LOCALIZATION OF A HETEROTRIMERIC G-PROTEIN GAMMA-SUBUNIT TO FOCAL ADHESIONS AND ASSOCIATED STRESS FIBERS

Signal transducing heterotrimeric G proteins are responsible for coupl ing a large number of cell surface receptors to the appropriate effect or(s). Of the three subunits, 16 alpha, 4 beta, and 5 gamma subunits h ave been characterized, indicating a potential for over 300 unique com binations of heterotrimeric G proteins. To begin deciphering the uniqu e G protein combinations that couple specific receptors with effecters , we examined the subcellular localization of the gamma subunits. Usin g anti-peptide antibodies specific for each of the known gamma subunit s, neonatal cardiac fibroblasts were screened by standard immunocytoch emistry. The anti-gamma(5) subunit antibody yielded a highly distincti ve pattern of intensely fluorescent regions near the periphery of cell that tended to protrude into the cell in a fibrous pattern. Dual stai ning with anti-vinculin anti-body showed co-localization of the gamma( 5) subunit with vinculin. In addition, the gamma(5) subunit staining e xtended a short distance out from the vinculin pattern along the protr uding stress fiber, as revealed by double staining with phalloidin. Th ese data indicated that the ys subunit was localized to areas of focal adhesion. Dual staining of rat aortic smooth muscle cells and Schwann cells also indicated co-localization of the ys subunit and vinculin, suggesting that the association of the ys subunit with areas of focal adhesion was widespread.