MUC1 (CD227) interacts with lck tyrosine kinase in Jurkat lymphoma cells and normal T cells

MUC1 is a potential target to overcome trastuzumab resistance in breast cancer therapy

Although resistance is its major obstacle in cancer therapy, trastuzumab is the most successful agent in treating epidermal growth factor receptor 2 positive (HER2 +) breast cancer (BC). Some patients show resistance to trastuzumab, and scientists want to circumvent this problem. This review elaborately discusses possible resistance mechanisms to trastuzumab and introduces mucin 1 (MUC1) as a potential target efficient for overcoming such resistance. MUC1 belongs to the mucin family, playing the oncogenic/mitogenic roles in cancer cells and interacting with several other oncogenic receptors and pathways, such as HER2, β-catenin, NF-κB, and estrogen receptor (ERα). Besides, it has been established that MUC1- Cytoplasmic Domain (MUC1-CD) accelerates the development of resistance to trastuzumab and that silencing MUC1-C proto-oncogene is associated with increased sensitivity of HER2⁺ cells to trastuzumab-induced growth inhibitors. We mention why targeting MUC1 can be useful in overcoming trastuzumab resistance in cancer therapy.

Biology, Significance and Immune Signaling of Mucin 1 in Hepatocellular Carcinoma

Mucin 1 (MUC 1) is a highly glycosylated tumor-associated antigen (TAA) overexpressed in hepatocellular carcinoma (HCC). This protein plays a critical role in various immune-mediated signaling pathways at its transcriptional and post-transcriptional levels, leading to immune evasion and metastasis in HCC. HCC cells maintain an immune-suppressive environment with the help of immunesuppressive tumor-associated antigens, resulting in a metastatic spread of the disease. The development of intense immunotherapeutic strategies to target tumor-associated antigen is critical to overcoming the progression of HCC. MUC 1 remains the most recognized tumor-associated antigen since its discovery over 30 years ago. A few promising immunotherapies targeting MUC 1 are currently under clinical trials, including CAR-T and CAR-pNK-mediated therapies. This review highlights the biosynthesis, significance, and clinical implication of MUC 1 as an immune target in HCC.

MUC1-Targeted Radiopharmaceuticals in Cancer Imaging and Therapy

Mucin 1 (MUC1) is a large, transmembrane mucin glycoprotein overexpressed in most adenocarcinomas and plays an important role in tumor progression. Regarding its cellular distribution, biochemical features, and function, tumor-related MUC1 varies from the MUC1 expressed in normal cells. Therefore, targeting MUC1 for cancer immunotherapy and imaging can exploit the difference between cancerous and normal cells. Radiopharmaceuticals have a potential use as carriers for the delivery of radionuclides to tumors for a diagnostic imaging and radiotherapy. Several radiolabeled targeting molecules like peptides, antibodies, and aptamers have been efficiently demonstrated in detecting and treating cancer by targeting MUC1. This review provides a brief overview of the current status of developments and applications of MUC1-targeted radiopharmaceuticals in cancer imaging and therapy.

Mammalian and Avian Host Cell Influenza A Restriction Factors

The threat of a new influenza pandemic is real. With past pandemics claiming millions of lives, finding new ways to combat this virus is essential. Host cells have developed a multi-modular system to detect incoming pathogens, a phenomenon called sensing. The signaling cascade triggered by sensing subsequently induces protection for themselves and their surrounding neighbors, termed interferon (IFN) response. This response induces the upregulation of hundreds of interferon-stimulated genes (ISGs), including antiviral effectors, establishing an antiviral state. As well as the antiviral proteins induced through the IFN system, cells also possess a so-called intrinsic immunity, constituted of antiviral proteins that are constitutively expressed, creating a first barrier preceding the induction of the interferon system. All these combined antiviral effectors inhibit the virus at various stages of the viral lifecycle, using a wide array of mechanisms. Here, we provide a review of mammalian and avian influenza A restriction factors, detailing their mechanism of action and in vivo relevance, when known. Understanding their mode of action might help pave the way for the development of new influenza treatments, which are absolutely required if we want to be prepared to face a new pandemic.

Gene Expression and Resistance to Glucocorticoid-Induced Apoptosis in Acute Lymphoblastic Leukemia: A Brief Review and Update

BACKGROUND

Resistance to glucocorticoid (GC)-induced apoptosis in Acute Lymphoblastic Leukemia (ALL), is considered one of the major prognostic factors for the disease. Prednisolone is a corticosteroid and one of the most important agents in the treatment of acute lymphoblastic leukemia. The mechanics of GC resistance are largely unknown and intense ongoing research focuses on this topic.

AIM

The aim of the present study is to review some aspects of GC resistance in ALL, and in particular of Prednisolone, with emphasis on previous and present knowledge on gene expression and signaling pathways playing a role in the phenomenon.

METHODS

An electronic literature search was conducted by the authors from 1994 to June 2019. Original articles and systematic reviews selected, and the titles and abstracts of papers screened to determine whether they met the eligibility criteria, and full texts of the selected articles were retrieved.

RESULTS

Identification of gene targets responsible for glucocorticoid resistance may allow discovery of drugs, which in combination with glucocorticoids may increase the effectiveness of anti-leukemia therapies. The inherent plasticity of clinically evolving cancer justifies approaches to characterize and prevent undesirable activation of early oncogenic pathways.

CONCLUSION

Study of the pattern of intracellular signal pathway activation by anticancer drugs can lead to development of efficient treatment strategies by reducing detrimental secondary effects.

A review on development of MUC1-based cancer vaccine

Mucin 1 (MUC1) is a transmembrane mucin glycoprotein expressed on the surface of almost all epithelial cells. Aberrantly glycosylated MUC1 is associated with cellular transformation from a normal to malignant phenotype in human cancers. Therefore, MUC1 is the major target for the design and development of cancer vaccines. MUC1-based cancer vaccines are a promising strategy for preventing cancer progression and metastasis. This review summarizes the most significant milestones achieved to date in the development of different MUC-1-based vaccine approaches in clinical trials. Further, it provides perspectives for future research that may promote clinical advances in infection-associated cancers.

