Identification of a monocyte specific pre-interleukin 1 beta convertase activity.
Interleukin 1 (IL-1) is a lymphokine secreted by monocytes in response to a variety of inflammatory stimuli. IL-1 beta, the predominant form of IL-1 produced by human monocytes, is synthesized as an inactive precursor of 31 kDa and is cleaved at Asp116-Ala117 to yield a 17.5-kDa extracellular form. The exact cellular site of cleavage and mechanism of secretion is at present unknown. We have prepared cell-free postnuclear extracts from freshly isolated human monocytes as well as THP.1 cells, a human monocyte-like cell line, and various blood lymphocytes and fibroblast cell lines. Using pre-IL-1 beta synthesized by in vitro transcription and translation, we have shown that only extracts derived from human monocytes and THP.1 cells were capable of cleaving precursor IL-1 beta to authentic mature IL-1 beta. Subcellular fractionation of the extracts suggested that the processing activity is found in the cytosol of monocytes or monocyte-like cell lines. The cleavage product of this protease is identical to authentic IL-1 beta as shown by mobility on SDS/PAGE and amino acid sequence analysis of the [3H]leucine-labeled product. The cleavage product is also capable of binding to the IL-1 receptor found on fibroblast membranes. Finally, mutation of Asp116----Ala116 rendered the IL-1 beta precursor resistant to cleavage by the processing activity. We conclude that a protease activity found only in monocytes will specifically process IL-1 beta to an active form.
Kostura
M J
MJ
Department of Biochemical and Molecular Pathology, Merck Sharp & Dohme Research Laboratories, Rahway, NJ 07065.
Tocci
M J
MJ
Limjuco
G
G
Chin
J
J
Cameron
P
P
Hillman
A G
AG
Chartrain
N A
NA
Schmidt
J A
JA
D020170:Caspase 1; D002460:Cell Line; D002474:Cell-Free System; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D006801:Humans; D007375:Interleukin-1 / Q000235:genetics* / Q000302:isolation & purification; D008666:Metalloendopeptidases / Q000097:blood*; D009000:Monocytes / Q000201:enzymology*; D009154:Mutation; D011498:Protein Precursors / Q000235:genetics* / Q000302:isolation & purification
D007375:Interleukin-1; D011498:Protein Precursors; C043830:interleukin 1 precursor; D020170:Caspase 1; D008666:Metalloendopeptidases