Metabolic pathways regulated by TAp73 in response to oxidative stress

Altered Mitochondrial Function and Accelerated Aging Phenotype in Neural Stem Cells Derived from Dnm1l Knockout Embryonic Stem Cells

Mitochondria are crucial for cellular energy metabolism and are involved in signaling, aging, and cell death. They undergo dynamic changes through fusion and fission to adapt to different cellular states. In this study, we investigated the effect of knocking out the dynamin 1-like protein (Dnm1l) gene, a key regulator of mitochondrial fission, in neural stem cells (NSCs) differentiated from Dnm1l knockout embryonic stem cells (Dnm1l-/- ESCs). Dnm1l-/- ESC-derived NSCs (Dnm1l-/- NSCs) exhibited similar morphology and NSC marker expression (Sox2, Nestin, and Pax6) to brain-derived NSCs, but lower Nestin and Pax6 expression than both wild-type ESC-derived NSCs (WT-NSCs) and brain-derived NSCs. In addition, compared with WT-NSCs, Dnm1l-/- NSCs exhibited distinct mitochondrial morphology and function, contained more elongated mitochondria, showed reduced mitochondrial respiratory capacity, and showed a metabolic shift toward glycolysis for ATP production. Notably, Dnm1l-/- NSCs exhibited impaired self-renewal ability and accelerated cellular aging during prolonged culture, resulting in decreased proliferation and cell death. Furthermore, Dnm1l-/- NSCs showed elevated levels of inflammation and cell stress markers, suggesting a connection between Dnm1l deficiency and premature aging in NSCs. Therefore, the compromised self-renewal ability and accelerated cellular aging of Dnm1l-/- NSCs may be attributed to mitochondrial fission defects.

Polyploid/Multinucleated Giant and Slow-Cycling Cancer Cell Enrichment in Response to X-ray Irradiation of Human Glioblastoma Multiforme Cells Differing in Radioresistance and TP53/PTEN Status

Radioresistance compromises the efficacy of radiotherapy for glioblastoma multiforme (GBM), the most devastating and common brain tumor. The present study investigated the relationship between radiation tolerance and formation of polyploid/multinucleated giant (PGCC/MGCC) and quiescent/senescent slow-cycling cancer cells in human U-87, LN-229, and U-251 cell lines differing in TP53/PTEN status and radioresistance. We found significant enrichment in MGCC populations of U-87 and LN-229 cell lines, and generation of numerous small mononuclear (called Raju cells, or RJ cells) U-87-derived cells that eventually form cell colonies, in a process termed neosis, in response to X-ray irradiation (IR) at single acute therapeutic doses of 2-6 Gy. For the first time, single-cell high-content imaging and analysis of Ki-67- and EdU-coupled fluorescence demonstrated that the IR exposure dose-dependently augments two distinct GBM cell populations. Bifurcation of Ki-67 staining suggests fast-cycling and slow-cycling populations with a normal-sized nuclear area, and with an enlarged nuclear area, including one resembling the size of PGCC/MGCCs, that likely underlie the highest radioresistance and propensity for repopulation of U-87 cells. Proliferative activity and anchorage-independent survival of GBM cell lines seem to be related to neosis, low level of apoptosis, fraction of prematurely stress-induced senescent MGCCs, and the expression of p63 and p73, members of p53 family transcription factors, but not to the mutant p53. Collectively, our data support the importance of the TP53wt/PTENmut genotype for the maintenance of cycling radioresistant U-87 cells to produce a significant amount of senescent MGCCs as an IR stress-induced adaptation response to therapeutic irradiation doses.

The Therapeutic Potential of the Restoration of the p53 Protein Family Members in the EGFR-Mutated Lung Cancer

Despite the recent development of precision medicine and targeted therapies, lung cancer remains the top cause of cancer-related mortality worldwide. The patients diagnosed with metastatic disease have a five-year survival rate lower than 6%. In metastatic disease, EGFR is the most common driver of mutation, with the most common co-driver hitting TP53. EGFR-positive patients are offered the frontline treatment with tyrosine kinase inhibitors, yet the development of resistance and the lack of alternative therapies make this group of patients only fit for clinical trial participation. Since mutant p53 is the most common co-driver in the metastatic setting, therapies reactivating the p53 pathway might serve as a promising alternative therapeutic approach in patients who have developed a resistance to tyrosine kinase inhibitors. This review focuses on the molecular background of EGFR-mutated lung cancer and discusses novel therapeutic options converging on the reactivation of p53 tumor suppressor pathways.

