RREB1 (Ras Responsive Element Binding Protein 1)

Review on RREB1 (Ras Responsive Element Binding Protein 1), with data on DNA, on the protein encoded, and where the gene is implicated

Cellular and molecular characterization of the sterol-regulatory element-binding protein-1

Human cells maintain lipid homeostasis by regulated cleavage of membranebound transcription factors, so-called sterol-regulatory element-binding proteins (SREBPs). The mature forms of SREBP-1 and -2 are transcriptional activators of lipogenic genes controlling cholesterol, fatty acids, and triglyceride biosynthesis and uptake. As the SREBPs play a central role in the regulation of the lipoprotein metabolism, we supposed that specific sequence variations, which correspond to single-nucleotide polymorphisms in these genes, and certain drugs, that influence the expression of SREBP, may result in alterations in plasma lipoprotein concentrations. A syndrome characterized by hypertriglyceridemia, hypercholesterolemia, hyperinsulinemia and lipodystrophy has been found to be associated with antiretroviral treatment (ART) including protease inhibitors. A marker predicting this syndrome has been identified in the gene encoding the sterolregulatory element-binding protein-1c (SREBP-1c), a regulator of triglycerides, cholesterol, insulin and adipocytes. A possible inhibition of SREBP-1c-dependent genes by the protease inhibitor indinavir and its possible reversal by the lipid-lowering drug simvastatin were studied in cell culture. The effects of indinavir and simvastatin on SREBP-1c-dependent genes were compared with the effects of indinavir and simvastatin on SREBP1c-independent genes. In fact, indinavir inhibited the SREBP-1c-dependent genes encoding the lipoprotein lipase and the fatty acid synthase in a dosedependent manner but not the SREBP-1c-independent gene encoding the low-density lipoprotein receptor. Furthermore, simvastatin antagonized the indinavir-induced SREBP-1c-inhibition. Thus, indinavir inhibits important effector genes of the SREBP-1c pathway, which may explain major antiretroviral treatment-related adverse effects. A single-nucleotide polymorphism (3' 322C/G SNP) identified in the sterolregulatory element-binding protein-1c (SREBP-1c) gene was predictive of highly active antiretroviral therapy-related hyperlipoproteinemia. Increases in cholesterol, triglyceride and insulin were less frequently associated with homozygous SREBP-1c-3' 322G (genotype 22) than with heterozygous/homozygous SREBP-1c-3'322C (genotypes 11/12). The differences in messenger RNA conformation can explain the pharmacogenetic basis of these findings. The mRNA stability of both homozygous genotypes of SREBP-1c-3’322C/G was compared in the stably transfected T-REx cell lines using a real-time quantitative polymerase chain reaction method. The mRNA of the SREBP-1c-3’322C isoform (genotype 11) was shown to have a more abundance decay rate than 3’322G isoform (genotype 22). Thus, the sequence variation (3’322C/G SNP) in the coding 3’ end of the gene affects the secondary structure of the SREBP-1c mRNA, influences its degradation rate and, therefore, causes differences in the regulation of SREBP-1c expression. In the process of this thesis, three new splice variants of the human SREBP-1 gene that shared different combinations of the SREBP-1a and -1c exons at the 3’ end of mRNA were identified. The splice variant containing exons 17, 18a and 18c was designated as SREBP-1d, the splice variant containing exons 17, 18a, 18c and 19c was termed as SREBP-1e, and the splice variant containing exons 17, 18c and 20f was named as SREBP-1f. Analysis of tissue distribution showed that the new splice variants SREBP-1e and -1d were ubiquitously found in various human tissues and tumor-derived cells, whereas wild-type SREBP-1c and SREBP-1f transcripts were relatively tissue-specific. This high abundance led us to the hypothesis that splice variants SREBP-1e and SREBP-1d play a more general role in regulating cellular lipid levels as compared to other isoforms. This thesis concludes that the sterol-regulatory element-binding protein (SREBP)-1c is crucial in the metabolic side-effects associated with highly active antiretroviral therapy using protease inhibitors. Moreover, regulation mechanism mediated by the transcription factor SREBP-1 is a model of a complex gene regulation system composed of different related levels: promoter regulation of effector genes, differences in mRNA stability and tissue specific splice variants in different quantities

Semi-quantitative analysis of endometrial receptivity marker mRNA expression in the mid-secretory endometrium of patients with uterine fibromas

