Yersinia deploys type III-secreted effectors to evade caspase-4 inflammasome activation in human cells

Abstract

ABSTRACT Yersinia are Gram-negative zoonotic bacteria that use a type III secretion system (T3SS) to inject Yersinia outer proteins into the host cytosol to subvert essential components of innate immune signaling. However, Yersinia virulence activities can elicit activation of inflammasomes, which lead to inflammatory cell death and cytokine release to contain infection. Yersinia activation and evasion of inflammasomes have been characterized in murine macrophages but remain poorly defined in human cells, particularly intestinal epithelial cells (IECs), a primary site of intestinal Yersinia infection. In contrast to murine macrophages, we find that in both human IECs and macrophages, Yersinia pseudotuberculosis T3SS effectors promote evasion of the caspase-4 inflammasome, which senses cytosolic lipopolysaccharide. The anti-phagocytic YopE and YopH, as well as the translocation regulator YopK, were collectively responsible for evading inflammasome activation, in part by inhibiting Yersinia internalization mediated by YadA and β1-integrin signaling. These data provide insight into the mechanisms of Yersinia- mediated inflammasome activation and evasion in human cells and reveal species-specific differences underlying the regulation of inflammasome responses to Yersinia . IMPORTANCE Yersinia are responsible for significant disease burden in humans, ranging from recurrent disease outbreaks (yersiniosis) to pandemics ( Yersinia pestis plague). Together with rising antibiotic resistance rates, there is a critical need to better understand Yersinia pathogenesis and host immune mechanisms, as this information will aid in developing improved immunomodulatory therapeutics. Inflammasome responses in human cells are less studied relative to murine models of infection, though recent studies have uncovered key differences in inflammasome responses between mice and humans. Here, we dissect human intestinal epithelial cell and macrophage inflammasome responses to Yersinia pseudotuberculosis . Our findings provide insight into species- and cell type-specific differences in inflammasome responses to Yersinia .