Gene Summary

Gene:RALGDS; ral guanine nucleotide dissociation stimulator
Aliases: RGF, RGDS, RalGEF
Summary:Guanine nucleotide dissociation stimulators (GDSs, or exchange factors), such as RALGDS, are effectors of Ras-related GTPases (see MIM 190020) that participate in signaling for a variety of cellular processes.[supplied by OMIM, Nov 2010]
Databases:OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:ral guanine nucleotide dissociation stimulator
Source:NCBIAccessed: 31 August, 2019


What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1994-2019)
Graph generated 31 August 2019 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • DNA Methylation
  • Cell Movement
  • Phosphatidylinositol 3-Kinases
  • rap GTP-Binding Proteins
  • Systems Biology
  • raf Kinases
  • Enzyme Activation
  • Signal Transduction
  • Molecular Sequence Data
  • ral GTP-Binding Proteins
  • Amino Acid Sequence
  • 3T3 Cells
  • Cell Line, Transformed
  • Pancreatic Cancer
  • Tumor Suppressor Proteins
  • Proto-Oncogene Proteins p21(ras)
  • Chromosome 9
  • Colorectal Cancer
  • Sequence Homology
  • RAS Genes
  • Transfection
  • Apoptosis
  • Promoter Regions
  • Mutation
  • Lung Cancer
  • Messenger RNA
  • Neoplastic Cell Transformation
  • Cancer Gene Expression Regulation
  • Cervical Cancer
  • Cell Proliferation
  • Neoplasm Invasiveness
  • Breast Cancer
  • Base Sequence
  • Monomeric GTP-Binding Proteins
  • alpha-Fetoproteins
  • Liver Cancer
  • rho GTP-Binding Proteins
  • ral Guanine Nucleotide Exchange Factor
  • Tumor Suppressor Gene
  • Gene Expression Profiling
Tag cloud generated 31 August, 2019 using data from PubMed, MeSH and CancerIndex

Specific Cancers (6)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: RALGDS (cancer-related)

Schmidt ML, Hobbing KR, Donninger H, Clark GJ
RASSF1A Deficiency Enhances RAS-Driven Lung Tumorigenesis.
Cancer Res. 2018; 78(10):2614-2623 [PubMed] Free Access to Full Article Related Publications
Mutant K-RAS has been shown to have both tumor-promoting and -suppressing functions, and growing evidence suggests that the RASSF family of tumor suppressors can act as RAS apoptosis and senescence effectors. It has been hypothesized that inactivation of the RASSF1A tumor suppressor facilitates K-RAS-mediated transformation by uncoupling it from apoptotic pathways such as the Hippo pathway. In human lung tumors, combined activation of K-RAS and inactivation of RASSF1A is closely associated with the development of the most aggressive and worst prognosis tumors. Here, we describe the first transgenic mouse model for activation of K-RAS in the lung in a RASSF1A-defective background. RASSF1A deficiency profoundly enhanced the development of K-RAS-driven lung tumors

Yang Q, Guo X, Yang L
Metformin Enhances the Effect of Regorafenib and Inhibits Recurrence and Metastasis of Hepatic Carcinoma After Liver Resection via Regulating Expression of Hypoxia Inducible Factors 2α (HIF-2α) and 30 kDa HIV Tat-Interacting Protein (TIP30).
Med Sci Monit. 2018; 24:2225-2234 [PubMed] Free Access to Full Article Related Publications
BACKGROUND Regorafenib (RGF) is the drug of choice for treating hepatic carcinoma (HCC), but the drug has drawbacks due to resistance and associated adverse effects. Thus, it becomes crucial to understand the causal 'map' of the resistance conferred by RGF, so that its clinical potency can be amplified, resulting in enhanced efficacy with reduced adverse effects. Metformin (MTF) has been reported to target NLK (Nemo-like kinase) to inhibit non-small lung cancer cells. Based on the literature, the present investigation was carried out to reveal the effect of RGF and MTF, with an expectation that MTF can synergize therapeutic potential as well reduce chances of resistance. MATERIAL AND METHODS Protein expression of hypoxia inducible factors (HIF)-2α, 30 kDa HIV Tat-interacting protein (TIP30), E-cadherin, N-cadherin, and pAMPK were assessed by Western blot analysis. RGF and MTF were exposed to MHCC97H cell and proliferation was quantified by assay of cell viability. Gene silencing and chromatin immunoprecipitation assay were done to reveal the relationship between TIP30 and HIF-2α. The impact of RGF and MTF together on postoperative recurrence and lung metastasis of hepatocellular carcinoma was investigated using tumor engrafted mice after administration of MTF and RGF once daily for 35 days. Immunohistochemistry was used to reveal CD31, Ki67, and TUNEL. RESULTS The results suggested MTF-RGF combination lowered expression of HIF-2α gene silencing and suggested increased TIP30 after reduction of HIF-2α. The chromatin immunoprecipitation study indicated that under hypoxia, HIF-2α could bind with TIP30 promoter. Cell number quantification (CCK8), viable cell count, and apoptosis data (using Annexin V-FITC) indicated co-administration of RGF and MTF reduced cell proliferation, encouraging cell apoptosis, and reduced epithelial-mesenchymal transition course. Thus, in orthotopic mice, the RGF-MTF combination exhibited substantial reduction of HCC in lung metastasis and postoperative relapse. CONCLUSIONS MTF can enhance the potential of RGF and inhibit the recurrence and metastasis of HCC after postoperative liver section by regulating the levels of TIP30 and HIF-2α.

Khan AQ, Kuttikrishnan S, Siveen KS, et al.
RAS-mediated oncogenic signaling pathways in human malignancies.
Semin Cancer Biol. 2019; 54:1-13 [PubMed] Related Publications
Abnormally activated RAS proteins are the main oncogenic driver that governs the functioning of major signaling pathways involved in the initiation and development of human malignancies. Mutations in RAS genes and or its regulators, most frequent in human cancers, are the main force for incessant RAS activation and associated pathological conditions including cancer. In general, RAS is the main upstream regulator of the highly conserved signaling mechanisms associated with a plethora of important cellular activities vital for normal homeostasis. Mutated or the oncogenic RAS aberrantly activates a web of interconnected signaling pathways including RAF-MEK (mitogen-activated protein kinase kinase)-ERK (extracellular signal-regulated kinase), phosphoinositide-3 kinase (PI3K)/AKT (protein kinase B), protein kinase C (PKC) and ral guanine nucleotide dissociation stimulator (RALGDS), etc., leading to uncontrolled transcriptional expression and reprogramming in the functioning of a range of nuclear and cytosolic effectors critically associated with the hallmarks of carcinogenesis. This review highlights the recent literature on how oncogenic RAS negatively use its signaling web in deregulating the expression and functioning of various effector molecules in the pathogenesis of human malignancies.