Multiple cancer-specific antigens are targeted by a chimeric antigen receptor on a single cancer cell

Human cancer cells were eradicated by adoptive transfer of T cells transduced with a chimeric antigen receptor (CAR) made from an antibody (237Ab) that is highly specific for the murine Tn-glycosylated podoplanin (Tn-PDPN). The objectives were to determine the specificity of these CAR-transduced T (CART) cells and the mechanism for the absence of relapse. We show that although the 237Ab bound only to cell lines expressing murine Tn-PDPN, the 237Ab-derived 237CART cells lysed multiple different human and murine cancers not predicted by the 237Ab binding. Nevertheless, the 237CART cell reactivities remained cancer specific because all recognitions were dependent on the Tn glycosylation that resulted from COSMC mutations that were not present in normal tissues. While Tn was required for the recognition by 237CART, Tn alone was not sufficient for 237CART cell activation. Activation of 237CART cells required peptide backbone recognition but tolerated substitutions of up to 5 of the 7 amino acid residues in the motif recognized by 237Ab. Together, these findings demonstrate what we believe is a new principle whereby simultaneous recognition of multiple independent Tn-glycopeptide antigens on a cancer cell makes tumor escape due to antigen loss unlikely.

Modulating MUC1 Function on T Cells

Immunotherapy is a promising approach to treating cancer. Mucin1 (MUC1), an epithelial glycoprotein, is hypo-glycosylated and overexpressed on epithelial cancers. This renders it a promising target for potential immunotherapeutic approaches. However, MUC1 has also been identified on T cells, which might complicate its potential as a target for immunotherapies.

MUC1 Mucin: A Putative Regulatory (Checkpoint) Molecule of T Cells

T lymphocytes are at the center of inducing an effective adaptive immune response and maintaining homeostasis. T cell responses are initiated through interactions between antigen presenting cells (APCs) and T cells. The type and strength of signals delivered through the T cell receptor (TCR) may modulate how the cells respond. The TCR-MHC (T cell receptor-major histocompatibility complex molecules) complex dictates the specificity, whereas co-stimulatory signals induced by interaction of various accessory cell surface molecules strengthen and optimize T cell responses. Multiple immune regulatory mechanisms brought about by co-inhibitory molecules expressed on T cells play a key role in orchestrating successful and non-damaging immunity. These co-inhibitory molecules are also referred to as initiators of immune check-points or co-inhibitory pathways. Knowledge of co-inhibitory pathways associated with activated T lymphocytes has allowed a better understanding of (a) the inflammatory and anti-inflammatory processes associated with infectious diseases and autoimmune diseases, and (b) mechanisms by which tumors evade immune attack. Many of these regulatory pathways are non-redundant and function in a highly concerted manner. Targeting them has provided effective approaches in treating cancer and autoimmune diseases. For this reason, it is valuable to identify any co-inhibitory molecules that affect these pathways. MUC1 mucin (CD227) has long been known to be expressed by epithelial cells and overexpressed by a multitude of adenocarcinomas. As long ago as 1998 we made a surprising discovery that MUC1 is also expressed by activated human T cells and we provided the first evidence of the role of MUC1 as a novel T cell regulator. Subsequent studies from different laboratories, as well as ours, supported an immuno-regulatory role of MUC1 in infections, inflammation, and autoimmunity that corroborated our original findings establishing MUC1 as a novel T cell regulatory molecule. In this article, we will discuss the experimental evidence supporting MUC1 as a putative regulatory molecule or a “checkpoint molecule” of T cells with implications as a novel biomarker and therapeutic target in chronic diseases such as autoimmunity, inflammation and cancer, and possibly infections.

Multiple Roles of Glycans in Hematological Malignancies

The three types of blood cells (red blood cells for carrying oxygen, white blood cells for immune protection, and platelets for wound clotting) arise from hematopoietic stem/progenitor cells in the adult bone marrow, and function in physiological regulation and communication with local microenvironments to maintain systemic homeostasis. Hematological malignancies are relatively uncommon malignant disorders derived from the two major blood cell lineages: myeloid (leukemia) and lymphoid (lymphoma). Malignant clones lose their regulatory mechanisms, resulting in production of a large number of dysfunctional cells and destruction of normal hematopoiesis. Glycans are one of the four major types of essential biological macromolecules, along with nucleic acids, proteins, and lipids. Major glycan subgroups are N-glycans, O-glycans, glycosaminoglycans, and glycosphingolipids. Aberrant expression of glycan structures, resulting from dysregulation of glycan-related genes, is associated with cancer development and progression in terms of cell signaling and communication, tumor cell dissociation and invasion, cell-matrix interactions, tumor angiogenesis, immune modulation, and metastasis formation. Aberrant glycan expression occurs in most hematological malignancies, notably acute myeloid leukemia, myeloproliferative neoplasms, and multiple myeloma, etc. Here, we review recent research advances regarding aberrant glycans, their related genes, and their roles in hematological malignancies. Our improved understanding of the mechanisms that underlie aberrant patterns of glycosylation will lead to development of novel, more effective therapeutic approaches targeted to hematological malignancies.

Mechanism of anticancer action of novel berenil complex of platinum(II) combined with anti-MUC1 in MCF-7 breast cancer cells

Mucin 1 (MUC1) is a high molecular weight transmembrane glycoprotein, that is overexpressed in >90% of breast cancers. It serves a crucial role in anti-apoptosis and tumor progression. MUC1 interacts with proteins in the extracellular matrix, at the cell membrane, in the cytoplasm and in the nucleus. The aim of the present study was to investigate the mechanism of anticancer action induced by novel berenil complex of platinum(II) (Pt12) together with a monoclonal antibody against MUC1 in breast cancer MCF-7 cells. The effect of combined treatment on the concentration of selected markers of apoptosis including proapoptotic B-cell lymphoma 2 associated X protein (Bax), caspase-8, cytochrome c and caspase-9, as well as selected proteins involved in intracellular signal transduction pathways including p53, phosphoinositide 3-kinase and phosphorylated protein kinase B (p-Akt) were analyzed. The results of the present study demonstrated that combined treatment may be a promising strategy in anticancer treatment and represents an alternative to monotherapy. All compounds used alone (Pt12, cisplatin and the anti-MUC1 antibody) increased the concentration of proapoptotic Bax, cytochrome c and caspase-9 in comparison with control, thus suggesting that they activated the mitochondrial apoptotic pathway. Pt12 alone significantly increased the concentration of caspase-8, which is responsible for the initiation of the extrinsic apoptotic pathway. However, the strongest effect was observed following Pt12 (20 µM) treatment combined with the anti-MUC1 antibody (10 µg/ml). These two compounds together strongly induced apoptosis in MCF-7 breast cancer cells via the external and internal apoptotic pathways. It was also demonstrated that combined treatment based on Pt12 and the anti-MUC1 antibody significantly reduced p-Akt concentration.

