The expanding universe of p53 targets

p53-mediated regulation of mitochondrial dynamics plays a pivotal role in the senescence of various normal cells as well as cancer cells

The tumor suppressor p53 is known as a critical mediator of many cellular processes, including cellular senescence, but its role in mitochondrial dynamics is not fully understood. We have previously shown that p53 regulates mitochondrial dynamics via the PKA-Drp1 pathway to induce cellular senescence. In this study, to further understand the role of p53-dependent regulation of mitochondrial dynamics, the effect of p53 expression on mitochondrial morphology was examined in various cancer cell lines and normal human cells. We found that p53 induced remarkable mitochondrial elongation and cellular senescence in various cancer cells regardless of their p53 status. p53 also induced mitochondrial elongation in various human primary normal cells, suggesting that p53-mediated mitochondrial elongation is a general phenomenon. Moreover, we found that p53 plays an essential role in mitochondrial elongation in H-Ras-induced cellular senescence and in the replicative senescence of normal human cells. Treatment with the MDM-2 antagonist Nutlin-3a also induced mitochondrial elongation through the PKA-Drp1 pathway in IMR90 normal human cells. Furthermore, the inhibition of PKA activity in late-passage normal cells significantly reduced both mitochondrial elongation and cellular senescence, suggesting that the p53-PKA pathway is essential for maintaining the senescence phenotype in normal cells. Together, these results further confirm the direct regulation of mitochondrial dynamics by p53 and the important role of p53-mediated mitochondrial elongation in cellular senescence.

Insight to Functional Conformation and Noncovalent Interactions of Protein-Protein Assembly Using MALDI Mass Spectrometry

Noncovalent interactions are the keys to the structural organization of biomolecule e.g., proteins, glycans, lipids in the process of molecular recognition processes e.g., enzyme-substrate, antigen-antibody. Protein interactions lead to conformational changes, which dictate the functionality of that protein-protein complex. Besides biophysics techniques, noncovalent interaction and conformational dynamics, can be studied via mass spectrometry (MS), which represents a powerful tool, due to its low sample consumption, high sensitivity, and label-free sample. In this review, the focus will be placed on Matrix-Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-MS) and its role in the analysis of protein-protein noncovalent assemblies exploring the relationship within noncovalent interaction, conformation, and biological function.

Context is key: Understanding the regulation, functional control, and activities of the p53 tumour suppressor

The p53 tumour suppressor is considered one of the most critical genes in cancer biology. By upregulating apoptosis, cell cycle arrest, and DNA damage repair in normal cells, p53 prevents the propagation of cells with tumorigenic potential; therefore, mutations in p53 are associated with carcinogenic transformation and can be accompanied by the accumulation of a novel gain-of-function oncogenic protein, mutant p53. Although p53 is most often understood to utilize context-dependent post-translational modifications to achieve regulation of its many target genes, recent research has also sought to define other mechanisms of regulating p53 gene expression prior to translation and to understand how this alternative regulation of p53 may influence target gene expression and cellular outcome. This review attempts to summarize what is known about p53 regulation at the transcriptional, post-transcriptional, and post-translational levels while paying special attention to the ways in which context may influence p53 regulation and subsequent regulation of its target genes.

MuRF1/TRIM63, Master Regulator of Muscle Mass

The E3 ubiquitin ligase MuRF1/TRIM63 was identified 20 years ago and suspected to play important roles during skeletal muscle atrophy. Since then, numerous studies have been conducted to decipher the roles, molecular mechanisms and regulation of this enzyme. This revealed that MuRF1 is an important player in the skeletal muscle atrophy process occurring during catabolic states, making MuRF1 a prime candidate for pharmacological treatments against muscle wasting. Indeed, muscle wasting is an associated event of several diseases (e.g., cancer, sepsis, diabetes, renal failure, etc.) and negatively impacts the prognosis of patients, which has stimulated the search for MuRF1 inhibitory molecules. However, studies on MuRF1 cardiac functions revealed that MuRF1 is also cardioprotective, revealing a yin and yang role of MuRF1, being detrimental in skeletal muscle and beneficial in the heart. This review discusses data obtained on MuRF1, both in skeletal and cardiac muscles, over the past 20 years, regarding the structure, the regulation, the location and the different functions identified, and the first inhibitors reported, and aim to draw the picture of what is known about MuRF1. The review also discusses important MuRF1 characteristics to consider for the design of future drugs to maintain skeletal muscle mass in patients with different pathologies.

