MUC1 is a receptor for the Salmonella SiiE adhesin that enables apical invasion into enterocytes.

The cellular invasion machinery of the enteric pathogen Salmonella consists of a type III secretion system (T3SS) with injectable virulence factors that induce uptake by macropinocytosis. Salmonella invasion at the apical surface of intestinal epithelial cells is inefficient, presumably because of a glycosylated barrier formed by transmembrane mucins that prevents T3SS contact with host cells. We observed that Salmonella is capable of apical invasion of intestinal epithelial cells that express the transmembrane mucin MUC1. Knockout of MUC1 in HT29-MTX cells or removal of MUC1 sialic acids by neuraminidase treatment reduced Salmonella apical invasion but did not affect lateral invasion that is not hampered by a defensive barrier. A Salmonella deletion strain lacking the SiiE giant adhesin was unable to invade intestinal epithelial cells through MUC1. SiiE-positive Salmonella closely associated with the MUC1 layer at the apical surface, but invaded Salmonella were negative for the adhesin. Our findings uncover that the transmembrane mucin MUC1 is required for Salmonella SiiE-mediated entry of enterocytes via the apical route.

Mucin 1 regulates the hypoxia response in head and neck cancer cells.

Mucin 1 (MUC1) is a transmembrane glycoprotein that contributes to the cellular response in hypoxic conditions in different carcinomas. We investigated the gene expression pattern of MUCs (1, 2, 4, 5AC, 5B, 6, 15, 16, and 19) in isogenic primary (HN4 and HN30) and metastatic (HN12 and HN31) head and neck squamous cell carcinoma (HNSCC) cell lines. MUC1 was significantly up-regulated at the mRNA and protein levels in HN12 and HN31 cells, whereas, other MUCs exhibited diverse expression patterns between HNSCC cell lines. Immunohistochemistry demonstrated that MUC1 was exclusively expressed in cancer cells; however, there was no significant correlation between MUC1 expression and malignancy grading. Inducing hypoxia with CoCl2 significantly increased cell viability, MUC1, hypoxia-inducible factor alpha (HIF-1α), and vascular endothelial growth factor A (VEGF-A) expression in HN12 cells, but not HN31 cells. Interestingly, in hypoxia, cell viability, HIF-1α and VEGF-A expression were significantly reduced in MUC1-knockdown HN12 cells. The current report is the first to demonstrate that MUC1 is required in the regulation of hypoxia-related genes in HNSCC cells. Thus, our results suggest that MUC1 modulates the hypoxic effects in HNSCC cells through HIF-1α regulation.

MUC1-mediated induction of myeloid-derived suppressor cells in patients with acute myeloid leukemia.

Myeloid-derived suppressor cells (MDSCs) play a critical role in promoting immune tolerance and disease growth. The mechanism by which tumor cells evoke the expansion of MDSCs in acute myeloid leukemia (AML) has not been well described. We have demonstrated that patients with AML exhibit increased presence of MDSCs in their peripheral blood, in comparison with normal controls. Cytogenetic studies demonstrated that MDSCs in patients with AML may be derived from leukemic or apparently normal progenitors. Engraftment of C57BL/6 mice with TIB-49 AML led to an expansion of CD11b+ Gr1+ MDSCs in bone marrow and spleen. Coculture of the AML cell lines MOLM-4, THP-1 or primary AML cells with donor peripheral blood mononuclear cells elicited a cell contact-dependent expansion of MDSCs. MDSCs were suppressive of autologous T-cell responses as evidenced by reduced T-cell proliferation and a switch from a Th1 to a Th2 phenotype. We hypothesized that the expansion of MDSCs in AML is accomplished by tumor-derived extracellular vesicles (EVs). Using tracking studies, we demonstrated that AML EVs are taken-up myeloid progenitor cells, resulting in the selective proliferation of MDSCs in comparison with functionally competent antigen-presenting cells. The MUC1 oncoprotein was subsequently identified as the critical driver of EV-mediated MDSC expansion. MUC1 induces increased expression of c-myc in EVs that induces proliferation in the target MDSC population via downstream effects on cell cycle proteins. Moreover, we demonstrate that the microRNA miR34a acts as the regulatory mechanism by which MUC1 drives c-myc expression in AML cells and EVs.

