CD146: biosynthesis and production of a soluble form in human cultured endothelial cells

We previously identified the S‐Endo 1‐associated antigen (CD146), an endothelial member of the immunoglobulin superfamily with a characteristic V‐V‐C2‐C2‐C2 Ig domain structure. In cultured human endothelial cells, we investigated its biosynthesis by immunoprecipitation and pulse‐chase labeling. CD146 was synthesized as a 100 kDa precursor form, which was processed into a 120 kDa mature form. In the culture media of endothelial cells, we observed a CD146 soluble form that was about 10 kDa smaller than cell‐associated CD146. In parallel with soluble forms of other members of the immunoglobulin superfamily, soluble CD146 could modulate and control the functions of the molecule.