Positively regulates lysosome peripheral distribution and ruffled border formation in osteoclasts (PubMed:27777970). Involved in bone resorption (PubMed:27777970). Interacts (via C-terminus) with PLEKHM1; this interaction is weak but increased in a RAB7A-dependent manner (PubMed:27777970). Abundantly expressed in peripheral blood leukocytes. Highly expressed in B-cells. Also present in lymph node and appendix. Down-regulated upon macrophage/granulocyte differentiation. Weakly expressed in bone marrow and spleen. Weakly or not expressed in thymus and fetal liver. Abundantly expressed during embryogenesis. Belongs to the DEF8 family.