Identification of an alternative transcript of ABCA1 gene in different human cell types

We have observed two ABCA1 gene transcripts in human skin fibroblasts. The RT-PCR amplification of the exon 3-exon 8 region generated a normal fragment (740 bp) and an abnormal fragment (600 bp) in a ratio ranging from 3:1 to 8/9:1. These two transcripts were present in other cells such as leukemia T-cells, endothelial and smooth muscle cells as well human hepatoma cells (HepG2). Restriction enzyme analysis and sequencing indicated that in the abnormal fragment exon 3 was followed by exon 5. The complete skipping of exon 4 leads to a premature stop and a predicted translation product of 74 amino acids. The ratio between the normal and alternative transcript is not affected by variation in ABCA1 gene expression induced by incubating cells in serum-free medium and in the presence of cholesterol. It is possible that this alternative splicing represents as mechanism that regulates the ABCA1 content in tissues.