Glia maturation factor-gamma modulation of signaling pathways in macrophages

单核细胞迁移需要整合素的动态再分配，通过一个受调节的胞内-胞外循环，但这一过程背后的复杂分子机制尚未完全阐明。神经胶质成熟因子- （Glia maturity factor-， GMFG）是Arp2/3复合物的一种新型调节剂，已被证明可以调节中性粒细胞和t淋巴细胞的定向迁移。在这项研究中，我们探讨了GMFG在单核细胞趋化、粘附和1-整合素转换中的重要作用。我们发现，单核细胞中GMFG的敲低导致向甲酰基met - leu - phe （fMLP）和基质细胞衍生因子1 （SDF-1）的趋化迁移受损，以及51整合素介导的趋化剂刺激的粘附减少。这些GMFG敲低受损效应可以通过共转染gfp标记的全长GMFG来逆转。GMFG敲低的细胞减少了51-整合素的细胞表面和总蛋白水平，增加了51-整合素的降解。重要的是，我们证明GMFG通过敲低或过表达介导1-整合素的泛素化。此外，在51-整合素的正常内吞作用后，GMFG敲低延缓了1-整合素回到质膜的有效循环，这表明GMFG参与维持51-整合素的稳定性可能部分是通过阻止泛素介导的降解和促进1-整合素的循环来实现的。此外，我们观察到GMFG与syntaxin 4 （STX4）和syntaxin binding protein 4 （STXBP4）相互作用；然而，只有STXBP4基因表达下调，而STX4基因不表达下调，单核细胞迁移减少，1-整合素细胞表面表达降低。STXBP4的敲低也显著抑制了人单核细胞中1-整合素的循环。这些结果表明，GMFG对单核细胞迁移和粘附的影响可能是通过阻止泛素介导的51-整合素蛋白酶体降解和促进有效的1-整合素循环回质膜来实现的。

Monocyte migration requires the dynamic redistribution of integrins through a regulated endo-exocytosis cycle, but the complex molecular mechanisms underlying this process have not been fully elucidated. Glia maturation factor- (GMFG), a novel regulator of the Arp2/3 complex, has been shown to regulate directional migration of neutrophils and T-lymphocytes. In this study, we explored the important role of GMFG in monocyte chemotaxis, adhesion, and 1-integrin turnover. We found that knockdown of GMFG in monocytes resulted in impaired chemotactic migration toward formyl-Met-Leu-Phe (fMLP) and stromal cell-derived factor 1 (SDF-1) as well as decreased 51-integrin-mediated chemoattractant-stimulated adhesion. These GMFG knockdown impaired effects could be reversed by cotransfection of GFP-tagged full-length GMFG. GMFG knockdown cells reduced the cell surface and total protein levels of 51-integrin and increased its degradation. Importantly, we demonstrate that GMFG mediates the ubiquitination of 1-integrin through knockdown or overexpression of GMFG. Moreover, GMFG knockdown retarded the efficient recycling of 1-integrin back to the plasma membrane following normal endocytosis of 51-integrin, suggesting that the involvement of GMFG in maintaining 51-integrin stability may occur in part by preventing ubiquitin-mediated degradation and promoting 1-integrin recycling. Furthermore, we observed that GMFG interacted with syntaxin 4 (STX4) and syntaxin-binding protein 4 (STXBP4); however, only knockdown of STXBP4, but not STX4, reduced monocyte migration and decreased 1-integrin cell surface expression. Knockdown of STXBP4 also substantially inhibited 1-integrin recycling in human monocytes. These results indicate that the effects of GMFG on monocyte migration and adhesion probably occur through preventing ubiquitin-mediated proteasome degradation of 51-integrin and facilitating effective 1-integrin recycling back to the plasma membrane.