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.