Transcriptional Regulation of the Apolipoprotein B-100 Gene: Identification of cis-Acting Elements in the First Nontranslated Exon of the Human Apolipoprotein B-100 Gene

Apolipoprotein B-100, produced primarily in the human liver, is the sole protein component of low-density lipoprotein and serves as a ligand for the LDL receptor. Two cis-acting positive elements between -128 and -70 control hepatic cell-specific expression of the human apoB gene (H. K. Das, T. Leff, and J. L. Breslow, J. Biol. Chem. 263: 11452-11458, 1988). In this study, two apoB cis-acting elements (+20 to +40; +43 to +53) have been identified using DNase I footprint analysis. Through in vitro mutagenesis and transient transfection experiments in Hep G2 and HeLa cells, the element (+20 to +40) was observed to have a negative effect on transcription of the apoB gene. The element (+43 to +53) was found to have a strong positive effect on apoB gene transcription in Hep G2 cells and mild positive effect in HeLa cells. Therefore these two cis-acting elements mediate hepatic-cell specific expression of the apolipoprotein gene by interacting with trans-acting protein factors.