The role of collagen-specific molecular chaperone HSP47

HSP47最初被鉴定为一种位于内质网(ER)的胶原特异性应激蛋白。在新生的前胶原链进入内质网后，HSP47立即与内质网中的前胶原结合，并在顺式高尔基体网络中与之解离。Biacore生物传感器显示，HSP47与包括I-V型胶原在内的各种胶原蛋白的结合亲和力相似。HSP47的表达与不同细胞系和小鼠胚胎发育过程中I型到IV型胶原的表达密切相关。HSP47和I型、III型胶原在某些病理条件下也被诱导，如在四氯化碳引起的大鼠肝纤维化过程中。我们获得了几个稳定的转染体，其中HSP47的合成和积累受到适度和几乎完全的抑制。在低水平的HSP47细胞中，从蛋白质合成和mRNA积累的水平上观察到前胶原的表达受到抑制。除了对胶原合成的抑制外，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较低，这种抑制作用并不明显。接下来，我们尝试将编码I型胶原蛋白a1链的c DNA导入HSP47-反义转染细胞。在该双转染细胞中，HSP47的表达水平较低，而前胶原链的含量与对照细胞相当。在这些细胞中，我们发现在洗涤剂不溶部分中恢复了前胶原，这表明HSP47参与了内质网中前胶原链的溶解。

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 BALB c/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 al 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 al 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 a chains of procollagen in the ER.