GAB2 induces tumor angiogenesis in NRAS-driven melanoma

Comparative Whole-Genome Sequencing Analysis of In-situ and Invasive Acral Lentiginous Melanoma: Markedly Increased Copy Number Gains of GAB2 , PAK1 , UCP2 , and CCND1 are Associated with Melanoma Invasion

Acral lentiginous melanoma (ALM) is the most common subtype of acral melanoma. Even though recent genetic studies are reported in acral melanomas, the genetic differences between in-situ and invasive ALM remain unclear. We aimed to analyze specific genetic changes in ALM and compare genetic differences between in-situ and invasive lesions to identify genetic changes associated with the pathogenesis and progression of ALM. We performed whole genome sequencing of 71 tissue samples from 29 patients with ALM. Comparative analyses were performed, pairing in-situ ALMs with normal tissues and, furthermore, invasive ALMs with normal and in-situ tissues. Among 21 patients with in-situ ALMs, 3 patients (14.3%) had SMIM14 , SLC9B1 , FRG1 , FAM205A , ESRRA , and ESPN mutations, and copy number (CN) gains were identified in only 2 patients (9.5%). Comparing 13 invasive ALMs with in-situ tissues, CN gains were identified in GAB2 in 8 patients (61.5%), PAK1 in 6 patients (46.2%), and UCP2 and CCND1 in 5 patients (38.5%). Structural variants were frequent in in-situ and invasive ALM lesions. Both in-situ and invasive ALMs had very low frequencies of common driver mutations. Structural variants were common in both in-situ and invasive ALMs. Invasive ALMs had markedly increased CN gains, such as GAB2 , PAK1 , UCP2 , and CCND1 , compared with in-situ lesions. These results suggest that they are associated with melanoma invasion.

Somatic structural variants drive distinct modes of oncogenesis in melanoma

The diversity of structural variants (SVs) in melanoma and how they impact oncogenesis are incompletely known. We performed harmonized analysis of SVs across melanoma histologic and genomic subtypes, and we identified distinct global properties between subtypes. These included the frequency and size of SVs and SV classes, their relation to chromothripsis events, and the impact on cancer-related genes of SVs that alter topologically associated domain (TAD) boundaries. Following our prior identification of double-stranded break repair deficiency in a subset of triple-wild-type cutaneous melanoma, we identified MRE11 and NBN loss-of-function SVs in melanomas with this mutational signature. Experimental knockouts of MRE11 and NBN, followed by olaparib cell viability assays in melanoma cells, indicated that dysregulation of each of these genes may cause sensitivity to PARP inhibitors in cutaneous melanomas. Broadly, harmonized analysis of melanoma SVs revealed distinct global genomic properties and molecular drivers, which may have biological and therapeutic impact.

New insights into RAS in head and neck cancer

RAS genes are known to be dysregulated in cancer for several decades, and substantial effort has been dedicated to develop agents that reduce RAS expression or block RAS activation. The recent introduction of RAS inhibitors for cancer patients highlights the importance of comprehending RAS alterations in head and neck cancer (HNC). In this regard, we examine the published findings on RAS alterations and pathway activations in HNC, and summarize their role in HNC initiation, progression, and metastasis. Specifically, we focus on the intrinsic role of mutated-RAS on tumor cell signaling and its extrinsic role in determining tumor-microenvironment (TME) heterogeneity, including promoting angiogenesis and enhancing immune escape. Lastly, we summarize the intrinsic and extrinsic role of RAS alterations on therapy resistance to outline the potential of targeting RAS using a single agent or in combination with other therapeutic agents for HNC patients with RAS-activated tumors.

Hypoxia in Skin Cancer: Molecular Basis and Clinical Implications

Skin cancer is one of the most prevalent cancers in the Caucasian population. In the United States, it is estimated that at least one in five people will develop skin cancer in their lifetime, leading to significant morbidity and a healthcare burden. Skin cancer mainly arises from cells in the epidermal layer of the skin, where oxygen is scarce. There are three main types of skin cancer: malignant melanoma, basal cell carcinoma, and squamous cell carcinoma. Accumulating evidence has revealed a critical role for hypoxia in the development and progression of these dermatologic malignancies. In this review, we discuss the role of hypoxia in treating and reconstructing skin cancers. We will summarize the molecular basis of hypoxia signaling pathways in relation to the major genetic variations of skin cancer.

