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, antiestrog en- and chemotherapy-resistant phenotype with highly invasive and meta static growth properties, This progression is usually accompanied by a ltered function of the estrogen receptor (ER) or outgrowth of PR-negat ive cancer cells, To understand the molecular mechanisms responsible f or 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-neg ative (MDA-MB-231 and MDA-MB-435) human breast cancer cell lines, NF-k appa B, which is usually maintained in an inactive state by protein-pr otein interaction with inhibitor I kappa Bs, was found to be constitut ively active in ER-negative breast cancer cell lines, Constitutive DNA binding of NF-kappa B was also observed with extracts from ER-negativ e, 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 phe notype) was also accompanied by constitutive activation of NF-kappa B, Analysis of individual subunits of NF-kappa B revealed that all ER-ne gative cell lines, including RM22-F5 cells of F phenotype, contain a u nique 37-kDa protein which is antigenically related to the RelA subuni t, Cell-type-specific differences in I kappa B alpha, -beta, and -gamm a were also observed, In transient-transfection experiments, constitut ive activity of an NF-kappa B-dependent promoter was observed in MDA-M B-231 and RM22-F5 cells of F phenotype, and this activity was efficien tly repressed by cotransfected ER, Since ER inhibits the constitutive as well as inducible activation function of NF-kappa B in a dose-depen dent manner, we propose that breast cancers that lack functional ER ov erexpress NF-kappa B-regulated genes, Furthermore, since recent data i ndicate that NF-kappa B protects cells from tumor necrosis factor alph a-, ionizing radiation-, and chemotherapeutic agent daunorubicin-media ted apoptosis, our results provide an explanation for chemotherapeutic resistance in ER-negative breast cancers.