p53 and metabolism

PGC-1α regulates translocated in liposarcoma activity: role in oxidative stress gene expression

Translocated in liposarcoma (TLS) is a poorly characterized multifunctional protein involved in the genotoxic response. TLS regulates gene expression at several steps, including splicing and mRNA transport, possibly connecting transcriptional and posttranscriptional events.

AIMS

In this study we aimed to idenfity molecular targets and regulatory partners of TLS.

RESULTS AND INNOVATION

Here we report that TLS transcriptionally regulates the expression of oxidative stress protection genes. This regulation requires interaction with the transcriptional coactivator peroxisome proliferator activated receptor γ-coactivator 1α (PGC-1α), a master regulator of mitochondrial function that coordinately induces the expression of genes involved in detoxification of mitochondrial reactive oxygen species (ROS). Microarray gene expression analysis showed that TLS transcriptional activity is impaired in the absence of PGC-1α, and is thus largely dependent on PGC-1α.

CONCLUSION

These results suggest the existence of a regulatory circuit linking the control of ROS detoxification to the coordinated cross-talk between oxidative metabolism and the cellular response to genomic DNA damage.

Tumor suppressor p53 regulates bile acid homeostasis via small heterodimer partner

Metabolic changes in cancer have been observed for almost a century. The mechanisms underlying these changes have begun to emerge from the recent studies implicating the tumor suppressor p53 in multiple metabolic pathways. The ability of p53 to regulate metabolism may also play important roles in the physiology of normal cells and organs. Here we demonstrate that p53 lowers bile acid (BA) levels under both normal and stressed conditions primarily through up-regulating expression of small heterodimer partner, a critical inhibitor of BA synthesis. Our results uncover a unique metabolic regulatory axis that unexpectedly couples p53 to BA homeostasis. Our results also warrant future studies to investigate a possible role of this axis in the tumor suppression by p53, because excessive quantities of BAs are cytotoxic and can cause liver damage and promote gastrointestinal cancers.

Mitochondrial recoupling: a novel therapeutic strategy for cancer?

Recent findings link metabolic transformation of cancer cells to aberrant functions of mitochondrial uncoupling proteins (UCPs). By inducing proton leak, UCPs interfere with mitochondrial synthesis of adenosine 5'-triphosphate, which is also a key determinant of glycolytic pathways. In addition, UCP suppress the generation of superoxide, a byproduct of mitochondrial electron transport and a major source of oxidative stress. The near ubiquitous UCP2 becomes highly abundant in some cancers and may advance metabolic reprogramming, further disrupt tumour suppression, and promote chemoresistance. Here we review current evidence to suggest that inhibition of mitochondrial uncoupling may eliminate these responses and reveal novel anti-cancer strategies.

E4F1 deficiency results in oxidative stress-mediated cell death of leukemic cells

The multifunctional E4F1 protein was originally discovered as a target of the E1A viral oncoprotein. Growing evidence indicates that E4F1 is involved in key signaling pathways commonly deregulated during cell transformation. In this study, we investigate the influence of E4F1 on tumorigenesis. Wild-type mice injected with fetal liver cells from mice lacking CDKN2A, the gene encoding Ink4a/Arf, developed histiocytic sarcomas (HSs), a tumor originating from the monocytic/macrophagic lineage. Cre-mediated deletion of E4F1 resulted in the death of HS cells and tumor regression in vivo and extended the lifespan of recipient animals. In murine and human HS cell lines, E4F1 inactivation resulted in mitochondrial defects and increased production of reactive oxygen species (ROS) that triggered massive cell death. Notably, these defects of E4F1 depletion were observed in HS cells but not healthy primary macrophages. Short hairpin RNA-mediated depletion of E4F1 induced mitochondrial defects and ROS-mediated death in several human myeloid leukemia cell lines. E4F1 protein is overexpressed in a large subset of human acute myeloid leukemia samples. Together, these data reveal a role for E4F1 in the survival of myeloid leukemic cells and support the notion that targeting E4F1 activities might have therapeutic interest.

Cell cycle arrest is not senescence

DNA damaging agents and radiation, cytotoxins and anti-cancer drugs, telomere erosion and cytokines, culture shock and mitogenic stimuli, oncogenes and tumor suppressors can induce both cell cycle arrest and cellular senescence. Due to this semi-coincidence, senescence is confused with cell cycle arrest, or even more misleadingly, with growth inhibition. With such misconceptions, cellular senescence cannot be linked to organismal aging. Also, the relation between cancer and senescence is distorted. Here I discuss why the link between arrest and senescence is semi-coincidental and how senescence is related to aging and cancer.

Inhibition of p53 by adenovirus type 12 E1B-55K deregulates cell cycle control and sensitizes tumor cells to genotoxic agents

Adenovirus E1B-55K represses p53-mediated transcription. However, the phenotypic consequence of p53 inhibition by E1B-55K for cell cycle regulation and drug sensitivity in tumor cells has not been examined. In HCT116 cells with constitutive E1B-55K expression, the activation of p53 target genes such as the p21, Mdm2, and Puma genes was attenuated, despite markedly elevated p53 protein levels. HCT116 cells with E1B-55K expression displayed a cell cycle profile similar to that of the isogenic HCT116p53(-/-) cells, including unhindered S-phase entry despite DNA damage. Surprisingly, E1B-55K-expressing cells were more sensitive to drug treatment than parental cells. Compared to HCT116 cells, HCT116p53(-/-) cells were more susceptible to both doxorubicin and etoposide, and E1B-55K expression had no effects on drug treatment. E1B-55K expression increased the rate of cell proliferation in HCT116 but not in HCT116p53(-/-) cells. Thus, deregulation of p53-mediated cell cycle control by E1B-55K probably underlies sensitization of HCT116 cells to anticancer drugs. Consistently, E1B-55K expression in A549, A172, and HepG2 cells, all containing wild-type (wt) p53, also enhanced etoposide-induced cytotoxicity, whereas in p53-null H1299 cells, E1B-55K had no effects. We generated several E1B-55K mutants with mutations at positions occupied by the conserved Phe/Trp/His residues. Most of these mutants showed no or reduced binding to p53, although some of them could still stabilize p53, suggesting that binding might not be essential for E1B-55K-induced p53 stabilization. Despite heightened p53 protein levels in cells expressing certain E1B-55K mutants, p53 activity was largely suppressed. Furthermore, most of these E1B-55K mutants could sensitize HCT116 cells to etoposide and doxorubicin. These results indicate that E1B-55K might have utility for enhancing chemotherapy.

