TY - JOUR
T1 - Regulated endoplasmic reticulum-associated degradation of a polytopic protein
T2 - p97 recruits proteasomes to Insig-1 before extraction from membranes
AU - Ikeda, Yukio
AU - DeMartino, George N.
AU - Brown, Michael S.
AU - Lee, Joon No
AU - Goldstein, Joseph L.
AU - Ye, Jin
PY - 2009/12/11
Y1 - 2009/12/11
N2 - Polytopic membrane proteins subjected to endoplasmic reticulum (ER)-associated degradation are extracted from membranes and targeted to proteasomes for destruction. The extraction mechanism is poorly understood. One polytopic ER protein subjected to ER-associated degradation is Insig-1, a negative regulator of cholesterol synthesis. Insig-1 is rapidly degraded by proteasomes when cells are depleted of cholesterol, and its degradation is inhibited when sterols accumulate in cells. Insig-2, a functional homologue of Insig-1, is degraded slowly, and its degradation is not regulated by sterols. Here, we report that a single amino acid substitution in Insig-2, Insig-2(L210A), causes Insig-2 to be degraded in an accelerated and sterol-regulated manner similar to Insig-1. In seeking an explanation for the accelerated degradation, we found that proteasomes bind to wild type Insig-1 and mutant Insig-2(L210A) but not to wild type Insig-2, whereas the proteins are still embedded in cell membranes. This binding depends on at least two factors, ubiquitination of Insig and association with the ATPase p97/ VCP complex. These data suggest that p97 recruits proteasomes to polytopic ER proteins even before they are extracted from membranes.
AB - Polytopic membrane proteins subjected to endoplasmic reticulum (ER)-associated degradation are extracted from membranes and targeted to proteasomes for destruction. The extraction mechanism is poorly understood. One polytopic ER protein subjected to ER-associated degradation is Insig-1, a negative regulator of cholesterol synthesis. Insig-1 is rapidly degraded by proteasomes when cells are depleted of cholesterol, and its degradation is inhibited when sterols accumulate in cells. Insig-2, a functional homologue of Insig-1, is degraded slowly, and its degradation is not regulated by sterols. Here, we report that a single amino acid substitution in Insig-2, Insig-2(L210A), causes Insig-2 to be degraded in an accelerated and sterol-regulated manner similar to Insig-1. In seeking an explanation for the accelerated degradation, we found that proteasomes bind to wild type Insig-1 and mutant Insig-2(L210A) but not to wild type Insig-2, whereas the proteins are still embedded in cell membranes. This binding depends on at least two factors, ubiquitination of Insig and association with the ATPase p97/ VCP complex. These data suggest that p97 recruits proteasomes to polytopic ER proteins even before they are extracted from membranes.
UR - http://www.scopus.com/inward/record.url?scp=71749117369&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=71749117369&partnerID=8YFLogxK
U2 - 10.1074/jbc.M109.044875
DO - 10.1074/jbc.M109.044875
M3 - Article
C2 - 19815544
AN - SCOPUS:71749117369
SN - 0021-9258
VL - 284
SP - 34889
EP - 34900
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 50
ER -