p53 drives a transcriptional program that elicits a non-cell-autonomous response and alters cell state in vivo

Cell stress and DNA damage activate the tumor suppressor p53, triggering transcriptional activation of a myriad of target genes. The molecular, morphological, and physiological consequences of this activation remain poorly understood in vivo. We activated a p53 transcriptional program in mice by deletion of Mdm2, a gene that encodes the major p53 inhibitor. By overlaying tissue-specific RNA-sequencing data from pancreas, small intestine, ovary, kidney, and heart with existing p53 chromatin immunoprecipitation (ChIP) sequencing, we identified a large repertoire of tissue-specific p53 genes and a common p53 transcriptional signature of seven genes, which included Mdm2 but not p21 Global p53 activation caused a metaplastic phenotype in the pancreas that was missing in mice with acinar-specific p53 activation, suggesting non-cell-autonomous effects. The p53 cellular response at single-cell resolution in the intestine altered transcriptional cell state, leading to a proximal enterocyte population enriched for genes within oxidative phosphorylation pathways. In addition, a population of active CD8+ T cells was recruited. Combined, this study provides a comprehensive profile of the p53 transcriptional response in vivo, revealing both tissue-specific transcriptomes and a unique signature, which were integrated to induce both cell-autonomous and non-cell-autonomous responses and transcriptional plasticity.

Construction and validation of a TP53-associated immune prognostic model for gastric cancer

Increasing evidence indicates that TP53 mutation impacts the patients' prognosis by regulating the gastric cancer (GC) immunophenotype. An immune prognostic signature (IPS) was constructed based on TP53 status. The effects of the IPS on the immune microenvironment of GC were analyzed. We also constructed a nomogram integrating the IPS and other clinical factors. An IPS was constructed in the TCGA cohort and validated in the meta-GEO cohort. TP53 mutation resulted in the downregulation of the immune response in GC. Concretely, high-risk patients were characterized by increased monocyte, macrophage M0 and T cell follicular helper infiltration; increased stromal score, ESTIMATE score and immune score; higher TIM3 and BTLA expression; and decreased dendritic cell and T cell CD4 memory-activated infiltration and tumor purity. The nomogram also showed good predictive performance. These results suggest that the IPS is an effective prognostic indicator for GC patients, which might provide a theoretical foundation for immunotherapy.

Loss of p53 in mesenchymal stem cells promotes alteration of bone remodeling through negative regulation of osteoprotegerin

p53 plays a pivotal role in controlling the differentiation of mesenchymal stem cells (MSCs) by regulating genes involved in cell cycle and early steps of differentiation process. In the context of osteogenic differentiation of MSCs and bone homeostasis, the osteoprotegerin/receptor activator of NF-κB ligand/receptor activator of NF-κB (OPG/RANKL/RANK) axis is a critical signaling pathway. The absence or loss of function of p53 has been implicated in aberrant osteogenic differentiation of MSCs that results in higher bone formation versus erosion, leading to an unbalanced bone remodeling. Here, we show by microCT that mice with p53 deletion systemically or specifically in mesenchymal cells possess significantly higher bone density than their respective littermate controls. There is a negative correlation between p53 and OPG both in vivo by analysis of serum from p53^+/+, p53^+/-, and p53^-/- mice and in vitro by p53 knockdown and ChIP assay in MSCs. Notably, high expression of Opg or its combination with low level of p53 are prominent features in clinical cancer lesion of osteosarcoma and prostate cancer respectively, which correlate with poor survival. Intra-bone marrow injection of prostate cancer cells, together with androgen can suppress p53 expression and enhance local Opg expression, leading to an enhancement of bone density. Our results support the notion that MSCs, as osteoblast progenitor cells and one major component of bone microenvironment, represent a cellular source of OPG, whose amount is regulated by the p53 status. It also highlights a key role for the p53-OPG axis in regulating the cancer associated bone remodeling.

