More severe type 2 diabetes-associated ischemic stroke injury is alleviated in aldose reductase-deficient mice.

Aldose reductase (AR), the first enzyme in the polyol pathway, has been implicated in a wide variety of physiological and pathological functions, such as diabetic vascular and neural complications. It is known that diabetes mellitus can exacerbate brain and retina damage after ischemic injuries. However, the underlying mechanisms are not clear. In the present study, we made use of db/db mice with an AR null mutation (AR(-/-)db/db) to understand better the role of AR in the pathogenesis of brain and retina ischemic injuries under diabetic conditions. Cerebral and retinal ischemia was induced by transient middle cerebral artery occlusion in control and diabetic mice either with or without an AR null mutation. Mice were evaluated for neurological deficits after 30 min of ischemia and 23.5 hr of reperfusion. Our results showed that the diabetic db/db mice had significantly more severe neurological deficit and larger brain infarct size than the nondiabetic mice. Compared with wild-type db/db mice, the AR(-/-)db/db mice had significantly lower neurological scores, smaller brain infarct areas, and less hemispheric brain swelling. Retinal swelling was also significantly decreased in the AR(-/-)db/db mice. Less swelling in the brain and retina of the AR(-/-)db/db mice correlated with less expression of the water channel aquaporin 4. Taken together, these data clearly show that deletion of AR leads to less severe brain and retinal ischemic injuries in the diabetic db/db mouse. The present study indicates that inhibition of AR in diabetics may protect against damage in the brain and retina following ischemic reperfusion injury.

Chemical composition and antiproliferative activity of essential oil from the leaves of a medicinal herb, Schefflera heptaphylla.

Schefflera heptaphylla (L.) Frodin is a medicinal herb widely used as a main ingredient of the popular health tea formulation against infections in Southern China. Twenty-seven volatile compounds were identified by GC-MS analysis from the essential oil obtained from the leaves of S. heptaphylla, and 17 of them belonged to monoterpenes or sesquiterpenes. The main volatile constituent in S. heptaphylla was found to be a monoterpene, beta-pinene, comprising about 22% of the total volatile components. The essential oil showed significant antiproliferative activity against three cancer cell lines, MCF-7, A375 and HepG2 cells, with IC50 values of 7.3 microg/mL, 7.5 microg/mL and 6.9 microg/mL, respectively. The result of the cytotoxicity assay indicates that (-)-beta-pinene and (+)-beta-pinene (commercially available from Sigma) also possessed antiproliferative activity against the cancer cells MCF-7, A375 and HepG2 with IC50 values ranging from 147.1 to 264.7 microm.

Establishment and characterization of a new cell line derived from human colorectal laterally spreading tumor.

AIM: To study the molecular mechanism of laterally spreading tumor (LST), a cell line [Laterally Spreading Tumor-Rectum 1 (LST-R1)] was derived and the characteristics of this cell line were investigated. METHODS: A new cell line (LST-R1) originated from laterally spreading tumor was established. Properties of the cell line were characterized using scanning and transmission electron microscopy, immunohistochemistry method, cytogenetic analysis and nude mice xenograft experiments. In vitro invasion assay, cDNA microarray and Western blotting were used to compare the difference between the LST-R1 and other colorectal cancer cell lines derived from prudent colon cancer. RESULTS: Our study demonstrated that both epithelial special antigen (ESA) and cytokeratin-20 (CK20) were expressed in LST-R1. The cells presented microvilli and tight junction with large nuclei. The karyotypic analysis showed hyperdiploid features with structural chromosome aberrations. The in vivo tumorigenicity was also demonstrated in nude mice xenograft experiments. The invasion assay suggested this cell line has a higher invasive ability. cDNA microarray and Western blotting show the loss of the expression of E-cadherin in LST-R1 cells. CONCLUSION: We established and characterized a colorectal cancer cell line, LST-R1 and LST-R1 has an obvious malignant tendency, which maybe partially attributed to the changes of the expression of some adhesion molecules, such as E-cadherin. It is also a versatile tool for exploring the original and progressive mechanisms of laterally spreading tumor and the early colon cancer genesis.

