RESUMO
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.
Assuntos
Antígenos de Neoplasias/metabolismo , Moléculas de Adesão Celular/metabolismo , Núcleo Celular/metabolismo , Proliferação de Células , Transformação Celular Neoplásica/metabolismo , Mitose/fisiologia , Transdução de Sinais/fisiologia , Proteínas ADAM/metabolismo , Proteína ADAM17 , Transporte Ativo do Núcleo Celular/fisiologia , Animais , Antígenos de Neoplasias/genética , Carcinoma/genética , Carcinoma/metabolismo , Moléculas de Adesão Celular/genética , Membrana Celular/genética , Membrana Celular/metabolismo , Núcleo Celular/genética , Transformação Celular Neoplásica/genética , Neoplasias do Colo/genética , Neoplasias do Colo/metabolismo , Molécula de Adesão da Célula Epitelial , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Humanos , Proteínas com Homeodomínio LIM , Fator 1 de Ligação ao Facilitador Linfoide/genética , Fator 1 de Ligação ao Facilitador Linfoide/metabolismo , Masculino , Camundongos , Proteínas Musculares/genética , Proteínas Musculares/metabolismo , Células NIH 3T3 , Presenilina-2/metabolismo , Estrutura Terciária de Proteína , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , beta Catenina/genética , beta Catenina/metabolismoRESUMO
Epithelial cell adhesion molecule (EpCAM) is a membrane glycoprotein expressed on adenomatous and simple epithelia, where it is involved in homophilic adhesion at the basolateral membrane. Carcinomas strongly overexpress EpCAM through an, as yet, unknown mechanism. Interestingly, otherwise EpCAM-negative squamous epithelia are seen to express EpCAM concomitant with their transformation and de-differentiation. The amount of EpCAM and the number of expressing cells both increase with the grade of dysplasia. Despite an important amount of data correlating the expression of EpCAM with cellular proliferation and de-differentiation, such as the coexpression with Ki-67, a marker for proliferation, it is unknown whether EpCAM may directly contribute to carcinogenesis. Here, we show that EpCAM has a direct impact on cell cycle and proliferation, and the ability to rapidly upregulate the proto-oncogene c-myc and cyclin A/E. Human epithelial 293 cells as well as murine NIH3T3 fibroblasts expressing EpCAM had a decreased requirement for growth factors, enhanced metabolic activity and colony formation capacity. Importantly, the inhibition of EpCAM expression with antisense mRNA led to a strong decrease in proliferation and metabolism in human carcinoma cells. Moreover, domain swapping experiments demonstrated that the intracellular part of EpCAM is necessary and sufficient to transduce the effects described. Thus, the data presented here highlight the role of EpCAM, demonstrating for the first time a direct link to cell cycle and proliferation.
Assuntos
Antígenos de Neoplasias/metabolismo , Moléculas de Adesão Celular/metabolismo , Proteínas Proto-Oncogênicas c-myc/genética , Células 3T3/metabolismo , Células 3T3/patologia , Animais , Antígenos de Neoplasias/genética , Testes de Carcinogenicidade , Carcinoma/genética , Carcinoma/metabolismo , Carcinoma/patologia , Moléculas de Adesão Celular/genética , Ciclo Celular/fisiologia , Divisão Celular/fisiologia , Células Cultivadas , Ciclina A/genética , Ciclina A/metabolismo , Ciclina E/genética , Ciclina E/metabolismo , Molécula de Adesão da Célula Epitelial , Células Epiteliais/metabolismo , Células Epiteliais/patologia , Regulação da Expressão Gênica , Humanos , Camundongos , Estrutura Terciária de Proteína , Proto-Oncogene Mas , Proteínas Proto-Oncogênicas c-myc/metabolismo , Regulação para CimaRESUMO
The tissue-specific glycosylation of the carcinoma (CA)-associated antigen epithelial cell adhesion molecule (EpCAM) was studied in 60 patients suffering from head and neck CAs, and 26 pairs of autologous healthy thyroid and CA biopsies. EpCAM was glycosylated in all tumor samples in which its expression was detectable (73%). Additionally, in 80.7% of patients, tumor-derived EpCAM was heavily glycosylated while EpCAM derived from autologous thyroid was not (76.2%) or weakly (23.8%). Four cases showed a similar glycosylation pattern (15.3%) and one case displayed a reverse pattern (3.8%). Additionally, the expression and glycosylation of EpCAM were assessed in tumor adjacent and distant tissue. EpCAM was glycosylated in tumor-adjacent while it was not or only weakly expressed in tumor distant tissue where it was unglycosylated. Thus, EpCAM is differentially glycosylated in healthy tissue and tumor cells of the head and neck area.