Niu Yamei, Roy François, Saltel Frédéric, Andrieu-Soler Charlotte, Dong Wen, Chantegrel Anne-Lise, Accardi Rosita, Thépot Amélie, Foiselle Nadège, Tommasino Massimo, Jurdic Pierre, Sylla Bakary S
Infections and Cancer Biology Group, International Agency for Research on Cancer, 150 cours Albert-Thomas, 69008 Lyon, France.
Mol Cell Biol. 2006 Jun;26(11):4288-301. doi: 10.1128/MCB.01817-05.
Dok1 is believed to be a mainly cytoplasmic adaptor protein which down-regulates mitogen-activated protein kinase activation, inhibits cell proliferation and transformation, and promotes cell spreading and cell migration. Here we show that Dok1 shuttles between the nucleus and cytoplasm. Treatment of cells with leptomycin B (LMB), a specific inhibitor of the nuclear export signal (NES)-dependent receptor CRM1, causes nuclear accumulation of Dok1. We have identified a functional NES (348LLKAKLTDPKED359) that plays a major role in the cytoplasmic localization of Dok1. Src-induced tyrosine phosphorylation prevented the LMB-mediated nuclear accumulation of Dok1. Dok1 cytoplasmic localization is also dependent on IKKbeta. Serum starvation or maintaining cells in suspension favor Dok1 nuclear localization, while serum stimulation, exposure to growth factor, or cell adhesion to a substrate induce cytoplasmic localization. Functionally, nuclear NES-mutant Dok1 had impaired ability to inhibit cell proliferation and to promote cell spreading and cell motility. Taken together, our results provide the first evidence that Dok1 transits through the nucleus and is actively exported into the cytoplasm by the CRM1 nuclear export system. Nuclear export modulated by external stimuli and phosphorylation may be a mechanism by which Dok1 is maintained in the cytoplasm and membrane, thus regulating its signaling functions.
Dok1被认为是一种主要位于细胞质的衔接蛋白，它可下调丝裂原活化蛋白激酶的激活，抑制细胞增殖和转化，并促进细胞铺展和迁移。在此我们表明，Dok1在细胞核和细胞质之间穿梭。用核输出信号（NES）依赖性受体CRM1的特异性抑制剂 leptomycin B（LMB）处理细胞，会导致Dok1在细胞核中积累。我们鉴定出一个功能性NES（348LLKAKLTDPKED359），它在Dok1的细胞质定位中起主要作用。Src诱导的酪氨酸磷酸化可阻止LMB介导的Dok1核积累。Dok1的细胞质定位也依赖于IKKβ。血清饥饿或使细胞保持悬浮状态有利于Dok1的核定位，而血清刺激、暴露于生长因子或细胞黏附于底物则诱导细胞质定位。在功能上，核NES突变型Dok1抑制细胞增殖以及促进细胞铺展和细胞运动的能力受损。综上所述，我们的结果提供了首个证据，即Dok1穿梭于细胞核，并通过CRM1核输出系统被主动输出到细胞质中。由外部刺激和磷酸化调节的核输出可能是一种机制，通过该机制Dok1被维持在细胞质和细胞膜中，从而调节其信号传导功能。