In-depth proteomics characterization of ∆Np73 effectors identifies key proteins with diagnostic potential implicated in lymphangiogenesis, vasculogenesis and metastasis in colorectal cancer

Colorectal cancer (CRC) is the third most common cancer and the second leading cause of cancer‐related death worldwide. Alterations in proteins of the p53‐family are a common event in CRC. ΔNp73, a p53‐family member, shows oncogenic properties and its effectors are largely unknown. We performed an in‐depth proteomics characterization of transcriptional control by ∆Np73 of the secretome of human colon cancer cells and validated its clinical potential. The secretome was analyzed using high‐density antibody microarrays and stable isotopic metabolic labeling. Validation was performed by semiquantitative PCR, ELISA, dot‐blot and western blot analysis. Evaluation of selected effectors was carried out using 60 plasma samples from CRC patients, individuals carrying premalignant colorectal lesions and colonoscopy‐negative controls. In total, 51 dysregulated proteins were observed showing at least 1.5‐foldchange in expression. We found an important association between the overexpression of ∆Np73 and effectors related to lymphangiogenesis, vasculogenesis and metastasis, such as brain‐derived neurotrophic factor (BDNF) and the putative aminoacyl tRNA synthase complex‐interacting multifunctional protein 1 (EMAP‐II)–vascular endothelial growth factor C–vascular endothelial growth factor receptor 3 axis. We further demonstrated the usefulness of BDNF as a potential CRC biomarker able to discriminate between CRC patients and premalignant individuals from controls with high sensitivity and specificity.

The p53 family member p73 in the regulation of cell stress response

During oncogenesis, cells become unrestrictedly proliferative thereby altering the tissue homeostasis and resulting in subsequent hyperplasia. This process is paralleled by resumption of cell cycle, aberrant DNA repair and blunting the apoptotic program in response to DNA damage. In most human cancers these processes are associated with malfunctioning of tumor suppressor p53. Intriguingly, in some cases two other members of the p53 family of proteins, transcription factors p63 and p73, can compensate for loss of p53. Although both p63 and p73 can bind the same DNA sequences as p53 and their transcriptionally active isoforms are able to regulate the expression of p53-dependent genes, the strongest overlap with p53 functions was detected for p73. Surprisingly, unlike p53, the p73 is rarely lost or mutated in cancers. On the contrary, its inactive isoforms are often overexpressed in cancer. In this review, we discuss several lines of evidence that cancer cells develop various mechanisms to repress p73-mediated cell death. Moreover, p73 isoforms may promote cancer growth by enhancing an anti-oxidative response, the Warburg effect and by repressing senescence. Thus, we speculate that the role of p73 in tumorigenesis can be ambivalent and hence, requires new therapeutic strategies that would specifically repress the oncogenic functions of p73, while keeping its tumor suppressive properties intact.

The p53 Family: A Role in Lipid and Iron Metabolism

The p53 family of tumor suppressors, which includes p53, p63, and p73, has a critical role in many biological processes, such as cell cycle arrest, apoptosis, and differentiation. In addition to tumor suppression, the p53 family proteins also participate in development, multiciliogenesis, and fertility, indicating these proteins have diverse roles. In this review, we strive to cover the relevant studies that demonstrate the roles of p53, p63, and p73 in lipid and iron metabolism.

