Cell surface-associated mucins in signal transduction

MUC1 mucin stabilizes and activates hypoxia-inducible factor 1 alpha to regulate metabolism in pancreatic cancer

Aberrant glucose metabolism is one of the hallmarks of cancer that facilitates cancer cell survival and proliferation. Here, we demonstrate that MUC1, a large, type I transmembrane protein that is overexpressed in several carcinomas including pancreatic adenocarcinoma, modulates cancer cell metabolism to facilitate growth properties of cancer cells. MUC1 occupies the promoter elements of multiple genes directly involved in glucose metabolism and regulates their expression. Furthermore, MUC1 expression enhances glycolytic activity in pancreatic cancer cells. We also demonstrate that MUC1 expression enhances in vivo glucose uptake and expression of genes involved in glucose uptake and metabolism in orthotopic implantation models of pancreatic cancer. The MUC1 cytoplasmic tail is known to activate multiple signaling pathways through its interactions with several transcription factors/coregulators at the promoter elements of various genes. Our results indicate that MUC1 acts as a modulator of the hypoxic response in pancreatic cancer cells by regulating the expression/stability and activity of hypoxia-inducible factor-1α (HIF-1α). MUC1 physically interacts with HIF-1α and p300 and stabilizes the former at the protein level. By using a ChIP assay, we demonstrate that MUC1 facilitates recruitment of HIF-1α and p300 on glycolytic gene promoters in a hypoxia-dependent manner. Also, by metabolomic studies, we demonstrate that MUC1 regulates multiple metabolite intermediates in the glucose and amino acid metabolic pathways. Thus, our studies indicate that MUC1 acts as a master regulator of the metabolic program and facilitates metabolic alterations in the hypoxic environments that help tumor cells survive and proliferate under such conditions.

Quantitative analyses of genes associated with mucin synthesis of broiler chickens with induced necrotic enteritis

Clostridial infection of the intestine can result in necrotic enteritis (NE), compromising production and health of poultry. Mucins play a major role in protecting the intestinal epithelium from infection. The relative roles of different mucins in gut pathology following bacterial challenge are unclear. This study was designed to quantify the expression of mucin and mucin-related genes, using intestinal samples from an NE challenge trial where birds were fed diets with or without in-feed antimicrobials. A method for quantifying mucin gene expression was established using a suite of reference genes to normalize expression data. This method was then used to quantify the expression of 11 candidate genes involved in mucin, inflammatory cytokine, or growth factor biosynthesis (IL-18, KGF, TLR4, TFF2, TNF-α, MUC2, MUC4, MUC5ac, MUC5b, MUC13, and MUC16). The only genes that were differentially expressed in the intestine among treatment groups were MUC2, MUC13, and MUC5ac. Expression of MUC2 and MUC13 was depressed by co-challenge with Eimeria spp. and Clostridium perfringens. Antimicrobial treatment prevented an NE-induced decrease in MUC2 expression but did not affect MUC13. The expression of MUC5ac was elevated in birds challenged with Eimeria spp./C. perfringens compared with unchallenged controls and antimicrobial treatment. Changes to MUC gene expression in challenged birds is most likely a consequence of severe necrosis of the jejunal mucosa.

Enhanced self-association of mucins possessing the T and Tn carbohydrate cancer antigens at the single-molecule level

Mucins are linear O-glycosylated glycoproteins involved in inflammation, cell adhesion, and tumorigenesis. Cancer-associated mucins often possess increased expression of the T (Galβ1,3GalNAcαThr/Ser) and Tn (GalNAcαThr/Ser) cancer antigens, which are diagnostic markers for several cancers, including colon cancer. We have used AFM based single-molecule forced unbinding under near physiological conditions to investigate the self-interactions between porcine submaxillary mucin (PSM) as well as between PSM analogs possessing various carbohydrates including the T- and Tn-antigen. Distributions of unbinding forces and corresponding force loading rates were determined for force loading rates from 0.18 nN/s to 39 nN/s, and processed to yield most probable unbinding forces f* and lifetimes of the interactions. Parameter f* varied in the range 27 to 50 pN at force loading rates of about 2 nN/s among the various mucins. All mucin samples investigated showed self-interaction, but the tendency was greatest for PSM displaying only the Tn-antigen (Tn-PSM) or a mixture of Tn-, T-antigen, and the trisaccharide Fucα1,2Galβ1,3GalNAc (Tri-PSM). Weaker self-interactions were observed for native PSM (Fd-PSM), which consists of a nearly equal mixture of the longer core 1 blood group A tetrasaccharide (GalNAcα1,3(Fucα1,2)Galβ1,3GalNAcαSer/Thr) and Tn-antigen. The data are consistent with the truncated Tn and T glycans enhancing self-interaction of the mucins. These carbohydrate cancer antigens may, thus, play an active role in the disease by constitutively activating mucin and mucin-type receptors by self-association on cells.

The regulation of filamentous growth in yeast

Filamentous growth is a nutrient-regulated growth response that occurs in many fungal species. In pathogens, filamentous growth is critical for host-cell attachment, invasion into tissues, and virulence. The budding yeast Saccharomyces cerevisiae undergoes filamentous growth, which provides a genetically tractable system to study the molecular basis of the response. Filamentous growth is regulated by evolutionarily conserved signaling pathways. One of these pathways is a mitogen activated protein kinase (MAPK) pathway. A remarkable feature of the filamentous growth MAPK pathway is that it is composed of factors that also function in other pathways. An intriguing challenge therefore has been to understand how pathways that share components establish and maintain their identity. Other canonical signaling pathways-rat sarcoma/protein kinase A (RAS/PKA), sucrose nonfermentable (SNF), and target of rapamycin (TOR)-also regulate filamentous growth, which raises the question of how signals from multiple pathways become integrated into a coordinated response. Together, these pathways regulate cell differentiation to the filamentous type, which is characterized by changes in cell adhesion, cell polarity, and cell shape. How these changes are accomplished is also discussed. High-throughput genomics approaches have recently uncovered new connections to filamentous growth regulation. These connections suggest that filamentous growth is a more complex and globally regulated behavior than is currently appreciated, which may help to pave the way for future investigations into this eukaryotic cell differentiation behavior.

