Reduction in Gh protein expression is associated with cytodifferentiation of vascular smooth muscle cells

Gh, a high molecular weight GTP-binding protein that couples alpha 1-adrenoceptors in heart and liver to phosphatidylinositol (PtdIns)-specific phospholipase C (PLC), has recently been shown to be a tissue transglutaminase type II. Transglutaminases have been suggested to play a role in the maintenance of blood vessel structure, and therefore it is possible that changes in their expression may accompany pathological states which involve phenotypic modulation of smooth muscle. Hence, we investigated the expression of Gh during differentiation of rat aortic smooth muscle cells in culture. Gh content was reduced markedly in cultured smooth muscle cells compared to freshly isolated cells as determined by Western blotting using a Gh-specific monoclonal antibody. In contrast, the level of Gq, a heterotrimeric G-protein that couples alpha 1-adrenoceptors to PLC, was maintained throughout the culture period. These findings indicate that changes in Gh expression accompany phenotypic modulation of vascular smooth muscle cells. These changes in Gh protein expression may be important in the altered responsiveness of vessels in pathological disease states.