Engagement of CD46 and α5β1 integrin by group A streptococci is required for efficient invasion of epithelial cells

Abstract

SummaryMembrane cofactor protein (MCP or CD46), a widely distributed complement regulatory human protein, is a cell surface receptor for many pathogens including group A streptococci (GAS). The surface M protein of GAS binds CD46 and mediates GAS adherence to keratinocytes. In the present study, we studied the role of CD46 in GAS invasion of human lung epithelial cells, A549. Anti-CD46 antibody which specifically blocks the domain to which M protein binds inhibited adherence to and invasion of A549 cells by GAS. Moreover, downregulation of CD46 expression on A549 by RNA interference resulted in reduced invasion of these cells by GAS. A mutant form of CD46 with a deletion in the cytoplasmic domain was overexpressed in A549 cells, which resulted in partial inhibition of invasion. This indicates that the cytoplasmic tail is required for CD46 to promote invasion by GAS. Invasion assays with Lactococcus lactis that express M protein demonstrated the dependence of CD46-promoted invasion on interaction with M protein. In addition, CD46-mediated invasion was also found to be dependent on the extracellular matrix protein fibronectin.

CD46 Contributes to the Severity of Group A Streptococcal Infection

“…Interestingly, the expression of ␤1 integrin was slightly reduced at 24 h (Fig. 1C), supporting that CD46 is linked to ␤1 integrin, as was previously reported (38). Control experiments showed that bacteria pretreated with ethanol or heat did not mediate the loss of CD46 in FaDu cells, suggesting that the process required viable bacteria (data not shown).…”

“…These data suggest that human CD46 plays an important role during S. pyogenes infection. CD46 serves as a receptor for several pathogens including strains of measles virus (10), human herpesvirus type 6 (42), group A streptococci (38), adenovirus (13,45), and Neisseria (24). Among these pathogens, infection by certain strains of measles virus (33,43), human herpesvirus type 6 (42), serogroup B adenovirus (41), and Neisseria gonorrhoeae (15) has been shown to cause CD46 downregulation from the cell surface.…”

“…This process prevents the formation of the membrane attack complex and consequently protects human cells from complement-mediated lysis (30). It was shown that S. pyogenes interacts with CD46 during invasion of epithelial cells (38). Furthermore, the interaction between S. pyogenes and CD46 triggers cell signaling pathways that induce an immunosuppressive/regulatory phenotype in T cells (37).…”

“…An important virulence factor used by S. pyogenes is the M protein, which has been shown to mediate binding to keratinocytes (8,36) and to participate in the invasion of epithelial cells (38). To colonize and cause disease, the bacteria must overcome early defense mechanisms that normally should eliminate and remove bacteria from the mucosal surface.…”

MAP1272c Encodes an NlpC/P60 Protein, an Antigen Detected in Cattle with Johne's Disease

“…Surface-exposed proteins are best positioned to be major contributors of host cell invasion, and antibodies against such proteins have been shown to be effective at blocking invasion (26,28). NlpC contains invasion-associated domains in addition to the P60 domain mentioned in the introduction.…”