Mutation of the gene encoding the circadian clock component PERIOD2 in oncogenic cells confers chemoresistance by up-regulating the gene.

Disruption of circadian rhythms has been implicated in an increased risk for cancer development. The Period2 () gene encodes one of the major components of the mammalian circadian clock, which plays a key role in controlling the circadian rhythms in physiology and behavior. PER2 has also been reported to suppress the malignant transformation of cells, but its role in the regulation of cancer susceptibility to chemotherapeutic drugs remains unclear. In this study, we found that oncogene-transformed embryonic fibroblasts prepared from -mutant ( ) mice, which are susceptible to both spontaneous and radiation-induced tumorigenesis, were resistant against common chemotherapeutic drugs and that this resistance is associated with up-regulation of the aldehyde dehydrogenase 3a1 () gene. Co-expression of the oncogenes and SV40 large T-antigen induced malignant transformation of both WT and cells, but the cytotoxic effects of the chemotherapeutic agents methotrexate, gemcitabine, etoposide, vincristine, and oxaliplatin were significantly alleviated in the oncogene-transformed cells. Although introduction of the two oncogenes increased the expression of in both WT and cells, the ALDH3A1 protein levels in the cells were ∼7-fold higher than in WT cells. The elevated ALDH3A1 levels in the oncogene-transformed cells were sufficient to prevent chemotherapeutic drug-induced accumulation of reactive oxygen species. Consequently, shRNA-mediated suppression of Aldh3a1 expression relieved the chemoresistance of the cells. These results suggest a role for mutated PER2 in the development of multiple drug resistance and may inform therapeutic strategies for cancer management.