Targeted Disruption of the Mouse apobec-1 Gene Abolishes Apolipoprotein B mRNA Editing and Eliminates Apolipoprotein B48

Ken-Ichi Hirano,Stephen G Young,Robert V Jr Farese,Jennifer Ng,Eric Sande,Cara Warburton,Lyn M Powell-Braxton,Nicholas O Davidson

doi:10.1074/jbc.271.17.9887

Abstract

A site-specific C to U editing reaction modifies nuclear apolipoprotein B100 (apoB100) mRNA, producing apolipoprotein B48 in the mammalian small intestine. This reaction is mediated by a multicomponent enzyme complex, which contains a catalytic subunit, Apobec-1. We have used gene targeting to disrupt mouse apobec-1 in order to establish its requisite importance in apoB mRNA editing and also, in view of its widespread tissue distribution in rodents, as a preliminary indication of other potential roles. Both heterozygous (apobec-1+/-) and homozygous (apobec-1-/-) gene-targeted mice appear healthy and fertile with no alterations in serum cholesterol or triglyceride concentrations. The apobec-1+/- mice demonstrated reduced levels of hepatic apoB mRNA editing. By contrast, levels of small intestinal apoB mRNA editing were indistinguishable in wild-type and apobec-1+/- animals, suggesting that Apobec-1 is expressed in limited quantities in the liver but not in the small intestine. The apobec-1-/- mice lacked detectable levels of Apobec-1 mRNA, expressed only unedited apoB mRNA in all tissues, and contained no apoB48 in their serum, demonstrating that there is no functional duplication of this gene.

Highlights

A common structural gene encodes two distinct forms of mammalian apolipoprotein B,1 in proportions that are
ApoB mRNA editing is mediated by a multicomponent enzyme complex that includes a 27-kDa component, Apobec-1, as well as other as yet uncharacterized factors that are required for the functional integrity of the complex [12,13,14]
In attempting to ascribe an integrated, biological role for Apobec-1, it was difficult to make a priori predictions, since recent reports suggest a range of potential functions

Summary

Introduction

A common structural gene encodes two distinct forms of mammalian apolipoprotein B (apoB),1 in proportions that are. Restricted to the gastrointestinal tract in humans and rabbits [21,22,23,24], the broad tissue distribution of Apobec-1 in rats and mice, taken together with the RNA binding and cytidine deaminase activity alluded to above, implies the possibility that potential functions exist for this protein beyond its role in apoB mRNA editing.

Results

Conclusion