RESUMEN
Lysosomal degradation of the endoplasmic reticulum (ER) via autophagy (ER-phagy) is emerging as a critical regulator of cell homeostasis and function. The recent identification of ER-phagy receptors has shed light on the molecular mechanisms underlining this process. However, the signaling pathways regulating ER-phagy in response to cellular needs are still largely unknown. We found that the nutrient responsive transcription factors TFEB and TFE3-master regulators of lysosomal biogenesis and autophagy-control ER-phagy by inducing the expression of the ER-phagy receptor FAM134B. The TFEB/TFE3-FAM134B axis promotes ER-phagy activation upon prolonged starvation. In addition, this pathway is activated in chondrocytes by FGF signaling, a critical regulator of skeletal growth. FGF signaling induces JNK-dependent proteasomal degradation of the insulin receptor substrate 1 (IRS1), which in turn inhibits the PI3K-PKB/Akt-mTORC1 pathway and promotes TFEB/TFE3 nuclear translocation and enhances FAM134B transcription. Notably, FAM134B is required for protein secretion in chondrocytes, and cartilage growth and bone mineralization in medaka fish. This study identifies a new signaling pathway that allows ER-phagy to respond to both metabolic and developmental cues.
Asunto(s)
Autofagia , Factores de Transcripción Básicos con Cremalleras de Leucinas y Motivos Hélice-Asa-Hélice/metabolismo , Núcleo Celular/metabolismo , Retículo Endoplásmico/metabolismo , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Proteínas de la Membrana/metabolismo , Transducción de Señal , Transporte Activo de Núcleo Celular , Animales , Factores de Transcripción Básicos con Cremalleras de Leucinas y Motivos Hélice-Asa-Hélice/genética , Núcleo Celular/genética , Retículo Endoplásmico/genética , Células HeLa , Humanos , Péptidos y Proteínas de Señalización Intracelular/genética , Diana Mecanicista del Complejo 1 de la Rapamicina/genética , Diana Mecanicista del Complejo 1 de la Rapamicina/metabolismo , Proteínas de la Membrana/genética , Ratones , OryziasRESUMEN
Autophagy is a cytosolic quality control process that recognizes substrates through receptor-mediated mechanisms. Procollagens, the most abundant gene products in Metazoa, are synthesized in the endoplasmic reticulum (ER), and a fraction that fails to attain the native structure is cleared by autophagy. However, how autophagy selectively recognizes misfolded procollagens in the ER lumen is still unknown. We performed siRNA interference, CRISPR-Cas9 or knockout-mediated gene deletion of candidate autophagy and ER proteins in collagen producing cells. We found that the ER-resident lectin chaperone Calnexin (CANX) and the ER-phagy receptor FAM134B are required for autophagy-mediated quality control of endogenous procollagens. Mechanistically, CANX acts as co-receptor that recognizes ER luminal misfolded procollagens and interacts with the ER-phagy receptor FAM134B. In turn, FAM134B binds the autophagosome membrane-associated protein LC3 and delivers a portion of ER containing both CANX and procollagen to the lysosome for degradation. Thus, a crosstalk between the ER quality control machinery and the autophagy pathway selectively disposes of proteasome-resistant misfolded clients from the ER.
Asunto(s)
Calnexina/metabolismo , Retículo Endoplásmico/metabolismo , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Proteínas de la Membrana/metabolismo , Procolágeno/metabolismo , Animales , Autofagia , Calnexina/genética , Línea Celular , Técnicas de Silenciamiento del Gen , Células HeLa , Humanos , Péptidos y Proteínas de Señalización Intracelular/genética , Proteínas de la Membrana/genética , Ratones , Proteínas Asociadas a Microtúbulos/metabolismo , Oryzias , Pliegue de ProteínaRESUMEN
Protein biogenesis within the endoplasmic reticulum (ER) is crucial for organismal function. Errors during protein folding necessitate the removal of faulty products. ER-associated protein degradation and ER-phagy target misfolded proteins for proteasomal and lysosomal degradation. The mechanisms initiating ER-phagy in response to ER proteostasis defects are not well understood. By studying mouse primary cells and patient samples as a model of ER storage disorders (ERSDs), we show that accumulation of faulty products within the ER triggers a response involving SESTRIN2, a nutrient sensor controlling mTORC1 signaling. SESTRIN2 induction by XBP1 inhibits mTORC1's phosphorylation of TFEB/TFE3, allowing these transcription factors to enter the nucleus and upregulate the ER-phagy receptor FAM134B along with lysosomal genes. This response promotes ER-phagy of misfolded proteins via FAM134B-Calnexin complex. Pharmacological induction of FAM134B improves clearance of misfolded proteins in ERSDs. Our study identifies the interplay between nutrient signaling and ER quality control, suggesting therapeutic strategies for ERSDs.