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

Dual targeting of the androgen receptor and PI3K/AKT/mTOR pathways in prostate cancer models improves antitumor efficacy and promotes cell apoptosis

Prostate cancer is a frequent malignancy in older men and has a very high 5-year survival rate if diagnosed early. The prognosis is much less promising if the tumor has already spread outside the prostate gland. Targeted treatments mainly aim at blocking androgen receptor (AR) signaling and initially show good efficacy. However, tumor progression due to AR-dependent and AR-independent mechanisms is often observed after some time, and novel treatment strategies are urgently needed. Dysregulation of the PI3K/AKT/mTOR pathway in advanced prostate cancer and its implication in treatment resistance has been reported. We compared the impact of PI3K/AKT/mTOR pathway inhibitors with different selectivity profiles on in vitro cell proliferation and on caspase 3/7 activation as a marker for apoptosis induction, and observed the strongest effects in the androgen-sensitive prostate cancer cell lines VCaP and LNCaP. Combination treatment with the AR inhibitor darolutamide led to enhanced apoptosis in these cell lines, the effects being most pronounced upon cotreatment with the pan-PI3K inhibitor copanlisib. A subsequent transcriptomic analysis performed in VCaP cells revealed that combining darolutamide with copanlisib impacted gene expression much more than individual treatment. A comprehensive reversal of the androgen response and the mTORC1 transcriptional programs as well as a marked induction of DNA damage was observed. Next, an in vivo efficacy study was performed using the androgen-sensitive patient-derived prostate cancer (PDX) model LuCaP 35 and a superior efficacy was observed after the combined treatment with copanlisib and darolutamide. Importantly, immunohistochemistry analysis of these treated tumors showed increased apoptosis, as revealed by elevated levels of cleaved caspase 3 and Bcl-2-binding component 3 (BBC3). In conclusion, these data demonstrate that concurrent blockade of the PI3K/AKT/mTOR and AR pathways has superior antitumor efficacy and induces apoptosis in androgen-sensitive prostate cancer cell lines and PDX models.

Proteomic analysis identifies deregulated metabolic and oxidative-associated proteins in Italian intrahepatic cholangiocarcinoma patients

Background

Cholangiocarcinoma (CCA) is an aggressive disease with poor prognosis. A molecular classification based on mutational, methylation and transcriptomic features could allow identifying tailored therapies to improve CCA patient outcome. Proteomic remains partially unexplored; here, we analyzed the proteomic profile of five intrahepatic cholangiocarcinoma (ICC) derived from Italian patients undergone surgery and one normal bile duct cell line.

Methods

Proteome profile was investigated by using 2D electrophoresis followed by Mass Spectrometry (MS). To validate proteomic data, the expression of four overexpressed proteins (CAT, SOD, PRDX6, DBI/ACBP) was evaluated by immunohistochemistry in an independent cohort of formalin fixed, paraffin-embedded (FFPE) ICC tissues. We also compared proteomic data with those obtained by transcriptomic profile evaluated by microarray analysis of the same tissues.

Results

We identified 19 differentially expressed protein spots, which were further characterized by MS; 13 of them were up- and 6 were down-regulated in ICC. These proteins are mainly involved in redox processes (CAT, SODM, PRDX2, PRDX6), in metabolism (ACBP, ACY1, UCRI, FTCD, HCMS2), and cell structure and organization (TUB2, ACTB). CAT is overexpressed in 86% of patients, PRDX6 in 73%, SODM in 100%, and DBI/ACBP in 81% compared to normal adjacent tissues. A concordance of 50% between proteomic and transcriptomic data was observed.

Conclusions

This study pointed out that the impairment of the metabolic and antioxidant systems, with a subsequent accumulation of free radicals, might be a key step in CCA development and progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08576-z.

Protein identification from the parotoid macrogland secretion of Duttaphrynus melanostictus

Background:

Bufonid parotoid macrogland secretion contains several low molecular mass molecules, such as alkaloids and steroids. Nevertheless, its protein content is poorly understood. Herein, we applied a sample preparation methodology that allows the analysis of viscous matrices in order to examine its proteins.

Methods:

Duttaphrynus melanostictus parotoid macrogland secretion was submitted to ion-exchange batch sample preparation, yielding two fractions: salt-displaced fraction and acid-displaced fraction. Each sample was then fractionated by anionic-exchange chromatography, followed by in-solution proteomic analysis.

Results:

Forty-two proteins could be identified, such as acyl-CoA-binding protein, alcohol dehydrogenase, calmodulin, galectin and histone. Moreover, de novo analyses yielded 153 peptides, whereas BLAST analyses corroborated some of the proteomic-identified proteins. Furthermore, the de novo peptide analyses indicate the presence of proteins related to apoptosis, cellular structure, catalysis and transport processes.

Conclusions:

Proper sample preparation allowed the proteomic and de novo identification of different proteins in the D. melanostictus parotoid macrogland secretion. These results may increase the knowledge about the universe of molecules that compose amphibian skin secretion, as well as to understand their biological/physiological role in the granular gland.

Quantitative Analysis of Seven New Prostate Cancer Biomarkers and the Potential Future of the 'Biomarker Laboratory'

Prostate cancer is the third highest cause of male mortality in the developed world, with the burden of the disease increasing dramatically with demographic change. There are significant limitations to the current diagnostic regimens and no established effective screening modality. To this end, research has discovered hundreds of potential ‘biomarkers’ that may one day be of use in screening, diagnosis or prognostication. However, the barriers to bringing biomarkers to clinical evaluation and eventually into clinical usage have yet to be realised. This is an operational challenge that requires some new thinking and development of paradigms to increase the efficiency of the laboratory process and add ‘value’ to the clinician. Value comes in various forms, whether it be a process that is seamlessly integrated into the hospital laboratory environment or one that can provide additional ‘information’ for the clinical pathologist in terms of risk profiling. We describe, herein, an efficient and tissue-conserving pipeline that uses Tissue Microarrays in a semi-automated process that could, one day, be integrated into the hospital laboratory domain, using seven putative prostate cancer biomarkers for illustration.

GABA withdrawal syndrome: GABAA receptor, synapse, neurobiological implications and analogies with other abstinences

The sudden interruption of the increase of the concentration of the gamma-aminobutyric acid (GABA), determines an increase in neuronal activity. GABA withdrawal (GW) is a heuristic analogy, with withdrawal symptoms developed by other GABA receptor-agonists such as alcohol, benzodiazepines, and neurosteroids. GW comprises a model of neuronal excitability validated by electroencephalogram (EEG) in which high-frequency and high-amplitude spike-wave complexes appear. In brain slices, GW was identified by increased firing synchronization of pyramidal neurons and by changes in the active properties of the neuronal membrane. GW induces pre- and postsynaptic changes: a decrease in GABA synthesis/release, and the decrease in the expression and composition of GABAA receptors associated with increased calcium entry into the cell. GW is an excellent bioassay for studying partial epilepsy, epilepsy refractory to drug treatment, and a model to reverse or prevent the generation of abstinences from different drugs.