Deletion of aldose reductase leads to protection against cerebral ischemic injury.

Previously, we reported that transgenic mice overexpressing endothelin-1 in astrocytes showed more severe neurological deficits and increased infarct after transient focal ischemia. In those studies, we also observed increased level of aldose reductase (AR), the first and rate-limiting enzyme of the polyol pathway, which has been implicated in osmotic and oxidative stress. To further understand the involvement of the polyol pathway, the mice with deletion of enzymes in the polyol pathway, AR, and sorbitol dehydrogenase (SD), which is the second enzyme in this pathway, were challenged with similar cerebral ischemic injury. Deletion of AR-protected animals from severe neurological deficits and large infarct, whereas similar protection was not observed in mice with SD deficiency. Most interestingly, AR(-/-) brains showed lowered expression of transferrin and transferrin receptor with less iron deposition and nitrotyrosine accumulation. The protection against oxidative stress in AR(-/-) brain was also associated with less poly(adenosine diphosphate-ribose) polymerase (PARP) and caspase-3 activation. Pharmacological inhibition of AR by Fidarestat also protected animals against cerebral ischemic injury. These findings are the first to show that AR contributes to iron- and transferrin-related oxidative stress associated with cerebral ischemic injury, suggesting that inhibition of AR but not SD may have therapeutic potential against cerebral ischemic injury.

Cells of the anterior pituitary.

The anterior pituitary is made up of a number of cell types that are essential for such physiological processes as growth, development, homeostasis, metabolism, and reproduction. These include the hormonal cells corticotropes, thyrotropes, gonadotropes, somatotropes, lactotropes and a small population of mammosomatotropes, together with a non-hormonal cell type called the folliculo-stellate cells. The anterior pituitary hormonal cells are highly differentiated and are committed very early on during embryonic development. Their development is tightly regulated by both extrinsic signals as well as by endogenous gene expression. Many transcription factors that shape the development and functions of the anterior pituitary cells have been identified. Even after differentiation, pituitary cells continue to undergo mitosis and this process could be augmented under certain conditions in adulthood. Some anterior pituitary cells are multifunctional and exhibit mixed phenotypes. Pituitary tumors, which are mostly monoclonal in nature, are rather common. The molecular pathogenesis of pituitary tumorigenesis involves complex and diverse mechanisms. Aberrant intra- and extra-pituitary factors are involved. Mutations of some genes specific to pituitary tumors also play a role.

Seabream ghrelin: cDNA cloning, genomic organization and promoter studies.

Recent studies have indicated that ghrelin stimulates growth hormone release from the pituitary via the growth hormone secretagogue receptor (GHSR). We have previously isolated two GHSR subtypes from the pituitary of the black seabream Acanthopagrus schlegeli. In the present study, we have cloned and characterized ghrelin from the same fish species at both the cDNA and gene levels. The full-length seabream ghrelin cDNA, isolated from sea-bream stomach using a novel approach by exploiting a single conserved region in the coding region, was found to encode a prepropeptide of 107 amino acids, with the predicted mature ghrelin peptide consisting of 20 amino acids (GSSFLSPSQKPQNRGKSSRV). Embedded in this full-length cDNA is a putative fish orthologue of the recently reported mammalian obestatin peptide. The ghrelin gene in black seabream, obtained by genomic PCR, was found to encompass four exons and three introns, possessing the same structural organization as in tilapia and goldfish, but different from that in rainbow trout. In addition, a 2230-bp 5'-flanking region of the seabream ghrelin gene was obtained by genome walking. Sequence analysis revealed that, as in the case of the human ghrelin gene, there is neither a GC box nor a CAAT box present in the isolated 5'-flanking region. However, a number of putative transcription factor-binding sites different from the human counterpart were found in the 5'-flanking region of the seabream ghrelin gene, suggesting that different cis- and trans-acting elements are involved in controlling their gene expression. Functional activity of this 5'-flanking region was examined by cloning it into the pGL3-Basic vector upstream of the luciferase reporter gene and transfected into various cell lines. Positive promoter activity could only be recorded in the colon-derived Caco-2 cells, suggesting that the cloned 5'-flanking region represents the functional promoter of the seabream ghrelin gene, which exhibits tissue-specific promoter activity. Using reverse transcriptase PCR analysis, expression of ghrelin was detected only in the seabream stomach, but not in the other tissues examined, including the brain, gill, intestine, kidney, liver and spleen. This stomach-specific expression of ghrelin in seabream is subject to regulation, as administration of growth hormone or ipamorelin to the fish in vivo was demonstrated to enhance its expression. Reminiscent of the homologous upregulation found in the transcriptional control of the seabream GHSR gene, a similar homologous regulatory mechanism might also exist in controlling the expression of seabream ghrelin. The identification of both GHSR and ghrelin from a single fish species would facilitate our subsequent studies on the elucidation of the physiological functions of the ghrelin/GHSR system in teleost. The possible existence of obestatin in teleost opens up new research avenues on the somatotropic axis in fish.

