Caspase-4 dimerisation and D289 auto-processing elicit an interleukin-1β-converting enzyme.

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• The noncanonical inflammasome is crucial for cellular defense against Gram-negative bacteria.
• Caspase-4 activation within this complex is essential for initiating inflammatory responses.
• The precise mechanisms of caspase-4 activation and substrate cleavage were previously unclear.

Purpose of the Study:

• To elucidate the molecular mechanisms governing caspase-4 activation and proteolytic activity.
• To identify the substrates and signaling pathways regulated by caspase-4.
• To understand the role of caspase-4 in inflammasome-mediated immunity.

Main Methods:

• Investigated caspase-4 dimerization and self-cleavage using biochemical assays.
• Analyzed the proteolytic activity of caspase-4 species.
• Examined caspase-4-mediated cleavage of gasdermin-D (GSDMD) and pro-IL-1β in human myeloid and epithelial cells.

Main Results:

• Caspase-4 dimerizes and undergoes self-cleavage at D270 and D289 to become fully active.
• Self-cleavage at D289 generates a p34/p9 caspase-4 species.
• This active caspase-4 species directly cleaves pro-IL-1β, independent of the NLRP3 inflammasome, leading to IL-1β maturation and secretion.

Conclusions:

• Caspase-4 activation involves dimerization and specific self-cleavage events.
• Caspase-4 directly processes pro-IL-1β, revealing a novel inflammasome-independent IL-1β maturation pathway.
• This study clarifies key molecular events in noncanonical inflammasome signaling and identifies IL-1β as a direct caspase-4 substrate.