The role of collagen-specific molecular chaperone HSP47

HSP47最初被确定为位于内质网（ER）的胶原特异性应激蛋白。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，并在顺式高尔基网络中与之分离。利用BIAcore生物传感器发现，HSP47对包括I型到V型在内的各种类型胶原的结合亲和力相似。HSP47在各种细胞系和小鼠胚胎发育过程中与I ~ IV型胶原的表达密切相关。在一些病理条件下，如在四氯化碳致大鼠肝纤维化的进展过程中，HSP47和I型和III型胶原也被诱导。我们展示了HSP47反义RNA转染BALB c/3T3细胞的结果。我们获得了几种稳定的转染物，其中HSP47的合成和积累被适度和几乎完全抑制。在含有低水平HSP47的细胞中，前胶原蛋白的表达在蛋白合成和mRNA积累水平上均受到抑制。除了抑制胶原合成外，这些细胞的前胶原分泌也受到抑制，但由于胶原合成水平低，抑制作用不那么明显。接下来，我们尝试将编码I型胶原al链的cDNA转染到hsp47反义转染的细胞中。在这种双转染中，HSP47水平较低，而前胶原链的数量与对照细胞相当。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，这表明HSP47参与了前胶原链在内质网中的溶解性。

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 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.