title: Regulation of the PDK4 isozyme by the Rb-E2F1 complex.
abstract: Loss of the transcription factor E2F1 elicits a complex metabolic phenotype in mice underscored by reduced adiposity and protection from high fat diet-induced diabetes. Here, we demonstrate that E2F1 directly regulates the gene encoding PDK4 (pyruvate dehydrogenase kinase 4), a key nutrient sensor and modulator of glucose homeostasis that is chronically elevated in obesity and diabetes and acutely induced under the metabolic stress of starvation or fasting. We show that loss of E2F1 in vivo blunts PDK4 expression and improves myocardial glucose oxidation. The absence of E2F1 also corresponds to lower blood glucose levels, improved plasma lipid profile, and increased sensitivity to insulin stimulation. Consistently, enforced E2F1 expression up-regulates PDK4 levels and suppresses glucose oxidation in C(2)C(12) myoblasts. Furthermore, inactivation of Rb, the repressor of E2F-dependent transcription, markedly induces PDK4 and triggers the enrichment of E2F1 occupancy onto the PDK4 promoter as detected by chromatin immunoprecipitation analysis. Two overlapping E2F binding sites were identified on this promoter. Transactivation assays later verified E2F1 responsiveness of this promoter element in C(2)C(12) myoblasts and IMR90 fibroblasts, an effect that was completely abrogated following mutation of the E2F sites. Taken together, our data illustrate how the E2F1 mitogen directly regulates PDK4 levels and influences cellular bioenergetics, namely mitochondrial glucose oxidation. These results are relevant to the pathophysiology of chronic diseases like obesity and diabetes, where PDK4 is dysregulated and could have implications pertinent to the etiology of tumor metabolism, especially in cancers with Rb pathway defects.
authors.affiliation: Department of Medicine, Washington University, St. Louis, Missouri 63110.
authors.forename: Michael C F
authors.initials: MCF
authors.lastname: Hsieh
authors.affiliation: Life Sciences Division, Ernest O. Lawrence Berkeley National Laboratory, Berkeley, California 94270.
authors.forename: Debopriya
authors.initials: D
authors.lastname: Das
authors.affiliation: Department of Medicine, Washington University, St. Louis, Missouri 63110.
authors.forename: Nandakumar
authors.initials: N
authors.lastname: Sambandam
authors.affiliation: Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724.
authors.forename: Michael Q
authors.initials: MQ
authors.lastname: Zhang
authors.affiliation: Department of Medicine, Washington University, St. Louis, Missouri 63110. Electronic address: znahle@DOM.wustl.edu.
authors.forename: Zaher
authors.initials: Z
authors.lastname: Nahlé
mesh_terms: D050154:Adiposity / Q000502:physiology; D000818:Animals; D003920:Diabetes Mellitus / Q000139:chemically induced / Q000201:enzymology / Q000235:genetics; D004041:Dietary Fats / Q000378:metabolism; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D005215:Fasting / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000201:enzymology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D005947:Glucose / Q000378:metabolism*; D006706:Homeostasis / Q000502:physiology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008929:Mitochondria, Heart / Q000201:enzymology / Q000235:genetics; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D032446:Myoblasts / Q000201:enzymology; D009206:Myocardium / Q000201:enzymology; D009369:Neoplasms / Q000201:enzymology / Q000235:genetics; D010084:Oxidation-Reduction; D011401:Promoter Regions, Genetic / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis* / Q000235:genetics; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism*; D013217:Starvation / Q000201:enzymology / Q000235:genetics; D015854:Up-Regulation / Q000502:physiology
chemical_list: D004041:Dietary Fats; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; D046912:Multiprotein Complexes; C000631439:Pdk4 protein, mouse; D000081382:Pyruvate Dehydrogenase Acetyl-Transferring Kinase; D016160:Retinoblastoma Protein; D017346:Protein Serine-Threonine Kinases; D005947:Glucose