INHIBITION OF ADENYLYL-CYCLASE BY CAVEOLIN PEPTIDES

Caveolae and their principal component caveolin have been implicated i n playing a major role in G protein-mediated transmembrane signaling. We examined whether caveolin interacts with adenylyl cyclase, an effec tor of G protein signaling, using a 20-mer peptide derived from the N- terminus scaffolding domain of caveolin-1. When tissue adenylyl cyclas es were examined, cardiac adenylyl cyclase was inhibited more potently than other tissue adenylyl cyclases. The caveolin-1 peptide inhibited type V, as well as type III adenylyl cyclase, overexpressed in insect cells, whereas the same peptide had no effect on type II. The caveoli n-3 scaffolding domain peptide similarly inhibited type V adenylyl cyc lase. In contrast, peptides derived from the caveolin-2 scaffolding do main and a caveolin-1 nonscaffolding domain had no effect. Kinetic stu dies showed that the caveolin-1 peptide decreased the maximal rate (V- max) value of type V without changing the Michaelis constant (Km) valu e for the substrate ATP. Studies with various truncations and point mu tations of this peptide revealed that a minimum of 16 amino acid resid ues and intact aromatic residues are important for the inhibitory effe ct. The potency of inhibition was greater when adenylyl cyclase was in stimulated condition vs. basal condition. Thus, caveolin may be anoth er cellular component that regulates adenylyl cyclase catalytic activi ty. Our results also suggest that the caveolin peptide may be used as an isoform-selective inhibitor of adenylyl cyclase.