Autophagic elimination of misfolded procollagen aggregates in the endoplasmic reticulum as a means of cell protection.
Type I collagen is a major component of the extracellular matrix, and mutations in the collagen gene cause several matrix-associated diseases. These mutant procollagens are misfolded and often aggregated in the endoplasmic reticulum (ER). Although the misfolded procollagens are potentially toxic to the cell, little is known about how they are eliminated from the ER. Here, we show that procollagen that can initially trimerize but then aggregates in the ER are eliminated by an autophagy-lysosome pathway, but not by the ER-associated degradation (ERAD) pathway. Inhibition of autophagy by specific inhibitors or RNAi-mediated knockdown of an autophagy-related gene significantly stimulated accumulation of aggregated procollagen trimers in the ER, and activation of autophagy with rapamycin resulted in reduced amount of aggregates. In contrast, a mutant procollagen which has a compromised ability to form trimers was degraded by ERAD. Moreover, we found that autophagy plays an essential role in protecting cells against the toxicity of the ERAD-inefficient procollagen aggregates. The autophagic elimination of aggregated procollagen occurs independently of the ERAD system. These results indicate that autophagy is a final cell protection strategy deployed against ER-accumulated cytotoxic aggregates that are not able to be removed by ERAD.
Department of Molecular and Cellular Biology, Institute for Frontier Medical Sciences, Kyoto University, Kyoto, Japan.
Yoshihito
Y
Ishida
Akitsugu
A
Yamamoto
Akira
A
Kitamura
Shireen R
SR
Lamandé
Tamotsu
T
Yoshimori
John F
JF
Bateman
Hiroshi
H
Kubota
Kazuhiro
K
Nagata
D000818:Animals; D001343:Autophagy; D015153:Blotting, Western; D002460:Cell Line; D024042:Collagen Type I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D036681:Fluorescence Recovery After Photobleaching; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D050958:HSP47 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D047468:Immunoprecipitation; D007976:Leupeptins / Q000494:pharmacology; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism*; D018942:Macrolides / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D009154:Mutation; D017510:Protein Folding; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection
D024042:Collagen Type I; D004791:Enzyme Inhibitors; D050958:HSP47 Heat-Shock Proteins; D007976:Leupeptins; D018942:Macrolides; D011993:Recombinant Fusion Proteins; C494661:Serpinh1 protein, mouse; C057620:bafilomycin A; D049452:Green Fluorescent Proteins; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde