Cell surface MUC16 is sensitive to proteolysis. A, Binding of OC125 and VK8 to OVCAR-3 cells that were harvested with trypsin or EDTA containing media was determined by flow cytometry. A significant decrease in VK8 binding to cells harvested after trypsin treatment was observed whereas under these conditions, OC125 binding was less affected. B, Reduction of the trypsinized OVCAR-3 cells with dithiothreitol (DTT) or 2-mercaptoethanol (2-ME) did not result in additional loss of OC125 binding to the cells. In all experiments, a fluorescently tagged goat anti-mouse antibody was used for detection.