Pathogenic phosphorylation of linear ubiquitin machinery causes inflammasome sensor degradation

Area of Science:

• Immunology
• Microbiology
• Molecular Biology

Background:

• Host immune cells utilize cytosolic sensors to detect pathogens and mount anti-infectious responses.
• Mechanisms by which pathogens evade intracellular surveillance for persistent infections remain incompletely understood.

Purpose of the Study:

• To investigate how Mycobacterium tuberculosis (Mtb) subverts host intracellular surveillance.
• To identify bacterial factors involved in evading inflammasome-mediated immunity.

Main Methods:

• Investigated the role of Mtb protein kinase PknG in targeting the host linear ubiquitin chain assembly complex (LUBAC).
• Utilized biochemical assays to analyze the phosphorylation of HOIL-1L by PknG and its impact on LUBAC formation and ubiquitination.
• Assessed the effect of PknG on NLRP3 inflammasome assembly, cytokine release, and pyroptosis.
• Evaluated the in vivo anti-Mtb immunity in mice with disrupted PknG kinase activity or HOIL-1L-interacting regions.

Main Results:

• Mtb PknG targets the LUBAC complex, specifically phosphorylating the HOIL-1L subunit.
• PknG-mediated phosphorylation of HOIL-1L inhibits LUBAC formation and ASC ubiquitination, thereby suppressing NLRP3 inflammasome assembly.
• Phosphorylated HOIL-1L is stabilized and activated, leading to K48-linked ubiquitination and degradation of NLRP3.
• Disruption of PknG's kinase activity or HOIL-1L-binding site enhances NLRP3-dependent anti-Mtb immunity in mice.

Conclusions:

• Mtb PknG subverts host inflammasome surveillance by disrupting the linear ubiquitin machinery.
• The bacterial kinase hijacks LUBAC to promote NLRP3 degradation, facilitating immune evasion for persistent infection.
• Targeting the PknG-LUBAC interaction represents a potential strategy to bolster host anti-mycobacterial immunity.