ARAF

Gene Summary

Gene:ARAF; A-Raf proto-oncogene, serine/threonine kinase
Aliases: PKS2, A-RAF, ARAF1, RAFA1
Location:Xp11.4-p11.2
Summary:This proto-oncogene belongs to the RAF subfamily of the Ser/Thr protein kinase family, and maybe involved in cell growth and development. Alternatively spliced transcript variants encoding different isoforms have been found for this gene.[provided by RefSeq, Jan 2012]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:serine/threonine-protein kinase A-Raf
HPRD
Source:NCBIAccessed: 17 March, 2015

Ontology:

What does this gene/protein do?
Show (16)

Cancer Overview

Research Indicators

Publications Per Year (1990-2015)
Graph generated 17 March 2015 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.

  • Apoptosis
  • Neoplastic Cell Transformation
  • alpha Catenin
  • Tumor Suppressor Proteins
  • FOXM1
  • Follicular Lymphoma
  • Xenograft Models
  • Thyroid Cancer
  • Bladder Cancer
  • BRAF
  • Polycomb Repressive Complex 2
  • Molecular Targeted Therapy
  • Trans-Activators
  • ERBB2
  • Genome-Wide Association Study
  • Proto-Oncogene Proteins A-raf
  • Mitogen-Activated Protein Kinases
  • Nuclear Proteins
  • Base Sequence
  • Cell Cycle Proteins
  • MYD88
  • Cancer Gene Expression Regulation
  • DNA Mutational Analysis
  • Signal Transduction
  • CREB-Binding Protein
  • X Chromosome
  • Adenocarcinoma
  • Gene Expression
  • Phosphatidylinositol 3-Kinases
  • Disease Progression
  • Cohort Studies
  • Polymerase Chain Reaction
  • Tumor Markers
  • High-Throughput Nucleotide Sequencing
  • Histones
  • DNA Sequence Analysis
  • CRAF
  • Mutation
  • raf Kinases
  • MAP Kinase Signaling System
Tag cloud generated 17 March, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (1)

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: ARAF (cancer-related)

Kim JH, Hong SK, Wu PK, et al.
Raf/MEK/ERK can regulate cellular levels of LC3B and SQSTM1/p62 at expression levels.
Exp Cell Res. 2014; 327(2):340-52 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
While cellular LC3B and SQSTM1 levels serve as key autophagy markers, their regulation by different signaling pathways requires better understanding. Here, we report the mechanisms by which the Raf/MEK/ERK pathway regulates cellular LC3B and SQSTM1 levels. In different cell types, ΔRaf-1:ER- or B-Raf(V600E)-mediated MEK/ERK activation increased LC3B-I, LC3B-II, and SQSTM1/p62 levels, which was accompanied by increased BiP/GRP78 expression. Use of the autophagy inhibitors chloroquine and bafilomycin A1, or RNA interference of ATG7, suggested that these increases in LC3B and SQSTM1 levels were in part attributed to altered autophagic flux. However, intriguingly, these increases were also attributed to their increased expression. Upon Raf/MEK/ERK activation, mRNA levels of LC3B and SQSTM1 were also increased, and subsequent luciferase reporter analyses suggested that SQSTM1 upregulation was mediated at transcription level. Under this condition, transcription of BiP/GRP78 was also increased, which was necessary for Raf/MEK/ERK to regulate LC3B at the protein, but not mRNA, level. This suggests that BiP has a role in regulating autophagy machinery when Raf/MEK/ERK is activated. In conclusion, these results suggest that, under a Raf/MEK/ERK-activated condition, the steady-state cellular levels of LC3B and SQSTM1 can also be determined by their altered expression wherein BiP is utilized as an effector of the signaling.

Aldea MD, Petrushev B, Soritau O, et al.
Metformin plus sorafenib highly impacts temozolomide resistant glioblastoma stem-like cells.
J BUON. 2014 Apr-Jun; 19(2):502-11 [PubMed] Related Publications
PURPOSE: Glioblastoma stem cells (GSCs), responsible for the dismal disease prognosis after conventional treatments, are driven by overactive signaling pathways, such as PI3K/ AKT/mTOR and RAS/RAF/MAPK. The objective of our study was to target in vitro-GSCs by combining metformin (Met) as a mTOR inhibitor, with sorafenib (Soraf) as a RAF inhibitor.
METHODS: GSCs cultured under basal conditions were treated with Met, temozolomide (TMZ), Soraf, Met+TMZ and Met+Soraf; as untreated arm served as control. At 4 hrs of drug exposure, we measured the level of reactive oxygen species (ROS) by 2',7'-dichlorofluorescein diacetate (DCFDA) assay, apoptosis by prodium iodide (PI)-V Annexin staining and efflux pump activity by using the fluorescent dye rhodamine 123. At 24 hrs, we measured cell proliferation by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assay, apoptosis and malondialdehyde (MDA) levels. MTT results were compared with corresponding measurements on cultures of non-stem glioblastoma cells and osteoblasts.
RESULTS: Met+Soraf exerted the highest antiproliferative effects in GSCs and non-stem glioblastoma cells (p<0.001). Both Met and Soraf monotherapy exhibited a selective cytotoxic effect on GSCs (p<0.001), while no effect was detected on non-stem glioblastoma cells (p>0.05). Soraf, but not Met, impacted the proliferation of normal cells. Soraf displayed synergism with Met in producing high levels of ROS, decreasing efflux pump activity and generating the highest apoptotic rates when compared to either drug alone (p<0.001).
CONCLUSION: GSCs were highly sensitive to the combination of Met and Soraf which reduced cell proliferation, increased oxidative stress, inhibited efflux pump activity and ultimately killed GSCs. We strongly believe that these results warrant further in vivo exploration.

