TY - JOUR
T1 - CpG hypermethylation contributes to decreased expression of PTEN during acquired resistance to gefitinib in human lung cancer cell lines
AU - Maeda, Masashi
AU - Murakami, Yuichi
AU - Watari, Kosuke
AU - Kuwano, Michihiko
AU - Izumi, Hiroto
AU - Ono, Mayumi
N1 - Funding Information:
This work was supported by the 3rd Term Comprehensive Control Research for Cancer from the Ministry of Health, Labor, and Welfare in Japan and also by a Grant-in-Aid for challenging Exploratory Research from the Japan Society for the Promotion of Science (JSPS) (M.K.) and supported by Life Science Foundation (M.O).
Publisher Copyright:
© 2015 Elsevier Ireland Ltd.
PY - 2015/3/1
Y1 - 2015/3/1
N2 - Objectives: We have previously reported that decreased expression of PTEN in lung cancer PC9 cells harboring an EGFR-activating mutation (del E746-A750) results in acquisition of resistance to EGFR-TKIs, gefitinib and erlotinib, accompanied by enhanced phosphorylation of Akt and decreased nuclear translocation of a transcription factor EGR-1 [8]. In the present study, PTEN promoter methylation accounted for the decreased expression of PTEN in our gefitinib-resistant mutant. Material and methods: DNA methylation status of the PTEN promoter in PC9 and gefitinib-resistant cells were examined using methylation-specific PCR. The effect of DNA methylation on PTEN expression was evaluated by treatment of lung cancer cell lines with 5-aza-2'-deoxycytidine (5AZA-CdR). Results: We observed the characteristics of two gefitinib-resistant sublines, GEF1-1 and GEF2-1, derived from PC9 as follows. (1) PTEN overexpression suppressed AKT phosphorylation and restored the sensitivity to gefitinib and erlotinib in GEF1-1 cells. (2) EGR-1 siRNA mediated knockdown suppressed the expression of cyclin D1 and ICAM-1 genes but not of PTEN gene in PC9 cells. (3) Transfection of EGR-1 cDNA into a drug-resistant subline induced the expression of cyclin D1 and ICAM-1 but not of PTEN. (4) Treatment with 5AZA-CdR induced the expression of PTEN in resistant sublines but not in the parental line PC9. (5) A CpG site near the translational start point of the 5'-regulatory region was methylated in GEF1-1 and GEF2-1 but not in PC9. Conclusion: Our results strongly suggest that CpG hypermethylation of the PTEN gene contributes to the decreased expression of PTEN during acquired resistance to gefitinib or erlotinib.
AB - Objectives: We have previously reported that decreased expression of PTEN in lung cancer PC9 cells harboring an EGFR-activating mutation (del E746-A750) results in acquisition of resistance to EGFR-TKIs, gefitinib and erlotinib, accompanied by enhanced phosphorylation of Akt and decreased nuclear translocation of a transcription factor EGR-1 [8]. In the present study, PTEN promoter methylation accounted for the decreased expression of PTEN in our gefitinib-resistant mutant. Material and methods: DNA methylation status of the PTEN promoter in PC9 and gefitinib-resistant cells were examined using methylation-specific PCR. The effect of DNA methylation on PTEN expression was evaluated by treatment of lung cancer cell lines with 5-aza-2'-deoxycytidine (5AZA-CdR). Results: We observed the characteristics of two gefitinib-resistant sublines, GEF1-1 and GEF2-1, derived from PC9 as follows. (1) PTEN overexpression suppressed AKT phosphorylation and restored the sensitivity to gefitinib and erlotinib in GEF1-1 cells. (2) EGR-1 siRNA mediated knockdown suppressed the expression of cyclin D1 and ICAM-1 genes but not of PTEN gene in PC9 cells. (3) Transfection of EGR-1 cDNA into a drug-resistant subline induced the expression of cyclin D1 and ICAM-1 but not of PTEN. (4) Treatment with 5AZA-CdR induced the expression of PTEN in resistant sublines but not in the parental line PC9. (5) A CpG site near the translational start point of the 5'-regulatory region was methylated in GEF1-1 and GEF2-1 but not in PC9. Conclusion: Our results strongly suggest that CpG hypermethylation of the PTEN gene contributes to the decreased expression of PTEN during acquired resistance to gefitinib or erlotinib.
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U2 - 10.1016/j.lungcan.2015.01.009
DO - 10.1016/j.lungcan.2015.01.009
M3 - Article
C2 - 25638724
AN - SCOPUS:84924071051
VL - 87
SP - 265
EP - 271
JO - Lung Cancer
JF - Lung Cancer
SN - 0169-5002
IS - 3
ER -
