Multiple Liver-Specific Factors Bind to a 64-bp Element and Activate Apo(a) Gene

Abstract

The high plasma levels of lipoprotein(a) [Lp(a)] are associated with atherosclerosis. The apo(a) gene is responsible for the variance of Lp(a) concentration and its expression is liver-specific. By 5′-deletion analysis, we, in a luciferase gene reporter assay, have identified a 64-bp AT-rich region of upstream apo(a) gene (−703 to −640) that binds to multiple liver-specific factors. The 64 bp cis-element contained three dyad symmetry elements (DSEs) that are crucial for synergistic binding to the factors. We have demonstrated that both DSE-2 and -3 together are responsible for factor binding in vitro, and for gene activation in liver cells. Further, we have purified one of the UV cross-linked DNA–protein complexes to homogeneity by streptavidin magnetic bead chromatography. The identification of a further upstream negative regulatory region (−1432 to −704) led us to predict that as yet unidentified transcriptional repressor(s) might also repress apo(a) gene transcription.