D'Aloia A, Berruti G, Costa B, et al.
RalGPS2 is involved in tunneling nanotubes formation in 5637 bladder cancer cells.
Exp Cell Res. 2018; 362(2):349-361 [PubMed] Related Publications
RalGPS2 is a Ras-independent Guanine Nucleotide Exchange Factor (GEF) for RalA containing a PH domain and an SH3-binding region and it is involved in several cellular processes, such as cytokinesis, control of cell cycle progression, differentiation, cytoskeleton organization and rearrangement. Up to now, few data have been published regarding RalGPS2 role in cancer cells, and its involvement in bladder cancer is yet to be established. In this paper we demonstrated that RalGPS2 is expressed in urothelial carcinoma-derived 5637 cancer cells and is essential for cellular growth. These cells produces thin membrane protrusions that displayed the characteristics of actin rich tunneling nanotubes (TNTs) and here we show that RalGPS2 is involved in the formation of these cellular protrusions. In fact the overexpression of RalGPS2 or of its PH-domain increased markedly the number and the length of nanotubes, while the knock-down of RalGPS2 caused a strong reduction of these structures. Moreover, using a series of RalA mutants impaired in the interaction with different downstream components (Sec5, Exo84, RalBP1) we demonstrated that the interaction of RalA with Sec5 is required for TNTs formation. Furthermore, we found that RalGPS2 interacts with the transmembrane MHC class III protein leukocyte specific transcript 1 (LST1) and RalA, leading to the formation of a complex which promotes TNTs generation. These findings allow us to add novel elements to molecular models that have been previously proposed regarding TNTs formation.

Marisa L, Svrcek M, Collura A, et al.
The Balance Between Cytotoxic T-cell Lymphocytes and Immune Checkpoint Expression in the Prognosis of Colon Tumors.
J Natl Cancer Inst. 2018; 110(1) [PubMed] Related Publications
Background: Immune checkpoint (ICK) expression might represent a surrogate measure of tumor-infiltrating T cell (CTL) exhaustion and therefore be a more accurate prognostic biomarker for colorectal cancer (CRC) patients than CTL enumeration as measured by the Immunoscore.
Methods: The expression of ICKs, Th1, CTLs, cytotoxicity-related genes, and metagenes, including Immunoscore-like metagenes, were evaluated in three independent cohorts of CRC samples (260 microsatellite instable [MSI], 971 non-MSI). Their associations with patient survival were analyzed by Cox models, taking into account the microsatellite instability (MSI) status and affiliation with various Consensus Molecular Subgroups (CMS). PD-L1 and CD8 expression were examined on a subset of tumors with immunohistochemistry. All statistical tests were two-sided.
Results: The expression of Immunoscore-like metagenes was statistically significantly associated with improved outcome in non-MSI tumors displaying low levels of both CTLs and immune checkpoints (ICKs; CMS2 and CMS3; hazard ratio [HR] = 0.63, 95% confidence interval [CI] = 0.43 to 0.92, P = .02; and HR = 0.55, 95% CI = 0.34 to 0.90, P = .02, respectively), but clearly had no prognostic relevance in CRCs displaying higher levels of CTLs and ICKs (CMS1 and CMS4; HR = 0.46, 95% CI = 0.10 to 2.10, P = .32; and HR = 1.13, 95% CI = 0.79 to 1.63, P = .50, respectively), including MSI tumors. ICK metagene expression was statistically significantly associated with worse prognosis independent of tumor staging in MSI tumors (HR = 3.46, 95% CI = 1.41 to 8.49, P = .007). ICK expression had a negative impact on the proliferation of infiltrating CD8 T cells in MSI neoplasms (median = 0.56 in ICK low vs median = 0.34 in ICK high, P = .004).
Conclusions: ICK expression cancels the prognostic relevance of CTLs in highly immunogenic colon tumors and predicts a poor outcome in MSI CRC patients.

Erkoc P, Cingöz A, Onder TB, Kizilel S
Quinacrine Mediated Sensitization of Glioblastoma (GBM) Cells to TRAIL through MMP-Sensitive PEG Hydrogel Carriers.
Macromol Biosci. 2017; 17(2) [PubMed] Related Publications
Overcoming drug resistance is a major challenge for cancer therapy. Tumor necrosis factor α-related apoptosis-inducing ligand (TRAIL) is a potent therapeutic as an activator of apoptosis, particularly in tumor but not in healthy cells. However, its efficacy is limited by the resistance of tumor cell populations to the therapeutic substance. Here, we have addressed this limitation through the development of a controlled release system, matrix-metalloproteinase (MMP)-sensitive and arg-gly-asp-ser (RGDS) peptide functionalized poly (ethylene-glycol) (PEG) particles which are synthesized via visible-light-induced water-in-water emulsion polymerization. Quinacrine (QC), a recently discovered TRAIL sensitizer drug, is loaded into the hydrogel carriers and the influence of this system on the apoptosis of a malignant type of brain cancer, glioblastoma multiforme (GBM), has been investigated in detail. The results suggest that MMP-sensitive particles are cytocompatible and superior to promote TRAIL-induced apoptosis in GBM cells when loaded with QC. Compared to QC and TRAIL alone, combination of QC-loaded PEG hydrogel and TRAIL demonstrates synergistic apoptotic inducing behavior. Furthermore, QC-loaded particles, but not QC or PEG-hydrogels alone, enhance apoptosis as is measured through expression of apoptosis-related genes. This system is promising to significantly improve the efficacy of chemotherapeutic drugs and suggests a combination treatment for GBM therapy.

Madureira PA, Bharadwaj AG, Bydoun M, et al.
Cell surface protease activation during RAS transformation: Critical role of the plasminogen receptor, S100A10.
Oncotarget. 2016; 7(30):47720-47737 [PubMed] Free Access to Full Article Related Publications
The link between oncogenic RAS expression and the acquisition of the invasive phenotype has been attributed to alterations in cellular activities that control degradation of the extracellular matrix. Oncogenic RAS-mediated upregulation of matrix metalloproteinase 2 (MMP-2), MMP-9 and urokinase-type plasminogen activator (uPA) is critical for invasion through the basement membrane and extracellular matrix. The uPA converts cell surface-bound plasminogen to plasmin, a process that is regulated by the binding of plasminogen to specific receptors on the cell surface, however, the identity of the plasminogen receptors that function in this capacity is unclear. We have observed that transformation of cancer cells with oncogenic forms of RAS increases plasmin proteolytic activity by 2- to 4-fold concomitant with a 3-fold increase in cell invasion. Plasminogen receptor profiling revealed RAS-dependent increases in both S100A10 and cytokeratin 8. Oncogenic RAS expression increased S100A10 gene expression which resulted in an increase in S100A10 protein levels. Analysis with the RAS effector-loop mutants that interact specifically with Raf, Ral GDS pathways highlighted the importance of the RalGDS pathways in the regulation of S100A10 gene expression. Depletion of S100A10 from RAS-transformed cells resulted in a loss of both cellular plasmin generation and invasiveness. These results strongly suggest that increases in cell surface levels of S100A10, by oncogenic RAS, plays a critical role in RAS-stimulated plasmin generation, and subsequently, in the invasiveness of oncogenic RAS expressing cancer cells.

