scholarly journals Dislocation of HMG-CoA Reductase and Insig-1, Two Polytopic Endoplasmic Reticulum Proteins, En Route to Proteasomal Degradation

2009 ◽  
Vol 20 (14) ◽  
pp. 3330-3341 ◽  
Author(s):  
Gil S. Leichner ◽  
Rachel Avner ◽  
Dror Harats ◽  
Joseph Roitelman
Keyword(s):  
Endoplasmic Reticulum ◽  
Proteasomal Degradation ◽  
Metabolic Energy ◽  
Wild Type ◽  
Hmg Coa Reductase ◽  
Aaa Atpase ◽  
Rate Limiting Step ◽  
Coa Reductase ◽  
Rate Limiting ◽  
Membrane Region

The endoplasmic reticulum (ER) glycoprotein HMG-CoA reductase (HMGR) catalyzes the rate-limiting step in sterols biosynthesis. Mammalian HMGR is ubiquitinated and degraded by the proteasome when sterols accumulate in cells, representing the best example for metabolically controlled ER-associated degradation (ERAD). This regulated degradation involves the short-lived ER protein Insig-1. Here, we investigated the dislocation of these ERAD substrates to the cytosol en route to proteasomal degradation. We show that the tagged HMGR membrane region, HMG350-HA, the endogenous HMGR, and Insig-1-Myc, all polytopic membrane proteins, dislocate to the cytosol as intact full-length polypeptides. Dislocation of HMG350-HA and Insig-1-Myc requires metabolic energy and involves the AAA-ATPase p97/VCP. Sterols stimulate HMG350-HA and HMGR release to the cytosol concurrent with removal of their N-glycan by cytosolic peptide:N-glycanase. Sterols neither accelerate dislocation nor stimulate deglycosylation of ubiquitination-defective HMG350-HA(K89 + 248R) mutant. Dislocation of HMG350-HA depends on Insig-1-Myc, whose dislocation and degradation are sterol independent. Coimmunoprecipitation experiments demonstrate sterol-stimulated association between HMG350-HA and Insig-1-Myc. Sterols do not enhance binding to Insig-1-Myc of HMG350-HA mutated in its sterol-sensing domain or of HMG350-HA(K89 + 248R). Wild-type HMG350-HA and Insig-1-Myc coimmunoprecipitate from the soluble fraction only when both proteins were coexpressed in the same cell, indicating their encounter before or during dislocation, raising the possibility that they are dislocated as a tightly bound complex.

The effects of tunicamycin, mevinolin and mevalonic acid on HMG-CoA reductase activity and nuclear division in the myxomycete Physarum polycephalum

1989 ◽  
Vol 92 (3) ◽  
pp. 341-344
Author(s):  
W. Engstrom ◽  
O. Larsson ◽  
W. Sachsenmaier
Keyword(s):  
Physarum Polycephalum ◽  
Nuclear Division ◽  
Reductase Activity ◽  
Mevalonic Acid ◽  
Minor Effect ◽  
Hmg Coa Reductase ◽  
Rate Limiting Step ◽  
Coa Reductase ◽  
A Minor ◽  
Rate Limiting

The effects of two inhibitors of 3-hydroxy 3-methyl glutaryl-coenzyme A reductase (tunicamycin and mevinolin) on nuclear division in the myxomycete Physarum polycephalum were examined. Tunicamycin exerted a minor effect on division in synchronized cultures, whereas mevinolin delayed the second, third and fourth nuclear divisions with increasing efficiency. Mevinolin also appeared to be the more potent inhibitor of HMG-CoA reductase, which catalyses the rate-limiting step in the biosynthesis of cholesterol and other isoprene derivatives. These effects of mevinolin could be partially reversed by the addition of mevalonate, suggesting that mevinolin exerts its inhibitory effects on Physarum nuclear division by decreasing the activity of HMG-CoA reductase.

