PERIOD (PER) proteins are transcriptional regulators that are involved in circadian rhythms, sleep homeostasis, cell proliferation and tumour progression. We previously showed that the expression of PER1 was related to the regulation of apoptosis in human pancreatic cancer and hepatocellular carcinoma cells. However, the significance of PER in oral cancer has not been reported, and the detailed molecular mechanisms by which anti-tumour drug induces apoptosis in gingival cancer cells are not well understood. We examined whether PER1 and PER3 are involved in the regulation of apoptosis in human gingival cancer CA9-22 cells. The expression of PER1 and PER3 was upregulated and downregulated, respectively, by cis-diamminedichloroplatinum (II) (cisplatin: CDDP) treatment in CA9-22 cells, whereas CDDP treatment had little effects on the expression of PER1 and PER3 in human gingival fibroblasts (HGF-1). We found that short interference RNA (siRNA)-mediated knockdown of PER1 enhanced apoptosis of CA9-22 cells, and that PER1 regulated the amount of Bim, an apoptosis-related molecule. On the other hand, PER3 knockdown had an inhibitory effect on the apoptosis of CA9-22 cells induced by CDDP treatment. These results suggest that the alternation of expression of PER1 and PER3 was related to the apoptosis of CA9-22 cells. Furthermore, PER1 was intensely stained in the gingival cancer tissues, whereas PER3 was significantly stained in the non-tumour tissues by immunohistochemistry. These findings suggest that PER1 and PER3 have anti-apoptotic and pro-apoptotic effects in human gingival cancer CA9-22 cells, respectively. The balance of PER1 and PER3 may modulate apoptotic reactions in gingival cancer cells.
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