Abnormal expressions of RasGRPs in autoimmune diseases

RAS鸟苷释放蛋白(RasGRPs)是RAS的鸟嘌呤交换因子。其中，RASGRP1在T细胞中优先表达。我们研究了RASGRP1在系统性红斑狼疮患者中的异常表达，先前报道RASGRP1的选择性剪接在狼疮T细胞中大量存在，选择性剪接与该信号分子的低蛋白水平有关。在目前的研究中，我们首先测试了无意义介导的mRNA衰退和/或泛素-蛋白酶体途径是否在狼疮T细胞中RASGRP1的低蛋白水平中起作用。抑制无意义介导的mRNA衰退或蛋白酶体影响RASGRP1蛋白的表达水平或模式。然后，我们决定产生在T细胞中专门表达RASGRP1剪接变体A的TG小鼠，RASGRP1剪接变体A是最常见的选择性剪接RASGRP1亚型。我们成功地培育出在胸腺表达RASGRP1剪接变异体A蛋白的小鼠。虽然胸腺中单阳性/双阴性T细胞的比例没有受到这种剪接变异体的明显影响，但我们正在研究抗CD3/28抗体刺激Tg T细胞时Ras-Erk通路的激活。

Ras guanyl nucleotide-releasing proteins (RasGRPs) are guanine exchange factors for Ras. Among them, RasGRP1 is preferentially expressed in T cells. We have investigated abnormal expressions of RasGRP1 in patients with systemic lupus erythematosus and previously reported that alternative splicing of RasGRP1 is abundant in lupus T cells that alternative splicing is related to lower protein levels of this signaling molecule. In the present study, we at first tested if nonsense-mediated mRNA decay and/or ubiquitine-proteasome pathway play a role in lower protein levels of RasGRP1 in lupus T cells. Inhibition of nonsense-mediated mRNA decay nor proteasome impact the expression levels or patterns of RasGRP1 protein. Then we decided to generate Tg mice expressing RasGRP1 splice variant A, the most frequent alternatively-spliced RasGRP1 isoform, exclusively in T cells. We successfully generate mice that express RasGRP1 splice variant A protein in their thymus. Although proportion of single positive/double negative T cells in the thymus was not apparently affected by this splice variant, we are investigating activation of Ras-Erk pathway in Tg Tcells when stimulated by anti-CD3/28 antibodies.