Forskolin and phorbol ester have opposite effects on the expression of mucin-associated sialyl-Lewis(a) in pancreatic cancer cells

The carbohydrate antigen sialyl-Lewis(a) is important to pancreatic tumour biology because the circulating antigen is used in serological tests for ma lignancy and because cell surface antigen is involved in tumour cell bindin g to the endothelial adhesion molecule, E-selectin, in extravasation. In th is study, we examined the effects of the adenylyl cyclase activator, forsko lin, and the diacylglycerol analogue, phorbol 12-myristate 13-acetate (PMA) , on the expression and release of sialyl-Lewis(a) in human pancreatic canc er cells. Increases in the release of sialyl-Lewis(a) from SW1990 cells pro duced by forskolin and PMA were associated with increases in the activities of protein kinases A and C, respectively, and could be blocked by inhibito rs specific for these enzymes. Immunoprecipitation experiments showed that sialyl-Lewis(a) was associated with MUC1 mucin. Forskolin also increased th e cellular content of antigen and MUC1 mRNA. Actinomycin D and a protein ki nase A inhibitor, Hg, blocked these effects. In contrast, PMA reduced cellu lar antigen and MUC1 mRNA levels, although it produced a temporary increase in release of the antigen. The effects of PMA were blocked by the protein kinase C inhibitor, H7. PMA also reduced cell binding to the adhesion molec ule E-selectin. In summary, PKA and PKC alter cell MUC1-associated sialyl-L ewis(a) in opposite directions. These changes may have clinical utility in the diagnosis of pancreatic cancer and the prevention of metastases. (C) 20 00 Elsevier Science Ltd. All rights reserved.