Transcriptional control mechanism for the expression of type I collagen gene in fibrotic skin disorders and related diseases

I型胶原是真皮中含量最丰富的一种蛋白质，由两个α(I)链和一个α2(I)链组成，它们是协同表达的。ColF1是一种DNA结合蛋白，它与α2(I)胶原启动子转录起始上游-400bp处的一段特异结合，在体外激活α2(I)胶原基因的转录。我们对α2(I)胶原蛋白基因的部分多肽序列及其转录因子的克隆进行了研究。序列特异性DNA亲和层析纯化的蛋白质由42 kDa和40.5 kDa两种多肽组成。42 kDa多肽的多肽序列与Purα完全相同，Purα是一种核蛋白，已报道与人c-myc基因的上游区域结合。其中一些40 kDa多肽与Purβ完全相同，已被部分测序，并与Purα有很强的同源性。Purα和Purβ的推导氨基酸序列具有61.4%的同源性。已有研究表明，在体外老化的成纤维细胞培养中，真皮中含量最丰富的I型胶原蛋白的表达减少，但控制I型胶原蛋白表达减少的机制尚不清楚。我们发现在晚期传代的成纤维细胞中，α(I)型胶原、转化生长因子β、转化生长因子β受体I和II的mRNA水平降低，并且晚期传代的成纤维细胞的转化生长因子β受体结合量低于早期传代的成纤维细胞。

Collagen type I,a most abundant protein in the dermis, consists of two alphal(I) chain and one alpha2(I) chain which are coordinately expressed. ColFl, a DNA binding protein which specifically binds to a segment of the alpha2(I)collagen promoter at -400bp upstream of the start of transcription, activates transcription of the alpha2(I)collagen gene in vitro. We investigated on the partial sequences of polypeptide and the cDNA cloning of this transcriptional factor of the alpha2(I)collagen gene. The protein purified by sequence-specific DNA affinity chromatography were found to consist of 42kDa and 40.5 kDa polypeptides. Sequences of peptide fragments from 42kDa polypeptide were identical to Pur alpha, is a nuclear protein which has been reported to binds to a upstream region of human c-myc gene. Some of those from 40kDa polypeptide were identical to Pur beta, has been partially sequenced and has regions of strong homology to Pur alpha Full length of Pur beta cDNA were sequenced. The deductive amino acid sequences of Pur alpha and Pur beta showed 61.4% homology. Previous studies have demonstrated that the expression of type I collagen, the most abundant protein in the dermis, is reduced in in vitro aging fibroblast cultures, but the mechanism controlling the reduction of type I collagen expression is not understood. We found that the mRNA levels of alphal(I) collagen, TGFbeta, and TGFbeta receptors I and II in late-passage fibroblasts were reduced, and the TGF beta receptor binding in late-passage fibroblasts was lower than that in early-passage fibroblasts.