Mediates transcriptional and post-transcriptional regulation of SLC5A1. Inhibits a dynamin and PKC-dependent exocytotic pathway of SLC5A1. Also involved in transcriptional regulation of SLC22A2. Exhibits glucose-dependent, short-term inhibition of SLC5A1 and SLC22A2 by inhibiting the release of vesicles from the trans-Golgi network. Interacts with YRDC. Localizes at the inner side of the plasma membrane. Expressed in small intestine, kidney and brain. The tripeptides QCP and QSP mediate post-transcriptional down-regulation of SLC5A1 at the trans-Golgi network. They inhibit a monosaccharide-dependent exocytotic pathway of SLC5A1.