Adipose Triglyceride Lipase is needed for homeostatic control of Sterol Element-Binding Protein-1c driven hepatic lipogenesis

AbstractSterol Regulatory Element-Binding Protein-1c (SREBP-1c) is translated as an inactive precursor-protein that is proteolytically activated to promote fatty-acid (FA) biosynthesis, when unsaturated (u)FAs are scarce. During fasting, however, lipogenesis is low, and adipose-tissue lipolysis supplies the organism with FAs. Adipose TriGlyceride Lipase (ATGL) is the rate-limiting enzyme for lipolysis, and it preferentially hydrolyzes uFAs. Therefore, we hypothesized that ATGL-derived FAs may suppress the proteolytic activation of SREBP-1c in the liver. Here we show that (i) SREBP-1c is inactive during fasting but active after refeeding, (ii) uFA species liberated by ATGL suppress SREBP-1c activation in vitro, (iii) SREBP-1c is hyper-activated in livers of mice lacking ATGL, and (iv) pharmacological inhibition of ATGL selectively activates SREBP-1c in hepatocytes. Our findings highlight an ATGL/SREBP-1c axis, instrumental to coordinate lipogenesis and lipolysis, whose homeostatic regulation is crucial to avoid severe diseases including diabetes, cardiomyopathy, and even cancer.

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A New Role for Sterol Regulatory Element Binding Protein 1 Transcription Factors in the Regulation of Muscle Mass and Muscle Cell Differentiation

Molecular and Cellular Biology ◽

10.1128/mcb.00690-09 ◽

2009 ◽

Vol 30 (5) ◽

pp. 1182-1198 ◽

Cited By ~ 54

Author(s):

Virginie Lecomte ◽

Emmanuelle Meugnier ◽

Vanessa Euthine ◽

Christine Durand ◽

Damien Freyssenet ◽

...

Keyword(s):

Transcription Factors ◽

Muscle Mass ◽

Target Genes ◽

Binding Protein ◽

Regulatory Element ◽

Element Binding Protein ◽

Sterol Regulatory Element ◽

Myogenic Program

ABSTRACT The role of the transcription factors sterol regulatory element binding protein 1a (SREBP-1a) and SREBP-1c in the regulation of cholesterol and fatty acid metabolism has been well studied; however, little is known about their specific function in muscle. In the present study, analysis of recent microarray data from muscle cells overexpressing SREBP1 suggested that they may play a role in the regulation of myogenesis. We then demonstrated that SREBP-1a and -1c inhibit myoblast-to-myotube differentiation and also induce in vivo and in vitro muscle atrophy. Furthermore, we have identified the transcriptional repressors BHLHB2 and BHLHB3 as mediators of these effects of SREBP-1a and -1c in muscle. Both repressors are SREBP-1 target genes, and they affect the expression of numerous genes involved in the myogenic program. Our findings identify a new role for SREBP-1 transcription factors in muscle, thus linking the control of muscle mass to metabolic pathways.

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Insulin activates the rat sterol-regulatory-element-binding protein 1c (SREBP-1c) promoter through the combinatorial actions of SREBP, LXR, Sp-1 and NF-Y cis-acting elements

Biochemical Journal ◽

10.1042/bj20040162 ◽

2004 ◽

Vol 385 (1) ◽

pp. 207-216 ◽

Cited By ~ 104

Author(s):

Lauren M. CAGEN ◽

Xiong DENG ◽

Henry G. WILCOX ◽

Edwards A. PARK ◽

Rajendra RAGHOW ◽

...

Keyword(s):

