Abstract: Objective To study the p53 signal pathway in keratinocytes damaged by ultraviolet B (UVB) irradiation.Methods Cultured normal human epidermal keratinocytes isolated from the foreskins of healthy children were irradiated with UVB in a dose of 20,60 and 120 mJ/cm²,respectively.The mRNA and protein expression of p53 and its downstream molecules p21,mouse double minute 2 (MDM2),Bax,and growth arrest and DNA damage induced gene 45 (GADD45) was detected by reverse transcription-PCR and Western blotting at 0,2,24,and 48 h after the irradiation.Results The mRNA and protein expression of p53 increased significantly at 2 h after UVB irradiation,and the increase continued until 48 h after the irradiation.None of the p53 effector genes (MDM2,p21,GADD45 and Bax) was transcriptionally induced significantly (P >0.05) after irradiation with low dose of UVB.When the dose of UVB reached 60 mJ/cm²,the mRNA and protein expression of both p21 and Bax increased significantly (both P<0.05) in a time-dependant manner,while those of MDM2 increased only transiently at 2 hrs after the irradiation.Conclusions UVB can trigger the activation of p53 signal pathway in keratinocytes.The expression of p53 downstream molecules is increased by UVB irradiation in a dose-and time-dependent manner in keratinocytes.

Key words: Ultraviolet rays, Keratinocytes, Protein p53, Signal transduction