GAB2

Gene Summary

Gene:GAB2; GRB2 associated binding protein 2
Location:11q14.1
Summary:This gene is a member of the GRB2-associated binding protein (GAB) gene family. These proteins contain pleckstrin homology (PH) domain, and bind SHP2 tyrosine phosphatase and GRB2 adapter protein. They act as adapters for transmitting various signals in response to stimuli through cytokine and growth factor receptors, and T- and B-cell antigen receptors. The protein encoded by this gene is the principal activator of phosphatidylinositol-3 kinase in response to activation of the high affinity IgE receptor. Two alternatively spliced transcripts encoding different isoforms have been described for this gene. [provided by RefSeq, Nov 2009]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:GRB2-associated-binding protein 2
Source:NCBIAccessed: 09 March, 2017

Ontology:

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 (1992-2017)
Graph generated 10 March 2017 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.

  • Phosphorylation
  • Messenger RNA
  • Intracellular Signaling Peptides and Proteins
  • Fusion Proteins, bcr-abl
  • Single Nucleotide Polymorphism
  • Breast Cancer
  • Enzyme Activation
  • Pyrimidines
  • siRNA
  • Cancer Gene Expression Regulation
  • FISH
  • Biomarkers, Tumor
  • Cell Proliferation
  • Gene Expression Profiling
  • Western Blotting
  • Protein Tyrosine Phosphatase, Non-Receptor Type 11
  • Protein-Tyrosine Kinases
  • Colorectal Cancer
  • Signal Transduction
  • Oligonucleotide Array Sequence Analysis
  • Gene Expression
  • Phosphatidylinositol 3-Kinases
  • Signal Transducing Adaptor Proteins
  • Cell Movement
  • Neoplasm Invasiveness
  • GRB2 Adaptor Protein
  • fms-Like Tyrosine Kinase 3
  • Acute Myeloid Leukaemia
  • src Homology Domains
  • Cell Survival
  • Drug Resistance
  • Chronic Myelogenous Leukemia
  • Gene Amplification
  • Neoplastic Cell Transformation
  • Protein Kinase Inhibitors
  • Mutation
  • Chromosome 11
  • Phosphoproteins
  • Ovarian Cancer
  • Genomics
Tag cloud generated 09 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (5)

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: GAB2 (cancer-related)

Hu X, He B, Zhou L, et al.
Expression Pattern and Clinical Significance of Gab2 Protein in Hepatocellular Carcinoma.
Clin Lab. 2016; 62(6):1087-92 [PubMed] Related Publications
BACKGROUND: To investigate the expression pattern of Gab2 in hepatocellular carcinoma (HCC) and explore the correlation between Gab2 expression and clinicopathological features of HCC patients. The prognostic significance of Gab2 expression is evaluated to determine the possible role in the progression of HCC.
METHODS: Gab2 expression was detected by immunohistochemistry in 90 HCC samples and matched adjacent noncancerous liver tissues. The mRNA and protein of Gab2 in HCC and normal liver cell lines were examined by quantitative RT-PCR and western blot, respectively. The correlation between Gab2 expression of tumor tissues and clinicopathological parameters was analyzed by Chi-squared test or Fisher's exact test. The association between Gab2 expression and overall survival percentage after surgery was evaluated by Kaplan-Meier method.
RESULTS: Gab2 expression was elevated in HCC tissues compared with matched normal liver tissues (p < 0.001). Gab2 was upregulated in a subset of HCC cell lines. Among the clinical and pathological features, Gab2 expression was correlated to the histologic grade of HCC tissues (p < 0.05). Kaplan-Meier analysis of the cumulative survival rate after surgery indicated that no statistical difference existed between high-Gab2 and low-Gab2 expression group (p = 0.8297).
CONCLUSIONS: Gab2 may be involved in the onset and progression of HCC. Gab2 expression is unable to serve as an independent prognosis factor in HCC patients.

Tian LQ, Liu EQ, Zhu XD, et al.
MicroRNA-197 inhibits cell proliferation by targeting GAB2 in glioblastoma.
Mol Med Rep. 2016; 13(5):4279-88 [PubMed] Related Publications
Glioblastoma is the most common type of primary brain tumor in adults, and is usually fatal in a short duration. Acquiring a better understanding of the pathogenic mechanisms of glioblastoma is essential to the design of effective therapeutic strategies. Grb2-associated binding protein 2 (GAB2) is a member of the daughter of sevenless/Gab family of scaffolding adapters, and has been reported to be important in the development and progression of human cancer. Previously, it has been reported that GAB2 is expressed at high levels in glioma, and may serve as a useful prognostic marker for glioma and a novel therapeutic target for glioma invasion intervention. Elucidating why GAB2 is overexpressed in glioma, and investigating how to downregulate it will assist in further understanding the pathogenesis and progression of the disease, and to offer novel targets for therapy. The present study used in situ hybridization to detect microRNA (miR)‑197 expression levels and Targetscan to predict that the 3'-UTR of GAB2 was targeted by miR-197. Northern blotting and reverse transcription‑quantitative polymerase chain reaction were also conducted in the current study. miR-197 is downregulated in glioblastoma tissues, compared with adjacent normal tissues, however it involvement continues to be detected in the disease. The results of the present study demonstrated that miR‑197, as a tumor suppressor gene, inhibited proliferation by regulating GAB2 in glioblastoma cells. Furthermore, GAB2 was not only upregulated in glioma, but its expression levels were also associated with the grades of glioma severity. In addition, overexpression of GAB2 suppressed the expression of miR‑197 in glioblastoma cells. Therefore, restoration of miR‑197 and targeting GAB2 may be used, in conjunction with other therapies, to prevent the progression of glioblastoma.

