A novel acyl-CoA-binding protein from bovine liver. Effect on fatty acid synthesis

Acyl-coenzyme A binding protein MoAcb1 regulates conidiation and pathogenicity in Magnaporthe oryzae

Magnaporthe oryzae is a filamentous fungus that causes rice blast. Rice blast seriously threatens the safety of food production. The normal synthesis and metabolism of fatty acids are extremely important for eukaryotes, and acyl-CoA is involved in fatty acid metabolism. Acyl-CoA binding (ACB) proteins specifically bind both medium-chain and long-chain acyl-CoA esters. However, the role of the Acb protein in plant-pathogenic fungi has not yet been investigated. Here, we identified MoAcb1, a homolog of the Acb protein in Saccharomyces cerevisiae. Disruption of MoACB1 causes delayed hyphal growth, significant reduction in conidial production and delayed appressorium development, glycogen availability, and reduced pathogenicity. Using immunoblotting and chemical drug sensitivity analysis, MoAcb1 was found to be involved in endoplasmic reticulum autophagy (ER-phagy). In conclusion, our results suggested that MoAcb1 is involved in conidia germination, appressorium development, pathogenicity and autophagy processes in M. oryzae.

DNA G-quadruplex structure participates in regulation of lipid metabolism through acyl-CoA binding protein

G-quadruplex structure (G4) is a type of DNA secondary structure that widely exists in the genomes of many organisms. G4s are believed to participate in multiple biological processes. Acyl-CoA binding protein (ACBP), a ubiquitously expressed and highly conserved protein in eukaryotic cells, plays important roles in lipid metabolism by transporting and protecting acyl-CoA esters. Here, we report the functional identification of a G4 in the promoter of the ACBP gene in silkworm and human cancer cells. We found that G4 exists as a conserved element in the promoters of ACBP genes in invertebrates and vertebrates. The BmACBP G4 bound with G4-binding protein LARK regulated BmACBP transcription, which was blocked by the G4 stabilizer pyridostatin (PDS) and G4 antisense oligonucleotides. PDS treatment with fifth instar silkworm larvae decreased the BmACBP expression and triacylglycerides (TAG) level, resulting in reductions in fat body mass, body size and weight and growth and metamorphic rates. PDS treatment and knocking out of the HsACBP G4 in human hepatic adenocarcinoma HepG2 cells inhibited the expression of HsACBP and decreased the TAG level and cell proliferation. Altogether, our findings suggest that G4 of the ACBP genes is involved in regulation of lipid metabolism processes in invertebrates and vertebrates.

From benzodiazepines to fatty acids and beyond: revisiting the role of ACBP/DBI

Four decades ago Costa and colleagues identified a small, secreted polypeptide in the brain that can displace the benzodiazepine diazepam from the GABA_A receptor, and was thus termed diazepam binding inhibitor (DBI). Shortly after, an identical polypeptide was identified in liver by its ability to induce termination of fatty acid synthesis, and was named acyl-CoA binding protein (ACBP). Since then, ACBP/DBI has been studied in parallel without a clear and integrated understanding of its dual roles. The first genetic loss-of-function models have revived the field, allowing targeted approaches to better understand the physiological roles of ACBP/DBI in vivo. We discuss the roles of ACBP/DBI in central and tissue-specific functions in mammals, with an emphasis on metabolism and mechanisms of action.

Cytoprotective and Neurotrophic Effects of Octadecaneuropeptide (ODN) in in vitro and in vivo Models of Neurodegenerative Diseases

Octadecaneuropeptide (ODN) and its precursor diazepam-binding inhibitor (DBI) are peptides belonging to the family of endozepines. Endozepines are exclusively produced by astroglial cells in the central nervous system of mammals, and their release is regulated by stress signals and neuroactive compounds. There is now compelling evidence that the gliopeptide ODN protects cultured neurons and astrocytes from apoptotic cell death induced by various neurotoxic agents. In vivo, ODN causes a very strong neuroprotective action against neuronal degeneration in a mouse model of Parkinson's disease. The neuroprotective activity of ODN is based on its capacity to reduce inflammation, apoptosis, and oxidative stress. The protective effects of ODN are mediated through its metabotropic receptor. This receptor activates a transduction cascade of second messengers to stimulate protein kinase A (PKA), protein kinase C (PKC), and mitogen-activated protein kinase (MAPK)-extracellular signal-regulated kinase (ERK) signaling pathways, which in turn inhibits the expression of proapoptotic factor Bax and the mitochondrial apoptotic pathway. In N2a cells, ODN also promotes survival and stimulates neurite outgrowth. During the ODN-induced neuronal differentiation process, numerous mitochondria and peroxisomes are identified in the neurites and an increase in the amount of cholesterol and fatty acids is observed. The antiapoptotic and neurotrophic properties of ODN, including its antioxidant, antiapoptotic, and pro-differentiating effects, suggest that this gliopeptide and some of its selective and stable derivatives may have therapeutic value for the treatment of some neurodegenerative diseases.

Characterization and function of a sunflower (Helianthus annuus L.) Class II acyl-CoA-binding protein

Acyl-CoA-binding proteins (ACBP) bind to long-chain acyl-CoA esters and phospholipids, enhancing the activity of different acyltransferases in animals and plants. Nevertheless, the role of these proteins in the synthesis of triacylglycerols (TAGs) remains unclear. Here, we cloned a cDNA encoding HaACBP1, a Class II ACBP from sunflower (Helianthus annuus), one of the world's most important oilseed crop plants. Transcriptome analysis of this gene revealed strong expression in developing seeds from 16 to 30 days after flowering. The recombinant protein (rHaACBP1) was expressed in Escherichia coli and purified to be studied by in vitro isothermal titration calorimetry and for phospholipid binding. Its high affinity for saturated palmitoyl-CoA (16:0-CoA; K_D 0.11 μM) and stearoyl-CoA (18:0-CoA; K_D 0.13 μM) esters suggests that rHaACBP1 could act in acyl-CoA transfer pathways that involve saturated acyl derivatives. Furthermore, rHaACBP1 also binds to both oleoyl-CoA (18:1-CoA; K_D 6.4 μM) and linoleoyl-CoA (18:2-CoA; K_D 21.4 μM) esters, the main acyl-CoA substrates used to synthesise the TAGs that accumulate in sunflower seeds. Interestingly, rHaACBP1 also appears to bind to different species of phosphatidylcholines (dioleoyl-PC and dilinoleoyl-PC), glycerolipids that are also involved in TAG synthesis, and while it interacts with dioleoyl-PA, this is less prominent than its binding to the PC derivative. Expression of rHaACBP in yeast alters its fatty acid composition, as well as the composition and size of the host acyl-CoA pool. These results suggest that HaACBP1 may potentially fulfil a role in the transport and trafficking of acyl-CoAs during sunflower seed development.

