Cue D, Dombek P E, Lam H, Cleary P P
Department of Microbiology, University of Minnesota, Minneapolis, Minnesota, USA.
Infect Immun. 1998 Oct;66(10):4593-601. doi: 10.1128/IAI.66.10.4593-4601.1998.
The ability of a serotype M1 strain of Streptococcus pyogenes to efficiently invade A549 human lung epithelial cells was previously shown to be dependent on bacterial exposure to human or bovine serum proteins or synthetic peptides containing the sequence RGD. In this study, stimulation by invasion agonists was determined to be dependent on expression of the streptococcal cell surface protein, M1. Fetal bovine serum (FBS), fibronectin (Fn), the extracellular matrix protein laminin (Lm), and RGD-containing peptides were tested for their abilities to promote epithelial cell invasion and adherence by isogenic M1(+) and M1(-) strains of S. pyogenes. In the absence of an agonist, invasion and adherence were comparable for the two bacterial strains. FBS, Fn, and Lm stimulated invasion of the M1(+) strain as much as 70-fold but failed to significantly affect invasion by the M1(-) mutant. Adherence of the wild-type strain was stimulated by these same agonists. Epithelial cell adherence by the M1(-) strain, however, was unaffected by the presence of Fn or Lm. Several RGD-containing peptides were found to promote invasion independently of M1 expression. Binding of 125I-Fn was reduced 88% by the M1(-) mutation and Fn was found to bind purified M1 protein, suggesting that Fn mediates invasion by direct binding to M1. To determine if host integrins might be involved in internalization of streptococci, several anti-integrin monoclonal antibodies (MAbs) were tested for their abilities to inhibit invasion. Antibody directed against integrin beta1 inhibited FBS-, Fn-, and Lm-mediated invasion but did not abrogate RGD-peptide-stimulated invasion. MAb directed against the epithelial cell Fn receptor, integrin alpha5beta1, inhibited Fn and FBS-mediated invasion but did not specifically inhibit Lm-mediated invasion. These results indicate that S. pyogenes has evolved multiple mechanisms for invasion of eukaryotic cells, at least two of which involve interactions between M1 protein, host integrins, and integrin ligands.
先前研究表明，化脓性链球菌M1血清型菌株有效侵袭A549人肺上皮细胞的能力取决于细菌与人或牛血清蛋白或含有RGD序列的合成肽的接触。在本研究中，侵袭激动剂的刺激作用被确定取决于链球菌细胞表面蛋白M1的表达。检测了胎牛血清（FBS）、纤连蛋白（Fn）、细胞外基质蛋白层粘连蛋白（Lm）以及含RGD的肽促进化脓性链球菌同基因M1(+)和M1(-)菌株侵袭和黏附上皮细胞的能力。在没有激动剂的情况下，两种细菌菌株的侵袭和黏附能力相当。FBS、Fn和Lm刺激M1(+)菌株的侵袭能力高达70倍，但对M1(-)突变体的侵袭没有显著影响。这些相同的激动剂刺激野生型菌株的黏附。然而，Fn或Lm的存在对M1(-)菌株的上皮细胞黏附没有影响。发现几种含RGD的肽可独立于M1表达促进侵袭。M1(-)突变使125I-Fn的结合减少了88%，并且发现Fn可结合纯化的M1蛋白，这表明Fn通过直接结合M1介导侵袭。为了确定宿主整合素是否可能参与链球菌的内化过程，检测了几种抗整合素单克隆抗体（MAb）抑制侵袭的能力。针对整合素β1的抗体抑制FBS、Fn和Lm介导的侵袭，但不消除RGD肽刺激的侵袭。针对上皮细胞Fn受体整合素α5β1的MAb抑制Fn和FBS介导的侵袭，但不特异性抑制Lm介导的侵袭。这些结果表明，化脓性链球菌已经进化出多种侵袭真核细胞的机制，其中至少两种涉及M1蛋白、宿主整合素和整合素配体之间的相互作用。
