Mucins in cancer: function, prognosis and therapy

Measuring kinetic dissociation/association constants between Lactococcus lactis bacteria and mucins using living cell probes

In this work we focused on quantifying adhesion between Lactococcus lactis, the model for lactic acid bacteria (LAB) and mucins. Interactions between two strains of L. lactis (IBB477 and MG1820 as control) and pig gastric mucin-based coating were measured and compared with the use of atomic force microscopy. Analysis of retraction force-distance curves shed light on the differential contributions of nonspecific and specific forces. An increased proportion of specific adhesive events was obtained for IBB477 (20% vs. 5% for the control). Blocking assays with free pig gastric mucin and its O-glycan moiety showed that oligosaccharides play a major (but not exclusive) role in L. lactis-mucins interactions. Specific interactions were analyzed in terms of kinetic constants. An increase in the loading rate of atomic force microscope tip led to a higher force between interacting biological entities, which was directly linked to the kinetic dissociation constant (K(off)). Enhancing the contact time between the tip and the sample allowed an increase in the interaction probability, which can be related to the kinetic association constant (K(on)). Variations in the loading rate and contact time enabled us to determine K(on) (3.3 × 10(2) M(-1)·s(-1)) and K(off) (0.46 s(-1)), and the latter was consistent with values given in the literature for sugar-protein interactions.

EGFR-mediated carcinoma cell metastasis mediated by integrin αvβ5 depends on activation of c-Src and cleavage of MUC1

Receptor tyrosine kinases and integrins play an essential role in tumor cell invasion and metastasis. We previously showed that EGF and other growth factors induce human carcinoma cell invasion and metastasis mediated by integrin αvβ5 that is prevented by Src blockade [1]. MUC1, a transmembrane glycoprotein, is expressed in most epithelial tumors as a heterodimer consisting of an extracellular and a transmembrane subunit. The MUC1 cytoplasmic domain of the transmembrane subunit (MUC1.CD) translocates to the nucleus where it promotes the transcription of a metastatic gene signature associated with epithelial to mesenchymal transition. Here, we demonstrate a requirement for MUC1 in carcinoma cell metastasis dependent on EGFR and Src without affecting primary tumor growth. EGF stimulates Src-dependent MUC1 cleavage and nuclear localization leading to the expression of genes linked to metastasis. Moreover, expression of MUC1.CD results in its nuclear localization and is sufficient for transcription of the metastatic gene signature and tumor cell metastasis. These results demonstrate that EGFR and Src activity contribute to carcinoma cell invasion and metastasis mediated by integrin αvβ5 in part by promoting proteolytic cleavage of MUC1 and highlight the ability of MUC1.CD to promote metastasis in a context-dependent manner. Our findings may have implications for the use and future design of targeted therapies in cancers known to express EGFR, Src, or MUC1.

Beyond the genome and proteome: targeting protein modifications in cancer

Nearly all proteins are modified in post translational events, indeed, understanding the control and function of post translational modifications (PTMs) is arguably the 'next frontier' for cancer cell biologists. The most well understood PTMs include glycosylation, phosphorylation, ubiquitination, methylation and palmitylation. Each of these modifications has been observed to be altered in cancer, affecting key cellular pathways including signal transduction, cell membrane receptor function, and protein-protein interactions. A number of strategies have been proposed that aim to target the modified proteins themselves, the enzymes that construct them, or that boost host-cellular immunity against modified residues aberrantly expressed in cancer.

Emerging avenues linking inflammation and cancer

The role of inflammation in carcinogenesis has been extensively investigated and well documented. Many biochemical processes that are altered during chronic inflammation have been implicated in tumorigenesis. These include shifting cellular redox balance toward oxidative stress; induction of genomic instability; increased DNA damage; stimulation of cell proliferation, metastasis, and angiogenesis; deregulation of cellular epigenetic control of gene expression; and inappropriate epithelial-to-mesenchymal transition. A wide array of proinflammatory cytokines, prostaglandins, nitric oxide, and matricellular proteins are closely involved in premalignant and malignant conversion of cells in a background of chronic inflammation. Inappropriate transcription of genes encoding inflammatory mediators, survival factors, and angiogenic and metastatic proteins is the key molecular event in linking inflammation and cancer. Aberrant cell signaling pathways comprising various kinases and their downstream transcription factors have been identified as the major contributors in abnormal gene expression associated with inflammation-driven carcinogenesis. The posttranscriptional regulation of gene expression by microRNAs also provides the molecular basis for linking inflammation to cancer. This review highlights the multifaceted role of inflammation in carcinogenesis in the context of altered cellular redox signaling.

Cancer imaging: Gene transcription-based imaging and therapeutic systems

Molecular-genetic imaging of cancer is in its infancy. Over the past decade gene reporter systems have been optimized in preclinical models and some have found their way into the clinic. The search is on to find the best combination of gene delivery vehicle and reporter imaging system that can be translated safely and quickly. The goal is to have a combination that can detect a wide variety of cancers with high sensitivity and specificity in a way that rivals the current clinical standard, positron emission tomography with [(18)F]fluorodeoxyglucose. To do so will require systemic delivery of reporter genes for the detection of micrometastases, and a nontoxic vector, whether viral or based on nanotechnology, to gain widespread acceptance by the oncology community. Merger of molecular-genetic imaging with gene therapy, a strategy that has been employed in the past, will likely be necessary for such imaging to reach widespread clinical use.

Oral drug delivery with polymeric nanoparticles: the gastrointestinal mucus barriers

Oral delivery is the most common method for drug administration. However, poor solubility, stability, and bioavailability of many drugs make achieving therapeutic levels via the gastrointestinal (GI) tract challenging. Drug delivery must overcome numerous hurdles, including the acidic gastric environment and the continuous secretion of mucus that protects the GI tract. Nanoparticle drug carriers that can shield drugs from degradation and deliver them to intended sites within the GI tract may enable more efficient and sustained drug delivery. However, the rapid secretion and shedding of GI tract mucus can significantly limit the effectiveness of nanoparticle drug delivery systems. Many types of nanoparticles are efficiently trapped in and rapidly removed by mucus, making controlled release in the GI tract difficult. This review addresses the protective barrier properties of mucus secretions, how mucus affects the fate of orally administered nanoparticles, and recent developments in nanoparticles engineered to penetrate the mucus barrier.

The MUC1-C oncoprotein binds to the BH3 domain of the pro-apoptotic BAX protein and blocks BAX function

The pro-apoptotic BAX protein contains a BH3 domain that is necessary for its dimerization and for activation of the intrinsic apoptotic pathway. The MUC1 (mucin 1) heterodimeric protein is overexpressed in diverse human carcinomas and blocks apoptosis in the response to stress. In this study, we demonstrate that the oncogenic MUC1-C subunit associates with BAX in human cancer cells. MUC1-C·BAX complexes are detectable in the cytoplasm and mitochondria and are induced by genotoxic and oxidative stress. The association between MUC1-C and BAX is supported by the demonstration that the MUC1-C cytoplasmic domain is sufficient for the interaction with BAX. The results further show that the MUC1-C cytoplasmic domain CQC motif binds directly to the BAX BH3 domain at Cys-62. Consistent with binding to the BAX BH3 domain, MUC1-C blocked BAX dimerization in response to (i) truncated BID in vitro and (ii) treatment of cancer cells with DNA-damaging agents. In concert with these results, MUC1-C attenuated localization of BAX to mitochondria and the release of cytochrome c. These findings indicate that the MUC1-C oncoprotein binds directly to the BAX BH3 domain and thereby blocks BAX function in activating the mitochondrial death pathway.

