Tyrosine Phosphatases in the HER2-Directed Motility of Ovarian Cancer Cells: Involvement of PTPN12, ERK5 and FAK

Background: HER2 activation in tumours supports multiple signalling pathways, including those regulating invasion and metastasis. Among the involved genes, Tyrosine and Dual Specificity Phosphatases (PTPs and DSPs) may play a relevant, though not completely clear role. Methods: HER2 was silenced in ovarian SKOV-3 cells, a genome-wide expression analysis of PTPs and DSPs was performed, the effects on cell motility were analysed and compared with those of PTPN12-silencing, focusing on FAK. Results: HER2-silencing altered the expression of 4 PTPs and 6 DSPs; PTPN12 displayed also 3-4-fold protein increase. Conversely, PTPN12-silencing enhanced migration, suggesting that PTPN12 down-modulation by HER2 favours motility. HER2-silencing inactivated FAK, in quiescent and migrating cells, involving FAK dephosphorylation at Y397 and S910. Conversely, in PTPN12-silenced cells FAK activity was close to control, altogether suggesting that PTPN12 targets Y397. As regards to S910, cell-treatment with the MEK inhibitor UO126 and ERK5-silencing indicated its targeting by ERK5. Loss of pS910 and decreased ERK5 kinase activity in HER2-silenced cells confirmed their control by HER2. Conclusions: The results indicate the contribution of PTPN12, targeting FAK Y397, and ERK5, targeting FAK S910, to the HER2-driven cell motility, thus depicting new aspects of the complex cross­talk between HER2 and the motility machinery.