STIMULATION OF TYPE-II ADENYLYL-CYCLASE BY CHEMOATTRACTANT FORMYL PEPTIDE AND C5A RECEPTORS

The capacity of N-formylmethionyl-leucyl-phenylalanine (fMLP) acid C5a receptors to regulate type II adenylyl cyclase was examined in transi ent transfection studies, Coexpression of either one of the chemoattra ctant receptors with type II adenylyl cyclase in human embryonic kidne y 293 cells allowed the corresponding chemotactic factor to stimulate cAMP accumulation in a dose-dependent manner. The chemoattractant-indu ced stimulation of type II adenylyl cyclase was absolutely dependent o n the presence of GTP-bound alpha subunit of G(s), as revealed by the coexpression of alpha(s)-Q227L, a constitutively activated mutant of a lpha(s). Stimulation of type II adenylyl cyclase by either fMLP or C5a was mediated via pertussis toxin-sensitive G(i)-like proteins, becaus e the response was abrogated by the toxin. The ability of G(z) (a pert ussis toxin-insensitive G protein that can couple to a number of G(i)- linked receptors) to replace G(i) in chemoattractant-induced stimulati on of type II adenylyl cyclase was examined. The chemoattractant-induc ed response became insensitive to pertussis toxin upon coexpression of the alpha subunit of G(z). Interestingly, coexpression of alpha(z) si gnificantly enhanced the chemotactic factor-stimulated type II adenyly l cyclase activities. When other G protein alpha subunits were tested under similar experimental conditions, all three forms of alpha(i) and alpha(o1) were able to potentiate the fMLP response to various extent s, whereas alpha(q) and alpha(t) slightly inhibited the fMLP response. The alpha subunit-mediated potentiation of the type II adenylyl cycla se response appears to reflect a productive coupling between alpha sub units and the fMLP receptor, because such enhancements were not seen w ith the constitutively activated alpha subunit mutants. Coexpression o f the constitutively activated mutants of alpha(z), alpha(q), alpha(o1 ) and alpha(i1-3) neither enhanced nor inhibited the fMLP-stimulated c AMP accumulation. These results indicated that the observed enhancemen t of type II adenylyl cyclase responses was dependent on the ability o f the wild-type alpha subunits to functionally interact with the fMLP receptor and that the fMLP receptor can couple to G(i1-3), G(z), and G (o1) but not to G(s), G(q), or G(t).