title: Context dependent reversion of tumor phenotype by connexin-43 expression in MDA-MB231 cells and MCF-7 cells: role of β-catenin/connexin43 association.
abstract: Connexins (Cx), gap junction (GJ) proteins, are regarded as tumor suppressors, and Cx43 expression is often down regulated in breast tumors. We assessed the effect of Cx43 over-expression in 2D and 3D cultures of two breast adenocarcinoma cell lines: MCF-7 and MDA-MB-231. While Cx43 over-expression decreased proliferation of 2D and 3D cultures of MCF-7 by 56% and 80% respectively, MDA-MB-231 growth was not altered in 2D cultures, but exhibited 35% reduction in 3D cultures. C-terminus truncated Cx43 did not alter proliferation. Untransfected MCF-7 cells formed spherical aggregates in 3D cultures, and MDA-MB-231 cells formed stellar aggregates. However, MCF-7 cells over-expressing Cx43 formed smaller sized clusters and Cx43 expressing MDA-MB-231 cells lost their stellar morphology. Extravasation ability of both MCF-7 and MDA-MB-231 cells was reduced by 60% and 30% respectively. On the other hand, silencing Cx43 in MCF10A cells, nonneoplastic human mammary cell line, increased proliferation in both 2D and 3D cultures, and disrupted acinar morphology. Although Cx43 over-expression did not affect total levels of β-catenin, α-catenin and ZO-2, it decreased nuclear levels of β-catenin in 2D and 3D cultures of MCF-7 cells, and in 3D cultures of MDA-MB-231 cells. Cx43 associated at the membrane with α-catenin, β-catenin and ZO-2 in 2D and 3D cultures of MCF-7 cells, and only in 3D conditions in MDA-MB-231 cells. This study suggests that Cx43 exerts tumor suppressive effects in a context-dependent manner where GJ assembly with α-catenin, β-catenin and ZO-2 may be implicated in reducing growth rate, invasiveness, and, malignant phenotype of 2D and 3D cultures of MCF-7 cells, and 3D cultures of MDA-MB-231 cells, by sequestering β-catenin away from nucleus.
authors.affiliation: Department of Biology, Faculty of Arts and Sciences, American University of Beirut, P.O. Box 11-0236, Beirut, Lebanon. Electronic address: rtalhouk@aub.edu.lb.
authors.forename: Rabih S
authors.initials: RS
authors.lastname: Talhouk
authors.forename: Mohamed-Bilal
authors.initials: MB
authors.lastname: Fares
authors.forename: Gilbert J
authors.initials: GJ
authors.lastname: Rahme
authors.forename: Hanaa H
authors.initials: HH
authors.lastname: Hariri
authors.forename: Tina
authors.initials: T
authors.lastname: Rayess
authors.forename: Hashem A
authors.initials: HA
authors.lastname: Dbouk
authors.forename: Dana
authors.initials: D
authors.lastname: Bazzoun
authors.forename: Dania
authors.initials: D
authors.lastname: Al-Labban
authors.forename: Marwan E
authors.initials: ME
authors.lastname: El-Sabban
mesh_terms: D018031:Connexin 43 / Q000235:genetics* / Q000378:metabolism*; D020869:Gene Expression Profiling; D006801:Humans; D061986:MCF-7 Cells; D009369:Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D010641:Phenotype; D011485:Protein Binding; D060888:Real-Time Polymerase Chain Reaction; D014407:Tumor Cells, Cultured; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism*
chemical_list: D018031:Connexin 43; D051176:beta Catenin
keywords: Breast Cancer; Catenin; Connexin; Gap junction intercellular communication