SLC7A5 and breast cancer: LLGL2 is highly expressed in estrogen receptor-positive (ER+) breast cancer, and LLGL2 regulates the cell surface levels of the leucine transporter protein SLC7A5 through the formation of a trimeric complex with SLC7A5 and the membrane fusion regulator YKT6 to promote leucine uptake and cell proliferation; LLGL2 is also involved in tamoxifen resistance [17].