Acyl-CoA-Binding Protein Drives Glioblastoma Tumorigenesis by Sustaining Fatty Acid Oxidation

Glioblastoma multiforme (GBM) undergoes metabolic reprogramming to meet the high ATP and anabolic demands of the tumor cells. However, the role of fatty acid oxidation (FAO) and its regulators in the GBM context has been largely unknown. Here, we show that the neural stem cell pro-proliferative factor acyl-CoA-binding protein (ACBP, also known as DBI) is highly expressed in GBM, and by binding to acyl-CoAs, it cell-autonomously maintains high proliferation rates, promoting tumor growth and poor survival in several preclinical models. Mechanistic experiments using ACBP-acyl-CoA binding affinity variants and pharmacological FAO modulators suggest that ACBP supports tumor growth by controlling the availability of long-chain fatty acyl-CoAs to mitochondria, promoting FAO in GBM. Thus, our findings uncover a critical link between lipid metabolism and GBM progression established by ACBP and offer a potential therapeutic strategy for an effective anti-proliferative metabolic management of GBM.

Glial Endozepines Inhibit Feeding-Related Autonomic Functions by Acting at the Brainstem Level

Endozepines are endogenous ligands for the benzodiazepine receptors and also target a still unidentified GPCR. The endozepine octadecaneuropeptide (ODN), an endoproteolytic processing product of the diazepam-binding inhibitor (DBI) was recently shown to be involved in food intake control as an anorexigenic factor through ODN-GPCR signaling and mobilization of the melanocortinergic signaling pathway. Within the hypothalamus, the DBI gene is mainly expressed by non-neuronal cells such as ependymocytes, tanycytes, and protoplasmic astrocytes, at levels depending on the nutritional status. Administration of ODN C-terminal octapeptide (OP) in the arcuate nucleus strongly reduces food intake. Up to now, the relevance of extrahypothalamic targets for endozepine signaling-mediated anorexia has been largely ignored. We focused our study on the dorsal vagal complex located in the caudal brainstem. This structure is strongly involved in the homeostatic control of food intake and comprises structural similarities with the hypothalamus. In particular, a circumventricular organ, the area postrema (AP) and a tanycyte-like cells forming barrier between the AP and the adjacent nucleus tractus solitarius (NTS) are present. We show here that DBI is highly expressed by ependymocytes lining the fourth ventricle, tanycytes-like cells, as well as by proteoplasmic astrocytes located in the vicinity of AP/NTS interface. ODN staining observed at the electron microscopic level reveals that ODN-expressing tanycyte-like cells and protoplasmic astrocytes are sometimes found in close apposition to neuronal elements such as dendritic profiles or axon terminals. Intracerebroventricular injection of ODN or OP in the fourth ventricle triggers c-Fos activation in the dorsal vagal complex and strongly reduces food intake. We also show that, similarly to leptin, ODN inhibits the swallowing reflex when microinjected into the swallowing pattern generator located in the NTS. In conclusion, we hypothesized that ODN expressing cells located at the AP/NTS interface could release ODN and modify excitability of NTS neurocircuitries involved in food intake control.

Deciphering the roles of acyl-CoA-binding proteins in plant cells

Lipid trafficking is vital for metabolite exchange and signal communications between organelles and endomembranes. Acyl-CoA-binding proteins (ACBPs) are involved in the intracellular transport, protection, and pool formation of acyl-CoA esters, which are important intermediates and regulators in lipid metabolism and cellular signaling. In this review, we highlight recent advances in our understanding of plant ACBP families from a cellular and developmental perspective. Plant ACBPs have been extensively studied in Arabidopsis thaliana (a dicot) and to a lesser extent in Oryza sativa (a monocot). Thus far, they have been detected in the plasma membrane, vesicles, endoplasmic reticulum, Golgi apparatus, apoplast, cytosol, nuclear periphery, and peroxisomes. In combination with biochemical and molecular genetic tools, the widespread subcellular distribution of respective ACBP members has been explicitly linked to their functions in lipid metabolism during development and in response to stresses. At the cellular level, strong expression of specific ACBP homologs in specialized cells, such as embryos, stem epidermis, guard cells, male gametophytes, and phloem sap, is of relevance to their corresponding distinct roles in organ development and stress responses. Other interesting patterns in their subcellular localization and spatial expression that prompt new directions in future investigations are discussed.

Involvement of the Acyl-CoA binding domain containing 7 in the control of food intake and energy expenditure in mice

Acyl-CoA binding domain-containing 7 (Acbd7) is a paralog gene of the diazepam-binding inhibitor/Acyl-CoA binding protein in which single nucleotide polymorphism has recently been associated with obesity in humans. In this report, we provide converging evidence indicating that a splice variant isoform of the Acbd7 mRNA is expressed and translated by some POMC and GABAergic-neurons in the hypothalamic arcuate nucleus (ARC). We have demonstrated that the ARC ACBD7 isoform was produced and processed into a bioactive peptide referred to as nonadecaneuropeptide (NDN) in response to catabolic signals. We have characterized NDN as a potent anorexigenic signal acting through an uncharacterized endozepine G protein-coupled receptor and subsequently via the melanocortin system. Our results suggest that ACBD7-producing neurons participate in the hypothalamic leptin signalling pathway. Taken together, these data suggest that ACBD7-producing neurons are involved in the hypothalamic control exerted on food intake and energy expenditure by the leptin-melanocortin pathway.

DOI:http://dx.doi.org/10.7554/eLife.11742.001

Obesity is an increasingly common problem worldwide. To treat it effectively, we must understand how the body controls how much food a person consumes and how much energy they expend. The hypothalamus is one region of the brain that plays a critical role in regulating this energy balance. Some of the neurons in the hypothalamus can change their activity when they detect satiety hormones including the leptin, which is produced by fat cells and suppresses appetite. However, it is not clear exactly how the neurons respond to leptin and other energy-related signals.

Recent studies have linked the gene that encodes a protein called ACBD7 with obesity, and showed that it is one of the genes that is overexpressed in neurons that are sensitive to leptin. Now, Lanfray et al. have discovered a population of neurons that produce a new variant of the protein in the hypothalamus of mice. When this protein variant matures, it can be cut down to form a small protein-like molecule called NDN. Further experiments showed that leptin stimulates the production of both the new ABCD7 variant and NDN.

Lanfray et al. then injected mice that had been denied food for a several hours with NDN. The injected mice ate less than untreated mice, and burn more energy.

NDN appears to form part of the signaling pathway through which leptin signals to the hypothalamus to control appetite. In the future, creating mice in which the activity of the gene that encodes ACBD7 can be easily disrupted could help to reveal more about how the hypothalamus helps to control energy balance.

