Control mechanisms in germ cells mediated by p53 family proteins

Activation of P53 pathway contributes to Xenopus hybrid inviability

Hybrid incompatibility as a kind of reproductive isolation contributes to speciation. The nucleocytoplasmic incompatibility between Xenopus tropicalis eggs and Xenopus laevis sperm (te×ls) leads to specific loss of paternal chromosomes 3L and 4L. The hybrids die before gastrulation, of which the lethal causes remain largely unclear. Here, we show that the activation of the tumor suppressor protein P53 at late blastula stage contributes to this early lethality. We find that in stage 9 embryos, P53-binding motif is the most enriched one in the up-regulated Assay for Transposase-Accessible Chromatin with high-throughput sequencing (ATAC-seq) peaks between te×ls and wild-type X. tropicalis controls, which correlates with an abrupt stabilization of P53 protein in te×ls hybrids at stage 9. Inhibition of P53 activity via either tp53 knockout or overexpression of a dominant-negative P53 mutant or Murine double minute 2 proto-oncogene (Mdm2), a negative regulator of P53, by mRNA injection can rescue the te×ls early lethality. Our results suggest a causal function of P53 on hybrid lethality prior to gastrulation.

Evo-devo perspectives on cancer

The integration of evolutionary and developmental approaches into the field of evolutionary developmental biology has opened new areas of inquiry- from understanding the evolution of development and its underlying genetic and molecular mechanisms to addressing the role of development in evolution. For the last several decades, the terms 'evolution' and 'development' have been increasingly linked to cancer, in many different frameworks and contexts. This mini-review, as part of a special issue on Evolutionary Developmental Biology, discusses the main areas in cancer research that have been addressed through the lenses of both evolutionary and developmental biology, though not always fully or explicitly integrated in an evo-devo framework. First, it briefly introduces the current views on carcinogenesis that invoke evolutionary and/or developmental perspectives. Then, it discusses the main mechanisms proposed to have specifically evolved to suppress cancer during the evolution of multicellularity. Lastly, it considers whether the evolution of multicellularity and development was shaped by the threat of cancer (a cancer-evo-devo perspective), and/or whether the evolution of developmental programs and life history traits can shape cancer resistance/risk in various lineages (an evo-devo-cancer perspective). A proper evolutionary developmental framework for cancer, both as a disease and in terms of its natural history (in the context of the evolution of multicellularity and development as well as life history traits), could bridge the currently disparate evolutionary and developmental perspectives and uncover aspects that will provide new insights for cancer prevention and treatment.

Enhanced pro-apoptosis gene signature following the activation of TAp63α in oocytes upon γ irradiation

Specialized surveillance mechanisms are essential to maintain the genetic integrity of germ cells, which are not only the source of all somatic cells but also of the germ cells of the next generation. DNA damage and chromosomal aberrations are, therefore, not only detrimental for the individual but affect the entire species. In oocytes, the surveillance of the structural integrity of the DNA is maintained by the p53 family member TAp63α. The TAp63α protein is highly expressed in a closed and inactive state and gets activated to the open conformation upon the detection of DNA damage, in particular DNA double-strand breaks. To understand the cellular response to DNA damage that leads to the TAp63α triggered oocyte death we have investigated the RNA transcriptome of oocytes following irradiation at different time points. The analysis shows enhanced expression of pro-apoptotic and typical p53 target genes such as CDKn1a or Mdm2, concomitant with the activation of TAp63α. While DNA repair genes are not upregulated, inflammation-related genes become transcribed when apoptosis is initiated by activation of STAT transcription factors. Furthermore, comparison with the transcriptional profile of the ΔNp63α isoform from other studies shows only a minimal overlap, suggesting distinct regulatory programs of different p63 isoforms.

Drosophila p53 isoforms have overlapping and distinct functions in germline genome integrity and oocyte quality control

p53 gene family members in humans and other organisms encode a large number of protein isoforms whose functions are largely undefined. Using Drosophila as a model, we find that a p53B isoform is expressed predominantly in the germline where it colocalizes with p53A into subnuclear bodies. It is only p53A, however, that mediates the apoptotic response to ionizing radiation in the germline and soma. In contrast, p53A and p53B are both required for the normal repair of meiotic DNA breaks, an activity that is more crucial when meiotic recombination is defective. We find that in oocytes with persistent DNA breaks p53A is also required to activate a meiotic pachytene checkpoint. Our findings indicate that Drosophila p53 isoforms have DNA lesion and cell type-specific functions, with parallels to the functions of mammalian p53 family members in the genotoxic stress response and oocyte quality control.

