title: The p16INK4a tumor suppressor controls p21WAF1 induction in response to ultraviolet light.
abstract: p16INK4a and p21WAF1, two major cyclin-dependent kinase inhibitors, are the products of two tumor suppressor genes that play important roles in various cellular metabolic pathways. p21WAF1 is up-regulated in response to different DNA damaging agents. While the activation of p21WAF1 is p53-dependent following -rays, the effect of ultraviolet (UV) light on p21WAF1 protein level is still unclear. In the present report, we show that the level of the p21WAF1 protein augments in response to low UVC fluences in different mammalian cells. This up-regulation is mediated through the stabilization of p21WAF1 mRNA in a p16INK4a-dependent manner in both human and mouse cells. Furthermore, using p16-siRNA treated human skin fibroblast; we have shown that p16 controls the UV-dependent cytoplasmic accumulation of the mRNA binding HuR protein. In addition, HuR immunoprecipitations showed that UV-dependent binding of HuR to p21 mRNA is p16-related. This suggests that p16 induces p21 by enabling the relocalization of HuR from the nucleus to the cytoplasm. Accordingly, we have also shown that p16 is necessary for efficient UV-dependent p53 up-regulation, which also requires HuR. These results indicate that, in addition to its role in cell proliferation, p16INK4a is also an important regulator of the cellular response to UV damage.
authors.affiliation: King Faisal Specialist Hospital and Research Center, Department of Biological and Medical Research, MBC # 03-66, PO BOX 3354, Riyadh 11211, KSA.
authors.forename: Mai A
authors.initials: MA
authors.lastname: Al-Mohanna
authors.forename: Huda H
authors.initials: HH
authors.lastname: Al-Khalaf
authors.forename: Nujoud
authors.initials: N
authors.lastname: Al-Yousef
authors.forename: Abdelilah
authors.initials: A
authors.lastname: Aboussekhra
mesh_terms: D000818:Animals; D000954:Antigens, Surface / Q000032:analysis / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis* / Q000235:genetics; D003593:Cytoplasm / Q000737:chemistry; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D034622:RNA Interference; D020871:RNA Stability; D016601:RNA-Binding Proteins / Q000032:analysis / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis; D014466:Ultraviolet Rays; D015854:Up-Regulation
chemical_list: D000954:Antigens, Surface; C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; C098770:ELAVL1 protein, human; D016601:RNA-Binding Proteins; D016159:Tumor Suppressor Protein p53