N6-Methyladenosine Modification of CIRCKRT17 Initiated by METTL3 Promotes Osimertinib Resistance of Lung Adenocarcinoma by EIF4A3 to Enhance YAP1 Stability

SIMPLE SUMMARY: Circular RNA KRT17 (circKRT17) is elevated in osimertinib-resistant lung cancer cells by a circRNA microarray analysis. However, the functional role of circKRT17 in the osimertinib resistance of lung adenocarcinoma (LUAD) remains undetermined. Herein, we found that circKRT17 and METTL3 were elevated in osimertinib-insensitive LUAD tissues and cells. CircKRT17 and METTL3 knockdown increased the sensitivity of LUAD cells to osimertinib. In mechanisms, we demonstrated that METTL3 enhanced the stability of circKRT17 by initiating m6A modification and, thus, promoting YAP1 nuclear localization through the recruitment of EIF4A3. These collective data provide novel insights into therapeutic strategies for osimertinib-resistant LUAD patients. CircKRT17 may act as a biomarker of osimertinib resistance of LUAD and a promising target for osimertinib-resistant LUAD treatment. ABSTRACT: Background: Circular RNAs (circRNAs) play a key role in regulating the drug resistance of numerous human tumors. However, whether circKRT17 involves in the osimertinib resistance of lung adenocarcinoma (LUAD) remains undetermined. Methods: Relative mRNA/circRNA and protein levels were detected by qRT-PCR and western blotting. Localization of circKRT17 and YAP1 was determined by FISH and immunofluorescence staining. Cell growth and apoptosis were evaluated using colony formation, EdU assays, and flow cytometry. The N6-methyladenosine (m6A) modification was analyzed by MeRIP. The interplay between EIF4A3 and circKRT17 or YAP1 was verified by RNA pull-down or/and RIP assays. Subcutaneous tumor growth was monitored in nude mice, and Ki-67 and TUNEL staining were carried out to evaluate cell proliferation and apoptosis, respectively. Results: CircKRT17 and METTL3 were elevated in osimertinib-insensitive LUAD tissues and cells. Knockdown of circKRT 17 and METTL3 increased the sensitivity of LUAD cells to osimertinib. Knockdown of METTL3 decreased the expression of circKRT17 by inhibiting m6A modification. CircKRT17 promoted the stability and nuclear transportation of YAP1 by recruiting EIF4A3 in LUAD cells. Overexpression of YAP1 abolished the impacts of circKRT17 knockdown on the osimertinib sensitivity of LUAD cells. CircKRT17 knockdown increased the repressive effects of osimertinib on tumor growth in vivo by inhibiting YAP1 signaling. Conclusion: METTL3 initiated the m6A modification of circKRT17, thus promoting osimertinib resistance of LUAD by enhancing YAP1 stability through EIF4A4 recruitment.