SH3GLB2 and neoplasm: Moreover, our previous studies [12-14] reported that benzo[a]pyrene diol epoxide (BPDE), a carcinogen present in tobacco smoke and environmental pollution, as well as bile acid, a tumor promoter in the gastrointestinal tract, inhibited RRIG1 expression, whereas retinoic acid induced RRIG1 expression, which was associated with downregulation of RAR-β2 expression by these carcinogens.