Submitted on March 15, 2006
Accepted on August 15, 2006
ApoB mRNA editing is mediated by a coordinated modulation of multiple apoB mRNA editing enzyme components
Zhigang Chen1, Thomas L. Eggerman2, and Amy P. Patterson3*
1 National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States
2 Division of Diabetes, Endocrinology and Metabolic Diseases, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland, United States; Dept. of Laboratory Medicine, W. G. Magnuson Clinical Center, National Institutes of Health, Bethasda, Maryland, United States
3 National Heart, Lung and Blood Institute, National Institutes of Health, 9000 Rockville Pike, 9/1N128, Bethesda, Maryland, 20892, United States; Office of Biotechnology Activities, National Institutes of Health, Bethesda, Maryland, United States
* To whom correspondence should be addressed. E-mail: pattersa{at}od.nih.gov.
Apolipoprotein B mRNA editing is accomplished by a large multi-protein complex. How these proteins interact to achieve the precise single nucleotide change induced by this complex remains unclear. We investigated the relationship between altered apoB mRNA editing and changes in editing enzyme components to evaluate their roles in editing regulation. In the mouse fetal small intestine, we found that the dramatic developmental up-regulation of apoB mRNA editing from ~3% to 88% begins with decreased levels of inhibitory CUGBP2 expression followed by increased levels of apobec-1 and ACF (4 and 8 fold) and then by decreased levels of the inhibitory components GRY-RBP and hnRNP-C1 (75% and 56%). In contrast, the expression of KSRP, ABBP1, ABBP2 and BAG4 were unaltered. In the human intestinal cell line Caco-2, the increase of apoB mRNA editing from ~1.7% to ~23% was associated with 6 and 3.2 fold increases of apobec-1 and CUGBP2 respectively. In the mouse large intestine, the editing was 48% and had a 2.7 fold relatively greater CUGBP2 level. Caco-2 and the large intestine thus have an increased instead of decreased CUGBP2 and a lower level of editing, suggesting that inhibitory CUGBP2 may play a critical role in the magnitude of editing regulation. siRNA mediated gene specific knock down of CUGBP2, GRY-RBP and hnRNP-C1 resulted in increased editing in Caco-2 cells, consistent with their known inhibitory function. These data suggest that a coordinated expression of editing components determines the magnitude and specificity of apoB mRNA editing.
