SNAT7 is the primary lysosomal glutamine exporter required for extracellular protein-dependent growth of cancer cells

Abstract

Lysosomes degrade cellular components sequestered by autophagy or extracellular material internalized by endocytosis and phagocytosis. The macromolecule building blocks released by lysosomal hydrolysis are then exported to the cytosol by lysosomal transporters, which remain undercharacterized. In this study, we designed an in situ assay of lysosomal amino acid export based on the transcription factor EB (TFEB), a master regulator of lysosomal biogenesis that detects lysosomal storage. This assay was used to screen candidate lysosomal transporters, leading to the identification of sodiumcoupled neutral amino acid transporter 7 (SNAT7), encoded by the SLC38A7 gene, as a lysosomal transporter highly selective for glutamine and asparagine. Cell fractionation confirmed the lysosomal localization of SNAT7, and flux measurements confirmed its substrate selectivity and showed a strong activation by the lysosomal pH gradient. Interestingly, gene silencing or editing experiments revealed that SNAT7 is the primary permeation pathway for glutamine across the lysosomal membrane and it is required for growth of cancer cells in a low free-glutamine environment, when macropinocytosis and lysosomal degradation of extracellular proteins are used as an alternative source of amino acids. SNAT7 may, thus, represent a novel target for glutamine-related anticancer therapies.lysosome | transporter | glutamine | cell nutrition | cancer

mTORC1 Activator SLC38A9 Is Required to Efflux Essential Amino Acids from Lysosomes and Use Protein as a Nutrient

“…Interestingly, while it has been appreciated that a lysosomal protein must exist for leucine efflux (Milkereit et al, 2015; Taylor, 2014), no such transporter had been identified. Recent work identified SLC38A7 as an effluxer of glutamine from lysosomes (Verdon et al, 2017). …”

Crystal structure of arginine-bound lysosomal transporter SLC38A9 in the cytosol-open state

“…In Homo sapiens, at least 17 known AAAP 31 members were found 9 , spanning across solute carrier families SLC32, SLC36 and SLC38, 32 although none of these structures have been determined to date. Thus far, 11 members of SLC38 33 have been identified in humans 10 , two of which, SLC38A7 and SLC38A9, localize at lysosomes 34 5,11,12 . SLC38A9 is the only member of this family known to participate in the Ragulator-Rag 35GTPases complex and in turn plays an important role in the amino acid dependent activation of 36 mTORC1 3,5,[13][14][15] .…”

Nutritional Stress Induced by Amino Acid Starvation Results in Changes for Slc38 Transporters in Immortalized Hypothalamic Neuronal Cells and Primary Cortex Cells

“…This theory can also be applied to SLC38A7 and SLC38A8 which also are phylogenetically closely related and co-expressed on most neurons (Hägglund et al, 2015 ) and initially regulated in the opposite direction after partial amino acid starvation, and in the hypothalamic cell line Slc38a7 was transcriptionally induced while Slc38a8 was not. In a previous study, SLC38A7 co-localized with lysosomes in HeLa cells and was found to mediate flux of glutamine and asparagine and hence crucial for growth of cancer cells (Verdon et al, 2017 ). SLC38A9 is located on lysosomes and is a component of the amino acid sensing Ragulator-Rag complex responsible for activation of mTORC1 (Jung et al, 2015 ; Rebsamen et al, 2015 ; Wang et al, 2015 ) and in mouse brain SLC38A9 immunostaining is detected in both GABAergic and glutamatergic neurons (Hellsten et al, 2017a ).…”