APOBEC-1, the catalytic subunit of the apolipoprotein B mRNA editing enzyme, is a mutifunctional cytidine deaminase with RNA binding activity

The apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3G (APOBEC3G or A3G) and its fellow cytidine deaminase family members are potent restrictive factors for human immunodeficiency virus type 1 (HIV-1) and many other retroviruses. A3G interacts with a vast spectrum of RNA-binding proteins and is located in processing bodies and stress granules. However, its cellular function remains to be further clarified. Using a luciferase reporter gene and green fluorescent protein reporter gene, we demonstrate that A3G and other APOBEC family members can counteract the inhibition of protein synthesis by various microRNAs (miRNAs) such as mir-10b, mir-16, mir-25, and let-7a. A3G could also enhance the expression level of miRNA-targeted mRNA. Further, A3G facilitated the association of microRNA-targeted mRNA with polysomes rather than with processing bodies. Intriguingly, experiments with a C288A/C291A A3G mutant indicated that this function of A3G is separable from its cytidine deaminase activity. Our findings suggest that the major cellular function of A3G, in addition to inhibiting the mobility of retrotransposons and replication of endogenous retroviruses, is most likely to prevent the decay of miRNA-targeted mRNA in processing bodies.

Download Full-text

The editosome for cytidine to uridine mRNA editing has a native complexity of 27S: identification of intracellular domains containing active and inactive editing factors

Journal of Cell Science ◽

10.1242/jcs.115.5.1027 ◽

2002 ◽

Vol 115 (5) ◽

pp. 1027-1039 ◽

Cited By ~ 5

Author(s):

Mark P. Sowden ◽

Nazzareno Ballatori ◽

Karen L. de Mesy Jensen ◽

Lakesha Hamilton Reed ◽

Harold C. Smith

Keyword(s):

Apolipoprotein B ◽

Rna Binding ◽

Binding Protein ◽

Rna Binding Protein ◽

Catalytic Subunit ◽

Cross Linking ◽

Primary Hepatocytes ◽

Mrna Editing ◽

Apob Mrna ◽

Rat Primary Hepatocytes

Apolipoprotein B mRNA cytidine to uridine editing requires the assembly of a multiprotein editosome comprised minimally of the catalytic subunit,apolipoprotein B mRNA editing catalytic subunit 1 (APOBEC-1), and an RNA-binding protein, APOBEC-1 complementation factor (ACF). A rat homolog has been cloned with 93.5% identity to human ACF (huACF). Peptide-specific antibodies prepared against huACF immunoprecipitated a rat protein of similar mass as huACF bound to apolipoprotein B (apoB) RNA in UV cross-linking reactions, thereby providing evidence that the p66, mooring sequence-selective, RNA-binding protein identified previously in rat liver by UV cross-linking and implicated in editosome assembly is a functional homolog of huACF. The rat protein (p66/ACF) was distributed in both the nucleus and cytoplasm of rat primary hepatocytes. Within a thin section, a significant amount of total cellular p66/ACF was cytoplasmic, with a concentration at the outer surface of the endoplasmic reticulum. Native APOBEC-1 co-fractionated with p66/ACF in the cytoplasm as 60S complexes. In the nucleus, the biological site of apoB mRNA editing, native p66/ACF, was localized to heterochromatin and fractionated with APOBEC-1 as 27S editosomes. When apoB mRNA editing was stimulated in rat primary hepatocytes with ethanol or insulin, the abundance of p66/ACF in the nucleus markedly increased. It is proposed that the heterogeneity in size of complexes containing editing factors is functionally significant and reflects functionally engaged editosomes in the nucleus and an inactive cytoplasmic pool of factors.

Download Full-text

Developmental regulation of the catalytic subunit of the apolipoprotein B mRNA editing enzyme (APOBEC-1) in human small intestine.

The Journal of Lipid Research ◽

10.1016/s0022-2275(20)41486-5 ◽

1995 ◽

Vol 36 (8) ◽

pp. 1664-1675

Author(s):

F. Giannoni ◽

S.C. Chou ◽

S.F. Skarosi ◽

M.S. Verp ◽

F.J. Field ◽

...

Keyword(s):

Small Intestine ◽

Apolipoprotein B ◽

Developmental Regulation ◽

Catalytic Subunit ◽

Mrna Editing ◽

Human Small Intestine ◽

Editing Enzyme

Download Full-text

ARCD-1, an apobec-1-related cytidine deaminase, exerts a dominant negative effect on C to U RNA editing

AJP Cell Physiology ◽

10.1152/ajpcell.2001.281.6.c1904 ◽

2001 ◽

Vol 281 (6) ◽

pp. C1904-C1916 ◽

Cited By ~ 38

Author(s):

Shrikant Anant ◽

Debnath Mukhopadhyay ◽

Vakadappu Sankaranand ◽

Susan Kennedy ◽

Jeffrey O. Henderson ◽

...

Keyword(s):

Rna Editing ◽

Rna Binding ◽

Cytidine Deaminase ◽

Binding Activity ◽

Dominant Negative ◽

Dominant Negative Effect ◽

Mrna Editing ◽

Apob Mrna

Mammalian apolipoprotein B (apoB) C to U RNA editing is catalyzed by a multicomponent holoenzyme containing a single catalytic subunit, apobec-1. We have characterized an apobec-1 homologue, ARCD-1, located on chromosome 6p21.1, and determined its role in apoB mRNA editing. ARCD-1 mRNA is ubiquitously expressed; phylogenetic analysis reveals it to be a distant member of the RNA editing family. Recombinant ARCD-1 demonstrates cytidine deaminase and apoB RNA binding activity but does not catalyze C to U RNA editing, either in vitro or in vivo. Although not competent itself to mediate deamination of apoB mRNA, ARCD-1 inhibits apobec-1-mediated C to U RNA editing. ARCD-1 interacts and heterodimerizes with both apobec-1 and apobec-1 complementation factor (ACF) and localizes to both the nucleus and cytoplasm of transfected cells. Together, the data suggest that ARCD-1 is a novel cytidine deaminase that interacts with apobec-1 and ACF to inhibit apoB mRNA editing, possibly through interaction with other protein components of the apoB RNA editing holoenzyme.

Download Full-text