Evolutionary distinct mechanisms regulate apolipoprotein A-I gene expression: differences between avian and mammalian apoA-I gene transcription control regions

Evolutionary analysis of apolipoprotein E by Maximum Likelihood and complex network methods

Apolipoprotein E (apo E) is a human glycoprotein with 299 amino acids, and it is a major component of very low density lipoproteins (VLDL) and a group of high-density lipoproteins (HDL). Phylogenetic studies are important to clarify how various apo E proteins are related in groups of organisms and whether they evolved from a common ancestor. Here, we aimed at performing a phylogenetic study on apo E carrying organisms. We employed a classical and robust method, such as Maximum Likelihood (ML), and compared the results using a more recent approach based on complex networks. Thirty-two apo E amino acid sequences were downloaded from NCBI. A clear separation could be observed among three major groups: mammals, fish and amphibians. The results obtained from ML method, as well as from the constructed networks showed two different groups: one with mammals only (C1) and another with fish (C2), and a single node with the single sequence available for an amphibian. The accordance in results from the different methods shows that the complex networks approach is effective in phylogenetic studies. Furthermore, our results revealed the conservation of apo E among animal groups.

Isolation and function analysis of apolipoprotein A-I gene response to virus infection in grouper

Apolipoproteins, synthesized mainly in liver and intestine and bounded to lipids, play important roles in lipid transport and uptake through the circulation system. In this study, an apolipoprotein A-I gene homologue was cloned from orange-spotted grouper Epinephelus coioides (designed as Ec-ApoA-I) by rapid amplification of cDNA ends (RACE) PCR. The full-length cDNA of Ec-ApoA-I was comprised of 1278 bp with a 792 bp open reading frame (ORF) that encodes a putative protein of 264 amino acids. Quantitative real-time PCR (qPCR) analysis revealed that Ec-ApoA-I was abundant in liver and intestine, and the expression in liver was significantly (P < 0.01) up-regulated after the stimulation of LPS, Poly(I:C), Vibrio alginolyticus, and Singapore grouper iridovirus (SGIV). Recombinant Ec-ApoA-I (rEc-ApoA-I) was produced in Escherichia coli BL21 (DE3) expression system exhibited bacteriolyticactivity against Microcococcus lysodeikticus and Aeromonas hydrophila. Intracellular localization revealed that Ec-ApoA-I distributed in both cytoplasm and nucleus, and predominantly in the cytoplasm. Overexpression of Ec-ApoA-I in grouper Brain (GB) cells could inhibit the replication of SGIV. These results together indicated that Ec-ApoA-I perhaps is involved in the responses to bacterial and viral challenge.

A novel estrogen-regulated avian apolipoprotein

In search for yet uncharacterized proteins involved in lipid metabolism of the chicken, we have isolated a hitherto unknown protein from the serum lipoprotein fraction with a buoyant density of ≤1.063 g/ml. Data obtained by protein microsequencing and molecular cloning of cDNA defined a 537 bp cDNA encoding a precursor molecule of 178 residues. As determined by SDS-PAGE, the major circulating form of the protein, which we designate apolipoprotein-VLDL-IV (Apo-IV), has an apparent M_r of approximately 17 kDa. Northern Blot analysis of different tissues of laying hens revealed Apo-IV expression mainly in the liver and small intestine, compatible with an involvement of the protein in lipoprotein metabolism. To further investigate the biology of Apo-IV, we raised an antibody against a GST-Apo-IV fusion protein, which allowed the detection of the 17-kDa protein in rooster plasma, whereas in laying hens it was detectable only in the isolated ≤1.063 g/ml density lipoprotein fraction. Interestingly, estrogen treatment of roosters caused a reduction of Apo-IV in the liver and in the circulation to levels similar to those in mature hens. Furthermore, the antibody crossreacted with a 17-kDa protein in quail plasma, indicating conservation of Apo-IV in avian species. In search for mammalian counterparts of Apo-IV, alignment of the sequence of the novel chicken protein with those of different mammalian apolipoproteins revealed stretches with limited similarity to regions of ApoC-IV and possibly with ApoE from various mammalian species. These data suggest that Apo-IV is a newly identified avian apolipoprotein.

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Apo-VLDL-IV (Apo-IV) is a newly identified avian apolipoprotein.

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Apo-IV expression is suppressed by estrogen.

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Apo-IV containing VLDL particles are excluded from uptake into yolk.

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Apo-IV has limited similarity to mammalian ApoC-IV.