The BH3-only protein, PUMA, is involved in oxaliplatin-induced apoptosis in colon cancer cells.

Oxaliplatin, the first line chemotherapeutic of colon cancer, induces damage to tumors via induction of apoptosis. PUMA (p53 up-regulate modulator of apoptosis) is an important pro-apoptotic member of Bcl-2 family and regulated mainly by p53. Here we investigated the role of PUMA in oxalipaltin-induced apoptosis and the potential mechanism. We showed that oxaliplatin-induced PUMA expression in a time- and dose-dependent manner and suppression of PUMA expression by stable transfecting anti-sense PUMA plasmid decreased oxaliplatin-induced apoptosis in colon cancer cells. By abrogating the function of p53, we further demonstrated that the induction was p53-independent. We also found that oxaliplatin could inactivate ERK and suppression of ERK activity by its specific inhibitor (PD98059), and dominant negative plasmid (DN-MEK1) enhanced the oxaliplatin-induced PUMA expression and apoptosis in a p53-independent manner. Taken together, our data suggest that PUMA plays an important role in oxaliplatin-induced apoptosis and the induction could be both p53-dependent and p53-independent. Moreover, PUMA expression and apoptosis in oxaliplatin-treated colon cancer cells could be regulated partly by ERK inactivation. Identification of the molecular components involved in regulating the cellular sensitivity to oxaliplatin may provide potential targets for development of novel compounds that may be useful in enhancement of oxaliplatin cytotoxicity in p53 deficient colon cancer.

Characterization of a new upstream GnRH receptor promoter in human ovarian granulosa-luteal cells.

GnRH has been implicated as an important local autocrine and paracrine factor in regulating ovarian function. However, to date, the transcriptional regulation of GnRH receptor (GnRHR) gene in human ovary remains poorly understood. Here we report the characterization of a new upstream promoter for the GnRHR gene in human granulosa-luteal cells. Using progressive deletion analysis, a region between nucleotide -1300 and -1018 (relative to the translation start site) was shown to exhibit the highest promoter activities in two immortalized human granulosa-luteal cell lines, SVOG-4o and SVOG-4m. Two putative CCAAT/enhancer binding protein (C/EBP) motifs and one GATA motif were identified within this region. Mutational studies showed that these three motifs cooperated synergistically to regulate GnRHR gene transcription in the granulosa cells but not in other cell types including human ovarian carcinoma OVCAR-3, human embryonic kidney-293 (HEK-293) and mouse pituitary gonadotrope-derived alphaT3-1 cells. Surprisingly, by competitive EMSAs, we found that an Oct-1 consensus sequence was able to inhibit protein complex formation with the distal C/EBP motif, suggesting a possible cross-talk between the Oct-1 transcription factor and this C/EBP motif. Taken together, our results strongly indicate a role of the C/EBP and GATA motifs in regulating GnRHR gene transcription in human granulosa-luteal cells and further suggest that tissue-specific expression of human GnRHR gene is mediated by differential promoter usage.

