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Proton-assisted amino-acid transporters are conserved regulators of proliferation and amino-acid-dependent mTORC1 activation

Abstract

The phosphoinositide3-kinase (PI3K)/Akt and downstream mammalian target of rapamycin complex 1 (mTORC1) signalling cascades promote normal growth and are frequently hyperactivated in tumour cells. mTORC1 is also regulated by local nutrients, particularly amino acids, but the mechanisms involved are poorly understood. Unexpectedly, members of the proton-assisted amino-acid transporter (PAT or SLC36) family emerged from in vivo genetic screens in Drosophila as transporters with uniquely potent effects on mTORC1-mediated growth. In this study, we show the two human PATs that are widely expressed in normal tissues and cancer cell lines, namely PAT1 and PAT4, behave similarly to fly PATs when expressed in Drosophila. Small interfering RNA knockdown shows that these molecules are required for the activation of mTORC1 targets and for proliferation in human MCF-7 breast cancer and HEK-293 embryonic kidney cell lines. Furthermore, activation of mTORC1 in starved HEK-293 cells stimulated by amino acids requires PAT1 and PAT4, and is elevated in PAT1-overexpressing cells. Importantly, in HEK-293 cells, PAT1 is highly concentrated in intracellular compartments, including endosomes, wherein mTOR shuttles upon amino-acid stimulation. Therefore our data are consistent with a model in which PATs modulate the activity of mTORC1 not by transporting amino acids into the cell but by modulating the intracellular response to amino acids.

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Acknowledgements

We thank Toshiro Aigaki, Hugo Bellen and the Bloomington Stock Centre for fly strains, Robert Edwards (UCSF) for generously providing the PAT1 antisera and Vuk Stambolic (Toronto) for the GFP-Rheb construct. We are grateful to Dr David Meredith (Oxford Brookes University) for helpful discussion and to Bass Hassan and Claudia Buehnemann for comments on the paper. This work was supported by Cancer Research-UK grants (C19591/A9093, C191591/A6181 and C7713/A6174), funding from the Studienstiftung des deutschen Volkes and the Max Weber Programm Bayern to SH and a University of Oxford, Newton Abraham Studentship and Overseas Research Student Award to MHO.

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Correspondence to D C I Goberdhan.

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Heublein, S., Kazi, S., Ögmundsdóttir, M. et al. Proton-assisted amino-acid transporters are conserved regulators of proliferation and amino-acid-dependent mTORC1 activation. Oncogene 29, 4068–4079 (2010). https://doi.org/10.1038/onc.2010.177

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