Binding Protein ◽

Regulatory Element ◽

Ectopic Expression ◽

Rat Hepatocytes ◽

Luciferase Reporter ◽

Luciferase Reporter Gene ◽

Cis Acting ◽

Element Binding Protein ◽

Sterol Regulatory Element

The enhanced synthesis of fatty acids in the liver and adipose tissue in response to insulin is critically dependent on the transcription factor SREBP-1c (sterol-regulatory-element-binding protein 1c). Insulin increases the expression of the SREBP-1c gene in intact liver and in hepatocytes cultured in vitro. To learn the mechanism of this stimulation, we analysed the activation of the rat SREBP-1c promoter and its truncated or mutated congeners driving a luciferase reporter gene in transiently transfected rat hepatocytes. The rat SREBP-1c promoter contains binding sites for LXR (liver X receptor), Sp1, NF-Y (nuclear factor-Y) and SREBP itself. We have found that each of these sites is required for the full stimulatory response of the SREBP-1c promoter to insulin. Mutation of either the putative LXREs (LXR response elements) or the SRE (sterol response element) in the proximal SREBP-1c promoter reduced the stimulatory effect of insulin by about 50%. Insulin and the LXR agonist TO901317 increased the association of SREBP-1 with the SREBP-1c promoter. Ectopic expression of LXRα or SREBP-1c increased activity of the SREBP-1c promoter, and this effect is further enhanced by insulin. The Sp1 and NF-Y sites adjacent to the SRE are also required for full activation of the SREBP-1c promoter by insulin. We propose that the combined actions of the SRE, LXREs, Sp1 and NF-Y elements constitute an insulin-responsive cis-acting unit of the SREBP-1c gene in the liver.

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Abstract 109: Preliminary Structural Into the Sterol Regulatory Element-Binding Protein (SREBP) Interaction With SREBP Cleavage-Activating Protein (SCAP)

Arteriosclerosis Thrombosis and Vascular Biology ◽

10.1161/atvb.33.suppl_1.a109 ◽

2013 ◽

Vol 33 (suppl_1) ◽

Author(s):

Joshua J Ziarek ◽

Gerhard Wagner

Keyword(s):

Drug Targets ◽

Binding Protein ◽

Protein Localization ◽

Recombinant Expression ◽

Regulatory Element ◽

Future Research ◽

Binding Interface ◽

Element Binding Protein ◽

Sterol Regulatory Element

Maintenance of cholesterol and fatty acid homeostasis is critical for membrane architecture, protein localization, and protein trafficking. Dysregulation can lead to severe health concerns including obesity, diabetes, heart attack and stroke. Vital to the management of lipid molecules are the sterol regulatory element binding protein (SREBP) family of transcription factors, which transcribe more than 30 genes controlling lipid homeostasis. The activation of SREBP is tightly regulated through association with SREBP cleavage-activating protein (SCAP). When sterol levels are high, SCAP maintains SREBP in the endoplasmic reticulum. As sterol concentrations are reduced, SCAP escorts SREBP to the Golgi apparatus where it is activated. Liver-specific knockout of SCAP results in a 70-80% decrease in lipid biosynthesis and germline knockout is hypothesized to be embryonic lethal. Nonetheless, how SCAP recognizes and restricts the location of SREBP is relatively unknown. Structural insight to this protein-protein interface may yield future drug targets; however, their large molecular mass makes them challenging. We hypothesize both CTDs can be functionally produced in vitro to investigate the complex affinity, stoichiometry, and architecture. So far, we have recombinantly produced milligram quantities of both proteins. Circular dichroism and 1D NMR spectroscopy support in vitro SCAP refolding into a β-propeller fold. In contrast to previously published suggestions of a seven-bladed propeller motif, our sequence analysis and homology modeling support an eight-bladed architecture. Both X-ray crystallography and NMR are currently being pursued to elucidate the SCAP structure. In conclusion, recombinant expression of SCAP and SREBP is feasible and future research will use a combined biochemical and cell-based approach to determine the complex affinity, dynamics, and binding interface.

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Proteolytic Activation of Sterol Regulatory Element-binding Protein Induced by Cellular Stress through Depletion of Insig-1

Journal of Biological Chemistry ◽

10.1074/jbc.m408235200 ◽

2004 ◽

Vol 279 (43) ◽

pp. 45257-45265 ◽

Cited By ~ 138

Author(s):

Joon No Lee ◽

Jin Ye

Keyword(s):

Binding Protein ◽

Regulatory Element ◽

Cellular Stress ◽

Proteolytic Activation ◽

Element Binding Protein ◽

Sterol Regulatory Element

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Sterol regulatory element-binding protein 1 is negatively modulated by PKA phosphorylation

AJP Cell Physiology ◽

10.1152/ajpcell.00374.2005 ◽

2006 ◽

Vol 290 (6) ◽

pp. C1477-C1486 ◽

Cited By ~ 58

Author(s):