DOI:http://dx.doi.org/10.7554/eLife.11742.002

Acyl-CoA-Binding Proteins (ACBPs) in Plant Development

Acyl-CoA-binding proteins (ACBPs) play a pivotal role in fatty acid metabolism because they can transport medium- and long-chain acyl-CoA esters. In eukaryotic cells, ACBPs are involved in intracellular trafficking of acyl-CoA esters and formation of a cytosolic acyl-CoA pool. In addition to these ubiquitous functions, more specific non-redundant roles of plant ACBP subclasses are implicated by the existence of multigene families with variable molecular masses, ligand specificities, functional domains (e.g. protein-protein interaction domains), subcellular locations and gene expression patterns. In this chapter, recent progress in the characterization of ACBPs from the model dicot plant, Arabidopsis thaliana, and the model monocot, Oryza sativa, and their emerging roles in plant growth and development are discussed. The functional significance of respective members of the plant ACBP families in various developmental and physiological processes such as seed development and germination, stem cuticle formation, pollen development, leaf senescence, peroxisomal fatty acid β-oxidation and phloem-mediated lipid transport is highlighted.

The binding versatility of plant acyl-CoA-binding proteins and their significance in lipid metabolism

Acyl-CoA esters are the activated form of fatty acids and play important roles in lipid metabolism and the regulation of cell functions. They are bound and transported by nonenzymic proteins such as the acyl-CoA-binding proteins (ACBPs). Although plant ACBPs were so named by virtue of amino acid homology to existing yeast and mammalian counterparts, recent studies revealed that ligand specificities of plant ACBPs are not restricted to acyl-CoA esters. Arabidopsis and rice ACBPs also interact with phospholipids, and their affinities to different acyl-CoA species and phospholipid classes vary amongst isoforms. Their ligands also include heavy metals. Interactors of plant ACBPs are further diversified due to the evolution of protein-protein interacting domains. This review summarizes our current understanding of plant ACBPs with a focus on their binding versatility. Their broad ligand range is of paramount significance in serving a multitude of functions during development and stress responses as discussed herein. This article is part of a Special Issue entitled: Plant Lipid Biology edited by Kent D. Chapman and Ivo Feussner.

Compromised epidermal barrier stimulates Harderian gland activity and hypertrophy in ACBP-/- mice

Acyl-CoA binding protein (ACBP) is a small, ubiquitously expressed intracellular protein that binds C14-C22 acyl-CoA esters with very high affinity and specificity. We have recently shown that targeted disruption of the Acbp gene leads to a compromised epidermal barrier and that this causes delayed adaptation to weaning, including the induction of the hepatic lipogenic and cholesterogenic gene programs. Here we show that ACBP is highly expressed in the Harderian gland, a gland that is located behind the eyeball of rodents and involved in the production of fur lipids and lipids used for lubrication of the eye lid. We show that disruption of the Acbp gene leads to a significant enlargement of this gland with hypertrophy of the acinar cells and increased de novo synthesis of monoalkyl diacylglycerol, the main lipid species produced by the gland. Mice with conditional targeting of the Acbp gene in the epidermis recapitulate this phenotype, whereas generation of an artificial epidermal barrier during gland development reverses the phenotype. Our findings indicate that the Harderian gland is activated by the compromised epidermal barrier as an adaptive and protective mechanism to overcome the barrier defect.

Long-chain acyl-CoA esters in metabolism and signaling: Role of acyl-CoA binding proteins

Long-chain fatty acyl-CoA esters are key intermediates in numerous lipid metabolic pathways, and recognized as important cellular signaling molecules. The intracellular flux and regulatory properties of acyl-CoA esters have been proposed to be coordinated by acyl-CoA-binding domain containing proteins (ACBDs). The ACBDs, which comprise a highly conserved multigene family of intracellular lipid-binding proteins, are found in all eukaryotes and ubiquitously expressed in all metazoan tissues, with distinct expression patterns for individual ACBDs. The ACBDs are involved in numerous intracellular processes including fatty acid-, glycerolipid- and glycerophospholipid biosynthesis, β-oxidation, cellular differentiation and proliferation as well as in the regulation of numerous enzyme activities. Little is known about the specific roles of the ACBDs in the regulation of these processes, however, recent studies have gained further insights into their in vivo functions and provided further evidence for ACBD-specific functions in cellular signaling and lipid metabolic pathways. This review summarizes the structural and functional properties of the various ACBDs, with special emphasis on the function of ACBD1, commonly known as ACBP.

Endozepines

Since their introduction in the 1960s, benzodiazepines (BZs) remain one of the most commonly prescribed medications, acting as potent sedatives, hypnotics, anxiolytics, anticonvulsants, and muscle relaxants. The primary neural action of BZs and related compounds is augmentation of inhibitory transmission, which occurs through allosteric modulation of the gamma-aminobutyric acid (GABA)-induced current at the gamma-aminobutyric acid receptor (GABAAR). The discovery of the BZ-binding site on GABAARs encouraged many to speculate that the brain produces its own endogenous ligands to this site (Costa & Guidotti, 1985). The romanticized quest for endozepines, endogenous ligands to the BZ-binding site, has uncovered a variety of ligands that might fulfill this role, including oleamides (Cravatt et al., 1995), nonpeptidic endozepines (Rothstein et al., 1992), and the protein diazepam-binding inhibitor (DBI) (Costa & Guidotti, 1985). Of these ligands, DBI, and affiliated peptide fragments, is the most extensively studied endozepine. The quest for the "brain's Valium" over the decades has been elusive as mainly negative allosteric modulatory effects have been observed (Alfonso, Le Magueresse, Zuccotti, Khodosevich, & Monyer, 2012; Costa & Guidotti, 1985), but recent evidence is accumulating that DBI displays regionally discrete endogenous positive modulation of GABA transmission through activation of the BZ receptor (Christian et al., 2013). Herein, we review the literature on this topic, focusing on identification of the endogenous molecule and its region-specific expression and function.

Acyl-coenzyme A-binding protein regulates Beta-oxidation required for growth and survival of non-small cell lung cancer

We identified acyl-coenzyme A-binding protein (ACBP) as part of a proteomic signature predicting the risk of having lung cancer. Because ACBP is known to regulate β-oxidation, which in turn controls cellular proliferation, we hypothesized that ACBP contributes to regulation of cellular proliferation and survival of non-small cell lung cancer (NSCLC) by modulating β-oxidation. We used matrix-assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS) and immunohistochemistry (IHC) to confirm the tissue localization of ABCP in pre-invasive and invasive NSCLCs. We correlated ACBP gene expression levels in NSCLCs with clinical outcomes. In loss-of-function studies, we tested the effect of the downregulation of ACBP on cellular proliferation and apoptosis in normal bronchial and NSCLC cell lines. Using tritiated-palmitate ((3)H-palmitate), we measured β-oxidation levels and tested the effect of etomoxir, a β-oxidation inhibitor, on proliferation and apoptosis. MALDI-IMS and IHC analysis confirmed that ACBP is overexpressed in pre-invasive and invasive lung cancers. High ACBP gene expression levels in NSCLCs correlated with worse survival (HR = 1.73). We observed a 40% decrease in β-oxidation and concordant decreases in proliferation and increases in apoptosis in ACBP-depleted NSCLC cells as compared with bronchial airway epithelial cells. Inhibition of β-oxidation by etomoxir in ACBP-overexpressing cells produced dose-dependent decrease in proliferation and increase in apoptosis (P = 0.01 and P < 0.001, respectively). These data suggest a role for ACBP in controlling lung cancer progression by regulating β-oxidation.

