THE TYROSINE PHOSPHATASE PTP1C ASSOCIATES WITH VAV, GRB2, AND MSOS1 IN HEMATOPOIETIC-CELLS

The association of the murine motheaten phenotype of severe hemopoieti c dysregulation with loss of PTP1C tyrosine phosphatase activity indic ates a critical role for this SH2 domain-containing phosphotyrosine ph osphatase in the regulation of hemopoietic cell growth and differentia tion. To explore the molecular basis for PTP1C effects on hematopoiesi s, we have investigated the possibility that this enzyme interacts wit h the product of the Vav proto-oncogene, a putative guanine nucleotide exchange factor expressed exclusively in hemopoietic cells. Our data indicate that PTP1C physically associates with Vav in murine spleen ce lls and in EL4 T lymphoma and P815 mastocytoma cells, and that this in teraction is increased following mitogenic stimulation and the inducti on of both PTP1C and Vav tyrosine phosphorylation. The results also re veal tyrosine phosphatase activity to be present in Vav immunoprecipit ates from stimulated splenic and P815 cells and suggest that a major p ortion of total cellular PTP1C catalytic activity is associated with V av. As Vav-associated tyrosine phosphatase activity was not detected i n PTP1C deficient motheaten splenic cells, it appears that PTP1C accou nts for most, if not all, Vav coprecipitable tyrosine phosphatase acti vity in normal cells. The data also demonstrate the capacity of the Va v SH2 domain alone to bind to PTP1C in activated P815 cells, but sugge st a role for the two Vav SH3 domains in enhancing this interaction. I n addition, the results reveal PTP1C association with two other molecu les implicated in Ras activation, the Grb2 adaptor protein and mSos1, a GTP/GDP exchanger for Ras. PTP1C therefore has the capacity to bind and potentially modulate various signaling effecters involved in activ ation of Ras or Ras-related proteins, and, accordingly, regulation of Ras activation represents a possible mechanism whereby PTP1C influence s hemopoietic cellular responses.