Lehrstuhl Zellbiologie X908, Universität Konstanz, Universitätsstr. 10, 78457 Konstanz, Germany.
J Cell Sci. 2010 Dec 15;123(Pt 24):4280-91. doi: 10.1242/jcs.064006. Epub 2010 Nov 23.
Staphylococcus aureus, which is a leading cause of hospital-acquired infections, binds via fibronectin to integrin α5β1, a process that can promote host colonization in vivo. Integrin engagement induces actin cytoskeleton rearrangements that result in the uptake of S. aureus by non-professional phagocytic cells. Interestingly, we found that fibronectin-binding S. aureus trigger the redistribution of membrane microdomain components. In particular, ganglioside GM1 and GPI-linked proteins were recruited upon integrin β1 engagement, and disruption of membrane microdomains blocked bacterial internalization. Several membrane-microdomain-associated proteins, such as flotillin-1 and flotillin-2, as well as caveolin, were recruited to sites of bacterial attachment. Whereas dominant-negative versions of flotillin-2 did not affect bacterial attachment or internalization, cells deficient for caveolin-1 (Cav1(-/-)) showed increased uptake of S. aureus and other Fn-binding pathogens. Recruitment of membrane microdomains to cell-associated bacteria was unaltered in Cav1(-/-) cells. However, fluorescence recovery after photobleaching (FRAP) revealed an enhanced mobility of membrane-microdomain-associated proteins in the absence of caveolin-1. Enhanced membrane microdomain mobility and increased uptake of S. aureus was repressed by expression of wild-type caveolin-1, but not caveolin-1 G83S, which harbors a point mutation in the caveolin scaffolding domain. Similarly, chemical or physical stimulation of membrane fluidity led to increased uptake of S. aureus. These results highlight a crucial role for caveolin-1 in negative regulation of membrane microdomain mobility, thereby affecting endocytosis of bacteria-engaged integrins. This process might not only limit host cell invasion by integrin-binding bacterial pathogens, but might also be physiologically relevant for integrin-mediated cell adhesion.
金黄色葡萄球菌是医院获得性感染的主要原因，它通过纤维连接蛋白与整合素 α5β1 结合，这一过程可以促进宿主在体内的定植。整合素的结合诱导细胞骨架的重排，导致非专业吞噬细胞摄取金黄色葡萄球菌。有趣的是，我们发现纤维连接蛋白结合的金黄色葡萄球菌触发了膜微区成分的再分布。特别是，神经节苷脂 GM1 和 GPI 连接蛋白在整合素 β1 结合后被募集，而破坏膜微区会阻止细菌内化。几种与膜微区相关的蛋白质，如 flotillin-1 和 flotillin-2，以及 caveolin，被募集到细菌附着的部位。虽然 flotillin-2 的显性失活突变体不会影响细菌的附着或内化，但 caveolin-1 缺陷型（Cav1(-/-)）细胞对金黄色葡萄球菌和其他 Fn 结合病原体的摄取增加。Cav1(-/-)细胞中膜微区向细胞相关细菌的募集没有改变。然而，光漂白后荧光恢复（FRAP）显示在缺乏 caveolin-1 的情况下，膜微区相关蛋白的流动性增强。在 caveolin-1 表达的情况下，膜微区的流动性增强和金黄色葡萄球菌的摄取增加受到抑制，但 caveolin-1 G83S 不受抑制，后者在 caveolin 支架结构域中存在一个点突变。同样，膜流动性的化学或物理刺激导致金黄色葡萄球菌摄取增加。这些结果突出了 caveolin-1 在负调控膜微区流动性从而影响整合素结合细菌内化中的关键作用。这个过程不仅可以限制整合素结合的细菌病原体对宿主细胞的入侵，而且可能对整合素介导的细胞黏附具有生理相关性。