Targeting metabolic remodeling in glioblastoma multiforme

A key aberrant biological difference between tumor cells and normal differentiated cells is altered metabolism, whereby cancer cells acquire a number of stable genetic and epigenetic alterations to retain proliferation, survive under unfavorable microenvironments and invade into surrounding tissues. A classic biochemical adaptation is the metabolic shift to aerobic glycolysis rather than mitochondrial oxidative phosphorylation, regardless of oxygen availability, a phenomenon termed the “Warburg Effect”. Aerobic glycolysis, characterized by high glucose uptake, low oxygen consumption and elevated production of lactate, is associated with a survival advantage as well as the generation of substrates such as fatty acids, amino acids and nucleotides necessary in rapidly proliferating cells. This review discusses the role of key metabolic enzymes and their association with aerobic glycolysis in Glioblastoma Multiforme (GBM), an aggressive, highly glycolytic and deadly brain tumor. Targeting key metabolic enzymes involved in modulating the “Warburg Effect” may provide a novel therapeutic approach either singularly or in combination with existing therapies in GBMs.

p53 transactivation and the impact of mutations, cofactors and small molecules using a simplified yeast-based screening system

Background

The p53 tumor suppressor, which is altered in most cancers, is a sequence-specific transcription factor that is able to modulate the expression of many target genes and influence a variety of cellular pathways. Inactivation of the p53 pathway in cancer frequently occurs through the expression of mutant p53 protein. In tumors that retain wild type p53, the pathway can be altered by upstream modulators, particularly the p53 negative regulators MDM2 and MDM4.

Methodology/Principal Findings

Given the many factors that might influence p53 function, including expression levels, mutations, cofactor proteins and small molecules, we expanded our previously described yeast-based system to provide the opportunity for efficient investigation of their individual and combined impacts in a miniaturized format. The system integrates i) variable expression of p53 proteins under the finely tunable GAL1,10 promoter, ii) single copy, chromosomally located p53-responsive and control luminescence reporters, iii) enhanced chemical uptake using modified ABC-transporters, iv) small-volume formats for treatment and dual-luciferase assays, and v) opportunities to co-express p53 with other cofactor proteins. This robust system can distinguish different levels of expression of WT and mutant p53 as well as interactions with MDM2 or 53BP1.

Conclusions/Significance

We found that the small molecules Nutlin and RITA could both relieve the MDM2-dependent inhibition of WT p53 transactivation function, while only RITA could impact p53/53BP1 functional interactions. PRIMA-1 was ineffective in modifying the transactivation capacity of WT p53 and missense p53 mutations. This dual-luciferase assay can, therefore, provide a high-throughput assessment tool for investigating a matrix of factors that can influence the p53 network, including the effectiveness of newly developed small molecules, on WT and tumor-associated p53 mutants as well as interacting proteins.

Oncosuppressive functions of autophagy

Macroautophagy (herein referred to as autophagy) constitutes a phylogenetically old mechanism leading to the lysosomal degradation of cytoplasmic structures. At baseline levels, autophagy exerts homeostatic functions by ensuring the turnover of potentially harmful organelles and long-lived aggregate-prone proteins. Moreover, the autophagic flow can be dramatically upregulated in response to a plethora of stressful conditions, including glucose, amino acid, oxygen, or growth factor deprivation, accumulation of unfolded proteins in the endoplasmic reticulum, and invasion by intracellular pathogens. In some experimental settings, stress-induced autophagy has been shown to contribute to programmed cell death. Nevertheless, autophagy most often confers cytoprotection by providing cells with new metabolic substrates or by ridding them of noxious intracellular entities including protein aggregates and invading organisms. Thus, autophagy has been implicated in an ever-increasing number of human diseases including cancer. Autophagy inhibition accelerates the demise of tumor cells that are subjected to chemo- or radiotherapy, thereby constituting an interesting target for the development of anticancer strategies. However, several oncosuppressor proteins and oncoproteins have been recently shown to stimulate and inhibit the autophagic flow, respectively, suggesting that autophagy exerts bona fide tumor-suppressive functions. In this review, we will discuss the mechanisms by which autophagy may prevent oncogenesis.

Prazosin induces p53-mediated autophagic cell death in H9C2 cells

Prazosin, a quinazoline-based α(1)-adrenoceptor antagonist, is known to induce cell death, and this effect is independent of its α-blockade activity. However, the detailed molecular mechanisms involved are still not fully understood. In this study, we found that prazosin, but not doxazosin, could induce patterns of autophagy in H9C2 cells, including intracellular vacuole formation, microtubule-associated protein 1 light chain 3 (LC3) conversion, and acidic vesicular organelle (AVO) augmentation. Western blot analysis of phosphorylated proteins showed that exposure to prazosin increased the levels of phospho-p53 and phospho-adenosine monophosphate-activated protein kinase (AMPK) but dramatically decreased the levels of phospho-mammalian target of rapamycin (mTOR), phospho-protein kinase B (Akt), and phospho-ribosomal protein S6 kinase (p70S6K). Furthermore, although pretreatments with the pharmacological autophagy inhibitor 3-methyladenine and the p53 inhibitor pifithrin-α suppressed prazosin-induced AVO formation, they did not reverse prazosin-induced decline in cell viability but enhanced prazosin-induced caspase-3 activation. From these results we suggest that prazosin induces autophagic cell death via a p53-mediated mechanism. When the autophagy pathway was inhibited, prazosin still induced programmed cell death, at least in part through apoptotic caspase-3 cascade enhancement. Thus, our results indicate a potential new target in prazosin-induced cell death.

Reciprocal influence of the p53 and the hypoxic pathways

When cells sense a decrease in oxygen availability (hypoxia), they develop adaptive responses in order to sustain this condition and survive. If hypoxia lasts too long or is too severe, the cells eventually die. Hypoxia is also known to modulate the p53 pathway, in a manner dependent or not of HIF-1 (hypoxia-inducible factor-1), the main transcription factor activated by hypoxia. The p53 protein is a transcription factor, which is rapidly stabilised by cellular stresses and which has a major role in the cell responses to these stresses. The aim of this review is to compile what has been reported until now about the interconnection between these two important pathways. Indeed, according to the cell line, the severity and the duration of hypoxia, oxygen deficiency influences very differently p53 protein level and activity. Conversely, p53 is also described to affect HIF-1α stability, one of the two subunits of HIF-1, and HIF-1 activity. The direct and indirect interactions between HIF-1α and p53 are described as well as the involvement in this complex network of their respective ubiquitin ligases von Hippel Lindau protein and murine double minute 2. Finally, the synergistic or antagonistic effects of p53 and HIF-1 on some important cellular pathways are discussed.

