Overexpression of MUC1 enhances proangiogenic activity of non-small-cell lung cancer cells through activation of Akt and extracellular signal-regulated kinase pathways. Lung. 2011;189:453-460. [PMID: 21959954 DOI: 10.1007/s00408-011-9327-y]

The multifaceted role of MUC1 in tumor therapy resistance

Tumor therapeutic resistances are frequently linked to the recurrence and poor prognosis of cancers and have been a key bottleneck in clinical tumor treatment. Mucin1 (MUC1), a heterodimeric transmembrane glycoprotein, exhibits abnormally overexpression in a variety of human tumors and has been confirmed to be related to the formation of therapeutic resistance. In this review, the multifaceted roles of MUC1 in tumor therapy resistance are summarized from aspects of pan-cancer principles shared among therapies and individual mechanisms dependent on different therapies. Concretely, the common mechanisms of therapy resistance across cancers include interfering with gene expression, promoting genome instability, modifying tumor microenvironment, enhancing cancer heterogeneity and stemness, and activating evasion and metastasis. Moreover, the individual mechanisms of therapy resistance in chemotherapy, radiotherapy, and biotherapy are introduced. Last but not least, MUC1-involved therapy resistance in different types of cancers and MUC1-related clinical trials are summarized.

EGFR-Dependent Extracellular Matrix Protein Interactions Might Light a Candle in Cell Behavior of Non-Small Cell Lung Cancer

Lung cancer remains the leading cause of cancer-related death and is associated with a poor prognosis. Lung cancer is divided into 2 main types: the major in incidence is non-small cell lung cancer (NSCLC) and the minor is small cell lung cancer (SCLC). Although NSCLC progression depends on driver mutations, it is also affected by the extracellular matrix (ECM) interactions that activate their corresponding signaling molecules in concert with integrins and matrix metalloproteinases (MMPs). These signaling molecules include cytoplasmic kinases, small GTPases, adapter proteins, and receptor tyrosine kinases (RTKs), particularly the epidermal growth factor receptor (EGFR). In NSCLC, the interplay between ECM and EGFR regulates ECM stiffness, angiogenesis, survival, adhesion, migration, and metastasis. Furthermore, some tumor-promoting ECM components (e.g., glycoproteins and proteoglycans) enhance activation of EGFR and loss of PTEN. On the other hand, other tumor-suppressing glycoproteins and -proteoglycans can inhibit EGFR activation, suppressing cell invasion and migration. Therefore, deciphering the molecular mechanisms underlying EGFR and ECM interactions might provide a better understanding of disease pathobiology and aid in developing therapeutic strategies. This review critically discusses the crosstalk between EGFR and ECM affecting cell behavior of NSCLC, as well as the involvement of ECM components in developing resistance to EGFR inhibition.

Crosstalk between MUC1 and VEGF in angiogenesis and metastasis: a review highlighting roles of the MUC1 with an emphasis on metastatic and angiogenic signaling

VEGF and its receptor family (VEGFR) members have unique signaling transduction system that play significant roles in most pathological processes, such as angiogenesis in tumor growth and metastasis. VEGF-VEGFR complex is a highly specific mitogen for endothelial cells and any de-regulation of the angiogenic balance implicates directly in endothelial cell proliferation and migration. Moreover, it has been shown that overexpressing Mucin 1 (MUC1) on the surface of many tumor cells resulting in upregulation of numerous signaling transduction cascades, such as growth and survival signaling pathways related to RTKs, loss of cell-cell and cell-matrix adhesion, and EMT. It promotes gene transcription of pro-angiogenic proteins such as HIF-1α during periods of oxygen scarcity (hypoxia) to enhance tumor growth and angiogenesis stimulation. In contrast, the cytoplasmic domain of MUC1 (MUC1-C) inhibits apoptosis, which in turn, impresses upon cell fate. Besides, it has been established that reduction in VEGF expression level correlated with silencing MUC1-C level indicating the anti-angiogenic effect of MUC1 downregulation. This review enumerates the role of MUC1-C oncoprotein and VEGF in angiogenesis and metastasis and describes several signaling pathways by which MUC1-C would mediate the pro-angiogenic activities of cancer cells.

