Role of caspase-1 in nuclear translocation of IL-37, release of the cytokine, and IL-37 inhibition of innate immune responses.
IL-37 is a fundamental inhibitor of innate immunity. Human IL-37 has a caspase-1 cleavage site and translocates to the nucleus upon LPS stimulation. Here, we investigated whether caspase-1 processing affects IL-37-mediated suppression of LPS-induced cytokines and the release from cells by analyzing a caspase-1 cleavage site mutant IL-37 (IL-37D20A). Nuclear translocation of IL-37D20A is significantly impaired compared with WT IL-37 in transfected cells. LPS-induced IL-6 was decreased in cells expressing WT IL-37 but not IL-37D20A. The function of IL-37 in transfected bone marrow-derived macrophages is nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome-dependent, because IL-37 transfection in apoptosis-associated speck-like protein containing a carboxyl-terminal caspase recruitment domain- and NLRP3-deficient cells does not reduce levels of IL-6 and IL-1β upon LPS stimulation. IL-37-expressing macrophages release both precursor and mature IL-37, but only the externalization of mature IL-37 was dependent on ATP. Precursor and mature IL-37 was also secreted from human dendritic cells and peripheral blood mononuclear cells. To determine whether IL-37 is active in the extracellular compartment, we pretreated IL-37 transgenic mice with IL-37-neutralizing antibodies before LPS challenge. In IL-37-expressing mice, neutralizing IL-37 antibodies reversed the suppression of LPS-induced serum IL-6. In contrast, the addition of neutralizing antibody did not reverse suppression of LPS-induced IL-6 in mouse macrophages transfected with IL-37. Although caspase-1 is required for nuclear translocation of intracellular IL-37 and for secretion of mature IL-37, the release of the IL-37 precursor is independent of caspase-1 activation. IL-37 now emerges as a dual-function cytokine with intra- and extracellular properties for suppressing innate inflammation.
Department of Pediatrics, Dr. von Hauner Children's Hospital, Ludwig Maximilians University, D-80337 Munich, Germany.
Ana-Maria
AM
Bulau
Marcel F
MF
Nold
Suzhao
S
Li
Claudia A
CA
Nold-Petry
Michaela
M
Fink
Ashley
A
Mansell
Tobias
T
Schwerd
Jaewoo
J
Hong
Anna
A
Rubartelli
Charles A
CA
Dinarello
Philip
P
Bufler
D021581:Active Transport, Cell Nucleus / Q000276:immunology; D000818:Animals; D057134:Antibodies, Neutralizing / Q000276:immunology*; D015153:Blotting, Western; D020170:Caspase 1 / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D004926:Escherichia coli; D005455:Fluorescent Antibody Technique; D006801:Humans; D007113:Immunity, Innate / Q000276:immunology*; D007375:Interleukin-1 / Q000378:metabolism*; D015850:Interleukin-6 / Q000097:blood; D008070:Lipopolysaccharides; D051379:Mice; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D016297:Mutagenesis, Site-Directed
D057134:Antibodies, Neutralizing; C508587:IL37 protein, human; D007375:Interleukin-1; D015850:Interleukin-6; D008070:Lipopolysaccharides; D020170:Caspase 1