Napsin A is negatively associated with EMT-mediated EGFR-TKI resistance in lung cancer cells

Abstract

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKI) have been used as a standard therapy for patients with lung cancer with EGFR-activating mutations. Epithelial-mesenchymal transition (EMT) has been reported to be associated with the development of EGFR-TKI resistance, which limits the clinical efficacy of EGFR-TKI. Therefore, investigating the resistance-associated mechanism is required in order to elucidate an effective therapeutic approach to enhance the sensitivity of lung cancer to EGFR-TKI. In the present study, EGFR-TKI erlotinib-sensitive H358, H322 and H441 lung cancer cells, erlotinib-moderately sensitive A549 cells, and erlotinib-insensitive HCC827 cells with EGFR-mutation (exon 19 deletion) were used to detect the mRNA and protein expression of the EMT-associated proteins E-cadherin and vimentin, and napsin A, by reverse transcription-quantitative polymerase chain reaction analysis and western blotting. It was observed that the E-cadherin expression level in erlotinib-sensitive cells was increased compared with the moderately sensitive A549 cells and HCC827 cells; however, vimentin exhibited opposite expression, suggesting a correlation between EMT and erlotinib sensitivity in lung cancer cells. The napsin A expression level was observed to be positively associated with erlotinib sensitivity. In addition, napsin A highly-expressingH322 cells were used and napsin A-silenced cells were constructed using small interfering RNA (siRNA) technology, and were induced by transforming growth factor (TGF)-ßl. It was observed that TGF-ßl partially induced the alterations in E-cadherin and vimentin expression and the occurrence of EMT in napsin A highly-expressing cells, while TGF-ßl significantly induced EMT via downregulation of E-cadherin and upregulation of vimentin in napsin A-silenced cells; cell proliferation and apoptosis assays demonstrated that TGF-ßl induced marked resistance to erlotinib in napsin A-silenced cells compared with napsin A-expression cells. These data indicated that napsin A expression may inhibit TGF-ßl-induced EMT and was negatively associated with EMT-mediated erlotinib resistance, suggesting that napsin A expression may improve the sensitivity of lung cancer cells to EGFR-TKI through the inhibition of EMT.