Alfonso-Jaume Maria Alejandra, Mahimkar Rajeev, Lovett David H
The Department of Medicine, San Francisco VAMC/University of California, 111J Medical Service, 4150 Clement Street, San Francisco, CA 94121, USA.
Biochem J. 2004 Jun 15;380(Pt 3):735-47. doi: 10.1042/BJ20031281.
The transition of normally quiescent glomerular MCs (mesangial cells) to a highly proliferative phenotype with characteristics of myofibroblasts is a process commonly observed in inflammatory diseases affecting the renal glomerulus, the ultimate result of which is glomerulosclerosis. Generation of proteolytically active MMP (matrix metalloproteinase)-2 by the membrane-associated membrane type 1 (MT1)-MMP is responsible for the transition of mesangial cells to the myofibroblast phenotype [Turck, Pollock, Lee, Marti and Lovett (1996) J. Biol. Chem. 271, 15074-15083]. In the present study, we show that the expression of MT1-MMP within the context of MCs is mediated by three discrete cis -acting elements: a proximal non-canonical Sp1 site that preferentially binds Sp1; an overlapping Sp1/Egr-1-binding site that preferentially binds Egr-1; and a more distal binding site for the NFAT (nuclear factor of activated T cells) that binds the NFAT c1 isoform present in MC nuclear extracts. Transfection with an NFAT c1 expression plasmid, or activation of calcineurin with a calcium ionophore, yielded major increases in NFAT c1 nuclear DNA-binding activity, MT1-MMP transcription and protein synthesis, which were additive with the lower levels of transactivation provided by the proximal Sp1 and the overlapping Sp1/Egr-1 sites. Specific binding of NFAT c1 to the MT1-MMP promoter was confirmed by chromatin immunoprecipitation studies, while MT1-MMP expression was suppressed by treatment with the calcineurin inhibitor, cyclosporin A. These studies are the first demonstration that a specific NFAT isoform enhances transcription of an MMP (MT1-MMP) that plays a major role in the proteolytic events that are a dominant feature of acute glomerular inflammation. Suppression of MT1-MMP by commonly used calcineurin inhibitors may play a role in the development of renal fibrosis following renal transplantation.
正常静止的肾小球系膜细胞（MCs）向具有肌成纤维细胞特征的高增殖表型转变，是影响肾小球的炎症性疾病中常见的过程，其最终结果是肾小球硬化。膜相关的膜型1（MT1）-基质金属蛋白酶（MMP）-2产生的蛋白水解活性负责系膜细胞向肌成纤维细胞表型的转变[Turck、Pollock、Lee、Marti和Lovett（1996年）《生物化学杂志》271卷，第15074 - 15083页]。在本研究中，我们表明MCs环境中MT1-MMP的表达由三个离散的顺式作用元件介导：一个优先结合Sp1的近端非典型Sp1位点；一个优先结合Egr-1的重叠Sp1/Egr-1结合位点；以及一个更远端的活化T细胞核因子（NFAT）结合位点，该位点结合MC细胞核提取物中存在的NFAT c1亚型。用NFAT c1表达质粒转染，或用钙离子载体激活钙调神经磷酸酶，导致NFAT c1核DNA结合活性、MT1-MMP转录和蛋白质合成大幅增加，这与近端Sp1和重叠Sp1/Egr-1位点提供的较低水平反式激活具有累加作用。通过染色质免疫沉淀研究证实了NFAT c1与MT1-MMP启动子的特异性结合，而用钙调神经磷酸酶抑制剂环孢素A处理可抑制MT1-MMP表达。这些研究首次证明特定的NFAT亚型增强了一种MMP（MT1-MMP）的转录，该MMP在蛋白水解事件中起主要作用，而蛋白水解事件正是急性肾小球炎症的主要特征。常用的钙调神经磷酸酶抑制剂对MT1-MMP的抑制作用可能在肾移植后肾纤维化的发展中起作用。
