Melanoma chondroitin sulfate proteoglycan activates FAK and ERK via separate integrin-dependent mechanisms

4905 Melanoma chondroitin sulfate proteoglycan (MCSP) is a major melanoma-associated cell-surface antigen that is incrementally expressed during the transition from early stages of melanoma progression to metastatic melanoma. MCSP has been implicated in melanoma cell proliferation, migration, invasion. This proteoglycan also enhances α4β1 integrin-mediated melanoma cell spreading, however, its signaling mechanisms are not well understood. Focal adhesion kinase (FAK) plays a vital role in integrin-mediated focal adhesion signaling pathways, and recently the activation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) has also been linked to melanoma cell proliferation and survival. In the current studies, we demonstrate that in vertical growth phase (VGP) melanoma WM1341D cells, which express endogenous MCSP, simultaneous engagement of α4β1 integrin and MCSP promoted extensive cell spreading and robust phosphorylation of FAK at Tyr397. This is not observed in radial growth phase (RGP) WM1552C cells, which did not express endogenous MCSP. We have cloned MCSP and expressed wild-type MCSP in WM1552C cells. Stable expression of MCSP stimulated both integrin-mediated cell spreading and FAK phosphorylation in WM1552C cells. Furthermore, phosphorylation of ERK1/2 was enhanced by stable expression of MCSP. The phosphorylation of FAK and ERK1/2 by MCSP involves independent mechanisms, since inhibition of FAK activation by focal adhesion kinase related non-kinase (FRNK) had no effect on ERK1/2 phosphorylation. Finally, chondroitinase ABC treatment of melanoma cells to remove the glycosaminoglycan chondroitin sulfate (CS) also had no effect on cell spreading, FAK, or ERK1/2 activation. These results indicate that MCSP core protein may facilitate primary melanoma progression by enhancing the activation of key signaling pathways important for tumor invasion and growth.