Specific combinations of G-protein subunits discriminate hormonal signalling in rat pituitary (GH(3)) cells in culture

It was previously shown that hormone receptor coupling to voltage-dependent calcium channels in prolactin and growth hormone producing GH(3) cells was heavily dependent on the specific heterotrimeric combinations of alpha, be ta, and gamma subunits of the guanosine triphosphate (GTP)-binding protein family. Consequently, we assessed whether this was also the case for hormon al modulation of the adenylate cyclase (AC) and phospholipase C (PL-C) effe ctor enzymes in GH(3) cells in culture. By employing polyclonal antibodies directed towards C-terminal decapeptides of various ol subunits in membrane assays, as well as antisense oligonucleotides towards certain beta and gam ma subunit genes in whole-cell incubations, it was possible to unravel a te ntative profile of heterotrimers preferred by some of the seven-transmembra ne-stretch receptors in their modulation of AC and PL-C activities. Vasoact ive intestinal peptide (VIP) and thyroliberin (TRH) activate membrane-bound AC through alpha (s)beta (2)gamma (2), while somatostatin (SRM) and dopami ne (DA) inhibited the AC through alpha (i2)beta (1)gamma (3). TRH activated membrane-bound PL-C through alpha (q/11)beta (4)gamma (2), while DA inhibi tion of the PL-C was accomplished via alpha (0)beta (3)gamma (1). Hence, it seems that not only the specificity of alpha subunits determines the coupl ing between G protein-associated receptors in GH cells, the receptor bindin g to G proteins also requires certain combinations of beta and gamma subuni ts. (C) 2001 Elsevier Science Inc. All rights reserved.