Intracellular lipid-binding proteins and their genes

Tissue-specific transcriptional modulation of fatty acid-binding protein genes, fabp2, fabp3 and fabp6, by fatty acids and the peroxisome proliferator, clofibrate, in zebrafish (Danio rerio)

All fabp genes, except fabp2, fabp3 and fabp6, exist as duplicates in the zebrafish genome owing to a whole genome duplication event ~230-400 million years ago. Transcription of some duplicated fabp genes is modulated by fatty acids (FAs) and/or clofibrate, a peroxisome proliferator-activated receptor (PPAR) agonist. We had also shown previously that the steady-state level of acyl-CoA oxidase 1 (acox1) mRNA, a marker of PPARα activation, was elevated in liver, intestine, heart and muscle of fish fed clofibrate demonstrating that zebrafish, unlike some fishes, is responsive to this drug. acox1 transcripts were not induced in the brain of fish fed clofibrate, which suggests this drug may not cross the blood brain barrier. Here, we investigated the effect of dietary FAs and clofibrate on the transcription of single copy fabp genes, fabp2, fabp3 and fabp6, in five tissues of inbred zebrafish. The steady-state level of fabp2 transcripts increased in intestine, while fabp3 mRNA increased in liver of fish fed diets differing in FA content. In fish fed clofibrate, fabp3 mRNA in intestine, and fabp6 mRNA in intestine and heart, were elevated. Based on these findings, modulation of fabp2, fabp3 and fabp6 transcription by FAs and/or clofibrate in zebrafish implicates control of these genes by PPAR interaction with peroxisome proliferator response elements (PPRE) most likely in fabp promoters. Moreover, transcriptional induction of these fabp genes by dietary FAs and/or clofibrate is over-ridden by a tissue-specific mechanism(s), e.g., transcriptional activator or repressor proteins.

Duplicated crabp1 and crabp2 genes in medaka (Oryzias latipes): gene structure, phylogenetic relationship and tissue-specific distribution of transcripts

Here we report the genomic organization of duplicated cellular retinoic acid-binding protein genes, crabp1 and crabp2, in medaka (Japanese ricefish; Oryzias latipes), the phylogenetic relationship of medaka Crabp1a, Crabp1b, Crabp2a and Crabp2b with other Crabp/CRABP sequences from teleosts/tetrapods, and the tissue-specific distribution of crabp1a, crabp1b, crabp2a, and crabp2b transcripts in adult medaka. The duplicated medaka crabp1 and crabp2 genes contain four exons separated by three introns, which encode polypeptides of 137 and 142 amino acids, respectively. Sequence alignment revealed that medaka Crabp sequences share highest sequence identity and similarity with their orthologs from vertebrates. Phylogenetic analysis confirmed the orthology of the medaka Crabps as they form a distinct clade with their orthologous polypeptides from vertebrates. Conserved gene synteny was evident between the duplicated crabp1 and crabp2 genes from medaka, and CRABP1 and CRABP2 genes from human, which provides compelling evidence that the identified duplicated crabp1 and crabp2 genes from medaka most likely arose owing to teleost-specific whole-genome duplication. The tissue-specific distribution of zebrafish (Danio rerio) and medaka crabp1a, crabp1b, crabp2a, and crabp2b gene transcripts suggests acquisition of new function by these genes in medaka, which may explain potential evolutionary processes that led to the retention of sister duplicates of crabp1 and crabp2 genes in the medaka genome.

CRABP2 promotes myoblast differentiation and is modulated by the transcription factors MyoD and Sp1 in C2C12 cells

Cellular retinoic acid binding protein 2 (CRABP2), a member of a family of specific carrier proteins for Vitamin A, belongs to a family of small cytosolic lipid binding proteins. Our previous study suggested that CRABP2 was involved in skeletal muscle development; however, the molecular function and regulatory mechanism of CRABP2 in myogenesis remained unclear. In this study, we found that the expression of the CRABP2 gene was upregulated during C2C12 differentiation. An over-expression assay revealed that CRABP2 promotes myogenic transformation by regulating the cell cycle during C2C12 differentiation. The region from -459 to -4 bp was identified as the core promoter and contains a TATA box, a GC box and binding sites for the transcription factors MyoD and Sp1. Over-expression, site-directed mutagenesis and EMSA assays indicated that the transcription factors MyoD and Sp1 regulate CRABP2 expression and promote myoblast differentiation in C2C12 cells.

The simulation approach to lipid-protein interactions

The interactions between lipids and proteins are crucial for a range of biological processes, from the folding and stability of membrane proteins to signaling and metabolism facilitated by lipid-binding proteins. However, high-resolution structural details concerning functional lipid/protein interactions are scarce due to barriers in both experimental isolation of native lipid-bound complexes and subsequent biophysical characterization. The molecular dynamics (MD) simulation approach provides a means to complement available structural data, yielding dynamic, structural, and thermodynamic data for a protein embedded within a physiologically realistic, modelled lipid environment. In this chapter, we provide a guide to current methods for setting up and running simulations of membrane proteins and soluble, lipid-binding proteins, using standard atomistically detailed representations, as well as simplified, coarse-grained models. In addition, we outline recent studies that illustrate the power of the simulation approach in the context of biologically relevant lipid/protein interactions.

Comparative evolutionary genomics of medaka and three-spined stickleback fabp2a and fabp2b genes with fabp2 of zebrafish

Here we describe the evolutionary relationship of the duplicated intestinal fatty acid binding protein genes fabp2a and fabp2b from medaka and three-spined stickleback by comparing them to the well-studied fabp2 gene from zebrafish. The duplicated fabp2 genes from medaka and three-spined stickleback consist of four exons separated by three introns, which code for a polypeptide of 132 amino acids. Fabp2a and Fabp2b of medaka and three-spined stickleback share highest sequence identity with zebrafish Fabp2. All Fabp2/FABP2 sequences from vertebrates form a distinct clade in a neighbor-joining phylogenetic tree with a robust 100% bootstrap value, which indicates that the medaka and three-spined stickleback fabp2a and fabp2b are orthologs of zebrafish fabp2. The syntenic genes of fabp2a and fabp2b from medaka and three-spined stickleback were shown to be conserved with the syntenic genes of fabp2/FABP2 from zebrafish and human, evidence that the duplicated fabp2 genes from medaka and three-spined stickleback most likely arose from the teleost-specific whole-genome duplication. The tissue-specific distribution of medaka and three-spined stickleback fabp2a and fabp2b transcripts, and zebrafish fabp2 transcripts, assayed by RT-qPCR suggests the acquisition of new function(s) by the medaka fabp2a, and the distinct evolution of fabp2b compared with fabp2a in the medaka and three-spined stickleback genomes.

