P19(Arf) is required for the cellular response to chronic DNA damage.

Abstract

The p53 tumor suppressor is a stress sensor, driving cell-cycle arrest or apoptosis in response to DNA damage or oncogenic signals. p53 activation by oncogenic signals relies on the p19Arf tumor suppressor, while p53 activation downstream of acute DNA damage is reported to be p19Arf-independent. Accordingly, p19Arf-deficient mouse embryo fibroblasts (MEFs) arrest in response to acute DNA damage. However, p19Arf is required for replicative senescence, a condition associated with an activated DNA damage response, as p19Arf−/− MEFs do not senesce after serial passage. A possible explanation for these seemingly disparate roles for p19Arf is that acute and chronic DNA damage responses are mechanistically distinct. Replicative senescence may result from chronic, low-dose DNA damage responses in which p19Arf has a specific role. We therefore examined the role of p19Arf in cellular responses to chronic, low-dose DNA damaging agent treatment by maintaining MEFs in low oxygen and administering 0.5 Gy γ-irradiation daily or 150μM hydroxyurea, a replication stress-inducer. In contrast to their response to acute DNA damage, p19Arf−/− MEFs exposed to chronic DNA damage do not senesce, revealing a selective role for p19Arf in senescence upon low-level, chronic DNA damage. We show further that p53 pathway activation in p19Arf−/− MEFs exposed to chronic DNA damage is attenuated relative to wild-type MEFs, suggesting a role for p19Arf in fine-tuning p53 activity. However, combined Nutlin3a and chronic DNA damaging agent treatment is insufficient to promote senescence in p19Arf−/− MEFs, suggesting that the role of p19Arf in the chronic DNA damage response may be partially p53-independent. These data suggest the importance of p19Arf for the cellular response to the low-level DNA damage incurred in culture or upon oncogene expression, providing new insight into how p19Arf serves as a tumor suppressor. Moreover, our study helps reconcile reports suggesting crucial roles for both p19Arf and DNA damage signaling pathways in tumor suppression.