Deciphering the Nature of Trp73 Isoforms in Mouse Embryonic Stem Cell Models: Generation of Isoform-Specific Deficient Cell Lines Using the CRISPR/Cas9 Gene Editing System

Simple Summary

The Trp73 gene is involved in the regulation of multiple biological processes such as response to stress, differentiation and tissue architecture. This gene gives rise to structurally different N and C-terminal isoforms which lead to differences in its biological activity in a cell type dependent manner. However, there is a current lack of physiological models to study these isoforms. The aim of this study was to generate specific p73-isoform-deficient mouse embryonic stem cell lines using the CRISPR/Cas9 system. Their special features, self-renewal and pluripotency, make embryonic stem cells a useful research tool that allows the generation of cells from any of the three germ layers carrying specific inactivation of p73-isoforms. Characterization of the generated cell lines indicates that while the individual elimination of TA- or DN-p73 isoform is compatible with pluripotency, it results in alterations of the transcriptional profiles and the pluripotent state of the embryonic stem cells in an isoform-specific manner.

Abstract

The p53 family has been widely studied for its role in various physiological and pathological processes. Imbalance of p53 family proteins may contribute to developmental abnormalities and pathologies in humans. This family exerts its functions through a profusion of isoforms that are generated by different promoter usage and alternative splicing in a cell type dependent manner. In particular, the Trp73 gene gives rise to TA and DN-p73 isoforms that confer p73 a dual nature. The biological relevance of p73 does not only rely on its tumor suppression effects, but on its pivotal role in several developmental processes. Therefore, the generation of cellular models that allow the study of the individual isoforms in a physiological context is of great biomedical relevance. We generated specific TA and DN-p73-deficient mouse embryonic stem cell lines using the CRISPR/Cas9 gene editing system and validated them as physiological bona fide p73-isoform knockout models. Global gene expression analysis revealed isoform-specific alterations of distinctive transcriptional networks. Elimination of TA or DN-p73 is compatible with pluripotency but prompts naïve pluripotent stem cell transition into the primed state, compromising adequate lineage differentiation, thus suggesting that differential expression of p73 isoforms acts as a rheostat during early cell fate determination.

The Janus-like role of proline metabolism in cancer

The metabolism of the non-essential amino acid L-proline is emerging as a key pathway in the metabolic rewiring that sustains cancer cells proliferation, survival and metastatic spread. Pyrroline-5-carboxylate reductase (PYCR) and proline dehydrogenase (PRODH) enzymes, which catalyze the last step in proline biosynthesis and the first step of its catabolism, respectively, have been extensively associated with the progression of several malignancies, and have been exposed as potential targets for anticancer drug development. As investigations into the links between proline metabolism and cancer accumulate, the complexity, and sometimes contradictory nature of this interaction emerge. It is clear that the role of proline metabolism enzymes in cancer depends on tumor type, with different cancers and cancer-related phenotypes displaying different dependencies on these enzymes. Unexpectedly, the outcome of rewiring proline metabolism also differs between conditions of nutrient and oxygen limitation. Here, we provide a comprehensive review of proline metabolism in cancer; we collate the experimental evidence that links proline metabolism with the different aspects of cancer progression and critically discuss the potential mechanisms involved.

The Undervalued Avenue to Reinstate Tumor Suppressor Functionality of the p53 Protein Family for Improved Cancer Therapy-Drug Repurposing

p53 and p73 are critical tumor suppressors that are often inactivated in human cancers through various mechanisms. Owing to their high structural homology, the proteins have many joined functions and recognize the same set of genes involved in apoptosis and cell cycle regulation. p53 is known as the 'guardian of the genome' and together with p73 forms a barrier against cancer development and progression. The TP53 is mutated in more than 50% of all human cancers and the germline mutations in TP53 predispose to the early onset of multiple tumors in Li-Fraumeni syndrome (LFS), the inherited cancer predisposition. In cancers where TP53 gene is intact, p53 is degraded. Despite the ongoing efforts, the treatment of cancers remains challenging. This is due to late diagnoses, the toxicity of the current standard of care and marginal benefit of newly approved therapies. Presently, the endeavors focus on reactivating p53 exclusively, neglecting the potential of the restoration of p73 protein for cancer eradication. Taken that several small molecules reactivating p53 failed in clinical trials, there is a need to develop new treatments targeting p53 proteins in cancer. This review outlines the most advanced strategies to reactivate p53 and p73 and describes drug repurposing approaches for the efficient reinstatement of the p53 proteins for cancer therapy.

