Rb independent inhibition of cell growth by p15(INK4B)

The INK4 cyclin dependent kinase inhibitors (CDKI), such as p15(INK4B) and p16(INK4A), block cell cycle progression from G to S phase. This is mediate d by inhibition of phosphorylation of proteins, including the retinoblastom a susceptibility protein (Rb), by cyclin dependent kinases. Ectopic over-ex pression of the p16(INK4A) CDKI can inhibit growth of cell lines depending on Rb status. Cell lines lacking Rb, with few exceptions, are resistant to growth inhibition by p16(INK4A). The effects of ectopic over-expression of p15(INK4B) in cell lines with and without wild type Rb were examined by mea suring cell recovery. Proliferation was inhibited in cells lacking Rb as we ll as in cells with wild type Rb expression. Experiments analyzing the effe ctiveness of chimeric p15(INK4B)/p16(INK4A) proteins indicated that the Rb independent growth inhibition required N-terminal residues of p15(INK4B). L inker insertion mutation of p15(INK4B) showed that the inhibition was depen dent on intact ankyrin structures. Double staining flow cytometry found tha t the growth inhibition correlated with a decrease in cells in G2/M phases of the cell cycle. These findings are consistent with Rb independent inhibi tion of the progression hom G1 to S caused by overexpression of p15(INK4B) (C) 1999 Academic Press.