The particles of the embryonic cerebrospinal fluid: how could they influence brain development?

During brain development, the embryonic cerebrospinal fluid (E-CSF) allows brain expansion and promotes neuroepithelial cell survival, proliferation or differentiation. Previous analyses of E-CSF content have revealed a high protein concentration and the presence of membranous particles. The role of these particles in the E-CSF remains poorly investigated. In this study we showed that the E-CSF contains at least two pools of particles: lipoproteins and exosome-like particles. We showed that these two populations of particles strongly interact with neuropithelial cells via an endocytic process, which display regional specificity along the developing neural tube. Finally, we explore and discuss the possibility that these interactions may influence brain development through the regulation of morphogen and growth factor signaling transduction.

Amyloid contained in the knee joint meniscus is formed from apolipoprotein A-I

OBJECTIVE

To determine the chemical nature of amyloid deposits found in knee joint menisci.

METHODS

Amyloid was extracted from the menisci of 3 adults who underwent knee joint replacement surgery. The primary structural features of the purified proteins were determined by sequential Edman degradation and tandem mass spectrometry (MS/MS). Tissue specimens were also subjected to in situ hybridization analysis, as well as complementary DNA cloning by reverse transcriptase-polymerase chain reaction (RT-PCR). Additionally, specimens from these 3 patients, as well as other patients with amyloid in the knee joint menisci, were examined immunohistochemically.

RESULTS

Amino acid sequence and MS/MS analyses of the extracts revealed the presence of 60-77-residue components identical to the N-terminal portion of apolipoprotein A-I (Apo A-I). The Apo A-I nature of the amyloid was confirmed by the demonstration that the green birefringent congophilic deposits in the 7 meniscus samples were recognized by an anti-human Apo A-I antibody. That the meniscus itself was the source of the amyloidogenic protein was evidenced through Southern blot analysis, in which an Apo A-I product was generated by RT-PCR from synovial tissue, and further, by the demonstration that the cytoplasm of chondrocytes reacted with the specific Apo A-I probe used for in situ hybridization and was immunostained by the anti-Apo A-I antiserum.

CONCLUSION

Amyloid in the knee joint menisci is formed from Apo A-I that is produced by chondrocytes within the meniscal cartilage. This entity represents yet another localized form of amyloidosis associated with the aging process and may be of pathophysiologic import.

Undetectable apolipoprotein A-I gene expression suggests an unusual mechanism of dietary lipid mobilisation in the intestine of Cyprinus carpio

High density lipoprotein (HDL) has been shown to play an important role in the dietary lipid mobilisation in the carp. In spite of this, previous studies have failed to demonstrate the synthesis of the major protein component of HDL, apolipoprotein A-I (apoA-I), in the proximal intestine of the carp. Therefore, the aim of the present study was to evaluate the expression of apoA-I throughout the entire intestine. Curiously, no transcription of the apoA-I gene could be detected either by northern blot or RT-PCR assays in the intestinal mucosa, in clear contrast with the abundant cytosolic immunoreactive apoA-I detected in almost all intestinal segments, which suggests a different origin for this protein. In addition, the detection of specific, but low affinity, binding sites for apoA-I in the carp intestinal brush-border membranes (BBM), and the strong interaction with BBM, which is highly dependent on temperature, points to an important contribution of membrane lipids in apoA-I binding to the intestinal mucosa. This idea was reinforced by the ability of carp apoA-I to associate with multilamellar phospholipid vesicles.

Characterization of the pufferfish Takifugu rubripes apolipoprotein multigene family

We have characterized the apolipoprotein multigene family of the pufferfish Takifugu rubripes. The pufferfish mainly contains 28-kDa, 27-kDa, and 14-kDa apolipoproteins in its plasma and was designated apo-28 kDa, apo-27 kDa, and apo-14 kDa, respectively. N-terminal amino acid sequencing revealed that pufferfish apo-28 kDa and apo-27 kDa have an identical amino acid sequence except an additional propeptide in the former; and both are homologues of apoA-I from other animals. The sequence of pufferfish apo-14 kDa is homologous to that of eel apo-14 kDa previously reported, both being apparently specific to fish. In silico screening, using the publicly available Fugu genome database confirmed the pufferfish apoA-I and apo-14 kDa genes. The database further contained the genes encoding four types of apoA-IV, one apoC-II and two types of apoE. Thus, pufferfish contains nine genes encoding apolipoprotein multigene family. Two apoA-IV and one apoE genes were tandemly arrayed and located on one scaffold. Thus two sets of these genes formed two gene clusters. The apoC-II and apo-14 kDa genes are also located on a single scaffold. apoA-I and apo-14 kDa gene transcripts were mainly expressed in liver and less abundantly in brain. The transcripts of the former gene were also observed in intestine. In contrast, the transcripts encoding four apoA-IVs, one apoC-II, and two apoEs were mainly expressed in intestine. These structural details of pufferfish apolipoproteins and tissue distribution of their gene transcripts provide a novel evidence for better understanding of evolutionary relationships of apolipoprotein multigene family.

