Endometrial carcinoma expresses gonadotropin-releasing hormone receptor (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 membranes. 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 protein antibodies. G protein-associated membrane event was observed by phosphotyrosine 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 significant levels of 42-kDa and 46-kDa proteins in endometrial carcinoma membranes, respectively. The nonhydrolyzable GTP analog GTP-gamma-S stimulated the phosphatase activity in a dose-dependent manner: a half maximal effect occurred with 30 nM. These findings demonstrate the expression of G proteins and the presence G proteins-associated membrane event in endometrial carcinoma.

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