MUC1 oncoprotein blocks nuclear targeting of c-Abl in the apoptotic response to DNA damage

MUC15 is an independent prognostic factor that promotes metastases of MYCN non-amplified neuroblastoma

Background: Neuroblastoma (NB) is a cancer that arises from neural-crest-derived sympathoadrenal lineage. Less is known about the pathogenesis and molecular characteristics of MYCN non-amplified (MYCN-NA) NB. Methods: We constructed a signature model targeting mucin family according to RNA sequencing data from GSE49710 dataset, and validated the prognostic performance. We also analyzed the gene expression matrix using DESeq2 R packages to screen the most differential mucin in high-risk NB samples. We further assessed its prognostic value, particularly in MYCN-NA NB samples. Moreover, we performed functional experiments to evaluate the impact of MUC15 overexpression on the migration of MYCN-NA NB cell lines. Results: The 8-mucin signature model showed good prognostic performance in the GSE49710 dataset. Among the mucin genes, MUC15 was significantly upregulated in the high-risk NB cohort and was associated with poor prognosis, especially in MYCN-NA NB samples. Furthermore, MUC15 overexpression and exogenous MUC15 protein enhanced the migration of MYCN-NA NB cell lines. Mechanistically, MUC15 promoted the phosphorylation of focal adhesion kinase (FAK) by inhibiting the expression of MYCT1, a target of c-Myc. Conclusions: Our findings suggested a potential network in controlling NB cell metastasis. Targeting MUC15 in MYCN-NA NB patients could be a promising therapeutic strategy.

Pathological Implications of Mucin Signaling in Metastasis

The dynamic mucosal layer provides a selective protective barrier for the epithelial cells lining the body cavities. Diverse human malignancies exploit their intrinsic role to protect and repair epithelia for promoting growth and survival. Aberrant expression of mucin has been known to be associated with poor prognosis of many cancers. However, the emergence of new paradigms in the study of metastasis recognizes the involvement of MUC1, MUC4, MUC5AC, MUC5B, and MUC16 during metastasis initiation and progression. Hence mucins can be used as an attractive target in future diagnostic and therapeutic strategies. In this review, we discuss in detail about mucin family and its domains and the role of different mucins in regulating cancer progression and metastasis. In addition, we briefly discuss insights into mucins as a therapeutic agent.

Genotoxicity-Stimulated and CYLD-Driven Malignant Transformation

Oxidative stress, which can cause DNA damage, can both activate TNF-R1 directly in the absence of TNF stimulation and phosphorylate c-Abl, thus promoting its cytoplasmic translocation. Persistent cytoplasmic localization of c-Abl has been associated with cellular transformation. c-Abl phosphorylates OTULIN at tyrosine 56, thereby disrupting its relationship with LUBAC. OTULIN-released LUBAC interacts with SPATA2 and is recruited to the TNF-R1sc, facilitating SPATA2-CYLD interaction. All these interactions are required for the activation of IKKβ to stimulate NF-κB transcriptional activity following genotoxic stress. IKKβ also induces the critical phosphorylation of CYLD at serine 568 to increase its deubiquitinating (DUB) activity required for the termination of signaling cascades. Contrary to the widespread belief that CYLD is an absolute tumor suppressor, CYLD initiates and terminates NF-κB activity by alternately using its oncoprotein and tumor suppressor activities, respectively. If IKKβ fails to achieve the DUB activity-inducing phosphorylation at serine 568, CYLD would operate in a sustained mode of oncogenic activity. The resulting dysregulated NF-κB activation and other accompanying pathologies will disrupt cellular homeostasis in favor of transformation.

Robust Principal Component Analysis Based On Hypergraph Regularization for Sample Clustering and Co-Characteristic Gene Selection

Extracting genes involved in cancer lesions from gene expression data is critical for cancer research and drug development. The method of feature selection has attracted much attention in the field of bioinformatics. Principal Component Analysis (PCA) is a widely used method for learning low-dimensional representation. Some variants of PCA have been proposed to improve the robustness and sparsity of the algorithm. However, the existing methods ignore the high-order relationships between data. In this paper, a new model named Robust Principal Component Analysis via Hypergraph Regularization (HRPCA) is proposed. In detail, HRPCA utilizes L2,1-norm to reduce the effect of outliers and make data sufficiently row-sparse. And the hypergraph regularization is introduced to consider the complex relationship among data. Important information hidden in the data are mined, and this method ensures the accuracy of the resulting data relationship information. Extensive experiments on multi-view biological data demonstrate that the feasible and effective of the proposed approach.

Mucin1 and Mucin16: Therapeutic Targets for Cancer Therapy

The mucin (MUC) family is a group of highly glycosylated macromolecules that are abundantly expressed in mammalian epithelial cells. MUC proteins contribute to the formation of the mucus barrier and thus have protective functions against infection. Interestingly, some MUC proteins are aberrantly expressed in cancer cells and are involved in cancer development and progression, including cell growth, proliferation, the inhibition of apoptosis, chemoresistance, metabolic reprogramming, and immune evasion. With their unique biological and structural features, MUC proteins have been considered promising therapeutic targets and also biomarkers for human cancer. In this review, we discuss the biological roles of the transmembrane mucins MUC1 and MUC16 in the context of hallmarks of cancer and current efforts to develop MUC1- and MUC16-targeted therapies.

Luteolin alters MUC1 extracellular domain, sT antigen, ADAM-17, IL-8, IL-10 and NF-κB expression in Helicobacter pylori-infected gastric cancer CRL-1739 cells: A preliminary study

Luteolin is a natural flavonoid possessing certain beneficial pharmacological properties, including anti-oxidant, anti-inflammatory, anti-microbial and anti-cancer properties. The majority of types of gastric cancer with chronic gastritis are caused by infection with Helicobacter pylori (H. pylori). The present study evaluated the effect of luteolin on a number of selected factors that are potentially involved in gastric cancer development. The study was performed using gastric cancer CRL-1739 cells treated with 30 µM luteolin and H. pylori alone or combined. ELISA and reverse transcription PCR were used to assess the expression levels of MUC1, GalNAcα-R (Tn antigen) and NeuAcα2-3Galβ1-3GalNAc-R (sT antigen), ADAM-17, IL-8, IL-10 and NF-κB. H. pylori and luteolin independently and in combination significantly reduced the expression levels of the extracellular domain of MUC1 in gastric cancer cells compared with the untreated control cells. ADAM-17 expression was reduced by treatment with the pathogen and luteolin. Additionally, both factors reduced sT antigen expression. Treatment with 30 ≤M luteolin significantly induced IL-8 expression at the mRNA and protein level, and the mRNA expression levels of IL-10 and NF-κB compared with the control. Both H. pylori and luteolin induced IL-8 protein expression. The present preliminary results suggest that luteolin may be used to treat patients with gastric cancer.

