Calcium-independent phospholipase A2 beta is dispensable in inflammasome activation and its inhibition by bromoenol lactone.
Calcium-independent phospholipase A2 (iPLA2) has been suggested to play an important role in the activation of caspase-1 induced by lipopolysaccharides (LPS). Here, we used pharmacological and genetic approaches to study the role of iPLA 2 in the activation of caspase-1. Bromoenol lactone (BEL), an inhibitor that was originally used to support a role for iPLA2 in the secretion of IL-1 beta, prevented caspase-1 activation induced by LPS and ATP as described, and also activation triggered by Salmonella infection and cytosolic flagellin, which rely on the Nlrc4 inflammasome. Analysis of BEL enantiomers showed that the S-BEL form was more effective than R-BEL in inhibiting the inflammasome, suggesting a role for iPLA2 . However, caspase-1 activation and IL-1 beta secretion and their inhibition by BEL were unimpaired in macrophages deficient in iPLA2 beta. BEL was originally identified as an inhibitor of serine proteases. Consistent with the latter, the serine proteases inhibitors TPCK, TLCK and AAF-cmk prevented the activation of the Nlrc4 and Nlrp3 inflammasomes while pan-cathepsin inhibitors were ineffective. These results indicate that iPLA2 beta is not critical for caspase-1 activation as currently proposed. Instead, the results suggest that serine protease(s) targeted by BEL may play a critical role in the activation of the inflammasome triggered by microbial stimuli.
Franchi
Luigi
L
Department of Pathology and Comprehensive Cancer Center, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
Chen
Grace
G
Marina-Garcia
Noemi
N
Abe
Akira
A
Qu
Yan
Y
Bao
Shunzhong
S
Shayman
James A
JA
Turk
John
J
Dubyak
George R
GR
Núñez
Gabriel
G
D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000276:immunology / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000276:immunology / Q000378:metabolism; D002352:Carrier Proteins / Q000276:immunology / Q000378:metabolism; D020170:Caspase 1 / Q000276:immunology / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology*; D054513:Group IV Phospholipases A2 / Q000276:immunology / Q000378:metabolism*; D015151:Immunoblotting; D007249:Inflammation / Q000201:enzymology / Q000276:immunology; D008264:Macrophages / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D009281:Naphthalenes / Q000494:pharmacology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D054512:Phospholipases A2, Calcium-Independent / Q000276:immunology / Q000378:metabolism*; D011753:Pyrones / Q000494:pharmacology*; D013237:Stereoisomerism
D051017:Apoptosis Regulatory Proteins; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; C512299:Ipaf protein, mouse; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D009281:Naphthalenes; C492716:Nlrp3 protein, mouse; D010726:Phosphodiesterase Inhibitors; D011753:Pyrones; C068314:6-(bromomethylene)tetrahydro-3-(1-naphthaleneyl)-2H-pyran-2-one; D054513:Group IV Phospholipases A2; D054512:Phospholipases A2, Calcium-Independent; D020170:Caspase 1