p53: at the crossroad between cancer and ageing

The landscape of aging

Aging is characterized by a progressive deterioration of physiological integrity, leading to impaired functional ability and ultimately increased susceptibility to death. It is a major risk factor for chronic human diseases, including cardiovascular disease, diabetes, neurological degeneration, and cancer. Therefore, the growing emphasis on “healthy aging” raises a series of important questions in life and social sciences. In recent years, there has been unprecedented progress in aging research, particularly the discovery that the rate of aging is at least partly controlled by evolutionarily conserved genetic pathways and biological processes. In an attempt to bring full-fledged understanding to both the aging process and age-associated diseases, we review the descriptive, conceptual, and interventive aspects of the landscape of aging composed of a number of layers at the cellular, tissue, organ, organ system, and organismal levels.

Sphingosine 1-Phosphate Receptor 5 (S1P5) Deficiency Promotes Proliferation and Immortalization of Mouse Embryonic Fibroblasts

Simple Summary

Sphingosine 1-phosphate (S1P) is a lipid metabolite involved in cell proliferation, survival or migration. S1P is a ligand for five high-affinity G protein-coupled receptors (S1P1-5), which differ in their tissue distribution, and the specific effects of S1P depend on the suite of S1P receptor subtypes expressed. To date, information regarding the role of S1P5 in cell proliferation is limited and ambiguous. Our results suggest that, unlike other S1P receptors, the S1P5 receptor has an anti-proliferative function. We found that S1P5 deficiency promotes cell immortalization and proliferation by controlling the spatial activation of ERK.

Abstract

Sphingosine 1-phosphate (S1P), a bioactive lipid, interacts with five widely expressed G protein-coupled receptors (S1P1-5), regulating a variety of downstream signaling pathways with overlapping but also opposing functions. To date, data regarding the role of S1P5 in cell proliferation are ambiguous, and its role in controlling the growth of untransformed cells remains to be fully elucidated. In this study, we examined the effects of S1P5 deficiency on mouse embryonic fibroblasts (MEFs). Our results indicate that lack of S1P5 expression profoundly affects cell morphology and proliferation. First, S1P5 deficiency reduces cellular senescence and promotes MEF immortalization. Second, it decreases cell size and leads to cell elongation, which is accompanied by decreased cell spreading and migration. Third, it increases proliferation rate, a phenotype rescued by the reintroduction of exogenous S1P5. Mechanistically, S1P5 promotes the activation of FAK, controlling cell spreading and adhesion while the anti-proliferative function of the S1P/S1P5 signaling is associated with reduced nuclear accumulation of activated ERK. Our results suggest that S1P5 opposes the growth-promoting function of S1P1-3 through spatial control of ERK activation and provides new insights into the anti-proliferative function of S1P5.

Transcriptome analysis of immune response against Siniperca chuatsi rhabdovirus infection in mandarin fish Siniperca chuatsi

As one of the piscine rhabdoviruses, Siniperca chuatsi rhabdovirus (SCRV) has caused considerable losses to mandarin fish aquaculture industry. RNA-seq, as efficient transcriptome research method, has been widely used to study the immune response of fish to pathogens. This study reported the effect of SCRV infection at 0, 24 and 60 hr on S. chuatsi at the transcriptome level. A total of 61,527 unigenes with high quality were obtained, and 3,095, 1,854 and 227 differentially expressed genes (DEGs) were labelled between the Sc24 and Sc0 groups, the Sc60 and Sc0 groups and the Sc60 and Sc24 groups, respectively. Genes involved in innate and adaptive immunity were highlighted. In Gene Ontology analysis, the DEGs that participated in immune response, innate immune response and the regulation of apoptotic process were identified as enriched classes. Kyoto Encyclopedia of Genes and Genomes pathway results indicated that most DEGs caused by SCRV infection were identified in the immune system (retinoic acid-inducible gene-I-like receptor/Toll-like receptor/nucleotide-binding oligomerization domain-like receptor/C-type lectin receptor signalling pathway), cellular processes, cell growth and death (p53 signalling pathway, cellular senescence, apoptosis and phagosome), and metabolism. Quantitative real-time PCR was used to further verify the expression levels of 15 immune-related DEGs. The transcriptome database obtained in this study provided further in-depth insight into the immune response of S. chuatsi against SCRV.

PLA2R1 promotes DNA damage and inhibits spontaneous tumor formation during aging

Although aging is a major risk factor for most types of cancers, it is barely studied in this context. The transmembrane protein PLA2R1 (phospholipase A2 receptor) promotes cellular senescence, which can inhibit oncogene-induced tumor initiation. Functions and mechanisms of action of PLA2R1 during aging are largely unknown. In this study, we observed that old Pla2r1 knockout mice were more prone to spontaneously develop a wide spectrum of tumors compared to control littermates. Consistently, these knockout mice displayed increased Parp1, a master regulator of DNA damage repair, and decreased DNA damage, correlating with large human dataset analysis. Forced PLA2R1 expression in normal human cells decreased PARP1 expression, induced DNA damage and subsequent senescence, while the constitutive expression of PARP1 rescued cells from these PLA2R1-induced effects. Mechanistically, PARP1 expression is repressed by a ROS (reactive oxygen species)-Rb-dependent mechanism upon PLA2R1 expression. In conclusion, our results suggest that PLA2R1 suppresses aging-induced tumors by repressing PARP1, via a ROS-Rb signaling axis, and inducing DNA damage and its tumor suppressive responses.

HMGB1 modulates the balance between senescence and apoptosis in response to genotoxic stress

High mobility group box-1 (HMGB1) is involved in various diseases and is associated with the resistance of many types of human cancers to chemotherapy; however, its role in cancer metastasis remains unexplored. This study examined the HMGB1 status of both highly and poorly metastatic cancer cells in response to genotoxic stress. The weakly and highly metastatic mouse melanoma cell lines (B16 vs. B16-F10), human melanoma cell lines (SK-MEL-28 vs. SK-MEL-24), colon cancer cell lines (DLD-1 vs. LS174T), and wild-type (WT) vs. HMGB1 knockout (KO) mouse embryonic fibroblasts (MEFs) were treated with doxorubicin (Dox) and camptothecin (CPT), and then cellular morphology, senescence-associated β-galactosidase staining, lactate dehydrogenase release, and caspase-3 activation were used to assess cell fate. To investigate the role of HMGB1 in p21 expression, HMGB1 and p21 expressions were examined by Western blotting, and the HMGB1-mediated p21 promoter luciferase assay was performed after small interfering RNA or overexpression of HMGB1 prior to Dox treatment. Although highly metastatic mouse melanoma B16-F10 cells preferred senescence, with persistent HMGB1 expression, poorly metastatic B16 cells entered apoptosis, with decreasing HMGB1 levels via cleavage under Dox treatment. Similarly, more metastatic human melanoma SK-MEL-24 and human colon cancer LS174T cells underwent senescence, whereas fewer metastatic melanoma SK-MEL-28 and DLD-1 cells exhibited apoptosis under Dox stimulation. In senescent B16-F10, SK-MEL-24, and LS174T cells treated with Dox, p21 levels were increased by persistent HMGB1 expression. Furthermore, HMGB1 depletion caused a senescence-apoptosis shift with p21 down-regulation in B16-F10 cells, and HMGB1 overexpression switched from apoptosis to senescence concomitantly with increased p21 expression in B16 cells after Dox treatment. The same effects were observed in both cell pairs of mouse melanoma and human colon cancer cells treated with CPT, another genotoxic stressor. Indeed, although WT MEF entered senescence accompanied by p21 increase, HMGB1 KO underwent apoptosis with p21 decrease by Dox treatment. In our cell model system, we demonstrated that highly metastatic cancer cells preferentially enter senescence, whereas apoptosis predominates in weakly metastatic cancer cells under genotoxic stress, which depends on the presence or absence of HMGB1, suggesting that the HMGB1-p21 axis is required for genotoxic stress-induced senescence. These findings suggest that HMGB1 modulation of cancers with different metastatic status could be a strategy for selectively enforcing tumor suppression.-Lee, J.-J., Park, I. H., Rhee, W. J., Kim, H. S., Shin, J.-S. HMGB1 modulates the balance between senescence and apoptosis in response to genotoxic stress.

