Effect of green tea Polyphenon 60 on microRNA expression in MCF-7 breast cancer cells

Abstract

In Western countries, breast cancer is the most common form of cancer and it is the second leading cause of female cancer death in America. The biochemical basis of the observed anti-oncogenic properties of green tea has been linked to the cellular effects of polyphenols found in the Camellia sinensis leaf. In this study we obtained dose-response data for the cellular effects of Polyphenon 60 green tea extract on MCF-7 breast cancer cells. Growth inhibition and cell death was observed after 48 hours at concentrations as low as 6 ug/ml (IC10). Results indicate that Polyphenon 60 induces a reduction in cellular metabolism on a similar dose-response starting at a concentration of 10 ug/ml. Cell cycle progression was unaffected by treatment with this tea extract and the method of cell death remained consistent across the treatment concentrations as analyzed by acridine orange/ethidium bromide fluorescence analysis. The specific regulatory mechanism behind how polyphenols affect gene expression and cancer cell survival has yet to be identified but current data suggests that small, non-protein coding microRNAs (miRNAs) may be responsible. In the present study, the effect of Polyphenon 60 green tea extract on MCF-7 breast cancer cell miRNA expression was investigated. Twenty-three miRNAs were identified by microarray analysis with differential expression after a 48 hour treatment of 10 ug/ml Polyphenon 60. This study further investigated the relationship between Polyphenon 60 dosage and miRNA responsiveness using let-7g, let-7e, miR-21, miR-26b, miR-27a, miR-92a, miR-548m, and miR-720, eight of the previously identified microarray miRNAs of interest. Additionally, miR-10b, miR-15a, miR-16, and miR-200c were investigated based on previous reports of their connection to breast cancer. Several miRNAs showed a change in expression at concentrations as low as 1 ug/ml and did not fluctuate significantly even at the IC80 value of 15 ug/ml. Time-dependent data was also generated for miR-27a, miR-92a, miR-200c, and miR-720 following 24, 48, and 72 hour treatment with low and high dose Polyphenon 60 treatment. At low-doses and short treatment times, miR-720 and miR-200c were up-regulated and directly reversed their typical breast cancer expression. miR-27a, an oncomir, was down-regulated. The subtle changes that low-dose green tea extract can induce in the miRNA expression profile of MCF-7 cells may help substantiate the previous epidemiological claims that green tea can influence breast cancer pathogenesis.