Mucin glycoproteins block apoptosis; promote invasion, proliferation, and migration; and cause chemoresistance through diverse pathways in epithelial cancers

Overexpression of mucin glycoproteins has been demonstrated in many epithelial-derived cancers. The significance of this overexpression remains uncertain. The aim of this paper was to define the association of mucin glycoproteins with apoptosis, cell growth, invasion, migration, adhesion, and clonogenicity in vitro as well as tumor growth, tumorigenicity, and metastasis in vivo in epithelial-derived cancers by performing a systematic review of all published data. A systematic review of PubMed, Embase, and the Cochrane Central Register of Controlled Trials was performed to identify all papers that evaluated the association between mucin glycoproteins with apoptosis, cell growth, invasion, migration, adhesion, and clonogenicity in vitro as well as tumor growth, tumorigenicity, and metastasis in vivo in epithelial-derived cancers. PRISMA guidelines were adhered to. Results of individual studies were extracted and pooled together based on the organ in which the cancer was derived from. The initial search revealed 2031 papers, of which 90 were deemed eligible for inclusion in the study. The studies included details on MUC1, MUC2, MUC4, MUC5AC, MUC5B, MUC13, and MUC16. The majority of studies evaluated MUC1. MUC1 overexpression was consistently associated with resistance to apoptosis and resistance to chemotherapy. There was also evidence that overexpression of MUC2, MUC4, MUC5AC, MUC5B, MUC13, and MUC16 conferred resistance to apoptosis in epithelial-derived cancers. The overexpression of mucin glycoproteins is associated with resistance to apoptosis in numerous epithelial cancers. They cause resistance through diverse signaling pathways. Targeting the expression of mucin glycoproteins represents a potential therapeutic target in the treatment of epithelial-derived cancers.

MUC1-C Integrates Chromatin Remodeling and PARP1 Activity in the DNA Damage Response of Triple-Negative Breast Cancer Cells

The oncogenic MUC1-C protein is overexpressed in triple-negative breast cancer (TNBC) cells and contributes to their epigenetic reprogramming and chemoresistance. Here we show that targeting MUC1-C genetically or pharmacologically with the GO-203 inhibitor, which blocks MUC1-C nuclear localization, induced DNA double-strand breaks and potentiated cisplatin (CDDP)-induced DNA damage and death. MUC1-C regulated nuclear localization of the polycomb group proteins BMI1 and EZH2, which formed complexes with PARP1 during the DNA damage response. Targeting MUC1-C downregulated BMI1-induced H2A ubiquitylation, EZH2-driven H3K27 trimethylation, and activation of PARP1. As a result, treatment with GO-203 synergistically sensitized both mutant and wild-type BRCA1 TNBC cells to the PARP inhibitor olaparib. These findings uncover a role for MUC1-C in the regulation of PARP1 and identify a therapeutic strategy for enhancing the effectiveness of PARP inhibitors against TNBC. SIGNIFICANCE: These findings demonstrate that targeting MUC1-C disrupts epigenetics of the PARP1 complex, inhibits PARP1 activity, and is synergistic with olaparib in TNBC cells.

Mucins: Structural diversity, biosynthesis, its role in pathogenesis and as possible therapeutic targets

Mucins are the main structural components of mucus that create a selective protective barrier for epithelial surface and also execute wide range of other physiological functions. Mucins can be classified into two types, namely secreted mucins and membrane bounded mucins. Alterations in mucin expression or glycosylation and mislocalization have been seen in various types of pathological conditions such as cancers, inflammatory bowel disease and ocular disease, which highlight the importance of mucin in maintaining homeostasis. Hence mucins can be used as attractive target for therapeutic intervention. In this review, we discuss in detail about the structural diversity of mucins; their biosynthesis; its role in pathogenesis; regulation and as possible therapeutic targets.

MUC1-Mediated Metabolic Alterations Regulate Response to Radiotherapy in Pancreatic Cancer

Purpose:MUC1, an oncogene overexpressed in multiple solid tumors, including pancreatic cancer, reduces overall survival and imparts resistance to radiation and chemotherapies. We previously identified that MUC1 facilitates growth-promoting metabolic alterations in pancreatic cancer cells. The present study investigates the role of MUC1-mediated metabolism in radiation resistance of pancreatic cancer by utilizing cell lines and in vivo models.Experimental Design: We used MUC1-knockdown and -overexpressed cell line models for evaluating the role of MUC1-mediated metabolism in radiation resistance through in vitro cytotoxicity, clonogenicity, DNA damage response, and metabolomic evaluations. We also investigated whether inhibition of glycolysis could revert MUC1-mediated metabolic alterations and radiation resistance by using in vitro and in vivo models.Results: MUC1 expression diminished radiation-induced cytotoxicity and DNA damage in pancreatic cancer cells by enhancing glycolysis, pentose phosphate pathway, and nucleotide biosynthesis. Such metabolic reprogramming resulted in high nucleotide pools and radiation resistance in in vitro models. Pretreatment with the glycolysis inhibitor 3-bromopyruvate abrogated MUC1-mediated radiation resistance both in vitro and in vivo, by reducing glucose flux into nucleotide biosynthetic pathways and enhancing DNA damage, which could again be reversed by pretreatment with nucleoside pools.Conclusions: MUC1-mediated nucleotide metabolism plays a key role in facilitating radiation resistance in pancreatic cancer and targeted effectively through glycolytic inhibition. Clin Cancer Res; 23(19); 5881-91. ©2017 AACR.

MUC1-ARF-A Novel MUC1 Protein That Resides in the Nucleus and Is Expressed by Alternate Reading Frame Translation of MUC1 mRNA