The role of mucin 1 in respiratory diseases

Recent evidence has demonstrated that mucin 1 (MUC1) is involved in many pathological processes that occur in the lung. MUC1 is a transmembrane protein mainly expressed by epithelial and hematopoietic cells. It has a receptor-like structure, which can sense the external environment and activate intracellular signal transduction pathways through its cytoplasmic domain. The extracellular domain of MUC1 can be released to the external environment, thus acting as a decoy barrier to mucosal pathogens, as well as serving as a serum biomarker for the diagnosis and prognosis of several respiratory diseases such as lung cancer and interstitial lung diseases. Furthermore, bioactivated MUC1-cytoplasmic tail (CT) has been shown to act as an anti-inflammatory molecule in several airway infections and mediates the expression of anti-inflammatory genes in lung diseases such as chronic rhinosinusitis, chronic obstructive pulmonary disease and severe asthma. Bioactivated MUC1-CT has also been reported to interact with several effectors linked to cellular transformation, contributing to the progression of respiratory diseases such as lung cancer and pulmonary fibrosis. In this review, we summarise the current knowledge of MUC1 as a promising biomarker and drug target for lung disease.

Comprehensive analysis of the mechanism and treatment significance of Mucins in lung cancer

Aberrant expression of mucin proteins has played a complex and essential role in cancer development and metastasis. Members of the mucin family have been intimately implicated in lung cancer progression, metastasis, survival and chemo-resistance. During the progression of lung cancer, mucin proteins have involved all of the procession of lung cancer, which is interacted with many receptor tyrosine kinases signal pathways and mediated cell signals for tumor cell growth and survival. Mucins thus have been considerable as the indicator of negative prognosis and desirable therapeutic targets of lung cancers. In this review, we comprehensively analyzed the role of each member of the mucin family in lung cancer by combining open-accessed database analysis and assembling cutting-edge information about these molecules.

Endomucin inhibits VEGF-induced endothelial cell migration, growth, and morphogenesis by modulating VEGFR2 signaling

Angiogenesis is central to both normal and pathologic processes. Endothelial cells (ECs) express O-glycoproteins that are believed to play important roles in vascular development and stability. Endomucin-1 (EMCN) is a type I O-glycosylated, sialic-rich glycoprotein, specifically expressed by venous and capillary endothelium. Evidence has pointed to a potential role for EMCN in angiogenesis but it had not been directly investigated. In this study, we examined the role of EMCN in angiogenesis by modulating EMCN levels both in vivo and in vitro. Reduction of EMCN in vivo led to the impairment of angiogenesis during normal retinal development in vivo. To determine the cellular basis of this inhibition, gain- and loss-of-function studies were performed in human retinal EC (HREC) in vitro by EMCN over-expression using adenovirus or EMCN gene knockdown by siRNA. We show that EMCN knockdown reduced migration, inhibited cell growth without compromising cell survival, and suppressed tube morphogenesis of ECs, whereas over-expression of EMCN led to increased migration, proliferation and tube formation. Furthermore, knockdown of EMCN suppressed VEGF-induced signaling as measured by decreased phospho-VEGFR2, phospho-ERK1/2 and phospho-p38-MAPK levels. These results suggest a novel role for EMCN as a potent regulator of angiogenesis and point to its potential as a new therapeutic target for angiogenesis-related diseases.

MUC1: The First Respiratory Mucin with an Anti-Inflammatory Function

MUC1 is a membrane-bound mucin expressed on the apical surfaces of most mucosal epithelial cells. In normal lung epithelia, MUC1 is a binding site for Pseudomonas aeruginosa, an opportunistic human pathogen of great clinical importance. It has now been established that MUC1 also serves an anti-inflammatory role in the airways that is initiated late in the course of a bacterial infection and is mediated through inhibition of Toll-like receptor (TLR) signaling. MUC1 expression was initially shown to interfere with TLR5 signaling in response to P. aeruginosa flagellin, but has since been extended to other TLRs. These new findings point to an immunomodulatory role for MUC1 during P. aeruginosa lung infection, particularly during the resolution phase of inflammation. This review briefly summarizes the recent characterization of MUC1’s anti-inflammatory properties in both the respiratory tract and extrapulmonary tissues.