In fertile women, expression of molecular marker of endometrial receptivity, HOXA11, leukemia inhibitory factor (LIF) and basic transcriptional element binding protein 1 (BTEB1), rises during the luteal phase with the peak occurring during the implantation window. We evaluated the transcript levels of HOXA-11, LIF and BTEB1 in the mid-secretory endometrium of infertile patients with uterine fibroid infertility (n = 8) and from normal fertile women (n = 8). Expression levels of HOXA11, LIF and BTEB1 mRNA were measured in endometrium during the mid-secretory phase using semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Endometrial HOXA11, LIF and BTEB1 mRNA expression levels (normalized to ß-actin expression) were significantly decreased in endometrium of infertile patients with uterine fibroid as compared with healthy fertile controls at the time of implantation (P<0.05). The results suggest that the alteration in expression pattern of some genes could account for some aspects of infertility in patients with uterine fibroma.Key words: Myoma, fibromas, implantation, HOXA11, leukemia inhibitory factor, basic transcriptional element binding protein 1

Novel roles of sterol regulatory element-binding protein-1 in liver

Indiana University-Purdue University Indianapolis (IUPUI)Sterol Regulatory Element Binding Protein-1 (SREBP-1) is a conserved transcription factor of the basic helix-loop-helix leucine zipper family (bHLH-Zip) that primarily regulates glycolytic and lipogenic enzymes such as L-pyruvate kinase, acetyl-CoA carboxylase, fatty acid synthase, stearoyl-CoA desaturase 1, and mitochondrial glycerol-3-phosphate acyltransferase 1. SREBP-1c activity is higher in the liver of human obese patients, as well as ob/ob and db/db mouse models of obesity and type 2 diabetes, underscoring the role of this transcription factor as a contributor to hepatic steatosis and insulin resistance. Nonetheless, SREBP-1 deficient ob/ob mice, do not display improved glycemia despite a significant decrease in hepatic lipid accumulation, suggesting that SREBP-1 might play a role at regulating carbohydrate metabolism. By silencing SREBP-1 in the liver of normal and type 2 diabetes db/db mice, we showed that indeed, SREBP-1 is needed for appropriate regulation of glycogen synthesis and gluconeogenesis enzyme gene expression. Depleting SREBP-1 activity more than 90%, resulted in a significant loss of glycogen deposition and increased expression of Pck1 and G6pc. Hence, the benefits of reducing de novo lipogenesis in db/db mice were offset by the negative impact on gluconeogenesis and glycogen synthesis. Some studies had also indicated that SREBP-1 regulates the insulin signaling pathway, through regulation of IRS2 and a subunit of the PI3K complex, p55g. To gain insight on the consequences of silencing SREBP-1 on insulin sensitivity, we analyzed the insulin signaling and mTOR pathways, as both are interconnected through feedback mechanisms. These studies suggest that SREBP-1 regulates S6K1, a downstream effector of mTORC1, and a key molecule to activate the synthesis of protein. Furthermore, these analyses revealed that depletion of SREBP-1 leads to reduced insulin sensitivity. Overall, our data indicates that SREBP-1 regulates pathways important for the fed state, including lipogenesis, glycogen and protein synthesis, while inhibiting gluconeogenesis. Therefore, SREBP-1 coordinates multiple aspects of the anabolic response in response to nutrient abundance. These results are in agreement with emerging studies showing that SREBP-1 regulates a complex network of genes to coordinate metabolic responses needed for cell survival and growth, including fatty acid metabolism; phagocytosis and membrane biosynthesis; insulin signaling; and cell proliferation

Lipid storage and autophagy in melanoma cancer cells

Cancer stem cells (CSC) represent a key cellular subpopulation controlling biological features such as cancer progression in all cancer types. By using melanospheres established from human melanoma patients, we compared less differentiated melanosphere-derived CSC to differentiating melanosphere-derived cells. Increased lipid uptake was found in melanosphere-derived CSC vs. differentiating melanosphere-derived cells, paralleled by strong expression of lipogenic factors Sterol Regulatory Element-Binding Protein-1 (SREBP-1) and Peroxisome Proliferator-Activated Receptor-γ (PPAR-γ). An inverse relation between lipid-storing phenotype and autophagy was also found, since microtubule-associated protein 1A/1B-Light Chain 3 (LC3) lipidation is reduced in melanosphere-derived CSC. To investigate upstream autophagy regulators, Phospho-AMP activated Protein Kinase (P-AMPK) and Phospho-mammalian Target of Rapamycin (P-mTOR) were analyzed; lower P-AMPK and higher P-mTOR expression in melanosphere-derived CSC were found, thus explaining, at least in part, their lower autophagic activity. In addition, co-localization of LC3-stained autophagosome spots and perilipin-stained lipid droplets was demonstrated mainly in differentiating melanosphere-derived cells, further supporting the role of autophagy in lipid droplets clearance. The present manuscript demonstrates an inverse relationship between lipid-storing phenotype and melanoma stem cells differentiation, providing novel indications involving autophagy in melanoma stem cells biology