Differences of immune disorders between Alzheimer's disease and breast cancer based on transcriptional regulation

Although chronic inflammation and immune disorders are of great importance to the pathogenesis of both dementia and cancer, the pathophysiological mechanisms are not clearly understood. In recent years, growing epidemiological evidence and meta-analysis data suggest an inverse association between Alzheimer’s disease (AD), which is the most common form of dementia, and cancer. It has been revealed that some common genes and biological processes play opposite roles in AD and cancer; however, the biological immune mechanism for the inverse association is not clearly defined. An unsupervised matrix decomposition two-stage bioinformatics procedure was adopted to investigate the opposite behaviors of the immune response in AD and breast cancer (BC) and to discover the underlying transcriptional regulatory mechanisms. Fast independent component analysis (FastICA) was applied to extract significant genes from AD and BC microarray gene expression data. Based on the extracted data, the shared transcription factors (TFs) from AD and BC were captured. Second, the network component analysis (NCA) algorithm in this study was presented to quantitatively deduce the TF activities and regulatory influences because quantitative dynamic regulatory information for TFs is not available via microarray techniques. Based on the NCA results and reconstructed transcriptional regulatory networks, inverse regulatory processes and some known innate immune responses were described in detail. Many of the shared TFs and their regulatory processes were found to be closely related to the adaptive immune response from dramatically different directions and to play crucial roles in both AD and BC pathogenesis. From the above findings, the opposing cellular behaviors demonstrate an invaluable opportunity to gain insights into the pathogenesis of these two types of diseases and to aid in developing new treatments.

p16INK4A enhances the transcriptional and the apoptotic functions of p53 through DNA-dependent interaction

p16^INK4A and p53 are two important tumor suppressor proteins that play essential roles during cell proliferation and aging through regulating the expression of several genes. Here, we report that p16^INK4A and p53 co-regulate a plethora of transcripts. Furthermore, both proteins colocalize in the nucleus of human primary skin fibroblasts and breast luminal cells, and form a heteromer whose level increases in response to genotoxic stress as well as aging of human fibroblasts and various mouse organs. CDK4 is also present in this heteromeric complex, which is formed only in the presence of DNA both in vitro using pure recombinant proteins and in vivo. We have also shown that p16^INK4A enhances the binding efficiency of p53 to its cognate sequence presents in the CDKN1A promoter in vitro, and both proteins are present at the promoters of CDKN1A and BAX in vivo. Importantly, the fourth ankyrin repeat of p16^INK4A and the C-terminal domain of p53 were necessary for the physical association between these two proteins. The physiologic importance of this association was revealed by the inability of cancer-associated p16^INK4A mutants to interact with p53 and to transactivate the expression of its major targets CDKN1A and BAX in the p16-defective U2OS cells expressing either wild-type or mutated p16^INK4A . Furthermore, the association between p16^INK4A and p53 was capital for their nuclear colocalization, the X-ray-dependent induction of p21 and Bax proteins as well as the induction of apoptosis in various types of cells. Together, these results show DNA-dependent physical interaction between p16^INK4A and p53.

Rb and p53 Liver Functions Are Essential for Xenobiotic Metabolism and Tumor Suppression

The tumor suppressors Retinoblastoma (Rb) and p53 are frequently inactivated in liver diseases, such as hepatocellular carcinomas (HCC) or infections with Hepatitis B or C viruses. Here, we discovered a novel role for Rb and p53 in xenobiotic metabolism, which represent a key function of the liver for metabolizing therapeutic drugs or toxins. We demonstrate that Rb and p53 cooperate to metabolize the xenobiotic 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). DDC is metabolized mainly by cytochrome P450 (Cyp)3a enzymes resulting in inhibition of heme synthesis and accumulation of protoporphyrin, an intermediate of heme pathway. Protoporphyrin accumulation causes bile injury and ductular reaction. We show that loss of Rb and p53 resulted in reduced Cyp3a expression decreased accumulation of protoporphyrin and consequently less ductular reaction in livers of mice fed with DDC for 3 weeks. These findings provide strong evidence that synergistic functions of Rb and p53 are essential for metabolism of DDC. Because Rb and p53 functions are frequently disabled in liver diseases, our results suggest that liver patients might have altered ability to remove toxins or properly metabolize therapeutic drugs. Strikingly the reduced biliary injury towards the oxidative stress inducer DCC was accompanied by enhanced hepatocellular injury and formation of HCCs in Rb and p53 deficient livers. The increase in hepatocellular injury might be related to reduce protoporphyrin accumulation, because protoporphrin is well known for its anti-oxidative activity. Furthermore our results indicate that Rb and p53 not only function as tumor suppressors in response to carcinogenic injury, but also in response to non-carcinogenic injury such as DDC.

Anti-tumor effects and cellular mechanisms of resveratrol

Resveratrol (3, 5, 4'-trihydroxystilbene) is a phytoalexin contained in a variety of plants, such as grapes, berries and especially in the dried roots of Polygonum cuspidatum Sieb. et Zucc. It has been shown to exhibit anti-oxidative and anti-inflammation activity, and to reverse the effects of aging. Its ability to suppress cell proliferation, induce apoptosis and suppress the metastasis and invasion in a number of cell lines has prompted a large interest from people for its use as an anti-tumor component. In this review, evidence of resveratrol's anti-tumor effects and molecular mechanisms are recapitulated. First, we present the anti-apoptosis, anti-invasion/metastasis and anti-inflammation effect of resveratrol; second, the main signaling pathways involved in these activities are described and summarized with the studies of different tumors involved. Resveratrol not only induces apoptosis of tumor cells through intrinsic/extrinsic pathways and cell cycle arrest, but also inhibits the invasion and metastasis abilities of tumors via modulating collagen degradation-related molecular targets. Altogether, the present findings suggest the anti-tumor potential of resveratrol against various types of cancers.

