p14ARF activates a Tip60-dependent and p53-independent ATM/ATR/CHK pathway in response to genotoxic stress

p14(ARF) is a tumor suppressor that controls a well-described p53/Mdm2-dependent checkpoint in response to oncogenic signals. Here, new insights into the tumor-suppressive function of p14(ARF) are provided. We previously showed that p14(ARF) can induce a p53-independent G(2) cell cycle arrest. In this study, we demonstrate that the activation of ATM/ATR/CHK signaling pathways contributes to this G(2) checkpoint and highlight the interrelated roles of p14(ARF) and the Tip60 protein in the initiation of this DNA damage-signaling cascade. We show that Tip60 is a new direct p14(ARF) binding partner and that its expression is upregulated and required for ATM/CHK2 activation in response to p14(ARF). Strikingly, both p14(ARF) and Tip60 products accumulate following a cell treatment with alkylating agents and are absolutely required for ATM/CHK2 activation in this setting. Moreover, and consistent with p14(ARF) being a determinant of CHK2 phosphorylation in lung carcinogenesis, a strong correlation between p14(ARF) and phospho-CHK2 (Thr68) protein expression is observed in human lung tumors (P < 0.00006). Overall, these data point to a novel regulatory pathway that mediates the p53-independent negative-cell-growth control of p14(ARF). Inactivation of this pathway is likely to contribute to lung carcinogenesis.