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Cloning & Expression of the Apo-B mRNA Editing Factor

Institution: J. David Gladstone Institutes
Investigator(s): Thomas Innerarity, Ph.D.
Award Cycle: 1994 (Cycle 3) Grant #: 3RT-0404 Award: $254,743
Subject Area: Cardiovascular Disease
Award Type: Research Project Awards
Abstracts

Final Report
An RNA-binding cytidine deaminase (APOBEC-1) and unidentified auxiliary protein(s) are required for apolipoprotein (apo-) B mRNA editing. A sequence motif on apo-B mRNA ("mooring sequence," nucleotides 6671-6681) is obligatory for the editing of cytidine 6666 (C6666), the only cytidine on apo-B mRNA converted to uridine in normal animals. Transgenic animals with hepatic overexpression of APOBEC-1 develop liver tumors, and other non-apo-B mRNAs are edited, suggesting a loss of the normally precise specificity. By using a modified differential display technique, we found a novel mRNA was extensively edited. The protein coded by this mRNA has homology to one of the eukaryotic translation initiation factor (EIF) subunits. The protein is found in every tissue and organ examined, has a GUG start codon, and is very highly conserved. We also examined apo-B mRNA from these transgenic animals to determine if cytidines besides C6666 are edited. Multiple cytidines downstream from C6666 in apo-B mRNA were edited extensively by the overexpressed APOBEC-1. This pathophysiological "hyperediting" could be mimicked in vitro by incubating a synthetic apo-B RNA substrate with the transgenic mouse liver extracts. Multiple cytidines in the synthetic apo-B RNA were edited by recombinant APOBEC-1, but only with supplementation of the auxiliary protein(s). Mutations in the mooring sequence markedly decreased the normal editing of C6666 but, surprisingly, increased the hyperediting of downstream cytidines. Furthermore, cytidines in an apo-B RNA substrate lacking the mooring sequence were also edited in vitro. These results indicate that the hyperediting of apo-B mRNA by overexpressed APOBEC- 1 depends upon auxiliary protein(s), but is independent of the exact mooring sequence motif.
Publications

Cloning and mutagenesis of the rabbit apoB mRNA editing protein. A zinc motif is essential for catalytic activity and non-catalytic auxillary factor(s) of the editing complex are widely distributed
Periodical: Journal of Biological Chemistry Index Medicus:
Authors: Yamanaka S, Poksay KS, Balestra ME, Zeng G-Q, Innerarity TL ART
Yr: 1994 Vol: 269 Nbr: 34 Abs: Pg: 21725-21734

Apolipoprotein B mRNA editing protein induces hepatocellular carcinoma and dysplasia in transgenic animals
Periodical: Proceedings of the National Academy of Sciences of the United States of America Index Medicus:
Authors: Yamanaka S, Balestra ME, Ferrell LD, et al ART
Yr: 1995 Vol: 92 Nbr: 18 Abs: Pg: 8483-8487

Hyperediting of multiple cytidines of apolipoprotein B mRNA by APOBEC-1 requires auxiliary protein(s) but not a mooring sequence motif
Periodical: Journal of Biological Chemistry Index Medicus:
Authors: Yamanaka S, Poksay KS, Driscoll DM, Innerarity TL ART
Yr: 1996 Vol: 271 Nbr: Abs: Pg: 11506-11510