Induction of the cholesterol metabolic pathway regulates the farnesylation of RAS in embryonic chick heart cells: a new role for ras in regulating the expression of muscarinic receptors and G proteins.

Abstract

We propose a novel mechanism for the regulation of the processing of Ras and demonstrate a new function for Ras in regulating the expression of cardiac autonomic receptors and their associated G proteins. We have demonstrated previously that induction of endogenous cholesterol synthesis in cultured cardiac myocytes resulted in a coordinated increase in expression of muscarinic receptors, the G protein alpha-subunit, G-alphai2, and the inward rectifying K+ channel, GIRK1. These changes in gene expression were associated with a marked increase in the response of heart cells to parasympathetic stimulation. In this study, we demonstrate that the induction of the cholesterol metabolic pathway regulates Ras processing and that Ras regulates expression of G-alphai2. We show that in primary cultured myocytes most of the RAS is localized to the cytoplasm in an unfarnesylated form. Induction of the cholesterol metabolic pathway results in increased farnesylation and membrane association of RAS. Studies of Ras mutants expressed in cultured heart cells demonstrate that activation of Ras by induction of the cholesterol metabolic pathway results in increased expression of G-alphai2 mRNA. Hence farnesylation of Ras is a regulatable process that plays a novel role in the control of second messenger pathways.