Aberrant expression of mucin core proteins and o-linked glycans associated with progression of pancreatic cancer

Abstract

Purpose: Mucin expression is a common feature of most adenocarcinomas and features prominently in current attempts to improve diagnosis and therapy for pancreatic cancer and other adenocarcinomas. We investigated the expression of a number of mucin core proteins and associated O-linked glycans expressed in pancreatic adenocarcinoma-sialyl Tn (STn), Tn, T antigen, sialyl Lewis A (CA19-9), sialyl Lewis C (SLeC), Lewis X (LeX), and sialyl LeX (SLeX)-during the progression of pancreatic cancer from early stages to metastatic disease.

Experimental design: Immunohistochemical analyses of mucin and associated glycan expression on primary tumor and liver metastatic tumor samples were conducted with matched sets of tissues from 40 autopsy patients diagnosed with pancreatic adenocarcinoma, 14 surgically resected tissue samples, and 8 normal pancreata.

Results: There were significant changes in mucin expression patterns throughout disease progression. MUC1 and MUC4 were differentially glycosylated as the disease progressed from early pancreatic intraepithelial neoplasias to metastatic disease. De novo expression of several mucins correlated with increased metastasis indicating a potentially more invasive phenotype, and we show the expression of MUC6 in acinar cells undergoing acinar to ductal metaplasia. A "cancer field-effect" that included changes in mucin protein expression and glycosylation in the adjacent normal pancreas was also seen.

Conclusions: There are significant alterations in mucin expression and posttranslational processing during progression of pancreatic cancer from early lesions to metastasis. The results are presented in the context of how mucins influence the biology of tumor cells and their microenvironment during progression of pancreatic cancer.

Figure 1

Antigen expression profiles. (A) Heat maps show the relative expression levels of each antigen analyzed in samples from normal pancreas tissue (8 normal organ donors), and matched sets of 38 primary tumors and 34 liver metastases (4 patients did not show tumor cells in liver samples) from rapid autopsies of individual patients. The matched results for autopsy patients are presented by increasing degrees of morphological differentiation of the primary tumor (since well differentiated tumors are hypothesized to express higher quantities of mucin). Higher intensity of color corresponds to higher levels of expression based on immunohistochemical score (materials and methods). Asterisks denote statistically different antigen expression levels between the normal pancreas and the primary tumor at p<0.05. (B) Heat map showing comparative changes in expression levels between matched sets of primary tumor and liver metastasis. Asterisks indicate statistically significant differences in antigen expression between matched primary tumor and liver metastasis at p<0.05.

Figure 2

Antigen expression patterns in areas of normal pancreas from 8 organ donors, PanIN lesions and malignant tumor from resection tissue samples, and corresponding recurring primary tumor tissues samples from autopsy patients (A). Uninvolved acini and ducts in the resection tissues were individually characterized and compared to normal tissue (B).

Figure 3

Cancer field-effect on antigen expression. Heat maps represent changes in relative expression levels of the indicated antigens in ducts (A) and acinar cells (B) of normal and uninvolved normal tissue as compared to areas of primary tumor. (C) Immunohistochemical analysis of the field effects seen in side-by-side comparisons between normal pancreas tissues and a mixed tissue section that contains both tumor and adjacent, uninvolved tissue from patient 34. Images photographed at 200x magnification. Area of the tissue section containing the tumor is labeled with “T” whereas the adjacent uninvolved tissue is labeled with “AU.”

Figure 4

Immunofluorescence staining of MUC6 and cytokeratin 19 in uninvolved acini from autopsy patients 15(A), 45 (B) and 44 (C), showing evidence of acinar to ductal metaplasia. Immunohistochemical staining for MUC6 on adjacent sections (I) is provided to show tissue structure, followed by DAPI (II), cytokeratin 19 (III), MUC6 (IV), and overlay (V) images. 200x magnification.