Metabolic regulation by p53 family members

Quantitative proteomics analysis of mitochondrial proteins in lung adenocarcinomas and normal lung tissue using iTRAQ and tandem mass spectrometry

Lung adenocarcinoma is the most common type of lung cancer. Unfortunately, lung adenocarcinoma has a poor prognosis and the pathogenesis remains unclear. Mitochondria are important mediators of tumorigenesis. However, the proteomics profile of lung adenocarcinoma mitochondrial proteins has not been elucidated. In this study, we investigated differences in the mitochondrial protein profiles between lung adenocarcinomas and normal tissue. Laser capture microdissection (LCM) was used to isolate the target cells from lung adenocarcinomas and normal tissue. The differential expression of mitochondrial proteins was determined using isobaric tags for relative and absolute quantitation (iTRAQ) combined with two-dimensional liquid chromatography-tandem mass spectrometry (2D-LC-MS/MS). Bioinformatics analysis was performed using Gene Ontology and KEGG databases. As a result, 510 differentially expressed proteins were identified, 315 of which were upregulated and 195 that were downregulated. Of these proteins, 35.5% were mitochondrial or mitochondrial-related and were involved in binding, catalysis, molecular transduction, transport, and molecular structure. Based on the differentially expressed proteins, 63 pathways were significantly enriched through KEGG. The overexpression and cellular distribution of the mitochondrial protein C1QBP in the lung cancer samples was confirmed and verified by Western blotting. The relationship between C1QBP expression and clinicopathological features in lung cancer patients was likewise evaluated using immunohistochemistry, which revealed that the upregulation of C1QBP was associated with lymph node metastasis, pathological grade and clinical stage of TNM. The results indicate that the iTRAQ 2D-LC-MS/MS technique is a potential method for comparing mitochondrial protein profiles between tumor and normal tissue and could aid in identifying novel biomarkers and the mechanisms underlying carcinogenesis.

Aging: Molecular Pathways and Implications on the Cardiovascular System

The world's population over 60 years is growing rapidly, reaching 22% of the global population in the next decades. Despite the increase in global longevity, individual healthspan needs to follow this growth. Several diseases have their prevalence increased by age, such as cardiovascular diseases, the leading cause of morbidity and mortality worldwide. Understanding the aging biology mechanisms is fundamental to the pursuit of cardiovascular health. In this way, aging is characterized by a gradual decline in physiological functions, involving the increased number in senescent cells into the body. Several pathways lead to senescence, including oxidative stress and persistent inflammation, as well as energy failure such as mitochondrial dysfunction and deregulated autophagy, being ROS, AMPK, SIRTs, mTOR, IGF-1, and p53 key regulators of the metabolic control, connecting aging to the pathways which drive towards diseases. In addition, senescence can be induced by cellular replication, which resulted from telomere shortening. Taken together, it is possible to draw a common pathway unifying aging to cardiovascular diseases, and the central point of this process, senescence, can be the target for new therapies, which may result in the healthspan matching the lifespan.

Conditionally Immortal Slc4a11-/- Mouse Corneal Endothelial Cell Line Recapitulates Disrupted Glutaminolysis Seen in Slc4a11-/- Mouse Model

Purpose

To establish conditionally immortal mouse corneal endothelial cell lines with genetically matched Slc4a11+/+ and Slc4a11-/- mice as a model for investigating pathology and therapies for SLC4A11 associated congenital hereditary endothelial dystrophy (CHED) and Fuchs' endothelial corneal dystrophy.

Methods

We intercrossed H-2Kb-tsA58 mice (Immortomouse) expressing an IFN-γ dependent and temperature-sensitive mutant of the SV40 large T antigen (tsTAg) with Slc4a11+/+ and Slc4a11-/- C57BL/6 mice. The growth characteristics of the cell lines was assessed by doubling time. Ion transport activities (Na+/H+ exchange, bicarbonate, lactate, and Slc4a11 ammonia transport) were analyzed by intracellular pH measurement. The metabolic status of the cell lines was assessed by analyzing TCA cycle intermediates via gas chromatography mass spectrometry (GC-MS).

Results

The immortalized Slc4a11+/+ and Slc4a11-/- mouse corneal endothelial cells (MCECs) remained proliferative through passage 49 and maintained similar active ion transport activity. As expected, proliferation was temperature sensitive and IFN-γ dependent. Slc4a11-/- MCECs exhibited decreased proliferative capacity, reduced NH3:H+ transport, altered expression of glutaminolysis enzymes similar to the Slc4a11-/- mouse, and reduced proportion of TCA cycle intermediates derived from glutamine with compensatory increases in glucose flux compared with Slc4a11+/+ MCECs.

Conclusions

This is the first report of the immortalization of MCECs. Ion transport of the immortalized endothelial cells remains active, except for NH3:H+ transporter activity in Slc4a11-/- MCECs. Furthermore, Slc4a11-/- MCECs recapitulate the glutaminolysis defects observed in Slc4a11-/- mouse corneal endothelium, providing an excellent tool to study the pathogenesis of SLC4A11 mutations associated with corneal endothelial dystrophies and to screen potential therapeutic agents.

DNA methylation of candidate genes in peripheral blood from patients with type 2 diabetes or the metabolic syndrome

INTRODUCTION

The prevalence of type 2 diabetes (T2D) and the metabolic syndrome (MetS) is increasing and several studies suggested an involvement of DNA methylation in the development of these metabolic diseases. This study was designed to investigate if differential DNA methylation in blood can function as a biomarker for T2D and/or MetS.

METHODS

Pyrosequencing analyses were performed for the candidate genes KCNJ11, PPARγ, PDK4, KCNQ1, SCD1, PDX1, FTO and PEG3 in peripheral blood leukocytes (PBLs) from 25 patients diagnosed with only T2D, 9 patients diagnosed with T2D and MetS and 11 control subjects without any metabolic disorders.

RESULTS

No significant differences in gene-specific methylation between patients and controls were observed, although a trend towards significance was observed for PEG3. Differential methylation was observed between the groups in 4 out of the 42 single CpG loci located in the promoters regions of the genes FTO, KCNJ11, PPARγ and PDK4. A trend towards a positive correlation was observed for PEG3 methylation with HDL cholesterol levels.

DISCUSSION

Altered levels of DNA methylation in PBLs of specific loci might serve as a biomarker for T2D or MetS, although further investigation is required.

Cold-water immersion following sprint interval training does not alter endurance signaling pathways or training adaptations in human skeletal muscle

We investigated the underlying molecular mechanisms by which postexercise cold-water immersion (CWI) may alter key markers of mitochondrial biogenesis following both a single session and 6 wk of sprint interval training (SIT). Nineteen men performed a single SIT session, followed by one of two 15-min recovery conditions: cold-water immersion (10°C) or a passive room temperature control (23°C). Sixteen of these participants also completed 6 wk of SIT, each session followed immediately by their designated recovery condition. Four muscle biopsies were obtained in total, three during the single SIT session (preexercise, postrecovery, and 3 h postrecovery) and one 48 h after the last SIT session. After a single SIT session, phosphorylated (p-)AMPK, p-p38 MAPK, p-p53, and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) mRNA were all increased (P < 0.05). Postexercise CWI had no effect on these responses. Consistent with the lack of a response after a single session, regular postexercise CWI had no effect on PGC-1α or p53 protein content. Six weeks of SIT increased peak aerobic power, maximal oxygen consumption, maximal uncoupled respiration (complexes I and II), and 2-km time trial performance (P < 0.05). However, regular CWI had no effect on changes in these markers, consistent with the lack of response in the markers of mitochondrial biogenesis. Although these observations suggest that CWI is not detrimental to endurance adaptations following 6 wk of SIT, they question whether postexercise CWI is an effective strategy to promote mitochondrial biogenesis and improvements in endurance performance.

