Involvement of a calpain-like protease in the processing of the murine interleukin 1 alpha precursor.
Interleukin (IL) 1 alpha is synthesized as a 33-kDa precursor that is enzymatically cleaved to the 15-17-kDa forms that are found in the culture supernatants of activated macrophages. We have explored the possibility that calcium might enhance IL-1 processing and secretion via the stimulation of a calcium-dependent protease. We have found that lysates prepared from human peripheral blood monocytes, the human histiocytic lymphoma cell line U937, and the murine macrophage cell line P388D1 contain a calcium-dependent IL-1 alpha processing activity that cleaves the IL-1 alpha precursor to its mature form. Although NIH 3T3 mouse fibroblast cell lysates also contain IL-1 processing activity, lysates from the murine thymoma EL-4, the human epidermoid cell line HEp-2, and the human foreskin fibroblast line FS-4 lack this activity. IL-1 processing activity is inhibited by leupeptin and exhibits a molecular mass of 80-110 kDa. The processing activity is also inhibited by a monoclonal antibody directed against calpain type I. These results indicate that the processing of the IL-1 alpha precursor is mediated, at least in part, by a member of the calpain family of proteases. Mixing experiments revealed that lysates from EL-4 or HEp-2 cells contain an inhibitor(s) of the calpain-like protease in macrophage extracts. It is, therefore, likely that many non-macrophage cell types are unable to process the IL-1 alpha precursor because the calpain present in these cells is only weakly active due to the presence of a specific inhibitor(s) such as calpastatin.
Carruth
L M
LM
Department of Microbiology and Immunology, Wake Forest University Medical Center, Winston-Salem, North Carolina 27103.
Demczuk
S
S
Mizel
S B
SB
D000818:Animals; D015153:Blotting, Western; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002154:Calpain / Q000378:metabolism*; D002460:Cell Line; D002850:Chromatography, Gel; D010450:Endopeptidases / Q000378:metabolism*; D006868:Hydrolysis; D007375:Interleukin-1 / Q000235:genetics / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D016297:Mutagenesis, Site-Directed; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*
D007375:Interleukin-1; D011498:Protein Precursors; D000001:Calcimycin; D015759:Ionomycin; D010450:Endopeptidases; D002154:Calpain; D002118:Calcium