The incidence of breast cancer has risen over the past 50 years, and it is now the second leading cause of death among American women. In an attempt to find the reasons for this increase in incidence, genetic, environmental and dietary factors are being studied. The NF-KB family of dimeric transcription factors, which controls genes critical for neoplastic transformation, cell proliferation and survival, consists of five members: 3 with transactivation domains (c-Rel, RelA, RelB), and 2 without (p50 and p52), which promote stronger binding. NF-KB factors are sequestered in the cytoplasm in inactive complexes in most cells. Collaborative studies by members of the Program Project demonstrated constitutive aberrant activation of c-Rel, RelA or p50 NF-KB subunits in -90% of primary human breast cancers, and that exposure to polycyclic aromatic hydrocarbons (PAHs), such as 7,12-dimethylbenz(a)anthracene (DMBA) or benzo(a)pyrene, up-regulated NF-KB in breast cancer. This led us to the central hypothesis in the original application that carcinogens can constitutively activate NF-KB, which will promote transformation. In collaboration with Projects 1 and 2, we have more recently shown that NF-KB complexes, which are induced by PAH exposure, play key roles in promoting an invasive phenotype of breast cancer via epithelial to mesenchymal transition (EMT). (1) PAH exposure of mice activated multiple NF-KB complexes, the IKKe/i kinase and an invasive phenotype of mammary tumors;(2) PAH exposure of c-Rel-driven breast cancer cells further activated NF-KB, which was required for an invasive phenotype;(3) the c-Rel subunit can play a causal role in mammary tumorigenesis and cooperated with protein kinase CK2 to induce the AhR and Slug, a master regulator of EMT;(4) a novel de novo RelB synthesis pathway was identified, which promoted EMT via induction of Bcl-2;(5) RelB was induced by DMBA or c-Rel and expressed in human breast cancer specimens. Of note, green tea and its polyphenol epigallocatechin-3 gallate (EGCG) reduced invasive phenotype of DMBA-induced mammary tumors and breast cancer cells. EGCG slowed proliferation of Her-2/neu breast cancer cell lines resistant to trastuzumab, suggesting translational applications of green tea polyphenols. Thus, environmental carcinogens are known to induce genetic as well as epigenetic events in mammary tissue. In this revised renewal application, we propose to test the hypothesis that these perturbations induce or enhance the activity of multiple NF-KB complexes thereby promoting a more invasive phenotype of breast cancer: thus inhibition of these pathways will revert the process of EMT.
Three aims are proposed: (1) elucidate the roles of c-Rel and RelB NF-KB in promoting carcinogenesis;(2) determine the function of IKKe/i in carcinogenesis, and the mechanism of IKKs/i promoter activation;(3) perform pre-clinical in vivo testing of the ability of green tea polyphenols to reduce Her-2/neu-mediated transformation. These studies will provide important information on the mechanisms of activation of aberrant expression of NF-KB factors by environmental carcinogens, and characterize their roles in promoting invasive breast cancer. Green tea polyphenols are potential inhibitors of breast cancer that can readily be translated to the clinic for combinatorial therapies.
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