Translation of mRNA in alternate reading frames (ARF) is a naturally occurring process heretofore underappreciated as a generator of protein diversity. The MUC1 gene encodes MUC1-TM, a signal-transducing trans-membrane protein highly expressed in human malignancies. Here we show that an AUG codon downstream to the MUC1-TM initiation codon initiates an alternate reading frame thereby generating a novel protein, MUC1-ARF. MUC1-ARF, like its MUC1-TM 'parent’ protein, contains a tandem repeat (VNTR) domain. However, the amino acid sequence of the MUC1-ARF tandem repeat as well as N- and C- sequences flanking it differ entirely from those of MUC1-TM. In vitro protein synthesis assays and extensive immunohistochemical as well as western blot analyses with MUC1-ARF specific monoclonal antibodies confirmed MUC1-ARF expression. Rather than being expressed at the cell membrane like MUC1-TM, immunostaining showed that MUC1-ARF protein localizes mainly in the nucleus: Immunohistochemical analyses of MUC1-expressing tissues demonstrated MUC1-ARF expression in the nuclei of secretory luminal epithelial cells. MUC1-ARF expression varies in different malignancies. While the malignant epithelial cells of pancreatic cancer show limited expression, in breast cancer tissue MUC1-ARF demonstrates strong nuclear expression. Proinflammatory cytokines upregulate expression of MUC1-ARF protein and co-immunoprecipitation analyses demonstrate association of MUC1-ARF with SH3 domain-containing proteins. Mass spectrometry performed on proteins coprecipitating with MUC1-ARF demonstrated Glucose-6-phosphate 1-dehydrogenase (G6PD) and Dynamin 2 (DNM2). These studies not only reveal that the MUC1 gene generates a previously unidentified MUC1-ARF protein, they also show that just like its ‘parent’ MUC1-TM protein, MUC1-ARF is apparently linked to signaling and malignancy, yet a definitive link to these processes and the roles it plays awaits a precise identification of its molecular functions. Comprising at least 524 amino acids, MUC1-ARF is, furthermore, the longest ARF protein heretofore described.

MUC1 in hematological malignancies

Mucin1 (MUC1) is a transmembrane oncogenic protein that plays a central role in malignant transformation and disease evolution, including cell proliferation, survival, self-renewal, and metastatic invasion. MUC1 has been shown to interact with diverse effectors such as β-catenin, receptor tyrosine kinases, and c-Abl, which are of importance in the pathogenesis of various hematological malignancies. In myeloid leukemia, MUC1 has been shown to have an essential role in leukemia stem-cell function, the induction of reactive oxygen species (ROS), and the promotion of terminal myeloid differentiation. As such, MUC1 is an attractive therapeutic target in hematologic malignancies. Targeting MUC1 has been shown to be an effective approach for inducing cell death in tumor in in vivo and in vitro models. Furthermore, MUC1 inhibition is synergistic with other therapeutic agents in the treatment of hematologic disorders. This review will explore the role of MUC1 in hematological malignancies, and strategies for targeting this oncoprotein.

Inside the biochemical pathways of thymidylate synthase perturbed by anticancer drugs: Novel strategies to overcome cancer chemoresistance

Our current understanding of the mechanisms of action of antitumor agents and the precise mechanisms underlying drug resistance is that these two processes are directly linked. Moreover, it is often possible to delineate chemoresistance mechanisms based on the specific mechanism of action of a given anticancer drug. A more holistic approach to the chemoresistance problem suggests that entire metabolic pathways, rather than single enzyme targets may better explain and educate us about the complexity of the cellular responses upon cytotoxic drug administration. Drugs, which target thymidylate synthase and folate-dependent enzymes, represent an important therapeutic arm in the treatment of various human malignancies. However, prolonged patient treatment often provokes drug resistance phenomena that render the chemotherapeutic treatment highly ineffective. Hence, strategies to overcome drug resistance are primarily designed to achieve either enhanced intracellular drug accumulation, to avoid the upregulation of folate-dependent enzymes, and to circumvent the impairment of DNA repair enzymes which are also responsible for cross-resistance to various anticancer drugs. The current clinical practice based on drug combination therapeutic regimens represents the most effective approach to counteract drug resistance. In the current paper, we review the molecular aspects of the activity of TS-targeting drugs and describe how such mechanisms are related to the emergence of clinical drug resistance. We also discuss the current possibilities to overcome drug resistance by using a molecular mechanistic approach based on medicinal chemistry methods focusing on rational structural modifications of novel antitumor agents. This paper also focuses on the importance of the modulation of metabolic pathways upon drug administration, their analysis and the assessment of their putative roles in the networks involved using a meta-analysis approach. The present review describes the main pathways that are modulated by TS-targeting anticancer drugs starting from the description of the normal functioning of the folate metabolic pathway, through the protein modulation occurring upon drug delivery to cultured tumor cells as well as cancer patients, finally describing how the pathways are modulated by drug resistance development. The data collected are then analyzed using network/netwire connecting methods in order to provide a wider view of the pathways involved and of the importance of such information in identifying additional proteins that could serve as novel druggable targets for efficacious cancer therapy.

The combined treatment with novel platinum(II) complex and anti-MUC1 increases apoptotic response in MDA-MB-231 breast cancer cells

New strategy of cancer’s targeting treatment is combining monoclonal antibodies with chemotherapeutic agents. An important goal of targeted therapy appears to be a transmembrane glycoprotein type I—mucin 1 (MUC1), which is overexpressed in tumors of epithelial origin, especially in breast cancer. The goal of the study was to check the effect of monoclonal antibody against MUC1 with novel platinum(II) complex (Pt12) on selected aspects of apoptosis in human MDA-MB-231 breast cancer cells. The number of apoptotic and necrotic cells was measured using annexin V binding assay. The decrease of mitochondrial membrane potential (MMP) and DNA fragmentation was analyzed. Finally, the influence of novel platinum(II) complex (Pt12) used with anti-MUC1 on the concentration of selected markers of apoptosis such as Bax, caspase-8, -9, and caspase-3 was performed using ELISA. The results from combined treatment were compared with those obtained using monotherapy. In our study, we proved that anti-MUC1 used in combination with Pt12 strongly induced apoptosis in MDA-MB-231 breast cancer cell line. The effect was stronger than treatment with Pt12, cisplatin, anti-MUC1, and anti-MUC1 used with cisplatin. We also observed the highest decrease of MMP and the strongest DNA fragmentation after such a combined treatment. The results obtained from ELISA showed increased concentration of Bax, caspases-8, -9, -3 compared to monotherapy. Our study proved that Pt12 together with anti-MUC1 strongly induced apoptosis in estrogen-negative breast cancer cell line (MDA-MB-231). The apoptosis may go through extrinsic pathway associated with caspase-8 as well as intrinsic pathway connected with caspase-9.

PPARγ E3 ubiquitin ligase regulates MUC1-C oncoprotein stability

MUC1-C oncoprotein is associated with colon, breast, ovarian, lung and pancreatic cancers. MUC1-C interacts with intracellular proteins to elicit signaling cascades that induce cell proliferation and tumor growth. Here we report that peroxisome proliferator-activated receptor gamma (PPARγ), an E3 ubiquitin ligase, is an inhibitor of MUC1-C-mediated cell proliferation. PPARγ does so by binding to and inducing MUC1-C proteasome-dependent degradation that was independent of PPARγ transcriptional activity. Lys134 residue was found to be critically important for PPARγ-mediated MUC1-C degradation, as it terminated MUC1-C-mediated cell proliferation. These findings demonstrate PPARγ induces MUC1-C ubiquitination and degradation that is critical to terminate MUC1-C signaling pathway-elicited cancer.

