Artemisinin, a sesquiterpene phytolactone derived from Artemisia annua, is a potent antimalarial compound with promising anticancer properties, although the mechanism of its anticancer signaling is not well understood. Artemisinin inhibited proliferation and induced a strong G1 cell cycle arrest of cultured MCF7 cells, an estrogen-responsive human breast cancer cell line that represents an early-stage cancer phenotype, and effectively inhibited the in-vivo growth of MCF7 cell-derived tumors from xenografts in athymic nude mice. Artemisinin also induced a growth arrest of tumorigenic human breast cancer cell lines with preneoplastic and late stage cancer phenotypes, but failed to arrest the growth of a nontumorigenic human mammary cell line. Concurrent with the cell cycle arrest of MCF7 cells, artemisinin selectively downregulated the transcript and protein levels of the CDK2 and CDK4 cyclin-dependent kinases, cyclin E, cyclin D1, and the E2F1 transcription factor. Analysis of CDK2 promoter-luciferase reporter constructs showed that the artemisinin ablation of CDK2 gene expression was accounted for by the loss of CDK2 promoter activity. Chromatin immunoprecipitation revealed that artemisinin inhibited E2F1 interactions with the endogenous MCF7 cell CDK2 and cyclin E promoters. Moreover, constitutive expression of exogenous E2F1 prevented the artemisinin-induced cell cycle arrest and downregulation of CDK2 and cyclin E gene expression. Taken together, our results demonstrate that the artemisinin disruption of E2F1 transcription factor expression mediates the cell cycle arrest of human breast cancer cells and represents a critical transcriptional pathway by which artemisinin controls human reproductive cancer cell growth.
Department of Cell and Molecular Biology, Cancer Research Laboratory, University of California, Berkeley, California, USA
Antony S. Tin and Shyam N. Sundar contributed equally to this study
Correspondence to Gary L. Firestone, Department of Cell and Molecular Biology, 591 LSA, University of California, Berkeley, CA 94720-3200, USA Tel: +1 510 642 8319; fax: +1 510 643 6791; e-mail: firstname.lastname@example.org
Received August 31, 2011
Accepted November 18, 2011