Methylation status of promoters and expression of MUC2 and MUC5AC mucins in pancreatic cancer cells

Anomalous expression of certain types of mucins occurs in pancreatic tumors, but little is known about the causes. MUC2 and MUC5AC are not expressed in normal pancreas. In the present study an immunohistochemical screening showed that MUC2 antigen was expressed in 6% of invasive tumors. Of the pancreatic cell lines, 2.4% expressed MUC2 message and antigen. In contrast, MUC5AC antigen was expressed in 86-100% of invasive adenocarcinoma (depending on the antibody). MUC5AC message and antigen were expressed in 66.7% of the cell lines tested. A polymerase chain reaction based assay was used to determine if methylation of CpG sites immediately 5' of the transcription initiation sites of the MUC2 and MUC5AC genes could be related to mucin expression in the cell lines. Digestibility by the methylation sensitive restriction enzyme HpaII correlated with the presence or absence of mRNA in 100% and 77.8% of the cell lines for MUC2 and MUC5AC, respectively. Treatment of a cell line that did not express MUC2 or MUC5AC gene products with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine resulted in an increase in MUC2 message but no change in MUC5AC message. In summary, the expression of MUC2 gene products correlated well with methylation of the proximal region of the promoter whereas expression of MUC5AC may involve additional regions or other mechanisms.