Class 3 PI3K coactivates the circadian clock to promote rhythmic de novo purine synthesis.

Metabolic demands fluctuate rhythmically and rely on coordination between the circadian clock and nutrient-sensing signalling pathways, yet mechanisms of their interaction remain not fully understood. Surprisingly, we find that class 3 phosphatidylinositol-3-kinase (PI3K), known best for its essential role as a lipid kinase in endocytosis and lysosomal degradation by autophagy, has an overlooked nuclear function in gene transcription as a coactivator of the heterodimeric transcription factor and circadian driver Bmal1-Clock. Canonical pro-catabolic functions of class 3 PI3K in trafficking rely on the indispensable complex between the lipid kinase Vps34 and regulatory subunit Vps15. We demonstrate that although both subunits of class 3 PI3K interact with RNA polymerase II and co-localize with active transcription sites, exclusive loss of Vps15 in cells blunts the transcriptional activity of Bmal1-Clock. Thus, we establish non-redundancy between nuclear Vps34 and Vps15, reflected by the persistent nuclear pool of Vps15 in Vps34-depleted cells and the ability of Vps15 to coactivate Bmal1-Clock independently of its complex with Vps34. In physiology we find that Vps15 is required for metabolic rhythmicity in liver and, unexpectedly, it promotes pro-anabolic de novo purine nucleotide synthesis. We show that Vps15 activates the transcription of Ppat, a key enzyme for the production of inosine monophosphate, a central metabolic intermediate for purine synthesis. Finally, we demonstrate that in fasting, which represses clock transcriptional activity, Vps15 levels are decreased on the promoters of Bmal1 targets, Nr1d1 and Ppat. Our findings open avenues for establishing the complexity for nuclear class 3 PI3K signalling for temporal regulation of energy homeostasis.

Asymmetric Dimethylation of Ribosomal S6 Kinase 2 Regulates Its Cellular Localisation and Pro-Survival Function.

Ribosomal S6 kinases (S6Ks) are critical regulators of cell growth, homeostasis, and survival, with dysregulation of these kinases found to be associated with various malignancies. While S6K1 has been extensively studied, S6K2 has been neglected despite its clear involvement in cancer progression. Protein arginine methylation is a widespread post-translational modification regulating many biological processes in mammalian cells. Here, we report that p54-S6K2 is asymmetrically dimethylated at Arg-475 and Arg-477, two residues conserved amongst mammalian S6K2s and several AT-hook-containing proteins. We demonstrate that this methylation event results from the association of S6K2 with the methyltransferases PRMT1, PRMT3, and PRMT6 in vitro and in vivo and leads to nuclear the localisation of S6K2 that is essential to the pro-survival effects of this kinase to starvation-induced cell death. Taken together, our findings highlight a novel post-translational modification regulating the function of p54-S6K2 that may be particularly relevant to cancer progression where general Arg-methylation is often elevated.

Design and Evaluation of Autophagy-Inducing Particles for the Treatment of Abnormal Lipid Accumulation.

Autophagy is a fundamental housekeeping process by which cells degrade their components to maintain homeostasis. Defects in autophagy have been associated with aging, neurodegeneration and metabolic diseases. Non-alcoholic fatty liver diseases (NAFLDs) are characterized by hepatic fat accumulation with or without inflammation. No treatment for NAFLDs is currently available, but autophagy induction has been proposed as a promising therapeutic strategy. Here, we aimed to design autophagy-inducing particles, using the autophagy-inducing peptide (Tat-Beclin), and achieve liver targeting in vivo, taking NAFLD as a model disease. Polylactic acid (PLA) particles were prepared by nanoprecipitation without any surfactant, followed by surface peptide adsorption. The ability of Tat-Beclin nanoparticles (NP T-B) to modulate autophagy and to decrease intracellular lipid was evaluated in vitro by LC3 immunoblot and using a cellular model of steatosis, respectively. The intracellular localization of particles was evaluated by transmission electron microscopy (TEM). Finally, biodistribution of fluorescent NP T-B was evaluated in vivo using tomography in normal and obese mice. The results showed that NP T-B induce autophagy with a long-lasting and enhanced effect compared to the soluble peptide, and at a ten times lower dose. Intracellular lipid also decreased in a cellular model of NAFLD after treatment with T-B and NP T-B under the same dose conditions. Ultrastructural studies revealed that NP T-B are internalized and located in endosomal, endolysosomal and autolysosomal compartments, while in healthy and obese mice, NP T-B could accumulate for several days in the liver. Given the beneficial effects of autophagy-inducing particles in vitro, and their capacity to target the liver of normal and obese mice, NP T-B could be a promising therapeutic tool for NAFLDs, warranting further in vivo investigation.

