The Roles of Protein Kinase C βI and βII in Vascular Smooth Muscle Cell Proliferation

Abstract

The role of protein kinase C (PKC) on proliferation of A10 vascular smooth muscle cells (VSMC) was studied by overexpressing specific PKC-βI and -βII isozymes. PKC-βI and -βII are derived from alternative splicing of the exon encoding the carboxy-terminal (C-terminal) 50 or 52 amino acids, respectively. The differential functions of the two isozymes with regard to cell proliferation, DNA synthesis, and the cell cycle were investigated in A10 cells, a clonal cell line of VSMC from rat aorta, and in A10 cells overexpressing PKC-βI and PKC-βII (βI-A10 and βII-A10). PKC levels were increased three- to fourfold in heterogeneous cultures of stably transfected cells. Although doubling time of A10 cells was 36 h, the cell doubling time in βI-A10 cells decreased by 12 h, and, in contrast, the doubling time of βII-A10 cells increased by 12 h compared to A10 cells. The increase of [3H]thymidine (TdR) incorporation was accelerated and increased in βI-A10 cells, but slowed and diminished in βII-A10 cells compared to A10 and control cells transfected with empty vector. Cell cycle analysis of βI-A10 cells showed an acceleration of S phase entry while βII-A10 cells slowed S phase entry. These results suggest that PKC-βI and PKC-βII regulate cell proliferation bidirectionally and that PKC-βI and PKC-βII may have distinct and opposing functions as cell cycle check point mediators during late G1phase and may regulate S phase entry in A10 VSMC.