Abstract
The autophagy-lysosome pathway is a major protein degradation pathway stimulated by multiple cellular stresses, including nutrient or growth factor deprivation, hypoxia, misfolded proteins, damaged organelles, and intracellular pathogens. Recent studies have revealed that transcription factor EB (TFEB) and transcription factor E3 (TFE3) play a pivotal role in the biogenesis and functions of autophagosome and lysosome. Here we report that three translation inhibitors (cycloheximide, lactimidomycin, and rocaglamide A) can facilitate the nuclear translocation of TFEB/TFE3 via dephosphorylation and 14-3-3 dissociation. In addition, the inhibitor-mediated TFEB/TFE3 nuclear translocation significantly increases the transcriptional expression of their downstream genes involved in the biogenesis and function of autophagosome and lysosome. Furthermore, we demonstrated that translation inhibition increased autophagosome biogenesis but impaired the degradative autolysosome formation because of lysosomal dysfunction. These results highlight the previously unrecognized function of the translation inhibitors as activators of TFEB/TFE3, suggesting a novel biological role of translation inhibition in autophagy regulation.
Highlights
Macroautophagy, hereafter referred to as autophagy, is a normal degradative pathway that exists in all eukaryotic cells [1,2]
Our results showed that transcription factor EB (TFEB)-enhanced green fluorescent protein (EGFP) was mainly localized in the cytoplasm, whereas EGFP alone was distributed in the cell under basal conditions (Supplemental Figure S1A)
We determined whether TFEB-EGFP nuclear translocation can be induced by starvation or mechanistic target of rapamycin complex 1 inhibition in the established mouse embryonic fibroblast (MEF)-TFEB-EGFP cell line
Summary
Macroautophagy, hereafter referred to as autophagy, is a normal degradative pathway that exists in all eukaryotic cells [1,2]. Autophagy involves sequestration of cytoplasmic contents, including organelles, by double membranes, to form a unique nascent autophagic vacuole (hereafter autophagosome) and their delivery to lysosomes for digestion [3,4,5]. A number of autophagy-related proteins are implicated in the formation of the autophagosome, such as microtubule-associated proteins 1A/1B light chain 3B (LC3B). LC3B produced as a precursor (pro-LC3B) is cleaved by the ATG4 protease into a cytosolic form referred to as LC3B(I). Increased LC3B(II) is routinely used as a marker of autophagy activation. LC3B is widely used as a microscopic marker of phagophores and autophagosomes [6,7]
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