Forskolin increases the expression of the pancreatic tumor antigen, Nd2, and uptake of Nd2 antibody

Nd2 antibody recognizes an antigen that is tumor specific in pancreas. It h as been used successfully in clinical radioimmunodetection studies to ident ify exocrine pancreatic tumors. In the present study we show that the uptak e of radiolabeled Nd2 antibody by SW1990 pancreatic carcinoma cells was inc reased by the adenyl cyclase activator, forskolin. Dibutyryl cyclic AMP and forskolin were both effective in increasing the level of Nd2 antigen in SW 1990 cells. Immunoprecipitation studies showed that the Nd2 epitope is asso ciated with MUC1 mucin. Forskolin increased Nd2/MUC1 antigen in both a memb rane fraction and a high buoyant density mucin-like fraction. Nd2 immunorea ctivity was reduced by treatment of mucins with proteases and B-mercaptoeth anol. Immunohistochemical studies showed that periodate catalyzed beta-elim ination greatly reduced Nd2 immunoreactivity. These results suggest that th e Nd2 epitope is unusual in having characteristics of both a peptide and a carbohydrate, protease and conformation sensitivities and involvement of O- linked oligosaccharides. Nd2 antibody does not react with several known pan creatic cancer antigens. In summary, activation of the cyclic AMP pathway i ncreased cellular uptake of Nd2 antibody and the cellular expression of the tumor-specific, mucin-associated Nd2 antigen. These results suggest a mean s of improving the effectiveness of monoclonal antibodies in targeting tumo r antigens for the diagnosis and treatment of malignancy.