Differential regulation of class IA phosphoinositide 3-kinase catalytic subunits p110α and β by protease-activated receptor 2 and β-arrestins

Abstract

PAR-2 (protease-activated receptor 2) is a GPCR (G-protein-coupled receptor) that can elicit both G-protein-dependent and -independent signals. We have shown previously that PAR-2 simultaneously promotes Gαq/Ca2+-dependent activation and β-arrestin-1-dependent inhibition of class IA PI3K (phosphoinositide 3-kinase), and we sought to characterize further the role of β-arrestins in the regulation of PI3K activity. Whereas the ability of β-arrestin-1 to inhibit p110α (PI3K catalytic subunit α) has been demonstrated, the role of β-arrestin-2 in PI3K regulation and possible differences in the regulation of the two catalytic subunits (p110α and p110β) associated with p85α (PI3K regulatory subunit) have not been examined. In the present study we have demonstrated that: (i) PAR-2 increases p110α- and p110β-associated lipid kinase activities, and both p110α and p110β are inhibited by over-expression of either β-arrestin-1 or -2; (ii) both β-arrestin-1 and -2 directly inhibit the p110α catalytic subunit in vitro, whereas only β-arrestin-2 directly inhibited p110β; (iii) examination of upstream pathways revealed that PAR-2-induced PI3K activity required the small GTPase Cdc (cell-division cycle)42, but not tyrosine phosphorylation of p85; and (iv) β-arrestins inhibit PAR-2-induced Cdc42 activation. Taken together, these results indicated that β-arrestins could inhibit PAR-2-stimulated PI3K activity, both directly and through interference with upstream pathways, and that the two β-arrestins differ in their ability to inhibit the p110α and p110β catalytic subunits. These results are particularly important in light of the growing interest in PAR-2 as a pharmacological target, as commonly used biochemical assays that monitor G-protein coupling would not screen for β-arrestin-dependent signalling events.