E-cadherin is required for the proper activation of the Lifr/Gp130 signaling pathway in mouse embryonic stem cells

The leukemia inhibitory factor (Lif) signaling pathway is a crucial determinant for mouse embryonic stem (mES) cell self-renewal and pluripotency. One of the hallmarks of mES cells, their compact growth morphology, results from tight cell adhesion mediated through E-cadherin, beta-catenin (Ctnnb1) and alpha-catenin with the actin cytoskeleton. beta-catenin is also involved in canonical Wnt signaling, which has also been suggested to control mES cell stemness. Here, we analyze Ctnnb1(-/-) mES cells in which cell adhesion is preserved by an E-cadherin-alpha-catenin (E alpha) fusion protein (Ctnnb1(-/-)E alpha mES cells), and show that mimicking only the adhesive function of beta-catenin is necessary and sufficient to maintain the mES cell state, making beta-catenin/Wnt signaling obsolete in this process. Furthermore, we propose a role for E-cadherin in promoting the Lif signaling cascade, showing an association of E-cadherin with the Lifr-Gp130 receptor complex, which is most likely facilitated by the extracellular domain of E-cadherin. Without E alpha, and thus without maintained cell adhesion, Ctnnb1(-/-) mES cells downregulate components of the Lif signaling pathway, such as Lifr, Gp130 and activated Stat3, as well as pluripotency-associated markers. From these observations, we hypothesize that the changes in gene expression accompanying the loss of pluripotency are a direct consequence of dysfunctional cell adhesion. Supporting this view, we find that the requirement for intact adhesion can be circumvented by the forced expression of constitutively active Stat3. In summary, we put forward a model in which mES cells can be propagated in culture in the absence of Ctnnb1, as long as E-cadherin-mediated cell adhesion is preserved.