DPP9's Enzymatic Activity and Not Its Binding to CARD8 Inhibits Inflammasome Activation

Area of Science:

• Immunology
• Molecular Biology
• Biochemistry

Background:

• Inflammasomes are critical pathogen sensors. NLRP1 and CARD8 are inflammasome components with unelucidated activation mechanisms.
• Serine dipeptidyl peptidases DPP8 and DPP9 (DPP8/9) are known to activate NLRP1 and CARD8 inflammasomes. DPP9 directly binds both NLRP1 and CARD8.

Purpose of the Study:

• To investigate the molecular mechanisms underlying the DPP9-CARD8 interaction and its role in inflammasome regulation.
• To determine whether DPP9 binding or catalytic activity is responsible for restraining the CARD8 inflammasome.

Main Methods:

• Activity-based probes and mass spectrometry-based proteomics were employed to study the DPP9-CARD8 interaction.
• Reconstituted inflammasome assays and cell death rescue experiments in DPP9 knockout cells were performed.

Main Results:

• The DPP9-CARD8 interaction is independent of DPP9 inhibitors and CARD8 autoproteolysis mutations.
• Wild-type DPP9, but not a catalytically inactive mutant, rescued CARD8-mediated cell death in DPP9 knockout cells.

Conclusions:

• DPP9's catalytic activity, rather than its direct binding to CARD8, restrains the CARD8 inflammasome.
• The physical interaction between DPP9 and CARD8 likely serves a distinct biological function unrelated to inflammasome inhibition.