O Santos A, Parrini MC, Camonis J
RalGPS2 Is Essential for Survival and Cell Cycle Progression of Lung Cancer Cells Independently of Its Established Substrates Ral GTPases.
PLoS One. 2016; 11(5):e0154840 [PubMed] Free Access to Full Article Related Publications
The human genome contains six genes coding for proteins validated in vitro as specific activators of the small GTPases "Ras-related protein Ral-A" and "Ras-related protein Ral-B", generically named Ral-guanine nucleotide exchange factors (RalGEF). Ral proteins are important contributors to Ras oncogenic signaling, and RAS oncogenes are important in human Non-Small Cell Lung Carcinoma (NSCLC). Therefore in this work, RalGEF contribution to oncogenic and non-oncogenic features of human NSCLC cell lines, as anchorage-dependent and independent growth, cell survival, and proliferation, was investigated. Among all human RalGEF, silencing of RGL1 and RALGPS1 had no detectable effect. However, silencing of either RGL2, RGL3, RALGDS or, to a larger extent, RALGPS2 inhibited cell population growth in anchorage dependent and independent conditions (up to 90 and 80%, respectively). RALGPS2 silencing also caused an increase in the number of apoptotic cells, up to 45% of the cell population in transformed bronchial BZR cells. In H1299 and A549, two NSCLC cell lines, RALGPS2 silencing caused an arrest of cells in the G0/G1-phase of cell cycle. Furthermore, it was associated with the modulation of important cell cycle regulators: the E3 Ubiquitin Protein Ligase S-phase kinase-associated protein 2 (Skp2) was strongly down-regulated (both at mRNA and protein levels), and its targets, the cell cycle inhibitors p27 and p21, were up-regulated. These molecular effects were not mimicked by silencing RALA, RALB, or both. However, RALB silencing caused a modest inhibition of cell cycle progression, which in H1299 cells was associated with Cyclin D1 regulation. In conclusion, RALGPS2 is implicated in the control of cell cycle progression and survival in the in vitro growth of NSCLC cell lines. This function is largely independent of Ral GTPases and associated with modulation of Skp2, p27 and p21 cell cycle regulators.

Dunne PD, Dasgupta S, Blayney JK, et al.
EphA2 Expression Is a Key Driver of Migration and Invasion and a Poor Prognostic Marker in Colorectal Cancer.
Clin Cancer Res. 2016; 22(1):230-242 [PubMed] Free Access to Full Article Related Publications
PURPOSE: EphA2, a member of the Eph receptor tyrosine kinases family, is an important regulator of tumor initiation, neovascularization, and metastasis in a wide range of epithelial and mesenchymal cancers; however, its role in colorectal cancer recurrence and progression is unclear.
EXPERIMENTAL DESIGN: EphA2 expression was determined by immunohistochemistry in stage II/III colorectal tumors (N = 338), and findings correlated with clinical outcome. The correlation between EphA2 expression and stem cell markers CD44 and Lgr5 was examined. The role of EphA2 in migration/invasion was assessed using a panel of KRAS wild-type (WT) and mutant (MT) parental and invasive colorectal cancer cell line models.
RESULTS: Colorectal tumors displayed significantly higher expression levels of EphA2 compared with matched normal tissue, which positively correlated with high CD44 and Lgr5 expression levels. Moreover, high EphA2 mRNA and protein expression were found to be associated with poor overall survival in stage II/III colorectal cancer tissues, in both univariate and multivariate analyses. Preclinically, we found that EphA2 was highly expressed in KRASMT colorectal cancer cells and that EphA2 levels are regulated by the KRAS-driven MAPK and RalGDS-RalA pathways. Moreover, EphA2 levels were elevated in several invasive daughter cell lines, and downregulation of EphA2 using RNAi or recombinant EFNA1 suppressed migration and invasion of KRASMT colorectal cancer cells.
CONCLUSIONS: These data show that EpHA2 is a poor prognostic marker in stage II/III colorectal cancer, which may be due to its ability to promote cell migration and invasion, providing support for the further investigation of EphA2 as a novel prognostic biomarker and therapeutic target.

Sehgal M, Gupta R, Moussa A, Singh TR
An Integrative Approach for Mapping Differentially Expressed Genes and Network Components Using Novel Parameters to Elucidate Key Regulatory Genes in Colorectal Cancer.
PLoS One. 2015; 10(7):e0133901 [PubMed] Free Access to Full Article Related Publications
For examining the intricate biological processes concerned with colorectal cancer (CRC), a systems biology approach integrating several biological components and other influencing factors is essential to understand. We performed a comprehensive system level analysis for CRC which assisted in unravelling crucial network components and many regulatory elements through a coordinated view. Using this integrative approach, the perceptive of complexity hidden in a biological phenomenon is extensively simplified. The microarray analyses facilitated differential expression of 631 significant genes employed in the progression of disease and supplied interesting associated up and down regulated genes like jun, fos and mapk1. The transcriptional regulation of these genes was deliberated widely by examining transcription factors such as hnf4, nr2f1, znf219 and dr1 which directly influence the expression. Further, interactions of these genes/proteins were evaluated and crucial network motifs were detected to associate with the pathophysiology of CRC. The available standard statistical parameters such as z-score, p-value and significance profile were explored for the identification of key signatures from CRC pathway whereas a few novel parameters representing over-represented structures were also designed in the study. The applied approach revealed 5 key genes i.e. kras, araf, pik3r5, ralgds and akt3 via our novel designed parameters illustrating high statistical significance. These novel parameters can assist in scrutinizing candidate markers for diseases having known biological pathways. Further, investigating and targeting these proposed genes for experimental validations, instead being spellbound by the complicated pathway will certainly endow valuable insight in a well-timed systematic understanding of CRC.