Protein mislocalization: mechanisms, functions and clinical applications in cancer

The changes from normal cells to cancer cells are primarily regulated by genome instability, which foster hallmark functions of cancer through multiple mechanisms including protein mislocalization. Mislocalization of these proteins, including oncoproteins, tumor suppressors, and other cancer-related proteins, can interfere with normal cellular function and cooperatively drive tumor development and metastasis. This review describes the cancer-related effects of protein subcellular mislocalization, the related mislocalization mechanisms, and the potential application of this knowledge to cancer diagnosis, prognosis, and therapy.

The MUC1 mucin regulates the tumorigenic properties of human esophageal adenocarcinomatous cells

MUC1 is a membrane-bound mucin known to participate in tumor proliferation. It has been shown that MUC1 pattern of expression is modified during esophageal carcinogenesis, with a progressive increase from metaplasia to adenocarcinoma. The principal cause of development of esophageal adenocarcinoma is gastro-esophageal reflux and MUC1 was previously shown to be up-regulated by several bile acids present in reflux. In this report, our aim was thus to determine whether MUC1 plays a role in biological properties of human esophageal cancer cells. For that, a stable MUC1-deficient esophageal cancer cell line was established using a shRNA approach. In vitro (proliferation, migration and invasion) and in vivo (tumor growth following subcutaneous xenografts in SCID mice) biological properties of MUC1-deficient cells were analyzed. Our results show that esophageal cancer cells lacking MUC1 were less proliferative and had decreased migration and invasion properties. These alterations were accompanied by a decreased activity of NFKB p65, Akt and MAPK (p44/42, JNK and p38) pathways. MCM6 and TSG101 tumor-associated markers were also decreased. Subcutaneous xenografts showed a significant decrease in tumor size when cells did not express MUC1. Altogether, the data indicate that MUC1 plays a key role in proliferative, migrating and invasive properties of esophageal cancer cells as well as in tumor growth promotion. MUC1 mucin appears thus as a good therapeutic target to slow down esophageal tumor progression.

Pemetrexed induces S-phase arrest and apoptosis via a deregulated activation of Akt signaling pathway

Pemetrexed is approved for first-line and maintenance treatment of patients with advanced or metastatic non-small-cell lung cancer (NSCLC). The protein kinase Akt/protein kinase B is a well-known regulator of cell survival which is activated by pemetrexed, but its role in pemetrexed-mediated cell death and its molecular mechanisms are unclear. This study showed that stimulation with pemetrexed induced S-phase arrest and cell apoptosis and a parallel increase in sustained Akt phosphorylation and nuclear accumulation in the NSCLC A549 cell line. Inhibition of Akt expression by Akt specific siRNA blocked S-phase arrest and protected cells from apoptosis, indicating an unexpected proapoptotic role of Akt in the pemetrexed-mediated toxicity. Treatment of A549 cells with pharmacological inhibitors of phosphatidylinositol 3-kinase (PI3K), wortmannin and Ly294002, similarly inhibited pemetrexed-induced S-phase arrest and apoptosis and Akt phosphorylation, indicating that PI3K is an upstream mediator of Akt and is involved in pemetrexed-mediated cell death. Previously, we identified cyclin A-associated cyclin-dependent kinase 2 (Cdk2) as the principal kinase that was required for pemetrexed-induced S-phase arrest and apoptosis. The current study showed that inhibition of Akt function and expression by pharmacological inhibitors as well as Akt siRNA drastically inhibited cyclin A/Cdk2 activation. These pemetrexed-mediated biological and molecular events were also observed in a H1299 cell line. Overall, our results indicate that, in contrast to its normal prosurvival role, the activated Akt plays a proapoptotic role in pemetrexed-mediated S-phase arrest and cell death through a mechanism that involves Cdk2/cyclin A activation.

Mucin 1 gene (MUC1) and gastric-cancer susceptibility

Gastric cancer (GC) is one of the major malignant diseases worldwide, especially in Asia. It is classified into intestinal and diffuse types. While the intestinal-type GC (IGC) is almost certainly caused by Helicobacter pylori (HP) infection, its role in the diffuse-type GC (DGC) appears limited. Recently, genome-wide association studies (GWAS) on Japanese and Chinese populations identified chromosome 1q22 as a GC susceptibility locus which harbors mucin 1 gene (MUC1) encoding a cell membrane-bound mucin protein. MUC1 has been known as an oncogene with an anti-apoptotic function in cancer cells; however, in normal gastric mucosa, it is anticipated that the mucin 1 protein has a role in protecting gastric epithelial cells from a variety of external insults which cause inflammation and carcinogenesis. HP infection is the most definite insult leading to GC, and a protective function of mucin 1 protein has been suggested by studies on Muc1 knocked-out mice.

Mucins and tumor resistance to chemotherapeutic drugs

Epithelial cancer patients not considered eligible for surgical resection frequently benefit from chemotherapy. Chemotherapy is the treatment of cancer with one or combination of cytotoxic or cytostatic drugs. Recent advances in chemotherapy allowed a great number of cancer patients to receive treatment with significant results. Unfortunately, resistance to chemotherapeutic drug treatment is a major challenge for clinicians in the majority of epithelial cancers because it is responsible for the inefficiency of therapies. Mucins belong to a heterogeneous group of large O-glycoproteins that can be either secreted or membrane-bound. Implications of mucins have been described in relation to cancer cell behavior and cell signaling pathways associated with epithelial tumorigenesis. Because of the frequent alteration of the pattern of mucin expression in cancers as well as their structural and functional characteristics, mucins are thought to also be involved in response to therapies. In this report, we review the roles of mucins in chemoresistance and the associated underlying molecular mechanisms (physical barrier, resistance to apoptosis, drug metabolism, cell stemness, epithelial-mesenchymal transition) and discuss the therapeutic tools/strategies and/or prognosis biomarkers for personalized chemotherapy that could be proposed from these studies.

Immunotherapy for lung cancer: ongoing clinical trials

ABSTRACT: Modulation of a patient’s immune system so that it acts against lung cancer cells has not been successful in the past decades. Advances in our understanding of the immune response to tumors resulted in the development of different kinds of novel immunotherapeutic agents. This has resulted in the development of two major approaches. First, antigen-specific immunotherapy or cancer vaccination, with the MAGE-A3 vaccine in resected early-stage non-small-cell lung cancer (NSCLC), the L-BLP25 vaccine in locally advanced NSCLC after chemoradiotherapy and belagenpumatucel-L and the TG4010 vaccine in advanced-stage NSCLC. Second, non-antigen-specific immunotherapy or cancer immunomodulation is reviewed, including how monoclonal antibodies modulate the interaction between antigen-presenting cells, T-lymphocytes and tumor cells (e.g., antibodies against CTLA-4, or against PD-1 receptor or its ligands). Recent Phase II trials with these treatments have shown promising results of efficacy and tolerability, which has led to testing in several large Phase III trials. Some of these are fully recruited, while others are still ongoing, and important results are be expected in the near future.