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.

High fat diet feeding exaggerates perfluorooctanoic acid-induced liver injury in mice via modulating multiple metabolic pathways

High fat diet (HFD) is closely linked to a variety of health issues including fatty liver. Exposure to perfluorooctanoic acid (PFOA), a synthetic perfluorinated carboxylic acid, also causes liver injury. The present study investigated the possible interactions between high fat diet and PFOA in induction of liver injury. Mice were pair-fed a high-fat diet (HFD) or low fat control with or without PFOA administration at 5 mg/kg/day for 3 weeks. Exposure to PFOA alone caused elevated plasma alanine aminotransferase (ALT) and alkaline phosphatase (ALP) levels and increased liver weight along with reduced body weight and adipose tissue mass. HFD alone did not cause liver damage, but exaggerated PFOA-induced hepatotoxicity as indicated by higher plasma ALT and AST levels, and more severe pathological changes including hepatocyte hypertrophy, lipid droplet accumulation and necrosis as well as inflammatory cell infiltration. These additive effects of HFD on PFOA-induced hepatotoxicity correlated with metabolic disturbance in liver and blood as well as up-regulation of hepatic proinflammatory cytokine genes. Metabolomic analysis demonstrated that both serum and hepatic metabolite profiles of PFOA, HFD, or HFD-PFOA group were clearly differentiated from that of controls. PFOA affected more hepatic metabolites than HFD, but HFD showed positive interaction with PFOA on fatty acid metabolites including long chain fatty acids and acylcarnitines. Taken together, dietary high fat potentiates PFOA-induced hepatic lipid accumulation, inflammation and necrotic cell death by disturbing hepatic metabolism and inducing inflammation. This study demonstrated, for the first time, that HFD increases the risk of PFOA in induction of hepatotoxicity.

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.

Specific regulation of low-abundance transcript variants encoding human Acyl-CoA binding protein (ACBP) isoforms

Despite intensive efforts on annotation of eukaryotic transcriptoms, little is known about the regulation of low-abundance transcripts. To address this question, we analysed the regulation of novel low-abundance transcript variants of human acyl-CoA binding protein (ACBP), an important multifunctional housekeeping protein, which we have identified by screening of human expressed sequence tags in combination with ab initio gene prediction. By using RT-, real-time RT- and rapid amplification of cDNA ends-PCR in five human tissues, we find these transcripts, which are generated by a consequent use of alternative promoters and alternate first or first two exons, to be authentic ones. They show a tissue-specific distribution and intrinsic responsiveness to glucose and insulin. Promoter analyses of the corresponding transcripts revealed a differential regulation mediated by sterol regulatory element-binding protein-2, hepatocyte nuclear factor-4α and nuclear factor κB (NF-κB), central transcription factors of fat and glucose metabolism and inflammation. Subcellular localization studies of deduced isoforms in liver HepG2 cells showed that they are distributed in different compartments. By demonstrating that ACBP is a target of NF-κB, our findings link fatty acid metabolism with inflammation. Furthermore, our findings show that low-abundance transcripts are regulated in a similar mode than their high-abundance counterparts.

Serotonin regulates an acyl-CoA-binding protein (ACBP) gene expression in the midgut of Rhodnius prolixus

Acyl-CoA esters have many intracellular functions, acting as energy source, substrate for metabolic processes and taking part in cell signaling. The acyl-CoA-binding protein (ACBP), a highly conserved 10 kDa intracellular protein, binds long- and medium-chain acyl-CoA esters with very high affinity, directing them to specific metabolic routes and protecting them from hydrolysis. An ACBP gene sequence was identified in the genome of Rhodnius prolixus. This ACBP gene (RpACBP-1) was expressed in all analyzed tissues and quantitative PCR showed that expression was highest in posterior midgut. In this tissue, ACBP gene expression increased in the first day after blood meal ( approximately 10-fold) and then decreased to unfed levels in the seventh day after meal. Injection of serotonin (5-hydroxytryptamine; 5-HT), a neuroamine released in the hemolymph after the start of feeding, increased the expression of this gene in the midgut of unfed females, reaching levels similar to those observed in fed insects. This effect of injected 5-HT was inhibited by spiperone, an antagonist of 5-HT mammalian receptors, that was also able to block the physiological increase in RpACBP-1 expression observed after feeding. Injection of cholera toxin or dibutyryl-cAMP also resulted in the stimulation of this gene expression. These data reveal a transcriptional regulatory mechanism in R. prolixus, that is triggered by 5-HT. In this way, a novel role for 5-HT is proposed, as a regulator of ACBP gene expression and, consequently, taking part in the control of lipid metabolism.

Mouse Elovl-6 promoter is an SREBP target

Elovl-6, a long fatty acid elongase, contributes to de novo synthesis of fatty acids and regulates hepatic insulin sensitivity. Hepatic regulation of Elovl-6 gene expression in various nutritional conditions suggested that, like other lipogenic enzyme genes, Elovl-6 is a target of SREBP-1, a transcription factor governing fatty acid synthesis. Supportively, adenoviral RNAi knockdown of SREBP-1 in mouse liver suppressed Elovl-6 mRNA and fatty acid synthase levels. Therefore, we analyzed mouse Elovl-6 gene promoter to determine its role as an SREBP-1 target. Luciferase reporter assays of 1.4-kb 5' flanking region of mouse Elovl-6 gene in HepG2 cells demonstrated that nuclear SREBPs activated the Elovl-6 promoter, highlighting two SREBP binding sites: proximal SRE-1 and distal SRE-2. EMSA indicated that SRE-1 had higher affinity than SRE-2 for SREBP. ChIP assays confirmed in vivo binding of hepatic nuclear SREBP-1c protein. These data demonstrated that Elovl-6 is regulated directly and primarily by SREBP-1c.

Structural and functional characterization of a new recombinant histidine-tagged acyl coenzyme A binding protein (ACBP) from mouse

Acyl coenzyme A binding protein (ACBP) has been proposed to transport fatty acyl CoAs intracellularly, facilitating their metabolism. In this study, a new mouse recombinant ACBP was produced by insertion of a histidine (his) tag at the C-terminus to allow efficient purification by Ni-affinity chromatography. The his-tag was inserted at the C-terminus since ACBP is a small molecular size (10 kDa) protein whose structure and activity are sensitive to amino acid substitutions in the N-terminus. The his-tag had no or little effect on ACBP structure or ligand binding affinity and specificity. His-ACBP bound the naturally occurring fluorescent cis-parinaroyl-CoA with very high affinity (K(d)=2.15 nM), but exhibited no affinity for non-esterified cis-parinaric acid. To determine if the presence of the C-terminal his-tag altered ACBP interactions with other proteins, direct binding to hepatocyte nuclear factor-4alpha (HNF-4alpha), a nuclear receptor regulating transcription of genes involved in lipid metabolism, was examined. His-ACBP and HNF-4alpha were labeled with Cy5 and Cy3, respectively, and direct interaction was determined by a novel fluorescence resonance energy transfer (FRET) binding assay. FRET analysis showed that his-ACBP directly interacted with HNF-4alpha (intermolecular distance of 73 A) at high affinity (K(d)=64-111 nM) similar to native ACBP. The his-tag also had no effect on ACBPs ability to interact with and stimulate microsomal enzymes utilizing or forming fatty acyl CoA. Thus, C-terminal his-tagged-ACBP maintained very similar structural and functional features of the untagged native protein and can be used in further in vitro experiments that require pure recombinant ACBP.