Metabolic rewiring in mutant Kras lung cancer

Lung cancer is the leading cause of cancer-related death worldwide, reflecting an unfortunate combination of very high prevalence and low survival rates, as most cases are diagnosed at advanced stages when treatment efficacy is limited. Lung cancer comprises several disease groups with non small cell lung cancer (NSCLC) accounting for ~ 85% of cases and lung adenocarcinoma being its most frequent histological subtype. Mutations in Kirsten rat sarcoma viral oncogene homologue (KRAS) affect ~ 30% of lung adenocarcinomas but unlike other commonly altered proteins (EGFR and ALK, affected in ~ 14% and 7% of cases respectively), mutant KRAS remains untargetable. Therapeutic strategies that rely instead on the inhibition of mutant KRAS functional output or the targeting of mutant KRAS cellular dependencies (i.e. synthetic lethality) are an appealing alternative approach. Recent studies focused on the metabolic properties of mutant KRAS lung tumours have uncovered unique metabolic features that can potentially be exploited therapeutically. We review these findings here with a particular focus on in vivo, physiologic, mutant KRAS activity.

The effect of endurance training with and without vitamin E on expression of p53 and PTEN tumor suppressing genes in prostate glands of male rats

The aim of this study was to investigate the effect of endurance training with and without vitamin E on the expression of p53 and Phosphatase and tension homolog (PTEN) tumor suppressor genes of prostate glands in male rats. For this purpose, 50 Sprague-Dawley male rats were randomly assigned into 5 groups: (1) control group (CON, n = 10), (2) sham (S, n = 10), (3) endurance training (ET, n = 10), (4) endurance training + vitamin E (ET + VE, n = 10), (5) vitamin E (VE, n = 10). Endurance training protocol was implemented for 6 weeks, 6 days per week, in accordance with the overload principle. To measure expression changes of p53 and PTEN genes in rats' prostate, real-time PCR method was used and HPLC method was used to measure vitamin E in this tissue. After 6 weeks of taking vitamin E, its level in all groups, except for group VE (p < 0.000) did not significantly increase. After implementing training protocol, p53 expression reduced significantly in ET group (p < 0.026). Vitamin E supplementation along with endurance training did not cause any significant change either p53 or PTEN (respectively; p < 0.2, p < 0.11). Instead, vitamin E supplementation without endurance training caused significant increase in PTEN, but did not cause any significant changes in p53 (respectively; p < 0.016, p < 0.15). These results indicate that endurance training reduces p53 and PTEN tumor suppressing genes expression, and taking vitamin E supplement could increase expression of these genes in some extent.

Hepatic p63 regulates steatosis via IKKβ/ER stress

p53 family members control several metabolic and cellular functions. The p53 ortholog p63 modulates cellular adaptations to stress and has a major role in cell maintenance and proliferation. Here we show that p63 regulates hepatic lipid metabolism. Mice with liver-specific p53 deletion develop steatosis and show increased levels of p63. Down-regulation of p63 attenuates liver steatosis in p53 knockout mice and in diet-induced obese mice, whereas the activation of p63 induces lipid accumulation. Hepatic overexpression of N-terminal transactivation domain TAp63 induces liver steatosis through IKKβ activation and the induction of ER stress, the inhibition of which rescues the liver functions. Expression of TAp63, IKKβ and XBP1s is also increased in livers of obese patients with NAFLD. In cultured human hepatocytes, TAp63 inhibition protects against oleic acid-induced lipid accumulation, whereas TAp63 overexpression promotes lipid storage, an effect reversible by IKKβ silencing. Our findings indicate an unexpected role of the p63/IKKβ/ER stress pathway in lipid metabolism and liver disease.

Discovery of Mieap-regulated mitochondrial quality control as a new function of tumor suppressor p53

The tumor suppressor p53 gene is frequently mutated in human cancers, and the p53 protein suppresses cancer. However, the mechanism behind the p53-mediated tumor suppression is still unclear. Recently, the mitochondria-eating protein (Mieap) was identified as a p53-inducible protein. Mieap induces the accumulation of lysosomal proteins within mitochondria (Mieap-induced accumulation of lysosome-like organelles within mitochondria, or MALM) in response to mitochondrial damage, and eliminates the oxidized mitochondrial proteins to repair unhealthy mitochondria. Furthermore, Mieap also induces vacuole-like structures (Mieap-induced vacuole, or MIV) to eat and degrade unhealthy mitochondria. Therefore, Mieap controls mitochondrial quality by repairing or eliminating unhealthy mitochondria by MALM or MIV, respectively. This mechanism is not mediated by canonical autophagy. Mieap-deficient Apc^Min/+ mice show strikingly high rates of intestinal tumor development as well as advanced-grade adenomas and adenocarcinomas. The p53/Mieap/BCL2 interacting protein 3 mitochondrial quality control pathway is frequently inactivated in human colorectal cancers. Defects in Mieap-regulated mitochondrial quality control lead to accumulation of unhealthy mitochondria in cancer cells. Cancer-specific unhealthy mitochondria could contribute to cancer development and aggressiveness through mitochondrial reactive oxygen species and altered metabolism. Mieap-regulated mitochondrial quality control is a newly discovered function of p53 that plays a critical role in tumor suppression.

Argininosuccinate synthase 1 is an intrinsic Akt repressor transactivated by p53

The transcription factor p53 is at the core of a built-in tumor suppression system that responds to varying degrees of stress input and is deregulated in most human cancers. Befitting its role in maintaining cellular fitness and fidelity, p53 regulates an appropriate set of target genes in response to cellular stresses. However, a comprehensive understanding of this scheme has not been accomplished. We show that argininosuccinate synthase 1 (ASS1), a citrulline-aspartate ligase in de novo arginine synthesis pathway, was directly transactivated by p53 in response to genotoxic stress, resulting in the rearrangement of arginine metabolism. Furthermore, we found that x-ray irradiation promoted the systemic induction of Ass1 and concomitantly increased plasma arginine levels in p53^+/+ mice but not in p53^-/- mice. Notably, Ass1^+/- mice exhibited hypersensitivity to whole-body irradiation owing to increased apoptosis in the small intestinal crypts. Analyses of ASS1-deficient cells generated using the CRISPR (clustered regularly interspaced short palindromic repeats)-Cas9 (CRISPR-associated 9) system revealed that ASS1 plays a pivotal role in limiting Akt phosphorylation. In addition, aberrant activation of Akt resulting from ASS1 loss disrupted Akt-mediated cell survival signaling activity under genotoxic stress. Building on these results, we demonstrated that p53 induced an intrinsic Akt repressor, ASS1, and the perturbation of ASS1 expression rendered cells susceptible to genotoxic stress. Our findings uncover a new function of p53 in the regulation of Akt signaling and reveal how p53, ASS1, and Akt are interrelated to each other.

The Chaperone TRAP1 As a Modulator of the Mitochondrial Adaptations in Cancer Cells

Mitochondria can receive, integrate, and transmit a variety of signals to shape many biochemical activities of the cell. In the process of tumor onset and growth, mitochondria contribute to the capability of cells of escaping death insults, handling changes in ROS levels, rewiring metabolism, and reprograming gene expression. Therefore, mitochondria can tune the bioenergetic and anabolic needs of neoplastic cells in a rapid and flexible way, and these adaptations are required for cell survival and proliferation in the fluctuating environment of a rapidly growing tumor mass. The molecular bases of pro-neoplastic mitochondrial adaptations are complex and only partially understood. Recently, the mitochondrial molecular chaperone TRAP1 (tumor necrosis factor receptor associated protein 1) was identified as a key regulator of mitochondrial bioenergetics in tumor cells, with a profound impact on neoplastic growth. In this review, we analyze these findings and discuss the possibility that targeting TRAP1 constitutes a new antitumor approach.

