CpG hypermethylation contributes to decreased expression of PTEN during acquired resistance to gefitinib in human lung cancer cell lines |
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| Affiliation: | 1. Department of Pharmaceutical Oncology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka 812-8582, Japan;2. St Mary''s Institute of Health Sciences, St Mary''s Hospital, Kurume 830-8543, Japan;3. Laboratory of Molecular Cancer Biology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka 812-8582, Japan;4. Department of Occupational Pneumology, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, Kitakyushu 807-8555, Japan;1. Oncological Ward, Independent Public Health Care Unit, Voivodeship Specialized Hospital, Rybnik, Poland;2. Department of Clinical Biochemistry, Medical University of Silesia, Zabrze, Poland;3. Department of Biochemistry, Medical University of Silesia, Zabrze, Poland;4. Department of Toxicology and Occupational Health Protection, Public Health Faculty, Medical University of Silesia, Katowice, Poland;1. Department of Experimental Oncology, IEO, European Institute of Oncology IRCCS, Milan, Italy;2. Department of Pharmacology and Toxicology, Faculty of Pharmacy, Ain Shams University, Cairo, Egypt;1. Department of Experimental Oncology, IEO, European Institute of Oncology IRCCS, Milan, Italy;2. Department of Biosciences, University of Milan, Milan, Italy;1. Medical Oncology, Santa Maria della Misericordia Hospital, Azienda Ospedaliera di Perugia, Perugia, Italy;2. Medical Oncology, University of Rome ‘La Sapienza’, Sant’Andrea Hospital, Rome, Italy;3. Department of Experimental Medicine, Division of Pathology and Histology, University of Perugia, Perugia, Italy;1. Department of Radiology, The University of Chicago, Chicago, IL, USA;2. Department of Pathology, The University of Chicago, Chicago, IL, USA;3. Section of Hematology/Oncology, Department of Medicine, The University of Chicago, Chicago, IL, USA;4. Department of Surgery, The University of Chicago, Chicago, IL, USA;1. Thoracic Oncology Program, Earle A Chiles Research Institute, 5251 NE Glisan Ave., Bldg. A, Portland, OR 97213-2967, United States;2. Fariborz Maseeh Department of Mathematics and Statistics, Portland State University, 724 SW Harrison, Portland, OR 97207, United States |
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| Abstract: | ObjectivesWe 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 methodsDNA 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).ResultsWe 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.ConclusionOur 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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| Keywords: | Gefitinib-resistance PTEN DNA methylation Lung cancer EGR-1 EGFR-tyrosine kinase inhibitor |
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