Mucin 16 (cancer antigen 125) expression in human tissues and cell lines and correlation with clinical outcome in adenocarcinomas of the pancreas, esophagus, stomach, and colon

Mucin 16 (cancer antigen 125) is a cell surface glycoprotein that plays a role in promoting cancer cell growth in ovarian cancer. The aims of this study were to examine mucin 16 expression in a large number of digestive tract adenocarcinomas and precursors and to determine whether mucin 16 up-regulation is correlated with patient outcome. Tissue microarrays were constructed using surgical resection tissues and included pancreatic (115 normal, 29 precursors, 200 pancreatic ductal adenocarcinomas), esophageal (86 normal, 104 precursors, 95 esophageal adenocarcinomas, 35 lymph node metastases), gastric (211 normal, 8 precursors, 119 gastric adenocarcinomas, 62 lymph node metastases), and colorectal (34 normal, 17 precursors, 39 colorectal adenocarcinomas) tissues. Mucin 16 was detected in 81.5%, 69.9%, 41.2%, and 64.1% of the pancreatic ductal adenocarcinomas, esophageal adenocarcinomas, gastric adenocarcinomas, and colorectal adenocarcinomas, respectively. Mucin 16 was seen in a subset of the precursors. On multivariate analysis, moderate/diffuse mucin 16 in pancreatic ductal adenocarcinomas was strongly associated with poor survival (P < .001), independent of other prognosis predictors. A similar trend was observed for esophageal adenocarcinomas (P = .160) and gastric adenocarcinomas (P = .080). Focal mucin 16 in colorectal adenocarcinomas was significantly correlated (P = .044) with a better patient outcome, when compared with mucin 16-negative cases. Using Western blot analysis, we found mucin 16 expression in 3 of 6 pancreatic ductal adenocarcinoma and 1 of 2 esophageal adenocarcinoma cell lines. We conclude that most of the digestive tract adenocarcinomas and a subset of their precursors express mucin 16. Mucin 16 expression is an independent predictor of poor outcome in pancreatic ductal adenocarcinomas and potentially in esophageal adenocarcinomas and gastric adenocarcinomas. We propose that mucin 16 may function as a prognostic marker and therapeutic target in the future.

Antibody targeting of cell-bound MUC1 SEA domain kills tumor cells

The cell-surface glycoprotein MUC1 is a particularly appealing target for antibody targeting, being selectively overexpressed in many types of cancers and a high proportion of cancer stem-like cells. However the occurrence of MUC1 cleavage, which leads to the release of the extracellular α subunit into the circulation where it can sequester many anti-MUC1 antibodies, renders the target problematic to some degree. To address this issue, we generated a set of unique MUC1 monoclonal antibodies that target a region termed the SEA domain that remains tethered to the cell surface after MUC1 cleavage. In breast cancer cell populations, these antibodies bound the cancer cells with high picomolar affinity. Starting with a partially humanized antibody, DMB5F3, we created a recombinant chimeric antibody that bound a panel of MUC1+ cancer cells with higher affinities relative to cetuximab (anti-EGFR1) or tratuzumab (anti-erbB2) control antibodies. DMB5F3 internalization from the cell surface occurred in an efficient temperature-dependent manner. Linkage to toxin rendered these DMB5F3 antibodies to be cytotoxic against MUC1+ cancer cells at low picomolar concentrations. Our findings show that high-affinity antibodies to cell-bound MUC1 SEA domain exert specific cytotoxicity against cancer cells, and they point to the SEA domain as a potential immunogen to generate MUC1 vaccines.

A monoclonal antibody against the oncogenic mucin 1 cytoplasmic domain

Mucin 1 (MUC1) is a heterodimeric protein that is aberrantly overexpressed in diverse human carcinomas and certain hematologic malignancies. The transmembrane MUC1-C subunit confers tumorigenicity and is a target for anti-cancer drug development. In this regard, the MUC1-C cytoplasmic domain interacts with multiple effectors that have been linked to transformation. Here we report on the generation of a mouse monoclonal antibody (MAb) against the human MUC1-C cytoplasmic domain (MUC1-CD). This IgG1 MAb, designated anti-MUC1-CD, reacts with the NYGQLDIFP epitope. We show that anti-MUC1-CD is useful in immunoblotting and immunoprecipitation experiments. In addition, anti-MUC1-CD can be used to detect expression of the MUC1-C subunit in formalin-fixed, paraffin-embedded tissues. The MUC1-C inhibitor has entered Phase I evaluation for patients with refractory solid tumors. The present results indicate that the anti-MUC1-CD antibody could be useful as a biomarker to identify patients with tumors that may be responsive to MUC1-C inhibitors.

Labeling of anti-MUC-1 binding single chain Fv fragments to surface modified upconversion nanoparticles for an initial in vivo molecular imaging proof of principle approach

In vivo optical Imaging is an inexpensive and highly sensitive modality to investigate and follow up diseases like breast cancer. However, fluorescence labels and specific tracers are still works in progress to bring this promising modality into the clinical day-to-day use. In this study an anti-MUC-1 binding single-chain antibody fragment was screened, produced and afterwards labeled with newly designed and surface modified NaYF₄:Yb,Er upconversion nanoparticles as fluorescence reporter constructs. The MUC-1 binding of the conjugate was examined in vitro and in vivo using modified state-of-the-art small animal Imaging equipment. Binding of the newly generated upconversion nanoparticle based probe to MUC-1 positive cells was clearly shown via laser scanning microscopy and in an initial proof of principal small animal optical imaging approach.

Clinical utility of serum tumor markers and circulating tumor cell assays in the treatment of breast cancer

OPINION STATEMENT

Though serum tumor markers and circulating tumor cells (CTCs) have been available to the oncologist for many years, their place in the management of breast cancer remains unclear. Due to issues with sensitivity and specificity, tumor markers are unreliable for the detection of metastases in early stage breast cancer. For patients with metastatic breast cancer without measurable disease (e.g., bone-only disease, pleural effusions, or ascites), it is reasonable to obtain baseline values of serum tumor markers and attempt to correlate them with the first set of scans. In patients with elevated markers at baseline whose tumor marker levels decrease in correlation with an improvement in clinical symptoms, it may be reasonable to use them in conjunction with imaging to help determine whether there is progression of disease. CTCs have been found to hold strong prognostic value for breast cancer in both the early stage and metastatic settings. No large prospective studies to date, however, have shown any predictive value for CTCs and their clinical utility is therefore limited. Whether changing treatment in response to an increase in CTCs without radiologic progression results in improvements in quality of life or survival remains to be seen. CTCs hold great promise in the management of breast cancer and future studies will help delineate their role more appropriately.

Genetic variation in MUC1, MUC2 and MUC6 genes and evolution of gastric cancer precursor lesions in a long-term follow-up in a high-risk area in Spain

In order to assess whether inherited genetic variability in the mucin genes associates with the evolution of gastric cancer precursor lesions (GCPLs), we genotyped 22 tagSNPs in MUC1, MUC6 and MUC2 genes of 387 patients with GCPLs that had been followed up for 12.8 years. According to the diagnosis at recruitment and at the end of follow-up, the lesions did not change in 43.1% of the patients, regressed in 28.7% and progressed in 28.2%. Three SNPs in the 3'-moiety of MUC2 were significantly associated with a decreased risk of progression of the lesions, whereas another four SNPs, located at the 5'-moiety, were found to be significantly associated either with increased [one single-nucleotide polymorphism (SNP)] or decreased (three SNPs) probability of regression. Stratified analysis indicated that significance was maintained only in those subjects positive for Helicobacter pylori infection and in those not consuming non-steroidal anti-inflammatory drugs, which were found protective against lesion progression. Haplotype analyses indicated the presence of two haplotypes, one in each moiety of the gene, that were significantly associated with decreased risk of progression of the lesions [odds ratio (OR) = 0.49 and 0.46; 95% confidence interval (CI) = 0.28-0.85 and 0.25-0.86, respectively]. The 5'-end haplotype was also associated with increased probability of regression (OR = 1.67; 95% CI = 1.02-2.73), altogether suggesting a protective role against progression of the precancerous lesions. No significant association was found with variants in MUC1 and MUC6 genes. These results indicate, for the first time, that genetic variability in MUC2 is associated with evolution of GCPLs, especially in H.pylori infected patients, suggesting a role of this secreted mucin in gastric carcinogenesis.

Therapeutic cancer vaccines: current status and moving forward

Concurrent with U.S. Food and Drug Administration (FDA) approval of the first therapeutic cancer vaccine, a wide spectrum of other cancer vaccine platforms that target a diverse range of tumor-associated antigens is currently being evaluated in randomized phase II and phase III trials. The profound influence of the tumor microenvironment and other immunosuppressive entities, however, can limit the effectiveness of these vaccines. Numerous strategies are currently being evaluated both preclinically and clinically to counteract these immunosuppressive entities, including the combined use of vaccines with immune checkpoint inhibitors, certain chemotherapeutics, small-molecule targeted therapies, and radiation. The potential influence of the appropriate patient population and clinical trial endpoint in vaccine therapy studies is discussed, as well as the potential importance of biomarkers in future directions of this field.

Extracellular leucine-rich repeat proteins are required to organize the apical extracellular matrix and maintain epithelial junction integrity in C. elegans

Epithelial cells are linked by apicolateral junctions that are essential for tissue integrity. Epithelial cells also secrete a specialized apical extracellular matrix (ECM) that serves as a protective barrier. Some components of the apical ECM, such as mucins, can influence epithelial junction remodeling and disassembly during epithelial-to-mesenchymal transition (EMT). However, the molecular composition and biological roles of the apical ECM are not well understood. We identified a set of extracellular leucine-rich repeat only (eLRRon) proteins in C. elegans (LET-4 and EGG-6) that are expressed on the apical surfaces of epidermal cells and some tubular epithelia, including the excretory duct and pore. A previously characterized paralog, SYM-1, is also expressed in epidermal cells and secreted into the apical ECM. Related mammalian eLRRon proteins, such as decorin or LRRTM1-3, influence stromal ECM or synaptic junction organization, respectively. Mutants lacking one or more of the C. elegans epithelial eLRRon proteins show multiple defects in apical ECM organization, consistent with these proteins contributing to the embryonic sheath and cuticular ECM. Furthermore, epithelial junctions initially form in the correct locations, but then rupture at the time of cuticle secretion and remodeling of cell-matrix interactions. This work identifies epithelial eLRRon proteins as important components and organizers of the pre-cuticular and cuticular apical ECM, and adds to the small but growing body of evidence linking the apical ECM to epithelial junction stability. We propose that eLRRon-dependent apical ECM organization contributes to cell-cell adhesion and may modulate epithelial junction dynamics in both normal and disease situations.

MUC1-C oncoprotein induces TCF7L2 transcription factor activation and promotes cyclin D1 expression in human breast cancer cells

MUC1 is a heterodimeric glycoprotein that is overexpressed in breast cancers. The present studies demonstrate that the oncogenic MUC1 C-terminal subunit (MUC1-C) associates with the TCF7L2 transcription factor. The MUC1-C cytoplasmic domain (MUC1-CD) binds directly to the TCF7L2 C-terminal region. MUC1-C blocks the interaction between TCF7L2 and the C-terminal-binding protein (CtBP), a suppressor of TCF7L2-mediated transcription. TCF7L2 and MUC1-C form a complex on the cyclin D1 gene promoter and MUC1-C promotes TCF7L2-mediated transcription by the recruitment of β-catenin and p300. Silencing MUC1-C in human breast cancer cells down-regulated activation of the cyclin D1 promoter and decreased cyclin D1 expression. In addition, a MUC1-C inhibitor blocked the interaction with TCF7L2 and suppressed cyclin D1 levels. These findings indicate that the MUC1-C oncoprotein contributes to TCF7L2 activation and thereby promotes cyclin D1 expression in breast cancer cells.

MUC1 regulates PDGFA expression during pancreatic cancer progression

Pancreatic Ductal Adenocarcinoma (PDA) has one of the worst prognoses of all cancers. Mucin 1 (MUC1), a transmembrane mucin glycoprotein, is a key modulator of several signaling pathways that affect oncogenesis, motility, and metastasis. Its expression is known to be associated with poor prognosis in patients. However, the precise mechanism remains elusive. We report a novel association of MUC1 with Platelet-Derived Growth Factor-A (PDGFA). PDGFA is one of the many drivers of tumor growth, angiogenesis, and metastasis in PDA. Using mouse PDA models as well as human samples, we show clear evidence that MUC1 regulates the expression and secretion of PDGFA. This, in turn, influences proliferation and invasion of pancreatic cancer cells leading to higher tumor burden in vivo. In addition, we reveal that MUC1 over expressing cells are heavily dependent on PDGFA both for proliferation and invasion while MUC1-null cells are not. Moreover, PDGFA and MUC1 are critical for translocation of βcatenin to the nucleus for oncogenesis to ensue. Finally, we elucidate the underlying mechanism by which MUC1 regulates PDGFA expression and secretion in pancreatic cancer cells. We show that MUC1 associates with Hif1-α, a known transcription factor involved in controlling PDGFA expression. Furthermore, MUC1 facilitates Hif1-α translocation to the nucleus. In summary, we have demonstrated that MUC1-induced invasion and proliferation occurs via increased exogenous production of PDGFA. Thus, impeding MUC1 regulation of PDGFA signaling may be therapeutically beneficial for patients with PDA.

Membrane-tethered MUC1 mucin is phosphorylated by epidermal growth factor receptor in airway epithelial cells and associates with TLR5 to inhibit recruitment of MyD88

MUC1 is a membrane-tethered mucin glycoprotein expressed on the apical surface of mucosal epithelial cells. Previous in vivo and in vitro studies established that MUC1 counterregulates airway inflammation by suppressing TLR signaling. In this article, we elucidate the mechanism by which MUC1 inhibits TLR5 signaling. Overexpression of MUC1 in HEK293 cells dramatically reduced Pseudomonas aeruginosa-stimulated IL-8 expression and decreased the activation of NF-κB and MAPK compared with cells not expressing MUC1. However, overexpression of MUC1 in HEK293 cells did not affect NF-κB or MAPK activation in response to TNF-α. Overexpression of MyD88 abrogated the ability of MUC1 to inhibit NF-κB activation, and MUC1 overexpression inhibited flagellin-induced association of TLR5/MyD88 compared with controls. The MUC1 cytoplasmic tail associated with TLR5 in all cells tested, including HEK293T cells, human lung adenocarcinoma cell line A549 cells, and human and mouse primary airway epithelial cells. Activation of epidermal growth factor receptor tyrosine kinase with TGF-α induced phosphorylation of the MUC1 cytoplasmic tail at the Y46EKV sequence and increased association of MUC1/TLR5. Finally, in vivo experiments demonstrated increased immunofluorescence colocalization of Muc1/TLR5 and Muc1/phosphotyrosine staining patterns in mouse airway epithelium and increased Muc1 tyrosine phosphorylation in mouse lung homogenates following P. aeruginosa infection. In conclusion, epidermal growth factor receptor tyrosine phosphorylates MUC1, leading to an increase in its association with TLR5, thereby competitively and reversibly inhibiting recruitment of MyD88 to TLR5 and downstream signaling events. This unique ability of MUC1 to control TLR5 signaling suggests its potential role in the pathogenesis of chronic inflammatory lung diseases.

MUC1 and MUC4: switching the emphasis from large to small

The MUC1 and MUC4 membrane mucins are each composed of a large alpha (α) and a small beta (β) subunit. The α subunits are fully exposed at the cell surface and contain variable numbers of repeated amino acid sequences that are heavily glycosylated. In contrast, the β subunits are much smaller and are anchored within the cell membrane, with their amino-terminal portions exposed at the cell surface and their carboxy-terminal tails facing the cytosol. Studies over the last several years are challenging the long-held belief that α subunits play the predominant role in cancer by conferring cellular properties that allow tumor cells to evade immune recognition and destruction. Indeed, the β subunits of MUC1 and MUC4 have emerged as oncogenes, as they engage signaling pathways responsible for tumor initiation and progression. Thus, a switch in the emphasis from the large α to the small β subunits offers attractive possibilities for successful clinical application. Such a focus shift is further supported by the absence of allelic polymorphism and variable glycosylation in the β subunit as well as by the presence of the β subunit in most MUC1 and MUC4 isoforms expressed by tumors. MUC1α, also known as CA15.3, is a Food and Drug Administration-approved serum biomarker for breast cancer, but its use is no longer recommended by the American Society of Clinical Oncology. However, comparison of β subunit expression in normal and malignant breast tissues may offer a novel approach to the exploitation of membrane mucins as biomarkers, as MUC1β-induced gene signatures with prognostic and predictive values in breast cancer have been reported. Preclinical studies with peptides that interfere with MUC1β oncogenic functions also look promising.

A novel anti-MUC1 antibody against the MUC1 cytoplasmic tail domain: use in sensitive identification of poorly differentiated cells in adenocarcinoma of the stomach

BACKGROUND

Isolated cancer cells of non-solid type poorly differentiated adenocarcinoma (por2) or signet-ring cell carcinoma (sig) are frequently seen in scirrhous gastric cancers with a very poor prognosis. These cells are often scattered in granulation tissue or desmoplastic fibrotic tissue and tend to be overlooked in routine pathological examination. We aimed to raise a novel antibody that can identify the isolated cancer cells easily.

METHODS

Because the MUC1 cytoplasmic tail domain (CTD) has many biological roles including tumor progression and cell adhesion disturbance and is expected to be expressed in isolated cancer cells, we raised a novel monoclonal antibody (MAb) MUC1-014E against an intracellular nonrepeating 19-amino-acid sequence (RYVPPSSTDRSPYEKVSAG: N-1217-1235-C) of the MUC1 CTD, using a synthetic peptide including the 7-amino-acid epitope (STDRSPY: N-1223-1229-C).

RESULTS

In the immunohistochemical staining of 107 gastrectomy specimens including 48 por2 and 31 sig lesions, the MAb MUC1-014E showed high rates of positive staining (≥5% of carcinoma cells stained) for por2 (100%) and sig (97%), and of the highest intensity staining (4+, ≥75% of carcinoma cells stained) for por2 (100%) and sig (90%). In the 89 biopsy specimens including 82 por2 and 38 sig lesions, the MAb MUC1-014E showed high rates of positive staining for por2 (100%) and sig (100%) and of 4+ staining for por2 (87%) and sig (84%). All the rates were significantly higher than those with cytokeratins (AE1/AE3 or CAM5.2).

CONCLUSIONS

The MAb MUC1-014E is very useful for accurate detection of isolated cancer cells in scirrhous gastric cancers.

MUC1 membrane trafficking: protocols for assessing biosynthetic delivery, endocytosis, recycling, and release through exosomes

MUC1 is normally apical in polarized epithelial cells but is aberrantly localized in tumor cells. To better understand the mechanism of this altered localization as well as the normal functions of MUC1, we are focused on characterizing the features of MUC1 that regulate the membrane trafficking of this mucin-like transmembrane protein. Previous studies using heterologous expression of MUC1 in CHO and MDCK cells revealed that trafficking to the cell surface as well as endocytosis and recycling is modulated by glycosylation, palmitoylation, and docking of adaptor protein complexes. Protocols for assessing MUC1 trafficking have utilized membrane-impermeant cell surface biotinylation and subsequent stripping with reducing reagents, such as MESNA. The cumulative data have been used for computer modeling and calculation of rate constants. As MUC1 is released through trafficking to exosomes, we have devised protocols for the affinity isolation of MUC1-containing lipid rafts from nanovesicular subpopulations to perform proteomic mapping of protein constituents in these sorting platforms. Our studies to date have shown that plasma membranous MUC1 traffics via lipid raft-associated pathways to exosomes, which are independent of caveolin-1 or dynamin, but dependent on flotillin.

Targeting cysteine-mediated dimerization of the MUC1-C oncoprotein in human cancer cells

The MUC1 heterodimeric protein is aberrantly overexpressed in diverse human carcinomas and contributes to the malignant phenotype. The MUC1-C transmembrane subunit contains a CQC motif in the cytoplasmic domain that has been implicated in the formation of dimers and in its oncogenic function. The present study demonstrates that MUC1-C forms dimers in human breast and lung cancer cells. MUC1-C dimerization was detectable in the cytoplasm and was independent of MUC1-N, the N-terminal mucin subunit that extends outside the cell. We show that the MUC1-C cytoplasmic domain forms dimers in vitro that are disrupted by reducing agents. Moreover, dimerization of the MUC1-C subunit in cancer cells was blocked by reducing agents and increased by oxidative stress, supporting involvement of the CQC motif in forming disulfide bonds. In support of these observations, mutation of the MUC1-C CQC motif to AQA completely blocked MUC1-C dimerization. Importantly, this study was performed with MUC1-C devoid of fluorescent proteins, such as GFP, CFP and YFP. In this regard, we show that GFP, CFP and YFP themselves form dimers that are readily detectable with cross-linking agents. The present results further demonstrate that a cell-penetrating peptide that targets the MUC1-C CQC cysteines blocks MUC1-C dimerization in cancer cells. These findings provide definitive evidence that: i) the MUC1-C cytoplasmic domain cysteines are necessary and sufficient for MUC1-C dimerization, and ii) these CQC motif cysteines represent an Achilles' heel for targeting MUC1-C function.

Expression patterns of MUC1, MUC2 and MUC3 in gastric hyperplastic polyps Juan Li, Li-Hua Wu, Yan Shi, Yu-Fei Jiao

AIM: To evaluate the expression patterns of MUC1, MUC2 and MUC3 in gastric hyperplastic polyps (GHP) and to analyze their value as markers for judging the malignant potential of GHP.

METHODS: A total of 238 GHP biopsy or surgical specimens, including 188 cases without dysplasia, 35 cases with low grade dysplasia (LGD), 8 cases with high grade dysplasia(HGD), and 7 cases with carcinoma (Ca), were used in this study. Thirty normal gastric mucosal specimens were used as controls. Immunohistochemistry was performed to detect the expression patterns of mucin proteins (MUC1, MUC2 and MUC3) in these specimens.

RESULTS: Cytoplasmic and membranous expression of MUC1 was observed in 85.60% of GHP cases without dysplasia or carcinoma. Glandular luminal expression of MUC1 was observed in 80.0% of GHP cases with LGD and 100% of GHP cases with HGD/Ca. The positive rate of MUC2 expression was 8.11% in GHP, 21.93% in GHP with LGD, and 31.42% in GHP with HGD/Ca. MUC3 expression was detected in one case of GHP with LGD and three cases of GHP with HGD/Ca but not in GHP without dysplasia.

CONCLUSION: MUC1 and MUC2 may be useful markers for judging the malignant potential of GHP.

