Sp1 and C/EBP-related factor regulate the transcription of human Cu/Zn SOD gene

The Cu/Zn superoxide dismutase (SOD1) is one of the key enzymes that protect cells against oxidative stress. It catalyzes the dismutation of superoxide radicals (O2-) to oxygen and hydrogen peroxide. To study the transcriptional regulation of the human Cu/Zn SOD gene, we began by analyzing the 1.5-kb upstream region of the gene (see Kim et al., 1994). The element from nucleotides (nt) -116 to -45 increased the transcriptional activity of Cu/Zn SOD. Analyses by DNase I footprinting and electrophoretic mobility shift assay (EMSA) showed that Sp1 binds to the region from nt -104 to -89 and C/EBP-related factors to the region from nt -64 to -55. Studies using two mutant versions of this promoter, in which the Sp1 and C/EBP-related factor binding sites were deleted, respectively, revealed that Sp1 and C/EBP-related factors activate the transcription of SOD1 gene. An Sp1 expression plasmid, pPacSp1, stimulated the SOD1-linked CAT expression. Cotransfection of the element from nt -116 to -45 with the C/EBP alpha expression vector, pMSV-C/EBP, increased the transcriptional activity of the Cu/Zn SOD in HepG2 cells, but barely in HeLa cells. Because Sp1 is a ubiquitously expressed transcriptional factor, the binding of Sp1 to the proximal upstream region of the Cu/Zn SOD might explain the expression of Cu/Zn SOD in a wide variety of cells.