2B1 antigen characteristically expressed on extracellular matrices of human malignant tumors is a large chondroitin sulfate proteoglycan, PG-M/versican.

2B1 is a monoclonal antibody against a large proteoglycan isolated from human yolk sac tumor (M. Sobue et al., Histochem. J., 21: 455-460, 1989). The antigen is expressed in a variety of embryonal tissues as well as most if not all malignant tumor tissues. However, the expression in normal adult tissues is limited to some tissues, such as the smooth muscle layers of the aorta. We characterized the 2B1 antigen isolated from the conditioned medium of human malignant fibrous histiocytoma and found that immunological and biochemical properties are identical to those of a large chondroitin sulfate proteoglycan, PG-M/versican. Partial amino acid sequences of peptides obtained from the core protein by V8 protease digestion and subsequent SDS-PAGE were detected in the reported amino acid sequence of human PG-M/versican with a complete identity. Furthermore, 2B1 was distinctly reactive to the expressed protein by transfection of the cDNA for the shortest form into mouse cells. The results indicate that the antigen is the PG-M core protein, and the epitope may be in one of the globular domains. It is thus likely that PG-M/versican is one of the extracellular matrix components characteristic of human malignant tumors.