Genistein affects HER2 protein concentration, activation, and promoter regulation in BT-474 human breast cancer cells

Abstract

The HER2 proto-oncogene, a member of the epidermal growth factor receptor family, is overexpressed in 20-30% of breast cancers. Genistein, the main soy isoflavone, interacts with estrogen receptors (ER) and it is also a potent tyrosine kinase inhibitor. Previously, our laboratory found that genistein delayed mammary tumor onset in transgenic mice that overexpress HER2 gene. Our goal was to define the mechanism through which genistein affects mammary tumorigenesis in HER2 overexpressing mice. We hypothesized that genistein inhibits HER2 activation and expression through ER-dependent and ER-independent mechanisms. Genistein inhibited total HER2 protein expression and tyrosine phosphorylation in BT-474, an ERalpha (-) and ERbeta (+) human breast cancer cell line, however, E2 had no effect. Taken together, these data suggest that genistein has an ER-independent inhibitory effect, presumably, through tyrosine kinase inhibition activity. Genistein at 1.0 microM mimicked E2 and down-regulated HER2 protein phosphorylation when BT-474 was co-transfected with ERalpha, but not ERbeta. Although E2 and overexpression of HER2 can promote mammary tumorigenesis, an inverse relationship between ER expression and HER2 overexpression has been found in human breast cancer. We cloned a 500-bp promoter region upstream of the HER2 transcription initiation site. Co-transfection with ERalpha, but not with ERbeta, down-regulated HER2 promoter reporter in BT-474. At concentrations > or =1 microM, genistein inhibited HER2 promoter reporter in the absence of ERalpha. In conclusion, genistein at > or =1 microM inhibited HER2 protein expression, phosphorylation, and promoter activity through an ER-independent mechanism. In the presence of ERalpha, genistein mimicked E2 and inhibited HER2 protein phosphorylation. These data support genistein's chemo-prevention and potential chemo-therapeutic roles in breast cancer.

Multi-targeted therapy of cancer by genistein

“…Sakla et al recently reported that genistein inhibits the protooncogene HER-2 protein tyrosine phosphorylation in breast cancer cells as well as delaying tumor onset in transgenic mice that overexpress the HER-2 gene This data support its potential anticancer role in chemotherapy of breast cancer [16]. However, effects independent of this activity have also been demonstrated [17].…”

Identification of novel signaling components in genistein-regulated signaling pathways by quantitative phosphoproteomics

“…In vitro experiment demonstrated that genistein repressed tyrosine-specific protein kinase activity of EGFR, pp60 v-src , and pp110 gag-fes [24]. Genistein also inhibited the pro-oncogene HER2 protein tyrosine phosphorylation in breast cancer cells and delayed tumor onset in transgenic mice over-expressing HER2 gene [27]. Kim et al further showed that the phosphorylation of AKT and ERK was significantly downregulated by genistein after HeLa and CaSki cells were treated with genistein for 48 h [28].…”

Understanding genistein in cancer: The “good” and the “bad” effects: A review

“…In a study performed using a low micromolar (about 1 lM) concentration of genistein on BT-474 human BC cells (expressing only ERb), the molecule inhibited HER2 expression, phosphorylation and promoter activity throughout an ER-independent mechanism. When these cells were genetically transformed to express ERa, genistein mimicked E2 and inhibited HER2 protein phosphorylation (Sakla, Shenouda, Ansell, Macdonald, & Lubahn, 2007). In a different study, the authors documented an anti-proliferative and apoptotic effect of genistein and quercetin, using a canonical MCF-7 cell line and MCF-7 overexpressing HER2.…”