Persistent inhibition of ABL tyrosine kinase causes enhanced apoptotic response to TRAIL and disrupts the pro-apoptotic effect of chloroquine

TNF-Related Apoptosis Inducing Ligand (TRAIL) binds to and activates death receptors to stimulate caspase-8 and apoptosis with higher efficiency in cancer than normal cells but the development of apoptosis resistance has limited its clinical efficacy. We found that stable, but not transient knockdown of the ABL tyrosine kinase enhanced the apoptotic response to TRAIL. Re-expression of Abl, but not its nuclear import- or kinase-defective mutant, in the ABL-knockdown cells re-established apoptosis suppression. TRAIL is known to stimulate caspase-8 ubiquitination (Ub-C8), which can facilitate caspase-8 activation or degradation by the lysosomes. In the ABL-knockdown cells, we found a higher basal level of Ub-C8 that was not further increased by lysosomal inhibition. Re-expression of Abl in the ABL-knockdown cells reduced the basal Ub-C8, correlating with apoptosis suppression. We found that lysosomal inhibition by chloroquine (CQ) could also enhance TRAIL-induced apoptosis. However, this pro-apoptotic effect of CQ was lost in the ABL-knockdown cells but restored by Abl re-expression. Interestingly, kinase inhibition at the time of TRAIL stimulation was not sufficient to enhance apoptosis. Instead, persistent treatment for several days with imatinib, an ABL kinase inhibitor, was required to cause the enhanced and the CQ-insensitive apoptotic response to TRAIL. Together, these results show that persistent loss of nuclear ABL tyrosine kinase function can sensitize cells to TRAIL and suggest that long-term exposure to the FDA-approved ABL kinase inhibitors may potentiate apoptotic response to TRAIL-based cancer therapy.

MUC1 has prognostic significance in malignant peritoneal mesothelioma

BACKGROUND

Overexpression of MUC1 predicts poor survival in most cancers. Routine immunohistochemical detection of MUC1 is performed for differential diagnosis in malignant peritoneal mesothelioma (MPM). However, the prognostic significance of MUC1 in MPM has not been determined. 


METHOD

We investigated MUC1 expression and other prognostic factors in relation to survival in 42 patients (20 males and 22 females) for whom archival samples were available, using immunohistochemistry. MUC1 was expressed in 38/42 (90%) patients. Its prognostic significance was statistically analyzed using the Kaplan-Meier method.


RESULTS

High expression of MUC1 (immunohistochemical score of 5-8), was correlated with poor survival in several categories: all subtypes of tumors (p=0.001), male gender (p=0.017), female gender (p=0.001), epitheloid tumors (p=0.001), epitheloid tumors in males (p=0.005), epitheloid tumors in females (p=0.003), and age at diagnosis (AAD) <60 years (p=0.001). Amongst the other clinicopathological variables, univariate analysis also showed that male gender (p=0.007), sarcomatoid histology (p=0.001), peritoneal cancer index (PCI) ≥20 (p=0.013) and AAD ≥60 (p=0.001), correlated with poor survival. Multivariate analysis showed that only AAD ≥60 (p=0.049) was an independent prognostic factor, and that high MUC1 expression significantly correlated with the following categories: all subtypes of tumors (p=0.001), male gender (p=0.002), female gender (p=0.031), epitheloid tumors (p=0.031), and AAD <60y (p=0.012).


CONCLUSION

AAD and high MUC1 expression in the tumor are indicators of poor prognosis. MUC1 evaluation by immunohistochemistry may serve as a useful prognostic tool in MPM, but may need further confirmation in a larger patients' cohort.

MUC1 activates JNK1 and inhibits apoptosis under genotoxic stress

The MUC1 transmembrane glycoprotein is aberrantly overexpressed in diverse human carcinomas and has been shown to inhibit apoptosis induced by genotoxic agents. In the present work, we report that MUC1 binds to and activates JNK1, an important member of the mitogen-activated protein kinases (MAPK) superfamily. The physical interaction between MUC1 cytoplasmic domain (MUC1-CD) and JNK1 was established by GST-pull-down assay in vitro and co-immunoprecipitation assay in vivo. We show that MUC1 activates JNK1 and inhibits cisplatin-induced apoptosis in human colon cancer HCT116 cells. Pharmacological inhibition of JNK or knockdown of JNK significantly reduces the ability of MUC1 to inhibit cisplatin-induced apoptosis. Together, our data indicate that MUC1 can inhibit apoptosis via activating JNK1 pathway in response to genotoxic anticancer agents.

Chemoresistance is associated with MUC1 and Lewis y antigen expression in ovarian epithelial cancers

Objective

The aim of this study was to analyze the correlation and clinical significance between the expression of Mucin-1 (MUC1) and the Lewis y antigen with chemoresistance in ovarian epithelial cancers.

Methods

Ovarian cancer patients (n = 92) treated at our hospital from May 2005 to July 2009 were divided, according to their treatment and follow-up outcomes, into a resistant group (n = 37) or sensitive group (n = 55). The expression of MUC1 and Lewis y antigen in ovarian cancer tissues was detected using immunohistochemistry and correlated with chemoresistance.

Results

The positive rates of MUC1 and Lewis y antigen in the resistant group were both 91.89%, significantly higher than their positive rates in the sensitive group (65.45% and 69.09%, respectively, and both p < 0.05). MUC1 or Lewis y expression and the pathological stage of the tissue were independent risk factors for chemoresistance (all p < 0.05).

Conclusion

The increased expression of MUC1 and the Lewis y antigen is a significant risk factor for chemoresistance in patients with ovarian epithelial cancer.

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

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

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.

Activation of abl family kinases in solid tumors

Although c-Abl and Arg non-receptor tyrosine kinases are well known for driving leukemia development, their role in solid tumors has not been appreciated until recently. Accumulating evidence now indicates that c-Abl and/or Arg are activated in some solid tumor cell lines via unique mechanisms that do not involve gene mutation/translocation, and c-Abl/Arg activation promotes matrix degradation, invasion, proliferation, tumorigenesis, and/or metastasis, depending on the tumor type. However, some data suggest that c-Abl also may suppress invasion, proliferation, and tumorigenesis in certain cell contexts. Thus, c-Abl/Arg may serve as molecular switches that suppress proliferation and invasion in response to some stimuli (e.g., ephrins) or when inactive/regulated, or as promote invasion and proliferation in response to other signals (e.g., activated growth factor receptors, loss of inhibitor expression), which induce sustained activation. Clearly, more data are required to determine the extent and prevalence of c-Abl/Arg activation in primary tumors and during progression, and additional animal studies are needed to substantiate in vitro findings. Furthermore, c-Abl/Arg inhibitors have been used in numerous solid tumor clinical trials; however, none of these trials were restricted to patients whose tumors expressed highly activated c-Abl/Arg (targeted trial). Targeted trials are critical for determining whether c-Abl/Arg inhibitors can be effective treatment options for patients whose tumors are driven by c-Abl/Arg.

