Connexin Restrains EMT by Dual-Domain Mechanisms to Preserve Epithelial Identity

Epithelial-mesenchymal transition (EMT) contributes to fibrotic disease in multiple organs and underlies post-surgical complications such as posterior capsule opacification (PCO), the leading cause of vision loss following cataract surgery. The molecular mechanisms that preserve epithelial integrity and restrain EMT remain poorly defined. Connexins are conventionally regarded as gap junction proteins mediating intercellular communication, but here we identify connexin 50 (Cx50) as a previously unrecognized key regulator of EMT. Using in vitro, ex vivo, and in vivo chick and mouse models, we show that transforming growth factor-β2 (TGF-β2) downregulates Cx50 and induces EMT markers including α-smooth muscle actin and fibronectin, changes reversed by Cx50 overexpression. Mechanistically, the extracellular E2 domain of Cx50 mediates adhesive interactions that limit epithelial migration and EMT, while the C-terminal domain stabilizes β-catenin-E-cadherin complexes and prevents TGF-β2-driven E-cadherin loss and β-catenin nuclear translocation. Dominant-negative E2 mutants abolish protection, and Cx50 knockout mice exhibit accelerated EMT after extracapsular lens extraction. These findings redefine connexins beyond their classical role as gap junction proteins, establishing Cx50 as a dual-domain regulator of EMT and epithelial plasticity with implications for fibrotic responses in ocular and other epithelial tissues.