Ding C, Luo J, Li L, et al.
Gab2 facilitates epithelial-to-mesenchymal transition via the MEK/ERK/MMP signaling in colorectal cancer.
J Exp Clin Cancer Res. 2016; 35:5 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Grb2-associated binder 2 (Gab2), a scaffolding adaptor protein, has recently been implicated in cancer progression. However, the role of Gab2 in the progression and metastasis of colorectal cancer (CRC) remains unclear.
METHODS: Gab2 expression was assessed in CRC patient specimens as well as in CRC cell lines. Recombinant lentivirus vector containing Gab2 gene and its small interfering RNAs were constructed and introduced into CRC cells. Cell migration and invasion ability were evaluated by transwell assays in vitro, and in vivo metastasis was performed on nude mice model. Moreover, the expression of Gab2 and epithelial-to-mesenchymal transition (EMT)-associated proteins (E-cadherin and vimentin) were assessed by western blot and qRT-PCR in CRC cells to evaluate the correlation between Gab2 and EMT. Finally, we evaluated the impact of Gab2 on the activation of its downstream signaling effectors, and furthermore the effects of these pathways on Gab2 induced-EMT were also detected.
RESULTS: We confirmed that increased Gab2 expression correlated with higher tumor node metastasis stage and highly invasive CRC cell lines. Ectopic expression of Gab2 promoted metastasis of CRC cells, whereas silencing of Gab2 resulted in inhibited metastasis both in vitro and in vivo. Overexpression of Gab2 in CRC cells induced EMT, whereas knockdown of Gab2 had the opposite effect. Furthermore, upregulation of Gab2 expression obviously stimulated the activation of extracellular signal-regulated kinase-1/2 (ERK1/2), and increased the expression of matrix metalloproteinase-7 (MMP7) and matrix metalloproteinase-9 (MMP9) in CRC cells. Conversely, downregulation of Gab2 expression significantly decreased the activation of ERK1/2, and inhibited MMP7 and MMP9 expression. U0126, an inhibitor of mitogen-activated protein kinase (MEK), can reverse the effects of Gab2 on EMT.
CONCLUSIONS: Our work highlights that Gab2 induces EMT through the MEK/ERK/MMP pathway, which in turn promotes intestinal tumor metastasis.

Wang WJ, Mou K, Wu XF, et al.
Grb2-associated binder 2 silencing impairs growth and migration of H1975 cells via modulation of PI3K-Akt signaling.
Int J Clin Exp Pathol. 2015; 8(9):10575-84 [PubMed] Free Access to Full Article Related Publications
Non-small cell lung cancer (NSCLC) is a leading cause of cancer-related death and often has a poor prognosis. Investigation of NSCLC cancer cell migration, invasion and development of strategies to block this process is essential to improve the disease prognosis. In this study, we tested our hypothesis that Grb2-associated binder 2 (Gab2) regulate NSCLC cancer cell H1975 malignant biological behaviors, and silencing Gab2 reduced H1975 cellular colony forming ability, migration and invasion. Moreover, silenced cells present defects in phosphatidylinositol 3-kinase (PI3K)-serine/threonine kinase (Akt) signaling, and reduced expression/activity of matrix metallopeptidase (MMP)-2/9. Furthermore, in Gab2 siRNA-transfected cells, we detected a decrease in signal transducer and activator of transcription 3 (STAT3) phosphorylation and nuclear translocation. In vivo, Gab2 siRNA cells inoculated subcutaneously in nude mice demonstrated decreased tumor growth and PI3K-Akt signaling inhibition. These results indicate that Gab2 is a key factor in H1975 tumor migration, invasion, suggesting that Gab2 can be a novel therapeutic target in NSCLC.

Luo LY, Hahn WC
Oncogenic Signaling Adaptor Proteins.
J Genet Genomics. 2015; 42(10):521-9 [PubMed] Free Access to Full Article Related Publications
Signal transduction pathways activated by receptor tyrosine kinases (RTK) play a critical role in many aspects of cell function. Adaptor proteins serve an important scaffolding function that facilitates key signaling transduction events downstream of RTKs. Recent work integrating both structural and functional genomic approaches has identified several adaptor proteins as new oncogenes. In this review, we focus on the discovery, structure and function, and therapeutic implication of three of these adaptor oncogenes, CRKL, GAB2, and FRS2. Each of the three genes is recurrently amplified in lung adenocarcinoma or ovarian cancer, and is essential to cancer cell lines that harbor such amplification. Overexpression of each gene is able to transform immortalized human cell lines in in vitro or in vivo models. These observations identify adaptor protein as a distinct class of oncogenes and potential therapeutic targets.

Yang L, Ma Y, Han W, et al.
Proteinase-activated receptor 2 promotes cancer cell migration through RNA methylation-mediated repression of miR-125b.
J Biol Chem. 2015; 290(44):26627-37 [PubMed] Free Access to Full Article Related Publications
Proteinase activated-receptor 2 (PAR2) participates in cancer metastasis promoted by serine proteinases. The current study aimed to test the molecular mechanism by which PAR2 promotes cancer cell migration. In different cancer cells, activation of PAR2 by activating peptide (PAR2-AP) dramatically increased cell migration, whereas knock down of PAR2 inhibited cellular motility. The PAR2 activation also repressed miR-125b expression while miR-125b mimic successfully blocked PAR2-induced cell migration. Moreover, Grb associated-binding protein 2 (Gab2) was identified as a novel target gene of miR-125b and it mediated PAR2-induced cell migration. The correlation of PAR2 with miR-125b and Gab2 was further supported by the findings obtained from human colorectal carcinoma specimens. Remarkably, knock down of NOP2/Sun domain family, member 2 (NSun2), a RNA methyltransferase, blocked the reduction in miR-125b induced by PAR2. Furthermore, PAR2 activation increased the level of N(6)-methyladenosine (m(6)A)-containing pre-miR-125b in NSun2-dependent manner. Taken together, our results demonstrated that miR-125b mediates PAR2-induced cancer cell migration by targeting Gab2 and that NSun2-dependent RNA methylation contributes to the down-regulation of miR-125b by PAR2 signaling. These findings suggest a novel epigenetic mechanism by which microenvironment regulates cancer cell migration by altering miRNA expression.

Wu T, Wang X, Li J, et al.
Identification of Personalized Chemoresistance Genes in Subtypes of Basal-Like Breast Cancer Based on Functional Differences Using Pathway Analysis.
PLoS One. 2015; 10(6):e0131183 [PubMed] Free Access to Full Article Related Publications
Breast cancer is a highly heterogeneous disease that is clinically classified into several subtypes. Among these subtypes, basal-like breast cancer largely overlaps with triple-negative breast cancer (TNBC), and these two groups are generally studied together as a single entity. Differences in the molecular makeup of breast cancers can result in different treatment strategies and prognoses for patients with different breast cancer subtypes. Compared with other subtypes, basal-like and other ER+ breast cancer subtypes exhibit marked differences in etiologic factors, clinical characteristics and therapeutic potential. Anthracycline drugs are typically used as the first-line clinical treatment for basal-like breast cancer subtypes. However, certain patients develop drug resistance following chemotherapy, which can lead to disease relapse and death. Even among patients with basal-like breast cancer, there can be significant molecular differences, and it is difficult to identify specific drug resistance proteins in any given patient using conventional variance testing methods. Therefore, we designed a new method for identifying drug resistance genes. Subgroups, personalized biomarkers, and therapy targets were identified using cluster analysis of differentially expressed genes. We found that basal-like breast cancer could be further divided into at least four distinct subgroups, including two groups at risk for drug resistance and two groups characterized by sensitivity to pharmacotherapy. Based on functional differences among these subgroups, we identified nine biomarkers related to drug resistance: SYK, LCK, GAB2, PAWR, PPARG, MDFI, ZAP70, CIITA and ACTA1. Finally, based on the deviation scores of the examined pathways, 16 pathways were shown to exhibit varying degrees of abnormality in the various subgroups, indicating that patients with different subtypes of basal-like breast cancer can be characterized by differences in the functional status of these pathways. Therefore, these nine differentially expressed genes and their associated functional pathways should provide the basis for novel personalized clinical treatments of basal-like breast cancer.

