Mucins are high molecular weight
glycoproteins having
oligosaccharides attached to the
apomucin protein backbone by O-glycosidic linkages. Biochemical studies on the structures and the organ specificities of several
mucin core
proteins (MUC1-MUC7) have been reported during the past several years. In the present study of pancreas and intrahepatic bile duct
tumors,
MUC1 mucin (membrane bound
mucin detected by
monoclonal antibody, DF3) was highly expressed in invasive
ductal carcinomas of the pancreas (IDC) and invasive
cholangiocarcinomas of the liver (ICC), which show invasive growth and a poor prognosis, but it was rarely expressed in intraductal papillary mucinous
tumors of the pancreas (IPMT) and bile duct
cystadenocarcinomas of the liver (BDCC), which show a favorable prognosis. In contrast, MUC2
mucin (intestinal type secretory
mucin detected by polyclonal antibody, anti-MRP) was rarely expressed in IDC and ICC, whereas it was highly expressed in IPMT and BDCC. The results suggest that the differences in the expression of MUC1 and MUC2
mucins are a useful prognostic
indicator of
malignancy potential in the
neoplasms of the pancreas and intrahepatic bile duct. Moreover, the expression of MUC1 and MUC2
mucins was a useful
indicator of the
malignancy potential of
tumors derived from other organs, such as the ampulla of Vater, stomach and breast. In another study on the expression of several
MUC1 mucin antigens with different patterns of glycosylation, sialylated-MUC1
mucin detected by
monoclonal antibody, MY.1E12, was found to be expressed in all the invasive
carcinomas (IDC and ICC) but was not frequently seen in the non-invasive type
tumors (IPMT and BDCC), although the other types of MUC1
mucins did not show such contrast between the invasive and non-invasive type
tumors. The results suggest that sialylation of
MUC1 mucin is associated with invasive growth of
neoplasms. In contrast, our study of the expression of MUC2
mRNA (transcript of intestinal type
mucin) and MUC5AC
mRNA (transcript of gastric type
mucin) by in situ hybridization in the
tumors of the pancreas and intrahepatic bile duct found that the non-invasive type
tumors (IPMT and BDCC) synthesize MUC2
mRNA and MUC5AC
mRNA, whereas most of the invasive
carcinomas (IDC and ICC) do not. Furthermore, patients positive for MUC2
mRNA or MUC5AC
mRNA expression in the
tumors showed significantly better survival than the patients with no expression. The production of MUC2 or MUC5AC, an abundant extracellular intestinal or gastric type secretory
mucin with high viscosity may be correlated, by a majority of the non-invasive type
tumors, with the expansive growth of the
tumors that display lower levels of invasion and
metastasis.