PLATELET-DERIVED GROWTH-FACTOR AND ANGIOTENSIN-II INDUCE DIFFERENT SPATIAL-DISTRIBUTION OF PROTEIN KINASE-C-ALPHA AND KINASE-C-BETA IN VASCULAR SMOOTH-MUSCLE CELLS

Protein kinase C is an important second-messenger system that is translocated from the cytosol to the cell membrane on cell stimulation. We used confocal microscopy to study the spatial distribution of protein kinase C isoforms after stimulation of cultured vascular smooth muscle cells with platelet-derived growth factor and angiotensin II (Ang II). Monoclonal antibodies for the isoforms alpha and beta were used. Translocation was also assessed by Western blot. Isoform alpha was evenly distributed in the cytosol, whereas the beta isoform formed coarse granules in the perinuclear region. Both isoforms shifted from the cytosolic to the membrane fraction after exposure to Ang II (10(-7) mol/L) and platelet-derived growth factor (100 ng/mL at 6, 12, and 20 minutes). Confocal microscopy showed a rapid assembly of isoform alpha along cytosolic fibers at 6 minutes followed by a translocation toward the nucleus at 12 minutes with Ang II. Platelet-derived growth factor engendered a similar response; however, a cytoskeletal distribution was not observed. The beta isoform was rapidly translocated by both inducers to the perinuclear region and the nucleus. Our results show that inducers cause a translocation of protein kinase C isoforms not only into the cell membrane but also into the cell nucleus. We suggest that protein kinase C may also be important for nuclear signaling.