Project description:Autophagy is the primary catabolic process triggered in response to starvation. Although autophagic regulation within the cytosolic compartment is well established, it is becoming clear that nuclear events also regulate the induction or repression of autophagy. Nevertheless, a thorough understanding of the mechanisms by which sequence-specific transcription factors modulate expression of genes required for autophagy is lacking. Here, we identify Foxk proteins (Foxk1 and Foxk2) as transcriptional repressors of autophagy in muscle cells and fibroblasts. Interestingly, Foxk1/2 serve to counter-balance another forkhead transcription factor, Foxo3, which induces an overlapping set of autophagic and atrophic targets in muscle. Foxk1/2 specifically recruits Sin3A-HDAC complexes to restrict acetylation of histone H4 and expression of critical autophagy genes. Remarkably, mTOR promotes the transcriptional activity of Foxk1 by facilitating nuclear entry to specifically limit basal levels of autophagy in nutrient-rich conditions. Our study highlights an ancient, conserved mechanism whereby nutritional status is interpreted by mTOR to restrict autophagy by repressing essential autophagy genes via Foxk-Sin3-mediated transcriptional control. Examination of (1) chromatin binding of Foxk1 and Sin3A in non-starved myoblasts and (2) gene expression profiling upon either starvation or siRNA-mediated depletion of Foxk1 relative to a non-starved control.
Project description:Autophagy is the primary catabolic process triggered in response to starvation. Although autophagic regulation within the cytosolic compartment is well established, it is becoming clear that nuclear events also regulate the induction or repression of autophagy. Nevertheless, a thorough understanding of the mechanisms by which sequence-specific transcription factors modulate expression of genes required for autophagy is lacking. Here, we identify Foxk proteins (Foxk1 and Foxk2) as transcriptional repressors of autophagy in muscle cells and fibroblasts. Interestingly, Foxk1/2 serve to counter-balance another forkhead transcription factor, Foxo3, which induces an overlapping set of autophagic and atrophic targets in muscle. Foxk1/2 specifically recruits Sin3A-HDAC complexes to restrict acetylation of histone H4 and expression of critical autophagy genes. Remarkably, mTOR promotes the transcriptional activity of Foxk1 by facilitating nuclear entry to specifically limit basal levels of autophagy in nutrient-rich conditions. Our study highlights an ancient, conserved mechanism whereby nutritional status is interpreted by mTOR to restrict autophagy by repressing essential autophagy genes via Foxk-Sin3-mediated transcriptional control.
Project description:Foxk proteins are transcriptional regulators implicated in key biological processes such as glycolysis, autophagy and cell cycle regulation, among others. Here we employ targeted morpholino knockdown to deplete Foxk1, Fokx2, and Foxk2-1 proteins in developing zebrafish embryos. We demonstrate that the loss of Foxk transcription factors causes genome-wide transcriptional misregulation, characterised by upregulation of autophagy-related genes and downregulation of cell cycle regulators. The phenotype is embryonic lethal with the majority of embryos not surviving past 24hpf.
Project description:In order to investigate the genome-wide binding profile of the forkhead transcription factor FOXK2 in human embryonic stem cells (ESCs) and downstream cell types, we generated the RNA-seq data with FOXK1/2 and SIN3A siRNA in H1 ESC cells and FOXK1/2 siRNA in the differentiated NPC cells.
Project description:Autophagy phenomenon is an essential mechanism to regulate cell homeostasis and is activated by various stresses such as nutrient starvation. It is well known that when autophagy is activated and how important components in the cytoplasm cause a series of reactions, but the regulatory mechanism of transcription in the nucleus is poorly known. Here, we identify that histone demethylase KDM3A plays a crucial role in the transcription of autophagy and lysosomal genes. Notably, KDM3A is increased in transcriptional levels in both glucose and amino acid starvation. Especially, transcriptional increase of histone demethylase in response to glucose starvation is dependent on AMP-activated protein kinase (AMPK). Furthermore, genome-wide analysis reveals that KDM3A acts as a co-activator in the expression of autophagy and lysosomal genes. Our finding of histone demethylase signaling cascade in nucleus, modulating histone demethylation signature is one of the predominant epigenetic event in autophagy activation, thereby providing the functional and mechanistic link between epigenetic control and transcriptional regulation of autophagy upon nutrient starvation.
