Deng C, Kaplan M J, Yang J, Ray D, Zhang Z, McCune W J, Hanash S M, Richardson B C
University of Michigan and the Ann Arbor VA Hospital, USA.
Arthritis Rheum. 2001 Feb;44(2):397-407. doi: 10.1002/1529-0131(200102)44:2<397::AID-ANR59>3.0.CO;2-N.
Previous studies have shown that inhibiting T cell DNA methylation causes a lupus-like disease by modifying gene expression. T cells from patients with lupus exhibit diminished levels of DNA methyltransferase (MTase) enzyme activity, hypomethylated DNA, and changes in gene expression similar to those exhibited by T cells treated with methylation inhibitors, suggesting that DNA hypomethylation may contribute to human lupus. Since it is known that DNA MTase levels are regulated by the ras-mitogen-activated protein kinase (MAPK) pathway, this study sought to determine whether decreased ras-MAPK signaling could account for the DNA hypomethylation in lupus T cells.
DNA MTase messenger RNA (mRNA) from lupus patients and from healthy controls was quantitated by Northern analysis, and ras-MAPK signaling was determined by immunoblotting with antibodies to the activated forms of extracellular receptor-associated kinase (ERK). Results were compared with those in T cells in which ras-MAPK signaling was inhibited with a soluble inhibitor of MAPK ERK I (MEK1).
T cells from patients with active lupus had diminished DNA MTase mRNA levels and decreased signaling through the ras-MAPK pathway. Inhibiting signaling through the ras-MAPK pathway with the MEK1 inhibitor decreased DNA MTase mRNA and enzyme activity to the levels seen in lupus T cells, and resulted in DNA hypomethylation resembling that seen in lupus T cells.
These results suggest that a decrease in signaling through the ras-MAPK pathway may be responsible for the decreased MTase activity and DNA hypomethylation in patients with lupus.
既往研究表明，抑制T细胞DNA甲基化可通过改变基因表达引发狼疮样疾病。狼疮患者的T细胞表现出DNA甲基转移酶（MTase）酶活性水平降低、DNA低甲基化以及基因表达变化，类似于用甲基化抑制剂处理的T细胞所表现出的变化，这表明DNA低甲基化可能与人类狼疮有关。由于已知DNA MTase水平受ras-丝裂原活化蛋白激酶（MAPK）途径调控，本研究旨在确定ras-MAPK信号传导降低是否可解释狼疮T细胞中的DNA低甲基化。
通过Northern分析定量狼疮患者和健康对照者的DNA MTase信使核糖核酸（mRNA），并用针对细胞外受体相关激酶（ERK）活化形式的抗体进行免疫印迹来确定ras-MAPK信号传导。将结果与用MAPK ERK I（MEK1）的可溶性抑制剂抑制ras-MAPK信号传导的T细胞中的结果进行比较。
活动性狼疮患者的T细胞DNA MTase mRNA水平降低，且通过ras-MAPK途径的信号传导减少。用MEK1抑制剂抑制通过ras-MAPK途径的信号传导，可使DNA MTase mRNA和酶活性降低至狼疮T细胞中的水平，并导致类似于狼疮T细胞中的DNA低甲基化。
这些结果表明，通过ras-MAPK途径的信号传导减少可能是狼疮患者MTase活性降低和DNA低甲基化的原因。