Understanding p53 functions through p53 antibodies

TP53 is the most frequently mutated gene across all cancer types. Our understanding of its functions has evolved since its discovery four decades ago. Initially thought to be an oncogene, it was later realized to be a critical tumour suppressor. A significant amount of our knowledge about p53 functions have come from the use of antibodies against its various forms. The early anti-p53 antibodies contributed to the recognition of p53 accumulation as a common feature of cancer cells and to our understanding of p53 DNA-binding and transcription activities. They led to the concept that conformational changes can facilitate p53’s activity as a growth inhibitory protein. The ensuing p53 conformational-specific antibodies further underlined p53’s conformational flexibility, collectively forming the basis for current efforts to generate therapeutic molecules capable of altering the conformation of mutant p53. A subsequent barrage of antibodies against post-translational modifications on p53 has clarified p53’s roles further, especially with respect to the mechanistic details and context-dependence of its activity. More recently, the generation of p53 mutation-specific antibodies have highlighted the possibility to go beyond the general framework of our comprehension of mutant p53—and promises to provide insights into the specific properties of individual p53 mutants. This review summarizes our current knowledge of p53 functions derived through the major classes of anti-p53 antibodies, which could be a paradigm for understanding other molecular events in health and disease.

TP53 dysfunction in chronic lymphocytic leukemia: clinical relevance in the era of B-cell receptors and BCL-2 inhibitors

INTRODUCTION

Patients with TP53 dysfunction, assessed by del(17p) or TP53 mutations, respond poorly to chemo-immunotherapy and fare better with the new therapies (BCR and BCL-2 inhibitors); however, it is unclear whether their response is similar to that of patients without anomalies or whether there is currently an adequate determination of TP53 dysfunction.

AREA COVERED

A literature search was undertaken on clinical trials and real-world experience data on patients with TP53 dysfunction treated with different protocols. Moreover, data on the TP53 biological function and on the tests currently employed for its assessment were reviewed.

EXPERT OPINION

Although TP53 dysfunction has less negative influence on the new biological therapies, patients with these alterations, particularly those with biallelic inactivation of TP53, have a worst outcome with these therapies than those without alterations. At present, a determination of TP53, particularly with next generation sequencing (NGS) methodologies, may be sufficient for the identifications of the patients unsuitable for chemo-immunotherapy, although integration with del(17p) would be advisable. For the future, more extensive determinations of the TP53 status, including functional assays, may become part of the current armamentarium for a better patient stratification and treatment with newer protocols.

p53-responsive TLR8 SNP enhances human innate immune response to respiratory syncytial virus

The Toll-like receptor 8 (TLR8) has an important role in innate immune responses to RNA viral infections, including respiratory syncytial virus (RSV). We previously reported that TLR8 expression was increased directly by the tumor suppressor and transcription factor p53 via a single nucleotide polymorphism (SNP) (rs3761624) in the TLR8 promoter, thereby placing TLR8 in the p53/immune axis. Because this SNP is in linkage disequilibrium with other SNPs associated with several infectious diseases, we addressed the combined influence of p53 and the SNP on downstream inflammatory signaling in response to a TLR8 cognate ssRNA ligand. Using human primary lymphocytes, p53 induction by chemotherapeutic agents such as ionizing radiation caused SNP-dependent synergistic increases in IL-6 following incubation with an ssRNA ligand, as well as TLR8 RNA and protein expression along with p53 binding at the TLR-p53 SNP site. Because TLR8 is X-linked, the increases were generally reduced in heterozygous females. We found a corresponding association of the p53-responsive allele with RSV disease severity in infants hospitalized with RSV infection. We conclude that p53 can strongly influence TLR8-mediated immune responses and that knowledge of the p53-responsive SNP can inform diagnosis and prognosis of RSV disease and other diseases that might have a TLR8 component, including cancer.

