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PTP-PEST is a cytoplasmic tyrosine phosphatase implicated in control of cell motility. Intriguingly, overexpression of PTP-PEST and deletion of the PTP-PEST gene both inhibit motility. The role of the phosphatase has therefore remained unclear, as has its mode of action — PTP-PEST contains binding sites for numerous proteins and therefore could function as an enzyme and/or a scaffold. Sarita Sastry and co-workers have examined the role of PTP-PEST in migrating CHOK1 and Rat1 cells (see p. 4305). They show that PTP-PEST transiently localizes to matrix-contact sites at the leading edge of migrating cells and that its activity increases following integrin-mediated attachment. They also show that PTP-PEST inhibits growth-factor-dependent cell migration, using a phosphatase-dead PTP-PEST mutant to demonstrate that this requires PTP-PEST phosphatase activity. Finally, the authors show that PTP-PEST suppresses integrin- and growth-factor-induced activation of Rac1 — a small GTPase required for cell migration — and that coexpression of activated Rac1 can alleviate the inhibitory effects of the phosphatase. Sastry and co-workers conclude that PTP-PEST, by inhibiting activation of Rac1, modulates signalling downstream of integrins and growth factor receptors to control lamellipodial protrusion.
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