title: Staphylococcus aureus protects its immune-evasion proteins against degradation by neutrophil serine proteases.
abstract: Neutrophils store large quantities of neutrophil serine proteases (NSPs) that contribute, via multiple mechanisms, to antibacterial immune defences. Even though neutrophils are indispensable in fighting Staphylococcus aureus infections, the importance of NSPs in anti-staphylococcal defence is yet unknown. However, the fact that S. aureus produces three highly specific inhibitors for NSPs [the extracellular adherence proteins (EAPs) Eap, EapH1 and EapH2], suggests that these proteases are important for host defences against this bacterium. In this study we demonstrate that NSPs can inactivate secreted virulence factors of S. aureus and that EAP proteins function to prevent this degradation. Specifically, we find that a large group of S. aureus immune-evasion proteins is vulnerable to proteolytic inactivation by NSPs. In most cases, NSP cleavage leads to functional inactivation of virulence proteins. Interestingly, proteins with similar immune-escape functions appeared to have differential cleavage sensitivity towards NSPs. Using targeted mutagenesis and complementation analyses in S. aureus, we demonstrate that all EAP proteins can protect other virulence factors from NSP degradation in complex bacterial supernatants. These findings show that NSPs inactivate S. aureus virulence factors. Moreover, the protection by EAP proteins can explain why this antibacterial function of NSPs was masked in previous studies. Furthermore, our results indicate that therapeutic inactivation of EAP proteins can help to restore the natural host immune defences against S. aureus.
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, Utrecht, the Netherlands.
authors.forename: D A C
authors.initials: DA
authors.lastname: Stapels
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, Utrecht, the Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Kuipers
authors.affiliation: Department of Physiological Chemistry, University of Veterinary Medicine Hannover, Hannover, Germany.
authors.forename: M
authors.initials: M
authors.lastname: von Köckritz-Blickwede
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, Utrecht, the Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Ruyken
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, Utrecht, the Netherlands.
authors.forename: A T
authors.initials: AT
authors.lastname: Tromp
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool, UK.
authors.forename: M J
authors.initials: MJ
authors.lastname: Horsburgh
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, Utrecht, the Netherlands.
authors.forename: C J C
authors.initials: CJ
authors.lastname: de Haas
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, Utrecht, the Netherlands.
authors.forename: J A G
authors.initials: JA
authors.lastname: van Strijp
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, Utrecht, the Netherlands.
authors.forename: K P M
authors.initials: KP
authors.lastname: van Kessel
authors.affiliation: Medical Microbiology, University Medical Center Utrecht, Utrecht, the Netherlands.
authors.forename: S H M
authors.initials: SH
authors.lastname: Rooijakkers
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D057131:Immune Evasion; D009504:Neutrophils / Q000201:enzymology* / Q000276:immunology; D059748:Proteolysis; D057057:Serine Proteases / Q000378:metabolism*; D015842:Serine Proteinase Inhibitors / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000276:immunology* / Q000472:pathogenicity / Q000502:physiology; D037521:Virulence Factors / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D015842:Serine Proteinase Inhibitors; D037521:Virulence Factors; D057057:Serine Proteases
keywords: Stapylococci; degradation; granules; immunology; virulence