P53 Is A Direct Transcriptional Repressor Of Keratin 17 Gene In Radiation Epidermis

Ionizing radiation(IR)is a common therapeutic agent in cancer therapy.When IR kill the cancer cells it also damage normal tissue and induces lots of side effects such as dermatitis and mucositis.Excess ultraviolet radiation may also cause similar skin reactions to ionizing radiation.The tumor supressor p53 is actived when the skin exposure to IR or ultraviolet.p53 is the key regulator protein in cell involved in stabilizing the genome,repairing the DNA damage and controlling the cell cycle processing.Keratins are a family of intermediate filaments that are critical for providing structural stability to epithelial cells.Recently,keratins have been found to have a wide array of additional functions,including the control of metabolic processes and regulation of cellular growth,proliferation,migration and apoptosis.Of special interest is keratin 17(Krt17),which is involved in wound healing,the regulation of nail and hair growth via impacting e.g.on TNF-alpha production,protein synthesis and epithelial growth,immune responses and tumorigenesis.Recent studies show that the expression of Krtl7 is regulated by c-Jun,Glil,STAT1/3 and ERK1/2.However,our current knowledge on the transcription factors which regulate Krt 17 expression during IR or ultraviolet,and their complex interplay,remains sparse.To investigate expression changes of Krt17 and regulating factors in the radiation damage skin model,the skin damage model of ionizing radiation was established in the rat.At the different times after radiation,skin samples were made for gene expression analysis.Results show that at the third and sixth day after ionizing radiation,the expression of Krt17 decrease,the expression of p21-downstream of the p53 gene-rise.Western blot analysis found that Krt17 protein levels drop,at the same time,p53 activated in the immunostaining assay.In order to further explore whether there is a regulation relationship between p53 and Krt17,the skin of wild-type and p53-/-mice were radiated by ionizing and ultraviolet.It proves that p53 negative regulate the expression of Krt17 by quantitative real-time PCR and immunostaining.The analysis of Krt17 promoter luciferase reporter assay also confirmed it.Meanwhile,the CHIP assay found-978--675 area in Krt17 promoter contains p53 binding sites.Finally,p53 binding sites were found on the promoter sequences of Krt17,through the Krt17 promoter analysis and EMSA experiments.In summary,we define Krt17 was a novel p53 target gene though establishing radiation damage skin model.Meanwhile,p53 binding sites was found on the promoter region of Krt17.The findings provide new ideas and methods for mitigation and clinical treatment of skin damage caused by the radiation.