Association of acyl-CoA-binding protein (ACBP) single nucleotide polymorphisms and type 2 diabetes in two German study populations

The human acyl-CoA-binding protein (ACBP) is a potential candidate gene of type 2 diabetes (T2D), since it plays a central role in determining the intracellular concentration of activated fatty acids which contribute to insulin resistance. The aim of our study was to evaluate whether single nucleotide polymorphisms (SNPs) of the ACBP gene are associated with risk of T2D. Genotyping of eight SNPs (rs2084202, rs3731607, rs8192501, rs8192504, rs2244135, rs2276596, rs8192506, rs2289948) was performed in 192 incident T2D subjects and 384 matched controls of the European Prospective Investigation into Cancer and Nutrition-Potsdam cohort. A putative promoter SNP (rs2084202) of splice variant ACBP 1c showed decreased risk of T2D (odds ratio (OR) 0.63, 95% CI 0.41-0.96). The haplotype, that contained the mutant base of rs2084202 showed similar evidence for the association with disease risk as single SNP rs2084202. In a second population-based study, Cooperative Health Research in the Augsburg Region of 226 individuals with T2D and 863 control subjects a borderline significant association between rs2084202 and T2D (OR 0.72, 95% CI 0.51-1.01) was observed. In summary, we obtained evidence from two Caucasian study populations that the minor allele of ACBP rs2084202 might be associated with reduced risk of T2D.

Expression profiling of heat stress effects on mice fed ergot alkaloids

Fescue toxicosis affects wild and domestic animals consuming ergot alkaloids contained in tall fescue forage infected with the endophytic fungus, Neotyphodium coenophialum. When animals are consuming infected fescue (E+) forage during periods of elevated ambient temperatures (summer), a range of phenotypic disorders collectively called summer slump is observed. It is characterized by hyperthermia, with an accompanying decrease in feed intake, growth, milk yield, and reproductive fitness. Laboratory mice also exhibit symptoms of fescue toxicosis at thermoneutral (TN) temperature, as indicated by reduced growth rate and reproductive fitness. Our goal was to characterize the differences in gene expression in liver of mice exposed to summer-type heat stress (HS) and E+ when compared to mice fed E+ at TN temperature. Mice were fed E+ diet under HS (34 +/- 1 degrees C; n = 13; E+HS) or TN conditions (24 +/- 1 degrees C; n = 14; E+TN) for a period of 2 weeks between 47 and 60 days of age. Genes differentially expressed between E+HS versus E+TN were identified using DNA microarrays. Forty-one genes were differentially expressed between treatment groups. Expressions of eight genes were measured using quantitative real-time PCR. Genes coding for phase I detoxification enzymes were upregulated in E+HS mouse liver. This detoxification pathway is known to produce reactive oxidative species. We observed an upregulation of genes involved in the protection against reactive oxidative species. Key genes involved in de novo lipogenesis and lipid transport were also upregulated. Finally, genes involved in DNA damage control and unfolded protein responses were downregulated.

Role of androgens and glucocorticoids in the regulation of diazepam-binding inhibitor mRNA levels in male mouse hypothalamus

In peripheral organs, gonadal and adrenal steroids regulate diazepam-binding inhibitor (DBI) mRNA expression. In order to further investigate the involvement of peripheral steroid hormones in the modulation of brain DBI mRNA expression, we studied by semiquantitative in situ hybridization the effect of adrenalectomy (ADX) and castration (CX) and short-term replacement therapy on DBI mRNA levels in the male mouse hypothalamus. Cells expressing DBI mRNA were mostly observed in the arcuate nucleus, the median eminence and the ependyma bordering the third ventricle. In the median eminence and the ependyma bordering the third ventricule, the DBI gene expression was decreased in ADX rats and a single injection of corticosterone to ADX rats induced a significant increase in DBI gene expression at 3 and 12 h time intervals without completely restoring the basal DBI mRNA expression observed in intact mice. In the arcuate nucleus, ADX and corticosterone administration did not modify DBI mRNA expression. CX down-regulated DBI gene expression in the ependyma bordering the third ventricle. The administration of dihydrotestosterone (3-24 h) completely reversed the inhibitory effect of CX. In the median eminence and arcuate nucleus, neither CX or dihydrotestosterone administration modified DBI mRNA levels. These results suggest that the effects of glucocorticoids on the hypothalamo-pituitary-adrenocortical axis and androgens on the hypothalamo-pituitary-gonadal axis are mediated by DBI.

Androgen activation of the sterol regulatory element-binding protein pathway: Current insights

The cellular effects of androgens are mediated by a cognate receptor, the androgen receptor. Typically, the androgen receptor is viewed to exert its activity by binding to androgen response elements located in or near the promoter region of target genes, thereby directly affecting the expression of these genes. However, increasing evidence indicates that androgens may also indirectly influence the expression of genes that do not contain androgen response elements by modulating the activity of secondary transcription factors, mediating the expression of growth factors acting in a paracrine or autocrine fashion, or by inducing changes in the production of other hormones. These indirect effects of androgens can induce cascade-like actions and may play an important role in more complex processes involving coordinated responses of genes, cells, and organs. Previously, our laboratory has identified and characterized a novel indirect mechanism of androgen action involving proteolytical activation of the key lipogenic transcription factor sterol regulatory element-binding protein (SREBP), resulting in the coordinate up-regulation of entire cellular lipogenic pathways. Interestingly, activation of SREBPs by androgens occurs not only under normal physiological conditions but has also been observed in a growing number of pathologies, and more in particular in the setting of steroid-regulated cancers, where increased lipogenesis has been shown to have remarkable diagnostic and prognostic potential and is considered a prime target for novel therapeutic approaches. This review aims to analyze current insights into the molecular mechanism(s) underlying androgen activation of the SREBP pathway and to ascertain the extent to which this phenomenon can be generalized to androgen-responsive cell systems.

