Napsin A is negatively associated with EMT­mediated EGFR­TKI resistance in lung cancer cells.

ABSTRACT

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR­TKI) have been used as a standard therapy for patients with lung cancer with EGFR­activating mutations. Epithelial­mesenchymal transition (EMT) has been reported to be associated with the development of EGFR­TKI resistance, which limits the clinical efficacy of EGFR­TKI. Therefore, investigating the resistance­associated mechanism is required in order to elucidate an effective therapeutic approach to enhance the sensitivity of lung cancer to EGFR­TKI. In the present study, EGFR­TKI erlotinib­sensitive H358, H322 and H441 lung cancer cells, erlotinib­moderately sensitive A549 cells, and erlotinib­insensitive HCC827 cells with EGFR­mutation (exon 19 deletion) were used to detect the mRNA and protein expression of the EMT­associated proteins E­cadherin and vimentin, and napsin A, by reverse transcription­quantitative polymerase chain reaction analysis and western blotting. It was observed that the E­cadherin expression level in erlotinib­sensitive 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 highly­expressingH322 cells were used and napsin A­silenced cells were constructed using small interfering RNA (siRNA) technology, and were induced by transforming growth factor (TGF)­ßl. It was observed that TGF­ßl partially induced the alterations in E­cadherin and vimentin expression and the occurrence of EMT in napsin A highly­expressing cells, while TGF­ßl significantly induced EMT via downregulation of E­cadherin and upregulation of vimentin in napsin A­silenced cells; cell proliferation and apoptosis assays demonstrated that TGF­ßl induced marked resistance to erlotinib in napsin A­silenced cells compared with napsin A­expression cells. These data indicated that napsin A expression may inhibit TGF­ßl­induced EMT and was negatively associated with EMT­mediated erlotinib resistance, suggesting that napsin A expression may improve the sensitivity of lung cancer cells to EGFR­TKI through the inhibition of EMT.