Abstract 4058: CSPG4 mediates melanoma cell survival in response to BRAFV600E inhibition.

Resistance to chemotherapy remains a major cause of malignant melanoma treatment failure. While recent clinical trials have shown significant patient response to chemotherapeutics targeting BRAF V600E , e.g. dabrafenib, tumors eventually become resistant and disease recurs. Development of additional novel therapies is therefore critical to better manage melanoma patients. Analysis of patient-derived melanoma lesions has revealed robust expression of the cell adhesion protein chondroitin sulfate proteoglycan 4 (CSPG4). While not prognostic due to its expression in premalignant nevi, CSPG4 has been revealed to promote melanoma progression by enhancing cell growth, migration and invasion in vitro and in vivo. Previous studies have shown CSPG4 to enhance activation of ERK1/2, PI3K and FAK, suggesting that CSPG4 likely contributes to oncogenic growth and survival through activation of a number of parallel signaling cascades. CSPG4 therefore represents a potential avenue for melanoma cell survival in response to chemotherapy. In support of this hypothesis, melanoma cells expressing endogenous or exogenous CSPG4 are more resistant to cell death induced by dabrafenib than cells lacking endogenous expression of CSPG4. Likewise, suppression of CSPG4 via siRNA reduced melanoma cell survival in response to dabrafenib. Melanoma cells expressing CSPG4 show enhanced growth in soft agar versus cells lacking CSPG4 expression, even in the presence of BRAF V600E inhibition. To determine the mechanism of CSPG4-driven resistance to BRAF V600E inhibition, activation of a number of oncogenic growth and survival pathways was interrogated. While ERK1/2 phosphorylation in the presence of BRAF V600E inhibition is unaffected by CSPG4, AKT phosphorylation is enhanced by expression of CSPG4. Moreover, this CSPG4-driven AKT activation in response to dabrafenib is dependent on PI3K, as treatment of melanoma cells with the PI3K inhibitor LY294002 eliminated increased AKT phosphorylation by CSPG4 in response to dabrafenib. CSPG4 enhances Src-FAK complex assembly, membrane lipid subdomain localization, and activation in melanoma cells through syntenin-1-dependent scaffolding. A mutant of CSPG4 engineered to eliminate lipid microdomain localization of CSPG4, termed CSPG4C2230A, was unable to recapitulate this phenotype.CSPG4C2230A also failed to protect melanoma cells from cytotoxicity or promote growth in soft agar in the presence of BRAF V600E inhibition. Altogether, these data indicate that CSPG4 confers protection against cytotoxicity induced by BRAF V600E inhibition by organizing progression-associated signalosomes involved in AKT activation, making CSPG4 an attractive target for the development of adjuvant therapies. Ongoing studies focus on determining the mechanism of CSPG4-mediated AKT activation and on developing CSPG4-targeting melanoma treatments for use in preclinical models. Citation Format: Leah E. Colvin Wanshura, Jianbo Yang, Matthew A. Price, Jennifer H. Carlson, Arkadiusz Z. Dudek, James B. McCarthy. CSPG4 mediates melanoma cell survival in response to BRAFV600E inhibition. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4058. doi:10.1158/1538-7445.AM2013-4058