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and MAPK
6 Section of Pulmonary and
Critical Care Medicine and
2 Section of Nephrology,
Particulate matter (PM) is a major by-product
from the combustion of fossil fuels. The biological target of inhaled
PM is the pulmonary epithelium and resident macrophages. In this study, we demonstrate that cultured macrophages (RAW 264.7 cells) exposed continously to a well-defined model of PM
[benzo[a]pyrene adsorbed on carbon black
(CB+BaP)] exhibit a time-dependent expression and release of the
cytokine tumor necrosis factor-
(TNF-
). CB+BaP also evoked
programmed cell death or apoptosis in cultured macrophages as assessed
by genomic DNA-laddering assays. The CB+BaP-induced apoptosis was
inhibited when macrophages were treated with CB+BaP in the presence of
a neutralizing antibody to TNF-
, suggesting that TNF-
plays an
important role in mediating CB+BaP-induced apoptosis in macrophages.
Interestingly, neither untreated carbon black nor
benzo[a]pyrene alone induced apoptosis or caused
the release of TNF-
in RAW 264.7 cells. Moreover, we observed that TNF-
activates mitogen-activated protein kinase (MAPK) activity, the
extracellular signal-regulated kinases p42/p44, in a time-dependent manner. RAW 264.7 cells treated with PD-098059, a selective inhibitor of MAPK kinase activity, did not exhibit CB+BaP-induced apoptosis and
TNF-
secretion. Furthermore, cells treated with the MAPK kinase
inhibitor did not undergo TNF-
-induced apoptosis. Taken together,
our data suggest that TNF-
mediates PM-induced apoptosis and that
the MAPK pathway may play an important role in regulating this pathway.
tumor necrosis factor-
; mitogen-activated protein kinase; programmed cell death; cytokines; carbon; signal transduction; macrophages
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