Mucin 1 (Muc1) is a heavily glycosylated protein that coats mucosal epithelial cells of the lungs, intestines, and other organs. Muc1 is thought to protect cells by binding to pathogens and responding to infections. During trafficking to the plasma membrane Muc1 is proteolytically cleaved in the endoplasmic reticulum to form a stable heterodimeric complex of two fragments. The smaller C-terminal region contains the cytoplasmic tail and transmembrane domain and is non-covalently bound to the larger glycosylated extracellular domain. Further cleavage or processing of the extracellular domain can cause release or shedding into the extracellular space and is thought to be involved in protein turnover and degradation or could potentially trigger a signaling response in the cytoplasmic domain. Muc1 is highly overexpressed in breast, ovarian, and prostate cancers and is correlated with metastasis and poor survival. Overexpressed Muc1 localizes throughout the cell in these cancers and the shed extracellular domain detected in patient sera serves as a prognostic indicator and a measure of response to therapy.
Whiteman et al. used the Mucin 1 antibody for immunofluorescence to monitor epithelial polarity in the lung cells of normal and mutant mice (1). In their study Crumbs knockout mice displayed defects in epithelial morphogenesis with abnormalities in the lungs, intestines, and kidneys. The Bagchi group at the University of Illinois Urbana-Champaign investigated tissue interactions during mouse embryo implantation (2). They identified Msx1 and Msx2 as important genes involved in regulating tissue interactions. Using the Mucin 1 antibody for immunohistochemistry they showed mice mutant for Msx1 and Mxs2 display persistent levels of Muc1 preventing embryo implantation and causing infertility. Desmetz et al. sought to identify autoantibodies that can serve as markers of early-stage breast cancer (3). They used ELISAs to compare their candidates to the currently used Mucin 1 antibody. They showed their panel of autoantibodies was able to accurately discriminate between healthy tissue and early-stage breast cancer. The Clausen group of the University of Copenhagen sought to develop a cancer immunotherapy based on the Muc1 overexpression in cancers (4). They used chemically synthesized Muc1 glycopeptides as immunogens to elicit immune responses in Muc1 expressing mice. Using the Mucin 1 antibody in ELISAs they were able to monitor the immunogenicity of their synthetic peptides. Dr. Taylor-Papadimitriou’s group used a Mucin 1 antibody specific to the cancer-associated SM3 epitope for FACS analysis (5). This allowed the identification of the glycosylase ST3Gal-1, whose expression is increased in breast cancer, as being important for generating this cancer-associated Muc1 epitope.
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