Isolation and structure-function studies of a glucagon-like peptide 1 receptor from goldfish Carassius auratus: identification of three charged residues in extracellular domains critical for receptor function.

A better understanding of the molecular mechanism of ligand-receptor interaction of glucagon-like peptide 1 (GLP-1) receptors (GLP-1Rs) is useful for the design of potent GLP-1 analogs that could potentially be used as a treatment for diabetic patients. Changes in the ligand and receptor sequences during evolution provide invaluable clues to evaluate the functional motifs of the receptor that are responsible for ligand interaction. For these reasons, in the present study, we have isolated and functionally characterized a GLP-1R from goldfish. Its amino acid sequence shows 50.8% and 52.3% identity with the human glucagon (hGLU) and GLP-1Rs, respectively, and 84.1% with the zebrafish GLP-1R (the only other GLP-1R isolated from teleost fish). Peptides that are structurally different from goldfish (gf)GLP-1, such as gfGLU and hGLU and human GLP-1 (7-36)amide, are also capable of stimulating this receptor, albeit with lower potencies than gfGLP-1. gfGLP-1 stimulates the formation of cAMP through the recombinant gfGLP-1R with EC(50) = 0.18 nM, whereas EC(50) values for gfGLU, human GLP-1 (7-36)amide, and hGLU are 0.53 nM, 0.9 nM, and 1.2 nM, respectively. These results indicate that the gfGLP-1R is structurally more flexible than its mammalian counterpart and that its binding pocket can accommodate a wider spectrum of peptide ligands. Previous studies demonstrated that the charged residues in the extracellular domains of mammalian GLP-1R, particularly those found in the N-terminal domain and the first exoloop, are important for ligand binding. We investigated the roles of the conserved charged residues in the function of the gfGLP-1R. Eleven mutant receptors were constructed, and the effects of mutations were determined by functional assays. Our results demonstrated that three charged residues (D(113), R(197), and D(205)) present in the extracellular domains are critical for receptor function.

Identification and characterization of a glucagon receptor from the goldfish Carassius auratus: implications for the evolution of the ligand specificity of glucagon receptors in vertebrates.

The structural basis of ligand selectivity of G protein-coupled receptors for metabolic hormones has been an area of intense investigation, and yet it remains unresolved. One approach to delineating the mechanism of ligand-receptor interactions is to compare the ligand specificities of receptors expressed in species that emerged at different times within vertebrate evolution. In this paper we describe the isolation, functional, and phylogenetic characterization of the glucagon receptor from the goldfish Carassius auratus (Teleostei, order Cypriniformes), and compare its ligand specificity with that of the homologous rat receptor. Goldfish (gf) glucagon stimulated glucose production in a dose-dependent manner from isolated goldfish hepatocytes, resulting in 5-fold increase at 1 microm. The goldfish glucagon receptor (gfGlucR) shares 56, 51, 50, and 52% amino acid identities with frog Rana tigrina regulosa, mouse, rat, and human glucagon receptors, respectively. In competitive binding experiments, the recombinant gfGlucR displays high affinity toward goldfish, zebrafish, and human glucagons (IC(50) = 0.6, 9, and 13 nm, respectively) but not toward goldfish glucagon-like peptide-1 or human glucagon-like peptide-1 (7-36) amide. Whereas both goldfish and human glucagons stimulated dose-dependent increases in intracellular cAMP through the recombinant gfGlucR, the recombinant rat GlucR interacted only with human glucagon, analogous to the specificity of the previously characterized glucagon receptor from the frog R. tigrina regulosa. Our results demonstrate that the binding pocket of gfGlucR can accommodate a broad range of glucagon structures and that in the frogs and mammals, there is a structural switch to a more restrictive conformation of glucagon receptors.

Oct-1 is involved in the transcriptional repression of the gonadotropin-releasing hormone receptor gene.