ATGL-dependent white adipose tissue lipolysis controls hepatocyte PPARα activity.

In hepatocytes, peroxisome proliferator-activated receptor α (PPARα) orchestrates a genomic and metabolic response required for homeostasis during fasting. This includes the biosynthesis of ketone bodies and of fibroblast growth factor 21 (FGF21). Here we show that in the absence of adipose triglyceride lipase (ATGL) in adipocytes, ketone body and FGF21 production is impaired upon fasting. Liver gene expression analysis highlights a set of fasting-induced genes sensitive to both ATGL deletion in adipocytes and PPARα deletion in hepatocytes. Adipose tissue lipolysis induced by activation of the ß3-adrenergic receptor also triggers such PPARα-dependent responses not only in the liver but also in brown adipose tissue (BAT). Intact PPARα activity in hepatocytes is required for the cross-talk between adipose tissues and the liver during fat mobilization.

Class 3 phosphoinositide 3-kinase promotes hepatic glucocorticoid receptor stability and transcriptional activity.

AIM: Lipid kinase class 3 phosphoinositide 3-kinase (PI3K) and nuclear receptor transcription factor glucocorticoid receptor (GR) play essential physiological roles in metabolic adaptation to fasting by activating lysosomal degradation by autophagy and metabolic gene expression, yet their functional interaction is unknown. The requirement of class 3 PI3K for GR function was investigated in liver tissue. METHODS: Inactivation of class 3 PI3K was achieved through deletion of its essential regulatory subunit Vps15, by expressing Cre-recombinase in the livers of Vps15f/f mice. The response to both 24-h fasting and synthetic GR ligand, dexamethasone (DEX) was evaluated in control and mutant mice. Liver tissue was analysed by immunoblot, RT-qPCR, and LC-MS. RESULTS: Vps15 mutant mice show decreased transcript levels of GR targets, coupled with lower nuclear levels of total and phosphorylated on Ser211, GR protein. Acute DEX treatment and 24-h fasting both failed to re-activate expression of GR targets in the livers of Vps15 mutant mice to the levels observed in controls. Decreased levels of endogenous GR ligand corticosterone and lower expression of 11ß-hydroxysteroid dehydrogenase 1 (11ß-HSD1), a metabolic enzyme that controls corticosterone availability, were found in the livers of Vps15 mutants. Hepatic Vps15 depletion resulted in the activation of nuclear Akt1 signalling, which was paralleled by increased polyubiquitination of GR. CONCLUSION: In the liver, class 3 PI3K is required for corticosterone metabolism and GR transcriptional activity.

Dual regulation of fatty acid synthase (FASN) expression by O-GlcNAc transferase (OGT) and mTOR pathway in proliferating liver cancer cells.

Fatty acid synthase (FASN) participates in many fundamental biological processes, including energy storage and signal transduction, and is overexpressed in many cancer cells. We previously showed in a context of lipogenesis that FASN is protected from degradation by its interaction with O-GlcNAc transferase (OGT) in a nutrient-dependent manner. We and others also reported that OGT and O-GlcNAcylation up-regulate the PI3K/AKT/mTOR pathway that senses mitogenic signals and nutrient availability to drive cell cycle. Using biochemical and microscopy approaches, we show here that FASN co-localizes with OGT in the cytoplasm and, to a lesser extent, in the membrane fraction. This interaction occurs in a cell cycle-dependent manner, following the pattern of FASN expression. Moreover, we show that FASN expression depends on OGT upon serum stimulation. The level of FASN also correlates with the activation of the PI3K/AKT/mTOR pathway in hepatic cell lines, and in livers of obese mice and in a chronically activated insulin and mTOR signaling mouse model (PTEN-null mice). These results indicate that FASN is under a dual control of O-GlcNAcylation and mTOR pathways. In turn, blocking FASN with the small-molecule inhibitor C75 reduces both OGT and O-GlcNAcylation levels, and mTOR activation, highlighting a novel reciprocal regulation between these actors. In addition to the role of O-GlcNAcylation in tumorigenesis, our findings shed new light on how aberrant activity of FASN and mTOR signaling may promote the emergence of hepatic tumors.

Alteration of splicing factors' expression during liver disease progression: impact on hepatocellular carcinoma outcome.