The acyl-CoA binding protein is required for normal epidermal barrier function in mice

The acyl-CoA binding protein (ACBP) is a 10 kDa intracellular protein expressed in all eukaryotic species. Mice with targeted disruption of Acbp (ACBP(-/-) mice) are viable and fertile but present a visible skin and fur phenotype characterized by greasy fur and development of alopecia and scaling with age. Morphology and development of skin and appendages are normal in ACBP(-/-) mice; however, the stratum corneum display altered biophysical properties with reduced proton activity and decreased water content. Mass spectrometry analyses of lipids from epidermis and stratum corneum of ACBP(+/+) and ACBP(-/-) mice showed very similar composition, except for a significant and specific decrease in the very long chain free fatty acids (VLC-FFA) in stratum corneum of ACBP(-/-) mice. This finding indicates that ACBP is critically involved in the processes that lead to production of stratum corneum VLC-FFAs via complex phospholipids in the lamellar bodies. Importantly, we show that ACBP(-/-) mice display a ∼50% increased transepidermal water loss compared with ACBP(+/+) mice. Furthermore, skin and fur sebum monoalkyl diacylglycerol (MADAG) levels are significantly increased, suggesting that ACBP limits MADAG synthesis in sebaceous glands. In summary, our study shows that ACBP is required for production of VLC-FFA for stratum corneum and for maintaining normal epidermal barrier function.

Tissue- and paralogue-specific functions of acyl-CoA-binding proteins in lipid metabolism in Caenorhabditis elegans

ACBP (acyl-CoA-binding protein) is a small primarily cytosolic protein that binds acyl-CoA esters with high specificity and affinity. ACBP has been identified in all eukaryotic species, indicating that it performs a basal cellular function. However, differential tissue expression and the existence of several ACBP paralogues in many eukaryotic species indicate that these proteins serve distinct functions. The nematode Caenorhabditis elegans expresses seven ACBPs: four basal forms and three ACBP domain proteins. We find that each of these paralogues is capable of complementing the growth of ACBP-deficient yeast cells, and that they exhibit distinct temporal and tissue expression patterns in C. elegans. We have obtained loss-of-function mutants for six of these forms. All single mutants display relatively subtle phenotypes; however, we find that functional loss of ACBP-1 leads to reduced triacylglycerol (triglyceride) levels and aberrant lipid droplet morphology and number in the intestine. We also show that worms lacking ACBP-2 show a severe decrease in the β-oxidation of unsaturated fatty acids. A quadruple mutant, lacking all basal ACBPs, is slightly developmentally delayed, displays abnormal intestinal lipid storage, and increased β-oxidation. Collectively, the present results suggest that each of the ACBP paralogues serves a distinct function in C. elegans.

Disruption of the acyl-CoA-binding protein gene delays hepatic adaptation to metabolic changes at weaning

The acyl-CoA-binding protein (ACBP)/diazepam binding inhibitor is an intracellular protein that binds C(14)-C(22) acyl-CoA esters and is thought to act as an acyl-CoA transporter. In vitro analyses have indicated that ACBP can transport acyl-CoA esters between different enzymatic systems; however, little is known about the in vivo function in mammalian cells. We have generated mice with targeted disruption of ACBP (ACBP(-/-)). These mice are viable and fertile and develop normally. However, around weaning, the ACBP(-/-) mice go through a crisis with overall weakness and a slightly decreased growth rate. Using microarray analysis, we show that the liver of ACBP(-/-) mice displays a significantly delayed adaptation to weaning with late induction of target genes of the sterol regulatory element-binding protein (SREBP) family. As a result, hepatic de novo cholesterogenesis is decreased at weaning. The delayed induction of SREBP target genes around weaning is caused by a compromised processing and decreased expression of SREBP precursors, leading to reduced binding of SREBP to target sites in chromatin. In conclusion, lack of ACBP interferes with the normal metabolic adaptation to weaning and leads to delayed induction of the lipogenic gene program in the liver.

Involvement of low molecular mass soluble acyl-CoA-binding protein in seed oil biosynthesis

Acyl-CoA-binding protein (ACBP), a low molecular mass (m) (∼ 10 kDa) soluble protein ubiquitous in eukaryotes, plays an important housekeeping role in lipid metabolism by maintaining the intracellular acyl-CoA pool. ACBP is involved in lipid biosynthesis and transport, gene expression, and membrane biogenesis. In plants, low m ACBP and high m ACBPs participate in response mechanisms to biotic and abiotic factors, acyl-CoA transport in phloem, and biosynthesis of structural and storage lipids. In light of current research on the modification of seed oil, insight into mechanisms of substrate trafficking within lipid biosynthetic pathways is crucial for developing rational strategies for the production of specialty oils with the desired alterations in fatty acid composition. In this review, we summarize our knowledge of plant ACBPs with emphasis on the role of low m ACBP in seed oil biosynthesis, based on in vitro studies and analyses of transgenic plants. Future prospects and possible applications of low m ACBP in seed oil modification are discussed.

Unraveling the pheromone biosynthesis activating neuropeptide (PBAN) signal transduction cascade that regulates sex pheromone production in moths

Studies over the past three decades have demonstrated that female moths usually produce sex pheromones as multicomponent blends in which the ratios of the individual components are precisely controlled, making it possible to generate species-specific pheromone blends. Most moth pheromone components are de novo synthesized from acetyl-CoA in the pheromone gland (PG) through modifications of fatty acid biosynthetic pathways. Pheromone biosynthesis activating neuropeptide (PBAN), a neurohormone produced by a cephalic organ (subesophageal ganglion) stimulates sex pheromone biosynthesis in the PG via an influx of extracellular Ca(2+). In recent years, we have expanded our knowledge of the precise mechanisms underlying silkmoth (Bombyx mori) sex pheromone production by characterizing a number of key molecules. In this review, we want to highlight our efforts in elucidating these mechanisms in B. mori and to understand how they relate more broadly to lepidopteran sex pheromone production in general.