High expression of GRB2 associated binding protein 3 mRNA predicts positive prognosis in melanoma

Malignant melanoma is the most aggressive form of skin cancer, and it is characterized by poor prognosis in patients with metastatic diseases. Accurate prediction of prognosis is crucial for therapeutic decisions. In this study, bioinformatics analysis was used to explore the prognostic value of growth factor receptor-bound protein 2-associated binding protein 3 (GAB3) mRNA. RNA transcriptome sequencing data and clinical data from The Cancer Genome Atlas and genotype-tissue expression (GTEx) were analyzed for differentially expressed genes in high and low GAB3 mRNA expression groups in melanoma. Performing gene enrichment analysis and constructing protein-protein interaction networks. High expression of GAB3 was significantly correlated with a lower T stage, melanoma Clark level, Breslow depth, and melanoma ulceration. And high GAB3 expression was also associated with better progression-free interval in T1 and T2 stages and N0 stage and longer overall survival in T1 and T2 stages, N0 stage, and N1 stage. GAB3 promoted high levels of infiltration of macrophages and activated natural killer cells in melanoma. High expression of GAB3 predicted a positive prognosis in early-stage melanoma that may be mediated by the anticancer immune response.

Cutaneous Melanoma: Mutational Status and Potential Links to Tertiary Lymphoid Structure Formation

Recent advances in immunotherapy have enabled rapid evolution of novel interventional approaches designed to reinvigorate and expand patient immune responses against cancer. An emerging approach in cancer immunology involves the conditional induction of tertiary lymphoid structures (TLS), which are non-encapsulated ectopic lymphoid structures forming at sites of chronic, pathologic inflammation. Cutaneous melanoma (CM), a highly-immunogenic form of solid cancer, continues to rise in both incidence and mortality rate, with recent reports supporting a positive correlation between the presence of TLS in melanoma and beneficial treatment outcomes amongst advanced-stage patients. In this context, TLS in CM are postulated to serve as dynamic centers for the initiation of robust anti-tumor responses within affected regions of active disease. Given their potential importance to patient outcome, significant effort has been recently devoted to gaining a better understanding of TLS neogenesis and the influence these lymphoid organs exert within the tumor microenvironment. Here, we briefly review TLS structure, function, and response to treatment in the setting of CM. To uncover potential tumor-intrinsic mechanisms that regulate TLS formation, we have taken the novel perspective of evaluating TLS induction in melanomas impacted by common driver mutations in BRAF, PTEN, NRAS, KIT, PRDM1, and MITF. Through analysis of The Cancer Genome Atlas (TCGA), we show expression of DNA repair proteins (DRPs) including BRCA1, PAXIP, ERCC1, ERCC2, ERCC3, MSH2, and PMS2 to be negatively correlated with expression of pro-TLS genes, suggesting DRP loss may favor TLS development in support of improved patient outcome and patient response to interventional immunotherapy.

MicroRNA‑218 inhibits tumor angiogenesis of human renal cell carcinoma by targeting GAB2

Renal cell carcinoma (RCC) is one of the most common malignant cancers in the adult urinary system worldwide. Tumor angiogenesis is a critical process during cancer progression, as it modulates carcinogenesis and metastasis. In recent years, microRNA-218 (miR-218) has been confirmed to play a crucial role in tumor suppression. However, the role of miR-218 in RCC angiogenesis remains unclear. In the present study, it was found that the expression of miR-218 was decreased in RCC tumor tissues and cell lines as detected by real-time PCR analysis. Tube formation assays and migration assays also confirmed that miR-218 inhibited the interaction between RCC cells and vascular endothelial cells by suppressing proangiogenic factor vascular endothelial growth factor A (VEGFA) in RCC cells. miR-218 also repressed the subcutaneous tumorigenesis of RCC cells in nude mice, and the corneal angiogenesis in rabbit eyes. The underlying molecular mechanism was elucidated; miR-218 targets GRB2-associated binding protein 2 (GAB2), thereby inhibiting the PI3K/AKT/mTOR/VEGFA pathway. These results provide new insights into the mechanism of RCC carcinogenesis and progression, suggesting that miRNA-218 may be a therapeutic target for the treatment of RCC.