ABL regulation by AXL promotes cisplatin resistance in esophageal cancer

Esophageal adenocarcinoma (EAC) is characterized by resistance to chemotherapy and poor outcome. Although cisplatin (CDDP) has been used as a first-line therapy in patients with EAC, resistance remains a major clinical problem. The AXL receptor tyrosine kinase, originally isolated as a transforming gene from leukemia, is overexpressed in several solid tumors. Herein, we assessed AXL protein expression in human EACs and examined its role in CDDP resistance in human EAC cells. AXL overexpression was detected in more than 50% of tumors examined. Elevating AXL in nonoverexpressing cells doubled the CDDP IC(50) and increased cell survival three-fold, while attenuating AXL in overexpressing cells reduced survival two-fold. The effects of AXL modulation on cell survival were associated with changes in cellular and molecular markers of apoptosis. Mechanistic investigations revealed that AXL blocked CDDP-induced activation of endogenous p73β (TP73), reducing its protein half-life, and inhibited CDDP-induced levels of p-c-ABL(Y412) and p-p73β(Y99). These changes were associated with a disruption of c-ABL/p73β protein interactions due to association with c-ABL in the cytoplasm, thereby blocking nuclear accumulation of c-ABL and phosphorylation of p73β in response to DNA damage. Together, our results establish that AXL promotes CDDP resistance in esophageal adenocarcinoma and argue that therapeutic targeting of AXL may sensitize these cancers to DNA-damaging drugs.

Inhibition of the MUC1-C oncoprotein is synergistic with cytotoxic agents in the treatment of breast cancer cells

Mucin 1 (MUC1) is a heterodimeric glycoprotein that is aberrantly overexpressed in most human breast cancers. The oncogenic MUC1-C subunit promotes survival and blocks the apoptotic response to genotoxic anticancer agents. In the present studies, human MCF-7 and ZR-75-1 breast cancer cells were treated with the MUC1-C inhibitor, GO-203, a cell-penetrating peptide that blocks MUC1-C homodimerization and thereby its oncogenic function. Treatment with GO-203 was found to promote the apoptotic response of MCF-7 and ZR-75-1 cells to the therapeutic drugs taxol and doxorubicin (DOX). This effect was (1) attenuated by a pan-caspase inhibitor, and (2) mediated, at least in part, by activation of the effector caspase-7 and cleavage of the downstream substrate PARP. Further analysis of the interaction between GO-203 and taxol using isobolograms, which evaluate the nature of the interaction of two drugs, demonstrated that the combination is highly synergistic. These results were supported by combination index (CI) analysis with values of less than 1. GO-203 was also highly synergistic with DOX in studies of both MCF-7 and ZR-75-1 breast cancer cells. These findings indicate that blocking MUC1-C function could be effective in combination with taxol and DOX for the treatment of breast cancer.

MUC1c regulates cell survival in pancreatic cancer by preventing lysosomal permeabilization

BACKGROUND

MUC1 is a type I transmembrane glycoprotein aberrantly overexpressed in various cancer cells including pancreatic cancer. The cytosolic end of MUC1 (MUC1-c) is extensively involved in a number of signaling pathways. MUC1-c is reported to inhibit apoptosis in a number of cancer cells, but the mechanism of inhibition is unclear.

METHOD

Expression of MUC1-c was studied in the pancreatic cancer cell line MIAPaCa-2 at the RNA level by using qRTPCR and at the protein level by Western blotting. MUC1-c expression was inhibited either by siRNA or by a specific peptide inhibitor, GO-201. Effect of MUC1-c inhibition on viability and proliferation and lysosomal permeabilization were studied. Association of MUC1-c with HSP70 was detected by co-immunoprecipitation of MUC1-c and HSP70. Localization of MUC1-c in cellular organelles was monitored by immunofluorescence and with immuno- blotting by MUC1-c antibody after subcellular fractionation.

RESULTS

Inhibition of MUC1-c by an inhibitor (GO-201) or siRNA resulted in reduced viability and reduced proliferation of pancreatic cancer cells. Furthermore, GO-201, the peptide inhibitor of MUC1-c, was effective in reducing tumor burden in pancreatic cancer mouse model. MUC1-c was also found to be associated with HSP70 in the cytosol, although a significant amount of MUC1 was also seen to be present in the lysosomes. Inhibition of MUC1 expression or activity showed an enhanced Cathepsin B activity in the cytosol, indicating lysosomal permeabilization. Therefore this study indicates that MUC1-c interacted with HSP70 in the cytosol of pancreatic cancer cells and localized to the lysosomes in these cells. Further, our results showed that MUC1-c protects pancreatic cancer cells from cell death by stabilizing lysosomes and preventing release of Cathepsin B in the cytosol.

The MUC1 Ectodomain: A Novel and Efficient Target for Gold Nanoparticle Clustering and Vapor Nanobubble Generation

MUC1 is a large, heavily glycosylated transmembrane glycoprotein that is proposed to create a protective microenvironment in many adenocarcinomas. Here we compare MUC1 and the well studied cell surface receptor target, EGFR, as gold nanoparticle (AuNP) targets and their subsequent vapor nanobubble generation efficacy in the human epithelial cell line, HES. Although EGFR and MUC1 were both highly expressed in these cells, TEM and confocal images revealed MUC1 as a superior target for nanoparticle intracellular accumulation and clustering. The MUC1-targeted AuNP intracellular clusters also generated significantly larger vapor nanobubbles. Our results demonstrate the promising opportunities MUC1 offers to improve the efficacy of targeted nanoparticle based approaches.

