Division of Immunogenetics, Department of Immunobiology and Neuroscience, Medical Institute of Bioregulation, Kyushu University, Fukuoka, Japan.
PLoS One. 2012;7(9):e46277. doi: 10.1371/journal.pone.0046277. Epub 2012 Sep 26.
The migratory properties of lymphocytes depend on DOCK2, an atypical Rac activator predominantly expressed in hematopoietic cells. Although DOCK2 does not contain the Dbl homology domain typically found in guanine nucleotide exchange factors (GEFs), DOCK2 mediates the GTP-GDP exchange reaction for Rac via its DOCK homology region (DHR)-2 (also known as CZH2 or Docker) domain. DOCK2 DHR-2 domain is composed of three lobes, and Rac binding site and catalytic center are generated entirely from lobes B and C. On the other hand, lobe A has been implicated in dimer formation, yet its physiological significance remains unknown. Here, we report that lobe A-mediated DOCK2 dimerization is crucial for Rac activation and lymphocyte migration. We found that unlike wild-type DOCK2, DOCK2 mutant lacking lobe A failed to restore motility and polarity when expressed in thymoma cells and primary T cells lacking endogenous expression of DOCK2. Similar results were obtained with the DOCK2 point mutant having a defect in dimerization. Deletion of lobe A from the DHR-2 domain did not affect Rac GEF activity in vitro. However, fluorescence resonance energy transfer analyses revealed that lobe A is required for DOCK2 to activate Rac effectively during cell migration. Our results thus indicate that DOCK2 dimerization is functionally important under the physiological condition where only limited amounts of DOCK2 and Rac are localized to the plasma membrane.
淋巴细胞的迁移特性取决于 DOCK2，DOCK2 是一种主要在造血细胞中表达的非典型 Rac 激活蛋白。虽然 DOCK2 不包含通常在鸟嘌呤核苷酸交换因子 (GEF) 中发现的 Dbl 同源结构域，但 DOCK2 通过其 DOCK 同源结构域 (DHR)-2（也称为 CZH2 或 Docker）结构域介导 Rac 的 GTP-GDP 交换反应。DOCK2 DHR-2 结构域由三个叶组成，Rac 结合位点和催化中心完全由叶 B 和 C 生成。另一方面，叶 A 已被牵连到二聚体形成中，但它的生理意义仍然未知。在这里，我们报告说，叶 A 介导的 DOCK2 二聚化对于 Rac 激活和淋巴细胞迁移至关重要。我们发现，与野生型 DOCK2 不同，缺乏叶 A 的 DOCK2 突变体在表达缺乏内源性 DOCK2 表达的胸腺瘤细胞和原代 T 细胞中无法恢复运动性和极性。具有二聚化缺陷的 DOCK2 点突变体也获得了类似的结果。从 DHR-2 结构域中删除叶 A 不会影响体外 Rac GEF 活性。然而，荧光共振能量转移分析表明，叶 A 是 DOCK2 在细胞迁移过程中有效激活 Rac 所必需的。因此，我们的研究结果表明，在仅将有限量的 DOCK2 和 Rac 定位到质膜的生理条件下，DOCK2 二聚化在功能上是重要的。
