Identification and characterization of a new human gene (APOC4) in the apolipoprotein E, C-I, and C-II gene locus.
ABSTRACT We have identified and characterized a previously unreported human gene that is found within the apolipoprotein (apo) E/C-I/C-II gene locus. On the basis of its location and its properties, this new gene has been designated APOC4. Nucleotide sequence analysis of genomic DNA and liver cDNA clones revealed a 3.3-kb gene consisting of three exons and two introns. Its 3' terminus lies 555 bp upstream of APOC2, giving both genes the same transcriptional orientation. The promoter of the APOC4 gene lacks a typical TATA box, consistent with an apparent heterogeneity in transcription start sites. RNase protection analysis indicated relatively low apoC-IV mRNA levels in human liver, compared to apoC-II mRNA levels. The predicted apoC-IV protein sequence, comprising 127 amino acid residues, contains a putative 25-residue signal peptide and two potential amphipathic alpha-helical domains. Amino acid sequence comparisons indicate a limited homology between apoC-IV and either apoC-I or apoC-II. Since its hepatic expression and predicted protein structure are characteristic of the other genes in this cluster, we propose that the APOC4 gene is a member of the apolipoprotein gene family.
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ABSTRACT: Apolipoprotein CII (apoCII) is a specific activator of lipoprotein lipase and plays an important role in triglyceride metabolism. The aim of our work was to elucidate the regulatory mechanisms involved in apoCII gene modulation in macrophages. Using Chromosome Conformation Capture we demonstrated that multienhancer 2 (ME.2) physically interacts with the apoCII promoter and this interaction facilitates the transcriptional enhancement of the apoCII promoter by the transcription factors bound on ME.2. We revealed that the transcription factor STAT1, previously shown to bind to its specific site on ME.2, is functional for apoCII gene upregulation. We found that siRNA-mediated inhibition of STAT1 gene expression significantly decreased the apoCII levels, while STAT1 overexpression in RAW 264.7 macrophages increased apoCII gene expression. Using transient transfections, DNA pull down and chromatin immunoprecipitation assays, we revealed a novel STAT1 binding site in the -500/-493 region of the apoCII promoter, which mediates apoCII promoter upregulation by STAT1. Interestingly, STAT1 could not exert its upregulatory effect when the RXRα/T3Rβ binding site located on the apoCII promoter was mutated, suggesting physical and functional interactions between these factors. Using GST pull-down and co-immunoprecipitation assays, we demonstrated that STAT1 physically interacts with RXRα. Taken together, these data revealed that STAT1 bound on ME.2 cooperates with RXRα located on apoCII promoter and upregulates apoCII expression only in macrophages, due to the specificity of the long-range interactions between the proximal and distal regulatory elements. Moreover, we showed for the first time that STAT1 and RXRα physically interact to exert their regulatory function.PLoS ONE 01/2012; 7(7):e40463. · 4.09 Impact Factor
Article: Apolipoprotein E genotype affects plasma lipid response to atorvastatin in a gender specific manner.[show abstract] [hide abstract]
ABSTRACT: The response to therapy with hypolipidemic agents shows considerable individual variation. These differences may be due to the interaction of environmental and genetic factors that affect drug bioavailability, receptor function or ligand structure. Our objective was to assess the effect of apolipoprotein (apo) E genotype and gender on lipid-lowering response to the HMG CoA reductase inhibitor, atorvastatin. Genotyping was carried out on DNA from 328 male and female subjects who participated in a multicentric, double-blind clinical trial, and received 10 mg/day of atorvastatin. Our data demonstrate no significant gender differences for LDL cholesterol levels at baseline. Moreover, mean LDL-C lowering was similar in men (-36.2%, range -2.7 to -57.8%) and in women (-38.1%, range -9.5 to -58.5%) as compared to baseline. However, men carrying the epsilon2 allele had a significantly higher mean LDL-C response (-44%) than epsilon3 homozygotes (-37%) and epsilon4 carriers (-34%); P=0.01 for apoE group by treatment interaction. No such gene/treatment interactions were noted in women, with those carrying the epsilon2 allele showing a similar mean response (-34%) as epsilon3 homozygotes (-39%) and epsilon4 carriers (-34%). Mean plasma triglyceride lowering with atorvastatin was 17%. A significant apoE group by treatment interaction (P=0.010) was also observed in men, with epsilon2 carriers being more responsive (-27%) than epsilon3/3 (-13%) and epsilon4 (-22%). This interaction was not observed in women. In summary, atorvastatin treatment had similar effects on plasma lipid levels in both men and women; however, the apoE gene locus was a significant predictor of LDL-C and TG responses to atorvastatin therapy in men, but not in women.Atherosclerosis 10/2001; 158(1):183-93. · 3.79 Impact Factor
Article: DNA sequence variation in human apolipoprotein C4 gene and its effect on plasma lipid profile.[show abstract] [hide abstract]
ABSTRACT: Human apolipoprotein C-IV (apoC-IV, protein; APOC4, gene) is a new member of the APO E/C1/C2 gene cluster. In transgenic mice, human apoC-IV is predominantly associated with very low-density lipoprotein (VLDL) and thus may play an important role in lipid metabolism. To our knowledge, the extent and nature of APOC4 genetic variation and its role in lipid metabolism are unknown. In this study we have assessed the presence of genetic variation in all three exons of APOC4 and their flanking intronic sequence by SSCP and DNA sequencing. A total of five point mutations were observed, including two in the non-coding part of exon 1 (A609G and G620A), two in exon 2 (codons 36 and 52) and one in exon 3 (codon 96). The three mutations in exons 2 and 3 predict amino acid substitutions, Leu36Pro, Gly52Asp, and Leu96Arg. The frequencies of the variant alleles were: 0.010 for 609G, 0.039 for 620A, 0.502 for Pro36, 0.003 for Asp52 and 0.357 for Arg96. Significant pairwise linkage disequilibrium was observed between five of the ten APOC4 pairs, including nt. 620/codon 36, nt. 620/codon 96, codon 36/codon 52, codon 36/codon 96 and codon 52/codon 96. A general linear model analysis reveled a significant association of the Leu36Pro and the Leu96Arg polymorphisms with triglyceride levels in women. This is consistent with the proposed role of apoC-IV in triglyceride metabolism. The characterization of APOC4 genetic variation may lead to the identification of a specific role of apoC-IV in lipid metabolism or in other physiologic pathways.Atherosclerosis 10/2000; 152(1):193-201. · 3.79 Impact Factor