Aiba Yuichi, Oh-hora Masatsugu, Kiyonaka Shigeki, Kimura Yayoi, Hijikata Atsushi, Mori Yasuo, Kurosaki Tomohiro
Laboratories of Lymphocyte Differentiation and Immunogenomics, RIKEN Research Center for Allergy and Immunology, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.
Proc Natl Acad Sci U S A. 2004 Nov 23;101(47):16612-7. doi: 10.1073/pnas.0407468101. Epub 2004 Nov 15.
The Ras signaling pathway plays a critical role in B lymphocyte development and activation, but its activation mechanism has not been well understood. At least one mode of Ras regulation in B cells involves a Ras-guanyl nucleotide exchange factor, RasGRP3. We demonstrate here that RasGRP3 undergoes phosphorylation at Thr-133 upon B cell receptor cross-linking, thereby resulting in its activation. Deletion of phospholipase C-gamma2 or pharmacological interference with conventional PKCs resulted in marked reduction in both Thr-133 phosphorylation and Ras activation. Moreover, mutation of Thr-133 in RasGRP3 alone severely impaired its ability to activate Ras in B cell receptor signaling. Hence, our data suggest that PKC, after being activated by diacylglycerol, phosphorylates RasGRP3, thereby contributing to its full activation.
Ras信号通路在B淋巴细胞的发育和激活过程中起着关键作用，但其激活机制尚未完全明确。B细胞中Ras调节的至少一种模式涉及一种Ras鸟苷酸交换因子RasGRP3。我们在此证明，在B细胞受体交联后，RasGRP3的苏氨酸-133位点会发生磷酸化，从而导致其激活。删除磷脂酶C-γ2或用药物干扰传统蛋白激酶C会导致苏氨酸-133磷酸化和Ras激活均显著降低。此外，单独将RasGRP3中的苏氨酸-133位点突变会严重损害其在B细胞受体信号传导中激活Ras的能力。因此，我们的数据表明，蛋白激酶C在被二酰基甘油激活后，会使RasGRP3磷酸化，从而促进其完全激活。
