IDENTIFICATION AND FUNCTIONAL-CHARACTERIZATION OF THE BOVINE MANGANOUS SUPEROXIDE-DISMUTASE PROMOTER

Manganous superoxide dismutase (MnSOD) gene expression is stimulated by endotoxin, tumor necrosis factor, and interleukin-1, agents thought to cause cellular damage through intracellular generation of reactive oxygen species. To study the molecular mechanisms underlying the induction of MnSOD mRNA by these stimuli, we cloned a bovine MnSOD cDNA and used it to isolate the promoter region of the bovine MnSOD gene. A 14 kb genomic DNA fragment (lambdaBS1) containing the first and second exons and 5' flanking region of the gene was characterized. The transcription start site was determined by primer extension and S1 nuclease protection assays and found to be 88 bp upstream of the translation initiation codon. The sequence of approximately 1 kb of DNA upstream of the start site was determined and examined for potential regulatory elements. DNA immediately upstream of the transcription start site was GC-rich and contained two AP-2 and eight Sp-1 consensus sequences. It did not contain either a CCAAT or TATA box. A 956 bp fragment of this DNA fragment was transcriptionally active when fused to a luciferase reporter gene and transfected into both bovine pulmonary artery endothelial and hamster insulinoma tumor cells. Transfection analysis of three additional deletion mutants, whose 5' end-points were -317, -182, and -70 bp, respectively, showed a step-like reduction in transfection efficiency, suggesting the presence of regulatory elements throughout this DNA fragment that contribute to transcriptional activity of the MnSOD promoter. Despite the high homology of the bovine MnSOD cDNA to other mammalian MnSODs, the promoter sequences of bovine and rat MnSOD genes showed a virtual lack of similarity. The divergence of the regulatory sequences in these two species suggests that the MnSOD gene from larger mammals may be regulated differently from that in rodents.