M1 protein triggers a phosphoinositide cascade for group A Streptococcus invasion of epithelial cells.
Invasion of nonphagocytic cells by bacteria provides a favorable niche for persistence and evasion of host defenses and antibiotics. M protein is a major virulence factor because it promotes high-frequency invasion of epithelial cells by group A Streptococcus (GAS) and also renders the bacterium resistant to phagocytosis. In this study, we investigated the role of M1 protein from serotype M1 strain 90-226 in regulating mammalian signal transduction and cytoskeletal rearrangement for bacterial entry. LY294002 and wortmannin, which are inhibitors of phosphatidylinositol 3-kinase (PI 3-K) blocked invasion of epithelial cells by GAS by 75 and 80%, respectively, but failed to inhibit invasion by Salmonella enterica serovar Typhimurium. Also, epithelial cells transiently transfected with dominant negative p85 and p110 genes, the regulatory and catalytic subunits of PI 3-K, respectively, were less able to be invaded by GAS. To separate the influence of other streptococcal virulence factors from M protein, Lactococcus lactis was engineered to express M1 protein on its surface. L. lactis(pLM1) invaded epithelial cells efficiently in vitro, and PI 3-K inhibitors blocked 90% of this invasion. Purified soluble M1 protein stimulated the formation of stress fibers and actin tuffs on epithelial cells. LY294002 and wortmannin inhibited these cellular changes. A phosphoinositide analogue also inhibited the invasion of epithelial cells by GAS. Therefore, M1 protein, either directly or via bound fibronectin, initiates signals that depend on the lipid kinase PI 3-K pathway, which paves the way for cytoskeletal rearrangement that internalize the bacterium.
D000942:Antigens, Bacterial; D001422:Bacterial Adhesion / Q000187:drug effects; D001425:Bacterial Outer Membrane Proteins / Q000502:physiology*; D002352:Carrier Proteins / Q000502:physiology*; D002460:Cell Line; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000378:metabolism / Q000382:microbiology; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism* / Q000494:pharmacology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D015398:Signal Transduction; D013297:Streptococcus pyogenes / Q000187:drug effects / Q000472:pathogenicity* / Q000502:physiology; D014774:Virulence / Q000502:physiology; D018631:ras Proteins / Q000378:metabolism
D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D005353:Fibronectins; D019869:Phosphatidylinositol 3-Kinases; D010716:Phosphatidylinositols; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D011505:Protein-Tyrosine Kinases; D018631:ras Proteins; C014689:streptococcal M protein