RESUMEN
The X-linked inhibitor of apoptosis protein (XIAP) is a potent caspase inhibitor, best known for its anti-apoptotic function in cancer. During apoptosis, XIAP is antagonized by SMAC, which is released from the mitochondria upon caspase-mediated activation of BID. Recent studies suggest that XIAP is involved in immune signaling. Here, we explore XIAP as an important mediator of an immune response against the enteroinvasive bacterium Shigella flexneri, both in vitro and in vivo. Our data demonstrate for the first time that Shigella evades the XIAP-mediated immune response by inducing the BID-dependent release of SMAC from the mitochondria. Unlike apoptotic stimuli, Shigella activates the calpain-dependent cleavage of BID to trigger the release of SMAC, which antagonizes the inflammatory action of XIAP without inducing apoptosis. Our results demonstrate how the cellular death machinery can be subverted by an invasive pathogen to ensure bacterial colonization.
Asunto(s)
Proteína Proapoptótica que Interacciona Mediante Dominios BH3/fisiología , Proteínas Portadoras/metabolismo , Disentería Bacilar/inmunología , Mitocondrias/inmunología , Proteínas Mitocondriales/metabolismo , Shigella/inmunología , Proteína Inhibidora de la Apoptosis Ligada a X/fisiología , Animales , Apoptosis , Proteínas Reguladoras de la Apoptosis , Western Blotting , Caspasas/metabolismo , Proliferación Celular , Células Cultivadas , Disentería Bacilar/microbiología , Disentería Bacilar/patología , Femenino , Hepatocitos/inmunología , Hepatocitos/metabolismo , Hepatocitos/patología , Técnicas para Inmunoenzimas , Integrasas/metabolismo , Masculino , Potencial de la Membrana Mitocondrial , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Mitocondrias/metabolismo , Mitocondrias/patología , Proteínas Mitocondriales/inmunología , ARN Mensajero/genética , Reacción en Cadena en Tiempo Real de la Polimerasa , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Shigella/patogenicidad , Transducción de Señal , Espectrometría de Masa por Ionización de Electrospray , Espectrometría de Masas en TándemRESUMEN
In this study, we show for the first time that the therapeutic antagonization of inhibitor of apoptosis proteins (IAPs) inhibits B16 melanoma growth by disrupting tumor vasculature. Specifically, the treatment of mice bearing B16 melanoma with an IAP antagonist compound A (Comp A) inhibits tumor growth not by inducing direct cytotoxicity against B16 cells but rather by a hitherto unrecognized antiangiogenic activity against tumor vessels. Our detailed analysis showed that Comp A treatment induces NF-κB activity in B16 tumor cells and facilitates the production of TNF. In the presence of Comp A, endothelial cells (ECs) become highly susceptible to TNF and undergo apoptotic cell death. Accordingly, the antiangiogenic and growth-attenuating effects of Comp A treatment were completely abolished in TNF-R knockout mice. This novel targeting approach could be of clinical value in controlling pathological neoangiogenesis under inflammatory condition while sparing blood vessels under normal condition.
Asunto(s)
Inhibidores de la Angiogénesis/farmacología , Endotelio Vascular/patología , Proteínas Inhibidoras de la Apoptosis/antagonistas & inhibidores , Melanoma Experimental/irrigación sanguínea , Melanoma Experimental/tratamiento farmacológico , Animales , Apoptosis/efectos de los fármacos , Inflamación/fisiopatología , Melanoma Experimental/metabolismo , Melanoma Experimental/patología , Ratones , Ratones Noqueados , FN-kappa B/metabolismo , Neovascularización Patológica , Receptores del Factor de Necrosis Tumoral/genética , Factor de Necrosis Tumoral alfa/metabolismoRESUMEN
The BH3-only protein NOXA represents one of the critical mediators of DNA-damage-induced cell death. In particular, its involvement in cellular responses to cancer chemotherapy is increasingly evident. Here, we identify a strategy of cancer cells to escape genotoxic chemotherapy by increasing proteasomal degradation of NOXA. We show that the deubiquitylating enzyme UCH-L1 is a key regulator of NOXA turnover, which protects NOXA from proteasomal degradation by removing Lys(48)-linked polyubiquitin chains. In the majority of tumors from patients with melanoma or colorectal cancer suffering from high rates of chemoresistance, NOXA fails to accumulate because UCH-L1 expression is epigenetically silenced. Whereas UCH-L1/NOXA-positive tumor samples exhibit increased sensitivity to genotoxic chemotherapy, downregulation of UCH-L1 or inhibition of its deubiquitylase activity resulted in reduced NOXA stability and resistance to genotoxic chemotherapy in both human and C. elegans cells. Our data identify the UCH-L1/NOXA interaction as a therapeutic target for overcoming cancer chemoresistance.