MUC1-positive Cells Research Articles

MUC1 Expression Is Regulated by DNA Methylation and Histone H3 Lysine 9 Modification in Cancer Cells

MUC1 is a transmembrane mucin that is highly expressed in various cancers and correlates with malignant potential. Important cancer-related genes such as p16 and E-cadherin are controlled epigenetically; however, MUC1 has been overlooked in epigenetics. Herein, we provide the first report that MUC1 gene expression is regulated by DNA methylation and histone H3 lysine 9 (H3-K9) modification of the MUC1 promoter. The recently developed MassARRAY assay was performed to investigate the DNA methylation status of 184 CpG sites from -2,753 to +263. Near the transcriptional start site, the DNA methylation level of MUC1-negative cancer cell lines (e.g., MDA-MB-453) was high, whereas that of MUC1-positive cell lines (e.g., MCF-7) was low. Histone H3-K9 modification status was also closely related to MUC1 gene expression. Furthermore, MUC1 mRNA expression in MUC1-negative cells was restored by treatment with the DNA methylation inhibitor 5-aza-2'-deoxycytidine. Our results indicate that DNA methylation and histone H3-K9 modification in the 5' flanking region play a critical role in MUC1 gene expression, and this study defines MUC1 as a new member of the class of epigenetically controlled genes. An understanding of the epigenetic changes of MUC1 may be of importance for diagnosis of carcinogenic risk and prediction of outcome for cancer patients.

Epitope Mapping of PR81 anti-MUC1 Monoclonal Antibody Following PEPSCAN and Phage Display Techniques

PR81 is an anti-MUC1 monoclonal antibody (MAb) which was generated against human MUC1 mucin that reacted with breast cancerous tissue, MUC1 positive cell line (MCF-7, BT-20, and T-4 7 D), and synthetic peptide, including the tandem repeat sequence of MUC1. Here we characterized the binding properties of PR81 against the tandem repeat of MUC1 by two different epitope mapping techniques, namely, PEPSCAN and phage display. Epitope mapping of PR81 MAb by PEPSCAN revealed a minimal consensus binding sequence, PDTRP, which is found on MUC1 peptide as the most important epitope. Using the phage display peptide library, we identified the motif PD(T/S/G)RP as an epitope and the motif AVGLSPDGSRGV as a mimotope recognized by PR81. Results of these two methods showed that the two residues, arginine and aspartic acid, have important roles in antibody binding and threonine can be substituted by either glycine or serine. These results may be of importance in tailor making antigens used in immunoassay.

Radioimmunoscintigraphy of Breast Tumor Xenografts in Mouse Model by 99mTc Direct Radiolabeling of a Monoclonal Antibody PR81

Introduction: The radioimmunoscintigraphy (RIS) has found widespread clinical applications in tumor diagnosis. Human epithelial mucin, MUC1, is commonly over expressed in adenocarcinoma including 80% of breast cancers and represents a useful target for RIS. The PR81 is a new murine anti-MUC1 monoclonal antibody that was found to react with the membrane extracts of several human breast cancerous tissues and the cell surface of some MUC1 positive cell lines. In this study, a direct method which is very simple, rapid and efficient for the labeling of this MAb with 99mTc, particularly suitable for the development of a ‘kit’, was developed. The quality control of new radiopharmaceutical and immunoscintigraphy studies in BALB/c mice bearing breast tumor xenografts were also performed. Materials and Methods: The Ab reduction was performed with 2-mercaptoethanol (2-ME) at a molar ratio of 2000:1 (2-ME:MAb) and reduced Ab was labeled with 99mTc via methylene diphosphonate (MDP) as a transchelator. The labeling efficiency was determined by ITLC. The amount of radiocolloids was measured by cellulose nitrate electrophoresis. The stability of the labeled product was checked in fresh human serum by gel filtration chromatography (FPLC) over 24 hrs. The integrity of the labeled MAb was checked by the means of SDS-PAGE. Cell-binding assay was used to test the binding ability of 99mTc-PR81 to MCF7 cells. Biodistribution was studied in normal BALB/c mice at 4 and 24 hrs post-injection. The tumor imaging was performed in female BALB/c mice with breast tumor xenografts 24 hrs after the new complex injection. Results: The labeling efficiency was 94.2%±2.3 and radiocolloids were 2.5%±1.7. In vitro stability was 70%±5.7 in fresh human serum over 24 hrs. There was no significant Ab fragmentation due to the labeling procedure. Both the labeled and unlabeled PR81 were able to compete for binding to MCF7 cells. The biodistribution studies in normal BALB/c mice showed that there was no important accumulation in any organ. The immunoscintigraphy studies demonstrated definite localization of the preparation at the site of tumors with high sensitivity. Discussion and Conclusion: The results show that by using the Schwarz method of radiolabeling MAb PR81, a labeling yield higher than 90% with high stability of the complex in human serum can be obtained. These findings demonstrated that the new radiopharmaceutical can be considered as a promising candidate for imaging of human breast cancer.