Ding C, Luo J, Yu W, et al.
Gab2 is a novel prognostic factor for colorectal cancer patients.
Int J Clin Exp Pathol. 2015; 8(3):2779-86 [PubMed] Free Access to Full Article Related Publications
Gab2 (Grb2-associated binder 2), a member of the DOS/Gab family of scaffolding adapters, serves as a critical signal amplifier downstream of various growth factor receptors. Recent studies have identified that Gab2 is overexpressed in several cancer types and that increased Gab2 expression promotes cell proliferation, cell transformation, and tumor progression. Here, we show for the first time that Gab2 protein is overexpressed in clinical colorectal cancer (CRC) specimens. Elevated mRNA (P=0.014) expression and protein (P=0.003) expression of Gab2 were found in most CRC tissues compared with the matched adjacent non-tumor tissues using real-time quantitative reverse transcription PCR (qRT-PCR) and western blotting, respectively. Immunohistochemical analyses showed that Gab2 protein was upregulated in CRC tissues relative to adjacent normal tissues (P<0.001), and this overexpression was significantly correlated with lymph node metastasis (P=0.007), distant metastasis (P<0.001) and TNM stage (P=0.002). According to Kaplan-Meier model, CRC patients with Gab2-positive had a significantly poorer prognosis compared to those with Gab2-negative (P=0.007). Multivariate analysis suggested that the positive expression of Gab2 protein was an independent prognostic factor for CRC patients. In conclusion, our data demonstrated that Gab2 expression may play an important role in the progression of CRC, and underscored that Gab2 has the potential value as a prognostic predictor for CRC patients.

Davis SJ, Sheppard KE, Anglesio MS, et al.
Enhanced GAB2 Expression Is Associated with Improved Survival in High-Grade Serous Ovarian Cancer and Sensitivity to PI3K Inhibition.
Mol Cancer Ther. 2015; 14(6):1495-503 [PubMed] Related Publications
Identification of genomic alterations defining ovarian carcinoma subtypes may aid the stratification of patients to receive targeted therapies. We characterized high-grade serous ovarian carcinoma (HGSC) for the association of amplified and overexpressed genes with clinical outcome using gene expression data from 499 HGSC patients in the Ovarian Tumor Tissue Analysis cohort for 11 copy number amplified genes: ATP13A4, BMP8B, CACNA1C, CCNE1, DYRK1B, GAB2, PAK4, RAD21, TPX2, ZFP36, and URI. The Australian Ovarian Cancer Study and The Cancer Genome Atlas datasets were also used to assess the correlation between gene expression, patient survival, and tumor classification. In a multivariate analysis, high GAB2 expression was associated with improved overall and progression-free survival (P = 0.03 and 0.02), whereas high BMP8B and ATP13A4 were associated with improved progression-free survival (P = 0.004 and P = 0.02). GAB2 overexpression and copy number gain were enriched in the AOCS C4 subgroup. High GAB2 expression correlated with enhanced sensitivity in vitro to the dual PI3K/mTOR inhibitor PF-04691502 and could be used as a genomic marker for identifying patients who will respond to treatments inhibiting PI3K signaling.

Sun L, Zhang B, Liu Y, et al.
MiR125a-5p acting as a novel Gab2 suppressor inhibits invasion of glioma.
Mol Carcinog. 2016; 55(1):40-51 [PubMed] Related Publications
Poor prognosis of glioma is due to the characteristics of high invasiveness. Recently, it was demonstrated that Gab2 was over-expressed and related to cellular migration and invasion in glioma, however, the mechanisms of regulation are still unknown. A better understanding of molecular events key to the carcinogenesis and tumor progression may facilitate development of new therapeutic targets and anti-glioma strategies. This study is the first to focus on miR125a-5p, which was predicted to regulate Gab2 with directly targeting the 3' un-translated region (3'UTR) of Gab2 and could inhibit migration and invasion of glioma cells by mediating Gab2 to affect cytoskeleton rearrangement and matrix metalloproteinases expression. Interestingly, further evaluation revealed that the miR125a-5p promoter was hypermethylated and that attenuating promoter methylation was sufficient to up-regulate miR125a-5p expression in glioma cells. Additionally, we reported that miR125a-5p was down-regulated in glioma as well as statistical analysis suggested that its expression level correlated with the World Health Organization grades of glioma (P < 0.05) and that patients with a low miR125a-5p level exhibited shorter survival time (P < 0.05). Taken together, these results reveal that miR125a-5p represents potential therapeutic targets in glioma by modulating Gab2.

Matsumura T, Sugimachi K, Takahashi Y, et al.
Clinical significance of GAB2, a scaffolding/docking protein acting downstream of EGFR in human colorectal cancer.
Ann Surg Oncol. 2014; 21 Suppl 4:S743-9 [PubMed] Related Publications
PURPOSE: Recent studies indicated that the scaffolding adaptor protein GAB2 (GRB2-associated binding protein 2) plays a critical role in the proliferation and migration of various cancers. This study aimed to determine the role of aberrant GAB2 expression in human colorectal cancer (CRC).
METHODS: Quantitative real-time reverse transcription polymerase chain reaction was used to evaluate GAB2 mRNA expression in 152 CRC tissues samples to determine the clinicopathological significance of GAB2 expression. We also performed in vitro proliferation assays using siGAB2-transfected CRC cells.
RESULTS: GAB2 expression in tumor colorectal tissues was significantly higher than in normal colorectal tissues (p = 0.0212). High GAB2 expression levels were associated with malignant clinicopathologic potential factors, including lymphatic invasion (p = 0.0003), venous invasion (p = 0.0170), and liver metastasis (p = 0.0144). The survival rate of patients with high GAB2 expression levels was significantly lower than that of patients with low GAB2 expression (p = 0.0074). Multivariate analysis indicated that GAB2 expression was a factor affecting lymph node metastasis. Cell proliferation was significantly suppressed by siGAB2 expression in CRC cells in vitro.
CONCLUSIONS: GAB2 expression was associated with lymph node metastasis and may play a role in the growth and metastasis of CRC. These results suggest that GAB2 is a potential therapeutic target in CRC.

