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Mol. Cell. Biol., Jul 1997, 3629-3639, Vol 17, No. 7
H Nakshatri, P Bhat-Nakshatri, DA Martin, RJ Goulet Jr and GW Sledge Jr
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.
Copyright © 1997, American Society for Microbiology
Constitutive activation of NF-kappaB during progression of breast cancer to hormone-independent growth
Department of Surgery, Indiana University School of Medicine, Indianapolis 46202, USA. Harikrishna_Nakshatri@iucc.iupui.edu
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