Ablation of the ASCT2 (SLC1A5) gene encoding a neutral amino acid transporter reveals transporter plasticity and redundancy in cancer cells

Abstract

The neutral amino acid transporter solute carrier family 1 member 5 (SLC1A5 or ASCT2) is overexpressed in many cancers. To identify its roles in tumors, we employed 143B osteosarcoma cells and HCC1806 triple-negative breast cancer cells with or without ASCT2 deletion. ASCT2ko 143B cells grew well in standard culture media, but ASCT2 was required for optimal growth at <0.5 mM glutamine, with tumor spheroid growth and monolayer migration of 143B ASCT2ko cells being strongly impaired at lower glutamine concentrations. However, the ASCT2 deletion did not affect matrix-dependent invasion. ASCT2ko 143B xenografts in nude mice exhibited a slower onset of growth and a higher number of small tumors than ASCT2wt 143B xenografts, but did not differ in average tumor size 25 days after xenotransplantation. ASCT2 deficiency was compensated by increased levels of sodium neutral amino acid transporter 1 (SNAT1 or SLC38A1) and SNAT2 (SLC38A2) in ASCT2ko 143B cells, mediated by a GCN2 EIF2␣ kinase (GCN2)-dependent pathway, but this compensation was not observed in ASCT2ko HCC1806 cells. Combined SNAT1 silencing and GCN2 inhibition significantly inhibited growth of ASCT2ko HCC1806 cells, but not of ASCT2ko 143B cells. Similarly, pharmacological inhibition of L-type amino acid transporter 1 (LAT1) and GCN2 significantly inhibited growth of ASCT2ko HCC1806 cells, but not of ASCT2ko 143B cells. We conclude that cancer cells with reduced transporter plasticity are more vulnerable to disruption of amino acid homeostasis than cells with a full capacity to up-regulate redundant transporters by an integrated stress response.

Increased expression of glutamine transporter SNAT2/SLC38A2 promotes glutamine dependence and oxidative stress resistance, and is associated with worse prognosis in triple-negative breast cancer

“…35,55 However, in contrast to SLC1A5, we found an increase in ROS production mainly in low Gln medium after SLC38A2 knockdown, confirming recent suggestions that SLC38A2 acts as a rescue transporter providing AA intake under stress conditions. 9 The role of SLC38A2 in maintaining mitochondrial function and ROS production in low Gln might be beyond the exchange with cysteine. In pancreatic cancer, SLC38A2 represents the major AAT for alanine, which is then deaminated to pyruvate (which can maintain the tricarboxylic acid cycle) in the presence of pyruvate carboxylase.…”

“…58 However, redundancy associated with other AATs after long-term silencing of SLC1A5 has been shown. 9 Due to its transmembrane localisation and the vulnerability of the TNBC cell lines to Gln depletion and SLC38A2 knockdown, SLC38A2 is potentially a useful target for this cancer subtype. However, apart from the canonical competitive inhibitor of system A transport, MeAIB, no pharmacological agent specifically targeting SLC38A2 has been identified so far.…”

Take Advantage of Glutamine Anaplerosis, the Kernel of the Metabolic Rewiring in Malignant Gliomas

“…LAT2 inhibition disturbs glutamine import and disrupts chemoresistance [ 46 ]. ASCT2 blockage impairs cancer metabolic remodeling, affecting cancer cell survival [ 47 , 48 , 49 , 50 ], thus specific inhibitors are under investigation for future clinical application [ 51 ]. However, the redundant activity of glutamine transporters [ 51 , 52 ] can be a mechanism of resistance to a glutamine uptake-targeted therapy.…”

Amino acid transporters in the regulation of insulin secretion and signalling

“…SNAT2 is a ubiquitously expressed sodium-dependent symporter of, predominately, small neutral amino acids alanine, serine, glycine, and cysteine but can also transport glutamine, asparagine, methionine, proline, and histidine (183, 184) ( Table 1). SNAT2 is regulated by various metabolic signals such as amino acid availability, amino acid starvation, hypertonic stress, and insulin (185)(186)(187)(188)(189)(190). The increase of amino acid uptake by insulin was first identified in rat skeletal muscle (185,191) but was subsequently shown to stimulate plasma clearance of leucine in humans (3).…”