Bozok Cetintas V, Tezcanli Kaymaz B, Aktug H, et al.
Capsaicin induced apoptosis and gene expression dysregulation of human acute lymphoblastic leukemia CCRF-CEM cells.
J BUON. 2014 Jan-Mar; 19(1):183-90 [PubMed] Related Publications
PURPOSE: Capsaicin, an ingredient of red chili pepper, has possible tumorigenicity/genotoxicity properties. We aimed to determine the effects of capsaicin on the proliferation and gene expression profiles of acute lymphoblastic leukemia (ALL) CCRF-CEM cell line.
METHODS: Cell viability and IC50 dose was determined by WST cytotoxicity assay. qRT-PCR, immunohistochemical staining and western blot methods were used to determine target genes' expression levels. Apoptosis was evaluated by measuring the caspase-3 activity.
RESULTS: Capsaicin inhibited the proliferation of CCRFCEM cells in a dose-dependent manner. Increased mRNA expressions of caspase gene family members, activated caspase-3 and decreased mRNA and protein expression of BCL-2 gene indicated apoptotic response to capsaicin. Moreover capsaicin treatment suppressed significantly the expression of the key cell signaling pathways of KRAS, AKT, GAB2, PTPN11, BRAF, INPP5D, MAPK7.
CONCLUSION: Capsaicin induces apoptosis in CCRF-CEM cells and this response is associated with downregulation of cell signaling pathways.

Dunn GP, Cheung HW, Agarwalla PK, et al.
In vivo multiplexed interrogation of amplified genes identifies GAB2 as an ovarian cancer oncogene.
Proc Natl Acad Sci U S A. 2014; 111(3):1102-7 [PubMed] Free Access to Full Article Related Publications
High-grade serous ovarian cancers are characterized by widespread recurrent copy number alterations. Although some regions of copy number change harbor known oncogenes and tumor suppressor genes, the genes targeted by the majority of amplified or deleted regions in ovarian cancer remain undefined. Here we systematically tested amplified genes for their ability to promote tumor formation using an in vivo multiplexed transformation assay. We identified the GRB2-associated binding protein 2 (GAB2) as a recurrently amplified gene that potently transforms immortalized ovarian and fallopian tube secretory epithelial cells. Cancer cell lines overexpressing GAB2 require GAB2 for survival and show evidence of phosphatidylinositol 3-kinase (PI3K) pathway activation, which was required for GAB2-induced transformation. Cell lines overexpressing GAB2 were as sensitive to PI3K inhibition as cell lines harboring mutant PIK3CA. Together, these observations nominate GAB2 as an ovarian cancer oncogene, identify an alternative mechanism to activate PI3K signaling, and underscore the importance of PI3K signaling in this cancer.

Ding J, Romani J, Zaborski M, et al.
Inhibition of PI3K/mTOR overcomes nilotinib resistance in BCR-ABL1 positive leukemia cells through translational down-regulation of MDM2.
PLoS One. 2013; 8(12):e83510 [PubMed] Free Access to Full Article Related Publications
Chronic myeloid leukemia (CML) is a cytogenetic disorder resulting from formation of the Philadelphia chromosome (Ph), that is, the t(9;22) chromosomal translocation and the formation of the BCR-ABL1 fusion protein. Tyrosine kinase inhibitors (TKI), such as imatinib and nilotinib, have emerged as leading compounds with which to treat CML. t(9;22) is not restricted to CML, 20-30% of acute lymphoblastic leukemia (ALL) cases also carry the Ph. However, TKIs are not as effective in the treatment of Ph+ ALL as in CML. In this study, the Ph+ cell lines JURL-MK2 and SUP-B15 were used to investigate TKI resistance mechanisms and the sensitization of Ph+ tumor cells to TKI treatment. The annexin V/PI (propidium iodide) assay revealed that nilotinib induced apoptosis in JURL-MK2 cells, but not in SUP-B15 cells. Since there was no mutation in the tyrosine kinase domain of BCR-ABL1 in cell line SUP-B15, the cells were not generally unresponsive to TKI, as evidenced by dephosphorylation of the BCR-ABL1 downstream targets, Crk-like protein (CrkL) and Grb-associated binder-2 (GAB2). Resistance to apoptosis after nilotinib treatment was accompanied by the constitutive and nilotinib unresponsive activation of the phosphoinositide 3-kinase (PI3K) pathway. Treatment of SUP-B15 cells with the dual PI3K/mammalian target of rapamycin (mTOR) inhibitor BEZ235 alone induced apoptosis in a low percentage of cells, while combining nilotinib and BEZ235 led to a synergistic effect. The main role of PI3K/mTOR inhibitor BEZ235 and the reason for apoptosis in the nilotinib-resistant cells was the block of the translational machinery, leading to the rapid downregulation of the anti-apoptotic protein MDM2 (human homolog of the murine double minute-2). These findings highlight MDM2 as a potential therapeutic target to increase TKI-mediated apoptosis and imply that the combination of PI3K/mTOR inhibitor and TKI might form a novel strategy to combat TKI-resistant BCR-ABL1 positive leukemia.

Chang X, Shi L, Gao F, et al.
Genomic and transcriptome analysis revealing an oncogenic functional module in meningiomas.
Neurosurg Focus. 2013; 35(6):E3 [PubMed] Related Publications
OBJECT: Meningiomas are among the most common primary adult brain tumors. Although typically benign, roughly 2%-5% display malignant pathological features. The key molecular pathways involved in malignant transformation remain to be determined.
METHODS: Illumina expression microarrays were used to assess gene expression levels, and Illumina single-nucleotide polymorphism arrays were used to identify copy number variants in benign, atypical, and malignant meningiomas (19 tumors, including 4 malignant ones). The authors also reanalyzed 2 expression data sets generated on Affymetrix microarrays (n = 68, including 6 malignant ones; n = 56, including 3 malignant ones). A weighted gene coexpression network approach was used to identify coexpression modules associated with malignancy.
RESULTS: At the genomic level, malignant meningiomas had more chromosomal losses than atypical and benign meningiomas, with average length of 528, 203, and 34 megabases, respectively. Monosomic loss of chromosome 22 was confirmed to be one of the primary chromosomal level abnormalities in all subtypes of meningiomas. At the transcriptome level, the authors identified 23 coexpression modules from the weighted gene coexpression network. Gene functional enrichment analysis highlighted a module with 356 genes that was highly related to tumorigenesis. Four intramodular hubs within the module (GAB2, KLF2, ID1, and CTF1) were oncogenic in other cancers such as leukemia. A putative meningioma tumor suppressor MN1 was also identified in this module with differential expression between malignant and benign meningiomas.
CONCLUSIONS: The authors' genomic and transcriptome analysis of meningiomas provides novel insights into the molecular pathways involved in malignant transformation of meningiomas, with implications for molecular heterogeneity of the disease.

