Cholesterol-enrichment reduces oa subunits in arterial smooth muscle cells: relationship to POI2 synthesis
Alterations in G-protein-mediated production of secondary messengers have been documented in atherosclerosis. However, the influence of cholesterol (CH) accumulation on G-protein-mediated signalling events leading to PGI2 synthesis are unknown. We tested the hypothesis that CHenrichment alters Ga expression and PGI2 synthesis. CH-enrichment reduced membrane-associated Gαi(1-3) protein without altering steady state mRNA levels. Our data suggest that reduced Ga expression may be due to reduced y-subunit prenylation since: (1) The effect of CH-enrichment on Gai was mimicked by 25-OH-CH, and was attenuated by mevalonate; and (2) CH-enrichment also diminished βγ content. Activities of Gai, which include thrombin-induced GTPase activity and thrombininduced inhibition of cAMP, were also reduced by CH-enrichment. In contrast, G-protein agonists (AlF4 -, GTP-yS, and ATP) stimulated PGI2 production through activation of PLA2, which was augmented over two-fold following CH-enrichment. This occured in spite of the observation that CH-enrichment reduced AlF4 --induction of MAP-kinase, which activates cPLA2. Collectively, these data suggest that CH-enrichment may alter signalling pathways specific for G-protein-mediated PGI2 production.