The circadian gene Period2 plays an important role in tumor suppression and DNA damage response in vivo.

The Period2 gene plays a key role in controlling circadian rhythm in mice. We report here that mice deficient in the mPer2 gene are cancer prone. After gamma radiation, these mice show a marked increase in tumor development and reduced apoptosis in thymocytes. The core circadian genes are induced by gamma radiation in wild-type mice but not in mPer2 mutant mice. Temporal expression of genes involved in cell cycle regulation and tumor suppression, such as Cyclin D1, Cyclin A, Mdm-2, and Gadd45alpha, is deregulated in mPer2 mutant mice. In particular, the transcription of c-myc is controlled directly by circadian regulators and is deregulated in the mPer2 mutant. Our studies suggest that the mPer2 gene functions in tumor suppression by regulating DNA damage-responsive pathways.