Apolipoprotein(a) gene transcription is regulated by liver-enriched trans-acting factor hepatocyte nuclear factor 1 alpha.

Abstract

Elevated levels of lipoprotein(a) (Lp(a)) in the plasma are a risk factor for coronary artery disease and stroke. Plasma Lp(a) concentrations are highly heritable and predominantly determined by the liver-specific apolipoprotein(a) (apo(a)) gene. In this report we show by deletion analysis that sequences from -98 to +130 of the apo(a) gene are sufficient to direct liver-specific transcription. DNase I protection analysis of this region using HepG2 nuclear extracts revealed six major protein-binding sites, designated A to F. A mutation within footprint C, situated in the 5'-untranslated region of the gene, resulted in a marked reduction of luciferase expression from a reporter construct to 12% of wild type. This was not due to a decrease in mRNA stability. Gel mobility shift assays demonstrated that site C binds hepatocyte nuclear factor 1 alpha (HNF-1 alpha), and overexpression of HNF-1 alpha in HepG2 cells resulted in a significant stimulation of transcription from this promoter fragment. Mutation of footprint B resulted in a 2-fold enhancement of transcription. These results show that positive regulation of transcription of the apo(a) gene is dependent on the binding of HNF-1 alpha to a regulatory element situated downstream of the mRNA start site, and suggest that an as yet unidentified protein may negatively regulate apo(a) transcription by binding to a discrete sequence within the 5'-untranslated region.