Huang YJ, Frazier ML, Zhang N, et al.
Reverse-phase protein array analysis to identify biomarker proteins in human pancreatic cancer.
Dig Dis Sci. 2014; 59(5):968-75 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Pancreatic cancer is the fourth leading cause of cancer death in the United States. The high mortality rate of patients with pancreatic cancer is primarily due to the difficulty of early diagnosis and a lack of effective therapies. There is an urgent need to discover novel molecular targets for early diagnosis and new therapeutic approaches to improve the clinical outcome of this deadly disease.
AIM: We utilized the reverse-phase protein assay (RPPA) to identify differentially expressed biomarker proteins in tumors and matched adjacent, normal-appearing tissue samples from 15 pancreatic cancer patients.
METHODS: The antibody panel used for the RPPA included 130 key proteins involved in various cancer-related pathways. The paired t test was used to determine the significant differences between matched pairs, and the false discovery rate-adjusted p values were calculated to take into account the effect of multiple comparisons.
RESULTS: After correcting for multiple comparisons, we found 19 proteins that had statistically significant differences in expression between matched pairs. However, only four (AKT, β-catenin, GAB2, and PAI-1) of them met the conservative criteria (both a q value <0.05 and a fold-change of ≥3/2 or ≤2/3) to be considered differentially expressed. Overexpression of AKT, β-catenin, and GAB2 in pancreatic cancer tissues identified by RPPA has also been further confirmed by western blot analysis. Further analysis identified several significantly associated canonical pathways and overrepresented network functions.
CONCLUSION: GAB2, a newly identified protein in pancreatic cancer, may provide additional insight into this cancer's pathogenesis. Future studies in a larger population are warranted to further confirm our results.

Davis SJ, Sheppard KE, Pearson RB, et al.
Functional analysis of genes in regions commonly amplified in high-grade serous and endometrioid ovarian cancer.
Clin Cancer Res. 2013; 19(6):1411-21 [PubMed] Related Publications
PURPOSE: Ovarian cancer has the highest mortality rate of all the gynecologic malignancies and is responsible for approximately 140,000 deaths annually worldwide. Copy number amplification is frequently associated with the activation of oncogenic drivers in this tumor type, but their cytogenetic complexity and heterogeneity has made it difficult to determine which gene(s) within an amplicon represent(s) the genuine oncogenic driver. We sought to identify amplicon targets by conducting a comprehensive functional analysis of genes located in the regions of amplification in high-grade serous and endometrioid ovarian tumors.
EXPERIMENTAL DESIGN: High-throughput siRNA screening technology was used to systematically assess all genes within regions commonly amplified in high-grade serous and endometrioid cancer. We describe the results from a boutique siRNA screen of 272 genes in a panel of 18 ovarian cell lines. Hits identified by the functional viability screen were further interrogated in primary tumor cohorts to determine the clinical outcomes associated with amplification and gene overexpression.
RESULTS: We identified a number of genes as critical for cellular viability when amplified, including URI1, PAK4, GAB2, and DYRK1B. Integration of primary tumor gene expression and outcome data provided further evidence for the therapeutic use of such genes, particularly URI1 and GAB2, which were significantly associated with survival in 2 independent tumor cohorts.
CONCLUSION: By taking this integrative approach to target discovery, we have streamlined the translation of high-resolution genomic data into preclinical in vitro studies, resulting in the identification of a number of genes that may be specifically targeted for the treatment of advanced ovarian tumors.

Yang Y, Wu J, Demir A, et al.
GAB2 induces tumor angiogenesis in NRAS-driven melanoma.
Oncogene. 2013; 32(31):3627-37 [PubMed] Free Access to Full Article Related Publications
GAB2 is a scaffold protein with diverse upstream and downstream effectors. MAPK and PI3K signaling pathways are known effectors of GAB2. It is amplified and overexpressed in a variety of human tumors including melanoma. Here we show a previously undescribed role for GAB2 in NRAS-driven melanoma. Specifically, we found that GAB2 is co-expressed with mutant NRAS in melanoma cell lines and tumor samples and its expression correlated with metastatic potential. Co-expression of GAB2(WT) and NRAS(G12D) in melanocytes and in melanoma cells increased anchorage-independent growth by providing GAB2-expressing cells a survival advantage through upregulation of BCL-2 family of anti-apoptotic factors. Of note, collaboration of GAB2 with mutant NRAS enhanced tumorigenesis in vivo and led to an increased vessel density with strong CD34 and VEGFR2 activity. We found that GAB2 facilitiated an angiogenic switch by upregulating HIF-1α and VEGF levels. This angiogenic response was significantly suppressed with the MEK inhibitor PD325901. These data suggest that GAB2-mediated signaling cascades collaborate with NRAS-driven downstream activation for conferring an aggressive phenotype in melanoma. Second, we show that GAB2/NRAS signaling axis is non-linear and non-redundant in melanocytes and melanoma, and thus are acting independent of each other. Finally, we establish a link between GAB2 and angiogenesis in melanoma for the first time. In conclusion, our findings provide evidence that GAB2 is a novel regulator of tumor angiogenesis in NRAS-driven melanoma through regulation of HIF-1α and VEGF expressions mediated by RAS-RAF-MEK-ERK signaling.

Zhang X, Zhang Y, Tao B, et al.
Docking protein Gab2 regulates mucin expression and goblet cell hyperplasia through TYK2/STAT6 pathway.
FASEB J. 2012; 26(11):4603-13 [PubMed] Related Publications
Goblet cell hyperplasia (GCH) and mucous hypersecretion are common pathological features of chronic pulmonary diseases, including asthma, chronic obstructive pulmonary disease (COPD), lung cancer, and cystic fibrosis. Despite numerous studies, the molecular basis for this condition remains elusive. Gab2 is a member of the Dos/Gab subfamily scaffolding molecules and plays important roles in regulating growth, differentiation, and inflammation. We found that an elevated level of Gab2 correlates with up-regulated mucus in airway epithelia from patients with lung cancer or COPD, suggesting the potential involvement of Gab2 in pathological lesions in lungs. Knockdown of Gab2 in human airway epithelial cells in vitro decreases IL-13-induced expression of mucin genes. To address the in vivo role of Gab2 in lungs, Gab2-knockout (Gab2(-/-)) mice were sensitized and challenged with ovalbumin (OVA). Further analysis of lungs in an OVA-induced allergy model suggested that GCH and mucus production are remarkably reduced in Gab2(-/-) mice. Mechanistically, Gab2 positively regulates IL-13-induced activation of TYK2/STAT6 by decreasing SOCS3-mediated degradation of TYK2. Together, we define a novel role for Gab2 in mediating mucin gene expression and GCH; these findings have important implications for the pathogenesis and therapy of airway inflammatory diseases.

