CDKN2A and colorectal cancer: For example, the PER1 protein has been shown to inhibit the cell cycle by interacting with checkpoint proteins ATM and CHK2 in colorectal cancer cells (Gery et al., 2006); similarly, NONO was found to influence the p16-Ink4A site by binding to PER1/PER2 proteins during the G1 phase, linking the cell cycle with the circadian rhythm (Kowalska et al., 2013).