Osteoactivin is an intracellular glycoprotein belongs to the NMB/pMEL-17 family, which is asscociated with cell endosomal/lysomal compartments. Human Osteoactivin is a 560 amino acid type I transmembrane protein, and one alternate splice form shows a 12 amino acid insert between amino acid 339-340. An additional 206 amino acid isoform shows a mutation at position 181 that results in a 26 amino acid substitution for the C-terminal 380 amino acids. Cells knowns to express Osteoactivin include fibroblast, osteoblasts, myeloid dendritic cell, melanocytes, plus fetal chondrocytes and stratum basale keratinocytes, macrophages/keratinocytes.