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

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

MUC1 in human and murine mammary carcinoma cells decreases the expression of core 2 β1,6-N-acetylglucosaminyltransferase and β-galactoside α2,3-sialyltransferase

A good correlation between the expression of mucin1 (MUC1) and T antigen was found in breast cancer tumors and breast cancer cell lines, especially after treatment with neuraminidase. The association between the appearance of T antigen and the overexpression of MUC1 was further confirmed by transfecting MDA-MB-231 cells and murine 4T1 mammary carcinoma cells with cDNA for MUC1 and using an RNAi approach to inhibit the expression of MUC1 gene in T47D cells. Furthermore, we discovered that in 4T1 cells which express the sialyl Le(X) antigen, overexpression of MUC1 caused not only appearance of T antigen, but also loss of the sialyl Le(X) structure. As the observed changes in O-glycan synthesis can be associated with changes in the expression of specific glycosyltransferases, core 1 β1,3-galactosyltransferase, core 2 β1,6-N-acetylglucosaminyltransferase (C2GnT1) and β-galactoside α2,3-sialyltransferase (ST3Gal I), we studied their expression in parental, vector-transfected and MUC1-transfected MDA-MB-231 and 4T1 cells as well as T47D cells transduced with small hairpin RNA targeted MUC1 mRNA. It was found that the expression of C2GnT1 and ST3Gal I is highly decreased in MUC1-expressing MDA-MB-231 and 4T1 cells and increased in T47D cells with suppressed expression of MUC1. Therefore, we found that changes in the structure of O-linked oligosaccharides, resulting in the occurrence of T antigen, are at least partially associated with MUC1 overexpression which down-regulates the expression of C2GnT1 and ST3Gal I. We showed also that the overexpression of MUC1 in 4T1 cells changes their adhesive properties, as MUC1-expressing cells do not adhere to E-selectin, but bind galectin-3.

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.

Transmembrane mucins as novel therapeutic targets

Membrane-tethered mucin glycoproteins are abundantly expressed at the apical surfaces of simple epithelia, where they play important roles in lubricating and protecting tissues from pathogens and enzymatic attack. Notable examples of these mucins are MUC1, MUC4 and MUC16 (also known as cancer antigen 125). In adenocarcinomas, apical mucin restriction is lost and overall expression is often highly increased. High-level mucin expression protects tumors from killing by the host immune system, as well as by chemotherapeutic agents, and affords protection from apoptosis. Mucin expression can increase as the result of gene duplication and/or in response to hormones, cytokines and growth factors prevalent in the tumor milieu. Rises in the normally low levels of mucin fragments in serum have been used as markers of disease, such as tumor burden, for many years. Currently, several approaches are being examined that target mucins for immunization or nanomedicine using mucin-specific antibodies.

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.

Dependence on the MUC1-C oncoprotein in non-small cell lung cancer cells

Non-small cell lung cancer (NSCLC) cells are often associated with constitutive activation of the phosphoinositide 3-kinase (PI3K) → Akt → mTOR pathway. The mucin 1 (MUC1) heterodimeric glycoprotein is aberrantly overexpressed in NSCLC cells and induces gene signatures that are associated with poor survival of NSCLC patients. The present results show that the MUC1 C-terminal subunit (MUC1-C) cytoplasmic domain associates with PI3K p85 in NSCLC cells. We show that inhibition of MUC1-C with cell-penetrating peptides blocks this interaction with PI3K p85 and suppresses constitutive phosphorylation of Akt and its downstream effector, mTOR. In concert with these results, treatment of NSCLC cells with the MUC1-C peptide inhibitor GO-203 was associated with downregulation of PI3K → Akt signaling and inhibition of growth. GO-203 treatment was also associated with increases in reactive oxygen species (ROS) and induction of necrosis by a ROS-dependent mechanism. Moreover, GO-203 treatment of H1975 (EGFR L858R/T790M) and A549 (K-Ras G12S) xenografts growing in nude mice resulted in tumor regressions. These findings indicate that NSCLC cells are dependent on MUC1-C both for activation of the PI3K → Akt pathway and for survival.

The c-Abl tyrosine kinase stabilizes Pitx1 in the apoptotic response to DNA damage

In the DNA damage response, c-Abl tyrosine kinase is transiently accumulated in the nucleus and induces apoptosis; however, little is known about the mechanism underlying apoptosis induction via nuclear c-Abl. Here we demonstrate that the expression of human pituitary homeobox 1 (Pitx1) transcription factor is increased after DNA damage. Notably, c-Abl controls augmentation of Pitx1 at the post-transcriptional level. Overexpression of c-Abl induces tyrosine phosphorylation of Pitx1, either directly or indirectly. We also show that, upon exposure to genotoxic stress, overexpression of Pitx1 is associated with marked induction of apoptosis that is independent of p53 status. Importantly, inhibition of c-Abl kinase activity substantially attenuates Pitx1-mediated apoptosis. These findings provide evidence that c-Abl participates in modulating Pitx1 expression in the apoptotic response to DNA damage.

DNA damage stress response in germ cells: role of c-Abl and clinical implications

Cells experiencing DNA damage undergo a complex response entailing cell-cycle arrest, DNA repair and apoptosis, the relative importance of the three being modulated by the extent of the lesion. The observation that Abl interacts in the nucleus with several proteins involved in different aspects of DNA repair has led to the hypothesis that this kinase is part of the damage-sensing mechanism. However, the mechanistic details underlying the role of Abl in DNA repair remain unclear. Here, I will review the evidence supporting our current understanding of Abl activation following DNA insults, while focusing on the relevance of these mechanisms in protecting DNA-injured germ cells. Early studies have shown that Abl transcripts are highly expressed in the germ line. Abl-deficient mice exhibit multiple abnormalities, increased perinatal mortality and reduced fertility. Recent findings have implicated Abl in a cisplatin-induced signaling pathway eliciting death of immature oocytes. A p53-related protein, TAp63, is an important immediate downstream effector of this pathway. Of note, pharmacological inhibition of Abl protects the ovarian reserve from the toxic effects of cisplatin. This suggests that the extent of Abl catalytic outputs may shift the balance between survival (likely through DNA repair) and activation of a death response. Taken together, these observations are consistent with the evolutionary conserved relationship between DNA damage and activation of the p53 family of transcription factors, while shedding light on the key role of Abl in dictating the fate of germ cells upon genotoxic insults.

Terminal differentiation of chronic myelogenous leukemia cells is induced by targeting of the MUC1-C oncoprotein

Chronic myelogenous leukemia (CML) is caused by expression of the Bcr-Abl fusion protein in hematopoietic stem cells. The MUC1-C oncoprotein is expressed in CML blasts and stabilizes Bcr-Abl. The present studies demonstrate that treatment of KU812 and K562 CML cells with GO-201, a cell-penetrating peptide inhibitor of MUC1-C oligomerization, downregulates Bcr-Abl expression and inhibits cell growth. In concert with decreases in Bcr-Abl levels, KU812 and K562 cells responded to GO-201 with induction of a differentiated myeloid phenotype as evidenced by increased expression of CD11b, CD11c and CD14. The results also show that the GO-201-treated cells undergo a late apoptotic/necrotic response, consistent with induction of terminal differentiation. Primary CML blasts expressing MUC1 similarly responded to GO-201 with induction of a more differentiated phenotype and late apoptosis/necrosis. In addition, treatment of KU812 xenografts in nude mice was associated with upregulation of CD11 and tumor regression. These findings indicate that CML blasts respond to targeting of the MUC1-C oncoprotein with induction of terminal differentiation.