MiRNA-137-mediated modulation of mitochondrial dynamics regulates human neural stem cell fate

The role of miRNAs in determining human neural stem cell (NSC) fate remains elusive despite their high expression in the developing nervous system. In this study, we investigate the role of miR‐137, a brain‐enriched miRNA, in determining the fate of human induced pluripotent stem cells‐derived NSCs (hiNSCs). We show that ectopic expression of miR‐137 in hiNSCs reduces proliferation and accelerates neuronal differentiation and migration. TargetScan and MicroT‐CDS predict myocyte enhancer factor‐2A (MEF2A), a transcription factor that regulates peroxisome proliferator‐activated receptor‐gamma coactivator (PGC1α) transcription, as a target of miR‐137. Using a reporter assay, we validate MEF2A as a downstream target of miR‐137. Our results indicate that reduced levels of MEF2A reduce the transcription of PGC1α, which in turn impacts mitochondrial dynamics. Notably, miR‐137 accelerates mitochondrial biogenesis in a PGC1α independent manner by upregulating nuclear factor erythroid 2 (NFE2)‐related factor 2 (NRF2) and transcription factor A of mitochondria (TFAM). In addition, miR‐137 modulates mitochondrial dynamics by inducing mitochondrial fusion and fission events, resulting in increased mitochondrial content and activation of oxidative phosphorylation (OXPHOS) and oxygen consumption rate. Pluripotency transcription factors OCT4 and SOX2 are known to have binding sites in the promoter region of miR‐137 gene. Ectopic expression of miR‐137 elevates the expression levels of OCT4 and SOX2 in hiNSCs which establishes a feed‐forward self‐regulatory loop between miR‐137 and OCT4/SOX2. Our study provides novel molecular insights into NSC fate determination by miR‐137.

Mitochondria as central regulators of neural stem cell fate and cognitive function

Emerging evidence now indicates that mitochondria are central regulators of neural stem cell (NSC) fate decisions and are crucial for both neurodevelopment and adult neurogenesis, which in turn contribute to cognitive processes in the mature brain. Inherited mutations and accumulated damage to mitochondria over the course of ageing serve as key factors underlying cognitive defects in neurodevelopmental disorders and neurodegenerative diseases, respectively. In this Review, we explore the recent findings that implicate mitochondria as crucial regulators of NSC function and cognition. In this respect, mitochondria may serve as targets for stem-cell-based therapies and interventions for cognitive defects.

TAp73 regulates ATP7A: possible implications for ageing-related diseases

The p53 family member p73 controls a wide range of cellular function. Deletion of p73 in mice results in increased tumorigenesis, infertility, neurological defects and altered immune system. Despite the extensive effort directed to define the molecular underlying mechanism of p73 function a clear definition of its transcriptional signature and the extent of overlap with the other p53 family members is still missing. Here we describe a novel TAp73 target, ATP7A a member of a large family of P-type ATPases implicated in human neurogenerative conditions and cancer chemoresistance. Modulation of TAp73 expression influences basal expression level of ATP7A in different cellular models and chromatin immunoprecipitation confirmed a physical direct binding of TAp73 on ATP7A genomic regions. Bioinformatic analysis of expression profile datasets of human lung cancer patients suggests a possible implication of TAp73/ATP7A axis in human cancer. These data provide a novel TAp73-dependent target which might have implications in ageing-related diseases such as cancer and neurodegeneration.

TAp73 Modifies Metabolism and Positively Regulates Growth of Cancer Stem-Like Cells in a Redox-Sensitive Manner

PURPOSE

Stem-like cancer cells, with characteristic self-renewal abilities, remain highly refractory to various clinical interventions. As such, stemness-inhibiting entities, such as tumor suppressor p53, are therapeutically pursued for their anticancer activities. Interestingly, similar implications for tumor suppressor TAp73 in regulating stemness features within stem-like cancer cells remain unknown.Experimental Design: This study utilizes various in vitro molecular biology techniques, including immunoblotting, qRT-PCR, and mass spectrometry-based proteomics, and metabolomics approaches to study the role of TAp73 in human and murine embryonal carcinoma stem-like cells (ECSLC) as well as human breast cancer stem-like cells (BCSLC). These findings were confirmed using patient-derived brain tumor-initiating cells (BTIC) and in vivo xenograft models.