Lipid synthetic transcription factor SREBP-1a activates p21WAF1/CIP1, a universal cyclin-dependent kinase inhibitor

Sterol regulatory element-binding proteins (SREBPs) are membrane-bound transcription factors that regulate lipid synthetic genes. In contrast to SREBP-2, which regulates cellular cholesterol level in normal cells, SREBP-1a is highly expressed in actively growing cells and activates entire programs of genes involved in lipid synthesis such as cholesterol, fatty acids, triglycerides, and phospholipids. Previously, the physiological relevance of this potent activity of SREBP-1a has been thought to regulate the supply of membrane lipids in response to cell growth. Here we show that nuclear SREBP-1a and SREBP-2 bind directly to a novel SREBP binding site in the promoter of the p21(WAF1/CIP1) gene, the major cyclin-dependent kinase inhibitor, and strongly activate its promoter activity. Only the SREBP-1a isoform consistently causes induction of p21 at both the mRNA and protein levels. Colony formation assays and polyploidy of livers from transgenic mice suggest that activation of p21 by SREBP-1a could inhibit cell growth. Activation of endogenous SREBPs in lipid deprivation conditions was associated with induction of p21 mRNA and protein. Expression of p21 was reduced in SREBP-1 null mice. These data suggest a physiological role of SREBP-1a in p21 regulation. Identification of p21 as a new SREBP target might implicate a new paradigm in the link between lipid synthesis and cell growth.

Identification of new acyl-CoA binding protein transcripts in human and mouse

The ubiquitously expressed acyl-CoA binding protein (ACBP) is involved in lipid metabolism and is regulated by hormones and feeding status via transcription factors such as sterol regulatory element-binding protein 1 and peroxisome proliferator-activated receptor-gamma (PPARgamma). In humans, two transcripts encoding proteins of 86 and 104 amino acids are known, whereas in mouse only one protein of 86 amino acids is described. We identified new transcripts in human and mouse tissues, that had been generated by alternative first exon usage. Quantitative RT-PCR analyses showed a high expression of the new human transcript, ACBP-1c, in adipose tissue. By promoter reporter gene assays, specific regulation of this transcript by PPARgamma2 was revealed, implicating the usage of an alternative promoter that contains a PPARgamma responsive element. Subcellular localizations of the known human proteins and the new variant showed an occurrence in cytoplasma and nucleus. Reported studies concerning ACBP gene regulation should be re-evaluated with respect to a new ACBP gene model. Given the fact that the new variant is highly expressed in adipose tissue and a PPARgamma target, it might be relevant for diseases like diabetes and obesity.

Somatostatin down-regulates the expression and release of endozepines from cultured rat astrocytes via distinct receptor subtypes

Endozepines, a family of regulatory peptides related to diazepam-binding inhibitor (DBI), are synthesized and released by astroglial cells. Because rat astrocytes express various subtypes of somatostatin receptors (sst), we have investigated the effect of somatostatin on DBI mRNA level and endozepine secretion in rat astrocytes in secondary culture. Somatostatin reduced in a concentration-dependent manner the level of DBI mRNA in cultured astrocytes. This inhibitory effect was mimicked by the selective sst4 receptor agonist L803-087 but not by the selective sst1, sst2 and sst3 receptor agonists L779-591, L779-976 and L797-778, respectively. Somatostatin was unable to further reduce DBI mRNA level in the presence of the MEK inhibitor U0126. Somatostatin and the sst1, sst2 and sst4 receptor agonists induced a concentration-dependent inhibition of endozepine release. Somatostatin and the sst1, sst2 and sst4 receptor agonists also inhibited cAMP formation dose-dependently. In addition, somatostatin reduced forskolin-induced endozepine release. H89 mimicked the inhibitory effect of somatostatin on endozepine secretion. In contrast the PLC inhibitor U73122, the PKC activator PMA and the PKC inhibitor calphostin C had no effect on somatostatin-induced inhibition of endozepine release. The present data demonstrate that somatostatin reduces DBI mRNA level mainly through activation of sst4 receptors negatively coupled to the MAPK pathway, and inhibits endozepine release through activation of sst1, sst2 and sst4 receptors negatively coupled to the adenylyl cyclase/PKA pathway.

Expression of genes encoding proteins involved in ecdysteroidogenesis in the female mosquito, Aedes aegypti

A blood meal induces the ovaries of female Aedes aegypti mosquitoes to produce ecdysteroid hormones that regulate many processes required for egg maturation. Various proteins involved in the intracellular transport and biosynthesis of ecdysteroid precursors have been identified by analysis of Drosophila melanogaster mutants and by biochemical and molecular techniques in other insects. To begin examining these processes in mosquito ovaries, complete cDNAs were cloned for putative orthologs of diazepam-binding inhibitor (DBI), StAR-related lipid transfer domain containing protein (Start1), aldo/keto reductase (A/KR), adrenodoxin reductase (AR), and the cytochrome P450 enzymes, CYP302a1 (22-hydroxylase), CYP315a1 (2-hydroxylase) and CYP314a1 (20-hydroxylase). As shown by RT-PCR, transcripts for all seven genes were present in ovaries and other tissues both before and following a blood meal. Expression of these genes likely supports the low level of ecdysteroids produced in vitro (7-10 pg /tissue/6 h) by tissues other than ovaries. Ovaries from females not blood fed and up to 6 h post blood meal (PBM) also produced low amounts of ecdysteroids in vitro, but by 18 and 30 h PBM, ecdysteroid production was greatly increased (75-106 pg/ovary pair/6h) and thereafter (48 and 72 h PBM) returned to low levels. As determined by real-time PCR analysis, gene transcript abundance for AedaeCYP302 and AedaeCYP315a1 was significantly greater (9 and 12 fold, respectively) in ovaries during peak ecdysteroid production relative to that in ovaries from females not blood fed or 2 h PBM. AedaeStart1, AedaeA/KR and AedaeAR also had high transcript levels in ovaries during peak ecdysteroid production, and AedaeDBI transcripts had the greatest increase at 48 h PBM. In contrast, gene transcript abundance of AedaeCYP314a1 decreased PBM. This study shows for the first time that transcription of a few key genes for proteins involved in ecdysteroid biosynthesis is positively correlated with the rise in ecdysteroid production by ovaries of a female insect.

