Connexin 32 constrains a mesenchymal-like switch in differentiated urothelium and luminal cancers

We reveal a coordinating role for Cx32-mediated cell–cell communication in maintaining mitotic-quiescence and limiting migration-associated TGFβ signalling, extracellular matrix remodelling and mesenchymal-like changes in human urothelium. These features establish a dichotomy in the biology of luminal muscle invasive bladder cancers. The molecular programming of epithelial wound repair provides the origin for the signalling pathways that drive the growth and spread of carcinoma cells. Urothelium is the mitotically quiescent, barrier-forming transitional epithelium of the urinary tract, characterised by uniquely specialised superficial cells and a remarkable regenerative capacity in response to damage. Connexin 32 (Cx32) was expressed by differentiated human urothelium where it predominantly localised to the basolateral borders of superficial urothelial cells. Suppression of Cx32 gap junction intercellular communication did not affect differentiation but instigated the switch to a highly migratory, wound healing phenotype marked by TGFβ-SMAD signalling, ECM-remodelling, and induction of mesenchymal and cell-cycle markers. Immunohistological classification of muscle-invasive bladder cancers revealed Cx32 expression to be informative in luminal tumour biology, with non-membrane localised Cx32 defining a Ki67-high, vimentin-expressing, and TGFβ-activated subset of luminal tumours. Our findings identify Cx32 cell–cell communication as suppressing migratory and proliferative behaviours in normal urothelial differentiation and suggest that Cx32 assessment, within the context of luminal muscle-invasive bladder cancer, can predict more invasive biology. This reveals the potential for differentiated cancers to exhibit EMT.