Overexpression of cell cycle inhibitors (p16(INK4) and p21(Cip1)) and cyclin D1 using adenovirus vectors regulates proliferation of rat mesangial cells

To elucidate the mechanisms of the cell cycle of mesangial cells, adenovirus vectors containing coding sequences of cyclin D1 (AxCAD1), p16(INK4) (AxCAp16) and p21(Cip1) (AxCAp21) were produced and investigated to determine whether transfer of these genes changes serum- and PDGF-induced proliferation of rat mesangial cells. Efficiency of the transfer of the genes was examined by Northern and Western blot analyses. The cell cycle of mesangial cells was evaluated by measurement of [H-3]-thymidine incorporation, flow cytometry, and cyclin-dependent kinase 4 kinase assay. Expression of cyclin D1, p16(INK4) and p21(Cip1) was observed from 24 h after the infection, and the expression increased up to 48 h. AxCAp16 and AxCAp21 caused a significant inhibition in the [H-3]-thymidine incorporation to 47% and 76%, respectively. AxCAp16 and AxCAp21 also inhibited the mitogen-induced increase in cyclin-dependent kinase 4 kinase activity and reduced the percentage of cells in S phase, Coinfection of AxCAp16 with AxCAp21 showed no additive inhibition. Overexpression of cyclin D1 reduced cell size and increased the percentage of the cells in S and G2 phase. These findings suggest that p16(INK4) and p21(Cip1) function as inhibitors of the proliferation of mesangial cells induced by growth-promoting factors and that deregulated expression of cyclin D1 causes cell cycle disturbances. Adenovirus-mediated gene transfer of p16(INK4) and p21(Cip1) serves as a potential therapeutic approach to mesangial proliferative diseases.