Promyelocytic Leukemia Protein, a Protein at the Crossroad of Oxidative Stress and Metabolism

SIGNIFICANCE

Cellular metabolic activity impacts the production of reactive oxygen species (ROS), both positively through mitochondrial oxidative processes and negatively by promoting the production of reducing agents (including NADPH and reduced glutathione). A defined metabolic state in cancer cells is critical for cell growth and long-term self-renewal, and such state is intrinsically associated with redox balance. Promyelocytic leukemia protein (PML) regulates several biological processes, at least in part, through its ability to control the assembly of PML nuclear bodies (PML NBs). Recent Advances: PML is oxidation-prone, and oxidative stress promotes NB biogenesis. These nuclear subdomains recruit many nuclear proteins and regulate their SUMOylation and other post-translational modifications. Some of these cargos-such as p53, SIRT1, AKT, and mammalian target of rapamycin (mTOR)-are key regulators of cell fate. PML was also recently shown to regulate oxidation.

CRITICAL ISSUES

While it was long considered primarily as a tumor suppressor protein, PML-regulated metabolic switch uncovered that this protein could promote survival and/or stemness of some normal or cancer cells. In this study, we review the recent findings on this multifunctional protein.

FUTURE DIRECTIONS

Studying PML scaffolding functions as well as its fine role in the activation of p53 or fatty acid oxidation will bring new insights in how PML could bridge oxidative stress, senescence, cell death, and metabolism. Antioxid. Redox Signal. 26, 432-444.

Alkaline ceramidase 2 is a novel direct target of p53 and induces autophagy and apoptosis through ROS generation

ACER2 is a critical sphingolipid metabolizing enzyme, and has been shown to be remarkably up-regulated following various stimuli such as DNA damage. However, the transcriptional regulatory mechanism of ACER2 gene and its potential role in the regulation of autophagy remain unknown. In this study, we have for the first time identified the human ACER2 gene promoter, and found that human ACER2 transcription is directly regulated by p53 and ACER2 is implicated in the induction of autophagy as well as apoptosis. A series of luciferase reporter assay demonstrated that ACER2 major promoter is located within its first intron where the consensus p53-binding sites exist. Consistently, forced expression of p53 significantly stimulated ACER2 transcription. Notably, p53-mediated autophagy and apoptosis were markedly enhanced by ACER2. Depletion of the essential autophagy gene ATG5 revealed that ACER2-induced autophagy facilitates its effect on apoptosis. Further studies clearly showed that ACER2-mediated autophagy and apoptosis are accompanied by ROS generation. In summary, our present study strongly suggests that ACER2 plays a pivotal role in p53-induced autophagy and apoptosis, and thus might serve as a novel and attractive molecular target for cancer treatment.

p53: Multiple Facets of a Rubik's Cube

The p53 tumor suppressor has been studied for decades, and still there are many questions left unanswered. In this review, we first describe the current understanding of the wild-type p53 functions that determine cell survival or death, and regulation of the protein, with a particular focus on the negative regulators, the murine double minute family of proteins. We also summarize tissue-, stress-, and age-specific p53 activities and the potential underlying mechanisms. Among all p53 gene alterations identified in human cancers, p53 missense mutations predominate, suggesting an inherent biological advantage. Numerous gain-of-function activities of mutant p53 in different model systems and contexts have been identified. The emerging theme is that mutant p53, which retains a potent transcriptional activation domain, also retains the ability to modify gene transcription, albeit indirectly. Lastly, because mutant p53 stability is necessary for its gain of function, we summarize the mechanisms through which mutant p53 is specifically stabilized. A deeper understanding of the multiple pathways that impinge upon wild-type and mutant p53 activities and how these, in turn, regulate cell behavior will help identify vulnerabilities and therapeutic opportunities.

Zinc finger protein ZPR9 functions as an activator of AMPK-related serine/threonine kinase MPK38/MELK involved in ASK1/TGF-β/p53 signaling pathways

Murine protein serine-threonine kinase 38 (MPK38), an AMP-activated protein kinase (AMPK)-related kinase, has been implicated in the induction of apoptosis signal-regulating kinase 1 (ASK1)-, transforming growth factor-β (TGF-β)-, and p53-mediated activity involved in metabolic homeostasis. Here, zinc finger protein ZPR9 was found to be an activator of MPK38. The association of MPK38 and ZPR9 was mediated by cysteine residues present in each of these two proteins, Cys²⁶⁹ and Cys²⁸⁶ of MPK38 and Cys³⁰⁵ and Cys³⁰⁸ of ZPR9. MPK38 phosphorylated ZPR9 at Thr²⁵². Wild-type ZPR9, but not the ZPR9 mutant T252A, enhanced ASK1, TGF-β, and p53 function by stabilizing MPK38. The requirement of ZPR9 Thr²⁵² phosphorylation was validated using CRISPR/Cas9-mediated ZPR9 (T252A) knockin cell lines. The knockdown of endogenous ZPR9 showed an opposite trend, resulting in the inhibition of MPK38-dependent ASK1, TGF-β, and p53 function. This effect was also demonstrated in mouse embryonic fibroblast (MEF) cells that were haploinsufficient (+/-) for ZPR9, NIH 3T3 cells with inducible knockdown of ZPR9, and CRISPR/Cas9-mediated ZPR9 knockout cells. Furthermore, high-fat diet (HFD)-fed mice displayed reduced MPK38 kinase activity and ZPR9 expression compared to that in mice on control chow, suggesting that ZPR9 acts as a physiological activator of MPK38 that may participate in obesity.

TAp73 upregulates IL-1β in cancer cells: Potential biomarker in lung and breast cancer?

p73 is a transcription factor belonging to the p53 tumour suppressor family. p73^−/− mice exhibit a range of phenotypes including neurological, reproductive and inflammatory defects. Although the role of p73 in the control of genomic stability explains part of these phenotypes, a clear mechanism of how p73 participates in the inflammatory response is still elusive. Interleukin-1β (IL-1β) has a crucial role in mediating the inflammatory response. Because of its high potency to induce inflammation, the activation and secretion of IL-1β is tightly regulated by large protein complexes, named inflammasomes. Inflammasomes regulate activation of proinflammatory caspase-1, which in turn proteolytically processes its substrates, including pro-IL-1β. Caspase-1 gene transcription is strongly activated by p53 protein family members including p73. Here, we have addressed whether p73 might be directly involved in IL-1β regulation and therefore in the control of the inflammatory response. Our results show that TAp73β upregulates pro-IL-1β mRNA and processed IL-1β protein. In addition, analysis of breast and lung cancer patient cohorts demonstrated that interaction between p73 and IL-1β predicts a negative survival outcome in these human cancers.

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The p53 family member p73 controls a wide a range of biological processes required for its tumour suppressor functions.

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p73 regulates IL-1β expression, thus potentially affecting inflammasomes and inflammatory response.

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p73/IL-1β axis correlates with poor prognosis in lung and breast cancer.

Liver p53 is stabilized upon starvation and required for amino acid catabolism and gluconeogenesis

The ability to adapt cellular metabolism to nutrient availability is critical for survival. The liver plays a central role in the adaptation to starvation by switching from glucose-consuming processes and lipid synthesis to providing energy substrates like glucose to the organism. Here we report a previously unrecognized role of the tumor suppressor p53 in the physiologic adaptation to food withdrawal. We found that starvation robustly increases p53 protein in mouse liver. This induction was posttranscriptional and mediated by a hepatocyte-autonomous and AMP-activated protein kinase-dependent mechanism. p53 stabilization was required for the adaptive expression of genes involved in amino acid catabolism. Indeed, acute deletion of p53 in livers of adult mice impaired hepatic glycogen storage and induced steatosis. Upon food withdrawal, p53-deleted mice became hypoglycemic and showed defects in the starvation-associated utilization of hepatic amino acids. In summary, we provide novel evidence for a p53-dependent integration of acute changes of cellular energy status and the metabolic adaptation to starvation. Because of its tumor suppressor function, p53 stabilization by starvation could have implications for both metabolic and oncological diseases of the liver.-Prokesch, A., Graef, F. A., Madl, T., Kahlhofer, J., Heidenreich, S., Schumann, A., Moyschewitz, E., Pristoynik, P., Blaschitz, A., Knauer, M., Muenzner, M., Bogner-Strauss, J. G., Dohr, G., Schulz, T. J., Schupp, M. Liver p53 is stabilized upon starvation and required for amino acid catabolism and gluconeogenesis.