Effects of sterol regulatory element-binding protein (SREBP) in chickens

Sterol regulatory element binding protein- 1 and -2 (SREBP-1 and -2) are key transcription factors involved in the biosynthesis of cholesterol and fatty acids. The SREBP have mostly been studied in rodents in which lipogenesis is regulated in both liver and adipose tissue. There is, though, a paucity of information on birds, in which lipogenesis occurs essentially in the liver as in humans. Since a prelude to the investigation of the role of SREBP in lipid metabolism regulation in chicken, we review Size and Tissue expression Pattern of SREBP and role of this protein in chickens

Sterol regulatory element binding protein-1 (SREBP1) gene expression is similarly increased in polycystic ovary syndrome and endometrial cancer

Introduction: Women with polycystic ovary syndrome (PCOS) have a 3-fold higher risk of endometrial cancer (EC). Insulin resistance and hyperlipidaemia may be pertinent factors in the pathogenesis of both conditions. The aim of this study was to investigate endometrial Sterol Regulatory Element Binding Protein-1 gene (SREBP1) expression in PCOS and EC endometrium, and to correlate endometrial SREBP1 expression with serum lipid profiles. Material and methods: A cross-sectional study was performed at Nottingham University Hospital, United Kingdom. A total of 102 women (PCOS, EC and controls; 34 participants in each group) were recruited. Clinical and biochemical assessments were performed before endometrial biopsies were obtained from all participants. Taqman real-time PCR for endometrial SREBP1 and its systemic protein expression were analysed. Results: The BMI of women with PCOS (29.28 (±2.91) kg/m2) and controls (28.58 (±2.62) kg/m2) was not significantly different. Women with EC had a higher mean BMI (32.22 (±5.70) kg/m2). SREBP1 gene expression was significantly increased in PCOS and EC endometrium compared to controls (p<0.0001). SREBP1 gene expression was positively correlated with BMI (r=0.017, p=0.921) and waist-hip ratio (r=0.023, p=0.544) in PCOS, but this was not statistically significant. Similarly, statistically insignificant positive correlations were found between endometrial SREBP1 gene expression and BMI in EC (r=0.643, p=0.06) and waist-hip ratio (r=0.096, p=0.073). SREBP1 expression was significantly positively correlated with triglyceride in both PCOS and EC (p= 0.028 and p=0.027). Quantitative serum SREBP1 correlated with endometrial gene expression (p<0.05). Conclusions: SREBP1 gene expression is significantly increased in the endometrium of PCOS and EC women compared with controls and positively correlates with serum triglyceride in both PCOS and EC

Phytochrome-regulated EBL1 contributes to ACO1 upregulation in rice

The 1-aminocyclopropane-1-carboxylate oxidase gene (ACO1) was upregulated in rice (Oryza sativa L.) phyAphyBphyC mutants lacking any phytochrome and containing the GCC box element, a binding site for rice ethylene-responsive element binding protein 1 (OsEREBP1), in its promoter region. Since the OsEREBP1-like gene EBL1 (OsEREBP1-LIKE 1) was significantly downregulated in phyAphyBphyC mutants, EBL1 was suspected to repress ACO1 expression in wild-type plants. However, ACO1 was downregulated in EBL1 RNA interference plants, and the total length of these plants was slightly shorter than that of wild-type plants. This study shows that EBL1 is positively regulated by phytochrome B and associated with ACO1 upregulation

Insulin-Like Growth Factor-1 Induces Lipid Production in Human SEB-1 Sebocytes Via Sterol Response Element-Binding Protein-1

An understanding of the molecular signaling involved in sebaceous gland lipid production is needed to develop therapeutic targets to improve acne. Treatment with methylisobutylxanthine, dexamethasone, and a high dose of insulin (MDI) has been shown to differentiate 3T3-L1 preadipocytes into adipocytes, a differentiation marked by an increase in lipid production. The present study has the following aims: (1) Since high doses of insulin, as found in MDI, will activate the IGF-1 receptor, we sought to determine if IGF-1 is capable of reproducing the lipogenic effect seen with MDI treatment, and (2) to determine if the sterol response element-binding protein-1 (SREBP-1) pathway mediates the increase in lipogenesis. Here we report that MDI increases lipogenesis and that this effect can be attributed wholly to the high-dose insulin in SEB-1 cells. Further, we show that a physiologically relevant dose of IGF-1 or high-dose (1μm) insulin induces an increase in SREBP-1 mRNA, protein, and total lipid production; while 100nm insulin induces lipogenesis yet the SREBP protein levels remain unchanged. These data indicate that activation of the IGF-1 receptor increases lipogenesis in SEB-1 cells through both SREBP-dependent and SREBP-independent pathways