Inhibition of ERK and p38 MAP kinases inhibits binding of Nrf2 and induction of GCS genes.

Genes encoding the catalytic (GCS(h)) and regulatory (GCS(l)) subunits of human gamma-glutamylcysteine synthetase (gammaGCS), which catalyzes the rate limiting step in glutathione synthesis, are up-regulated in response to xenobiotics through Electrophile Response Elements (EpREs). Exposure of HepG2 cells to the GCS-inducing agent, Pyrrolidine dithiocarbamate (PDTC), results in ERK and p38 MAP kinase activation. Inhibition of ERK or p38 kinases by PD98059 or SB202190, respectively, results in approximately 50% reduction in GCS gene induction, while simultaneous inhibition completely eliminates induction. Induction of GCS expression is associated with an increase in Nrf2 and JunD binding to GCS EpREs. Pretreatment with the MAPK inhibitors significantly reduces binding of both transcription factors. These studies indicate that ERK and p38 contribute to the transcriptional up-regulation of the GCS subunit genes following PDTC treatment. Furthermore, supershift analyses suggest that binding of Nrf2 and JunD to the EpRE is a downstream consequence of ERK and p38 phosphorylation events.