Regulation of the Catalase Gene Promoter by Sp1, CCAAT-Recognizing Factors, and a WT1/Egr-Related Factor in Hydrogen Peroxide-Resistant HP100 Cells.

Reactive oxygen species (ROS) play a critical role in the onset of apoptosis induced by various extracellular stimuli, including ionizing radiation. Therefore active regulation of ROS-metabolizing enzymes may be one response to an apoptotic stimulus. In this regard HP100 cells, H2O2-resistant variants derived from human leukemia HL60 cells, display an interesting phenotype wherein the activity of catalase is constitutively high, while its mRNA is reduced after X ray-irradiation. In the present study, we investigated the molecular mechanisms underlying this phenomenon. By combining analyses from nuclear run-on, reporter gene transient transfection, genomic footprinting, site-directed mutagenesis, EMSA, and Western blotting experiments, we found that constitutively elevated catalase expression is strongly regulated at the transcriptional level by both Sp1 and CCAAT-recognizing factors, and that much higher levels of nuclear Sp1 and NF-Y are present in HP100 as compared to HL60 nuclei. In addition, we demonstrated an X ray-inducible association of a WT1/Egr-related factor with an overlapping Sp1/Egr-1 recognition sequence located within the core promoter of the catalase gene. This association may lead to inactivation of the promoter by disturbing, or competing with, the transactivating ability of Sp1.41st Annual Meeting, The American Society for Cell Biolog