A role for smooth endoplasmic reticulum membrane cholesterol ester in determining the intracellular location and regulation of sterol-regulatory-element-binding protein-2

2001 ◽  
Vol 358 (2) ◽  
pp. 415-422 ◽  
Author(s):  
Christopher R. IDDON ◽  
Jane WILKINSON ◽  
Andrew J. BENNETT ◽  
Julie BENNETT ◽  
Andrew M. SALTER ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Cholesterol Ester ◽  
Smooth Endoplasmic Reticulum ◽  
Regulatory Element ◽  
Membrane Cholesterol ◽  
Endoplasmic Reticulum Membrane ◽  
Cellular Cholesterol ◽  
Element Binding Protein ◽  
Sterol Regulatory Element ◽  
Coa Reductase

Cellular cholesterol homoeostasis is regulated through proteolysis of the membrane-bound precursor sterol-regulatory-element-binding protein (SREBP) that releases the mature transcription factor form, which regulates gene expression. Our aim was to identify the nature and intracellular site of the putative sterol-regulatory pool which regulates SREBP proteolysis in hamster liver. Cholesterol metabolism was modulated by feeding hamsters control chow, or a cholesterol-enriched diet, or by treatment with simvastatin or with the oral acyl-CoA:cholesterol acyltransferase inhibitor C1-1011 plus cholesterol. The effects of the different treatments on SREBP activation were confirmed by determination of the mRNAs for the low-density lipoprotein receptor and hydroxymethylglutaryl-CoA (HMG-CoA) reductase and by measurement of HMG-CoA reductase activity. The endoplasmic reticulum was isolated from livers and separated into subfractions by centrifugation in self-generating iodixanol gradients. Immunodetectable SREBP-2 accumulated in the smooth endoplasmic reticulum of cholesterol-fed animals. Cholesterol ester levels of the smooth endoplasmic reticulum membrane (but not the cholesterol levels) increased after cholesterol feeding and fell after treatment with simvastatin or C1-1011. The results suggest that an increased cellular cholesterol load causes accumulation of SREBP-2 in the smooth endoplasmic reticulum and, therefore, that membrane cholesterol ester may be one signal allowing exit of the SREBP-2/SREBP-cleavage-regulating protein complex to the Golgi.

scholarly journals Effectors of Rapid Homeostatic Responses of Endoplasmic Reticulum Cholesterol and 3-Hydroxy-3-methylglutaryl-CoA Reductase

2007 ◽  
Vol 283 (3) ◽  
pp. 1445-1455 ◽  
Author(s):  
Yvonne Lange ◽  
Daniel S. Ory ◽  
Jin Ye ◽  
Michael H. Lanier ◽  
Fong-Fu Hsu ◽  
...  
Keyword(s):  
Gene Expression ◽  
Endoplasmic Reticulum ◽  
Regulatory Element ◽  
Cholesterol Content ◽  
Cholesterol Levels ◽  
Element Binding Protein ◽  
Sterol Regulatory Element ◽  
Hmgr Activity ◽  
Coa Reductase ◽  
Cholesterol Precursors

The cholesterol content of the endoplasmic reticulum (ER) and the activity of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) imbedded therein respond homeostatically within minutes to changes in the level of plasma membrane cholesterol. We have now examined the roles of sterol regulatory element-binding protein (SREBP)-dependent gene expression, side chain oxysterol biosynthesis, and cholesterol precursors in the short term regulation of ER cholesterol levels and HMGR activity. We found that SREBP-dependent gene expression is not required for the response to changes in cell cholesterol of either the pool of ER cholesterol or the rate of cholesterol esterification. It was also found that the acute proteolytic inactivation of HMGR triggered by cholesterol loading required the conversion of cholesterol to 27-hydroxycholesterol. High levels of exogenous 24,25-dihydrolanosterol drove the inactivation of HMGR; lanosterol did not. However, purging endogenous 24,25-dihydrolanosterol, lanosterol, and other biosynthetic sterol intermediates by treating cells with NB-598 did not greatly affect either the setting of their ER cholesterol pool or the inactivation of their HMGR. In summary, neither SREBP-regulated genes nor 27-hydroxycholesterol is involved in setting the ER cholesterol pool. On the other hand, 27-hydroxycholesterol, rather than cholesterol itself or biosynthetic precursors of cholesterol, stimulates the rapid inactivation of HMGR in response to high levels of cholesterol.

New insights into the activation of sterol regulatory element-binding proteins by proteolytic processing

2013 ◽  
Vol 4 (4) ◽  
pp. 417-423 ◽  
Author(s):  
Jun Inoue ◽  
Ryuichiro Sato
Keyword(s):  
Endoplasmic Reticulum ◽  
Small Molecules ◽  
Recent Progress ◽  
Binding Proteins ◽  
Regulatory Element ◽  
Acid Synthesis ◽  
Proteolytic Processing ◽  
Endoplasmic Reticulum Membrane ◽  
Post Translational Modification ◽  
Sterol Regulatory Element

AbstractSterol regulatory element-binding proteins (SREBPs) are transcription factors that regulate a wide variety of genes involved in cholesterol and fatty acid synthesis. After transcription, SREBPs are controlled at multiple post-transcriptional levels, including proteolytic processing and post-translational modification. Among these, proteolytic processing is a crucial regulatory step that activates SREBPs, which are synthesized as inactive endoplasmic reticulum membrane proteins. In this review, we focus on recent progress with regard to signaling pathways and small molecules that affect activation of SREBPs by proteolytic processing.