Kanekiyo S, Iizuka N, Tsunedomi R, et al.
Preoperative serum methylation signature as prognostic tool after curative hepatectomy in patients with hepatocellular carcinoma.
Anticancer Res. 2015; 35(2):997-1007 [PubMed] Related Publications
AIM: This study aimed to investigate the relationship between prognosis after curative hepatectomy and serum methylation signature (SMS), defined by methylation levels of six specific genes (cyclin D2, Ras association (RalGDS/AF-6) domain family member 1, serine peptidase inhibitor Kunitz type 2, cystic fibrosis transmembrane conductance regulator, brain abundant membrane attached signal protein 1, and steroid-5-alpha-reductase alpha polypeptide 2).
PATIENTS AND METHODS: Serum samples were collected preoperatively from 125 patients with hepatocellular carcinoma associated with hepatitis C virus infection who underwent curative hepatectomy. We measured the methylation levels of the preceding six genes. We defined the methylation of three genes or more in the serum as SMS-positive in this study. We investigated the prognosis of SMS-positive patients.
RESULTS: SMS-positive patients exhibited significantly shorter disease-free survival (DFS) and overall survival (OS) than SMS-negative patients (p=0.0002 and p<0.0001, respectively). Multivariate analysis showed that SMS positivity was an independent risk factor for shorter DFS (hazard ratio (HR)=2.182; p<0.001) and OS (HR=4.198; p<0.001).
CONCLUSION: SMS is useful as a prognostic predictor in patients with hepatocellular carcinoma after curative hepatectomy.

Villanueva A, Portela A, Sayols S, et al.
DNA methylation-based prognosis and epidrivers in hepatocellular carcinoma.
Hepatology. 2015; 61(6):1945-56 [PubMed] Related Publications
UNLABELLED: Epigenetic deregulation has emerged as a driver in human malignancies. There is no clear understanding of the epigenetic alterations in hepatocellular carcinoma (HCC) and of the potential role of DNA methylation markers as prognostic biomarkers. Analysis of tumor tissue from 304 patients with HCC treated with surgical resection allowed us to generate a methylation-based prognostic signature using a training-validation scheme. Methylome profiling was done with the Illumina HumanMethylation450 array (Illumina, Inc., San Diego, CA), which covers 96% of known cytosine-phosphate-guanine (CpG) islands and 485,000 CpG, and transcriptome profiling was performed with Affymetrix Human Genome U219 Plate (Affymetrix, Inc., Santa Clara, CA) and miRNA Chip 2.0. Random survival forests enabled us to generate a methylation signature based on 36 methylation probes. We computed a risk score of mortality for each individual that accurately discriminated patient survival both in the training (221 patients; 47% hepatitis C-related HCC) and validation sets (n = 83; 47% alcohol-related HCC). This signature correlated with known predictors of poor outcome and retained independent prognostic capacity of survival along with multinodularity and platelet count. The subset of patients identified by this signature was enriched in the molecular subclass of proliferation with progenitor cell features. The study confirmed a high prevalence of genes known to be deregulated by aberrant methylation in HCC (e.g., Ras association [RalGDS/AF-6] domain family member 1, insulin-like growth factor 2, and adenomatous polyposis coli) and other solid tumors (e.g., NOTCH3) and describes potential candidate epidrivers (e.g., septin 9 and ephrin B2).
CONCLUSIONS: A validated signature of 36 DNA methylation markers accurately predicts poor survival in patients with HCC. Patients with this methylation profile harbor messenger RNA-based signatures indicating tumors with progenitor cell features.

Tang SC, Chen YC
Novel therapeutic targets for pancreatic cancer.
World J Gastroenterol. 2014; 20(31):10825-44 [PubMed] Free Access to Full Article Related Publications
Pancreatic cancer has become the fourth leading cause of cancer death in the last two decades. Only 3%-15% of patients diagnosed with pancreatic cancer had 5 year survival rate. Drug resistance, high metastasis, poor prognosis and tumour relapse contributed to the malignancies and difficulties in treating pancreatic cancer. The current standard chemotherapy for pancreatic cancer is gemcitabine, however its efficacy is far from satisfactory, one of the reasons is due to the complex tumour microenvironment which decreases effective drug delivery to target cancer cell. Studies of the molecular pathology of pancreatic cancer have revealed that activation of KRAS, overexpression of cyclooxygenase-2, inactivation of p16(INK4A) and loss of p53 activities occurred in pancreatic cancer. Co-administration of gemcitabine and targeting the molecular pathological events happened in pancreatic cancer has brought an enhanced therapeutic effectiveness of gemcitabine. Therefore, studies looking for novel targets in hindering pancreatic tumour growth are emerging rapidly. In order to give a better understanding of the current findings and to seek the direction in future pancreatic cancer research; in this review we will focus on targets suppressing tumour metastatsis and progression, KRAS activated downstream effectors, the relationship of Notch signaling and Nodal/Activin signaling with pancreatic cancer cells, the current findings of non-coding RNAs in inhibiting pancreatic cancer cell proliferation, brief discussion in transcription remodeling by epigenetic modifiers (e.g., HDAC, BMI1, EZH2) and the plausible therapeutic applications of cancer stem cell and hyaluronan in tumour environment.

Vu HL, Aplin AE
Targeting TBK1 inhibits migration and resistance to MEK inhibitors in mutant NRAS melanoma.
Mol Cancer Res. 2014; 12(10):1509-19 [PubMed] Free Access to Full Article Related Publications
UNLABELLED: Melanoma is a devastating form of skin cancer with limited therapeutic options. Fifteen to 20% of patients with melanoma have an activating mutation in the GTPase, NRAS. The major downstream effectors of RAS are RAFs (ARAF, BRAF, and CRAF), phosphoinositide 3-kinase (PI3K), and the Ral guanine exchange factors (RalGEF). TANK-binding kinase 1 (TBK1) is an atypical IκB kinase family member that acts downstream of RalGEFs. Whereas many studies have analyzed RAF and PI3K signaling in mutant NRAS melanoma, the role of RalGEF/Ral is understudied and TBK1 has not been examined. To address this, TBK1 was modulated with knockdown approaches and targeted therapies to determine the role of TBK1 in motility, apoptosis, and signaling. In melanoma, NRAS overexpression increased TBK1 phosphorylation. TBK1 depletion inhibited migration and invasion, whereas its constitutive overexpression led to an increase in invasion. In three-dimensional systems that mimic the dermal microenvironment, TBK1 depletion or inhibition cooperated with MEK inhibitors to promote apoptosis, particularly in the context of MEK-insensitive mutant NRAS. This effect was absent in melanoma cells that are wild-type for NRAS. These results suggest the utility of TBK1 inhibitors as part of a treatment regimen for patients with mutant NRAS melanoma, for whom there are no current effective therapies.
IMPLICATIONS: TBK1 promotes the malignant properties of NRAS-mutant melanoma and its targeting, in combination with MEK, promotes apoptosis, thus providing a potential novel targeted therapeutic option.