Latest developments in MUC1 immunotherapy.

Currently, there is renewed interest in attempting to recruit the host immune system to eliminate cancers, and within this renewed activity, MUC1 continues to arouse interest. MUC1 has been considered a possible therapeutic target for the past 30 years as it is up-regulated, aberrantly glycosylated and its polarization is lost in many adenocarcinomas. Moreover, MUC1 is expressed by some haematopoietic cancers, including acute myeloid leukaemia and myeloma. Although multiple clinical trials have been initiated and immune responses have been documented, effective clinical benefit worthy of approval for general application has not as yet been achieved. However, this does not appear to have quelled the interest in MUC1 as a therapeutic target, as shown by the increase in the number of MUC1-based clinical trials initiated in 2017 ( Figure 1). As with all translational studies, incorporating new relevant research findings into therapeutic strategy is difficult. Decisions are made to commit to a specific strategy based on the information and data available when the trial is initiated. However, the time required for preclinical studies and early trials can render the founding concept not always appropriate for proceeding to a larger definitive trial. Here, we summarize the attempts made, to date, to bring MUC1 into the world of cancer immunotherapy and discuss how research findings regarding MUC1 structure and function together with expanded knowledge of its interactions with the tumour environment and immune effector cells could lead to improved therapeutic approaches. ppbiost;46/3/659/BST20170400CF1F1BST-2017-0400CF1Figure 1.Number of MUC1-targeted trials initiated each year.

Muc1 knockout potentiates murine lung carcinogenesis involving an epiregulin-mediated EGFR activation feedback loop.

Mucin 1 (MUC1) is a tumor antigen that is aberrantly overexpressed in various cancers, including lung cancer. Our previous in vitro studies showed that MUC1 facilitates carcinogen-induced EGFR activation and transformation in human lung bronchial epithelial cells (HBECs), which along with other reports suggests an oncogenic property for MUC1 in lung cancer. However, direct evidence for the role of MUC1 in lung carcinogenesis is lacking. In this study, we used the 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced A/J mouse lung tumor model to investigate the effect of whole-body Muc1 knockout (KO) on carcinogen-induced lung carcinogenesis. Surprisingly, lung tumor multiplicity was significantly increased in Muc1 KO compared to wild-type (WT) mice. The EGFR/AKT pathway was unexpectedly activated, and expression of the EGFR ligand epiregulin (EREG) was increased in the lung tissues of the Muc1 KO compared to the WT mice. EREG stimulated proliferation and protected against cigarette smoke extract (CSE)-induced cytotoxicity in in vitro cultured human bronchial epithelial cells. Additionally, we determined that MUC1 was expressed in human fibroblast cell lines where it suppressed CSE-induced EREG production. Further, suppression of MUC1 cellular activity with GO-201 enhanced EREG production in lung cancer cells, which in turn protected cancer cells from GO-201-induced cell death. Moreover, an inverse association between MUC1 and EREG was detected in human lung cancer, and EREG expression was inversely associated with patient survival. Together, these results support a promiscuous role of MUC1 in lung cancer development that may be related to cell-type specific functions of MUC1 in the tumor microenvironment, and MUC1 deficiency in fibroblasts and malignant cells results in increased EREG production that activates the EGFR pathway for lung carcinogenesis.

Mucin-1 Increases Renal TRPV5 Activity In Vitro, and Urinary Level Associates with Calcium Nephrolithiasis in Patients.

