KSHV-encoded ORF45 activates human NLRP1 inflammasome

Area of Science:

• Immunology
• Virology
• Molecular Biology

Background:

• The NOD-like receptor (NLR)-containing pyrin domain (PYD) (NLRP)1 inflammasome is crucial for immune responses.
• At steady state, NLRP1 is auto-inhibited by dipeptidyl peptidases 8 and 9 (DPP8/DPP9) and activated by pathogen proteases.

Purpose of the Study:

• To investigate the mechanism of human NLRP1 (hNLRP1) inflammasome activation by Kaposi's sarcoma-associated herpesvirus (KSHV).
• To identify the specific regions and interactions involved in KSHV-mediated hNLRP1 activation.

Main Methods:

• Biochemical assays to study protein interactions and inflammasome activation.
• Analysis of the role of the Linker1 region in hNLRP1 auto-inhibition and activation.
• Comparative studies of KSHV-mediated activation in human and murine inflammasomes.

Main Results:

• KSHV ORF45 protein activates hNLRP1 inflammasome in a non-protease-dependent manner.
• The Linker1 region of hNLRP1 is essential for both auto-inhibition and non-protease-dependent activation.
• ORF45 binding to Linker1 disrupts the auto-inhibitory complex by displacing UPA, facilitating inflammasome assembly.
• ORF45-induced NLRP1 activation is conserved in primates but not in mice.

Conclusions:

• KSHV ORF45 utilizes a novel, protease-independent pathway to activate the hNLRP1 inflammasome.
• The Linker1 region is a critical regulatory hub for hNLRP1 inflammasome activation.
• Understanding this mechanism provides insights into viral immune evasion strategies and inflammasome regulation.