Expression of HER-2 in MCF-7 breast cancer cells modulates anti-apoptotic proteins Survivin and Bcl-2 via the extracellular signal-related kinase (ERK) and phosphoinositide-3 kinase (PI3K) signalling pathways

To understand the initial event(s) that take place by HER-2 over expression, we studied the effect of short term induction of HER-2 expression in the MCF7 breast cancer cell line.We examined the modulation of apoptotic pathways by tetracycline-regulated HER-2 expression for 48 hrs in the MCF7 breast cancer cell line. Specific inhibitors were used to determine signalling pathways that are required for HER-2 induced up-regulation of survivin.Tetracycline regulated short term over expression of HER-2 in the MCF7 cell line increased the antiapoptotic proteins Bcl-2 and survivin levels. Significant increase of extracellular signal-related kinase (ERK) activation but not AKT1, AKT2 and STAT3 was observed in HER-2 over-expressing MCF7 cells. Specific inhibitors of ERK, and phosphoinositide-3 kinase (PI3K), inhibited the HER-2 induced up-regulation of survivin. We did not observe a change in survivin and NF-κB promoter activity in HER-2 expressing MCF7 cells.Our results indicate that short term over expression of HER-2 up regulates antiapoptotic proteins Bcl-2 and survivin in MCF7 cells. We determined that survivin is up-regulated via ERK activation and PI3K signalling. Additionally we show that survivin up-regulation is not at transcriptional level. These data provide insight into the mechanism(s) by which induction of HER-2 over expression up-regulates survivin and Bcl-2 and identifies new targets for therapy of breast cancer.Impaired apoptosis is critical in cancer development and is a major barrier to effective treatment. Apoptosis is executed by intracellular cysteine proteases called caspases. Two pathways lead to the caspase activation – the extrinsic and intrinsic pathways. The extrinsic pathway is initiated by ligation of death receptors [1]. The intrinsic pathway requires disruption of mitochondrial membranes and release of cytochrome C [2]. Molecules and signalling events that regulate apoptosis affect disease progression and the efficacy of chemotherapy because