Ortiz-Padilla C, Gallego-Ortega D, Browne BC, et al.
Functional characterization of cancer-associated Gab1 mutations.
Oncogene. 2013; 32(21):2696-702 [PubMed] Related Publications
Grb2-associated binder 1 (Gab1) is a docking protein that transduces signals from a variety of tyrosine kinases, including Met and the epidermal growth factor receptor (EGFR). Although the related protein Gab2 is strongly implicated in human cancer, a role for Gab1 has been less clear. However, a screen for gene mutations in breast cancer identified two somatic mutations in Gab1, Y83C and T387N. In this paper we describe the functional characterization of these Gab1 mutants. MCF-10A immortalized mammary epithelial cells overexpressing Gab1 Y83C and T387N exhibited a more elongated, fibroblastic phenotype compared with wild-type Gab1 controls. Expression of Gab1 or the mutants promoted epidermal growth factor (EGF)-independent proliferation in monolayer culture to a similar degree. However, in Matrigel culture, both mutants enhanced the formation of acini exhibiting an aberrant, branched morphology. In addition, expression of the mutants modestly increased Erk activation. The two mutants also enhanced branching morphogenesis in a different mammary epithelial cell line, HC11. To gain further insights into the mechanism of action of these mutations, we mapped Gab1 phosphorylation sites by mass spectrometry. This detected phosphorylation of T387 but ;not Y83. Cellular stimulation with EGF or hepatocyte growth factor (HGF) led to a transient, or sustained, induction of T387 phosphorylation, respectively. As T387 corresponds in position to Gab2 T391, which suppresses Gab2 signaling in a phosphorylation-dependent manner, these data support a model in which the T387N mutation abrogates negative-feedback regulation of Gab1. Interrogation of publically-available databases revealed additional cancer-associated mutations at, or in close proximity to, identified serine/threonine phosphorylation sites in other docking proteins. These data indicate that aberrant Gab1 signaling can directly contribute to breast cancer progression, and that negative feedback sites in docking proteins can be targeted by oncogenic mutations.

Quintás-Cardama A, Qiu YH, Post SM, et al.
Reverse phase protein array profiling reveals distinct proteomic signatures associated with chronic myeloid leukemia progression and with chronic phase in the CD34-positive compartment.
Cancer. 2012; 118(21):5283-92 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Chronic myeloid leukemia (CML) is a clonal stem cell malignancy whose pathogenesis is driven by constitutive activation of the breakpoint cluster region-v-abl Abelson murine leukemia viral oncogene homolog 1 (BCR-ABL1) kinase. Although BCR-ABL1 activation is present in all patients with CML, patients can present in 3 different phases characterized by an increasingly worse prognosis and diminished responsiveness to tyrosine kinase inhibitors: chronic phase, accelerated phase, or blastic phase. The biologic basis for progression from chronic phase to blastic phase and for regulating the homeostasis of tyrosine kinase inhibitor-resistant CML stem cells is not entirely understood.
METHODS: To shed some light into these aspects of CML biology, the authors used reverse phase protein arrays probed with 112 individual monoclonal antibodies to compare protein expression patterns in 40 samples of leukemia-enriched fractions from patients with CML (25 in chronic phase, 5 in accelerated phase, and 10 in phase).
RESULTS: An analysis of variance (significance cutoff, P < .01) unveiled a set of proteins that were overexpressed in blastic phase, including heat-shock protein 90 (hsp90); retinoblastoma (Rb); apoptosis-inducing factor (AIF); serine/threonine-protein phosphatase 2A (PP2A); B-cell leukemia 2 (Bcl-2); X-linked inhibitor of apoptosis protein (Xiap); human homolog of Drosophila Mad (mothers against decapentaplegic) and related Caenorhabditis elegans gene Sma, family member 1 (Smad1); single-stranded DNA binding protein 2 alpha (SSBP2α); poly(adenosine diphosphate-ribose) polymerase (PARP); GRB2-associated binding protein 2 (Gab2); and tripartite motif containing 24 (Trim24). It is noteworthy that several of these proteins also were overexpressed in the CD34-positive compartment, which putatively contains the CML stem cell population.
CONCLUSIONS: The results from this study indicated that reverse phase protein array analysis can unveil differentially expressed proteins in advanced phase CML that can be exploited therapeutically with targeted approaches.

Gadd S, Beezhold P, Jennings L, et al.
Mediators of receptor tyrosine kinase activation in infantile fibrosarcoma: a Children's Oncology Group study.
J Pathol. 2012; 228(1):119-30 [PubMed] Related Publications
Infantile fibrosarcoma (IFS; also known as cellular congenital mesoblastic nephroma, CMN, when in the kidney) is a rare, undifferentiated tumour often characterized by the ETV6-NTRK3 fusion transcript. Our goal was to identify downstream pathways, diagnostic markers and potential therapeutic targets for IFS/CMN. Global gene expression, reverse-phase protein array and ETV6-NTRK3 fusion analyses were performed on 14 IFS/CMN and compared with 41 other paediatric renal tumours. These analyses confirm significant receptor tyrosine kinase (RTK) activation, with evidence of PI3-Akt, MAPK and SRC activation. In particular, GAB2 docking protein, STAT5-pTyr-694, STAT3-pSer-729 and YAP-pSer-127 were elevated, and TAZ-pSer-89 was decreased. This provides mRNA and proteomic evidence that GAB2, STAT activation and phosphorylation of the Hippo pathway transcription co-activators YAP and TAZ contribute to the RTK signal transduction in IFS/CMN. All IFS/CMN tumours displayed a distinctive gene expression pattern that may be diagnostically useful. Unexpectedly, abundant ETV6-NTRK3 transcript copies were present in only 7/14 IFS, with very low copy number in 3/14. An additional 4/14 were negative by RT-PCR and absence of ETV6-NTRK3 was confirmed by FISH for both ETV6 and NTRK3. Therefore, molecular mechanisms other than ETV6-NTRK3 fusion are responsible for the development of some IFS/CMNs and the absence of ETV6-NTRK3 fusion products should not exclude IFS/CMN as a diagnosis.