Identification and expression analysis of a putative fatty acidbinding protein gene in the Asian honeybee, Apis cerana cerana

Fatty acid-binding proteins (FABPs) play pivotal roles in cellular signaling, gene transcription, and lipid metabolism in vertebrates and invertebrates. In this study, a putative FABP gene, referred to as AccFABP, was isolated from the Asian honeybee, Apis cerana cerana Fabricius (Hymenoptera: Apidae). The full-length cDNA consisted of 725 bp, and encoded a protein of 204 amino acids. Homology and phylogenetic analysis indicated that AccFABP was a member of the FABP multifamily. The genomic structure of this gene, which was common among FABP multifamily members, spanned 1,900 bp, and included four exons and three introns. Gene expression analysis revealed that AccFABP was highly expressed in the dark-pigmented phase of pupal development, with peak expression observed in the fat bodies of the dark-pigmented phase pupae. The AccFABP transcripts in the fat body were upregulated by exposure to dietary fatty acids such as conjugated linoleic acid, docosahexaenoic acid, and arachidonic acid. Transcription factor binding sites for Caudal-Related Homeobox and functional CCAAT/enhancer binding site, which were respectively associated with tissue expression and lipid metabolism, were detected in the 5' promoter sequence. The evidence provided in the present study suggests that AccFABP may regulate insect growth and development, and lipid metabolism.

Tissue-specific differential induction of duplicated fatty acid-binding protein genes by the peroxisome proliferator, clofibrate, in zebrafish (Danio rerio)

Background

Force, Lynch and Conery proposed the duplication-degeneration-complementation (DDC) model in which partitioning of ancestral functions (subfunctionalization) and acquisition of novel functions (neofunctionalization) were the two primary mechanisms for the retention of duplicated genes. The DDC model was tested by analyzing the transcriptional induction of the duplicated fatty acid-binding protein (fabp) genes by clofibrate in zebrafish. Clofibrate is a specific ligand of the peroxisome proliferator-activated receptor (PPAR); it activates PPAR which then binds to a peroxisome proliferator response element (PPRE) to induce the transcriptional initiation of genes primarily involved in lipid homeostasis. Zebrafish was chosen as our model organism as it has many duplicated genes owing to a whole genome duplication (WGD) event that occurred ~230-400 million years ago in the teleost fish lineage. We assayed the steady-state levels of fabp mRNA and heterogeneous nuclear RNA (hnRNA) transcripts in liver, intestine, muscle, brain and heart for four sets of duplicated fabp genes, fabp1a/fabp1b.1/fabp1b.2, fabp7a/fabp7b, fabp10a/fabp10b and fabp11a/fabp11b in zebrafish fed different concentrations of clofibrate.

Result

Electron microscopy showed an increase in the number of peroxisomes and mitochondria in liver and heart, respectively, in zebrafish fed clofibrate. Clofibrate also increased the steady-state level of acox1 mRNA and hnRNA transcripts in different tissues, a gene with a functional PPRE. These results demonstrate that zebrafish is responsive to clofibrate, unlike some other fishes. The levels of fabp mRNA and hnRNA transcripts for the four sets of duplicated fabp genes was determined by reverse transcription, quantitative polymerase chain reaction (RT-qPCR). The level of hnRNA coded by a gene is an indirect estimate of the rate of transcriptional initiation of that gene. Clofibrate increased the steady-state level of fabp mRNAs and hnRNAs for both the duplicated copies of fabp1a/fabp1b.1, and fabp7a/fabp7b, but in different tissues. Clofibrate also increased the steady-state level of fabp10a and fabp11a mRNAs and hnRNAs in liver, but not for fabp10b and fabp11b.

Conclusion

Some duplicated fabp genes have, most likely, retained PPREs, but induction by clofibrate is over-ridden by an, as yet, unknown tissue-specific mechanism(s). Regardless of the tissue-specific mechanism(s), transcriptional control of duplicated zebrafish fabp genes by clofibrate has markedly diverged since the WGD event.

Sex differences in transcriptional expression of FABPs in zebrafish liver after chronic perfluorononanoic acid exposure

Perfluorononanoic acid (PFNA), a nine carbon backbone of perfluorinated acids (PFAAs), has wide production applications and is found in environmental matrices as a contaminant. To understand the adverse effects of PFNA, adult male and female zebrafish were exposed to differing PFNA dosages (0, 0.01, 0.1, and 1.0 mg/L) for 180 days using a flow-through exposure system. Results showed body weight, body length, and hepatosomatic index (HSI) decreased in both sexes. The HPLC-MS/MS analysis found that PFNA concentrations were higher in male livers than in female livers with increasing significance in a dose-dependent manner. Total cholesterol levels increased in the livers of both sexes, whereas triglyceride (TG) levels increased in males and decreased in females. With the exception of FABP1b, the transcriptional expression levels of fatty acid binding proteins (FABPs) were up-regulated in males and down-regulated in females. A similar trend between sexes occurred for peroxisome proliferator-activated receptors (PPARs) and Ccaat-enhancer-binding proteins (C/EBPs), which may be the upstream regulatory elements of FABPs. The results indicated that PFNA exposure caused opposite adverse effects on liver TG levels between the sexes in zebrafish possibly due to the opposite expression of FABPs and its upstream genes.

Identification and expression analysis of fabp2 gene from common carp Cyprinus carpio

Two complementary (c)DNA fragments, including the complete open reading frame of fabp2 from the common carp Cyprinus carpio, were cloned by reverse-transcription polymerase chain reaction (RT-PCR). Both were putative intestinal-type fabp genes, named fabp2a and fabp2b. fabp2b was mainly expressed in the intestine and the brain. This gene, however, was nearly not expressed in the liver, heart, pancreas and muscle. fabp2a was only expressed at a very low level in the intestine. Western blot also showed that Fabp2 is relatively highly expressed in the intestine and the brain. Immunohistochemical analysis revealed that Fabp2 is widely distributed in the mucosa of the intestine. These findings provide novel insights into the fabp2 gene molecular evolution, as well as its potential features in the intestine and the brain.

Small lipid-binding proteins in regulating endothelial and vascular functions: focusing on adipocyte fatty acid binding protein and lipocalin-2

Dysregulated production of adipokines from adipose tissue plays a critical role in the development of obesity-associated cardiovascular abnormalities. A group of adipokines, including adipocyte fatty acid binding protein (A-FABP) and lipocalin-2, possess specific lipid-binding activity and are up-regulated in obese human subjects and animal models. They act as lipid chaperones to promote lipotoxicity in endothelial cells and cause endothelial dysfunction under obese conditions. However, different small lipid-binding proteins modulate the development of vascular complications in distinctive manners, which are partly attributed to their specialized structural features and functionalities. By focusing on A-FABP and lipocalin-2, this review summarizes recent advances demonstrating the causative roles of these newly identified adipose tissue-derived lipid chaperones in obesity-related endothelial dysfunction and cardiovascular complications. The specific lipid-signalling mechanisms mediated by these two proteins are highlighted to support their specialized functions. In summary, A-FABP and lipocalin-2 represent potential therapeutic targets to design drugs for preventing vascular diseases associated with obesity.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Cloning and characterization of a midgut-specific fatty acid binding protein in Spodoptera litura

A fatty acid binding protein (FABP) gene (Slfabp1) was cloned from the midgut of Spodoptera litura larvae. The gene consists of four exons and three introns and encodes a peptide of 134 amino acid residues with a predicted molecular mass of 14.7 kDa, which was confirmed by in vitro protein expression. Northern blot and Western blot analyses indicated that both of Slfabp1 mRNA and protein were highly and specifically expressed in the midgut during the fifth and sixth instar feeding larval stages. In situ hybridization and immunohistochemistry analyses confirmed the midgut-specific localization of Slfabp1 mRNA and protein. The result of Western blot showed that expression of the protein was downregulated by starvation and upregulated by refeeding in sixth instar larvae. All of the results taken together suggest that the SlFABP1 plays important role(s) in FA uptake and transport in the midgut during the larval feeding stages of the insect.

