TY - JOUR
T1 - Sterol-regulated degradation of insig-1 mediated by the membrane-bound ubiquitin ligase gp78
AU - Joon, No Lee
AU - Song, Baoliang
AU - DeBose-Boyd, Russell A.
AU - Ye, Jin
PY - 2006/12/22
Y1 - 2006/12/22
N2 - Insig-1 and Insig-2, closely related endoplasmic reticulum membrane proteins, mediate transcriptional and post-transcriptional mechanisms that assure cholesterol homeostasis through their sterol-induced binding to Scap (SREBP cleavage-activating protein) and 3-hydroxy-3-methylglutaryl coenzyme A reductase. Recent studies show that Insig-1 (but not Insig-2) is ubiquitinated and rapidly degraded when cells are depleted of sterols. Conversely, ubiquitination of Insig-1 is blocked, and the protein is stabilized when intracellular sterols accumulate. Here, we report that the ubiquitin ligase gp78, which binds with much higher affinity to Insig-1 than Insig-2, is required for ubiquitination and degradation of Insig-1 in sterol-depleted cells. Sterols prevent Insig-1 ubiquitination and degradation by displacing gp78 from Insig-1, an event that results from sterol-induced binding of Scap to Insig-1. In addition to providing a mechanism for sterol-regulated degradation of Insig-1, these results help to explain why Scap is subject to endoplasmic reticulum retention upon Insig-1 binding, whereas 3-hydroxy-3-methylglutaryl coenzyme A reductase is ubiquitinated and degraded.
AB - Insig-1 and Insig-2, closely related endoplasmic reticulum membrane proteins, mediate transcriptional and post-transcriptional mechanisms that assure cholesterol homeostasis through their sterol-induced binding to Scap (SREBP cleavage-activating protein) and 3-hydroxy-3-methylglutaryl coenzyme A reductase. Recent studies show that Insig-1 (but not Insig-2) is ubiquitinated and rapidly degraded when cells are depleted of sterols. Conversely, ubiquitination of Insig-1 is blocked, and the protein is stabilized when intracellular sterols accumulate. Here, we report that the ubiquitin ligase gp78, which binds with much higher affinity to Insig-1 than Insig-2, is required for ubiquitination and degradation of Insig-1 in sterol-depleted cells. Sterols prevent Insig-1 ubiquitination and degradation by displacing gp78 from Insig-1, an event that results from sterol-induced binding of Scap to Insig-1. In addition to providing a mechanism for sterol-regulated degradation of Insig-1, these results help to explain why Scap is subject to endoplasmic reticulum retention upon Insig-1 binding, whereas 3-hydroxy-3-methylglutaryl coenzyme A reductase is ubiquitinated and degraded.
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U2 - 10.1074/jbc.M608999200
DO - 10.1074/jbc.M608999200
M3 - Article
C2 - 17043353
AN - SCOPUS:33846013601
SN - 0021-9258
VL - 281
SP - 39308
EP - 39315
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 51
ER -