Role of epithelial mucins during airway infection

Airway surface fluid contains two layers of mucins consisting mainly of 5 different mucin gene products. While the outer layer contains two gel-forming mucins (MUC5AC and MUC5B) that are tightly associated with various biologically active, defensive molecules, the inner layer contains three membrane-tethered mucins (MUC1, MUC4 and MUC16) shed from the apical cell surface. During airway infection, all of these mucins serve as a major protective barrier against pathogens. MUC1 mucin produced by virtually all the surface columnar epithelial cells in the respiratory tract as well as Type II pneumocytes in the alveoli plays an additional, perhaps more critical role during respiratory infection by controlling the resolution of inflammation that is essential to prevent the development of inflammatory lung disease.

MUC1 protein expression in tumor cells regulates transcription of proinflammatory cytokines by forming a complex with nuclear factor-κB p65 and binding to cytokine promoters: importance of extracellular domain

MUC1 is a transmembrane glycoprotein abnormally expressed in all stages of development of human adenocarcinomas. Overexpression and hypoglycosylation of MUC1 in cancer cells compared with normal epithelial cells are likely to alter its function and affect the behavior of cancer cells. The extracellular domain, specifically the highly O-glycosylated VNTR (variable number of tandem repeats) region, plays an important role in cell-cell communication; however, we show here that it also participates intracellularly in activation of the NF-κB pathway. Transfection of MUC1(-) tumor cells with cDNA encoding MUC1 with 22 tandem repeats (MUC1/22TR) or two tandem repeats (MUC1/2TR) or two isoforms that lack the VNTR region (MUC1/Z and MUC1/Y) showed that the highest expression levels of NF-κB family members correlated with the presence of VNTR and the highest number of tandem repeats. Because expression of MUC1 with VNTR on tumors was previously associated with chemotactic activity for cells of the innate immune system, we investigated the influence of MUC1 expression on the NF-κB-dependent transcriptional regulation of proinflammatory cytokines. ChIP and real-time PCR experiments revealed that MUC1/22TR up-regulated IL-6 and TNF-α expression by binding to their promoter regions in a NF-κB p65-dependent manner in both MUC1-transfected and human breast cancer cells that express endogenous MUC1. This newly detected complex of MUC1 and p65 is a novel mechanism that tumors can use to promote inflammation and cancer development.

MUC1-C oncoprotein regulates glycolysis and pyruvate kinase M2 activity in cancer cells

Aerobic glycolysis in cancer cells is regulated by multiple effectors that include Akt and pyruvate kinase M2 (PKM2). Mucin 1 (MUC1) is a heterodimeric glycoprotein that is aberrantly overexpressed by human breast and other carcinomas. Here we show that transformation of rat fibroblasts by the oncogenic MUC1-C subunit is associated with Akt-mediated increases in glucose uptake and lactate production, consistent with the stimulation of glycolysis. The results also demonstrate that the MUC1-C cytoplasmic domain binds directly to PKM2 at the B- and C-domains. Interaction between the MUC1-C cytoplasmic domain Cys-3 and the PKM2 C-domain Cys-474 was found to stimulate PKM2 activity. Conversely, epidermal growth factor receptor (EGFR)-mediated phosphorylation of the MUC1-C cytoplasmic domain on Tyr-46 conferred binding to PKM2 Lys-433 and inhibited PKM2 activity. In human breast cancer cells, silencing MUC1-C was associated with decreases in glucose uptake and lactate production, confirming involvement of MUC1-C in the regulation of glycolysis. In addition, EGFR-mediated phosphorylation of MUC1-C in breast cancer cells was associated with decreases in PKM2 activity. These findings indicate that the MUC1-C subunit regulates glycolysis and that this response is conferred in part by PKM2. Thus, the overexpression of MUC1-C oncoprotein in diverse human carcinomas could be of importance to the Warburg effect of aerobic glycolysis.

Inhibition of the MUC1-C oncoprotein induces multiple myeloma cell death by down-regulating TIGAR expression and depleting NADPH

The MUC1-C oncoprotein is aberrantly expressed in most multiple myeloma cells. However, the functional significance of MUC1-C expression in multiple myeloma is not known. The present studies demonstrate that treatment of multiple myeloma cells with a MUC1-C inhibitor is associated with increases in reactive oxygen species (ROS), oxidation of mitochondrial cardiolipin, and loss of the mitochondrial transmembrane potential. The MUC1-C inhibitor-induced increases in ROS were also associated with down-regulation of the p53-inducible regulator of glycolysis and apoptosis (TIGAR). In concert with the decrease in TIGAR expression, which regulates the pentose phosphate pathway, treatment with the MUC1-C inhibitor reduced production of NADPH, and in turn glutathione (GSH) levels. TIGAR protects against oxidative stress-induced apoptosis. The suppression of TIGAR and NADPH levels thus contributed to ROS-mediated late apoptosis/necrosis of multiple myeloma cells. These findings indicate that multiple myeloma cells are dependent on MUC1-C and TIGAR for maintenance of redox balance and that targeting MUC1-C activates a cascade involving TIGAR suppression that contributes to multiple myeloma cell death.

MUC1-C Oncoprotein Blocks Terminal Differentiation of Chronic Myelogenous Leukemia Cells by a ROS-Mediated Mechanism

Chronic myelogenous leukemia (CML) inevitably progresses to a blast phase by mechanisms that are not well understood. The MUC1-C oncoprotein is expressed in CML blasts but not chronic phase cells. The present studies demonstrate that treatment of KU812 and K562 CML cells with a cell-penetrating MUC1-C inhibitor, designated GO-203, is associated with increases in reactive oxygen species (ROS) and depletion of glutathione. GO-203 treatment resulted in the complete downregulation of Bcr-Abl expression and induced cell cycle arrest by a ROS-mediated mechanism that was blocked by the antioxidant N-acetylcysteine. Progression of CML to blast crisis has been linked to dysregulation of Wnt/β-catenin signaling and an arrest of differentiation. The present results show that inhibition of MUC1-C induces ROS-mediated suppression of β-catenin expression and induction of a differentiated myeloid phenotype. Our studies also show that GO-203 treatment is associated with ROS-induced decreases in ATP and loss of survival by late apoptosis/necrosis. These findings demonstrate that inhibition of the MUC1-C oncoprotein in CML cells disrupts redox balance and thereby 1) downregulates expression of both Bcr-Abl and β-catenin and 2) induces terminal myeloid differentiation by ROS-mediated mechanisms.

The role of mucin in GERD and its complications

Acid, pepsin and other noxious material reach the esophageal mucosa and interact with the luminal aspect of the squamous epithelium. The first protective barrier to these potentially injurious substances is the mucus buffer layer that covers the mucosa. In healthy people, the esophagus has a protective surface adherent mucus gel barrier. Levels of mucin glycoprotein are considerably increased in response to acid and pepsin. A wide spectrum of mucin genes are expressed in normal esophageal mucosa, squamous cell carcinoma of the esophagus, Barrett epithelium and esophageal adenocarcinoma. The mucins MUC5AC and MUC6 are expressed to a similar degree in Barrett metaplasia and gastric mucosa, as is MUC2 in Barrett intestinal metaplasia and small bowel mucosa. Increased expression of MUC1 is associated with progression from dysplasia to adenocarcinoma of the esophagus. Thus, mucins have an important role in the defense of esophageal mucosa against the acid, pepsin and bile that are present in the refluxate. Changes in the expression of mucins occur in patients with GERD, and might lead to the development of new drugs.

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.

