Laboratory of Immunodynamics, Department of Microbiology and Immunology, Osaka University, Graduate School of Medicine, Osaka, Japan.
Cancer Sci. 2010 Feb;101(2):363-8. doi: 10.1111/j.1349-7006.2009.01398.x. Epub 2009 Oct 12.
Focal adhesion (FA) consists of multiple cellular proteins including paxillin and serves as a center for adhesion-mediated signaling. The assembly and disassembly of FAs is regulated by locally produced intracellular signals, and tyrosine phosphorylation of paxillin has been implicated in this process. A Lin-11 Isl-1 Mec-3 (LIM) domain-containing adaptor protein, leupaxin, a member of the paxillin family, is expressed in leukocytes as well as in certain cancer cells, and shares overall structural characteristics with paxillin. However, it remains unknown whether leupaxin and paxillin cooperate with or antagonize each other in integrin signaling. Here we show that leupaxin potently represses the tyrosine phosphorylation of paxillin. When expressed in mouse thymoma BW5147 cells bound to ICAM-1, leupaxin accumulated in FA-like patches in the cell periphery. When expressed in NIH3T3 and HEK293T cells, leupaxin localized to FAs upon cell adhesion to fibronectin and strongly suppressed the integrin-induced tyrosine phosphorylation of paxillin. In integrin-stimulated HEK293T cells, leupaxin's LIM3 domain appeared essential for selective FA localization and the suppression of paxillin tyrosine phosphorylation. Leupaxin's LD3 motif, which is critical for stable association with FAK, was dispensable for leupaxin's suppressive ability. In addition, leupaxin reduced the spreading of NIH3T3 cells on fibronectin, which required both the LD3 motif and LIM3 domain. When expressed in human leukocytic K562 cells, leupaxin significantly suppressed integrin alpha5beta1-mediated cell adhesion to fibronectin and the tyrosine phosphorylation of paxillin. These findings indicate that leupaxin functions as a paxillin counterpart that potently suppresses the tyrosine phosphorylation of paxillin during integrin signaling.
焦点黏附（FA）由多种细胞蛋白组成，包括桩蛋白，作为黏附介导信号的中心。FA 的组装和拆卸受局部产生的细胞内信号调节，桩蛋白的酪氨酸磷酸化已被牵涉到这个过程中。Lin-11 Isl-1 Mec-3（LIM）结构域包含衔接蛋白，leupaxin，桩蛋白家族的成员，在白细胞以及某些癌细胞中表达，并与桩蛋白具有总体结构特征。然而，尚不清楚 leupaxin 和桩蛋白在整合素信号传导中是相互合作还是相互拮抗。在这里，我们显示 leupaxin 强烈抑制桩蛋白的酪氨酸磷酸化。当与 ICAM-1 结合表达在小鼠胸腺瘤 BW5147 细胞中时，leupaxin 在细胞外周的 FA 样斑片中积累。当在 NIH3T3 和 HEK293T 细胞中表达时，leupaxin 在细胞黏附到纤维连接蛋白时定位于 FA，并强烈抑制整合素诱导的桩蛋白酪氨酸磷酸化。在整合素刺激的 HEK293T 细胞中，leupaxin 的 LIM3 结构域似乎对于选择性 FA 定位和抑制桩蛋白酪氨酸磷酸化是必需的。对于与 FAK 的稳定关联至关重要的 leupaxin 的 LD3 基序对于 leupaxin 的抑制能力是可有可无的。此外，leupaxin 减少了 NIH3T3 细胞在纤维连接蛋白上的扩展，这需要 LD3 基序和 LIM3 结构域。当在人类白细胞性 K562 细胞中表达时，leupaxin 显著抑制整合素 alpha5beta1 介导的细胞黏附到纤维连接蛋白和桩蛋白的酪氨酸磷酸化。这些发现表明，leupaxin 作为一种桩蛋白对应物发挥作用，在整合素信号传导过程中强烈抑制桩蛋白的酪氨酸磷酸化。
