HER-2 over expression mediates the transition to aerobic glycolysis and stress/REDOX signaling in progressively transformed human mammary epithelial cells.

Abstract

Abstract Abstract #6032 The goal of this study was to use a computational strategy to identify HER-2 regulated-gene expression networks in an isogenic series of cell lines in which HER-2 functions as a proto-oncogene, as an oncogene driving partial transformation, and as an oncogene driving full malignant transformation. The cells used for these experiments include non-transformed, immortalized MCF10A cells grown in media containing EGF and insulin; MCF10HER2 cells that over express HER-2 and are insulin-independent for growth; and MCF10HER2/E7 cells (also E7 transduced), which are insulin and EGF-independent for growth and fully malignant in vivo. We obtained whole-genome expression data every 3 hours for 45 hours while HER-2 signaling and cell proliferation were blocked by treatment with specific small molecule kinase inhibitors. A dynamic linear finite difference model was used to derive phenomenological gene expression networks from the time-series gene expression data. In these networks each gene is rank-ordered by its degree of connectivity, and hub genes are identified as those with the highest connectivity level. We then compared the hub genes regulated by HER-2 in each cell line, and used Ingenuity Pathway Analysis to identify the biological networks differentially regulated by HER-2. Results show that both normal and transformed gene expression networks have scale-free topology. Using the same connectivity value to define hubs, we found that HER-2 regulated the expression of more hub genes in transformed cells. These findings suggested that the HER-2 signal was integrated differently in progressively transformed cells and led us to map functional association networks for each cell-specific list of hubs. In MCF-10HER-2 cells, which are partially transformed and insulin-independent for growth, two hubs differentially regulated by HER-2 include VAMP8 and PHGDH. These genes influence cell surface expression of glucose transporters, and activate anabolic pathways from glycolysis intermediates, respectively. Thus, HER-2-mediated insulin independence is associated with constitutive glucose transport and the transition to aerobic glycolysis. HER-2/E7 cells are fully transformed, and in these cells, differentially regulated hub genes such as HSP1A1 and GPX4 are part of the coordinated regulation of the stress-protective heat shock response and enzymatic pathways of oxidative defense. In concert with these modular changes, the CITED2 hub gene, a negative regulator of HIF1α, is specifically down-regulated by HER-2 signaling in the MCF10A/HER2 and MCF10A/HER2/E7 cell lines, which results in enhanced HIF1α expression and transcriptional activity. In summary, our systems biology approach resulted in the identification of distinct gene expression and functional association networks that arise when HER-2 transitions from being a proto-oncogene to a fully transforming gene. These results provide evidence regarding the mechanisms by which HER-2 acts as a transforming gene when over expressed. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6032.