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      Functions of EpCAM in physiological processes and diseases (Review)

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          Abstract

          EpCAM (epithelial cell adhesion molecule) is a type I transmembrane glycoprotein, which was originally identified as a tumor-associated antigen due to its high expression level in rapidly growing epithelial tumors. Germ line mutations of the human EpCAM gene have been indicated as the cause of congenital tufting enteropathy. Previous studies based on cell models have revealed that EpCAM contributes to various biological processes including cell adhesion, signaling, migration and proliferation. Due to the previous lack of genetic animal models, the in vivo functions of EpCAM remain largely unknown. However, EpCAM genetic animal models have recently been generated, and are useful for understanding the functions of EpCAM. The authors here briefly review the functions and mechanisms of EpCAM in physiological processes and different diseases.

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          Most cited references118

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          Nuclear signalling by tumour-associated antigen EpCAM.

          EpCAM was found to be overexpressed on epithelial progenitors, carcinomas and cancer-initiating cells. The role of EpCAM in proliferation, and its association with cancer is poorly explained by proposed cell adhesion functions. Here we show that regulated intramembrane proteolysis activates EpCAM as a mitogenic signal transducer in vitro and in vivo. This involves shedding of its ectodomain EpEX and nuclear translocation of its intracellular domain EpICD. Cleavage of EpCAM is sequentially catalysed by TACE and presenilin-2. Pharmacological inhibition or genetic silencing of either protease impairs growth-promoting signalling by EpCAM, which is compensated for by EpICD. Released EpICD associates with FHL2, beta-catenin and Lef-1 to form a nuclear complex that contacts DNA at Lef-1 consensus sites, induces gene transcription and is oncogenic in immunodeficient mice. In patients, EpICD was found in nuclei of colon carcinoma but not of normal tissue. Nuclear signalling of EpCAM explains how EpCAM functions in cell proliferation.
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            Claudin-2 expression induces cation-selective channels in tight junctions of epithelial cells.

            Tight junctions seal the paracellular pathway of epithelia but, in leaky tissues, also exhibit specific permeability. In order to characterize the contribution of claudin-2 to barrier and permeability properties of the tight junction in detail, we studied two strains of Madin-Darby canine kidney cells (MDCK-C7 and MDCK-C11) with different tight junctional permeabilities. Monolayers of C7 cells exhibited a high transepithelial resistance (>1 kOhms cm(2)), compared with C11 cells (<100 Ohms cm(2)). Genuine expression of claudin-1 and claudin-2, but not of occludin or claudin-3, was reciprocal to transepithelial resistance. However, confocal microscopy revealed a marked subjunctional localization of claudin-1 in C11 cells, indicating that claudin-1 is not functionally related to the low tight junctional resistance of C11 cells. Strain MDCK-C7, which endogenously does not express junctional claudin-2, was transfected with claudin-2 cDNA. In transfected cells, but not in vector controls, the protein was detected in colocalization with junctional occludin by means of immunohistochemical analyses. Overexpression of claudin-2 in the originally tight epithelium with claudin-2 cDNA resulted in a 5.6-fold higher paracellular conductivity and relative ion permeabilities of Na(+) identical with 1, K(+)=1.02, NMDG(+)=0.79, choline(+)=0.71, Cl(-)=0.12, Br(-)=0.10 (vector control, 1:1.04:0.95:0.94:0.85:0.83). By contrast, fluxes of (radioactively labeled) mannitol and lactulose and (fluorescence labeled) 4 kDa dextran were not changed. Hence, with regular Ringer's, Na(+) conductivity was 0.2 mS cm(-2) in vector controls and 1.7 mS cm(-2) in claudin-2-transfected cells, while Cl(-) conductivity was 0.2 mS cm(-2) in both cells. Thus, presence of junctional claudin-2 causes the formation of cation-selective channels sufficient to transform a 'tight' tight junction into a leaky one.
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              Tight junctions and cell polarity.

              The tight junction is an intracellular junctional structure that mediates adhesion between epithelial cells and is required for epithelial cell function. Tight junctions control paracellular permeability across epithelial cell sheets and also serve as a barrier to intramembrane diffusion of components between a cell's apical and basolateral membrane domains. Recent genetic and biochemical studies in invertebrates and vertebrates indicate that tight junction proteins play an important role in the establishment and maintenance of apico-basal polarity. Proteins involved in epithelial cell polarization form evolutionarily conserved multiprotein complexes at the tight junction, and these protein complexes regulate the architecture of epithelia throughout the polarization process. Accumulating information regarding the regulation of these polarity proteins will lead to a better understanding of the molecular mechanisms whereby cell polarity is established.
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                Author and article information

                Journal
                Int J Mol Med
                Int. J. Mol. Med
                IJMM
                International Journal of Molecular Medicine
                D.A. Spandidos
                1107-3756
                1791-244X
                October 2018
                11 July 2018
                11 July 2018
                : 42
                : 4
                : 1771-1785
                Affiliations
                [1 ]Guangdong Metabolic Disease Research Center of Integrated Chinese and Western Medicine
                [2 ]Institute of Chinese Medicinal Sciences
                [3 ]School of Traditional Chinese Medicine, Guangdong Pharmaceutical University, Guangzhou Higher Education Mega Center, Guangzhou, Guangdong 510006
                [4 ]The First Affiliated Hospital, School of Clinical Medicine, Guangdong Pharmaceutical University, Guangzhou, Guangdong 510080, P.R. China
                Author notes
                Correspondence to: Dr Zili Lei or Dr Jiao Guo, Institute of Chinese Medicinal Sciences, Guangdong Pharmaceutical University, Guangzhou Higher Education Mega Center, 280 Waihuan East Road, Center, Panyu, Guangzhou, Guangdong 510006, P.R. China, E-mail: 3182683090@ 123456qq.com , E-mail: gyguoyz@ 123456163.com
                [*]

                Contributed equally

                Article
                ijmm-42-04-1771
                10.3892/ijmm.2018.3764
                6108866
                30015855
                c3136b16-2352-4ec3-a07d-e681475b2c57
                Copyright: © Huang et al.

                This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

                History
                : 25 March 2018
                : 04 July 2018
                Categories
                Articles

                epithelial cell adhesion molecule,cell-cell junctions,stem cell,cancer,congenital tufting enteropathy

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