MUC1 Cytoplasmic Domain Coactivates Wnt Target Gene Transcription and Confers Transformation

The DF3/MUC1 mucin-like transmembrane oncoprotein is overexpressed by most human carcinomas. The MUC1 cytoplasmic domain (CD) binds directly to the Wnt effector, beta-catenin, and colocalizes with beta-catenin in the nucleus; however, the nuclear function of MUC1 is unknown. The present results demonstrate that MUC1 coactivates transcription of beta-catenin-Tcf-binding sites in the pTOPFLASH reporter. Activation of transcription was abrogated by expression of MUC1 with a Y-46->F mutation in the CD that attenuates binding of MUC1 and beta-catenin. We also show that transcription of the Wnt responsive cyclin D1 promoter is activated by MUC1, but not MUC1(Y46F), and that the cyclin D1 gene is upregulated in MUC1-positive cells. In concert with these results, MUC1-induced anchorage-independent growth and tumorigenicity were also abrogated by mutating MUC1 at the Y-46 site. These findings support a model in which the MUC1 functions as a transforming protein by coactivating transcription of Wnt target genes.

Human DF3/MUC1 carcinoma-associated protein functions as an oncogene.

The human DF3/MUC1 mucin-like glycoprotein is aberrantly overexpressed by most carcinomas of the breast and other epithelia. The contribution of MUC1 overexpression to the malignant phenotype is, however, not known. In the present studies, we have stably expressed MUC1 in rat 3Y1 fibroblasts. MUC1-positive cells were selected from independent transfections. The results demonstrate that, as found in human carcinomas, MUC1 is expressed on the cell surface and as a complex with beta-catenin in the nucleus of the transfectants. Colony formation in soft agar demonstrates that cells expressing MUC1, but not the empty vector, exhibit anchorage-independent growth. The results also show that MUC1 expression confers tumor formation in nude mice. These findings provide the first evidence that MUC1 induces cellular transformation.

Production of monoclonal antibody, PR81, recognizing the tandem repeat region of MUC1 mucin.

A monoclonal antibody (MAb) was generated by immunizing BALB/c mice with homogenized breast cancerous tissues. This antibody (PR81) was found to be of IgG(1) class and subclass, containing kappa light chain. PR81 reacted with either the membrane extracts of several breast cancerous tissues or the cell surface of some MUC1 positive cell lines (MCF-7, BT-20 and T-47D) tested by enzyme immunoassay and for MCF-7 by immunofluorescence method. PR81 also reacted with two synthetic 27 and 16-amino acid peptides, TSA-P1-24 and A-P1-15, respectively, which included the core tandem repeat sequence of MUC1. However, this antibody did not react with a synthetic 14 amino acid peptide that has no similarity with tandem repeat found in MUC1. The generated antibody had good and similar affinities (2.19 x 10(8) M(-1)) toward TSA-P1-24 and A-P1-15, which are mainly shared in the hydrophilic sequence of PDTRPAP. Through Western blot analysis of homogenized breast tissues, PR81 recognized only a major band of 250 kDa. This band is stronger in malignant tissue than benign and normal tissues.

MUC1 as a human tumor marker

MUC1 mucin serves as a tumor-associated antigen in various carcinomas. We have reported the expression of MUC1 in multiple myeloma (MM) cells and the establishment of an HLA-unrestricted cytotoxic T lymphocyte (CTL) that recognized MUC1 from peripheral lymphocytes in a patient with MM. In this study, we successfully induced MUC1-specific CTLs from bone marrow cells in two MM patients. Both CTLs lysed MUC1-positive cell lines with different kinds of HLA, and the cytotoxicity was inhibited by anti-CD3, anti-αβ T cell receptor and anti-MUC1 monoclonal antibodies. The treatment with O-glycosylation inhibitor augmented the cytotoxicity of the CTLs. These data showed that HLA-unrestricted CTLs that recognize the underglycosylated form of MUC1 could be induced from MM patients. MUC1 is also an important factor in cancer metastasis. We previously reported that MUC1 mucin has anti-adhesion effects that contribute to the separation of tumor cells from the primary site. We next investigated the involvement of MUC1 in tumor invasion that is a second step of metastasis. MUC1-transfectants transplanted subcutaneously into nude mice invaded the muscular layer. The treatment with O-glycosylation inhibitor abolished these effects of MUC1. Our data indicated that MUC1 mucin increases the invasive ability of tumor cells, while O-glycan plays an essential role.

MUC1 expression in primary breast cancer: the effect of tamoxifen treatment.

This was a non-randomised single institution retrospective study. Forty-six banked frozen tumour specimens were obtained from a group of patients who had undergone 3 weeks of neoadjuvant treatment with tamoxifen between biopsy and surgery. Fifty-one comparison specimens were randomly selected from a group of concomitantly treated primary breast cancer patients who did not receive neoadjuvant tamoxifen. Specimen selection was not based on prognostic factors: hormone receptor status, patient age, or menopausal status. MUC1 expression and cell cycle distribution were assessed by flow cytometry. S-phase fraction of MUC1 positive and MUC1 negative cells were compared. A lower percentage of cells expressed MUC1 following 3-week tamoxifen treatment 18.2% versus 28.5% (p = 0.03, Mann-Whitney) and lower levels of MUC1 expression were seen following tamoxifen treatment 31,519 molecules/cell versus 39,387 (p = 0.04, Mann-Whitney). MUC1 positive cells, irrespective of treatment group, had a greater proportion of cells in S-phase of the cell cycle 27.9% versus 16.8% (p = 0.0004, Mann-Whitney) and demonstrated more cases of aneuploidy 80.65% versus 42.6% (p < 0.0001). MUC1 levels in primary tumours treated neoadjunctively with 3 weeks of tamoxifen were lower than a comparison group which did not receive tamoxifen. MUC1 should be explored further as an intermediate biomarker for assessment of treatment and prognosis.

