CpG hypermethylation contributes to decreased expression of PTEN during acquired resistance to gefitinib in human lung cancer cell lines.

Abstract

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.

• Authors: Masashi Maeda, Yuichi Murakami, Kosuke Watari, Michihiko Kuwano, Hiroto Izumi, Mayumi Ono
• Journal: Lung cancer (Amsterdam, Netherlands) (Lung Cancer) Vol. 87 Issue 3 Pg. 265-71 (Mar 2015) ISSN: 1872-8332 [Electronic] Ireland
• PMID: 25638724 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Chemical References

• Antineoplastic Agents
• EGR1 protein, human
• Early Growth Response Protein 1
• Protein Kinase Inhibitors
• Quinazolines
• Intercellular Adhesion Molecule-1
• Cyclin D1
• Proto-Oncogene Proteins c-akt
• PTEN Phosphohydrolase
• Gefitinib

Topics

• Antineoplastic Agents (pharmacology)
• Cell Line, Tumor
• CpG Islands
• Cyclin D1 (genetics)
• DNA Methylation
• Drug Resistance, Neoplasm (genetics)
• Early Growth Response Protein 1 (genetics)
• Gefitinib
• Gene Expression
• Gene Expression Regulation, Neoplastic
• Gene Knockdown Techniques
• Humans
• Intercellular Adhesion Molecule-1 (genetics)
• Lung Neoplasms (genetics)
• PTEN Phosphohydrolase (genetics)
• Phosphorylation
• Promoter Regions, Genetic
• Protein Kinase Inhibitors (pharmacology)
• Proto-Oncogene Proteins c-akt (metabolism)
• Quinazolines (pharmacology)