Nrf2 up-regulates the induction of acidic sphingomyelinase by electrophiles

Acidic sphingomyelinase (ASMase) catalyses the generation of ceramide from sphingomyelin. Ceramide is a lipid mediator and is implicated in mediating and regulating various cellular processes including cell proliferation, differentiation, stress response and inflammation. We have previously reported that electrophiles including diethyl maleate (DEM), heavy metals and cigarette smoke extracts induced ASMase expression in human bladder carcinoma ECV-304 cells, but the mechanism of ASMase mRNA induction by electrophiles remains unknown. In this study, we clarified the involvement of NF-E2-related factor 2 (Nrf2) in the induction of ASMase mRNA by DEM. Promoter analysis using a series of deletion mutants of the human ASMase gene showed that ARE-like element1 located in a region between -200 and -160 bp upstream of the transcription start point is mainly a DEM-responsive element. Moreover, an electrophoretic mobility shift assay using ARE-like element1 revealed that Nrf2 is a candidate transcription factor that binds to ARE-like element1 in response to DEM. Finally, alteration of Nrf2 expression by overexpression and knockdown could regulate the induction of ASMase mRNA by DEM. This is the first evidence that supports the possibility that sphingolipid metabolism is affected via the induction of ASMase by the Nrf2 pathway.