Lin TY, Ki CS, Lin CC
Manipulating hepatocellular carcinoma cell fate in orthogonally cross-linked hydrogels.
Biomaterials. 2014; 35(25):6898-906 [PubMed] Related Publications
De-differentiation and loss of function in hepatocytes during two-dimensional (2D) tissue culture significantly hinders the progress of liver research. An ideal three-dimensional (3D) in vitro liver parenchymal cell culture platform should restore cell-cell and cell-matrix interactions, as well as normal hepatocyte polarity. Here, we report an orthogonal thiol-ene hydrogel system for culturing liver cell lines (e.g. Huh7 and HepG2). The hydrogels were prepared by a radical-mediated orthogonal thiol-norbornene photo-click chemistry using poly(ethylene glycol)-tetra-norbornene (PEG4NB) macromer and di-thiol containing linker (e.g., dithiothreitol (DTT) or bis-cysteine matrix metalloproteinase (MMP)-sensitive peptide). This system also allows facile incorporation of bioactive peptides (e.g., fibronectin-derived RGDS) to improve cell-matrix interactions. Encapsulated Huh7 and HepG2 cells showed elevated urea secretion and CYP3A4 enzymatic activities, as well as up-regulated mRNA levels of multiple hepatocyte genes (e.g., CYP3A4, BESP, and NTCP). Importantly, this is the first 3D hydrogel system that up-regulates the expression of NCTP in encapsulated Huh7 and HepG2 cell lines without any genetic modification or the addition of growth factors and chemical additives. Furthermore, the encapsulated cells displayed hepatocyte-like polarity distinctively different from the polarity displayed in 2D culture. These characteristics not only allow the study of hepatology in 3D using inexpensive cell lines, but also permit large-scale small-molecule screening. The up-regulation of NTCP expression and restoration of hepatocyte-like polarity in our hydrogels also shed light on future study of hepatitis B virus infection in vitro.

Ezzeldin M, Borrego-Diaz E, Taha M, et al.
RalA signaling pathway as a therapeutic target in hepatocellular carcinoma (HCC).
Mol Oncol. 2014; 8(5):1043-53 [PubMed] Free Access to Full Article Related Publications
Ral (Ras like) leads an important proto-oncogenic signaling pathway down-stream of Ras. In this work, RalA was found to be significantly overactivated in hepatocellular carcinoma (HCC) cells and tissues as compared to non-malignant samples. Other elements of RalA pathway such as RalBP1 and RalGDS were also expressed at higher levels in malignant samples. Inhibition of RalA by gene-specific silencing caused a robust decrease in the viability and invasiveness of HCC cells. Additionally, the use of geranyl-geranyl transferase inhibitor (GGTI, an inhibitor of Ral activation) and Aurora kinase inhibitor II resulted in a significant decrease in the proliferation of HCC cells. Furthermore, RalA activation was found to be at a higher level of activation in HCC stem cells that express CD133. Transgenic mouse model for HCC (FXR-Knockout) also revealed an elevated level of RalA-GTP in the liver tumors as compared to background animals. Finally, subcutaneous mouse model for HCC confirmed effectiveness of inhibition of aurora kinase/RalA pathway in reducing the tumorigenesis of HCC cells in vivo. In conclusion, RalA overactivation is an important determinant of malignant phenotype in differentiated and stem cells of HCC and can be considered as a target for therapeutic intervention.

Naushad SM, Hussain T, Al-Attas OS, et al.
Molecular insights into the association of obesity with breast cancer risk: relevance to xenobiotic metabolism and CpG island methylation of tumor suppressor genes.
Mol Cell Biochem. 2014; 392(1-2):273-80 [PubMed] Related Publications
Obesity, genetic polymorphisms of xenobiotic metabolic pathway, hypermethylation of tumor suppressor genes, and hypomethylation of proapoptotic genes are known to be independent risk factors for breast cancer. The objective of this study is to evaluate the combined effect of these environmental, genetic, and epigenetic risk factors on the susceptibility to breast cancer. PCR-RFLP and multiplex PCR were used for the genetic analysis of six variants of xenobiotic metabolic pathway. Methylation-specific PCR was used for the epigenetic analysis of four genetic loci. Multifactor dimensionality reduction analysis revealed a significant interaction between the body mass index (BMI) and catechol-O-methyl transferase H108L variant alone or in combination with cytochrome P450 (CYP) 1A1m1 variant. Women with "Luminal A" breast cancer phenotype had higher BMI compared to other phenotypes and healthy controls. There was no association between the BMI and tumor grade. The post-menopausal obese women exhibited lower glutathione levels. BMI showed a positive association with the methylation of extracellular superoxide dismutase (r = 0.21, p < 0.05), Ras-association (RalGDS/AF-6) domain family member 1 (RASSF1A) (r = 0.31, p < 0.001), and breast cancer type 1 susceptibility protein (r = 0.19, p < 0.05); and inverse association with methylation of BNIP3 (r = -0.48, p < 0.0001). To conclude based on these results, obesity increases the breast cancer susceptibility by two possible mechanisms: (i) by interacting with xenobiotic genetic polymorphisms in inducing increased oxidative DNA damage and (ii) by altering the methylome of several tumor suppressor genes.

Kashatus DF
Ral GTPases in tumorigenesis: emerging from the shadows.
Exp Cell Res. 2013; 319(15):2337-42 [PubMed] Free Access to Full Article Related Publications
Oncogenic Ras proteins rely on a series of key effector pathways to drive the physiological changes that lead to tumorigenic growth. Of these effector pathways, the RalGEF pathway, which activates the two Ras-related GTPases RalA and RalB, remains the most poorly understood. This review will focus on key developments in our understanding of Ral biology, and will speculate on how aberrant activation of the multiple diverse Ral effector proteins might collectively contribute to oncogenic transformation and other aspects of tumor progression.

Huang C, Wang WM, Gong JP, Yang K
Oncogenesis and the clinical significance of K-ras in pancreatic adenocarcinoma.
Asian Pac J Cancer Prev. 2013; 14(5):2699-701 [PubMed] Related Publications
The RAS family genes encode small GTP-binding cytoplasmic proteins. Activated KRAS engages multiple effector pathways, notably the RAF-mitogen-activated protein kinase, phosphoinositide-3-kinase (PI3K) and RalGDS pathways. In the clinical field, K-ras oncogene activation is frequently found in human cancers and thus may serve as a potential diagnostic marker for cancer cells in circulation. This mini-review aims to summarise information on Ras-induced oncogenesis and the clinical significance of K-ras.

