Department of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda University, Shinjuku, Tokyo, 169-8555, Japan.
Nippi Research Institute of Biomatrix, 520-11 Kuwabara, Toride, Ibaraki, 302-0017, Japan.
Sci Rep. 2019 Nov 22;9(1):17433. doi: 10.1038/s41598-019-53962-0.
Heat shock protein 47 (HSP47) is an endoplasmic reticulum (ER)-resident molecular chaperone that specifically recognizes triple helical portions of procollagens. The chaperone function of HSP47 is indispensable in mammals, and hsp47-null mice show an embryonic lethal phenotype accompanied by severe abnormalities in collagen-based tissue structures. Two leading hypotheses are currently accepted for the molecular function of HSP47 as a procollagen-specific chaperone. One is facilitation of procollagen folding by stabilizing thermally unstable triple helical folding intermediates, and the other is inhibition of procollagen aggregation or lateral association in the ER. The aim of this study was to elucidate the functional essence of this unique chaperone using fibroblasts established from hsp47-/- mouse embryos. When the cells were cultured at 37 °C, various defects in procollagen biosynthesis were observed, such as accumulation in the ER, over-modifications including prolyl hydroxylation, lysyl hydroxylation, and further glycosylation, and unusual secretion of type I collagen homotrimer. All defects were corrected by culturing the cells at a lower temperature of 33 °C. These results indicated that lowering the culture temperature compensated for the loss of HSP47. This study elucidated that HSP47 stabilizes the elongating triple helix of procollagens, which is otherwise unstable at the body temperature of mammals.
热休克蛋白 47（HSP47）是一种内质网（ER）驻留的分子伴侣，它特异性地识别前胶原的三螺旋部分。在哺乳动物中，HSP47 的伴侣功能是不可或缺的，hsp47 基因敲除小鼠表现出胚胎致死表型，并伴有基于胶原蛋白的组织结构严重异常。目前，HSP47 作为前胶原特异性伴侣的分子功能有两个主要假说。一种假说认为它通过稳定热不稳定的三螺旋折叠中间体来促进前胶原折叠，另一种假说认为它抑制 ER 中前胶原的聚集或侧向缔合。本研究旨在利用从 hsp47-/- 小鼠胚胎中建立的成纤维细胞来阐明这种独特伴侣的功能本质。当细胞在 37°C 下培养时，观察到前胶原生物合成的各种缺陷，如在 ER 中的积累、过度修饰，包括脯氨酰羟化、赖氨酰羟化和进一步糖基化，以及 I 型胶原同源三聚体的异常分泌。所有缺陷都可以通过在 33°C 的较低温度下培养细胞来纠正。这些结果表明，降低培养温度可以弥补 HSP47 的缺失。本研究阐明了 HSP47 稳定了前胶原延伸的三螺旋，否则在哺乳动物体温下是不稳定的。
