Contribution of the tandem repeat and cytoplasmic tail domains of MUC1 to anti-tumor immunity and metastatic potential of tumors

MUC1 is a polymorphic, highly glycosylated, type I transmembrane protein expressed by ductal epithelial cells of many organs including pancreas, breast, gastrointestinal tract, and airway. MUC1 is overexpressed and differentially glycosylated by adenocarcinomas that arise in these organs. Alterations of expression pattern and/or glycosylation may expose previous hidden epitopes or generate novel epitopes sufficiently recognized by the immune system to mount an immune response directed towards MUC1. Accordingly, antibodies and cytolytic T lymphocytes specific for MUC1 can be detected in patients with MUC1-positive tumors; however, these immune responses do not completely eliminate these tumors. In the first and second set of studies described in this dissertation, we investigated in vivo immune responses directed against tumor-associated MUC1 in a well defined murine model to define portion(s) of the molecule that are required for effective anti-tumor immune responses utilizing tumor cell lines (B16, and Panc02) that expressed constructs of MUC1 in which portions of the protein were deleted. Based on results obtained from these studies, we developed vaccination strategies using peptides derived from the amino acid sequence of MUC1 CT to generate protective immune responses against MUC1-expressing tumors in wt and MUC1.Tg mice.; Additional functions in tumor cells have been proposed for MUC1. MUC1 is believed to contribute to invasive and metastatic potential by contributing to cell surface adhesion properties (via the tandem repeat domain) by interfering with cell-cell and/or cell-extracellular matrix (ECM) interactions and thereby facilitates detachment of tumor cells from the primary growth; secondly, through morphogenetic signal transduction (via the cytoplasmic tail). In the third set of studies reported in this dissertation, we investigated the contribution of the tandem repeat domain and the cytoplasmic tail of MUC1 to the in vivo invasive and metastatic potential of the human pancreatic tumor cell line S2-013. These studies demonstrated expression of endogenous MUC1 or deletion of either the cytoplasmic tail or tandem repeat of MUC1 resulted in an increased propensity of tumor cells to invade vessels and metastasize to lymph nodes compared to a cell line expressing full length MUC1. In the final set of experiments, we attempted to gain insights into the mechanisms, affected by MUC1 overexpression, which may contribute to the observed in vivo phenotypes. These studies showed overexpression of full length MUC1 down regulated both MMP7 and CD24, and S2-013 cells having the highest MMP7 and CD24 expression demonstrated the most invasive and metastatic behavior in vivo.