Utility of KL-6/MUC1 in the clinical management of interstitial lung diseases

Interstitial lung diseases (ILDs) are a diverse group of pulmonary disorders characterized by various patterns of inflammation and fibrosis in the interstitium of the lung. Because injury and/or regeneration of type II pneumocytes are prominent histological features of ILDs, substances derived from type II pneumocytes have been the focus of research investigating potential biomarkers for ILD. One important biomarker for ILD is the high-molecular-weight glycoprotein, Krebs von den Lungen-6 (KL-6). KL-6 is now classified as a human MUC1 mucin protein, and regenerating type II pneumocytes are the primary cellular source of KL-6/MUC1 in the affected lungs of patients with ILD. KL-6/MUC1 is detectable in the serum of patients with ILD, and extensive investigations performed primarily in Japan have revealed that serum KL-6/MUC1 is elevated in 70-100% of patients with various ILDs, including idiopathic interstitial pneumonias, collagen vascular disease-associated interstitial pneumonia, hypersensitivity pneumonia, radiation pneumonitis, drug-induced ILDs, acute respiratory distress syndrome, pulmonary sarcoidosis, and pulmonary alveolar proteinosis. The results from these various studies have supported the utility of KL-6/MUC1 as a serum biomarker for detecting these various ILDs. Moreover, KL-6/MUC1 serum levels have been demonstrated to be useful for evaluating disease activity and predicting the clinical outcomes of various ILD types. Based on these observations, we believe that KL-6/MUC1 is currently one of the best and most reliable serum biomarkers available for ILD management.

A metalloproteinase secreted by Streptococcus pneumoniae removes membrane mucin MUC16 from the epithelial glycocalyx barrier

The majority of bacterial infections occur across wet-surfaced mucosal epithelia, including those that cover the eye, respiratory tract, gastrointestinal tract and genitourinary tract. The apical surface of all these mucosal epithelia is covered by a heavily glycosylated glycocalyx, a major component of which are membrane-associated mucins (MAMs). MAMs form a barrier that serves as one of the first lines of defense against invading bacteria. While opportunistic bacteria rely on pre-existing defects or wounds to gain entry to epithelia, non opportunistic bacteria, especially the epidemic disease-causing ones, gain access to epithelial cells without evidence of predisposing injury. The molecular mechanisms employed by these non opportunistic pathogens to breach the MAM barrier remain unknown. To test the hypothesis that disease-causing non opportunistic bacteria gain access to the epithelium by removal of MAMs, corneal, conjunctival, and tracheobronchial epithelial cells, cultured to differentiate to express the MAMs, MUCs 1, 4, and 16, were exposed to a non encapsulated, non typeable strain of Streptococcus pneumoniae (SP168), which causes epidemic conjunctivitis. The ability of strain SP168 to induce MAM ectodomain release from epithelia was compared to that of other strains of S. pneumoniae, as well as the opportunistic pathogen Staphylococcus aureus. The experiments reported herein demonstrate that the epidemic disease-causing S. pneumoniae species secretes a metalloproteinase, ZmpC, which selectively induces ectodomain shedding of the MAM MUC16. Furthermore, ZmpC-induced removal of MUC16 from the epithelium leads to loss of the glycocalyx barrier function and enhanced internalization of the bacterium. These data suggest that removal of MAMs by bacterial enzymes may be an important virulence mechanism employed by disease-causing non opportunistic bacteria to gain access to epithelial cells to cause infection.

MUC1 is a novel costimulatory molecule of human T cells and functions in an AP-1-dependent manner

MUC1 mucin, primarily known as an epithelial antigen, has been demonstrated to be expressed on activated human T cells. In the present study, we first examined the expression of MUC1 on different subsets of T cells (naive, effector, effector/memory). MUC1 appears to be strongly upregulated on activated CD4(+) T cells in comparison with CD8(+) T cells. The cytoplasmic tail of MUC1 contains both immune tyrosine-based activation and inhibitory motifs; therefore, we investigated whether MUC1 can also act as a costimulatory molecule on human T cells. Nonpurified T-cell cultures from human peripheral blood exhibited enhanced proliferation and an increase in cytokine production when CD3 and MUC1 were cross-linked and coligated. The intracellular mechanism of MUC1-mediated costimulation was determined to be mediated by the calcium-dependent NF-AT pathway. We further demonstrated that the cytoplasmic tail of MUC1 binds to the AP-1 transcription factors c-Fos and c-Jun, with c-Fos binding constitutively and c-Jun binding only after MUC1 stimulation. Their nuclear migration is then facilitated in a CD3-dependent manner. Our findings clearly demonstrate that MUC1 is a novel T-cell costimulatory molecule involved in immune regulation. These studies delineate important mechanisms of T-cell activation and regulation.

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.

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.

UDP-N-acetyl-α-D-galactosamine:polypeptide N-acetylgalactosaminyltransferases: completion of the family tree

The formation of mucin-type O-glycans is initiated by an evolutionarily conserved family of enzymes, the UDP-N-acetyl-α-D-galactosamine:polypeptide N-acetylgalactosaminyltransferases (GalNAc-Ts). The human genome encodes 20 transferases; 17 of which have been characterized functionally. The complexity of the GalNAc-T family reflects the differential patterns of expression among the individual enzyme isoforms and the unique substrate specificities which are required to form the dense arrays of glycans that are essential for mucin function. We report the expression patterns and enzymatic activity of the remaining three members of the family and the further characterization of a recently reported isoform, GalNAc-T17. One isoform, GalNAcT-16 that is most homologous to GalNAc-T14, is widely expressed (abundantly in the heart) and has robust polypeptide transferase activity. The second isoform GalNAc-T18, most similar to GalNAc-T8, -T9 and -T19, completes a discrete subfamily of GalNAc-Ts. It is widely expressed and has low, albeit detectable, activity. The final isoform, GalNAc-T20, is most homologous to GalNAc-T11 but lacks a lectin domain and has no detectable transferase activity with the panel of substrates tested. We have also identified and characterized enzymatically active splice variants of GalNAc-T13 that differ in the sequence of their lectin domain. The variants differ in their affinities for glycopeptide substrates. Our findings provide a comprehensive view of the complexities of mucin-type O-glycan formation and provide insight into the underlying mechanisms employed to heavily decorate mucins and mucin-like domains with carbohydrate.

Characterization of the Src/Abl hybrid kinase SmTK6 of Schistosoma mansoni

Cellular protein-tyrosine kinases play key roles in signal transduction processes in eukaryotes. SmTK4 was the first Syk kinase identified in a parasite and found to be tissue-specifically transcribed in the gonads of adult Schistosoma mansoni. Functional analyses confirmed its role in oogenesis and spermatogenesis. As an SmTK4 upstream binding partner, the cellular protein-tyrosine kinase SmTK6 was isolated from a yeast two-hybrid library. Phylogenetic analyses performed in this study confirmed the first suggestions of a hybrid character of SmTK6. Biochemical studies made in Xenopus oocytes using inhibitors against Src (herbimycin A) and Abl (imatinib) kinases exhibited a biochemical inhibition profile of SmTK6, which was intermediate of Src and Abl kinases. As SmTK6 upstream interaction partners, we identified among others the known Src kinase SmTK3 and the Venus kinase receptor SmVKR1 of S. mansoni by yeast two-hybrid analyses, all of which co-localized in the gonads. Co-immunoprecipitation experiments confirmed interactions between SmTK6 and SmTK3 or SmVKR1. In Xenopus oocytes, it was finally shown that SmVKR1 but also SmTK3 were able to activate SmTK6 enzymatic activity indicating its functions in a receptor tyrosine kinase signal transduction cascade. These results not only demonstrate an intermediate but Src-biased profile of the unusual kinase SmTK6. They also strongly substantiate previous indications for a kinase complex, consisting of a receptor tyrosine kinase, Syk and Src kinases, which has been hypothesized to be involved in proliferation and differentiation processes in the gonads of schistosomes.

