title: TNFα-induced apoptosis enabled by CCN1/CYR61: pathways of reactive oxygen species generation and cytochrome c release.
abstract: Although TNFα is a strong inducer of apoptosis, its cytotoxicity in most normal cells in vitro requires blockade of NFκB signaling or inhibition of de novo protein synthesis, typically by the addition of cycloheximide. However, several members of CCN (CYR61/CTGF/NOV) family of extracellular matrix proteins enable TNFα-dependent apoptosis in vitro without inhibiting NFκB or de novo protein synthesis, and CCN1 (CYR61) is essential for optimal TNFα cytotoxicity in vivo. Previous studies showed that CCN1 unmasks the cytotoxicity of TNFα by binding integrins α(v)β(5), α(6)β(1), and the cell surface heparan sulfate proteoglycan syndecan 4 to induce the accumulation of a high level of reactive oxygen species (ROS), leading to a biphasic activation of JNK necessary for apoptosis. Here we show for the first time that CCN1 interacts with the low density lipoprotein receptor-related protein 1 (LRP1) in a protein complex, and that binding to LRP1 is critical for CCN1-induced ROS generation and apoptotic synergism with TNFα. We also found that neutral sphingomyelinase 1 (nSMase1), which contributes to CCN1-induced ROS generation, is required for CCN1/TNFα-induced apoptosis. Furthermore, CCN1 promotes the activation of p53 and p38 MAPK, which mediate enhanced cytochrome c release to amplify the cytotoxicity of TNFα. By contrast, LRP1, nSMase1, p53, and p38 MAPK are not required when TNFα-dependent apoptosis is facilitated by the presence of cycloheximide, indicating that they function in the CCN1 signaling pathway that converges with TNFα-induced signaling events. Since CCN1/CYR61 is a physiological regulator of TNFα cytotoxicity at least in some contexts, these findings may reveal important mediators of TNFα-induced apoptosis in vivo and identify potential therapeutic targets for thwarting TNFα-dependent tissue damage.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Illinois College of Medicine, Chicago, Illinois, United States of America.
authors.forename: Vladislava
authors.initials: V
authors.lastname: Juric
authors.forename: Chih-Chiun
authors.initials: CC
authors.lastname: Chen
authors.forename: Lester F
authors.initials: LF
authors.lastname: Lau
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D003513:Cycloheximide / Q000494:pharmacology; D055515:Cysteine-Rich Protein 61 / Q000378:metabolism*; D045304:Cytochromes c / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000378:metabolism; D008954:Models, Biological; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D055515:Cysteine-Rich Protein 61; C475476:LRP1 protein, human; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D017382:Reactive Oxygen Species; D014409:Tumor Necrosis Factor-alpha; D016159:Tumor Suppressor Protein p53; D045304:Cytochromes c; D003513:Cycloheximide; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D013108:Sphingomyelin Phosphodiesterase