Sterol-regulated transport of SREBPs from endoplasmic reticulum to Golgi: Insig renders sorting signal in Scap inaccessible to COPII proteins

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Abstract

Two classes of sterols, cholesterol and oxysterols, block export of sterol regulatory element-binding proteins (SREBPs) from the endoplasmic reticulum (ER) to the Golgi by preventing the binding of COPII-coated proteins to a hexapeptide sorting signal (MELADL) in Scap, the SREBP-escort protein. Here, we show that anti-MELADL blocks COPII binding in vitro, and microinjection of Fab anti-MELADL blocks Scap·SREBP movement in cells. Cholesterol and oxysterols block COPII binding to MELADL by binding to different intracellular receptors, cholesterol to Scap and oxysterols to Insig. Cysteine labeling shows that both binding events produce a conformational change near the MELADL sequence, abrogating COPII binding but not anti-MELADL binding. Mutagenesis experiments raise the possibility that the distance of MELADL from the ER membrane is crucial for COPII binding, and we speculate that sterols and Insig block SREBP transport by altering the location of MELADL with respect to the membrane, rendering it inaccessible to COPII proteins.

Original languageEnglish (US)
Pages (from-to)6519-6526
Number of pages8
JournalProceedings of the National Academy of Sciences of the United States of America
Volume104
Issue number16
DOIs
StatePublished - Apr 17 2007

Keywords

  • COPII vesicles
  • Cholesterol homeostasis
  • Oxysterols
  • SREBP pathway

ASJC Scopus subject areas

  • General

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