Abnormal expressions of RasGRPs in autoimmune diseases

Ras鸟嘌呤核苷酸释放蛋白（Ras grps）是Ras的鸟嘌呤交换因子。其中，RasGRP1优先在T细胞中表达。我们已经研究了RasGRP1在系统性红斑狼疮患者中的异常表达，并且之前报道了RasGRP1的选择性剪接在狼疮T细胞中丰富，选择性剪接与该信号分子的蛋白水平较低有关。在本研究中，我们首先测试了无意义介导的mRNA衰减和/或泛素-蛋白酶体途径是否在狼疮T细胞中降低RasGRP1蛋白水平中起作用。无义介导的mRNA衰变或蛋白酶体的抑制影响RasGRP1蛋白的表达水平或模式。然后，我们决定产生只在T细胞中表达RasGRP1剪接变体A的Tg小鼠，这是最常见的交替剪接RasGRP1亚型。我们成功地产生了在胸腺中表达RasGRP1剪接变异体A蛋白的小鼠。虽然胸腺中单阳性/双阴性T细胞的比例不受这种剪接变体的明显影响，但我们正在研究抗cd3 /28抗体刺激下Tg T细胞中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.