A zinc transporter, transmembrane protein 163 (TMEM163), is critical for the biogenesis of platelet dense granules.

Lysosome-related organelles (LROs) are a category of secretory organelles enriched with ions such as Ca2+, which are maintained by ion transporters or channels. Homeostasis of these ions is important for LRO biogenesis and secretion. Hermansky-Pudlak syndrome (HPS) is a recessive disorder with defects in multiple LROs, typically platelet dense granules (DGs) and melanosomes. However, the underlying mechanism of DG deficiency is largely unknown. Using quantitative proteomics, we identified a previously unreported platelet Zn2+ transporter TMEM163, which was significantly reduced in BLOC-1 (Dtnbp1 sdy and Pldn pa), BLOC-2 (Hps6 ru) or AP-3 (Ap3b1 pe) deficient mice and HPS patients (HPS2, 3, 5, 6, or 9). We observed similar platelet DG defects and abnormal intracellular zinc accumulation in platelets of mice deficient in either TMEM163 or dysbindin (a BLOC-1 subunit). In addition, we discovered that BLOC-1 was required for the trafficking of TMEM163 to perinuclear DG and late endosome (LE) marker-positive compartments (likely DG precursors) in MEG-01 cells. Our results suggest that TMEM163 is critical for DG biogenesis and BLOC-1 is required for the trafficking of TMEM163 to putative DG precursors. These new findings suggest that loss of TMEM163 function results in disruption of intracellular zinc homeostasis, and provide insights into the pathogenesis of HPS or platelet storage pool deficiency.