Inhibition of the conversion of pre-interleukins-1 alpha and 1 beta to mature cytokines by p-benzoquinone, a metabolite of benzene.
Chronic exposure of humans to benzene causes severe bone marrow cell depression leading to aplastic anemia. Marrow stromal macrophage dysfunction and deficient interleukin-1 production has been reported for patients with severe aplastic anemia. The stromal macrophage, a target of benzene toxicity, is involved in hematopoietic regulation through the synthesis of several cytokines including interleukin-1, which is required for production by stromal fibroblasts of a number of cytokines required for the survival of hematopoietic progenitor cells. We have previously demonstrated that hydroquinone, a major toxic metabolite of benzene in marrow, prevents the proteolytic conversion of 31 kDa pre-interleukin-1 alpha to the 17 kDa cytokine by calpain in purified murine stromal macrophages. Furthermore, stromal macrophages from benzene-treated mice produce the 31 kDa pre-interleukin-1 alpha when stimulated in culture with endotoxin, but cannot convert the precursor to interleukin-1 alpha. In this report, we show that 1,4-benzoquinone, the oxidation product of hydroquinone in the cell, causes a concentration-dependent inhibition of highly purified human platelet calpain with an IC50 of 3 microM. Hydroquinone also inhibits the processing of pre-interleukin-1 beta by interleukin-1 beta convertase. The addition of 2 microM hydroquinone to B1 cells that undergo autocrine stimulation by interleukin-1 beta resulted in the cessation of autocrine cell growth and interleukin-1 beta secretion into the culture medium, as determined by Western immunoblots of the culture supernatants. Purified converting enzyme treated with 3 microM benzoquinone was incapable of converting 31 kDa recombinant pre-interleukin-1 beta to the 17 kDa mature cytokine as analyzed by polyacrylamide gel electrophoresis and Western immunoblotting. These findings support our observations in a mouse model that benzene-induced bone marrow cell depression results from a lack of interleukin-1 alpha subsequent to an inhibition by benzoquinone of calpain, the protease required for converting pre-interleukin-1 alpha to active cytokine. The results may provide a basis for studying benzene-induced aplastic anemia in a mouse model.
Department of Biochemistry and Molecular Biology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA.
R
R
Niculescu
H N
HN
Bradford
R W
RW
Colman
G F
GF
Kalf
D001554:Benzene / Q000378:metabolism / Q000633:toxicity; D016227:Benzoquinones / Q000633:toxicity*; D015153:Blotting, Western; D002154:Calpain / Q000037:antagonists & inhibitors*; D020170:Caspase 1; D002455:Cell Division / Q000187:drug effects; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000633:toxicity; D006801:Humans; D006873:Hydroquinones / Q000633:toxicity; D007213:Indomethacin / Q000633:toxicity; D007375:Interleukin-1 / Q000378:metabolism*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014407:Tumor Cells, Cultured
D016227:Benzoquinones; D015853:Cysteine Proteinase Inhibitors; D006873:Hydroquinones; D007375:Interleukin-1; D011498:Protein Precursors; D011994:Recombinant Proteins; C043830:interleukin 1 precursor; C004532:quinone; D002154:Calpain; D003546:Cysteine Endopeptidases; D020170:Caspase 1; D001554:Benzene; C031927:hydroquinone; D007213:Indomethacin