Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205.
Proc Natl Acad Sci U S A. 2013 Dec 3;110(49):E4723-32. doi: 10.1073/pnas.1312540110. Epub 2013 Nov 18.
During chemotaxis, cells sense extracellular chemical gradients and position Ras GTPase activation and phosphatidylinositol (3,4,5)-triphosphate (PIP3) production toward chemoattractants. These two major signaling events are visualized by biosensors in a crescent-like zone at the plasma membrane. Here, we show that a Dictyostelium Rho GTPase, RacE, and a guanine nucleotide exchange factor, GxcT, stabilize the orientation of Ras activation and PIP3 production in response to chemoattractant gradients, and this regulation occurred independently of the actin cytoskeleton and cell polarity. Cells lacking RacE or GxcT fail to persistently direct Ras activation and PIP3 production toward chemoattractants, leading to lateral pseudopod extension and impaired chemotaxis. Constitutively active forms of RacE and human RhoA are located on the portion of the plasma membrane that faces lower concentrations of chemoattractants, opposite of PIP3 production. Mechanisms that control the localization of the constitutively active form of RacE require its effector domain, but not PIP3. Our findings reveal a critical role for Rho GTPases in positioning Ras activation and thereby establishing the accuracy of directional sensing.
在趋化作用过程中，细胞感知细胞外化学梯度，并将 Ras GTP 酶的激活和磷脂酰肌醇（3,4,5）-三磷酸（PIP3）的产生定位到趋化剂。这两个主要的信号事件可以通过生物传感器在质膜的新月形区域可视化。在这里，我们表明，粘菌的 RacE Rho GTP 酶和鸟嘌呤核苷酸交换因子 GxcT 稳定了 Ras 激活和 PIP3 产生的方向，以响应趋化剂梯度，这种调节独立于肌动蛋白细胞骨架和细胞极性发生。缺乏 RacE 或 GxcT 的细胞无法持续将 Ras 激活和 PIP3 产生定向到趋化剂，导致侧向伪足延伸和趋化性受损。组成性激活形式的 RacE 和人 RhoA 位于面向较低浓度趋化剂的质膜部分，与 PIP3 产生相反。控制 RacE 组成性激活形式定位的机制需要其效应结构域，但不需要 PIP3。我们的发现揭示了 Rho GTP 酶在定位 Ras 激活方面的关键作用，从而建立了定向感应的准确性。
