Constitutive activation of NF-kappa B 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 PR-negative cancer cells, To understand the molecular mechanisms responsible for metastatic growth of ER-negative breast cancers, the activities of the transcription factor NF-kappa B (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-kappa B, which is usually maintained in an inactive state by protein-protein interaction with inhibitor I kappa Bs, was found to be constitutively active in ER-negative breast cancer cell lines, Constitutive DNA binding of NF-kappa B 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-kappa B, Analysis of individual subunits of NF-kappa B 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 I kappa B alpha, -beta, and -gamma were also observed, In transient-transfection experiments, constitutive activity of an NF-kappa B-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-kappa B in a dose-dependent manner, we propose that breast cancers that lack functional ER overexpress NF-kappa B-regulated genes, Furthermore, since recent data indicate that NF-kappa B 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.