Mazur PK, Reynoird N, Khatri P, et al.
SMYD3 links lysine methylation of MAP3K2 to Ras-driven cancer.
Nature. 2014; 510(7504):283-7 [PubMed] Article available free on PMC after 01/10/2015 Related Publications
Deregulation of lysine methylation signalling has emerged as a common aetiological factor in cancer pathogenesis, with inhibitors of several histone lysine methyltransferases (KMTs) being developed as chemotherapeutics. The largely cytoplasmic KMT SMYD3 (SET and MYND domain containing protein 3) is overexpressed in numerous human tumours. However, the molecular mechanism by which SMYD3 regulates cancer pathways and its relationship to tumorigenesis in vivo are largely unknown. Here we show that methylation of MAP3K2 by SMYD3 increases MAP kinase signalling and promotes the formation of Ras-driven carcinomas. Using mouse models for pancreatic ductal adenocarcinoma and lung adenocarcinoma, we found that abrogating SMYD3 catalytic activity inhibits tumour development in response to oncogenic Ras. We used protein array technology to identify the MAP3K2 kinase as a target of SMYD3. In cancer cell lines, SMYD3-mediated methylation of MAP3K2 at lysine 260 potentiates activation of the Ras/Raf/MEK/ERK signalling module and SMYD3 depletion synergizes with a MEK inhibitor to block Ras-driven tumorigenesis. Finally, the PP2A phosphatase complex, a key negative regulator of the MAP kinase pathway, binds to MAP3K2 and this interaction is blocked by methylation. Together, our results elucidate a new role for lysine methylation in integrating cytoplasmic kinase-signalling cascades and establish a pivotal role for SMYD3 in the regulation of oncogenic Ras signalling.

Nguyen TV, Sleiman M, Moriarty T, et al.
Sorafenib resistance and JNK signaling in carcinoma during extracellular matrix stiffening.
Biomaterials. 2014; 35(22):5749-59 [PubMed] Related Publications
Tumor progression is coincident with mechanochemical changes in the extracellular matrix (ECM). We hypothesized that tumor stroma stiffening, alongside a shift in the ECM composition from a basement membrane-like microenvironment toward a dense network of collagen-rich fibers during tumorigenesis, confers resistance to otherwise powerful chemotherapeutics. To test this hypothesis, we created a high-throughput drug screening platform based on our poly(ethylene glycol)-phosphorylcholine (PEG-PC) hydrogel system, and customized it to capture the stiffness and integrin-binding profile of in vivo tumors. We report that the efficacy of a Raf kinase inhibitor, sorafenib, is reduced on stiff, collagen-rich microenvironments, independent of ROCK activity. Instead, sustained activation of JNK mediated this resistance, and combining a JNK inhibitor with sorafenib eliminated stiffness-mediated resistance in triple negative breast cancer cells. Surprisingly, neither ERK nor p38 appears to mediate sorafenib resistance, and instead, either ERK or p38 inhibition rescued sorafenib resistance during JNK inhibition, suggesting negative crosstalk between these signaling pathways on stiff, collagen-rich environments. Overall, we discovered that β1 integrin and its downstream effector JNK mediate sorafenib resistance during tumor stiffening. These results also highlight the need for more advanced cell culture platforms, such as our high-throughput PEG-PC system, with which to screen chemotherapeutics.

Kanazawa T, Morisaki K, Suzuki S, Takashima Y
Prolongation of life in rats with malignant glioma by intranasal siRNA/drug codelivery to the brain with cell-penetrating peptide-modified micelles.
Mol Pharm. 2014; 11(5):1471-8 [PubMed] Related Publications
New therapeutic strategies are required to develop candidate drugs and ensure efficient delivery of these drugs to the brain and the central nervous system (CNS). Small interfering RNA (siRNA)-based therapies have been investigated as potential novel approaches for the treatment of brain disorders. Previously, we showed that Tat, a cell-penetrating peptide derived from HIV-Tat, and the modified block copolymers (MPEG-PCL-Tat) can form stable complexes with siRNA or can be loaded with an anticancer drug and efficiently deliver the drugs to the brain tissue via intranasal delivery. In this study, to develop a novel, efficient, and safe therapeutic strategy for managing brain disorders, we used MPEG-PCL-Tat micelles with a nose-to-brain delivery system to investigate its therapeutic effects on a rat model of malignant glioma using siRNA with a Raf-1 (siRaf-1)/camptothecin (CPT) codelivery system. MPEG-PCL-Tat and CPT-loaded MPEG-PCL-Tat can form a stable complex with siRNA with a particle size from 60 to 200 nm and a positive charge at N/P ratios up to 5. Additionally, MPEG-PCL-Tat/siRaf-1 and CPT-loaded MPEG-PCL-Tat/siRaf-1 have fostered cell death in rat glioma cells after the high cellular uptake of siRaf-1/drug by the MPEG-PCL-Tat carrier. Furthermore, compared to the unloaded MPEG-PCL-Tat/siRaf-1 complex, a CPT-loaded MPEG-PCL-Tat/siRaf-1 complex achieved the high therapeutic effect because of the additive effects of CPT and siRaf-1. These results indicate that drug/siRNA codelivery using MPEG-PCL-Tat nanomicelles with nose-to-brain delivery is an excellent therapeutic approach for brain and CNS diseases.

Shilo A, Ben Hur V, Denichenko P, et al.
Splicing factor hnRNP A2 activates the Ras-MAPK-ERK pathway by controlling A-Raf splicing in hepatocellular carcinoma development.
RNA. 2014; 20(4):505-15 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
In recent years, it has become clear that splicing factors play a direct role in cancer development. We showed previously that splicing factors SRSF1, SRSF6, and hnRNP A2/B1 are up-regulated in several cancers and can act as oncogenes when up-regulated. Here we examined the role of splicing factors hnRNP A1/A1b and hnRNP A2/B1 in hepatocellular carcinoma (HCC). We show that the splicing factors hnRNP A1 and hnRNP A2 are up-regulated in HCC tumors derived from inflammation-induced liver cancer mouse model. Overexpression of hnRNP A1 or hnRNP A2, but not the splicing isoform hnRNP B1, induced tumor formation of immortalized liver progenitor cells, while knockdown of these proteins inhibited anchorage-independent growth and tumor growth of human liver cancer cell lines. In addition, we found that cells overexpressing hnRNP A2 showed constitutive activation of the Ras-MAPK-ERK pathway. In contrast, knockdown of hnRNP A2 inhibited the Ras-MAPK-ERK pathway and prevented ERK1/2 activation by EGF. Moreover, we found that hnRNP A2 regulates the splicing of A-Raf, reducing the production of a short dominant-negative isoform of A-Raf and elevating the full-length A-Raf transcript. Taken together, our data suggest that hnRNP A2 up-regulation in HCC induces an alternative splicing switch that down-regulates a dominant-negative isoform of A-Raf, leading to activation of the Raf-MEK-ERK pathway and cellular transformation.