Gene/protein expression level, immunolocalization and binding characteristics of fatty acid binding protein from Clonorchis sinensis (CsFABP)

Clonorchis sinensis fatty acid-binding protein (CsFABP) belongs to a multigene family of lipid-binding proteins and is considered to be a promising vaccine candidate for human clonorchiasis. In this study, binding characteristics of CsFABP have been examined for the first time. The recombinant CsFABP (rCsFABP) was found to bind 11-(dansylamino) undecanoic acid (DAUDA), causing a blue shift in the fluorescence emission from 543 to 531 nm with an excitation wavelength of 345 nm and a substantial increase in fluorescence intensity. Fluorimetric titration of rCsFABP with DAUDA exhibited an apparent dissociation constant (K (d)) of 1.58 ± 0.14 μM. In the competitive experiment, the rCsFABP efficiently bound saturated C(10)-C(18) fatty acids and unsaturated fatty acids (oleic acid and linoleic acid), and the latter presented the higher affinity. Furthermore, quantitative RT-PCR and western blotting analysis revealed that CsFABP mRNA and protein were differentially expressed throughout the developmental cycle stages of the parasite, which occur in the definitive host (metacercariae, adult worms, and eggs). In addition, immunolocalization assay showed that CsFABP was localized on the vitelline gland, tegument, intestine, seminal vesicle, eggs in uterus, ovary, and testicle of C. sinensis adult worm, as well as on the vitelline gland of metacercaria. Intriguingly, the surface tissue of the bile duct where C. sinensis resided in the infected Sprague-Dawley rat was also strongly labeled, implying that CsFABP may possibly mediate direct interactions with host cells as a component of excretory/secretory products.

Pro-bone and antifat effects of green tea and its polyphenol, epigallocatechin, in rat mesenchymal stem cells in vitro

Green tea has been demonstrated recently as a potent bone supportive agent. Our previous studies showed that green tea and its polyphenolic constituents can promote bone-forming osteoblast activities and inhibit the bone-resorpting osteoclast formation. The objective of the present study was to investigate whether green tea and its components can regulate the osteogenic and adipogenic differentiation in pluripotent rat mesenchymal stem cells (MSCs). The rat MSCs were isolated from the bone marrow of tibiae and femora. The cells were treated with decaffeinated green tea extract (GTE) and six tea polyphenols under osteogenic induction. The alkaline phosphatase (ALP) activities and matrix calcium (Ca) deposition were assessed after 7 and 14 days of treatment. Our results demonstrated that GTE could significantly increase ALP dose dependently in the concentrations without cytotoxicity (0-100 μg/mL). Among six tested tea polyphenols, epigallocatechin (EGC) was shown to be the most effective in promoting osteogenic differentiation. At 20 μM, EGC increased ALP levels and Ca deposition significantly by 2.3- and 1.7-fold, respectively, when compared with the control group. EGC also increased the mRNA expression of bone formation markers runt-related transcription factor 2, ALP, osteonectin, and osteopontin. Furthermore, EGC demonstrated its antiadipogenicity by decreasing the adipocyte formation and inhibiting the mRNA expression levels of the adipogenic markers peroxisome proliferator-activated receptor γ, ccaat/enhancer-binding protein β, and fatty acid binding protein 4. In conclusion, this is the first report of the dual action of green tea polyphenol EGC in promoting osteogenesis and inhibiting adipocyte formation in MSCs. Our results provide scientific evidence to support the potential use of green tea in supporting the bone against degenerative diseases such as osteoporosis.

The human fatty acid-binding protein family: evolutionary divergences and functions

Fatty acid-binding proteins (FABPs) are members of the intracellular lipid-binding protein (iLBP) family and are involved in reversibly binding intracellular hydrophobic ligands and trafficking them throughout cellular compartments, including the peroxisomes, mitochondria, endoplasmic reticulum and nucleus. FABPs are small, structurally conserved cytosolic proteins consisting of a water-filled, interior-binding pocket surrounded by ten anti-parallel beta sheets, forming a beta barrel. At the superior surface, two alpha-helices cap the pocket and are thought to regulate binding. FABPs have broad specificity, including the ability to bind long-chain (C16-C20) fatty acids, eicosanoids, bile salts and peroxisome proliferators. FABPs demonstrate strong evolutionary conservation and are present in a spectrum of species including Drosophila melanogaster, Caenorhabditis elegans, mouse and human. The human genome consists of nine putatively functional protein-coding FABP genes. The most recently identified family member, FABP12, has been less studied.

Liver fatty acid-binding protein and obesity

While low levels of unesterified long chain fatty acids (LCFAs) are normal metabolic intermediates of dietary and endogenous fat, LCFAs are also potent regulators of key receptors/enzymes and at high levels become toxic detergents within the cell. Elevated levels of LCFAs are associated with diabetes, obesity and metabolic syndrome. Consequently, mammals evolved fatty acid-binding proteins (FABPs) that bind/sequester these potentially toxic free fatty acids in the cytosol and present them for rapid removal in oxidative (mitochondria, peroxisomes) or storage (endoplasmic reticulum, lipid droplets) organelles. Mammals have a large (15-member) family of FABPs with multiple members occurring within a single cell type. The first described FABP, liver-FABP (L-FABP or FABP1), is expressed in very high levels (2-5% of cytosolic protein) in liver as well as in intestine and kidney. Since L-FABP facilitates uptake and metabolism of LCFAs in vitro and in cultured cells, it was expected that abnormal function or loss of L-FABP would reduce hepatic LCFA uptake/oxidation and thereby increase LCFAs available for oxidation in muscle and/or storage in adipose. This prediction was confirmed in vitro with isolated liver slices and cultured primary hepatocytes from L-FABP gene-ablated mice. Despite unaltered food consumption when fed a control diet ad libitum, the L-FABP null mice exhibited age- and sex-dependent weight gain and increased fat tissue mass. The obese phenotype was exacerbated in L-FABP null mice pair fed a high-fat diet. Taken together with other findings, these data suggest that L-FABP could have an important role in preventing age- or diet-induced obesity.

Molecular cloning and tissue expression of the fatty acid-binding protein (Es-FABP) gene in female Chinese mitten crab (Eriocheir sinensis)

Background

Fatty acid-binding proteins (FABPs), small cytosolic proteins that function in the uptake and utilization of fatty acids, have been extensively studied in higher vertebrates while invertebrates have received little attention despite similar nutritional requirements during periods of reproductive activity.