Hypercalciuria is a major risk factor for nephrolithiasis. We previously reported that Uromodulin (UMOD) protects against nephrolithiasis by upregulating the renal calcium channel TRPV5. This channel is crucial for calcium reabsorption in the distal convoluted tubule (DCT). Recently, mutations in the gene encoding Mucin-1 (MUC1) were found to cause autosomal dominant tubulointerstitial kidney disease, the same disease caused by UMOD mutations. Because of the similarities between UMOD and MUC1 regarding associated disease phenotype, protein structure, and function as a cellular barrier, we examined whether urinary MUC1 also enhances TRPV5 channel activity and protects against nephrolithiasis. We established a semiquantitative assay for detecting MUC1 in human urine and found that, compared with controls (n=12), patients (n=12) with hypercalciuric nephrolithiasis had significantly decreased levels of urinary MUC1. Immunofluorescence showed MUC1 in the thick ascending limb, DCT, and collecting duct. Applying whole-cell patch-clamp recording of HEK cells, we found that wild-type but not disease mutant MUC1 increased TRPV5 activity by impairing dynamin-2- and caveolin-1-mediated endocytosis of TRPV5. Coimmunoprecipitation confirmed a physical interaction between TRPV5 and MUC1. However, MUC1 did not increase the activity of N-glycan-deficient TRPV5. MUC1 is characterized by variable number tandem repeats (VNTRs) that bind the lectin galectin-3; galectin-3 siRNA but not galectin-1 siRNA prevented MUC1-induced upregulation of TRPV5 activity. Additionally, MUC1 lacking VNTRs did not increase TRPV5 activity. Our results suggest that MUC1 forms a lattice with the N-glycan of TRPV5 via galectin-3, which impairs TRPV5 endocytosis and increases urinary calcium reabsorption.

Membrane-Tethered MUC1 Mucin Counter-Regulates the Phagocytic Activity of Macrophages.

MUC1 (MUC in human; Muc in animals) is a transmembrane mucin glycoprotein expressed in mucosal epithelial cells and hematopoietic cells. MUC1 is involved in the resolution of inflammation during airway Pseudomonas aeruginosa (Pa) infection by suppressing Toll-like receptor signaling in airway epithelial cells. Although alveolar macrophages are recognized as critical mediators of cell-mediated immunity against microorganisms inhaled into the airways, the role of MUC1 in regulating their response is unknown. The aims of this study were to determine whether macrophages express MUC1, and, if so, whether MUC1 expression might be associated with macrophage M0/M1/M2 differentiation or phagocytic activity. Human and mouse MUC1/Muc1 expression was drastically up-regulated in classically activated (M1) macrophages compared with nonactivated (M0) and alternatively activated (M2) macrophages. M1 polarization and Pa stimulation each increased MUC1 ectodomain shedding from the macrophage surface in a TNF-α-converting enzyme-dependent manner. MUC1/Muc1 deficiency in M0 macrophages increased adhesion and phagocytosis of Pa and Escherichia coli compared with MUC1/Muc1-expressing cells, and attenuation of phagocytosis by MUC1 was augmented after polarization into M1 macrophages compared with M0 macrophages. Finally, MUC1/Muc1 deficiency in macrophages increased reactive oxygen species production and TNF-α release in response to Pa compared with MUC1/Muc1-sufficient cells. These results indicate that MUC1/Muc1 expression by macrophages is predominantly in the M1 subtype, and that MUC1/Muc1 expression in these cells decreases their phagocytic activity in an antiinflammatory manner.

MUC1 (CD227): a multi-tasked molecule.

Mucin 1 (MUC1 [CD227]) is a high-molecular weight (>400 kDa), type I membrane-tethered glycoprotein that is expressed on epithelial cells and extends far above the glycocalyx. MUC1 is overexpressed and aberrantly glycosylated in adenocarcinomas and in hematological malignancies. As a result, MUC1 has been a target for tumor immunotherapeutic studies in mice and in humans. MUC1 has been shown to have anti-adhesive and immunosuppressive properties, protects against infections, and is involved in the oncogenic process as well as in cell signaling. In addition, MUC1 plays a key role in the reproductive tract, in the immune system (affecting dendritic cells, monocytes, T cells, and B cells), and in chronic inflammatory diseases. Evidence for all of these roles for MUC1 is discussed herein and demonstrates that MUC1 is truly a multitasked molecule.