Imielinski M, Greulich H, Kaplan B, et al.
Oncogenic and sorafenib-sensitive ARAF mutations in lung adenocarcinoma.
J Clin Invest. 2014; 124(4):1582-6 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
Targeted cancer therapies often induce "outlier" responses in molecularly defined patient subsets. One patient with advanced-stage lung adenocarcinoma, who was treated with oral sorafenib, demonstrated a near-complete clinical and radiographic remission for 5 years. Whole-genome sequencing and RNA sequencing of primary tumor and normal samples from this patient identified a somatic mutation, ARAF S214C, present in the cancer genome and expressed at high levels. Additional mutations affecting this residue of ARAF and a nearby residue in the related kinase RAF1 were demonstrated across 1% of an independent cohort of lung adenocarcinoma cases. The ARAF mutations were shown to transform immortalized human airway epithelial cells in a sorafenib-sensitive manner. These results suggest that mutant ARAF is an oncogenic driver in lung adenocarcinoma and an indicator of sorafenib response.

Okosun J, Bödör C, Wang J, et al.
Integrated genomic analysis identifies recurrent mutations and evolution patterns driving the initiation and progression of follicular lymphoma.
Nat Genet. 2014; 46(2):176-81 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
Follicular lymphoma is an incurable malignancy, with transformation to an aggressive subtype representing a critical event during disease progression. Here we performed whole-genome or whole-exome sequencing on 10 follicular lymphoma-transformed follicular lymphoma pairs followed by deep sequencing of 28 genes in an extension cohort, and we report the key events and evolutionary processes governing tumor initiation and transformation. Tumor evolution occurred through either a 'rich' or 'sparse' ancestral common progenitor clone (CPC). We identified recurrent mutations in linker histone, JAK-STAT signaling, NF-κB signaling and B cell developmental genes. Longitudinal analyses identified early driver mutations in chromatin regulator genes (CREBBP, EZH2 and KMT2D (MLL2)), whereas mutations in EBF1 and regulators of NF-κB signaling (MYD88 and TNFAIP3) were gained at transformation. Collectively, this study provides new insights into the genetic basis of follicular lymphoma and the clonal dynamics of transformation and suggests that personalizing therapies to target key genetic alterations in the CPC represents an attractive therapeutic strategy.

Bödör C, Grossmann V, Popov N, et al.
EZH2 mutations are frequent and represent an early event in follicular lymphoma.
Blood. 2013; 122(18):3165-8 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
Gain of function mutations in the H3K27 methyltransferase EZH2 represent a promising therapeutic target in germinal center lymphomas. In this study, we assessed the frequency and distribution of EZH2 mutations in a large cohort of patients with follicular lymphoma (FL) (n = 366) and performed a longitudinal analysis of mutation during the disease progression from FL to transformed FL (tFL) (n = 33). Mutations were detected at 3 recurrent mutation hot spots (Y646, A682, and A692) in 27% of FL cases with variant allele frequencies (VAF) ranging from 2% to 61%. By comparing VAF of EZH2 with other mutation targets (CREBBP, MLL2, TNFRSF14, and MEF2B), we were able to distinguish patients harboring clonal EZH2 mutation from rarer cases with subclonal mutations. Overall, the high incidence of EZH2 mutations in FL and their stability during disease progression makes FL an appropriate disease to evaluate EZH2 targeted therapy.

Bronte F, Bronte G, Cusenza S, et al.
Targeted therapies in hepatocellular carcinoma.
Curr Med Chem. 2014; 21(8):966-74 [PubMed] Related Publications
The onset of hepatocellular carcinoma (HCC) is related to the development of non-neoplastic liver disease, such as viral infections and cirrhosis. Even though patients with chronic liver diseases undergo clinical surveillance for early diagnosis of HCC, this cancer is often diagnosed in advanced stage. In this case locoregional treatment is not possible and systemic therapies are the best way to control it. Until now sorafenib, a Raf and multi-kinase inhibitor has been the best, choice to treat HCC systemically. It showed a survival benefit in multicenter phase III trials. However the proper patient setting to treat is not well defined, since the results in Child-Pugh B patients are conflicting. To date various new target drugs are under developed and other biological treatments normally indicated in other malignancies are under investigation also for HCC. These strategies aim to target the different biological pathways implicated in HCC development and progression. The target drugs studied in HCC include anti-VEGF and anti-EGFR monoclonal antibodies, tyrosine kinase inhibitors and mTOR inhibitors. The most important challenge is represented by the best integration of these drugs with standard treatments to achieve improvement in overall survival and quality of life.

Molzan M, Kasper S, Röglin L, et al.
Stabilization of physical RAF/14-3-3 interaction by cotylenin A as treatment strategy for RAS mutant cancers.
ACS Chem Biol. 2013; 8(9):1869-75 [PubMed] Related Publications
One-third of all human cancers harbor somatic RAS mutations. This leads to aberrant activation of downstream signaling pathways involving the RAF kinases. Current ATP-competitive RAF inhibitors are active in cancers with somatic RAF mutations, such as BRAF(V600) mutant melanomas. However, they paradoxically promote the growth of RAS mutant tumors, partly due to the complex interplay between different homo- and heterodimers of A-RAF, B-RAF, and C-RAF. Based on pathway analysis and structure-guided compound identification, we describe the natural product cotylenin-A (CN-A) as stabilizer of the physical interaction of C-RAF with 14-3-3 proteins. CN-A binds to inhibitory 14-3-3 interaction sites of C-RAF, pSer233, and pSer259, but not to the activating interaction site, pSer621. While CN-A alone is inactive in RAS mutant cancer models, combined treatment with CN-A and an anti-EGFR antibody synergistically suppresses tumor growth in vitro and in vivo. This defines a novel pharmacologic strategy for treatment of RAS mutant cancers.

