B-216. Caspase-1 Activation in Macrophages Infected with Yersinia pestis KIM Requires the Type III Secretion System Effector YopJ

S. Lilo, Y. Zheng, J. B. Bliska;
State Univ. of New York, Stony Brook, NY.

Pathogenic Yersinia species utilize a type III secretion system (T3SS) to translocate effectors called Yersinia outer proteins (Yops) into infected host cells. Previous studies demonstrated a role for effector Yops in the inhibition of caspase-1-mediated cell death and secretion of IL-1β in naïve macrophages infected with Yersinia enterocolitica. Naïve murine bone marrow-derived macrophages were infected with a panel of different Yersinia pestis and Yersinia pseudotuberculosis strains to determine if Yops of these species inhibit caspase-1 activation. Cell death was measured by release of lactate dehydrogenase (LDH) and ELISA for secreted IL-1β was used to measure caspase-1 activation. Surprisingly, isolates derived from the Y. pestis KIM strain (e.g. KIM5), displayed an unusual ability to activate caspase-1 and kill infected macrophages as compared to other Y. pestis and Y. pseudotuberculosis strains tested. Secretion of IL-1β from macrophages infected with KIM5 was reduced in the presence of a caspase-1 inhibitor. However, release of LDH was not reduced under conditions of caspase-1 inhibition, indicating that cell death occurs independently of caspase-1. Analysis of KIM-derived strains defective for production of functional effector or translocator Yops indicated that translocation of catalytically active YopJ into macrophages was required for caspase-1 activation and cell death. Release of LDH and secretion of IL-1β was not reduced when actin polymerization was inhibited in KIM5-infected macrophages, indicating that extracellular bacteria translocating YopJ could trigger cell death and caspase-1 activation. This study uncovered a novel role for YopJ in the activation of caspase-1 in infected macrophages.