Autophagy in the cellular energetic balance

Autophagy mediates the degradation of cellular components in lysosomes, assuring removal of altered or dysfunctional proteins and organelles. Autophagy is not only activated in response to cellular damage; in fact, one of its strongest and better-characterized stimuli is starvation. Activation of autophagy when nutrients are scarce allows cells to reutilize their own constituents for energy. Besides protein breakdown, autophagy also contributes to the mobilization of diverse cellular energy stores. This recently discovered interplay between autophagy and lipid and carbohydrate metabolism reveals the existence of a dynamic feedback between autophagy and cellular energy balance.

Induction of autophagy by drug-resistant esophageal cancer cells promotes their survival and recovery following treatment with chemotherapeutics

We investigated the cell-death mechanisms induced in esophageal cancer cells in response to the chemotherapeutic drugs, 5-fluorouracil (5-FU) and cisplatin. Chemosensitive cell lines exhibited apoptosis whereas chemoresistant populations exhibited autophagy and a morphology resembling type II programmed cell death (PCD). Cell populations that respond with autophagy are more resistant and will recover following withdrawal of the chemotherapeutic agents. Specific inhibition of early autophagy induction with siRNA targeted to Beclin 1 and ATG7 significantly enhanced the effect of 5-FU and reduced the recovery of drug-treated cells. Pharmacological inhibitors of autophagy were evaluated for their ability to improve chemotherapeutic effect. The PtdIns 3-kinase inhibitor 3-methyladenine did not enhance the cytotoxicity of 5-FU. Disruption of lysosomal activity with bafilomycin A 1 or chloroquine caused extensive vesicular accumulation but did not improve chemotherapeutic effect. These observations suggest that an autophagic response to chemotherapy is a survival mechanism that promotes chemoresistance and recovery and that selective inhibition of autophagy regulators has the potential to improve chemotherapeutic regimes. Currently available indirect inhibitors of autophagy are, however, ineffective at modulating chemosensitivity in these esophageal cancer cell lines.

Otto Warburg's contributions to current concepts of cancer metabolism

Otto Warburg pioneered quantitative investigations of cancer cell metabolism, as well as photosynthesis and respiration. Warburg and co-workers showed in the 1920s that, under aerobic conditions, tumour tissues metabolize approximately tenfold more glucose to lactate in a given time than normal tissues, a phenomenon known as the Warburg effect. However, this increase in aerobic glycolysis in cancer cells is often erroneously thought to occur instead of mitochondrial respiration and has been misinterpreted as evidence for damage to respiration instead of damage to the regulation of glycolysis. In fact, many cancers exhibit the Warburg effect while retaining mitochondrial respiration. We re-examine Warburg's observations in relation to the current concepts of cancer metabolism as being intimately linked to alterations of mitochondrial DNA, oncogenes and tumour suppressors, and thus readily exploitable for cancer therapy.

Mitochondrial dysfunction impairs tumor suppressor p53 expression/function

Recently, mitochondria have been suggested to act in tumor suppression. However, the underlying mechanisms by which mitochondria suppress tumorigenesis are far from being clear. In this study, we have investigated the link between mitochondrial dysfunction and the tumor suppressor protein p53 using a set of respiration-deficient (Res(-)) mammalian cell mutants with impaired assembly of the oxidative phosphorylation machinery. Our data suggest that normal mitochondrial function is required for γ-irradiation (γIR)-induced cell death, which is mainly a p53-dependent process. The Res(-) cells are protected against γIR-induced cell death due to impaired p53 expression/function. We find that the loss of complex I biogenesis in the absence of the MWFE subunit reduces the steady-state level of the p53 protein, although there is no effect on the p53 protein level in the absence of the ESSS subunit that is also essential for complex I assembly. The p53 protein level was also reduced to undetectable levels in Res(-) cells with severely impaired mitochondrial protein synthesis. This suggests that p53 protein expression is differentially regulated depending upon the type of electron transport chain/respiratory chain deficiency. Moreover, irrespective of the differences in the p53 protein expression profile, γIR-induced p53 activity is compromised in all Res(-) cells. Using two different conditional systems for complex I assembly, we also show that the effect of mitochondrial dysfunction on p53 expression/function is a reversible phenomenon. We believe that these findings will have major implications in the understanding of cancer development and therapy.

Investigation of tumor hypoxia using a two-enzyme system for in vitro generation of oxygen deficiency

Background

Oxygen deficiency in tumor tissue is associated with a malign phenotype, characterized by high invasiveness, increased metastatic potential and poor prognosis. Hypoxia chambers are the established standard model for in vitro studies on tumor hypoxia. An enzymatic hypoxia system (GOX/CAT) based on the use of glucose oxidase (GOX) and catalase (CAT) that allows induction of stable hypoxia for in vitro approaches more rapidly and with less operating expense has been introduced recently. Aim of this work is to compare the enzymatic system with the established technique of hypoxia chamber in respect of gene expression, glucose metabolism and radioresistance, prior to its application for in vitro investigation of oxygen deficiency.

Methods

Human head and neck squamous cell carcinoma HNO97 cells were incubated under normoxic and hypoxic conditions using both hypoxia chamber and the enzymatic model. Gene expression was investigated using Agilent microarray chips and real time PCR analysis. ¹⁴C-fluoro-deoxy-glucose uptake experiments were performed in order to evaluate cellular metabolism. Cell proliferation after photon irradiation was investigated for evaluation of radioresistance under normoxia and hypoxia using both a hypoxia chamber and the enzymatic system.

Results

The microarray analysis revealed a similar trend in the expression of known HIF-1 target genes between the two hypoxia systems for HNO97 cells. Quantitative RT-PCR demonstrated different kinetic patterns in the expression of carbonic anhydrase IX and lysyl oxidase, which might be due to the faster induction of hypoxia by the enzymatic system. ¹⁴C-fluoro-deoxy-glucose uptake assays showed a higher glucose metabolism under hypoxic conditions, especially for the enzymatic system. Proliferation experiments after photon irradiation revealed increased survival rates for the enzymatic model compared to hypoxia chamber and normoxia, indicating enhanced resistance to irradiation. While the GOX/CAT system allows independent investigation of hypoxia and oxidative stress, care must be taken to prevent acidification during longer incubation.

Conclusion

The results of our study indicate that the enzymatic model can find application for in vitro investigation of tumor hypoxia, despite limitations that need to be considered in the experimental design.

