The p53
tumor suppressor is a mutational target of environmental
carcinogen anti-
benzo[a]pyrene-7,8-diol-9,10-
epoxide (
BPDE). We now demonstrate that p53 plays an important role in regulation of cellular responses to
BPDE. Exposure of p53-null H1299 human
lung cancer cells to
BPDE resulted in S and G(2) phase cell cycle arrest, but not mitotic block, which correlated with induction of
cyclin B1 protein expression, down-modulation of cell division cycle 25C (Cdc25C) and Cdc25B
protein levels, and hyperphosphorylation of Cdc25C (S216),
cyclin-dependent kinase 1 (Cdk1; Y15),
checkpoint kinase 1 (Chk1; S317 and S345) and Chk2 (T68). The
BPDE-induced S phase block, but not the G(2)/M phase arrest, was significantly attenuated by knockdown of Chk1
protein level. The
BPDE-mediated accumulation of sub-diploid fraction (apoptotic cells) was significantly decreased in H1299 cells transiently transfected with both Chk1 and Chk2 specific siRNAs. The H460 human
lung cancer cell line (wild-type p53) was relatively more sensitive to
BPDE-mediated growth inhibition and enrichment of sub-diploid apoptotic fraction compared with H1299 cells. The
BPDE exposure failed to activate either S or G(2) phase checkpoint in H460 cells. Instead, the
BPDE-treated H460 cells exhibited a nearly 8-fold increase in sub-diploid apoptotic cells that was accompanied by phosphorylation of p53 at multiple sites. Knockdown of p53
protein level in H460 cells attenuated
BPDE-induced apoptosis but enforced activation of S and G(2) phase checkpoints. In conclusion, the present study points towards an important role of p53 in regulation of cellular responses to
BPDE in human
lung cancer cells.