Zhang Libin, Lee Jerome E, Wilusz Jeffrey, Wilusz Carol J
Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, Colorado 80523, USA.
J Biol Chem. 2008 Aug 15;283(33):22457-63. doi: 10.1074/jbc.M802803200. Epub 2008 Jun 16.
Type I myotonic dystrophy (DM1) is caused by a triplet repeat expansion in the 3'-untranslated region (UTR) of the dystrophia myotonia protein kinase (DMPK) gene. Pathogenesis is closely linked with production of a toxic RNA from the mutant allele, which interferes with function of several RNA-binding proteins, including CUGBP1. Here we show that expression of a mutant DMPK 3'-UTR containing 960 CUG repeats is sufficient to increase expression and stability of an mRNA encoding the potent proinflammatory cytokine, tumor necrosis factor (TNF). CUGBP1 specifically recognizes sequences within the TNF 3'-UTR that are dissimilar from its canonical UG-rich binding site. Depletion of CUGBP1 from mouse myoblasts results in increased abundance of TNF mRNA through stabilization of the transcript. Moreover, activation of the protein kinase C pathway by treatment with phorbol ester, which has been shown previously to result in CUGBP1 phosphorylation, also causes TNF mRNA stabilization. Our results suggest that the elevated serum TNF seen in DM1 patients may be derived from muscle where it is induced by expression of toxic DMPK RNA. Importantly, overexpression of this potent cytokine could contribute to the muscle wasting and insulin resistance that are characteristic of this debilitating disease.
I型强直性肌营养不良症（DM1）由肌强直性营养不良蛋白激酶（DMPK）基因3'非翻译区（UTR）中的三联体重复扩增引起。发病机制与突变等位基因产生的有毒RNA密切相关，该RNA会干扰包括CUGBP1在内的几种RNA结合蛋白的功能。在此我们表明，含有960个CUG重复序列的突变型DMPK 3'-UTR的表达足以增加编码强效促炎细胞因子肿瘤坏死因子（TNF）的mRNA的表达和稳定性。CUGBP1特异性识别TNF 3'-UTR内与其典型富含UG的结合位点不同的序列。从小鼠成肌细胞中去除CUGBP1会通过稳定转录本而导致TNF mRNA丰度增加。此外，用佛波酯处理激活蛋白激酶C途径（先前已证明该途径会导致CUGBP1磷酸化）也会导致TNF mRNA稳定。我们的结果表明，DM1患者血清中升高的TNF可能源自肌肉，在肌肉中它由有毒的DMPK RNA的表达诱导产生。重要的是，这种强效细胞因子的过表达可能导致这种使人衰弱的疾病所特有的肌肉萎缩和胰岛素抵抗。
