Moulton Vaishali R, Kyttaris Vasileios C, Juang Yuang-Taung, Chowdhury Bhabadeb, Tsokos George C
Department of Medicine, Division of Rheumatology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02115, USA.
J Biol Chem. 2008 Jul 18;283(29):20037-44. doi: 10.1074/jbc.M710434200. Epub 2008 May 27.
T cell dysfunction is crucial to the pathogenesis of systemic lupus erythematosus (SLE); however, the molecular mechanisms involved in the deficient expression of the T cell receptor-associated CD3zeta chain in SLE are not clear. SLE T cells express abnormally increased levels of an alternatively spliced isoform of CD3zeta that lacks a 562-bp region in its 3'-untranslated region (UTR). We showed previously that two adenosine/uridine-rich elements (ARE) in this splice-deleted region of CD3zeta transcript are critical for the mRNA stability and protein expression of CD3zeta. In this study we show for the first time that the mRNA-stabilizing protein HuR binds to these two ARE bearing regions of CD3zeta 3'-UTR. Knockdown of HuR resulted in decreased expression of the CD3zeta chain, whereas overexpression led to the increase of CD3zeta chain levels. Additionally, overexpression of HuR in human T cells resulted in increased mRNA stability of CD3zeta. Our results identify the 3'-UTR of CD3zeta as a novel target for the mRNA-stabilizing protein HuR. Thus, the absence of two critical AREs in the alternatively spliced CD3zeta 3'-UTR found in SLE T cells may result in decreased HuR binding, representing a possible molecular mechanism contributing to the reduced stability and expression of CD3zeta in SLE.
T细胞功能障碍对系统性红斑狼疮（SLE）的发病机制至关重要；然而，SLE中T细胞受体相关CD3ζ链表达缺陷所涉及的分子机制尚不清楚。SLE T细胞异常表达一种剪接异构体形式的CD3ζ，其3'-非翻译区（UTR）缺少一个562 bp的区域。我们之前表明，CD3ζ转录本这个剪接缺失区域中的两个富含腺苷/尿苷元件（ARE）对CD3ζ的mRNA稳定性和蛋白表达至关重要。在本研究中，我们首次表明，mRNA稳定蛋白HuR与CD3ζ 3'-UTR的这两个含有ARE的区域结合。敲低HuR导致CD3ζ链表达降低，而过表达则导致CD3ζ链水平升高。此外，在人T细胞中过表达HuR导致CD3ζ的mRNA稳定性增加。我们的结果确定CD3ζ的3'-UTR是mRNA稳定蛋白HuR的一个新靶点。因此，在SLE T细胞中发现的剪接后CD3ζ 3'-UTR中两个关键ARE的缺失可能导致HuR结合减少，这代表了一种可能导致SLE中CD3ζ稳定性和表达降低的分子机制。
