A SINGLE NUCLEOTIDE SUBSTITUTION IN THE PROMOTER REGION OF THE APOLIPOPROTEIN C-II GENE IDENTIFIED IN INDIVIDUALS WITH CHYLOMICRONEMIA

Apolipoprotein (ape) C-II plays a major role as a cofactor for lipopro tein lipase, the enzyme involved in the hydrolysis of triglyceride-ric h particles. We identified in two relatives of a family (mother and so n) massive hypertriglyceridemia with chylomicronemia. In these individ uals apoC-II was not measurable in plasma by radial immunodiffusion. O n isoelectric focusing of very low density apolipoproteins, trace amou nts of apoC-II became obvious in the regular position. By sequencing, no abnormalities in the exons or neighboring intron sequences were det ected. However, three alterations in the DNA sequence were found upstr eam from the transcription initiation site. Two variations could be ex plained by differences in previously published DNA sequences. The thir d variation (A-->G; position -86; Das et al. 1987. J. Biol. Chem. 262: 4787-4793) was present only in the homozygous form in the two hypertr iglyceridemic probands. In 46 hypertriglyceridemic individuals outside the family, this mutation with not found. In electrophoretic mobility shift experiments with nuclear extracts from HepG2 cells, the 31 bp D NA fragment carrying the A-->G substitution resulted in a markedly dim inished protein binding compared with the wildtype DNA fragment. In pr omoter reporter gene assays, the activity of the basal promoter was re duced in the case of the A-->G substitution and the deletion of the ba ses -91 to -58. The pedigree analysis and the experimental results are evidence that this is the first mutation in the apolipoprotein CII ge ne where a single nucleotide substitution diminishes the binding of a transcription factor to a positive cis-acting element in the promoter resulting in a depletion of apolipoprotein C-II in plasma.-Streicher, R., J. Geisel, C. Weisshaar, H. Avci, K. Oette, D. Muller-Wieland, and W. Krone. A single nucleotide substitution in the promoter region of the apolipoprotein CII gene identified in individuals with chylomicron emia.