Araf S, Montoto S
The use of interim (18)F-fluorodeoxyglucose PET to guide therapy in lymphoma.
Future Oncol. 2013; 9(6):807-15 [PubMed] Related Publications
Over the past decade (18)F-fluorodeoxyglucose (FDG)-PET combined with computed tomography has gained a central role in the management of patients with lymphoma. The use of FDG-PET for staging and assessing treatment response in Hodgkin's and 'aggressive' non-Hodgkin's lymphoma is now well established, and the prognostic impact of the response to treatment assessed by FDG-PET is being increasingly recognized. Despite the widespread utilization of FDG-PET in clinical practice, key questions remain on its optimal use in certain contexts. One such area that is generating intense interest is the role of interim FDG-PET (typically performed after two to four cycles of chemotherapy) to guide treatment strategies. The author's will review the current available evidence in this area, highlighting questions in need of further study.

Hong SK, Jeong JH, Chan AM, Park JI
AKT upregulates B-Raf Ser445 phosphorylation and ERK1/2 activation in prostate cancer cells in response to androgen depletion.
Exp Cell Res. 2013; 319(12):1732-43 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
Upregulated ERK1/2 activity is often correlated with AKT activation during prostate cancer (PCa) progression, yet their functional relation needs elucidation. Using androgen-deprived LNCaP cells, in which ERK1/2 activation occurs in strong correlation with AKT activation, we found that AKT-mediated B-Raf regulation is necessary for ERK1/2 activation. Specifically, in response to androgen deprivation, AKT upregulated B-Raf phosphorylation at Ser445 without affecting A-Raf or C-Raf-1. This effect of AKT was abolished by Arg25 to Ala mutation or truncating (∆4-129) the pleckstrin homology domain of AKT, indicating that the canonical AKT regulation is important for this signaling. Intriguingly, although a constitutively active AKT containing N-terminal myristoylation signal could sufficiently upregulate B-Raf phosphorylation at Ser445 in LNCaP cells, subsequent MEK/ERK activation still required hormone deprivation. In contrast, AKT activity was sufficient to induce not only B-Raf phosphorylation but also MEK/ERK activation in the hormone refractory LNCaP variant, C4-2. These data indicate that androgen depletion may induce MEK/ERK activation through a synergy between AKT-dependent and -independent mechanisms and that the latter may become deregulated in association with castration resistance. In support, consistent AKT-mediated B-Raf regulation was also detected in a panel of PCa lines derived from the cPten(-/-)L mice before and after castration. Our results also demonstrate that AKT regulates androgen receptor levels partly via the Raf/MEK/ERK pathway. This study reveals a novel crosstalk between ERK1/2 and AKT in PCa cells.

Yang Z, Xu J, Fu Q, et al.
Antitumor activity of a polysaccharide from Pleurotus eryngii on mice bearing renal cancer.
Carbohydr Polym. 2013; 95(2):615-20 [PubMed] Related Publications
One water-soluble polysaccharide (PEPw), with an average molecular weight of 2.5×10(4)Da, was isolated from the fruiting bodies of Pleurotus eryngii and subjected to composition analysis and evaluated for the antitumor and immunomodulatory activity. PEPw was composed of arabinose, mannose and galactose in a molar ratio of 1.2:2.3:6.2 and had a backbone mainly consisting of 1,6-linked-Galp, 1,2,6-linked-Galp and 1,4-linked-Manp residues, which was occasionally terminated with terminal-Araf attached to O-2 of 1,2,6-linked-Galp residue. The animal experiment results showed that PEPw significantly increased relative thymus and spleen indices, promoted the spleen lymphocytes proliferation induced by ConA or LPS, elevated the activities of NK cell and CTL in spleen, and increased the serum concentration of TNF-α and IL-2 in Renca tumor-bearing mice. As a result, the tumor growth was significantly inhibited by PEPw treatment at the doses of 50, 100 and 200mg/kg in a dose-dependent manner. These data indicated that the anti-tumor activity of PEPw may be related to the activation of the immune response in tumor-bearing mice.

Turajlic S, Ali Z, Yousaf N, Larkin J
Phase I/II RAF kinase inhibitors in cancer therapy.
Expert Opin Investig Drugs. 2013; 22(6):739-49 [PubMed] Related Publications
INTRODUCTION: Aberrant activation of RAF signalling is a frequent finding in human cancers. BRAF is the only RAF family member that is commonly mutated, whilst CRAF and ARAF play important roles in the signal transduction from mutant RAS. BRAF-specific inhibitors have been more effective in the treatment of BRAF-mutant melanoma than BRAF-mutant thyroid and colorectal cancers.
AREAS COVERED: The review summarises the experience with RAF kinase inhibitors, including efficacy, modes of acquired resistance, and the mechanism behind the progression of pre-malignant RAS-mutant lesions observed with RAF kinase inhibitors. The authors review all the completed and ongoing Phase I or II clinical trials of RAF kinase inhibitors and discuss in detail the rationale behind the combinatorial approaches.
EXPERT OPINION: The success of RAF kinase inhibitors has demonstrated the necessity of genotype-driven treatment selection for cancer patients. The spectrum of responses in different tumour types is explained by feedback events that are determined by cell lineage. Dissection of these events and the mechanisms of acquired resistance will determine the appropriate combination therapies. Ongoing characterisation of RAS-MAPK regulation in malignant cells may aid the development of novel agents that have greater potency for the inhibition of activated RAF kinase, and lesser propensity for promotion of RAS-mutant tumours.

