Stabilization of E-cadherin adhesions by COX-2/GSK3ß signaling is a targetable pathway in metastatic breast cancer

Metastatic progression of epithelial cancers can be associated with epithelial-mesenchymal-transition (EMT) including transcriptional inhibition of E-cadherin (CDH1) expression. Recently, EM plasticity (EMP) and E-cadherin-mediated, cluster-based metastasis and treatment resistance have become more appreciated. However, the mechanisms that maintain E-cadherin expression in this context are less understood. Through studies of inflammatory breast cancer (IBC) and a 3D tumor cell "emboli" culture paradigm, we discovered that COX-2 (PTGS2), a target gene of C/EBPd (CEBPD), or its metabolite prostaglandin E2 (PGE2) promotes protein stability of E-cadherin, ß-catenin and p120 catenin through inhibition of GSK3ß. The COX-2 inhibitor celecoxib downregulated E-cadherin complex proteins and caused cell death. Co-expression of E-cadherin and COX-2 was seen in breast cancer patients with poor outcome and, along with inhibitory GSK3ß phosphorylation, in patient-derived xenografts (PDX) including triple negative breast cancer (TNBC). Celecoxib alone decreased E-cadherin protein expression within xenograft tumors, though CDH1 mRNA levels increased, and reduced circulating tumor cell (CTC) clusters, and in combination with paclitaxel attenuated or regressed lung metastases. This study uncovered a mechanism by which metastatic breast cancer cells can maintain E-cadherin-mediated cell-cell adhesions and cell survival, suggesting that some patients with COX-2+/E-cadherin+ breast cancer may benefit from targeting of the PGE2 signaling pathway.

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