Sandra Gendler

The MUC1 Cytoplasmic Tail and Tandem Repeat Domains Contribute to Mammary Oncogenesis in FVB Mice.

Background Though the importance of the transmembrane mucin MUC1 in mammary oncogenesis has long been recognized, the relative contributions of the cytoplasmic tail and tandem repeat domains are poorly understood. Methods To address this, mouse models of mammary carcinogenesis were created expressing full-length cytoplasmic tail-deleted, or tandem repeat-deleted MUC1 constructs. Results Overexpression of full-length MUC1 resulted in tumor formation in young mice (≤ 12 months); however, loss of either the cytoplasmic tail or the tandem repeat domain abrogated this oncogenic capacity. Aged mice in all strains developed late-onset mammary tumors similar to those previously described for the FVB background. Conclusions This study is the first spontaneous cancer model to address the relative importance of the cytoplasmic tail and tandem repeat domains to MUC1-driven mammary oncogenesis, and suggests that both of these domains are essential for tumor formation.

Molecular and Immunological Analysis of Mucin Molecules Produced by Normal and Malignant Human Mammary Epithelial Cells

The mammary gland is a complex tissue containing several lineages, including the luminal or secretory epithelial cells and the basal or myoepithelial cells which line the ducts and alveoli. These two cell types can be distinguished in tissue sections by immunohistochemical staining with monoclonal antibodies to structural components and to functional products characteristic of each cell type. Such studies have focused attention on the luminal or secretory epithelial cell lineage, since the dominant cell in breast cancers expresses both the simple epithelial keratins and the mucin molecules expressed by the luminal epithelial cells in the normal gland1. In these particulars the breast cancer cell resembles other adenocarcinomas, such as those from the colon, lung and ovary.

Epithelial Mucin Antibodies and Their Epitopes: Core Protein Epitopes of a Polymorphic Epithelial Mucin (PEM)

Largely because of their complexity, the detailed structure of the mucins has been difficult to analyze. This group of compounds is categorized mainly by the fact that they contain a high level of carbohydrate which is attached in O-linkage to serine and/or threonine via the linkage sugar N-acetylgalactosamine. The mucous secretions produced by some epithelial cells, particularly those lining the gastro-intestinal tract and the lungs, contain mucins along with other products and these components have been studied for some time at the biochemical level. However, other glandular epithelial cells, such as the salivary gland, breast, ovary, endometrium, and sweat glands, also produce mucins, and some of these simpler mucins have recently received much attention. This is because many antibodies selected for epithelial or tumor specificity have been found to react with high molecular weight glycoproteins which are produced by simple epithelial cells and have the properties of mucins.1–9

Aberrant glycosylation of anchor-optimized MUC1 peptides can enhance antigen binding affinity and reverse tolerance to cytotoxic T lymphocytes

Cancer vaccines have often failed to live up to their promise, although recent results with checkpoint inhibitors are reviving hopes that they will soon fulfill their promise. Although mutation-specific vaccines are under development, there is still high interest in an off-the-shelf vaccine to a ubiquitous antigen, such as MUC1, which is aberrantly expressed on most solid and many hematological tumors, including more than 90% of breast carcinomas. Clinical trials for MUC1 have shown variable success, likely because of immunological tolerance to a self-antigen and to poor immunogenicity of tandem repeat peptides. We hypothesized that MUC1 peptides could be optimized, relying on heteroclitic optimizations of potential anchor amino acids with and without tumor-specific glycosylation of the peptides. We have identified novel MUC1 class I peptides that bind to HLA-A*0201 molecules with significantly higher affinity and function than the native MUC1 peptides. These peptides elicited CTLs from normal donors, as well as breast cancer patients, which were highly effective in killing MUC1-expressing MCF-7 breast cancer cells. Each peptide elicited lytic responses in greater than 6/8 of normal individuals and 3/3 breast cancer patients. The CTLs generated against the glycosylated-anchor modified peptides cross reacted with the native MUC1 peptide, STAPPVHNV, suggesting these analog peptides may offer substantial improvement in the design of epitope-based vaccines.

Characterization and Evolution of an Expressed Hypervariable Gene for a Tumor-Associated Mucin, MUC-1

Mucins, present on highly polarized, secretory epithelial cells, have gained prominence in recent years as many monoclonal antibodies selected for their reactivity on differentiated or normal tissues react with epitopes present on these molecules. Although difficult to analyze biochemically because of their large size and large amount of O-linked carbohydrate, recent cloning studies from a number of different laboratories have produced structural information of the core protein. In most cases cDNA clones were obtained from λgt11 expression libraries following the development of antibodies to the stripped core protein. Thus far, three human mucin partial or full-length cDNA clones have been characterized as well as the porcine submaxillary mucin and a Xenopus integumentary mucin. In each case a domain of the core protein was found to consist of tandem repeats of a defined length. Although no homology exists between the tandem repeats of the various mucin genes at either the DNA or protein level, the repeated sequences in each case code for molecules which could be highly O-glycosylated. One characteristic feature of mucins is the presence of between 50 and 90% carbohydrate which is linked to serines or threonines via an O-glycosidic linkage to N-acetylgalactosamine. A second characteristic is the presence of prolines which along with glycosylation help to provide the extended core protein structure characteristic of mucins. All of the predicted proteins coded for by the mucin clones contain these features.