Long Term Exposure to Polyphenols of Artichoke (Cynara scolymus L.) Exerts Induction of Senescence Driven Growth Arrest in the MDA-MB231 Human Breast Cancer Cell Line

Polyphenolic extracts from the edible part of artichoke (Cynara scolymus L.) have been shown to be potential chemopreventive and anticancer dietary compounds. High doses of polyphenolic extracts (AEs) induce apoptosis and decrease the invasive potential of the human breast cancer cell line, MDA-MB231. However, the molecular mechanism underlying AEs antiproliferative effects is not completely understood. We demonstrate that chronic and low doses of AEs treatment at sublethal concentrations suppress human breast cancer cell growth via a caspases-independent mechanism. Furthermore, AEs exposure induces a significant increase of senescence-associated β-galactosidase (SA-β-gal) staining and upregulation of tumour suppressor genes, p16^INK4a and p21^Cip1/Waf1 in MDA-MB231 cells. AEs treatment leads to epigenetic alterations in cancer cells, modulating DNA hypomethylation and lysine acetylation levels in total proteins. Cell growth arrest correlates with increased reactive oxygen species (ROS) production in AEs treated breast cancer cells. Inhibition of ROS generation by N-acetylcysteine (NAC) attenuates the antiproliferative effect. These findings demonstrate that chronic AEs treatment inhibits breast cancer cell growth via the induction of premature senescence through epigenetic and ROS-mediated mechanisms. Our results suggest that artichoke polyphenols could be a promising dietary tool either in cancer chemoprevention or/and in cancer treatment as a nonconventional, adjuvant therapy.

BIS targeting induces cellular senescence through the regulation of 14-3-3 zeta/STAT3/SKP2/p27 in glioblastoma cells

Cellular senescence is an important mechanism for preventing tumor progression. The elevated expression of Bcl-2-interacting cell death suppressor (BIS), an anti-apoptotic and anti-stress protein, often correlates with poor prognosis in several cancers including glioblastoma; however, the role of BIS in the regulation of senescence has not been well defined. Here, we describe for the first time that the depletion of BIS induces G1 arrest and cellular senescence through the accumulation of p27 that is independent of p53, p21 or p16. The increase in p27 expression in BIS-depleted cells was attributable to an impairment of the ubiquitin-mediated degradation of p27, which was caused by a decrease in S-phase kinase-associated protein 2 (SKP2) at the transcriptional level. As an underlying molecular mechanism, we demonstrate that the loss of activity of signal transducer and activator of transcription 3 (STAT3) was specifically linked to the suppression of SKP2 expression. Despite a reduction in phospho-STAT3 levels, total STAT3 levels were unexpectedly increased by BIS depletion, specifically in the insoluble fraction. Our results show that 14-3-3ζ expression is decreased by BIS knockdown and that 14-3-3ζ depletion per se significantly induced senescence phenotypes. In addition, the ectopic expression of 14-3-3ζ blocked senescence caused by BIS depletion, which was paralleled with a decrease in insoluble STAT3 in A172 glioblastoma cells. These findings indicate that the impairment of the protein quality control conferred by BIS and/or 14-3-3ζ is critical for BIS depletion-induced senescence. Moreover, BIS knockdown also induced senescence along with an accumulation of total STAT3 and p27 in several different cell types as well as embryonic fibroblasts derived from Bis-knock out mice with/without variations in 14-3-3ζ levels. Therefore, our findings suggest that a downregulation of BIS expression could serve as a potential strategy for restricting tumor progression via an induction of senescence through the regulation of STAT3/SKP2/p27 pathway.

Regulation of mitochondrial apoptosis by Pin1 in cancer and neurodegeneration

Mitochondria are sensitive and efficient organelles that regulate essential biological processes including: energy metabolism, decoding and transduction of intracellular signals, and balance between cell death and survival. Of note, dysfunctions in mitochondrial physiology are a general hallmark of cancer cells, leading to transformation-related features such as altered cellular metabolism, survival under stress conditions and reduced apoptotic response to chemotherapy. Mitochondrial apoptosis is a finely regulated process that derives from activation of multiple signaling networks. A crucial biochemical requirement for transducing pro-apoptotic stimuli is represented by kinase-dependent phosphorylation cascades. In this context a pivotal role is played by the prolyl-isomerase Pin1, which translates Ser/Thr-Pro phosphorylation into conformational changes able to modify the activities of its substrates. In this review we will discuss the impact of Pin1 in regulating various aspects of apoptosis in different biological contexts with particular emphasis on cancer and neurodegenerative diseases.

Collaborator of ARF (CARF) regulates proliferative fate of human cells by dose-dependent regulation of DNA damage signaling

Collaborator of ARF (CARF) has been shown to directly bind to and regulate p53, a central protein that controls tumor suppression via cellular senescence and apoptosis. However, the cellular functions of CARF and the mechanisms governing its effect on senescence, apoptosis, or proliferation are still unknown. Our previous studies have shown that (i) CARF is up-regulated during replicative and stress-induced senescence, and its exogenous overexpression caused senescence-like growth arrest of cells, and (ii) suppression of CARF induces aneuploidy, DNA damage, and mitotic catastrophe, resulting in apoptosis via the ATR/CHK1 pathway. In the present study, we dissected the cellular role of CARF by investigating the molecular pathways triggered by its overexpression in vitro and in vivo. We found that the dosage of CARF is a critical factor in determining the proliferation potential of cancer cells. Most surprisingly, although a moderate level of CARF overexpression induced senescence, a very high level of CARF resulted in increased cell proliferation. We demonstrate that the level of CARF is crucial for DNA damage and checkpoint response of cells through ATM/CHK1/CHK2, p53, and ERK pathways that in turn determine the proliferative fate of cancer cells toward growth arrest or proproliferative and malignant phenotypes. To the best of our knowledge, this is the first report that demonstrates the capability of a fundamental protein, CARF, in controlling cell proliferation in two opposite directions and hence may play a key role in tumor biology and cancer therapeutics.

Resveratrol inhibits the growth of gastric cancer by inducing G1 phase arrest and senescence in a Sirt1-dependent manner

Resveratrol, a naturally occurring polyphenolic compound, has been reported to exert anticancer activity by affecting diverse molecular targets. In this study, we examined the effects and the underlying mechanisms of resveratrol on gastric cancer. We found that resveratrol inhibited the proliferation of gastric cancer cells in a dose-dependent manner. At the concentration of 25 and 50 µM, resveratrol inhibited the cell viability and diminished the clonogenic potential of gastric cancer cells. Resveratrol treatment arrested gastric cancer cells in the G1 phase and led to senescence instead of apoptosis. Regulators of the cell cycle and senescence pathways, including cyclin D1, cyclin-dependent kinase (CDK4 and 6), p21 and p16, were dysregulated by resveratrol treatment. The inhibitory effects of resveratrol on gastric cancer were also verified in vivo using a nude mice xenograft model. Resveratrol (40 mg/kg/d) exerted inhibitory activities on gastric cancer development and significantly decreased the fractions of Ki67-positive cells in the tumor specimens from the nude mice. After resveratrol treatment, the induction of senescence and the changes in the expression of the regulators involved in the cell cycle and senescence pathways were similar to what we observed in vitro. However, the depletion of Sirtuin (Sirt)1 reversed the above-described effects of resveratrol both in vitro and in vivo. Our data suggest that resveratrol inhibits gastric cancer in a Sirt1-dependent manner and provide detailed evidence for the possibility of applying resveratrol in gastric cancer prevention and therapy.

p21 both attenuates and drives senescence and aging in BubR1 progeroid mice

BubR1 insufficiency occurs with natural aging and induces progeroid phenotypes in both mice and children with mosaic variegated aneuploidy syndrome. In response to BubR1 insufficiency, skeletal muscle, fat, and lens tissue engage p19(Arf) to attenuate senescence and age-related deterioration. Here, we address how p19(Arf) exerts this caretaker role using BubR1 progeroid mice lacking p53 or its transcriptional target p21. We show that p53 delays functional decline of skeletal muscle and fat in a p21-dependent fashion by inhibiting p16(Ink4a)-mediated senescence of progenitor cells. Strikingly, p53 also attenuates the formation of cataractous lenses, but here its antiaging effect is p21 independent, as we found p21 to promote senescence of lens epithelial cells and cataract formation. Together, these results demonstrate that p53 counteracts tissue destruction in response to BubR1 insufficiency through diverse mechanisms and uncover a causal link between senescence of the progenitor cell compartment and age-related dysfunction.

