title: Lysosomal trafficking of beta-catenin induced by the tea polyphenol epigallocatechin-3-gallate.
abstract: beta-Catenin is a cadherin-binding protein involved in cell-cell adhesion, which also functions as a transcriptional activator when complexed in the nucleus with members of the T-cell factor (TCF)/lymphoid enhancer factor (LEF) family of proteins. There is considerable interest in mechanisms that down-regulate beta-catenin, since this provides an avenue for the prevention of colorectal and other cancers in which beta-catenin is frequently over-expressed. We show here that physiologically relevant concentrations of the tea polyphenol epigallocatechin-3-gallate (EGCG) inhibited beta-catenin/TCF-dependent reporter activity in human embryonic kidney 293 cells transfected with wild type or mutant beta-catenins, and there was a corresponding decrease in beta-catenin protein levels in the nuclear, cytosolic and membrane-associated fractions. However, beta-catenin accumulated as punctate aggregates in response to EGCG treatment, including in human colon cancer cells over-expressing beta-catenin endogenously. Confocal microscopy studies revealed that the aggregated beta-catenin in HEK293 cells was extra-nuclear and co-localized with lysosomes, suggesting that EGCG activated a pathway involving lysosomal trafficking of beta-catenin. Lysosomal inhibitors leupeptin and transepoxysuccinyl-l-leucylamido(4-guanido)butane produced an increase in beta-catenin protein in total cell lysates, without a concomitant increase in beta-catenin transcriptional activity. These data provide the first evidence that EGCG facilitates the trafficking of beta-catenin into lysosomes, presumably as a mechanism for sequestering beta-catenin and circumventing further nuclear transport and activation of beta-catenin/TCF/LEF signaling.
authors.affiliation: Linus Pauling Institute, 571 Weniger Hall, Oregon State University, Corvallis, OR 97331-6512, USA.
authors.forename: Wan-Mohaiza
authors.initials: WM
authors.lastname: Dashwood
authors.forename: Orianna
authors.initials: O
authors.lastname: Carter
authors.forename: Mohamed
authors.initials: M
authors.lastname: Al-Fageeh
authors.forename: Qingjie
authors.initials: Q
authors.lastname: Li
authors.forename: Roderick H
authors.initials: RH
authors.lastname: Dashwood
mesh_terms: D016588:Anticarcinogenic Agents / Q000737:chemistry / Q000378:metabolism*; D015820:Cadherins / Q000378:metabolism; D002392:Catechin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D002460:Cell Line; D003110:Colonic Neoplasms / Q000378:metabolism; D015179:Colorectal Neoplasms / Q000378:metabolism; D017930:Genes, Reporter; D006801:Humans; D008247:Lysosomes / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D051820:TCF Transcription Factors / Q000235:genetics / Q000378:metabolism; D013662:Tea / Q000737:chemistry*; D058118:Transcription Factor 7-Like 2 Protein; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
chemical_list: D016588:Anticarcinogenic Agents; D015820:Cadherins; D011993:Recombinant Fusion Proteins; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; D013662:Tea; D058118:Transcription Factor 7-Like 2 Protein; D051176:beta Catenin; D002392:Catechin; C045651:epigallocatechin gallate