MUC13 mucin augments pancreatic tumorigenesis

The high death rate of pancreatic cancer is attributed to the lack of reliable methods for early detection and underlying molecular mechanisms of its aggressive pathogenesis. Although MUC13, a newly identified transmembrane mucin, is known to be aberrantly expressed in ovarian and gastro-intestinal cancers, its role in pancreatic cancer is unknown. Herein, we investigated the expression profile and functions of MUC13 in pancreatic cancer progression. The expression profile of MUC13 in pancreatic cancer was investigated using a recently generated monoclonal antibody (clone PPZ0020) and pancreatic tissue microarrays. The expression of MUC13 was significantly (P < 0.005) higher in cancer samples compared with normal/nonneoplastic pancreatic tissues. For functional analyses, full-length MUC13 was expressed in MUC13 null pancreatic cancer cell lines, MiaPaca and Panc1. MUC13 overexpression caused a significant (P < 0.05) increase in cell motility, invasion, proliferation, and anchorage-dependent or -independent clonogenicity while decreasing cell-cell and cell-substratum adhesion. Exogenous MUC13 expression significantly (P < 0.05) enhanced pancreatic tumor growth and reduced animal survival in a xenograft mouse model. These tumorigenic characteristics correlated with the upregulation/phosphorylation of HER2, p21-activated kinase 1 (PAK1), extracellular signal-regulated kinase (ERK), Akt, and metastasin (S100A4), and the suppression of p53. Conversely, suppression of MUC13 in HPAFII pancreatic cancer cells by short hairpin RNA resulted in suppression of tumorigenic characteristics, repression of HER2, PAK1, ERK, and S100A4, and upregulation of p53. MUC13 suppression also significantly (P < 0.05) reduced tumor growth and increased animal survival. These results imply a role of MUC13 in pancreatic cancer and suggest its potential use as a diagnostic and therapeutic target.

Mucins in human neoplasms: clinical pathology, gene expression and diagnostic application

Mucins are high molecular weight glycoproteins that play important roles in carcinogenesis and tumor invasion. Our immunohistochemical studies demonstrated that MUC1 or MUC4 expression is related to the aggressive behavior and poor outcome of human neoplasms. MUC2 is expressed in indolent pancreatobiliary neoplasms, but these tumors sometimes show invasive growth with MUC1 expression in invasive areas. MUC5AC shows de novo high expression in many types of precancerous lesions of pancreatobiliary cancers and is an effective marker for early detection of the neoplasms. The combination of MUC1, MUC2, MUC4 and MUC5AC expression may be useful for early detection and evaluation of the potential for malignancy of pancreatobiliary neoplasms. Regarding the mechanism of mucin expression, we have recently reported that expression of the mucin genes is regulated epigenetically in cancer cell lines, using quantitative MassARRAY analysis, methylation-specific polymerase chain reaction analysis and chromatin immunoprecipitation analysis, with confirmation by the treatment with 5-aza-2'-deoxycytidine and trichostatin A. We have also developed a monoclonal antibody against the MUC1 cytoplasmic tail domain, which has many biological roles. Based on all of the above findings, we suggest that translational research into mucin gene expression mechanisms, including epigenetics, may provide new tools for early and accurate detection of human neoplasms.

Molecular characterization of the region 7q22.1 in splenic marginal zone lymphomas

Splenic marginal zone lymphomas (SMZL) are an uncommon type of B-cell non-Hodgkin's lymphoma (NHL-B) in which no specific chromosomal translocations have been described. In contrast, the most frequent cytogenetic abnormality is the loss of the long arm of chromosome 7 (7q). Previous reports have located this loss in the 7q32 region. In order to better characterize the genomic imbalances in SMZL, molecular studies were carried out in 73 patients with SMZL. To gain insight into the mapping at 7q a tiling array was also used. The results confirmed the loss of 7q as the most frequent change. In addition, several abnormalities, including 4q22.1, 1q21.3–q22, 6q25.3, 20q13.33, 3q28, 2q23.3–q24.1 and 17p13, were also present. A loss of 7q22.1 at 99925039–101348479 bp was observed in half of the cases. The region of 7q22.1 has not previously been characterised in SMZL. Our results confirmed the presence of a new region of loss on chromosome 7 in these NHL.

Core-glycosylated mucin-like repeats from MUC1 are an apical targeting signal

MUC1 is efficiently delivered to the apical surface of polarized Madin-Darby canine kidney (MDCK) cells by transit through apical recycling endosomes, a route associated with delivery of apical proteins with glycan-dependent targeting signals. However, a role for glycans in MUC1 sorting has not been established. A key feature of MUC1 is a heavily O-glycosylated mucin-like domain with a variable number of nearly perfect tandem repeats and adjacent imperfect repeats. Metabolic labeling, cell surface biotinylation, immobilized lectins, and confocal immunofluorescence microscopy were used to characterize the polarized delivery of MUC1 mutants and chimeras in MDCK cells to identify the apical targeting signal. Both the interleukin-2 receptor α subunit (Tac) and a chimera where the Tac ectodomain replaced that of MUC1 were delivered primarily to the basolateral surface. Attachment of the MUC1 mucin-like domain to the N terminus of Tac enhanced apical but not basolateral delivery when compared with Tac. Conversely, deletions within the mucin-like domain in MUC1 reduced apical but not basolateral delivery when compared with MUC1. In pull-down assays with lectins, we found a notable difference in the presence of core 1 O-glycans, but not poly-N-acetyllactosamine, in apically targeted MUC1 and chimeras when compared with Tac. Consistent with these data, we found no effect on MUC1 targeting when galectin-3, with preference for poly-N-acetyllactosamine, was depleted from polarized MDCK cells. However, we did block the apical targeting activity of the mucin-like repeats when we overexpressed CMP-Neu5Ac:GalNAc-Rα2,6-sialyltransferase-1 to block core O-glycan synthesis. The cumulative data indicate that the core-glycosylated mucin-like repeats of MUC1 constitute an apical targeting signal.

Membrane-active host defense peptides--challenges and perspectives for the development of novel anticancer drugs

Although much progress has been achieved in the development of cancer therapies in recent decades, problems continue to arise particularly with respect to chemotherapy due to resistance to and low specificity of currently available drugs. Host defense peptides as effector molecules of innate immunity represent a novel strategy for the development of alternative anticancer drug molecules. These cationic amphipathic peptides are able to discriminate between neoplastic and non-neoplastic cells interacting specifically with negatively charged membrane components such as phosphatidylserine (PS), sialic acid or heparan sulfate, which differ between cancer and non-cancer cells. Furthermore, an increased number of microvilli has been found on cancer cells leading to an increase in cell surface area, which may in turn enhance their susceptibility to anticancer peptides. Thus, part of this review will be devoted to the differences in membrane composition of non-cancer and cancer cells with a focus on the exposure of PS on the outer membrane. Normally, surface exposed PS triggers apoptosis, which can however be circumvented by cancer cells by various means.

Host defense peptides, which selectively target differences between cancer and non-cancer cell membranes, have excellent tumor tissue penetration and can thus reach the site of both primary tumor and distant metastasis. Since these molecules kill their target cells rapidly and mainly by perturbing the integrity of the plasma membrane, resistance is less likely to occur. Hence, a chapter will also describe studies related to the molecular mechanisms of membrane damage as well as alternative non-membrane related mechanisms. In vivo studies have demonstrated that host defense peptides display anticancer activity against a number of cancers such as e.g. leukemia, prostate, ascite and ovarian tumors, yet so far none of these peptides has made it on the market. Nevertheless, optimization of host defense peptides using various strategies to enhance further selectivity and serum stability is expected to yield novel anticancer drugs with improved properties in respect of cancer cell toxicity as well as reduced development of drug resistance.

