Abstract
Substance P receptor (SPR) stably expressed in Chinese hamster ovary (CHO) cells stimulates at least three second messenger systems including phosphoinositide hydrolysis, cyclic AMP (cAMP) formation, and arachidonic acid release. Whether these second messenger systems are activated via single or multiple G proteins is not known. Therefore, in the present study we examined whether human SPR (hSPR) stably expressed in CHO cells activates multiple G proteins. This was achieved by photoaffinity labeling of Gα-subunits with [32P]azidoanilido-GTP ([32P]AA-GTP) upon hSPR stimulation in CHO-hSPR membranes followed by immunoprecipitation of the labeled Gα-subunits with antibodies specific for various Gα-subunits. These experiments reveal that hSPR directly activates Gαq/11, Gαs and Gαo. While hSPR is known to couple Gαq/11, the present study provides the first evidence that hSPR can also activate Gαs and Gαo in a mammalian system.