Stefanovic B, Hellerbrand C, Brenner D A
Departments of Medicine and Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
Mol Cell Biol. 1999 Jun;19(6):4334-42. doi: 10.1128/MCB.19.6.4334.
Three fibrillar collagen mRNAs, alpha1(I), alpha2(I), and alpha1(III), are coordinately upregulated in the activated hepatic stellate cell (hsc) in liver fibrosis. These three mRNAs contain sequences surrounding the start codon that can be folded into a stem-loop structure. We investigated the role of this stem-loop structure in expression of collagen alpha1(I) reporter mRNAs in hsc's and fibroblasts. The stem-loop dramatically decreases accumulation of mRNAs in quiescent hsc's and to a lesser extent in activated hsc's and fibroblasts. The stem-loop decreases mRNA stability in fibroblasts. In activated hsc's and fibroblasts, a protein complex binds to the stem-loop, and this binding requires the presence of a 7mG cap on the RNA. Placing the 3' untranslated region (UTR) of collagen alpha1(I) mRNA in a reporter mRNA containing this stem-loop further increases the steady-state level in activated hsc's. This 3' UTR binds alphaCP, a protein implicated in increasing stability of collagen alpha1(I) mRNA in activated hsc's (B. Stefanovic, C. Hellerbrand, M. Holcik, M. Briendl, S. A. Liebhaber, and D. A. Brenner, Mol. Cell. Biol. 17:5201-5209, 1997). A set of protein complexes assembles on the 7mG capped stem-loop RNA, and a 120-kDa protein is specifically cross-linked to this structure. Thus, collagen alpha1(I) mRNA is regulated by a complex interaction between the 5' stem-loop and the 3' UTR, which may optimize collagen production in activated hsc's.
在肝纤维化过程中，三种原纤维胶原蛋白mRNA，即α1(I)、α2(I)和α1(III)，在活化的肝星状细胞（hsc）中协同上调。这三种mRNA在起始密码子周围包含可折叠成茎环结构的序列。我们研究了这种茎环结构在hsc和成纤维细胞中胶原蛋白α1(I)报告基因mRNA表达中的作用。该茎环显著降低了静止hsc中mRNA的积累，在活化的hsc和成纤维细胞中降低程度较小。茎环降低了成纤维细胞中mRNA的稳定性。在活化的hsc和成纤维细胞中，一种蛋白质复合物与茎环结合，这种结合需要RNA上存在7mG帽。将胶原蛋白α1(I) mRNA的3'非翻译区（UTR）置于含有该茎环的报告基因mRNA中，可进一步提高活化hsc中的稳态水平。该3'UTR结合αCP，αCP是一种与活化hsc中胶原蛋白α1(I) mRNA稳定性增加有关的蛋白质（B. Stefanovic、C. Hellerbrand、M. Holcik、M. Briendl、S. A. Liebhaber和D. A. Brenner，《分子细胞生物学》17:5201 - 5209，1997）。一组蛋白质复合物在7mG加帽的茎环RNA上组装，一种120 kDa的蛋白质与该结构特异性交联。因此，胶原蛋白α1(I) mRNA受5'茎环和3'UTR之间复杂相互作用的调节，这可能在活化的hsc中优化胶原蛋白的产生。
