title: YopJ-induced caspase-1 activation in Yersinia-infected macrophages: independent of apoptosis, linked to necrosis, dispensable for innate host defense.
abstract: Yersinia outer protein J (YopJ) is a type III secretion system (T3SS) effector of pathogenic Yersinia (Yersinia pestis, Yersinia enterocolitica and Yersinia pseudotuberculosis) that is secreted into host cells. YopJ inhibits survival response pathways in macrophages, causing cell death. Allelic variation of YopJ is responsible for differential cytotoxicity in Yersinia strains. YopJ isoforms in Y. enterocolitica O:8 (YopP) and Y. pestis KIM (YopJ(KIM)) strains have high cytotoxic activity. In addition, YopJ(KIM)-induced macrophage death is associated with caspase-1 activation and interleukin-1β (IL-1β secretion. Here, the mechanism of YopJ(KIM)-induced cell death, caspase-1 activation, and IL-1β secretion in primary murine macrophages was examined. Caspase-3/7 activity was low and the caspase-3 substrate poly (ADP-ribose) polymerase (PARP) was not cleaved in Y. pestis KIM5-infected macrophages. In addition, cytotoxicity and IL-1β secretion were not reduced in the presence of a caspase-8 inhibitor, or in B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax)/Bcl-2 homologous antagonist/killer (Bak) knockout macrophages, showing that YopJ(KIM)-mediated cell death and caspase-1 activation occur independent of mitochondrial-directed apoptosis. KIM5-infected macrophages released high mobility group protein B1 (HMGB1), a marker of necrosis, and microscopic analysis revealed that necrotic cells contained active caspase-1, indicating that caspase-1 activation is associated with necrosis. Inhibitor studies showed that receptor interacting protein 1 (RIP1) kinase and reactive oxygen species (ROS) were not required for cytotoxicity or IL-β release in KIM5-infected macrophages. IL-1β secretion was reduced in the presence of cathepsin B inhibitors, suggesting that activation of caspase-1 requires cathepsin B activity. Ectopically-expressed YopP caused higher cytotoxicity and secretion of IL-1β in Y. pseudotuberculosis-infected macrophages than YopJ(KIM). Wild-type and congenic caspase 1 knockout C57BL/6 mice were equally susceptible to lethal infection with Y. pseudotuberculosis ectopically expressing YopP. These data suggest that YopJ-induced caspase-1 activation in Yersinia-infected macrophages is a downstream consequence of necrotic cell death and is dispensable for innate host resistance to a strain with enhanced cytotoxicity.
authors.affiliation: Department of Molecular Genetics and Microbiology, and Center for Infectious Diseases, Stony Brook University, Stony Brook, New York, United States of America.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zheng
authors.forename: Sarit
authors.initials: S
authors.lastname: Lilo
authors.forename: Patricio
authors.initials: P
authors.lastname: Mena
authors.forename: James B
authors.initials: JB
authors.lastname: Bliska
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D020170:Caspase 1 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D061945:Caspase Inhibitors; D002401:Cathepsin B / Q000037:antagonists & inhibitors / Q000378:metabolism; D002478:Cells, Cultured; D004789:Enzyme Activation; D005260:Female; D020690:GTPase-Activating Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D024243:HMGB1 Protein / Q000378:metabolism; D007113:Immunity, Innate; D053583:Interleukin-1beta / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism* / Q000382:microbiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008928:Mitochondria / Q000378:metabolism; D009336:Necrosis / Q000378:metabolism* / Q000473:pathology; D011480:Protease Inhibitors / Q000494:pharmacology; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D015007:Yersinia / Q000378:metabolism* / Q000472:pathogenicity; D015009:Yersinia Infections / Q000378:metabolism / Q000382:microbiology / Q000473:pathology; D015008:Yersinia enterocolitica / Q000378:metabolism / Q000472:pathogenicity; D015010:Yersinia pestis / Q000378:metabolism / Q000472:pathogenicity; D015011:Yersinia pseudotuberculosis / Q000378:metabolism / Q000472:pathogenicity; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000172:deficiency / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D061945:Caspase Inhibitors; D020690:GTPase-Activating Proteins; D024243:HMGB1 Protein; D053583:Interleukin-1beta; D011480:Protease Inhibitors; D020033:Protein Isoforms; C490620:Ralbp1 protein, mouse; D017382:Reactive Oxygen Species; C109227:YopP protein, Yersinia; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D053148:Caspase 3; D053179:Caspase 7; D053181:Caspase 8; D002401:Cathepsin B; D020170:Caspase 1