Blood glucose levels are maintained by the balance between glucose uptake by peripheral tissues and glucose secretion by the liver. Gluconeogenesis is strongly stimulated during fasting and is aberrantly activated in diabetes mellitus. Here we show that the transcriptional coactivator PGC-1 is strongly induced in liver in fasting mice and in three mouse models of insulin action deficiency: streptozotocin-induced diabetes, ob/ob genotype and liver insulin-receptor knockout. PGC-1 is induced synergistically in primary liver cultures by cyclic AMP and glucocorticoids. Adenoviral-mediated expression of PGC-1 in hepatocytes in culture or in vivo strongly activates an entire programme of key gluconeogenic enzymes, including phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase, leading to increased glucose output. Full transcriptional activation of the PEPCK promoter requires coactivation of the glucocorticoid receptor and the liver-enriched transcription factor HNF-4alpha (hepatic nuclear factor-4alpha) by PGC-1. These results implicate PGC-1 as a key modulator of hepatic gluconeogenesis and as a central target of the insulin-cAMP axis in liver.

Hepatic gluconeogenesis is absolutely required for survival during prolonged fasting or starvation, but is inappropriately activated in diabetes mellitus. Glucocorticoids and glucagon have strong gluconeogenic actions on the liver. In contrast, insulin suppresses hepatic gluconeogenesis. Two components known to have important physiological roles in this process are the forkhead transcription factor FOXO1 (also known as FKHR) and peroxisome proliferative activated receptor-gamma co-activator 1 (PGC-1alpha; also known as PPARGC1), a transcriptional co-activator; whether and how these factors collaborate has not been clear. Using wild-type and mutant alleles of FOXO1, here we show that PGC-1alpha binds and co-activates FOXO1 in a manner inhibited by Akt-mediated phosphorylation. Furthermore, FOXO1 function is required for the robust activation of gluconeogenic gene expression in hepatic cells and in mouse liver by PGC-1alpha. Insulin suppresses gluconeogenesis stimulated by PGC-1alpha but co-expression of a mutant allele of FOXO1 insensitive to insulin completely reverses this suppression in hepatocytes or transgenic mice. We conclude that FOXO1 and PGC-1alpha interact in the execution of a programme of powerful, insulin-regulated gluconeogenesis.

Summary Aneuploidy has been recognized as a hallmark of cancer for over 100 years, yet no general theory to explain the recurring patterns of aneuploidy in cancer has emerged. Here we develop Tumor Suppressor and Oncogene (TUSON) Explorer, a computational method that analyzes the patterns of mutational signatures in tumors and predicts the likelihood that any individual gene functions as a tumor suppressor (TSG) or oncogene (OG). By analyzing >8200 tumor-normal pairs we provide statistical evidence suggesting many more genes possess cancer driver properties than anticipated, forming a continuum of oncogenic potential. Integrating our driver predictions with information on somatic copy number alterations, we find that the distribution and the potency of TSGs (STOP genes), OGs and essential genes (GO genes) on chromosomes can predict the complex patterns of aneuploidy and copy number variation characteristic of cancer genomes. We propose that the cancer genome is shaped through a process of cumulative haploinsufficiency and triplosensitivity.

Cachexia is a chronic state of negative energy balance and muscle wasting that is a severe complication of cancer and chronic infection. While cytokines such as IL-1alpha, IL-1beta, and TNFalpha can mediate cachectic states, how these molecules affect energy expenditure is unknown. We show here that many cytokines activate the transcriptional PPAR gamma coactivator-1 (PGC-1) through phosphorylation by p38 kinase, resulting in stabilization and activation of PGC-1 protein. Cytokine or lipopolysaccharide (LPS)-induced activation of PGC-1 in cultured muscle cells or muscle in vivo causes increased respiration and expression of genes linked to mitochondrial uncoupling and energy expenditure. These data illustrate a direct thermogenic action of cytokines and p38 MAP kinase through the transcriptional coactivator PGC-1.

The liver plays several critical roles in the metabolic adaptation to fasting. We have shown previously that the transcriptional coactivator peroxisome proliferator-activated receptor ␥ coactivator-1␣ (PGC-1␣) is induced in fasted or diabetic liver and activates the entire program of gluconeogenesis. PGC-1␣ interacts with several nuclear receptors known to bind gluconeogenic promoters including the glucocorticoid receptor, hepatocyte nuclear factor 4␣ (HNF4␣), and the peroxisome proliferator-activated receptors. However, the genetic requirement for any of these interactions has not been determined. Using hepatocytes from mice lacking HNF4␣ in the liver, we show here that PGC-1␣ completely loses its ability to activate key genes of gluconeogenesis such as phosphoenolpyruvate carboxykinase and glucose-6-phosphatase when HNF4␣ is absent. It is also shown that PGC-1␣ can induce genes of ␤-oxidation and ketogenesis in hepatocytes, but these effects do not require HNF4␣. Analysis of the glucose-6-phosphatase promoter indicates a key role for HNF4␣-binding sites that function robustly only when HNF4␣ is coactivated by PGC-1␣. These data illustrate the involvement of PGC-1␣ in several aspects of the hepatic fasting response and show that HNF4␣ is a critical component of PGC-1␣-mediated gluconeogenesis.A crucial function of the liver is the regulation of systemic fuel availability. During prolonged fasting, the liver activates gluconeogenesis to maintain blood glucose levels. Gluconeogenesis begins 4-6 h after the onset of fasting and reaches maximal activity as hepatic glycogen stores are reduced. Fatty acid oxidation is also activated during fasting and provides ATP for the liver. The very rapid oxidation of fatty acids also leads to generation and export of ketone bodies, which provide an important alternative fuel source to glucose, especially for the central nervous system. Gluconeogenesis, ␤-oxidation of fatty acids, and ketogenesis all are suppressed by insulin and elevated in poorly controlled diabetes. Elevated gluconeogenesis is a major contributor to the hyperglycemia of diabetes.Peroxisome proliferator-activated receptor (PPAR)␥ coactivator-1␣ (PGC-1␣) is a transcriptional coactivator that regulates a wide range of processes involved in energy production and utilization, namely adaptive thermogenesis, mitochondrial biogenesis, glucose uptake in muscle, and skeletal muscle fiber-type switching (1-4). PGC-1␣ is induced in the liver in fasting or diabetes and is a potent stimulator of the entire program of hepatic gluconeogenesis (5, 6). Primary murine hepatocytes and rats receiving recombinant PGC-1␣ through adenoviral delivery exhibit a dramatic rise in the expression of key gluconeogenic enzymes in the liver, such as phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase), and in the subsequent production of glucose. The function of PGC-1␣ in other aspects of the hepatic fasting response is unknown, although PGC-1␣ has been shown to induce mitochondrial fatty acid oxidation in cardiac myo...