Galectin-3 binds to MUC1-N-terminal domain and triggers recruitment of ß-catenin in MUC1-expressing mouse 3T3 cells.

BACKGROUND: Galectin-3 is expressed in a variety of tumors and its expression level is related with tumor progression. Aberrant expression of MUC1 in various tumors is also associated with a poor prognosis. It has been reported that MUC1 is a natural ligand of galectin-3. METHODS: A stable MUC1 transfectant was produced by introducing MUC1 cDNA into mouse 3T3 fibroblasts (MUC1/3T3 cells). MUC1 was prepared from MUC1/3T3 cells; MUC1-N-terminal domain (MUC1-ND) and -C-terminal domain (MUC1-CD) were separated by CsCl ultracentrifugation, and then the galectin-3-binding domain was determined by co-immuniprecipitation assay. After ligation of galectin-3 to 3T3/MUC1 cells, MUC1-CD was immunoprecipitated from the cell lysate. The immunoprecipitate was subjected to SDS-PAGE and Western blotting, followed by detection of co-immunoprecipitated ß-catenin. RESULTS: Galectin-3 binds to the N-terminal domain of MUC1 but not to the C-terminal one. Galectin-3 present on the cell surface increased with the expression of MUC1 and is colocalized with MUC1. It should be noted that ß-catenin was detected in the immunoprecipitate with anti-MUC1-CD Ab from a lysate of galectin-3-treated 3T3/MUC1 cells. CONCLUSIONS: Galectin-3 binds to MUC1-ND and triggers MUC1-mediated signaling in 3T3/MUC1 cells, leading to recruitment of ß-catenin to MUC1-CD. GENERAL SIGNIFICANCE: This signaling may be another MUC1-mediated pathway and function in parallel with a growth factor-dependent MUC1-mediated pathway.

The MUC1 oncomucin regulates pancreatic cancer cell biological properties and chemoresistance. Implication of p42-44 MAPK, Akt, Bcl-2 and MMP13 pathways.

MUC1 is an oncogenic mucin overexpressed in several epithelial cancers, including pancreatic ductal adenocarcinoma, and is considered as a potent target for cancer therapy. To this aim, we undertook to study MUC1 biological effects on pancreatic cancer cells and identify pathways mediating these effects. Our in vitro experiments indicate that inhibiting MUC1 expression decreases cell proliferation, cell migration and invasion, cell survival and increases cell apoptosis. Moreover, lack of MUC1 in these cells profoundly altered their sensitivity to gemcitabine and 5-Fluorouracil chemotherapeutic drugs. In vivo MUC1-KD cell xenografts in SCID mice grew slower. Altogether, we show that MUC1 oncogenic mucin alters proliferation, migration, and invasion properties of pancreatic cancer cells and that these effects are mediated by p42-44 MAPK, Akt, Bcl-2 and MMP13 pathways.

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.

The adenocarcinoma cell surface mucin receptor for alpha-fetoprotein: is the same receptor present on circulating monocytes and macrophages? A commentary.

