Reciprocal positive regulation between Cx26 and PI3K/Akt pathway confers acquired gefitinib resistance in NSCLC cells via GJIC-independent induction of EMT.

J Yang,L Pan,G Qin,M Luo,Q Zhang,S Qin,J Chen,L Li

doi:10.1038/cddis.2015.197

Abstract

Gefitinib efficiency in non-small-cell lung cancer (NSCLC) therapy is limited due to development of drug resistance. The molecular mechanisms of gefitinib resistance remain still unclear. In this study, we first found that connexin 26 (Cx26) is the predominant Cx isoform expressed in various NSCLC cell lines. Then, two gefitinib-resistant (GR) NSCLC cell lines, HCC827 GR and PC9 GR, from their parental cells were established. In these GR cells, the results showed that gefitinib resistance correlated with changes in cellular EMT phenotypes and upregulation of Cx26. Cx26 was detected to be accumulated in the cytoplasm and failed to establish functional gap-junctional intercellular communication (GJIC) either in GR cells or their parental cells. Ectopic expression of GJIC-deficient chimeric Cx26 was sufficient to induce EMT and gefitinib insensitivity in HCC827 and PC9 cells, while knockdown of Cx26 reversed EMT and gefitinib resistance in their GR cells both in vitro and in vivo. Furthermore, Cx26 overexpression could activate PI3K/Akt signaling in these cells. Cx26-mediated EMT and gefitinib resistance were significantly blocked by inhibition of PI3K/Akt pathway. Specifically, inhibition of the constitutive activation of PI3K/Akt pathway substantially suppressed Cx26 expression, and Cx26 was confirmed to functionally interplay with PI3K/Akt signaling to promote EMT and gefitinib resistance in NSCLC cells. In conclusion, the reciprocal positive regulation between Cx26 and PI3K/Akt signaling contributes to acquired gefitinib resistance in NSCLC cells by promoting EMT via a GJIC-independent manner.

Highlights

Epithelial-mesenchymal transition (EMT), during which cancer cells lose epithelial markers such as E-cadherin but gain mesenchymal markers such as vimentin, is known to be deeply involved in cancer progression and chemotherapy resistance
In vivo studies showed that treatment with LY294002 (25 mg/kg, twice a week, i.p.) induced marked tumor regression of connexin 26 (Cx26)-overexpressing group to the level comparable to that of mock control group (Figure 6f). These findings suggest that activation of phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway is sufficient to account for Cx26-promoted EMT and gefitinib resistance in non-small-cell lung cancer (NSCLC) cells
We present here that a reciprocal positive regulation exists between Cx26 and PI3K/Akt signaling, providing insights into the molecular mechanism underlying the dysregulation of Cx26 and PI3K/Akt in NSCLC cells

Summary

Introduction

Epithelial-mesenchymal transition (EMT), during which cancer cells lose epithelial markers such as E-cadherin but gain mesenchymal markers such as vimentin, is known to be deeply involved in cancer progression and chemotherapy resistance. There are ~ 21 isoforms of Cxs that distribute in almost all human organs in tissue-specific patterns.[17] Cx26, one of the most common isoforms of Cxs, is predominantly expressed in lung tissue.[18,19] Despite Cx26 has been considered as a potential tumor suppressor or chemotherapy sensitizer in some types of tumors,[20,21] Ito et al.[22] found that Cx26 helps lung squamous cell carcinoma (SCC, one histological type of NSCLC), acquire aggressive phenotypes, lymph node metastasis, and poor prognosis, indicating that a potential role of Cx26 on the malignant development of SCC. The roles of Cx26 and its derived GJIC in the development of gefitinib resistance in NSCLC have not been explored

Methods

Results

Conclusion