American ginseng transcriptionally activates p21 mRNA in breast cancer cell lines

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 p2l 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 (E-2), genistein or cycloheximide (CHX). Northern blot analyses were performed using human p21Cip1 and 36134 cDNA probes. Cell lines were transiently transfected with select mouse p2l CAT reporter constructs, including those lacking a p53 binding site. Cell cycle analyses was performed by FACScan. The results revealed that AG induced p2l mRNA expression in MCF-7 and MDA-MB-231 cells (p=0.0004; pless than or equal to0.0001, respectively). Neither E-2 nor genistein alter p21 mRNA expression. CHX, a protein synthesis inhibitor, did not block p2l mRNA expression induced by AG, indicating that p2l is induced as an immediate early gene. AG activated p2l reporter constructs in transfected cells, independent of p53 binding sites, The cell cycle proliferative phase was significantly decreased by AG and increased by E-2 (pless than or equal to0.0001). AG may inhibit breast cancer cell growth by transcriptional activation of the p2l gene, independent of p53.