Regulation by estrogen of synthesis and secretion of apolipoprotein A-I in the chicken hepatoma cell line, LMH-2A

The synthesis and secretion of apolipoprotein A-I (apoA-I) in response to the treatment with estrogen were investigated in the chicken hepatoma cell line, LMH-2A. Exposure of these cells to exogenous estrogen for up to 48 h results in a decrease of apoA-I production, as evident from Western blotting, immunoprecipitation, and immunofluorescence experiments. Likewise, the secretion of apoA-I is also decreased in estrogen-treated cells when compared to controls. However, under both conditions, the disappearance of the apoprotein from the cells occurs very rapidly and with similar kinetics. The bulk of apoA-I secreted from LMH-2A cells is recovered on lipoprotein particles with a buoyant density of > or =1.10 g/ml, corresponding to HDL and heavy LDL. Interestingly, apoA-I is detectable on apoB-containing lipoproteins by sequential immunoprecipitation, suggesting that the two apoproteins co-reside at least on a subfraction of the secreted particles, or that apoB- and apoA-I-containing particles interact. These interactions are more pronounced in estrogen-treated cells, most likely due to the dramatic estrogen-mediated induction of apoB synthesis and secretion.

Genistein activates apolipoprotein A-I gene expression in the human hepatoma cell line Hep G2

Soy phytoestrogens have been shown to increase plasma levels of HDL cholesterol and apolipoprotein (apo) A-I, its major protein component, in animal studies and in some human studies. The human hepatoma cell line Hep G2 was used to study the effect of the phytoestrogens genistein and daidzein on apo A-I secretion and gene expression in liver cells. Both genistein and daidzein increased apo A-I secretion in a dose-dependent fashion. Apo A-I concentration in the media of treated cells was increased approximately fivefold by 10 micromol/L genistein (P: < 0.001) and approximately onefold by 10 micromol/L daidzein (P: < 0.001) compared with control cells. The effect of genistein on apo A-I secretion was similar to that observed with 17-beta-estradiol. Treatment of cells with genistein for 24 h increased the transcriptional activity of the apo A-I gene as measured by nuclear run-on assay. Transfection experiments with plasmids containing regulatory regions of the apo A-I gene cloned in front of the luciferase reporter gene indicated that the 5' region of the apo A-I gene contained between nucleotides -256 and -41 is responsible for the increased expression of this gene by genistein.

Uptake of lipoproteins for axonal growth of sympathetic neurons

Lipoproteins originating from axon and myelin breakdown in injured peripheral nerves are believed to supply cholesterol to regenerating axons. We have used compartmented cultures of rat sympathetic neurons to investigate the utilization of lipids from lipoproteins for axon elongation. Lipids and proteins from human low density lipoproteins (LDL) and high density lipoproteins (HDL) were taken up by distal axons and transported to cell bodies, whereas cell bodies/proximal axons internalized these components from only LDL, not HDL. Consistent with these observations, the impairment of axonal growth, induced by inhibition of cholesterol synthesis, was reversed when LDL or HDL were added to distal axons or when LDL, but not HDL, were added to cell bodies. LDL receptors (LDLRs) and LR7/8B (apoER2) were present in cell bodies/proximal axons and distal axons, with LDLRs being more abundant in the former. Inhibition of cholesterol biosynthesis increased LDLR expression in cell bodies/proximal axons but not distal axons. LR11 (SorLA) was restricted to cell bodies/proximal axons and was undetectable in distal axons. Neither the LDL receptor-related protein nor the HDL receptor, SR-B1, was detected in sympathetic neurons. These studies demonstrate for the first time that lipids are taken up from lipoproteins by sympathetic neurons for use in axonal regeneration.