Haarberg HE, Paraiso KH, Wood E, et al.
Inhibition of Wee1, AKT, and CDK4 underlies the efficacy of the HSP90 inhibitor XL888 in an in vivo model of NRAS-mutant melanoma.
Mol Cancer Ther. 2013; 12(6):901-12 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
The HSP90 inhibitor XL888 is effective at reversing BRAF inhibitor resistance in melanoma, including that mediated through acquired NRAS mutations. The present study has investigated the mechanism of action of XL888 in NRAS-mutant melanoma. Treatment of NRAS-mutant melanoma cell lines with XL888 led to an inhibition of growth, G2-M phase cell-cycle arrest, and the inhibition of cell survival in three-dimensional spheroid and colony formation assays. In vitro, HSP90 inhibition led to the degradation of ARAF, CRAF, Wee1, Chk1, and cdc2 and was associated with decreased mitogen-activated protein kinase (MAPK), AKT, mTOR, and c-jun NH2 kinase (JNK) signaling. Apoptosis induction was associated with increased BIM expression and a decrease in the expression of the prosurvival protein Mcl-1. The critical role of increased BIM and decreased Mcl-1 expression in the survival of NRAS-mutant melanoma cell lines was shown through siRNA knockdown and overexpression studies. In an animal xenograft model of NRAS-mutant melanoma, XL888 treatment led to reduced tumor growth and apoptosis induction. Important differences in the pattern of client degradation were noted between the in vivo and in vitro studies. In vivo, XL888 treatment led to degradation of CDK4 and Wee1 and the inhibition of AKT/S6 signaling with little or no effect observed upon ARAF, CRAF, or MAPK. Blockade of Wee1, using either siRNA knockdown or the inhibitor MK1775, was associated with significant levels of growth inhibition and apoptosis induction. Together, these studies have identified Wee1 as a key target of XL888, suggesting novel therapeutic strategies for NRAS-mutant melanoma.

Yun SM, Jung KH, Lee H, et al.
Synergistic anticancer activity of HS-173, a novel PI3K inhibitor in combination with Sorafenib against pancreatic cancer cells.
Cancer Lett. 2013; 331(2):250-61 [PubMed] Related Publications
The RAF/MEK/ERK and PI3K/AKT pathways are highly implicated in the development of pancreatic cancer. The principal objective of this study was to assess the synergic effect between Sorafenib (a RAF inhibitor) and HS-173 (a novel PI3K inhibitor) to gain insight into novel therapeutic strategies for treating pancreatic cancer. We first investigated the cytotoxic effect of co-treatment with Sorafenib and HS-173 using the Calcusyn program. Combined treatment of the two drugs synergistically inhibited the viability of Panc-1 cells (combination index<1). Concomitantly, the co-treatment induced G2/M arrest and increased apoptosis with the loss of mitochondrial membrane potential. Apoptosis resulting from the co-treatment was accompanied by increased levels of cleaved caspase-3 and PARP as well as greater numbers of TUNEL-positive apoptotic cells compared to treatment with either drug alone. Furthermore, combined treatment with these drugs decreased the expression of HIF-1α and VEGF which play an important role in angiogenesis. This anti-angiogenic effect was confirmed by the suppressed tube formation of VEGF-induced human umbilical vein endothelial cells and inhibition of blood vessel formation in a Matrigel plug assay in mice. Taken together, our study demonstrates that combined treatment with Sorafenib and HS-173 has a synergistic anti-cancer effect on pancreatic cancer cells, indicating that simultaneously targeting the RAF/MEK and PI3K/AKT pathways can induce a synergistic inhibitory effect on pancreatic cancers in which both pathways are activated. Based on the observations from our study, we suggest that the combined administration of these two drugs may be considered to be a new therapeutic regimen for treating pancreatic cancer.

Kim HY, Jung SK, Byun S, et al.
Raf and PI3K are the molecular targets for the anti-metastatic effect of luteolin.
Phytother Res. 2013; 27(10):1481-8 [PubMed] Related Publications
Metastases are the primary cause of human cancer deaths. Luteolin, a naturally occurring phytochemical, has chemopreventive and/or anticancer properties in several cancer cell lines. However, anti-metastatic effects of luteolin in vivo and the underlying molecular mechanisms and target(s) remain unknown. Luteolin suppresses matrix metalloproteinase (MMP)-2 and -9 activities and invasion in murine colorectal cancer CT-26 cells. Western blot and kinase assay data revealed that luteolin inhibited Raf and phosphatidylinositol 3-kinase (PI3K) activities and subsequently attenuated phosphorylation of MEK and Akt. A pull-down assay indicated that luteolin non-competitively bound with ATP to suppress Raf activity and competitively bound with ATP to inhibit PI3K activity. GW5074, a Raf inhibitor, and LY294002, a PI3K inhibitor, inhibited MMP-2 and -9 activities and invasion in CT-26 cells. An in vivo mouse study showed that oral administration (10 or 50 mg/kg) of luteolin significantly inhibited tumor nodules and tumor volume of lung metastasis induced by intravenous injection of CT-26 cells. Luteolin also inhibited MMP-9 expression and activity in CT-26-induced mouse lung tissue. These results suggest that luteolin may have considerable potential for development as an anti-metastatic agent.

Craig DW, O'Shaughnessy JA, Kiefer JA, et al.
Genome and transcriptome sequencing in prospective metastatic triple-negative breast cancer uncovers therapeutic vulnerabilities.
Mol Cancer Ther. 2013; 12(1):104-16 [PubMed] Related Publications
Triple-negative breast cancer (TNBC) is characterized by the absence of expression of estrogen receptor, progesterone receptor, and HER-2. Thirty percent of patients recur after first-line treatment, and metastatic TNBC (mTNBC) has a poor prognosis with median survival of one year. Here, we present initial analyses of whole genome and transcriptome sequencing data from 14 prospective mTNBC. We have cataloged the collection of somatic genomic alterations in these advanced tumors, particularly those that may inform targeted therapies. Genes mutated in multiple tumors included TP53, LRP1B, HERC1, CDH5, RB1, and NF1. Notable genes involved in focal structural events were CTNNA1, PTEN, FBXW7, BRCA2, WT1, FGFR1, KRAS, HRAS, ARAF, BRAF, and PGCP. Homozygous deletion of CTNNA1 was detected in 2 of 6 African Americans. RNA sequencing revealed consistent overexpression of the FOXM1 gene when tumor gene expression was compared with nonmalignant breast samples. Using an outlier analysis of gene expression comparing one cancer with all the others, we detected expression patterns unique to each patient's tumor. Integrative DNA/RNA analysis provided evidence for deregulation of mutated genes, including the monoallelic expression of TP53 mutations. Finally, molecular alterations in several cancers supported targeted therapeutic intervention on clinical trials with known inhibitors, particularly for alterations in the RAS/RAF/MEK/ERK and PI3K/AKT/mTOR pathways. In conclusion, whole genome and transcriptome profiling of mTNBC have provided insights into somatic events occurring in this difficult to treat cancer. These genomic data have guided patients to investigational treatment trials and provide hypotheses for future trials in this irremediable cancer.

