Inhibition of cyclooxygenase-2 gene expression by p53

Oncogenes enhance the expression of cyclooxygenase (Cox)-2, but interaction s between tumor suppressor genes and Cox-a have not been studied. In the pr esent work, we have compared the levels of Cox-2 and the production of pros taglandin E-2 in mouse embryo fibroblasts that do not express any p53 ((10) 1) versus the same cell line ((10.1)Val5) engineered to overexpress wild-ty pe (wt) p53 at 32 degrees C or mutant p53 at 39 degrees C. Cells expressing wt p53 showed about a 10-fold decrease in synthesis of prostaglandin E-2 c ompared with those expressing mutant p53. Levels of Cox-2 protein and mRNA were markedly suppressed by wt p53 but not by mutant p53. Nuclear run-offs revealed decreased rates of Cox-2 transcription in cells expressing wt p53. The activity of the Cox-2 promoter was reduced by 85% in cells expressing wt p53 but was reduced only by 30% in cells express ing mutant p53 compared with cells null for p53. The effect of p53 on the suppression of Cox-2 pro moter activity was localized to the first 40 base pairs 5' from the transcr iption start site. Electrophoretic mobility shift assay revealed that p53 c ompeted with TATA-binding protein for binding to mouse Cox-2 or human Cox-2 promoter extending from -50 to +52 base pairs. The results of this study s uggest that interactions between p53 and Cox-2 could be important for under standing why levels of Cox-2 are undetectable in normal cells and increased in many tumors.