Signal Transduction in Atria and Ventricles of Mice With Transient Cardiac Expression of Activated G Protein α q

Abstract

Abstract —We recently showed that the transient expression of a hemagglutinin (HA) epitope–tagged, constitutively active mutant of the G protein α q subunit (HAα q *) in the hearts of transgenic mice is sufficient to induce cardiac hypertrophy and dilatation that continue to progress after HAα q * protein becomes undetectable. We demonstrated that the activity of phospholipase Cβ, the immediate downstream target of activated Gα q , is increased at 2 weeks, when HAα q * is expressed, but also at 10 weeks, when HAα q * is no longer detectable. This observation suggested that the transient HAα q * expression causes multiple, persistent changes in cellular signaling pathways. We now demonstrate changes in the level, activity, or both of several signaling components, including changes in the amount and hormone responsiveness of phospholipase Cβ enzymes, in the basal level of diacylglycerol (which predominantly reflects activation of phospholipase D), in the amount or distribution of protein kinase C (PKC) isoforms (PKCα, PKCδ, and PKCε), and in the amount of several endogenous G proteins. These changes vary depending on the isoform of the signaling molecule, the chamber in which it is expressed, and the presence or absence of HAα q *. Our results suggest that a network of linked signaling functions determines the development of hypertrophy. They also suggest that atria and ventricles represent different signaling domains. It is likely that such changes occur in other model systems in which the activity of a single signaling component is increased, either due to an activating mutation or due to overexpression of the wild type.