Transmembrane protein that binds to and facilitates the assembly of lysosomal proton-transporting V-type ATPase (v-ATPase), resulting in enhanced lysosomal acidification and trafficking . By bringing the v-ATPase accessory protein ATP6AP2 and the v-ATPase subunit ATP6V0D1 together, allows v-ATPase complex formation and activation . TMEM9-controlled vesicular acidification induces hyperactivation of Wnt/beta-catenin signaling, involved in development, tissue homeostasis and tissue regeneration, through lysosomal degradation of adenomatous polyposis coli/APC (, ). In the liver, involved in hepatic regeneration .
Subcellular locations: Lysosome membrane, Late endosome membrane, Endosome, Multivesicular body membrane
Highly expressed in adrenal gland, thyroid gland, testis, ovary and prostate . Moderate expression in trachea, spinal cord, stomach, colon, small intestine and spleen (, ). Low expression in bone marrow, lymph node, thymus and peripheral blood lymphocytes . Expression is detected in hematopoietic cell lines including those of myeloid, erythroid, B- and T-cell origin .