S100A1 blocks the interaction between p53 and mdm2 and decreases cell proliferation activity

About 50% of human cancers across the globe arise due to a mutation in the p53 gene which gives rise to its functional inactive form, and in the rest of the cancer the efficacy of active p53 (wild-type) is hindered by MDM2-mediated degradation. Breakdown of the p53-MDM2 association may constitute an effective strategy to stimulate or reinstate the activity of wild type p53, thereby reviving the p53 tumor suppressor capability. S100A1 has been revealed to associate with the N-terminal domain of MDM2 and p53 protein. We utilized NMR spectroscopy to study the interface amongst the S100A1 and N-terminal domain of MDM2. Additionally, the S100A1-MDM2 complex generated through the HADDOCK program was then superimposed with the p53 (peptide) -MDM2 complex reported earlier. The overlay indicated that a segment of S100A1 could block the interaction of p53 (peptide) -MDM2 complex significantly. To further justify our assumption, we performed HSQC-NMR titration for the S100A1 and p53 N-terminal domain (p53-TAD). The data obtained indicated that the S100A1 segment comprising nearly 17 residues have some common residues that interact with both MDM2 and p53-TAD. Further, we synthesized the 17-residue peptide derived from the S100A1 protein and attached it to the cell-penetrating HIV-TAT peptide. The HSQC-NMR competitive binding experiment revealed that Peptide 1 could successfully interfere with the p53-MDM2 interaction. Furthermore, functional effects of the peptide was validated in cancer cells. The results showed that Peptide 1 effectively inhibited cell proliferation, and increased the protein levels of p53 and its downstream p21 in MCF-7 cells. Treatment of Peptide 1 resulted in cell cycle arrest at G2/M phase, and also induced apoptotic cell death at higher concentration. Taken together, the results suggest that disruption of the interaction of p53 and MDM2 by Peptide 1 could activate normal p53 functions, leading to cell cycle arrest and apoptotic cell death in cancer cells. We proposed here that S100A1 could influence the p53-MDM2 interaction credibly and possibly reactivates the wild type p53 pathway.

Emerging roles of long non-coding RNAs in the p53 network

Transcription factor p53 is activated in response to numerous stress stimuli in order to promote repair and survival or death of abnormal cells. For decades, regulatory mechanisms and downstream targets that execute the many biological functions of tumour suppressor p53 largely focused on the products of protein-coding genes. Recently, an entirely new class of molecules, termed long non-coding RNAs (lncRNAs), were discovered as key regulatory players in shaping p53 activity and biological outcomes. Many p53-regulated lncRNAs are now reported to either directly or indirectly intervene in p53-regulatory networks, generally in fine-tuning p53's tumour surveillance programme. Recent studies reveal that signals that converge upon p53 to regulate its activity, and molecules that implement downstream p53-response include both proteins and lncRNAs. In this review, we discuss the non-proteomic component of p53-regulatory networks, focusing on lncRNAs regulated by p53 and/or that regulate p53 activity, and their impact on biological outcomes.

Cytotoxic Property of Grias neuberthii Extract on Human Colon Cancer Cells: A Crucial Role of Autophagy

