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. The purpose of the present proposal is to understand the relationship between two transcription factors involved in metabolic control: the glucose-sensing transcription factor, carbohydrate response element binding protein (ChREBP), and the proto-oncogene, Myc (formally c-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 bound to target genes, additional poorly defined molecular events, and dependent on glucose, must take place for ChREBP transactivation. Dysregulated Myc, and recently ChREBP, have both been implicated in the increased glycolysis (the 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 sates. Our challenge, reflected in this proposal, is to understand more completely the molecular relationship between Myc and ChREBP within the context of the physiological role that Myc plays in glucose homeostasis. Our overarching hypothesis is that Myc is required for the ChREBP-dependent glucose response, and for transitions between metabolic phenotypes. To test this hypothesis we will accomplish the following Specific Aims: 1) determine if glucose alters Myc activity and is therefore a glucose-sensing transcription factor. Using a proteomic approach we will determine if glucose alters the posttranslational modification of Myc, and the domains of Myc required for recruitment to glucose-responsive genes will be determined in a rescue assay. 2) Determine how Myc promotes glucose-activated gene transcription by ChREBP. Using a quantitative chromatin immunoprecipitation, we will determine the epigenetic environment created by Myc in a glucose-dependent manner, the domains of Myc required for the glucose-mediated recruitment of ChREBP, and the elongation of paused RNA polymerase by glucose, and if glucose affects nucleosome positioning or replacement. 3) Determine the molecular, metabolic, and physiological consequences of depleting Myc activity in the liver. Using a Cre-lox approach, we will determine the effects of depleting Myc in the liver, measuring gene expression, transcription factor recruitment, and whole body glucose metabolism.
Cells must adapt to changes in metabolic environment, and failure to do so results in diabetes and metabolic syndrome. ChREBP and Myc are transcription factors involved in the perception and regulation of cellular metabolism. Understanding how they interact to regulate metabolism will provide crucial information for informed therapies for the treatment of diabetes and cancer.
