SLC38A2 and breast cancer: Similar to MDA-MB-231 cells, the effects of hSPAR on SLC38A2, P27KIP1, mTOR signaling, and cell proliferation were also observed in breast cancer MCF7 cells (Luminal-A subtype) (Fig. EV4I–L) and MDA-MB-468 cells (triple-negative subtype) (Fig. EV4E-H), but not in HEK293T cells (Fig. EV4A–D).