Traditional herbal medicine has become an important alternative in the treatment of various cancer types, including colon cancer, which represents one of the main health problems around the world. Therefore, the search for new therapies to counteract this disease is very active. Grias neuberthii is an endemic plant located in the Ecuadorian Amazon region, which has been used in traditional medicine for its pharmacological properties, including its ability to inhibit tumor cell growth, although scientific studies are limited. We have analyzed the effect of this plant on two colon carcinoma cell lines, that is, RKO (normal p53) and SW613-B3 (mutated p53) cells. Among several extracts obtained from various parts of G. neuberthii plant, we identified the extract with the greatest cytotoxic potential, derived from the stem bark. The cytotoxic effect was similar on both cell lines, thus indicating that it is independent of the status of p53. However, significant differences were observed after the analysis of colony formation, with RKO cells being more sensitive than SW613-B3. No evidence for apoptotic markers was recorded; nevertheless, both cell lines showed signs of autophagy after the treatment, including increased Beclin-1 and LC3-II and decreased p62. Finally, three chemical compounds, possibly responsible for the effect observed in both cell lines, were identified: lupeol (1), 3′-O-methyl ellagic acid 4-O-β-D-rhamnopyranoside (2), and 19-α-hydroxy-asiatic acid monoglucoside (3).

PABPN1, a Target of p63, Modulates Keratinocyte Differentiation through Regulation of p63α mRNA Translation

p63 is expressed from two promoters and produces two N-terminal isoforms, TAp63 and ΔNp63. Alternative splicing creates three C-terminal isoforms p63α, p63β, and p63δ, whereas alternative polyadenylation (APA) in coding sequence creates two more C-terminal isoforms p63γ and p63ε. Although several transcription factors have been identified to differentially regulate the N-terminal p63 isoforms, it is unclear how the C-terminal p63 isoforms are regulated. Thus, we determined whether PABPN1, a key regulator of APA, may differentially regulate the C-terminal p63 isoforms. We found that PABPN1 deficiency increases p63γ mRNA through APA in coding sequence. We also found that PABPN1 is necessary for p63α translation by modulating the binding of translation initiation factors eIF4E and eIF4G to p63α mRNA. Moreover, we found that the p53 family, especially p63α, regulates PABPN1 transcription, suggesting that the mutual regulation between p63 and PABPN1 forms a feedback loop. Furthermore, we found that PABPN1 deficiency inhibits keratinocyte cell growth, which can be rescued by ectopic ΔNp63α. Finally, we found that PABPN1 controls the terminal differentiation of HaCaT keratinocytes by modulating ΔNp63α expression. Taken together, our findings suggest that PABPN1 is a key regulator of the C-terminal p63 isoforms through APA in coding sequence and mRNA translation and that the p63-PABPN1 loop modulates p63 activity and the APA landscape.

Ipr1 Regulation by Cyclic GMP-AMP Synthase/Interferon Regulatory Factor 3 and Modulation of Irgm1 Expression via p53

Intracellular pathogen resistance 1 (Ipr1) has been found to be a mediator to integrate cyclic GMP-AMP synthase (cGAS)-interferon regulatory factor 3 (IRF3), activated by intracellular pathogens, with the p53 pathway. Previous studies have shown the process of Ipr1 induction by various immune reactions, including intracellular bacterial and viral infections. The present study demonstrated that Ipr1 is regulated by the cGAS-IRF3 pathway during pathogenic infection. IRF3 was found to regulate Ipr1 expression by directly binding the interferon-stimulated response element motif of the Ipr1 promoter. Knockdown of Ipr1 decreased the expression of immunity-related GTPase family M member 1 (Irgm1), which plays critical roles in autophagy initiation. Irgm1 promoter characterization revealed a p53 motif in front of the transcription start site. P53 was found to participate in regulation of Irgm1 expression and IPR1-related effects on P53 stability by affecting interactions between ribosomal protein L11 (RPL11) and transformed mouse 3T3 cell double minute 2 (MDM2). Our results indicate that Ipr1 integrates cGAS-IRF3 with p53-modulated Irgm1 expression.