The cell surface mucin MUC1 limits the severity of influenza A virus infection

Cell surface mucin (cs-mucin) glycoproteins are constitutively expressed at the surface of respiratory epithelia where pathogens such as influenza A virus (IAV) gain entry into cells. Different members of the cs-mucin family each express a large and heavily glycosylated extracellular domain that towers above other receptors on the epithelial cell surface, a transmembrane domain that enables shedding of the extracellular domain, and a cytoplasmic tail capable of triggering signaling cascades. We hypothesized that IAV can interact with the terminal sialic acids presented on the extracellular domain of cs-mucins, resulting in modulation of infection efficiency. Utilizing human lung epithelial cells, we found that IAV associates with the cs-mucin MUC1 but not MUC13 or MUC16. Overexpression of MUC1 by epithelial cells or the addition of sialylated synthetic MUC1 constructs, reduced IAV infection in vitro. In addition, Muc1^-/- mice infected with IAV exhibited enhanced morbidity and mortality, as well as greater inflammatory mediator responses compared to wild type mice. This study implicates the cs-mucin MUC1 as a critical and dynamic component of the innate host response that limits the severity of influenza and provides the foundation for exploration of MUC1 in resolving inflammatory disease.

EMMPRIN (CD147) is induced by C/EBPβ and is differentially expressed in ALK+ and ALK- anaplastic large-cell lymphoma

Anaplastic lymphoma kinase-positive (ALK+) anaplastic large-cell lymphoma (ALCL) is characterized by expression of oncogenic ALK fusion proteins due to the translocation t(2;5)(p23;q35) or variants. Although genotypically a T-cell lymphoma, ALK+ ALCL cells frequently show loss of T-cell-specific surface antigens and expression of monocytic markers. C/EBPβ, a transcription factor constitutively overexpressed in ALK+ ALCL cells, has been shown to play an important role in the activation and differentiation of macrophages and is furthermore capable of transdifferentiating B-cell and T-cell progenitors to macrophages in vitro. To analyze the role of C/EBPβ for the unusual phenotype of ALK+ ALCL cells, C/EBPβ was knocked down by RNA interference in two ALK+ ALCL cell lines, and surface antigen expression profiles of these cell lines were generated using a Human Cell Surface Marker Screening Panel (BD Biosciences). Interesting candidate antigens were further analyzed by immunohistochemistry in primary ALCL ALK+ and ALK- cases. Antigen expression profiling revealed marked changes in the expression of the activation markers CD25, CD30, CD98, CD147, and CD227 after C/EBPβ knockdown. Immunohistochemical analysis confirmed a strong, membranous CD147 (EMMPRIN) expression in ALK+ ALCL cases. In contrast, ALK- ALCL cases showed a weaker CD147 expression. CD274 or PD-L1, an immune inhibitory receptor ligand, was downregulated after C/EBPβ knockdown. PD-L1 also showed stronger expression in ALK+ ALCL compared with ALK- ALCL, suggesting an additional role of C/EBPβ in ALK+ ALCL in generating an immunosuppressive environment. Finally, no expression changes of T-cell or monocytic markers were detected. In conclusion, surface antigen expression profiling demonstrates that C/EBPβ plays a critical role in the activation state of ALK+ ALCL cells and reveals CD147 and PD-L1 as important downstream targets. The multiple roles of CD147 in migration, adhesion, and invasion, as well as T-cell activation and proliferation suggest its involvement in the pathogenesis of ALCL.

Muc1 enhances the β-catenin protective pathway during ischemia-reperfusion injury

The hypoxia-inducible factor (HIF)-1 and β-catenin protective pathways represent the two most significant cellular responses that are activated in response to acute kidney injury. We previously reported that murine mucin (Muc)1 protects kidney function and morphology in a mouse model of ischemia-reperfusion injury (IRI) by stabilizing HIF-1α, enhancing HIF-1 downstream signaling, and thereby preventing metabolic stress (Pastor-Soler et al. Muc1 is protective during kidney ischemia-reperfusion injury. Am J Physiol Renal Physiol 308: F1452-F1462, 2015). We asked if Muc1 regulates the β-catenin protective pathway during IRI as 1) β-catenin nuclear targeting is MUC1 dependent in cultured human cells, 2) β-catenin is found in coimmunoprecipitates with human MUC1 in extracts of both cultured cells and tissues, and 3) MUC1 prevents β-catenin phosphorylation by glycogen synthase kinase (GSK)3β and thereby β-catenin degradation. Using the same mouse model of IRI, we found that levels of active GSK3β were significantly lower in kidneys of control mice compared with Muc1 knockout (KO) mice. Consequently, β-catenin was significantly upregulated at 24 and 72 h of recovery and appeared in the nuclear fraction at 72 h in control mouse kidneys. Both β-catenin induction and nuclear targeting were absent in Muc1 KO mice. We also found downstream induction of β-catenin prosurvival factors (activated Akt, survivin, transcription factor T cell factor 4 (TCF4), and its downstream target cyclin D1) and repression of proapoptotic factors (p53, active Bax, and cleaved caspase-3) in control mouse kidneys that were absent or aberrant in kidneys of Muc1 KO mice. Altogether, the data clearly indicate that Muc1 protection during acute kidney injury proceeds by enhancing both the HIF-1 and β-catenin protective pathways.

MUC1 (CD227): a multi-tasked molecule

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

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.

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.

Binding of the sialic acid-binding lectin, Siglec-9, to the membrane mucin, MUC1, induces recruitment of β-catenin and subsequent cell growth

Because MUC1 carries a variety of sialoglycans that are possibly recognized by the siglec family, we examined MUC1-binding siglecs and found that Siglec-9 prominently bound to MUC1. An immunochemical study showed that Siglec-9-positive immune cells were associated with MUC1-positive cells in human colon, pancreas, and breast tumor tissues. We investigated whether or not this interaction has any functional implications for MUC1-expressing cells. When mouse 3T3 fibroblast cells and a human colon cancer cell line, HCT116, stably transfected with MUC1cDNA were ligated with recombinant soluble Siglec-9, β-catenin was recruited to the MUC1 C-terminal domain, which was enhanced on stimulation with soluble Siglec-9 in dose- and time-dependent manners. A co-culture model of MUC1-expressing cells and Siglec-9-expressing cells mimicking the interaction between MUC1-expressing malignant cells, and Siglec-9-expressing immune cells in a tumor microenvironment was designed. Brief co-incubation of Siglec-9-expressing HEK293 cells, but not mock HEK293 cells, with MUC1-expressing cells similarly enhanced the recruitment of β-catenin to the MUC1 C-terminal domain. In addition, treatment of MUC1-expressing cells with neuraminidase almost completely abolished the effect of Siglec-9 on MUC1-mediated signaling. The recruited β-catenin was thereafter transported to the nucleus, leading to cell growth. These findings suggest that Siglec-9 expressed on immune cells may play a role as a potential counterreceptor for MUC1 and that this signaling may be another MUC1-mediated pathway and function in parallel with a growth factor-dependent pathway.

