XPLN, a guanine nucleotide exchange factor for RhoA and RhoB, but not RhoC
XPLN, a guanine nucleotide exchange factor for RhoA and RhoB, but not RhoC
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DOI：
10.1074/jbc.m207401200
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发表时间：
2002-11-08
影响因子：
4.8
通讯作者：
Wennerberg, K
中科院分区：
文献类型：
--
作者：
Arthur, WT;Ellerbroek, SM;Wennerberg, K
Rho蛋白在GDP结合的非活性状态和GTP结合的活性状态之间循环。这些GTP酶的激活是由鸟嘌呤核苷酸交换因子(GEF)介导的，GEF促进GDP到GTP的交换。在这项研究中，我们鉴定了XPLN，一个Rho家族的全环基金。与其他Rho GEF一样，XPLN包含串联的DBL同源结构域和Pleckstrin同源结构域，但缺乏与其他已知功能结构域或基序的同源性。XPLN蛋白在脑、骨骼肌、心脏、肾脏、血小板、巨噬细胞和神经细胞系中表达。在体外，XPLN刺激RhoA和RhoB上的鸟核苷酸交换，但不刺激RhoC、RhoG、rac1或Cdc42。与这些数据一致，XPLN优先与RhoA和RhoB关联。XPLN对RhoA和RhoB的特异性，而不是RhoC，令人惊讶，因为它们有超过85%的序列同源性。我们确定XPLN不能交换RhoC是由RhoC中的异亮氨酸43介导的，异亮氨酸在RhoA和RhoB中占据一个位置。当XPLN在细胞中表达时，XPLN激活RhoA和RhoB，但不激活RhoC，并以Rho激酶依赖的方式刺激应激纤维和局灶性粘连的组装。通过焦点形成实验，我们还发现XPLN具有转化活性。综上所述，我们描述了一个能够区分密切相关的RhoA、Rholl和RhoC的Rho家族的全长蛋白，这可能有助于我们深入了解这三种蛋白的不同功能。
Rho proteins cycle between an inactive, GDP-bound state and an active, GTP-bound state. Activation of these GTPases is mediated by guanine nucleotide exchange factors (GEFs), which promote GDP to GTP exchange. In this study we have characterized XPLN, a Rho family GEF. Like other Rho GEFs, XPLN contains a tandem Dbl homology and pleckstrin homology domain topography, but lacks homology with other known functional domains or motifs. XPLN protein is expressed in the brain, skeletal muscle, heart, kidney, platelets, and macrophage and neuronal cell lines. In vitro, XPLN stimulates guanine nucleotide exchange on RhoA and RhoB, but not RhoC, RhoG, Rac1, or Cdc42. Consistent with these data, XPLN preferentially associates with RhoA and RhoB. The specificity of XPLN for RhoA and RhoB, but not RhoC, is surprising given that they share over 85% sequence identity. We determined that the inability of XPLN to exchange RhoC is mediated by isoleucine 43 in RhoC, a position occupied by valine in RhoA and RhoB. When expressed in cells, XPLN activates RhoA and RhoB, but not RhoC, and stimulates the assembly of stress fibers and focal adhesions in a Rho kinase-dependent manner. We also found that XPLN possesses transforming activity, as determined by focus formation assays. In conclusion, here we describe a Rho family GEF that can discriminate between the closely related RhoA, Rholl, and RhoC, possibly giving insight to the divergent functions of these three proteins.