The mucin family of proteins is largely expressed on sedentary epithelial cells lining the gastrointestinal, pulmonary, and reproductive tracts and their associated organs and malignant tumors. It is less well-known that mucins are also expressed on circulatory cells of the immune and inflammatory systems, such as monocytes, macrophages, leukemic, and lymphoma cells. The epithelial mucins function in (a) protection and lubrication of mucosal linings, (b) cell adhesion and cell-to-cell contact, (c) cell migration and metastasis, and (d) signal transduction. It would be logical to presume that mucins expressed on circulating mononuclear cells could perform similar functions. Recently, it was proposed that the alpha-fetoprotein (AFP) receptor, known to be present on solid epithelial-derived malignant tumor cells, can be identified as a mucin glycoprotein. Interestingly, it was also reported that AFP binds to a receptor on circulating cells and sedentary tumor cells of lymphoreticular origin, especially monocytes associated with lymphomas and leukemias. The primary objective of the present commentary is to present literature-based evidence that some of the cell surface mucins on sedentary epithelial tumor cells and certain mucins expressed on circulating monocytes/macrophages are identical to the AFP receptor. The secondary objective is to discuss the role of AFP and its derived peptides in the growth suppression of adenocarcinomas and lymphomas using the AFP-mucin receptor concept as a key to the mechanism of tumor growth inhibition.

MUC1 oncoprotein activates the IkappaB kinase beta complex and constitutive NF-kappaB signalling.

Nuclear factor-kappaB (NF-kappaB) is constitutively activated in diverse human malignancies by mechanisms that are not understood. The MUC1 oncoprotein is aberrantly overexpressed by most human carcinomas and, similarly to NF-kappaB, blocks apoptosis and induces transformation. This study demonstrates that overexpression of MUC1 in human carcinoma cells is associated with constitutive activation of NF-kappaB p65. We show that MUC1 interacts with the high-molecular-weight IkappaB kinase (IKK) complex in vivo and that the MUC1 cytoplasmic domain binds directly to IKKbeta and IKKgamma. Interaction of MUC1 with both IKKbeta and IKKgamma is necessary for IKKbeta activation, resulting in phosphorylation and degradation of IkappaBalpha. Studies in non-malignant epithelial cells show that MUC1 is recruited to the TNF-R1 complex and interacts with IKKbeta-IKKgamma in response to TNFalpha stimulation. TNFalpha-induced recruitment of MUC1 is dependent on TRADD and TRAF2, but not the death-domain kinase RIP1. In addition, MUC1-mediated activation of IKKbeta is dependent on TAK1 and TAB2. These findings indicate that MUC1 is important for physiological activation of IKKbeta and that overexpression of MUC1, as found in human cancers, confers sustained induction of the IKKbeta-NF-kappaB p65 pathway.

Mucin 1 (MUC1) signalling contributes to increase the resistance to cell death in human bronchial epithelial cells exposed to nickel acetate.

We have previously reported that nickel acetate (Ni(2+)), a well-known human carcinogenic agents, differentially affected apoptosis in two different airway epithelial cell lines derived from the human respiratory tract (A549 and Beas-2B, respectively), suggesting a potential involvement of epidermal growth factor receptor (EGFR)/Neu receptors in mediating this effect. Since ErbBs are closely associated to Mucin 1 (MUC1), a glycoprotein component of airway mucus that is overexpressed in lung tumors, we have investigated the role of this signaling system in the survival response of airway epithelial cells against Ni(2+)-induced cell death. We found that A549 cells exposed to Ni(2+) do not show any significant increase of MUC1 levels. Conversely, Beas-2B cells exposed to equivalent concentrations of Ni(2+) showed increased expression of MUC1 levels and this correlated with increased phosphorylation of both EGFR and of the extracellular-regulated kinase 1/2 (ERK1/2) and increase resistance to apoptosis, as indicated by cell viability assessments and DNA damage. Interestingly, suppression of MUC1 by small interfering RNA inhibited the EGFR activation in Beas-2B cells, leading to a significant decrease of survival and enhancement of DNA fragmentation and cleaved Caspase-3 expression. These results strongly suggest a role for MUC1 in Ni(2+)-induced neoplastic transformation, which likely involves the activation of the EGFR-mediated cell survival pathway, highlighting new avenues in the molecular approach to lung cancer prevention.

Higher susceptibility to experimental autoimmune encephalomyelitis in Muc1-deficient mice is associated with increased Th1/Th17 responses.

