Proteasome-mediated regulation of interleukin-1beta turnover and export in human monocytes.
Interleukin-1beta is a secreted protein that accumulates in the cytosol as an inactive precursor (pIL-1beta) before processing and release of biologically active protein. To understand the impact of this property on IL-1beta production, we examined the intracellular stability of pIL-1beta in lipopolysaccharide (LPS)-stimulated human monocytes. Precursor IL-1beta was degraded with a relatively short half-life of 2.5 h in the promonocytic cell line, THP-1, and in primary monocytes. MG132 (carbobenzoxyl-leucinyl-leucinyl-leucinal) stabilized pIL-1beta levels in THP-1 cells, suggesting that degradation was proteasome-mediated, but this inhibitor was toxic for primary monocytes, causing release of pIL-1beta as well as the cytoplasmic enzyme, lactate dehydrogenase (LDH) into supernatants. In contrast, clasto-lactacystin beta-lactone, a specific inhibitor of the proteasome, caused a dose-dependent stabilization of intracellular pIL-1beta, and this led to a corresponding increase in mIL-1beta and pIL-1beta but not LDH release into culture supernatants. Therefore, by regulating intracellular levels of precursor IL-1beta, the proteasome plays an important and previously unrecognized role in controlling the amount of biologically active IL-1beta that is exported by activated monocytes.
Moors
M A
MA
Department of Microbiology and Immunology, Wake Forest University Medical Center, Winston-Salem, North Carolina 27157, USA.
Mizel
S B
SB
D000179:Acrylates / Q000494:pharmacology; D003546:Cysteine Endopeptidases / Q000502:physiology*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology / Q000633:toxicity; D006207:Half-Life; D006801:Humans; D007375:Interleukin-1 / Q000378:metabolism*; D007783:Lactones / Q000494:pharmacology; D007930:Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D007948:Leukemia, Monocytic, Acute / Q000473:pathology; D007976:Leupeptins / Q000494:pharmacology / Q000633:toxicity; D008070:Lipopolysaccharides / Q000494:pharmacology; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000502:physiology*; D009363:Neoplasm Proteins / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
D000179:Acrylates; D015853:Cysteine Proteinase Inhibitors; D007375:Interleukin-1; D007783:Lactones; D007976:Leupeptins; D008070:Lipopolysaccharides; D009097:Multienzyme Complexes; D009363:Neoplasm Proteins; C100442:PD 150606; C098869:clasto-lactacystin beta-lactone; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D007930:Leucine; C108192:aloxistatin; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde