O-glycosylation of MUC1 mucin in prostate cancer and the effects of its expression on tumor growth in a prostate cancer xenograft model

Mucin Glycans: A Target for Cancer Therapy

Mucin glycans are an important component of the mucus barrier and a vital defence against physical and chemical damage as well as pathogens. There are 20 mucins in the human body, which can be classified into secreted mucins and transmembrane mucins according to their distributions. The major difference between them is that secreted mucins do not have transmembrane structural domains, and the expression of each mucin is organ and cell-specific. Under physiological conditions, mucin glycans are involved in the composition of the mucus barrier and thus protect the body from infection and injury. However, abnormal expression of mucin glycans can lead to the occurrence of diseases, especially cancer, through various mechanisms. Therefore, targeting mucin glycans for the diagnosis and treatment of cancer has always been a promising research direction. Here, we first summarize the main types of glycosylation (O-GalNAc glycosylation and N-glycosylation) on mucins and the mechanisms by which abnormal mucin glycans occur. Next, how abnormal mucin glycans contribute to cancer development is described. Finally, we summarize MUC1-based antibodies, vaccines, radio-pharmaceuticals, and CAR-T therapies using the best characterized MUC1 as an example. In this section, we specifically elaborate on the recent new cancer therapy CAR-M, which may bring new hope to cancer patients.

Narrative review of urinary glycan biomarkers in prostate cancer

Prostate cancer (PC) is the second most common cancer in men worldwide. The application of the prostate-specific antigen (PSA) test has improved the diagnosis and treatment of PC. However, the PSA test has become associated with overdiagnosis and overtreatment. Therefore, there is an unmet need for novel diagnostic, prognostic, and predictive biomarkers of PC. Urinary glycoproteins and exosomes are a potential source of PC glycan biomarkers. Urinary glycan profiling can provide noninvasive monitoring of tumor heterogeneity and aggressiveness throughout a treatment course. However, urinary glycan profiling is not popular due to technical disadvantages, such as complicated structural analysis that requires specialized expertise. The technological development of glycan analysis is a rapidly advancing field. A lectin-based microarray can detect aberrant glycoproteins in urine, including PSA glycoforms and exosomes. Glycan enrichment beads can enrich the concentration of N-linked glycans specifically. Capillary electrophoresis, liquid chromatography-tandem mass spectrometry, and matrix-assisted laser desorption/ionization-time of flight mass spectrometry can detect glycans directory. Many studies suggest potential of urinary glycoproteins, exosomes, and glycosyltransferases as a biomarker of PC. Although further technological challenges remain, urinary glycan analysis is one of the promising approaches for cancer biomarker discovery.

Lewis(y) antigen promotes the progression of epithelial ovarian cancer by stimulating MUC1 expression

MUC1 is a type I transmembrane glycoprotein and is overexpressed in various epithelial tumor tissues. Some researchers have demonstrated that the glycosylation status of MUC1 can affect MUC1-mediated tumor growth and cell differentiation. In our previous study, we proved that the abilities of cell proliferation, adhesion, invasion and metastasis, and drug resistance were enhanced in ovarian cancer cells stably expressing Lewis(y). Therefore, we hypothesized that Lewis(y) antigen may play a central role in regulating MUC1 expression, and MUC1-mediated cell growth and differentiation may be closely associated with Lewis(y) antigen. This study aimed to examine the correlation between MUC1 expression and Lewis(y) antigen levels in ovarian cancer cell lines and tissue samples. A series of techniques, including RT-qPCR, western blot anlaysis, immunoprecipitation, immunohistochemistry and double-labeling immunofluorescence were applied to detect the expression of Lewis(y) and MUC1. In malignant epithelial ovarian tumors, the positive expression rates of Lewis(y) antigen and MUC1 were 88.33 and 86.67%, respectively, which were markedly higher than those in borderline (60.00 and 53.33%, P<0.05), benign (33.33 and 30%, P<0.01) and normal (0 and 25%, P<0.01) ovarian samples. There was no correlation between the positive expression rates of Lewis(y) or MUC1 and clinicopathological parameters in ovarian cancers (P>0.05). The expression levels of Lewis(y) and MUC1 correlated with the clinical FIGO stage (P<0.05). Both MUC1 and Lewis(y) were highly expressed in ovarian cancer tissues, and their expression levels were positively correlated (P<0.01). In α1,2-fucosyltransferase (α1,2-FT)-transfected cells, the gene and protein expression levels of MUC1 were significantly upregulated compared with the cells that did not overexpress α1,2-FT (P<0.05). The ratio of Lewis(y) immunoprecipitated with MUC1 to total MUC1 increased 1.55-fold in α1,2-FT-overexpressing cells (P<0.05). The overexpression of Lewis(y) resulted in the upregulation of MUC1. On the whole, our data indicate that both MUC1 and Lewis(y) are associated with the occurrence and development of ovarian cancers.

MUC1 Expression by Immunohistochemistry Is Associated with Adverse Pathologic Features in Prostate Cancer: A Multi-Institutional Study

Background

The uncertainties inherent in clinical measures of prostate cancer (CaP) aggressiveness endorse the investigation of clinically validated tissue biomarkers. MUC1 expression has been previously reported to independently predict aggressive localized prostate cancer. We used a large cohort to validate whether MUC1 protein levels measured by immunohistochemistry (IHC) predict aggressive cancer, recurrence and survival outcomes after radical prostatectomy independent of clinical and pathological parameters.

Material and Methods

MUC1 IHC was performed on a multi-institutional tissue microarray (TMA) resource including 1,326 men with a median follow-up of 5 years. Associations with clinical and pathological parameters were tested by the Chi-square test and the Wilcoxon rank sum test. Relationships with outcome were assessed with univariable and multivariable Cox proportional hazard models and the Log-rank test.

Results

The presence of MUC1 expression was significantly associated with extracapsular extension and higher Gleason score, but not with seminal vesicle invasion, age, positive surgical margins or pre-operative serum PSA levels. In univariable analyses, positive MUC1 staining was significantly associated with a worse recurrence free survival (RFS) (HR: 1.24, CI 1.03–1.49, P = 0.02), although not with disease specific survival (DSS, P>0.5). On multivariable analyses, the presence of positive surgical margins, extracapsular extension, seminal vesicle invasion, as well as higher pre-operative PSA and increasing Gleason score were independently associated with RFS, while MUC1 expression was not. Positive MUC1 expression was not independently associated with disease specific survival (DSS), but was weakly associated with overall survival (OS).

Conclusion

In our large, rigorously designed validation cohort, MUC1 protein expression was associated with adverse pathological features, although it was not an independent predictor of outcome after radical prostatectomy.

Intra- and Extra-Cellular Events Related to Altered Glycosylation of MUC1 Promote Chronic Inflammation, Tumor Progression, Invasion, and Metastasis

Altered glycosylation of mucin 1 (MUC1) on tumor cells compared to normal epithelial cells was previously identified as an important antigenic modification recognized by the immune system in the process of tumor immunosurveillance. This tumor form of MUC1 is considered a viable target for cancer immunotherapy. The importance of altered MUC1 glycosylation extends also to its role as a promoter of chronic inflammatory conditions that lead to malignant transformation and cancer progression. We review here what is known about the role of specific cancer-associated glycans on MUC1 in protein-protein interactions and intracellular signaling in cancer cells and in their adhesion to each other and the tumor stroma. The tumor form of MUC1 also creates a different landscape of inflammatory cells in the tumor microenvironment by controlling the recruitment of inflammatory cells, establishing specific interactions with dendritic cells (DCs) and macrophages, and facilitating tumor escape from the immune system. Through multiple types of short glycans simultaneously present in tumors, MUC1 acquires multiple oncogenic properties that control tumor development, progression, and metastasis at different steps of the process of carcinogenesis.

Ocular Surface Membrane-Associated Mucins

Ocular surface epithelial cells produce and secrete mucins that form a hydrophilic barrier for protection and lubrication of the eye. This barrier, the glycocalyx, is formed by high molecular weight heavily glycosylated membrane-associated mucins (MAMs) that include MUC1, MUC4, and MUC16. These mucins extend into the tear film from the anterior surfaces of the conjunctiva and cornea, and, through interactions with galectin-3, prevent penetrance of pathogens into the eye. Due primarily to the glycosylation of the mucins, the glycocalyx also creates less friction during blinking and enables the tear film to maintain wetting of the eye. The secretory mucins include soluble MUC7 and gel-forming MUC5AC. These mucins, particularly MUC5AC, assist with removal of debris from the tear film and contribute to the hydrophilicity of the tear film. While new methodologies and cell culture models have expanded our understanding of mucin structure and function on the ocular surface, there is still a paucity of studies characterizing the glycosylation of MAMs on a normal ocular surface and a diseased ocular surface. Although studies have shown alterations in mucin production and expression in dry eye diseases, the relationship between changes in mucins and functional consequences is unclear. This review focuses on comparing what is known about MAMs in wet-surfaced epithelia of the body to what has been studied on the eye.

Epithelial MUC1 promotes cell migration, reduces apoptosis and affects levels of mucosal modulators during acetylsalicylic acid (aspirin)-induced gastropathy

MUC1, a transmembrane mucin highly expressed in the stomach, is up-regulated after acetylsalicylic acid (ASA) intake in humans and mice. Epithelial Muc1/MUC1 facilitates mucosal wound healing by enhancing cell migration and proliferation, protecting against apoptosis and mediating expression of mucosal modulators.

Pleomorphic adenoma of oral minor salivary glands: An investigation of its neoplastic potential based on apoptosis, mucosecretory activity and cellular proliferation

OBJECTIVE

The aim of this study was to investigate the neoplastic potential of the PA of minor oral salivary glands measured by apoptosis (Bcl-2, Bax and p53), mucosecretory activity (MUC1), and cellular proliferation (Ki-67).

DESIGN

Thirty-one cases of PA of the oral cavity and four controls (C) taken from normal oral minor salivary glands were analyzed using the immunohistochemistry technique. The proteins were detected utilizing a semi-quantitative method (scores) as follows: (-) negative ≤5%, (+) low 6-25%, (++) moderate 26-50% and (+++) high >50% of positive tumour cells. The apoptotic indices were evaluated by the ratio Bcl-2/Bax. Non-parametric comparison and correlation tests were used for analysis.

RESULTS

The data showed high staining of anti-apoptotic protein Bcl-2 in both groups (PA=57.9%; C=67.7%) and a significantly lower expression of pro-apoptotic protein Bax (PA=22.7%; C=97.7%) and MUC1 (PA=14%; C=82.3%) in PA than in C (p<0.001). On the other hand, a similar expression of Ki-67 and p53 proteins (≤5%) was seen in both PA and C. In PA, only 2/31 cases showed the ratio Bcl-2/Bax<1.There was no difference in cellular expression with regard to clinical variables or clinical outcome (p>0.05).

CONCLUSION

The neoplastic potential of PA could be associated with an imbalance in apoptotic processes and a lower index of cellular proliferation. Mucosecretory activity does not play a significant role in primary PA.

Increased understanding of the biochemistry and biosynthesis of MUC2 and other gel-forming mucins through the recombinant expression of their protein domains

The gel-forming mucins are large and heavily O-glycosylated proteins which build up mucus gels. The recombinant production of full-length gel-forming mucins has not been possible to date. In order to study mucin biosynthesis and biochemistry, we and others have taken the alternative approach of constructing different recombinant proteins consisting of one or several domains of these large proteins and expressing them separately in different cell lines. Using this approach, we have determined that MUC2, the intestinal gel-forming mucin, dimerizes via its C-terminal cysteine-knot domain and also trimerizes via one of the N-terminal von Willebrand D domains. Both of these interactions are disulfide bond mediated. Via this assembly, a molecular network is built by which the mucus gel is formed. Here we discuss not only the functional understanding obtained from studies of the recombinant proteins, but also highlight the difficulties encountered when these proteins were produced recombinantly. We often found an accumulation of the proteins in the ER and consequently no secretion. This was especially apparent when the cysteine-rich domains of the N- and C-terminal parts of the mucins were expressed. Other proteins that we constructed were either not secreted or not expressed at all. Despite these problems, the knowledge of mucin biosynthesis and assembly has advanced considerably through the studies of these recombinant proteins.

Expression of human full-length MUC1 inhibits the proliferation and migration of a B16 mouse melanoma cell line

Mucin 1 (MUC1) is a large transmembrane glycoprotein that is aberrantly overexpressed in most adenocarcinomas and certain hematological malignancies. MUC1 is known to function as an oncogene with roles in both tumor formation and progression, making it a potential target for immunotherapy. B16-MUC1 cells with human full-length MUC1 are frequently used to study the antitumor activities of MUC1-based vaccines. However, we found that the growth of B16-MUC1 cells was significantly reduced in vitro. Therefore, in this study, we established two MUC1-positive clones, B16-MUC1 9-12 and B16-MUC1 9-23, and one empty vector control clone, B16-neo, to investigate the effects of MUC1 on the cancer-related characteristics of B16 cells in vitro and in vivo. Our results demonstrated that, compared with MUC1-negative cells, cells expressing MUC1 exhibited decreased cell proliferation, increased cell cycle arrest and reduced cell migratory and invasive capacities. We further investigated several MUC1-related molecules of the β-catenin pathway, and found that the expression of MUC1 decreased the translocation of β-catenin into the nucleus, reduced the activity of T cell factor (TCF) and blocked the expression of cyclin D1 and c-Myc. Moreover, when inoculated into BALB/c nude mice, cells expressing MUC1 developed smaller tumors compared with the control cells. These results demonstrate that MUC1 expression negatively affects the malignancy of B16 cells, and suggest that the regulatory mechanisms of MUC1 as an oncoprotein are more complex than previously appreciated.

Glycosylation potential of human prostate cancer cell lines

Altered glycosylation is a universal feature of cancer cells and altered glycans can help cancer cells escape immune surveillance, facilitate tumor invasion, and increase malignancy. The goal of this study was to identify specific glycoenzymes, which could distinguish prostate cancer cells from normal prostatic cells. We investigated enzymatic activities and gene expression levels of key glycosyl- and sulfotransferases responsible for the assembly of O- and N-glycans in several prostatic cells. These cells included immortalized RWPE-1 cells derived from normal prostatic tissues, and prostate cancer cells derived from metastasis in bone (PC-3), brain (DU145), lymph node (LNCaP), and vertebra (VCaP). We found that all cells were capable of synthesizing complex N-glycans and O-glycans with the core 1 structure, and each cell line had characteristic biosynthetic pathways to modify these structures. The in vitro measured activities corresponded well to the mRNA levels of glycosyltransferases and sulfotransferases. Lectin and antibody binding to whole cells supported these results, which form the basis for the development of tumor cell-specific targeting strategies.

Implications of the Golgi apparatus in prostate cancer

The classical view of the Golgi apparatus is of a small membranous organelle involved in protein transport and secretion. Recent descriptions of the molecular network connecting the Golgi to other organelles demonstrate the essential roles of the Golgi in cellular activities as a stress sensor, apoptosis trigger, lipid/protein modifier, mitotic checkpoint, and a mediator of malignant transformation. Thus, the Golgi function should have a fundamental impact on cancer cell survival. Prostate cancer is initially responsive to androgenic hormones; however, it almost invariably progresses to a castration-refractory or hormone-insensitive state. Nevertheless, androgen signaling remains active at this stage and is important as a therapeutic target. Certain Golgi-associated molecules have recently been demonstrated to be regulated by androgen action, and the Golgi is emerging as a new therapeutic target in prostate cancer. The key Golgi-associated molecules essential for prostate cancer development and the potential therapeutic options targeting the Golgi apparatus are discussed.

Glycoproteomics-based identification of cancer biomarkers

Protein glycosylation is one of the most common posttranslational modifications in mammalian cells. It is involved in many biological pathways and molecular functions and is well suited for proteomics-based disease investigations. Aberrant protein glycosylation may be associated with disease processes. Specific glycoforms of glycoproteins may serve as potential biomarkers for the early detection of disease or as biomarkers for the evaluation of therapeutic efficacy for treatment of cancer, diabetes, and other diseases. Recent technological developments, including lectin affinity chromatography and mass spectrometry, have provided researchers the ability to obtain detailed information concerning protein glycosylation. These in-depth investigations, including profiling and quantifying glycoprotein expression, as well as comprehensive glycan structural analyses may provide important information leading to the development of disease-related biomarkers. This paper describes methodologies for the detection of cancer-related glycoprotein and glycan structural alterations and briefly summarizes several current cancer-related findings.