Antigenic differences between metastatic cells in bone marrow and primary tumours and the anti-MUC1 humoral immune response induced in breast cancer patients

Breast cancer cutaneous metastases are associated to uMUC1 and sialyl Lewis x and to highly malignant primary tumors

Breast cancer spreading to different organs have been related to different molecules and mechanisms, but cutaneous metastasis remains unexplored. Increasing evidence showed that MUC1 and some of its carbohydrate associated antigens may be implicated in breast cancer metastasis. In this study we analyzed these tumor markers in order to identify breast cancer cutaneous metastatic profiles. A cohort of 26 primary tumors from breast cancer patients with cutaneous metastases were included; also, cutaneous and lymphatic node metastatic samples and primary tumors from breast cancer patients without metastases were analysed. Immunohistochemical (IHC) studies demonstrated that both underglycosylated MUC1 (uMUC1) and sialyl Lewis x (sLex) to be positively associated with cutaneous metastatic primary tumors (p < 0.05). Notably, a high percentage of tumors with cutaneous metastases were characterized as triple negative and Her2+ tumors (37.5 % and 29 %, respectively). Some discordant results were found between primary tumors and their matched cutaneous metastases. To determine if MUC1 variants may be carriers of carbohydrate antigens, subcellular fractions from a cutaneous metastatic lesion were obtained, immunoprecipitated and analyzed by Western blot. We found that the isolated uMUC1 with a molecular weight of>200 kDa was also the site for binding of anti-sLex MAb; in coincidence, a high correlation of positive IHC expression of both markers was observed. Our findings confirm that breast cancer cutaneous metastases were associated to highly malignant primary tumors and sustain the hypothesis that u-MUC1 and sLe x may drive breast cancer cutaneous metastases.

Nuclear localization of MUC1 extracellular domain in breast, head and neck, and colon cancer

Background

The glycoprotein MUC1 is overexpressed and underglycosylated in cancer cells. MUC1 is translated as a single polypeptide that undergoes autocleavage into 2 subunits (the extracellular domain and the cytoplasmic tail), and forms a stable heterodimer at the apical membrane of normal epithelial cells. The MUC1 cytoplasmic tail localizes to the cytoplasm of transformed cells and is targeted to the nucleus.

Aims

To study the expression of the MUC1 extracellular subunit in cell nuclei of neoplastic breast, head and neck, and colon samples.

Materials and Methods

330 primary tumor samples were analyzed: 166 invasive breast carcinomas, 127 head and neck tumors, and 47 colon tumors; 10 benign breast disease (BBD) and 40 normal specimens were also included. A standard immunohistochemical method with antigen retrieval was performed. Nuclear fractions from tissue homogenates and breast cancer cell lines (ZR-75, MDA-MB-231, MCF7, and T47D) were obtained and analyzed by Western blotting (WB). The anti-MUC1 extracellular subunit monoclonal antibody HMFG1 was used for immunohistochemistry.

Results

37/166 breast cancer specimens, 5/127 head and neck cancer specimens, 2/47 colon cancer samples, and 3/10 BBD samples showed immunohistochemical staining at the nuclear level. No nuclear reaction was detected in normal samples. By WB, breast and colon cancer purified nuclear fractions showed reactivity at 200 kDa in 3/30 breast and 3/20 colon cancer samples as well as purified nuclear fractions obtained from breast cancer cell lines.

Conclusions

This study shows that the MUC1 extracellular domain might be translocated to the cell nucleus in breast, head and neck, and colon cancer as well as BBD.

Transmembrane mucins as novel therapeutic targets

Membrane-tethered mucin glycoproteins are abundantly expressed at the apical surfaces of simple epithelia, where they play important roles in lubricating and protecting tissues from pathogens and enzymatic attack. Notable examples of these mucins are MUC1, MUC4 and MUC16 (also known as cancer antigen 125). In adenocarcinomas, apical mucin restriction is lost and overall expression is often highly increased. High-level mucin expression protects tumors from killing by the host immune system, as well as by chemotherapeutic agents, and affords protection from apoptosis. Mucin expression can increase as the result of gene duplication and/or in response to hormones, cytokines and growth factors prevalent in the tumor milieu. Rises in the normally low levels of mucin fragments in serum have been used as markers of disease, such as tumor burden, for many years. Currently, several approaches are being examined that target mucins for immunization or nanomedicine using mucin-specific antibodies.

Sialylated Lewis x antigen bearing glycoproteins in human plasma

Recent studies have shown that antibodies targeting Lewis x (Le(x)) antigen are a valuable tool in the isolation and identification of glycoproteins in plasma. A focus of this study was to determine whether sialylated Lewis x (sLe(x)) antigen carrying glycoproteins occur in human plasma and whether an antibody targeting this antigen could be used to isolate and identify glycoproteins bearing this antigen. An additional objective was to determine the degree to which proteins conjugated to Le(x) and sLe(x) antigens are similar in structure. A specific anti-sLe(x) antibody (anti-sLe(x)Ab), CHO-131, immobilized in an immunoaffinity column was used to select a set of specific sLe(x) bearing proteins from human plasma, after which they were identified by either of two analytical strategies. One approach was to further resolve the affinity selected proteins by reversed phase chromatography (RPC), tryptic digest the RPC fractions, and identify peptide fragments by MALDI-MS/MS. The second was to tryptic digest the affinity selected protein fraction, further resolve the tryptic fragments by RPC, and identify peptides from RPC fractions by MALDI-MS/MS. Histidine-rich glycoprotein, plasminogen, apolipoprotein A-I, vitronectin, proteoglycan-4, clusterin, Ig gamma-2 chain C region, Ig mu chain C region, and interalpha-trypsin inhibitor heavy chain H4 were found to change three folds or more in association with breast cancer. Fifty percent of the glycoproteins carrying either sLe(x) antigen from CHO-131 selection, Le(x) antigen from selection with TG-1 antibody, or both were found to be changed three folds or more in concentration in breast cancer plasma relative to controls.