Gab2 promotes cancer stem cell like properties and metastatic growth of ovarian cancer via downregulation of miR-200c

Scaffolding adaptor Gab2 is overexpressed in a subset of high-grade ovarian cancer. Our published work shows that Gab2 via PI3K enhances migratory behaviors and epithelial to mesenchymal transition (EMT) features of ovarian cancer cells in vitro. However, it is still unclear how Gab2/PI3K pathway reuglates EMT characteristics and whether Gab2 promotes the growth of ovarian cancer stem cell (CSC)-like population and metastatic growth. In this study, we examined the effects of Gab2 expression on CSC-like cell growth using Aldefluor and tumorshpere assays commonly used for assessing ovarian cancer cells with CSC properties. Gab2 overexpression increased the number of ALDH⁺ cells and tumorsphere formation in two different ovarian cancer cell lines OVCAR5 and OVCAR8, whereas knockdown of Gab2 decreased the number of ALDH⁺ cells and tumorsphere formation in Caov-3 cells. Furthermore, Gab2 promoted metastatic tumor growth of OVCAR5 in nude mice. Mechanistically, we uncovered that Gab2 via PI3K specifically inhibited miR-200c expression. miR-200c downregulation contributed to the Gab2-enhanced cell migratory behaviors, EMT properties, and the expansion of ALDH⁺ cells and tumorspheres. Furthermore, Gab2 promoted CD44 expression and cell migration/invasion through miR-200c downregulation. Our findings support a model that Gab2-PI3K pathway via miR-200c downregulation promotes CD44 expression, EMT characteristics, and CSC-like cell growth. Therapies involving miR-200c or targeting CD44 should help treat ovarian cancer with high Gab2 expression.

Synergistic effects of SHP2 and PI3K pathway inhibitors in GAB2-overexpressing ovarian cancer

The scaffold/adaptor growth factor receptor bound 2 (GRB2)-associated binding protein 2 (GAB2) is frequently amplified and/or overexpressed in primary high-grade serous ovarian cancers (HGSOCs). Here we investigate a novel treatment strategy by targeting SHP2 and PI3K signaling in HGSOCs with GAB2 amplification/overexpression (GAB2^High). The expression of GAB2 was analyzed in primary HGSOCs and ovarian cancer cell lines. In vitro and in vivo assays were performed to demonstrate the effect of SHP2 and PI3K-mediated GAB2^High HGSOC progression. Analysis of gene expression data reveals that primary GAB2^High HGSOCs are associated with increased ERBB, RAS, and MAPK activity signatures. Inhibition of SHP2 by an allosteric inhibitor SHP099 selectively inhibits ERK1/2 activity, proliferation, and survival of GAB2^High ovarian cancer cell lines. Treatment with SHP099 has a synergistic effect with BKM120, a pan-class I PI3K inhibitor, at suppressing proliferation and survival of GAB2^High ovarian cancer cells in vitro and in vivo by more effectively activating both BIM and BAD and inhibiting c-MYC compared with individual inhibitor. Our findings identify an important role of SHP2 in promoting proliferation and survival of GAB2^High ovarian cancer cells, and combinatorial SHP2 and PI3K inhibition may be a promising therapeutic approach for such cancer.

Gab2 mediates hepatocellular carcinogenesis by integrating multiple signaling pathways

Our previous studies have found that Growth factor receptor-bound protein 2-associated binding protein 2 (Gab2)-a docking protein-governs the development of fatty liver disease. Here, we further demonstrate that Gab2 mediates hepatocarcinogenesis. Compared with a faint expression in para-carcinoma tissue, Gab2 was highly expressed in ∼60-70% of human hepatocellular carcinoma (HCC) specimens. Deletion of Gab2 dramatically suppressed diethylnitrosamine-induced HCC in mice. The oncogenic effects of Gab2 in HepG2 cells were promoted by Gab2 overexpression but were rescued by Gab2 knockdown. Furthermore, Gab2 knockout in HepG2 cells restrained cell proliferation, migration and tumor growth in nude mice. Signaling pathway analysis with protein kinase inhibitors demonstrated that oncogenic regulation by Gab2 in hepatic cells involved multiple signaling molecules, including ERK, Akt, and Janus kinases (Jaks), especially those that mediate inflammatory signaling. IL-6 signaling was increased by Gab2 overexpression and impaired by Gab2 deletion via regulation of Jak2 and signal transducer and activator of transcription 3 phosphorylation and the expression of downstream genes, such as Bcl-2 (B-cell lymphoma 2), c-Myc, MMP7 (matrix metalloproteinase-7), and cyclin D1in vitro and in vivo These data indicate that Gab2 mediates the pathologic progression of HCC by integrating multiple signaling pathways and suggest that Gab2 might be a powerful therapeutic target for HCC.-Cheng, J., Zhong, Y., Chen, S., Sun, Y., Huang, L., Kang, Y., Chen, B., Chen, G., Wang, F., Tian, Y., Liu, W., Feng, G.-S., Lu, Z. Gab2 mediates hepatocellular carcinogenesis by integrating multiple signaling pathways.