Estrogen increases apolipoprotein (apo) A-I secretion in hep G2 cells by modulating transcription of the apo A-I gene promoter

Estrogen administration to postmenopausal women has been shown to increase plasma levels of apolipoprotein (apo) A-I. A human hepatoma cell line, Hep G2, was used to test the hypothesis that estrogen increases the hepatic production of apo A-I by modulating gene expression. When Hep G2 cells were treated for 24 hours with E(2), the apo A-I content in the medium increased 4.3+/-1.0-fold at 10 micromol/L E(2) and 1.8+/-0.4-fold at 1 micromol/L E(2) compared with untreated cells. A time-course experiment indicated that there was no E(2)-dependent (10 micromol/L) increase in apo A-I medium content at 1 hour and 2 hours and that apo A-I was 165% of controls at 6 hours and 440% at 24 hours. Hep G2 cells were transfected, by the cationic lipid method, with constructs containing serial deletions of the 5' region of the apo A-I gene (-41/+397, -256/+397, and -2500/+397) cloned in front of the luciferase gene and with or without a 7-kb region spanning the apo C-III/A-IV intergenic region, which has been shown to contain regulatory elements for the expression of the apo A-I gene. With the exception of the construct containing only the basal promoter (-41/+397), the expression of all constructs was 2- to 3-fold greater in the presence of E(2). The smallest construct that maintained E(2) responsiveness, the -256/+397 construct, does not contain a typical estrogen-responsive element. In the same transfection experiments, the 4-fold increase in apo A-I in the culture medium was preserved. However, when the same set of transfections was performed by the calcium phosphate precipitation method, the E(2) effect on the apo A-I content in the culture medium and on transcription activation was nearly abolished. This effect was probably mediated by Ca(2+), because incubation of cells with 20 mmol/L CaCl(2) abolished the E(2) response. In conclusion, E(2) increases apo A-I production in hepatic cells by increasing the transcription of the apo A-I gene.

Transcriptional regulatory sequences within the first intron of the chicken apolipoproteinAI (apoAI) gene

Previous studies demonstrated that the -82 to +87 nucleotides (nt) 5'-upstream region of the chicken apolipoprotein (apoAI) gene are necessary for maximum reporter chloramphenicol acetyl transferase (cat) gene activation in chicken hepatocarcinoma (LMH) cells [Bhattacharyya, N., Chattapadhyay, R., Oddoux, C., Banerjee, D., 1993. Characterisation of the chicken apolipoprotein A-I gene 5'-flanking region. DNA Cell Biol. 12, 597-604]. The -82 to +87nt contain the 5'-untranslated nt, part of the first intron, and the upstream regulatory sequences. In this study, we examined the role of the first intron in the transcriptional regulation of the chicken apoAI gene. Six different reporter cat gene constructs with or without part of the first intron were prepared and transfected into LMH, normal rat kidney (NRK) and human hepatocarcinoma (HepG2) cells. Cell extracts were prepared from each transfected cell line, and CAT activities were measured. All three cell-lines readily expressed CAT, indicating that transcriptional regulatory sequences are present within the first intron region of the chicken apoAI gene. In an enhancer assay, the first intron containing cat construct exhibited a 5.4-fold increase of reporter activity in NRK cells when compared to a SV 40 promoter containing cat plasmid, suggesting the presence of a moderate enhancer element within +29 to +87nt of the first intron. DNase I protection assays, electrophoretic mobility shift assays and binding experiments with nuclear proteins isolated from different chicken tissues and LMH cells showed interaction with +29 to +87nt. Nuclear proteins isolated from tissues like liver and intestine, that actively express apoAI gene, failed to interact with +29 to +87nt, whereas nuclear proteins isolated from tissues that are less active in apoAI gene expression readily interacted with this region. To show the binding of the LMH-specific trans-acting factors to the +50 to +68nt intron region, DNA-affinity chromatography step was performed by using 3H-labeled nuclear proteins. These studies demonstrate that the first intron region of the apoAI gene interacts with trans-acting proteins and plays an important role in transcriptional regulation of the apoAI gene.

