Jak3 Enables Chemokine-Dependent Actin Cytoskeleton Reorganization by Regulating Cofilin and Rac/Rhoa GTPases Activation

We have previously shown that Jak3 is involved in the signaling pathways of CCR7, CCR9 and CXCR4 in murine T lymphocytes and that Jak3−/− lymphocytes display an intrinsic defect in homing to peripheral lymph nodes. However, the molecular mechanism underlying the defective migration observed in Jak3−/− lymphocytes remains elusive. Here, it is demonstrated for the first time, that Jak3 is required for the actin cytoskeleton reorganization in T lymphocytes responding to chemokines. It was found that Jak3 regulates actin polymerization by controlling cofilin inactivation in response to CCL21 and CXCL12. Interestingly, cofilin inactivation was not precluded in PTX- treated cells despite their impaired actin polymerization. Additionally, Jak3 was required for small GTPases Rac1 and RhoA activation, which are indispensable for acquisition of the migratory cell phenotype and the generation of a functional leading edge and uropod, respectively. This defect correlates with data obtained by time-lapse video-microscopy showing an incompetent uropod formation and impaired motility in Jak3-pharmacologically inhibited T lymphocytes. Our data support a new model in which Jak3 and heterotrimeric G proteins can use independent, but complementary, signaling pathways to regulate actin cytoskeleton dynamics during cell migration in response to chemokines.我们此前已证实，Jak3可参与小鼠T淋巴细胞中CCR7、CCR9及CXCR4的信号通路，且Jak3基因敲除（Jak3−/−）的T淋巴细胞在向外周淋巴结归巢方面存在固有缺陷。然而，Jak3−/−淋巴细胞迁移缺陷背后的分子机制仍未阐明。本研究首次证实，在趋化因子（chemokines）刺激的T淋巴细胞中，Jak3是肌动蛋白细胞骨架重排（actin cytoskeleton reorganization）所必需的。研究发现，在受到CCL21与CXCL12刺激时，Jak3可通过调控丝切蛋白（cofilin）的失活来调节肌动蛋白聚合。有趣的是，尽管经百日咳毒素（pertussis toxin，PTX）处理的细胞肌动蛋白聚合受损，但其丝切蛋白的失活并未受到阻断。此外，小GTP酶（small GTPases）Rac1与RhoA的激活依赖于Jak3，而这两种酶分别对于细胞获得迁移表型并形成功能性前沿，以及形成功能性尾足（uropod）不可或缺。该缺陷与延时视频显微镜技术所得结果一致：经Jak3药理学抑制的T淋巴细胞无法形成正常尾足，且迁移能力受损。我们的研究结果支持一种新模型：在趋化因子诱导的细胞迁移过程中，Jak3与异源三聚体G蛋白（heterotrimeric G proteins）可通过相互独立但功能互补的信号通路来调控肌动蛋白细胞骨架的动态变化。