The Gene Encoding Acyl-CoA-binding Protein Is Subject to Metabolic Regulation by Both Sterol Regulatory Element-binding Protein and Peroxisome Proliferator-activated Receptor α in Hepatocytes

The acyl-CoA-binding protein (ACBP) is a 10-kDa intracellular lipid-binding protein that transports acylCoA esters. The protein is expressed in most cell types at low levels; however, expression is particularly high in cells with a high turnover of fatty acids. Here we confirm a previous observation that ACBP expression in rodent liver is down-regulated by fasting, and we show that insulin but not glucose is the inducer of ACBP expression in primary rat hepatocytes. In keeping with the regulation by insulin, we show that ACBP is a sterol regulatory element-binding protein 1c (SREBP-1c) target gene in hepatocytes. Members of the SREBP family activate the rat ACBP gene through binding sites for SREBP and the auxiliary factors Sp1 and nuclear factor Y in the proximal promoter. In addition, we show that ACBP is a peroxisome proliferator-activated receptor (PPAR) alpha target gene in cultured hepatocytes and is induced in the liver by fibrates in a PPARalpha-dependent manner. Thus, ACBP is a dual PPARalpha and SREBP-1c target gene in hepatocytes. Fasting leads to reduced activity of SREBP but increased activity of PPARalpha in hepatocytes, and in keeping with ACBP being a dual target gene, we show that ACBP expression is significantly lower in livers from PPARalpha knock-out mice than in livers from wild type mice. In conclusion, expression of ACBP in rodent hepatocytes is subject to dual metabolic regulation by PPARalpha and SREBP-1c, which may reflect the need for ACBP during lipogenic as well as lipo-oxidative conditions.

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.

Novel role for a sterol response element binding protein in directing spermatogenic cell-specific gene expression

Sperm are highly specialized cells, and their formation requires the synthesis of a large number of unique mRNAs. However, little is known about the transcriptional mechanisms that direct male germ cell differentiation. Sterol response element binding protein 2gc (SREBP2gc) is a spermatogenic cell-enriched isoform of the ubiquitous transcription factor SREBP2, which in somatic cells is required for homeostatic regulation of cholesterol. SREBP2gc is selectively enriched in spermatocytes and spermatids, and, due to its novel structure, its synthesis is not subject to cholesterol feedback control. This suggested that SREBP2gc has unique cell- and stage-specific functions during spermatogenesis. Here, we demonstrate that this factor activates the promoter for the spermatogenesis-related gene proacrosin in a cell-specific manner. Multiple SREBP2gc response elements were identified within the 5'-flanking and proximal promoter regions of the proacrosin promoter. Mutating these elements greatly diminished in vivo expression of this promoter in spermatogenic cells of transgenic mice. These studies define a totally new function for an SREBP as a transactivator of male germ cell-specific gene expression. We propose that SREBP2gc is part of a cadre of spermatogenic cell-enriched isoforms of ubiquitously expressed transcriptional coregulators that were specifically adapted in concert to direct differentiation of the male germ cell lineage.

Dysregulation of sterol response element-binding proteins and downstream effectors in prostate cancer during progression to androgen independence

Androgen ablation, the most common therapeutic treatment used for advanced prostate cancer, triggers the apoptotic regression of prostate tumors. However, remissions are temporary because surviving prostate cancer cells adapt to the androgen-deprived environment and form androgen-independent (AI) tumors. We hypothesize that adaptive responses of surviving tumor cells result from dysregulated gene expression of key cell survival pathways. Therefore, we examined temporal alterations to gene expression profiles in prostate cancer during progression to androgen independence at several time points using the LNCaP xenograft tumor model. Two key genes, sterol response element-binding protein (SREBP)-1 and -2 (SREBP-1a,-1c, and -2), were consistently dysregulated. These genes are known to coordinately control the expression of the groups of enzymes responsible for lipid and cholesterol synthesis. Northern blots revealed modest increased expression of SREBP-1a, -1c, and -2 after castration, and at androgen independence (day 21-28), the expression levels of both SREBP-1a and -1c were significantly greater than precastrate levels. Changes in SREBP-1 and -2 protein expression were observed by Western analysis. SREBP-1 68-kDa protein levels were maintained throughout progression, however, SREBP-2 68-kDa protein expression increased after castration and during progression (3-fold). SREBPs are transcriptional regulators of over 20 functionally related enzymes that coordinately control the metabolic pathways of lipogenesis and cholesterol synthesis, some of which were likewise dysregulated during progression to androgen independence. RNA levels of acyl-CoA-binding protein/diazepam-binding inhibitor and fatty acid synthase decreased significantly after castration, and then, during progression, increased to levels greater than or equal to precastrate levels. Expression of farnesyl diphosphate synthase did not decrease after castration but did increase significantly during progression to androgen independence. Levels of SREBP cleavage-activating protein, a regulator of SREBP transcriptional activity, decreased after castration and increased significantly at androgen independence. In clinical prostate cancer specimens from patients with varying grades of disease, the stained tissue sections showed high levels of SREBP-1 protein compared with noncancerous prostate tissue. After hormone withdrawal therapy, tumor levels of SREBP-1 decreased significantly after 6 weeks. AI tumors expressed significantly higher levels of SREBP-1. In summary, the LNCaP xenograft model of human prostate cancer as well as clinical specimens of prostate cancer demonstrated an up-regulation of SREBPs and their downstream effector genes during progression to androgen independence. As the AI phenotype emerges, enzymes critical for lipogenesis and cholesterol synthesis are activated and likely contribute significantly to cell survival of AI prostate cancer.

Pathogenesis of peroxisomal deficiency disorders (Zellweger syndrome) may be mediated by misregulation of the GABAergic system via the diazepam binding inhibitor

Background

Zellweger syndrome (ZS) is a fatal inherited disease caused by peroxisome biogenesis deficiency. Patients are characterized by multiple disturbances of lipid metabolism, profound hypotonia and neonatal seizures, and distinct craniofacial malformations. Median live expectancy of ZS patients is less than one year. While the molecular basis of peroxisome biogenesis and metabolism is known in considerable detail, it is unclear how peroxisome deficiency leads to the most severe neurological symptoms. Recent analysis of ZS mouse models has all but invalidated previous hypotheses.

Hypothesis

We suggest that a regulatory rather than a metabolic defect is responsible for the drastic impairment of brain function in ZS patients.

Testing the hypothesis

Using microarray analysis we identify diazepam binding inhibitor/acyl-CoA binding protein (DBI) as a candidate protein that might be involved in the pathogenic mechanism of ZS. DBI has a dual role as a neuropeptide antagonist of GABA(A) receptor signaling in the brain and as a regulator of lipid metabolism. Repression of DBI in ZS patients could result in an overactivation of GABAergic signaling, thus eventually leading to the characteristic hypotonia and seizures. The most important argument for a misregulation of GABA(A) in ZS is, however, provided by the striking similarity between ZS and "benzodiazepine embryofetopathy", a malformation syndrome observed after the abuse of GABA(A) agonists during pregnancy.

Implications of the hypothesis

We present a tentative mechanistic model of the effect of DBI misregulation on neuronal function that could explain some of the aspects of the pathology of Zellweger syndrome.

