Inhibition of T24 human bladder carcinoma cell migration by RNA interference suppressing the expression of HD-PTP.

Cell migration is fundamental for invasion and metastasis and is modulated by the reversible phosphorylation of tyrosine residues on target proteins. Here we report that the tyrosine phosphatase HD-PTP has a role in modulating the motility of T24 bladder carcinoma cells. Indeed, HD-PTP silencing by RNA interference (RNAi) markedly induced cell migration in a Src dependent fashion. We therefore investigated the interaction and the regulation of Src and HD-PTP. We found that, in Epidermal Growth Factor (EGF) stimulated cells, Src binds to and phosphorylates HD-PTP on tyrosine residues. On the contrary, HD-PTP does not modulate the levels of Src phosphorylation. Interestingly, HD-PTP also binds to FAK, another regulator of cell migration, and this interaction is inhibited after exposure to EGF. FAK phosphorylates HD-PTP and this event reduced the interactions between the two proteins. Interestingly, in cells silencing HD-PTP the phosphorylation of FAK is enhanced and this correlates with its localization in focal complexes both in the presence and in the absence of EGF. We hypothesize that in unstimulated T24 cells HD-PTP does not interact with Src, while it binds to FAK. Following stimulation with EGF, HD-PTP is tyrosine-phosphorylated and releases FAK which will ultimately contribute to the turn-over of focal adhesion and, therefore, to cell motility.