Method: Studies utilized human melanoma WM1552C cells, stably overexpressing CSPG4 (WM1552C-CSPG4) or empty vector (WM1552C-Mock). The BRAFV600E inhibitor used was SB590885. In vitro transformation was assessed by soft agar assay. Protein expression was evaluated by western blot.
Result: Evaluating both size and number of colonies, CSPG4 promoted anchorage-independent growth in soft agar and dramatically decreased sensitivity to SB590885 in WM1552C-CSPG4 cells relative to WM1552C-Mock cells. Western blot analysis demonstrated a loss of ERK1/2 phosphorylation in WM1552C-Mock and WM1552C-CSPG4 cells; synchronously, WM1552C-CSPG4 cells exhibited substantial AKT phosphorylation unobserved in mock cells treated with SB590885.
Conclusion: These results suggest that CSPG4 plays a central role in the survival and resistance to BRAFV600E–targeting therapies of human melanoma cells. These data suggest that not only does CSPG4 significantly increase the oncogenic potential of melanoma, but expression of CSPG4 may also enable tumors to evade the cytotoxicity of BRAFV600E inhibitors by concomitantly upregulating the PI3K/AKT survival pathway. As such, CSPG4 may be an attractive novel target in patients developing BRAFV600E inhibitor resistant metastatic melanoma.