Senescence regulation by the p53 protein family

p53, a guardian of the genome, exerts its tumor suppression activity by regulating a large number of downstream targets involved in cell cycle arrest, DNA repair, apoptosis, and cellular senescence. Although p53-mediated apoptosis is able to kill cancer cells, a role for cellular senescence in p53-dependent tumor suppression is becoming clear. Mouse studies showed that activation of p53-induced premature senescence promotes tumor regression in vivo. However, p53-mediated cellular senescence also leads to aging-related phenotypes, such as tissue atrophy, stem cell depletion, and impaired wound healing. In addition, several p53 isoforms and two p53 homologs, p63 and p73, have been shown to play a role in cellular senescence and/or aging. Importantly, p53, p63, and p73 are necessary for the maintenance of adult stem cells. Therefore, understanding the dual role the p53 protein family in cancer and aging is critical to solve cancer and longevity in the future. In this chapter, we provide an overview on how p53, p63, p73, and their isoforms regulate cellular senescence and aging.

Clair D, Butterfield DA. Lack of p53 affects the expression of several brain mitochondrial proteins: insights from proteomics into important pathways regulated by p53

The tumor suppressor protein p53 has been described "as the guardian of the genome" for its crucial role in regulating the transcription of numerous genes responsible for cells cycle arrest, senescence, or apoptosis in response to various stress signals. Although p53 promotes longevity by decreasing the risk of cancer through activation of apoptosis or cellular senescence, several findings suggest that an increase of its activity may have deleterious effects leading to selected aspects of the aging phenotype and neurodegenerative diseases. There is the link between p53 and oxidative stress, the latter a crucial factor that contributes to neurodegenerative processes like Alzheimer disease (AD). In the present study, using a proteomics approach, we analyzed the impact of lack of p53 on the expression of several brain mitochondrial proteins involved in different pathways, and how lack of p53 may present a target to restore neuronal impairments. Our investigation on isolated brain mitochondria from p53((-/-)) mice also provides a better understanding of the p53-mitochondria relationship and its involvement in the development of many diseases.

Pifithrin-μ increases mitochondrial COX biogenesis and MnSOD activity in skeletal muscle of middle-aged mice

We investigated the biogenesis and mitochondrial antioxidant capacity of cytochrome c oxidase (COX) within the skeletal muscle under the treatments of p53 inhibitors (pifithrin, PFTα and PFTμ). Significantly, PFTμ increased mtDNA content and COX biogenesis. These changes coincided with increases in the activity and expression of manganese superoxide dismutase (MnSOD), the key antioxidant enzyme in mitochondria. Conversely, PFTα caused muscle loss, increased oxidative damage and decreased MnSOD activity in intermyofibrillar (IMF) mitochondria. Mechanically, PFTμ inhibited p53 translocation to mitochondria and thus increased its transcriptional activity for expression of synthesis of cytochrome c oxidase 2 (SCO2), an important assembly protein for COX. This study provides in vivo evidence that PFTμ, superior to PFTα, preserves muscle mass and increases mitochondrial antioxidant activity.

Regulation of glucose metabolism by p53: emerging new roles for the tumor suppressor

p53 is well known as the "guardian of the genome" for differentiated and neoplastic cells. p53 induces cell-cycle arrest and cell death after DNA damage and thus contributes to the maintenance of genomic stability. In addition to this tumor suppressor function for pro-oncogenic cells, p53 also plays an important role as the central regulator of stress response by maintaining cellular homeostasis at the molecular and biochemical level. p53 regulates aerobic respiration at the glycolytic and oxidative phosphorylation (OXPHOS) steps via transcriptional regulation of its downstream genes TP53-induced glycolysis regulator (TIGAR) and synthesis of cytochrome c oxidase (SCO2). p53 negatively regulates glycolysis through activation of TIGAR (an inhibitor of the fructose-2,6-bisphosphate). On the contrary p53 positively regulates OXPHOS through upregulation of SCO2, a member of the COX-2 assembly involved in the electron-transport chain. It is interesting to notice that p53 antagonistically regulates the inter-dependent glycolytic and OXPHOS cycles. It is important to understand whether the p53-mediated transcriptional regulation of TIGAR and SCO2 is temporally segregated in cancer cells and what is the relation between these paradoxical regulations of glycolytic pathway with the tumor suppressor activity of p53. In this review we will elucidate the importance of p53-mediated regulation of glycolysis and OXPHOS and its relation with the tumor suppressor function of p53. Further since cellular metabolism shares great relation with the process of aging we will also try and establish the role of p53 in regulation of aging via its transcriptional control of cellular metabolism.

Apoptosis of human fibrosarcoma HT-1080 cells by epigallocatechin-3-O-gallate via induction of p53 and caspases as well as suppression of Bcl-2 and phosphorylated nuclear factor-κB

Animal tumor bioassays and in vitro cell culture systems have demonstrated that epigallocatechin-3-O-gallate (EGCG), the predominant catechin in green tea, possesses anti-proliferative and pro-apoptotic effects on various cancer cells and tumors. In this study, we investigated the effects of EGCG on cell growth, cell cycle progression, and apoptosis in human fibrosarcoma HT-1080 cells. The involvement of p53, Bcl-2, Bax, caspases, and nuclear factor-κB (NF-κB) was examined as a mechanism for the anti-cancer activity of EGCG. Time-dependent intracellular trafficking of EGCG was also determined using fluorescein isothiocyanate (FITC)-conjugated EGCG (FITC-EGCG). Our data show that EGCG treatment caused dose-dependent cell growth inhibition, cell cycle arrest at the G(0)/G(1) phase, and DNA fragmentation suggesting the induction of apoptosis in HT-1080 cells. Immunoblot analysis revealed that the expression of p53, caspase-7 and -9 as well as the ratio of Bax/Bcl-2 protein increased significantly with higher EGCG concentrations and longer incubation times. Moreover, expression of phosphorylated NF-κB/p65 in HT-1080 cells was inhibited by EGCG treatment in a dose-dependent manner, while that of unphosphorylated NF-κB/p65 remained unaffected. Here we also reveal time-dependent internalization of FITC-EGCG into the cytosol of HT-1080 cells and its subsequent nuclear translocation. These results suggest that EGCG may interrupt exogenous signals directed towards genes involved in proliferation and cell cycle progression. Taken together, our data indicate that HT-1080 apoptosis may be mediated through the induction of p53 and caspases by the pro-oxidant activity of internalized EGCG, as well as suppression of Bcl-2 and phosphorylated NF-κB by the antioxidant activity of EGCG.

