Staphylococcus aureus Keratinocyte Invasion Is Dependent upon Multiple High-Affinity Fibronectin-Binding Repeats within FnBPA

Abstract

Staphylococcus aureus is a commensal organism and a frequent cause of skin and soft tissue infections, which can progress to serious invasive disease. This bacterium uses its fibronectin binding proteins (FnBPs) to invade host cells and it has been hypothesised that this provides a protected niche from host antimicrobial defences, allows access to deeper tissues and provides a reservoir for persistent or recurring infections. FnBPs contain multiple tandem fibronectin-binding repeats (FnBRs) which bind fibronectin with varying affinity but it is unclear what selects for this configuration. Since both colonisation and skin infection are dependent upon the interaction of S. aureus with keratinocytes we hypothesised that this might select for FnBP function and thus composition of the FnBR region. Initial experiments revealed that S. aureus attachment to keratinocytes is rapid but does not require FnBRs. By contrast, invasion of keratinocytes was dependent upon the FnBR region and occurred via similar cellular processes to those described for endothelial cells. Despite this, keratinocyte invasion was relatively inefficient and appeared to include a lag phase, most likely due to very weak expression of α5β1 integrins. Molecular dissection of the role of the FnBR region revealed that efficient invasion of keratinocytes was dependent on the presence of at least three high-affinity (but not low-affinity) FnBRs. Over-expression of a single high-affinity or three low-affinity repeats promoted invasion but not to the same levels as S. aureus expressing an FnBPA variant containing three high-affinity repeats. In summary, invasion of keratinocytes by S. aureus requires multiple high-affinity FnBRs within FnBPA, and given the importance of the interaction between these cell types and S. aureus for both colonisation and infection, may have provided the selective pressure for the multiple binding repeats within FnBPA.

Fibronectin Binding Proteins SpsD and SpsL Both Support Invasion of Canine Epithelial Cells by Staphylococcus pseudintermedius

“…In S. aureus Fn-binding proteins FnBPA and FnBPB both promote invasion of mammalian cells, where Fn acts as a bridge between the bacterial surface protein which binds to the N-terminal N29 domain by the tandem ␤ zipper mechanism and the ␣ 5 ␤ 1 integrin, which recognizes an RGD motif within C-terminal repeat 10 of Fn (18,31). The finding that the N-terminal region of Fn and an RGD-containing peptide inhibited S. pseudintermedius invasion of CPEK strongly suggests that the same mechanism is employed and involves the Fn binding domains of SpsD and SpsL.…”

Temporins A and B Stimulate Migration of HaCaT Keratinocytes and Kill Intracellular Staphylococcus aureus

“…However, there is clear evidence that it can enter host cells to facilitate escape from immune attack, cellular barriers, and AMPs (54). Transient or persistent infections can occur in healthy individuals (e.g., impetigo and folliculitis), as well as in those with skin lesions due to wounds, inserted medical devices, or chronic autoimmune diseases (55).…”

The Staphylococcal Biofilm: Adhesins, Regulation, and Host Response

“…In place of the SD repeat region, the FNBPs have a region of 10–11 tandem repeats that recognize fibronectin (106). FnBP binding to fibronectin induces bacterial invasion into epithelial cells, endothelial cells, and keratinocytes (107–109). The FnBPs have been found to affect biofilm formation and virulence.…”