CYSTIC-FIBROSIS AND PANCREATIC-CANCER CELLS SYNTHESIZE AND SECRETE MUC1 TYPE MUCIN GENE-PRODUCT

The purpose of this study was to determine the biochemical and molecul ar characteristics of mucin synthesized by cystic fibrosis cells (CFPA C-1), a pancreatic cancer cell line derived from a patient with cystic fibrosis, and pancreatic cancer (SW-1990) cell lines. High molecular weight glycoproteins (HMG) were quantified by [H-3]-glucosamine labeli ng and chromatography on sepharose CL-4B. Mucin gene expression was de termined by using cDNA probes for 2 distinct intestinal mucins (MUC2 a nd MUC3) and one stomach mucin (MUC1). The specific mucin core epitope s were confirmed by immunoblots using antibodies that recognize T, Tn, sialosyl Tn, MUC1, MUC2, and MUC3. The results of these experiments d emonstrate that CFPAC-1 cells contained 1.25 fold and 1.4 fold more HM G in the membrane and cytosolic fractions, however, secreted 4-fold mo re HMG into the medium compared to SW-1990 cells. The HMG of SW-1990 w as found to be mucinous in nature and not proteoglycans, as it was not susceptible to hyalurinidase, heparinase and chondroitinase ABC. The HMG of CFPAC-1 was also predominantly (80%) mucinous but with small am ounts of proteoglycans. mRNA and immunoblot analysis suggest that thes e CFPAC-1 and SW-1990 cells predominantly express MUC1 apomucin, small amounts of MUC2 apomucin, and no MUC3. Pulse chase labeling and immun oprecipitation of MUC1 type mucin using the 139H2 monoclonal antibody demonstrated that different sizes of mucin gene product were present i n both cell lines, corresponding to the known length polymorphism of t his mucin. Both T and Tn antigens were significantly higher in CFPAC-1 and SW-1990 cells as compared to sialosyl Tn antigen. These findings were associated with the increased activities of polypeptidyl N-acetyl galactosaminyl transferase and b1,3-galactosyltransferase. These inves tigations demonstrate for the first time that cystic fibrosis cells (C FPAC-1) secrete and synthesize high amounts of mucin which is associat ed with high levels of MUC1 mRNA, low levels of MUC2 mRNA and non dete ctable MUC3 mRNA.