Characterization of the human alpha 2-macroglobulin gene promoter: identification of a novel, triple TRE/RARE/ERE response element.

Human alpha 2-macroglobulin is synthesized in the liver and in some extra-hepatic tissues but the physiological role of the protein remains unexplained. We initiated studies to characterize the promoter of the gene. In transient transfections 240 bp of the proximal promoter were necessary and sufficient for CAT-expression in HepG2 cells and lung fibroblasts. This promoter was silent in skin fibroblasts. In DNAase I footprint analyses, five regions bound nuclear factors from expressing and non-expressing cells. FPII (-144 to -104) was most prominent with extracts from HepG2 cells and lung fibroblasts. In mobility shifts, FPII bound nuclear factors present in the order: HepG2 > lung >> skin fibroblasts. This region contains a canonical TRE/RARE/ERE half-site (TGACCT) flanked by 2 related hexamers in the combinations PR4 (palindromic repeat, spacing 4) and ER1 (everted repeat, spacing 1). The interplay of (orphan) members of the steroid receptor family could explain the tissue- and species-specific regulation of the alpha 2M gene.