Transmembrane Mucins: Signaling Receptors at the Intersection of Inflammation and Cancer

Mucosal surfaces line our body cavities and provide the interaction surface between commensal and pathogenic microbiota and the host. The barrier function of the mucosal layer is largely maintained by gel-forming mucin proteins that are secreted by goblet cells. In addition, mucosal epithelial cells express cell-bound mucins that have both barrier and signaling functions. The family of transmembrane mucins consists of diverse members that share a few characteristics. The highly glycosylated extracellular mucin domains inhibit invasion by pathogenic bacteria and can form a tight mesh structure that protects cells in harmful conditions. The intracellular tails of transmembrane mucins can be phosphorylated and connect to signaling pathways that regulate inflammation, cell-cell interactions, differentiation, and apoptosis. Transmembrane mucins play important roles in preventing infection at mucosal surfaces, but are also renowned for their contributions to the development, progression, and metastasis of adenocarcinomas. In general, transmembrane mucins seem to have evolved to monitor and repair damaged epithelia, but these functions can be highjacked by cancer cells to yield a survival advantage. This review presents an overview of the current knowledge of the functions of transmembrane mucins in inflammatory processes and carcinogenesis in order to better understand the diverse functions of these multifunctional proteins.

Chinese herbal medicine Fuzheng Kang-Ai decoction sensitized the effect of gefitinib on inhibition of human lung cancer cells through inactivating PI3-K/Akt -mediated suppressing MUC1 expression

ETHNOPHARMACOLOGICAL RELEVANCE

Chinese herbal medicine (CHM) Fuzheng Kang-Ai (FZKA for short) decoction has been used as adjuvant treatment strategies in lung cancer patients for decades. However, the molecular mechanism underlying the therapeutic potential especially in sensitizing the effect of EGFR-TKI gefitinib has not been well elucidated.

MATERIALS AND METHODS

Cell viability was detected by MTT assay. Cell cycle distribution was detected by flow cytometry. Western blot were used to examine phosphorylation and protein levels of Akt, p65, p50 and MUC1. The mRNA level of MUC1 was measured by qRT-PCR. Transient transfection experiments were used to overexpression of Akt, p65 and MUC1. Tumor xenograft and bioluminescent imaging experiments were carried out to confirm the in vitro findings.

RESULTS

Cell viability was inhibited by FZKA treatment and showed more significant when treated with FZKA and gefitinib in combine in lung cancer cells. FZKA induced the cell arrest at G0/G1 phase. Mechanistically, we showed that the phosphorylation of Akt, protein expressions of p65 and MUC1 were suppressed by FZKA and even more responses were observed in the FZKA and gefitinib combining. Overexpressed Akt overcame the effect of FZKA on p65 protein, and exogenously expressed p65 resisted the inhibitory effect of MUC1 protein expression by FZKA. On the contrary, while overexpressed MUC1 had no effect on p65 expression, it feedback increased phosphorylation of Akt, and more importantly, reversed the cell growth inhibition affected by FZKA. In line with the above, our results confirmed the synergistic effects of FZKA and gefitinib combination on tumor growth, the phosphorylation of Akt, and protein expression of p65 and MUC1 in vivo.

CONCLUSION

This study shows that FZKA decoction inhibits the growth of NSCLC cells through Akt-mediated inhibition of p65, followed by reducing the expression of MUC1. More importantly, there is a synergistic effect of FZKA decoction and gefitinib combination with greater suppression. The positive feedback regulatory loop of MUC1 to Akt signaling pathway further added the important role of MUC1 in mediating the overall responses of FZKA decoction in this process. The in vitro and in vivo study provides an additional and a novel mechanism by which the FZKA decoction enhances the growth inhibition of gefitinib in gefitinib-resistant NSCLC cells.

