GTP-BINDING PROTEIN AND ITS ASSOCIATED EVENT IN MEMBRANES FROM ENDOMETRIAL CARCINOMA

Endometrial carcinoma expresses gonadotropin-releasing hormone recepto r (Gn-RHR) known to be linked by heterotrimeric GTP-binding proteins ( G proteins). We have examined endometrial carcinomas for the presence of G protein and its associated membrane event in isolated plasma memb ranes. Endometrial carcinomas surgically removed had been screened for Gn-RHR expression prior to plasma membrane isolation. G protein level was observed by immunoblotting of membrane extracts with anti-G prote in antibodies. G protein-associated membrane event was observed by pho sphotyrosine phosphatase (PTP) activity determined with the synthetic substrate p-nitrophenyl in a spectrophotometric assay. Immunoblotting with the specific G alpha 11 and G alpha s antibodies showed significa nt levels of 42-kDa and 46-kDa proteins in endometrial carcinoma membr anes, respectively. The nonhydrolyzable GTP analog GTP-gamma-S stimula ted the phosphatase activity in a dose-dependent manner: a half maxima l effect occurred with 30 nM. These findings demonstrate the expressio n of G proteins and the presence G proteins-associated membrane event in endometrial carcinoma.