Abstract:

Background and purpose: Tumor metastasis is a main reason of breast cancer patients’ death.This study aimed to discuss whether or how the transcription factor ETS2 regulate CXCR4 transcription and the molecular mechanism of ETS2 modulating transcriptional activity of CXCR4 gene in human breast cancer cells. Methods: In MCF-7 breast cancer cell lines and MDA-MB-231 breast cancer cell lines, through transient transfection, as well as RNAi technology, the expression of ETS2 was overexpressed or inhibited was detected. RT-PCR and ELISA was used respectively to detect CXCR4 mRNA expression and protein level. Luciferase reporter gene assay was applied to detect CXCR4 promoter activity, and ChIP for detecting the amount of ETS2 protein binding to CXCR4 promoter. Two binding sites of CXCR4 promoter were mutated to detect the impact on the activity of CXCR4 promoter by gene mutations. Results: After transfected with ETS2 expression vector in MCF-7 and MDA-MB-231 breast cancer cell lines, the mRNA expression and protein level of CXCR4 were elevated. The result of luciferase reporter gene assay indicated that overexpression of ETS2 activated CXCR4 promoter. ChIP assay demonstrated that the amount of ETS2 protein binding to CXCR4 promoter increased after ETS2 transfection. This result indicated that ETS2 may activate CXCR4 promoter through directly binding with CXCR4 promoter. Inhibition of ETS2 expression using RNAi could significantly attenuate CXCR4 promoter activity and reduce expression of CXCR4. Two ETS binding sites of CXCR4 promoter were mutated and the result of luciferase reporter gene assay proved that, an arbitrary point mutations attenuated CXCR4 promoter activity, while mutation of both binding sites further attenuated CXCR4 activity. Conclusion: In MCF-7 and MDA-MB-231 breast cancer cell lines, overexpression of ETS2 could activate CXCR4 promoter and the transcription of CXCR4 through directly binding to two ETS2 binding sites (-540 to -535 and -240 to -235) of CXCR4 promoter.

Key words: Breast cancer, ETS2, Transcription, CXCR4, Promoter