The central Sirtuin 1/p53 pathway is essential for the orexigenic action of ghrelin

OBJECTIVE

Ghrelin is a stomach-derived peptide that increases food intake through the activation of hypothalamic AMP-activated protein kinase (AMPK). However, the molecular mechanisms initiated by the activation of the ghrelin receptor, which in turn lead to AMPK activation, remain unclear. Sirtuin 1 (SIRT1) is a deacetylase activated in response to calorie restriction that acts through the tumor suppressor gene p53. We tested the hypothesis that the central SIRT1/p53 pathway might be mediating the orexigenic action of ghrelin.

RESEARCH DESIGN AND METHODS

SIRT1 inhibitors, such as Ex527 and sirtinol, and AMPK activators, such as AICAR, were administered alongside ghrelin in the brain of rats and mice (wild-type versus p53 knockout [KO]). Their hypothalamic effects on lipid metabolism and changes in transcription factors and neuropeptides were assessed by Western blot and in situ hybridization.

RESULTS

The central pretreatment with Ex527, a potent SIRT1 inhibitor, blunted the ghrelin-induced food intake in rats. Mice lacking p53, a target of SIRT1 action, failed to respond to ghrelin in feeding behavior. Ghrelin failed to phosphorylate hypothalamic AMPK when rats were pretreated with Ex527, as it did in p53 KO mice. It is noteworthy that the hypothalamic SIRT1/p53 pathway seems to be specific for mediating the orexigenic action of ghrelin, because central administration of AICAR, a potent AMPK activator, increased food intake in p53 KO mice. Finally, blockade of the central SIRT1 pathway did not modify ghrelin-induced growth hormone secretion.

CONCLUSIONS

Ghrelin specifically triggers a central SIRT1/p53 pathway that is essential for its orexigenic action, but not for the release of growth hormone.

SPATA18, a spermatogenesis-associated gene, is a novel transcriptional target of p53 and p63

The transcription factor p53 functions not only to suppress tumorigenesis but also to maintain normal development and homeostasis. Although p53 was implicated in different aspects of fertility, including spermatogenesis and implantation, the mechanism underlying p53 involvement in spermatogenesis is poorly resolved. In this study we describe the identification of a spermatogenesis-associated gene, SPATA18, as a novel p53 transcriptional target and show that SPATA18 transcription is induced by p53 in a variety of cell types of both human and mouse origin. p53 binds a consensus DNA motif that resides within the first intron of SPATA18. We describe the spatiotemporal expression patterns of SPATA18 in mouse seminiferous tubules and suggest that SPATA18 transcription is regulated in vivo by p53. We also demonstrate the induction of SPATA18 by p63 and suggest that p63 can compensate for the loss of p53 activity in vivo. Our data not only enrich the known collection of p53 targets but may also provide insights on spermatogenesis defects that are associated with p53 deficiency.

AMP-activated protein kinase inhibits NF-κB signaling and inflammation: impact on healthspan and lifespan

Adenosine monophosphate-activated protein kinase (AMPK) is a crucial regulator of energy metabolic homeostasis and thus a major survival factor in a variety of metabolic stresses and also in the aging process. Metabolic syndrome is associated with a low-grade, chronic inflammation, primarily in adipose tissue. A low-level of inflammation is also present in the aging process. There are emerging results indicating that AMPK signaling can inhibit the inflammatory responses induced by the nuclear factor-κB (NF-κB) system. The NF-κB subunits are not direct phosphorylation targets of AMPK, but the inhibition of NF-κB signaling is mediated by several downstream targets of AMPK, e.g., SIRT1, PGC-1α, p53, and Forkhead box O (FoxO) factors. AMPK signaling seems to enhance energy metabolism while it can repress inflammatory responses linked to chronic stress, e.g., in nutritional overload and during the aging process. AMPK can inhibit endoplasmic reticulum and oxidative stresses which are involved in metabolic disorders and the aging process. Interestingly, many target proteins of AMPK are so-called longevity factors, e.g., SIRT1, p53, and FoxOs, which not only can increase the stress resistance and extend the lifespan of many organisms but also inhibit the inflammatory responses. The activation capacity of AMPK declines in metabolic stress and with aging which could augment the metabolic diseases and accelerate the aging process. We will review the AMPK pathways involved in the inhibition of NF-κB signaling and suppression of inflammation. We also emphasize that the capacity of AMPK to repress inflammatory responses can have a significant impact on both healthspan and lifespan.

AMP-activated protein kinase inhibits NF-κB signaling and inflammation: impact on healthspan and lifespan

Adenosine monophosphate-activated protein kinase (AMPK) is a crucial regulator of energy metabolic homeostasis and thus a major survival factor in a variety of metabolic stresses and also in the aging process. Metabolic syndrome is associated with a low-grade, chronic inflammation, primarily in adipose tissue. A low-level of inflammation is also present in the aging process. There are emerging results indicating that AMPK signaling can inhibit the inflammatory responses induced by the nuclear factor-κB (NF-κB) system. The NF-κB subunits are not direct phosphorylation targets of AMPK, but the inhibition of NF-κB signaling is mediated by several downstream targets of AMPK, e.g., SIRT1, PGC-1α, p53, and Forkhead box O (FoxO) factors. AMPK signaling seems to enhance energy metabolism while it can repress inflammatory responses linked to chronic stress, e.g., in nutritional overload and during the aging process. AMPK can inhibit endoplasmic reticulum and oxidative stresses which are involved in metabolic disorders and the aging process. Interestingly, many target proteins of AMPK are so-called longevity factors, e.g., SIRT1, p53, and FoxOs, which not only can increase the stress resistance and extend the lifespan of many organisms but also inhibit the inflammatory responses. The activation capacity of AMPK declines in metabolic stress and with aging which could augment the metabolic diseases and accelerate the aging process. We will review the AMPK pathways involved in the inhibition of NF-κB signaling and suppression of inflammation. We also emphasize that the capacity of AMPK to repress inflammatory responses can have a significant impact on both healthspan and lifespan.