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.

MUC1-C Oncoprotein Interacts Directly with ATM and Promotes the DNA Damage Response to Ionizing Radiation

The ataxia-telangiectasia mutated (ATM) kinase is activated in the cellular response to ionizing radiation (IR) and is of importance to the repair of DNA double strand breaks (DSBs). The MUC1 oncoprotein is aberrantly overexpressed in human breast carcinomas. The present work demonstrates that the MUC1 C-terminal subunit (MUC1-C) constitutively interacts with ATM in human breast cancer cells. We show that the MUC1-C cytoplasmic domain binds directly to ATM HEAT repeats. Our results also demonstrate that the MUC1-C cytoplasmic domain binds to the ATM substrate H2AX. The functional significance of these interactions is supported by the finding that MUC1-C promotes removal of IR-induced nuclear γH2AX foci. MUC1-C also protects against IR-induced chromosomal aberrations. In concert with these results, MUC1-C blocks IR-induced death by promoting repair of potentially lethal DNA damage. These findings indicate that the overexpression of MUC1 can protect against IR-induced DNA DSBs and may represent a physiologic response that has been exploited by malignant cells.

c-Abl and Arg tyrosine kinases regulate lysosomal degradation of the oncoprotein Galectin-3

Galectin-3 (Gal3) has important roles in tumor transformation and metastasis. This study shows that c-Abl and Abl-related gene (Arg) associate with and phosphorylate Gal3. The SH (Src homology)3 domains of c-Abl/Arg bind to a P(80)GPPSGP motif of Gal3, and Tyr79 and Tyr118 are the major tyrosine phosphorylation sites. A consequence of this interaction and phosphorylation is the significant impairment of chaperone-mediated autophagy of Gal3. Cells expressing Gal3 and treated with the c-Abl/Arg inhibitor STI571, Gal3-depleted cells, and Gal3-depleted cells expressing Gal3 phosphorylation mutants all display an increased sensitivity to apoptosis-inducing agents. In addition, tumor cells expressing the phosphorylation mutants show impaired tumorigenicity. These results partially explain the antiapoptotic effect of Abl and Arg. As tumors frequently overexpress Gal3, a c-Abl/Arg-specific inhibitor may potentially be applied along with other antitumor drugs to target the lysosomal degradation of Gal3 in tumor therapy.

Temporal gene expression changes induced by a low concentration of benzo[a]pyrene diol epoxide in a normal human cell line

(+ or -)-anti-Benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE), which causes bulky-adduct DNA damage, is well-characterized as the ultimate carcinogen of benzo[a]pyrene (BaP). In this study, we have employed Affymetrix HG-U133 Plus 2.0 microarray and quantitative real-time RT-PCR methods to investigate a temporal transcriptomic response triggered by a low concentration (0.05 microM) of BPDE at 1, 10, and 22 h after exposure in normal human cells. The differential gene expression profiles at the three time points varied greatly, and generally reflected a cellular responsive process from initiation to progression and to recovery after the BPDE-caused damage. The dynamic regulation of the genes related with cell cycle progression and cell fate exhibited a tendency from inhibition to survival, which was accordant with the cell cycle arrest and cytotoxicity data induced by the low-dose BPDE exposure. In silico comparison of the genomic data revealed that BPDE and ultraviolet induced a panel of common transcriptional responses, which might be related with a series of similar molecular processes elicited by these two DNA-damaging agents. In conclusion, this whole-genome time-course study has identified a dynamically regulated transcriptional signature after low-dose BPDE exposure, which may help to understand the complex mechanisms of mutagenesis and carcinogenesis induced by BPDE.

c-Abl regulates estrogen receptor alpha transcription activity through its stabilization by phosphorylation

Estrogen receptors are members of the steroid hormone superfamily of nuclear receptors that act as ligand-activated transcription factors. Similar to other steroid hormone receptors, estrogen receptor alpha (ERalpha) is a substrate for protein kinases, and phosphorylation has profound effects on the function of this receptor. In this study, we show that ERalpha associates with c-Abl nonreceptor tyrosine kinase. The direct interaction is mediated by two PXXP motifs of ERalpha and the c-Abl SH3 domain. Mutational analysis and in vitro kinase assays show that ERalpha can be phosphorylated on two sites, tyrosine 52 (Y-52) and tyrosine 219 (Y-219). ERalpha phosphorylation by c-Abl stabilizes ERalpha, resulting in enhanced ERalpha transcriptional activity and increased expression of endogenous ERalpha target genes. Furthermore, ERalpha phosphorylation at the Y-219 site affects DNA binding and dimerization by ERalpha. Both the c-Abl inhibitor and the c-Abl kinase dead mutation abolish the c-Abl-induced accumulation of ERalpha and enhancement of ERalpha transcriptional activity, indicating that c-Abl kinase activity is required for regulation of the ERalpha function. Moreover, the ERalpha (Y52,219F) mutant shows reduced breast cancer cell growth and invasion. Taken together, these results show that c-Abl is a novel kinase that upregulates ERalpha expression and promotes breast cancer cell proliferation, suggesting a great potential for this kinase to function as a therapeutic target for breast cancer.

Cooperativity of the MUC1 oncoprotein and STAT1 pathway in poor prognosis human breast cancer

Signal transducer and activator of transcription 1 (STAT1) is activated in the inflammatory response to interferons. The MUC1 oncoprotein is overexpressed in human breast cancers. Analysis of genes differentially expressed in MUC1-transformed cells has identified a network linking MUC1 and STAT1 that is associated with cellular growth and inflammation. The results further demonstrate that the MUC1-C subunit associates with STAT1 in cells and that the MUC1-C cytoplasmic domain binds directly to the STAT1 DNA binding domain. The interaction between MUC1-C and STAT1 is inducible by IFNγ in non-malignant epithelial cells and constitutive in breast cancer cells. Moreover, the MUC1-STAT1 interaction contributes to the activation of STAT1 target genes, including MUC1 itself. Analysis of two independent databases demonstrated that MUC1 and STAT1 are coexpressed in about 15% of primary human breast tumors. Coexpression of MUC1 and the STAT1 pathway was found to be significantly associated with decreased recurrence-free and overall survival. These findings indicate that (i) MUC1 and STAT1 function in an auto-inductive loop, and (ii) activation of both MUC1 and the STAT1 pathway in breast tumors confers a poor prognosis for patients.