RESULTS

TAp73 inhibition decreases the expression of stem cell transcription factors Oct4, Nanog, and Sox-2, as well as tumorsphere formation capacity in ECSLCs. In vivo, TAp73-deficient ECSLCs and BCSLCs demonstrate decreased tumorigenic potential when xenografted in mice. Mechanistically, TAp73 modifies the proline regulatory axis through regulation of enzymes GLS, OAT, and PYCR1 involved in the interconversion of proline-glutamine-ornithine. Further, TAp73 deficiency exacerbates glutamine dependency, enhances accumulation of reactive oxygen species through reduced superoxide dismutase 1 (SOD1) expression, and promotes differentiation by arresting cell cycle and elevating autophagy. Most importantly, the knockdown of TAp73 in CD133^HI BTICs, separated from three different glioblastoma patients, strongly decreases the expression of prosurvival factors Sox-2, BMI-1, and SOD1, and profoundly decreases their self-renewal capacity as evidenced through their reduced tumorsphere formation ability.

CONCLUSIONS

Collectively, we reveal a clinically relevant aspect of cancer cell growth and stemness regulation through TAp73-mediated redox-sensitive metabolic reprogramming.

Integrin-β4 is a novel transcriptional target of TAp73

As a member of p53 family, p73 has attracted intense investigations due to its structural and functional similarities to p53. Among more than ten p73 variants, the transactivation (TA) domain-containing isoform TAp73 is the one that imitates the p53's behavior most. TAp73 induces apoptosis and cell cycle arrest, which endows it the capacity of tumour suppression. Also, it can exert diverse biological influences on cells through activating a complex and context dependent transcriptional programme. The transcriptional activities further broaden its roles in more intricate biological processes. In this article, we report that p73 is a positive regulator of a cell adhesion related gene named integrin β4 (ITGB4). This finding may have implications for the dissection of the biological mechanisms underlining p73 functions.

TAp73 is a marker of glutamine addiction in medulloblastoma

Medulloblastoma is the most common solid primary brain tumor in children. Remarkable advancements in the understanding of the genetic and epigenetic basis of these tumors have informed their recent molecular classification. However, the genotype/phenotype correlation of the subgroups remains largely uncharacterized. In particular, the metabolic phenotype is of great interest because of its druggability, which could lead to the development of novel and more tailored therapies for a subset of medulloblastoma. p73 plays a critical role in a range of cellular metabolic processes. We show overexpression of p73 in a proportion of non-WNT medulloblastoma. In these tumors, p73 sustains cell growth and proliferation via regulation of glutamine metabolism. We validated our results in a xenograft model in which we observed an increase in survival time in mice on a glutamine restriction diet. Notably, glutamine starvation has a synergistic effect with cisplatin, a component of the current medulloblastoma chemotherapy. These findings raise the possibility that glutamine depletion can be used as an adjuvant treatment for p73-expressing medulloblastoma.

Mitochondrial dynamics in the regulation of neurogenesis: From development to the adult brain

Mitochondria are classically known to be the cellular energy producers, but a renewed appreciation for these organelles has developed with the accumulating discoveries of additional functions. The importance of mitochondria within the brain has been long known, particularly given the high-energy demanding nature of neurons. The energy demands imposed by neurons require the well-orchestrated morphological adaptation and distribution of mitochondria. Recent studies now reveal the importance of mitochondrial dynamics not only in mature neurons but also during neural development, particularly during the process of neurogenesis and neural stem cell fate decisions. In this review, we will highlight the recent findings that illustrate the importance of mitochondrial dynamics in neurodevelopment and neural stem cell function. Developmental Dynamics 247:47-53, 2018. © 2017 Wiley Periodicals, Inc.

