Identification of constitutively active interleukin 33 (IL-33) splice variant

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Interleukin-33 (IL-33) is an IL-1 family cytokine that elicits T helper immune responses.
• IL-33 signals through ST2 and IL-1 receptor accessory protein (IL-1RAcP), activating NF-κB and MAPK pathways.
• A caspase-1 cleavage site is proposed within IL-33.

Purpose of the Study:

• To identify and characterize a novel splice variant of IL-33.
• To investigate the functional activity and signaling pathways of the new variant.
• To determine the role of caspase-1 in the activity of the IL-33 variant.

Main Methods:

• Isolation of spIL-33 cDNA from Huh7 cells.
• Expression and purification of recombinant spIL-33 and pro-IL-33 in E. coli.
• Functional assays in HMC-1 and Raw 264.7 cells, including cytokine production and protein phosphorylation analysis.
• Treatment with anti-ST2 monoclonal antibody.

Main Results:

• A novel short splice variant of IL-33 (spIL-33) was identified, lacking exon 3.
• Recombinant spIL-33 and pro-IL-33 were not cleaved by caspase-1.
• spIL-33 demonstrated constitutive activity, inducing inflammatory cytokine production independently of caspase-1.
• spIL-33 activated IRAK1, NF-κB, p38 MAPK, p44/42 MAPK, and JNK signaling.
• Anti-ST2 antibody blocked spIL-33-induced cytokine production.

Conclusions:

• A constitutively active IL-33 splice variant (spIL-33) has been identified and characterized.
• The activity of spIL-33 is independent of caspase-1 cleavage.
• The findings suggest diverse mechanisms for IL-33 activation and highlight its potential role in inflammatory disorders.