The Role of Myc in ChREBP-dependent, Glucose-stimulated Gene Expression

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DESCRIPTION (provided by applicant): The ability of cells to sense and respond to changes in their metabolic environment is crucial to preventing the pathophysiological consequences of metabolic syndrome and diabetes. Cellular adaptation to changes in metabolic fuel availability includes coordinated changes in patterns of gene expression, mediated by nutrient- sensing transcription factors, and this process is disrupted in diabetes, with cells trapped in the fasted state despite abundant metabolic fuel. The purpose of the present proposal is to understand the relationship between two transcription factors involved in nutrient sensing and the hepatic fasted-to-fed transition, the glucose-sensing transcription factor carbohydrate response element binding protein (ChREBP), and Myc. ChREBP mediates transcriptional activation of glucose-responsive target genes in metabolically relevant tissues such as the liver and pancreatic beta cells. Glucose stimulates translocation of ChREBP to the nucleus, and once ChREBP is bound to target genes, additional poorly defined molecular events, dependent on glucose, must take place for transactivation. Dysregulated Myc, and recently ChREBP, have both been implicated in the increased glycolysis (Warburg effect) associated with transformation in cancer. Our published and Preliminary Data demonstrate that Myc is required for ChREBP-dependent glucose-stimulated gene expression, is recruited to regulatory regions of glucose-responsive genes, and is necessary for the recruitment of ChREBP and other activating transcription factors of the glucose response. We hypothesize that Myc works in a larger context to allow transition between metabolic phenotypes, e.g., the fasted and fed states. Our challenge, reflected in this proposal is to understand more completely the molecular relationship between Myc and ChREBP within the context of the physiological roles they play in glucose homeostasis, so that we can better understand how to manipulate them therapeutically in disease states. Our overarching hypothesis is that Myc is required for the ChREBP-dependent glucose response, and for transitions between metabolic phenotypes. Specific Aim 1) is to determine the physiological, metabolic, and molecular consequences of depleting Myc activity in the liver. Using a CRE-Lox approach, we will determine the effect of hepatic Myc depletion on the fasting-to-fed transition by measuring gene expression with RT-PCR and SOLID SAGE; by measuring ChREBP and other transcription factor occupancies by ChIP and by ChIP-seq; and by measuring glycolysis, lipogenesis, lipid storage and oxidation, ketogenesis, and glucose output, as well as whole body and hepatic insulin resistance and glucose tolerance. Specific Aim 2 is to determine how Myc promotes ChREBP-dependent glucose-activated gene transcription. We will use a proteomic approach to test if glucose alters the posttranslational modification of Myc; we will determine if Myc alters the epigenetic environment of glucose responsive genes in a glucose-dependent manner; and will map the domains of Myc required for the glucose-specific functions of Myc. Accomplishing these Aims will provide the framework for understanding the normal physiological relationship between Myc and ChREBP, and will allow informed design of therapies for metabolic disorders such as metabolic syndrome and diabetes, and may well provide insights towards the metabolic perturbations of cancer.