Lito P, Pratilas CA, Joseph EW, et al.
Relief of profound feedback inhibition of mitogenic signaling by RAF inhibitors attenuates their activity in BRAFV600E melanomas.
Cancer Cell. 2012; 22(5):668-82 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
BRAF(V600E) drives tumors by dysregulating ERK signaling. In these tumors, we show that high levels of ERK-dependent negative feedback potently suppress ligand-dependent mitogenic signaling and Ras function. BRAF(V600E) activation is Ras independent and it signals as a RAF-inhibitor-sensitive monomer. RAF inhibitors potently inhibit RAF monomers and ERK signaling, causing relief of ERK-dependent feedback, reactivation of ligand-dependent signal transduction, increased Ras-GTP, and generation of RAF-inhibitor-resistant RAF dimers. This results in a rebound in ERK activity and culminates in a new steady state, wherein ERK signaling is elevated compared to its initial nadir after RAF inhibition. In this state, ERK signaling is RAF inhibitor resistant, and MEK inhibitor sensitive, and combined inhibition results in enhancement of ERK pathway inhibition and antitumor activity.

Wakelee HA, Lee JW, Hanna NH, et al.
A double-blind randomized discontinuation phase-II study of sorafenib (BAY 43-9006) in previously treated non-small-cell lung cancer patients: eastern cooperative oncology group study E2501.
J Thorac Oncol. 2012; 7(10):1574-82 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
INTRODUCTION: Sorafenib is a raf kinase and angiogenesis inhibitor with activity in multiple cancers. This phase-II study in heavily pretreated non-small-cell lung cancer (NSCLC) patients (≥ 2 prior therapies) used a randomized discontinuation design.
METHODS: Patients received 400 mg of sorafenib orally twice daily for two cycles (2 months) (step 1). Responding patients on step 1 continued on sorafenib; progressing patients went off study, and patients with stable disease were randomized to placebo or sorafenib (step 2), with crossover from placebo allowed upon progression. The primary endpoint of this study was the proportion of patients having stable or responding disease 2 months after randomization.
RESULTS: There were 299 patients evaluated for step 1; of these, 81 eligible patients were randomized on step 2 and received sorafenib (n = 50) or placebo (n = 31). The 2-month disease control rates after randomization were 54% and 23% for patients initially receiving sorafenib and placebo, respectively, p = 0.005. The hazard ratio for progression on step 2 was 0.51 (95% [confidence interval] CI 0.30, 0.87, p = 0.014) favoring sorafenib. A trend in favor of overall survival with sorafenib was also observed (13.7 versus 9.0 months from time of randomization), hazard ratio 0.67 (95% CI 0.40-1.11), p = 0.117. A dispensing error occurred, which resulted in the unblinding of some patients, but not before completion of the 8-week initial step 2 therapy. Toxicities were manageable and as expected.
CONCLUSIONS: The results of this randomized discontinuation trial suggest that sorafenib has single-agent activity in a heavily pretreated, enriched patient population with advanced NSCLC. These results support further investigation with sorafenib as a single agent in larger, randomized studies in NSCLC.

Somnay Y, Chen H, Kunnimalaiyaan M
Synergistic effect of pasireotide and teriflunomide in carcinoids in vitro.
Neuroendocrinology. 2013; 97(2):183-92 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
BACKGROUND/AIM: Somatostatin (SST) analogs are mainstay for controlling tumor proliferation and hormone secretion in carcinoid patients. Recent data suggest that extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation may potentiate the anti-tumor effects of SST analogs in carcinoids. Additionally, ERK1/2 phosphorylating agents have been shown to suppress biomarker expression in carcinoids. Thus, Raf-1/MEK/ERK1/2 pathway activating drugs may be synergistic with SST analogs such as pasireotide (SOM230), which may be more effective than others in its class given its elevated receptor affinity and broader binding spectrum. Here, we investigate the effects of SOM230 in combination with teriflunomide (TFN), a Raf-1 activator, in a human carcinoid cell line.
METHODS: Human pancreatic carcinoid cells (BON) were incubated in TFN, SOM230 or a combination. Cell proliferation was measured using a rapid colorimetric assay. Western analysis was performed to analyze expression levels of achaete-scute complex-like 1 (ASCL1), chromogranin A (CgA), phosphorylated and total ERK1/2, and markers for apoptosis.
RESULTS: Combination treatment with SOM230 and TFN reduced cell growth beyond the additive effect of either drug alone. Combination indices (CI) fell below 1, thus quantifiably verifying synergy between both drugs as per the Chou-Talalay CI scale. Combined treatment also reduced ASCL1 and CgA expression beyond the additive effect of either drug alone. Furthermore, it increased levels of phosphorylated ERK1/2, cleaved poly(ADP)-ribose polymerase and caspase-3, and reduced levels of anti-apoptotic biomarkers. Elevated phosphorylated ERK1/2 expression following combination therapy may underlie the synergistic interaction between the two drugs.
CONCLUSION: Since efficacy is achieved at lower doses, combination therapy may palliate symptoms at low toxicity levels. Because each drug has already been evaluated in clinical trials, combinatorial drug trials are warranted.