Posttranslational Regulation of HMG CoA Reductase, the Rate-Limiting Enzyme in Synthesis of Cholesterol

2021 ◽  
Vol 90 (1) ◽  
pp. 659-679
Author(s):  
Marc M. Schumacher ◽  
Russell A. DeBose-Boyd
Keyword(s):  
Endoplasmic Reticulum ◽  
Cholesterol Metabolism ◽  
Posttranslational Regulation ◽  
Hmg Coa Reductase ◽  
Feedback Mechanisms ◽  
Genetically Manipulated ◽  
Coa Reductase ◽  
Rate Limiting

The polytopic, endoplasmic reticulum (ER) membrane protein 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase produces mevalonate, the key intermediate in the synthesis of cholesterol and many nonsterol isoprenoids including geranylgeranyl pyrophosphate (GGpp). Transcriptional, translational, and posttranslational feedback mechanisms converge on this reductase to ensure cells maintain a sufficient supply of essential nonsterol isoprenoids but avoid overaccumulation of cholesterol and other sterols. The focus of this review is mechanisms for the posttranslational regulation of HMG CoA reductase, which include sterol-accelerated ubiquitination and ER-associated degradation (ERAD) that is augmented by GGpp. We discuss how GGpp-induced ER-to-Golgi trafficking of the vitamin K2 synthetic enzyme UbiA prenyltransferase domain–containing protein-1 (UBIAD1) modulates HMG CoA reductase ERAD to balance the synthesis of sterol and nonsterol isoprenoids. We also summarize the characterization of genetically manipulated mice, which established that sterol-accelerated, UBIAD1-modulated ERAD plays a major role in regulation of HMG CoA reductase and cholesterol metabolism in vivo.

Cholesterol metabolism in estrogen-sensitive progestin synthesis by rabbit corpus luteum

1986 ◽  
Vol 251 (4) ◽  
pp. E457-E463
Author(s):  
F. M. Wittmaack ◽  
J. A. Holt ◽  
J. R. Schreiber
Keyword(s):  
Cholesteryl Ester ◽  
De Novo ◽  
Reductase Activity ◽  
Side Chain ◽  
Inner Mitochondrial Membrane ◽  
Hmg Coa Reductase ◽  
Rate Limiting Step ◽  
Chain Cleavage ◽  
Coa Reductase ◽  
Rate Limiting

To learn whether either reduced de novo cholesterol synthesis and/or altered cholesteryl ester metabolism is responsible for the deficient progestin production induced by estrogen withdrawal from pseudopregnant rabbits, we measured the luteal activity of three enzymes: 1) 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (the rate-limiting step in de novo cholesterol synthesis), 2) cholesteryl ester hydrolase, and 3) acyl coenzyme A:cholesterol acyltransferase (ACAT) in estrogen-stimulated and estrogen-deprived rabbits. The only change in the activity of these enzymes and of the enzyme NADPH-cytochrome c reductase (a microsomal marker enzyme) after estrogen capsule removal for 12 or 24 h was a 30% decrease in HMG-CoA reductase activity after 24 h. The decrease in HMG-CoA reductase activity was not accompanied by a detectable change in either the content or localization of cellular free cholesterol. Previous data from our laboratory have demonstrated that 24 h of estrogen deprivation has no effect on inner mitochondrial membrane P-450 side-chain cleavage activity (a rate-limiting step in the conversion of cholesterol to steroid hormones). These data, and our earlier finding that estrogen deprivation leads to accumulation of cholesteryl ester in the luteal cells, indicate that estrogen maintains rabbit luteal progestin production by stimulating the transfer of cytoplasmic cholesterol to the active site of P-450 side-chain cleavage on the inner mitochondrial membrane.

scholarly journals Type 1 polyisoprenoid diphosphate phosphatase modulates geranylgeranyl-mediated control of HMG CoA reductase and UBIAD1

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Rania Elsabrouty ◽  
Youngah Jo ◽  
Seonghwan Hwang ◽  
Dong-Jae Jun ◽  
Russell A DeBose-Boyd
Keyword(s):  
Endoplasmic Reticulum ◽  
Vitamin K ◽  
Feedback Mechanism ◽  
Hmg Coa Reductase ◽  
Golgi Transport ◽  
Coa Reductase ◽  
Rate Limiting ◽  
Hydrolysis Of ◽  
Alcohol Derivative

