REGULATION OF HUMAN CELL DEATH RESPONSES TO YERSINIA INFECTION

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Degree type
Doctor of Philosophy (PhD)
Graduate group
Immunology
Discipline
Immunology and Infectious Disease
Microbiology
Biology
Subject
Caspase
host defense
Yersinia
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Copyright date
2023
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Author
Nataraj, Neha, Mahalakshmi
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Abstract

Regulated cell death in response to microbial infection plays an important role in immune defense and is triggered by pathogen disruption of essential cellular pathways. Gram-negative bacterial pathogens in the Yersinia genus disrupt NF-κB signaling via translocated effectors injected by a type III secretion system (T3SS), thereby preventing induction of cytokine production and antimicrobial defense. In murine models of infection, Yersinia blockade of NF-κB signaling triggers cell-extrinsic apoptosis through Receptor Interacting Serine-Threonine Protein Kinase 1 (RIPK1) and caspase-8, which is required for bacterial clearance and host survival. However, significant differences in immune genes exist between humans and mice. Using in vitro infection models and CRISPR-Cas9 technology, we sought to uncover how Yersinia-induced cell death signaling works in human macrophages. Unexpectedly, we find that human macrophages undergo apoptosis independently of RIPK1 in response to Yersinia or chemical blockade of IKKβ. Instead, IKK blockade led to decreased cFLIP expression, and overexpression of cFLIP contributed to protection from IKK blockade-induced apoptosis in human macrophages. Importantly, IKK blockade also induces RIPK1 kinase-independent apoptosis in human T cells and human pancreatic cells. Altogether, our data indicate that, in contrast to murine cells, blockade of IKK activity in human cells triggers a distinct apoptosis pathway that is independent of RIPK1. These findings have implications for the contribution of RIPK1 to cell death in humans and the efficacy of RIPK1 inhibition in human diseases.

Advisor
Brodsky, Igor, E
Shin, Sunny
Date of degree
2023
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