RESUMEN
NF-κB-inducing kinase (NIK) is well-known for its role in promoting p100/NF-κB2 processing into p52, a process defined as the alternative, or non-canonical, NF-κB pathway. Here we reveal an unexpected new role of NIK in TNFR1-mediated RIP1-dependent apoptosis, a consequence of TNFR1 activation observed in c-IAP1/2-depleted conditions. We show that NIK stabilization, obtained by activation of the non-death TNFRs Fn14 or LTßR, is required for TNFα-mediated apoptosis. These apoptotic stimuli trigger the depletion of c-IAP1/2, the phosphorylation of RIP1 and the RIP1 kinase-dependent assembly of the RIP1/FADD/caspase-8 complex. In the absence of NIK, the phosphorylation of RIP1 and the formation of RIP1/FADD/caspase-8 complex are compromised while c-IAP1/2 depletion is unaffected. In vitro kinase assays revealed that recombinant RIP1 is a bona fide substrate of NIK. In vivo, we demonstrated the requirement of NIK pro-death function, but not the processing of its substrate p100 into p52, in a mouse model of TNFR1/LTßR-induced thymus involution. In addition, we also highlight a role for NIK in hepatocyte apoptosis in a mouse model of virus-induced TNFR1/RIP1-dependent liver damage. We conclude that NIK not only contributes to lymphoid organogenesis, inflammation and cell survival but also to TNFR1/RIP1-dependent cell death independently of the alternative NF-κB pathway.
Asunto(s)
Proteínas Activadoras de GTPasa/metabolismo , FN-kappa B/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Receptores Tipo I de Factores de Necrosis Tumoral/metabolismo , Animales , Apoptosis/efectos de los fármacos , Caspasa 8/química , Caspasa 8/metabolismo , Línea Celular , Proteína de Dominio de Muerte Asociada a Fas/química , Proteína de Dominio de Muerte Asociada a Fas/metabolismo , Proteínas Activadoras de GTPasa/química , Células HEK293 , Humanos , Proteínas Inhibidoras de la Apoptosis/genética , Proteínas Inhibidoras de la Apoptosis/metabolismo , Hígado/efectos de los fármacos , Hígado/metabolismo , Hígado/patología , Receptor beta de Linfotoxina/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Fosforilación , Proteínas Serina-Treonina Quinasas/deficiencia , Proteínas Serina-Treonina Quinasas/genética , Transducción de Señal/efectos de los fármacos , Timo/metabolismo , Timo/patología , Factor de Necrosis Tumoral alfa/farmacología , Quinasa de Factor Nuclear kappa BRESUMEN
Decidualization of endometrial stromal cells (ESCs) is critical for a successful pregnancy but the molecular mechanisms of the process are poorly understood. In this study, we investigated whether the insulin-like growth factor (IGF) network is involved in this cellular process. Expression kinetics of members of the IGF system was examined at both mRNA and protein levels during in-vitro decidualization of cultured human ESCs. We found a significant up-regulation of IGF-II as well as of IGF-I receptor and the A and B insulin receptor (InsR) isoforms. In addition, levels of the key adaptor proteins insulin receptor substrate 1 (IRS-1) and IRS-2 increased, suggesting a potential involvement of the IGF signalling pathway in the decidualization process. Expression of two IGF binding proteins, IGFBP-1 and IGFBP-4, which can inhibit IGF action, also increased. In order to determine whether IGF signalling was activated during decidualization, the phosphorylation status of the receptors and the adaptor proteins was estimated. Only IRS-2 was slightly phosphorylated in decidualized cells and was further activated by the addition of exogenous IGF-II. These results suggest that the IGF signalling pathway could play a crucial role in the functions of decidualized endometrial cells.
