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

Abstract

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.

Nuclear Factor-κB (NF-κB) Regulates Proliferation and Branching in Mouse Mammary Epithelium

“…In addition, overexpression and enhanced nuclear localization of p50, p52, c-Rel, and Bcl-3 have been reported in breast cancer cell lines and in human tumors (Dejardin et al, 1995;Mukhopadhyay et al, 1995;Cogswell et al, 2000). In addition, the induction of NF-B activity may be an early event in chemical carcinogenesis, because NF-B activity was induced in vivo and in cell culture by 7,12-dimethylbenz[␣]anthracene before neoplastic transformation (Kim et al, 2000). Further investigation is required to delineate precisely the role NF-B plays in breast cancer and may lead to identification of new molecular targets for therapeutic interventions.…”

Gene expression profiling in the mammary gland of rats treated with 7,12‐dimethylbenz[a]anthracene

“…The mechanisms for the upregulation of cyclin D1 in the rat mammary gland are not yet known, but several factors have been shown to regulate cyclin D1 gene expression. [19][20][21][22] Interestingly, NF-Kb/Rel activation was reported to be an early event in the mammary gland of DMBA-treated rats, and NF-Kb is known to regulate cyclin D1 expression. 22 One family of genes shown to be differentially expressed in the preneoplastic stage of DMBA-induced rat mammary gland carcinogenesis is the heat shock proteins.…”

“…[19][20][21][22] Interestingly, NF-Kb/Rel activation was reported to be an early event in the mammary gland of DMBA-treated rats, and NF-Kb is known to regulate cyclin D1 expression. 22 One family of genes shown to be differentially expressed in the preneoplastic stage of DMBA-induced rat mammary gland carcinogenesis is the heat shock proteins. Heat shock proteins have many cellular functions in protein homeostasis, including protein folding, aggregation and trafficking.…”

Antiestrogen resistance in breast cancer and the role of estrogen receptor signaling

“…Several aspects of normal mammary gland development appear dependent upon NFkB activity (Clarkson and Watson, 1999), likely reflecting its regulation by both estrogens and growth factors (Nakshatri et al, 1997;Biswas et al, 2000). Elevated NFkB activity arises early during neoplastic transformation in the rat mammary gland (Kim et al, 2000). Widely expressed in human and rat mammary tumors (Sovak et al, 1997;Cogswell et al, 2000), upregulation of NFkB is associated with estrogen independence (Nakshatri et al, 1997;Clarkson and Watson, 1999).…”