The nuclear receptor peroxisome proliferator-activated receptor ␥ regulates adipose differentiation and systemic insulin signaling via ligand-dependent transcriptional activation of target genes. However, the identities of the biologically relevant target genes are largely unknown. Here we describe the isolation and characterization of a novel target gene induced by PPAR␥ ligands, termed PGAR (for PPAR␥ angiopoietin related), which encodes a novel member of the angiopoietin family of secreted proteins. The transcriptional induction of PGAR follows a rapid time course typical of immediate-early genes and occurs in the absence of protein synthesis. The expression of PGAR is predominantly localized to adipose tissues and placenta and is consistently elevated in genetic models of obesity. Hormone-dependent adipocyte differentiation coincides with a dramatic early induction of the PGAR transcript. Alterations in nutrition and leptin administration are found to modulate the PGAR expression in vivo. Taken together, these data suggest a possible role for PGAR in the regulation of systemic lipid metabolism or glucose homeostasis.The past several years have witnessed an increasing recognition of the adipocyte as a remarkably dynamic entity that uses diverse signaling pathways to interact with other tissues. A compelling body of evidence now implicates adipocyte-derived proteins such as leptin (25a, 31) and tumor necrosis factor ␣ (10) as endocrine and/or autocrine modulators of distant and local targets. This enables the adipose tissue to exercise feedback regulation over systemic energy homeostasis and metabolism.In parallel with the improved functional understanding of the adipocyte, there has been a burgeoning interest in studying the molecular control of adipose differentiation. Research efforts directed at the transcriptional regulation of adipogenesis have led to the elucidation of several transcription factors that play key roles in this process, including the peroxisome proliferator-activated receptor ␥ (PPAR␥) (26) and the CCAAT/ enhancer binding protein (6) family members. PPAR␥, a member of the PPAR subfamily of nuclear hormone receptors, is a ligand-dependent transcription factor expressed in a tissueselective manner, with the highest levels in the adipose tissue. Much evidence from gain-and loss-of-function studies indicates that PPAR␥ is a central regulator of adipogenesis and systemic insulin action (reviewed in references 15 and 24), providing a crucial link between these two major aspects of adipocyte biology. PPAR␥ has been demonstrated to stimulate adipose conversion in a variety of fibroblastic cell lines ectopically expressing PPAR␥, as well as in preadipocyte and mesenchymal precursor cell lines (26). Committed myoblasts stably infected with PPAR␥ and CCAAT/enhancer binding protein ␣ can be induced to undergo transdifferentiation into adipocytes upon PPAR␥ activation (11). More recently, lossof-function experiments using PPAR␥ Ϫ/Ϫ mice or embryonic stem cells have confirmed the requirement of PPAR␥ f...

Summary Completion of DNA replication after replication stress depends on PCNA, which undergoes mono-ubiquitination to stimulate direct bypass of DNA lesions by specialized DNA polymerases or is poly-ubiquitinated to promote recombination dependent DNA synthesis across DNA lesions by template switching mechanisms. Here we report that the ZRANB3 translocase, a SNF2 family member related to the SIOD disorder SMARCAL1 protein, is recruited by poly-ubiquitinated PCNA to promote fork restart following replication arrest. ZRANB3 depletion in mammalian cells results in an increased frequency of sister chromatid exchange and DNA damage sensitivity after treatment with agents that cause replication stress. Using in vitro biochemical assays, we show that recombinant ZRANB3 remodels DNA structures mimicking stalled replication forks and disassembles recombination intermediates. We therefore propose that ZRANB3 maintains genomic stability at stalled or collapsed replication forks by facilitating fork restart and limiting inappropriate recombination that could occur during template switching events.

Mitochondria serve a critical role in physiology and disease. The genetic basis of mitochondrial regulation in mammalian cells has not yet been detailed. We performed a large-scale RNAi screen to systematically identify genes that affect mitochondrial abundance and function. This screen revealed previously unrecognized roles for >150 proteins in mitochondrial regulation. We report that increased Wnt signals are a potent activator of mitochondrial biogenesis and reactive oxygen species (ROS) generation, leading to DNA damage and acceleration of cellular senescence in primary cells. The signaling protein insulin receptor substrate-1 (IRS-1), shown here to be a transcriptional target of Wnt, is induced in this setting. The increased level of IRS-1 drives activation of mitochondrial biogenesis; furthermore, in insulin-responsive cell types, it enhances insulin signaling, raising the possibility that Wnt proteins may be used to modulate glucose homeostasis. Our results identify a key component of the mitochondrial regulatory apparatus with a potentially important link to metabolic and degenerative disorders.[Keywords: RNAi screen; mitochondria; Wnt signaling; IRS-1] Supplemental material is available at http://www.genesdev.org.