Understanding the Regulation of TFEB and Rab7 and Their Contributions to Lysosomal Adaptation

Lysosomes can adapt their activity and biogenesis through alterations in genetic expression of lysosomal genes by transcription factor EB (TFEB), and potentially by modifying membrane trafficking through increased activation and recruitment of Rab7 to lysosomes. This research investigated how TFEB is differentially modified and what the relationship between Rab7 and mTOR inhibition is within the context of membrane trafficking. 

Mass spectrometry revealed 6 novel phosphorylated sites on TFEB: S108, S113, T329, T330, S331 and S465. S108 and S113 showed evidence of mTOR mediated phosphorylation, while phosphorylation on S465 is hypothesized to be mTOR-independent. All phosphorylated sites are hypothesized to result in cytoplasmic retention and TFEB inactivation. Additionally, mTOR inhibition resulted in increased lysosomal-bound Rab7 and subsequent increase in cargo trafficking and degradation. Delineating TFEB activation patterns and understanding the mechanistic pathway of Rab7 activation along with its downstream effects may help improve our understanding of key regulators of lysosomal adaptation.