PFKFB3, a Direct Target of p63, Is Required for Proliferation and Inhibits Differentiation in Epidermal Keratinocytes

p63 is a transcription factor essential for epidermal development and homeostasis. p63 is a member of the p53 family of transcription factors, which are increasingly understood to be regulators of cellular metabolism. How p63 regulates metabolism in epidermal keratinocytes is incompletely understood, and it is unknown whether glycolytic regulation is essential to maintain the balance between proliferation and differentiation within the epidermis. We found that p63 promotes glycolytic metabolism in epidermal keratinocytes. p63 bound to consensus sites within the PFKFB3 gene and was required for PFKFB3 mRNA and protein expression. PFKFB3 overexpression inhibited differentiation of keratinocytes, whereas knockdown inhibited proliferation and increased the rate of differentiation. Furthermore, we found that PFKFB3 was highly expressed in psoriatic epidermis. Our results show that PFKFB3 is a key regulator of epidermal homeostasis and may represent a therapeutic target for epidermal diseases associated with hyperproliferation and impaired differentiation.

Employing Metabolism to Improve the Diagnosis and Treatment of Pancreatic Cancer

Pancreatic ductal adenocarcinoma is on pace to become the second leading cause of cancer-related death. The high mortality rate results from a lack of methods for early detection and the inability to successfully treat patients once diagnosed. Pancreatic cancer cells have extensively reprogrammed metabolism, which is driven by oncogene-mediated cell-autonomous pathways, the unique physiology of the tumor microenvironment, and interactions with non-cancer cells. In this review, we discuss how recent efforts delineating rewired metabolic networks in pancreatic cancer have revealed new in-roads to develop detection and treatment strategies for this dreadful disease.

1H NMR metabolomic signatures related to giant cell tumor of the bone

¹H NMR metabolomic profiling for giant cell tumor of the bone.

Mitochondria and Cancer

Mitochondria are bioenergetic, biosynthetic, and signaling organelles that are integral in stress sensing to allow for cellular adaptation to the environment. Therefore, it is not surprising that mitochondria are important mediators of tumorigenesis, as this process requires flexibility to adapt to cellular and environmental alterations in addition to cancer treatments. Multiple aspects of mitochondrial biology beyond bioenergetics support transformation, including mitochondrial biogenesis and turnover, fission and fusion dynamics, cell death susceptibility, oxidative stress regulation, metabolism, and signaling. Thus, understanding mechanisms of mitochondrial function during tumorigenesis will be critical for the next generation of cancer therapeutics.

p53 as a Regulator of Lipid Metabolism in Cancer

Enhanced proliferation and survival are common features of cancer cells. Cancer cells are metabolically reprogrammed which aids in their survival in nutrient-poor environments. Indeed, changes in metabolism of glucose and glutamine are essential for tumor progression. Thus, metabolic reprogramming is now well accepted as a hallmark of cancer. Recent findings suggest that reprogramming of lipid metabolism also occurs in cancer cells, since lipids are used for biosynthesis of membranes, post-translational modifications, second messengers for signal transduction, and as a source of energy during nutrient deprivation. The tumor suppressor p53 is a transcription factor that controls the expression of proteins involved in cell cycle arrest, DNA repair, apoptosis, and senescence. p53 also regulates cellular metabolism, which appears to play a key role in its tumor suppressive activities. In this review article, we summarize non-canonical functions of wild-type and mutant p53 on lipid metabolism and discuss their association with cancer progression.

Proteomic Analysis Reveals GMP Synthetase as p53 Repression Target in Liver Cancer

Disruption of the tumor-suppressive p53 network is a key event in human malignancies, including primary liver cancer. In response to different types of stress, p53 mediates several antiproliferative cellular outcomes, such as cell cycle arrest, apoptosis, and senescence, by activation or repression of its target genes. Metabolic alterations initiating or being part of the p53 response have become an actively studied research area in the p53 field, with several aspects that still remain to be elucidated. Herein, we identified GMP synthetase (GMPS), a key enzyme of de novo purine biosynthesis, as an important p53 repression target using a large-scale proteomics approach. This p53-mediated repression of GMPS could be validated by immunoblotting in Sk-Hep1, HepG2, and HuH6 cells. Moreover, we found GMPS transcriptionally repressed in a p21-dependent manner and its repression maintained in the context of p53-mediated cellular senescence. More important, direct knockdown of GMPS by RNA interference resulted in reduced cell viability and was sufficient to trigger cellular senescence. Finally, by comparing murine hepatocellular carcinomas, which developed in p53 wild-type (^+/+) versus p53 null (^-/-) mice, we observed higher GMPS expression in the latter, supporting the in vivo relevance of our findings. We conclude that repression of GMPS by p53 through p21 is a functionally relevant part of the p53-mediated senescence program limiting tumor cell growth in liver cancer.

TP53 Mutations in Head and Neck Squamous Cell Carcinoma and Their Impact on Disease Progression and Treatment Response

Recent studies describing the mutational landscape of head and neck squamous cell carcinoma (HNSCC) on a genomic scale by our group and others, including The Cancer Genome Atlas, have provided unprecedented perspective for understanding the molecular pathogenesis of HNSCC progression and response to treatment. These studies confirmed that mutations of the TP53 tumor suppressor gene were the most frequent of all somatic genomic alterations in HNSCC, alluding to the importance of the TP53 gene in suppressing the development and progression of this disease. Clinically, TP53 mutations are significantly associated with short survival time and tumor resistance to radiotherapy and chemotherapy in HNSCC patients, which makes the TP53 mutation status a potentially useful molecular factor for risk stratification and predictor of clinical response in these patients. In addition to loss of wild-type p53 function and the dominant-negative effect on the remaining wild-type p53, some p53 mutants often gain oncogenic functions to promote tumorigenesis and progression. Different p53 mutants may possess different gain-of-function properties. Herein, we review the most up-to-date information about TP53 mutations available via The Cancer Genome Atlas-based analysis of HNSCC and discuss our current understanding of the potential tumor-suppressive role of p53, focusing on gain-of-function activities of p53 mutations. We also summarize our knowledge regarding the use of the TP53 mutation status as a potential evaluation or stratification biomarker for prognosis and a predictor of clinical response to radiotherapy and chemotherapy in HNSCC patients. Finally, we discuss possible strategies for targeting HNSCCs bearing TP53 mutations. J. Cell. Biochem. 117: 2682-2692, 2016. © 2016 Wiley Periodicals, Inc.

The Double Role of p53 in Cancer and Autoimmunity and Its Potential as Therapeutic Target

p53 is a sequence-specific short-lived transcription factor expressed at low concentrations in various tissues while it is upregulated in damaged, tumoral or inflamed tissue. In normally proliferating cells, p53 protein levels and function are tightly controlled by main regulators, i.e., MDM2 (mouse double minute 2) and MDM4 proteins. p53 plays an important role due to its ability to mediate tumor suppression. In addition to its importance as a tumor suppressor, p53 coordinates diverse cellular responses to stress and damage and plays an emerging role in various physiological processes, including fertility, cell metabolism, mitochondrial respiration, autophagy, cell adhesion, stem cell maintenance and development. Interestingly, it has been recently implicated in the suppression of autoimmune and inflammatory diseases in both mice and humans. In this review based on current knowledge on the functional properties of p53 and its regulatory pathways, we discuss the potential utility of p53 reactivation from a therapeutic perspective in oncology and chronic inflammatory disorders leading to autoimmunity.