Selective identification of macrophages and cancer cells based on thermal transport through surface-imprinted polymer layers

In this article, we describe a novel straightforward method for the specific identification of viable cells (macrophages and cancer cell lines MCF-7 and Jurkat) in a buffer solution. The detection of the various cell types is based on changes of the heat transfer resistance at the solid-liquid interface of a thermal sensor device induced by binding of the cells to a surface-imprinted polymer layer covering an aluminum chip. We observed that the binding of cells to the polymer layer results in a measurable increase of heat transfer resistance, meaning that the cells act as a thermally insulating layer. The detection limit was found to be on the order of 10(4) cells/mL, and mutual cross-selectivity effects between the cells and different types of imprints were carefully characterized. Finally, a rinsing method was applied, allowing for the specific detection of cancer cells with their respective imprints while the cross-selectivity toward peripheral blood mononuclear cells was negligible. The concept of the sensor platform is fast and low-cost while allowing also for repetitive measurements.

Downregulation of hematopoietic MUC1 during experimental colitis increases tumor-promoting myeloid-derived suppressor cells

PURPOSE

MUC1 is a tumor-associated antigen that is aberrantly expressed in cancer and inflammatory bowel disease (IBD). Even though immune cells express low MUC1 levels, their modulations of MUC1 are important in tumor progression. Consistent with previous clinical data that show increased myeloid-derived suppressor cells (MDSCs) in IBD, we now show that downregulation of MUC1 on hematopoietic cells increases MDSCs in IBD, similar to our data in tumor-bearing mice. We hypothesize that MDSC expansion in IBD is critical for tumor progression.

EXPERIMENTAL DESIGN

To mechanistically confirm the linkage between Muc1 downregulation and MDSC expansion, we generated chimeric mice that did not express Muc1 in the hematopoietic compartment (KO→WT). These mice were used in two models of colitis and colitis-associated cancer (CAC) and their responses were compared with wild-type (WT) chimeras (WT→WT).

RESULTS

KO→WT mice show increased levels of MDSCs during colitis and increased protumorigenic signaling in the colon during CAC, resulting in larger colon tumors. RNA and protein analysis show increased upregulation of metalloproteinases, collagenases, defensins, complements, growth factors, cytokines, and chemokines in KO→WT mice as compared with WT→WT mice. Antibody-mediated depletion of MDSCs in mice during colitis reduced colon tumor formation during CAC.

CONCLUSION

Development of CAC is a serious complication of colitis and our data highlight MDSCs as a targetable link between inflammation and cancer. In addition, the lack of MUC1 expression on MDSCs can be a novel marker for MDSCs, given that MDSCs are still not well characterized in human cancers.

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

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

Integration of activating and inhibitory receptor signaling by regulated phosphorylation of Vav1 in immune cells

Natural killer (NK) cells are effector cells of the immune system whose activation is carefully regulated by the interplay of signals from activating and inhibitory receptors. Signals from activating receptors induce phosphorylation of the guanine nucleotide exchange factor Vav1, whereas those from inhibitory receptors lead to the dephosphorylation of Vav1 by the Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1). Here, we used mathematical modeling and experiments with NK cells to gain insight into this integration of positive and negative signals at a molecular level. Our data showed a switch-like regulation of Vav1 phosphorylation, the extent of which correlated with the cytotoxic activity of NK cells. Comparison of our experimental results with the predictions that we derived from an ensemble of 72 mathematical models showed that a physical association between Src family kinases and activating receptors on NK cells was essential to generate the cytotoxic response. Our data support a central role for Vav1 in determining the cytotoxic activity of NK cells and provide insight into the molecular mechanism of the integration of positive and negative signals during lymphocyte activation.

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

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

RNA interference suppression of mucin 5AC (MUC5AC) reduces the adhesive and invasive capacity of human pancreatic cancer cells

BACKGROUND

MUC5AC is a secretory mucin normally expressed in the surface muconous cells of stomach and bronchial tract. It has been known that MUC5AC de novo expression occurred in the invasive ductal carcinoma and pancreatic intraepithelial neoplasm with no detectable expression in normal pancreas, however, its function remains uncertain. Here, we report the impact of MUC5AC on the adhesive and invasive ability of pancreatic cancer cells.

METHODS

We used two MUC5AC expressing cell lines derived from human pancreatic cancer, SW1990 and BxPC3. Small-interfering (si) RNA directed against MUC5AC were used to assess the effects of MUC5AC on invasion and adhesion of pancreas cancer cells in vitro and in vivo. We compared parental cells (SW1990 and BxPC3) with MUC5AC suppressed cells by si RNA (si-SW1990 and si-BxPC3).

RESULTS

MUC5AC was found to express in more than 80% of pancreatic ductal carcinoma specimens. Next we observed that both of si-SW1990 and si-BxPC3 showed significantly lower adhesion and invasion to extracellular matrix components compared with parental cell lines. Expression of genes associated with adhesion and invasion including several integerins, matrix metalloproteinase (MMP) -3 and vascular endothelial growth factor (VEGF) were down-regulated in both MUC5AC suppressed cells. Furthermore, production of VEGF and phosphorylation of VEGFR-1 were significantly reduced by MUC5AC down regulation. Both of si-SW1990 and si-BxPC3 attenuated activation of Erk1/2. In vivo, si-SW1990 did not establish subcutaneous tumor in nude mice.

CONCLUSIONS

Knockdown of MUC5AC reduced the ability of pancreatic cancer cells to adhesion and invasion, suggesting that MUC5AC might contribute to the invasive motility of pancreatic cancer cells by enhancing the expression of integrins, MMP-3, VEGF and activating Erk pathway.

