Gab2-Mediated Signaling Promotes Melanoma Metastasis

Abstract

Metastatic melanoma is a disease with a poor prognosis that currently lacks effective treatments. Critical biological features of metastasis include acquisition of migratory competence, growth factor independence, and invasive potential. In an attempt to identify genes that contribute to melanoma pathogenesis, a genomewide search using bacterial artificial chromosome array comparative genomic hybridization and single nucleotide polymorphism arrays in a series of 64 metastatic melanoma samples and 20 melanoma cell lines identified increased copy numbers of Gab2 located on 11q14.1. Gab2 is an adaptor protein that potentiates the activation of the Ras-Erk and PI3K-Akt pathways and has recently been implicated in human cancer; however, its role in melanoma has not been explored. In this study, we found that Gab2 was either amplified (ϳ11%) and/or overexpressed (ϳ50%) in melanoma. Gab2 protein expression correlated with clinical melanoma progression, and higher levels of expression were seen in metastatic melanomas compared with primary melanoma and melanocytic nevi. We found that overexpression of Gab2 potentiates, whereas silencing of Gab2 reduces, migration and invasion of melanoma cells. Gab2 mediated the hyperactivation of Akt signaling in the absence of growth factors, whereas inhibition of the PI3K-Akt pathway decreased Gab2-mediated tumor cell migration and invasive potential. Gab2 overexpression resulted in enhanced tumor growth and metastatic potential in vivo. These studies demonstrate a previously undefined role for Gab2 in melanoma tumor progression and metastasis.

In vivo multiplexed interrogation of amplified genes identifies GAB2 as an ovarian cancer oncogene

“…GAB2 resides on the fourth most significant amplicon in high-grade serous ovarian cancer (3), the focal peak located on 11q14.1. This amplified region has been identified as a recurrent alteration in breast (9,22) and ovarian cancer (19) as well as in metastatic melanoma (24). Across over 6,300 different TCGA samples, this region is among the 26 most amplified regions in all cancers (21).…”

“…GAB2 is required for BCR/ABL-mediated transformation in chronic myeloid leukemia (CML) (31) and also HER2-mediated mammary carcinogenesis through ERK activation (16). Moreover, GAB2 is overexpressed in breast cancer (9,22) and some metastatic melanomas (24) and promotes survival in breast cancer (22) and migration in both malignancies (17,24). Several ovarian cancer cell lines also overexpress GAB2, which was linked to increased migration and the epithelial-mesenchymal transition (26).…”

“…However, analysis of the TCGA dataset revealed that alterations in known PI3K pathway components including PTEN, PIK3CA, AKT1, and AKT2 were present in only about one-third of ovarian cancer samples (3). Although prior studies have shown that GAB2-mediated migration of melanoma (24) and ovarian cancer cells (26) can be reduced by PI3K inhibitors, we hypothesized that GAB2 amplification represents an additional mechanism of PI3K activation in ovarian cancer. We tested whether increased GAB2 expression activated AKT1.…”

“…Prior work has implicated GAB2 as a signaling intermediate in both SHP2-dependent activation of MAPK signaling (16,17) and activation of phosphatidylinositol 3-kinase (PI3K) (24). To assess the effects of suppressing GAB2 on these signaling pathways in cell lines expressing elevated or normal levels of GAB2, we interrogated the phosphorylation levels of PI3K/AKT/mTOR pathway components AKT1 and S6 as well as the MAPK pathway component ERK.…”

“…Having shown that the PI3K pathway was required for GAB2-mediated transformation and that activated AKT1 could partially rescue GAB2-dependent cell lines depleted of GAB2, we next determined whether GAB2 alterations represented a feature that correlated with enhanced sensitivity to PI3K pathway inhibition. Several studies suggest that PI3K inhibition attenuated GAB2-dependent migration phenotypes (24,26) and pointed to the types of pathway alterations that activate AKT1 (28). However, although recent work has been directed at correlating PI3K pathway alterations with sensitivity to pathway inhibition in breast cancer (29), it is unclear whether increased GAB2 expression increases cell sensitivity to PI3K pathway inhibition in a manner similar to the sensitivity conferred by canonical mutations in PIK3CA and PTEN.…”