Constitutive activation of NF-kappaB during progression of breast cancer to hormone-independent growth.
Breast cancers often progress from a hormone-dependent, nonmetastatic, antiestrogen-sensitive phenotype to a hormone-independent, antiestrogen- and chemotherapy-resistant phenotype with highly invasive and metastatic growth properties. This progression is usually accompanied by altered function of the estrogen receptor (ER) or outgrowth of ER-negative cancer cells. To understand the molecular mechanisms responsible for metastatic growth of ER-negative breast cancers, the activities of the transcription factor NF-kappaB (which modulates the expression of genes involved in cell proliferation, differentiation, apoptosis, and metastasis) were compared in ER-positive (MCF-7 and T47-D) and ER-negative (MDA-MB-231 and MDA-MB-435) human breast cancer cell lines. NF-kappaB, which is usually maintained in an inactive state by protein-protein interaction with inhibitor IkappaBs, was found to be constitutively active in ER-negative breast cancer cell lines. Constitutive DNA binding of NF-kappaB was also observed with extracts from ER-negative, poorly differentiated primary breast tumors. Progression of the rat mammary carcinoma cell line RM22-F5 from an ER-positive, nonmalignant phenotype (E phenotype) to an ER-negative, malignant phenotype (F phenotype) was also accompanied by constitutive activation of NF-kappaB. Analysis of individual subunits of NF-kappaB revealed that all ER-negative cell lines, including RM22-F5 cells of F phenotype, contain a unique 37-kDa protein which is antigenically related to the RelA subunit. Cell-type-specific differences in IkappaB alpha, -beta, and -gamma were also observed. In transient-transfection experiments, constitutive activity of an NF-kappaB-dependent promoter was observed in MDA-MB-231 and RM22-F5 cells of F phenotype, and this activity was efficiently repressed by cotransfected ER. Since ER inhibits the constitutive as well as inducible activation function of NF-kappaB in a dose-dependent manner, we propose that breast cancers that lack functional ER overexpress NF-kappaB-regulated genes. Furthermore, since recent data indicate that NF-kappaB protects cells from tumor necrosis factor alpha-, ionizing radiation-, and chemotherapeutic agent daunorubicin-mediated apoptosis, our results provide an explanation for chemotherapeutic resistance in ER-negative breast cancers.
Nakshatri
H
H
Department of Surgery, Indiana University School of Medicine, Indianapolis 46202, USA. HarikrishnavNakshatri@iucc.iupui.edu
Bhat-Nakshatri
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P
Martin
D A
DA
Goulet
R J
RJ
Sledge
G W
GW
D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology*; D002455:Cell Division; D004273:DNA, Neoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008325:Mammary Neoplasms, Experimental / Q000235:genetics* / Q000473:pathology*; D016328:NF-kappa B / Q000502:physiology*; D009361:Neoplasm Invasiveness; D009362:Neoplasm Metastasis; D011401:Promoter Regions, Genetic; D051381:Rats; D011960:Receptors, Estrogen / Q000502:physiology; D051996:Transcription Factor RelA; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D016328:NF-kappa B; D011960:Receptors, Estrogen; D051996:Transcription Factor RelA