title: Mutation of lasA and lasB reduces Pseudomonas aeruginosa invasion of epithelial cells.
abstract: Pseudomonas aeruginosa is an opportunistic bacterial pathogen implicated in a variety of devastating conditions. Its flexibility as a pathogen is attributed to a myriad of virulence factors and regulatory elements that respond to prevailing environmental conditions. ExoS and ExoT are type III secreted effector proteins, regulated by the transcriptional activator ExsA, that can inhibit invasion of epithelial cells by cytotoxic strains of P. aeruginosa. This study sought to understand why invasive strains, which can secrete both ExoS and ExoT, still invade epithelial cells. The results showed that LasA and elastase (LasB), which are regulated by the Las and Rhl quorum-sensing systems, modulated P. aeruginosa invasion. Mutation of lasA and/or lasB reduced P. aeruginosa invasion, which was not fully restored by extracellularly added LasB, P. aeruginosa conditioned medium containing LasA and LasB, or EGTA pretreatment of cells. This indicated that protease effects on invasion involved factors additional to tight junction disruption and subsequent alterations to cell polarity. Upon mutation of lasA and/or lasB, steady-state levels of ExoS and ExoT were increased in culture medium of P. aeruginosa grown under conditions stimulatory for these toxins. The increase in ExoS was significantly correlated with reduced invasion. In vitro experiments showed that purified LasB degraded recombinant ExoS. Taken together, these studies suggest a mechanism by which invasive strains can synthesize inhibitors of invasion, ExoS and ExoT, yet still invade epithelial cells. By this mechanism, LasA and LasB decrease the levels of the toxins directly or indirectly, and thus reduce inhibition of invasion.
authors.affiliation: School of Optometry, University of California, Berkeley 94720-2020, CA, USA.
authors.forename: Brigitte A
authors.initials: BA
authors.lastname: Cowell
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI, USA.
authors.forename: Sally S
authors.initials: SS
authors.lastname: Twining
authors.affiliation: Department of Microbiology, Wayne State University, Detroit, MI, USA.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Hobden
authors.affiliation: School of Optometry, University of California, Berkeley 94720-2020, CA, USA.
authors.forename: Mary S F
authors.initials: MSF
authors.lastname: Kwong
authors.affiliation: School of Optometry, University of California, Berkeley 94720-2020, CA, USA.
authors.forename: Suzanne M J
authors.initials: SMJ
authors.lastname: Fleiszig
mesh_terms: D036002:ADP Ribose Transferases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism; D002364:Caseins / Q000378:metabolism; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004549:Elastin / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism; D004847:Epithelial Cells / Q000382:microbiology; D020690:GTPase-Activating Proteins; D066298:In Vitro Techniques; D008666:Metalloendopeptidases / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D011550:Pseudomonas aeruginosa / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity*; D011817:Rabbits; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014774:Virulence / Q000235:genetics / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D002364:Caseins; D004268:DNA-Binding Proteins; C477521:ExoT protein, Pseudomonas aeruginosa; C095092:ExsA protein, bacteria; D020690:GTPase-Activating Proteins; D011994:Recombinant Proteins; D015534:Trans-Activators; D004549:Elastin; D036002:ADP Ribose Transferases; C444820:exoenzyme S; D010450:Endopeptidases; D008666:Metalloendopeptidases; C043859:pseudolysin, Pseudomonas aeruginosa; C087822:alkaline protease; C066371:staphylolytic protease