Gastric cancer: basic aspects

Gastric cancer (GC) is a world health burden, ranging as the second cause of cancer death worldwide. Etiologically, GC arises not only from the combined effects of environmental factors and susceptible genetic variants but also from the accumulation of genetic and epigenetic alterations. In the last years, molecular oncobiology studies brought to light a number of genes that are implicated in gastric carcinogenesis. This review is intended to focus on the recently described basic aspects that play key roles in the process of gastric carcinogenesis. Genetic variants of the genes IL-10, IL-17, MUC1, MUC6, DNMT3B, SMAD4, and SERPINE1 have been reported to modify the risk of developing GC. Several genes have been newly associated with gastric carcinogenesis, both through oncogenic activation (GSK3β, CD133, DSC2, P-Cadherin, CDH17, CD168, CD44, metalloproteinases MMP7 and MMP11, and a subset of miRNAs) and through tumor suppressor gene inactivation mechanisms (TFF1, PDX1, BCL2L10, XRCC, psiTPTE-HERV, HAI-2, GRIK2, and RUNX3). It also addressed the role of the inflammatory mediator cyclooxygenase-2 (COX-2) in the process of gastric carcinogenesis and its importance as a potential molecular target for therapy.

Androgen receptor regulates expression of the MUC1-C oncoprotein in human prostate cancer cells

BACKGROUND

The MUC1 heterodimeric oncoprotein is aberrantly overexpressed in human prostate cancers with more aggressive pathologic and clinical features. However, the signals that regulate MUC1 expression in prostate cancer cells are not well understood.

METHODS

MUC1 expression was studied in androgen-dependent and -independent prostate cancer cell lines by quantitative RT-PCR, immunoblotting and assessment of MUC1 promoter activation. Chromatin immunoprecipitation (ChIP) studies were performed to assess androgen receptor (AR) occupancy on the MUC1 promoter. Post-transcriptional regulation of MUC1 expression was assessed by miR-125b-mediated effects on activity of the MUC1 3' untranslated region (3'UTR).

RESULTS

The present studies demonstrate that AR occupies a consensus AR element on the MUC1 promoter in androgen-dependent LNCaP, but not in androgen-independent DU145 and PC3, prostate cancer cells. The results further show that AR downregulates MUC1 gene transcription. Stable introduction of exogenous AR in PC3 (PC3/AR) cells and then silencing of AR confirmed AR-mediated repression of the MUC1 promoter. AR signaling has also been shown to drive miR-125b expression. The present studies further demonstrate that miR-125b suppresses MUC1 translation in LNCaP cells and that an anti-sense miR-125b upregulates expression of MUC1 protein. In addition, stable expression of miR-125b in DU145 cells resulted in decreases in MUC1 levels.

CONCLUSIONS

These findings demonstrate that AR signaling regulates MUC1 expression by transcriptional and posttranscriptional mechanisms in prostate cancer cells.

Post-translational regulation of signaling mucins

Signaling mucins are large transmembrane glycoproteins that regulate signal transduction pathways. Recent advances have shown that two major types of post-translational modifications, protein glycosylation and proteolytic processing, play important and unexpected roles in regulating signaling mucin function. New O-glycosyltransferases and proteases have been identified, and the structure of the domain that undergoes auto-proteolysis has been solved. A picture is beginning to emerge where specific glycosyl modifications and regulated processing control the signaling and adherence properties of signaling glycoproteins and contribute to the routing of signals to specific pathways.

Protein biomarkers for the early detection of breast cancer

Advances in breast cancer control will be greatly aided by early detection so as to diagnose and treat breast cancer in its preinvasive state prior to metastasis. For breast cancer, the second leading cause of cancer-related death among women in the United States, early detection does allow for increased treatment options, including surgical resection, with a corresponding better patient response. Unfortunately, however, many patients' tumors are diagnosed following metastasis, thus making it more difficult to successfully treat the malignancy. There are, at present, no existing validated plasma/serum biomarkers for breast cancer. Only a few biomarkers (such as HER-2/neu, estrogen receptor, and progesterone receptor) have utility for diagnosis and prognosis. Thus, there is a great need for new biomarkers for breast cancer. This paper will focus on the identification of new serum protein biomarkers with utility for the early detection of breast cancer.

Case-control study for colorectal cancer genetic susceptibility in EPICOLON: previously identified variants and mucins

Background

Colorectal cancer (CRC) is the second leading cause of cancer death in developed countries. Familial aggregation in CRC is also important outside syndromic forms and, in this case, a polygenic model with several common low-penetrance alleles contributing to CRC genetic predisposition could be hypothesized. Mucins and GALNTs (N-acetylgalactosaminyltransferase) are interesting candidates for CRC genetic susceptibility and have not been previously evaluated. We present results for ten genetic variants linked to CRC risk in previous studies (previously identified category) and 18 selected variants from the mucin gene family in a case-control association study from the Spanish EPICOLON consortium.

Methods

CRC cases and matched controls were from EPICOLON, a prospective, multicenter, nationwide Spanish initiative, comprised of two independent stages. Stage 1 corresponded to 515 CRC cases and 515 controls, whereas stage 2 consisted of 901 CRC cases and 909 controls. Also, an independent cohort of 549 CRC cases and 599 controls outside EPICOLON was available for additional replication. Genotyping was performed for ten previously identified SNPs in ADH1C, APC, CCDN1, IL6, IL8, IRS1, MTHFR, PPARG, VDR and ARL11, and 18 selected variants in the mucin gene family.

Results

None of the 28 SNPs analyzed in our study was found to be associated with CRC risk. Although four SNPs were significant with a P-value < 0.05 in EPICOLON stage 1 [rs698 in ADH1C (OR = 1.63, 95% CI = 1.06-2.50, P-value = 0.02, recessive), rs1800795 in IL6 (OR = 1.62, 95% CI = 1.10-2.37, P-value = 0.01, recessive), rs3803185 in ARL11 (OR = 1.58, 95% CI = 1.17-2.15, P-value = 0.007, codominant), and rs2102302 in GALNTL2 (OR = 1.20, 95% CI = 1.00-1.44, P-value = 0.04, log-additive 0, 1, 2 alleles], only rs3803185 achieved statistical significance in EPICOLON stage 2 (OR = 1.34, 95% CI = 1.06-1.69, P-value = 0.01, recessive). In the joint analysis for both stages, results were only significant for rs3803185 (OR = 1.12, 95% CI = 1.00-1.25, P-value = 0.04, log-additive 0, 1, 2 alleles) and borderline significant for rs698 and rs2102302. The rs3803185 variant was not significantly associated with CRC risk in an external cohort (MCC-Spain), but it still showed some borderline significance in the pooled analysis of both cohorts (OR = 1.08, 95% CI = 0.98-1.18, P-value = 0.09, log-additive 0, 1, 2 alleles).

Conclusions

ARL11, ADH1C, GALNTL2 and IL6 genetic variants may have an effect on CRC risk. Further validation and meta-analyses should be undertaken in larger CRC studies.

Natural and Induced Humoral Responses to MUC1

MUC1 is a membrane-tethered mucin expressed on the ductal cell surface of glandular epithelial cells. Loss of polarization, overexpression and aberrant glycosylation of MUC1 in mucosal inflammation and in adenocarcinomas induces humoral immune responses to the mucin. MUC1 IgG responses have been associated with a benefit in survival in patients with breast, lung, pancreatic, ovarian and gastric carcinomas. Antibodies bound to the mucin may curb tumor progression by restoring cell-cell interactions altered by tumor-associated MUC1, thus preventing metastatic dissemination, as well as counteracting the immune suppression exerted by the molecule. Furthermore, anti-MUC1 antibodies are capable of effecting tumor cell killing by antibody-dependent cell-mediated cytotoxicity. Although cytotoxic T cells are indispensable to achieve anti-tumor responses in advanced disease, abs to tumor-associated antigens are ideally suited to address minimal residual disease and may be sufficient to exert adequate immune surveillance in an adjuvant setting, destroying tumor cells as they arise or maintaining occult disease in an equilibrium state. Initial evaluation of MUC1 peptide/glycopeptide mono and polyvalent vaccines has shown them to be immunogenic and safe; anti-tumor responses are scarce. Progress in carbohydrate synthesis has yielded a number of sophisticated substrates that include MUC1 glycopeptide epitopes that are at present in preclinical testing. Adjuvant vaccination with MUC1 glycopeptide polyvalent vaccines that induce strong humoral responses may prevent recurrence of disease in patients with early stage carcinomas. Furthermore, prophylactic immunotherapy targeting MUC1 may be a strategy to strengthen immune surveillance and prevent disease in subjects at hereditary high risk of breast, ovarian and colon cancer.