Rebocho AP, Marais R
ARAF acts as a scaffold to stabilize BRAF:CRAF heterodimers.
Oncogene. 2013; 32(26):3207-12 [PubMed] Related Publications
The RAF proteins are cytosolic protein kinases that regulate cell responses to extracellular signals. There are three RAF proteins in cells, ARAF, BRAF and CRAF, and recent studies have shown that the formation of complexes by these different isoforms has an important role in their activation, particularly in response to RAF inhibitors. Here, we investigated the role of ARAF in cancer cell signaling and examined the role of ARAF in mediating paradoxical activation of the MAPK pathway in cells treated with RAF inhibitors. We show that two mutations that occur in ARAF in cancer inactivate the kinase. We also show that ARAF is not functionally redundant with CRAF and cannot substitute for CRAF downstream of RAS. We further show that ARAF binds to and is activated by BRAF and that ARAF also forms complexes with CRAF. Critically, ARAF seems to stabilize BRAF:CRAF complexes in cells treated with RAF inhibitors and thereby regulate cell signaling in a subtle manner to ensure signaling efficiency.

Subramanian RR, Yamakawa A
Combination therapy targeting Raf-1 and MEK causes apoptosis of HCT116 colon cancer cells.
Int J Oncol. 2012; 41(5):1855-62 [PubMed] Related Publications
Members of the Ras protooncogene family are mutated in approximately 75% of colon cancers. The Raf kinases (Raf-1, b-Raf and a-Raf) directly interact with Ras and serve as mediators of mitogenic signals. Expression of the constitutively active alleles of Raf or Ras gene families results in oncogenesis in a number of model systems. Previous studies emphasized the importance of Raf-1 and b-Raf in preventing apoptosis in addition to their roles in cell growth. In the present study, we examined whether inhibition of the Raf-1 or b-Raf kinase decreases cell growth and increases apoptosis in colon cancer cells. c-Raf and b-Raf were depleted in colon cancer cell lines, such as HCT116, HT29 and Colo205, containing Ras or b-Raf mutations by RNA interference (RNAi). The results showed that colon cancer cells with activating Ras mutations undergo apoptosis following Raf-1 inhibition, as determined by cell cycle analysis and the release of cytochrome c. Moreover, in b-Raf mutant colon cancers, the inhibition of b-Raf as compared to Raf-1 is crucial for cancer cell death. There is increasing evidence for both MEK-independent Raf signaling and Raf-independent MEK signaling. Thus, we investigated whether targeting multiple points of the mitogen-activated protein kinase (MAPK) pathway with a MEK inhibitor and Raf RNAi increases cancer cell death. The results showed that combination therapy, inhibiting Raf and MEK kinases simultaneously, increased apoptosis in colon cancer cells. Taken together, our data demonstrate that combination therapy targeting the MAPK pathway at two distinct points, Raf kinase and MEK, has greater efficacy in increasing cancer cell death and is likely to improve therapeutic outcomes for patients.

Kang Z, Xu F, Zhang QA, et al.
Oncogenic mutations in extramammary Paget's disease and their clinical relevance.
Int J Cancer. 2013; 132(4):824-31 [PubMed] Related Publications
Extramammary Paget's disease (EMPD) is a rare cutaneous malignant neoplasm. The genetic alterations underlying its pathogenesis have less been described. Therefore, we analyzed the possible mutations in the KRAS, HRAS, NRAS, BRAF, ARAF, RAF1, PIK3CA, AKT1, CTNNB1 and APC genes as well as methylation and expression of CDH1 in 144 EMPD cases and 42 matched normal skin tissues. A distinct mutation profile was identified in EMPDs with 27 (19%) cases mutant for RAS and RAF genes and 50 (35%) cases harboring oncogenic mutations in PIK3CA and AKT1. Moreover, a mutually exclusive pattern was observed in the genetic variants in these two signaling pathways. No mutation was detected in CTNNB1 and APC genes. High prevalence of low expression and hypermethylation of CDH1 gene was detected in 33 and 48% of the EMPD cases, respectively. Furthermore, PIK3CA and AKT1 mutations were significantly correlated with CDH1 hypermethylation which could explain why the majority of EMPD cases with mutant PIK3CA and AKT1 were invasive. Our study demonstrates that genetic variants associated with constitutive activation of RAS/RAF and PI3K/AKT pathways are involved in the pathogenesis of EMPD. This may represent novel therapeutic targets for this skin cancer.

Lau KS, Zhang T, Kendall KR, et al.
BAY61-3606 affects the viability of colon cancer cells in a genotype-directed manner.
PLoS One. 2012; 7(7):e41343 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
BACKGROUND: K-RAS mutation poses a particularly difficult problem for cancer therapy. Activating mutations in K-RAS are common in cancers of the lung, pancreas, and colon and are associated with poor response to therapy. As such, targeted therapies that abrogate K-RAS-induced oncogenicity would be of tremendous value.
METHODS: We searched for small molecule kinase inhibitors that preferentially affect the growth of colorectal cancer cells expressing mutant K-RAS. The mechanism of action of one inhibitor was explored using chemical and genetic approaches.
RESULTS: We identified BAY61-3606 as an inhibitor of proliferation in colorectal cancer cells expressing mutant forms of K-RAS, but not in isogenic cells expressing wild-type K-RAS. In addition to its anti-proliferative effects in mutant cells, BAY61-3606 exhibited a distinct biological property in wild-type cells in that it conferred sensitivity to inhibition of RAF. In this context, BAY61-3606 acted by inhibiting MAP4K2 (GCK), which normally activates NFκβ signaling in wild-type cells in response to inhibition of RAF. As a result of MAP4K2 inhibition, wild-type cells became sensitive to AZ-628, a RAF inhibitor, when also treated with BAY61-3606.
CONCLUSIONS: These studies indicate that BAY61-3606 exerts distinct biological activities in different genetic contexts.