Mucin-interacting proteins: from function to therapeutics

Mucins are high molecular weight glycoproteins that are involved in regulating diverse cellular activities both in normal and pathological conditions. Mucin activity and localization is mediated by several molecular mechanisms, including discrete interactions with other proteins. An understanding of the biochemistry behind the known interactions between mucins and other proteins, coupled with an appreciation of their pathophysiological significance, can lend insight into the development of novel therapeutic agents. Indeed, a recent study demonstrated that a cell permeable inhibitor, PMIP, that disrupts the MUC1-EGFR interaction, is effective in killing breast cancer cells in vitro and in tumor models.

Early over expression of messenger RNA for multiple genes, including insulin, in the Pancreatic Lymph Nodes of NOD mice is associated with Islet Autoimmunity

BACKGROUND

Autoimmune diabetes (T1D) onset is preceded by a long inflammatory process directed against the insulin-secreting beta cells of the pancreas. Deciphering the early autoimmune mechanisms represents a challenge due to the absence of clinical signs at early disease stages. The aim of this study was to identify genes implicated in the early steps of the autoimmune process, prior to inflammation, in T1D. We have previously established that insulin autoantibodies (E-IAA) predict early diabetes onset delineating an early phenotypic check point (window 1) in disease pathogenesis. We used this sub-phenotype and applied differential gene expression analysis in the pancreatic lymph nodes (PLN) of 5 weeks old Non Obese Diabetic (NOD) mice differing solely upon the presence or absence of E-IAA. Analysis of gene expression profiles has the potential to provide a global understanding of the disease and to generate novel hypothesis concerning the initiation of the autoimmune process.

METHODS

Animals have been screened weekly for the presence of E-IAA between 3 and 5 weeks of age. E-IAA positive or negative NOD mice at least twice were selected and RNAs isolated from the PLN were used for microarray analysis. Comparison of transcriptional profiles between positive and negative animals and functional annotations of the resulting differentially expressed genes, using software together with manual literature data mining, have been performed.

RESULTS

The expression of 165 genes was modulated between E-IAA positive and negative PLN. In particular, genes coding for insulin and for proteins known to be implicated in tissue remodelling and Th1 immunity have been found to be highly differentially expressed. Forty one genes showed over 5 fold differences between the two sets of samples and 30 code for extracellular proteins. This class of proteins represents potential diagnostic markers and drug targets for T1D.

CONCLUSION

Our data strongly suggest that the immune related mechanisms taking place at this early age in the PLN, correlate with homeostatic changes influencing tissue integrity of the adjacent pancreatic tissue. Functional analysis of the identified genes suggested that similar mechanisms might be operating during pre-inflammatory processes deployed in tissues i) hosting parasitic microorganisms and ii) experiencing unrestricted invasion by tumour cells.

Lack of Muc1-regulated beta-catenin stability results in aberrant expansion of CD11b+Gr1+ myeloid-derived suppressor cells from the bone marrow

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of myeloid cells that inhibit T-cell activity and contribute to the immune suppression characteristic of most tumors. We discovered that bone marrow (BM) progenitor cells from the Muc1 knockout (KO) mice differentiated into CD11b(+)Gr1(+) MDSCs in vitro under granulocyte macrophage colony-stimulating factor and interleukin-4 signaling. MUC1 is a tumor-associated mucin and its cytoplasmic tail (MUC1-CT) can regulate beta-catenin to promote oncogenesis. Given the importance of beta-catenin in hematopoiesis, we hypothesized that the MUC1 regulation of beta-catenin is important for MDSC development. Our current study shows that the aberrant development of BM progenitors into CD11b(+)Gr1(+) MDSCs is dependent on the down-regulation of beta-catenin levels that occurs in the absence of Muc1. In light of this, KO mice showed enhanced EL4 tumor growth and were able to better tolerate allogeneic BM185 tumor growth, with an accumulation of CD11b(+)Gr1(+) cells in the blood and tumor-draining lymph nodes. WT mice were able to similarly tolerate allogeneic tumor growth when they were injected with CD11b(+)Gr1(+) cells from tumor-bearing KO mice, suggesting that tolerance of allogeneic tumors is dependent on MDSC-mediated immune suppression. This further delineates the ability of Muc1 to control MDSC development, which could directly affect tumorigenesis. Knowledge of the biology by which Muc1 regulates the development of myeloid progenitors into MDSCs would also be very useful in enhancing the efficacy of cancer vaccines in the face of tumor immune suppression.

Mucin 1 (MUC1) is a novel partner for MAL2 in breast carcinoma cells

BACKGROUND

The MAL2 gene, encoding a four-transmembrane protein of the MAL family, is amplified and overexpressed in breast and other cancers, yet the significance of this is unknown. MAL-like proteins have trafficking functions, but their molecular roles are largely obscure, partly due to a lack of known binding partners.

METHODS

Yeast two-hybrid screening of a breast carcinoma cDNA expression library was performed using a full-length MAL2 bait, and subsequent deletion mapping experiments were performed. MAL2 interactions were confirmed by co-immunoprecipitation analyses and confocal microscopy was employed to compare protein sub-cellular distributions. Sucrose density gradient centrifugation of membranes extracted in cold Triton X-100 was employed to compare protein distributions between Triton X-100-soluble and -insoluble fractions.

RESULTS

The tumor-associated protein mucin 1 (MUC1) was identified as a potential MAL2 partner, with MAL2/MUC1 interactions being confirmed in myc-tagged MAL2-expressing MCF-10A cells using co-immunoprecipitation assays. Deletion mapping experiments demonstrated a requirement for the first MAL2 transmembrane domain for MUC1 binding, whereas the MAL2 N-terminal domain was required to bind D52-like proteins. Confocal microscopy identified cytoplasmic co-localisation of MUC1 and MAL2 in breast cell lines, and centrifugation of cell lysates to equilibrium in sucrose density gradients demonstrated that MAL2 and MUC1 proteins were co-distributed between Triton X-100-soluble and -insoluble fractions. However co-immunoprecipitation analyses detected MAL2/MUC1 interactions in Triton X-100-soluble fractions only. Myc-MAL2 expression in MCF-10A cells was associated with both increased MUC1 detection within Triton X-100-soluble and -insoluble fractions, and increased MUC1 detection at the cell surface.

CONCLUSION

These results identify MUC1 as a novel MAL2 partner, and suggest a role for MAL2 in regulating MUC1 expression and/or localisation.