Results

Therefore, a cDNA encoding Eriocheir sinensis FABP (Es-FABP) was cloned based upon EST analysis of a hepatopancreas cDNA library. The full length cDNA was 750 bp and encoded a 131 aa polypeptide that was highly homologous to related genes reported in shrimp. The 9108 bp Es-FABP gene contained four exons that were interrupted by three introns, a genomic organization common among FABP multigene family members in vertebrates. Gene expression analysis, as determined by RT-PCR, revealed the presence of Es-FABP transcripts in hepatopancreas, hemocytes, ovary, gills, muscle, thoracic ganglia, heart, and intestine, but not stomach or eyestalk. Real-time quantitative RT-PCR analysis revealed that Es-FABP expression in ovary, hemocytes, and hepatopancreas was dependent on the status of ovarian development, with peak expression observed in January.

Conclusions

Evidence provided in the present report supports a role of Es-FABP in lipid transport during the period of rapid ovarian growth in E. sinensis, and indirectly confirms the participation of the hepatopancreas, ovary, and hemocytes in lipid nutrient absorption and utilization processes.

The duplicated retinol-binding protein 7 (rbp7) genes are differentially transcribed in embryos and adult zebrafish (Danio rerio)

Genomic and cDNA sequences coding for two cellular retinol-binding proteins (rbp) in zebrafish were retrieved from DNA sequence databases. Phylogenetic analysis revealed that these proteins were most similar to mammalian RBP7/Rbp7 proteins. Hence, the genes coding for these proteins were named rbp7a and rbp7b. Using a radiation hybrid panel, rbp7a and rbp7b were mapped to the zebrafish chromosomes 23 and 6, respectively. Conserved gene synteny indicated that these genes most likely arose as a result of a fish-specific whole-genome duplication event that had occurred 230-400 million years ago. Whole-mount in situ hybridization to zebrafish embryos detected rbp7a transcripts from the sphere stage (4h post-fertilization (hpf)) in the forerunner cells and the yolk syncytial layer, as well as in Kuppfer's vesicle and the periderm at 12 hpf. The transcripts of rbp7b were seen primarily in the somite stages (10-24 hpf) of zebrafish embryos, but also in the floor plate and hypochord, and did not overlap with the distribution of rbp7a transcripts in embryos. The hybridization signal for rbp7a and rbp7b transcripts was not detected in embryos after 12 hpf and 24 hpf, respectively. While transcripts for both rbp7a and rbp7b were found in all adult tissues assayed by RT-qPCR, the steady-state level of rbp7a transcripts were significantly higher than that of rbp7b transcripts in gill and ovary, whereas rbp7b transcripts were significantly higher than rbp7a transcripts in muscle and brain. The distribution of rbp7a and rbp7b transcripts in embryos and adult zebrafish indicate that the cis-elements that control the transcriptional regulation of the rbp7a and rbp7b genes have diverged considerably since their duplication.

Tandem duplication of the fabp1b gene and subsequent divergence of the tissue-specific distribution of fabp1b.1 and fabp1b.2 transcripts in zebrafish (Danio rerio)

We describe a fatty acid-binding protein 1 (fabp1b.2) gene and its tissue-specific expression in zebrafish embryos and adults. The 3.5 kb zebrafish fabp1b.2 gene is the paralog of the previously described zebrafish fabp1a and fabp1b genes. Using the LN54 radiation hybrid mapping panel, we assigned the zebrafish fabp1b.2 gene to linkage group 8, the same linkage group to which fabp1b.1 was mapped. fabp1b.1 and fabp1b.2 appear to have arisen by a tandem duplication event. Whole-mount in situ hybridization of a riboprobe to embryos and larvae detected fabp1b.2 transcripts in the diencephalon and as spots in the periphery of the yolk sac. In adult zebrafish, in situ hybridization revealed fabp1b.2 transcripts in the anterior intestine and skin, and reverse transcription PCR (RT-PCR) detected fabp1b.2 transcripts in the intestine, brain, heart, ovary, skin, and eye. By contrast, fabp1b.1 transcripts were detected by RT-PCR in the liver, intestine, heart, testis, ovary, and gills. The tissue-specific distribution of transcripts for the tandemly duplicated fabp1b.1 and fabp1b.2 genes in adult tissues and during development suggests that the duplicated fabp1b genes of zebrafish have acquired additional functions compared with the ancestral fabp1 gene, i.e., by neofunctionalization. Furthermore, these functions were subsequently divided between fabp1b.1 and fabp1b.2 owing to subfunctionalization.

FABP4: a novel candidate gene for polycystic ovary syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) is a complex multifactorial disorder involving a number of genetic and environmental factors. Adipocyte-fatty acid-binding protein (FABP4) is an adipokine regulating systemic insulin sensitivity, lipid and glucose metabolism. In humans serum FABP4 levels correlate significantly with features of PCOS. Previous researches showed strong evidences that FABP4 impacted the developing of PCOS possibly through its protein alteration or transcription regulation. Thus, the present study is the first attempt to identify the possible genetic role of FABP4 gene in the development of PCOS.

METHODS

About 1000 bp of the promoter region and four exons of FABP4 gene of 178 PCOS patients and 171 healthy controls were directly sequenced.

RESULTS

Three polymorphisms, rs16909225, rs3834363, and rs16909220, were identified, of which rs16909225 and rs16909220 were completely linked (r² = 1) and not associated with the development of PCOS, while the -2-bp/-2-bp genotype of rs3834363 was significantly higher in PCOS than in the controls (χ² = 7.39, df = 1, P = 0.007, OR = 1.80 95% CI: 1.18-2.75).

CONCLUSION

The present study is the first to establish an association between FABP4 gene polymorphisms and the development of PCOS.

Evidence for the Thr79Met polymorphism of the ileal fatty acid binding protein (FABP6) to be associated with type 2 diabetes in obese individuals

The ileal fatty acid binding protein (FABP6) is known to be involved in enterohepatic bile acid metabolism. We have previously found a significant association between the rare allele of the FABP6 Thr79Met polymorphism and lower type 2 diabetes risk in a small case-control study (192 cases and 384 controls) embedded in the large EPIC-Potsdam cohort. A priori functional implication of the amino acid change was gained from in-silico analysis. In this study, we analysed an independent nested case-cohort including 543 incident type 2 diabetes cases from the EPIC-Potsdam cohort and a case-control study including 939 type 2 diabetes cases from KORA to confirm the association with type 2 diabetes and performed association analyses with quantitative disease-related measures in 2112 non-diabetic individuals. Homozygosity for the Met-allele was associated with lower risk of type 2 diabetes (EPIC-Potsdam: 0.70, P=0.04; KORA: 0.79, P=0.06) if adjusted for age, sex, body mass index (BMI), and waist circumference. The homozygous rare variant showed a significant interaction (P=0.006) with BMI. Relative risks in different categories (BMI <25, 25-30, and >30 kg/m(2)) showed an association exclusively in obese (BMI >30 kg/m(2)) individuals (combined risk ratio: 0.62, 95% CI 0.45-0.86). In non-diabetic individuals from the general adult population, no significant associations were observed with plasma total cholesterol, LDL-, and HDL-cholesterol, triglyceride, insulin and glucose concentration. In summary, we found evidence that the-putative functional-Thr79Met substitution of FABP6 confers a protective effect on type 2 diabetes in obese individuals.