Compound heterozygosity for an apolipoprotein A1 gene promoter mutation and a structural nonsense mutation with apolipoprotein A1 deficiency

Apolipoprotein (apo) A1 plays a central role in the metabolism of HDL. We describe a novel genetic variant of the apoA1 gene identified in a patient with low concentrations of plasma HDL cholesterol. The proband, a 12-year-old Japanese boy, exhibited markedly low levels of both plasma apoA1 and HDL cholesterol. Genomic DNA sequencing of apoA1 genes of the patient showed a compound heterozygosity for an A to C substitution at 27 bp upstream of the transcription start site of 1 apoA1 allele, and a C to T substitution in another allele at residue 84 resulting in aberrant termination. The point mutation at nucleotide position -27 changed ATAAATA of the putative TATA box signal sequence to ATACATA. In addition to this mutation, the patient was heterozygous for a G to A substitution at position -75. Immunoblotting of an isoelectric focusing electrophoresis gel of the proband's plasma showed a trace amount of normal apoA1. No measurable plasma apoA1 and HDL cholesterol in a patient with homozygosity for nonsense mutation at residue 84 has been reported previously. To determine the effects of substitution either at position -27 or -75, plasmids containing the 5'-flanking region of the human apoA1 promoter fused to the CAT reporter gene were constructed and transfected in HepG2 cells. A construct with the A to C substitution at position -27 showed 41. 8+/-4.2%, and G to A substitution at position -75 showed 72.8+/-15. 2% (means+/-SD, n=3) of CAT activities, compared with the wild-type promoter sequence. A construct with the double substitutions at positions -27 and -75 showed only 22.8+/-1.3% (mean+/-SD, n=3) activity relative to the wild type. Our patient is the first case with a TATA box mutation etiologically related to lipoprotein disorders.

Both apolipoprotein E and A-I genes are present in a nonmammalian vertebrate and are highly expressed during embryonic development

Apolipoprotein E (apoE) is associated with several classes of plasma lipoproteins and mediates uptake of lipoproteins through its ability to interact with specific cell surface receptors. Besides its role in cardiovascular diseases, accumulating evidence has suggested that apoE could play a role in neurodegenerative diseases, such as Alzheimer disease. In vertebrates, apoA-I is the major protein of high-density lipoprotein. ApoA-I may play an important role in regulating the cholesterol content of peripheral tissues through the reverse cholesterol transport pathway. We have isolated cDNA clones that code for apoE and apoA-I from a zebrafish embryo library. Analysis of the deduced amino acid sequences showed the presence of a region enriched in basic amino acids in zebrafish apoE similar to the lipoprotein receptor-binding region of human apoE. We demonstrated by whole-mount in situ hybridization that apoE and apoA-I genes are highly expressed in the yolk syncytial layer, an extraembryonic structure implicated in embryonic and larval nutrition. ApoE transcripts were also observed in the deep cell layer during blastula stage, in numerous ectodermal derivatives after gastrulation, and after 3 days of development in a limited number of cells both in brain and in the eyes. Our data indicate that apoE can be found in a nonmammalian vertebrate and that the duplication events, from which apoE and apoA-I genes arose, occurred before the divergence of the tetrapod and teleost ancestors. Zebrafish can be used as a simple and useful model for studying the role of apolipoproteins in embryonic and larval nutrition and of apoE in brain morphogenesis and regeneration.

Transcription factor Sp1 is essential for early embryonic development but dispensable for cell growth and differentiation

Transcription factor Sp1 has been implicated in the expression of many genes. Moreover, it has been suggested that Sp1 is linked to the maintenance of methylation-free CpG islands, the cell cycle, and the formation of active chromatin structures. We have inactivated the mouse Sp1 gene. Sp1-/- embryos are retarded in development, show a broad range of abnormalities, and die around day 11 of gestation. In Sp1-/- embryos, the expression of many putative target genes, including cell cycle-regulated genes, is not affected, CpG islands remain methylation free, and active chromatin is formed at the globin loci. However, the expression of the methyl-CpG-binding protein MeCP2 is greatly reduced in Sp1-/- embryos. MeCP2 is thought to be required for the maintenance of differentiated cells. We suggest that Sp1 is an important regulator of this process.

