PRKCD and hepatoblastoma: Although PKC-mediated phosphorylation of Nrf2 at Serine 40 has been linked to HO-1 induction in cancer cell lines, PKCδ seems to be the isoform involved.45 Moreover, at least in hepatoblastoma cells, PKCε may phosphorylate Keap1 (INrf2) and so target Nrf2 for degradation.