Genomic organization of Atlantic salmon (Salmo salar) fatty acid binding protein (fabp2) genes reveals independent loss of duplicate loci in teleosts

Gene and genome duplications are considered to be driving forces of evolution. The relatively recent genome duplication in the common ancestor of salmonids makes this group of fish an excellent system for studying the re-diploidization process and the fates of duplicate genes. We characterized the structure and genome organization of the intestinal fatty acid binding protein (fabp2) genes in Atlantic salmon as a means of understanding the evolutionary fates of members of this protein family in teleosts. A survey of EST databases identified three unique salmonid fabp2 transcripts (fabp2aI, fabp2aII and fabp2b) compared to one transcript in zebrafish. We screened the CHORI-214 Atlantic salmon BAC library and identified BACs containing each of the three fabp2 genes. Physical mapping, genetic mapping and fluorescence in situ hybridization of Atlantic salmon chromosomes revealed that Atlantic salmon fabp2aI, fabp2aII and fabp2b correspond to separate genetic loci that reside on different chromosomes. Comparative genomic analyses indicated that these genes are related to one another by two genome duplications and a gene loss. The first genome duplication occurred in the common ancestor of all teleosts, giving rise to fabp2a and fabp2b, and the second in the common ancestor of salmonids, producing fabp2aI, fabp2aII, fabp2bI and fabp2bII. A subsequent loss of fabp2bI or fabp2bII gave the complement of fabp2 genes seen in Atlantic salmon today. There is also evidence for independent losses of fabp2b genes in zebrafish and tetraodon. Although there is no evidence for partitioning of tissue expression of fabp2 genes (i.e., sub-functionalization) in Atlantic salmon, the pattern of amino acid substitutions in Atlantic salmon and rainbow trout fabp2aI and fabp2aII suggests that neo-functionalization is occurring.

Prediction of functional class of proteins and peptides irrespective of sequence homology by support vector machines

Various computational methods have been used for the prediction of protein and peptide function based on their sequences. A particular challenge is to derive functional properties from sequences that show low or no homology to proteins of known function. Recently, a machine learning method, support vector machines (SVM), have been explored for predicting functional class of proteins and peptides from amino acid sequence derived properties independent of sequence similarity, which have shown promising potential for a wide spectrum of protein and peptide classes including some of the low- and non-homologous proteins. This method can thus be explored as a potential tool to complement alignment-based, clustering-based, and structure-based methods for predicting protein function. This article reviews the strategies, current progresses, and underlying difficulties in using SVM for predicting the functional class of proteins. The relevant software and web-servers are described. The reported prediction performances in the application of these methods are also presented.

Beta-glucan extracts inhibit the in vitro intestinal uptake of long-chain fatty acids and cholesterol and down-regulate genes involved in lipogenesis and lipid transport in rats

BACKGROUND

Dietary fiber reduces the intestinal absorption of nutrients and the blood concentrations of cholesterol and triglycerides.

AIM

We wished to test the hypothesis that high-viscosity (HV) and low-viscosity preparations of barley and oat beta-glucan modify the expression of selected genes of lipid-binding proteins in the intestinal mucosa and reduce the intestinal in vitro uptake of lipids.

METHODS

Five different beta-glucan extracts were separately added to test solutions at concentrations of 0.1-0.5% (wt/wt), and the in vitro intestinal uptake of lipids into the intestine of rats was assessed. An intestinal cell line was used to determine the effect of beta-glucan extracts on the expression of intestinal genes involved in lipid metabolism and fatty acid transport.

RESULTS

All extracts reduced the uptake of 18:2 when the effective resistance of the unstirred water layer was high. When the unstirred layer resistance was low, the HV oat beta-glucan extract reduced jejunal 18:2 uptake, while most extracts reduced ileal 18:2 uptake. Ileal 18:0 uptake was reduced by the HV barley extract, while both jejunal and ileal cholesterol uptakes were reduced by the medium-purity HV barley extract. The inhibitory effect of HV barley beta-glucan on 18:0 and 18:2 uptake was more pronounced at higher fatty acid concentrations. The expression of genes involved in fatty acid synthesis and cholesterol metabolism was down-regulated with the HV beta-glucan extracts. beta-Glucan extracts also reduced intestinal fatty-acid-binding protein and fatty acid transport protein 4 mRNA.

CONCLUSIONS

The reduced intestinal fatty acid uptake observed with beta-glucan is associated with inhibition of genes regulating intestinal uptake and synthesis of lipids. The inhibitory effect of beta-glucan on intestinal lipid uptake raises the possibility of their selective use to reduce their intestinal absorption.

A novel polymorphism in the chicken adipocyte fatty acid-binding protein gene (FABP4) that alters ligand-binding and correlates with fatness

Similar to the mammalian FABP4 gene, the chicken (Gallus gallus) FABP4 gene consists of four exons separated by three introns and encodes a 132 amino acid protein termed the adipocyte fatty acid-binding protein (AFABP). In the current study, a novel G/A polymorphism in exon 3 of the chicken FABP4 gene was identified associated with different chicken breeds that leads to either Ser or Asn at amino acid 89 of the AFABP protein. The Baier chicken averages 0.89+/-0.12% abdominal fat and expresses the G allele (Ser 89 isoform) while the Broiler chicken typically has 3.74+/-0.23% abdominal fat and expresses the A allele (Asn 89 isoforms). cDNAs corresponding to the two AFABP isoforms were cloned and expressed in Escherichia coli as GST fusions, purified by using glutathione sepharose 4B chromatography and evaluated for lipid binding using the fluorescent surrogate ligand 1-anilinonaphthalene 8-sulphonic acid (1,8-ANS). The results showed that AFABP Ser89 exhibited a lower ligand-binding affinity with apparent dissociation constants (Kd) of 7.31+/-3.75 microM, while the AFABP Asn89 isoform bound 1,8-ANS with an apparent dissociation constant of 2.99+/-1.00 microM (P=0.02). These results suggest that the Ser89Asn polymorphism may influence chicken AFABP function and ultimately lipid deposition through changing the ligand-binding activity of AFABP.

All-trans-retinoic acid represses obesity and insulin resistance by activating both peroxisome proliferation-activated receptor beta/delta and retinoic acid receptor

Many biological activities of all-trans-retinoic acid (RA) are mediated by the ligand-activated transcription factors termed retinoic acid receptors (RARs), but this hormone can also activate the nuclear receptor peroxisome proliferation-activated receptor beta/delta (PPARbeta/delta). We show here that adipocyte differentiation is accompanied by a shift in RA signaling which, in mature adipocytes, allows RA to activate both RARs and PPARbeta/delta, thereby enhancing lipolysis and depleting lipid stores. In vivo studies using a dietary-induced mouse model of obesity indicated that onset of obesity is accompanied by downregulation of adipose PPARbeta/delta expression and activity. RA treatment of obese mice induced expression of PPARbeta/delta and RAR target genes involved in regulation of lipid homeostasis, leading to weight loss and improved insulin responsiveness. RA treatment also restored adipose PPARbeta/delta expression. The data indicate that suppression of obesity and insulin resistance by RA is largely mediated by PPARbeta/delta and is further enhanced by activation of RARs. By targeting two nuclear receptors, RA may be a uniquely efficacious agent in the therapy and prevention of the metabolic syndrome.

