Tumor Necrosis Factor-α Generates Reactive Oxygen Species via a Cytosolic Phospholipase A2-linked Cascade

• Published in: The Journal of biological chemistry 2000-10, Vol.275 (41), p.32357
• Main Authors: Chang-Hoon Woo, Young-Woo Eom, Min-Hyuk Yoo, Hae-Jin You, Ho Jae Han, Woo Keun Song, Yung Joon Yoo, Jang-Soo Chun, Jae-Hong Kim
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M005638200

Reactive oxygen species (ROS) are important regulatory molecules implicated in the signaling cascade triggered by tumor necrosis factor (TNF)-α, although the events through which TNF-α induces ROS generation are not yet well characterized. We therefore investigated selected candidates likely to mediate TNF-α-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-α-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-α-induced ROS generation was blocked by inhibition of cPLA 2 or 5-LO, but not cyclooxygenase, suggesting that TNF-α-induced ROS generation is dependent on synthesis of AA and its subsequent metabolism to leukotrienes. Consistent with that hypothesis, TNF-α 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-α.