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BHLHE40 and ChREBP associate with hepatic enhancer clusters containing PPARα, RXRα, and HNF4 nuclear receptors.

BHLHE40/DEC1 is a basic helix-loop-helix transcription factor (TF) that regulates circadian rhythm and T-cell responses. In hepatocytes, its function and interplay with other TFs are poorly understood. Employing a genome-wide approach, we show that its genomic binding strongly overlapped with that of carbohydrate response-element binding protein, a sugar-sensing TF and known inducer of BHLHE40 expression. Transcriptomic analysis of primary mouse hepatocytes revealed reduced expression of genes involved in genomic stability on Bhlhe40 knockdown by siRNA. Bhlhe40 depletion potentiated fructose responsiveness of genes involved in cell-cycle regulation. Strikingly, genomic binding of BHLHE40 extensively overlapped with enhancers occupied by PPARα, RXRα, and HNF4 nuclear receptors and BHLHE40 fine-tuned the expression of PPARα target genes. Using HEK293 cells, we further observed that BHLHE40 physically interacted with RXRα and PPARα cofactors. Collectively, our data suggest that through cooperation with carbohydrate response-element binding protein and nuclear receptors, BHLHE40 is a central regulator of hepatic gene expression with potential to integrate inputs from nutrient signals contributing to the metabolic flexibility of the liver.

Animals

Histone demethylase PHF2 drives olanzapine-induced dyslipidemia via epigenomic rewiring of hepatic lipogenic genes.

Olanzapine, an atypical antipsychotic agent, is widely used in treating psychotic disorders, yet its metabolic side effects remain a clinical concern. Emerging evidence suggests that dynamic alterations in histone methylation are implicated in olanzapine-induced hepatic lipid metabolic disorders. PHF2, a JmjC family histone demethylase mediating H3K9me2 demethylation, functions as a transcriptional repressor by regulating downstream targets. To elucidate PHF2's role in this process, we utilized an olanzapine-induced dyslipidemia rat model. ChIP-qPCR analysis demonstrated a significant reduction in dimethylated histone H3 lysine 9 (H3K9me2) on the promoters of lipogenic genes (Fasn, Acc1, Scd1) in the liver, accompanied by elevated nuclear expression of PHF2 in olanzapine-treated rats. Co-immunoprecipitation (Co-IP) assays revealed a physical interaction between PHF2 and ChREBP, a glucose-responsive lipogenic transcription factor. Olanzapine was found to enhance the formation of this complex. Overexpression of PHF2 led to upregulated protein levels of FASN/ACC1 and intracellular lipid accumulation, whereas knockdown of PHF2 using siRNA attenuated these effects. Notably, the upregulation of FASN/ACC1 expression induced by olanzapine was markedly diminished in PHF2-deficient AML12 cells via ChREBP-PHF2-mediated H3K9me2 demethylation. Additionally, olanzapine inhibited the nuclear translocation of FOXA2, a PHF2 transcriptional regulator, thereby augmenting PHF2 expression. These findings uncover a novel epigenetic mechanism underlying olanzapine-induced dyslipidemia, positioning the FOXA2-PHF2-ChREBP axis as a potential therapeutic target through modulation of hepatic histone methylation.

Animals

MondoA mediates transcriptional coordination between the MYC network and the integrated stress response in pancreatic cancer.

MYC amplification contributes to poor survival and outcome in pancreatic ductal adenocarcinoma (PDAC). Here we show that in PDAC cell lines with amplified MYC, MondoA is required for viability, facilitating proliferation while suppressing apoptosis in vitro and in vivo. Transcriptional and genomic profiling demonstrates that loss of MondoA leads to altered expression of direct MondoA targets as well as MYC target genes and is accompanied by shifts in genomic occupancy of MYC, MNT, and the MondoA paralog ChREBP. This altered genomic binding by MYC network members is associated with transcriptional perturbation of multiple metabolic and stress pathways, as well as global changes in N6-methyladenosine modification (m6A) of messenger RNA (mRNA). MondoA inhibition disrupts coordination between MYC network members and the Integrated Stress Response (ISR), resulting in decreased translation of ATF4 mRNA, discordant gene regulation of shared targets of MYC and ATF4 and, ultimately, apoptosis. Reestablishing ATF4 protein expression rescues the diminished viability due to loss of MondoA expression or activity, providing direct evidence of a link between deregulated MYC and the transcriptional machinery of the ISR. Last, we find that small-molecule inhibition of MondoA is lethal in a subset of PDAC cell lines, including patient-derived organoids, suggesting that the ability to target MYC via chemical inhibition of MondoA transcriptional activity may have broad efficacy.

Humans

MondoA mediates transcriptional coordination between the MYC network and the integrated stress response in pancreatic ductal adenocarcinoma.

MYC amplification contributes to poor survival and outcome in pancreatic ductal adenocarcinoma (PDAC). Here we show that in PDAC cell lines with amplified MYC, MondoA is required for viability, facilitating proliferation while suppressing apoptosis in vitro and in vivo. Transcriptional and genomic profiling demonstrates that loss of MondoA leads to altered expression of direct MondoA targets as well as MYC target genes and is accompanied by shifts in genomic occupancy of MYC, MNT, and the MondoA paralog ChREBP. This altered genomic binding by MYC network members is associated with transcriptional perturbation of multiple metabolic and stress pathways, as well as global changes in N6-methyladenosine modification (m6A) of mRNA. MondoA inhibition disrupts coordination between MYC network members and the Integrated Stress Response (ISR), resulting in decreased translation of ATF4 mRNA, discordant gene regulation of shared targets of MYC and ATF4 and, ultimately, apoptosis. Re-establishing ATF4 protein expression rescues the diminished viability due to loss of MondoA expression or activity, providing direct evidence of a link between deregulated MYC and the transcriptional machinery of the ISR. Lastly, we find that small-molecule inhibition of MondoA is lethal in a subset of PDAC cell lines, including patient-derived organoids, suggesting that the ability to target MYC via chemical inhibition of MondoA transcriptional activity may have broad efficacy.

Cell Biology