RESUMO
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.
Assuntos
Inibidor p16 de Quinase Dependente de Ciclina/fisiologia , Inibidor de Quinase Dependente de Ciclina p21/biossíntese , Raios Ultravioleta , Animais , Antígenos de Superfície/análise , Antígenos de Superfície/metabolismo , Linhagem Celular , Células Cultivadas , Inibidor p16 de Quinase Dependente de Ciclina/antagonistas & inibidores , Inibidor p16 de Quinase Dependente de Ciclina/genética , Inibidor de Quinase Dependente de Ciclina p21/genética , Citoplasma/química , Proteínas ELAV , Proteína Semelhante a ELAV 1 , Humanos , Camundongos , Camundongos Knockout , Interferência de RNA , Estabilidade de RNA , Proteínas de Ligação a RNA/análise , Proteínas de Ligação a RNA/metabolismo , Proteína Supressora de Tumor p53/biossíntese , Regulação para CimaRESUMO
p16(INK4a) (hereafter referred to as p16), a major cyclin-dependent kinase (CDK) inhibitor, is the product of a tumor-suppressor gene that has been found inactivated in different cancer types. In the present study, we sought to investigate the role of p16 in apoptosis induced by ultraviolet light (the most important etiological cause of skin cancer) and cisplatin (an anticancer DNA damaging agent). It is clearly shown that p16-compromised osteosarcoma U2OS cell line and p16-/- mouse embryo fibroblasts are sensitive to UV-induced apoptosis, as compared to their respective isogenic p16-expressing cells (EH1, EH2) and p16 +/+, indicating that p16 protects cells from undergoing apoptosis in response to UV light. Importantly, this reduction in UV-mediated apoptosis was associated with downregulation of the proapoptotic Bax protein, with no effect on Bcl-2 expression, suggesting that this antiapoptotic role of p16 is mediated via the intrinsic-mitochondrial pathway. On the other hand, p16 sensitized cells to cisplatin-mediated apoptosis through Bcl-2 decline. Interestingly, only proliferating but not G1-arrested EH1 cells underwent apoptosis in response to the anticancer drug. These novel findings provide further insight into the role of p16 in carcinogenesis, and has potential implications for future therapy strategies.