Qu Y, Dang S, Hou P
Gene methylation in gastric cancer.
Clin Chim Acta. 2013; 424:53-65 [PubMed] Related Publications
Gastric cancer is one of the most common malignancies and remains the second leading cause of cancer-related death worldwide. Over 70% of new cases and deaths occur in developing countries. In the early years of the molecular biology revolution, cancer research mainly focuses on genetic alterations, including gastric cancer. Epigenetic mechanisms are essential for normal development and maintenance of tissue-specific gene expression patterns in mammals. Disruption of epigenetic processes can lead to altered gene function and malignant cellular transformation. Recent advancements in the rapidly evolving field of cancer epigenetics have shown extensive reprogramming of every component of the epigenetic machinery in cancer, including DNA methylation, histone modifications, nucleosome positioning, noncoding RNAs, and microRNAs. Aberrant DNA methylation in the promoter regions of gene, which leads to inactivation of tumor suppressor and other cancer-related genes in cancer cells, is the most well-defined epigenetic hallmark in gastric cancer. The advantages of gene methylation as a target for detection and diagnosis of cancer in biopsy specimens and non-invasive body fluids such as serum and gastric washes have led to many studies of application in gastric cancer. This review focuses on the most common and important phenomenon of epigenetics, DNA methylation, in gastric cancer and illustrates the impact epigenetics has had on this field.

Guerrero-Setas D, Pérez-Janices N, Blanco-Fernandez L, et al.
RASSF2 hypermethylation is present and related to shorter survival in squamous cervical cancer.
Mod Pathol. 2013; 26(8):1111-22 [PubMed] Related Publications
Ras association (RalGDS/AF-6) domain family member 2 (RASSF2) is a gene involved in the progression of several human cancers, including breast, colorectal and lung cancer. The aims of this study were to determine the hypermethylation of the gene in squamous cervical cancer and precursor lesions, along with that of RASSF1 and the recently described EPB41L3, and to analyze the potential prognostic role of these genes. Methylation-specific PCR and bisulfite sequencing were used to analyze the methylation status of RASSF2 and EPB41L3 gene in 60 squamous cervical cancer, 76 cervical intraepithelial neoplasias grade III, 16 grade II, 14 grade I and 13 cases of normal tissue adjacent to cervical intraepithelial neoplasia. RASSF2 expression was evaluated by immunohistochemistry and the re-expression of RASSF2 and EPB41L3 was analyzed by quantitative reverse-transcription PCR in HeLa, SiHa, C33A and A431 cell lines treated with 5-aza-2'-deoxycytidine and/or trichostatin. RASSF1 hypermethylation and human papillomavirus type were also analyzed in all the cases by methylation-specific PCR and reverse line blot, respectively. RASSF2 hypermethylation was predominant in squamous cervical cancer (60.9%) compared with cervical intraepithelial neoplasias (4.2%) and was associated with a lower level of RASSF2 expression and vascular invasion in squamous cervical cancer. EPB41L3 and RASSF1 hypermethylations were also more frequent in cancer than in precursor lesions. Patients with RASSF2 hypermethylation had shorter survival time, independent of tumor stage (hazard ratio: 6.0; 95% confidence interval: 1.5-24.5). Finally, the expressions of RASSF2 and EPB41L3 were restored in several cell lines treated with 5-aza-2'-deoxycytidine. Taken together, our results suggest that RASSF2 potentially functions as a new tumor-suppressor gene that is inactivated through hypermethylation in cervical cancer and is related to the bad prognosis of these patients.

Monica V, Familiari U, Chiusa L, et al.
Messenger RNA and protein expression of thymidylate synthase and DNA repair genes in thymic tumors.
Lung Cancer. 2013; 79(3):228-35 [PubMed] Related Publications
BACKGROUND: Thymic epithelial tumors include several entities with different biologic behavior. Chemotherapy is indicated in advanced disease, but limited data exist on gene expression correlation with the response to chemotherapeutic agents.
PATIENTS AND METHODS: A series of 69 thymic neoplasms (7 A-, 6 AB-, 6 B1-, 10 B2-, 14 B3-thymomas, 22 carcinomas and 4 combined tumors) was collected to assess gene expression of thymidylate synthase (TS), excision repair cross complementing-1 (ERCC1), ribonucleotide reductase subunit 1 (RRM1), topoisomerase 2α (TOP2A) and mTOR.
RESULTS: A strong linear correlation between TS gene and protein expression was observed (P<0.0001, R=0.40). TS expression was significantly lower in pure A-thymomas and thymic carcinomas (P<0.0001) and progressively decreasing from B1-type to thymic carcinomas (B1>B2>B3>C; P<0.0001). RRM1 and TOP2A mRNA expression levels were significantly correlated with TS levels (both P=0.03) with a similar trend of expression among histotypes. RRM1 and TOP2A high levels were significantly correlated with high TS (P=0.03) and low tumor stages (I-II) (P<0.0001 and P<0.01, respectively). No relevant changes of ERCC1 and mTOR were detected.
CONCLUSIONS: Low TS and, to a minor extent, RRM1 and TOP2A expression were detected in aggressive thymic tumors. These findings should be prospectively considered in selecting the most appropriate chemotherapy.

Miranda E, Bianchi P, Destro A, et al.
Genetic and epigenetic alterations in primary colorectal cancers and related lymph node and liver metastases.
Cancer. 2013; 119(2):266-76 [PubMed] Related Publications
BACKGROUND: Colorectal cancer (CRC) prognosis and survival are strictly related to the development of distant metastases. New targeted therapies have increased patient survival, but the objective response rate is still very limited, partially because of a traditional focus on designing treatment according to the molecular profile of the primary tumor regardless the diversity between the primary tumor and metastases. The objective of this study was to evaluate the presence of molecular heterogeneity during metastatic progression and its potential impact on clinical treatment.
METHODS: The authors analyzed v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) codon 12 mutations, the v-Raf murine sarcoma viral oncogene homolog B1 (BRAF) thymine to adenine substitution at codon 1788, and tumor protein 53 (p53) mutations and investigated promoter methylation of Ras association (RalGDS/AF-6) domain family member 1 protein (RASSF1a), E-cadherin, and cyclin-dependent kinase inhibitor 2A (p16INK4a) in 101 primary CRCs (67 stage III and 34 stage IV) and related lymph node and liver metastases.
RESULTS: Lymph node metastases were characterized by fewer alterations compared with primary tumors and liver metastases, especially KRAS (P = .03) and p16INK4a (P = .05). Genetic changes, when detectable in metastases, mostly were retained from the primary tumor, whereas epigenetic changes more frequently were acquired de novo. Overall, 31 distinct CRC molecular profiles were detected, none of which characterized a particular tumor stage. When the metastatic lesions also were included in the profiles, there were 53 distinct molecular profiles in 67 patients with stage III disease and 34 distinct molecular profiles in 34 patients with stage IV disease.
CONCLUSIONS: Lymph node and liver metastases appear to originate in clonally different processes, with more molecular alterations occurring in distant metastases than in lymph node metastases and with elevated heterogeneity of the primary tumor. Thus, potential prognostic targets should be carefully evaluated for their heterogeneity in both primary tumors and distant metastases to avoid erroneous misclassification.

