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Calcium-Independent Phospholipase A2β Is Dispensable in Inflammasome Activation and Its Inhibition by Bromoenol LactoneFranchi L.a · Chen G.a · Marina-Garcia N.a · Abe A.b · Qu Y.c · Bao S.d · Shayman J.A.b · Turk J.d · Dubyak G.R.c · Núñez G.a
aDepartment of Pathology and Comprehensive Cancer Center, and bDepartment of Internal Medicine, University of Michigan Medical School, Ann Arbor, Mich., cDepartment of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio, and dDepartment of Medicine, Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Mo., USA Corresponding Author
Dr. Gabriel Núñez
Department of Pathology and Comprehensive Cancer Center
University of Michigan Medical School
1500 E. Medical Center Drive, Ann Arbor, MI 48109 (USA)
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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 iPLA2 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-1β, 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 iPLA2β. However, caspase-1 activation and IL-1β secretion and their inhibition by BEL were unimpaired in macrophages deficient in iPLA2β. 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 iPLA2β 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.
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