Molecular characterization of a mucin-type antigen associated with human pancreatic cancer. The DU-PAN-2 antigen

This work describes the molecular characterization of a human pancreatic cancer-associated antigen defined by a murine monoclonal antibody (DU-PAN-2). DU-PAN-2 antigen was isolated from a pancreatic adenocarcinoma cell line (HPAF) or patient's ascitic fluid, and the antigenic activity was monitored by competitive inhibition radioimmunoassay. Affinity chromatography and CsCl/guanidine HCl density gradient centrifugation were employed to remove other populations of mucin-type glycoproteins and noncovalently associated proteins, respectively. Three electrophoretically distinct components were detected by 1% agarose gel electrophoresis and were resolved by chromatography on Sepharose CL-4B. The major fraction (FII) was subjected to carbohydrate and amino acid analyses. The sum of threonine, serine, proline, glycine, and alanine comprised more than 50% of the amino acid residues. The saccharide units, O-glycosidically linked to the peptide via GalNAc, contained fucose, galactose, GlcNAc, GalNAc, and sialic acid. The total carbohydrate content of FI and FII was 80.8% and 77.4% by weight, respectively. The molecular weight of FII antigen showed two species of molecules of 1.45 X 10(6) and 4.59 X 10(6) by analytical sedimentation equilibrium. DU-PAN-2 antigen was susceptible to neuraminidase, pepsin, Pronase, and papain digestion. These results suggest that both protein components and sialic acid residues may play important roles in the binding of DU-PAN-2 antibody.