Wang Y, Sheng Q, Spillman MA, et al.
Gab2 regulates the migratory behaviors and E-cadherin expression via activation of the PI3K pathway in ovarian cancer cells.
Oncogene. 2012; 31(20):2512-20 [PubMed] Free Access to Full Article Related Publications
Ovarian cancer, the most deadly gynecologic malignancy, is often diagnosed late and at the advanced stage when the cancer cells have already migrated and invaded into other tissues and organs. Better understanding of the mechanism of metastasis in ovarian cancer cells is essential to the design of effective therapy. In this study, we investigated the function of scaffolding adaptor protein Gab2 in ovarian cancer cells. Gab2 is found to be overexpressed in a subset of ovarian tumors and cancer cell lines. Gab2 expression mainly regulates the migratory behaviors of ovarian cancer cells. Overexpression of Gab2 promotes the migration and invasion, and downregulates E-cadherin expression in ovarian cancer cells with low-Gab2 expression. Conversely, knockdown of Gab2 expression inhibits the migration and invasion, and promotes E-cadherin expression in ovarian cancer cells with high-Gab2 expression. By expressing Gab2 wild-type and Gab2 mutants that are defective in activation of the PI3K and Shp2-Erk pathways, we find that Gab2 inhibits E-cadherin expression and enhances the expression of Zeb1, a transcription factor involved in epithelial-to-mesenchymal transition (EMT), and cell migration and invasion through the activation of the PI3K pathway. Knockdown of Zeb1 expression blocks Gab2-induced suppression of E-cadherin expression and increase in cell invasion. LY294002 and GDC-0941, inhibitors of PI3K, or Rapamycin, an inhibitor of PI3K downstream target mTOR, can reverse the effects of Gab2 on migration and invasion. Overall, our studies reveal that Gab2 overexpression, via activation of the PI3K-Zeb1 pathway, promotes characteristics of EMT in ovarian cancer cells.

Karlsson E, Waltersson MA, Bostner J, et al.
High-resolution genomic analysis of the 11q13 amplicon in breast cancers identifies synergy with 8p12 amplification, involving the mTOR targets S6K2 and 4EBP1.
Genes Chromosomes Cancer. 2011; 50(10):775-87 [PubMed] Related Publications
The chromosomal region 11q13 is amplified in 15-20% of breast cancers; an event not only associated with estrogen receptor (ER) expression but also implicated in resistance to endocrine therapy. Coamplifications of the 11q13 and 8p12 regions are common, suggesting synergy between the amplicons. The aim was to identify candidate oncogenes in the 11q13 region based on recurrent amplification patterns and correlations to mRNA expression levels. Furthermore, the 11q13/8p12 coamplification and its prognostic value, was evaluated at the DNA and the mRNA levels. Affymetrix 250K NspI arrays were used for whole-genome screening of DNA copy number changes in 29 breast tumors. To identify amplicon cores at 11q13 and 8p12, genomic identification of significant targets in cancer (GISTIC) was applied. The mRNA expression levels of candidate oncogenes in the amplicons [RAD9A, RPS6KB2 (S6K2), CCND1, FGF19, FGF4, FGF3, PAK1, GAB2 (11q13); EIF4EBP1 (4EBP1), PPAPDC1B, and FGFR1 (8p12)] were evaluated using real-time PCR. Resulting data revealed three main amplification cores at 11q13. ER expression was associated with the central 11q13 amplification core, encompassing CCND1, whereas 8p12 amplification/gene expression correlated to S6K2 in a proximal 11q13 core. Amplification of 8p12 and high expression of 4EBP1 or FGFR1 was associated with a poor outcome in the group. In conclusion, single nucleotide polymorphism arrays have enabled mapping of the 11q13 amplicon in breast tumors with high resolution. A proximal 11q13 core including S6K2 was identified as involved in the coamplification/coexpression with 8p12, suggesting synergy between the mTOR targets S6K2 and 4EBP1 in breast cancer development and progression.

Peng Z, Luo HW, Yuan Y, et al.
Growth of chronic myeloid leukemia cells is inhibited by infection with Ad-SH2-HA adenovirus that disrupts Grb2-Bcr-Abl complexes.
Oncol Rep. 2011; 25(5):1381-8 [PubMed] Related Publications
The persistence of Bcr-Abl-positive cells in patients on imatinib therapy indicates that inhibition of the Bcr-Abl kinase activity alone might not be sufficient to eradicate the leukemia cells. Many downstream effectors of Bcr-Abl have been described, including activation of both the Grb2-SoS-Ras-MAPK and Grb2-Gab2-PI3K-Akt pathways. The Bcr-Abl-Grb2 interaction, which is mediated by the direct interaction of the Grb2 SH2 domain with the phospho-Bcr-Abl Y177, is required for activation of these signaling pathways. Therefore, disrupting their interaction represents a potential therapeutic strategy for inhibiting the oncogenic downstream signals of Bcr-Abl. Adenovirus Ad-SH2-HA expressing the Grb2 SH2 domain was constructed and applied in this study. As expected, Ad-SH2-HA efficiently infected CML cells and functioned by binding to the phospho-Bcr-Abl Y177 site, competitively disrupting the Grb2 SH2-phospho-Bcr-Abl Y177 complex. They induced potent anti-proliferation and apoptosis-inducing effects in CML cell lines. Moreover, the Ras, MAPK and Akt activities were significantly reduced in the Ad-SH2-HA treated cells. These were not observed with the point-mutated control adenovirus Ad-Sm-HA with abolished phospho-Bcr-Abl Y177 binding sites. These data indicate that, in addition to the direct targeting of Bcr-Abl, selective inhibition of its downstream signaling pathways may be a therapeutic option for CML, and the Ad-SH2-HA-mediated killing strategy could be explored as a promising anti-leukemia agent in CML.

Herrera Abreu MT, Hughes WE, Mele K, et al.
Gab2 regulates cytoskeletal organization and migration of mammary epithelial cells by modulating RhoA activation.
Mol Biol Cell. 2011; 22(1):105-16 [PubMed] Free Access to Full Article Related Publications
The docking protein Gab2 is overexpressed in several human malignancies, including breast cancer, and is associated with increased metastatic potential. Here we report that Gab2 overexpression in MCF-10A mammary epithelial cells led to delayed cell spreading, a decrease in stress fibers and mature focal adhesions, and enhanced cell migration. Expression of a Gab2 mutant uncoupled from 14-3-3-mediated negative feedback (Gab2(2xA)) led to a more mesenchymal morphology and acquisition of invasive potential. Expression of either Gab2 or Gab2(2xA) led to decreased activation of RhoA, but only the latter increased levels of Rac-GTP. Expression of constitutively active RhoA in MCF-10A/Gab2 cells restored stress fibers and focal adhesions, indicating that Gab2 signals upstream of RhoA to suppress these structures. Mutation of the two Shp2-binding sites to phenylalanine (Gab2(ΔShp2)) markedly reduced the effects of Gab2 on cellular phenotype and RhoA activation. Expression of Gab2 or Gab2(2xA), but not Gab2(ΔShp2), promoted Vav2 phosphorylation and plasma membrane recruitment of p190A RhoGAP. Knockdown of p190A RhoGAP reversed Gab2-mediated effects on stress fibers and focal adhesions. The identification of a novel pathway downstream of Gab2 involving negative regulation of RhoA by p190A RhoGAP sheds new light on the role of Gab2 in cancer progression.