Min Lu ◽

John Y.-J. Shyy

Keyword(s):

Chromatin Immunoprecipitation ◽

Hepg2 Cells ◽

Binding Protein ◽

Regulatory Element ◽

Phosphorylation Site ◽

Chromatin Immunoprecipitation Assay ◽

Element Binding Protein ◽

Sterol Regulatory Element ◽

Pka Pathway

Sterol regulatory element-binding protein (SREBP)-1a and -1c are key transcription factors that regulate lipid biosynthesis in cells. We identified that Ser338 located at the NH2 terminus of SREBP-1a is a PKA phosphorylation site in vitro and in HepG2 cells. PKA phosphorylation of this site attenuated DNA occupancy, as revealed by chromatin immunoprecipitation assay, and the ensuing transactivation. In contrast, replacing Ser with Ala [SREBP-1a(N)-S338A] increased transactivation. Although it forms heterodimers with the wild-type SREBP-1a(N) or S338A but not a homodimer with itself, SREBP-1a(N)-S338D (replacing Ser with Asp) decreased DNA binding. Ser314 of SREBP-1c, the counterpart of SREBP-1a Ser338, was also phosphorylated by PKA. Accordingly, the adenovirus-mediated expression of SREBP-1c(N)-S314D in HepG2 cells retarded lipogenesis. Our results indicate that the cAMP-PKA pathway, by phosphorylating SREBP-1, may modulate lipid metabolism in liver cell lines.

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Docosahexaenoic Acid Suppresses Expression of Adipogenic Tetranectin through Sterol Regulatory Element-Binding Protein and Forkhead Box O Protein in Pigs

Nutrients ◽

10.3390/nu13072315 ◽

2021 ◽

Vol 13 (7) ◽

pp. 2315

Author(s):

Jui-Ting Yang ◽

Yu-Jen Chen ◽

Chao-Wei Huang ◽

Ya-Chin Wang ◽

Harry J. Mersmann ◽

...

Keyword(s):

Fatty Acids ◽

Binding Sites ◽

Binding Protein ◽

Regulatory Element ◽

Forkhead Box ◽

Transcriptional Suppression ◽

Element Binding Protein ◽

Sterol Regulatory Element

Tetranectin (TN), a plasminogen-binding protein originally involved in fibrinolysis and bone formation, was later identified as a secreted adipokine from human and rat adipocytes and positively correlated with adipogenesis and lipid metabolism in adipocytes. To elucidate the nutritional regulation of adipogenic TN from diets containing different sources of fatty acids (saturated, n-6, n-3) in adipocytes, we cloned the coding region of porcine TN from a cDNA library and analyzed tissue expressions in weaned piglets fed with 2% soybean oil (SB, enriched in n-6 fatty acids), docosahexaenoic acid oil (DHA, an n-3 fatty acid) or beef tallow (BT, enriched in saturated and n-9 fatty acids) for 30 d. Compared with tissues in the BT- or SB-fed group, expression of TN was reduced in the adipose, liver and lung tissues from the DHA-fed group, accompanied with lowered plasma levels of triglycerides and cholesterols. This in vivo reduction was also confirmed in porcine primary differentiated adipocytes supplemented with DHA in vitro. Then, promoter analysis was performed. A 1956-bp putative porcine TN promoter was cloned and transcription binding sites for sterol regulatory-element binding protein (SREBP)-1c or forkhead box O proteins (FoxO) were predicted on the TN promoter. Mutating binding sites on porcine TN promoters showed that transcriptional suppression of TN by DHA on promoter activity was dependent on specific response elements for SREBP-1c or FoxO. The inhibited luciferase promoter activity by DHA on the TN promoter coincides with reduced gene expression of TN, SREBP-1c, and FoxO1 in human embryonic kidney HEK293T cells supplemented with DHA. To conclude, our current study demonstrated that the adipogenic TN was negatively regulated by nutritional modulation of DHA both in pigs in vivo and in humans/pigs in vitro. The transcriptional suppression by DHA on TN expression was partly through SREBP-1c or FoxO. Therefore, down-regulation of adipogenic tetranectin associated with fibrinolysis and adipogenesis may contribute to the beneficial effects of DHA on ameliorating obesity-induced metabolic syndromes such as atherosclerosis and adipose dysfunctions.

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