Multiple missense mutations in the diazepam binding inhibitor (DBI) gene identified in schizophrenia but lack of disease association

The diazepam binding inhibitor (DBI), alternatively known as the acyl-CoA binding protein (ACBP), is involved in multiple biological actions. The polypeptide binds to the peripheral, or mitochondrial, benzodiazepine receptor and facilitates transport of cholesterol to the inner membrane to stimulate steroid synthesis. Through this action, DBI indirectly modulates gamma-aminobutyric acid (GABA)-mediated inhibitory neurotransmission. DBI can be postulated as a candidate gene for psychiatric phenotypes including anxiety, mood, and psychotic disorders. In an examination of the DBI gene among 112 individuals with schizophrenia, our laboratory has identified 18 novel single nucleotide polymorphisms (SNPs), including three missense changes in conserved amino acids, a coding region microdeletion, and multiple SNPs in the putative promoter region. Case-control association analyses were performed for the missense changes, but none was found to be significantly associated with disease.

Novel putative SREBP and LXR target genes identified by microarray analysis in liver of cholesterol-fed mice

High-cholesterol diets elicit changes in gene expression via such transcription factors as sterol-regulatory element binding proteins (SREBPs) and liver X receptors (LXRs). We used Affymetrix microarrays to identify genes in mouse liver regulated by dietary cholesterol (0.0% vs. 0.5% cholesterol wt/wt). Three independent experiments were performed, and data were analyzed with Affymetrix Microarray Suite and ANOVA statistical software. There were 69 unique Unigene clusters consistently regulated by dietary cholesterol (37 downregulated and 32 upregulated). The array results were confirmed by quantitative RT-PCR (Q-PCR) for seven of nine downregulated genes and five of six upregulated genes. A time course of dietary cholesterol feeding over 1 week revealed different temporal patterns of gene regulation for these confirmed genes. Six downregulated genes were examined in transgenic mice overexpressing truncated nuclear forms of SREBP-1a and SREBP-2, and all were induced in these mice. A second microarray analysis of mice treated with the LXR agonist TO901317 confirmed that 13 of the 32 cholesterol upregulated genes were also LXR-activated. This array result was confirmed by Q-PCR for three of three genes. In summary, these studies identified and confirmed six novel dietary cholesterol-regulated genes, three putative SREBP target genes (calcium/calmodulin-dependent protein kinase 1D, fatty acid binding protein 5, and proprotein convertase subtilisin/kexin 9), and three putative LXR target genes (a disintegrin and metalloprotease domain 11, apoptosis-inhibitory 6, and F-box-only protein 3).

Androgens stimulate coordinated lipogenic gene expression in normal target tissues in vivo

In prostate cancer cell lines in culture androgens cause a marked and coordinated upregulation of the expression of several lipogenic genes. Here, using castrated male Wistar rats as an experimental paradigm, we investigated whether coordinated androgen stimulation of lipogenic gene expression represents a more general physiological regulation in non-cancerous androgen-responsive cells as well. In typical target tissues for androgen action such as the ventral prostate and the lacrimal gland, androgen deprivation resulted in a marked reduction in the mRNA and protein levels of genes involved in fatty acid (fatty acid synthase and acetyl-CoA-carboxylase) and cholesterol synthesis (HMG-CoA-reductase and farnesyl diphosphate synthase). Readministration of testosterone immediately following orchidectomy restored the expression of all four genes. Substitution of testosterone by the non-aromatizable androgen dihydrotestosterone gave rise to comparable changes in the mRNA and protein levels of the lipogenic genes under investigation, confirming the involvement of the androgen receptor in the observed effects. In support of the coordinate nature of this regulation, androgen-induced upregulation of lipogenic gene expression is accompanied by an increase in the nuclear content of SREBP, a key lipogenic transcription factor. Taken together, these findings provide evidence for a coordinate regulation of lipogenic gene expression not only in prostate cancer cell lines in culture but also in non-cancerous androgen-responsive tissues in vivo.

Sterol regulatory element-binding protein family as global regulators of lipid synthetic genes in energy metabolism

Sterol regulatory element-binding proteins (SREBPs) have been established as lipid synthetic transcription factors for cholesterol and fatty acid synthesis. SREBPs are synthesized as membrane-bound precursors with their N-terminal active portions entering the nucleus to activate target genes after proteolytic cleavage in a sterol-regulated manner. This cleavage step is regulated by a putative sterol-sensing molecule, SREBP-activating protein (SCAP), that forms a complex with SREBPs and traffics between the rough endoplasmic reticulum and Golgi. DNA cis-elements that SREBPs bind, originally identified as sterol-regulatory elements (SREs), now expands to a variety of SRE-like sequences and some of E-boxes, which makes SREBPs eligible to regulate a wide range of lipid genes. Animal experiments including transgenic and knockout mice suggest that three isoforms, SREBP-1a, -1c, and -2, have different roles in lipid synthesis. In differentiated tissues and organs, SREBP-1c is involved in fatty acid, whereas SREBP-2 plays a major role in regulation of cholesterol synthesis. SREBP-1a is expressed in growing cells, providing both cholesterol and fatty acids that are required for membrane synthesis. SREBP-1c seems to be a mediator for insulin/glucose signaling to lipogenesis, and could be involved in insulin resistance, remnant lipoproteins, and fatty livers. Future studies in this field will certainly focus on understanding the molecular mechanisms sensing cellular sterol and energy states leading to the activation of SREBP-mediated gene transcription.

The gene encoding the Acyl-CoA-binding protein is activated by peroxisome proliferator-activated receptor gamma through an intronic response element functionally conserved between humans and rodents

The acyl-CoA-binding protein (ACBP) is a 10-kDa intracellular protein that specifically binds acyl-CoA esters with high affinity and is structurally and functionally conserved from yeast to mammals. In vitro studies indicate that ACBP may regulate the availability of acyl-CoA esters for various metabolic and regulatory purposes. The protein is particularly abundant in cells with a high level of lipogenesis and de novo fatty acid synthesis and is significantly induced during adipocyte differentiation. However, the molecular mechanisms underlying the regulation of ACBP expression in mammalian cells have remained largely unknown. Here we report that ACBP is a novel peroxisome proliferator-activated receptor (PPAR)gamma target gene. The rat ACBP gene is directly activated by PPARgamma/retinoid X receptor alpha (RXRalpha) and PPARalpha/RXRalpha, but not by PPARdelta/RXRalpha, through a PPAR-response element in intron 1, which is functionally conserved in the human ACBP gene. The intronic PPAR-response element (PPRE) mediates induction by endogenous PPARgamma in murine adipocytes and confers responsiveness to the PPARgamma-selective ligand BRL49653. Finally, we have used chromatin immunoprecipitation to demonstrate that the intronic PPRE efficiently binds PPARgamma/RXR in its natural chromatin context in adipocytes. Thus, the PPRE in intron 1 of the ACBP gene is a bona fide PPARgamma-response element.