MUC1 enhances tumor progression and contributes toward immunosuppression in a mouse model of spontaneous pancreatic adenocarcinoma

MUC1, a membrane tethered mucin glycoprotein, is overexpressed and aberrantly glycosylated in >80% of human ductal pancreatic adenocarcinoma. However, the role of MUC1 in pancreatic cancer has been elusive, partly due to the lack of an appropriate model. We report the characterization of a novel mouse model that expresses human MUC1 as a self molecule (PDA.MUC1 mice). Pancreatic tumors arise in an appropriate MUC1-tolerant background within an immune-competent host. Significant enhancement in the development of pancreatic intraepithelial preneoplastic lesions and progression to adenocarcinoma is observed in PDA.MUC1 mice, possibly due to increased proliferation. Tumors from PDA.MUC1 mice express higher levels of cyclooxygenase-2 and IDO compared with PDA mice lacking MUC1, especially during early stages of tumor development. The increased proinflammatory milieu correlates with an increased percentage of regulatory T cells and myeloid suppressor cells in the pancreatic tumor and tumor draining lymph nodes. Data shows that during pancreatic cancer progression, MUC1-mediated mechanisms enhance the onset and progression of the disease, which in turn regulate the immune responses. Thus, the mouse model is ideally suited for testing novel chemopreventive and therapeutic strategies against pancreatic cancer.

The MUC1 Cytoplasmic Tail and Tandem Repeat Domains Contribute to Mammary Oncogenesis in FVB Mice

BACKGROUND

Though the importance of the transmembrane mucin MUC1 in mammary oncogenesis has long been recognized, the relative contributions of the cytoplasmic tail and tandem repeat domains are poorly understood.

METHODS

To address this, mouse models of mammary carcinogenesis were created expressing full-length, cytoplasmic tail-deleted, or tandem repeat-deleted MUC1 constructs.

RESULTS

Overexpression of full-length MUC1 resulted in tumor formation in young mice (≤12 months); however, loss of either the cytoplasmic tail or the tandem repeat domain abrogated this oncogenic capacity. Aged mice in all strains developed late-onset mammary tumors similar to those previously described for the FVB background.

CONCLUSIONS

This study is the first spontaneous cancer model to address the relative importance of the cytoplasmic tail and tandem repeat domains to MUC1-driven mammary oncogenesis, and suggests that both of these domains are essential for tumor formation.

Structure and Function of the Cell Surface (Tethered) Mucins

Cell surface mucins are large transmembrane glycoproteins involved in diverse functions ranging from shielding the airway epithelium against pathogenic infection to regulating cellular signaling and transcription. Although hampered by the relatively recent characterization of cell surface mucins and the difficulties inherent in working with molecules of their size, numerous studies have placed the tethered mucins in the thick of normal and diseased lung physiology. This review focuses on the three best-characterized cell surface mucins expressed in the respiratory tract: MUC1, MUC4, and MUC16.

MUC1 cell surface mucin is a critical element of the mucosal barrier to infection

Cell surface mucin glycoproteins are highly expressed by all mucosal tissues, yet their physiological role is currently unknown. We hypothesized that cell surface mucins protect mucosal cells from infection. A rapid progressive increase in gastrointestinal expression of mucin 1 (Muc1) cell surface mucin followed infection of mice with the bacterial pathogen Campylobacter jejuni. In the first week following oral infection, C. jejuni was detected in the systemic organs of the vast majority of Muc1(-/-) mice but never in Muc1(+/+) mice. Although C. jejuni entered gastrointestinal epithelial cells of both Muc1(-/-) and Muc1(+/+) mice, small intestinal damage as manifested by increased apoptosis and enucleated and shed villous epithelium was more common in Muc1(-/-) mice. Using radiation chimeras, we determined that prevention of systemic infection in wild-type mice was due exclusively to epithelial Muc1 rather than Muc1 on hematopoietic cells. Expression of MUC1-enhanced resistance to C. jejuni cytolethal distending toxin (CDT) in vitro and CDT null C. jejuni showed lower gastric colonization in Muc1(-/-) mice in vivo. We believe this is the first in vivo experimental study to demonstrate that cell surface mucins are a critical component of mucosal defence and that the study provides the foundation for exploration of their contribution to epithelial infectious and inflammatory diseases.

Muc1 mucin limits both Helicobacter pylori colonization of the murine gastric mucosa and associated gastritis

BACKGROUND & AIMS

The MUC1 mucin is expressed on the cell surface of epithelial cells lining the gastric mucosa. Epidemiologic studies suggest that functional allelic variations in the MUC1 gene may play a role in human susceptibility to Helicobacter pylori-associated pathologies, including gastric adenocarcinoma. We have evaluated the impact of Muc1 expression on the colonization and pathogenesis of gastric Helicobacter infections.

METHODS

Wild-type and Muc1-deficient mice were infected with H pylori and colonization and gastritis levels determined. Primary gastric cells were used to examine the impact of Muc1 expression on bacterial adherence.

RESULTS

Mice lacking Muc1 were colonized by 5-fold more H pylori within 1 day of infection, and this difference was maintained for at least 2 months postinfection. Mice heterozygous for the null Muc1 allele developed intermediate bacterial colonization. Although wild-type mice developed only a mild gastritis when infected for 2 months with H pylori, Muc1(-/-) mice developed an atrophic gastritis marked by loss of parietal cells. We demonstrate H pylori adhesion to purified MUC1 and significantly increased adhesion to cultured murine Muc1 null gastric epithelial cells, suggesting that Muc1 acts as a decoy limiting binding to the cell surface.

CONCLUSIONS

Muc1 provides a protective barrier, which limits both acute and chronic colonization by H pylori, as well as playing a major role in limiting the inflammation induced by Helicobacter infection. We propose that Muc1 restricts access of H pylori to the epithelial surface, hence reducing exposure of the host to proinflammatory bacterial products.

Down-regulation of MUC1 in cancer cells inhibits cell migration by promoting E-cadherin/catenin complex formation

MUC1, a tumor associated glycoprotein, is over-expressed in most cancers and can promote proliferation and metastasis. The objective of this research was to study the role of MUC1 in cancer metastasis and its potential mechanism. Pancreatic (PANC1) and breast (MCF-7) cancer cells with stable 'knockdown' of MUC1 expression were created using RNA interference. beta-Catenin and E-cadherin protein expression were upregulated in PANC1 and MCF-7 cells with decreased MUC1 expression. Downregulation of MUC1 expression also induced beta-catenin relocation from the nucleus to the cytoplasm, increased E-cadherin/beta-catenin complex formation and E-cadherin membrane localization in PANC1 cells. PANC1 cells with 'knockdown' MUC1 expression had decreased in vitro cell invasion. This study suggested that MUC1 may affect cancer cell migration by increasing E-cadherin/beta-catenin complex formation and restoring E-cadherin membrane localization.

