Two Proteins Essential for Apolipoprotein B mRNA Editing Are Expressed from a Single Gene through Alternative Splicing

• Published in: The Journal of biological chemistry 2002-04, Vol.277 (15), p.12703-12709
• Main Authors: Dance, Geoffrey S.C., Sowden, Mark P., Cartegni, Luca, Cooper, Ellen, Krainer, Adrian R., Smith, Harold C.
• Format: Article
• Language: English
• Subjects: ACF64 protein; ACF65 protein; Alternative Splicing; APOBEC-1 Deaminase; apolipoprotein B; Base Sequence; Cell Line; Cloning, Molecular; Cytidine Deaminase - genetics; Cytidine Deaminase - physiology; DNA, Complementary; Exons; Humans; Molecular Sequence Data; Promoter Regions, Genetic; Protein Isoforms - genetics; Protein Isoforms - physiology; RNA, Messenger - genetics; SC35 protein; SF2/ASF protein; SRp40 protein; SRp55 protein
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111337200

Apolipoprotein B (apoB) mRNA editing involves site-specific deamination of cytidine to form uridine, resulting in the production of an in-frame stop codon. Protein translated from edited mRNA is associated with a reduced risk of atherosclerosis, and hence the protein factors that regulate hepatic apoB mRNA editing are of interest. A human protein essential for apoB mRNA editing and an eight-amino acid-longer variant of no known function have been recently cloned. We report that both proteins, henceforth referred to as ACF64 and ACF65, supported APOBEC-1 (the catalytic subunit of the editosome) equivalently in editing of apoB mRNA. They are encoded by a single 82-kb gene on chromosome 10. The transcripts are encoded by 15 exons that are expressed from a tissue-specific promoter minimally contained within the −0.33-kb DNA sequence. ACF64 and ACF65 mRNAs are expressed in both liver and intestinal cells in an approximate 1:4 ratio. Exon 11 is alternatively spliced to include or exclude 24 nucleotides of exon 12, thereby encoding ACF65 and ACF64, respectively. Recognition motifs for the serine/arginine-rich (SR) proteins SC35, SRp40, SRp55, and SF2/ASF involved in alternative RNA splicing were predicted in exon 12. Overexpression of these SR proteins in liver cells demonstrated that alternative splicing of a minigene-derived transcript to express ACF65 was enhanced 6-fold by SRp40. The data account for the expression of two editing factors and provide a possible explanation for their different levels of expression.