Fowler T, Wann E R, Joh D, Johansson S, Foster T J, Höök M
Center for Extracellular Matrix Biology, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston 77030, USA.
Eur J Cell Biol. 2000 Oct;79(10):672-9. doi: 10.1078/0171-9335-00104.
Although Staphylococcus aureus is primarily considered an extracellular pathogen, recent evidence suggests that this bacterium can invade a variety of nonprofessional phagocytic cells. Here we investigate the early stages of cellular invasion by S. aureus and determine the bacterial and host components that are required for this process. S. aureus expresses two cell surface-associated fibronectin (FN)-binding proteins (FnbpA and FnbpB) that mediate the interaction of the bacteria with both soluble and solid-phase FN in vitro. Using a mutant of S. aureus that lacks the expression of both Fnbps, we show that the expression of either protein is necessary for efficient uptake by the mouse fibroblast line GD25beta1A. Invasion could be inhibited by soluble recombinant proteins encompassing either the FN-binding D repeat region or the A region (and B repeats) of FnbpA, suggesting that the activities of both regions are important in this process. We demonstrate that FN is also required for invasion of this cell line. In the presence of FN-depleted fetal bovine serum, the invasion level was reduced by approximately 40% compared to in the presence of whole fetal bovine serum. Invasion could be further reduced by the addition of anti-mouse FN antibodies to the assay. Finally, we utilize a mutant mouse fibroblast line, which lacks beta1 integrin expression, to demonstrate that host cell beta1 integrins are necessary for efficient cellular invasion. The level of invasion of the mutant cell line GD25 was reduced by approximately 97% compared to the beta1-expressing complemented cell line GD25beta1A. In addition, invasion of the GD25beta1A cell line could be inhibited by an RGD-containing peptide, further implicating a role for integrins in this process. Based on these observations, we put forward a model of S. aureus invasion in which host FN forms a bridge between the bacterial Fnbps and host cell beta1 integrins, leading to bacterial uptake.
尽管金黄色葡萄球菌主要被视为一种胞外病原体，但最近的证据表明这种细菌能够侵入多种非专职吞噬细胞。在此，我们研究了金黄色葡萄球菌细胞侵袭的早期阶段，并确定了该过程所需的细菌和宿主成分。金黄色葡萄球菌表达两种细胞表面相关的纤连蛋白（FN）结合蛋白（FnbpA和FnbpB），它们在体外介导细菌与可溶性和固相FN的相互作用。使用缺乏两种Fnbps表达的金黄色葡萄球菌突变体，我们发现任何一种蛋白的表达对于小鼠成纤维细胞系GD25β1A的有效摄取都是必需的。包含FnbpA的FN结合D重复区域或A区域（以及B重复区域）的可溶性重组蛋白可抑制侵袭，这表明这两个区域的活性在该过程中都很重要。我们证明FN对于该细胞系的侵袭也是必需的。在存在FN缺失的胎牛血清的情况下，与存在完整胎牛血清相比，侵袭水平降低了约40%。向试验中添加抗小鼠FN抗体可进一步降低侵袭。最后，我们利用缺乏β1整合素表达的突变小鼠成纤维细胞系，证明宿主细胞β1整合素对于有效的细胞侵袭是必需的。与表达β1的互补细胞系GD25β1A相比，突变细胞系GD25的侵袭水平降低了约97%。此外，含RGD的肽可抑制GD25β1A细胞系的侵袭，这进一步表明整合素在该过程中发挥作用。基于这些观察结果，我们提出了一个金黄色葡萄球菌侵袭模型，其中宿主FN在细菌Fnbps和宿主细胞β1整合素之间形成桥梁，导致细菌摄取。
