Immunochemical and Biosynthetic Analysis of Monoclonal Antibody-Defined Melanoma-Associated Antigen

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Abstract
Immunoprecipitation studies with application of monoclonal antibody Fll originally made to a partially purified spent medium antigen of melanoma cells, made it possible to delineate the molecular profiles of both the cell associated and spent medium antigens recognized on melanoma cells intrinsically labeled with glycoprotein precursors. F11 distinguishes a glycoprotein of Mr 100,000 (100 K) in the spent media of melanoma cells while a parallel analysis of detergent lysates of cells reveals a pattern of three glycoproteins of Mr 75, 77, and 100 K. Pulse-chase analysis of the biosynthesis of these antigens indicated that F11 first recognizes the 75 and 77 K antigens in the absence of a 100K component suggesting strongly that these molecules contain an antigenic site recognized by F11. The 100 K antigen appears later in the pulse-chase analysis with kinetics that suggest some of the 75 and 77 K antigens are biosynthetic precursors of the 100 K antigen. This molecule is ultimately secreted into the extracellular media and appears to be a sialoglycoprotein judging from its sensitivity to neuraminidase. A cross-reactive species with an approximate Mr 90 K is also recognized by F11 in indirect immunoprecipitation analysis of spent media from a neuroblastoma cell line indicating that a common antigenic site exists on this secreted but structurally different neuroblastoma antigen. Thus, a combination of immunochemical and biosynthetic analyses of cell-associated and secreted antigens recognized by monoclonal antibody F11 demonstrate such molecules can differ structurally when isolated from the same or different tumor cells. These findings indicate the necessity to establish molecular profiles of melanoma-associated glycoprotein antigens recognized by monoclonal antibodies to characterize and define their potential biological functions within tumor cells.