Protein Kinase Cα Mediates Erlotinib Resistance in Lung Cancer Cells

Overexpression and mutational activation of the epidermal growth factor receptor (EGFR) plays an important role in the pathogenesis of non-small cell lung cancer (NSCLC). EGFR tyrosine-kinase inhibitors (TKIs) are given as a primary therapy for advanced patients with EGFR-activating mutations; however, the majority of these tumors relapse and patients eventually develop resistance to TKIs. To address a potential role of protein kinase C (PKC) isozymes in the resistance to TKIs, we used the isogenic NSCLC H1650 cell line and its erlotinib-resistant derivative H1650-M3, a cell line that displays a mesenchymal-like morphology driven by transforming growth factor-beta signaling. We found that H1650-M3 cells display remarkable PKC alpha upregulation and PKC delta downregulation. Notably, silencing PKC alpha from H1650-M3 cells using RNA interference caused a significant reduction in the expression of epithelial-to-mesenchymal transition (EMT) markers vimentin, Zeb2, Snail, and Twist. Moreover, pharmacological inhibition or PKC alpha RNA interference depletion and PKC delta restoring sensitized H1650-M3 cells to erlotinib. Whereas ectopic overexpression of PKC alpha in parental H1650 cells was not sufficient to alter the expression of EMT genes or to confer resistance to erlotinib, it caused downregulation of PKC delta expression, suggesting a unidirectional crosstalk. Finally, mechanistic studies revealed that PKC alpha upregulation in H1650-M3 cells is driven by transforming growth factor-beta. Our results identified important roles for specific PKC isozymes in erlotinib resistance and EMT in lung cancer cells, and highlight PKC alpha as a potential target for lung cancer treatment.