Differentiation of breast cancer stem cells by knockdown of CD44: promising differentiation therapy

BACKGROUND

Breast cancer stem cells (BCSCs) are the source of breast tumors. Compared with other cancer cells, cancer stem cells show high resistance to both chemotherapy and radiotherapy. Targeting of BCSCs is thus a potentially promising and effective strategy for breast cancer treatment. Differentiation therapy represents one type of cancer stem-cell-targeting therapy, aimed at attacking the stemness of cancer stem cells, thus reducing their chemo- and radioresistance. In a previous study, we showed that down-regulation of CD44 sensitized BCSCs to the anti-tumor agent doxorubicin. This study aimed to determine if CD44 knockdown caused BCSCs to differentiate into breast cancer non-stem cells (non-BCSCs).

METHODS

We isolated a breast cancer cell population (CD44+CD24- cells) from primary cultures of malignant breast tumors. These cells were sorted into four sub-populations based on their expression of CD44 and CD24 surface markers. CD44 knockdown in the BCSC population was achieved using small hairpin RNA lentivirus particles. The differentiated status of CD44 knock-down BCSCs was evaluated on the basis of changes in CD44+CD24- phenotype, tumorigenesis in NOD/SCID mice, and gene expression in relation to renewal status, metastasis, and cell cycle in comparison with BCSCs and non-BCSCs.

RESULTS

Knockdown of CD44 caused BCSCs to differentiate into non-BCSCs with lower tumorigenic potential, and altered the cell cycle and expression profiles of some stem cell-related genes, making them more similar to those seen in non-BCSCs.

CONCLUSIONS

Knockdown of CD44 is an effective strategy for attacking the stemness of BCSCs, resulting in a loss of stemness and an increase in susceptibility to chemotherapy or radiation. The results of this study highlight a potential new strategy for breast cancer treatment through the targeting of BCSCs.

A novel mechanism of increased infections in contact lens wearers

PURPOSE

It is well documented that contact lens wearers have much higher incidences of corneal infections compared with those of non-contact lens wearers, although the exact cause(s) of this increased susceptibility has not been identified. A distinct subset of mucins (MUCs) is present on the ocular surface, acting to protect the integrity of the corneal epithelium. This study was performed to determine whether multipurpose contact lens solutions (MPCLSs) can cause increased infections in the cornea by destroying the protective cell-bound mucin layer.

METHODS

An immortalized human corneal limbal epithelial cell line was treated in the presence of four commonly used MPCLSs or PBS and the expression and release of MUC-16 was assessed. Cells were also cultured with Pseudomonas aeruginosa after MPCLS treatment and internalization of bacteria was assessed by quantitative genomic PCR. Loss of MUC-16 was then correlated with infection rates.

RESULTS

Each of the four commonly used MPCLSs examined in this study differentially affected mucin release. The relative effect was correlated with an increase in infection of corneal epithelial cells by P. aeruginosa.

CONCLUSIONS

The results of this study are consistent with the hypothesis that MPCLSs cause increased infections in the cornea by destroying the protective cell-bound mucin layer.

Impact of MUC1 mucin downregulation in the phenotypic characteristics of MKN45 gastric carcinoma cell line

Background

Gastric carcinoma is the second leading cause of cancer-associated death worldwide. The high mortality associated with this disease is in part due to limited knowledge about gastric carcinogenesis and a lack of available therapeutic and prevention strategies. MUC1 is a high molecular weight transmembrane mucin protein expressed at the apical surface of most glandular epithelial cells and a major component of the mucus layer above gastric mucosa. Overexpression of MUC1 is found in approximately 95% of human adenocarcinomas, where it is associated with oncogenic activity. The role of MUC1 in gastric cancer progression remains to be clarified.

Methodology

We downregulated MUC1 expression in a gastric carcinoma cell line by RNA interference and studied the effects on cellular proliferation (MTT assay), apoptosis (TUNEL assay), migration (migration assay), invasion (invasion assay) and aggregation (aggregation assay). Global gene expression was evaluated by microarray analysis to identify alterations that are regulated by MUC1 expression. In vivo assays were also performed in mice, in order to study the tumorigenicity of cells with and without MUC1 downregulation in MKN45 gastric carcinoma cell line.

Results

Downregulation of MUC1 expression increased proliferation and apoptosis as compared to controls, whereas cell-cell aggregation was decreased. No significant differences were found in terms of migration and invasion between the downregulated clones and the controls. Expression of TCN1, KLK6, ADAM29, LGAL4, TSPAN8 and SHPS-1 was found to be significantly different between MUC1 downregulated clones and the control cells. In vivo assays have shown that mice injected with MUC1 downregulated cells develop smaller tumours when compared to mice injected with the control cells.

Conclusions

These results indicate that MUC1 downregulation alters the phenotype and tumorigenicity of MKN45 gastric carcinoma cells and also the expression of several molecules that can be involved in tumorigenic events. Therefore, MUC1 should be further studied to better clarify its potential as a novel therapeutic target for gastric cancer.

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.

Apoptosis signaling kinases: from stress response to health outcomes

Apoptosis is a highly regulated process essential for the development and homeostasis of multicellular organisms. Whereas caspases, a large family of intracellular cysteine proteases, play central roles in the execution of apoptosis, other proapoptotic and antiapoptotic regulators such as the members of the Bcl-2 family are also critically involved in the regulation of apoptosis. A large body of evidence has revealed that a number of protein kinases are among such regulators and regulate cellular sensitivity to various proapoptotic signals at multiple steps in apoptosis. However, recent progress in the analysis of these apoptosis signaling kinases demonstrates that they generally act as crucial regulators of diverse cellular responses to a wide variety of stressors, beyond their roles in apoptosis regulation. In this review, we have cataloged apoptosis signaling kinases involved in cellular stress responses on the basis of their ability to induce apoptosis and discuss their roles in stress responses with particular emphasis on health outcomes upon their dysregulation.

Association of placental inflammation with fetomaternal hemorrhage and loss of placental mucin-1

BACKGROUND

Fetomaternal hemorrhage (FMH) poses an immediate risk to the fetus and, in case of Rhesus-immunization, to future pregnancies. Given that altered endothelial permeability is part of the pathophysiology of inflammation, in this study we investigated whether placental inflammatory processes like chorioamnionitis (ChoA) or preeclampsia (PE) lead to increased rates of FMH compared to the established risk factor of placenta previa (PP). Putative accompanying markers of trophoblastic damage were also explored.

