The expression of apoB mRNA editing factors is not the sole determinant for the induction of editing in differentiating Caco-2 cells

Apobec1 complementation factor (A1CF) and RBM47 interact in tissue-specific regulation of C to U RNA editing in mouse intestine and liver

Mammalian C to U RNA is mediated by APOBEC1, the catalytic deaminase, together with RNA binding cofactors (including A1CF and RBM47) whose relative physiological requirements are unresolved. Although A1CF complements APOBEC1 for in vitro RNA editing, A1cf^-/- mice exhibited no change in apolipoproteinB (apoB) RNA editing, while Rbm47 mutant mice exhibited impaired intestinal RNA editing of apoB as well as other targets. Here we examined the role of A1CF and RBM47 in adult mouse liver and intestine, following deletion of either one or both gene products and also following forced (liver or intestinal) transgenic A1CF expression. There were minimal changes in hepatic and intestinal apoB RNA editing in A1cf^-/- mice and no changes in either liver- or intestine-specific A1CF transgenic mice. Rbm47 liver-specific knockout (Rbm47^LKO ) mice demonstrated reduced editing in a subset (11 of 20) of RNA targets, including apoB. By contrast, apoB RNA editing was virtually eliminated (<6% activity) in intestine-specific (Rbm47^IKO ) mice with only five of 53 targets exhibiting C-to-U RNA editing. Double knockout of A1cf and Rbm47 in liver (AR^LKO ) eliminated apoB RNA editing and reduced editing in the majority of other targets, with no changes following adenoviral APOBEC1 administration. Intestinal double knockout mice (AR^IKO ) demonstrated further reduced editing (<10% activity) in four of five of the residual APOBEC1 targets identified in AR^IKO mice. These data suggest that A1CF and RBM47 each function independently, yet interact in a tissue-specific manner, to regulate the activity and site selection of APOBEC1 dependent C-to-U RNA editing.

Apobec-1 Complementation Factor (A1CF) Inhibits Epithelial-Mesenchymal Transition and Migration of Normal Rat Kidney Proximal Tubular Epithelial Cells

Apobec-1 complementation factor (A1CF) is a member of the heterogeneous nuclear ribonucleoproteins (hnRNP) family, which participates in site-specific posttranscriptional RNA editing of apolipoprotein B (apoB) transcript. The posttranscriptional editing of apoB mRNA by A1CF in the small intestine is required for lipid absorption. Apart from the intestine, A1CF mRNA is also reported to be highly expressed in the kidneys. However, it is remained unknown about the functions of A1CF in the kidneys. The aim of this paper is to explore the potential functions of A1CF in the kidneys. Our results demonstrated that in C57BL/6 mice A1CF was weakly expressed in embryonic kidneys from E15.5dpc while strongly expressed in mature kidneys after birth, and it mainly existed in the tubules of inner cortex. More importantly, we identified A1CF negatively regulated the process of epithelial-mesenchymal transition (EMT) in kidney tubular epithelial cells. Our results found ectopic expression of A1CF up-regulated the epithelial markers E-cadherin, and down-regulated the mesenchymal markers vimentin and α-smooth muscle actin (α-SMA) in NRK52e cells. In addition, knockdown of A1CF enhanced EMT contrary to the overexpression effect. Notably, the two A1CF variants led to the similar trend in the EMT process. Taken together, these data suggest that A1CF may be an antagonistic factor to the EMT process of kidney tubular epithelial cells.

Intestine-specific expression of Apobec-1 rescues apolipoprotein B RNA editing and alters chylomicron production in Apobec1 -/- mice

Intestinal apolipoprotein B (apoB) mRNA undergoes C-to-U editing, mediated by the catalytic deaminase apobec-1, which results in translation of apoB48. Apobec1(-/-) mice produce only apoB100 and secrete larger chylomicron particles than those observed in wild-type (WT) mice. Here we show that transgenic rescue of intestinal apobec-1 expression (Apobec1(Int/O)) restores C-to-U RNA editing of apoB mRNA in vivo, including the canonical site at position 6666 and also at approximately 20 other newly identified downstream sites present in WT mice. The small intestine of Apobec1(Int/O) mice produces only apoB48, and the liver produces only apoB100. Serum chylomicron particles were smaller in Apobec1(Int/O) mice compared with those from Apobec1(-/-) mice, and the predominant fraction of serum apoB48 in Apobec1(Int/O) mice migrated in lipoproteins smaller than chylomicrons, even when these mice were fed a high-fat diet. Because apoB48 arises exclusively from the intestine in Apobec1(Int/O) mice and intestinal apoB48 synthesis and secretion rates were comparable to WT mice, we were able to infer the major sites of origin of serum apoB48 in WT mice. Our findings imply that less than 25% of serum apoB48 in WT mice arises from the intestine, with the majority originating from the liver.