Activation of NF-kappa B/Rel occurs early during neoplastic transformationof mammary cells

NF-kappa B/Rel is a family of transcription factors which are expressed in all cells; however, in most non-B cells, they are sequestered in the cytopl asm in inactive complexes with specific inhibitory proteins, termed I kappa Bs. We have recently shown that NF-kappa B/Rel factors are aberrantly acti vated in human breast cancer and rodent mammary tumors, and function to pro mote tumor cell survival and proliferation. Here, we have examined the time -course of induction of NF-kappa B/Rel factors upon carcinogen treatment of female Sprague-Dawley (S-D) rats in vivo and in human mammary epithelial c ells (HMECs) in culture. We observed that NF-kappa B/Rel activation is an e arly event, occurring prior to malignant transformation. In S-D rats, incre ased NF-kappa B/ Rel binding was detected in nuclear extracts of mammary gl ands from 40% of animals 3 weeks post-treatment with 15 mg/kg 7,12-dimethyl benz[a]anthracene (DMBA); this is prior to formation of tumors which normal ly begin to be detected after 7-9 weeks, In non-tumorigenic MCF-10F cells, ill vitro malignant transformation upon treatment with either DMBA or benzo [a]pyrene (B[a]P) resulted in a 4- to 12-fold increase in activity of class ical NF-kappa B (p65/ p50), NF-kappa B induction was corrrelated with a dec rease in the stability of the NF-kappa B-specific inhibitory protein I kapp a B-alpha. Ectopic expression of the transactivating p65 subunit of NF-kapp a B in MCF-10F cells induced the c-myc oncogene promoter, which is driven b y two NF-kappa B elements, and endogenous c-Myc levels. Furthermore, reduct ion mammoplasty-derived HMECs, immortalized following B[a]P exposure, showe d dysregulated induction of classical NF-kappa B prior to malignant transfo rmation. Together these findings suggest that activation of NF-kappa B play s an early, critical role in the carcinogen-driven transformation of mammar y glands.