METHODS

40 patients (14 PE; 6 ChoA; 9 PP; 11 normal controls) were evaluated for FMH using a flowcytometric test kit, which is able to quantify FMH of 0.06% fetal cells. Placental tissue samples were immunostained for human placental lactogen (hPL), human chorionic gonadotropin (hCG), and mucin-1 (MUC1). MUC1 was evaluated as a potential serum marker of FMH.

RESULTS

Patients with ChoA had a mean calculated FMH volume of 29 ml, compared to 4 ml in PE and 1 ml in PP and controls. MUC1 staining was reduced in PE and ChoA placenta samples, while elevated MUC1 serum concentration correlated positively with FMH.

CONCLUSION

Diseases of placental inflammation are associated with FMH. Placental MUC1 staining is reduced and serum concentrations are increased in cases of FMH.

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.

What role do mucins have in the development of laryngeal squamous cell carcinoma? A systematic review

Mucins are the dominant component in the protective mucus layer on mucosal surfaces including the larynx. Hence, they are part of the first line of defence against external stimuli including effect of smoking in the larynx. We asked whether existing published evidence supported the hypothesis that alteration in mucins expression/production is related to the laryngeal neoplastic process. The objective of this study is to review published evidence for mucins having an important role in normal laryngeal physiology and the development of laryngeal squamous cell carcinoma (SCC). We aimed to review all available literature on mucins in the larynx in order to develop hypotheses to be tested by future research. Thereby, new potential means of prevention and treatment of laryngeal cancer may be developed. A systematic search of all published literature was conducted. Systematic searches were done in the following databases: AMED, BNI, EMBASE, HMIC, MEDLINE, PsycINFO, CINAHL and HEALTH BUSINESS ELITE from their respective inception up to 11 February 2011. The following keywords were used in combination: mucin, larynx and squamous cell carcinoma. Altogether, 53 studies were identified; 43 studies were excluded following screening of the titles and abstracts. Full text manuscripts for ten studies were obtained for detailed evaluation and five studies were included in this review. No single study fulfilled all relevant criteria. Based on the included studies, we now know that MUC1 is definitely expressed in SCC larynx. However, there is no definitive evidence to suggest that MUC1 and MUC2 are aberrantly expressed in SCC larynx as compared to normal larynx. Further studies using the best available detection technique to detect MUC1, MUC2 and other possible relevant mucins i.e., MUC4 on adequate numbers of normal and SCC specimens are needed to confirm the findings of this review.

A functional single nucleotide polymorphism in mucin 1, at chromosome 1q22, determines susceptibility to diffuse-type gastric cancer

BACKGROUND & AIMS

Two major types of gastric cancer, intestinal and diffuse, develop through distinct mechanisms; the diffuse type is considered to be more influenced by genetic factors, although the mechanism is unknown. Our previous genome-wide association study associated 3 single nucleotide polymorphisms (SNPs) with diffuse-type gastric cancer (DGC); 1 was a functional SNP (rs2294008) in prostate stem cell antigen (PSCA), but the loci of the other 2 were not investigated.

METHODS

We performed high-density mapping to explore a linkage disequilibrium status of the 2 SNPs at chromosome 1q22. A DGC case-control study was conducted using DNA from 606 cases and 1264 controls (all Japanese individuals) and validated using DNA from Japanese (304 cases, 1465 controls) and Korean (452 cases, 372 controls) individuals. The effects of SNPs on function were analyzed by reporter assays and analyses of splice variants.

RESULTS

A region of a strong linkage disequilibrium with the 2 SNPs contained mucin 1 (MUC1) and other 4 genes and SNPs significantly associated with DGC (rs2070803: P = 4.33 × 10(-13); odds ratio [OR], 1.71 by meta-analysis of the studies on the 3 panels) but not with intestinal-type gastric cancer. Functional studies demonstrated that rs4072037 (P = 1.43 × 10(-11); OR, 1.66 by meta-analysis) in MUC1 affects promoter activity and determines the major splicing variants of MUC1 in the gastric epithelium. Individuals that carry both SNPs rs2294008 in PSCA and rs4072037 in MUC1 have a high risk for developing DGC (OR, 8.38).

CONCLUSIONS

MUC1 is the second major DGC susceptibility gene identified. The SNPs rs2070803 and rs4072037 in MUC1 might be used to identify individuals at risk for this type of gastric cancer.

The Tn antigen-structural simplicity and biological complexity

Glycoproteins in animal cells contain a variety of glycan structures that are added co- and/or posttranslationally to proteins. Of over 20 different types of sugar-amino acid linkages known, the two major types are N-glycans (Asn-linked) and O-glycans (Ser/Thr-linked). An abnormal mucin-type O-glycan whose expression is associated with cancer and several human disorders is the Tn antigen. It has a relatively simple structure composed of N-acetyl-D-galactosamine with a glycosidic α linkage to serine/threonine residues in glycoproteins (GalNAcα1-O-Ser/Thr), and was one of the first glycoconjugates to be chemically synthesized. The Tn antigen is normally modified by a specific galactosyltransferase (T-synthase) in the Golgi apparatus of cells. Expression of active T-synthase is uniquely dependent on the molecular chaperone Cosmc, which is encoded by a gene on the X chromosome. Expression of the Tn antigen can arise as a consequence of mutations in the genes for T-synthase or Cosmc, or genes affecting other steps of O-glycosylation pathways. Because of the association of the Tn antigen with disease, there is much interest in the development of Tn-based vaccines and other therapeutic approaches based on Tn expression.

Galectin-3 regulates MUC1 and EGFR cellular distribution and EGFR downstream pathways in pancreatic cancer cells

MUC1 is a transmembrane glycoprotein which is typically expressed at the apical membrane of normal epithelial cells. In cancer cells, the over-expression of MUC1 and its aberrant localization around the cell membrane and in the cytoplasm favours its interaction with different protein partners such as epidermal growth factor receptor (EGFR) and can promote tumour proliferation through the activation of oncogenic signalling pathways. Our aims were to study the mechanisms inducing MUC1 cytoplasmic localization in pancreatic cancer cells, and to decipher their impact on EGFR cellular localization and activation. Our results showed that galectin-3, an endogenous lectin, is co-expressed with MUC1 in human pancreatic ductal adenocarcinoma, and that it favours the endocytosis of MUC1 and EGFR. Depletion of galectin-3 by RNA interference increased the interaction between MUC1 and EGFR, EGFR and ERK-1,2 phosphorylation, and translocation of EGFR to the nucleus. On the contrary, silencing of galectin-3 led to a decrease of cyclin-D1 levels and of cell proliferation. The galectin-3-dependent regulation of MUC1/EGFR functions may represent an interesting mechanism modulating the EGFR-stimulated cell growth of pancreatic cancer cells.