MUC1 alters oncogenic events and transcription in human breast cancer cells

Introduction

MUC1 is an oncoprotein whose overexpression correlates with aggressiveness of tumors and poor survival of cancer patients. Many of the oncogenic effects of MUC1 are believed to occur through interaction of its cytoplasmic tail with signaling molecules. As expected for a protein with oncogenic functions, MUC1 is linked to regulation of proliferation, apoptosis, invasion, and transcription.

Methods

To clarify the role of MUC1 in cancer, we transfected two breast cancer cell lines (MDA-MB-468 and BT-20) with small interfering (si)RNA directed against MUC1 and analyzed transcriptional responses and oncogenic events (proliferation, apoptosis and invasion).

Results

Transcription of several genes was altered after transfection of MUC1 siRNA, including decreased MAP2K1 (MEK1), JUN, PDGFA, CDC25A, VEGF and ITGAV (integrin α_v), and increased TNF, RAF1, and MMP2. Additional changes were seen at the protein level, such as increased expression of c-Myc, heightened phosphorylation of AKT, and decreased activation of MEK1/2 and ERK1/2. These were correlated with cellular events, as MUC1 siRNA in the MDA-MB-468 line decreased proliferation and invasion, and increased stress-induced apoptosis. Intriguingly, BT-20 cells displayed similar levels of apoptosis regardless of siRNA, and actually increased proliferation after MUC1 siRNA.

Conclusion

These results further the growing knowledge of the role of MUC1 in transcription, and suggest that the regulation of MUC1 in breast cancer may be more complex than previously appreciated. The differences between these two cell lines emphasize the importance of understanding the context of cell-specific signaling events when analyzing the oncogenic functions of MUC1, and caution against generalizing the results of individual cell lines without adequate confirmation in intact biological systems.

MUC1/X protein immunization enhances cDNA immunization in generating anti-MUC1 alpha/beta junction antibodies that target malignant cells

MUC1 has generated considerable interest as a tumor marker and potential target for tumor killing. To date, most antibodies against MUC1 recognize epitopes within the highly immunogenic alpha chain tandem repeat array. A major shortcoming of such antibodies is that the MUC1 alpha chain is shed into the peripheral circulation, sequesters circulating antitandem repeat array antibodies, and limits their ability to even reach targeted MUC1-expressing cells. Antibodies recognizing MUC1 epitopes tethered to the cell surface would likely be more effective. MUC1 alpha subunit binding the membrane-tethered beta subunit provides such an epitope. By use of a novel protocol entailing immunization with cDNA encoding full-length MUC1 (MUC1/TM) followed by boosting with the alternatively spliced MUC1/X isoform from which the tandem repeat array has been deleted, we generated monoclonal antibodies, designated DMC209, which specifically bind the MUC1 alpha/beta junction. DMC209 is exquisitely unique for this site; amino acid mutations, which abrogate MUC1 cleavage, also abrogate DMC209 binding. Additionally, DMC209 specifically binds the MUC1 alpha/beta junction on full-length MUC1/TM expressed by breast and ovarian cancer cell lines and on freshly obtained, unmanipulated MUC1-positive malignant plasma cells of multiple myeloma. DMC209 is likely to have clinical application by targeting MUC1-expressing cells directly and as an immunotoxin conjugate. Moreover, the novel immunization procedure used in generating DMC209 can be used to generate additional anti-MUC1 alpha/beta junction antibodies, which may, analogously to Herceptin, have cytotoxic activity. Lastly, sequential immunization with MUC1/TM cDNA acting as a nonspecific adjuvant followed by protein of interest may prove to be a generalizable method to yield high-titer specific antibodies.

Cell surface-associated mucins in signal transduction

Mucins are heavily glycosylated high molecular weight glycoproteins, which are involved in the protection and lubrication of luminal epithelial surfaces. Transmembrane mucins also engage in signal transduction, through extracellular domain-mediated ligand binding or by interacting with receptors for growth and differentiation factors. The cytoplasmic tail of MUC1 (MUC1CT), the best characterized of the transmembrane mucins, is involved in several signaling pathways, including those involving Ras, beta-catenin, p120 catenin, p53 and estrogen receptor alpha. MUC1CT also forms complexes with transcription factors, and then translocates to the nucleus by an unknown mechanism, where it is believed to influence the transcription of their target genes. MUC1CT has also been proposed to localize to mitochondrial membranes under conditions of genotoxic stress, where it attenuates the apoptotic pathway in response and confers resistance to apoptosis-inducing drugs.

RNA interference suppression of MUC1 reduces the growth rate and metastatic phenotype of human pancreatic cancer cells

MUC1 is a highly glycosylated, type I transmembrane protein expressed by normal ductal epithelial cells of the pancreas, breast, lung, and gastrointestinal tract, and overexpressed in many cases of adenocarcinoma. We down-regulated MUC1 expression by RNA interference and investigated the effects on malignant and metastatic potential of a human pancreatic cancer cell line, S2-013. MUC1-suppressed clones, S2-013.MTII.C1 and S2-013.MTII.C2, were established by targeting a sequence 3,151 bp from the initiation codon and characterized in vitro for proliferation, invasion, and adhesion. We evaluated the effects of MUC1 suppression in vivo on tumor growth and metastatic properties following implantation into the cecum or pancreas of athymic mice. MUC1-suppressed clones showed significantly decreased proliferation in vitro and in vivo. Global gene expression was evaluated by oligonucleotide microarray analysis. Surprisingly, genes predicted to increase doubling times (cyclin B1 and cyclin D3) were overexpressed in MUC1-suppressed clones. There were alterations in expression of several genes that may affect the malignant properties of pancreatic cancer. Adhesion of MUC1-suppressed cells in vitro to type IV collagen and fibronectin was slightly increased, and adhesion was slightly decreased to type I collagen and laminin. Results of implantation to cecum and pancreas showed significant reduction of metastasis to lymph nodes, lung, or peritoneal sites compared with S2-013.gfp-neo control cells. These results support the hypothesis that MUC1 contributes significantly to growth and metastasis, and that down-regulation of MUC1 protein expression decreases the metastatic potential of pancreatic adenocarcinoma.

