Muc1/sec: A Secreted Alternative Splice Variant Of Muc1 That Promotes Tumor Immunity

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Microbiology and Immunology

First Committee Member

Diana M. Lopez, Committee Chair


Human MUC1/sec is a secreted form of the glycoprotein mucin 1 (MUC1). In order to characterize the role that MUC1 and MUC1/sec have in tumor progression, these genes were expressed in DA-3 mammary tumor cells. DA-3 cells and DA-3 cells expressing the full length transmembrane form of MUC1 (DA-3/TM) grow with similar kinetics in BALB/c mice. Surprisingly, DA-3 cells expressing and secreting MUC1/sec (DA-3/sec) fail to form tumors in vivo. The mechanism of rejection was evaluated using mice deficient in constituents of the immune system. All mice lacking IFN-gamma, NK, NKT, or macrophages formed DA-3/sec tumors that regressed shortly after implantation. However, progressively growing DA-3/sec tumors developed in mice devoid of T lymphocytes. The importance of T lymphocytes in the rejection of DA-3/sec tumors was further supported by detection of DA-3 specific CTL in mice challenged with the DA3/sec tumor. Recruitment of appropriate antigen presenting and effector cells is an important first step in the tumor clearance. Indeed, DA-3/sec cells or cell supernatants recruited 3--4 times as many macrophages as DA-3/TM cells in vivo, suggesting that a secreted chemotactic product is produced from DA-3/sec cells. RNA and protein analysis of DA-3/sec cells revealed that several genes are up-regulated by MUC1/sec expression, including monocyte chemotactic protein 1 (MCP-1).Further investigations into the production of chemokines in DA-3/sec cells revealed that MUC1/sec directly controls MCP-1 production. Incubation of DA-3/sec cells with a MUC1/sec-specific antibody reduced MCP-1 protein levels, and conversely, incubation of DA-3/sec cells with a MUC1/sec-derived peptide increased MCP-1 levels. MCP-1 regulation is dependent on several signaling pathways, including the p38MAP kinase and protein kinase C pathway. Using inhibitors of these pathways, MCP-1 production was abrogated in DA-3/sec cells, suggesting MUC1/sec may be activating MCP-1 through these signaling networks. Overall, these results point to a novel function for the secreted isoform of mucin 1, MUC1/sec, in the stimulation of both innate and T cell immunity in the prevention of tumor cell growth in vivo.


Biology, Microbiology; Health Sciences, Immunology

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