Activation of NF-kappaB/Rel occurs early during neoplastic transformation of mammary cells.
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.
Kim
D W
DW
Department of Biochemistry, Department of Pathology and Laboratory Medicine and Program in Research on Women's Health, Boston University Medical School, 715 Albany Street, Boston, MA 02118, USA.
Sovak
M A
MA
Zanieski
G
G
Nonet
G
G
Romieu-Mourez
R
R
Lau
A W
AW
Hafer
L J
LJ
Yaswen
P
P
Stampfer
M
M
Rogers
A E
AE
Russo
J
J
Sonenshein
G E
GE
D000818:Animals; D001483:Base Sequence; D002273:Carcinogens; D002471:Cell Transformation, Neoplastic; D005260:Female; D016259:Genes, myc; D006801:Humans; D008325:Mammary Neoplasms, Experimental / Q000378:metabolism* / Q000473:pathology; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000378:metabolism*; D010641:Phenotype; D051381:Rats; D017207:Rats, Sprague-Dawley; D014407:Tumor Cells, Cultured
D002273:Carcinogens; D016328:NF-kappa B