RESUMEN
The ubiquitin-proteasome system degrades viral oncoproteins and other microbial virulence factors; however, the role of endolysosomal degradation pathways in these processes is unclear. Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of Kaposi's sarcoma, and a constitutively active viral G protein-coupled receptor (vGPCR) contributes to the pathogenesis of KSHV-induced tumors. We report that a recently discovered autophagy-related protein, Beclin 2, interacts with KSHV GPCR, facilitates its endolysosomal degradation, and inhibits vGPCR-driven oncogenic signaling. Furthermore, monoallelic loss of Becn2 in mice accelerates the progression of vGPCR-induced lesions that resemble human Kaposi's sarcoma. Taken together, these findings indicate that Beclin 2 is a host antiviral molecule that protects against the pathogenic effects of KSHV GPCR by facilitating its endolysosomal degradation. More broadly, our data suggest a role for host endolysosomal trafficking pathways in regulating viral pathogenesis and oncogenic signaling.
Asunto(s)
Proteínas Reguladoras de la Apoptosis/fisiología , Herpesvirus Humano 8/fisiología , Lisosomas/fisiología , Receptores Acoplados a Proteínas G/metabolismo , Proteínas Virales/metabolismo , Animales , Proteínas Reguladoras de la Apoptosis/genética , Autofagia/fisiología , Beclina-1 , Transformación Celular Viral , Cruzamientos Genéticos , Modelos Animales de Enfermedad , Endocitosis/fisiología , Predisposición Genética a la Enfermedad , Células HEK293 , Herpesvirus Humano 8/inmunología , Herpesvirus Humano 8/patogenicidad , Heterocigoto , Humanos , Inmunidad Innata , Péptidos y Proteínas de Señalización Intercelular , Interleucina-6/biosíntesis , Interleucina-6/genética , Lisosomas/virología , Ratones , FN-kappa B/metabolismo , Proteínas/fisiología , Proteolisis , ARN Interferente Pequeño , Receptores de Quimiocina/metabolismo , Sarcoma de Kaposi/genética , Sarcoma de Kaposi/patología , Sarcoma de Kaposi/virología , Neoplasias Cutáneas/genética , Neoplasias Cutáneas/patología , Neoplasias Cutáneas/virologíaRESUMEN
A long-standing controversy is whether autophagy is a bona fide cause of mammalian cell death. We used a cell-penetrating autophagy-inducing peptide, Tat-Beclin 1, derived from the autophagy protein Beclin 1, to investigate whether high levels of autophagy result in cell death by autophagy. Here we show that Tat-Beclin 1 induces dose-dependent death that is blocked by pharmacological or genetic inhibition of autophagy, but not of apoptosis or necroptosis. This death, termed "autosis," has unique morphological features, including increased autophagosomes/autolysosomes and nuclear convolution at early stages, and focal swelling of the perinuclear space at late stages. We also observed autotic death in cells during stress conditions, including in a subpopulation of nutrient-starved cells in vitro and in hippocampal neurons of neonatal rats subjected to cerebral hypoxia-ischemia in vivo. A chemical screen of ~5,000 known bioactive compounds revealed that cardiac glycosides, antagonists of Na(+),K(+)-ATPase, inhibit autotic cell death in vitro and in vivo. Furthermore, genetic knockdown of the Na(+),K(+)-ATPase α1 subunit blocks peptide and starvation-induced autosis in vitro. Thus, we have identified a unique form of autophagy-dependent cell death, a Food and Drug Administration-approved class of compounds that inhibit such death, and a crucial role for Na(+),K(+)-ATPase in its regulation. These findings have implications for understanding how cells die during certain stress conditions and how such cell death might be prevented.