Connexin43 over-expression induces partial Mesenchymal-Epithelial-Transition in MDA-MB-231 breast cancer cells -

Abstract

Many studies have classified cancer in the category of connexin-related pathologies. Addressing the role of connexins (Cx) in breast cancer progression has yielded contradictory results. In order to investigate the role of Cx43 in highly invasive breast cancer cells, we over-expressed Cx43 in MDA-MB-231 cells, a human breast cancer cell line that expresses low endogenous Cx43 levels. Our data shows a decrease in cell proliferation in Cx43 overexpressing cells grown in 3D cultures on Matrigel, a milieu that more faithfully mimics the in vivo context. The decrease in cell proliferation was not noted in cells grown on 2D. This effect is mediated, in part, by up-regulation of cadherins in Cx43 over-expressing cells when grown on 3D. Our data also shows that E-cadherin and p21 are not expressed in Cx43 over-expressing MDA-MB-231 cells and that levels of Cyclin B, Cyclin D and p38 remain constant when comparing Cx43, sham transfected and untransfected cells in 2D and 3D conditions. As opposed to sham and untransfected cells, qRTPCR of Cx43 overexpressing cells showed a 2-fold decrease in Zeb1-GAPDH mRNA levels in 2D but not in 3D cultures. A similar trend was also noted in Vimentin-GAPDH levels, but both in 2D and 3D cultures. Examination of cell polarity marker Scribble shows that when Cx43, sham and untransfected cells are grown on 2D, the protein is cytoplasmic, an abnormal phenotype commonly found in breast cancer cells. However, growing Cx43, sham and untransfected cells on 3D localized Scribble predominantly to the membrane. The data suggests that Cx43 mediates a partial transcriptional down-regulation of certain Epithelial-Mesenchymal Transition markers, while the cellular context may also affect apico-basal polarity of breast cancer cells independently of the genetic background. In conclusion, Cx43 alters tumor phenotype of highly metastatic breast cancer cells in a context dependent manner and partially induces Mesenchymal-Epithelial Transition.