ELK1/MTOR/S6K1 Pathway Contributes to Acquired Resistance to Gefitinib in Non-Small Cell Lung Cancer
The development of acquired resistance to small molecule tyrosine kinase inhibitors (TKIs) targeting epidermal growth factor receptor (EGFR) signaling has hindered their efficacy in treating non-small cell lung cancer (NSCLC) patients. Our previous study showed that constitutive activation of the 70...
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MDPI AG
2024-02-01
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| Series: | International Journal of Molecular Sciences |
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| Online Access: | https://www.mdpi.com/1422-0067/25/4/2382 |
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| author | Lei Zhao Yifang Wang Xin Sun Xiujuan Zhang Nicole Simone Jun He |
| author_facet | Lei Zhao Yifang Wang Xin Sun Xiujuan Zhang Nicole Simone Jun He |
| author_sort | Lei Zhao |
| collection | DOAJ |
| description | The development of acquired resistance to small molecule tyrosine kinase inhibitors (TKIs) targeting epidermal growth factor receptor (EGFR) signaling has hindered their efficacy in treating non-small cell lung cancer (NSCLC) patients. Our previous study showed that constitutive activation of the 70 kDa ribosomal protein S6 kinase 1 (S6K1) contributes to the acquired resistance to EGFR-TKIs in NSCLC cell lines and xenograft tumors in nude mice. However, the regulatory mechanisms underlying S6K1 constitutive activation in TKI-resistant cancer cells have not yet been explored. In this study, we recapitulated this finding by taking advantage of a gefitinib-resistant patient-derived xenograft (PDX) model established through a number of passages in mice treated with increasing doses of gefitinib. The dissociated primary cells from the resistant PDX tumors (PDX-R) displayed higher levels of phosphor-S6K1 expression and were resistant to gefitinib compared to cells from passage-matched parental PDX tumors (PDX-P). Both genetic and pharmacological inhibition of S6K1 increased sensitivity to gefitinib in PDX-R cells. In addition, both total and phosphorylated mechanistic target of rapamycin kinase (MTOR) levels were upregulated in PDX-R and gefitinib-resistant PC9G cells. Knockdown of MTOR by siRNA decreased the expression levels of total and phosphor-S6K1 and increased sensitivity to gefitinib in PDX-R and PC9G cells. Moreover, a transcription factor ELK1, which has multiple predicted binding sites on the MTOR promoter, was also upregulated in PDX-R and PC9G cells, while the knockdown of ELK1 led to decreased expression of MTOR and S6K1. The chromatin immunoprecipitation (ChIP)-PCR assay showed the direct binding between ELK1 and the MTOR promoter, and the luciferase reporter assay further indicated that ELK1 could upregulate MTOR expression through tuning up its transcription. Silencing ELK1 via siRNA transfection improved the efficacy of gefitinib in PDX-R and PC9G cells. These results support the notion that activation of ELK1/MTOR/S6K1 signaling contributes to acquired resistance to gefitinib in NSCLC. The findings in this study shed new light on the mechanism for acquired EGFR-TKI resistance and provide potential novel strategies by targeting the ELK1/MTOR/S6K1 pathway. |
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| language | English |
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| spelling | doaj.art-117b2455d84c459987c1dafe97920c052024-02-23T15:20:48ZengMDPI AGInternational Journal of Molecular Sciences1661-65961422-00672024-02-01254238210.3390/ijms25042382ELK1/MTOR/S6K1 Pathway Contributes to Acquired Resistance to Gefitinib in Non-Small Cell Lung CancerLei Zhao0Yifang Wang1Xin Sun2Xiujuan Zhang3Nicole Simone4Jun He5Department of Pathology and Genomic Medicine, Sidney Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USADepartment of Pathology and Genomic Medicine, Sidney Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USADepartment