C2-O-sLeX glycoproteins are E-selectin ligands that regulate invasion of human colon and hepatic carcinoma cells

Similar to mechanisms of recruitment of activated leukocytes to inflamed tissues, selectins mediate adhesion and extravasation of circulating cancer cells. Our objective was to determine whether sialyl Lewis X modified core 2 O-glycans (C2-O-sLe^X) present on colon and hepatic carcinoma cells promote their adhesion and invasion. We examined membrane expression of C2-O-sLe^X, selectin binding, invasion of human colon and hepatic carcinoma cell lines, and mRNA levels of alpha-2,3 fucosyltransferase (FucT-III) and core 2 beta-1,6 N-acetylglucosaminyltransferase (C2GnT1) genes, necessary for C2-O-sLe^X synthesis, by quantitative reverse-transcriptase (RT) PCR. Synthesis of core 2 branched O-glycans decorated by sLe^X is dependent on C2GnT1 function and thus we determined enzyme activity of C2GnT1. The cell lines that expressed C2GnT1 and FucT-III mRNA by quantitative RT-PCR were highly positive for C2-O-sLe^X by flow cytometry, and colon carcinoma cells possessed highly active C2GnT1 enzyme. Cells bound avidly to E-selection but not to P- and L-selectin. Gene knock-down of C2GnT1 in colon and hepatic carcinoma cells using short hairpin RNAs (shRNA) resulted in a 40–90% decrease in C2-O-sLe^X and a 30–50% decrease in E-selectin binding compared to control cells. Invasion of hepatic and colon carcinoma cells containing C2GnT1 shRNA was significantly reduced compared to control cells in Matrigel assays and C2GnT1 activity was down-regulated in the latter cells. The sLe^X epitope was predominantly distributed on core 2 O-glycans on colon and hepatic carcinoma cells. Our findings indicate that C2GnT1 gene expression and the resulting C2-O-sLe^X carbohydrates produced mediate the adhesive and invasive behaviors of human carcinomas which may influence their metastatic potential.

Changes in the mucosal barrier during acute and chronic Trichuris muris infection

The intestinal mucosal barrier, part of the innate immune defence, is responsive to the external environment and changes in response to infection. There is disparate evidence for the epithelial and goblet cell products within the intrinsic barrier being part of a response to resolve infection. We comprehensively analysed the changes of mucosal glycoconjugates during acute and chronic infection by utilising the Trichuris muris (T. muris) model. Transcription factors, atonal homolog 1 (Math-1) and SAM pointed domain containing ETS transcription factor (Spdef) were activated during acute infection, which promoted stem cell fate towards a secretory cell phenotype. The thickness of the intermediate barrier, the carbohydrate-rich glycocalyx, composed of cell surface mucins increased with exposure to T. muris, with an increase in Muc4, Muc13 and Muc17. Overall, hypersecretion of glycoproteins into the extrinsic barrier (mediated by IL-13) via the gamma amino-butyric acid-α3 receptor (GABA-α3), was observed during acute infection. Furthermore, altered glycosylation was observed during acute and chronic infection; mucins were more highly charged during acute infection than during chronic infection. This study readdresses the changes within the mucosal barrier, in particular in the cell surface and secreted mucins during acute and chronic nematode infection.

Role of mucins in the skin during benign and malignant conditions

Skin-related diseases comprise a major health challenge to the practicing physician, and constitute a significant psychological, social and financial burden to the society. Further, skin cancer, especially non-melanoma skin cancer is currently the leading type of malignancy in the Western world. Given the huge burden of skin diseases, there is growing emphasis on understanding their pathophysiology, and towards their early detection. Mucins are high-molecular weight O- and N-linked glycoproteins that have emerged in recent years as important molecules in maintaining health and in promoting or protecting against inflammation and cancer. They have also begun to emerge as highly specific diagnostic and prognostic markers and novel therapeutic targets in several malignant disorders. However, their role in cutaneous pathologies has remained largely obscured. The present review provides the expression patterns and proposed role of mucins in the healthy skin and various benign and malignant skin diseases. The review has immense clinical significance as the availability of highly specific reagents including monoclonal antibodies against mucins makes them extremely attractive targets for specific diagnosis and/or immunotherapy of benign and malignant cutaneous diseases.

MUC1 enhances invasiveness of pancreatic cancer cells by inducing epithelial to mesenchymal transition

Increased motility and invasiveness of pancreatic cancer cells are associated with epithelial to mesenchymal transition (EMT). Snai1 and Slug are zinc-finger transcription factors that trigger this process by repressing E-cadherin and enhancing vimentin and N-cadherin protein expression. However, the mechanisms that regulate this activation in pancreatic tumors remain elusive. MUC1, a transmembrane mucin glycoprotein, is associated with the most invasive forms of pancreatic ductal adenocarcinomas (PDA). In this study, we show that over expression of MUC1 in pancreatic cancer cells triggers the molecular process of EMT, which translates to increased invasiveness and metastasis. EMT was significantly reduced when MUC1 was genetically deleted in a mouse model of PDA or when all seven tyrosines in the cytoplasmic tail of MUC1 were mutated to phenylalanine (mutated MUC1 CT). Using proteomics, RT-PCR and western blotting, we revealed a significant increase in vimentin, Slug and Snail expression with repression of E-Cadherin in MUC1-expressing cells compared with cells expressing the mutated MUC1 CT. In the cells that carried the mutated MUC1 CT, MUC1 failed to co-immunoprecipitate with β-catenin and translocate to the nucleus, thereby blocking transcription of the genes associated with EMT and metastasis. Thus, functional tyrosines are critical in stimulating the interactions between MUC1 and β-catenin and their nuclear translocation to initiate the process of EMT. This study signifies the oncogenic role of MUC1 CT and is the first to identify a direct role of the MUC1 in initiating EMT during pancreatic cancer. The data may have implications in future design of MUC1-targeted therapies for pancreatic cancer.

MUC1 immunotherapy

The overexpression and aberrant glycosylation of MUC1 is associated with a wide variety of cancers, making it an ideal target for immunotherapeutic strategies. This review highlights the main avenues of research in this field, focusing on adenocarcinomas, from the preclinical to clinical; the problems and possible solutions associated with each approach; and speculates on the direction of MUC1 immunotherapeutic research over the next 5-10 years.

Multivalent lectin-carbohydrate interactions energetics and mechanisms of binding

The biological signaling properties of lectins, which are carbohydrate-binding proteins, are due to their ability to bind and cross-link multivalent glycoprotein receptors on the surface of normal and transformed cells. While the crosslinking properties of lectins with multivalent carbohydrates and glycoproteins are relatively well understood, the mechanisms of binding of lectins to multivalent glycoconjugates are less well understood. Recently, the thermodynamics of binding of lectins to synthetic clustered glycosides, a multivalent globular glycoprotein, and to linear glycoproteins (mucins) have been described. The results are consistent with a dynamic binding mechanism in which lectins bind and jump from carbohydrate to carbohydrate epitope in these molecules. Importantly, the mechanism of binding of lectins to mucins is similar to that for a variety of protein ligands binding to DNA. Recent analysis also shows that high-affinity lectin-mucin crosslinking interactions are driven by favorable entropy of binding that is associated with the bind and jump mechanism. The results suggest that the binding of ligands to biopolymers, in general, may involve a common mechanism that involves enhanced entropic effects which facilitate binding and subsequent complex formation including enzymology.

