Sterol-regulated transport of SREBPs from endoplasmic reticulum to Golgi: Oxysterols block transport by binding to Insig

Radhakrishnan, Arun; Ikeda, Yukio; Kwon, Ho-Keun; Brown, Michael S.; Goldstein, Joseph L.

doi:10.1073/pnas.0700899104

Cited by 510 publications

(532 citation statements)

References 47 publications

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“…Although 25-HC does not bind Scap, this oxysterol eliminated cleavage in loop 4 in a manner similar to cholesterol (Fig. 6A, lanes 2 and 3) Previous studies showed that both cholesterol and 25-HC cause a conformational change in loop 6 of Scap that is dependent on Insigs (1), but they do it by different means (6,12,13). Cholesterol binds to Scap and causes Scap to bind to Insig proteins.…”

Section: Cholesterol-induced Changes In Loops 4 and 6 Of Scapmentioning

confidence: 99%

Cholesterol-induced conformational changes in the sterol-sensing domain of the Scap protein suggest feedback mechanism to control cholesterol synthesis

Gao¹,

Zhou²,

Goldstein

et al. 2017

Journal of Biological Chemistry

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Edited by George M. CarmanScap is a polytopic protein of endoplasmic reticulum (ER) membranes that transports sterol regulatory element-binding proteins to the Golgi complex for proteolytic activation. Cholesterol accumulation in ER membranes prevents Scap transport and decreases cholesterol synthesis. Previously, we provided evidence that cholesterol inhibition is initiated when cholesterol binds to loop 1 of Scap, which projects into the ER lumen. Within cells, this binding causes loop 1 to dissociate from loop 7, another luminal Scap loop. However, we have been unable to demonstrate this dissociation when we added cholesterol to isolated complexes of loops 1 and 7. We therefore speculated that the dissociation requires a conformational change in the intervening polytopic sequence separating loops 1 and 7. Here we demonstrate such a change using a protease protection assay in sealed membrane vesicles. In the absence of cholesterol, trypsin or proteinase K cleaved cytosolic loop 4, generating a protected fragment that we visualized with a monoclonal antibody against loop 1. When cholesterol was added to these membranes, cleavage in loop 4 was abolished. Because loop 4 is part of the so-called sterol-sensing domain separating loops 1 and 7, these results support the hypothesis that cholesterol binding to loop 1 alters the conformation of the sterol-sensing domain. They also suggest that this conformational change helps transmit the cholesterol signal from loop 1 to loop 7, thereby allowing separation of the loops and facilitating the feedback inhibition of cholesterol synthesis. These insights suggest a new structural model for cholesterol-mediated regulation of Scap activity.A membrane protein called Scap controls cholesterol homeostasis in animal cells. Scap facilitates the proteolytic activation of sterol regulatory element-binding proteins (SREBPs), 6 transcription factors that activate the genes encoding all of the enzymes required for synthesis of cholesterol and unsaturated fatty acids and their uptake from circulating plasma LDL (2). Scap is also the cholesterol sensor that turns off SREBP processing when cellular cholesterol levels are too high. Our laboratory has made recent progress in understanding the mechanism for this cholesterol regulation through a delineation of the conformational changes cholesterol produces when it binds to Scap (1, 3).Scap is a polytopic membrane protein with eight transmembrane helices that is synthesized on endoplasmic reticulum (ER) membranes (4). The carboxyl-terminal domain of Scap projects into the cytosol, where it binds to the cytosolic regulatory domain of SREBPs (5). Like Scap, SREBPs are synthesized on ER-bound ribosomes. Immediately after their synthesis, SREBPs bind to Scap. When ER cholesterol levels are low, Scap serves as the binding site for coat protein complex II (COPII) proteins that incorporate the Scap/SREBP complex into COPIIcoated vesicles that move to the Golgi (6). There the SREBPs are processed proteolytically to release their active transcription ...

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Section: Cholesterol-induced Changes In Loops 4 and 6 Of Scapmentioning

confidence: 99%

Cholesterol-induced conformational changes in the sterol-sensing domain of the Scap protein suggest feedback mechanism to control cholesterol synthesis

Gao¹,

Zhou²,

Goldstein

et al. 2017

Journal of Biological Chemistry

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“…The polytopic membrane region of SCAP contains a conserved sterol-sensing domain that is also found in other proteins involved in cholesterol regulation and signaling, such as HMG CoA reductase, NPC-1, and the hedgehog receptor Patched (Chang et al 2006). Cholesterol binds directly to mammalian SCAP and NPC-1 (Ohgami et al 2004;Radhakrishnan et al 2004;Infante et al 2008), and key metabolites modulate the binding of reductase and SCAP to the INSIG proteins (Sever et al 2003;Radhakrishnan et al 2007).…”

Section: Regulation Of Srebp Proteolytic Maturationmentioning

confidence: 99%

“…2; Sun et al 2007). The SCAP-INSIG association is regulated by the binding of regulatory sterols directly to INSIG or SCAP (Radhakrishnan et al 2007;Sun et al 2007). The polytopic membrane region of SCAP contains a conserved sterol-sensing domain that is also found in other proteins involved in cholesterol regulation and signaling, such as HMG CoA reductase, NPC-1, and the hedgehog receptor Patched (Chang et al 2006).…”

Section: Regulation Of Srebp Proteolytic Maturationmentioning

confidence: 99%

Evolutionary conservation and adaptation in the mechanism that regulates SREBP action: what a long, strange tRIP it's been

Osborne

Espenshade²

2009

Genes Dev.

230

249

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Sterol regulatory element-binding proteins (SREBPs) are a subfamily of basic helix–loop–helix leucine zipper (bHLH-LZ) transcription factors that are conserved from fungi to humans and are defined by two key features: a signature tyrosine residue in the DNA-binding domain, and a membrane-tethering domain that is a target for regulated proteolysis. Recent studies including genome-wide and model organism approaches indicate SREBPs coordinate cellular lipid metabolism with other cellular physiologic processes. These functions are broadly related as cellular adaptation to environmental changes ranging from nutrient fluctuations to toxin exposure. This review integrates classic features of the SREBP pathway with newer information regarding the regulation and sensing mechanisms that serve to assimilate different cellular physiologic processes for optimal function and growth.

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“…However, this oxysterol does not bind Scap, nor does it induce the conformational change in Scap (Adams et al 2004;Radhakrishnan et al 2004). Instead, 25-hydroxycholesterol binds to purified recombinant Insig proteins (Radhakrishnan et al 2007). Remarkably, Insigs do not bind to cholesterol.…”

Section: Regulation Of the Srebp Pathway In Cultured Cells Regulatedmentioning

confidence: 99%

Regulation of Cholesterol and Fatty Acid Synthesis

Jin

DeBose‐Boyd²

2011

Cold Spring Harbor Perspectives in Biology

207

148

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Sterol-regulated transport of SREBPs from endoplasmic reticulum to Golgi: Oxysterols block transport by binding to Insig

Cited by 510 publications

References 47 publications

Cholesterol-induced conformational changes in the sterol-sensing domain of the Scap protein suggest feedback mechanism to control cholesterol synthesis

Cholesterol-induced conformational changes in the sterol-sensing domain of the Scap protein suggest feedback mechanism to control cholesterol synthesis

Evolutionary conservation and adaptation in the mechanism that regulates SREBP action: what a long, strange tRIP it's been

Regulation of Cholesterol and Fatty Acid Synthesis

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