Functional characterization of the Bombyx mori fatty acid transport protein (BmFATP) within the silkmoth pheromone gland

Fatty acid transport protein (FATP) is an evolutionarily conserved membrane-bound protein that facilitates the uptake of extracellular long chain fatty acids. In humans and mice, six FATP isoforms have been identified and their tissue-specific distributions suggest that each plays a discrete role in lipid metabolism in association with fatty acid uptake. While the presence of FATP homologs in insects has been demonstrated, their functional role remains to be characterized. Pheromonogenesis is defined as the dynamic period in which all machinery required for sex pheromone biosynthesis is generated and organized within the pheromone gland (PG) cells. By exploiting this unique system in the PG of the silkmoth, Bombyx mori, we found that BmFATP is predominantly expressed in the PG and undergoes up-regulation 1 day prior to eclosion. Before eclosion, B. mori PG cells accumulate cytoplasmic lipid droplets (LDs), which play a role in storing the pheromone (bombykol) precursor fatty acid in the form of triacylglycerol. RNAi-mediated gene silencing of BmFATP in vivo significantly suppressed LD accumulation by preventing the synthesis of triacylglycerols and resulted in a significant reduction in bombykol production. These results, in conjunction with the findings that BmFATP stimulates the uptake of extracellular long-chain fatty acids and BmFATP knockdown reduces cellular long-chain acyl-CoA synthetase activity, suggest that BmFATP plays an essential role in bombykol biosynthesis by stimulating both LD accumulation and triacylglycerol synthesis via a process called vectorial acylation that couples the uptake of extracellular fatty acids with activation to CoA thioesters during pheromonogenesis.

Molecular mechanisms underlying sex pheromone production in the silkmoth, Bombyx mori: characterization of the molecular components involved in bombykol biosynthesis

Many species of female moths produce sex pheromones to attract conspecific males. To date, sex pheromones from more than 570 moth species have been chemically identified. Most moth species utilize Type I pheromones that consist of straight-chain compounds 10-18 carbons in length with a functional group of a primary alcohol, aldehyde, or acetate ester and usually with several double bonds. In contrast, some moth species use unsaturated hydrocarbons or hydrocarbon epoxides, classified as Type II lepidopteran pheromones, as sex pheromones. Studies over the past three decades have demonstrated that female moths usually produce sex pheromones as multi-component blends where the ratio of the individual components is precisely controlled, thus making it possible to generate species-specific pheromone blends. As for the biosynthesis of Type I pheromones, it is well established that they are de novo synthesized in the pheromone gland (PG) through modifications of fatty acid biosynthetic pathways. However, as many of the molecular components within the PG cells (i.e., enzymes, proteins, and small regulatory molecules) have not been functionally characterized, the molecular mechanisms underlying sex pheromone production in PG cells remain poorly understood. To address this, we have recently characterized some of the molecules involved in the biosynthesis of the sex pheromone bombykol in the silkmoth, Bombyx mori. Characterization of these, and other, key molecules will facilitate our understanding of the precise mechanisms underlying lepidopteran sex pheromone production.

Acyl-CoA binding proteins; structural and functional conservation over 2000 MYA

Besides serving as essential substrates for beta-oxidation and synthesis of triacylglycerols and more complex lipids like sphingolipids and sterol esters, long-chain fatty acyl-CoA esters are increasingly being recognized as important regulators of enzyme activities and gene transcription. Acyl-CoA binding protein, ACBP, has been proposed to play a pivotal role in the intracellular trafficking and utilization of long-chain fatty acyl-CoA esters. Depletion of acyl-CoA binding protein in yeast results in aberrant organelle morphology incl. fragmented vacuoles, multi-layered plasma membranes and accumulation of vesicles of variable sizes. In contrast to synthesis and turn-over of glycerolipids, the levels of very-long-chain fatty acids, long-chain bases and ceramide are severely affected by Acb1p depletion, suggesting that Acb1p, rather than playing a general role, serves specific roles in cellular lipid metabolism.

High resolution crystal structures of unliganded and liganded human liver ACBP reveal a new mode of binding for the acyl-CoA ligand

The acyl-CoA binding protein (ACBP) is essential for the fatty acid metabolism, membrane structure, membrane fusion, and ceramide synthesis. Here high resolution crystal structures of human cytosolic liver ACBP, unliganded and liganded with a physiological ligand, myristoyl-CoA are described. The binding of the acyl-CoA molecule induces only few structural differences near the binding pocket. The crystal form of the liganded ACBP, which has two ACBP molecules in the asymmetric unit, shows that in human ACBP the same acyl-CoA binding pocket is present as previously described for the bovine and Plasmodium falciparum ACBP and the mode of binding of the 3'-phosphate-AMP moiety is conserved. Unexpectedly, in one of the acyl-CoA binding pockets the acyl moiety is bound in a reversed mode as compared with the bovine and P. falciparum structures. In this binding mode, the myristoyl-CoA molecule is fully ordered and bound across the two ACBP molecules of the crystallographic asymmetric unit: the 3'-phosphate-AMP moiety is bound in the binding pocket of one ACBP molecule and the acyl chain is bound in the pocket of the other ACBP molecule. The remaining binding pocket cavities of these two ACBP molecules are filled by other ligand fragments. This novel binding mode shows that the acyl moiety can flip out of its classical binding pocket and bind elsewhere, suggesting a mechanism for the acyl-CoA transfer between ACBP and the active site of a target enzyme. This mechanism is of possible relevance for the in vivo function of ACBP.

MAA-1, a novel acyl-CoA-binding protein involved in endosomal vesicle transport in Caenorhabditis elegans

The budding and fission of vesicles during membrane trafficking requires many proteins, including those that coat the vesicles, adaptor proteins that recruit components of the coat, and small GTPases that initiate vesicle formation. In addition, vesicle formation in vitro is promoted by the hydrolysis of acyl-CoA lipid esters. The mechanisms by which these lipid esters are directed to the appropriate membranes in vivo, and their precise roles in vesicle biogenesis, are not yet understood. Here, we present the first report on membrane associated ACBP domain-containing protein-1 (MAA-1), a novel membrane-associated member of the acyl-CoA-binding protein family. We show that in Caenorhabditis elegans, MAA-1 localizes to intracellular membrane organelles in the secretory and endocytic pathway and that mutations in maa-1 reduce the rate of endosomal recycling. A lack of maa-1 activity causes a change in endosomal morphology. Although in wild type, many endosomal organelles have long tubular protrusions, loss of MAA-1 activity results in loss of the tubular domains, suggesting the maa-1 is required for the generation or maintenance of these domains. Furthermore, we demonstrate that MAA-1 binds fatty acyl-CoA in vitro and that this ligand-binding ability is important for its function in vivo. Our results are consistent with a role for MAA-1 in an acyl-CoA-dependent process during vesicle formation.

