CHEK2 and cancer: Furthermore, knockdown PAF-AH 1B2 caused caspases activation and cancer cells cycle arrest, apoptosis, as well as significant rise the phosphorylation levels of related regulatory proteins p53-Ser15, Akt-Ser473, CDC2-Tyr15, Chk2-Tyr68, and the protein level of p21Waf1 and CDC2 (Fig. 4E), all of which have been associated with relate regulation [32, 33].