Microarray and biochemical analysis of lovastatin-induced apoptosis of squamous cell carcinomas

We recently identified 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme of the mevalonate pathway, as a potential therapeutic target of the head and neck squamous cell carcinomas (HNSCC) and cervical carcinomas (CC). The products of this complex biochemical pathway, including de novo cholesterol, are vital for a variety of key cellular functions affecting membrane integrity, cell signaling, protein synthesis, and cell cycle progression. Lovastatin, a specific inhibitor of HMG-CoA reductase, induces a pronounced apoptotic response in a specific subset of tumor types, including HNSCC and CC. The mediators of this response are not well established. Identification of differentially expressed genes represents a feasible approach to delineate these mediators as lovastatin has the potential to modulate transcription indirectly by perturbing levels of sterols and other mevalonate metabolites. Expression analysis following treatment of the HNSCC cell lines SCC9 or SCC25 with 10 microM lovastatin for 1 day showed that less than 2% (9 cDNAs) of the 588 cDNAs on this microarray were affected in both cell lines. These included diazepam-binding inhibitor/acyl-CoA-binding protein, the activated transcription factor 4 and rhoA. Because the biosynthesis of mevalonate leads to its incorporation into more than a dozen classes of end products, their role in lovastatin-induced apoptosis was also evaluated. Addition of the metabolites of all the major branches of the mevalonate pathway indicated that only the nonsterol moiety, geranylgeranyl pyrophosphate (GGPP), significantly inhibited the apoptotic effects of lovastatin in HNSCC and CC cells. Because rhoA requires GGPP for its function, this links the microarray and biochemical data and identifies rhoA as a potential mediator of the anticancer properties of lovastatin. Our data suggest that the depletion of nonsterol mevalonate metabolites, particularly GGPP, can be potential mediators of lovastatin-induced apoptosis of HNSCC and CC cells.

Peroxisomal beta-oxidation and peroxisome proliferator-activated receptor alpha: an adaptive metabolic system

beta-Oxidation occurs in both mitochondria and peroxisomes. Mitochondria catalyze the beta-oxidation of the bulk of short-, medium-, and long-chain fatty acids derived from diet, and this pathway constitutes the major process by which fatty acids are oxidized to generate energy. Peroxisomes are involved in the beta-oxidation chain shortening of long-chain and very-long-chain fatty acyl-coenzyme (CoAs), long-chain dicarboxylyl-CoAs, the CoA esters of eicosanoids, 2-methyl-branched fatty acyl-CoAs, and the CoA esters of the bile acid intermediates di- and trihydroxycoprostanoic acids, and in the process they generate H2O2. Long-chain and very-long-chain fatty acids (VLCFAs) are also metabolized by the cytochrome P450 CYP4A omega-oxidation system to dicarboxylic acids that serve as substrates for peroxisomal beta-oxidation. The peroxisomal beta-oxidation system consists of (a) a classical peroxisome proliferator-inducible pathway capable of catalyzing straight-chain acyl-CoAs by fatty acyl-CoA oxidase, L-bifunctional protein, and thiolase, and (b) a second noninducible pathway catalyzing the oxidation of 2-methyl-branched fatty acyl-CoAs by branched-chain acyl-CoA oxidase (pristanoyl-CoA oxidase/trihydroxycoprostanoyl-CoA oxidase), D-bifunctional protein, and sterol carrier protein (SCP)x. The genes encoding the classical beta-oxidation pathway in liver are transcriptionally regulated by peroxisome proliferator-activated receptor alpha (PPAR alpha). Evidence derived from mice deficient in PPAR alpha, peroxisomal fatty acyl-CoA oxidase, and some of the other enzymes of the two peroxisomal beta-oxidation pathways points to the critical importance of PPAR alpha and of the classical peroxisomal fatty acyl-CoA oxidase in energy metabolism, and in the development of hepatic steatosis, steatohepatitis, and liver cancer.

Sterol regulatory element-binding proteins (SREBPs): transcriptional regulators of lipid synthetic genes

Roles of sterol regulatory element-binding proteins (SREBPs) have been established as lipid synthetic transcription factors especially for cholesterol and fatty acid synthesis. SREBPs have unique characteristics. Firstly, they are membrane-bound proteins and the N-terminal active portions enter nucleus to activate their target genes after proteolytic cleavage, which requires sterol-sensing molecule, SREBP-activating protein (SCAP) and is crucial for sterol-regulation. Secondly, they bind and activate sterol-regulatory (SREs) containing promoters as well as some E-boxes, which makes SREBPs eligible to regulate a wide range of lipid genes. Finally, three isoforms, SREBP-1a-1c, and have different roles in lipid synthesis. In vivo studies using transgenic and knockout mice suggest that SREBP-1 seems to be involved in energy metabolism including fatty acid and glucose/insulin metabolism, whereas SREBP-2 is specific to cholesterol synthesis. Future studies will be focused on understanding molecular mechanisms sensing cellular sterol and energy states where SREBPs are deeply involved.

Sterol regulatory element binding protein-1a regulation of the steroidogenic acute regulatory protein gene

The binding of tropic hormones to their specific receptors in steroidogenic cells stimulates the cAMP second-messenger system in the presence of steroidogenic factor-1 (SF-1) to increase expression of steroidogenic acute regulatory (StAR) protein, facilitating the transfer of cholesterol to the inner mitochondrial membrane. The increased use of cholesterol in steroidogenesis triggers activation of sterol- sensitive genes through a second regulatory pathway involving the binding of sterol regulatory element (SRE)-binding proteins (SREBP) to SREs located in the promoter regions of these genes. A search of the rat StAR promoter revealed five potential SRE sites, which demonstrated specific binding with recombinant SREBP-1a. Overexpression of SREBP-1a, -1c or -2 in HTB-9 cells cotransfected with the rat StAR promoter resulted in an increase in promoter-driven luciferase activity. In addition, SREBP-1a was able to activate the StAR promoter through an E-box but only in a promoter construct lacking SREs. SREBPs are known to be weak transcriptional activators and require the presence of additional coactivators like Sp1 and nuclear factor-Y (NF-Y) to elicit maximum activation. Electrophoretic mobility shift assays demonstrated that Sp1, SF-1, and NF-Y enhanced SREBP-1a binding to SREs in the StAR promoter. There was a 4-fold increase in StAR promoter luciferase reporter gene expression when HTB-9 cells were cotransfected with expression vectors for SREBP-1a and NF-Y. In addition, the combined action of SREBP-1a and SF-1 increased both basal (1.6-fold) and cAMP-induced (3.5-fold) activation of the rat StAR promoter. Although Sp1 enhanced SREBP-1a binding to an SRE, Sp1 was not able to increase StAR promoter activity in the presence of SREBP-1a. These results suggest that SREBP-induced regulation of the rat StAR gene is responsive to selective combinations of transcriptional cofactors that could necessitate the convergence of multiple regulatory pathways to enhance gene transcription.

