Nitric oxide inhibits tumor necrosis factor-α-induced apoptosis by reducing the generation of ceramide

^*Department of Neuroscience, DIBIT-H San Raffaele Institute, and Consiglio Nazionale delle Ricerche, Centre of Cellular and Molecular Pharmacology, 20132 Milan, Italy; ^†Institute of Pharmacology, University of Urbino, 61029, Italy; ^‡The Wolfson Institute for Biomedical Research, University College London, London WC1E 6BT, United Kingdom; and ^§Department of Pharmaco-Biology, University of Calabria, 87036 Rende, Italy

Contributed by Salvador Moncada

Abstract

Apoptosis triggered by death receptors proceeds after defined signal-transduction pathways. Whether signaling at the receptor level is regulated by intracellular messengers is still unknown. We have investigated the role of two messengers, ceramide and nitric oxide (NO), on the apoptotic pathway activated in human monocytic U937 cells by tumor necrosis factor-α (TNF-α) working at its p55 receptor. Two transduction events, the receptor recruitment of the adapter protein, TRADD, and the activation of the initiator caspase, caspase 8, were investigated. When administered alone, neither of the messengers had any effect on these events. In combination with TNF-α, however, ceramide potentiated, whereas NO inhibited, TNF-α-induced TRADD recruitment and caspase 8 activity. The effect of NO, which was cGMP-dependent, was due to inhibition of the TNF-α-induced generation of ceramide. Our results identify a mechanism of regulation of a signal-transduction pathway activated by death receptors.

Footnotes

↵ ¶ To whom reprint requests should be addressed at: DIBIT-H San Raffaele Scientific Institute, Via Olgettina 58, 20132 Milan, Italy. E-mail: clementi.emilio{at}hsr.it.
Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.070062397.
Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.070062397
Abbreviations:

TNF-α and TNF-R1,

tumor necrosis factor-α and its p55 receptor;

ODQ,

H-[1,2,4]oxadiazolo[4,3-α]quinoxalin-1-one;

PDMP,

dl-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol;

D609,

tricyclodecan-9-yl xanthate;

SNAP,

S-nitroso-acetylpenicillamine;

CHX,

cycloheximide