Correlation between deregulated expression of PER2 gene and degree of glioma malignancy

Growing evidence indicates that disruption of circadian rhythms may be a risk factor for the development of glioma. However, the molecular mechanisms underlying the genetic regulation of circadian rhythms in glioma cells have yet to be explored.

Using immunohistochemical staining and methylation-specific PCR techniques, we examined the expression of the period 2 (PER2) gene, one of the most important clock genes, epidermal growth factor receptor (EGFR), and proliferating cell nuclear antigen (PCNA) in 92 gliomas.

Our results revealed disturbances in the expression of PER2 in most (52.17%) glioma cells compared with the expression in nearby noncancerous cells, and indicated that PER2 gene deregulation most likely occurs via methylation of PER2 promoters. The protein expression of PCNA and EGFR was significantly higher in high-grade than low-grade gliomas (P < 0.05). Furthermore, a negative correlation was detected between the protein expression of PER2 and PCNA and EGFR in glioma.

Because the circadian clock regulates the expression of cell cycle-related genes, we suggest that disturbances in PER2 gene expression may disrupt the regulation of the circadian clock, thus enhancing the survival of cancer cells and promoting carcinogenesis.