Isoform-Specific Roles of Mutant p63 in Human Diseases

Simple Summary

The protein p63 belongs to the family of the p53 tumor suppressor. Mouse models have, however, shown that it is not a classical tumor suppressor but instead involved in developmental processes. Mutations in the p63 gene cause several developmental defects in human patients characterized by limb deformation, cleft lip/palate, and ectodermal dysplasia due to p63’s role as a master regulator of epidermal development. In addition, p63 plays a key role as a quality control factor in oocytes and p63 mutations can result either in compromised genetic quality control or premature cell death of all oocytes.

Abstract

The p63 gene encodes a master regulator of epidermal commitment, development, and differentiation. Heterozygous mutations in the DNA binding domain cause Ectrodactyly, Ectodermal Dysplasia, characterized by limb deformation, cleft lip/palate, and ectodermal dysplasia while mutations in in the C-terminal domain of the α-isoform cause Ankyloblepharon-Ectodermal defects-Cleft lip/palate (AEC) syndrome, a life-threatening disorder characterized by skin fragility, severe, long-lasting skin erosions, and cleft lip/palate. The molecular disease mechanisms of these syndromes have recently become elucidated and have enhanced our understanding of the role of p63 in epidermal development. Here we review the molecular cause and functional consequences of these p63-mutations for skin development and discuss the consequences of p63 mutations for female fertility.

Distinct p63 and p73 Protein Interactions Predict Specific Functions in mRNA Splicing and Polyploidy Control in Epithelia

Epithelial organs are the first barrier against microorganisms and genotoxic stress, in which the p53 family members p63 and p73 have both overlapping and distinct functions. Intriguingly, p73 displays a very specific localization to basal epithelial cells in human tissues, while p63 is expressed in both basal and differentiated cells. Here, we analyse systematically the literature describing p63 and p73 protein-protein interactions to reveal distinct functions underlying the aforementioned distribution. We have found that p73 and p63 cooperate in the genome stability surveillance in proliferating cells; p73 specific interactors contribute to the transcriptional repression, anaphase promoting complex and spindle assembly checkpoint, whereas p63 specific interactors play roles in the regulation of mRNA processing and splicing in both proliferating and differentiated cells. Our analysis reveals the diversification of the RNA and DNA specific functions within the p53 family.

Tumor suppressor p53: from engaging DNA to target gene regulation

The p53 transcription factor confers its potent tumor suppressor functions primarily through the regulation of a large network of target genes. The recent explosion of next generation sequencing protocols has enabled the study of the p53 gene regulatory network (GRN) and underlying mechanisms at an unprecedented depth and scale, helping us to understand precisely how p53 controls gene regulation. Here, we discuss our current understanding of where and how p53 binds to DNA and chromatin, its pioneer-like role, and how this affects gene regulation. We provide an overview of the p53 GRN and the direct and indirect mechanisms through which p53 affects gene regulation. In particular, we focus on delineating the ubiquitous and cell type-specific network of regulatory elements that p53 engages; reviewing our understanding of how, where, and when p53 binds to DNA and the mechanisms through which these events regulate transcription. Finally, we discuss the evolution of the p53 GRN and how recent work has revealed remarkable differences between vertebrates, which are of particular importance to cancer researchers using mouse models.

PACT/PRKRA and p53 regulate transcriptional activity of DMRT1

The transcription factor DMRT1 (doublesex and mab-3 related transcription factor) has two distinct functions, somatic-cell masculinization and germ-cell development in some vertebrate species, including mouse and the African clawed frog Xenopus laevis. However, its transcriptional regulation remains unclear. We tried to identify DMRT1-interacting proteins from X. laevis testes by immunoprecipitation with an anti-DMRT1 antibody and MS/MS analysis, and selected three proteins, including PACT/PRKRA (Interferon-inducible double-stranded RNA dependent protein kinase activator A) derived from testes. Next, we examined the effects of PACT/PRKRA and/or p53 on the transcriptional activity of DMRT1. In transfected 293T cells, PACT/PRKRA and p53 significantly enhanced and repressed DMRT1-driven luciferase activity, respectively. We also observed that the enhanced activity by PACT/PRKRA was strongly attenuated by p53. Moreover, in situ hybridization analysis of Pact/Prkra mRNA in tadpole gonads indicated high expression in female and male germline stem cells. Taken together, these findings suggest that PACT/PRKRA and p53 might positively and negatively regulate the activity of DMRT1, respectively, for germline stem cell fate.

p53, cancer and the immune response

The importance of cancer-cell-autonomous functions of the tumour suppressor p53 (encoded by TP53) has been established in many studies, but it is now clear that the p53 status of the cancer cell also has a profound impact on the immune response. Loss or mutation of p53 in cancers can affect the recruitment and activity of myeloid and T cells, allowing immune evasion and promoting cancer progression. p53 can also function in immune cells, resulting in various outcomes that can impede or support tumour development. Understanding the role of p53 in tumour and immune cells will help in the development of therapeutic approaches that can harness the differential p53 status of cancers compared with most normal tissue.

