The synthetic epoxyquinoids jesterone dimer and epoxyquinone A monomer induce apoptosis and inhibit REL (human c-Rel) DNA binding in an IkappaBalpha-deficient diffuse large B-cell lymphoma cell line.
ABSTRACT The NF-kappaB transcription factor signaling pathway is constitutively active in many human cancers, and inhibition of this pathway can often kill cancer cells by inducing apoptosis. In this study, we show that two synthetic epoxyquinoids, jesterone dimer (JD) and epoxyquinone A monomer (EqM), are equally effective at inhibiting the growth of two human lymphoma cell lines that have constitutively nuclear REL (human c-Rel) DNA-binding complexes, but either express (SUDHL-4 cells) or do not express (RC-K8 cells) the NF-kappaB inhibitor IkappaBalpha. Furthermore, in these cells, both JD and EqM dose-dependently induced apoptosis, inhibited REL DNA-binding activity, and converted REL to a high molecular weight form. In A293 cells, JD and EqM inhibited the DNA-binding activity of overexpressed REL, but not p50. Replacement of Cys-27 with Ser in REL reduced JD- and EqM-mediated inhibition of REL DNA-binding activity. These results suggest that JD and EqM can induce apoptosis in IkappaBalpha-deficient lymphoma cells through a mechanism involving direct inhibition of transcription factor REL.
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ABSTRACT: c-Rel is a member of the nuclear factor κB (NF-κB) transcription factor family. Unlike other NF-κB proteins that are expressed in a variety of cell types, high levels of c-Rel expression are found primarily in B and T cells, with many c-Rel target genes involved in lymphoid cell growth and survival. In addition to c-Rel playing a major role in mammalian B and T cell function, the human c-rel gene (REL) is a susceptibility locus for certain autoimmune diseases such as arthritis, psoriasis, and celiac disease. The REL locus is also frequently altered (amplified, mutated, rearranged), and expression of REL is increased in a variety of B and T cell malignancies and, to a lesser extent, in other cancer types. Thus, agents that modulate REL activity may have therapeutic benefits for certain human cancers and chronic inflammatory diseases.Genes & cancer 07/2011; 2(7):695-711.
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ABSTRACT: Recent genome-wide studies have shown that approximately 30% of diffuse large B-cell lymphoma (DLBCL) cases harbor mutations in the histone acetyltransferase (HAT) coactivators p300 or CBP, the majority of which inactivate the catalytic HAT domain. We previously demonstrated that the human DLBCL cell line RC-K8 expresses a C-terminally truncated, HAT-defective p300 protein (p300DeltaC-1087), whose expression was essential for normal cell proliferation. Using results from large-scale DLBCL studies, we have identified and characterized a second C-terminally truncated, HAT-defective p300 mutant, p300DeltaC-820, expressed in the SUDHL2 DLBCL cell line. Properties of p300DeltaC-820 were characterized in the SUDHL2 DLBCL cell line by Western blotting, co-immunoprecipitation, and shRNA gene knockdown, as well by using cDNA expression vectors for p300DeltaC-820 in pull-down assays, transcriptional reporter assays, and immunofluorescence experiments. A mass spectrometry-based method was used to compare the histone acetylation profile of DLBCL cell lines expressing various levels of wild-type p300. We show that the SUDHL2 cell line expresses a C-terminally truncated, HAT-defective form of p300 (p300DeltaC-820), but no wild-type p300. The p300DeltaC-820 protein has a wild-type ability to localize to subnuclear "speckles," but has a reduced ability to enhance transactivation by transcription factor REL. Knockdown of p300DeltaC-820 in SUDHL2 cells reduces their proliferation and soft agar colony-forming ability. In RC-K8 cells, knockdown of p300DeltaC-1087 results in increased expression of mRNA and protein for REL target genes A20 and IkappaBalpha, two genes that have been shown to limit the growth of RC-K8 cells when overexpressed. Among a panel of B-lymphoma cell lines, low-level expression of full-length p300 protein, which is characteristic of the SUDHL2 and RC-K8 cells, was associated with decreased acetylation of histone H3 at lysines 14 and 18. The high prevalence of p300 mutations in DLBCL suggests that HAT-deficient p300 activity defines a subtype of DLBCL, which we have investigated using human DLBCL cell lines RC-K8 and SUDHL2. Our results suggest that truncated p300 proteins contribute to DLBCL cell growth by affecting the expression of specific genes, perhaps through a mechanism that involves alterations in global histone acetylation.Molecular Cancer 02/2014; 13(1):29. · 5.13 Impact Factor
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ABSTRACT: MicroRNA-155 (miR-155) is the diced product of the MIR155HG gene. miR-155 regulates the expression of many immune-specific transcripts, is overexpressed in many human lymphomas, and has oncogenic activity in mouse transgenic models. MIR155HG has been proposed to be a target gene for transcription factor NF-kappaB largely due to the positive correlation between high nuclear NF-kappaB activity and increased miR-155 expression following treatment with NF-kappaB inducers or in subsets of hematopoietic cancers. Nevertheless, direct regulation of the human MIR155HG promoter by NF-kappaB has not been convincingly demonstrated previously. This report shows that induction of NF-kappaB activity rapidly leads to increased levels of both primary MIR155HG mRNA and mature miR-155 transcripts. We have mapped an NF-kappaB-responsive element to a position approximately 178 nt upstream of the MIR155HG transcription start site. The -178 site is specifically bound by the NF-kappaB p50/p65 heterodimer and is required for p65-induced reporter gene activation. Moreover, the levels of miR-155 in nine human B-lymphoma cell lines generally correlate with increased nuclear NF-kappaB proteins. Overall, the identification of an NF-kappaB-responsive site in the MIR155HG proximal promoter suggests that MIR155HG is a direct NF-kappaB target gene in vivo. Understanding NF-kappaB-mediated regulation of miR-155 could lead to improved immune cell-related diagnostic tools and targeted therapies.BMC Molecular Biology 09/2013; 14(1):24. · 2.80 Impact Factor