Samakoglu S, Deevi DS, Li H, et al.
Preclinical rationale for combining an EGFR antibody with cisplatin/gemcitabine for the treatment of NSCLC.
Cancer Genomics Proteomics. 2012 Mar-Apr; 9(2):77-92 [PubMed] Related Publications
BACKGROUND: Although the addition of epidermal growth factor receptor (EGFR) antibodies to various platinum-based chemotherapy regimens for non-small cell lung cancer (NSCLC) is being actively pursued in the clinic, rationale for the prioritization of specific regimens is lacking.
MATERIALS AND METHODS: We evaluated the antitumor effects of necitumumab, a recombinant human IgG1 antibody targeting EGFR, in combination with cisplatin plus gemcitabine, pemetrexed, or paclitaxel in a panel of 9 subcutaneous tumor models of NSCLC established in nu/nu athymic mice.
RESULTS: Necitumumab in combination with cisplatin/gemcitabine was particularly effective, although interestingly, the mechanisms underlying these benefits were model dependent. For example, increased tumor cell apoptosis contributed towards combination efficacy in the A549 model, in association with increased expression of hsa-miR-29b and reduced expression of antiapoptotic genes including DNA methyltransferase DNMT3B, commonly up-regulated in patients with NSCLC. Such inverse effects of combination therapy on DNMT3B and hsa-miR-29b expression were found in multiple models. Importantly, in the A549 model, hsa-miR-29b down-regulation of DMNT3b reduced promoter methylation of tumor suppressor genes such as Cell adhesion molecule 1 (CADM1), Ras associated (RalGDS/AF-6) domain family member 1 (RASSF1), and Fragile histidine triad gene (FHIT), increasing their expression.
CONCLUSION: These results offer a preclinical rationale for combining an EGFR antibody with cisplatin/gemcitabine for patients with NSCLC, and provide potential molecular biomarkers for tailoring therapy.

Gus-Brautbar Y, Johnson D, Zhang L, et al.
The anti-inflammatory TIPE2 is an inhibitor of the oncogenic Ras.
Mol Cell. 2012; 45(5):610-8 [PubMed] Free Access to Full Article Related Publications
The connection between cancer and inflammation is widely recognized, yet the underlying molecular mechanisms are poorly understood. We report here that TIPE2 provides a molecular bridge from inflammation to cancer by targeting the Ras signaling pathway. TIPE2 binds the Ras-interacting domain of the RalGDS family of proteins, which are essential effectors of activated Ras. This binding prevented Ras from forming an active complex, thereby inhibiting the activation of the downstream signaling molecules Ral and AKT. Consequently, TIPE2 deficiency led to heightened activation of Ral and AKT, resistance to cell death, increased migration, and dysregulation of exocyst complex formation. Conversely, TIPE2 overexpression induced cell death and significantly inhibited Ras-induced tumorigenesis in mice. Importantly, TIPE2 expression was either completely lost or significantly downregulated in human hepatic cancer. Thus, TIPE2 is an inhibitor of both inflammation and cancer, and a potential drug target for inflammatory and neoplastic diseases.

Buhmeida A, Merdad A, Al-Maghrabi J, et al.
RASSF1A methylation is predictive of poor prognosis in female breast cancer in a background of overall low methylation frequency.
Anticancer Res. 2011; 31(9):2975-81 [PubMed] Related Publications
Breast cancer (BC) is the most common cancer worldwide. The Kingdom of Saudi Arabia is no exception, with ever increasing incidence rates. An interesting feature of this disease is the relatively young age of the affected women. The average age in the present cohort of 100 sporadic cases of invasive ductal carcinomas was 45 years, with a median of 46 years (range between 19-81 years). In an effort to understand the molecular signature of BC in the Saudi population, we undertook this study to profile the methylation events in a series of key genes including Ras association (RalGDS/AF-6) domain family member 1 isoform a (RASSF1A), hypermethylated in cancer 1 (HIC1), cyclin-dependent kinase inhibitor 2A (CDKN2A), retinoic acid receptor beta (RARB2), estrogen receptor 1 (ESR1), progesterone receptor (PGR), paired-like homeodomain 2 (PITX2), secreted frizzled-related protein 1 (SFRP1), myogenic differentiation 1 (MYOD1), and slit homolog 2 (SLIT2), using MethyLight analysis in archival tumour samples. Interestingly, the overall methylation levels were low in this cohort, with only 84% of the cases displaying methylation in one or more of the analysed genes. The frequency of RASSF1A methylation was the highest (65%), while there was almost complete absence of methylation of the ESR1 and the CDH1 genes (1% and 3%, respectively). Several statistically significant correlations were identified between specific methylation events and clinical parameters which gained more significance when analysis was limited to the estrogen receptor positive samples. Although there was no significant correlations between any methylation event and disease-specific survival, methylation of MYOD1 or RASSF1A was associated with lower disease-free survival and increased chance of disease recurrence. Furthermore, multivariate (Cox) regression analysis identified RASSF1A as an independent predictor of poor prognosis in terms of disease-free survival in this cohort. Our findings provide further evidence on the usefulness of RASSF1A methylation status as an informative prognostic biomarker in BC in a Saudi population.