Previous deletion analysis of the 5'-flanking region of human GnRH receptor (GnRHR) gene has revealed a powerful negative regulatory element (NRE) located between nucleotide -1017 and -771. In the present study, we demonstrated that this NRE could repress the homologous promoter, irrespective of its position and completely abolish the activity of a heterologous thymidine kinase promoter in an orientation-dependent manner. Progressive 3'-deletion analysis revealed that most of the silencing activity of the NRE resided in a putative octamer regulatory sequence (5'AAGCAAACT3'), which alone could repress the promoter activities by 69-90% in ovarian OVCAR-3, placental JEG-3, and gonadotrope-derived alphaT3-1 cells. Mutation of the AAAC residues of the octamer sequence completely removed its silencing activity. Interestingly, conversion of the octamer sequence into that of the rodent GnRHR promoter (5'AAGCAAAGT3') did not attenuate its silencing effect, indicating that the repressive role of the octamer sequence is evolutionarily conserved. EMSAs showed that common DNA-protein complexes of the same mobility were formed with nuclear extracts from the reproductive cells and gonadotropes, and a consensus octamer transcription factor-1 (Oct-1) binding sequence could dose dependently inhibit the complex formation. Antibody supershift and Southwestern blot assays confirmed that the protein binding to the octamer sequence was the ubiquitously expressed transcription factor Oct-1. Overexpression of Oct-1 augmented the silencing activity of the octamer sequence in alphaT3-1 cells. Taken together, our results clearly indicate a role of Oct-1 in the transcriptional repression of the human GnRHR gene.

Isolation and characterization of the 5'-flanking region of the growth hormone secretagogue receptor gene from black seabream Acanthopagrus schlegeli.

Ghrelin, the recently discovered endogenous ligand for growth hormone secretagogue receptor (GHSR), is widely expressed and involved in regulating diverse physiological functions in addition to stimulation of growth hormone (GH) secretion. Previous studies have demonstrated the functional significance of the ghrelin/GHSR system, yet the transcriptional regulation of the ghrelin and GHSR genes are poorly understood. We have recently cloned the GHSR cDNA from the pituitary of black seabream Acanthopagrus schlegeli. In the present study, we have isolated a 2.1 kb 5'-flanking region of the GHSR gene from the same species and have investigated, for the first time, the transcriptional regulation of GHSR from a non-human species. The 5'-flanking region of the seabream GHSR gene was found to contain a number of unique putative transcription factor-binding sites different from the human counterpart. Functional characterization of the 5'-flanking region in several cell lines indicates that the region between -1423 and +19 contains sufficient elements for promoter function. Moreover, progressive 3'-deletion analysis suggests the presence of negative regulatory element(s) and essential cis-acting element(s) at -514/+19 and -928/-515, respectively. Furthermore, we have shown that the promoter activity is significantly enhanced by a GHSR agonist in a cell line stably expressing the seabream GHSR, and this stimulatory effect could be completely blocked by a GHSR antagonist. These results suggest that homologous up-regulation plays an important role in the transcriptional control of the teleostean GHSR gene. This is in big contrast to the human situation in which a homologous down-regulation of the GHSR gene transcription by its own ligand has been previously demonstrated.

Lycium barbarum extracts protect the brain from blood-brain barrier disruption and cerebral edema in experimental stroke.

BACKGROUND AND PURPOSE: Ischemic stroke is a destructive cerebrovascular disease and a leading cause of death. Yet, no ideal neuroprotective agents are available, leaving prevention an attractive alternative. The extracts from the fruits of Lycium barbarum (LBP), a Chinese anti-aging medicine and food supplement, showed neuroprotective function in the retina when given prophylactically. We aim to evaluate the protective effects of LBP pre-treatment in an experimental stroke model. METHODS: C57BL/6N male mice were first fed with either vehicle (PBS) or LBP (1 or 10 mg/kg) daily for 7 days. Mice were then subjected to 2-hour transient middle cerebral artery occlusion (MCAO) by the intraluminal method followed by 22-hour reperfusion upon filament removal. Mice were evaluated for neurological deficits just before sacrifice. Brains were harvested for infarct size estimation, water content measurement, immunohistochemical analysis, and Western blot experiments. Evans blue (EB) extravasation was determined to assess blood-brain barrier (BBB) disruption after MCAO. RESULTS: LBP pre-treatment significantly improved neurological deficits as well as decreased infarct size, hemispheric swelling, and water content. Fewer apoptotic cells were identified in LBP-treated brains by TUNEL assay. Reduced EB extravasation, fewer IgG-leaky vessels, and up-regulation of occludin expression were also observed in LBP-treated brains. Moreover, immunoreactivity for aquaporin-4 and glial fibrillary acidic protein were significantly decreased in LBP-treated brains. CONCLUSIONS: Seven-day oral LBP pre-treatment effectively improved neurological deficits, decreased infarct size and cerebral edema as well as protected the brain from BBB disruption, aquaporin-4 up-regulation, and glial activation. The present study suggests that LBP may be used as a prophylactic neuroprotectant in patients at high risk for ischemic stroke.

