DIRECT BINDING OF THE PROLINE-RICH REGION OF PROTEIN-TYROSINE-PHOSPHATASE-1B TO THE SRC HOMOLOGY-3 DOMAIN OF P130(CAS)

Protein tyrosine phosphatase 1B (PTP1B) is an abundant intracellular e nzyme that is thought to act as a negative regulator of certain signal ing pathways. The C terminus of PTP1B contains two proline-rich region s which conform to the canonical class II Src homology 3 domain bindin g motif, Pro-X-X-Pro-X-Arg. In this study, we establish that PTP1B int eracts with Crk, Grb2, and p130(Cas) in vitro and with at least one of these, p130(Cas), in intact cells. The interaction of PTP1B and p130( Cas) is independent of tyrosine phosphorylation but can be disrupted b y replacing two critical proline residues in the proline rich domain o f PTP1B between amino acids 301 and 315. When wild-type PTP1B is expre ssed in 3Y1-v-crk cells, p130(Cas) shows substantial dephosphorylation , whereas the PTP1B proline mutant does not have this effect. In 3Y1 a nd 3Y1 v-crk-transformed fibroblasts, almost all of the total PTP1B an d about 40% of total p130(Cas) co-sediment with membranes composed pri marily of endoplasmic reticulum. These results suggest that the prolin e-rich domain between amino acids 301 and 315 in PTP1B binds Src homol ogy 3-containing proteins and that p130(Cas) may be a physiological ta rget of this phosphatase in cells.