Autolysosome biogenesis and developmental senescence are regulated by both Spns1 and v-ATPase

Spns1 (Spinster homolog 1 [Drosophila]) in vertebrates, as well as Spin (Spinster) in Drosophila, is a hypothetical lysosomal H⁺-carbohydrate transporter, which functions at a late stage of macroautophagy (hereafter autophagy). The Spin/Spns1 defect induces aberrant autolysosome formation that leads to developmental senescence in the embryonic stage and premature aging symptoms in adulthood. However, the molecular mechanism by which loss of Spin/Spns1 leads to the specific pathogenesis remains to be elucidated. Using chemical, genetic and CRISPR/Cas9-mediated genome-editing approaches in zebrafish, we investigated and determined a mechanism that suppresses embryonic senescence as well as autolysosomal impairment mediated by Spns1 deficiency. Unexpectedly, we found that a concurrent disruption of the vacuolar-type H⁺-ATPase (v-ATPase) subunit gene, atp6v0ca (ATPase, H⁺ transporting, lysosomal, V0 subunit ca) led to suppression of the senescence induced by the Spns1 defect, whereas the sole loss of Atp6v0ca led to senescent embryos similar to the single spns1 mutation. Moreover, we discovered that the combined stable defect seen in the presence of both the spns1 and atp6v0ca mutant genes still subsequently induced premature autophagosome-lysosome fusion marked by insufficient acidity, while extending developmental life span, compared with the solely mutated spns1 defect. Our data suggest that Spns1 and the v-ATPase orchestrate proper autolysosomal biogenesis with optimal acidification that is critically linked to developmental senescence and survival.

The role of the p53 tumor suppressor in metabolism and diabetes

In the context of tumor suppression, p53 is an undisputedly critical protein. Functioning primarily as a transcription factor, p53 helps fend off the initiation and progression of tumors by inducing cell cycle arrest, senescence or programmed cell death (apoptosis) in cells at the earliest stages of precancerous development. Compelling evidence, however, suggests that p53 is involved in other aspects of human physiology, including metabolism. Indeed, recent studies suggest that p53 plays a significant role in the development of metabolic diseases, including diabetes, and further that p53's role in metabolism may also be consequential to tumor suppression. Here, we present a review of the literature on the role of p53 in metabolism, diabetes, pancreatic function, glucose homeostasis and insulin resistance. Additionally, we discuss the emerging role of genetic variation in the p53 pathway (single-nucleotide polymorphisms) on the impact of p53 in metabolic disease and diabetes. A better understanding of the relationship between p53, metabolism and diabetes may one day better inform the existing and prospective therapeutic strategies to combat this rapidly growing epidemic.

Uncovering metabolism in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a myogenic tumor classified as the most frequent soft tissue sarcoma affecting children and adolescents. The histopathological classification includes 5 different histotypes, with 2 most predominant referred as to embryonal and alveolar, the latter being characterized by adverse outcome. The current molecular classification identifies 2 major subsets, those harboring the fused Pax3-Foxo1 transcription factor generating from a recurrent specific translocation (fusion-positive RMS), and those lacking this signature but harboring mutations in the RAS/PI3K/AKT signaling axis (fusion-negative RMS). Since little attention has been devoted to RMS metabolism until now, in this review we summarize the "state of art" of metabolism and discuss how some of the molecular signatures found in this cancer, as observed in other more common tumors, can predict important metabolic challenges underlying continuous cell growth, oxidative stress resistance and metastasis, which could be the subject of future targeted therapies.

Activation of SAT1 engages polyamine metabolism with p53-mediated ferroptotic responses

Although p53-mediated cell-cycle arrest, senescence, and apoptosis remain critical barriers to cancer development, the emerging role of p53 in cell metabolism, oxidative responses, and ferroptotic cell death has been a topic of great interest. Nevertheless, it is unclear how p53 orchestrates its activities in multiple metabolic pathways into tumor suppressive effects. Here, we identified the SAT1 (spermidine/spermine N¹-acetyltransferase 1) gene as a transcription target of p53. SAT1 is a rate-limiting enzyme in polyamine catabolism critically involved in the conversion of spermidine and spermine back to putrescine. Surprisingly, we found that activation of SAT1 expression induces lipid peroxidation and sensitizes cells to undergo ferroptosis upon reactive oxygen species (ROS)-induced stress, which also leads to suppression of tumor growth in xenograft tumor models. Notably, SAT1 expression is down-regulated in human tumors, and CRISPR-cas9-mediated knockout of SAT1 expression partially abrogates p53-mediated ferroptosis. Moreover, SAT1 induction is correlated with the expression levels of arachidonate 15-lipoxygenase (ALOX15), and SAT1-induced ferroptosis is significantly abrogated in the presence of PD146176, a specific inhibitor of ALOX15. Thus, our findings uncover a metabolic target of p53 involved in ferroptotic cell death and provide insight into the regulation of polyamine metabolism and ferroptosis-mediated tumor suppression.

Oncogenic Mutant p53 Gain of Function Nourishes the Vicious Cycle of Tumor Development and Cancer Stem-Cell Formation

More than half of human tumors harbor an inactivated p53 tumor-suppressor gene. It is well accepted that mutant p53 shows an oncogenic gain-of-function (GOF) activity that facilitates the transformed phenotype of cancer cells. In addition, a growing body of evidence supports the notion that cancer stem cells comprise a seminal constituent in the initiation and progression of cancer development. Here, we elaborate on the mutant p53 oncogenic GOF leading toward the acquisition of a transformed phenotype, as well as placing mutant p53 as a major component in the establishment of cancer stem cell entity. Therefore, therapy targeted toward cancer stem cells harboring mutant p53 is expected to pave the way to eradicate tumor growth and recurrence.

Increased obesity resistance and insulin sensitivity in mice lacking the isocitrate dehydrogenase 2 gene

Reactive oxygen species (ROS) are a byproduct of normal metabolism and play important roles in cell signaling and homeostasis. Mitochondria, the main organelles involved in intracellular ROS production, play central roles in modulating redox-dependent cellular processes such as metabolism and apoptosis. We recently reported an important role for mitochondrial NADP⁺-dependent isocitrate dehydrogenase (IDH2) in cellular redox regulation. Here, we show that mice with targeted disruption of IDH2 exhibit resistance to obesity, with lower body weight and reduced visceral fat, and increased insulin sensitivity accompanied by enhanced energy expenditure relative to controls. This function of IDH2 is linked to its capacity to suppress lipogenesis in visceral adipose tissue, partly via transcriptional repression of SREBP1, and to increase thermogenesis in adipocytes by transcriptional activation of UCP1 via activation of the p38 signaling axis. Our results highlight the importance of redox balance in the regulation of metabolism and demonstrate that IDH2 plays a major role in modulating both insulin sensitivity and fuel metabolism, thereby establishing this protein as a potential therapeutic target in the treatment of type 2 diabetes and obesity.

Reprogramming glucose metabolism in cancer: can it be exploited for cancer therapy?

In recent years there has been a growing interest among cancer biologists in cancer metabolism. This Review summarizes past and recent advances in our understanding of the reprogramming of glucose metabolism in cancer cells, which is mediated by oncogenic drivers and by the undifferentiated character of cancer cells. The reprogrammed glucose metabolism in cancer cells is required to fulfil anabolic demands. This Review discusses the possibility of exploiting the reprogrammed glucose metabolism for therapeutic approaches that selectively target cancer cells.

