SLC9A5 and central nervous system cancer: NHE5 cycles between recycling endosomes and the plasma membrane [15], and acidifies the lumen of recycling endosomes [16], thereby playing a critical role in regulating the cell-surface availability of the high-affinity nerve growth factor receptor TrkA in PC12 pheochromocytoma cells of adrenal gland origin [17] and the hepatocyte growth factor/scatter factor (HGF) receptor MET in C6 glioma cells [14].