The effect on transcription efficiency of the apolipoprotein Al gene of DNA variants at the 5 ' untranslated region

Elevated circulating levels of high-density lipoprotein and apolipoprotein AI are associated with reduced coronary artery disease risk. We have shown that a C to T substitution at +83 bp and a G to A substitution at -75 bp of the apolipoprotein AI gene are both related to increased high-density lipo protein levels in a healthy population but not in a coronary population, am ong whom the same mutations are associated with increased disease severity. In the present study, we explored the effects of these base changes on tra nscriptional efficiency in vitro. We directionally cloned (using polymerase chain reaction) the 5' region of the apolipoprotein AI gene (-281 to + 330 bp) with GC, GT, and AC haplotypes into a pG13-luciferase reporter gene ba sic vector, and transfected the constructed vectors into HepG2 cells. The c ells carrying the T allele at the +83 bp site (GT 112.3+/-12.4) had the sam e transcriptional efficiency as those bearing the C allele (GC 126.3+/-9.6) . However, for cells with the A allele at -75 bp there was a twofold decrea se in transcription (AC 63.1+/-9.3) accompanied by similar changes in LucmRNA levels; this reduced transcription was only present if the apolipoprot ein AI leader sequence was included in the insert. While the findings are i nconsistent with the T or A allele being associated with higher high-densit y lipoprotein levels, they are consistent with the finding that the alleles are associated with an increased coronary artery disease risk, and demonst rate that the 5' leader region of the apolipoprotein Al gene participates i n regulating apolipoprotein AI transcription. They also suggest that other regions of the apolipoprotein AI gene may have an active role in such regul ation, and that environmental effects may influence allele-specific express ion.