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The prenyltransferase UBIAD1 is the target of geranylgeraniol in degradation of HMG CoA reductase.

Schumacher MM, Elsabrouty R, Seemann J, Jo Y, DeBose-Boyd RA - Elife (2015)

Bottom Line: Here, we show that sterols stimulate binding of UBIAD1 to the cholesterol biosynthetic enzyme HMG CoA reductase, which is subject to sterol-accelerated, endoplasmic reticulum (ER)-associated degradation augmented by the nonsterol isoprenoid geranylgeraniol through an unknown mechanism.CRISPR-CAS9-mediated knockout of UBIAD1 relieves the geranylgeraniol requirement for reductase degradation.The current results identify UBIAD1 as the elusive target of geranylgeraniol in reductase degradation, the inhibition of which may contribute to accumulation of cholesterol in SCD.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States.

ABSTRACT
Schnyder corneal dystrophy (SCD) is an autosomal dominant disorder in humans characterized by abnormal accumulation of cholesterol in the cornea. SCD-associated mutations have been identified in the gene encoding UBIAD1, a prenyltransferase that synthesizes vitamin K2. Here, we show that sterols stimulate binding of UBIAD1 to the cholesterol biosynthetic enzyme HMG CoA reductase, which is subject to sterol-accelerated, endoplasmic reticulum (ER)-associated degradation augmented by the nonsterol isoprenoid geranylgeraniol through an unknown mechanism. Geranylgeraniol inhibits binding of UBIAD1 to reductase, allowing its degradation and promoting transport of UBIAD1 from the ER to the Golgi. CRISPR-CAS9-mediated knockout of UBIAD1 relieves the geranylgeraniol requirement for reductase degradation. SCD-associated mutations in UBIAD1 block its displacement from reductase in the presence of geranylgeraniol, thereby preventing degradation of reductase. The current results identify UBIAD1 as the elusive target of geranylgeraniol in reductase degradation, the inhibition of which may contribute to accumulation of cholesterol in SCD.

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Insig-mediated, sterol-accelerated degradation of HMG CoA reductase in mammalian cells.DOI:http://dx.doi.org/10.7554/eLife.05560.004
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fig2: Insig-mediated, sterol-accelerated degradation of HMG CoA reductase in mammalian cells.DOI:http://dx.doi.org/10.7554/eLife.05560.004

Mentions: The ERAD of reductase is initiated by intracellular accumulation of sterols, which causes the enzyme to bind to ER membrane proteins called Insig-1 and Insig-2 (Sever et al., 2003a, 2003b) (Figure 2). Insig binding occurs through the membrane domain of reductase, which contains eight membrane-spanning helices and precedes a large cytosolic domain with enzymatic activity (Liscum et al., 1985; Roitelman et al., 1992). Insig-associated ubiquitin ligases gp78 and Trc8 facilitate ubiquitination of cytosolically exposed lysine residues in the membrane domain of reductase (Sever et al., 2003a; Song et al., 2005; Jo et al., 2011; Liu et al., 2012). This ubiquitination marks reductase for recognition by the AAA (ATPases associated with diverse cellular activities)-ATPase VCP/p97, which mediates extraction of reductase across ER membranes (Morris et al., 2014). Once extracted, ubiquitinated reductase is then released into the cytosol and delivered into the proteolytic chamber of the 20S proteasome through reactions mediated by the proteasome 19S regulatory particle, which contains six AAA-ATPases (Ehlinger and Walters, 2013). Geranylgeraniol, the alcohol derivative of geranylgeranyl pyrophosphate, augments sterol-accelerated ERAD of reductase but does not appreciably affect sterol-induced ubiquitination (Sever et al., 2003a). This observation led to the notion that geranylgeraniol augments post-ubiquitination steps in reductase ERAD (Figure 2). Indeed, geranylgeraniol enhances sterol-induced membrane extraction and cytosolic dislocation of reductase as judged by assays carried out in vitro and in intact cells (Song and DeBose-Boyd, 2004; Elsabrouty et al., 2013; Morris et al., 2014).10.7554/eLife.05560.004Figure 2.Insig-mediated, sterol-accelerated degradation of HMG CoA reductase in mammalian cells.