Integrated analysis of miRNA and mRNA expression profiles in p53-edited PFF cells

p53 is the most frequently mutated gene in human cancers, with over half of all tumors harboring mutation at this locus. R248 and R249 (corresponding to porcine R241 and R242), are among the hotspot mutations frequently mutated in liver, lung, breast, and some other cancers. In this study, p53 gene was knocked out or point-edited (R241 and R242 were converted to 241W and 242S) in porcine fetal fibroblast (PFF) cells via CRISPR-Cas9 technique. High throughput sequencing of miRNA and mRNA uncovered a total of 225 differentially expressed miRNAs (DEMs) and 738 differentially expressed genes (DEGs) in the p53 knockout (p53-KO) cells, and a total of 211 DEMs and 722 DEGs in the point-modified (p53-241W242S) cells. Totally 28 annotated DEMs were found to overlap between p53-KO/p53-WT and p53-241W242S/p53-WT miRNAs datasets, of which miR-34 c, miR-218, miR-205, miR-105-1, miR-105-2, miR-206, miR-224 and miR-429 play important roles in p53 regulatory network. Among the top 10 DEGs in p53-KO and p53-241W242S cells, most genes were reported to be involved in tumors, cell proliferation or cell migration. p53-KO and p53-241W242S cells showed a significantly higher (P < 0.01) proliferation rate compared with p53-WT cells. In conclusion, genetic modifications of p53 gene significantly affect the expression levels of a large number of genes and miRNAs in the PFF cells. The p53-edited PFF cells could be used as non-tumor cell models for investigating the p53 signaling network, and as donor cells for somatic nuclear transfer, with the aim to develop porcine models with the corresponding p53 mutations.Abbreviations: CRISPR-Cas9: Clustered regularly interspaced short palindromic repeats-associated protein 9; PFF: porcine fetal fibroblasts; SCNT: somatic cell nuclear transfer; RNA sequencing: small RNA sequencing and mRNA sequencing; DEGs: differentially expressed mRNAs; DEMs: differentially expressed miRNAs.

Chronic exposure to excess iron promotes EMT and cancer via p53 loss in pancreatic cancer

Based on the evidence that hemochromatosis, an iron-overload disease, drives hepatocellular carcinoma, we hypothesized that chronic exposure to excess iron, either due to genetic or environmental causes, predisposes an individual to cancer. Using pancreatic cancer as our primary focus, we employed cell culture studies to interrogate the connection between excess iron and cancer, and combined in vitro and in vivo studies to explore the connection further. Ferric ammonium citrate was used as an exogenous iron source. Chronic exposure to excess iron induced epithelial-mesenchymal transition (EMT) in normal and cancer cell lines, loss of p53, and suppression of p53 transcriptional activity evidenced from decreased expression of p53 target genes (p21, cyclin D1, Bax, SLC7A11). To further extrapolate our cell culture data, we generated EL-Kras^G12D (EL-Kras) mouse (pancreatic neoplastic mouse model) expressing Hfe^+/+and Hfe^−/− genetic background. p53 target gene expression decreased in EL-Kras/Hfe^−/− mouse pancreas compared to EL-Kras/Hfe^+/+ mouse pancreas. Interestingly, the incidence of acinar-to-ductal metaplasia and cystic pancreatic neoplasms (CPN) decreased in EL-Kras/Hfe^−/− mice, but the CPNs that did develop were larger in these mice than in EL-Kras/Hfe^+/+ mice. In conclusion, these in vitro and in vivo studies support a potential role for chronic exposure to excess iron as a promoter of more aggressive disease via p53 loss and SLC7A11 upregulation within pancreatic epithelial cells.

Chitinase 3 like 1 suppresses the stability and activity of p53 to promote lung tumorigenesis

Background

Chitinase 3 like 1 protein (Chi3L1) is expressed in several cancers, and a few evidences suggest that the secreted Chi3L1 contributes to tumor development. However, the molecular mechanisms of intracellular Chi3L1 are unknown in the lung tumor development. Methods: In the present study, we generated Chi3L1 knockout mice (Chi3L1^KO(−/−)) using CRISPR/Cas9 system to investigate the role of Chi3L1 on lung tumorigenesis.