Molecular cloning and tissue-specific expression of intestinal-type fatty acid binding protein in porcine

The intestinal fatty acid-binding protein (I-FABP) shows binding specificity for long-chain fatty acids and is proposed to be involved in the uptake of dietary fatty acids and their intracellular transport. In this study, the full-length cDNA of I-FABP was cloned from pig intestine by homology cloning approach combined with 3' and 5' RACE. Sequence analysis and bioinformatics study showed that this cDNA contained 614 nucleotides, with a 399 bp open reading frame (ORF) flanked by a 43 bp 5' UTR and a 172 bp 3' UTR. The encoded 132 amino acids of pig I-FABP with a molecular weight of approximately 15 kDa shared a high sequence identity of 68%-85% with those of other species. In addition, the phylogenetical analysis also indicated that the pig I-FABP was in the same branch with those of other species. The tissue-specific expression of pig I-FABP was measured by Northern hybridization and semi-quantitative RT-PCR. The results demonstrated that pig I-FABP mRNA was extensively present in various tissues, but I-FABP transcript of approximately 620 bp was more abundant in intestine than in other tissues.

A global metabolite profiling approach to identify protein-metabolite interactions

Understanding the biochemical functions of proteins is an important factor in elucidating their cellular and physiological functions. Due to the predominance of biopolymer interactions in biology, many methods have been designed to interrogate and identify biologically relevant interactions that proteins make to DNA, RNA, and other proteins. Complementary approaches that can elucidate binding interactions between proteins and small molecule metabolites will impact the understanding of protein-metabolite interactions and fill a need that is outside the scope of current methods. Here, we demonstrate the ability to identify natural protein-metabolite interactions from complex metabolite mixtures by combining a protein-mediated small molecule enrichment step with a global metabolite profiling platform.

A novel fatty acid-binding protein (FABP) gene resulting from tandem gene duplication in mammals: transcription in rat retina and testis

We have identified a new member of the FABP gene family, designated FABP12. FABP12 has the same structure as other FABP genes and resides in a cluster with FABP4/5/8/9 within 300,000 bp chromosomal region. FABP12 orthologs are found in mammals, but not in the zebrafish or chicken genomes. We demonstrate that FABP12 is expressed in rodent retina and testis, as well as in human retinoblastoma cell lines. In situ hybridization of adult rat retinal tissue indicates that FABP12 mRNA is expressed in ganglion and inner nuclear layer cells. Analysis of adult rat testis reveals a pattern of expression that is different from that of the known testis FABP (FABP9) in the testicular germ cells, suggesting distinct roles for these two genes during mammalian spermatogenesis. We propose that FABP12 arose as the result of tandem gene duplication, a mechanism that may have been instrumental to the expansion of the FABP family.

Functional assignment to JEV proteins using SVM

Identification of different protein functions facilitates a mechanistic understanding of Japanese encephalitis virus (JEV) infection and opens novel means for drug development. Support vector machines (SVM), useful for predicting the functional class of distantly related proteins, is employed to ascribe a possible functional class to Japanese encephalitis virus protein. Our study from SVMProt and available JE virus sequences suggests that structural and nonstructural proteins of JEV genome possibly belong to diverse protein functions, are expected to occur in the life cycle of JE virus. Protein functions common to both structural and non-structural proteins are iron-binding, metal-binding, lipid-binding, copper-binding, transmembrane, outer membrane, channels/Pores - Pore-forming toxins (proteins and peptides) group of proteins. Non-structural proteins perform functions like actin binding, zinc-binding, calcium-binding, hydrolases, Carbon-Oxygen Lyases, P-type ATPase, proteins belonging to major facilitator family (MFS), secreting main terminal branch (MTB) family, phosphotransfer-driven group translocators and ATP-binding cassette (ABC) family group of proteins. Whereas structural proteins besides belonging to same structural group of proteins (capsid, structural, envelope), they also perform functions like nuclear receptor, antibiotic resistance, RNA-binding, DNA-binding, magnesium-binding, isomerase (intra-molecular), oxidoreductase and participate in type II (general) secretory pathway (IISP).

Spatio-temporal distribution of fatty acid-binding protein 6 (fabp6) gene transcripts in the developing and adult zebrafish (Danio rerio)

We have determined the structure of the fatty acid-binding protein 6 (fabp6) gene and the tissue-specific distribution of its transcripts in embryos, larvae and adult zebrafish (Danio rerio). Like most members of the vertebrate FABP multigene family, the zebrafish fabp6 gene contains four exons separated by three introns. The coding region of the gene and expressed sequence tags code for a polypeptide of 131 amino acids (14 kDa, pI 6.59). The putative zebrafish Fabp6 protein shared greatest sequence identity with human FABP6 (55.3%) compared to other orthologous mammalian FABPs and paralogous zebrafish Fabps. Phylogenetic analysis showed that the zebrafish Fabp6 formed a distinct clade with the mammalian FABP6s. The zebrafish fabp6 gene was assigned to linkage group (chromosome) 21 by radiation hybrid mapping. Conserved gene synteny was evident between the zebrafish fabp6 gene on chromosome 21 and the FABP6/Fabp6 genes on human chromosome 5, rat chromosome 10 and mouse chromosome 11. Zebrafish fabp6 transcripts were first detected in the distal region of the intestine of embryos at 72 h postfertilization. This spatial distribution remained constant to 7-day-old larvae, the last stage assayed during larval development. In adult zebrafish, fabp6 transcripts were detected by RT-PCR in RNA extracted from liver, heart, intestine, ovary and kidney (most likely adrenal tissue), but not in RNA from skin, brain, gill, eye or muscle. In situ hybridization of a fabp6 riboprobe to adult zebrafish sections revealed intense hybridization signals in the adrenal homolog of the kidney and the distal region of the intestine, and to a lesser extent in ovary and liver, a transcript distribution that is similar, but not identical, to that seen for the mammalian FABP6/Fabp6 gene.

The evolutionary relationship between the duplicated copies of the zebrafish fabp11 gene and the tetrapod FABP4, FABP5, FABP8 and FABP9 genes

We describe the structure of a fatty acid-binding protein 11 (fabp11b) gene and its tissue-specific expression in zebrafish. The 3.4 kb zebrafish fabp11b is the paralog of the previously described zebrafish fabp11a, with a deduced amino acid sequence for Fabp11B exhibiting 65% identity with that of Fabp11A. Whole mount in situ hybridization of a riboprobe to embryos and larvae showed that zebrafish fabp11b transcripts were restricted solely to the retina and were first detected at 24 h postfertilization. In situ hybridization revealed fabp11b transcripts along the spinal cord in adult zebrafish. However, the highly sensitive RT-PCR assay detected fabp11b transcripts in the brain, heart, ovary and eye in adult tissues. By contrast, fabp11a transcripts had been previously detected in the liver, brain, heart, testis, muscle, ovary and skin of adult zebrafish. Using the LN54 radiation hybrid panel, we assigned zebrafish fabp11b to linkage group 16. Phylogenetic analysis and conserved gene synteny with tetrapod genes indicated that the emergence of two copies of fabp11 in the zebrafish genome may have resulted from a fish-specific whole genome duplication event. Furthermore, we propose that the FABP4-FABP5-FABP8-FABP9 (PERF15) gene cluster on a single chromosome in the tetrapod genome and the fabp11 genes in the zebrafish genome originated from a common ancestral gene, which, following their divergence, gave rise to the fabp11 genes of zebrafish, and the progenitor of the FABP4, FABP5, FABP8 and FABP9 genes in tetrapods after the separation of the fish and tetrapod lineages.

