Dataset Information

Antagonism of E2F-1 regulated Bnip3 transcription by NF-kappaB is essential for basal cell survival.

ABSTRACT: The transcription factor E2F-1 drives proliferation and death, but the mechanisms that differentially regulate these divergent actions are poorly understood. The hypoxia-inducible death factor Bnip3 is an E2F-1 target gene and integral component of the intrinsic mitochondrial death pathway. The mechanisms that govern Bnip3 gene activity remain cryptic. Herein we show that the transcription factor NF-kappaB provides a molecular switch that determines whether E2F-1 signals proliferation or death under physiological conditions. We show under basal nonapoptotic conditions that NF-kappaB constitutively occupies and transcriptionally silences Bnip3 gene transcription by competing with E2F-1 for Bnip3 promoter binding. Conversely, in the absence of NF-kappaB, or during hypoxia when NF-kappaB abundance is reduced, basal Bnip3 gene transcription is activated by the unrestricted binding of E2F-1 to the Bnip3 promoter. Genetic knock-down of E2F-1 or retinoblastoma gene product over-expression in cardiac and human pancreatic cancer cells deficient for NF-kappaB signaling abrogated basal and hypoxia-inducible Bnip3 transcription. The survival kinase PI3K/Akt inhibited Bnip3 expression levels in cells in a manner dependent upon NF-kappaB activation. Hence, by way of example, we show that the transcriptional inhibition of E2F-1-dependent Bnip3 expression by NF-kappaB highlights a survival pathway that overrides the E2F-1 tumor suppressor program. Our data may explain more fundamentally how cells, by selectively inhibiting E2F-1-dependent death gene transcription, avert apoptosis down-stream of the retinoblastoma/E2F-1 cell cycle pathway.

SUBMITTER: Shaw J

PROVIDER: S-EPMC2603431 | biostudies-literature |

REPOSITORIES: biostudies-literature

ACCESS DATA

Similar Datasets

Project description:Picroliv, an iridoid glycoside derived from the plant Picrorhiza kurroa, is used traditionally to treat fever, asthma, hepatitis, and other inflammatory conditions. However, the exact mechanism of its therapeutic action is still unknown. Because nuclear factor-kappaB (NF-kappaB) activation plays a major role in inflammation and carcinogenesis, we postulated that picroliv must interfere with this pathway by inhibiting the activation of NF-kappaB-mediated signal cascade. Electrophoretic mobility shift assay showed that pretreatment with picroliv abrogated tumor necrosis factor (TNF)-induced activation of NF-kappaB. The glycoside also inhibited NF-kappaB activated by carcinogenic and inflammatory agents, such as cigarette smoke condensate, phorbol 12-myristate 13-acetate, okadaic acid, hydrogen peroxide, lipopolysaccharide, and epidermal growth factor. When examined for the mechanism of action, we found that picroliv inhibited activation of IkappaBalpha kinase, leading to inhibition of phosphorylation and degradation of IkappaBalpha. It also inhibited phosphorylation and nuclear translocation of p65. Further studies revealed that picroliv directly inhibits the binding of p65 to DNA, which was reversed by the treatment with reducing agents, suggesting a role for a cysteine residue in interaction with picroliv. Mutation of Cys(38) in p65 to serine abolished this effect of picroliv. NF-kappaB inhibition by picroliv leads to suppression of NF-kappaB-regulated proteins, including those linked with cell survival (inhibitor of apoptosis protein 1, Bcl-2, Bcl-xL, survivin, and TNF receptor-associated factor 2), proliferation (cyclin D1 and cyclooxygenase-2), angiogenesis (vascular endothelial growth factor), and invasion (intercellular adhesion molecule-1 and matrix metalloproteinase-9). Suppression of these proteins enhanced apoptosis induced by TNF. Overall, our results show that picroliv inhibits the NF-kappaB activation pathway, which may explain its anti-inflammatory and anticarcinogenic effects.

Project description:BackgroundPancreatic beta-cells are the target of an autoimmune attack in type 1 diabetes mellitus (T1DM). This is mediated in part by cytokines, such as interleukin (IL)-1beta and interferon (IFN)-gamma. These cytokines modify the expression of hundreds of genes, leading to beta-cell dysfunction and death by apoptosis. Several of these cytokine-induced genes are potentially regulated by the IL-1beta-activated transcription factor (TF) nuclear factor (NF)-kappaB, and previous studies by our group have shown that cytokine-induced NF-kappaB activation is pro-apoptotic in beta-cells. To identify NF-kappaB-regulated gene networks in beta-cells we presently used a discriminant analysis-based approach to predict NF-kappaB responding genes on the basis of putative regulatory elements.ResultsThe performance of linear and quadratic discriminant analysis (LDA, QDA) in identifying NF-kappaB-responding genes was examined on a dataset of 240 positive and negative examples of NF-kappaB regulation, using stratified cross-validation with an internal leave-one-out cross-validation (LOOCV) loop for automated feature selection and noise reduction. LDA performed slightly better than QDA, achieving 61% sensitivity, 91% specificity and 87% positive predictive value, and allowing the identification of 231, 251 and 580 NF-kappaB putative target genes in insulin-producing INS-1E cells, primary rat beta-cells and human pancreatic islets, respectively. Predicted NF-kappaB targets had a significant enrichment in genes regulated by cytokines (IL-1beta or IL-1beta + IFN-gamma) and double stranded RNA (dsRNA), as compared to genes not regulated by these NF-kappaB-dependent stimuli. We increased the confidence of the predictions by selecting only evolutionary stable genes, i.e. genes with homologs predicted as NF-kappaB targets in rat, mouse, human and chimpanzee.ConclusionThe present in silico analysis allowed us to identify novel regulatory targets of NF-kappaB using a supervised classification method based on putative binding motifs. This provides new insights into the gene networks regulating cytokine-induced beta-cell dysfunction and death.

Dataset Information

Antagonism of E2F-1 regulated Bnip3 transcription by NF-kappaB is essential for basal cell survival.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets