CHARACTERIZATION OF AN SH2 CONTAINING PROTEIN-TYROSINE-PHOSPHATASE INRAT PAROTID-GLAND ACINAR-CELLS

Rat parotid glands were shown to possess protein phosphatase activity capable of catalyzing the dephosphorylation of several model phosphata se substrates, including p-nitrophenyl phosphate, tyrosine phosphoryla ted myelin basic protein and serine phosphorylated casein. A portion o f this activity closely resemble dephosphorylation patterns of known p rotein tyrosine phosphatases. The reaction showed sensitivity to sodiu m orthovanadate, proceeded efficiently in the presence of metal chelat ors and favored acidic pH for optimum activity. Cell lysates from EGF- or isoproterenol-stimulated parotid glands, when immunoprecipitated w ith anti-Syp antibody, showed the induction of protein tyrosine phosph atase activity significantly higher than the unstimulated controls. Th e protein of M(r) = 65kDa also had elevated levels of tyrosine phospho rylation following isolation from cells treated to undergo proliferati on. Thus parotid gland acinar cells possess protein tyrosine phosphata se activity of the PTPase 1D class associated with inducible cell grow th, in addition to other phosphatases.