Tumor necrosis factor-alpha generates reactive oxygen species via a cytosolic phospholipase A2-linked cascade.
Reactive oxygen species (ROS) are important regulatory molecules implicated in the signaling cascade triggered by tumor necrosis factor (TNF)-alpha, although the events through which TNF-alpha induces ROS generation are not yet well characterized. We therefore investigated selected candidates likely to mediate TNF-alpha-induced ROS generation. Consistent with the role of Rac in that process, stable expression of Rac(Asn-17), a dominant negative Rac1 mutant, completely blocked TNF-alpha-induced ROS generation. To understand better the mediators downstream of Rac, we investigated the involvement of cytosolic phospholipase A(2) (cPLA(2)) activation and metabolism of the resultant arachidonic acid (AA) by 5-lipoxygenase (5-LO). TNF-alpha-induced ROS generation was blocked by inhibition of cPLA(2) or 5-LO, but not cyclooxygenase, suggesting that TNF-alpha-induced ROS generation is dependent on synthesis of AA and its subsequent metabolism to leukotrienes. Consistent with that hypothesis, TNF-alpha Rac-dependently stimulated endogenous production of leukotriene B(4) (LTB(4)), while exogenous application of LTB(4) increased levels of ROS. In contrast, application of leukotrienes C(4), D(4), and E(4) or prostaglandin E(2) had little effect. Our findings suggest that LTB(4) production by 5-LO is situated downstream of the Rac-cPLA(2) cascade, and we conclude that Rac, cPLA(2), and LTB(4) play pivotal roles in the ROS-generating cascade triggered by TNF-alpha.
Department of Life Science, Kwangju Institute of Science and Technology, Kwangju 500-712, Korea.
C H
CH
Woo
Y W
YW
Eom
M H
MH
Yoo
H J
HJ
You
H J
HJ
Han
W K
WK
Song
Y J
YJ
Yoo
J S
JS
Chun
J H
JH
Kim
D000818:Animals; D001094:Arachidonate 5-Lipoxygenase / Q000378:metabolism; D016718:Arachidonic Acid / Q000378:metabolism; D001095:Arachidonic Acids / Q000494:pharmacology; D002460:Cell Line; D003600:Cytosol / Q000201:enzymology*; D004268:DNA-Binding Proteins / Q000502:physiology; D004789:Enzyme Activation; D005799:Genes, Dominant / Q000235:genetics; D016762:Genes, fos / Q000235:genetics; D007211:Indoles / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases; D007975:Leukotriene B4 / Q000378:metabolism / Q000494:pharmacology; D016859:Lipoxygenase Inhibitors; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism*; D018102:Receptors, Leukotriene B4 / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D026362:Serum Response Factor; D015398:Signal Transduction / Q000187:drug effects*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism; D002722:Chlorobenzenes
D001094:Arachidonate 5-Lipoxygenase; D016718:Arachidonic Acid; D001095:Arachidonic Acids; D004268:DNA-Binding Proteins; D007211:Indoles; D048031:JNK Mitogen-Activated Protein Kinases; D007975:Leukotriene B4; D016859:Lipoxygenase Inhibitors; D020928:Mitogen-Activated Protein Kinases; D009687:Nuclear Proteins; D019869:Phosphatidylinositol 3-Kinases; D010741:Phospholipases A; D054467:Phospholipases A2; D017382:Reactive Oxygen Species; D018102:Receptors, Leukotriene B4; D026362:Serum Response Factor; D014409:Tumor Necrosis Factor-alpha; D020830:rac1 GTP-Binding Protein; C081565:arachidonyltrifluoromethane; C060893:MK-886; D002722:Chlorobenzenes