Autoproteolysis of the SEA module of rMuc3 C-terminal domain modulates its functional composition

rMuc3 is a typical transmembrane mucin and contains a 174 amino acid domain called an SEA module in its C-terminal domain which is cleaved in eukaryotic cells. However, the mechanism by which the rMuc3 SEA module is proteolyzed and its biological significance has to be elucidated. In this study, we showed that the rMuc3 C-terminal domain was cleaved at LSKGSIVV motif within SEA module in prokaryotic cells, the time-dependence of the cleavage was found in the purified rMuc3 C-terminal domain carrying a mutated LSKASIVV motif expressed in bacteria. Thus, the cleavage of rMuc3 SEA module depended on autoproteolysis. The autoproteolysis of the SEA module of rMuc3 C-terminal domain played a critical role in the migration and invasion of the LoVo human colon cancer cells with rMuc3 C-terminal domain in vitro. The rMuc3 C-terminal domain induced a significant activation of HER/ErbB2 phosphorylated form (py1248) in LoVo cells. Inhibition of the phosphorylation by gefitinib (ZD1839) did attenuate migration and invasion of LoVo cells with rMuc3 C-terminal domain. Thus, rMuc3 C-terminal domain undergoes autoproteolysis at its SEA module, which maintains its availability for the potentiation of the signaling process that is modulated by HER/ErbB2 phosphorylation to promote the migration and invasion of LoVo cells.

The reactive tumor microenvironment: MUC1 signaling directly reprograms transcription of CTGF

The MUC1 cytoplasmic tail (MUC1.CT) conducts signals from spatial and extracellular cues (growth factor and cytokine stimulation) to evoke a reprogramming of the cellular transcriptional profile. Specific phosphorylated forms of the MUC1.CT achieve this function by differentially associating with transcription factors and redirecting their transcriptional regulatory capabilities at specific gene regulatory elements. The specificity of interaction between MUC1.CT and several transcription factors is dictated by the phosphorylation pattern of the 18 potential phosphorylation motifs within the MUC1.CT. To better appreciate the scope of differential gene expression triggered by MUC1.CT activation, we performed microarray gene expression analysis and ChIP-chip promoter analysis and identified the genome-wide transcriptional targets of MUC1.CT signaling in pancreatic cancer. On a global scale, MUC1.CT preferentially targets genes relating to invasion, angiogenesis and metastasis, suggesting that MUC1.CT signaling contributes to establishing a reactive tumor microenvironment during tumor progression to metastatic disease. We examined in detail the molecular mechanisms of MUC1.CT signaling that induces expression of connective tissue growth factor (CTGF/CCN2), a potent mediator of ECM remodeling and angiogenesis. We demonstrate a robust induction of CTGF synthesis and secretion in response to serum factors that is enabled only when MUC1 is highly expressed. We demonstrate the requirement of phosphorylation at distinct tyrosine motifs within the MUC1.CT for MUC1-induced CTGF expression and demonstrate a phosphorylation-specific localization of MUC1.CT to the CTGF promoter. We found that MUC1 reorganizes transcription factor occupancy of genomic regions upstream of the CTGF gene, directing β-catenin and mutant p53 to CTGF gene regulatory elements to promote CTGF expression and destabilizing the interaction at these regions of the transcriptional repressor, c-Jun. With this example we illustrate the capacity of MUC1.CT to mediate transcription factor activity in a context-dependent manner to achieve widespread and robust changes in gene expression and facilitate creation of the reactive tumor microenvironment.

Invasive lobular carcinoma with extracellular mucin production and HER-2 overexpression: a case report and further case studies

Invasive lobular carcinomas (ILC) of breast typically demonstrate intracytoplasmic mucin. We present a unique case of classical type ILC with abundant extracellular mucin and strong ERBB2 (HER2/neu) expression confirmed by immunohistochemistry and fluorescent in situ hybridization. Dual E-cadherin/p120 immunohistochemical stain demonstrated complete loss of membranous E-cadherin and the presence of diffuse cytoplasmic p120 staining, confirming the lobular phenotype. The tumor cells showed ductal-like cytoplasmic MUC1 staining, but were negative for MUC2 and other mucin gene markers. In addition, studies of tissue microarrays of 80 breast carcinomas with mucinous differentiation revealed 4 pure mucinous carcinomas showing significantly reduced E-cadherin staining without redistribution of p120 into cytoplasm. The findings suggest that the presence of extracellular mucin does not exclude a diagnosis of lobular carcinoma, and the morphologic and molecular characteristics of lobular and ductal carcinomas are more complex than previously appreciated.

Sho1 and Msb2-related proteins regulate appressorium development in the smut fungus Ustilago maydis

The dimorphic fungus Ustilago maydis switches from budding to hyphal growth on the plant surface. In response to hydrophobicity and hydroxy fatty acids, U. maydis develops infection structures called appressoria. Here, we report that, unlike in Saccharomyces cerevisiae and other fungi where Sho1 (synthetic high osmolarity sensitive) and Msb2 (multicopy suppressor of a budding defect) regulate stress responses and pseudohyphal growth, Sho1 and Msb2-like proteins play a key role during appressorium differentiation in U. maydis. Sho1 was identified through a two-hybrid screen as an interaction partner of the mitogen-activated protein (MAP) kinase Kpp6. Epistasis analysis revealed that sho1 and msb2 act upstream of the MAP kinases kpp2 and kpp6. Furthermore, Sho1 was shown to destabilize Kpp6 through direct interaction with the unique N-terminal domain in Kpp6, indicating a role of Sho1 in fine-tuning Kpp6 activity. Morphological differentiation in response to a hydrophobic surface was strongly attenuated in sho1 msb2 mutants, while hydroxy fatty acid-induced differentiation was unaffected. These data suggest that Sho1 and the transmembrane mucin Msb2 are involved in plant surface sensing in U. maydis.

Membrane-tethered mucins have multiple functions on the ocular surface

Membrane-tethered mucins are large glycoproteins present in the glycocalyx along the apical surface of all wet-surfaced epithelia of the body, including that of the ocular surface. Originally thought to function only in epithelial surface lubrication and hydration, data now indicate that the mucins are multifunctional molecules, each having unique as well as common functions. This review summarizes current knowledge regarding the three major membrane mucins of the ocular surface, MUC1, MUC4, and MUC16. The mucins vary in their ocular surface distribution, size, structural motifs, and functions. The ectodomains of each are released into the tear film and are, thus, a component of the soluble mucins of the tear film. Both animal and in vitro models for their study are herein described, as are alterations of the mucins in ocular surface disease.