Induction of LPL gene expression by sterols is mediated by a sterol regulatory element and is independent of the presence of multiple E boxes

Overexpression of the adipocyte differentiation and determination factor-1 (ADD-1) or sterol regulatory element binding protein-1 (SREBP-1) induces the expression of numerous genes involved in lipid metabolism, including lipoprotein lipase (LPL). Therefore, we investigated whether LPL gene expression is controlled by changes in cellular cholesterol concentration and determined the molecular pathways involved. Cholesterol depletion of culture medium resulted in a significant induction of LPL mRNA in the 3T3-L1 preadipocyte cell line, whereas addition of cholesterol reduced LPL mRNA expression to basal levels. Similar to the expression of the endogenous LPL gene, the activity of the human LPL gene promoter was enhanced by cholesterol depletion in transient transfection assays, whereas addition of cholesterol caused a reversal of its induction. The effect of cholesterol depletion upon the human LPL gene promoter was mimicked by cotransfection of expression constructs encoding the nuclear form of SREBP-1a, -1c (also called ADD-1) and SREBP-2. Bioinformatic analysis demonstrated the presence of 3 potential sterol regulatory elements (SRE) and 3 ADD-1 binding sequences (ABS), also known as E-box motifs. Using a combination of in vitro protein-DNA binding assays and transient transfection assays of reporter constructs containing mutations in each individual site, a sequence element, termed LPL-SRE2 (SRE2), was shown to be the principal site conferring sterol responsiveness upon the LPL promoter. These data furthermore underscore the importance of SRE sites relative to E-boxes in the regulation of LPL gene expression by sterols and demonstrate that sterols contribute to the control of triglyceride metabolism via binding of SREBP to the LPL regulatory sequences.

Sterols and isoprenoids: signaling molecules derived from the cholesterol biosynthetic pathway

Compounds derived from the isoprenoid/cholesterol biosynthetic pathway have recently been shown to have novel biological activities. These compounds include certain sterols, oxysterols, farnesol, and geranylgeraniol, as well as the diphosphate derivatives of isopentenyl, geranyl, farnesyl, geranylgeranyl, and presqualene. They regulate transcriptional and post-transcriptional events that in turn affect lipid synthesis, meiosis, apoptosis, developmental patterning, protein cleavage, and protein degradation.

Acyl-CoA-binding protein is a potent m-calpain activator

Acyl-CoA-binding protein, a 20-kDa homodimer that exerts many physiological functions, promotes activation of the classic calpain forms, most markedly that of the m-isozyme. This protein factor was purified from rat skeletal muscle and was also expressed in Escherichia coli. Both native and recombinant acyl-CoA-binding proteins show the same molecular properties and an identical capacity to decrease the [Ca(2+)] required for m-calpain activity. The binding of long-chain acyl-CoAs to acyl-CoA-binding protein does not modify the activating effect on calpains. Acyl-CoA-binding protein seems to be involved in the m-calpain regulation process, whereas the previously identified UK114 activator is a specific modulator of micro-calpain. Acyl-CoA-binding protein is proposed as a new component of the Ca(2+)-dependent proteolytic system. A comparative analysis among levels of classic calpains and their activator proteins is also reported.

Oxysterols: modulators of cholesterol metabolism and other processes

Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.

Sterol regulatory element-binding protein-1a binds to cis elements in the promoter of the rat high density lipoprotein receptor SR-BI gene

The high density lipoprotein (HDL) receptor, or scavenger receptor class B type I (SR-BI), is critical for cholesterol transport and a potential target for hypercholesterolemic drugs. Thus, elucidation of the mechanism underlying regulation of the HDL receptor SR-BI gene is essential. It has been previously shown that there is a correlation between depletion in ovarian cholesteryl ester content and increased HDL receptor SR-BI expression in response to hormonal stimulation. We wanted to determine whether the levels of mature sterol response element-binding protein-1a (SREBP-1a), a key protein in the transcriptional regulation of several genes by sterols, are affected under these conditions. Thus, Western blot analysis was carried out. Consistent with the possibility that SREBP-1a may be involved in the regulation of the HDL receptor SR-BI gene, we found that mature SREBP-1a levels increased up to 11-fold in the ovary after treatment with 50 U hCG. This increase in mature SREBP-1a protein levels correlated with a 30% decrease in ovarian cholesterol levels. These changes in both SREBP-1a and cholesterol levels preceded a 2-fold induction of HDL receptor SR-BI protein levels. To determine whether SREBP-1a could directly regulate the expression of the rat HDL receptor SR-BI gene, approximately 2.2 kb of the receptor SR-BI promoter were cloned and sequenced, and deletion analysis and mobility shift assays were performed. The results of these studies demonstrate that the rat HDL receptor SR-BI promoter contains two sterol response elements (pSRE and dSRE) through which SREBP-1a can bind and activate transcription of this gene. These motifs are similar to known SRE motifs reported for sterol-sensitive genes, and the pSRE is located between two Sp1 sites, similar to the SRE-1 motif in the low density lipoprotein receptor. The cysteine protease inhibitor N-acetyl-leucyl-leucyl-norleucinal, which inhibits SREBP degradation, enhanced the effect of SREBP-1a on the regulation of the rat HDL receptor SR-BI gene. It has previously been shown that tropic hormones such as hCG can also influence gene expression by increasing cAMP levels. Consistent with this fact, we have recently shown that steroidogenic factor-1 (SF-1) mediates cAMP activation of the HDL receptor SR-BI gene. Thus, we decided to examine whether SREBP-1a could cooperate with SF-1 to enhance transcription this gene. The results confirm that indeed both SF-1 and SREBP-1a synergize to induce HDL receptor SR-BI gene expression.

The molecular biology of the CCAAT-binding factor NF-Y

Protein coding genes are transcribed by Polymerase II, under the control of short discrete DNA elements in promoters and enhancers, recognized with high efficiency and specificity by trans-acting factors and by general transcription proteins (Tjian and Maniatis, 1994). The former regulate specific genes or set of genes, usually in a tissue-, developmental-, cell-cycle or stimuli-dependent way; the latter are involved in the activation of all promoters, as a whole multi-subunit holoenzyme (Parvis and Young, 1998). A limited set of elements, such as the GC and CCAAT-boxes, are present in a very high number of promoters. The whole process is further complicated by the need to operate in the context of higher order chromatin structures (Workman and Kingston, 1998). This review focuses on the CCAAT sequence and on the NF-Y protein, also known as CBF, which binds to it.

Indirect mechanisms and cascades of androgen action

Androgens are the main hormones responsible for the induction of the male phenotype. This process involves a complex combination of reversible and irreversible effects. As for other steroid hormones, many of the effects of androgens are mediated by a specific intracellular receptor that interacts with cis-acting regulatory regions (AREs) in the affected genes. Apart from these direct effects, however, androgens may indirectly affect the expression of a variety of genes that do not necessarily contain AREs. Indirect effects may be related to androgen-induced changes in the concentration or activity of secondary transcription factors, autocrine and paracrine mediators, and circulating hormones. Such indirect effects may induce cascade-like actions and may play an important role in more complex effects of androgens involving coordinated responses of genes, cells and organs.