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system in which dendritic cells (DC) play an important role in the development of inflammatory responses. Recently it has been shown that Muc1, a membrane tethered glycoprotein, has an ability to suppress inflammatory responses in cultured DC. The objective of this study was to investigate the possible involvement of Muc1 in the development of MS using experimental autoimmune encephalomyelitis (EAE) in mice, a widely used animal model of MS. Our results showed that: (1) Muc1(-/-) mice developed greater EAE severity compared with wild type (wt) mice, which correlated with increased numbers of Th1 and Th17 cells infiltrating into the CNS; (2) upon stimulation, splenic DC from Muc1(-/-) mice produced greater amounts of IL-1ß, IL-6, and IL-12 but less amounts of IL-10 compared with those from wt mice; and (3) the ability of splenic DC to differentiate antigen-specific CD4+ T cells into Th1 and Th17 cells was greater in Muc1(-/-) mice compared with wt mice. We conclude that Muc1 plays an anti-inflammatory role in EAE. This is the first report demonstrating the possible involvement of Muc1 in the development of MS and might provide a potential target for immunotherapy.

Human MUC1 oncoprotein regulates p53-responsive gene transcription in the genotoxic stress response.

The MUC1 oncoprotein is aberrantly overexpressed by most human carcinomas. The present work demonstrates that MUC1 associates with the p53 tumor suppressor, and that this interaction is increased by genotoxic stress. The MUC1 cytoplasmic domain binds directly to p53 regulatory domain. Chromatin immunoprecipitation assays demonstrate that MUC1 coprecipitates with p53 on the p53-responsive elements of the p21 gene promoter and coactivates p21 gene transcription. Conversely, MUC1 attenuates activation of Bax transcription. In concert with these results, MUC1 promotes selection of the p53-dependent growth arrest response and suppresses the p53-dependent apoptotic response to DNA damage. These findings indicate that MUC1 regulates p53-responsive genes and thereby cell fate in the genotoxic stress response.

Antiinflammatory role of MUC1 mucin during infection with nontypeable Haemophilus influenzae.

MUC1 (or Muc1 in nonhuman species) is a membrane-tethered mucin expressed on the apical surface of mucosal epithelia (including those of the airways) that suppresses Toll-like receptor (TLR) signaling. We sought to determine whether the anti-inflammatory effect of MUC1 is operative during infection with nontypeable Haemophilus influenzae (NTHi), and if so, which TLR pathway was affected. Our results showed that: (1) a lysate of NTHi increased the early release of IL-8 and later production of MUC1 protein by A549 cells in dose-dependent and time-dependent manners, compared with vehicle control; (2) both effects were attenuated after transfection of the cells with a TLR2-targeting small interfering (si) RNA, compared with a control siRNA; (3) the NTHi-induced release of IL-8 was suppressed by an overexpression of MUC1, and was enhanced by the knockdown of MUC1; (4) the TNF-α released after treatment with NTHi was sufficient to up-regulate MUC1, which was completely inhibited by pretreatment with a soluble TNF-α receptor; and (5) primary murine tracheal surface epithelial (MTSE) cells from Muc1 knockout mice exhibited an increased in vitro production of NTHi-stimulated keratinocyte chemoattractant compared with MTSE cells from Muc1-expressing animals. These results suggest a hypothetical feedback loop model whereby NTHi activates TLRs (mainly TLR2) in airway epithelial cells, leading to the increased production of TNF-α and IL-8, which subsequently up-regulate the expression of MUC1, resulting in suppressed TLR signaling and decreased production of IL-8. This report is the first, to the best of our knowledge, demonstrating that the inflammatory response in airway epithelial cells during infection with NTHi is controlled by MUC1 mucin, mainly through the suppression of TLR2 signaling.

MUC1-induced alterations in a lipid metabolic gene network predict response of human breast cancers to tamoxifen treatment.