Membrane-bound mucins: the mechanistic basis for alterations in the growth and survival of cancer cells

Mucins (MUC) are high molecular weight O-linked glycoproteins whose primary functions are to hydrate, protect, and lubricate the epithelial luminal surfaces of the ducts within the human body. The MUC family is comprised of large secreted gel forming and transmembrane (TM) mucins. MUC1, MUC4, and MUC16 are the well-characterized TM mucins and have been shown to be aberrantly overexpressed in various malignancies including cystic fibrosis, asthma, and cancer. Recent studies have uncovered the unique roles of these mucins in the pathogenesis of cancer. These mucins possess specific domains that can make complex associations with various signaling pathways, impacting cell survival through alterations of cell growth, proliferation, death, and autophagy. The cytoplasmic domain of MUC1 serves as a scaffold for interaction with various signaling proteins. On the other hand, MUC4 mediates its effect by stabilizing and enhancing the activity of growth factor receptor ErbB2. MUC16, previously known as CA125, is a well-known serum marker for the diagnosis of ovarian cancer and has a key role in stimulation and dissemination of ovarian cancer cells by interacting with mesothelin and galectin. Therefore, herein we discuss the function and divergent mechanisms of MUC1, MUC4, and MUC16 in carcinogenesis in the context of alteration in cell growth and survival.

Multiple signals converge on a differentiation MAPK pathway

An important emerging question in the area of signal transduction is how information from different pathways becomes integrated into a highly coordinated response. In budding yeast, multiple pathways regulate filamentous growth, a complex differentiation response that occurs under specific environmental conditions. To identify new aspects of filamentous growth regulation, we used a novel screening approach (called secretion profiling) that measures release of the extracellular domain of Msb2p, the signaling mucin which functions at the head of the filamentous growth (FG) MAPK pathway. Secretion profiling of complementary genomic collections showed that many of the pathways that regulate filamentous growth (RAS, RIM101, OPI1, and RTG) were also required for FG pathway activation. This regulation sensitized the FG pathway to multiple stimuli and synchronized it to the global signaling network. Several of the regulators were required for MSB2 expression, which identifies the MSB2 promoter as a target “hub” where multiple signals converge. Accessibility to the MSB2 promoter was further regulated by the histone deacetylase (HDAC) Rpd3p(L), which positively regulated FG pathway activity and filamentous growth. Our findings provide the first glimpse of a global regulatory hierarchy among the pathways that control filamentous growth. Systems-level integration of signaling circuitry is likely to coordinate other regulatory networks that control complex behaviors.

Signal integration is an essential feature of information flow through signal transduction pathways. The mechanisms by which signals from multiple pathways become integrated into a coordinated response remain unclear. We show that multiple pathways that regulate filamentous growth converge on a differentiation-dependent MAPK pathway. Our findings indicate that more extensive communication occurs between signaling pathways that control the filamentation response than has previously been appreciated. We suggest that global communication hierarchies regulate information flow in other systems, particularly higher eukaryotes where multiple pathways typically function simultaneously to modulate a complex response.

MUC4 down-regulation reverses chemoresistance of pancreatic cancer stem/progenitor cells and their progenies

The present study was undertaken to estimate the therapeutic benefit to down-regulate the MUC4 mucin for reversing chemoresistance of pancreatic cancer (PC) stem/progenitor cells and their progenies. The results have revealed that MUC4 mucin is overexpressed in CD133(+) and CD133(-) pancreatic cells (PCs) detected in patient's adenocarcinoma tissues while no significant expression was seen in normal pancreatic tissues. The gain- and loss-of-function analyses have indicated that the overexpression of MUC4 in PC lines is associated with a higher resistance to the anti-proliferative, anti-invasive and apoptotic effects induced by gemcitabine. Importantly, the treatment of the MUC4-overexpressing CD18/HPAF-Src cells with gemcitabine resulted in an enrichment of the side population (SP) cells expressing CD133 while the total PC cells including non-SP cells detected in MUC4 knockdown CD18/HPAF-shMUC4 cells were responsive to the cytotoxic effects induced by gemcitabine. These data suggest that the MUC4 down-regulation may constitute a potential therapeutic strategy for improving the efficacy of gemcitabine to eradicate the total PC cell mass, and thereby preventing disease relapse.

A Candida albicans cell wall-linked protein promotes invasive filamentation into semi-solid medium

Growth of cells in contact with an abiotic or biological surface profoundly affects cellular physiology. In the opportunistic human pathogen, Candida albicans, growth on a semi-solid matrix such as agar results in invasive filamentation, a process in which cells change their morphology to highly elongated filamentous hyphae that grow into the matrix. We hypothesized that a plasma membrane receptor-type protein would sense the presence of matrix and activate a signal transduction cascade, thus promoting invasive filamentation. In this communication, we demonstrate that during growth in contact with a semi-solid surface, activation of a MAP kinase, Cek1p, is promoted, in part, by a plasma membrane protein termed Dfi1p and results in invasive filamentation. A C. albicans mutant lacking Dfi1p showed reduced virulence in a murine model of disseminated candidiasis. Dfi1p is a relatively small, integral membrane protein that localizes to the plasma membrane. Some Dfi1p molecules become cross-linked to the carbohydrate polymers of the cell wall. Thus, Dfi1p is capable of linking the cell wall to the plasma membrane and cytoplasm.

Critical roles of mucin 1 glycosylation by transactivated polypeptide N-acetylgalactosaminyltransferase 6 in mammary carcinogenesis

The structure of O-glycosylated proteins is altered in breast cancer cells, but the mechanisms of such an aberrant modification have been largely unknown. We here report critical roles of a novel druggable target, polypeptide N-acetylgalactosaminyltransferase 6 (GALNT6), which is upregulated in a great majority of breast cancers and encodes a glycosyltransferase responsible for initiating mucin-type O-glycosylation. Knockdown of GALNT6 by small interfering RNA significantly enhanced cell adhesion function and suppressed the growth of breast cancer cells. Western blot and immunostaining analyses indicated that wild-type GALNT6 protein could glycosylate and stabilize an oncoprotein mucin 1 (MUC1), which was upregulated with GALNT6 in breast cancer specimens. Furthermore, knockdown of GALNT6 or MUC1 led to similar morphologic changes of cancer cells accompanied by the increase of cell adhesion molecules beta-catenin and E-cadherin. Our findings implied that overexpression of GALNT6 might contribute to mammary carcinogenesis through aberrant glycosylation and stabilization of MUC1 and that screening of GALNT6 inhibitors would be valuable for the development of novel therapeutic modalities against breast cancer.