PURPOSE: Trans-acting splicing factors (SF) shape the eukaryotic transcriptome by regulating alternative splicing (AS). This process is recurrently modulated in liver cancer suggesting its direct contribution to the course of liver disease. The aim of our study was to investigate the relationship between the regulation of SFs expression and liver damage. METHODS: The expression profile of 10 liver-specific SF and the AS events of 7 genes associated with liver disorders was assessed by western-blotting in 6 murine models representing different stages of liver damage, from inflammation to hepatocellular carcinoma (HCC). Relevant SFs (PSF, SRSF3, and SRSF6) and target genes (INSR, SRSF3, and SLK) modulated in mice were investigated in a cohort of 179 HCC patients. RESULTS: Each murine model of liver disease was characterized by a unique SF expression profile. Changes in the SF profile did not affect AS events of the selected genes despite the presence of corresponding splicing sites. In human HCC expression of SFs, including the tumor-suppressor SRSF3, and AS regulation of genes studied were frequently upregulated in tumor versus non-tumor tissues. Risk of tumor recurrence positively correlated with AS isoform of the INSR gene. In contrast, increased levels of SFs expression correlated with an extended overall survival of patients. CONCLUSIONS: Dysregulation of SF expression is an early event occurring during liver injury and not just at the stage of HCC. Besides impacting on AS regulation, overexpression of SF may contribute to preserving hepatocyte homeostasis during liver pathogenesis.

The class 3 PI3K coordinates autophagy and mitochondrial lipid catabolism by controlling nuclear receptor PPARα.

The class 3 phosphoinositide 3-kinase (PI3K) is required for lysosomal degradation by autophagy and vesicular trafficking, assuring nutrient availability. Mitochondrial lipid catabolism is another energy source. Autophagy and mitochondrial metabolism are transcriptionally controlled by nutrient sensing nuclear receptors. However, the class 3 PI3K contribution to this regulation is unknown. We show that liver-specific inactivation of Vps15, the essential regulatory subunit of the class 3 PI3K, elicits mitochondrial depletion and failure to oxidize fatty acids. Mechanistically, transcriptional activity of Peroxisome Proliferator Activated Receptor alpha (PPARα), a nuclear receptor orchestrating lipid catabolism, is blunted in Vps15-deficient livers. We find PPARα repressors Histone Deacetylase 3 (Hdac3) and Nuclear receptor co-repressor 1 (NCoR1) accumulated in Vps15-deficient livers due to defective autophagy. Activation of PPARα or inhibition of Hdac3 restored mitochondrial biogenesis and lipid oxidation in Vps15-deficient hepatocytes. These findings reveal roles for the class 3 PI3K and autophagy in transcriptional coordination of mitochondrial metabolism.

Genetics in biliary atresia.

PURPOSE OF REVIEW: Biliary atresia is a poorly understood deadly disease. Genetic predisposition factors are suspected albeit not firmly established. This review summarizes recent evidence of genetic alterations in biliary atresia. RECENT FINDINGS: Whole-genome association studies in biliary atresia patients identified four distinct predisposition loci with four different genes potentially involved in the disease occurrence. Variations in these genes were searched for, but none were found in patients with biliary atresia suggesting complex mechanisms. SUMMARY: Despite decades since its description and decades of intensive researches, cause of biliary atresia disease remains enigmatic. The inheritance of biliary atresia is not Mendelian. Genetic predisposition factor is one of the explored fields to explain biliary atresia pathogenicity. Biliary atresia has been associated with several inborn syndromes, chromosome anomalies, and gene polymorphisms in specific populations. Four predisposition loci encompassing genes relevant to the disease have been identified, but no pathogenic variations were found in biliary atresia patients. Few reported cases of isolated biliary atresia manifestation in the context of known genetic diseases suggest coincidental findings. Alternatives to classic genetic alterations are proposed to explain genetic predisposition in biliary atresia including noncoding and epigenetic factors. Biliary atresia is most likely related to complex traits making its genetic exploration challenging.

Intravenous administration of scAAV9-Hexb normalizes lifespan and prevents pathology in Sandhoff disease mice.

