DIFFERENTIAL COUPLING OF THE FORMYL PEPTIDE RECEPTOR TO ADENYLATE-CYCLASE AND PHOSPHOLIPASE-C BY THE PERTUSSIS TOXIN-INSENSITIVE G(Z) PROTEIN

In neutrophils, activation of receptors for the chemotactic peptide N- formylmethionyl-leucyl-phenylalanine (fMLP) leads to changes in intrac ellular events such as phosphoinositide turnover and Ca2+ mobilization . Studies have shown that activation of the cloned fMLP receptor can a lso lead to inhibition of cyclic AMP (cAMP) accumulation [Lang, Boulay , Li and Wollheim (1993) EMBO J. 12, 2671-2679; Uhing, Gettys, Tomhave , Snyderman and Didsbury (1992) Biochem. Biophys. Res. Commun. 183, 10 33-1039]. These responses are apparently mediated through pertussis to xin-sensitive G(i) proteins. Since other chemotactic factor receptors can couple to multiple G proteins, we examined the ability of the fMLP receptor to utilize a pertussis toxinin-sensitive G protein, G(z), in its signal transduction pathways. The human fMLP receptor was transie ntly expressed in 293 and Ltk(-) cells, and subsequently assayed for r eceptor-mediated inhibition of cAMP accumulation and stimulation of ph osphoinositide-specific phospholipase C. In transfected 293 cells, fML P inhibited choriogonadotropin-stimulated cAMP accumulation by 50% and the response could be abolished by pertussis toxin. Co-expression of the fMLP receptor with the alpha subunit of G(z) rendered the fMLP res ponse pertussis toxinin-sensitive, indicating that the endogenous Gi p roteins can be substituted efficiently by G(z). In contrast, Ltk(-) ce lls expressing the fMLP receptor were able to respond to fMLP with an increase in the production of inositol phosphates, but this response w as completely abolished by pertussis toxin even in cells co-expressing the alpha subunit of G(z). Thus, although both signalling pathways ap peared to utilize G(i)-like proteins, G(z) can only replace G(i) in me diating inhibition of cAMP accumulation, and not in the stimulation of phospholipase C. Differential interaction with G(z) might represent a novel mechanism by which fMLP receptors regulate intracellular events .