PHOSPHOTYROSINE PHOSPHATASE-ACTIVITY ASSOCIATED WITH C-SRC IN LARGE MULTIMERIC COMPLEXES ISOLATED FROM ADRENAL-MEDULLARY CHROMAFFIN CELLS

Chromaffin cells, which secrete catecholamines in response to acetylch oline, express high levels of the Src-famiiy tyrosine kinases. These k inases contain protein-protein interaction domains which bind signal t ransduction proteins that participate in a variety of cellular process es. To determine if signalling proteins bind c-Src in chromaffin cells , we examined c-Src immunocomplexes for co-precipitating proteins. We discovered a phosphotyrosine phosphatase (PTPase: EC 3.1.3.48) activit y which associates with specific subcellular pools of c-Src in vivo an d which preferentially binds the SH2 (Src homology 2) domain of c-Src in vitro. Known PTPases were not identified by blotting of c-Src immun ocomplexes with a panel of anti-PTPase antibodies, suggesting that the PTPase may be a novel family member. The c-Src-PTPase complex is enri ched in the plasma membrane fraction and exists in several large compl exes, as revealed by gel-filtration analysis. This PTPase activity is altered rapidly following stimulation by secretagogues, decreasing wit hin 30 s and returning to basal levels by 60 s of stimulation. Both th e subcellular localization and rapid activity changes suggest that the c-Src-associated PTPase may function in early signalling events emana ting from the nicotinic acetylcholine receptor. In support of this is the co-precipitation of a PTPase activity with the nicotinic acetylcho line receptor and co-chromatography of this receptor with one of the c -Src-PTPase complexes.