The balance between rRNA and ribosomal protein synthesis up- and downregulates the tumour suppressor p53 in mammalian cells

Data on the relationship between ribosome biogenesis and p53 function indicate that the tumour suppressor can be activated by either nucleolar disruption or ribosomal protein defects. However, there is increasing evidence that the induction of p53 does not always require these severe cellular changes, and data are still lacking on a possible role of ribosome biogenesis in the downregulation of p53. Here, we studied the effect of the up- and downregulation of the rRNA transcription rate on p53 induction in mammalian cells. We found that a downregulation of rRNA synthesis, induced by silencing the POLR1A gene coding for the RNA polymerase I catalytic subunit, stabilised p53 without altering the nucleolar integrity in human cancer cells. p53 stabilisation was due to the inactivation of the MDM2-mediated p53 degradation by the binding of ribosomal proteins no longer used for ribosome building. p53 stabilisation did not occur when rRNA synthesis downregulation was associated with a contemporary reduction of protein synthesis. Furthermore, we demonstrated that in three different experimental models characterised by an upregulation of rRNA synthesis, cancer cells treated with insulin or exposed to the insulin-like growth factor 1, rat liver stimulated by cortisol and regenerating rat liver after partial hepatectomy, the p53 protein level was reduced due to a lowered ribosomal protein availability for MDM2 binding. It is worth noting that the upregulation of rRNA synthesis was responsible for a decreased p53-mediated response to cytotoxic stresses. These findings demonstrated that the balance between rRNA and ribosomal protein synthesis controls the function of p53 in mammalian cells, that p53 can be induced without the occurrence of severe changes of the cellular components controlling ribosome biogenesis, and that conditions characterised by an upregulated rRNA synthesis are associated with a reduced p53 response.

The p53 target Wig-1: a regulator of mRNA stability and stem cell fate?

Wig-1 is a transcriptional target of the tumor suppressor p53 and encodes an unusual zinc-finger protein involved in post-transcriptional gene regulation. Wig-1 is expressed in all cell types investigated so far, with the highest levels in the brain, and is enriched in stem cells as compared with more differentiated cells of the same lineage. Wig-1 binds to both long double-stranded (ds) RNA and short microRNA-like dsRNA. We have shown that Wig-1 acts in a positive feedback loop that stabilizes p53 mRNA through an AU-rich element (ARE) in the p53 3'untranslated region. Our preliminary data indicate a more general effect of Wig-1 on ARE-containing mRNA. Here we shall summarize current knowledge about Wig-1 and discuss possible implications on p53 function and other cellular processes.

Defining the molecular nexus of cancer, type 2 diabetes and cardiovascular disease

The metabolic syndrome is characterized by a state of metabolic dysfunction resulting in the development of several chronic diseases that are potentially deadly. These metabolic deregulations are complex and intertwined and it has been observed that many of the mechanisms and pathways responsible for diseases characterizing the metabolic syndrome such as type 2 diabetes and cardiovascular disease are linked with cancer development as well. Identification of molecular pathways common to these diverse diseases may prove to be a critical factor in disease prevention and development of potential targets for therapeutic treatments. This review focuses on several molecular pathways, including AMPK, PPARs and FASN that interconnect cancer development, type 2 diabetes and cardiovascular disease. AMPK, PPARs and FASN are crucial regulators involved in the maintenance of key metabolic processes necessary for proper homeostasis. It is critical to recognize and identify common pathways deregulated in interrelated diseases as it may provide further information and a much more global picture in regards to disease development and prevention. Thus, this review focuses on three key metabolic regulators, AMPK, PPARs and FASN, that may potentially serve as therapeutic targets.

DNA damaging agents and p53 do not cause senescence in quiescent cells, while consecutive re-activation of mTOR is associated with conversion to senescence

When the cell cycle is arrested, growth-promoting pathways such as mTOR (Target of Rapamycin) drive cellular senescence, characterized by cellular hyper-activation, hypertrophy and permanent loss of the proliferative potential. While arresting cell cycle, p53 (under certain conditions) can inhibit the mTOR pathway. Senescence occurs when p53 fails to inhibit mTOR. Low concentrations of DNA-damaging drugs induce p53 at levels that do not inhibit mTOR, thus causing senescence. In quiescence caused by serum starvation, mTOR is deactivated. This predicts that induction of p53 will not cause senescence in such quiescent cells. Here we tested this prediction. In proliferating normal cells, etoposide caused senescence (cells could not resume proliferation after removal of etoposide). Serum starvation prevented induction of senescence, but not of p53, by etoposide. When etoposide was removed, such cells resumed proliferation upon addition of serum. Also, doxorubicin did not cause senescent morphology in the absence of serum. Re-addition of serum caused mTOR-dependent senescence in the presence of etoposide or doxorubicin. Also, serum-starvation prevented senescent morphology caused by nutlin-3a in MCF-7 and Mel-10 cells. We conclude that induction of p53 does not activate the senescence program in quiescent cells. In cells with induced p53, re-activation of mTOR by serum stimulation causes senescence, as an equivalent of cellular growth.

The biology of lysine acetylation integrates transcriptional programming and metabolism

The biochemical landscape of lysine acetylation has expanded from a small number of proteins in the nucleus to a multitude of proteins in the cytoplasm. Since the first report confirming acetylation of the tumor suppressor protein p53 by a lysine acetyltransferase (KAT), there has been a surge in the identification of new, non-histone targets of KATs. Added to the known substrates of KATs are metabolic enzymes, cytoskeletal proteins, molecular chaperones, ribosomal proteins and nuclear import factors. Emerging studies demonstrate that no fewer than 2000 proteins in any particular cell type may undergo lysine acetylation. As described in this review, our analyses of cellular acetylated proteins using DAVID 6.7 bioinformatics resources have facilitated organization of acetylated proteins into functional clusters integral to cell signaling, the stress response, proteolysis, apoptosis, metabolism, and neuronal development. In addition, these clusters also depict association of acetylated proteins with human diseases. These findings not only support lysine acetylation as a widespread cellular phenomenon, but also impel questions to clarify the underlying molecular and cellular mechanisms governing target selectivity by KATs. Present challenges are to understand the molecular basis for the overlapping roles of KAT-containing co-activators, to differentiate between global versus dynamic acetylation marks, and to elucidate the physiological roles of acetylated proteins in biochemical pathways. In addition to discussing the cellular 'acetylome', a focus of this work is to present the widespread and dynamic nature of lysine acetylation and highlight the nexus that exists between epigenetic-directed transcriptional regulation and metabolism.