CD4+ T-lymphocyte telomere length is related to fibrosis stage, clinical outcome and treatment response in chronic hepatitis C virus infection

BACKGROUND & AIMS

Increasing age is associated with impaired immune function and in chronic HCV infection specifically, with progressive fibrosis, liver failure, HCC and impaired responses to antiviral therapy. T-lymphocyte telomere length declines with age. We hypothesised that shorter T-lymphocyte telomere length would be associated with poor clinical outcome in HCV infection.

METHODS

Circulating T-lymphocyte telomere length, an objective measure of immune senescence, was measured by flow-FISH in 135 HCV-RNA-positive, treatment-naïve patients and 41 healthy controls in relation to clinical outcome.

RESULTS

Shorter CD4+CD45RO+ T-lymphocyte telomeres were associated with severe fibrosis (p=0.003), independent of male sex (p=0.04), CMV positivity (p=0.003), previous HBV infection (p=0.007), and age (p=ns) in viraemic patients compared to controls. There were inverse correlations between CD4+CD45RO+ telomere length and fibrosis stage (p<0.001), portal tract inflammatory grade (p=0.035), prothrombin time (p<0.001) and bilirubin (p=0.001). One hundred and twenty-four viraemic individuals were followed prospectively to a composite endpoint of death, hepatic decompensation or HCC. Independent of age, those with shorter CD4+CD45RO+ telomeres were less likely to be complication free after 2-years than those with longer telomeres (86% versus 96%, p=0.009) with an age-adjusted hazard ratio of 0.93 (0.90-0.96). In addition, CD4+CD45RO+ telomere length predicted successful antiviral therapy (p=0.001) independent of other factors.

CONCLUSIONS

CD4+ T-lymphocyte telomere length, independent of age, was related to inflammatory grade, fibrosis stage, laboratory indices of severity, subsequent hepatic decompensation and treatment outcome in patients with chronic HCV infection.

Genetics vs. entropy: longevity factors suppress the NF-kappaB-driven entropic aging process

Molecular studies in model organisms have identified potent longevity genes which can delay the aging process and extend the lifespan. Longevity factors promote stress resistance and cellular survival. It seems that the aging process itself is not genetically programmed but a random process involving the loss of molecular fidelity and subsequent accumulation of waste products. This age-related increase in cellular entropy is compatible with the disposable soma theory of aging. A large array of host defence systems has been linked to the NF-kappaB system which is an ancient signaling pathway specialized to host defence, e.g. functioning in immune system. Emerging evidence demonstrates that the NF-kappaB system is activated during aging. Oxidative stress and DNA damage increase with aging and elicit a sustained activation of the NF-kappaB system which has negative consequences, e.g. chronic inflammatory response, increase in apoptotic resistance, decline in autophagic cleansing, and tissue atrophy, i.e. processes that enhance the aging process. We will discuss the role of NF-kappaB system in the pro-aging signaling and will emphasize that several longevity factors seem to be inhibitors of NF-kappaB signaling and in that way they can suppress the NF-kappaB-driven entropic host defence catastrophe.

Glycolysis links p53 function with NF-kappaB signaling: impact on cancer and aging process

In 1930, Otto Warburg observed that cancer cells produce an increased amount of their energy through aerobic glycolysis and subsequently, this was called the Warburg effect. During aging, the capacity for mitochondrial respiration clearly declines and aerobic glycolysis appears to compensate for the deficiency in oxidative metabolism. This shift in energy production, both in aging and cancer, could protect from the toxic effects of oxygen free radicals whereas increased glycolysis can have adverse effects. It was recently demonstrated that the glycolysis-linked protein O-glycosylation can potentiate the catalytic activity of IKK beta and subsequently trigger NF-kappaB signaling. It seems that tumor suppressor oncogene p53 has an important role in the regulation of protein O-glycosylation since p53 is a potent inhibitor of glycolysis, for example, via TIGAR protein expression. Aging is known to repress the function of p53 and this could enhance glycolysis and NF-kappaB signaling. We will discuss the role of p53 in the regulation of glycolysis-dependent activation of NF-kappaB signaling in both cancer and aging process.

An oxidative analogue of gambogic acid-induced apoptosis of human hepatocellular carcinoma cell line HepG2 is involved in its anticancer activity in vitro

The objective of this study was to investigate the apoptosis-inducing effect of an oxidative analogue of gambogic acid (GA) on the human hepatocellular carcinoma cell line HepG2 and explore the related molecular mechanisms. HepG2 cells were treated with the analogue of GA and the growth inhibition was analysed by MTT assay. The morphological changes in cells were observed under an inverted light microscope and a fluorescence microscope. In addition, both the cell-cycle arrest and the apoptosis rate were detected by flow cytometry. Western blot was used to evaluate the alteration of protein expression. The viability of HepG2 cells was markedly inhibited in a concentration-dependent manner and obvious morphological changes were confirmed, including condensed chromatin and reduced volume. Increased percentage of apoptotic cells was displayed and altered expression level of several apoptosis-associated proteins, P53, Bcl-2, Bax and pro-caspase-3, was obtained. The newly synthesized analogue of GA exhibited potential anticancer activity, induced remarkable apoptosis in HepG2 cells, probably through the intrinsic mitochondrial pathway, and promised to be a new candidate for future cancer therapy.

TP53 Mutations and Pathologic Complete Response to Neoadjuvant Cisplatin and Fluorouracil Chemotherapy in Resected Oral Cavity Squamous Cell Carcinoma

Purpose

To find out if TP53 functional status predicts response to neoadjuvant chemotherapy and thus may be helpful during treatment decision making of oral cavity squamous cell carcinoma (SCC) patients.

Patients and Methods

We analyzed the predictive value of TP53 mutations and their functional status on the basis of the transactivation activity of p53 mutant proteins in 53 pretreatment biopsies of oral cavity SCC patients receiving primary cisplatin and fluorouracil chemotherapy followed by surgery.

Results

The surgical specimens showed that 15 patients (28%) achieved a pathologic complete remission (pCR) at both T and N sites, and 38 patients had residual tumor cells. Among the 53 pretreatment biopsies, 24 (45%) displayed TP53 mutations: 22 single-nucleotide substitutions and two deletions. According to functional status that could be determined only for the 22 substitutions, 21 mutations were nonfunctional and one was partially functional. TP53 mutation was found in four (27%) of 15 patients who achieved a pCR and in 20 (53%) of 38 nonresponder patients; the difference was not statistically significant (P = .12). In contrast, two (14%) of 14 cases with pCR carried a nonfunctional TP53 mutation, a frequency significantly less than that found in the nonresponders (19 [51%] of 37; P = .02). TP53 mutation predicted pCR in four (17%) of 24 patients and a nonfunctional mutation in only two (9%) of 22 patients.

Conclusion

The results indicate that the loss of function (transactivation activities) of p53 mutant proteins may predict a significant low pCR rate and suboptimal response to cisplatin-based neoadjuvant chemotherapy in patients with oral cavity SCC.