Construction of a diabody (small recombinant bispecific antibody) using a refolding system.

Diabodies are the recombinant bispecific antibodies (BsAbs), constructed from heterogeneous single-chain antibodies. Usually, diabodies have been prepared from bacterial periplasmic fraction using a co-expression vector (i.e. genes encoding two chains were tandemly located under the same promoter). Some diabodies, however, cannot be expressed as a soluble material owing to inclusion body formation, which limits the utilization of diabodies in various fields. Here we report an improved method for the construction of diabodies using a refolding system. As a model, a bispecific diabody binding to adenocarcinoma-associated antigen MUC1 and to CD3 on T cells was studied. One chain consisted of a VH specific for MUC1 linked to a VL specific for CD3 with a short polypeptide linker (GGGGS). The second was composed of a VL specific for MUC1 linked to a VH specific for CD3. The two hetero scFvs were independently obtained from intracellular insoluble fractions of Escherichia coli, purified, mixed stoichiometrically (at an equivalent molar ratio of 1:1) and refolded. The refolded two hetero scFv has a hetero-dimeric structure, with complete specificity for both target cells [i.e. MUC1 positive cells and CD3 positive lymphokine-activated killer cells with a T cell phenotype (T-LAK)]. Evaluation of the in vitro efficacy of T-LAK with the diabody by growth inhibition assay of cancer cells demonstrated maximum growth inhibition of cancer cells to reach approximately 98% at an effector:target ratio (E:T ratio) of 10, almost identical with that with anti-MUC1xanti-CD3 chemically synthesized BsAbs (c-BsAbs). This is the first report of the construction of a diabody using a refolding system.

Clinical significance of MUC1 and MUC2 mucin and p53 protein expression in colorectal carcinoma.

Up-regulation of MUC1, down-regulation of MUC2 and p53 overexpression are seen in colorectal carcinomas. However, there have been few reports about the associations between MUC1, MUC2 and p53 expression and metastatic potential. The aim of this study was to investigate MUC1, MUC2 and p53 expression in colorectal carcinoma with special reference to regional and distant metastasis. Eighty-six colorectal carcinomas were collected from patients undergoing tumor resection. Sections were used for MUC1, MUC2 and p53 immunostaining. Cancers were regarded as MUC1 or MUC2 positive when the positive cells were beyond 30% of cancer cells. Cancers with diffuse or nested patterns were regarded as having p53 overexpression. Of 86 cancers, 37 (43%) were MUC1 positive, 28 (33%) were MUC2 positive and 59 (69%) showed p53 overexpression. A difference was observed only in the frequency of MUC1 positivity with respect to depth of tumor invasion. Neither depth of tumor invasion nor histological differentiation had a positive correlation with MUC1, MUC2 and p53 overexpression. The frequency of MUC1 positive cells in Dukes' C and D tumors was significantly higher than that in Dukes' A and B tumors. The frequency of MUC1 positivity in tumors with hepatic involvement was significantly higher than that in tumors without hepatic involvement (100 vs 39%; p < 0.01). There was no difference in the frequency of MUC2 or p53 positivity in Dukes' stage or hepatic metastasis. MUC1 immunoreactivity of the surface was identical with that of the whole tumor in 81% (70/86) of carcinomas, MUC 2 in 87% and p53 in 100%. The results suggest that up-regulation of MUC1 is involved in the progression from the non-metastatic to the metastatic stage and that p53 abnormality is not directly involved in it. The data also imply that immunostaining of preoperative biopsy samples is useful for evaluating the immunoreactivity of the whole tumor.

Use of transcriptional regulatory elements of the MUC1 and ERBB2 genes to drive tumour-selective expression of a prodrug activating enzyme.

In order to exploit differences in gene expression between normal and malignant cells for genetic prodrug-activation therapy, we have generated recombinant retroviruses containing the herpes simplex virus thymidine kinase coding region cloned downstream of sequences derived from the 5'-flanking regions of the MUC1 and ERBB2 genes. Transduction with retroviruses containing MUC1 promoters resulted in an increase in GCV sensitivity in MUC1 positive cells. A further increase in GCV sensitivity was achieved when MUC1-positive cells were transduced with retroviruses containing chimeric-MUC1/ERBB2 promoters. No significant sensitization to GCV was observed when MUC1-negative cells were transduced with these recombinant retroviruses. These results suggest that one may be able to develop a tumour-selective therapy by utilizing the transcriptional regulatory regions of the MUC1 and ERBB2 genes to drive the expression of suicide genes.