Fleuren ED, O'Toole S, Millar EK, et al.
Overexpression of the oncogenic signal transducer Gab2 occurs early in breast cancer development.
Int J Cancer. 2010; 127(6):1486-92 [PubMed] Related Publications
Gab2, a docking-type signaling protein with demonstrated oncogenic potential, is overexpressed in breast cancer, but its prognostic significance and role in disease evolution remain unclear. Immunohistochemical detection of Gab2 in a large cohort of primary human breast cancers of known outcome revealed that while Gab2 expression was positively correlated with increased tumor grade, it did not correlate with disease recurrence or breast cancer-related death in the total cohort or in patients stratified according to lymph node, estrogen receptor (ER) or HER2 status. Interestingly, analysis of a "progression series" that included premalignant and preinvasive breast lesions as well as samples of metastatic disease revealed that Gab2 expression was significantly enhanced in the earliest lesion examined, usual ductal hyperplasia, with a further increase detected in ductal carcinoma in situ (DCIS). Furthermore, expression was less in invasive cancers and lymph node metastases than in DCIS, but still higher than in normal breast. These findings indicate that while Gab2 expression is not prognostic in breast cancer, its role in early disease evolution warrants further analysis, as Gab2 and its effectors may provide targets for novel strategies aimed at preventing breast cancer development.

Bocanegra M, Bergamaschi A, Kim YH, et al.
Focal amplification and oncogene dependency of GAB2 in breast cancer.
Oncogene. 2010; 29(5):774-9 [PubMed] Related Publications
DNA amplifications in breast cancer are frequent on chromosome 11q, in which multiple driver oncogenes likely reside in addition to cyclin D1 (CCND1). One such candidate, the scaffolding adapter protein, GRB2-associated binding protein 2 (GAB2), functions in ErbB signaling and was recently shown to enhance mammary epithelial cell proliferation, and metastasis of ERBB2 (HER2/neu)-driven murine breast cancer. However, the amplification status and function of GAB2 in the context of amplification remain undefined. In this study, by genomic profiling of 172 breast tumors, and fluorescence in situ hybridization validation in an independent set of 210 scorable cases, we observed focal amplification spanning GAB2 (11q14.1) independent of CCND1 (11q13.2) amplification, consistent with a driver role. Further, small interfering RNA (siRNA)-mediated knockdown of GAB2 in breast cancer lines (SUM52, SUM44PE and MDA468) with GAB2 amplification revealed a dependency on GAB2 for cell proliferation, cell-cycle progression, survival and invasion, likely mediated through altered phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) signaling. GAB2 knockdown also reduced proliferation and survival in a cell line (BT474) with ERBB2 amplification, consistent with the possibility that GAB2 can function downstream of ERBB2. Our studies implicate focal amplification of GAB2 in breast carcinogenesis, and underscore an oncogenic role of scaffolding adapter proteins, and a potential new point of therapeutic intervention.

Mira A, Isella C, Renzulli T, et al.
The GAB2 signaling scaffold promotes anchorage independence and drives a transcriptional response associated with metastatic progression of breast cancer.
Oncogene. 2009; 28(50):4444-55 [PubMed] Related Publications
Acquisition of independence from anchorage to the extracellular matrix is a critical event for onset and progression of solid cancers. To identify and characterize new genes conferring anchorage independence, we transduced MCF10A human normal breast cells with a retroviral cDNA expression library and selected them by growth in suspension. Microarray analysis targeted on library-derived transcripts revealed robust and reproducible enrichment, after selection, of cDNAs encoding the scaffolding adaptor Gab2. Gab2 was confirmed to strongly promote anchorage-independent growth when overexpressed. Interestingly, downregulation by RNA interference of endogenous Gab2 in neoplastic cells did not affect their adherent growth, but abrogated their growth in soft agar. Gab2-driven anchorage independence was found to specifically involve activation of the Src-Stat3 signaling axis. A transcriptional 'signature' of 205 genes was obtained from GAB2-transduced, anchorage-independent MCF10A cells, and found to contain two main functional modules, controlling proliferation and cell adhesion/migration/invasion, respectively. Extensive validation on breast cancer data sets showed that the GAB2 signature provides a robust prognostic classifier for breast cancer metastatic relapse, largely independent from existing clinical and genomic indicators and from estrogen receptor status. This work highlights a pivotal role for GAB2 and its transcriptional targets in anchorage-independent growth and breast cancer metastatic progression.

Chernoff KA, Bordone L, Horst B, et al.
GAB2 amplifications refine molecular classification of melanoma.
Clin Cancer Res. 2009; 15(13):4288-91 [PubMed] Free Access to Full Article Related Publications
PURPOSE: Gain-of-function mutations in BRAF, NRAS, or KIT are associated with distinct melanoma subtypes with KIT mutations and/or copy number changes frequently observed among melanomas arising from sun-protected sites, such as acral skin (palms, soles, and nail bed) and mucous membranes. GAB2 has recently been implicated in melanoma pathogenesis, and increased copy numbers are found in a subset of melanomas. We sought to determine the association of increased copy numbers of GAB2 among melanoma subtypes in the context of genetic alterations in BRAF, NRAS, and KIT.
EXPERIMENTAL DESIGN: A total of 85 melanomas arising from sun-protected (n = 23) and sun-exposed sites (n = 62) were analyzed for copy number changes using array-based comparative genomic hybridization and for gain-of-function mutations in BRAF, NRAS, and KIT.
RESULTS: GAB2 amplifications were found in 9% of the cases and were associated with melanomas arising from acral and mucosal sites (P = 0.005). Increased copy numbers of the KIT locus were observed in 6% of the cases. The overall mutation frequencies for BRAF and NRAS were 43.5% and 14%, respectively, and were mutually exclusive. Among the acral and mucosal melanomas studied, the genetic alteration frequency was 26% for GAB2, 13% for KIT, 30% for BRAF, and 4% for NRAS. Importantly, the majority of GAB2 amplifications occurred independent from genetic events in BRAF, NRAS, and KIT.
CONCLUSIONS: GAB2 amplification is critical for melanomas arising from sun-protected sites. Genetic alterations in GAB2 will help refine the molecular classification of melanomas.

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