PYK2 mediates the BRAF inhibitor (vermurafenib)-induced invadopodia formation and metastasis in melanomas

OBJECTIVE: The BRAF inhibitor, vemurafenib, has been widely used in the treatment of patients with melanoma-bearing BRAF(V600E) mutations. While the initial response to vemurafenib is usually excellent, the majority of patients eventually develop resistance and metastatic disease. However, the underlying molecular mechanism remains elusive. The objective of this study was therefore to identify additional molecular targets responsible for vemurafenib resistance. METHODS: Western blots and immunohistochemistry analyses were used to evaluate expressions of PYK2 and p-PYK2 in cultured cells and melanoma tissue microarrays. The relationships of p-PYK2 with clinicopathological parameters were statistically analyzed. Invadopodia cell invasion, and a Ca(2+) assay were used to determine the effect of vemurafenib resistance-induced p-PYK2 on melanoma progression. A mouse model was used to assess the effects of PYK2 on melanoma metastasis. RESULTS: Elevated p-PYK2 levels were detected in vemurafenib-resistant melanoma cells, and PYK2 was shown to regulate invadopodia formation in melanoma cells. Vemurafenib triggered invadopodia formation by activation of PYK2. Inhibition of PYK2 with either shRNA or the small molecule inhibitor, PF562711, dramatically reduced vemurafenib-induced invadopodia formation. Furthermore, knockdown of PYK2 significantly reduced melanoma lung metastasis in vivo. Increased expressions of p-PYK2 in melanoma patients were positively correlated with advanced stage (P = 0.002), metastasis (P < 0.001), and Clark grade (P < 0.001), and were also associated with short overall survival [hazard ratio (HR) = 3.304, P = 0.007] and progression-free survival (HR = 2.930, P = 0.001). CONCLUSIONS: PYK2 mediated vemurafenib-induced melanoma cell migration and invasion. Inhibition of PYK2 resensitized melanoma cells to vemurafenib. Phospho-PYK2 was a prognostic biomarker in melanoma patients.