Linxin Li

4th Year Prize Winner 2018

During my BSc in Biological Sciences at Tsinghua University, I worked on a systematic genetic screen for kinases involved in HDAC inhibitor-induced autophagy in budding yeast, under the supervision of Prof Li Yu. My interest in post-translational regulation of circadian rhythms extended my experience to another kinase screen soon after I started working with Prof Yi Rao at Peking University. Since then, understanding the molecular and cellular mechanisms underlying human diseases and finding a cure have become my biggest motivation.

I came to Oxford in 2014 and started my DPhil supported by the CSC scholarship. In Prof Colin Goding’s lab, I have been working on TFEB, a basic helix-loop-lelix leucine zipper transcription factor known as the master regulator of lysosomal biogenesis and autophagy, which also plays important roles in lipid and glucose metabolism, mitochondrial biogenesis, integrated stress response and immunity. The aberrant regulation of the TFE transcription factor family is often implicated in cancers such as melanoma, pancreatic ductal adenocarcinoma and renal cell carcinoma. The transcriptional activity of TFEB is determined by its subcellular localisation. Upon starvation, TFEB dissociates from cytoplasmic anchor and travels into the nucleus to activate gene transcription. This process is regulated by phosphorylation by multiple kinases including mTORC1, ERK2, MAP4K3 and AKT.

My DPhil project established that unlike amino acid starvation, glucose starvation-induced TFEB nuclear translocation and transcriptional activation is not due to loss of mTORC1 activity. Instead, glucose starvation leads to activation of mTORC2-AKT signalling cascade, which inactivates GSK3β. Our work showed that TFEB phosphorylation by GSK3β is primed by a prior phosphorylation by mTORC1 or ERK2, and that the hierarchical phosphorylation is required for the activation of our newly identified nuclear export signal (NES) of TFEB. Mutation of the consensus sequence in the NES does not prevent TFEB nuclear entry, but disables its nuclear export and inactivation upon nutrient replenishment. Therefore, this project expands the understanding of TFEB regulation in response to nutrient fluctuation, which is subject to a highly dynamic nuclear import-export equilibrium. This mechanism is also conserved in its related factor MITF. Targeting nuclear export of these factors can potentially be therapeutically effective against cancer.

The role in lysosomal biogenesis and autophagy also makes TFEB a promising target for treating lysosomal storage disorders including Alzheimer’s disease, Parkinson’s disease and Huntington’s disease, which leads to the 2nd part of my DPhil project. I designed and performed an image-based high throughput screen using 1,600 FDA-approved small compounds in collaboration with Dr Daniel Ebner’s group in the TDI, aimed at identifying chemical modulators of TFEB activity. Functional validation shortlisted around 50 compounds that both induce TFEB nuclear accumulation and lysosomal biogenesis, some of which also improve autophagy in a cell model. We are currently studying the modes of action of a few interesting hits using various tools and techniques, and we are planning to test them in disease models both in vitro and in vivo, hoping that our work will repurpose old drugs into effective therapeutics for neurodegenerative diseases.

 

Publications

Li, L., Friedrichsen, H.J., Andrews, S., Picaud, S., Volpon, L., Ngeow, K., Berridge, G., Fischer, R., Borden, K.L.B., Filippakopoulos, P., et al. (2018). A TFEB nuclear export signal integrates amino acid supply and glucose availability. Nat. Commun. 9, 2685.

Ngeow, K.C., Friedrichsen, H.J., Li, L., Zeng, Z., Andrews, S., Volpon, L., Brunsdon, H., Berridge, G., Picaud, S., Fischer, R., et al. (2018). BRAF/MAPK and GSK3 signaling converges to control MITF nuclear export. Proc. Natl. Acad. Sci. 115. E8868-E8877.