UbiA prenyltransferase domain-containing protein-1 (UBIAD1) utilizes geranylgeranyl pyrophosphate (GGpp) to synthesize the vitamin K2 subtype menaquinone-4. The prenyltransferase has emerged as a key regulator of sterol-accelerated, endoplasmic reticulum (ER)-associated degradation (ERAD) of HMG CoA reductase, the rate-limiting enzyme in synthesis of cholesterol and nonsterol isoprenoids including GGpp. Sterols induce binding of UBIAD1 to reductase, inhibiting its ERAD. Geranylgeraniol (GGOH), the alcohol derivative of GGpp, disrupts this binding and thereby stimulates ERAD of reductase and translocation of UBIAD1 to Golgi. We now show that overexpression of Type 1 polyisoprenoid diphosphate phosphatase (PDP1), which dephosphorylates GGpp and other isoprenyl pyrophosphates to corresponding isoprenols, abolishes protein geranylgeranylation as well as GGOH-induced ERAD of reductase and Golgi transport of UBIAD1. Conversely, these reactions are enhanced in the absence of PDP1. Our findings indicate PDP1-mediated hydrolysis of GGpp significantly contributes to a feedback mechanism that maintains optimal intracellular levels of the nonsterol isoprenoid.

scholarly journals Maturation of the Na,K-ATPase in the Endoplasmic Reticulum in Health and Disease

2021 ◽  
Author(s):  
Vitalii Kryvenko ◽  
Olga Vagin ◽  
Laura A. Dada ◽  
Jacob I. Sznajder ◽  
István Vadász
Keyword(s):  
Endoplasmic Reticulum ◽  
Intracellular Signaling ◽  
Loss Of Function ◽  
Α Subunit ◽  
Rate Limiting Step ◽  
Atpase Subunits ◽  
A Cell ◽  
Health And Disease ◽  
And Function ◽  
Rate Limiting

Abstract The Na,K-ATPase establishes the electrochemical gradient of cells by driving an active exchange of Na+ and K+ ions while consuming ATP. The minimal functional transporter consists of a catalytic α-subunit and a β-subunit with chaperon activity. The Na,K-ATPase also functions as a cell adhesion molecule and participates in various intracellular signaling pathways. The maturation and trafficking of the Na,K-ATPase include co- and post-translational processing of the enzyme in the endoplasmic reticulum (ER) and the Golgi apparatus and subsequent delivery to the plasma membrane (PM). The ER folding of the enzyme is considered as the rate-limiting step in the membrane delivery of the protein. It has been demonstrated that only assembled Na,K-ATPase α:β-complexes may exit the organelle, whereas unassembled, misfolded or unfolded subunits are retained in the ER and are subsequently degraded. Loss of function of the Na,K-ATPase has been associated with lung, heart, kidney and neurological disorders. Recently, it has been shown that ER dysfunction, in particular, alterations in the homeostasis of the organelle, as well as impaired ER-resident chaperone activity may impede folding of Na,K-ATPase subunits, thus decreasing the abundance and function of the enzyme at the PM. Here, we summarize our current understanding on maturation and subsequent processing of the Na,K-ATPase in the ER under physiological and pathophysiological conditions. Graphic Abstract

scholarly journals Retrograde trafficking of Argonaute 2 acts as a rate-limiting step for de novo miRNP formation on endoplasmic reticulum–attached polysomes in mammalian cells

2020 ◽  
Vol 3 (2) ◽  
pp. e201800161 ◽  
Author(s):  
Mainak Bose ◽  
Susanta Chatterjee ◽  
Yogaditya Chakrabarty ◽  
Bahnisikha Barman ◽  
Suvendra N Bhattacharyya
Keyword(s):  
Endoplasmic Reticulum ◽  
Mammalian Cells ◽  
De Novo ◽  
Mirna Biogenesis ◽  
Argonaute 2 ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Cellular Context ◽  
Subcellular Compartmentalization ◽  
Rate Limiting

