ASC amino acid transporter 2, defined by enzyme‐mediated activation of radical sources, enhances malignancy of GD2‐positive small‐cell lung cancer

Abstract

Ganglioside GD2 is specifically expressed in small‐cell lung cancer (SCLC) cells, leading to enhancement of malignant phenotypes, such as cell proliferation and migration. However, how GD2 promotes malignant phenotypes in SCLC cells is not well known. In this study, to reveal the mechanisms by which GD2 increases malignant phenotypes in SCLC cells, we used enzyme‐mediated activation of radical sources combined with mass spectrometry in GD2+ SCLC cells. Consequently, we identified ASC amino acid transporter 2 (ASCT2), a major glutamine transporter, which coordinately works with GD2. We showed that ASCT2 was highly expressed in glycolipid‐enriched microdomain/rafts in GD2+ SCLC cells, and colocalized with GD2 in both proximity ligation assay and immunocytostaining, and bound with GD2 in immunoprecipitation/TLC immunostaining. Malignant phenotypes of GD2+ SCLC cells were enhanced by glutamine uptake, and were suppressed by L‐γ‐glutamyl‐p‐nitroanilide, a specific inhibitor of ASCT2, through reduced phosphorylation of p70 S6K1 and S6. These results suggested that ASCT2 enhances glutamine uptake in glycolipid‐enriched microdomain/rafts in GD2+ SCLC cells, leading to the enhancement of cell proliferation and migration through increased phosphorylation of the mTOR complex 1 signaling axis.

New era of research on cancer‐associated glycosphingolipids

“…ASCT2 colocalized with GD2 in GEM/rafts, and they were associated with each other, as shown by multiple approaches such as co-immunoprecipitation and the proximity ligation assay. 35 Consequently, ASCT2 co-operated with GD2 and increased the uptake of glutamine, and increased activation levels of downstream molecules of mTOR1, such as p-p70 S6K1 and p-S6 35 (Figure 5B).…”

“…Labeled proteins were immunoprecipitated and applied for immunoblotting. Only the sample labeled with the anti‐ GD 2 mA b showed multiple bands . These proteins were applied to MS…”

“…B, By EMARS / MS , a glutamine transporter, ASCT 2, was defined as a GD 2‐associating molecule in SCLC . ASCT 2 cooperates with GD 2, resulting in the increased activation levels of mTOR 1 downstream molecules such as p70S6K1 and S6 in SCLC cells . These signals finally induce increased cell growth and migration…”

“…Therefore, novel Ab therapy targeting SCLC‐specific antigens has been long expected . As a result of EMARS/MS using anti‐GD2 mAb and GD2 synthase‐transfectants of SK‐LC‐17, approximately 20 molecules were identified as candidates of GD2‐associating molecules . These molecules consisted of CD109, uPAR, EphA2, and CD44.…”

“…34 As a result of EMARS/MS using anti-GD2 mAb and GD2 synthase-transfectants of SK-LC-17, 9 approximately 20 molecules were identified as candidates of GD2-associating molecules. 35 These molecules consisted of CD109, uPAR, EphA2, and CD44. Among them, ASCT2, a glutamine transporter, was most clearly localized in lipid rafts of GD2 + cells.…”