Epidermal growth factor activates telomerase activity by direct binding of Ets-2 to hTERT promoter in lung cancer cells

Abstract

Growth signals are directly or indirectly involved in telomerase regulation. In this study, we investigated molecular mechanisms of the effect of EGF (epidermal growth factor) on regulating hTERT (human telomerase reverse transcriptase) expression. To elucidate specific transcription factors involved in EGF-stimulated hTERT transcription in A549 and H1299 lung cancer cells, transcription factors drives hTERT promoter activity, such as Myc, Mad, and Ets-2, was evaluated on luciferase reporter assay. The upregulation of hTERT promoter by Ets-2 and Myc were abolished by Mad. Using DAPA (DNA affinity precipitation assay), Ets-2 binding to SNP (T) was stronger than Ets-2 binding to SNP (C) at -245 bp upstream of the transcription start site within the core promoter of hTERT. Ets-2 silence by siRNA decreased hTERT expression at mRNA and protein levels. The regulation of hTERT promoter by EGF/Ets-2 was diminished via the EGFR kinase signal pathway-specific inhibitors AG1478 and Iressa. Inhibitors of Erk and Akt inhibited Ets-2-activated hTERT promoter activity. These data suggested that Ets-2, a genuine cancer-specific transcription factor, is actively involved in EGFR kinase-induced hTERT overexpression pathway in lung cancer cells. Blockage of this pathway may contribute to targeted gene therapy in lung cancer.