Mucin-1 correlates with survival, smoking status, and growth patterns in lung adenocarcinoma

Mucin-1 (MUC1) affects cancer progression in lung adenocarcinoma, and its aberrant expression pattern has been correlated with poor tumor differentiation and impaired prognosis. In this study, the immunohistochemical expression of MUC1 and Mucin-4 (MUC4) was analyzed in a series of 106 surgically operated stage I-IV pulmonary adenocarcinomas. MUC1 immunohistochemistry was evaluated according to the Nagai classification, and the immunohistochemical profile of the tumors was correlated with detailed clinical and histological data. The effect of cigarette smoke on MUC1 expression in lung cancer cell lines was examined using real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) and immunoelectron microscopy (IEM). In contrast to the normal apical localization of MUC1, a basolateral and cytoplasmic (depolarized) MUC1 expression pattern was frequently encountered in the high-grade subtypes, i.e., solid predominant adenocarcinoma and the cribriform variant of acinar predominant adenocarcinoma (p < 0.001), and was rarely observed in tumors containing a non-predominant lepidic component (p < 0.001). Furthermore, the altered staining pattern of MUC1 correlated with stage (p = 0.002), reduced overall survival (p = 0.031), and was associated with smoking (p < 0.001). When H1650 adenocarcinoma cells were exposed to cigarette smoke and analyzed by RT-qPCR and IEM, the levels of the MUC1 transcript and protein were elevated (p = 0.042). In conclusion, MUC1 participates in the pathogenesis of lung adenocarcinoma and associates with smoking both in vitro and in vivo. In lung adenocarcinoma, depolarized MUC1 protein expression correlated with histological growth patterns, stage, and patient outcome.

MUC1-C Stabilizes MCL-1 in the Oxidative Stress Response of Triple-Negative Breast Cancer Cells to BCL-2 Inhibitors

Aberrant expression of myeloid cell leukemia-1 (MCL-1) is a major cause of drug resistance in triple-negative breast cancer (TNBC) cells. Mucin 1 (MUC1) is a heterodimeric oncoprotein that is aberrantly overexpressed in most TNBC. The present studies show that targeting the oncogenic MUC1 C-terminal subunit (MUC1-C) in TNBC cells with silencing or pharmacologic inhibition with GO-203 is associated with downregulation of MCL-1 levels. Targeting MUC1-C suppresses the MEK → ERK and PI3K → AKT pathways, and in turn destabilizes MCL-1. The small molecules ABT-737 and ABT-263 target BCL-2, BCL-XL and BCL-w, but not MCL-1. We show that treatment with ABT-737 increases reactive oxygen species and thereby MUC1-C expression. In this way, MUC1-C is upregulated in TNBC cells resistant to ABT-737 or ABT-263. We also demonstrate that MUC1-C is necessary for the resistance-associated increases in MCL-1 levels. Significantly, combining GO-203 with ABT-737 is synergistic in inhibiting survival of parental and drug resistant TNBC cells. These findings indicate that targeting MUC1-C is a potential strategy for reversing MCL-1-mediated resistance in TNBC.

Reduced miR-126 expression facilitates angiogenesis of gastric cancer through its regulation on VEGF-A

miR-126 is an endothelial-specific microRNA essential for governing vascular integrity and angiogenesis. Its role in tumor angiogenesis of gastric cancer (GC) is unclear. This study aimed at determining the role of miR-126 in GC angiogenesis. Down-regulation of miR-126 was found to inversely correlate with an increased microvessel density (MVD) and vascular endothelial growth factor A (VEGF-A) expression in gastric cancer tissues. Bioinformatics analysis and luciferase reporter assay revealed that miR-126 directly targeted the 3′-untranslated region (3′-UTR) of VEGF-A mRNA. In addition, the restoration of miR-126 expression by lentivirus-miR-126 (Lenti-miR-126) transfection obviously reduced the expression of VEGF-A and the activition of its downstream genes, Akt, mTOR and Erk1/2 in gastric cancer cell lines SGC-7901, MKN-28 and MKN-45. In contrast, the down-regulation of miR-126 expression by lentivirus-anti-miR-126 (Lenti-anti-miR-126) transfection obviously up-regulated the expression of VEGF-A and its downstream signaling pathways. In vivo xenograft mice model experiments clarified the down-regulation of VEGF-A and MVD as well as inhibition of tumor growth by up-regulation of miR-126. Overall, the results from our study suggested that miR-126 could suppress tumor growth and tumor angiogenesis of GC through VEGF-A signaling, and it is a novel potential therapeutic target for GC.