An miR-502-binding site single-nucleotide polymorphism in the 3'-untranslated region of the SET8 gene is associated with early age of breast cancer onset

PURPOSE

MicroRNAs regulate gene expression by binding to the 3'-untranslated region (UTR) of target genes. Single-nucleotide polymorphisms of critical genes may affect their regulation by microRNAs. We have identified a single-nucleotide polymorphism within the miR-502 seed binding region in the 3'-UTR of the SET8 gene. SET8 methylates TP53 and regulates genome stability. We investigated the role of this SET8 single-nucleotide polymorphism and in concert with the TP53 codon 72 single-nucleotide polymorphism in the propensity for onset of breast cancer.

EXPERIMENTAL DESIGN

We measured the SET8 single-nucleotide polymorphisms in a case-control study on 1,110 breast cancer cases and 1,097 controls.

RESULTS

The SET8 CC and TP53 GG genotypes were independently associated with an earlier age of breast cancer onset in an allele-dose-dependent manner (for SET8, 52.2 years for TT, 51.4 for TC, and 49.5 for CC; and for TP53, 53.1 years for CC, 51.5 for GC, 50.7 for GG). Individuals with combined SET8 CC and TP53 GG genotypes developed cancer at a median age of 47.7 years as compared with 54.6 years for individuals with combined SET8 TT and TP53 CC genotypes. In the 51 breast cancer tissue samples tested, the SET8 CC genotype was associated with reduced SET8, but not miR-502, transcript levels.

CONCLUSIONS

These data suggest that the miR-502-binding site single-nucleotide polymorphism in the 3'-UTR of SET8 modulates SET8 expression and contributes to the early development of breast cancer, either independently or together with the TP53 codon 72 single-nucleotide polymorphism. Larger studies with multiethnic groups are warranted to validate our findings.

Function of sirtuins in biological tissues

Sirtuins are protein deacetylases, which are dependent on nicotine adenine dinucleotide. They are phylogenetically conserved from bacteria to humans. Seven sirtuin proteins localized in a wide variety of subcellular locations have been identified in the human genome. The most important known function of sirtuins is their regulation of transcriptional repression, mediated through binding of a complex containing sirtuins and other proteins. Studies have shown that sirtuins have pathophysiological relevance to neurodegeneration, muscle differentiation, inflammation, obesity, and cancer. In addition, sirtuin activity extends the lifespan of several organisms. In this review, we discuss the mode(s) of action of sirtuins, and their biological role(s) in health and disease.

A common biological mechanism in cancer and Alzheimer's disease?

Cancer and Alzheimer's disease (AD) are two common disorders for which the final pathophysiological mechanism is not yet clearly defined. In a prospective longitudinal study we have previously shown an inverse association between AD and cancer, such that the rate of developing cancer in general with time was significantly slower in participants with AD, while participants with a history of cancer had a slower rate of developing AD. In cancer, cell regulation mechanisms are disrupted with augmentation of cell survival and/or proliferation, whereas conversely, AD is associated with increased neuronal death, either caused by, or concomitant with, beta amyloid (Abeta) and tau deposition. The possibility that perturbations of mechanisms involved in cell survival/death regulation could be involved in both disorders is discussed. Genetic polymorphisms, DNA methylation or other mechanisms that induce changes in activity of molecules with key roles in determining the decision to "repair and live"- or "die" could be involved in the pathogenesis of the two disorders. As examples, the role of p53, Pin1 and the Wnt signaling pathway are discussed as potential candidates that, speculatively, may explain inverse associations between AD and cancer.

Cellular stress response pathway system as a sentinel ensemble in toxicological screening

High costs, long test times, and societal concerns related to animal use have required the development of in vitro assays for the rapid and cost-effective toxicological evaluation and characterization of compounds in both the pharmaceutical and environmental arenas. Although the pharmaceutical industry has developed very effective, high-throughput in vitro assays for determining the therapeutic potential of compounds, the application of this approach to toxicological screening has been limited. A primary reason for this is that while drug candidate screens are directed to a specific target/mechanism, xenobiotics can cause toxicity through any of a myriad of undefined interactions with cellular components and processes. Given that it is not practical to design assays that can interrogate each potential toxicological target, an integrative approach is required if there is to be a rapid and low-cost toxicological evaluation of chemicals. Cellular stress response pathways offer a viable solution to the creation of a set of integrative assays as there is a limited and hence manageable set (a small ensemble of 10 or less) of major cellular stress response pathways through which cells mount a homoeostatic response to toxicants and which also participate in cell fate/death decisions. Further, over the past decades, these pathways have been well characterized at a molecular level thereby enabling the development of high-throughput cell-based assays using the components of the pathways. Utilization of the set of cellular stress response pathway-based assays as indicators of toxic interactions of chemicals with basic cellular machinery will potentially permit the clustering of chemicals based on biological response profiles of common mode of action (MOA) and also the inference of the specific MOA of a toxicant. This article reviews the biochemical characteristics of the stress response pathways, their common architecture that enables rapid activation during stress, their participation in cell fate decisions, the essential nature of these pathways to the organism, and the biochemical basis of their cross-talk that permits an assay ensemble screening approach. Subsequent sections describe how the stress pathway ensemble assay approach could be applied to screening potentially toxic compounds and discuss how this approach may be used to derive toxicant MOA from the biological activity profiles that the ensemble strategy provides. The article concludes with a review of the application of the stress assay concept to noninvasive in vivo assessments of chemical toxicants.

Implications of endoplasmic reticulum stress, the unfolded protein response and apoptosis for molecular cancer therapy. Part I: targeting p53, Mdm2, GADD153/CHOP, GRP78/BiP and heat shock proteins

BACKGROUND

In eukaryotes, endoplasmic reticulum stress (ERS) and the unfolded protein response (UPR) are coordinately regulated to maintain steady-state levels and activities of various cellular proteins to ensure cell survival.

OBJECTIVE

This review (Part I of II) focuses on specific ERS and UPR signalling regulators, their expression in the cancer phenotype and apoptosis, and proposes how their implication in these processes can be rationalised into proteasome inhibition, apoptosis induction and the development of more efficacious targeted molecular cancer therapies.

METHOD

In this review, we contextualise many ERS and UPR client proteins that are deregulated or mutated in cancers and show links between ERS and the UPR, their implication in oncogenic transformation, tumour progression and escape from immune surveillance, apoptosis inhibition, angiogenesis, metastasis, acquired drug resistance and poor cancer prognosis.

CONCLUSION

Evasion of programmed cell death or apoptosis is a hallmark of cancer that enables tumour cells to proliferate uncontrollably. Successful eradication of cancer cells through targeting ERS- and UPR-associated proteins to induce apoptosis is currently being pursued as a central tenet of anticancer drug discovery.

Cyclin D1 is frequently overexpressed in microsatellite unstable colorectal cancer, independent of CpG island methylator phenotype

AIMS

Cyclin D1 and cyclin-dependent kinases are commonly activated in colorectal cancer. Microsatellite instability (MSI) and CpG island methylator phenotype (CIMP) are important molecular classifiers in colorectal cancer. The aim was to clarify the relationship between cyclin D1, MSI and CIMP.

