NHE9 induces chemoradiotherapy resistance in esophageal squamous cell carcinoma by upregulating the Src/Akt/β-catenin pathway and Bcl-2 expression

Recently, we found that NHE9 mRNA was upregulated in chemoradiotherapy (CRT)-resistant esophageal squamous cell carcinoma (ESCC); however, the underlying mechanisms were unclear. Here, we aimed to clarify the functional contribution of NHE9 to CRT resistance, understand the molecular basis of NHE9-dependent resistance in ESCC, and identify potential therapeutic targets. Our results showed that NHE9 prevented CRT-induced apoptosis. Importantly, we found that RACK1 is a novel binding partner of NHE9 and that NHE9-dependent induction of CRT resistance requires the activation of RACK1-associated Src/Akt/beta-catenin signaling. Moreover, upregulated Bcl-2 protein was also observed in cells exhibiting NHE9-induced CRT resistance. A higher NHE9 level was associated with a poor response to CRT and less decrease in T and N stage in ESCC patients. Furthermore, combining either Dasatinib or ABT-737 with CRT significantly reduced tumor volume, and the response to CRT was restored when these inhibitors were used together with CRT in a xenograft nude mouse model with NHE9 overexpression. Taken together, our findings demonstrate that NHE9 can be an effective predictor of CRT response and may be useful in the development of targeted therapies for CRT-resistant ESCC.