ELEVATED P16 AT SENESCENCE AND EOSS OF P16 AT IMMORTALIZATION IN HUMAN PAPILLOMAVIRUS-16 E6, BUT NOT E7, TRANSFORMED HUMAN UROEPITHELIAL CELLS

CDKN2/p16 inhibits the cyclin D/cyclin-dependent kinase complexes that phosphorylate pRb, thus blocking cell cycle progression. We previousl y reported that p16 levels are low to undetectable in normal human uro epithelial cells (HUCs) and in immortalized uroepithelial cells with f unctional pRb, whereas p16 levels are markedly elevated in immortal HU Cs with altered pRb (T. Yeager et al., Cancer Res., 55: 493-597, 1995) . We now report that elevation of p16 levels occurs at senescence in H UCs, including HUCs transformed by human papillomavirus 16 E7 or E5, w hose oncoprotein products lead to functional toss of pRb and p53, resp ectively. We also report that six of six independently immortalized E7 HUCs show high levels of p16 similar to those observed at WC senescen ce, whereas p16 is undetectable in five of Eve immortal E6 HUCs. Four of the five independent E6 HUCs that lost p16 at immortalization shelv ed hemizygous deletion of the 9p21 region. However, no homozygous CDKN 2 deletions were detected, and only one CDKN2 mutation was identified. For the first time, these data associate elevated p16 with senescence in human epithelial cells. These data also suggest that a component o f immortalization may be abrogation, either by pRb inactivation (as in the E7-transformed HUCs) or by p16 inactivation (as in the E6-transfo rmed HUCs), of a p16-mediated senescence cell cycle block.