Piccinini G, Golay J, Flora A, Songia S, Luchetti M, Gabrielli A, Introna M
Department of Immunology and Cell Biology, Institute of Pharmacological Research Mario Negri, Milano, Italy.
J Invest Dermatol. 1999 Feb;112(2):191-6. doi: 10.1046/j.1523-1747.1999.00485.x.
C-myb and B-myb belong to the myb family of transcription factors. We have shown previously that c-myb is deregulated in fibroblasts from systemic sclerosis (scleroderma) patients relative to normal fibroblasts. Scleroderma fibroblasts are known to express elevated levels of collagen genes and transforming growth factor beta is known to be a pro-fibrotic cytokine and to induce transcription of type I collagen genes. We have therefore investigated the role of c-myb and B-myb in the regulation of type I collagen genes in response to transforming growth factor beta in normal human fibroblasts. We show that, in these cells, transforming growth factor beta treatment induces c-myb as well as collagen alpha1(I) and alpha2(I) gene expression, but not B-myb. Furthermore we demonstrate by cotransfection assays that c-myb can upregulate alpha1(I) and alpha2(I) collagen promoters by 6-10-fold whereas B-myb is inactive. The activity of c-myb on both type I collagen promoters requires a functional c-myb DNA binding domain suggesting a direct interaction between c-myb and these promoters. Indeed c-myb is active also on a 500 bp fragment of the alpha2(I) collagen promoter and can bind to this fragment in electrophoretic mobility shift assays. Finally, we show that anti-c-myb anti-sense treatment reduces alpha1(I) and to a lesser extent alpha2(I) collagen gene expression. These data strongly suggest that c-myb, but not B-myb, plays a direct role in the upregulation of type I collagen gene expression in response to transforming growth factor beta.
C-myb和B-myb属于转录因子的myb家族。我们之前已经表明，相对于正常成纤维细胞，系统性硬化症（硬皮病）患者的成纤维细胞中c-myb失调。已知硬皮病成纤维细胞表达升高水平的胶原蛋白基因，并且转化生长因子β是一种促纤维化细胞因子，已知其可诱导I型胶原蛋白基因的转录。因此，我们研究了c-myb和B-myb在正常人成纤维细胞中响应转化生长因子β时对I型胶原蛋白基因调控中的作用。我们发现，在这些细胞中，转化生长因子β处理可诱导c-myb以及胶原蛋白α1(I)和α2(I)基因的表达，但不诱导B-myb的表达。此外，我们通过共转染实验证明，c-myb可使α1(I)和α2(I)胶原蛋白启动子上调6至10倍，而B-myb则无活性。c-myb对两种I型胶原蛋白启动子的活性需要一个功能性的c-myb DNA结合结构域，这表明c-myb与这些启动子之间存在直接相互作用。实际上，c-myb对α2(I)胶原蛋白启动子的500 bp片段也有活性，并且在电泳迁移率变动分析中可与该片段结合。最后，我们表明抗c-myb反义处理可降低α1(I)胶原蛋白基因的表达，并在较小程度上降低α2(I)胶原蛋白基因的表达。这些数据强烈表明，c-myb而非B-myb在响应转化生长因子β时对I型胶原蛋白基因表达的上调中起直接作用。