Crosstalk between PTEN/PI3K/Akt Signalling and DNA Damage in the Oocyte: Implications for Primordial Follicle Activation, Oocyte Quality and Ageing

The preservation of genome integrity in the mammalian female germline from primordial follicle arrest to activation of growth to oocyte maturation is fundamental to ensure reproductive success. As oocytes are formed before birth and may remain dormant for many years, it is essential that defence mechanisms are monitored and well maintained. The phosphatase and tensin homolog of chromosome 10 (PTEN)/phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB, Akt) is a major signalling pathway governing primordial follicle recruitment and growth. This pathway also contributes to cell growth, survival and metabolism, and to the maintenance of genomic integrity. Accelerated primordial follicle activation through this pathway may result in a compromised DNA damage response (DDR). Additionally, the distinct DDR mechanisms in oocytes may become less efficient with ageing. This review considers DNA damage surveillance mechanisms and their links to the PTEN/PI3K/Akt signalling pathway, impacting on the DDR during growth activation of primordial follicles, and in ovarian ageing. Targeting DDR mechanisms within oocytes may be of value in developing techniques to protect ovaries against chemotherapy and in advancing clinical approaches to regulate primordial follicle activation.

Roles of p53 Family Structure and Function in Non-Canonical Response Element Binding and Activation

The p53 canonical consensus sequence is a 10-bp repeat of PuPuPuC(A/T)(A/T)GPyPyPy, separated by a spacer with up to 13 bases. C(A/T)(A/T)G is the core sequence and purine (Pu) and pyrimidine (Py) bases comprise the flanking sequence. However, in the p53 noncanonical sequences, there are many variations, such as length of consensus sequence, variance of core sequence or flanking sequence, and variance in number of bases making up the spacer or AT gap composition. In comparison to p53, the p53 family members p63 and p73 have been found to have more tolerance to bind and activate several of these noncanonical sequences. The p53 protein forms monomers, dimers, and tetramers, and its nonspecific binding domain is well-defined; however, those for p63 or p73 are still not fully understood. Study of p63 and p73 structure to determine the monomers, dimers or tetramers to bind and regulate noncanonical sequence is a new challenge which is crucial to obtaining a complete picture of structure and function in order to understand how p63 and p73 regulate genes differently from p53. In this review, we will summarize the rules of p53 family non-canonical sequences, especially focusing on the structure of p53 family members in the regulation of specific target genes. In addition, we will compare different software programs for prediction of p53 family responsive elements containing parameters with canonical or non-canonical sequences.

The Trp73 Mutant Mice: A Ciliopathy Model That Uncouples Ciliogenesis From Planar Cell Polarity

p73 transcription factor belongs to one of the most important gene families in vertebrate biology, the p53-family. Trp73 gene, like the other family members, generates multiple isoforms named TA and DNp73, with different and, sometimes, antagonist functions. Although p73 shares many biological functions with p53, it also plays distinct roles during development. Trp73 null mice (p73KO from now on) show multiple phenotypes as gastrointestinal and cranial hemorrhages, rhinitis and severe central nervous system defects. Several groups, including ours, have revisited the apparently unrelated phenotypes observed in total p73KO and revealed a novel p73 function in the organization of ciliated epithelia in brain and trachea, but also an essential role as regulator of ependymal planar cell polarity. Unlike p73KO or TAp73KO mice, tumor-prone Trp53−/− mice (p53KO) do not present ependymal ciliary or planar cell polarity defects, indicating that regulation of ciliogenesis and PCP is a p73-specific function. Thus, loss of ciliary biogenesis and epithelial organization might be a common underlying cause of the diverse p73KO-phenotypes, highlighting Trp73 role as an architect of the epithelial tissue. In this review we would like to discuss the data regarding p73 role as regulator of ependymal cell ciliogenesis and PCP, supporting the view of the Trp73-mutant mice as a model that uncouples ciliogenesis from PCP and a possible model of human congenital hydrocephalus.