Emerging roles of p53 and other tumour-suppressor genes in immune regulation

Tumour-suppressor genes are indispensable for the maintenance of genomic integrity. Recently, several of these genes, including those encoding p53, PTEN, RB1 and ARF, have been implicated in immune responses and inflammatory diseases. In particular, the p53 tumour- suppressor pathway is involved in crucial aspects of tumour immunology and in homeostatic regulation of immune responses. Other studies have identified roles for p53 in various cellular processes, including metabolism and stem cell maintenance. Here, we discuss the emerging roles of p53 and other tumour-suppressor genes in tumour immunology, as well as in additional immunological settings, such as virus infection. This relatively unexplored area could yield important insights into the homeostatic control of immune cells in health and disease and facilitate the development of more effective immunotherapies. Consequently, tumour-suppressor genes are emerging as potential guardians of immune integrity.

Preclinical model in HCC: the SGK1 kinase inhibitor SI113 blocks tumor progression in vitro and in vivo and synergizes with radiotherapy

The SGK1 kinase is pivotal in signal transduction pathways operating in cell transformation and tumor progression. Here, we characterize in depth a novel potent and selective pyrazolo[3,4-d]pyrimidine-based SGK1 inhibitor. This compound, named SI113, active in vitro in the sub-micromolar range, inhibits SGK1-dependent signaling in cell lines in a dose- and time-dependent manner. We recently showed that SI113 slows down tumor growth and induces cell death in colon carcinoma cells, when used in monotherapy or in combination with paclitaxel. We now demonstrate for the first time that SI113 inhibits tumour growth in hepatocarcinoma models in vitro and in vivo. SI113-dependent tumor inhibition is dose- and time-dependent. In vitro and in vivo SI113-dependent SGK1 inhibition determined a dramatic increase in apoptosis/necrosis, inhibited cell proliferation and altered the cell cycle profile of treated cells. Proteome-wide biochemical studies confirmed that SI113 down-regulates the abundance of proteins downstream of SGK1 with established roles in neoplastic transformation, e.g. MDM2, NDRG1 and RAN network members. Consistent with knock-down and over-expressing cellular models for SGK1, SI113 potentiated and synergized with radiotherapy in tumor killing. No short-term toxicity was observed in treated animals during in vivo SI113 administration. These data show that direct SGK1 inhibition can be effective in hepatic cancer therapy, either alone or in combination with radiotherapy.

Metabolic plasticity in heterogeneous pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) is one of the most lethal malignant neoplasms. The recognized hallmarks of PDA are regarded to be downstream events of metabolic reprogramming. Because PDA is a heterogeneous disease that is influenced by genetic polymorphisms and changes in the microenvironment, metabolic plasticity is a novel feature of PDA. As intrinsic factors for metabolic plasticity, K-ras activation and mutations in other tumor suppressor genes induce abnormal mitochondrial metabolism and enhance glycolysis, with alterations in glutamine and lipid metabolism. As extrinsic factors, the acidic and oxygen/nutrient-deprived microenvironment also induces cancer cells to reprogram their metabolic pathway and hijack stromal cells (mainly cancer-associated fibroblasts and immunocytes) to communicate, thereby adapting to metabolic stress. Therefore, a better understanding of the metabolic features of PDA will contribute to the development of novel diagnostic and therapeutic strategies.

Clinical Outcomes of TP53 Mutations in Cancers

High-throughput sequencing of cancer genomes is increasingly becoming an essential tool of clinical oncology that facilitates target identification and targeted therapy within the context of precision medicine. The cumulative profiles of somatic mutations in cancer yielded by comprehensive molecular studies also constitute a fingerprint of historical exposures to exogenous and endogenous mutagens, providing insight into cancer evolution and etiology. Mutational signatures that were first established by inspection of the TP53 gene somatic landscape have now been confirmed and expanded by comprehensive sequencing studies. Further, the degree of granularity achieved by deep sequencing allows detection of low-abundance mutations with clinical relevance. In tumors, they represent the emergence of small aggressive clones; in normal tissues, they signal a mutagenic exposure related to cancer risk; and, in blood, they may soon become effective surveillance tools for diagnostic purposes and for monitoring of cancer prognosis and recurrence.

Hypertonic Saline Primes Activation of the p53-p21 Signaling Axis in Human Small Airway Epithelial Cells That Prevents Inflammation Induced by Pro-inflammatory Cytokines

Uncontrolled inflammatory responses underlie the etiology of acute lung injury and acute distress respiratory syndrome, the most common late complications in trauma, the leading cause of death under the age of 59. Treatment with HTS decreases lung injury in clinical trials, rat models of trauma and hemorrhagic shock and inflammation in lung cell lines, although the mechanisms underlying these responses are still incompletely understood. Transcriptomics (RNaseq), proteomics, and U-¹³C-glucose tracing metabolomics experiments were performed to investigate the mechanisms of cellular responses to HTS treatment in primary small airway epithelial cells in the presence or absence of inflammatory injury mediated by a cocktail of cytokines (10 ng/mL of IFNγ, IL-1β, and TNFα). Modestly hyperosmolar HTS has an anti-inflammatory effect, triggers the p53-p21 signaling axis, and deregulates mitochondrial metabolism while inducing minimal apoptosis in response to a second hit by cytokines. Decreased transcription of pro-inflammatory cytokines suggested a role for the tumor suppressor protein p53 in mediating the beneficial effects of the HTS treatment. The anti-inflammatory mechanisms induced by HTS involves p53 gene regulation, promotes cell cycle arrest, and prevents ROS formation and mitochondria depolarization. Pharmaceutical targeting of the p53-p21 axis may mimic or reinforce the beneficial effects mediated by HTS when sustained hypertonicity cannot be maintained.

PTRF/Cavin-1 promotes efficient ribosomal RNA transcription in response to metabolic challenges

Ribosomal RNA transcription mediated by RNA polymerase I represents the rate-limiting step in ribosome biogenesis. In eukaryotic cells, nutrients and growth factors regulate ribosomal RNA transcription through various key factors coupled to cell growth. We show here in mature adipocytes, ribosomal transcription can be acutely regulated in response to metabolic challenges. This acute response is mediated by PTRF (polymerase I transcription and release factor, also known as cavin-1), which has previously been shown to play a critical role in caveolae formation. The caveolae–independent rDNA transcriptional role of PTRF not only explains the lipodystrophy phenotype observed in PTRF deficient mice and humans, but also highlights its crucial physiological role in maintaining adipocyte allostasis. Multiple post-translational modifications of PTRF provide mechanistic bases for its regulation. The role of PTRF in ribosomal transcriptional efficiency is likely relevant to many additional physiological situations of cell growth and organismal metabolism.

DOI:http://dx.doi.org/10.7554/eLife.17508.001

Obesity can cause several other health conditions to develop. Type 2 diabetes is one such condition, which arises in part because fat cells become unable to store excess fats. This makes certain tissues in the body less sensitive to the hormone insulin, and so the individual is less able to adapt to changing nutrient levels. Without treatment or a change in lifestyle, this insulin resistance may develop into diabetes. However, “healthy obese” individuals also exist, who can accommodate an overabundance of fat without developing insulin resistance and diabetes.

Some forms of rare genetic disorders called lipodystrophies, which result in an almost complete lack of body fat, can also lead to type 2 diabetes. This raises the question of whether lipodystrophy and obesity share some common mechanisms that cause fat cells to trigger insulin resistance. One possible player in such mechanisms is a protein called PTRF. In rare cases, individuals with lipodystrophy lack this protein, and mice that have been engineered to lack PTRF also largely lack body fat and develop insulin resistance.

Fat cells can respond rapidly to changes in nutrients during feeding or fasting, and to do so, they must produce new proteins. Structures called ribosomes, which are made up of proteins and ribosomal RNA, build proteins; thus when the cell needs to make new proteins, it also has to produce more ribosomes. PTRF is thought to play a role in ribosome production, but it is not clear how it does so.