Brain fatty acid binding protein (Fabp7) is diurnally regulated in astrocytes and hippocampal granule cell precursors in adult rodent brain

Brain fatty acid binding protein (Fabp7), which is important in early nervous system development, is expressed in astrocytes and neuronal cell precursors in mature brain. We report here that levels of Fabp7 mRNA in adult murine brain change over a 24 hour period. Unlike Fabp5, a fatty acid binding protein that is expressed widely in various cell types within brain, RNA analysis revealed that Fabp7 mRNA levels were elevated during the light period and lower during dark in brain regions involved in sleep and activity mechanisms. This pattern of Fabp7 mRNA expression was confirmed using in situ hybridization and found to occur throughout the entire brain. Changes in the intracellular distribution of Fabp7 mRNA were also evident over a 24 hour period. Diurnal changes in Fabp7, however, were not found in postnatal day 6 brain, when astrocytes are not yet mature. In contrast, granule cell precursors of the subgranular zone of adult hippocampus did undergo diurnal changes in Fabp7 expression. These changes paralleled oscillations in Fabp7 mRNA throughout the brain suggesting that cell-coordinated signals likely control brain-wide Fabp7 mRNA expression. Immunoblots revealed that Fabp7 protein levels also underwent diurnal changes in abundance, with peak levels occurring in the dark period. Of clock or clock-regulated genes, the synchronized, global cycling pattern of Fabp7 expression is unique and implicates glial cells in the response or modulation of activity and/or circadian rhythms.

Inflammatory biomarkers associated with obesity and insulin resistance: a focus on lipocalin-2 and adipocyte fatty acid-binding protein

Obesity is an important risk factor for a cluster of metabolic and cardiovascular diseases, including insulin resistance, Type 2 diabetes, nonalcoholic fatty liver disease and atherosclerosis. Systemic low-grade inflammation, characterized by elevated circulating concentrations of proinflammatory factors, has recently been proposed to be a key mediator that links obesity with its medical complications. Adipose tissue is now recognized as the major contributor to systemic inflammation associated with obesity. As obesity develops, adipose tissue is infiltrated with activated macrophages. The 'inflamed' adipose tissue secretes a large number of proinflammatory adipokines and/or cytokines, which can act either in an autocrine manner to perpetuate local inflammation or in an endocrine manner to induce insulin resistance and endothelial dysfunction. In this review, we summarize recent advances in several newly identified adipose tissue-derived inflammatory factors, with the focus on lipocalin-2 and adipocyte fatty acid-binding protein (A-FABP). Both lipocalin-2 and A-FABP possess lipid-binding properties and are important integrators of metabolic and inflammatory pathways. A growing body of evidence from experimental, epidemiological and genetic studies suggests that both lipocalin-2 and A-FABP represent a novel class of serum biomarkers for risk prediction and therapeutic intervention of obesity-related medical complications.

Interaction of the adipocyte fatty acid-binding protein with the hormone-sensitive lipase: regulation by fatty acids and phosphorylation

Adipocyte fatty acid-binding protein (AFABP/aP2) forms a physical complex with the hormone-sensitive lipase (HSL) and AFABP/aP2-null mice exhibit reduced basal and hormone-stimulated lipolysis. To identify the determinants affecting the interaction fluorescence resonance energy transfer (FRET) imaging was used in conjunction with a mutagenesis strategy to evaluate the roles AFABP/aP2 fatty acid binding and HSL phosphorylation have in complex formation as well as determine the HSL binding site on AFABP/aP2. The nonfatty acid binding mutant of AFABP/aP2 (R126Q) failed to form a FRET-competent complex with HSL either under basal or forskolin-stimulated conditions, indicating that lipid binding is required for association. Once bound to HSL and on the surface of the lipid droplet, YFP-AFABP/aP2 (but not YFP-HSL) exhibited energy transfer between the fusion protein and BODIPY-C12-labeled triacylglycerol. Serine to alanine mutations at the two PKA phosphorylation sites of HSL (659 and 660), or at the AMPK phosphorylation sites (565), blocked FRET between HSL and AFABP/aP2. Substitution of isoleucine for lysine at position 21 of AFABP/aP2 (K21I), but not 31 (K31I), resulted in a non-HSL-binding protein indicating that residues on helix alphaI of AFABP/aP2 define a component of the HSL binding site. These results indicate that the ligand-bound form of AFABP/aP2.interacts with the activated, phosphorylated HSL and that the association is likely to be regulatory; either delivering FA to inhibit HSL (facilitating feedback inhibition) or affecting multicomponent complex formation on the droplet surface.

The fabp4 gene of zebrafish (Danio rerio)--genomic homology with the mammalian FABP4 and divergence from the zebrafish fabp3 in developmental expression

Teleost fishes differ from mammals in their fat deposition and distribution. The gene for adipocyte-type fatty acid-binding protein (A-FABP or FABP4) has not been identified thus far in fishes. We have determined the cDNA sequence and defined the structure of a fatty acid-binding protein gene (designated fabp4) from the zebrafish genome. The polypeptide sequence encoded by zebrafish fabp4 showed highest identity to the H(ad)-FABP or H6-FABP from Antarctic fishes and the putative orthologs from other teleost fishes (83-88%). Phylogenetic analysis clustered the zebrafish FABP4 with all Antarctic fish H6-FABPs and putative FABP4s from other fishes in a single clade, and then with the mammalian FABP4s in an extended clade. Zebrafish fabp4 was assigned to linkage group 19 at a distinct locus from fabp3. A number of closely linked syntenic genes surrounding the zebrafish fabp4 locus were found to be conserved with human FABP4. The zebrafish fabp4 transcripts showed sequential distribution in the developing eye, diencephalon and brain vascular system, from the middle somitogenesis stage to 48 h postfertilization, whereas fabp3 mRNA was located widely in the embryonic and/or larval central nervous system, retina, myotomes, pancreas and liver from middle somitogenesis to 5 days postfertilization. Differentiation in developmental regulation of zebrafish fabp4 and fabp3 gene transcription suggests distinct functions for these two paralogous genes in vertebrate development.

Genes, diet and type 2 diabetes mellitus: a review

Diabetes mellitus is widely recognized as one of the leading causes of death and disability. While insulin insensitivity is an early phenomenon partly related to obesity, pancreatic beta-cell function declines gradually over time even before the onset of clinical hyperglycemia. Several mechanisms have been proposed to be responsible for insulin resistance, including increased non-esterified fatty acids, inflammatory cytokines, adipokines, and mitochondrial dysfunction, as well as glucotoxicity, lipotoxicity, and amyloid formation for beta-cell dysfunction. Moreover, the disease has a strong genetic component, although only a handful of genes have been identified so far. Diabetic management includes diet, exercise and combinations of antihyperglycemic drug treatment with lipid-lowering, antihypertensive, and antiplatelet therapy. Since many persons with type 2 diabetes are insulin resistant and overweight, nutrition therapy often begins with lifestyle strategies to reduce energy intake and increase energy expenditure through physical activity. These strategies should be implemented as soon as diabetes or impaired glucose homoeostasis (pre-diabetes) is diagnosed.

