p53 protein expression and increased SSCP mobility shifts in the p53 gene in normal urothelium cultured from smokers
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This study provides evidence of a significantly (P = 0.018) increased level of expression of the stable conformation of p53 in normal urothelial cells, cultured in vitro from bladder biopsies obtained from normal smokers without malignant disease of any site. With two significant exceptions, non-smokers showed low or no expression of this protein. Past smokers appeared to segregate into high or low p53 expressers, but the expression was not correlated with years since quitting smoking or with pack years smoked. The mean data in this group were not quite significantly different (P = 0.08) from the non-smoker group, due to the wide inter-patient variation. For most of the smoker group, pack years correlated with p53 expression with a mean unit of 1.7 +/- 0.37% p53 per pack year but there was a small group of very heavy smokers who showed lower than expected expression (approximately 0.3-0.8% p53 per pack year). These were statistical outliers (Grubbs test). No explanation could be found for this. Over-expression of p53 protein, often correlates with mutations in the gene, but may also indicate that breakdown of wild-type p53 has slowed. SSCP analysis of the biopsy material was not possible on all patients due to ethical constraints on the amounts of tissue which could be taken but in the cases where it was possible the association between loss of p53 protein function and mobility shifts in p53 exons 5-8 was confirmed with smokers having 3.5 times the number of mobility shifts detected in non-smoker DNA. Thus the results may point to a role for the early abrogation of p53 protein function in bladder carcinogenesis induced by cigarette smoking.
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