Cell cycle inhibitors (p27(Kip1) and p21(CIP1)) cause hypertrophy in LLC-PK1 cells

Background Angiotensin II has been reported to induce renal tubular hypertr ophy, but the mechanisms of this hypertrophy are not well known. We evaluat ed the roles of cyclin-dependent kinase (CDK) inhibitors in renal tubular h ypertrophy. Methods. To elucidate whether CDK inhibitors cause renal tubular hypertroph y, we produced adenovirus vectors containing coding sequences of the CDK in hibitors p27(Kip1) (AxCAp27), p21(CIP1) (AxCAp21), and p16(INK4) (AxCAp16) and we investigated the effect of these gene transfers on epidermal growth factor (EGF)-induced proliferation in LLC-PK1 cells. We evaluated the cell cycle and hypertrophy by measurements of the [H-3]- leucine and [H-3]-thymi dine incorporation, the protein DNA ratio, flow cytometry, and CDK4 and CDK 2 kinase assays. Results. AxCAp27 and AxCAp21 caused significant increases in [H-3]-leucine incorporation and the protein:DNA ratio but did not change the [H-3]-thymid ine incorporation. Conversely, AxCAp16 inhibited EGF-stimulated [H-3]-thymi dine incorporation but did not change the [H-3]-leucine incorporation. AxCA p27, AxCAp21, and AxCAp16 all inhibited EGF-stimulated CDK4 kinase activity (to 15.6, 14.1, and 21.9% of control, respectively). Forward light-scatter analysis demonstrated that AxCAp27 and AxCAp21 increased the cell size but that AxCAp16 effected no change in cell size. Conclusion. These findings suggest that p27(Kip1) and p21(CIP1) may play an important role in hypertrophy of renal tubule cells by reducing pRb phosph orylation. On the other hand, p16(INK4) was not found to cause hypertrophic changes in EGF-treated LLC-PK1 cells.