Frataxin participates to the hypoxia-induced response in tumors

Defective expression of frataxin is responsible for the degenerative disease Friedreich's ataxia. Frataxin is a protein required for cell survival since complete knockout is lethal. Frataxin protects tumor cells against oxidative stress and apoptosis but also acts as a tumor suppressor. The molecular bases of this apparent paradox are missing. We therefore sought to investigate the pathways through which frataxin enhances stress resistance in tumor cells. We found that frataxin expression is upregulated in several tumor cell lines in response to hypoxic stress, a condition often associated with tumor progression. Moreover, frataxin upregulation in response to hypoxia is dependent on hypoxia-inducible factors expression and modulates the activation of the tumor-suppressor p53. Importantly, we show for the first time that frataxin is in fact increased in human tumors in vivo. These results show that frataxin participates to the hypoxia-induced stress response in tumors, thus implying that modulation of its expression could have a critical role in tumor cell survival and/or progression.

p53 regulates biosynthesis through direct inactivation of glucose-6-phosphate dehydrogenase

Cancer cells consume large quantities of glucose and primarily use glycolysis for ATP production, even in the presence of adequate oxygen. This metabolic signature (aerobic glycolysis or the Warburg effect) enables cancer cells to direct glucose to biosynthesis, supporting their rapid growth and proliferation. However, both causes of the Warburg effect and its connection to biosynthesis are not well understood. Here we show that the tumour suppressor p53, the most frequently mutated gene in human tumours, inhibits the pentose phosphate pathway (PPP). Through the PPP, p53 suppresses glucose consumption, NADPH production and biosynthesis. The p53 protein binds to glucose-6-phosphate dehydrogenase (G6PD), the first and rate-limiting enzyme of the PPP, and prevents the formation of the active dimer. Tumour-associated p53 mutants lack the G6PD-inhibitory activity. Therefore, enhanced PPP glucose flux due to p53 inactivation may increase glucose consumption and direct glucose towards biosynthesis in tumour cells.

Regulation of cancer cell metabolism

Interest in the topic of tumour metabolism has waxed and waned over the past century of cancer research. The early observations of Warburg and his contemporaries established that there are fundamental differences in the central metabolic pathways operating in malignant tissue. However, the initial hypotheses that were based on these observations proved inadequate to explain tumorigenesis, and the oncogene revolution pushed tumour metabolism to the margins of cancer research. In recent years, interest has been renewed as it has become clear that many of the signalling pathways that are affected by genetic mutations and the tumour microenvironment have a profound effect on core metabolism, making this topic once again one of the most intense areas of research in cancer biology.

Deletion of the p53 tumor suppressor gene improves neuromotor function but does not attenuate regional neuronal cell loss following experimental brain trauma in mice

Deletion of the tumor suppressor gene p53 has been shown to improve the outcome in experimental models of focal cerebral ischemia and kainate-induced seizures. To evaluate the potential role of p53 in traumatic brain injury, genetically modified mice lacking a functional p53 gene (p53(-/-), n = 9) and their wild-type littermates (p53(+/+), n = 9) were anesthetized and subjected to controlled cortical impact (CCI) experimental brain trauma. After brain injury, neuromotor function was assessed by using composite neuroscore and rotarod tests. By 7 days posttrauma, p53(-/-) mice exhibited significantly improved neuromotor function, in the composite neuroscore (P = 0.002) as well as in two of three individual tests, when compared with brain-injured p53(+/+) animals. CCI resulted in the formation of a cortical cavity (mean volume = 6.1 mm(3)) 7 days postinjury in p53(+/+) as well as p53(-/-) mice. No difference in lesion volume was detected between the two genotypes (P = 0.95). Although significant cell loss was detected in the ipsilateral hippocampus and thalamus of brain-injured animals, no differences between p53(+/+) and p53(-/-) mice were detected. Although our results suggest that lack of the p53 gene results in augmented recovery of neuromotor function following experimental brain trauma, they do not support a role for p53 acting as a mediator of neuronal death in this context, underscoring the complexity of its role in the injured brain.

Guarding the 'translation apparatus': defective ribosome biogenesis and the p53 signaling pathway

Ribosomes, the molecular factories that carry out protein synthesis, are essential for every living cell. Ribosome biogenesis, the process of ribosome synthesis, is highly complex and energy consuming. Over the last decade, many exciting and novel findings have linked various aspects of ribosome biogenesis to cell growth and cell cycle control. Defects in ribosome biogenesis have also been linked to human diseases. It is now clear that disruption of ribosome biogenesis causes nucleolar stress that triggers a p53 signaling pathway, thus providing cells with a surveillance mechanism for monitoring ribosomal integrity. Although the exact mechanisms of p53 induction in response to nucleolar stress are still unknown, several ribosomal proteins have been identified as key players in this ribosome-p53 signaling pathway. Recent studies of human ribosomal pathologies in a variety of animal models have also highlighted the role of this pathway in the pathophysiology of these diseases. However, it remains to be understood why the effect of ribosomal malfunction is not a universal response in all cell types but is restricted to particular tissues, causing the specific phenotypes seen in ribosomal diseases. A challenge for future studies will be to identify additional players in this signaling pathway and to elucidate the underlying molecular mechanisms that link defective ribosome synthesis to p53.

Basal cell carcinomas arise from hair follicle stem cells in Ptch1(+/-) mice

Basal cell carcinomas (BCCs) are hedgehog-driven tumors that resemble follicular and interfollicular epidermal basal keratinocytes and hence long have been thought to arise from these cells. However, the actual cell of origin is unknown. Using cell fate tracking of X-ray induced BCCs in Ptch1(+/-) mice, we found their essentially exclusive origin to be keratin 15-expressing stem cells of the follicular bulge. However, conditional loss of p53 not only enhanced BCC carcinogenesis from the bulge but also produced BCCs from the interfollicular epidermis, at least in part by enhancing Smo expression. This latter finding is consistent with the lack of visible tumors on ears and tail, sites lacking Smo expression, in Ptch1(+/-) mice.

Autophagy as a therapeutic target in cancer

Autophagy is a self-catabolic process that maintains intracellular homeostasis and prolongs cell survival under stress via lysosomal degradation of cytoplasmic constituents and recycling of amino acids and energy. Autophagy is intricately involved in many aspects of human health and disease, including cancer. Autophagy is a double-edged sword in tumorigenesis, acting both as a tumor suppressor and a protector of cancer cell survival, and elucidation of its exact role at different stages of cancer progression and in treatment responsiveness is a complex and challenging task. Better understanding of autophagy regulation and its impact on treatment outcome will potentially allow us to identify novel therapeutic targets in cancer. In this review, we summarize current knowledge on the regulation and dual function of autophagy in tumorigenesis, as well as ongoing efforts in modulating autophagy for cancer treatment and prevention. This is a very exciting and highly promising area of cancer research, as pharmacologic modulation of autophagy appears to augment the efficacy of currently available anticancer regimens and opens the way to the development of new combinatorial therapeutic strategies that will hopefully contribute to cancer eradication.

