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

  1. Marc M Schumacher
  2. Rania Elsabrouty
  3. Joachim Seemann
  4. Youngah Jo
  5. Russell A DeBose-Boyd  Is a corresponding author
  1. University of Texas Southwestern Medical Center, United States
  2. University of Texas Southwestern Medial Center, United States
  3. Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, 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.

Article and author information

Author details

  1. Marc M Schumacher

    Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States
    Competing interests
    The authors declare that no competing interests exist.
  2. Rania Elsabrouty

    Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, United States
    Competing interests
    The authors declare that no competing interests exist.
  3. Joachim Seemann

    Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, United States
    Competing interests
    The authors declare that no competing interests exist.
  4. Youngah Jo

    Department of Molecular Genetics, University of Texas Southwestern Medial Center, Dallas, United States
    Competing interests
    The authors declare that no competing interests exist.
  5. Russell A DeBose-Boyd

    Department of Molecular Genetics, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, United States
    For correspondence
    Russell.Debose-Boyd@utsouthwestern.edu
    Competing interests
    The authors declare that no competing interests exist.

Reviewing Editor

  1. Ramanujan S Hegde, MRC Laboratory of Molecular Biology, United Kingdom

Publication history

  1. Received: November 11, 2014
  2. Accepted: March 4, 2015
  3. Accepted Manuscript published: March 5, 2015 (version 1)
  4. Version of Record published: March 26, 2015 (version 2)

Copyright

© 2015, Schumacher et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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  1. Marc M Schumacher
  2. Rania Elsabrouty
  3. Joachim Seemann
  4. Youngah Jo
  5. Russell A DeBose-Boyd
(2015)
The prenyltransferase UBIAD1 is the target of geranylgeraniol in degradation of HMG CoA reductase
eLife 4:e05560.
https://doi.org/10.7554/eLife.05560

Further reading

    1. Biochemistry and Chemical Biology
    2. Cell Biology
    Youngah Jo et al.
    Research Advance Updated

    Autosomal-dominant Schnyder corneal dystrophy (SCD) is characterized by corneal opacification owing to overaccumulation of cholesterol. SCD is caused by mutations in UBIAD1, which utilizes geranylgeranyl pyrophosphate (GGpp) to synthesize vitamin K2. Using cultured cells, we previously showed that sterols trigger binding of UBIAD1 to the cholesterol biosynthetic enzyme HMG CoA reductase (HMGCR), thereby inhibiting its endoplasmic reticulum (ER)-associated degradation (ERAD) (Schumacher et al. 2015). GGpp triggers release of UBIAD1 from HMGCR, allowing maximal ERAD and ER-to-Golgi transport of UBIAD1. SCD-associated UBIAD1 resists GGpp-induced release and is sequestered in ER to inhibit ERAD. We now report knockin mice expressing SCD-associated UBIAD1 accumulate HMGCR in several tissues resulting from ER sequestration of mutant UBIAD1 and inhibition of HMGCR ERAD. Corneas from aged knockin mice exhibit signs of opacification and sterol overaccumulation. These results establish the physiological significance of UBIAD1 in cholesterol homeostasis and indicate inhibition of HMGCR ERAD contributes to SCD pathogenesis.

    1. Biochemistry and Chemical Biology
    2. Chromosomes and Gene Expression
    Ryo Fujisawa et al.
    Research Article Updated

    The p97/Cdc48 ATPase and its ubiquitin receptors Ufd1-Npl4 are essential to unfold ubiquitylated proteins in many areas of eukaryotic cell biology. In yeast, Cdc48-Ufd1-Npl4 is controlled by a quality control mechanism, whereby substrates must be conjugated to at least five ubiquitins. Here, we show that mammalian p97-UFD1-NPL4 is governed by a complex interplay between additional p97 cofactors and the number of conjugated ubiquitins. Using reconstituted assays for the disassembly of ubiquitylated CMG (Cdc45-MCM-GINS) helicase by human p97-UFD1-NPL4, we show that the unfoldase has a high ubiquitin threshold for substrate unfolding, which can be reduced by the UBX proteins UBXN7, FAF1, or FAF2. Our data indicate that the UBX proteins function by binding to p97-UFD1-NPL4 and stabilising productive interactions between UFD1-NPL4 and K48-linked chains of at least five ubiquitins. Stimulation by UBXN7 is dependent upon known ubiquitin-binding motifs, whereas FAF1 and FAF2 use a previously uncharacterised coiled-coil domain to reduce the ubiquitin threshold of p97-UFD1-NPL4. We show that deleting the Ubnx7 and Faf1 genes impairs CMG disassembly during S-phase and mitosis and sensitises cells to reduced ubiquitin ligase activity. These findings indicate that multiple UBX proteins are important for the efficient unfolding of ubiquitylated proteins by p97-UFD1-NPL4 in mammalian cells.