SIRT1 participates in the response to methylglyoxal-dependent glycative stress in mouse oocytes and ovary

Methylglyoxal (MG), a highly reactive dicarbonyl derived from metabolic processes, is the most powerful precursor of advanced glycation end products (AGEs). Glycative stress has been recently associated with ovarian dysfunctions in aging and PCOS syndrome. We have investigated the role of the NAD⁺-dependent Class III deacetylase SIRT1 in the adaptive response to MG in mouse oocytes and ovary. In mouse oocytes, MG induced up-expression of glyoxalase 1 (Glo1) and glyoxalase 2 (Glo2) genes, components of the main MG detoxification system, whereas inhibition of SIRT1 by Ex527 or sirtinol reduced this response. In addition, the inhibition of SIRT1 worsened the effects of MG on oocyte maturation rates, while SIRT1 activation by resveratrol counteracted MG insult. Ovaries from female mice receiving 100 mg/kg MG by gastric administration for 28 days (MG mice) exhibited increased levels of SIRT1 along with over-expression of catalase, superoxide dismutase 2, SIRT3, PGC1α and mtTFA. Similar levels of MG-derived AGEs were observed in the ovaries from MG and control groups, along with enhanced protein expression of glyoxalase 1 in MG mice. Oocytes ovulated by MG mice exhibited atypical meiotic spindles, a condition predisposing to embryo aneuploidy. Our results from mouse oocytes revealed for the first time that SIRT1 could modulate MG scavenging by promoting expression of glyoxalases. The finding that up-regulation of glyoxalase 1 is associated with that of components of a SIRT1 functional network in the ovaries of MG mice provides strong evidence that SIRT1 participates in the response to methylglyoxal-dependent glycative stress in the female gonad.

p53 and reproduction

Tumor protein 53 (TP53) and its related family of p63 and p73 are tumor suppressor genes that regulate cellular activity to enhance longevity. p53 binds to specific response elements in DNA, modulating the transcription of genes that govern the major defenses against tumor growth. Additional members of the p53 family are involved with male and female germ cell survival. Although the majority of studies have focused on p53 as a tumor suppressor gene, little is known about its function in normal cellular processes. Polymorphisms of TP53 codon 72 that alter activity levels have been studied with respect to implantation in both the murine and human models. TP53 codon 72 (arginine) exhibits higher rates of apoptosis and leukemia inhibitory factor expression, whereas the C allele (proline) reduces leukemia inhibitory factor expression. Here, we review the role of p53 and the family of p53 proteins, along with the potential effect of p53 polymorphisms on reproduction.

TP53 gene Arg72Pro polymorphism and male infertility risk: A meta-analysis

To evaluate the association between TP53 codon72 polymorphism and male infertility risk. We conducted a search on Medline, Embase, Web of Science and CNKI up to April 30, 2017. Odds ratio (OR) and 95% confidence interval (95% CI) were used to assess the strength of the association. Seven studies including 1,818 cases and 2,278 controls met the inclusion criteria. The pooled results indicated that no significant association was observed between TP53 codon72 polymorphism and male infertility risk (G versus C: OR = 1.11, 95%CI = 0.94-1.32; GG versus CC: OR = 1.26, 95%CI = 0.90-1.78; GG versus GC+CC: OR = 1.16, 95%CI = 0.90-1.49; GG+GC versus CC: OR = 1.15, 95%CI = 0.88-1.49). In the subgroup analysis by ethnicity, significant association was observed between TP53 codon72 polymorphism and male infertility risk in non-Chinese (G versus C: OR = 1.47, 95%CI = 1.14-1.89), but not in Chinese population (G versus C: OR = 1.03, 95%CI = 0.87-1.22). In conclusion, this study suggested that TP53 codon72 polymorphism might be associated with an increased susceptibility to male infertility in non-Chinese population, but not in Chinese population. Studies with larger sample sizes and representative population-based cases and well-matched controls are needed to validate our results.

Detection of a novel, primate-specific 'kill switch' tumor suppression mechanism that may fundamentally control cancer risk in humans: an unexpected twist in the basic biology of TP53

The activation of TP53 is well known to exert tumor suppressive effects. We have detected a primate-specific adrenal androgen-mediated tumor suppression system in which circulating DHEAS is converted to DHEA specifically in cells in which TP53 has been inactivated DHEA is an uncompetitive inhibitor of glucose-6-phosphate dehydrogenase (G6PD), an enzyme indispensable for maintaining reactive oxygen species within limits survivable by the cell. Uncompetitive inhibition is otherwise unknown in natural systems because it becomes irreversible in the presence of high concentrations of substrate and inhibitor. In addition to primate-specific circulating DHEAS, a unique, primate-specific sequence motif that disables an activating regulatory site in the glucose-6-phosphatase (G6PC) promoter was also required to enable function of this previously unrecognized tumor suppression system. In human somatic cells, loss of TP53 thus triggers activation of DHEAS transport proteins and steroid sulfatase, which converts circulating DHEAS into intracellular DHEA, and hexokinase which increases glucose-6-phosphate substrate concentration. The triggering of these enzymes in the TP53-affected cell combines with the primate-specific G6PC promoter sequence motif that enables G6P substrate accumulation, driving uncompetitive inhibition of G6PD to irreversibility and ROS-mediated cell death. By this catastrophic 'kill switch' mechanism, TP53 mutations are effectively prevented from initiating tumorigenesis in the somatic cells of humans, the primate with the highest peak levels of circulating DHEAS. TP53 mutations in human tumors therefore represent fossils of kill switch failure resulting from an age-related decline in circulating DHEAS, a potentially reversible artifact of hominid evolution.

