THE ROLES OF PROTEIN-KINASE-C BETA-I AND BETA-II IN VASCULAR SMOOTH-MUSCLE CELL-PROLIFERATION

The role of protein kinase C (PKC) on proliferation of A10 vascular sm ooth muscle cells (VSMC) was studied by overexpressing specific PKC-be ta I and -beta II isozymes, PKC-beta I and -beta II are derived from a lternative splicing of the exon encoding the carboxy-terminal (C-termi nal) 50 or 52 amino acids, respectively. The differential functions of the two isozymes with regard to cell proliferation, DNA synthesis, an d the cell cycle were investigated in A10 cells, a clonal cell line of VSMC from rat aorta, and in A10 cells overexpressing PKC-beta I and P KC-beta II (beta I-A10 and beta II-A10), PKC levels were increased thr ee-to fourfold in heterogeneous cultures of stably transfected cells. Although doubling time of A10 cells was 36 h, the cell doubling time i n beta I-A10 cells decreased by 12 h, and, in contrast, the doubling t ime of beta II-A10 cells increased by 12 h compared to A10 cells. The increase of[H-3]thymidine (TdR) incorporation was accelerated and incr eased in beta I-A10 cells, but slowed and diminished in beta II-A10 ce lls compared to A10 and control cells transfected with empty vector. C ell cycle analysis of beta I-A10 cells showed an acceleration of S pha se entry while beta II-A10 cells slowed S phase entry. These results s uggest that PKC-beta I and PKC-beta II regulate cell proliferation bid irectionally and that PKC-beta I and PKC-beta II may have distinct and opposing functions as cell cycle check point mediators during late G( 1) phase and may regulate S phase entry in A10 VSMC. (C) 1998 Academic Press.