Activation of NF-kappaB/Rel occurs early during neoplastic transformation of mammary cells

• Published in: Carcinogenesis (New York) 2000-05, Vol.21 (5), p.871-879
• Main Authors: Kim, D W, Sovak, M A, Zanieski, G, Nonet, G, Romieu-Mourez, R, Lau, A W, Hafer, L J, Yaswen, P, Stampfer, M, Rogers, A E, Russo, J, Sonenshein, G E
• Format: Article
• Language: English
• Subjects: Animals; Base Sequence; Carcinogens; Cell Transformation, Neoplastic; Female; Genes, myc; Humans; Mammary Neoplasms, Experimental - metabolism; Mammary Neoplasms, Experimental - pathology; Molecular Sequence Data; NF-kappa B - metabolism; Phenotype; Rats; Rats, Sprague-Dawley; Tumor Cells, Cultured
• ISSN: 0143-3334; 1460-2180; 1460-2180
• DOI: 10.1093/carcin/21.5.871

NF-kappaB/Rel is a family of transcription factors which are expressed in all cells; however, in most non-B cells, they are sequestered in the cytoplasm in inactive complexes with specific inhibitory proteins, termed IkappaBs. We have recently shown that NF-kappaB/Rel factors are aberrantly activated in human breast cancer and rodent mammary tumors, and function to promote tumor cell survival and proliferation. Here, we have examined the time-course of induction of NF-kappaB/Rel factors upon carcinogen treatment of female Sprague-Dawley (S-D) rats in vivo and in human mammary epithelial cells (HMECs) in culture. We observed that NF-kappaB/Rel activation is an early event, occurring prior to malignant transformation. In S-D rats, increased NF-kappaB/Rel binding was detected in nuclear extracts of mammary glands from 40% of animals 3 weeks post-treatment with 15 mg/kg 7,12-dimethylbenz[a]anthracene (DMBA); this is prior to formation of tumors which normally begin to be detected after 7-9 weeks. In non-tumorigenic MCF-10F cells, in 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 classical NF-kappaB (p65/p50). NF-kappaB induction was corrrelated with a decrease in the stability of the NF-kappaB-specific inhibitory protein IkappaB-alpha. Ectopic expression of the transactivating p65 subunit of NF-kappaB in MCF-10F cells induced the c-myc oncogene promoter, which is driven by two NF-kappaB elements, and endogenous c-Myc levels. Furthermore, reduction mammoplasty-derived HMECs, immortalized following B[a]P exposure, showed dysregulated induction of classical NF-kappaB prior to malignant transformation. Together these findings suggest that activation of NF-kappaB plays an early, critical role in the carcinogen-driven transformation of mammary glands.