Elevated Gab2 induces tumor growth and angiogenesis in colorectal cancer through upregulating VEGF levels

Background

Grb2-associated binder 2 (Gab2) is a scaffolding protein that serves as a critical signaling amplifier downstream of tyrosine kinase receptors. Our previous study has shown that Gab2 induces epithelial-to-mesenchymal transition (EMT) and promotes metastasis in colorectal cancer (CRC). However, the role of Gab2 in CRC growth and angiogenesis remains unclear.

Methods

The expression of vascular endothelial growth factor (VEGF) in different colorectal tissues was detected by immunohistochemistry and qRT-PCR to evaluate its correlation with Gab2. Lentiviral vectors bearing Gab2 gene and its small interfering RNAs were constructed and transfected into CRC cell lines. The effects of Gab2 on the cell proliferation in vitro and tumorigenesis in vivo, were examined via CCK‑8 assay, colony formation assay as well as tumorigenicity assay respectively. Moreover, to assess its potential role in tumor growth and angiogenesis, the expression of Ki67, CD34 and vascular endothelial growth factor receptor-2 (VEGFR2) were detected by immunohistochemistry in CRC cells tumors. Finally, we evaluated the impact of Gab2 on the expression of c-Myc and VEGF, and the probable effect of mechanistic targeted extracellular signal-regulated kinase (ERK) pathway in suppressing tumor growth and angiogenesis.

Results

Up-regulation of Gab2 expression was found to be positively correlated with VEGF in CRC tissues. Exogenous expression of Gab2 obviously promoted, whereas silencing of Gab2 inhibited, proliferation and clone formation of human CRC cells in vitro. Of note, Gab2 enhanced tumorigenesis and tumor growth in mouse xenografts with high Ki67 expression, and led to an increased vessel density with strong CD34 and VEGFR2 activity. In addition, elevated Gab2 expression obviously up-regulated the expression of VEGF, and stimulated the activation of its downstream genes, ERK1/2 and c-Myc in CRC cells. Instead, down-regulated Gab2 expression significantly reduced the levels of VEGF, and inhibited the transduction of ERK/c-Myc pathway. Finally, we revealed that mechanistic target of mitogen-activated protein kinase (MEK) could attenuate Gab2-induced tumor growth and angiogenesis via altering VEGF and c-Myc levels.

Conclusions

The results from our study suggest that Gab2 promotes intestinal tumor growth and angiogenesis through upregulation of VEGF expression mediated by the MEK/ERK/c-Myc pathway.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-017-0524-2) contains supplementary material, which is available to authorized users.

Deciphering the RAS/ERK pathway in vivo

The RAS/ERK pathway has been intensely studied for about three decades, not least because of its role in human pathologies. ERK activation is observed in the majority of human cancers; in about one-third of them, it is driven by mutational activation of pathway components. The pathway is arguably one of the best targets for molecule-based pharmacological intervention, and several small-molecule inhibitors are in clinical use. Genetically engineered mouse models have greatly contributed to our understanding of signaling pathways in development, tissue homeostasis, and disease. In the specific case of the RAS/ERK pathway, they have revealed unique biological roles of structurally and functionally similar proteins, new kinase-independent effectors, and unsuspected relationships with other cascades. This short review summarizes the contribution of mouse models to our current understanding of the pathway.

