Differential and competitive regulation of human melanocortin 1 receptor signaling by β-arrestin isoforms.
Protease-activated receptor-2 (PAR-2) is a G-protein-coupled receptor (GPCR) activated upon proteolytic cleavage of its N-terminus by a number of serine proteases. We have previously reported that formation of a beta-arrestin-dependent signaling scaffold is required for PAR-2-stimulated activation of extracellular signal regulated kinases 1 and 2 and chemotaxis. beta-Arrestin-dependent pathways downstream of some GPCRs have been shown to function independently and sometimes in opposition to classic signaling through heterotrimeric G-proteins; however, this possibility has not been addressed with respect to PAR-2. Here we demonstrate that PAR-2 can increase PI3K activity through a Galphaq/Ca(2+)-dependent pathway involving PYK2 and a Src-family kinase, while inhibiting PI3K activity through a beta-arrestin-dependent mechanism, and that beta-arrestin-1 can directly associate with and inhibit the catalytic activity of p110alpha. Using size exclusion chromatography and co-immunoprecipitation, we demonstrate that the PI3K is recruited into a scaffolding complex containing PAR-2 and beta-arrestins. Inhibition of PI3K activity blocks PAR-2-stimulated chemotaxis, and beta-arrestin-1 colocalizes with p85 within the pseudopodia, suggesting that beta-arrestin-1 association with PI3K may spatially restrict its enzymatic activity and that this localized inhibition may be crucial for PAR-2-stimulated chemotaxis.