The role of substrate-specific molecular chaperone in the trimerization of procollagen.

HSP47最初被鉴定为位于内质网（ER）的胶原特异性应激蛋白。HSP47在原胶原的新生链进入ER后立即与ER中的原胶原结合，并在顺式高尔基体网络中与其解离。使用BIAcore生物传感器显示HSP 47与包括I型至V型的各种类型的胶原的结合亲和力是相似的。在小鼠胚胎发育过程中，HSP 47的表达与I型至IV型胶原的表达密切相关。在某些病理条件下，如四氯化碳诱导的大鼠肝纤维化过程中，HSP 47和I、III型胶原也被诱导。我们获得了几个稳定的转染子，其中HSP 47的合成和积累被中度抑制，几乎完全抑制。在低水平HSP 47的细胞中，前胶原的表达在蛋白质合成和mRNA积累的水平上被观察到抑制。除了抑制胶原合成外，这些细胞中的前胶原分泌也受到抑制，尽管由于胶原合成水平低，抑制作用不太明显。然后，我们尝试将编码I型胶原α 1链的cDNA转染到HSP 47反义转染的细胞中。在该双转染子中，HSP 47的水平较低，而前胶原α 1链的量与对照细胞的量相当。在这些细胞中，我们发现，前胶原在洗涤剂不溶性部分中被回收，表明HSP 47参与ER中前胶原α链的溶解性。

HSP47 was originally identified as a collagen-specific stress protein located in the endoplasmic reticulum (ER). HSP47 binds to procollagen in the ER immediately after the nascent chain of procollagen enters the ER and dissociates from it in the cis-Golgi network. Binding affinity of HSP47 to various types of collagens including types I to V was revealed to be similar using BIAcore biosensor. The expression of HSP47 closely correlates with that of collagens including types I to IV in various cell lines and during the development of mouse embryos. Both HSP47 and types I and III collagens were also induced in some pathological conditions such as during the progression of liver fibrosis caused by the administration of carbon tetrachrolide into rats.We showed the results of the transfection of antisense RNA for HSP47 into BALBc/3T3 cells. We obtained several stable transfectants where the synthesis and accumulation of HSP47 were inhibited moderately and almost completely. The expression of procollagen was observed to be inhibited at levels of both protein synthesis and mRNA accumulation in the cells containing low level of HSP47. In addition to the inhibition of collagen synthesis, the secretion of procollagen was inhibited in these cells although the inhibition was not so evident because of the low level of collagen synthesis. Next, we tried to transfect the cDNA encoding alpha1 chain of type I collagen into the HSP47-antisense transfected cells. In this double transfectants, the level of HSP47 was low while the amount of procollagen alpha1 chain was comparable with that of control cells. In these cells, we found that procollagen was recovered in the detergent-insoluble fraction, indicating that HSP47 is involved in the solubility of alpha chains of pprocollagen in the ER.