The membrane mucin MUC4 is elevated in breast tumor lymph node metastases relative to matched primary tumors and confers aggressive properties to breast cancer cells

Introduction

Previous studies indicate that overexpression of the membrane-associated mucin MUC4 is potently anti-adhesive to cultured tumor cells, and suppresses cellular apoptotic response to a variety of insults. Such observations raise the possibility that MUC4 expression could contribute to tumor progression or metastasis, but the potential involvement of MUC4 in breast cancer has not been rigorously assessed. The present study aimed to investigate the expression of the membrane mucin MUC4 in normal breast tissue, primary breast tumors and lymph node metastases, and to evaluate the role of MUC4 in promoting the malignant properties of breast tumor cells.

Methods

MUC4 expression levels in patient-matched normal and tumor breast tissue was initially examined by immunoblotting lysates of fresh frozen tissue samples with a highly specific preparation of anti-MUC4 monoclonal antibody 1G8. Immunohistochemical analysis was then carried out using tissue microarrays encompassing patient-matched normal breast tissue and primary tumors, and patient-matched lymph node metastases and primary tumors. Finally, shRNA-mediated knockdown was employed to assess the contribution of MUC4 to the cellular growth and malignancy properties of JIMT-1 breast cancer cells.

Results

Immunoblotting and immunohistochemistry revealed that MUC4 levels are suppressed in the majority (58%, p < 0.001) of primary tumors relative to patient-matched normal tissue. On the other hand, lymph node metastatic lesions from 37% (p < 0.05) of patients expressed higher MUC4 protein levels than patient-matched primary tumors. MUC4-positive tumor emboli were often found in lymphovascular spaces of lymph node metastatic lesions. shRNA-mediated MUC4 knockdown compromised the migration, proliferation and anoikis resistance of JIMT-1 cells, strongly suggesting that MUC4 expression actively contributes to cellular properties associated with breast tumor metastasis.

Conclusions

Our observations suggest that after an initial loss of MUC4 levels during the transition of normal breast tissue to primary tumor, the re-establishment of elevated MUC4 levels confers an advantage to metastasizing breast tumor cells by promoting the acquisition of cellular properties associated with malignancy.

Human embryonic stem cell-derived keratinocytes exhibit an epidermal transcription program and undergo epithelial morphogenesis in engineered tissue constructs

Human embryonic stem (hES) cells are an attractive source of cellular material for scientific, diagnostic, and potential therapeutic applications. Protocols are now available to direct hES cell differentiation to specific lineages at high purity under relatively defined conditions; however, researchers must establish the functional similarity of hES cell derivatives and associated primary cell types to validate their utility. Using retinoic acid to initiate differentiation, we generated high-purity populations of keratin 14+ (K14) hES cell-derived keratinocyte (hEK) progenitors and performed microarray analysis to compare the global transcriptional program of hEKs and primary foreskin keratinocytes. Transcriptional patterns were largely similar, though gene ontology analysis identified that genes associated with signal transduction and extracellular matrix were upregulated in hEKs. In addition, we evaluated the ability of hEKs to detect and respond to environmental stimuli such as Ca(2+), serum, and culture at the air-liquid interface. When cultivated on dermal constructs formed with collagen gels and human dermal fibroblasts, hEKs survived and proliferated for 3 weeks in engineered tissue constructs. Maintenance at the air-liquid interface induced stratification of surface epithelium, and immunohistochemistry results indicated that markers of differentiation (e.g., keratin 10, involucrin, and filaggrin) were localized to suprabasal layers. Although the overall tissue morphology was significantly different compared with human skin samples, organotypic cultures generated with hEKs and primary foreskin keratinocytes were quite similar, suggesting these cell types respond to this microenvironment in a similar manner. These results represent an important step in characterizing the functional similarity of hEKs to primary epithelia.

The role of mucin-type O-glycans in eukaryotic development

Newly emerging genetic studies have revealed that a subset of the family of glycosyltransferases responsible for the formation of mucin-type O glycans is essential for normal development. As additional genetic, biochemical and physical tools are developed to interrogate the complex structure and surface location of this under-studied class of carbohydrate, no doubt additional roles will be elucidated.

Altered global gene expressions of human placentae subjected to assisted reproductive technology treatments

BACKGROUND

Researchers are more and more concerning the safety of fetus or offspring derived from assisted reproductive technology (ART) treatment. As the placenta is a critical organ that sustains and protects the fetus, we hypothesize that altered global gene expression of the placenta subjected to ART manipulation may reflect changes associated with ART procedures and subsequently causal related to offspring health.

METHODS

Three term placenta samples were obtained from patients undergone in vitro fertilization and embryo transfer due to oviductal factors only. Other three control placentae were from those underwent normal pregnancy. A GeneChip Affymetrix HG-U133 Plus 2.0 Array was utilized to analyze the genes. Using qRT-PCR we certified microarray data from 10 dysregulated genes. Five genes were localized precisely in the placenta as per immunohistochemistry.

RESULTS

Twenty-six differentially expressed genes were identified in the ART-treated placentae: 17 up-regulated; 9 down-regulated. Eighteen of these were classified into six groups according to critical placental function: immune response; transmembrane transport; metabolism; oxidative stress; cell differentiation; and other functions. Genes involved in immune response, such as ERAP2 and STAT4, and those regulating cell differentiations, such as MUC1, were discerned to be differentially expressed. These gene products were expressed in the placental villus tissues, either in the cytoplasm or in the membrane of syncytiotrophoblastic cells.

CONCLUSION

To our knowledge, this is the first study in comparing differentially expressed genes in placentae from patients undergone ART treatment vs. those underwent normal pregnancy. Abnormal profiles of critical placental functioning genes, such as ERAP2, STAT4 and MUC1, may be valuable biomarkers to understand how the placenta affects fetal development and ART-derived offspring's health problems.

Recent insights into cerebral cavernous malformations: a complex jigsaw puzzle under construction

Cerebral cavernous malformations (CCM) are common vascular malformations with an unpredictable risk of hemorrhage, the consequences of which range from headache to stroke or death. Three genes, CCM1, CCM2 and CCM3, have been linked to the disease. The encoded CCM proteins interact with each other within a large protein complex. Within the past 2 years, a plethora of new data has emerged on the signaling pathways in which CCM proteins are involved. CCM proteins regulate diverse aspects of endothelial cell morphogenesis and blood vessel stability such as cell-cell junctions, cell shape and polarity, or cell adhesion to the extracellular matrix. Although fascinating, a global picture is hard to depict because little is known about how these pathways coordinate to orchestrate angiogenesis. Here we present what is known about the structural domain organization of CCM proteins, their association as a ternary complex and their subcellular localization. Numerous CCM partners have been identified using two-hybrid screens, genetic analyses or proteomic studies. We focus on the best-characterized partners and review data on the signaling pathways they regulate as a step towards a better understanding of the etiology of CCM disease.