β2-AR signaling controls trastuzumab resistance-dependent pathway

Currently, trastuzumab resistance is a major clinical problem in the treatment of Her2-overexpressing breast cancer. The underlying molecular mechanisms are not fully understood. Our previous study demonstrates that β2-adrenergic receptor (β2-AR) and Her2 comprise a positive feedback loop in human breast cancer cells and that crosstalk between Her2 and β2-AR affects the bio-behaviors of breast cancer cells, suggesting that the β2-AR activation may be involved in trastuzumab resistance. In this study, we show that the expression of β2-AR, which mediates most catecholamine-induced effects, negatively correlates with trastuzumab response in the patients with Her2-overexpressing breast cancer. Catecholamines potently antagonize the anti-proliferative effects of trastuzumab both in vitro and in vivo. Catecholamine stimulation upregulates the expression of miR-21 and MUC-1 by activating Her2 and STAT3, leading to deficiency of phosphatase and tensin homolog and activation of phosphatidylinositol-3-kinase (PI3K) and Akt. Through inhibition of miR-199a/b-3p, catecholamines induce the mammalian target of rapamycin (mTOR) activation. Thus, trastuzumab resistance-dependent PI3K/Akt/mTOR pathway is controlled by catecholamine-induced β2-AR activation. The data indicate that β2-AR is a reliable molecular marker for prediction of response probability to trastuzumab-based therapy in breast cancer. We also demonstrate that β-blocker propranolol not only enhances the antitumor activities of trastuzumab but also re-sensitizes the resistant cells to trastuzumab. Our retrospective study shows that concurrent treatment of β-blocker and trastuzumab significantly improved progression-free survival and overall survival in the patients with Her2-overexpressing metastatic breast cancer, implicating the possibility for combination therapy with trastuzumab plus β-blocker in Her2-overexpressing breast cancer.

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

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

Targeting the oncogenic MUC1-C protein inhibits mutant EGFR-mediated signaling and survival in non-small cell lung cancer cells

PURPOSE

Non-small cell lung cancers (NSCLC) that express EGF receptor with activating mutations frequently develop resistance to EGFR kinase inhibitors. The mucin 1 (MUC1) heterodimeric protein is aberrantly overexpressed in NSCLC cells and confers a poor prognosis; however, the functional involvement of MUC1 in mutant EGFR signaling is not known.

EXPERIMENTAL DESIGN

Targeting the oncogenic MUC1 C-terminal subunit (MUC1-C) in NSCLC cells harboring mutant EGFR was studied for effects on signaling, growth, clonogenic survival, and tumorigenicity.

RESULTS

Stable silencing of MUC1-C in H1975/EGFR(L858R/T790M) cells resulted in downregulation of AKT signaling and inhibition of growth, colony formation, and tumorigenicity. Similar findings were obtained when MUC1-C was silenced in gefitinib-resistant PC9GR cells expressing EGFR(delE746_A750/T790M). The results further show that expression of a MUC1-C(CQC → AQA) mutant, which blocks MUC1-C homodimerization, suppresses EGFR(T790M), AKT and MEK → ERK activation, colony formation, and tumorigenicity. In concert with these results, treatment of H1975 and PC9GR cells with GO-203, a cell-penetrating peptide that blocks MUC1-C homodimerization, resulted in inhibition of EGFR, AKT, and MEK → ERK signaling and in loss of survival. Combination studies of GO-203 and afatinib, an irreversible inhibitor of EGFR, further demonstrate that these agents are synergistic in inhibiting growth of NSCLC cells harboring the activating EGFR(T790M) or EGFR(delE746-A750) mutants.