METHODS AND RESULTS

Among 865 colorectal cancers with MSI and CIMP data, 246 tumours (28.4%) showed cyclin D1 overexpression by immunohistochemistry. DNA methylation in p14 and eight CIMP-specific promoters (CACNA1G, CDKN2A (p16), CRABP1, IGF2, MLH1, NEUROG1, RUNX3 and SOCS1) was quantified by real-time polymerase chain reaction (MethyLight). Both MSI-high and CIMP-high were associated with cyclin D1 overexpression (P < 0.0001). After tumours were stratified by MSI and CIMP status, the relationship between MSI-high and cyclin D1 persisted (P < or = 0.02), whereas the relationship between CIMP-high and cyclin D1 did not. Cyclin D1 overexpression was correlated with BRAF mutation (P = 0.0001), p27 loss (P = 0.0007) and p16 loss (P = 0.02), and inversely with p53 expression (P = 0.0002) and p21 loss (P < 0.0001). After stratification by MSI status, the inverse relationship between cyclin D1 and p21 loss still persisted (P < 0.008).

CONCLUSIONS

Cyclin D1 activation is associated with MSI and inversely with p21 loss in colorectal cancers. Cyclin D1 may play an important role in the development of MSI-high tumours, independent of CIMP status.

Increased levels of a particular phosphatidylcholine species in senescent human dermal fibroblasts in vitro

Plasma membranes are essential components of living cells, and phospholipids are major components of cellular membranes. Here, we used liquid chromatography/mass spectrometry to investigate changes in the membrane phospholipid content that occur in association with aging. Our results indicate that the levels of a particular species of phosphatidylcholine comprised of stearic acid and arachidonic acid increased with age. To determine the reason for the increased levels of this particular phosphatidylcholine, we examined the effect of highly unsaturated fatty acids, such as arachidonic acid and eicosapentaenoic acid, on cellular aging. Applied arachidonic acid was incorporated into phosphatidylcholine molecules, but neither arachidonic acid nor other related unsaturated fatty acids had any effect. We conclude that increased levels of this distinctive phosphatidylcholine are a result of in vitro senescence.

p73 regulates neurodegeneration and phospho-tau accumulation during aging and Alzheimer's disease

The genetic mechanisms that regulate neurodegeneration are only poorly understood. We show that the loss of one allele of the p53 family member, p73, makes mice susceptible to neurodegeneration as a consequence of aging or Alzheimer's disease (AD). Behavioral analyses demonstrated that old, but not young, p73+/- mice displayed reduced motor and cognitive function, CNS atrophy, and neuronal degeneration. Unexpectedly, brains of aged p73+/- mice demonstrated dramatic accumulations of phospho-tau (P-tau)-positive filaments. Moreover, when crossed to a mouse model of AD expressing a mutant amyloid precursor protein, brains of these mice showed neuronal degeneration and early and robust formation of tangle-like structures containing P-tau. The increase in P-tau was likely mediated by JNK; in p73+/- neurons, the activity of the p73 target JNK was enhanced, and JNK regulated P-tau levels. Thus, p73 is essential for preventing neurodegeneration, and haploinsufficiency for p73 may be a susceptibility factor for AD and other neurodegenerative disorders.

Explaining oscillations and variability in the p53-Mdm2 system

BACKGROUND

In individual living cells p53 has been found to be expressed in a series of discrete pulses after DNA damage. Its negative regulator Mdm2 also demonstrates oscillatory behaviour. Attempts have been made recently to explain this behaviour by mathematical models but these have not addressed explicit molecular mechanisms. We describe two stochastic mechanistic models of the p53/Mdm2 circuit and show that sustained oscillations result directly from the key biological features, without assuming complicated mathematical functions or requiring more than one feedback loop. Each model examines a different mechanism for providing a negative feedback loop which results in p53 activation after DNA damage. The first model (ARF model) looks at the mechanism of p14ARF which sequesters Mdm2 and leads to stabilisation of p53. The second model (ATM model) examines the mechanism of ATM activation which leads to phosphorylation of both p53 and Mdm2 and increased degradation of Mdm2, which again results in p53 stabilisation. The models can readily be modified as further information becomes available, and linked to other models of cellular ageing.

RESULTS

The ARF model is robust to changes in its parameters and predicts undamped oscillations after DNA damage so long as the signal persists. It also predicts that if there is a gradual accumulation of DNA damage, such as may occur in ageing, oscillations break out once a threshold level of damage is acquired. The ATM model requires an additional step for p53 synthesis for sustained oscillations to develop. The ATM model shows much more variability in the oscillatory behaviour and this variability is observed over a wide range of parameter values. This may account for the large variability seen in the experimental data which so far has examined ARF negative cells.

CONCLUSION

The models predict more regular oscillations if ARF is present and suggest the need for further experiments in ARF positive cells to test these predictions. Our work illustrates the importance of systems biology approaches to understanding the complex role of p53 in both ageing and cancer.

Diagnostic utility of p16INK4a: a reappraisal of its use in cervical biopsies

p16(INK4a), an indirect marker of cell cycle dysregulation, is commonly expressed in cervical dysplasias and carcinomas associated with high risk human papillomavirus (HR-HPV) infections. Although p16(INK4a) immunohistology is routinely used as a cost effective surrogate marker, many of the published articles are confusing and contradictory. The discrepancies can be ascribed to a multitude of factors operating at the molecular, technical and interpretative levels. In the first place, our simplistic model of viral mediated oncogenesis is speculative and fails to account for all the known biomolecular changes. Unresolved technical issues include the variables of tissue fixation, antibody dilution, antibody isotype and clone, and the sensitivity of the particular detection method. Within any controlled staining method, strong diffuse or 'block' immunoreactivity in squamous cells may be found in moderate/severe dysplasia (CIN 2/3) and invasive squamous carcinoma. In contrast, focal or multifocal reactivity in squamous cells may be artefactual, related to low risk or HR-HPV. p16(INK4a) is less reliable when dealing with glandular lesions since considerable overlap exists between reactive and dysplastic lesions. In addition not all glandular dysplasias/carcinomas are HR-HPV related, nor are all p16(INK4a) immunoreactive lesions associated with HR-HPV. We conclude that p16(INK4a) immunoperoxidase shows greater specificity than sensitivity for squamous lesions; in comparison, glandular dysplasias/carcinomas show reduced specificity and sensitivity. Like all cell cycle regulatory proteins, the future diagnostic role of p16(INK4a) is limited. The ideal diagnostic molecular test for cervical dysplasias will detect a HR-HPV related product after, but not before, cell transformation and will reliably predict those cases yet to experience disease progression.

CARF: an emerging regulator of p53 tumor suppressor and senescence pathway

Replicative senescence, a major outcome of normal cells with finite lifespan, is a widely accepted in vitro model for ageing studies. Limited repair and defense mechanisms of normal cells, in addition to DNA alterations and oncogene inductions under stress, are believed to result in senescence as a protective mechanism to prevent undesirable proliferation of cells. The ARF/p53/p21(cip1/waf1) tumor suppression pathway acts as a molecular sensor and regulator of cellular stress, senescence, and immortalization. Understanding the molecular regulation of this pathway by intrinsic and extrinsic signals is extremely important to address unsolved questions in senescence and cancer. CARF was first discovered as a binding partner of ARF and has since been shown to have both ARF-dependent and -independent functions that converge to regulate p53 pathway. CARF directly binds to p53 and HDM2, and functions in a negative feedback pathway. Whereas CARF transcriptionally represses HDM2 to increase p53 activity, HDM2 in return degrades CARF. Thus, CARF may act as a novel key regulator of the p53 pathway at multiple checkpoints. The aim of this article is to discuss the current knowledge about functions of CARF and its impact on p53 pathway in regulation of senescence and carcinogenesis.