Carr BI, Cavallini A, Lippolis C, et al.
Fluoro-Sorafenib (Regorafenib) effects on hepatoma cells: growth inhibition, quiescence, and recovery.
J Cell Physiol. 2013; 228(2):292-7 [PubMed] Related Publications
To evaluate the growth-inhibitory properties of the potent multi-kinase antagonist Regorafenib (Fluoro-Sorafenib), which was synthesized as a more potent Sorafenib, a Raf inhibitor and to determine whether similar mechanisms were involved, human hepatoma cell lines were grown in the presence or absence of Regorafanib and examined for growth inhibition. Western blots were performed for Raf targets, apoptosis, and autophagy. Regorafenib inhibited growth of human Hep3B, PLC/PRF/5, and HepG2 cells in a concentration- and time-dependent manner. Multiple signaling pathways were altered, including MAP kinases phospho-ERK and phospho-JNK and its target phospho-c-Jun. There was evidence for apoptosis by FACS, cleavage of caspases and increased Bax levels; as well as induction of autophagy, as judged by increased Beclin-1 and LC3 (II) levels. Prolonged drug exposure resulted in cell quiescence. Full growth recovery occurred after drug removal, unlike with doxorubicin chemotherapy. Regorafenib is a potent inhibitor of cell growth. Cells surviving Regorafenib treatment remain viable, but quiescent and capable of regrowth following drug removal. The reversibility of tumor cell growth suppression after drug removal may have clinical implications.

Spirli C, Morell CM, Locatelli L, et al.
Cyclic AMP/PKA-dependent paradoxical activation of Raf/MEK/ERK signaling in polycystin-2 defective mice treated with sorafenib.
Hepatology. 2012; 56(6):2363-74 [PubMed] Article available free on PMC after 01/04/2015 Related Publications
UNLABELLED: Mutations in polycystins are a cause of polycystic liver disease. In polycystin-2 (PC2)-defective mice, cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)-dependent activation of the Rat Sarcoma (Ras)/rapidly accelerated fibrosarcoma (Raf)/mitogen signal-regulated kinase-extracellular signal-regulated kinase (ERK) 1/2 pathway stimulates the growth of liver cysts. To test the hypothesis that sorafenib, a Raf inhibitor used for the treatment of liver and kidney cancers, inhibits liver cyst growth in PC2-defective mice, we treated PC2 (i.e., Pkd2(flox/-) :pCxCreER(TM) [Pkd2cKO]) mice with sorafenib-tosylate for 8 weeks (20-60 mg/kg/day). Sorafenib caused an unexpected increase in liver cyst area, cell proliferation (Ki67), and expression of phosphorylated ERK (pERK) compared with Pkd2cKO mice treated with vehicle. When given to epithelial cells isolated from liver cysts of Pkd2cKO mice (Pkd2cKO-cells), sorafenib progressively stimulated pERK1/2 and cell proliferation [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium and bromodeoxyuridine assay (MTS)] at doses between 0.001 and 1 μM; however, both pERK1/2 and cell proliferation significantly decreased at the dose of 10 μM. Raf kinase activity assay showed that whereas B-Raf is inhibited by sorafenib in both wild-type (WT) and Pkd2cKO cells, Raf-1 is inhibited in WT cells but is significantly stimulated in Pkd2cKO cells. In Pkd2cKO cells pretreated with the PKA inhibitor 14-22 amide, myristolated (1 μM) and in mice treated with octreotide in combination with sorafenib, the paradoxical activation of Raf/ERK1/2 was abolished, and cyst growth was inhibited.
CONCLUSION: In PC2-defective cells, sorafenib inhibits B-Raf but paradoxically activates Raf-1, resulting in increased ERK1/2 phosphorylation, cell proliferation, and cyst growth in vivo. These effects are consistent with the ability of Raf inhibitors to transactivate Raf-1 when a PKA-activated Ras promotes Raf-1/B-Raf heterodimerization, and are inhibited by interfering with cAMP/PKA signaling both in vitro and in vivo, as shown by the reduction of liver cysts in mice treated with combined octreotide and sorafenib.

Wang CM, Fleming KF, Hsu S
A case of vemurafenib-induced keratosis pilaris-like eruption.
Dermatol Online J. 2012; 18(4):7 [PubMed] Related Publications
Vemurafenib, a selective BRAF kinase inhibitor, is a new anti-cancer drug recently proven to improve survival in patients with metastatic melanoma harboring the BRAF V600E mutation. BRAF is one of three RAF kinases (ARAF, BRAF, CRAF) involved in the MAP kinase pathway. Mutations in BRAF are reported to be present in 40 to 70 percent of melanomas and in lower frequencies in various other malignancies. The BRAF V600E mutation is a specific valine to glutamic acid single substitution that constitutes 80 to 90 percent of reported BRAF mutations. Successful treatment of metastatic melanoma with vemurafenib is not without significant adverse effects. The most common toxic effects of this drug include rash, arthralgia, and fatigue. Less commonly, cases of follicular cystic lesions, keratoacanthoma, and squamous cell carcinoma have also been described. We report a case of a patient with metastatic melanoma treated with vemurafenib, who developed diffuse follicular hyperkeratosis resembling keratosis pilaris. To our knowledge, this is the first reported case of a keratosis pilaris-like side effect of vemurafenib.

Kim DH, Sim T
Novel small molecule Raf kinase inhibitors for targeted cancer therapeutics.
Arch Pharm Res. 2012; 35(4):605-15 [PubMed] Related Publications
Aberrant activation of Raf signaling pathway is frequently found in various human tumors, it has been considered as distinct and promising molecular target for cancer therapeutics. B-Raf is most attractive drug target out of three Raf isoforms (A-Raf, B-Raf and C-Raf) because it exhibits high kinase activity due to frequent mutations in human tumors. However, most recently, it has been reported that Raf isoforms show the cross-activation in the presence of specific B-Raf inhibitors, which brings about the paradoxical p-ERK activation as well as tumor promoting effect. According to these findings, it remains controversy whether pan-Raf kinase inhibitor is more valuable and promising rather than specific B-Raf inhibitor under certain conditions in terms of cancer therapeutics. In this short review, novel Raf kinase inhibitors undergoing clinical investigation are introduced. Moreover, the paradoxical p-ERK activation is discussed with specific B-Raf inhibitors, PLX4032/4720 compounds.

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