PER1 and central nervous system cancer: Functionally, PER1 and PER2 sustain the normal cell cycle via regulating the expression of P53 and c-Myc (101) Supporting these data, other studies demonstrated that high levels of PER2 in cancer cell lines and glioma xenografts correlated with increased induction of P53 and apoptosis (102) and overexpression of PER2 in irradiated glioma induces a decreased of c-Myc mRNA and protein levels (100).