Role of leukocyte specific adaptor protein leupaxin in T cell migration

尽管白细胞的黏附和运动在很大程度上依赖于整合素，但白细胞往往缺乏在其他黏附细胞中作为信号中心的可区分的焦点黏附(FA)。FAs的组装和拆解受局部产生的细胞内信号的调控，Paxlin的酪氨酸磷酸化参与了这一过程。白细胞特异性连接蛋白Leupasin是巴西林家族的成员，与巴西林具有相同的整体结构特征。亮蛋白由多个功能模块组成，包括LD基序和LIM结构域，提示亮蛋白也是参与整合素介导的信号转导的分子接头。然而，亮蛋白和巴西林在整合素信号转导中是相互合作还是相互拮抗仍是个未知数。我们发现亮帕新能有效地抑制巴西林的酪氨酸磷酸化。当在与细胞间黏附分子-1结合的小鼠胸腺瘤BW5147细胞中表达时，亮蛋白积累…BW5147细胞在ICAM-1上迁移时，细胞外有较多的FA样斑块，亮蛋白选择性地位于细胞的尾缘。当在NIH3T3和HEK293T细胞中表达时，亮蛋白在细胞与纤维连接蛋白黏附时定位于FAs，并强烈抑制整合素诱导的帕西林的酪氨酸磷酸化。在整合素刺激的HEK293T细胞中，亮蛋白的LIM3结构域似乎对FA的选择性定位和抑制帕西林酪氨酸磷酸化是必不可少的。亮帕新的LD3基序对于稳定地与FAK结合是至关重要的，而对于亮帕新的抑制能力则是必不可少的。此外，亮蛋白减少了NIH3T3细胞在纤维连接蛋白上的扩散，这需要LD3基序和LIM3结构域。当在人白细胞K562细胞中表达时，亮帕新显著抑制整合素α5β1介导的细胞与纤维连接蛋白的黏附和巴西林的酪氨酸磷酸化。这些发现表明，亮蛋白是一种白细胞特异性的对应物，在整合素信号传递较少的过程中，它能有效地抑制帕西林的酪氨酸磷酸化。

Although the adhesion and locomotion of leukocytes largely depend on integrins, leukocytes often lack the distinguishable focal adhesions (FAs) that serve as signaling centers in other adherent cells. The assembly and disassembly of FAs is regulated by locally produced intracellular signals, and tyrosine phosphorylation of paxillin has been implicated in this process. Aleukocyte-specific adaptor protein, leupaxin, is a member of the paxillin family and shares overall structural characteristics with paxillin. Leupaxin is composed of multiple functional trbodules, including LD motifs and LIM domains, suggesting that leupaxin also serves as a molecular adaptor that is involved in integrinmediated signaling. However, it remains unknown whether leupaxin and paxillin cooperate with or antagonize each other in integrin signaling. We found that leupaxin potently represses the tyrosine phosphorylation of paxillin. When expressed in mouse thymoma BW5147 cells bound to ICAM-1, leupaxin accumulate … More d in FA like patches in the cell periphery In BW5147 cells migrating on ICAM-1, leupaxin is selectively located at the trailing edge. When expressed in NIH3T3 and HEK293Tcells, leupaxin localized to FAs upon cell adhesion to fibronectin and strongly suppressed the integrin-induced tyrosine phosphorylation of paxillin. In integrin-stimulatecd HEK293Tcells, leupaxin's LIM3 domain appeared essential for the 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 α5β1-mediated cell adhesion to fibronectin and the tyrosine phosphorylation of paxillin. These findings indicate that leupaxin functions as a leukocyte-specific counterpart that potently suppresses the tyrosine phosphorylarion of paxillin during integrin signaling Less