Induction of p16ink4a and P19ARF by TGFβ1 Contributes to Growth Arrest and Senescence Response in Mouse Keratinocytes

TGF beta 1 acts as a potent negative regulator of the cell cycle and tumor suppressor in part through induction of cyclin dependent kinase inhibitors p15(ink4b), p21, and p57. We previously showed that primary mouse epidermal keratinocytes (MEK) expressing a v-ras(Ha) oncogene undergo hyperproliferation followed by growth arrest and senescence that was dependent on TGF beta 1 signaling and associated with increased levels of p16(ink4a) and p19(ARF). Here we show that the induction of both p16(ink4a), and p19(ARF) in v-ras(Ha) expressing keratinocytes is dependent on TGF beta 1 signaling, as TGF beta 1 treatment or Smad3 overexpression induces both p16(ink4a) and p19(ARF) protein and mRNA, while Smad3 depletion or Smad7 overexpression blocks induction. Genetic ablation of the cdkn2a (ink4alaf) locus reduced sensitivity to TGF beta 1 mediated cell cycle arrest and induction of senescence suggesting that alteration of TGF beta 1 responses may be an additional pathway impacted by the inactivation of cdkn2a locus during tumor development. (C) 2008 Wilev-Liss, Inc