Classification of breast cancer precursors through exhaled breath

Certain benign breast diseases are considered to be precursors of invasive breast cancer. Currently available techniques for diagnosing benign breast conditions lack accuracy. The purpose of this study was to deliver a proof-of-concept for a novel method that is based on breath testing to identify breast cancer precursors. Within this context, the authors explored the possibility of using exhaled alveolar breath to identify and distinguish between benign breast conditions, malignant lesions, and healthy states, using a small-scale, case-controlled, cross-sectional clinical trial. Breath samples were collected from 36 volunteers and were analyzed using a tailor-made nanoscale artificial NOSE (NA-NOSE). The NA-NOSE signals were analyzed using two independent methods: (i) principal component analysis, ANOVA and Student's t-test and (ii) support vector machine analysis to detect statistically significant differences between the sub-populations. The NA-NOSE could distinguish between all studied test populations. Breath testing with a NA-NOSE holds future potential as a cost-effective, fast, and reliable diagnostic test for breast cancer risk factors and precursors, with possible future potential as screening method.

Regulation of the mTOR complex 1 pathway by nutrients, growth factors, and stress

The large serine/threonine protein kinase mTOR regulates cellular and organismal homeostasis by coordinating anabolic and catabolic processes with nutrient, energy, and oxygen availability and growth factor signaling. Cells and organisms experience a wide variety of insults that perturb the homeostatic systems governed by mTOR and therefore require appropriate stress responses to allow cells to continue to function. Stress can manifest from an excess or lack of upstream signals or as a result of genetic perturbations in upstream effectors of the pathway. mTOR nucleates two large protein complexes that are important nodes in the pathways that help buffer cells from stresses, and are implicated in the progression of stress-associated phenotypes and diseases, such as aging, tumorigenesis, and diabetes. This review focuses on the key components of the mTOR complex 1 pathway and on how various stresses impinge upon them.

MicroRNA regulation of core apoptosis pathways in cancer

Recent research has demonstrated that microRNAs (miRNAs) are key regulators of many cell processes often deregulated in cancer, including apoptosis. Indeed, it is becoming clear that many miRNAs are anti-apoptotic and mediate this effect by targeting pro-apoptotic mRNAs or positive regulators of pro-apoptotic mRNAs. Conversely, many pro-apoptotic miRNAs target anti-apoptotic mRNAs or their positive regulators. We have reviewed the current knowledge in this area including evidence of miRNA involvement in cancer drug resistance.

Phospho-ΔNp63α/Rpn13-dependent regulation of LKB1 degradation modulates autophagy in cancer cells

Oxidative stress was shown to promote the translocation of Ataxia-telangiectasia mutated (ATM) to cytoplasm and trigger the LKB1-AMPK-tuberin pathway leading to a down-regulation of mTOR and subsequently inducing the programmed cell death II (autophagy). Cisplatin was previously found to induce the ATM-dependent phosphorylation of ΔNp63α in squamous cell carcinoma (SCC) cells. In this study, phosphorylated (p)-ΔNp63α was shown to bind the ATM promoter, to increase the ATM promoter activity and to enhance the ATM cytoplasmic accumulation. P-ΔNp63α protein was further shown to interact with the Rpn13 protein leading to a proteasome-dependent degradation of p-ΔNp63α and thereby protecting LKB1 from the degradation. In SCC cells (with an altered ability to support the ATM-dependent ΔNp63α phosphorylation), the non-phosphorylated ΔNp63α protein failed to form protein complexes with the Rpn13 protein and thereby allowing the latter to bind and target LKB1 into a proteasome-dependent degradation pathway thereby modulating a cisplatin-induced autophagy. We thus suggest that SCC cells sensitive to cisplatin-induced cell death are likely to display a greater ratio of p-ΔNp63α/non-phosphorylated ΔNp63α than cells with the innate resistant/impaired response to a cisplatin-induced cell death. Our data also suggest that the choice made by Rpn13 between p-ΔNp63α or LKB1 to be targeted for degradation is critical for cell death decision made by cancer cells in response to chemotherapy.

Short-term magnesium deficiency upregulates sphingomyelin synthase and p53 in cardiovascular tissues and cells: relevance to the de novo synthesis of ceramide

The present study tested the hypotheses that 1) short-term dietary deficiency of magnesium (21 days) in rats would result in the upregulation of sphingomyelin synthase (SMS) and p53 in cardiac and vascular (aortic) smooth muscles, 2) low levels of Mg(2+) added to drinking water would either prevent or greatly reduce the upregulation of both SMS and p53, 3) exposure of primary cultured vascular smooth muscle cells (VSMCs) to low extracellular Mg(2+) concentration ([Mg(2)](o)) would lead to the de novo synthesis of ceramide, 4) inhibition of either SMS or p53 in primary culture VSMCs exposed to low [Mg(2+)](o) would lead to reductions in the levels of de novo ceramide synthesis, and 5) inhibition of sphingomyelin palmitoyl-CoA transferase (SPT) or ceramide synthase (CS) in primary cultured VSMCs exposed to low [Mg(2+)](o) would lead to a reduction in the levels of de novo ceramide synthesis. The data indicated that short-term magnesium deficiency (10% normal dietary intake) resulted in the upregulation of SMS and p53 in both ventricular and aortic smooth muscles; even very low levels of water-borne Mg(2+) (e.g., 15 mg·l(-1)·day(-1)) either prevented or ameliorated the upregulation in SMS and p53. Our experiments also showed that VSMCs exposed to low [Mg(2+)](o) resulted in the de novo synthesis of ceramide; the lower the [Mg(2+)](o), the greater the synthesis of ceramide. In addition, the data indicated that inhibition of either SMS, p53, SPT, or CS in VSMCs exposed to low [Mg(2+)](o) resulted in marked reductions in the de novo synthesis of ceramide.

Negative regulation of autophagy

Autophagy is an evolutionarily conserved catabolic process that involves the invagination and degradation of cytoplasmic components through an autophagosomelysosome track. Autophagy functions as a quality control of cellular milieu and is implicated in a wide variety of pathological conditions. However, excessive or imbalanced autophagic flux may also be associated with cellular toxicity and may potentially contribute to the development of pathological conditions. Just as all membrane trafficking systems need to constantly strike a balance in their level of activation and inhibition to ensure proper spatial and temporal delivery of their cargo, autophagy must also be tightly regulated. Here, we provide an overview of the current knowledge regarding the negative regulation of mammalian autophagy in an effort to understand its physiological relevance and potential clinical importance.

