title: The Anoikis Effector Bit1 Inhibits EMT through Attenuation of TLE1-Mediated Repression of E-Cadherin in Lung Cancer Cells.
abstract: The mitochondrial Bcl-2 inhibitor of transcription 1 (Bit1) protein is part of an anoikis-regulating pathway that is selectively dependent on integrins. We previously demonstrated that the caspase-independent apoptotic effector Bit1 exerts tumor suppressive function in lung cancer in part by inhibiting anoikis resistance and anchorage-independent growth in vitro and tumorigenicity in vivo. Herein we show a novel function of Bit1 as an inhibitor cell migration and epithelial-mesenchymal transition (EMT) in the human lung adenocarcinoma A549 cell line. Suppression of endogenous Bit1 expression via siRNA and shRNA strategies promoted mesenchymal phenotypes, including enhanced fibroblastoid morphology and cell migratory potential with concomitant downregulation of the epithelial marker E-cadherin expression. Conversely, ectopic Bit1 expression in A549 cells promoted epithelial transition characterized by cuboidal-like epithelial cell phenotype, reduced cell motility, and upregulated E-cadherin expression. Specific downregulation of E-cadherin in Bit1-transfected cells was sufficient to block Bit1-mediated inhibition of cell motility while forced expression of E-cadherin alone attenuated the enhanced migration of Bit1 knockdown cells, indicating that E-cadherin is a downstream target of Bit1 in regulating cell motility. Furthermore, quantitative real-time PCR and reporter analyses revealed that Bit1 upregulates E-cadherin expression at the transcriptional level through the transcriptional regulator Amino-terminal Enhancer of Split (AES) protein. Importantly, the Bit1/AES pathway induction of E-cadherin expression involves inhibition of the TLE1-mediated repression of E-cadherin, by decreasing TLE1 corepressor occupancy at the E-cadherin promoter as revealed by chromatin immunoprecipitation assays. Consistent with its EMT inhibitory function, exogenous Bit1 expression significantly suppressed the formation of lung metastases of A549 cells in an in vivo experimental metastasis model. Taken together, our studies indicate Bit1 is an inhibitor of EMT and metastasis in lung cancer and hence can serve as a molecular target in curbing lung cancer aggressiveness.
authors.affiliation: Department of Biological and Public Health Sciences, Xavier University of Louisiana, New Orleans, Louisiana, United States of America.
authors.forename: Xin
authors.initials: X
authors.lastname: Yao
authors.affiliation: Department of Biological and Public Health Sciences, Xavier University of Louisiana, New Orleans, Louisiana, United States of America.
authors.forename: Tri
authors.initials: T
authors.lastname: Pham
authors.affiliation: Department of Biological and Public Health Sciences, Xavier University of Louisiana, New Orleans, Louisiana, United States of America.
authors.forename: Brandi
authors.initials: B
authors.lastname: Temple
authors.affiliation: Department of Biological and Public Health Sciences, Xavier University of Louisiana, New Orleans, Louisiana, United States of America.
authors.forename: Selena
authors.initials: S
authors.lastname: Gray
authors.affiliation: Department of Biological and Public Health Sciences, Xavier University of Louisiana, New Orleans, Louisiana, United States of America.
authors.forename: Cornita
authors.initials: C
authors.lastname: Cannon
authors.affiliation: Center for Bioengineering, University of California Santa Barbara, Santa Barbara, California, United States of America.
authors.forename: Renwei
authors.initials: R
authors.lastname: Chen
authors.affiliation: Tulane Cancer Center, Tulane University School of Medicine, New Orleans, Louisiana, United States of America.
authors.forename: Asim B
authors.initials: AB
authors.lastname: Abdel-Mageed
authors.affiliation: Department of Biological and Public Health Sciences, Xavier University of Louisiana, New Orleans, Louisiana, United States of America.
authors.forename: Hector
authors.initials: H
authors.lastname: Biliran
mesh_terms: D000072283:A549 Cells; D023102:Anoikis / Q000502:physiology*; D015820:Cadherins / Q000378:metabolism*; D002265:Carboxylic Ester Hydrolases / Q000502:physiology*; D056970:Co-Repressor Proteins; D015536:Down-Regulation; D058750:Epithelial-Mesenchymal Transition / Q000502:physiology*; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism / Q000473:pathology*; D024101:Mitochondrial Proteins / Q000502:physiology*; D009362:Neoplasm Metastasis; D012097:Repressor Proteins / Q000502:physiology*; D014158:Transcription, Genetic; D015854:Up-Regulation
chemical_list: D015820:Cadherins; D056970:Co-Repressor Proteins; D024101:Mitochondrial Proteins; D012097:Repressor Proteins; C499043:TLE1 protein, human; D002265:Carboxylic Ester Hydrolases; C483418:PTH2 protein, human