of Pathology and Genomic Medicine, Sidney Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USADepartment of Medicine, Center for Translational Medicine, Thomas Jefferson University, Philadelphia, PA 19107, USADepartment of Radiation Oncology, Sidney Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USADepartment of Pathology and Genomic Medicine, Sidney Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USAThe development of acquired resistance to small molecule tyrosine kinase inhibitors (TKIs) targeting epidermal growth factor receptor (EGFR) signaling has hindered their efficacy in treating non-small cell lung cancer (NSCLC) patients. Our previous study showed that constitutive activation of the 70 kDa ribosomal protein S6 kinase 1 (S6K1) contributes to the acquired resistance to EGFR-TKIs in NSCLC cell lines and xenograft tumors in nude mice. However, the regulatory mechanisms underlying S6K1 constitutive activation in TKI-resistant cancer cells have not yet been explored. In this study, we recapitulated this finding by taking advantage of a gefitinib-resistant patient-derived xenograft (PDX) model established through a number of passages in mice treated with increasing doses of gefitinib. The dissociated primary cells from the resistant PDX tumors (PDX-R) displayed higher levels of phosphor-S6K1 expression and were resistant to gefitinib compared to cells from passage-matched parental PDX tumors (PDX-P). Both genetic and pharmacological inhibition of S6K1 increased sensitivity to gefitinib in PDX-R cells. In addition, both total and phosphorylated mechanistic target of rapamycin kinase (MTOR) levels were upregulated in PDX-R and gefitinib-resistant PC9G cells. Knockdown of MTOR by siRNA decreased the expression levels of total and phosphor-S6K1 and increased sensitivity to gefitinib in PDX-R and PC9G cells. Moreover, a transcription factor ELK1, which has multiple predicted binding sites on the MTOR promoter, was also upregulated in PDX-R and PC9G cells, while the knockdown of ELK1 led to decreased expression of MTOR and S6K1. The chromatin immunoprecipitation (ChIP)-PCR assay showed the direct binding between ELK1 and the MTOR promoter, and the luciferase reporter assay further indicated that ELK1 could upregulate MTOR expression through tuning up its transcription. Silencing ELK1 via siRNA transfection improved the efficacy of gefitinib in PDX-R and PC9G cells. These results support the notion that activation of ELK1/MTOR/S6K1 signaling contributes to acquired resistance to gefitinib in NSCLC. The findings in this study shed new light on the mechanism for acquired EGFR-TKI resistance and provide potential novel strategies by targeting the ELK1/MTOR/S6K1 pathway.https://www.mdpi.com/1422-0067/25/4/2382EGFR-TKIgefitinibS6K1MTORELK1resistance |
| spellingShingle | Lei Zhao Yifang Wang Xin Sun Xiujuan Zhang Nicole Simone Jun He ELK1/MTOR/S6K1 Pathway Contributes to Acquired Resistance to Gefitinib in Non-Small Cell Lung Cancer International Journal of Molecular Sciences EGFR-TKI gefitinib S6K1 MTOR ELK1 resistance |
| title | ELK1/MTOR/S6K1 Pathway Contributes to Acquired Resistance to Gefitinib in Non-Small Cell Lung Cancer |
| title_full | ELK1/MTOR/S6K1 Pathway Contributes to Acquired Resistance to Gefitinib in Non-Small Cell Lung Cancer |
| title_fullStr | ELK1/MTOR/S6K1 Pathway Contributes to Acquired Resistance to Gefitinib in Non-Small Cell Lung Cancer |
| title_full_unstemmed | ELK1/MTOR/S6K1 Pathway Contributes to Acquired Resistance to Gefitinib in Non-Small Cell Lung Cancer |
| title_short | ELK1/MTOR/S6K1 Pathway Contributes to Acquired Resistance to Gefitinib in Non-Small Cell Lung Cancer |
| title_sort | elk1 mtor s6k1 pathway contributes to acquired resistance to gefitinib in non small cell lung cancer |
| topic | EGFR-TKI gefitinib S6K1 MTOR ELK1 resistance |
| url | https://www.mdpi.com/1422-0067/25/4/2382 |
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