Ribosomal protein L11 mutation in zebrafish leads to haematopoietic and metabolic defects

Mutations in ribosomal proteins are associated with a congenital syndrome, Diamond-Blackfan anaemia (DBA), manifested by red blood cell aplasia, developmental abnormalities and increased risk of malignancy. Recent studies suggest the involvement of p53 activation in DBA. However, which pathways are involved and how they contribute to the DBA phenotype remains unknown. Here we show that a zebrafish mutant for the rpl11 gene had defects both in the development of haematopoietic stem cells (HSCs) and maintenance of erythroid cells. The molecular signature of the mutant included upregulation of p53 target genes and global changes in metabolism. The changes in several pathways may affect haematopoiesis including upregulation of pro-apoptotic and cell cycle arrest genes, suppression of glycolysis, downregulation of biosynthesis and dysregulation of cytoskeleton. Each of these pathways has been individually implicated in haematological diseases. Inhibition of p53 partially rescued haematopoiesis in the mutant. Altogether, we propose that the unique phenotype of DBA is a sum of several abnormally regulated molecular pathways, mediated by the p53 protein family and p53-independent, which have synergistic impact on haematological and other cellular pathways affected in DBA. Our results provide new insights into the pathogenesis of DBA and point to the potential avenues for therapeutic intervention.

Correlation of high 18F-FDG uptake to clinical, pathological and biological prognostic factors in breast cancer

PURPOSE

The aim of this study was to determine the impact of the main clinicopathological and biological prognostic factors of breast cancer on (18)F-fluorodeoxyglucose (FDG) uptake. Only women with tumours larger than 20 mm (T2-T4) were included in order to minimize bias of partial volume effect.

METHODS

In this prospective study, 132 consecutive women received FDG PET/CT imaging before starting neoadjuvant chemotherapy. Maximum standardized uptake values (SUV(max)) were compared to tumour characteristics as assessed on core biopsy.

RESULTS

There was no influence of T and N stage on SUV. Invasive ductal carcinoma showed higher SUV than lobular carcinoma. However, the highest uptake was found for metaplastic tumours, representing 5% of patients in this series. Several biological features usually considered as bad prognostic factors were associated with an increase in FDG uptake: the median of SUV(max) was 9.7 for grade 3 tumours vs 4.8 for the lower grades (p < 0.0001); negativity for oestrogen receptors (ER) was associated with higher SUV (ER+ SUV = 5.5; ER- SUV = 7.6; p = 0.003); triple-negative tumours (oestrogen and progesterone receptor negative, no overexpression of c-erbB-2) had an SUV of 9.2 vs 5.8 for all others (p = 0005); p53 mutated tumours also had significantly higher SUV (7.8 vs 5.0; p < 0.0001). Overexpression of c-erbB-2 had no effect on the SUV value.

CONCLUSION

Knowledge of the factors influencing uptake is important when interpreting FDG PET/CT scans. Also, findings that FDG uptake is highest in those patients with poor prognostic features (high grade, hormone receptor negativity, triple negativity, metaplastic tumours) is helpful to determine who are the best candidates for baseline staging.

Translating p53 into the clinic

Mutations in the TP53 gene are a feature of 50% of all reported cancer cases. In the other 50% of cases, the TP53 gene itself is not mutated but the p53 pathway is often partially inactivated. Cancer therapies that target specific mutant genes are proving to be highly active and trials assessing agents that exploit the p53 system are ongoing. Many trials are aimed at stratifying patients on the basis of TP53 status. In another approach, TP53 is delivered as a gene therapy; this is the only currently approved p53-based treatment. The p53 protein is overexpressed in many cancers and p53-based vaccines are undergoing trials. Processed cell-surface p53 is being exploited as a target for protein-drug conjugates, and small-molecule drugs that inhibit the activity of MDM2, the E3 ligase that regulates p53 levels, have been developed by several companies. The first MDM2 inhibitors are being trialed in both hematologic and solid malignancies. Finally, the first agent found to restore the active function of mutant TP53 has just entered the clinic. Here we discuss the basis of these trials and the future of p53-based therapy.

Sugar-free approaches to cancer cell killing

Tumors show an increased rate of glucose uptake and utilization. For this reason, glucose analogs are used to visualize tumors by the positron emission tomography technique, and inhibitors of glycolytic metabolism are being tested in clinical trials. Upregulation of glycolysis confers several advantages to tumor cells: it promotes tumor growth and has also been shown to interfere with cell death at multiple levels. Enforcement of glycolysis inhibits apoptosis induced by cytokine deprivation. Conversely, antiglycolytic agents enhance cell death induced by radio- and chemotherapy. Synergistic effects are likely due to regulation of the apoptotic machinery, as glucose regulates activation and levels of proapoptotic BH3-only proteins such as Bim, Bad, Puma and Noxa, as well as the antiapoptotic Bcl-2 family of proteins. Moreover, inhibition of glucose metabolism sensitizes cells to death ligands. Glucose deprivation and antiglycolytic drugs induce tumor cell death, which can proceed through necrosis or through mitochondrial or caspase-8-mediated apoptosis. We will discuss how oncogenic pathways involved in metabolic stress signaling, such as p53, AMPK (adenosine monophosphate-activated protein kinase) and Akt/mTOR (mammalian target of rapamycin), influence sensitivity to inhibition of glucose metabolism. Finally, we will analyze the rationale for the use of antiglycolytic inhibitors in the clinic, either as single agents or as a part of combination therapies.

NFκB/p53 crosstalk-a promising new therapeutic target

The transcription factors p53 and NFκB determine cellular fate and are involved in the pathogenesis of most-if not all-cancers. The crosstalk between these transcription factors becomes increasingly appreciated as an important mechanism operative during all stages of tumorigenesis, metastasis, and immunological surveillance. In this review, we summarize molecular mechanisms regulating cross-signaling between p53 and NFκB proteins and how dysregulated interactions between p53 and NFκB family members contribute to oncogenesis. We furthermore analyze how such signaling modules represent targets for the design of novel intervention strategies using established compounds and powerful combination therapies.

Oxygenomics in environmental stress

Environmental stressors such as chemicals and physical agents induce various oxidative stresses and affect human health. To elucidate their underlying mechanisms, etiology and risk, analyses of gene expression signatures in environmental stress-induced human diseases, including neuronal disorders, cancer and diabetes, are crucially important. Recent studies have clarified oxidative stress-induced signaling pathways in human and experimental animals. These pathways are classifiable into several categories: reactive oxygen species (ROS) metabolism and antioxidant defenses, p53 pathway signaling, nitric oxide (NO) signaling pathway, hypoxia signaling, transforming growth factor (TGF)-beta bone morphogenetic protein (BMP) signaling, tumor necrosis factor (TNF) ligand-receptor signaling, and mitochondrial function. This review describes the gene expression signatures through which environmental stressors induce oxidative stress and regulate signal transduction pathways in rodent and human tissues.