Targeted disruption of genes in the Bombyx mori sex pheromone biosynthetic pathway

The sex pheromone biosynthetic pathways of lepidopterans require the concerted actions of multiple gene products. A number of pheromone gland (PG)-specific genes have been cloned in recent years and, whereas in vitro characterizations have indicated functions consistent with roles in pheromone production, there have been no clear demonstrations in vivo. Using an RNA interference-mediated loss-of-function approach, we injected newly formed Bombyx mori pupae with dsRNAs corresponding to genes of interest [i.e., PG fatty acyl reductase (pgFAR), B. mori PG Z11/Delta10,12 desaturase (Bmpgdesat1), PG acyl-CoA-binding protein (pgACBP), midgut ACBP, and pheromone biosynthesis activating neuropeptide receptor (PBANR)] to assess their specific roles during pheromonogenesis. In all cases, the introduced dsRNAs induced a dose-dependent reduction in sex pheromone production with the corresponding decrease in transcript levels. No effects on pupal development or adult emergence were observed. Disrupting the PBANR gene resulted in a loss of the lipase activity that liberates pheromone precursors, whereas knockout of the pgACBP gene prevented the daily accumulation and fluctuation of the triacylglycerols that function as the cellular deposits for the pheromone precursors. Taken together, our results provide unequivocal evidence that the pgACBP, Bmpgdesat1, pgFAR, and PBANR gene products are essential during pheromonogenesis and demonstrate the power of this methodology for dissecting the molecular interactions that comprise biosynthetic pathways.

Evolution of the acyl-CoA binding protein (ACBP)

Acyl-CoA-binding protein (ACBP) is a 10 kDa protein that binds C12-C22 acyl-CoA esters with high affinity. In vitro and in vivo experiments suggest that it is involved in multiple cellular tasks including modulation of fatty acid biosynthesis, enzyme regulation, regulation of the intracellular acyl-CoA pool size, donation of acyl-CoA esters for beta-oxidation, vesicular trafficking, complex lipid synthesis and gene regulation. In the present study, we delineate the evolutionary history of ACBP to get a complete picture of its evolution and distribution among species. ACBP homologues were identified in all four eukaryotic kingdoms, Animalia, Plantae, Fungi and Protista, and eleven eubacterial species. ACBP homologues were not detected in any other known bacterial species, or in archaea. Nearly all of the ACBP-containing bacteria are pathogenic to plants or animals, suggesting that an ACBP gene could have been acquired from a eukaryotic host by horizontal gene transfer. Many bacterial, fungal and higher eukaryotic species only harbour a single ACBP homologue. However, a number of species, ranging from protozoa to vertebrates, have evolved two to six lineage-specific paralogues through gene duplication and/or retrotransposition events. The ACBP protein is highly conserved across phylums, and the majority of ACBP genes are subjected to strong purifying selection. Experimental evidence indicates that the function of ACBP has been conserved from yeast to humans and that the multiple lineage-specific paralogues have evolved altered functions. The appearance of ACBP very early on in evolution points towards a fundamental role of ACBP in acyl-CoA metabolism, including ceramide synthesis and in signalling.

Expression analysis of androgen-responsive genes in the prostate of veal calves treated with anabolic hormones

In order to identify indirect molecular biomarkers of anabolic treatments in veal calves, an animal experiment was performed using two combinations of growth promoters (consisting of boldenone undecylenate and estradiol benzoate, and of testosterone enantate and estradiol benzoate). We selected a set of 12 genes that are known to be androgen responsive in other mammalian species. The expression profile of this set of genes was analysed on prostate samples of veal calves using a real-time RT-PCR approach. For each selected gene the corresponding bovine sequence was obtained and a gene specific real-time assay was optimised and validated. The amplification was shown to be highly specific, linear and efficient. High reproducibility (<1%) and low-test variability (<2.5%) were also been achieved. Messenger RNA levels were quantified in prostate samples, non-parametric analysis of variance showed significant up-regulation of three genes (MAF, ESR1 and AR) and significant down-regulation of four genes (HMGCS1, HPGD, DBI, and LIM) in treated samples when compared with untreated controls. To assess the possibility of identifying hormone-treated animals by molecular means we performed a discriminant analysis that was effective in classifying treated and non-treated samples with an accuracy of 93%. Our results indicate that identification of treatment with steroid hormones in veal calves by means of gene expression analysis is a feasible approach and could be improved increasing both the number of genes and the number of controls analysed.

Studies of plasma membrane fatty acid-binding protein and other lipid-binding proteins in human skeletal muscle

The first putative fatty acid transporter identified was plasma membrane fatty acid-binding protein (FABPpm). Later it was demonstrated that this protein is identical to the mitochondrial isoform of the enzyme aspartate aminotransferase. In recent years data from several cell types have emerged, indicating that FABPpm plays a role in the transport of long-chain saturated and unsaturated fatty acids. In the limited number of studies in human skeletal muscle it has been demonstrated that dietary composition and exercise training can influence the content of FABPpm. Ingestion of a fat-rich diet induces an increase in FABPpm protein content in human skeletal muscle in contrast to the decrease seen during consumption of a carbohydrate-rich diet. A similar effect of a fat-rich diet is also observed for cytosolic fatty acid-binding protein and fatty acid translocase/CD36 protein expression. Exercise training up regulates FABPpm protein content in skeletal muscle, but only in male subjects; no significant differences were observed in muscle FABPpm content in a cross-sectional study of female volunteers of varying training status, even though muscle FABPpm content did not depend on gender in the untrained state. A higher utilization of plasma long-chain fatty acids during exercise in males compared with females could explain the gender-dependent influence of exercise training on FABPpm. The mechanisms involved in the regulation of the function and expression of FABPpm protein remain to be clarified.

Modular kinetic analysis of the adenine nucleotide translocator-mediated effects of palmitoyl-CoA on the oxidative phosphorylation in isolated rat liver mitochondria

To test whether long-chain fatty acyl-CoA esters link obesity with type 2 diabetes through inhibition of the mitochondrial adenine nucleotide translocator, we applied a system-biology approach, dual modular kinetic analysis, with mitochondrial membrane potential (Deltapsi) and the fraction of matrix ATP as intermediates. We found that 5 mumol/l palmitoyl-CoA inhibited adenine nucleotide translocator, without direct effect on other components of oxidative phosphorylation. Indirect effects depended on how oxidative phosphorylation was regulated. When the electron donor and phosphate acceptor were in excess, and the mitochondrial "work" flux was allowed to vary, palmitoyl-CoA decreased phosphorylation flux by 38% and the fraction of ATP in the medium by 39%. Deltapsi increased by 15 mV, and the fraction of matrix ATP increased by 46%. Palmitoyl-CoA had a stronger effect when the flux through the mitochondrial electron transfer chain was maintained constant: Deltapsi increased by 27 mV, and the fraction of matrix ATP increased 2.6 times. When oxidative phosphorylation flux was kept constant by adjusting the rate using hexokinase, Deltapsi and the fraction of ATP were not affected. Palmitoyl-CoA increased the extramitochondrial AMP concentration significantly. The effects of palmitoyl-CoA in our model system support the proposed mechanism linking obesity and type 2 diabetes through an effect on adenine nucleotide translocator.

