Adenylate cyclase regulation via proteasome-mediated modulation of Galphas levels.

The adenylate cyclase (AC)/cyclic AMP (cAMP)/cAMP-dependent protein kinase pathway controls many biological phenomena. The ubiquitin/ proteasome system, controlling the levels of many proteins, modulates important cellular processes such as cell cycle and cell growth. Here we describe a novel mechanism for AC regulation by proteasome pathway. Pharmacological inhibition of proteasome function in human osteosarcoma U2OS cells results in up-regulation of AC activity, increase of levels of a subunit of heterotrimeric stimulatory GTP binding proteins (as) and, remarkably, also in preventing of h-adrenergic receptor-mediated down-regulation of as protein levels. Accumulation of as protein is also accompanied by the appearance of poly-ubiquitinated as species. Our results: (1) identify as protein as a novel proteasome substrate in mammalian cells; (2) indicate that proteasome might play a physiological role in controlling AC/cAMP mediated pathways by modulating the levels of Gas protein; (3) suggest a role for the proteasome also in controlling as-mediated signaling pathways other than those affecting AC complex.