AP-1 and STAT mediate hyperoxia-induced gene transcription of heme oxygenase-1

We have previously shown marked induction of the stress-inducible gene heme oxygenase-1 (HO-1) in vivo and in vitro after hyperoxia. In RAW 264.7 cell s, HO-1 induction is transcriptionally regulated and dependent on cooperati on between the HO-1 gene promoter and the 5' distal enhancer element SX2. I n our present study, further deletional and mutational analyses demonstrate that signal transducer and activator of transcription (STAT) DNA binding s ites located in the promoter of HO-1 and activator protein (AP)-1 DNA bindi ng sites in the distal enhancer element SX2 are necessary for optimal HO-1 gene activation after hyperoxia. Interestingly, a second 5' distal enhancer element, AB1, located 10 kb upstream from the HO-1 promoter, alone is acti vated after hyperoxia but cannot confer maximal hyperoxia-induced HO-1 gene transcription. Mutational analysis of the AB1 enhancer shows that AP-1 is essential for AB1-mediated HO-1 gene transcription after hyperoxia. Electro mobility shift assays show increased STAT1, STAT3, STAT5, and AP-1 DNA bind ing activity in RAW 264.7 cells after hyperoxia. Taken together, our data s uggest that the 5' distal enhancer elements of the HO-1 gene in concert wit h the promoter regulate HO-1 gene induction and highlight the complexity of HO-1 gene transcription in response to hyperoxia.