CONCLUSIONS

These findings indicate that targeting MUC1-C inhibits mutant EGFR signaling and survival, and thus represents a potential approach alone and in combination for the treatment of NSCLCs resistant to EGFR kinase inhibitors.

Targeted immunotherapy for non-small cell lung cancer

Targeted therapies that deliver the expected anti-tumor effects while mitigating the adverse effects are taking the cancer world by storm. The need for such therapies in non-small cell lung cancer (NSCLC), where systemic cytotoxic chemotherapies still remain the backbone of management, is felt more than ever before. Runway success of immunotherapies such as Ipilimumab for melanoma has brought excitement among oncologists. Immune-based treatments are in various stages of evaluation for NSCLC as well. Immunotherapies using strategies of antigen based or cell based vaccines, and blocking immune checkpoints are of substantial interest. Meaningful clinical responses are yet to be reaped from these new treatment modalities.

MUC1-C oncoprotein activates ERK→C/EBPβ signaling and induction of aldehyde dehydrogenase 1A1 in breast cancer cells

Aldehyde dehydrogenase 1A1 (ALDH1A1) activity is used as a marker of breast cancer stem cells; however, little is known about the regulation of ALDH1A1 expression. Mucin 1 (MUC1) is a heterodimeric protein that is aberrantly overexpressed in most human breast cancers. In studies of breast cancer cells stably silenced for MUC1 or overexpressing the oncogenic MUC1-C subunit, we demonstrate that MUC1-C is sufficient for induction of MEK → ERK signaling and that treatment with a MUC1-C inhibitor suppresses ERK activation. In turn, MUC1-C induces ERK-mediated phosphorylation and activation of the CCAAT/enhancer-binding protein β (C/EBPβ) transcription factor. The results further show that MUC1-C and C/EBPβ form a complex on the ALDH1A1 gene promoter and activate ALDH1A1 gene transcription. MUC1-C-induced up-regulation of ALDH1A1 expression is associated with increases in ALDH activity and is detectable in stem-like cells when expanded as mammospheres. These findings demonstrate that MUC1-C (i) activates a previously unrecognized ERK→C/EBPβ→ALDH1A1 pathway, and (ii) promotes the induction of ALDH activity in breast cancer cells.

Knockdown of the Bcl-2 gene increases sensitivity to EGFR tyrosine kinase inhibitors in the H1975 lung cancer cell line harboring T790M mutation

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are being widely used as targeted therapy in non-small cell lung cancer (NSCLC), but most cases acquire drug-resistance in 9 months. However, the mechanisms of resistance are still not fully understood. Since it has been demonstrated that EGFR-TKI-mediated repression of downstream signaling cascades and apoptosis induction is a key mechanism through which EGFR-TKIs exert their cytotoxic effects, we reasoned that activation of downstream signaling pathways and changes in the expression of apoptosis-related proteins contribute to the acquired resistance to EGFR-TKIs. We analyzed the protein levels of p-Akt, Bcl-2, Bax between gefitinib-sensitive and gefitinib-resistant lung cancer cell lines and evaluated whether targeting the anti-apoptotic protein Bcl-2 induces cell apoptosis and further sensitizes resistant H1975 cells to gefitinib. The data showed that p-Akt was activated and accompanied by substantial Bcl-2 in the H1975 lung cancer cell line, whereas no evidence was observed in HCC827 cells. Using small interfering RNA (siRNA) to silence Bcl-2 in H1975 cells led to significant downregulation of Bcl-2 protein expression, decreased cell viability in vitro and induced intrinsic apoptosis confirmed by flow cytometry and PARP cleavage. In Bcl-2 siRNA-transfected cells, adding gefitinib further reduced the number of viable cells, induced apoptosis to a greater extent compared to either treatment alone. These preclinical data suggested that downregulation of Bcl-2 by RNAi in the gefitinib-resistant H1975 lung cancer cell line with T790M mutation enhanced the effects of gefitinib and may offer a novel therapeutic strategy for the treatment of NSCLC.