The prenyltransferase UBIAD1 is the target of geranylgeraniol in degradation of HMG CoA reductase.

Schumacher MM, Elsabrouty R, Seemann J, Jo Y, DeBose-Boyd RA - Elife (2015)

Insig-mediated, sterol-accelerated degradation of HMG CoA reductase in mammalian cells.DOI:http://dx.doi.org/10.7554/eLife.05560.004
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4374513&req=5

fig2: Insig-mediated, sterol-accelerated degradation of HMG CoA reductase in mammalian cells.DOI:http://dx.doi.org/10.7554/eLife.05560.004
Mentions: The ERAD of reductase is initiated by intracellular accumulation of sterols, which causes the enzyme to bind to ER membrane proteins called Insig-1 and Insig-2 (Sever et al., 2003a, 2003b) (Figure 2). Insig binding occurs through the membrane domain of reductase, which contains eight membrane-spanning helices and precedes a large cytosolic domain with enzymatic activity (Liscum et al., 1985; Roitelman et al., 1992). Insig-associated ubiquitin ligases gp78 and Trc8 facilitate ubiquitination of cytosolically exposed lysine residues in the membrane domain of reductase (Sever et al., 2003a; Song et al., 2005; Jo et al., 2011; Liu et al., 2012). This ubiquitination marks reductase for recognition by the AAA (ATPases associated with diverse cellular activities)-ATPase VCP/p97, which mediates extraction of reductase across ER membranes (Morris et al., 2014). Once extracted, ubiquitinated reductase is then released into the cytosol and delivered into the proteolytic chamber of the 20S proteasome through reactions mediated by the proteasome 19S regulatory particle, which contains six AAA-ATPases (Ehlinger and Walters, 2013). Geranylgeraniol, the alcohol derivative of geranylgeranyl pyrophosphate, augments sterol-accelerated ERAD of reductase but does not appreciably affect sterol-induced ubiquitination (Sever et al., 2003a). This observation led to the notion that geranylgeraniol augments post-ubiquitination steps in reductase ERAD (Figure 2). Indeed, geranylgeraniol enhances sterol-induced membrane extraction and cytosolic dislocation of reductase as judged by assays carried out in vitro and in intact cells (Song and DeBose-Boyd, 2004; Elsabrouty et al., 2013; Morris et al., 2014).10.7554/eLife.05560.004Figure 2.Insig-mediated, sterol-accelerated degradation of HMG CoA reductase in mammalian cells.

Bottom Line: Here, we show that sterols stimulate binding of UBIAD1 to the cholesterol biosynthetic enzyme HMG CoA reductase, which is subject to sterol-accelerated, endoplasmic reticulum (ER)-associated degradation augmented by the nonsterol isoprenoid geranylgeraniol through an unknown mechanism.CRISPR-CAS9-mediated knockout of UBIAD1 relieves the geranylgeraniol requirement for reductase degradation.The current results identify UBIAD1 as the elusive target of geranylgeraniol in reductase degradation, the inhibition of which may contribute to accumulation of cholesterol in SCD.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States.

ABSTRACT
Schnyder corneal dystrophy (SCD) is an autosomal dominant disorder in humans characterized by abnormal accumulation of cholesterol in the cornea. SCD-associated mutations have been identified in the gene encoding UBIAD1, a prenyltransferase that synthesizes vitamin K2. Here, we show that sterols stimulate binding of UBIAD1 to the cholesterol biosynthetic enzyme HMG CoA reductase, which is subject to sterol-accelerated, endoplasmic reticulum (ER)-associated degradation augmented by the nonsterol isoprenoid geranylgeraniol through an unknown mechanism. Geranylgeraniol inhibits binding of UBIAD1 to reductase, allowing its degradation and promoting transport of UBIAD1 from the ER to the Golgi. CRISPR-CAS9-mediated knockout of UBIAD1 relieves the geranylgeraniol requirement for reductase degradation. SCD-associated mutations in UBIAD1 block its displacement from reductase in the presence of geranylgeraniol, thereby preventing degradation of reductase. The current results identify UBIAD1 as the elusive target of geranylgeraniol in reductase degradation, the inhibition of which may contribute to accumulation of cholesterol in SCD.

Show MeSH
Related in: MedlinePlus