Structure and function of phosphatidylcholine transfer protein (PC-TP)/StarD2

Phosphatidylcholine transfer protein (PC-TP) is a highly specific soluble lipid binding protein that transfers phosphatidylcholine between membranes in vitro. PC-TP is a member of the steroidogenic acute regulatory protein-related transfer (START) domain superfamily. Although its biochemical properties and structure are well characterized, the functions of PC-TP in vivo remain incompletely understood. Studies of mice with homozygous disruption of the Pctp gene have largely refuted the hypothesis that this protein participates in the hepatocellular selection and transport of biliary phospholipids, in the production of lung surfactant, in leukotriene biosynthesis and in cellular phosphatidylcholine metabolism. Nevertheless, Pctp(-/-) mice exhibit interesting defects in lipid homeostasis, the understanding of which should elucidate the biological functions of PC-TP.

Detection of Transcript for Brain-Type Fatty Acid-Binding Protein in Tumor and Urine of Patients with Renal Cell Carcinoma

OBJECTIVES

To clarify the gene expression patterns of fatty acid-binding protein (FABP) and evaluate it as a potential marker for the diagnosis of renal cell carcinoma (RCC). RCC is the most common renal neoplasm.

METHODS

The expression of eight FABP genes in normal human tissues, tumor cell lines, and surgically resected RCC tissues (n = 54) was evaluated by reverse transcriptase-polymerase chain reaction. Additionally, the gene expression of FABPs in the urine of healthy volunteers (n = 12) and patients with RCC (n = 5) was investigated.

RESULTS

In these results, the carcinoma tissues but not the noncancerous (normal) parts of the kidney samples resected from patients with RCC expressed the transcript for brain-type FABP (B-FABP), indicating that expression of the B-FABP gene is a novel marker for RCC. Furthermore, the B-FABP cDNA fragment was not amplified by reverse transcriptase-polymerase chain reaction in the urine samples of healthy donors or patients with RCC after surgical operation. However, B-FABP cDNA was amplified in the patients' urine samples collected before surgery.

CONCLUSIONS

This novel method can be used as a powerful ancillary in the diagnosis of RCC.

Evolutionary coupling of structural and functional sequence information in the intracellular lipid-binding protein family

We have mined the evolutionary record for the large family of intracellular lipid-binding proteins (iLBPs) by calculating the statistical coupling of residue variations in a multiple sequence alignment using methods developed by Ranganathan and coworkers (Lockless and Ranganathan, Science 1999:286;295-299). The 213 sequences analyzed have a wide range of ligand-binding functions as well as highly divergent phylogenetic origins, assuring broad sampling of sequence space. Emerging from this analysis were two major clusters of coupled residues, which when mapped onto the structure of a representative iLBP under study in our laboratory, cellular retinoic-acid binding protein I, are largely contiguous and provide useful points of comparison to available data for the folding of this protein. One cluster comprises a predominantly hydrophobic core away from the ligand-binding site and likely represents key structural information for the iLBP fold. The other cluster includes the portal region where ligand enters its binding site, regions of the ligand-binding cavity, and the region where the 10-stranded beta-barrel characteristic of this family closes (between strands 1' and 10). Linkages between these two clusters suggest that evolutionary pressures on this family constrain structural and functional sequence information in an interdependent fashion. The necessity of the structure to wrap around a hydrophobic ligand confounds the typical sequestration of hydrophobic side chains. Additionally, ligand entry and exit require these structures to have a capacity for specific conformational change during binding and release. We conclude that an essential and structurally apparent separation of local and global sequence information is conserved throughout the iLBP family.

Coordinate transcriptional repression of liver fatty acid-binding protein and microsomal triglyceride transfer protein blocks hepatic very low density lipoprotein secretion without hepatosteatosis

Unlike the livers of humans and mice, and most hepatoma cells, which accumulate triglycerides when treated with microsomal triglyceride transfer protein (MTP) inhibitors, L35 rat hepatoma cells do not express MTP and cannot secrete very low density lipoprotein (VLDL), yet they do not accumulate triglyceride. In these studies we show that transcriptional co-repression of the two lipid transfer proteins, liver fatty acid-binding protein (L-FABP) and MTP, which cooperatively shunt fatty acids into de novo synthesized glycerolipids and the transfer of lipids into VLDL, respectively, act together to maintain hepatic lipid homeostasis. FAO rat hepatoma cells express L-FABP and MTP and demonstrate the ability to assemble and secrete VLDL. In contrast, L35 cells, derived as a single cell clone from FAO cells, do not express L-FABP or MTP nor do they assemble and secrete VLDL. We used these hepatoma cells to elucidate how a conserved DR1 promoter element present in the promoters of L-FABP and MTP affects transcription, expression, and VLDL production. In FAO cells, the DR1 elements of both L-FABP and MTP promoters are occupied by peroxisome proliferator-activated receptor alpha-retinoid X receptor alpha (RXRalpha), with which PGC-1beta activates transcription. In contrast, in L35 cells the DR1 elements of both L-FABP and MTP promoters are occupied by chicken ovalbumin upstream promoter transcription factor II, and transcription is diminished. The combined findings indicate that peroxisome proliferator-activated receptor alpha-RXRalpha and PGC-1beta coordinately up-regulate L-FABP and MTP expression, by competing with chicken ovalbumin upstream promoter transcription factor II for the DR1 sites in the proximal promoters of each gene. Additional studies show that ablation of L-FABP prevents hepatic steatosis caused by treating mice with an MTP inhibitor. Our findings show that reducing both L-FABP and MTP is an effective means to reduce VLDL secretion without causing hepatic steatosis.

An Acute and Coincident Increase in FABP Expression and Lymphatic Lipid and Drug Transport Occurs During Intestinal Infusion of Lipid-Based Drug Formulations to Rats

PURPOSE

To determine a) whether administration of lipid-based formulations can acutely up-regulate the intestinal expression of I-FABP and L-FABP and b) whether this occurs coincidentally with an increase in intestinal lymphatic lipid and drug transport.

METHODS

The expression of I-FABP and L-FABP mRNA (using q-PCR) and protein (using immunohistochemistry and Western blotting) in enterocytes was compared with data describing transport of lipid and drug into intestinal lymph following infusion of a set of lipid-based formulations.

RESULTS

Administration of relatively small amounts of oleic acid (5-20 mg/h) over a 5 h period to rats acutely up-regulated the expression, and altered the intracellular distribution of, I-FABP and L-FABP in the enterocytes of the small intestinal epithelia. The increase in expression of I-FABP and L-FABP correlated well with previous data describing the transport of lipid and drug into intestinal lymph following infusion of the same formulations.

CONCLUSION

The expression and intracellular distribution of I-FABP and L-FABP are acutely influenced by lipid infusion over a time period relevant to feeding or the administration of pharmaceutical lipidic formulations, and these changes occur coincidentally with increased drug transport into the lymphatics.