C T POLYMORPHISM IN THE 5' UNTRANSLATED REGION OF THE APOLIPOPROTEIN(A) GENE INTRODUCES AN UPSTREAM ATG AND REDUCES IN-VITRO TRANSLATION/

Elevated plasma levels of lipoproteinz(a) [Lp(a)] are a significant in dependent risk factor for arteriosclerosis. Interindividual levels of Lp(a) vary nearly 1000-fold and are mainly due to inheritance that is linked to the locus of the apolipoprotein(a) [apo(a)] gene. A search w as made for sequence variants in the 5' flanking region of the apo(a) gene that affect its expression. A C to T transition at position +93 f rom the transcription start site was found with a frequency of 14% in the study population. In transient transfection assays in HepG2 cells, luciferase reporter gene constructs with a T at this position were as sociated with a 58% reduction in luciferase activity compared with the more common allele. This single base variant had no significant effec t on the binding of nuclear regulatory proteins; however, it introduce d an additional upstream ATG initiation codon with its own in-frame st op codon. Furthermore, equivalent levels of mRNA were produced in HepG 2 cells transfected with reporter gene constructs containing either a T or a C at position +93. In vitro translation experiments using trans cripts derived from either variant apo(a) promoter revealed a 60% redu ction in translation associated with the T allele. Hence, the addition al ATG created by the T at position +93 in the 5' flanking region of t he apo(a) gene impairs the efficiency of translation from the bona fid e ATG initiation codon.