Transcriptional control of the rat heme oxygenase gene by a nuclear protein that interacts with adenovirus 2 major late promoter

Induction of rat heme oxygenase is mediated by at least two factors: its substrate heme and heat shock (Shibahara, S., Muller, R.M., and Taguchi, H. (1987) J. Biol. Chem. 262, 12889-12892). We have identified the cis-acting element of the rat heme oxygenase gene (HO gene), that was specifically bound by a nuclear protein prepared from rat glioma cells. We have termed this protein as heme oxygenase transcription factor (HOTF), whose estimated molecular weight is about 40,000. The element identified is CCACCACGT-GACTCGAG (-51/-35) located just upstream of TATA-like sequence. The functional studies indicate that this sequence is required for the accurate and efficient initiation of transcription from the HO gene promoter. Since the HOTF-binding element is similar to the upstream promoter sequence (UPS) of the adenovirus 2 major late promoter (Ad2MLP), we examined whether rat HOTF is homologous to the upstream stimulatory factor (USF) or major late transcription factor previously identified in HeLa cells, which interacts with the UPS and activates the transcription from the Ad2MLP. HOTF specifically binds to the UPS of Ad2MLP, whereas HOTF failed to form a stable complex with the mutated HOTF-binding element lacking a GTGA sequence (-44/-42 of the HO gene), the sequence of which is identical to a core sequence of the USF-binding sites. Moreover, we show that like USF, HOTF is heat stable. These results suggest that HOTF may be homologous to USF or the major late transcription factor. Since USF is present in uninfected cells, it is conceivable that the expression of the HO gene is regulated at least in part by USF.