Sex difference in neural tube defects in p53-null mice is caused by differences in the complement of X not Y genes

To shed light on the biological origins of sex differences in neural tube defects (NTDs), we examined Trp53-null C57BL/6 mouse embryos and neonates at 10.5 and 18.5 days post coitus (dpc) and at birth. We confirmed that female embryos show more NTDs than males. We also examined mice in which the testis-determining gene Sry is deleted from the Y chromosome but inserted onto an autosome as a transgene, producing XX and XY gonadal females and XX and XY gonadal males. At birth, Trp53 nullizygous mice were predominantly XY rather than XX, irrespective of gonadal type, showing that the sex difference in the lethal effect of Trp53 nullizygosity by postnatal day 1 is caused by differences in sex chromosome complement. At 10.5 dpc, the incidence of NTDs in Trp53-null progeny of XY* mice, among which the number of the X chromosomes varies independently of the presence or absence of a Y chromosome, was higher in mice with two copies of the X chromosome than in mice with a single copy. The presence of a Y chromosome had no protective effect, suggesting that sex differences in NTDs are caused by sex differences in the number of X chromosomes.

Cellular and organismal ageing: Role of the p53 tumor suppressor protein in the induction of transient and terminal senescence

In recent years, an impact of the p53 tumor suppressor protein in the processes of cellular and organismal ageing became evident. First hints were found in model organisms like Saccharomyces cerevisiae, Caenorhabditis elegans, and Drosophila melanogaster where a clear connection between ageing phenotypes and pathways that are regulated by p53, were found. Interestingly, pathways that are central to the ageing process are usually also involved in energy metabolism and are highly conserved throughout evolution. This also supports the long known empiric finding that caloric restriction has a positive impact on the life span of a wide variety of organisms. Within the last years, on the molecular level, an involvement of the insulin-like growth factor and of the histone deacetylase SRIT1 could be shown. Insight on the impact of p53 on ageing at the organismal level came from mice expressing aberrant forms of the p53 protein. Obviously, the balance of the full length p53 protein and of the shorter p44/DeltaNp53 isomer bear a strong impact on ageing. The shorter isoform regulates full length p53 and in cases where there is too much of the longer isoform, this leads to elevated apoptosis resulting in decreased tumor incidence but also in premature ageing due to exhaustion of the renewal potential. Therefore, modulating the expression of the truncated p53 isoform accordingly, might lead to increased health-span and elevated life-span.

How does suppression of IGF-1 signaling by DNA damage affect aging and longevity?

Long-lived animals have evolved a robust set of defenses to maintain genomic integrity over their entire lifespan. The DNA damage response and DNA repair pathways are critical pillars of organismal defenses, minimizing somatic mutations in both post-mitotic and mitotic cells. These genomic maintenance systems not only prevent the premature emergence of cancers but may also maintain normal tissue function and organismal longevity. Genetic defects in a number of DNA repair and DNA damage response genes often leads to a dramatic increase in cancer incidence; in other cases, premature aging or progeroid syndromes may be induced. In this review, we discuss two recent reports of two nucleotide excision repair-deficient models that exhibit dramatic premature aging and shortened longevity. The DNA repair defects were also associated with a significant inhibition of the growth hormone/insulin-like growth factor 1 (GH/IGF-1) axis, an endocrine signaling pathway shown to influence aging and longevity in both vertebrates and invertebrates. Potential mechanisms of how DNA damage might affect IGF-1 signaling and aging are discussed, with a particular emphasis on the role of such signaling alterations in the adult tissue stem cell compartments.

Identification of a p53-response element in the promoter of the proline oxidase gene

Proline oxidase (POX) is a p53-induced proapoptotic gene. We investigated whether p53 could bind directly to the POX gene promoter. Chromatin immunoprecipitation (ChIP) assays detected p53 bound to POX upstream gene sequences. In support of the ChIP results, sequence analysis of the POX gene and its 5' flanking sequences revealed a potential p53-binding site, GGGCTTGTCTTCGTGTGACTTCTGTCT, located at 1161 base pairs (bp) upstream of the transcriptional start site. A 711-bp DNA fragment containing the candidate p53-binding site exhibited reporter gene activity that was induced by p53. In contrast, the same DNA region lacking the candidate p53-binding site did not show significant p53-response activity. Electrophoretic mobility shift assay (EMSA) in ACHN renal carcinoma cell nuclear lysates confirmed that p53 could bind to the 711-bp POX DNA fragment. We concluded from these experiments that a p53-binding site is positioned at -1161 to -1188bp upstream of the POX transcriptional start site.

Towards a pathway definition of Parkinson's disease: a complex disorder with links to cancer, diabetes and inflammation

We have previously established a first whole genome transcriptomic profile of sporadic Parkinson's disease (PD). After extensive brain tissue-based validation combined with cycles of iterative data analysis and by focusing on the most comparable cases of the cohort, we have refined our analysis and established a list of 892 highly dysregulated priority genes that are considered to form the core of the diseased Parkinsonian metabolic network. The substantia nigra pathways, now under scrutiny, contain more than 100 genes whose association with PD is known from the literature. Of those, more than 40 genes belong to the highly significantly dysregulated group identified in our dataset. Apart from the complete list of 892 priority genes, we present pathways revealing PD 'hub' as well as 'peripheral' network genes. The latter include Lewy body components or interact with known PD genes. Biological associations of PD with cancer, diabetes and inflammation are discussed and interactions of the priority genes with several drugs are provided. Our study illustrates the value of rigorous clinico-pathological correlation when analysing high-throughput data to make optimal use of the histopathological phenome, or morphonome which currently serves as the key diagnostic reference for most human diseases. The need for systematic human tissue banking, following the highest possible professional and ethical standard to enable sustainability, becomes evident.

Cellular signaling in normal and cancerous stem cells

Self-renewing divisions of normal and cancerous stem cells are responsible for the initiation and maintenance of normal and certain cancerous tissues, respectively. Recent findings suggest that tumor surveillance mechanisms can reduce regenerative capacity and frequency of normal stem cells, thereby contributing to tissue aging. Signaling pathways promoting self-renewal of stem cells can also drive proliferation in cancer. The BMI-1 proto-oncogene is required for the maintenance of tissue-specific stem cells and is involved in carcinogenesis within the same tissues. BMI-1 promotes self-renewal of stem cells largely by interfering with two central cellular tumor suppressor pathways, p16(Ink4a)/retinoblastoma protein (Rb) and ARF/p53, whose disruption is a hallmark of cancer. Nucleolin, an Rb-associated protein, is abundant in proliferating cancerous cells and likely contributes to the maintenance of human CD34-positive stem/progenitor cells of hematopoiesis. Elucidation of the involvement of proto-oncogenes and tumor suppressors in the maintenance of stem cells might have therapeutic implications.