Yoshikawa Y, Sato A, Tsujimura T, et al.
Frequent deletion of 3p21.1 region carrying semaphorin 3G and aberrant expression of the genes participating in semaphorin signaling in the epithelioid type of malignant mesothelioma cells.
Int J Oncol. 2011; 39(6):1365-74 [PubMed] Related Publications
Array-based comparative genomic hybridization analysis was performed on 21 malignant mesothelioma (MM) samples (16 primary cell cultures and 5 cell lines) and two reactive mesothelial hyperplasia (RM) primary cell cultures. The RM samples did not have any genomic losses or gains. In MM samples, deletions in 1p, 3p21, 4q, 9p21, 16p13 and 22q were detected frequently. We focused on 3p21 because this deletion was specific to the epithelioid type. Especially, a deletion in 3p21.1 region carrying seven genes including SEMA3G was found in 52% of MM samples (11 of 14 epithelioid samples). The allele loss of 3p21.1 might be a good marker for the epithelioid MM. A homozygous deletion in this region was detected in two MM primary cell cultures. A heterozygous deletion detected in nine samples contained the 3p21.1 region and 3p21.31 one carrying the candidate tumor suppressor genes such as semaphorin 3F (SEMA3F), SEMA3B and Ras association (RalGDS/AF-6) domain family member 1 (RASSF1A). SEMA3B, 3F and 3G are class 3 semaphorins and inhibit growth by competing with vascular endothelial growth factor (VEGF) through binding to neuropilin. All MM samples downregulated the expression of more than one gene for SEMA3B, 3F and 3G when compared with Met5a, a normal pleura-derived cell line. Moreover, in 12 of 14 epithelioid MM samples the expression level of SEMA3A was lower than that in Met5a and the two RM samples. An augmented expression of VEGFA was detected in half of the MM samples. The expression ratio of VEGFA/SEMA3A was significantly higher in the epithelioid MMs than in Met5a, RMs and the non-epithelioid MMs. Our data suggest that the downregulated expression of SEMA3A and several SEMA3s results in a loss of inhibitory activities in tumor angiogenesis and tumor growth of VEGFA; therefore, it may play an important role on the pathogenesis of the epithelioid type of MM.

Osei-Sarfo K, Martello L, Ibrahim S, Pellicer A
The human Rgr oncogene is overexpressed in T-cell malignancies and induces transformation by acting as a GEF for Ras and Ral.
Oncogene. 2011; 30(34):3661-71 [PubMed] Free Access to Full Article Related Publications
The Ras superfamily of GTPases is involved in the modification of many cellular processes including cellular motility, proliferation and differentiation. Our laboratory has previously identified the RalGDS-related (Rgr) oncogene in a DMBA (7,12-dimethylbenz[α]anthracene)-induced rabbit squamous cell carcinoma and its human orthologue, hRgr. In this study, we analyzed the expression levels of the human hRgr transcript in a panel of human hematopoietic malignancies and found that a truncated form (diseased-truncated (Dtr-hrgr)) was significantly overexpressed in many T-cell-derived neoplasms. Although the Rgr proto-oncogene belongs to the RalGDS family of guanine nucleotide exchange factors (GEFs), we show that upon the introduction of hRgr into fibroblast cell lines, it is able to elicit the activation of both Ral and Ras GTPases. Moreover, in vitro guanine nucleotide exchange assays confirm that hRgr promotes Ral and Ras activation through GDP dissociation, which is a critical characteristic of GEF proteins. hRgr has guanine nucleotide exchange activity for both small GTPases and this activity was reduced when a point mutation within the catalytic domain (CDC25) of the protein, (cd) Dtr-hRgr, was utilized. These observations prompted the analysis of the biological effects of hRgr and (cd) hRgr expression in cultured cells. Here, we show that hRgr increases proliferation in low serum, increases invasion, reduces anchorage dependence and promotes the progression into the S phase of the cell cycle; properties that are abolished or severely reduced in the presence of the catalytic dead mutant. We conclude that the ability of hRgr to activate both Ral and Ras is responsible for its transformation-inducing phenotype and it could be an important contributor in the development of some T-cell malignancies.

Martin TD, Samuel JC, Routh ED, et al.
Activation and involvement of Ral GTPases in colorectal cancer.
Cancer Res. 2011; 71(1):206-15 [PubMed] Free Access to Full Article Related Publications
Current approaches to block KRAS oncogene function focus on inhibition of K-Ras downstream effector signaling. We evaluated the antitumor activity of selumetinib (AZD6244, ARRY-142886), a potent and selective MEK1/2 inhibitor, on a panel of colorectal carcinoma (CRC) cells and found no inhibition of KRAS mutant CRC cell anchorage-independent growth. Although AKT activity was elevated in KRAS mutant cells, and PI3K inhibition did impair the growth of MEK inhibitor-insensitive CRC cell lines, concurrent treatment with selumetinib did not provide additional antitumor activity. Therefore, we speculated that inhibition of the Ral guanine exchange factor (RalGEF) effector pathway may be a more effective approach for blocking CRC growth. RalGEFs are activators of the related RalA and RalB small GTPases and we found activation of both in CRC cell lines and patient tumors. Interfering RNA stable suppression of RalA expression reduced CRC tumor cell anchorage-independent growth, but surprisingly, stable suppression of RalB greatly enhanced soft agar colony size and formation frequency. Despite their opposing activities, both RalA and RalB regulation of anchorage-independent growth required interaction with RalBP1/RLIP76 and components of the exocyst complex. Interestingly, RalA interaction with the Exo84 but not Sec5 exocyst component was necessary for supporting anchorage-independent growth, whereas RalB interaction with Sec5 but not Exo84 was necessary for inhibition of anchorage-independent growth. We suggest that anti-RalA-selective therapies may provide an effective approach for KRAS mutant CRC.

Vigil D, Martin TD, Williams F, et al.
Aberrant overexpression of the Rgl2 Ral small GTPase-specific guanine nucleotide exchange factor promotes pancreatic cancer growth through Ral-dependent and Ral-independent mechanisms.
J Biol Chem. 2010; 285(45):34729-40 [PubMed] Free Access to Full Article Related Publications
Our recent studies established essential and distinct roles for RalA and RalB small GTPase activation in K-Ras mutant pancreatic ductal adenocarcinoma (PDAC) cell line tumorigencity, invasion, and metastasis. However, the mechanism of Ral GTPase activation in PDAC has not been determined. There are four highly related mammalian RalGEFs (RalGDS, Rgl1, Rgl2, and Rgl3) that can serve as Ras effectors. Whether or not they share distinct or overlapping functions in K-Ras-mediated growth transformation has not been explored. We found that plasma membrane targeting to mimic persistent Ras activation enhanced the growth-transforming activities of RalGEFs. Unexpectedly, transforming activity did not correlate directly with total cell steady-state levels of Ral activation. Next, we observed elevated Rgl2 expression in PDAC tumor tissue and cell lines. Expression of dominant negative Ral, which blocks RalGEF function, as well as interfering RNA suppression of Rgl2, reduced PDAC cell line steady-state Ral activity, growth in soft agar, and Matrigel invasion. Surprisingly, the effect of Rgl2 on anchorage-independent growth could not be rescued by constitutively activated RalA, suggesting a novel Ral-independent function for Rgl2 in transformation. Finally, we determined that Rgl2 and RalB both localized to the leading edge, and this localization of RalB was dependent on endogenous Rgl2 expression. In summary, our observations support nonredundant roles for RalGEFs in Ras-mediated oncogenesis and a key role for Rgl2 in Ral activation and Ral-independent PDAC growth.

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