Project description:Autophagy is a highly conserved self-digestion process, essential to maintain homeostasis and viability in response to nutrient starvation. Although the components of autophagy in the cytoplasm have been well-studied, molecular basis for the epigenetic regulation of autophagy is poorly understood. Here, we identify histone arginine methyltransferase CARM1 as a critical component of autophagy. We found that nutrient starvation increased CARM1 protein level and subsequently histone H3R17 dimethylation. Genome-wide analyses reveal that CARM1 exerts transcriptional coactivator function on autophagy-related genes and lysosomal genes through TFEB. Our findings demonstrate a previously unrecognized role of CARM1-dependent histone arginine methylation as a critical nuclear event of autophagy.
Project description:Autophagy, a catabolic process to remove unnecessary or dysfunctional cells, is triggered by various signals including nutrient starvation. Depending on the type of the nutrient deficiency, diverse sensing mechanisms and pathways are used for autophagy, suggesting subsequent nutrient dependent transcriptional regulation. Still, however, our knowledge about nutrient specific transcriptional regulation during autophagy is limited. To understand nutrient type dependent transcriptional mechanisms during autophagy, we performed single cell RNA sequencing (scRNAseq) for the mouse embryonic fibroblasts (MEFs) before and after applying glucose- (GS) as well as amino acid starvation (AAS). Trajectory analysis using scRNAseq identified sequential induction of potential transcriptional regulators for each deficiency condition. Gene regulatory rules inferred using TENET newly identified CCAAT/enhancer binding protein γ (C/EBPγ) regulates autophagy processes specifically to AAS condition. Strikingly, knockdown of C/EBPγ attenuated the autophagic process only in the AAS condition. Cell biological and biochemical studies validated that C/EBPγ plays a switching role for ATF4 to activate autophagy genes under AAS, but not under GS. Together, our data identified C/EBPγ as a previously unidentified key regulator under amino acid starvation-induced autophagy.
Project description:Autophagy, a catabolic process to remove unnecessary or dysfunctional cells, is triggered by various signals including nutrient starvation. Depending on the type of the nutrient deficiency, diverse sensing mechanisms and pathways are used for autophagy, suggesting subsequent nutrient dependent transcriptional regulation. Still, however, our knowledge about nutrient specific transcriptional regulation during autophagy is limited. To understand nutrient type dependent transcriptional mechanisms during autophagy, we performed single cell RNA sequencing (scRNAseq) for the mouse embryonic fibroblasts (MEFs) before and after applying glucose- (GS) as well as amino acid starvation (AAS). Trajectory analysis using scRNAseq identified sequential induction of potential transcriptional regulators for each deficiency condition. Gene regulatory rules inferred using TENET newly identified CCAAT/enhancer binding protein γ (C/EBPγ) regulates autophagy processes specifically to AAS condition. Strikingly, knockdown of C/EBPγ attenuated the autophagic process only in the AAS condition. Cell biological and biochemical studies validated that C/EBPγ plays a switching role for ATF4 to activate autophagy genes under AAS, but not under GS. Together, our data identified C/EBPγ as a previously unidentified key regulator under amino acid starvation-induced autophagy.
Project description:Starvation causes the accumulation of lipid droplets in the liver, a somewhat counterintuitive phenomenon that is nevertheless conserved from flies to humans. Much like fatty liver resulting from overfeeding, hepatic lipid accumulation (steatosis) during undernourishment can lead to lipotoxicity and atrophy of the liver. Here, we found that while surface populations of Astyanax mexicanus undergo this evolutionarily conserved response to starvation, the starvation-resistant cavefish larvae of the same species do not display an accumulation of lipid droplets upon starvation. Moreover, cavefish are resistant to liver atrophy during starvation, providing a unique system to explore strategies for liver protection. Using comparative transcriptomics between zebrafish, surface fish, and cavefish, we identified the fatty acid transporter slc27a2a/fatp2 to be correlated with the development of fatty liver. Pharmacological inhibition of slc27a2a in zebrafish rescues steatosis and atrophy of the liver upon starvation. Further, down-regulation of FATP2 in drosophila larvae inhibits the development of starvation-induced steatosis, suggesting the evolutionary conserved importance of the gene in regulating fatty liver upon nutrition deprivation. Overall, our study identifies a conserved, druggable target to protect the liver from atrophy during starvation.