GPNMB, also known as glycoprotein nmb, is a transmembrane glycoprotein that is expressed in numerous cells, including osteoclasts, macrophages, dendritic cells, and tumor cells. It shows expression in the lowly metastatic human melanoma cell lines and xenografts but does not show expression in the highly metastatic cell lines. This protein participates in bone mineralization, and functions as a negative regulator of inflammation in macrophages. It may be involved in growth delay and reduction of metastatic potential. Recombinant human GPNMB protein, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.