Exploring the importance of cancer pathways by meta-analysis of differential protein expression networks in three different cancers

Background

It is believed that all cancers occur due to the mutation or change in one or more genes. In order to investigate the significance of the biological pathways which are interrupted by these genetic mutations, we pursue an integrated analysis using multiple cancer datasets released by the International Cancer Genome Consortium (ICGC). This dataset consists of expression profiles for genes/proteins of patients receiving treatment, for three types of cancer - Head and Neck Squamous Cell Carcinoma (HNSC), Lung Adenocarcinoma (LUAD) and Kidney Renal Clear Cell Carcinoma (KIRC). We consider pathway analysis to identify all the biological pathways which are active among the patients and investigate the roles of the significant pathways using a differential network analysis of the protein expression datasets for the three cancers separately. We then integrate the pathway based results of all the three cancers which provide a more comprehensive picture of the three cancers.

Results

From our analysis of the protein expression data, overall, RAS and PI3K signaling pathways appear to play the most significant roles in the three cancers - Head and Neck Squamous Cell Carcinoma (HNSC), Lung Adenocarcinoma (LUAD) and Kidney Renal Clear Cell Carcinoma (KIRC).

Conclusion

This analysis suggests that the RAS and PI3K signaling pathways are the two most important pathways in all the three cancers and should be investigated further for their potential roles in cancers.

Reviewers

This article was reviewed by Joaquin Dopazo and Samiran Ghosh.

Standard melanoma-associated markers do not identify the MM127 metastatic melanoma cell line

Reliable identification of different melanoma cell lines is important for many aspects of melanoma research. Common markers used to identify melanoma cell lines include: S100; HMB-45; and Melan-A. We explore the expression of these three markers in four different melanoma cell lines: WM35; WM793; SK-MEL-28; and MM127. The expression of these markers is examined at both the mRNA and protein level. Our results show that the metastatic cell line, MM127, cannot be detected using any of the commonly used melanoma-associated markers. This implies that it would be very difficult to identify this particular cell line in a heterogeneous sample, and as a result this cell line should be used with care.

NRAS mutant melanoma: an overview for the clinician for melanoma management

Melanoma is the deadliest form of skin cancer and the incidence continues to rise in the United States and worldwide. Activating mutations in RAS oncogenes are found in roughly a third of all human cancers. Mutations in NRAS occur in approximately a fifth of cutaneous melanomas and are associated with aggressive clinical behavior. Cells harboring oncogenic NRAS mutations exhibit activation of multiple signaling cascades, including PI3K/Akt, MEK-ERK and RAL, which collectively stimulate cancer growth. While strategies to target N-Ras itself have proven ineffective, targeting one or more N-Ras effector pathways has shown promise in preclinical models. Despite promising preclinical data, current therapies for NRAS mutant melanoma remain limited. Immune checkpoint inhibitors and targeted therapies for BRAF mutant melanoma are transforming the treatment of metastatic melanoma, but the ideal treatment for NRAS mutant melanoma remains unknown. Improved understanding of NRAS mutant melanoma and relevant N-Ras effector signaling modules will be essential to develop new treatment strategies.

Overexpression of GAB2 in ovarian cancer cells promotes tumor growth and angiogenesis by upregulating chemokine expression

We previously found that the scaffold adapter GRB2-associated binding protein 2 (GAB2) is amplified and overexpressed in a subset of primary high-grade serous ovarian cancers and cell lines. Ovarian cancer cells overexpressing GAB2 are dependent on GAB2 for activation of the phosphatidylinositol 3-kinase (PI3K) pathway and are sensitive to PI3K inhibition. In this study, we show an important role of GAB2 overexpression in promoting tumor angiogenesis by upregulating expression of multiple chemokines. Specifically, we found that suppression of GAB2 by inducible small hairpin RNA in ovarian cancer cells inhibited tumor cell proliferation, angiogenesis and peritoneal tumor growth in immunodeficient mice. Overexpression of GAB2 upregulated the secretion of several chemokines from ovarian cancer cells, including CXCL1, CXCL2 and CXCL8. The secreted chemokines not only signal through endothelial CXCR2 receptor in a paracrine manner to promote endothelial tube formation, but also act as autocrine growth factors for GAB2-induced transformation of fallopian tube secretory epithelial cells and clonogenic growth of ovarian cancer cells overexpressing GAB2. Pharmacological inhibition of inhibitor of nuclear factor kappa-B kinase subunit β (IKKβ), but not PI3K, mechanistic target of rapamycin (mTOR) or mitogen-activated protein kinase (MEK), could effectively suppress GAB2-induced chemokine expression. Inhibition of IKKβ augmented the efficacy of PI3K/mTOR inhibition in suppressing clonogenic growth of ovarian cancer cells with GAB2 overexpression. Taken together, these findings suggest that overexpression of GAB2 in ovarian cancer cells promotes tumor growth and angiogenesis by upregulating expression of CXCL1, CXCL2 and CXCL8 that is IKKβ-dependent. Co-targeting IKKβ and PI3K pathways downstream of GAB2 might be a promising therapeutic strategy for ovarian cancer that overexpresses GAB2.

