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Browsing by Author "Bhat-Nakshatri, P"
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Item Constitutive activation of NF-kappaB during progression of breast cancer to hormone-independent growth.(American Society for Microbiology, 1997-07) Nakshatri, H; Bhat-Nakshatri, P; Martin, D A; Goulet, R J; Sledge, G WBreast 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.Item Multiple parameters determine the specificity of transcriptional response by nuclear receptors HNF-4, ARP-1, PPAR, RAR and RXR through common response elements.(Oxford University Press, 1998-05-15) Nakshatri, H; Bhat-Nakshatri, PA number of nuclear receptors, including retinoic acid receptors (RARs), retinoid-X receptors (RXRs), hepatocyte nuclear factor 4 (HNF-4), chicken ovalbumin upstream promoter transcription factor I (COUP-TFI), apolipoprotein regulatory protein 1 (ARP-1) and peroxisome proliferator-activated receptor (PPAR), bind to response elements comprised of two core motifs, 5'-RG(G/T)TCA, or a closely related sequence separated by 1 nt (DR1 elements). The potential role of the precise sequence of the core motif as well as the spacer nucleotide in determining specificity and promiscuity of receptor-response element interactions was investigated. We show here that nucleotides at base positions 1, 2 and 4 of the core motif as well as the spacer nucleotide determine the binding preference of HNF-4 and ARP-1 homodimers and RAR:RXR and PPAR:RXR heterodimers. In transfection experiments transcriptional activation by HNF-4 and PPAR:RXR and repression by ARP-1 correlated with the relative in vitro binding affinity provided the element was located within the proper promoter context. Furthermore, promoter context also determined whether an element that binds to HNF-4 and PPAR:RXR with equal affinity functions as an HNF-4 response element or PPAR response element. Thus, apart from the element-specific differences in affinity for the receptors, additional promoter-specific transcription factors that interact with HNF-4 and PPAR:RXR determine the specificity of transcriptional response through DR1-type elements.Item Tumour necrosis factor and PI3-kinase control oestrogen receptor alpha protein level and its transrepression function(Springer Nature, 2004-02-23) Bhat-Nakshatri, P; Campbell, R A; Patel, N M; Newton, T R; King, A J; Marshall, M S; Ali, S; Nakshatri, H