Isolation and characterization of a humoral factor that stimulates transcription of the acyl-CoA-binding protein in the pheromone gland of the silkmoth, Bombyx mori

Acyl-CoA binding protein (ACBP) is a highly conserved 10-kDa intracellular lipid-binding protein that binds straight-chain (C14-C22) acyl-CoA esters with high affinity and is expressed in a wide variety of species ranging from yeast to mammals. Functionally, ACBP can act as an acyl-CoA carrier or as an acyl-CoA pool maker within the cell. Much work on the biochemical properties regarding the ACBP has been performed using various vertebrate and plant tissues, as well as different types of cells in culture, the regulatory mechanisms underlying ACBP gene expression have remained poorly understood. By exploiting the unique sex pheromone production system in the moth pheromone gland (PG), we report that transcription of a specific ACBP termed pheromone gland ACBP is triggered by a hemolymph-based humoral factor. Following purification and structure elucidation by means of high resolution electrospray ionization mass spectrometry and NMR analyses, in conjunction with stereochemical analyses using acid hydrolysates, the humoral factor was identified to be beta-D-glucosyl-O-L-tyrosine. Examination of the hemolymph titers during development revealed that the amount of beta-D-glucosyl-O-L-tyrosine dramatically rose prior to eclosion and reached a maximum of 5 mg/ml (about 1 mg/pupa) on the day preceding eclosion, which was consistent with the effective dose of beta-D-glucosyl-O-L-tyrosine in stimulating pheromone gland ACBP transcription in vivo. Furthermore, in vitro assays using trimmed PG indicated that beta-D-glucosyl-O-L-tyrosine acts directly on the PG. These results provide the first evidence that transcription of some ACBPs can be triggered by specific humoral factors.

Acyl-coenzyme A organizes laterally in membranes and is recognized specifically by acyl-coenzyme A binding protein

Long chain acyl-coenzyme A (acyl-CoA) is a biochemically important amphiphilic molecule that is known to partition strongly into membranes by insertion of the acyl chain. At present, microscopically resolved evidence is lacking on how acyl-CoA influences and organizes laterally in membranes. By atomic force microscopy (AFM) imaging of membranes exposed to acyl-CoA in microM concentrations, it is shown that aggregate formation takes place within the membrane upon long-time exposure. It is known that acyl-CoA is bound by acyl-CoA binding protein (ACBP) with high affinity and specificity and that ACBP may bind and desorb membrane-bound acyl-CoA via a partly unknown mechanism. Following incubation with acyl-CoA, it is shown that ACBP is able to reverse the formation of acyl-CoA aggregates and to associate peripherally with acyl-CoA on the membrane surface. Our microscopic results point to the role of ACBP as an intermembrane transporter of acyl-CoA and demonstrate the ability of AFM to reveal the remodelling of membranes by surfactants and proteins.

Catabolism of hydroxyacids and biotechnological production of lactones by Yarrowia lipolytica

The gamma- and delta-lactones of less than 12 carbons constitute a group of compounds of great interest to the flavour industry. It is possible to produce some of these lactones through biotechnology. For instance, gamma-decalactone can be obtained by biotransformation of methyl ricinoleate. Among the organisms used for this bioproduction, Yarrowia lipolytica is a yeast of choice. It is well adapted to growth on hydrophobic substrates, thanks to its efficient and numerous lipases, cytochrome P450, acyl-CoA oxidases and its ability to produce biosurfactants. Furthermore, genetic tools have been developed for its study. This review deals with the production of lactones by Y. lipolytica with special emphasis on the biotransformation of methyl ricinoleate to gamma-decalactone. When appropriate, information from the lipid metabolism of other yeast species is presented.

Control of mitochondrial beta-oxidation flux

The control of mitochondrial beta-oxidation, including the delivery of acyl moieties from the plasma membrane to the mitochondrion, is reviewed. Control of beta-oxidation flux appears to be largely at the level of entry of acyl groups to mitochondria, but is also dependent on substrate supply. CPTI has much of the control of hepatic beta-oxidation flux, and probably exerts high control in intact muscle because of the high concentration of malonyl-CoA in vivo. beta-Oxidation flux can also be controlled by the redox state of NAD/NADH and ETF/ETFH(2). Control by [acetyl-CoA]/[CoASH] may also be significant, but it is probably via export of acyl groups by carnitine acylcarnitine translocase and CPT II rather than via accumulation of 3-ketoacyl-CoA esters. The sharing of control between CPTI and other enzymes allows for flexible regulation of metabolism and the ability to rapidly adapt beta-oxidation flux to differing requirements in different tissues.

Overexpression of acyl-coA binding protein and its effects on the flux of free fatty acids in McA-RH 7777 cells

Overexpression of acyl-CoA binding protein (ACBP) was induced in a rat hepatoma cell line (McA-RH 7777) by stable integration of rat ACBP cDNA. The transfected cells (ACBP-27) had 3.5-fold higher concentrations of ACBP than control cells (14 vs. 4 ng/microg DNA). Both ACBP-27 and control cells were cultured in the presence of various concentrations of radiolabeled palmitic acid; and the effects of ACBP on lipogenesis and beta-oxidation were studied. Incubation of the cells with 100 microM palmitic acid resulted in 42% greater incorporation of the fatty acid in ACBP-27 cells as compared to that in the control cells. This increased incorporation of the fatty acid was observed predominantly in the triglyceride fraction. Higher concentrations of palmitic acid (200 to 400 microM) were associated with a significant decrease in the production of 14CO2 in the ACBP-27 cell line than in the control cells, while lower concentrations had no effect. Our data suggest a role for ACBP in the partitioning of fatty acids between esterification reactions leading to the formation of neutral lipids and beta-oxidation. ACBP may play a regulatory role by influencing this important branch point in intermediary lipid metabolism.

Characterization of acyl-CoA-binding protein (ACBP) in the pheromone gland of the silkworm, Bombyx mori

Various fatty acyl-CoAs are involved as intermediates or precursors of sex pheromone components in the biosynthetic pathway of the pheromones in many lepidopteran insects. We have purified a 10-kDa protein from the cytosolic fraction of Bombyx mori pheromone glands by using affinity chromatography with a palmitoyl-CoA-agarose column and reversed-phase HPLC. Amino acid sequence analysis of the fragment peptides obtained from the purified protein, and a homology search, revealed that this protein was a member of acyl-CoA-binding proteins (ACBPs). MALDI-TOF mass spectral analysis of the purified protein and cloning of the gene from a pheromone gland cDNA library confirmed B. mori ACBP to be a 90 amino acid protein with 78.9% identity to that of Manduca sexta ACBP. The secondary structure of the recombinant B. mori ACBP was determined by NMR spectroscopy. Northern blot analysis demonstrated that B. mori ACBP was predominantly expressed in the pheromone gland and the corresponding transcript was expressed from the day before adult eclosion. Present results suggest that ACBP plays a significant role in the production of sex pheromones regulated by the neurohormone, pheromone biosynthesis activating neuropeptide (PBAN).