The mucin 1 (MUC1) oncoprotein is aberrantly overexpressed in human breast cancers. Although MUC1 modulates the activity of estrogen receptor alpha (ER), there is no information regarding the effects of MUC1 on global gene expression patterns and the potential role of MUC1-induced genes in predicting outcome for breast cancer patients. We have developed an experimental model of MUC1-induced transformation that has identified the activation of genes involved in cholesterol and fatty acid metabolism. A 38-gene set of experimentally derived MUC1-induced genes associated with lipid metabolism was applied to the analysis of ER(+) breast cancer patients treated with tamoxifen. The results obtained from 2 independent databases demonstrate that patients overexpressing MUC1 and the lipid metabolic pathways are at significantly higher risk for death and recurrence/distant metastasis. By contrast, these genes were not predictive in untreated patients. Furthermore, a positive correlation was found between expression of the 38-gene set and the ER signaling pathway. These findings indicate that (i) MUC1 regulates cholesterol and fatty acid metabolism, and (ii) activation of these pathways in ER(+) breast cancers predicts failure to tamoxifen treatment.

Transmembrane Mucin 1 Blocks Fluorescein Ingress to Corneal Epithelium.

Purpose: To determine the role of transmembrane mucins in blocking fluorescein ingress to the corneal epithelium and its deficiency in contributing to corneal fluorescein punctate staining. Methods: A dry eye model was established by extirpating lacrimal and Harderian glands in rabbits to correlate the expression of mucins with fluorescein-stained areas on the corneal button using immunofluorescence. Expression of transmembrane mucins was promoted in human corneal epithelial cells (HCECs) by culturing with the mucin-promoting medium (MPM) or diquafosol treatment. Conversely, the expression of mucins was downregulated by knockdown with short hairpin RNA. The role of mucin1 extracellular domain in fluorescein ingress was further verified by overexpression of N-terminally truncated mucin1 in HCECs. Results: In the rabbit dry eye model, the expression level of mucin1 was significantly decreased in superficial corneal epithelial cells where fluorescein punctate staining was observed. Upregulation of mucin1 and mucin16 in HCECs promoted by MPM or by diquafosol treatment impeded intracellular fluorescein ingress. Downregulation of mucin1 and mucin16 enhanced fluorescence ingress in HCECs after fluorescein staining. Overexpression of truncated mucin1 did not alter the fluorescein intensity of fluorescein-stained HCECs, supporting the notion that the ability of mucin1 to block fluorescein ingress was primarily mediated by its extracellular domain. Minimal inherent expression of mucin16 in the rabbit cornea limited the validation of its role in blocking fluorescein ingress in vivo. Conclusion: Transmembrane mucin1 blocks fluorescein ingress in the corneal epithelium, explaining how fluorescein staining is positive when the level of transmembrane mucins is disturbed in dry eyes.

MUC1 induces metastasis in esophageal squamous cell carcinoma by upregulating matrix metalloproteinase 13.

Esophagus squamous cell carcinoma (ESCC) is one of the most deadly malignances because of its high frequency of metastasis. Given the associations of MUC1 with ESCC and tumor metastasis, we explored a potential role of MUC1 in ESCC metastasis. Among 40 ESCC and 20 paired normal tissue specimens examined, we found a significant increase of MUC1 expression in ESCC and more importantly, that expression of MUC1 and MMP13 are strongly correlated in patients who had lymph node metastasis. Studies with cell models indicated that overexpression of MUC1 upregulates the expression of MMP13, leading to increased cell migration. In support of a mode of transcriptional regulation, promoter analysis revealed that MUC1 stimulates MMP13 expression through the Runx-2-binding site. The link of MUC1 to cell motility was further confirmed by the finding that depletion of MUC1 resulted in reduced expression of MMP13 and cell migration, invasion and adhesion. Moreover, the loss of cell metastatic potential was rescued by overexpression of MMP13 completely. Collectively, our findings indicate that MUC1 contributes to ESCC metastasis by stimulating MMP13 expression, suggesting MUC1 as a novel diagnostic biomarker and therapeutic target in ESCC.