Disease relevance of Apobec1

• METHODS AND RESULTS: Transcutaneous injection of recombinant adenovirus expressing Apobec1 (AvApobec1) into the liver of newborn rabbits in vivo resulted in efficient Apobec1 expression until Day 50, as detected by PCR-Southern blot analysis [1].
• In comparison, over-expression of APOBEC-1 in HepG2 (HepG2-APOBEC) human hepatoma cells, induced promiscuous editing primarily 5' of the mooring sequence, but sites 3' of the C6666 were also used more efficiently [2].
• In colon cancer, apobec-1 protein levels decreased by 90% in the cancer tissue as compared to normal tissue, suggesting an inhibitory effect of the 5'UTR on apobec-1 translation [3].
• We speculate that the natural substrates of the APOBEC enzymes may extend to RNA viruses that do not replicate through DNA intermediates [4].
• Here we demonstrate that APOBEC-mediated cytidine deamination of human immunodeficiency virus (HIV) virion RNA can also occur [4].

High impact information on Apobec1

• A full-length complementary DNA clone encoding an apo B messenger RNA editing protein (REPR) was isolated from rat small intestine [5].
• HepG2 cell extracts acquire editing activity when mixed with REPR from oocyte extracts [5].
• The activity of the catalytic subunit of the editosome APOBEC-1 and mooring sequence RNA binding proteins of 66 and 44 kDa could not be demonstrated in AUX240 [6].
• A sequence-specific RNA-binding protein complements apobec-1 To edit apolipoprotein B mRNA [7].
• These data, together with the finding that all ACF variants were co-expressed in rat liver nuclei (the site of apoB mRNA editing), suggested that ACF variants might compete with one another for APOBEC-1 and apoB mRNA binding and thereby contribute to the regulation of apoB mRNA editing [8].

Chemical compound and disease context of Apobec1

• We used this physiologic hypercholesterolemia model to study the effect of adenovirus-mediated hepatic gene transfer of rat apolipoprotein B mRNA editing enzyme (Apobec1) on modulation of plasma cholesterol levels [1].

Biological context of Apobec1

• This dominant translational control of apobec-1 gene expression is most plausibly exerted through uAUGs [3].
• These findings were confirmed in transient transfection studies in vivo using HepG2 cells, where functional expression of apobec-1 was restored by mutagenesis of the uAUGs [3].
• Apobec-1 transcription in rat colon cancer: decreased apobec-1 protein production through alterations in polysome distribution and mRNA translation associated with upstream AUGs [3].
• By contrast, protein-protein interaction is important for the nuclear import of apobec-1 [9].
• In contrast, ACF43 bound strongly to APOBEC-1 but demonstrated weak binding to mooring sequence RNA [8].

Anatomical context of Apobec1

• Intravenous injection of AvREPR in mice resulted in efficient transduction of liver cells, where REPR mRNA and protein were overexpressed, reaching a peak at 7 and 12 days, returning toward control levels at 39 days after AvREPR administration [10].
• We have partially purified the editing activity from extracts of a McArdle cell line overexpressing His6-hemagglutinin-tagged, rat APOBEC-1 using metal-chelating affinity chromatography [11].
• The abundant hnRNP C1 protein, which is contiguously deposited on nascent pre-mRNA during transcription and is involved in spliceosome assembly and mRNA splicing, is a likely regulator of the editing of apo B mRNA which restricts the activity of APOBEC-1 to limited and specific editing events [12].

Associations of Apobec1 with chemical compounds

• This physiological level of Apobec1 expression was associated with the production of apoB-48-containing lipoprotein particles from rabbit liver, with a concomitant 30% reduction in total plasma cholesterol compared to AvLacZ-treated or untreated control animals [1].
• Experimental over-expression of APOBEC-1 resulted in an increased proportion of apoB mRNAs edited at C6666, as well as editing of sites that would otherwise not be recognized (promiscuous editing) [2].
• Retroviral DNA can be subjected to cytosine-to-uracil editing through the action of members of the APOBEC family of cytidine deaminases [4].
• In vitro deamination of cytosine to uracil in single-stranded DNA by apolipoprotein B editing complex catalytic subunit 1 (APOBEC1) [13].
• We also demonstrate that in the absence of alterations in APOBEC-1 expression, changes in edited apoB RNA induced by ethanol arise through the stimulation of nuclear editing activity [14].

Physical interactions of Apobec1

• Moreover, alkaline phosphatase treatment of nuclear extracts reduced the amount of APOBEC-1 co-immunoprecipitated with ACF and inhibited in vitro editing activity [15].
• Apolipoprotein B-editing complex catalytic subunit 1 (APOBEC1) is the catalytic component of an RNA-editing complex that deaminates C6666 --> U in apolipoprotein B RNA in gastrointestinal tissue, thereby generating a premature stop codon [13].

Enzymatic interactions of Apobec1

• Apobec-1 catalyzes C to U editing of apolipoprotein B (apoB) mRNA in the mammalian intestine [3].

Other interactions of Apobec1

• Induction of cytidine to uridine editing on cytoplasmic apolipoprotein B mRNA by overexpressing APOBEC-1 [14].
• VLDL from WHHL rabbits treated with Ad APOBEC-1 had the same particle size, lipid composition, and content of apolipoprotein E as VLDL from Ad LacZ-infected control animals [16].

Analytical, diagnostic and therapeutic context of Apobec1

• Using RNA affinity chromatography, we show that the complementing activity binds to a 280-nucleotide apo-B RNA in the absence of apobec-1 [7].
• Recombinant GST/APOBEC-1 binds with high specificity to a rat apoB RNA template as demonstrated by UV cross-linking and electrophoretic mobility shift assay (EMSA) [17].
• This report quantifies for the first time the effect of altering APOBEC-1 protein abundance on the proportion of edited apoB mRNAs using transfected McArdle rat hepatoma cells which had been sorted by flow cytometry into populations expressing different levels of green fluorescent protein-APOBEC-1 chimera, GFP-APOBEC [18].
• In situ hybridization demonstrated REPR mRNA to be distributed along the entire villus-crypt axis, while apoB mRNA distribution did not extend into the crypts [19].

References