Acyl-CoA-binding protein in the armadillo Harderian gland: its primary structure and possible role in lipid secretion

Similar to those of other species, the Harderian glands of armadillo produce an abundant lipid secretion, most of which is composed of 1-alkyl-2,3-diacylglycerol. Biosynthesis of this component is apparently performed with the participation of one cytosolic pool of acyl-CoA and another of free fatty acids. The acyl-CoA-binding protein (ACBP) is present at a concentration at least 7-fold that of the heart-type fatty acid-binding protein (H-FABP), though lower than that in other armadillo organs such as liver and brain. The ACBP complete amino acid sequence was determined by Edman degradation of peptides generated by cleavage of the protein with cyanogen bromide, endopeptidase Glu-C, and trypsin. ACBP consists of 86 residues and has a calculated molecular mass of 9783 Da, taking into account that an acetyl group is blocking the N-terminus. Identity percentages between armadillo Harderian gland ACBP and other known ACBPs show that the protein belongs to the liver-specific ACBP isoform (L-ACBP). The fact that the ACBP concentration is higher than that of FABP suggests that the Harderian gland is able to store acyl-CoA amounts in ACBP larger than those of fatty acids in H-FABP for 1-alkyl-2,3-diacylglycerol synthesis.

Microsomal fatty acyl-CoA transacylation and hydrolysis: fatty acyl-CoA species dependent modulation by liver fatty acyl-CoA binding proteins

arachidonoyl-CoA. In summary, the data established for the first time a role for both L-FABP and ACBP in microsomal phosphatidic acid biosynthesis. By preferentially stimulating microsomal transacylation of unsaturated long chain fatty acyl-CoAs while concomitantly exerting their differential protection from microsomal acyl-CoA hydrolase, L-FABP and ACBP can uniquely function in modulating the pattern of fatty acids esterified to phosphatidic acid, the de novo precursor of phospholipids and triacylglycerols. This may explain in part the simultaneous presence of these proteins in cell types involved in fatty acid absorption and lipoprotein secretion.

Role of acylCoA binding protein in acylCoA transport, metabolism and cell signaling

Long chain acylCoA esters (LCAs) act both as substrates and intermediates in intermediary metabolism and as regulators in various intracellular functions. AcylCoA binding protein (ACBP) binds LCAs with high affinity and is believed to play an important role in intracellular acylCoA transport and pool formation and therefore also for the function of LCAs as metabolites and regulators of cellular functions [1]. The major factors controlling the free concentration of cytosol long chain acylCoA ester (LCA) include ACBP [2], sterol carrier protein 2 (SCP2) [3] and fatty acid binding protein (FABP) [4]. Additional factors affecting the concentration of free LCA include feed back inhibition of the acylCoA synthetase [5], binding to acylCoA receptors (LCA-regulated molecules and enzymes), binding to membranes and the activity of acylCoA hydrolases [6].

Ontogeny of diazepam binding inhibitor/acyl-CoA binding protein mRNA and peripheral benzodiazepine receptor mRNA expression in the rat

The Diazepam Binding Inhibitor/Acyl-CoA Binding Protein (DBI/ACBP) has been implicated in different functions, as acyl-CoA transporter and as an endogenous ligand at the GABA(A) receptor and the peripheral benzodiazepine receptor (PBR). The latter is thought to be involved in control of steroidogenesis. We studied the ontogeny of DBI/ACBP and PBR mRNA expression in embryos and offspring of time-pregnant Long Evans rats by in-situ hybridization with 33P-endlabelled oligonucleotides. Both mRNAs were present in embryo and placenta at gestational day (G)11, the earliest stage studied. DBI/ACBP mRNA was strongly expressed from embryonic through mid-foetal stages in central nervous system (maximum in neuroepithelium), cranial and sympathetic ganglia, anterior pituitary, adrenal cortex, thyroid, thymus, liver and (late foetal) brown adipose tissue, moderately in testis, heart, lung and kidney. In brain, a late foetal decrease of DBI/ACBP mRNA was followed by an increase at postnatal day 6. Peripheral benzodiazepine receptor mRNA expression started very low and increased to moderate levels in adrenal cortex and medulla, testis, thyroid, brown adipose tissue, liver, heart, lung, salivary gland at mid- to late-foetal stages. Data suggest a significant role of DBI/ACBP at early developmental stages. Both proteins may be involved in the control of foetal steroidogenesis. However, differences in developmental patterns indicate that additional functions may be equally important during ontogeny, such as the involvement in lipid metabolism in the case of DBI/ACBP.

Identification of diazepam-binding Inhibitor/Acyl-CoA-binding protein as a sterol regulatory element-binding protein-responsive gene

Diazepam-binding inhibitor/acyl-CoA-binding protein (DBI/ACBP), a highly conserved 10-kDa polypeptide, has been implicated in various physiological processes including gamma-aminobutyric acid type A receptor binding, acyl-CoA binding and transport, steroidogenesis, and peptide hormone release. Both in LNCaP prostate cancer cells and 3T3-L1 preadipocytes, the expression of DBI/ACBP is stimulated under conditions that promote lipogenesis (treatment with androgens and insulin, respectively) and that involve the activation of sterol regulatory element-binding proteins (SREBPs). Accordingly, we investigated whether DBI/ACBP expression is under the direct control of SREBPs. Analysis of the human and rat DBI/ACBP promoter revealed the presence of a conserved sterol regulatory element (SRE)-like sequence. Gel shift analysis confirmed that this sequence is able to bind SREBPs. In support of the functionality of SREBP binding, coexpression of SREBP-1a with a DBI/ACBP promoter-reporter gene resulted in a 50-fold increase in transcriptional activity in LNCaP cells. Disruption of the SRE decreased basal expression and abolished SREBP-1a-induced transcriptional activation. In agreement with the requirement of a co-regulator for SREBP function, transcriptional activation by SREBP-1a overexpression was severely diminished when a neighboring NF-Y site was mutated. Cholesterol depletion or androgen treatment, conditions that activate SREBP function in LNCaP cells, led to an increase in DBI/ACBP mRNA expression and SRE-dependent transcriptional activation. These findings indicate that the promoter for DBI/ACBP contains a functional SRE that allows DBI/ACBP to be coregulated with other genes involved in lipid metabolism.

Antibacterial peptides are present in chromaffin cell secretory granules

1. Antibacterial activity has recently been associated with the soluble matrix of bovine chromaffin granules. Furthermore, this activity was detected in the contents secreted from cultured chromaffin cells following stimulation. 2. The agents responsible for the inhibition of Gram+ and Gram- bacteria growth are granular peptides acting in the micromolar range or below. In secretory granules, these peptides are generated from cleavage of chromogranins and proenkephalin A and are released together with catecholamines into the circulation. 3. Secretolytin and enkelytin are the best characterized; these two peptides share sequence homology and similar antibacterial activity with insect cecropins and intestinal diazepam-binding inhibitor. For some of the peptides derived from chromogranin A, posttranslational modifications were essential since antibacterial activity was expressed only when peptides were phosphorylated and/or glycosylated. 4. The significance of this activity is not yet understood. It may be reminiscent of some primitive defense mechanism or may serve as a first barrier to bacteria infection during stress, as these peptides are secreted along with catecholamines.