Lipopolysaccharide activates caspase-1 (interleukin-1-converting enzyme) in cultured monocytic and endothelial cells.
Interleukin-1 beta (IL-1 beta) is a pleiotropic proinflammatory cytokine. Mechanisms leading to its secretion include not only release of newly synthesized protein, but also cleavage of a preformed immature precursor protein into an active secretory form by the intracellular protease caspase-1 (formerly termed IL-1-converting enzyme [ICE]). Caspase-1 belongs to a rapidly growing family of cysteine proteases with substrate specificity for aspartate involved in cellular apoptosis. We have used an assay determining the caspase-1 activity based on cleavage of a fluorogenic peptide substrate to elucidate its role in lipopolysaccharide (LPS)-induced secretion of IL-1 beta. We show that LPS induces moderate caspase-1 activity in the monocytic cell line THP-1, in freshly isolated peripheral blood monocytes, and in human umbilical vein endothelial cells (HUVECs) in a time- and dose-dependent fashion. Caspase-1 activation by LPS was associated with cleavage of the IL-1 beta precursor protein that was followed by release of the mature IL-1 beta protein in monocytic cells. In contrast, subsequent release of IL-1 beta by HUVECs was not significant. LPS-induced caspase-1 activation appeared not to result from modulation of caspase-1 transcript accumulation and inhibition of caspase-1 activity was accomplished by two specific inhibitors, YVAD-CHO and YVAD-CMK, capable of alleviating the release of mature IL-1 beta. Taken together, these results show that LPS moderately activates caspase-1 and that caspase-1 activation contributes to LPS induction of IL-1 beta secretion.
Schumann
R R
RR
Molecular Sepsis Research Laboratory, Max-Delbrück-Center for Molecular Medicine, University Hospital Charité, Humboldt-University, Berlin, Germany.
Belka
C
C
Reuter
D
D
Lamping
N
N
Kirschning
C J
CJ
Weber
J R
JR
Pfeil
D
D
D020170:Caspase 1; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007375:Interleukin-1 / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D009000:Monocytes / Q000201:enzymology*
D007375:Interleukin-1; D008070:Lipopolysaccharides; D003546:Cysteine Endopeptidases; D020170:Caspase 1