SLC1A5 and cancer: While ASCT2 has not previously been described as a serine transporter in cancer cells, it has been extensively characterized as a glutamine transporter.47–49,60,61 Indeed, we find that knockout and overexpression of ASCT2 in MCF7 cells causes a decrease and increase, respectively, in acute glutamine uptake (Figures 4A and 4B), and that loss of ASCT2 sensitizes MCF7 cells to decreasing glutamine concentrations (Figures 4C and 4D).