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Relatively little is known about the antiproliferative effects of artemisinin, a naturally occurring antimalarial compound from Artemisia annua, or sweet wormwood, in human endometrial cancer cells. Artemisinin induced a G1 cell cycle arrest in cultured human Ishikawa endometrial cancer cells and downregulated cyclin-dependent kinase-2 (CDK2) and CDK4 transcript and protein levels. Analysis of CDK4 promoter-luciferase reporter constructs showed that the artemisinin ablation of CDK4 gene expression was accounted for by the loss of CDK4 promoter activity. Chromatin immunoprecipitation demonstrated that artemisinin inhibited nuclear factor [kappa]-light-chain-enhancer of activated B cells (NF-[kappa]B) subunit p65 and p50 interactions with the endogenous Ishikawa cell CDK4 promoter. Coimmunoprecipitation revealed that artemisinin disrupts endogenous p65 and p50 nuclear translocation through increased protein-protein interactions with I[kappa]B-[alpha], an NF-[kappa]B inhibitor, and disrupts its interaction with the CDK4 promoter, leading to a loss of CDK4 gene expression. Artemisinin treatment stimulated the cellular levels of I[kappa]B-[alpha] protein without altering the level of I[kappa]B-[alpha] transcripts. Finally, expression of exogenous p65 resulted in the accumulation of this NF-[kappa]B subunit in the nucleus of artemisinin-treated and artemisinin-untreated cells, reversed the artemisinin downregulation of CDK4 protein expression and promoter activity, and prevented the artemisinin-induced G1 cell cycle arrest. Taken together, our results demonstrate that a key event in the artemisinin antiproliferative effects in endometrial cancer cells is the transcriptional downregulation of CDK4 expression by disruption of NF-[kappa]B interactions with the CDK4 promoter.

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