Recycling of MUC1 is dependent on its palmitoylation

MUC1 is a mucin-like transmembrane protein expressed on the apical surface of epithelia, where it protects the cell surface. The cytoplasmic domain has numerous sites for phosphorylation and docking of proteins involved in signal transduction. In a previous study, we showed that the cytoplasmic YXXphi motif Y20HPM and the tyrosine-phosphorylated Y60TNP motif are required for MUC1 clathrin-mediated endocytosis through binding AP-2 and Grb2, respectively (Kinlough, C. L., Poland, P. A., Bruns, J. B., Harkleroad, K. L., and Hughey, R. P. (2004) J. Biol. Chem. 279, 53071-53077). Palmitoylation of transmembrane proteins can affect their membrane trafficking, and the MUC1 sequence CQC3RRK at the boundary of the transmembrane and cytoplasmic domains mimics reported site(s) of S-palmitoylation. [3H]Palmitate labeling of Chinese hamster ovary cells expressing MUC1 with mutations in CQC3RRK revealed that MUC1 is dually palmitoylated at the CQC motif independent of RRK. Lack of palmitoylation did not affect the cold detergent solubility profile of a chimera (Tac ectodomain and MUC1 transmembrane and cytoplasmic domains), the rate of chimera delivery to the cell surface, or its half-life. Calculation of rate constants for membrane trafficking of wild-type and mutant Tac-MUC1 indicated that the lack of palmitoylation blocked recycling, but not endocytosis, and caused the chimera to accumulate in a EGFP-Rab11-positive endosomal compartment. Mutations CQC/AQA and Y20N inhibited Tac-MUC1 co-immunoprecipitation with AP-1, although mutant Y20N had reduced rates of both endocytosis and recycling, but a normal subcellular distribution. The double mutant chimera AQA+Y20N had reduced endocytosis and recycling rates and accumulated in EGFP-Rab11-positive endosomes, indicating that palmitoylation is the dominant feature modulating MUC1 recycling from endosomes back to the plasma membrane.

The MUC1 SEA Module Is a Self-cleaving Domain

MUC1, a glycoprotein overexpressed by a variety of human adenocarcinomas, is a type I transmembrane protein (MUC1/TM) that soon after its synthesis undergoes proteolytic cleavage in its extracellular domain. This cleavage generates two subunits, alpha and beta, that specifically recognize each other and bind together in a strong noncovalent interaction. Proteolysis occurs within the SEA module, a 120-amino acid domain that is highly conserved in a number of heavily glycosylated mucin-like proteins. Post-translational cleavage of the SEA module occurs at a site similar to that in MUC1 in the glycoproteins IgHepta and MUC3. However, as in the case of other proteins containing the cleaved SEA module, the mechanism of MUC1 proteolysis has not been elucidated. Alternative splicing generates two transmembrane MUC1 isoforms, designated MUC1/Y and MUC1/X. We demonstrated here that MUC1/X, whose extracellular domain is comprised solely of the SEA module in addition to 30 MUC1 N-terminal amino acids, undergoes proteolytic cleavage at the same site as the MUC1/TM protein. In contrast, the MUC1/Y isoform, composed of an N-terminally truncated SEA module, is not cleaved. Cysteine or threonine mutations of the MUC1/X serine residue (Ser-63) immediately C-terminal to the cleavage site generated cleaved proteins, whereas mutation of the Ser-63 residue of MUC1/X to any other of 17 amino acids did not result in cleavage. In vitro incubation of highly purified precursor MUC1/X protein resulted in self-cleavage. Furthermore, addition of hydroxylamine, a strong nucleophile, markedly enhanced cleavage. Both these features are signature characteristics of self-cleaving proteins, and we concluded that MUC1 undergoes autoproteolysis mediated by an N --> O-acyl rearrangement at the cleavage site followed by hydrolytic resolution of the unstable ester and concomitant cleavage. It is likely that all cleaved SEA module-containing proteins follow a similar route.

Silencing OCILRP2 leads to intrinsic defects in T cells in response to antigenic stimulation

We have previously demonstrated that OCILRP2 interaction with its ligand NKRP1f provides a co-stimulatory signal for optimal T cell proliferation and IL-2 production. Here, using RNA interference technology, we will demonstrate that silencing OCILRP2 in vivo leads to intrinsic impairment in T cell response to CD3- and CD28-cross-linking as well as antigenic stimulation. OCILRP2-silenced T cells have reduced cell proliferation and IL-2 production, which can be bypassed by PMA and ionomycin treatment. OCILRP2-silenced T cells also failed to undergo TCR capping and had impaired cytoskeleton reorganization. Moreover, in OCILRP2-silenced T cells, tyrosine phosphorylation of Lck was diminished, while tyrosine phosphorylation of linkers for activation of T cells was unchanged. Interestingly, NF-kappaB activation was also impaired as the result of OCILRP2 silencing. Together, our data strongly support a novel role for OCILRP2 C-type lectin in TCR-mediated signal transduction. The observation that OCILRP2 is involved in TCR capping and cytoskeletal organization suggests that OCILRP2-NKRP1f may facilitate lipid rafts and immunological synapse formation during T cell interaction with antigen presenting cells.

A Novel Protein Derived from the MUC1 Gene by Alternative Splicing and Frameshifting

Genes that have been designated the name "MUC" code for proteins comprising mucin domains. These proteins may be involved in barrier and protective functions. The first such gene to be characterized and sequenced is the MUC1 gene. Here we report a novel small protein derived from the MUC1 gene by alternative splicing that does not contain the hallmark of mucin proteins, the mucin domain. This protein termed MUC1/ZD retains the same N-terminal MUC1 sequences as all of the other known MUC1 protein isoforms. The common N-terminal sequences comprise the signal peptide and a subsequent stretch of 30 amino acids. In contrast, the MUC1/ZD C-terminal 43 amino acids are novel and result from a reading frameshift engendered by a splicing event that forms MUC1/ZD. The expression of MUC1/ZD at the protein level in human tissues is demonstrated by Western blotting, immunohistochemistry, immunoprecipitation, and an ELISA. Utilization was made of affinity-purified MUC1/ZD-specific polyclonal antibodies as well as two different monoclonal antibodies that are monospecific for the MUC1/ZD protein. The MUC1/ZD protein is expressed in tissues as an oligomeric complex composed of monomers linked by disulfide bonds contributed by MUC1/ZD cysteine residues. MUC1/ZD protein expression did not parallel that of the tandem-repeat array-containing MUC1 protein. Results presented here demonstrate for the first time the expression of a novel MUC1 protein isoform MUC1/ZD, which is generated by an alternative splicing event that both deletes the tandem-repeat array and leads to a C-terminal reading frameshift.