Liu and Pilch analyzed normal mice as well as those that lacked the PTRF protein. This revealed that in response to cycles of fasting and feeding, PTRF increases the production of ribosomal RNA in fat cells, enabling the cells to produce more proteins. By contrast, the fat cells of mice that lack PTRF have much lower levels of ribosomal RNA and proteins.

Liu and Pilch then examined mouse fat cells that were grown in the laboratory. Exposing these cells to insulin caused phosphate groups to be attached to the PTRF proteins inside the cells. This modification caused PTRF to move into the cell’s nucleus, where it increased the production of ribosomal RNA.

Overall, the results show that fat cells that lack PTRF are unable to produce the proteins that they need to deal with changing nutrient levels, leading to an increased likelihood of diabetes. The next steps are to investigate the mechanism by which PTRF is modified, and to see whether the mechanisms uncovered in this study also apply to humans.

DOI:http://dx.doi.org/10.7554/eLife.17508.002

Integrated Omic Analysis of a Guinea Pig Model of Heart Failure and Sudden Cardiac Death

Here, we examine key regulatory pathways underlying the transition from compensated hypertrophy (HYP) to decompensated heart failure (HF) and sudden cardiac death (SCD) in a guinea pig pressure-overload model by integrated multiome analysis. Relative protein abundances from sham-operated HYP and HF hearts were assessed by iTRAQ LC-MS/MS. Metabolites were quantified by LC-MS/MS or GC-MS. Transcriptome profiles were obtained using mRNA microarrays. The guinea pig HF proteome exhibited classic biosignatures of cardiac HYP, left ventricular dysfunction, fibrosis, inflammation, and extravasation. Fatty acid metabolism, mitochondrial transcription/translation factors, antioxidant enzymes, and other mitochondrial procsses, were downregulated in HF but not HYP. Proteins upregulated in HF implicate extracellular matrix remodeling, cytoskeletal remodeling, and acute phase inflammation markers. Among metabolites, acylcarnitines were downregulated in HYP and fatty acids accumulated in HF. The correlation of transcript and protein changes in HF was weak (R(2) = 0.23), suggesting post-transcriptional gene regulation in HF. Proteome/metabolome integration indicated metabolic bottlenecks in fatty acyl-CoA processing by carnitine palmitoyl transferase (CPT1B) as well as TCA cycle inhibition. On the basis of these findings, we present a model of cardiac decompensation involving impaired nuclear integration of Ca(2+) and cyclic nucleotide signals that are coupled to mitochondrial metabolic and antioxidant defects through the CREB/PGC1α transcriptional axis.

p53-regulated autophagy is controlled by glycolysis and determines cell fate

The tumor suppressor p53 regulates downstream targets that determine cell fate. Canonical p53 functions include inducing apoptosis, growth arrest, and senescence. Non-canonical p53 functions include its ability to promote or inhibit autophagy and its ability to regulate metabolism. The extent to which autophagy and/or metabolic regulation determines cell fate by p53 is unclear. To address this, we compared cells resistant or sensitive to apoptosis by the p53 activator Nutlin-3a. In resistant cells, glycolysis was maintained upon Nutlin-3a treatment, and activated p53 promoted prosurvival autophagy. In contrast, in apoptosis sensitive cells activated p53 increased superoxide levels and inhibited glycolysis through repression of glycolytic pathway genes. Glycolysis inhibition and increased superoxide inhibited autophagy by repressing ATG genes essential for autophagic vesicle maturation. Inhibiting glycolysis increased superoxide and blocked autophagy in apoptosis-resistant cells, causing p62-dependent caspase-8 activation. Finally, treatment with 2-DG or the autophagy inhibitors chloroquine or bafilomycin A1 sensitized resistant cells to Nutlin-3a-induced apoptosis. Together, these findings reveal novel links between glycolysis and autophagy that determine apoptosis-sensitivity in response to p53. Specifically, the findings indicate 1) that glycolysis plays an essential role in autophagy by limiting superoxide levels and maintaining expression of ATG genes required for autophagic vesicle maturation, 2) that p53 can promote or inhibit autophagy depending on the status of glycolysis, and 3) that inhibiting protective autophagy can expand the breadth of cells susceptible to Nutlin-3a induced apoptosis.

Mitochondria, cholesterol and cancer cell metabolism

Given the role of mitochondria in oxygen consumption, metabolism and cell death regulation, alterations in mitochondrial function or dysregulation of cell death pathways contribute to the genesis and progression of cancer. Cancer cells exhibit an array of metabolic transformations induced by mutations leading to gain-of-function of oncogenes and loss-of-function of tumor suppressor genes that include increased glucose consumption, reduced mitochondrial respiration, increased reactive oxygen species generation and cell death resistance, all of which ensure cancer progression. Cholesterol metabolism is disturbed in cancer cells and supports uncontrolled cell growth. In particular, the accumulation of cholesterol in mitochondria emerges as a molecular component that orchestrates some of these metabolic alterations in cancer cells by impairing mitochondrial function. As a consequence, mitochondrial cholesterol loading in cancer cells may contribute, in part, to the Warburg effect stimulating aerobic glycolysis to meet the energetic demand of proliferating cells, while protecting cancer cells against mitochondrial apoptosis due to changes in mitochondrial membrane dynamics. Further understanding the complexity in the metabolic alterations of cancer cells, mediated largely through alterations in mitochondrial function, may pave the way to identify more efficient strategies for cancer treatment involving the use of small molecules targeting mitochondria, cholesterol homeostasis/trafficking and specific metabolic pathways.

Pharmacological and Genetic Manipulation of p53 in Brown Fat at Adult But Not Embryonic Stages Regulates Thermogenesis and Body Weight in Male Mice

p53 is a well-known tumor suppressor that plays multiple biological roles, including the capacity to modulate metabolism at different levels. However, its metabolic role in brown adipose tissue (BAT) remains largely unknown. Herein we sought to investigate the physiological role of endogenous p53 in BAT and its implication on BAT thermogenic activity and energy balance. To this end, we generated and characterized global p53-null mice and mice lacking p53 specifically in BAT. Additionally we performed gain-and-loss-of-function experiments in the BAT of adult mice using virogenetic and pharmacological approaches. BAT was collected and analyzed by immunohistochemistry, thermography, real-time PCR, and Western blot. p53-deficient mice were resistant to diet-induced obesity due to increased energy expenditure and BAT activity. However, the deletion of p53 in BAT using a Myf5-Cre driven p53 knockout did not show any changes in body weight or the expression of thermogenic markers. The acute inhibition of p53 in the BAT of adult mice slightly increased body weight and inhibited BAT thermogenesis, whereas its overexpression in the BAT of diet-induced obese mice reduced body weight and increased thermogenesis. On the other hand, pharmacological activation of p53 improves body weight gain due to increased BAT thermogenesis by sympathetic nervous system in obese adult wild-type mice but not in p53(-/-) animals. These results reveal that p53 regulates BAT metabolism by coordinating body weight and thermogenesis, but these metabolic actions are tissue specific and also dependent on the developmental stage.

p62/Sqstm1 promotes malignancy of HCV-positive hepatocellular carcinoma through Nrf2-dependent metabolic reprogramming

p62/Sqstm1 is a multifunctional protein involved in cell survival, growth and death, that is degraded by autophagy. Amplification of the p62/Sqstm1 gene, and aberrant accumulation and phosphorylation of p62/Sqstm1, have been implicated in tumour development. Herein, we reveal the molecular mechanism of p62/Sqstm1-dependent malignant progression, and suggest that molecular targeting of p62/Sqstm1 represents a potential chemotherapeutic approach against hepatocellular carcinoma (HCC). Phosphorylation of p62/Sqstm1 at Ser349 directs glucose to the glucuronate pathway, and glutamine towards glutathione synthesis through activation of the transcription factor Nrf2. These changes provide HCC cells with tolerance to anti-cancer drugs and proliferation potency. Phosphorylated p62/Sqstm1 accumulates in tumour regions positive for hepatitis C virus (HCV). An inhibitor of phosphorylated p62-dependent Nrf2 activation suppresses the proliferation and anticancer agent tolerance of HCC. Our data indicate that this Nrf2 inhibitor could be used to make cancer cells less resistant to anticancer drugs, especially in HCV-positive HCC patients.

