RESUMEN
The Wnt/ß-catenin signalling and autophagy pathways each play important roles during development, adult tissue homeostasis and tumorigenesis. Here we identify the Wnt/ß-catenin signalling pathway as a negative regulator of both basal and stress-induced autophagy. Manipulation of ß-catenin expression levels in vitro and in vivo revealed that ß-catenin suppresses autophagosome formation and directly represses p62/SQSTM1 (encoding the autophagy adaptor p62) via TCF4. Furthermore, we show that during nutrient deprivation ß-catenin is selectively degraded via the formation of a ß-catenin-LC3 complex, attenuating ß-catenin/TCF-driven transcription and proliferation to favour adaptation during metabolic stress. Formation of the ß-catenin-LC3 complex is mediated by a W/YXXI/L motif and LC3-interacting region (LIR) in ß-catenin, which is required for interaction with LC3 and non-proteasomal degradation of ß-catenin. Thus, Wnt/ß-catenin represses autophagy and p62 expression, while ß-catenin is itself targeted for autophagic clearance in autolysosomes upon autophagy induction. These findings reveal a regulatory feedback mechanism that place ß-catenin at a key cellular integration point coordinating proliferation with autophagy, with implications for targeting these pathways for cancer therapy.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales/metabolismo , Autofagia , Factores de Transcripción Básicos con Cremalleras de Leucinas y Motivos Hélice-Asa-Hélice/metabolismo , Neoplasias del Colon/patología , Lisosomas/metabolismo , Factores de Transcripción/metabolismo , Proteínas Wnt/metabolismo , beta Catenina/metabolismo , Proteínas Adaptadoras Transductoras de Señales/genética , Animales , Antígenos CD/genética , Antígenos CD/metabolismo , Factores de Transcripción Básicos con Cremalleras de Leucinas y Motivos Hélice-Asa-Hélice/genética , Western Blotting , Inmunoprecipitación de Cromatina , Neoplasias del Colon/genética , Neoplasias del Colon/metabolismo , Técnica del Anticuerpo Fluorescente , Humanos , Técnicas para Inmunoenzimas , Receptor Leucocitario Tipo Inmunoglobulina B1 , Ratones , Ratones Noqueados , Proteínas Asociadas a Microtúbulos/genética , Proteínas Asociadas a Microtúbulos/metabolismo , Fagosomas/metabolismo , Complejo de la Endopetidasa Proteasomal/metabolismo , Proteolisis , ARN Mensajero/genética , ARN Interferente Pequeño/genética , Reacción en Cadena en Tiempo Real de la Polimerasa , Receptores Inmunológicos/genética , Receptores Inmunológicos/metabolismo , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Proteína Sequestosoma-1 , Factor de Transcripción 4 , Factores de Transcripción/genética , Células Tumorales Cultivadas , Proteínas Wnt/genética , beta Catenina/antagonistas & inhibidores , beta Catenina/genéticaRESUMEN
Autophagy is a cell-protective and degradative process that recycles damaged and long-lived cellular components. Cancer cells are thought to take advantage of autophagy to help them to cope with the stress of tumorigenesis; thus targeting autophagy is an attractive therapeutic approach. However, there are currently no specific inhibitors of autophagy. ULK1, a serine/threonine protein kinase, is essential for the initial stages of autophagy, and here we report that two compounds, MRT67307 and MRT68921, potently inhibit ULK1 and ULK2 in vitro and block autophagy in cells. Using a drug-resistant ULK1 mutant, we show that the autophagy-inhibiting capacity of the compounds is specifically through ULK1. ULK1 inhibition results in accumulation of stalled early autophagosomal structures, indicating a role for ULK1 in the maturation of autophagosomes as well as initiation.