Lycium barbarum polysaccharides reduce neuronal damage, blood-retinal barrier disruption and oxidative stress in retinal ischemia/reperfusion injury.

Neuronal cell death, glial cell activation, retinal swelling and oxidative injury are complications in retinal ischemia/reperfusion (I/R) injuries. Lycium barbarum polysaccharides (LBP), extracts from the wolfberries, are good for "eye health" according to Chinese medicine. The aim of our present study is to explore the use of LBP in retinal I/R injury. Retinal I/R injury was induced by surgical occlusion of the internal carotid artery. Prior to induction of ischemia, mice were treated orally with either vehicle (PBS) or LBP (1 mg/kg) once a day for 1 week. Paraffin-embedded retinal sections were prepared. Viable cells were counted; apoptosis was assessed using TUNEL assay. Expression levels of glial fibrillary acidic protein (GFAP), aquaporin-4 (AQP4), poly(ADP-ribose) (PAR) and nitrotyrosine (NT) were investigated by immunohistochemistry. The integrity of blood-retinal barrier (BRB) was examined by IgG extravasations. Apoptosis and decreased viable cell count were found in the ganglion cell layer (GCL) and the inner nuclear layer (INL) of the vehicle-treated I/R retina. Additionally, increased retinal thickness, GFAP activation, AQP4 up-regulation, IgG extravasations and PAR expression levels were observed in the vehicle-treated I/R retina. Many of these changes were diminished or abolished in the LBP-treated I/R retina. Pre-treatment with LBP for 1 week effectively protected the retina from neuronal death, apoptosis, glial cell activation, aquaporin water channel up-regulation, disruption of BRB and oxidative stress. The present study suggests that LBP may have a neuroprotective role to play in ocular diseases for which I/R is a feature.

Pluronic L-81 ameliorates diabetic symptoms in db/db mice through transcriptional regulation of microsomal triglyceride transfer protein.

AIM: To test whether oral L-81 treatment could improve the condition of mice with diabetes and to investigate how L-81 regulates microsomal triglyceride transfer protein (MTP) activity in the liver. METHODS: Genetically diabetic (db/db) mice were fed on chow supplemented with or without L-81 for 4 wk. The body weight, plasma glucose level, plasma lipid profile, and adipocyte volume of the db/db mice were assessed after treatment. Toxicity of L-81 was also evaluated. To understand the molecular mechanism, HepG2 cells were treated with L-81 and the effects on apolipoprotein B (apoB) secretion and mRNA level of the MTP gene were assessed. RESULTS: Treatment of db/db mice with L-81 significantly reduced and nearly normalized their body weight, hyperphagia and polydipsia. L-81 also markedly decreased the fasting plasma glucose level, improved glucose tolerance, and attenuated the elevated levels of plasma cholesterol and triglyceride. At the effective dosage, little toxicity was observed. Treatment of HepG2 cells with L-81 not only inhibited apoB secretion, but also significantly decreased the mRNA level of the MTP gene. Similar to the action of insulin, L-81 exerted its effect on the MTP promoter. CONCLUSION: L-81 represents a promising candidate in the development of a selective insulin-mimetic molecule and an anti-diabetic agent.

The antidiabetic effects of a dry powder of dietary vegetable and fruit mixtures in diabetic db/db mice.

