Cdk5 is involved in retinoic acid affected cell fate of DU145 cells and HeLa cells

Cdk5 is a small serine/threonine protein kinase which belongs to Cdk family. Unlike other Cdk members, Cdk5 is known to be irrelevant in cell cycle so far. Cdk5 kinase activity is regulated by binding with its activator, p35. Our previous results indicate that Cdk5 and p35 are involved in drugs-induced apoptosis of prostate cancer cells. Retinoic acid (RA) is one of vitamin A-related compounds. Because of its potency on biological functions, it has been widely studied on its novel actions including the ability to inhibit cancer cell growth and to induce apoptosis. Here, we report that RA treatment decreased the growth of human prostate cancer cell line-DU145 and cervical cancer cell line-HeLa, and Cdk5 activity contributed to these inhibitory effects. We identified that RA-induced growth inhibition was correlated to G1 phase arrest in DU145 cells and RA-induced apoptosis of HeLa cells was observed by detecting cell cycle distribution of sub G1 phase. In addition, our results also indicated that RA-induced HeLa apoptosis was Cdk5 activity-dependent by annexin V staining . In conclusion, we provide the evidence implying that Cdk5 and p35 might play important roles in RA-induced DU145 growth inhibition and HeLa apoptosis and the detail mechanisms still need further investigation.