Modulation of human Niemann-Pick C1-like 1 gene expression by sterol: role of sterol regulatory element binding protein 2

2007 ◽  
Vol 292 (1) ◽  
pp. G369-G376 ◽  
Author(s):  
Waddah A. Alrefai ◽  
Fadi Annaba ◽  
Zaheer Sarwar ◽  
Alka Dwivedi ◽  
Seema Saksena ◽  
...  
Keyword(s):  
Promoter Activity ◽  
Binding Protein ◽  
Regulatory Element ◽  
Cholesterol Absorption ◽  
Cholesterol Depletion ◽  
Element Binding Protein ◽  
Sterol Regulatory Element ◽  
Niemann Pick ◽  
Coa Reductase

Niemann-Pick C1-like 1 (NPC1L1) is an essential intestinal component of cholesterol absorption. However, little is known about the molecular regulation of intestinal NPC1L1 expression and promoter activity. We demonstrated that human NPC1L1 mRNA expression was significantly decreased by 25-hydroxycholesterol but increased in response to cellular cholesterol depletion achieved by incubation with Mevinolin (an inhibitor of 3-hydroxy-3-methylglutaryl-CoA reductase) in human intestinal Caco-2 cells. We also showed that a −1741/+56 fragment of the NPC1L1 gene demonstrated high promoter activity in Caco-2 cells that was reduced by 25-hydroxycholesterol and stimulated by cholesterol depletion. Interestingly, we showed that the NPC1L1 promoter is remarkably transactivated by the overexpression of sterol regulatory element (SRE) binding protein (SREBP)-2, suggesting its involvement in the sterol-induced alteration in NPC1L1 promoter activity. Finally, we identified two putative SREs in the human NPC1L1 promoter and established their essential roles in mediating the effects of cholesterol on promoter activity. Our study demonstrated the modulation of human NPC1L1 expression and promoter activity by cholesterol in a SREBP-2-dependent mechanism.

Regulated intramembrane proteolysis: from the endoplasmic reticulum to the nucleus

2002 ◽  
Vol 38 ◽  
pp. 155-168 ◽  
Author(s):  
Robert B Rawson
Keyword(s):  
Endoplasmic Reticulum ◽  
Regulatory Element ◽  
Transmembrane Proteins ◽  
Intramembrane Proteolysis ◽  
Regulated Intramembrane Proteolysis ◽  
Class 1 ◽  
Element Binding Protein ◽  
Sterol Regulatory Element ◽  
Membrane Spanning ◽  
Highly Hydrophobic

Regulated intramembrane proteolysis (Rip) is an ancient and widespread process by which cells transmit information from one compartment (the endoplasmic reticulum) to another (the nucleus). Two separate cleavages that are carried out by two separate proteases are required for Rip. The first protease cleaves its protein substrate within an extracytoplasmic domain; the second cleaves it within a membrane-spanning domain, releasing a functionally active fragment of the target protein. In eukaryotes, examples of Rip can be divided into two classes, according to the proteases that are involved and the orientation of the substrates with the membrane. Class 1 Rip involves type 1 transmembrane proteins and requires presenilin for cleavage within a membrane-spanning domain. In Class 2 Rip, the highly hydrophobic metalloprotease, site-2 protease, is required for cleavage within a membrane-spanning domain and substrates are type 2 transmembrane proteins. Both classes of Rip are implicated in diseases that are important in modern societies, such as hyperlipidaemias (via the sterol regulatory element binding protein pathway) and Alzheimer's disease (via processing of the amyloid precursor protein.)

scholarly journals Subunit Architecture of the Golgi Dsc E3 Ligase Required for Sterol Regulatory Element-binding Protein (SREBP) Cleavage in Fission Yeast

2013 ◽  
Vol 288 (29) ◽  
pp. 21043-21054 ◽  
Author(s):  
S. Julie-Ann Lloyd ◽  
Sumana Raychaudhuri ◽  
Peter J. Espenshade
Keyword(s):  
Endoplasmic Reticulum ◽  
Fission Yeast ◽  
Binding Protein ◽  
Regulatory Element ◽  
E3 Ligase ◽  
E3 Ligases ◽  
Endoplasmic Reticulum Associated Degradation ◽  
Element Binding Protein ◽  
Uba Domain ◽  
Sterol Regulatory Element

The membrane-bound sterol regulatory element-binding protein (SREBP) transcription factors regulate lipogenesis in mammalian cells and are activated through sequential cleavage by the Golgi-localized Site-1 and Site-2 proteases. The mechanism of fission yeast SREBP cleavage is less well defined and, in contrast, requires the Golgi-localized Dsc E3 ligase complex. The Dsc E3 ligase consists of five integral membrane subunits, Dsc1 through Dsc5, and resembles membrane E3 ligases that function in endoplasmic reticulum-associated degradation. Using immunoprecipitation assays and blue native electrophoresis, we determined the subunit architecture for the complex of Dsc1 through Dsc5, showing that the Dsc proteins form subcomplexes and display defined connectivity. Dsc2 is a rhomboid pseudoprotease family member homologous to mammalian UBAC2 and a central component of the Dsc E3 ligase. We identified conservation in the architecture of the Dsc E3 ligase and the multisubunit E3 ligase gp78 in mammals. Specifically, Dsc1-Dsc2-Dsc5 forms a complex resembling gp78-UBAC2-UBXD8. Further characterization of Dsc2 revealed that its C-terminal UBA domain can bind to ubiquitin chains but that the Dsc2 UBA domain is not essential for yeast SREBP cleavage. Based on the ability of rhomboid superfamily members to bind transmembrane proteins, we speculate that Dsc2 functions in SREBP recognition and binding. Homologs of Dsc1 through Dsc4 are required for SREBP cleavage and virulence in the human opportunistic pathogen Aspergillus fumigatus. Thus, these studies advance our organizational understanding of multisubunit E3 ligases involved in endoplasmic reticulum-associated degradation and fungal pathogenesis.

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