Cyclin D1 Induction by Benzo[a]pyrene-7,8-diol-9,10-epoxide via the Phosphatidylinositol 3-Kinase/Akt/MAPK- and p70s6k-dependent Pathway Promotes Cell Transformation and Tumorigenesis

Benzoa]pyrene-7,8-diol-9,10-epoxide (Ba]PDE), the major metabolite of Ba]P, has been well recognized as one ubiquitous carcinogen, but the molecular mechanism involved in its carcinogenic effect remains obscure. In the present study, we found that bronchial epithelial cells (Beas-2B) and hepatocytes treated with Ba]PDE presented a significant increase of cyclin D1 expression. Moreover, Akt, p70^s6k, and MAPKs including JNK, Erks, and p38 were notably activated in Ba]PDE-treated Beas-2B cells, whereas NF-κB, NFAT, and Egr-1 were not. Our results demonstrated that JNK and Erks were required in Ba]PDE-induced cyclin D1 expression because the inhibition of JNK or Erks by a selective chemical inhibitor or dominant negative mutant robustly impaired the cyclin D1 induction by Ba]PDE. Furthermore, we found that overexpression of the dominant negative mutant of p85 (regulatory subunit of phosphatidylinositol 3-kinase) or Akt dramatically suppressed Ba]PDE-induced JNK and Erk activation as well as cyclin D1 expression, suggesting that cyclin D1 induction by Ba]PDE is via the phosphatidylinositol 3-kinase/Akt/MAPK-dependent pathway. In addition, we clarified that p70^s6k is also involved in Ba]PDE-induced cyclin D1 expression because rampamycin pretreatment dramatically reduced cyclin D1 induction by Ba]PDE. More importantly, we demonstrated that up-regulated cyclin D1 by Ba]PDE plays a critical role in oncogenic transformation and tumorigenesis of Beas-2B cells. These results not only broaden our knowledge of the molecular mechanism of Ba]PDE carcinogenicity but also lead to the further study of chemoprevention of Ba]PDE-associated human cancers.