Inhibition of benzo(a)pyrene-induced cell cycle progression by all-trans retinoic acid partly through cyclin D1/E2F-1 pathway in human embryo lung fibroblasts

Benzo(a)pyrene [B(a)P] is a potent environmental carcinogen, which induces cell cycle changes. All-trans retinoic acid (ATRA) is a promising agent in prevention and treatment of human cancers. In the present study, we investigated the inhibition of B(a)P-induced cell cycle progression by ATRA in human embryo lung fibroblast (HELF). Our results showed that after treatment with B(a)P, the expression of cyclin D1 and E2F-1 were both increased significantly in HELF. There were almost no changes of CDK4 and E2F-4 expression by treatment with B(a)P. As expected, pretreatment with ATRA could efficiently decrease B(a)P-induced overexpression of cyclin D1 and E2F-1. In a further study, we stably transfected antisense cyclin D1 and antisense CDK4 plasmid into HELF. The inhibition of cyclin D1 expression and the inhibition of CDK4 expression significantly impaired the B(a)P-induced overexpression of E2F-1 respectively. Pretreatment with ATRA, cells expressing antisense cyclinD1 or antisense CDK4 showed a lesser decrease of B(a)P-induced overexpression of E2F-1 compared with similarly treated HELF. Furthermore, flow cytometry analysis showed that B(a)P promoted cell cycle progression from G₁ phase to S phase, while pretreatment with ATRA could inhibit B(a)P-induced cell cycle progression by an accumulation of cells in the G₁ phase. It was suggested that ATRA could block B(a)P-induced cell cycle promotion partly through the cyclin D1/E2F-1 pathway in HELF.