Attenuation of p53 Response to PAHs by Tumor Promoters

Mukherjee, Jagat

Abstract

There is considerable evidence showing that the prototype polynuclear aromatic hydrocarbon (PAH) benzo[a] pyrene (BP) induces p53 in human and mouse cells, and that 12-O-tetradecanoylphorbol-13-acetate (TPA) and other tumor promoters attenuate this BP-induced p53 up-regulation. We hypothesize that the inhibition of p53 accumulation by TPA is due to (i) inhibition of BP-induced p53 transcription which is activated by nuclear factor kappaB (NF-kappaB) and (ii) decreased p53 protein stability, which is regulated by mouse double minute (MDM) 2 protein level and post-translational modifications of p53 and MDM2 proteins by signal transducing kinase-mediated phosphorylations. We have selected mouse epidermal JB6 (P+) cells and (+)-anti-BPDE (BP-derived ultimate carcinogen) for the proposed study. In order to test the above hypotheses, we propose (i) to investigate the effect of TPA on p53 transcript/protein levels, p53 protein stability and NF-kappaB activation in cells treated with (+)-anti-BPDE, (ii) to examine the effect of TPA on MDM2 protein expression and stability, (iii) to examine the effect of TPA on the activation of PI3-kinase and Akt (involved in mdm2 protein phosphorylation) in relation to p53 response and (iv) to determine the effect of TPA on the activation of ERK1/2 and PKC (involved in p53 protein phosphorylations) in relation to p53 response. The overall objective of the proposed research is to understand the mechanism by which TPA inhibits the (+)-anti-BPDE -induced up-regulation of p53, and thereby elucidate the mechanism(s) underlying the promotion of PAH-induced carcinogenicity by TPA and possibly other tumor promoters.