Sandhoff disease (SD) is a rare inherited disorder caused by a deficiency of ß-hexosaminidase activity which is fatal because no effective treatment is available. A mouse model of Hexb deficiency reproduces the key pathognomonic features of SD patients with severe ubiquitous lysosomal dysfunction, GM2 accumulation, neuroinflammation and neurodegeneration, culminating in death at 4 months. Here, we show that a single intravenous neonatal administration of a self-complementary adeno-associated virus 9 vector (scAAV9) expressing the Hexb cDNA in SD mice is safe and sufficient to prevent disease development. Importantly, we demonstrate for the first time that this treatment results in a normal lifespan (over 700 days) and normalizes motor function assessed by a battery of behavioral tests, with scAAV9-treated SD mice being indistinguishable from wild-type littermates. Biochemical analyses in multiple tissues showed a significant increase in hexosaminidase A activity, which reached 10-15% of normal levels. AAV9 treatment was sufficient to prevent GM2 and GA2 storage almost completely in the cerebrum (less so in the cerebellum), as well as thalamic reactive gliosis and thalamocortical neuron loss in treated Hexb-/- mice. In summary, this study demonstrated a widespread protective effect throughout the entire CNS after a single intravenous administration of the scAAV9-Hexb vector to neonatal SD mice.

Mutations in the X-linked ATP6AP2 cause a glycosylation disorder with autophagic defects.

The biogenesis of the multi-subunit vacuolar-type H+-ATPase (V-ATPase) is initiated in the endoplasmic reticulum with the assembly of the proton pore V0, which is controlled by a group of assembly factors. Here, we identify two hemizygous missense mutations in the extracellular domain of the accessory V-ATPase subunit ATP6AP2 (also known as the [pro]renin receptor) responsible for a glycosylation disorder with liver disease, immunodeficiency, cutis laxa, and psychomotor impairment. We show that ATP6AP2 deficiency in the mouse liver caused hypoglycosylation of serum proteins and autophagy defects. The introduction of one of the missense mutations into Drosophila led to reduced survival and altered lipid metabolism. We further demonstrate that in the liver-like fat body, the autophagic dysregulation was associated with defects in lysosomal acidification and mammalian target of rapamycin (mTOR) signaling. Finally, both ATP6AP2 mutations impaired protein stability and the interaction with ATP6AP1, a member of the V0 assembly complex. Collectively, our data suggest that the missense mutations in ATP6AP2 lead to impaired V-ATPase assembly and subsequent defects in glycosylation and autophagy.

Hepatocyte nuclear factor 1α suppresses steatosis-associated liver cancer by inhibiting PPARγ transcription.

Worldwide epidemics of metabolic diseases, including liver steatosis, are associated with an increased frequency of malignancies, showing the highest positive correlation for liver cancer. The heterogeneity of liver cancer represents a clinical challenge. In liver, the transcription factor PPARγ promotes metabolic adaptations of lipogenesis and aerobic glycolysis under the control of Akt2 activity, but the role of PPARγ in liver tumorigenesis is unknown. Here we have combined preclinical mouse models of liver cancer and genetic studies of a human liver biopsy atlas with the aim of identifying putative therapeutic targets in the context of liver steatosis and cancer. We have revealed a protumoral interaction of Akt2 signaling with hepatocyte nuclear factor 1α (HNF1α) and PPARγ, transcription factors that are master regulators of hepatocyte and adipocyte differentiation, respectively. Akt2 phosphorylates and inhibits HNF1α, thus relieving the suppression of hepatic PPARγ expression and promoting tumorigenesis. Finally, we observed that pharmacological inhibition of PPARγ is therapeutically effective in a preclinical murine model of steatosis-associated liver cancer. Taken together, our studies in humans and mice reveal that Akt2 controls hepatic tumorigenesis through crosstalk between HNF1α and PPARγ.

Class III PI3K regulates organismal glucose homeostasis by providing negative feedback on hepatic insulin signalling.

Defective hepatic insulin receptor (IR) signalling is a pathogenic manifestation of metabolic disorders including obesity and diabetes. The endo/lysosomal trafficking system may coordinate insulin action and nutrient homeostasis by endocytosis of IR and the autophagic control of intracellular nutrient levels. Here we show that class III PI3K--a master regulator of endocytosis, endosomal sorting and autophagy--provides negative feedback on hepatic insulin signalling. The ultraviolet radiation resistance-associated gene protein (UVRAG)-associated class III PI3K complex interacts with IR and is stimulated by insulin treatment. Acute and chronic depletion of hepatic Vps15, the regulatory subunit of class III PI3K, increases insulin sensitivity and Akt signalling, an effect that requires functional IR. This is reflected by FoxO1-dependent transcriptional defects and blunted gluconeogenesis in Vps15 mutant cells. On depletion of Vps15, the metabolic syndrome in genetic and diet-induced models of insulin resistance and diabetes is alleviated. Thus, feedback regulation of IR trafficking and function by class III PI3K may be a therapeutic target in metabolic conditions of insulin resistance.