Mapping functional chicken genes: an alternative approach

Functional genes were selected for linkage analysis mapping using the East Lansing (EL) reference population ¿[Jungle Fowl (JF) x White Leghorn (WL)] x WL¿. The approach used was based on the identification of DNA sequence polymorphisms in the introns of those genes found in JF and WL. Deoxyribonucleic acid sequence analysis revealed single base substitutions in introns of six Type I marker genes: adenylate kinase 1 (AK1), aldolase B (ALDOB), a lysosomal membrane protein gene (LAMP1), vitellogenin 2 (VTG2), apolipoprotein A1 (APOA1), and creatine kinase B (CKB). Transitions or transversions were found in introns of AK1, ALDOB, LAMP1, VTG2, APOA1, and CKB. A transversion in the intron of the JF allele of AK1 generated a unique BspHI cleavage site. The design of polymerase chain reaction (PCR) primers based on the site of base substitution led to the specific amplification of the JF allele in the remaining five genes. A size polymorphism in the PCR production derived from iron response element binding protein (IREBP) distinguished the JF from the WL allele. Linkage analysis of the EL reference population revealed that these candidate genes were located in the following EL linkage groups (E) or chromosomes (Chrom) of the chicken genome: AK1 (E41), VTG2 (E43), APOA1 (E49), CKB (E07), LAMP1 (E01), ALDOB (Chrom Z), and IREBP (Chrom Z). Provided that a base substitution can be found in the parents of the reference population, this PCR-based approach can be used to map any cloned candidate gene. This approach will lead to further information on synteny of the chicken genome with cognate genes of mammalian species.

Species-specific polymorphism in the promoter of the apolipoprotein A-I gene: restoration of human transcriptional efficiency by substitution at positions -189, -144 and -48 bp

Previous studies indicate that species-specific differences in apolipoprotein A-I (apo A-I) expression could be largely explained by cis-acting factors located within or near the 5' flanking region (-231 to +223 bp, where +1 is the start site of transcription). In the present studies, we have localized 7 sites within the (-231 to -15 bp) region of the African green monkey apo A-I gene that differ from the human apo A-I gene 5' flanking region. To identify which of the 7 polymorphic sites were essential for the species-specific differences in apo A-I gene expression, mutated promoter constructs were transfected into HepG2 cells and reporter gene expression was measured. Each of the 7 sites within a defined 5' flanking region of the human gene was individually mutated to the African green nucleotide sequence found at that position. Three of the sites (-189, -144 and -48) were found to raise the human apo A-I promoter activity to approx. 60-65% of the African green promoter. While double mutations (-144/-48 bp and -189/-144 bp), restored the human apo A-I promoter activity to 100% of that found with the African green monkey promoter. Additional studies revealed similar DNA: protein interactions with DNA probes from either human or African green monkey and HepG2 cell nuclear extract. In conclusion, these studies demonstrate that double and triple nucleotide substitutions within the human apo A-I promoter are sufficient to restore gene expression in HepG2 cells to levels seen with the African green monkey promoter. These data suggest that sites -189, -144 and -48 bp are involved in significantly altering the binding affinity of a nuclear factor determining the species-specific level of apo A-I gene transcription.

Transcriptional regulation of the gene encoding apolipoprotein AI in chicken LMH cells

Previous studies indicated that the differential expression of the chicken gene (ApoAI) encoding apolipoprotein AI (ApoAI) in the QMLA-29 and LMH cell lines may be the result of altered cis-elements and/or trans-acting factors. To examine the cis-elements, LMH DNA was used as a template and the 5'-upstream region of ApoAI was PCR amplified. The nucleotide sequence of the LMH ApoAI upstream region was identical to that obtained from young chicken liver DNA. Band shift analyses of the -87 to +90 bp upstream DNA of ApoAI showed differences in the shifting patterns when nuclear proteins from LMH and liver cells were used. Southwestern blots with the same DNA fragment and nuclear proteins from liver and LMH also showed differences. There was one common band of approx. 65 kDa. In addition, LMH had a trans-acting factor of approx. 26 kDa, while liver had an approx. 46-kDa protein. These data suggest that LMH has a different trans-acting factor which may downregulate ApoAI expression.

Characterization of the chicken apolipoprotein A-I gene 5'-flanking region

Apolipoprotein A-I (apoA-I) is a major protein component of plasma high-density lipoprotein in all species studied, and plays an important role in cholesterol homeostasis. In an earlier study, we cloned and structurally characterized the chicken apoA-I gene. In this study, the 5'-flanking region of the chicken apoA-I gene was sequenced and functionally characterized. Sequence analysis of the 510-nucleotide 5' upstream region revealed the presence of TATA and CCAAT boxes. In addition, we identified binding sites for several transcription factors such as Sp1, AP1, and NFI.2. When the 5' fragment was ligated into a promoterless CAT vector and transfected into a chicken hepatocarcinoma cell line (LMH), the bacterial chloramphenicol acetyl transferase (CAT) gene was expressed, suggesting transcriptional regulation is associated with this region. Transfection studies with other 5' deletion constructs revealed that the sequence spanning the region -82 to +87 contained the major transcriptional activity. DNase I footprinting, gel retardation, and Southwestern blot analyses showed that the fragment interacts with nuclear proteins.