Cancer Clocks Out for Lunch: Disruption of Circadian Rhythm and Metabolic Oscillation in Cancer

Circadian rhythms are 24-h oscillations present in most eukaryotes and many prokaryotes that synchronize activity to the day-night cycle. They are an essential feature of organismal and cell physiology that coordinate many of the metabolic, biosynthetic, and signal transduction pathways studied in biology. The molecular mechanism of circadian rhythm is controlled both by signal transduction and gene transcription as well as by metabolic feedback. The role of circadian rhythm in cancer cell development and survival is still not well understood, but as will be discussed in this Review, accumulated research suggests that circadian rhythm may be altered or disrupted in many human cancers downstream of common oncogenic alterations. Thus, a complete understanding of the genetic and metabolic alterations in cancer must take potential circadian rhythm perturbations into account, as this disruption itself will influence how gene expression and metabolism are altered in the cancer cell compared to its non-transformed neighbor. It will be important to better understand these circadian changes in both normal and cancer cell physiology to potentially design treatment modalities to exploit this insight.

Chromatin-Bound MDM2 Regulates Serine Metabolism and Redox Homeostasis Independently of p53

The mouse double minute 2 (MDM2) oncoprotein is recognized as a major negative regulator of the p53 tumor suppressor, but growing evidence indicates that its oncogenic activities extend beyond p53. Here, we show that MDM2 is recruited to chromatin independently of p53 to regulate a transcriptional program implicated in amino acid metabolism and redox homeostasis. Identification of MDM2 target genes at the whole-genome level highlights an important role for ATF3/4 transcription factors in tethering MDM2 to chromatin. MDM2 recruitment to chromatin is a tightly regulated process that occurs during oxidative stress and serine/glycine deprivation and is modulated by the pyruvate kinase M2 (PKM2) metabolic enzyme. Depletion of endogenous MDM2 in p53-deficient cells impairs serine/glycine metabolism, the NAD(+)/NADH ratio, and glutathione (GSH) recycling, impacting their redox state and tumorigenic potential. Collectively, our data illustrate a previously unsuspected function of chromatin-bound MDM2 in cancer cell metabolism.

p53 attenuates AKT signaling by modulating membrane phospholipid composition

The p53 tumor suppressor is the central component of a complex network of signaling pathways that protect organisms against the propagation of cells carrying oncogenic mutations. Here we report a previously unrecognized role of p53 in membrane phospholipids composition. By repressing the expression of stearoyl-CoA desaturase 1, SCD, the enzyme that converts saturated to mono-unsaturated fatty acids, p53 causes a shift in the content of phospholipids with mono-unsaturated acyl chains towards more saturated phospholipid species, particularly of the phosphatidylinositol headgroup class. This shift affects levels of phosphatidylinositol phosphates, attenuates the oncogenic AKT pathway, and contributes to the p53-mediated control of cell survival. These findings expand the p53 network to phospholipid metabolism and uncover a new molecular pathway connecting p53 to AKT signaling.

CerS6 Is a Novel Transcriptional Target of p53 Protein Activated by Non-genotoxic Stress

Our previous study suggested that ceramide synthase 6 (CerS6), an enzyme in sphingolipid biosynthesis, is regulated by p53: CerS6 was elevated in several cell lines in response to transient expression of p53 or in response to folate stress, which is known to activate p53. It was not clear, however, whether CerS6 gene is a direct transcriptional target of p53 or whether this was an indirect effect through additional regulatory factors. In the present study, we have shown that the CerS6 promoter is activated by p53 in luciferase assays, whereas transcriptionally inactive R175H p53 mutant failed to induce the luciferase expression from this promoter. In vitro immunoprecipitation assays and gel shift analyses have further demonstrated that purified p53 binds within the CerS6 promoter sequence spanning 91 bp upstream and 60 bp downstream of the transcription start site. The Promo 3.0.2 online tool for the prediction of transcription factor binding sites indicated the presence of numerous putative non-canonical p53 binding motifs in the CerS6 promoter. Luciferase assays and gel shift analysis have identified a single motif upstream of the transcription start as a key p53 response element. Treatment of cells with Nutlin-3 or low concentrations of actinomycin D resulted in a strong elevation of CerS6 mRNA and protein, thus demonstrating that CerS6 is a component of the non-genotoxic p53-dependent cellular stress response. This study has shown that by direct transcriptional activation of CerS6, p53 can regulate specific ceramide biosynthesis, which contributes to the pro-apoptotic cellular response.

Differentiation-Dependent Energy Production and Metabolite Utilization: A Comparative Study on Neural Stem Cells, Neurons, and Astrocytes

While it is evident that the metabolic machinery of stem cells should be fairly different from that of differentiated neurons, the basic energy production pathways in neural stem cells (NSCs) or in neurons are far from clear. Using the model of in vitro neuron production by NE-4C NSCs, this study focused on the metabolic changes taking place during the in vitro neuronal differentiation. O2 consumption, H(+) production, and metabolic responses to single metabolites were measured in cultures of NSCs and in their neuronal derivatives, as well as in primary neuronal and astroglial cultures. In metabolite-free solutions, NSCs consumed little O2 and displayed a higher level of mitochondrial proton leak than neurons. In stem cells, glycolysis was the main source of energy for the survival of a 2.5-h period of metabolite deprivation. In contrast, stem cell-derived or primary neurons sustained a high-level oxidative phosphorylation during metabolite deprivation, indicating the consumption of own cellular material for energy production. The stem cells increased O2 consumption and mitochondrial ATP production in response to single metabolites (with the exception of glucose), showing rapid adaptation of the metabolic machinery to the available resources. In contrast, single metabolites did not increase the O2 consumption of neurons or astrocytes. In "starving" neurons, neither lactate nor pyruvate was utilized for mitochondrial ATP production. Gene expression studies also suggested that aerobic glycolysis and rapid metabolic adaptation characterize the NE-4C NSCs, while autophagy and alternative glucose utilization play important roles in the metabolism of stem cell-derived neurons.

The MDM2-p53-pyruvate carboxylase signalling axis couples mitochondrial metabolism to glucose-stimulated insulin secretion in pancreatic β-cells

Mitochondrial metabolism is pivotal for glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells. However, little is known about the molecular machinery that controls the homeostasis of intermediary metabolites in mitochondria. Here we show that the activation of p53 in β-cells, by genetic deletion or pharmacological inhibition of its negative regulator MDM2, impairs GSIS, leading to glucose intolerance in mice. Mechanistically, p53 activation represses the expression of the mitochondrial enzyme pyruvate carboxylase (PC), resulting in diminished production of the TCA cycle intermediates oxaloacetate and NADPH, and impaired oxygen consumption. The defective GSIS and mitochondrial metabolism in MDM2-null islets can be rescued by restoring PC expression. Under diabetogenic conditions, MDM2 and p53 are upregulated, whereas PC is reduced in mouse β-cells. Pharmacological inhibition of p53 alleviates defective GSIS in diabetic islets by restoring PC expression. Thus, the MDM2-p53-PC signalling axis links mitochondrial metabolism to insulin secretion and glucose homeostasis, and could represent a therapeutic target in diabetes.