Abstract
Lysosomes are the terminal organelles of the autophagic-endocytic pathway and play a key role in the degradation of autophagic contents. We previously reported that a natural compound oblongifolin C (OC) increased the number of autophagosomes and impaired the degradation of P62, most likely via suppression of lysosomal function and blockage of autophagosome-lysosome fusion. However, the precise mechanisms of how OC inhibits the lysosome-autophagy pathway remain unclear. In the present study, we investigated the effect of OC on transcription factor EB (TFEB), a master regulator of lysosomal biogenesis, lysosomal function and autophagy. We showed that treatment with OC (15 μM) markedly enhanced the nuclear translocation of TFEB in HeLa cells, concomitantly reduced the interaction of TFEB with 14-3-3 proteins. We further demonstrated that OC caused significant inhibition of mTORC1 along with TFEB nuclear translocation, and OC-mediated TFEB nuclear translocation was dependent on mTORC1 suppression. Intriguingly, this increased nuclear TFEB was accompanied by reduced TFEB luciferase activity, increased lysosomal pH and impaired cathepsin enzyme activities. In HeLa cells, treatment with OC (7.5 μM) resulted in about 30% of cell death, whereas treatment with hydroxycitrate, a caloric restriction mimetic (20 μM) did not affect the cell viability. However, cotreatment with OC and hydroxycitrate caused significantly great cytotoxicity (>50%). Taken together, these results demonstrate that inhibition of lysosome function is mediated by OC, despite evident TFEB nuclear translocation.
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Acknowledgements
We are thankful to Dr. A Ballabio and N Mizushima for providing critical reagents. This work was supported by the National Natural Science Foundation of China (No. 81773951 and No. 81602990), Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning and research grants from NMRC (NMRC-CIRG/1430/2015) to HMS.
Author contributions
HXX, HMS, and YZL designed the research; MW and HST performed most of the experiments and analyzed the data; GL, YR, ZQZ and JY performed some of the Western blotting experiments; WWF contributed material support; YL and MW wrote the manuscript; and HXX and HMS revised the manuscript.
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Wu, M., Lao, Yz., Tan, Hs. et al. Oblongifolin C suppresses lysosomal function independently of TFEB nuclear translocation. Acta Pharmacol Sin 40, 929–937 (2019). https://doi.org/10.1038/s41401-018-0167-7
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DOI: https://doi.org/10.1038/s41401-018-0167-7
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