We evaluated the antidiabetic effects of a mixed vegetable powder-formula I (MVP-FI), which is a dry powder mixture of over 65 kinds of vegetables and fruits, using the db/db type 2 diabetes mouse model. The db/db mice at 8-10 weeks of age were randomly divided into three groups: vehicle treatment, 1.575 g/kg MVP-FI treatment, and 3.15 g/kg MVP-FI treatment. During 12 days of treatment, we measured food intake and body weight changes, fasting blood glucose levels, and plasma lipid levels. Our results showed that the food intake and the body weight of MVP-FI-treated group were decreased gradually. Moreover, the fasting blood glucose level of the treated group was significantly dropped to a normal level comparable to that of the lean mice. Furthermore, we also found that the plasma triglyceride level in the treated group was dropped, whereas the high-density lipoprotein (HDL) level was increased and total cholesterol/HDL-cholesterol ratio was decreased. Taken together, these results suggest that the diabetic conditions of the db/db mice have been improved after 12 days treatment with MVP-FI. The antihyperglycemic and antiobese activities of the MVP-FI, as demonstrated in the present study, may have important clinical implications for improving the management of type 2 diabetic patients.

Hepatocyte nuclear factor 1 binding element within the promoter of microsomal triglyceride transfer protein (MTTP) gene is crucial for MTTP basal expression and insulin responsiveness.

Insulin inhibits the transcription of the microsomal triglyceride transfer protein (MTTP), which plays a pivotal role in lipoprotein assembly and secretion. Here, we provide evidence that a hepatocyte nuclear factor 1 binding element (HNF1A element) within the MTTP promoter serves as a novel negative insulin-responsive element. Deletion/mutation mapping of the MTTP gene promoter identified a modified HNF1A element that is crucial to the negative insulin effect. Chimeric promoter containing this HNF1A element and minimal TEAD1 promoter also responded negatively toward insulin treatment. Gel shift assay demonstrated that HNF1A but not HNF1B binds to this element. Enforced expression of HNF1A was sufficient to reconstitute the negative insulin responsiveness of MTTP promoter in TM4SF1 myocytes that are HNF1A negative. Furthermore, replacing this element with consensus HNF1A element preserved the negative insulin response, suggesting that negative insulin responsiveness is a generic characteristic of HNF1A element. Given that many genes implicated in diabetes contain HNF1A element, the potential regulation of these genes by insulin via HNF1A element may provide important clues for the manifestation and treatment of diabetic metabolic syndromes.

Expression and transcriptional regulation of the GnRH receptor gene in human neuronal cells.

GnRH, acts via the GnRH receptor (GnRHR), plays a pivotal role in human reproduction by stimulating the synthesis and secretion of gonadotropins from pituitary gonadotropes. Studies have also suggested that it has other extra-pituitary functions. To date, the transcriptional regulation of human GnRHR gene in the brain remains largely unknown. Recently, the human cerebellar medulloblastoma cell line TE-671 is found to express GnRH. We report here for the first time that GnRHR is also expressed in this neuronal cell line. Treatment with GnRHR agonist stimulated the phosphorylation of both ERK1/2 and JNK in the cells. Moreover, transient transfection of various human GnRHR promoter-luciferase constructs into the cells identified an upstream promoter region located between -2197 and -1018. Important cis-acting regulatory elements were found at -1300/-1018 and -2197/- 1900, as deletion of either region caused a dramatic decrease in the promoter activity. An upstream GnRHR promoter element was identified to be important for basal transcription in the human neuronal TE-671 cells, in contrast to the previous finding that a downstream promoter is responsible for the gonadotrope-specific expression. Furthermore, we showed that antide (GnRHR antagonist) significantly stimulated the GnRHR promoter activity and inhibition of protein kinase C (PKC) pathway by staurosporine could also up-regulate the promoter activity in dose- and time-dependent manners. Taken together, these data suggest that activation of the GnRHR by interacting with GnRH may transcriptionally down-regulate itself via the PKC pathway in human neuronal cells.