title: IQGAP1 is important for activation of caspase-1 in macrophages and is targeted by Yersinia pestis type III effector YopM.
abstract: YopM is a leucine-rich repeat (LRR)-containing effector in several Yersinia species, including Yersinia pestis and Y. pseudotuberculosis. Different Yersinia strains encode distinct YopM isoforms with variable numbers of LRRs but conserved C-terminal tails. A 15-LRR isoform in Y. pseudotuberculosis YPIII was recently shown to bind and inhibit caspase-1 via a YLTD motif in LRR 10, and attenuation of YopM(-) YPIII was reversed in mice lacking caspase-1, indicating that caspase-1 inhibition is a major virulence function of YopM(YPIII). To determine if other YopM proteins inhibit caspase-1, we utilized Y. pseudotuberculosis strains natively expressing a 21-LRR isoform lacking the YLTD motif (YopM(32777)) or ectopically expressing a Y. pestis 15-LRR version with a functional (YopM(KIM)) or inactivated (YopM(KIM) D271A) YLTD motif. Results of mouse and macrophage infections with these strains showed that YopM(32777), YopM(KIM), and YopM(KIM) D271A inhibit caspase-1 activation, indicating that the YLTD motif is dispensable for this activity. Analysis of YopM(KIM) deletion variants revealed that LRRs 6 to 15 and the C-terminal tail are required to inhibit caspase-1 activation. YopM(32777), YopM(KIM), and YopM(KIM) deletion variants were purified, and binding partners in macrophage lysates were identified. Caspase-1 bound to YopM(KIM) but not YopM(32777). Additionally, YopM(KIM) bound IQGAP1 and the use of Iqgap1(-/-) macrophages revealed that this scaffolding protein is important for caspase-1 activation upon infection with YopM(-) Y. pseudotuberculosis. Thus, while multiple YopM isoforms inhibit caspase-1 activation, their variable LRR domains bind different host proteins to perform this function and the LRRs of YopM(KIM) target IQGAP1, a novel regulator of caspase-1, in macrophages. Importance: Activation of caspase-1, mediated by macromolecular complexes termed inflammasomes, is important for innate immune defense against pathogens. Pathogens can, in turn, subvert caspase-1-dependent responses through the action of effector proteins. For example, the Yersinia effector YopM inhibits caspase-1 activation by arresting inflammasome formation. This caspase-1 inhibitory activity has been studied in a specific YopM isoform, and in this case, the protein was shown to act as a pseudosubstrate to bind and inhibit caspase-1. Different Yersinia strains encode distinct YopM isoforms, many of which lack the pseudosubstrate motif. We studied additional isoforms and found that these YopM proteins inhibit caspase-1 activation independently of a pseudosubstrate motif. We also identified IQGAP1 as a novel binding partner of the Yersinia pestis YopM(KIM) isoform and demonstrated that IQGAP1 is important for caspase-1 activation in macrophages infected with Yersinia. Thus, this study reveals new insights into inflammasome regulation during Yersinia infection.
authors.affiliation: Department of Molecular Genetics and Microbiology and Center for Infectious Diseases, Stony Brook University, Stony Brook, New York, USA.
authors.forename: Lawton K
authors.initials: LK
authors.lastname: Chung
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA;
authors.forename: Naomi H
authors.initials: NH
authors.lastname: Philip
authors.affiliation: Department of Medicine, School of Medicine, Stony Brook University, Stony Brook, New York, USA.
authors.forename: Valentina A
authors.initials: VA
authors.lastname: Schmidt
authors.affiliation: Proteomics Center, School of Medicine, Stony Brook University, Stony Brook, New York, USA;
authors.forename: Antonius
authors.initials: A
authors.lastname: Koller
authors.affiliation: Department of Immunobiology and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA.
authors.forename: Till
authors.initials: T
authors.lastname: Strowig
authors.affiliation: Department of Immunobiology and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut, USA.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Flavell
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA;
authors.forename: Igor E
authors.initials: IE
authors.lastname: Brodsky
authors.affiliation: Department of Molecular Genetics and Microbiology and Center for Infectious Diseases, Stony Brook University, Stony Brook, New York, USA james.bliska@stonybrook.edu.
authors.forename: James B
authors.initials: JB
authors.lastname: Bliska
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism*; D020170:Caspase 1 / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D005260:Female; D008264:Macrophages / Q000201:enzymology*; D051379:Mice; D018345:Mice, Knockout; D015010:Yersinia pestis / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D020170:Caspase 1