Abstract
Abstractp53 is a transcription factor that drives the expression of down-stream effector genes when its activity is induced, such as by exposure to UV irradiation. The effector genes transactivated by p53 seem to play important roles in cellular DNA damage reponses, and leading to G1 arrest, repair, and apoptosis. Previous studies in our laboratory have shown that p53 in CHO. K1 contained a single missense mutation at codon 211, and the CHO.K1 cells on UV irradiation failed to arrest at G1 phase even when the cells were transfected with a wild type human p53 gene. Indicating that the failure probably was not caused by dysfunction of its p53. Our study proffers the possibility that CHO.K1 p53 protein is functional as a transcription activator and that the failure of G1 arrest is secondary to its interacting components. In accordance with the hypothesis, we analyzed the protein level of two p53-inducible gene, p21 ( waf1/cip1 ) and gadd45 . p21 ( waf1/cip1 ) is undetectable in the UV-treated cells, whereas GADD45 is UV inducible. The mRNA level of p21 ( waf1/cip1 ) is then analyzed by RT-PCR and northern blotting, the results shown that p21 ( waf1/cip1 ) mRNAs can not be detected in CHO.K1 cells on UV irradiation. As GADD45 is UV inducible in the cells, suggesting that the endogenous p53 is able to induce gadd45, the absence of p21 ( waf1/cip1 ) mRNAs is unlikely to be attributable to the dysfunction of p53. We suggest that it is probably due to the defect of the promoter sequence of p21 ( waf1/cip1 ), and the deficiency of p21 ( waf1/cip1 ) transcription may be responsible for the cell's failure to arrest at G1 following the UV irradiation.