MUC16 induced rapid G2/M transition via interactions with JAK2 for increased proliferation and anti-apoptosis in breast cancer cells

MUC16/CA125 is a tumor marker currently used in clinics for the follow-up of patients with ovarian cancer. However, MUC16 expression is not entirely restricted to ovarian malignancies and has been reported in other cancers including breast cancer. Although it is well established as a biomarker, function of MUC16 in cancer remains to be elucidated. In the present study, we investigated the role of MUC16 in breast cancer and its underlying mechanisms. Interestingly, our results showed that MUC16 is overexpressed in breast cancer tissues whereas not expressed in non-neoplastic ducts. Further, stable knockdown of MUC16 in breast cancer cells (MDA MB 231 and HBL100) resulted in significant decrease in the rate of cell growth, tumorigenicity and increased apoptosis. In search of a mechanism for breast cancer cell proliferation we found that MUC16 interacts with the ezrin/radixin/moesin domain-containing protein of Janus kinase (JAK2) as demonstrated by the reciprocal immunoprecipitation method. These interactions mediate phosphorylation of STAT3 (Tyr705), which might be a potential mechanism for MUC16-induced proliferation of breast cancer cells by a subsequent co-transactivation of transcription factor c-Jun. Furthermore, silencing of MUC16 induced G2/M arrest in breast cancer cells through downregulation of Cyclin B1 and decreased phosphorylation of Aurora kinase A. This in turn led to enhanced apoptosis in the MUC16-knockdown breast cancer cells through Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated extrinsic apoptotic pathway with the help of c-Jun N-terminal kinase signaling. Collectively, our results suggest that MUC16 has a dual role in breast cancer cell proliferation by interacting with JAK2 and by inhibiting the apoptotic process through downregulation of TRAIL.

Recent advances in mucin immunohistochemistry in salivary gland tumors and head and neck squamous cell carcinoma

This review focuses on the immunohistochemical expression of members of the MUC-type mucin family in salivary gland tumors and head and neck squamous cell carcinomas (HNSCC). Information is available on changes in the expression levels and distribution profiles of MUC1, MUC2, MUC3, MUC4, MUC5AC, MUC5B, MUC6 and MUC7 in tumors of the salivary glands; and of MUC1, MUC2 and MUC4 in HNSCC. In salivary gland tumors the expression patterns of MUC2, MUC3, MUC5AC and MUC6 appear to be very closely correlated with the histopathological tumor type indicating their potential use to improve diagnostic accuracy in salivary gland neoplasia. Some MUC-type mucins have emerged as valuable prognostic indicators in pleomorphic adenoma, mucoepidermoid carcinoma and HNSCC. Nine antibodies directed against different MUC1 antigens have thus far been examined in HNSCC of which monoclonal antibodies DF3, HMFG-1 and Ma695 have shown significant correlations with disease outcome. The importance of taking the specific anti-MUC antibody into consideration when comparing the results of different studies on MUC expression in salivary gland tumors and HNSCC is also highlighted in this review.

Soluble MUC1 and serum MUC1-specific antibodies are potential prognostic biomarkers for platinum-resistant ovarian cancer

MUC1 (CA15-3) and MUC16 (CA125) tumor-associated antigens are upregulated in ovarian cancer and can be detected in patients' sera by standardized tests. We postulated that increased MUC1 and MUC16 antigens augment antibody responses in platinum-resistant ovarian cancer patients and that the frequency and intensity of these responses can be used as immune biomarkers of treatment response and disease outcome. We measured MUC1 and MUC16 tumor expression by immunohistochemistry (IHC), assessed serum antigenic levels and quantitated circulating antibodies by ELISA in a cohort of 28 ovarian cancer patients with platinum-resistant or platinum-refractory ovarian cancer, and treated with intraperitoneal (IP) interleukin-2 (IL-2). MUC1 and MUC16 were overexpressed in tumor samples and showed differential distribution profiles. Serum MUC1 (CA15-3) measurements were elevated in all patients and significantly correlated with increased risk of death (P = 0.003). MUC1-specific IgM and IgG anitbodies were found in 92 and 50% of cases, respectively. Patients with progressive disease had higher mean anti-MUC1 IgG than responders at both early (P = 0.025) and late (P = 0.022) time points during IP IL-2 treatment. Anti-MUC1 IgM antibodies inversely correlated with overall survival at both early (P = 0.052) and late (P = 0.009) time points. In contrast to MUC1, neither soluble MUC16 nor MUC16-specific antibodies were significantly associated with clinical response or overall survival in this study. Increased serum MUC1 and high anti-MUC1 antibody levels are prognostic for poor clinical response and reduced overall survival in platinum-resistant or platinum-refractory ovarian cancer.

A novel potent tumour promoter aberrantly overexpressed in most human cancers

The complexity and heterogeneity of tumours have hindered efforts to identify commonalities among different cancers. Furthermore, because we have limited information on the prevalence and nature of ubiquitous molecular events that occur in neoplasms, it is unfeasible to implement molecular-targeted cancer screening and prevention. Here, we found that the FEAT protein is overexpressed in most human cancers, but weakly expressed in normal tissues including the testis, brain, and liver. Transgenic mice that ectopically expressed FEAT in the thymus, spleen, liver, and lung spontaneously developed invasive malignant lymphoma (48%, 19/40) and lung-metastasizing liver cancer (hepatocellular carcinoma) (35%, 14/40) that models human hepatocarcinogenesis, indicating the FEAT protein potently drives tumorigenesis in vivo. Gene expression profiling suggested that FEAT drives receptor tyrosine kinase and hedgehog signalling pathways. These findings demonstrate that integrated efforts to identify FEAT-like ubiquitous oncoproteins are useful and may provide promising approaches for cost-effective cancer screening and prevention.

Muc17 protects intestinal epithelial cells from enteroinvasive E. coli infection by promoting epithelial barrier integrity

The membrane-bound mucin MUC17 (mouse homolog Muc3) is highly expressed on the apical surface of intestinal epithelia and is thought to play a role in epithelial restitution and protection. Therefore, we hypothesized that MUC17 has a role in protection of the intestinal mucosa against luminal pathogens. Human intestinal cell lines were transfected by electroporation (Caco-2 and HT 29/19A) and by retroviral expression vector (LS174T, a cell line with high levels of MUC17 expression) using MUC17 siRNA. Transepithelial electrical resistance, permeability, tight-junction protein expression, adhesion, and invasion in response to enteroinvasive Escherichia coli (EIEC) were measured in all cell lines. In some experiments, the effect of the addition of exogenous purified crude mucin or recombinant Muc3 cysteine-rich domain protein (Muc3 CRD1-L-CRD2) as preventative or protective treatment was tested. Reduction of endogenous MUC17 is associated with increased permeability, inducible nitric oxide synthase and cyclooxygenase 2 induction, and enhanced bacterial invasion in response to EIEC exposure. Bacterial adhesion is not affected. Exogenous mucin (Muc3) and recombinant Muc3CRD treatment had a small but significant effect in attenuating the effects of EIEC infection. In conclusion, these data suggest that both native and exogenous MUC17 play a role in attachment and invasion of EIEC in colonic cell lines and in maintaining epithelial barrier function.