BACKGROUND: Some reports have indicated that ginseng might have an inhibitory effect on tumorogenesis. The p21 protein, a universal cell-cycle inhibitor, directly binds cyclin-CDK complexes. The aim of this study was to determine if ginseng induced p21 mRNA expression in hormone-sensitive (MCF-7) and -insensitive (MDA-MB-231) breast-cancer cell lines. METHODS: Cells were grown in a steroid stripped medium (SSM) and then treated with ginseng extracts, SSM, estradiol (10 9 M), genistein (10 6 M), and cycloheximide (CHX, 10 microgram/ml) for 1 to 48 hours. Northern blot analyses were performed using human p21 cip1 and 36B4 cDNA (control). Cell-cycle analyses using DNA measurements were performed by using 4FACScan flow-cytometry for ginseng extracts and estradiol. RESULTS: p21 mRNA increased in a time- and dose-dependent manner. Ginseng induced peak p21 mRNA expression at 4 hours in MCF-7 and MDA-MB-231 cells (p=0.0004 and p<0.0001, respectively) in comparison with the SSM controls. Neither E2 nor genistein induce p21 expression. CHX, a protein-synthesis inhibitor, did not block the p21 mRNA expression induced by the ginseng extracts, indicating that p21 is induced as an early immediate gene. The ginseng extracts significantly decreased the % S-phase fraction of the cell cycle (p<0.001). CONCLUSIONS: This study suggests that ginseng exhibits growth inhibitory properties due to transcriptional up-regulation of p21.
Blotting, Northern ; Breast Neoplasms ; Cell Cycle ; Cell Line* ; Cycloheximide ; DNA ; DNA, Complementary ; Estradiol ; Genes, Tumor Suppressor* ; Genistein ; Humans* ; Panax* ; Phytoestrogens ; RNA, Messenger ; Up-Regulation

American ginseng (AG) has been demonstrated to inhibit breast cancer cell growth in vitro. p21 protein, a universal cell cycle inhibitor, binds cyclin-CDK complexes, an important mechanism in cell cycle regulation. The purpose of this investigation was to determine if AG induces p21 gene expression in hormone sensitive (MCF-7) and insensitive (MDA-MB-231) breast cancer cell lines. Cells grown in steroid stripped medium (SSM) were treated with AG, 17-beta-estradiol (E2), genistein or cycloheximide (CHX). Northern blot analyses were performed using human p21Cip1 and 36B4 cDNA probes. Cell lines were transiently transfected with select mouse p21 CAT reporter constructs, including those lacking a p53 binding site. Cell cycle analyses was performed by FACScan. The results revealed that AG induced p21 mRNA expression in MCF-7 and MDA-MB-231 cells (p=0.0004; p< or =0.0001, respectively). Neither E2 nor genistein alter p21 mRNA expression. CHX, a protein synthesis inhibitor, did not block p21 mRNA expression induced by AG, indicating that p21 is induced as an immediate early gene. AG activated p21 reporter constructs in transfected cells, independent of p53 binding sites. The cell cycle proliferative phase was significantly decreased by AG and increased by E2 (p< or =0.0001). AG may inhibit breast cancer cell growth by transcriptional activation of the p21 gene, independent of p53.
Animal ; Binding Sites ; Breast Neoplasms ; Cell Division/drug effects ; Chloramphenicol O-Acetyltransferase/genetics ; Cyclins/*genetics ; Female ; Genes, Reporter ; HT29 Cells ; Human ; Mice ; *Panax ; Plant Extracts/pharmacology ; Protein p53/metabolism ; *RNA, Messenger ; *Trans-Activation (Genetics) ; Tumor Cells, Cultured