The capacity of oocytes for DNA repair

Female fertility and offspring health are critically dependent on the maintenance of an adequate supply of high-quality oocytes. Like somatic cells, oocytes are subject to a variety of different types of DNA damage arising from endogenous cellular processes and exposure to exogenous genotoxic stressors. While the repair of intentionally induced DNA double strand breaks in gametes during meiotic recombination is well characterised, less is known about the ability of oocytes to repair pathological DNA damage and the relative contribution of DNA repair to oocyte quality is not well defined. This review will discuss emerging data suggesting that oocytes are in fact capable of efficient DNA repair and that DNA repair may be an important mechanism for ensuring female fertility, as well as the transmission of high-quality genetic material to subsequent generations.

Control of metabolism by p53 - Cancer and beyond

p53 is an important tumour suppressor gene, with loss of p53 contributing to the development of most human cancers. However, the activation of p53 in response to stress signals underpins a role for p53 in diverse aspects of health and disease. Activities of p53 that regulate metabolism can play a role in maintaining homeostasis and protecting cells from damage - so preventing disease development. By contrast, either loss or over-activation of p53 can contribute to numerous metabolic pathologies, including aging, obesity and diabetes.

Programmed cell death in the human ovary

During a woman's reproductive life, only about 400 primordial follicles will develop into a preovulatory follicle and undergo ovulation, releasing an oocyte available for fertilization. The process of formation and selection of these follicles is complex and involves a multistep process characterized by a balance between survival and death of the oocytes and the surrounding follicular cells. Although the mechanisms underlying such process are not completely clarified yet, it is common idea that they can occur through various types of programmed cellular death (PCD). Since atresia is the principal destiny of the ovarian follicles, it is relevant to understand how this process takes place and how it is regulated. In this review, after a summary description of folliculogenesis in humans, the main mechanisms of atresia reported to occur during folliculogenesis from birth to adult age, in the human ovary and in other mammals when appropriate, are described.

Regulation of the Activity in the p53 Family Depends on the Organization of the Transactivation Domain

Despite high sequence homology among the p53 family members, the regulation of their transactivation potential is based on strikingly different mechanisms. Previous studies revealed that the activity of TAp63α is regulated via an autoinhibitory mechanism that keeps inactive TAp63α in a dimeric conformation. While all p73 isoforms are constitutive tetramers, their basal activity is much lower compared with tetrameric TAp63. We show that the dimeric state of TAp63α not only reduces DNA binding affinity, but also suppresses interaction with the acetyltransferase p300. Exchange of the transactivation domains is sufficient to transfer the regulatory characteristics between p63 and p73. Structure determination of the transactivation domains of p63 and p73 in complex with the p300 Taz2 domain further revealed that, in contrast to p53 and p73, p63 has a single transactivation domain. Sequences essential for stabilizing the closed dimer of TAp63α have evolved into a second transactivation domain in p73 and p53.

Oocyte DNA damage quality control requires consecutive interplay of CHK2 and CK1 to activate p63

The survival rate of cancer patients is steadily increasing, owing to more efficient therapies. Understanding the molecular mechanisms of chemotherapy-induced premature ovarian insufficiency (POI) could identify targets for prevention of POI. Loss of the primordial follicle reserve is the most important cause of POI, with the p53 family member p63 being responsible for DNA-damage-induced apoptosis of resting oocytes. Here, we provide the first detailed mechanistic insight into the activation of p63, a process that requires phosphorylation by both the priming kinase CHK2 and the executioner kinase CK1 in mouse primordial follicles. We further describe the structural changes induced by phosphorylation that enable p63 to adopt its active tetrameric conformation and demonstrate that previously discussed phosphorylation by c-Abl is not involved in this process. Inhibition of CK1 rescues primary oocytes from doxorubicin and cisplatin-induced apoptosis, thus uncovering a new target for the development of fertoprotective therapies.