Presence of a laminin-binding chondroitin sulfate proteoglycan at the cell surface of a human melanoma cell Mel-85

Working with Mel-85 (a human melanoma cell line), we have been able to detect a laminin-binding molecule with an apparent molecular mass of 100/110 kDa (Mel-85-LBM). Reduction with beta-mercaptoethanol decreases its molecular mass but does not affect its ability to bind laminin. This laminin interaction seems to be very specific since Mel-85-LBM binds laminin, but not fibronectin, vitronectin or type I collagen in affinity chromatography experiments. The molecule has a negative net charge at physiological pH and binds laminin in a divalent cation dependent way. Mel-85-LBM was metabolically radiolabeled with sodium [S-35]-sulfate and chemical beta-elimination of purified Mel-85-LBM releases chondroitin sulfate chains. Mel-85-LBM is also sensitive to chondroitinase ABC digestion. These findings show that this molecule is a chondroitin sulfate proteoglycan. The location of this proteoglycan at the cell surface is evidenced by experiments using a polyclonal antiserum raised against purified Mel-85LBM, that specifically reacts with just one molecule by western blotting among Mel-85 total cell extract as well as produces a positive signal by flow cytometry and a fluorescence profile of Mel-85 cells adhered on laminin.