This application proposes experiments that will explore the molecular mechanisms by which alternative splice variants of MUC1, a cell surface associated mucin, contribute to the diversification of MUC1 function in pancreatic adenocarcinoma. Previous work has established that MUC1 is overexpressed and differentially gycosylated in various adenocarcinomas and that this overexpression is associated with aggressive forms of pancreatic cancer. Most study has focused on the full-length MUC1 isoform that contains the VNTR and all seven exons, but alternative splicing of MUC1 yields a minimum of 26 isoforms and several of these forms have been linked to malignancy state in ovarian, cervical, and breast cancer. Specifically, splice variants A, D, X, Y and Z were more frequently expressed in malignant ovarian tumors than benign tumors. One intriguing study focusing on MUC1 expression in breast cancer demonstrated that MUC1/SEC and MUC1/Y isoforms were coexpressed and that the secreted form of MUC1, MUC1/SEC, interacts with MUC1/Y, inducing a change in the phosphorylation status of the cytoplasmic tail and altering cell morphology. The phosphorylation status of the MUC1 cytoplasmic tail (MUC1.CT) has more recently been shown to be important in cell signaling and is responsive to the extracellular environment. The MUC1.CT is a known substrate for GSK3?, c-Src, EGFR, PDGFR?, c-Met, and HGF and has a role in Wnt signaling. The regulation of MUC1.CT phosphorylation and resultant signaling is not well understood and alterations in the MUC1 isoform including the presence or absence of the MUC1 VNTR and/or the inclusion of sequences unique to specific MUC1 splice variants present on the cell surface could have an important role in defining how MUC1 signals through its cytoplasmic tail in response to its extracellular environment. Our initial work focusing on MUC1 alternative splicing has developed a splice-sensitive oligonucleotide array to analyze isoform expression and has shown increases in expression of 3 distinct splice variants in a moderately differentiated pancreatic cell line that is highly metastatic. The experiments proposed in this application will provide insight into MUC1 splice variant expression in pancreatic cancer and will seek to correlate specific isoform expression with disease aggressiveness. We will also determine if changes in splice variant expression alters MUC1 interaction with its microenvironment through the analysis of signaling cascades and phosphorylation status of the MUC1 cytoplasmic tail. These experiments have the potential to provide novel insights into the functionally distinct roles MUC1 alternative splice products have in pancreatic tumor oncogenesis and metastasis, as well as to serve as model for future studies into the diversification of protein function for genes with multiple alternate splice products.
This application proposes experiments that will explore the molecular mechanisms by which alternative splice variants of MUC1, a cell surface associated mucin, contribute to the diversification of MUC1 function in pancreatic adenocarcinoma. This application will investigate which MUC1 isoforms are expressed in pancreatic cancer and the mechanisms through which these alternatively spliced proteins are involved in signal transduction, tumor progression and metastasis.
