Hemin-induced activation of the thioredoxin gene by Nrf2 - A differential regulation of the antioxidant responsive element by a switch of its bindingfactors

Thioredoxin plays an important role in various cellular processes through r edox regulation. Here, we have demonstrated that thioredoxin expression is transcriptionally induced in K562 cells by hemin (ferriprotoporphyrin IX) t hrough activation of a regulatory region positioned from -452 to -420 bp of the thioredoxin gene. Insertion of a mutation in the antioxidant responsiv e element (ARE)/AP-1 consensus binding sequence in this region abolished th e response to hemin. With electrophoretic mobility shift and DNA affinity a ssays, we have shown that the NF-E2p45/small Maf complex constitutively bin ds to the ARE. The binding of the Nrf2/small Maf complex to ARE was induced by hemin, whereas the binding of Jun/Fos proteins to ARE was induced by ph orbol 12-myristate 13-acetate, but not hemin, Hemin induced nuclear translo cation of Nrf2 but did not affect nuclear expression of Jun/Fos proteins. O verexpression of Nrf2 augmented the response to hemin in a dose-dependent m anner. In contrast, overexpression of the dominant negative mutant of Nrf2 suppressed hemin-induced activation through the ARE. We show here hemin-ind uced activation of the thioredoxin gene by Nrf2 through the ARE and propose a novel mechanism of the regulation of the ARE through a switch of its bin ding factors.