LOCALIZATION AND DOWN-REGULATING ROLE OF THE PROTEIN-TYROSINE-PHOSPHATASE PTP2C IN MEMBRANE RUFFLES OF PDGF-STIMULATED CELLS

PTP2C (also known as Syp/SH-PTP2/PTP1D) is a soluble protein tyrosine phosphatase present in most cell types, It interacts directly with act ivated PDGF receptor via its SH2 domains, which results in its phospho rylation on tyrosine residue(s). The phosphorylated PTP2C in turn bind s to the SH2 domain of GRB2, serving as an adaptor in the transduction of mitogenic signals from the growth factor receptor to the Ras and M AP kinase signaling pathways, We investigated the interaction of PTP2C with the PDGF receptor by examining the localization of both proteins after PDGF stimulation of 293 cells which stably express the human PD GF receptor, In resting cells, transiently expressed PTP2C was distrib uted throughout the cytoplasm, Upon stimulation with PDGF, PTP2C was t ranslocated from the cytoplasm to membrane ruffles, Immunofluorescence examination revealed that PTP2C colocalized with actin, the PDGF rece ptors, and hyper-tyrosine-phosphorylated protein(s). Neither deletion of the SH2 domains nor point mutations at either the catalytic site or the major phosphorylation site affected membrane ruffling or the loca lization of PTP2C to the ruffles of PDGF-stimulated cells. However, th e expression of a catalytically inactive mutant PTP2C substantially pr olonged ruffling activity following PDGF stimulation, These results su ggest that PTP2C is involved in the down-regulation of the membrane ru ffling pathway, and in contrast to its positive function in the MAP ki nase pathway, the phosphatase activity negatively regulates ruffling a ctivity. (C) 1996 Academic Press, Inc.