Roy S G, Nozaki Y, Phan S H
Department of Pathology, University of Michigan Medical School, 48109-0602, Ann Arbor, MI, USA.
Int J Biochem Cell Biol. 2001 Jul;33(7):723-34. doi: 10.1016/s1357-2725(01)00041-3.
Myofibroblasts express alpha-smooth muscle actin and have a phenotype intermediate between fibroblasts and smooth muscle cells. Their emergence can be induced by cytokines such as transforming growth factor beta; but the regulatory mechanism for induction of alpha-smooth muscle actin gene expression in myofibroblast differentiation has not been determined. To examine this mechanism at the level of the alpha-smooth muscle actin promoter, rat lung fibroblasts were transfected with varying lengths of the alpha-smooth muscle actin promoter linked to the chloramphenicol acetyl transferase reporter gene and treated with transforming growth factor beta1. The results show that the shortest inducible promoter was 150 base pairs long, suggesting the presence in this region of cis-elements of potential importance in transforming growth factor beta1 induced myofibroblast differentiation. Transfection of "decoy" oligonucleotides corresponding to sequences for four suspected regulatory factors demonstrated that only the transforming growth factor beta control element is involved in the regulation of transforming growth factor beta1-induced alpha-smooth muscle actin expression in myofibroblast differentiation. Consistent with this conclusion is the finding that a mutation in the transforming growth factor beta control element caused a significant reduction in promoter activity. These observations taken together show that alpha-smooth muscle actin promoter regulation during myofibroblast differentiation is uniquely different from that in smooth muscle cells and other cell lines. Since myofibroblasts play a key role in wound contraction and synthesis of extracellular matrix, clarification of this differentiation mechanism should provide new insight into fibrogenesis and suggest future novel strategies for modulation of wound healing and controlling fibrosis.
肌成纤维细胞表达α-平滑肌肌动蛋白，其表型介于成纤维细胞和平滑肌细胞之间。它们的出现可由细胞因子如转化生长因子β诱导；但在肌成纤维细胞分化过程中诱导α-平滑肌肌动蛋白基因表达的调控机制尚未确定。为了在α-平滑肌肌动蛋白启动子水平研究这一机制，将与氯霉素乙酰转移酶报告基因相连的不同长度的α-平滑肌肌动蛋白启动子转染大鼠肺成纤维细胞，并用转化生长因子β1处理。结果表明，最短的可诱导启动子长度为150个碱基对，这表明在该区域存在对转化生长因子β1诱导的肌成纤维细胞分化可能具有重要意义的顺式元件。转染对应于四种疑似调控因子序列的“诱饵”寡核苷酸表明，只有转化生长因子β控制元件参与肌成纤维细胞分化过程中转化生长因子β1诱导的α-平滑肌肌动蛋白表达的调控。与这一结论一致的是，转化生长因子β控制元件中的突变导致启动子活性显著降低。这些观察结果共同表明，肌成纤维细胞分化过程中α-平滑肌肌动蛋白启动子的调控与平滑肌细胞和其他细胞系中的调控独特不同。由于肌成纤维细胞在伤口收缩和细胞外基质合成中起关键作用，阐明这种分化机制应为纤维生成提供新的见解，并为调节伤口愈合和控制纤维化提出未来的新策略。
