Post-translational regulation of transcription factor EB

The bHLH-LZ transcription factor EB (TFEB) is a master regulator of lysosomal biogenesis and autophagy, it also plays an important role in lipid and glucose metabolism, mitochondrial biogenesis, integrated stress response and immunity. Dysregulation of TFEB family is implicated in cancer as well as neurodegenerative diseases. TFEB subcellular localisation and transcriptional activity are regulated by cellular nutrient and energy status. Elucidating the mechanism of TFEB regulation is the key to understanding its role in maintaining cellular homeostasis as well as providing therapeutic insights. In this study we showed that TFEB subcellular localisation is regulated by both amino acids and glucose availability. Low glucose levels activate mTORC2-AKT signalling, leading to the inactivation of GSK3β, and GSK3β kinase activity is required for TFEB cytoplasmic localisation. We also demonstrated that GSK3β phosphorylates TFEB at S138 only after a priming phosphorylation event at S142. The sequential phosphorylation is required for CRM1-depedent nuclear export of TFEB via a novel nuclear export signal. This mechanism is important for the rapid cytoplasmic relocalisation and inactivation of TFEB upon nutrient replenishment. Additionally, we performed a high-throughput screen of 1,600 FDA-approved drugs and identified around 100 chemical modulators of TFEB and TFE3, of which around 50 % exhibited lysosomal biogenesis promoting potential. In particular, trifluoperazine, pimozide and loperamide induce TFEB nuclear translocation, lysosomal biogenesis and autophagy in an mTORC1- and AMPK- independent manner.