Oxidative stress promotes pathologic polyploidization in nonalcoholic fatty liver disease.

Polyploidization is one of the most dramatic changes that can occur in the genome. In the liver, physiological polyploidization events occur during both liver development and throughout adult life. Here, we determined that a pathological polyploidization takes place in nonalcoholic fatty liver disease (NAFLD), a widespread hepatic metabolic disorder that is believed to be a risk factor for hepatocellular carcinoma (HCC). In murine models of NAFLD, the parenchyma of fatty livers displayed alterations of the polyploidization process, including the presence of a large proportion of highly polyploid mononuclear cells, which are rarely observed in normal hepatic parenchyma. Biopsies from patients with nonalcoholic steatohepatitis (NASH) revealed the presence of alterations in hepatocyte ploidy compared with tissue from control individuals. Hepatocytes from NAFLD mice revealed that progression through the S/G2 phases of the cell cycle was inefficient. This alteration was associated with activation of a G2/M DNA damage checkpoint, which prevented activation of the cyclin B1/CDK1 complex. Furthermore, we determined that oxidative stress promotes the appearance of highly polyploid cells, and antioxidant-treated NAFLD hepatocytes resumed normal cell division and returned to a physiological state of polyploidy. Collectively, these findings indicate that oxidative stress promotes pathological polyploidization and suggest that this is an early event in NAFLD that may contribute to HCC development.

Regulation of YAP by mTOR and autophagy reveals a therapeutic target of tuberous sclerosis complex.

Genetic studies have shown that the tuberous sclerosis complex (TSC) 1-TSC2-mammalian target of Rapamycin (mTOR) and the Hippo-Yes-associated protein 1 (YAP) pathways are master regulators of organ size, which are often involved in tumorigenesis. The crosstalk between these signal transduction pathways in coordinating environmental cues, such as nutritional status and mechanical constraints, is crucial for tissue growth. Whether and how mTOR regulates YAP remains elusive. Here we describe a novel mouse model of TSC which develops renal mesenchymal lesions recapitulating human perivascular epithelioid cell tumors (PEComas) from patients with TSC. We identify that YAP is up-regulated by mTOR in mouse and human PEComas. YAP inhibition blunts abnormal proliferation and induces apoptosis of TSC1-TSC2-deficient cells, both in culture and in mosaic Tsc1 mutant mice. We further delineate that YAP accumulation in TSC1/TSC2-deficient cells is due to impaired degradation of the protein by the autophagosome/lysosome system. Thus, the regulation of YAP by mTOR and autophagy is a novel mechanism of growth control, matching YAP activity with nutrient availability under growth-permissive conditions. YAP may serve as a potential therapeutic target for TSC and other diseases with dysregulated mTOR activity.

Role of PI3K, mTOR and Akt2 signalling in hepatic tumorigenesis via the control of PKM2 expression.

To sustain increased growth, rapidly proliferating cells, such as tumour cells, undergo metabolic adaptations. In recent years, the mechanisms of glycolysis activation as a key metabolic adaptation in proliferating cells became the topic of intense research. Although this phenomenon was described more than 50 years ago by Otto Warburg, the molecular mechanisms remained elusive. Only recently, it was demonstrated that the expression of specific glycolytic enzymes, namely PKM2 (pyruvate kinase M2) and HK2 (hexokinase 2), occurs simultaneously with the glycolytic addiction of cancer cells. The PI3K (phosphoinositide 3-kinase)/mTOR [mammalian (or mechanistic) target of rapamycin] signalling pathway is a central signalling hub co-ordinating the growth in response to growth factor signalling and nutrient availability. Not surprisingly, it is found to be activated in the majority of the tumour cells. In the present article, we discuss the requirement of different PI3K/mTOR downstream effectors for the metabolic adaptation in liver cancer cells driven by this signalling pathway. We provide evidence for a selective involvement of the mTOR target Akt2 in tumoral growth. In addition, PTEN (phosphatase and tensin homologue deleted on chromosome 10)-negative human hepatocellular carcinoma cell lines display an up-regulation of PKM2 expression in an Akt2-dependent manner, providing an advantage for cell proliferation and anchorage-independent growth. Our data have implications on the link between the metabolic action of insulin signal transduction and tumorigenesis, identifying Akt2 as a potential therapeutical target in liver malignancies depending on cancer genotype.