Structure and function of Gab2 and its role in cancer (Review)

The docking proteins of the Grb-associated binder (Gab) family transduce cellular signals between receptors and intracellular downstream effectors, and provide a platform for protein-protein interactions. Gab2, a key member of the Gab family of proteins, is involved in the amplification and integration of signal transduction, evoked by a variety of extracellular stimuli, including growth factors, cytokines and antigen receptors. Gab2 protein lacks intrinsic catalytic activity; however, when phosphorylated by protein-tyrosine kinases (PTKs), Gab2 recruits several Src homology-2 (SH2) domain-containing proteins, including the SH2-containing protein tyrosine phosphatase 2 (SHP2), the p85 subunit of phosphoinositide-3 kinase (PI3K), phospholipase C-γ (PLCγ)1, Crk, and GC-GAP. Through these interactions, the Gab2 protein triggers various downstream signal effectors, including SHP2/rat sarcoma viral oncogene/RAF/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase and PI3K/AKT, involved in cell growth, differentiation, migration and apoptosis. It has been previously reported that aberrant Gab2 and/or Gab2 signaling is closely associated with human tumorigenesis, particularly in breast cancer, leukemia and melanoma. The present review aimed to focus on the structure and effector function of Gab2, its role in cancer and its potential for use as an effective therapeutic target.

Hypoxia-independent drivers of melanoma angiogenesis

Tumor angiogenesis is a process which is traditionally regarded as the tumor’s response to low nutrient supply occurring under hypoxic conditions. However, hypoxia is not a pre-requisite for angiogenesis. The fact that even single tumor cells or small tumor cell aggregates are capable of attracting blood vessels reveals the early metastatic capability of tumor cells. This review sheds light on the hypoxia-independent mechanisms of tumor angiogenesis in melanoma.

Mechanisms of tumour vascularization in cutaneous malignant melanoma: clinical implications

Malignant melanoma represents < 10% of all skin cancers but is responsible for the majority of skin-cancer-related deaths. Metastatic melanoma has historically been considered as one of the most therapeutically challenging malignancies. Fortunately, for the first time after decades of basic research and clinical investigation, new drugs have produced major clinical responses. Angiogenesis has been considered an important target for cancer treatment. Initial efforts have focused primarily on targeting endothelial and tumour-related vascular endothelial growth factor signalling. Here, we review different mechanisms of tumour vascularization described in melanoma and discuss the potential clinical implications.

Clinical significance of GAB2, a scaffolding/docking protein acting downstream of EGFR in human colorectal cancer

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.

GAB2--a scaffolding protein in cancer

Adaptor or scaffolding proteins mediate protein-protein interactions that drive the formation of protein complexes. Grb2-associated binding protein 2 (GAB2) scaffolding protein is an intermediary molecule that links plasma membrane receptor signaling including receptor tyrosine kinases with the downstream effectors, such as protein tyrosine phosphatase, nonreceptor type 11 (SHP2), p85 subunit of phosphoinositide-3 kinase (PI3-K), phospholipase C-gamma 1 (PLC-γ), v-crk sarcoma virus CT10 (CRK), Src homology 2 domain containing transforming protein 1 (SHC), and SH2 containing inositol phosphatase (SHIP). Although, well described in signal transduction, its role in cancer has recently been emerging especially in leukemia, breast and ovarian cancer, and melanoma. GAB2 is essential for two major signal transduction pathways in cancer, the PI3-K-AKT and extracellular signal-regulated kinase (ERK) signaling pathways, and thus regulates a number of key cellular processes. This review focuses on structure and function of GAB2, its regulatory proteins, emerging role in cancer, and potential as a therapeutic target.