p73 Regulates Primary Cortical Neuron Metabolism: a Global Metabolic Profile

The transcription factor p73 has been demonstrated to play a significant role in survival and differentiation of neuronal stem cells. In this report, by employing comprehensive metabolic profile and mitochondrial bioenergetics analysis, we have explored the metabolic alterations in cortical neurons isolated from p73 N-terminal isoform specific knockout animals. We found that loss of the TAp73 or ΔNp73 triggers selective biochemical changes. In particular, p73 isoforms regulate sphingolipid and phospholipid biochemical pathway signaling. Indeed, sphinganine and sphingosine levels were reduced in p73-depleted cortical neurons, and decreased levels of several membrane phospholipids were also observed. Moreover, in line with the complexity associated with p73 functions, loss of the TAp73 seems to increase glycolysis, whereas on the contrary, loss of ΔNp73 isoform reduces glucose metabolism, indicating an isoform-specific differential effect on glycolysis. These changes in glycolytic flux were not reflected by parallel alterations of mitochondrial respiration, as only a slight increase of mitochondrial maximal respiration was observed in p73-depleted cortical neurons. Overall, our findings reinforce the key role of p73 in regulating cellular metabolism and point out that p73 exerts its functions in neuronal biology at least partially through the regulation of metabolic pathways.

Impact of Mediterranean diet on metabolic syndrome, cancer and longevity

Obesity symbolizes a major public health problem. Overweight and obesity are associated to the occurrence of the metabolic syndrome and to adipose tissue dysfunction. The adipose tissue is metabolically active and an endocrine organ, whose dysregulation causes a low-grade inflammatory state and ectopic fat depositions. The Mediterranean Diet represents a possible therapy for metabolic syndrome, preventing adiposopathy or "sick fat" formation.The Mediterranean Diet exerts protective effects in elderly subjects with and without baseline of chronic diseases. Recent studies have demonstrated a relationship between cancer and obesity. In the US, diet represents amount 30-35% of death causes related to cancer. Currently, the cancer is the second cause of death after cardiovascular diseases worldwide. Furthermore, populations living in the Mediterranean area have a decreased incidence of cancer compared with populations living in Northern Europe or the US, likely due to healthier dietary habits. The bioactive food components have a potential preventive action on cancer. The aims of this review are to evaluate the impact of Mediterranean Diet on onset, progression and regression of metabolic syndrome, cancer and on longevity.

Impaired embryonic development in glucose-6-phosphate dehydrogenase-deficient Caenorhabditis elegans due to abnormal redox homeostasis induced activation of calcium-independent phospholipase and alteration of glycerophospholipid metabolism

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a commonly pervasive inherited disease in many parts of the world. The complete lack of G6PD activity in a mouse model causes embryonic lethality. The G6PD-deficient Caenorhabditis elegans model also shows embryonic death as indicated by a severe hatching defect. Although increased oxidative stress has been implicated in both cases as the underlying cause, the exact mechanism has not been clearly delineated. In this study with C. elegans, membrane-associated defects, including enhanced permeability, defective polarity and cytokinesis, were found in G6PD-deficient embryos. The membrane-associated abnormalities were accompanied by impaired eggshell structure as evidenced by a transmission electron microscopic study. Such loss of membrane structural integrity was associated with abnormal lipid composition as lipidomic analysis revealed that lysoglycerophospholipids were significantly increased in G6PD-deficient embryos. Abnormal glycerophospholipid metabolism leading to defective embryonic development could be attributed to the increased activity of calcium-independent phospholipase A₂ (iPLA) in G6PD-deficient embryos. This notion is further supported by the fact that the suppression of multiple iPLAs by genetic manipulation partially rescued the embryonic defects in G6PD-deficient embryos. In addition, G6PD deficiency induced disruption of redox balance as manifested by diminished NADPH and elevated lipid peroxidation in embryos. Taken together, disrupted lipid metabolism due to abnormal redox homeostasis is a major factor contributing to abnormal embryonic development in G6PD-deficient C. elegans.