Defects of Vps15 in skeletal muscles lead to autophagic vacuolar myopathy and lysosomal disease.

The complex of Vacuolar Protein Sorting 34 and 15 (Vps34 and Vps15) has Class III phosphatidylinositol 3-kinase activity and putative roles in nutrient sensing, mammalian Target Of Rapamycin (mTOR) activation by amino acids, cell growth, vesicular trafficking and autophagy. Contrary to expectations, here we show that Vps15-deficient mouse tissues are competent for LC3-positive autophagosome formation and maintain mTOR activation. However, an impaired lysosomal function in mutant cells is traced by accumulation of adaptor protein p62, LC3 and Lamp2 positive vesicles, which can be reverted to normal levels after ectopic overexpression of Vps15. Mice lacking Vps15 in skeletal muscles, develop a severe myopathy. Distinct from the autophagy deficient Atg7(-/-) mutants, pathognomonic morphological hallmarks of autophagic vacuolar myopathy (AVM) are observed in Vps15(-/-) mutants, including elevated creatine kinase plasma levels, accumulation of autophagosomes, glycogen and sarcolemmal features within the fibres. Importantly, Vps34/Vps15 overexpression in myoblasts of Danon AVM disease patients alleviates the glycogen accumulation. Thus, the activity of the Vps34/Vps15 complex is critical in disease conditions such as AVMs, and possibly a variety of other lysosomal storage diseases.

The role of the mTOR pathway during liver regeneration and tumorigenesis.

It is established that overnutrition is a risk factor for hepatocellular carcinoma. Il has been proposed that hepatic steatosis leads to a subinflammatory response and to the production of mitogenic cytokines. Our team is focused on the role of mammalian Target of Rapamycin (mTOR) in two pathophysiological conditions that modulate liver growth: liver regeneration after partial hepatectomy, and steatosis-associated tumorigenesis. Target kinases of mTOR seem more specifically involved in these processes: while S6K1 contributes to liver regeneration following hepatectomy, Akt2 is implicated in steatosis-associated tumorigenesis. In addition, recent data indicate that the transcription factor PPARγ, through an activation of glycolytic enzymes, could promote liver steatosis, hypertrophy and hyperplasia.

EDC4 interacts with and regulates the dephospho-CoA kinase activity of CoA synthase.

Coenzyme A synthase (CoAsy) is a bifunctional enzyme which facilitates the last two steps of Coenzyme A biogenesis in higher eukaryotes. Here we describe that CoAsy forms a complex with enhancer of mRNA-decapping protein 4 (EDC4), a central scaffold component of processing bodies. CoAsy/EDC4 complex formation is regulated by growth factors and is affected by cellular stresses. EDC4 strongly inhibits the dephospho-CoA kinase activity of CoAsy in vitro. Transient overexpression of EDC4 decreases cell proliferation, and further co-expression of CoAsy diminishes this effect. Here we report that EDC4 might contribute to regulation of CoA biosynthesis in addition to its scaffold function in processing bodies.

PPARγ contributes to PKM2 and HK2 expression in fatty liver.

Rapidly proliferating cells promote glycolysis in aerobic conditions, to increase growth rate. Expression of specific glycolytic enzymes, namely pyruvate kinase M2 and hexokinase 2, concurs to this metabolic adaptation, as their kinetics and intracellular localization favour biosynthetic processes required for cell proliferation. Intracellular factors regulating their selective expression remain largely unknown. Here we show that the peroxisome proliferator-activated receptor gamma transcription factor and nuclear hormone receptor contributes to selective pyruvate kinase M2 and hexokinase 2 gene expression in PTEN-null fatty liver. Peroxisome proliferator-activated receptor gamma expression, liver steatosis, shift to aerobic glycolysis and tumorigenesis are under the control of the Akt2 kinase in PTEN-null mouse livers. Peroxisome proliferator-activated receptor gamma binds to hexokinase 2 and pyruvate kinase M promoters to activate transcription. In vivo rescue of peroxisome proliferator-activated receptor gamma activity causes liver steatosis, hypertrophy and hyperplasia. Our data suggest that therapies with the insulin-sensitizing agents and peroxisome proliferator-activated receptor gamma agonists, thiazolidinediones, may have opposite outcomes depending on the nutritional or genetic origins of liver steatosis.