title: Type I collagen in Hsp47-null cells is aggregated in endoplasmic reticulum and deficient in N-propeptide processing and fibrillogenesis.
abstract: Heat-shock protein of 47 kDa (Hsp47) is a molecular chaperone that recognizes collagen triple helices in the endoplasmic reticulum (ER). Hsp47-knockout mouse embryos are deficient in the maturation of collagen types I and IV, and collagen triple helices formed in the absence of Hsp47 show increased susceptibility to protease digestion. We show here that the fibrils of type I collagen produced by Hsp47-/- cells are abnormally thin and frequently branched. Type I collagen was highly accumulated in the ER of Hsp47-/- cells, and its secretion rate was much slower than that of Hsp47+/+ cells, leading to accumulation of the insoluble aggregate of type I collagen within the cells. Transient expression of Hsp47 in the Hsp47-/- cells restored normal extracellular fibril formation and intracellular localization of type I collagen. Intriguingly, type I collagen with unprocessed N-terminal propeptide (N-propeptide) was secreted from Hsp47-/- cells and accumulated in the extracellular matrix. These results indicate that Hsp47 is required for correct folding and prevention of aggregation of type I collagen in the ER and that this function is indispensable for efficient secretion, processing, and fibril formation of collagen.
authors.affiliation: Department of Molecular and Cellular Biology, Institute for Frontier Medical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8397, Japan.
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Ishida
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kubota
authors.forename: Akitsugu
authors.initials: A
authors.lastname: Yamamoto
authors.forename: Akira
authors.initials: A
authors.lastname: Kitamura
authors.forename: Hans Peter
authors.initials: HP
authors.lastname: Bächinger
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Nagata
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D024042:Collagen Type I / Q000032:analysis / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D005347:Fibroblasts / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D050958:HSP47 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D017510:Protein Folding; D021381:Protein Transport; D012995:Solubility
chemical_list: D024042:Collagen Type I; D050958:HSP47 Heat-Shock Proteins; C494661:Serpinh1 protein, mouse