Puma is a novel target of soy isoflavone genistein but is dispensable for genistein-induced cell fate determination.

Here, we attempted to identify novel target genes of genistein in human A549 cells. Using analysis of proteins related to cell cycle and apoptotic pathways, we confirmed an elevated level of p53 accompanying p21 Waf1/Cip1 protein in genistein-treated or genistin-treated A549 and WI-38 cells, but not in HeLa cells. In addition, a p53-upregulated modulator of apoptosis (Puma) protein accumulated significantly in genistein-treated A549 and WI-38 cells, but not in genistin-treated or beta-estradiol-treated cells, though the growth of any ingredient-treated cells was severely inhibited. Intriguingly, the caspase-3 activity of genistein-treated A549 cells, in which Puma or p53 expression was knocked-down by RNA interference (RNAi), remained unaltered compared to that in cells transfected with irrelevant RNAi. These results raise a concern that molecular targets identified by powerful omic approaches may not necessarily represent key molecules responsible for given cellular phenotypes and thus must be verified by conclusive assays.