microRNAs are short regulatory RNAs in metazoan cells. Regulation of miRNA activity and abundance is evident in human cells where availability of target messages can influence miRNA biogenesis by augmenting the Dicer1-dependent processing of precursors to mature microRNAs. Requirement of subcellular compartmentalization of Ago2, the key component of miRNA repression machineries, for the controlled biogenesis of miRNPs is reported here. The process predominantly happens on the polysomes attached with the endoplasmic reticulum for which the subcellular Ago2 trafficking is found to be essential. Mitochondrial tethering of endoplasmic reticulum and its interaction with endosomes controls Ago2 availability. In cells with depolarized mitochondria, miRNA biogenesis gets impaired, which results in lowering of de novo–formed mature miRNA levels and accumulation of miRNA-free Ago2 on endosomes that fails to interact with Dicer1 and to traffic back to endoplasmic reticulum for de novo miRNA loading. Thus, mitochondria by sensing the cellular context regulates Ago2 trafficking at the subcellular level, which acts as a rate-limiting step in miRNA biogenesis process in mammalian cells.

scholarly journals Dissection of the asynchronous transport of intestinal microvillar hydrolases to the cell surface.

1988 ◽  
Vol 106 (6) ◽  
pp. 1853-1861 ◽  
Author(s):  
B Stieger ◽  
K Matter ◽  
B Baur ◽  
K Bucher ◽  
M Höchli ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Surface ◽  
Intracellular Transport ◽  
Colon Adenocarcinoma ◽  
Subcellular Fractionation ◽  
Adenocarcinoma Cell Line ◽  
Dipeptidylpeptidase Iv ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Novel subcellular fractionation procedures and pulse-chase techniques were used to study the intracellular transport of the microvillar membrane hydrolases sucrase-isomaltase and dipeptidylpeptidase IV in the differentiated colon adenocarcinoma cell line Caco-2. The overall rate of transport to the cell surface was two fold faster for dipeptidylpeptidase IV than for sucrase-isomaltase, while no significant differences were observed in transport rates from the site of complex glycosylation to the brush border. The delayed arrival of sucrase-isomaltase in the compartment where complex glycosylation occurs was only in part due to exit from the endoplasmic reticulum. A major slow-down could be ascribed to maturation in and transit of this enzyme through the Golgi apparatus. These results suggest that the observed asynchronism is due to more than one rate-limiting step along the rough endoplasmic reticulum to trans-Golgi pathway.

scholarly journals The sterol-responsive RNF145 E3 ubiquitin ligase mediates the degradation of HMG-CoA reductase together with gp78 and Hrd1

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Sam A Menzies ◽  
Norbert Volkmar ◽  
Dick JH van den Boomen ◽  
Richard T Timms ◽  
Anna S Dickson ◽  
...  
Keyword(s):  
Ubiquitin Ligase ◽  
Critical Role ◽  
E3 Ubiquitin Ligase ◽  
E3 Ligase ◽  
Editorial Note ◽  
Hmg Coa Reductase ◽  
Genome Wide ◽  
Cholesterol Biosynthetic Pathway ◽  
Coa Reductase ◽  
Rate Limiting

Mammalian HMG-CoA reductase (HMGCR), the rate-limiting enzyme of the cholesterol biosynthetic pathway and the therapeutic target of statins, is post-transcriptionally regulated by sterol-accelerated degradation. Under cholesterol-replete conditions, HMGCR is ubiquitinated and degraded, but the identity of the E3 ubiquitin ligase(s) responsible for mammalian HMGCR turnover remains controversial. Using systematic, unbiased CRISPR/Cas9 genome-wide screens with a sterol-sensitive endogenous HMGCR reporter, we comprehensively map the E3 ligase landscape required for sterol-accelerated HMGCR degradation. We find that RNF145 and gp78 independently co-ordinate HMGCR ubiquitination and degradation. RNF145, a sterol-responsive ER-resident E3 ligase, is unstable but accumulates following sterol depletion. Sterol addition triggers RNF145 recruitment to HMGCR via Insigs, promoting HMGCR ubiquitination and proteasome-mediated degradation. In the absence of both RNF145 and gp78, Hrd1, a third UBE2G2-dependent E3 ligase, partially regulates HMGCR activity. Our findings reveal a critical role for the sterol-responsive RNF145 in HMGCR regulation and elucidate the complexity of sterol-accelerated HMGCR degradation.Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (<xref ref-type="decision-letter" rid="SA1">see decision letter</xref>).

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