Anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (anti-BPDE) is a metabolite of benzo[a]pyrene (B[a]P) and acts as a potent mutagen in mammalian systems. However, the molecular mechanisms related to anti-BPDE-induced carcinogenesis are poorly understood. We have used malignant human bronchial epithelial cells (16HBE-T) transformed by exposure to anti-BPDE to help characterize these possible molecular mechanisms. We have previously observed overexpression of HER2/neu in 16HBE-T. To further investigate the effects of HER2/neu on 16HBE-T cell biologic phenotype, we inhibited HER2/neu expression using RNA interference. Silencing of HER2/neu in 16HBE-T cells was performed in vitro using retrovirus-delivered short hairpin RNA (shRNA). Silencing of HER2/neu in 16HBE-T cells resulted in significant increases and decreases in the proportions of cells in G0/G1 phase (67.1+/-2.1%) and in S phase (17.3+/-4.1%), respectively, and significantly reduced cell viability and colony formation rate. These results may help to explain epithelial cell transformation following exposure to anti-BPDE, and suggest an oncogenic role for HER2/neu in anti-BPDE-induced carcinogenesis.