MUC1 and metastatic cancer: expression, function and therapeutic targeting

MUC1 is a transmembrane mucin that is often overexpressed in metastatic cancers and often used as a diagnostic marker for metastatic progression. The extracellular domain of MUC1 can serve as a ligand for stromal and endothelial cell adhesion receptors, and the cytoplasmic domain engages in several interactions that can result in increased migration and invasion, as well as survival. In this review, we address the role of MUC1 in metastatic progression by assessing clinical studies reporting MUC1 levels at various disease stages, reviewing mouse models utilized to study the role of MUC1 in metastatic progression, discuss mechanisms of MUC1 upregulation, and detail MUC1 protein interactions and signaling events. We review interactions between MUC1 and the extracellular environment, with proteins colocalized in the plasma membrane and/or cytoplasmic proteins, and summarize the role of MUC1 in the nucleus as a transcriptional cofactor. Finally, we review recent publications describing current therapies targeting MUC1 in patients with advanced disease and the stage of these therapies in preclinical development or clinical trials.

MUC1 enhances hypoxia-driven angiogenesis through the regulation of multiple proangiogenic factors

Pancreatic cancer is one of the most lethal malignancies due to its aggressive growth and rapid development of distant metastases. In this context, mucin 1 (MUC1) overexpression and hypoxia are frequently observed events. However, their functional relationship remains largely unknown. This study provides evidence that MUC1 is overexpressed by hypoxia and contributes to hypoxia-driven angiogenesis. Using the conditioned medium obtained from hypoxia-stressed AsPC1 cells treated with MUC1 siRNAs, we demonstrated that MUC1 enhanced the endothelial tube formation, proliferation and migration ability, which induced by hypoxia-conditioned medium (HCM). In addition, MUC1 was significantly induced by hypoxia, especially in the pancreatic cancer cells derived from metastatic tumors (AsPC1, HPAF2 or Capan1), and MUC1-cytoplasmic tail (MUC1-CT) accumulated in the nucleus under hypoxia. As noted in a previous report, MUC1-CT was recruited to genomic regions upstream of the connective tissue growth factor (CTGF) accompanied with β-catenin and p53, resulting in the hypoxic induction of CTGF. Moreover, hypoxia-induced MUC1 partially regulated two other hypoxia-inducible proangiogenic factors including vascular endothelial growth factor-A and platelet-derived growth factor-B. The neutralization assay revealed that endothelial tube formation induced by HCM was clearly suppressed by antibodies against these three factors, suggesting the importance of these factors in hypoxia-driven angiogenesis. In summary, this is the first report demonstrating a pivotal role of MUC1 in controlling the hypoxia-driven angiogenesis through the regulation of multiple proangiogenic factors in pancreatic cancer. Our findings provide the novel insights into the understanding of complex interactions between pancreatic cancer cells and tumor microenvironments.

MUC1-C oncoprotein as a target in breast cancer: activation of signaling pathways and therapeutic approaches

Mucin 1 (MUC1) is a heterodimeric protein formed by two subunits that is aberrantly overexpressed in human breast cancer and other cancers. Historically, much of the early work on MUC1 focused on the shed mucin subunit. However, more recent studies have been directed at the transmembrane MUC1-C-terminal subunit (MUC1-C) that functions as an oncoprotein. MUC1-C interacts with EGFR (epidermal growth factor receptor), ErbB2 and other receptor tyrosine kinases at the cell membrane and contributes to activation of the PI3KAKT and mitogen-activated protein kinase kinase (MEK)extracellular signal-regulated kinase (ERK) pathways. MUC1-C also localizes to the nucleus where it activates the Wnt/β-catenin, signal transducer and activator of transcription (STAT) and NF (nuclear factor)-κB RelA pathways. These findings and the demonstration that MUC1-C is a druggable target have provided the experimental basis for designing agents that block MUC1-C function. Notably, inhibitors of the MUC1-C subunit have been developed that directly block its oncogenic function and induce death of breast cancer cells in vitro and in xenograft models. On the basis of these findings, a first-in-class MUC1-C inhibitor has entered phase I evaluation as a potential agent for the treatment of patients with breast cancers who express this oncoprotein.