RESUMEN
Palladin is a scaffold protein involved in the formation of actin-associated protein complexes. Gene expression array analysis on the poorly metastatic HCT116 colon cancer cell line and a metastatic derivative cell line (E1) with EMT (epithelial-mesenchymal transition) features showed a down-regulation of palladin gene expression in the latter. Knockdown of palladin expression in the HCT116 cells suppressed junctional localization of E-cadherin, reduced intercellular adhesion and collective cell migration, showing that palladin plays an important role in maintaining the integrity of adherens junctions. The acquisition of the EMT features by the E1 cell line was dependent on the Erk pathway. Inhibition of this pathway by U0126 treatment in E1 cells resulted in the re-expression of palladin, relocalization of E-cadherin to the adherens junctions and a reversal of EMT features. The re-establishment of intercellular adhesion was dependent on palladin expression. The down-regulation of palladin was also observed in poorly-differentiated tumor tubules and dissociated tumor cells that have undergone de-differentiation in human primary colon tumors. Our data show that palladin is an integral component of adherens junctions and plays a role in the localization of E-cadherin to the junctions. The loss of palladin may be an integral part of EMT, an early step in the metastatic spread of colon carcinoma.
Asunto(s)
Uniones Adherentes/metabolismo , Adhesión Celular , Movimiento Celular , Neoplasias Colorrectales/metabolismo , Proteínas del Citoesqueleto/metabolismo , Fosfoproteínas/metabolismo , Uniones Adherentes/efectos de los fármacos , Uniones Adherentes/patología , Animales , Antígenos CD , Cadherinas/metabolismo , Adhesión Celular/efectos de los fármacos , Desdiferenciación Celular , Movimiento Celular/efectos de los fármacos , Neoplasias Colorrectales/genética , Neoplasias Colorrectales/patología , Proteínas del Citoesqueleto/genética , Transición Epitelial-Mesenquimal , Quinasas MAP Reguladas por Señal Extracelular/antagonistas & inhibidores , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Femenino , Regulación Neoplásica de la Expresión Génica , Células HCT116 , Humanos , Neoplasias Hepáticas/metabolismo , Neoplasias Hepáticas/secundario , Ratones , Ratones Desnudos , Invasividad Neoplásica , Fenotipo , Fosfoproteínas/genética , Inhibidores de Proteínas Quinasas/farmacología , Interferencia de ARN , Neoplasias del Bazo/metabolismo , Neoplasias del Bazo/secundario , Factores de Tiempo , TransfecciónRESUMEN
BACKGROUND: Members of the TRIP-Br/SERTAD family of mammalian transcriptional coregulators have recently been implicated in E2F-mediated cell cycle progression and tumorigenesis. We, herein, focus on the detailed functional characterization of the least understood member of the TRIP-Br/SERTAD protein family, TRIP-Br2 (SERTAD2). METHODS: Oncogenic potential of TRIP-Br2 was demonstrated by (1) inoculation of NIH3T3 fibroblasts, which were engineered to stably overexpress ectopic TRIP-Br2, into athymic nude mice for tumor induction and (2) comprehensive immunohistochemical high-throughput screening of TRIP-Br2 protein expression in multiple human tumor cell lines and human tumor tissue microarrays (TMAs). Clinicopathologic analysis was conducted to assess the potential of TRIP-Br2 as a novel prognostic marker of human cancer. RNA interference of TRIP-Br2 expression in HCT-116 colorectal carcinoma cells was performed to determine the potential of TRIP-Br2 as a novel chemotherapeutic drug target. RESULTS: Overexpression of TRIP-Br2 is sufficient to transform murine fibroblasts and promotes tumorigenesis in nude mice. The transformed phenotype is characterized by deregulation of the E2F/DP-transcriptional pathway through upregulation of the key E2F-responsive genes CYCLIN E, CYCLIN A2, CDC6 and DHFR. TRIP-Br2 is frequently overexpressed in both cancer cell lines and multiple human tumors. Clinicopathologic correlation indicates that overexpression of TRIP-Br2 in hepatocellular carcinoma is associated with a worse clinical outcome by Kaplan-Meier survival analysis. Small interfering RNA-mediated (siRNA) knockdown of TRIP-Br2 was sufficient to inhibit cell-autonomous growth of HCT-116 cells in vitro. CONCLUSION: This study identifies TRIP-Br2 as a bona-fide protooncogene and supports the potential for TRIP-Br2 as a novel prognostic marker and a chemotherapeutic drug target in human cancer.