Results

We established lung metastasis induced by i.v. injections of B16F10 in Chi3L1^KO(−/−). The lung tumor nodules were significantly reduced in Chi3L1^KO(−/−) and protein levels of p53, p21, BAX, and cleaved-caspase 3 were significantly increased in Chi3L1^KO(−/−), while protein levels of cyclin E1, CDK2, and phsphorylation of STAT3 were decreased in Chi3L1^KO(−/−). Allograft mice inoculated with B16F10 also suppressed tumor growth and increased p53 and its target proteins including p21 and BAX. In addition, knockdown of Chi3L1 in lung cancer cells inhibited lung cancer cell growth and upregulated p53 expression with p21 and BAX, and a decrease in phosphorylation of STAT3. Furthermore, we found that intracellular Chi3L1 physically interacted and colocalized with p53 to inhibit its protein stability and transcriptional activity for target genes related with cell cycle arrest and apoptosis. In lung tumor patient, we clinically found that Chi3L1 expression was upregulated with a decrease in p53 expression, as well as we validated that intracellular Chi3L1 was colocalized, reversely expressed, and physically interacted with p53, which results in suppression of the expression and function of p53 in lung tumor patient.

Conclusions

Our studies suggest that intracellular Chi3L1 plays a critical role in the lung tumorigenesis by regulating its novel target protein, p53 in both an in vitro and in vivo system.

Nonsense mutation-dependent reinitiation of translation in mammalian cells

In-frame stop codons mark the termination of translation. However, post-termination ribosomes can reinitiate translation at downstream AUG codons. In mammals, reinitiation is most efficient when the termination codon is positioned close to the 5′-proximal initiation site and around 78 bases upstream of the reinitiation site. The phenomenon was studied mainly in the context of open reading frames (ORFs) found within the 5′-untranslated region, or polycicstronic viral mRNA. We hypothesized that reinitiation of translation following nonsense mutations within the main ORF of p53 can promote the expression of N-truncated p53 isoforms such as Δ40, Δ133 and Δ160p53. Here, we report that expression of all known N-truncated p53 isoforms by reinitiation is mechanistically feasible, including expression of the previously unidentified variant Δ66p53. Moreover, we found that significant reinitiation of translation can be promoted by nonsense mutations located even 126 codons downstream of the 5′-proximal initiation site, and observed when the reinitiation site is positioned between 6 and 243 bases downstream of the nonsense mutation. We also demonstrate that reinitiation can stabilise p53 mRNA transcripts with a premature termination codon, by allowing such transcripts to evade the nonsense mediated decay pathway. Our data suggest that the expression of N-truncated proteins from alleles carrying a premature termination codon is more prevalent than previously thought.

p53's Extended Reach: The Mutant p53 Secretome

p53 suppresses tumorigenesis by activating a plethora of effector pathways. While most of these operate primarily inside of cells to limit proliferation and survival of incipient cancer cells, many extend to the extracellular space. In particular, p53 controls expression and secretion of numerous extracellular factors that are either soluble or contained within extracellular vesicles such as exosomes. As part of the cellular secretome, they execute key roles in cell-cell communication and extracellular matrix remodeling. Mutations in the p53-encoding TP53 gene are the most frequent genetic alterations in cancer cells, and therefore, have profound impact on the composition of the tumor cell secretome. In this review, we discuss how the loss or dominant-negative inhibition of wild-type p53 in concert with a gain of neomorphic properties observed for many mutant p53 proteins, shapes a tumor cell secretome that creates a supportive microenvironment at the primary tumor site and primes niches in distant organs for future metastatic colonization.

Whole-body MRI within a surveillance program for carriers with clinically actionable germline TP53 variants - the Swedish constitutional TP53 study SWEP53

Background

The current guidelines in Sweden regarding individuals with a clinically actionable (i.e. pathogenic or likely pathogenic) germline TP53 variant recommend patients to take part of the national Swedish P53 Study (SWEP53).

Methods

The study comprises a patient registry (mandatory for all participants) and three optional parts: a biobank, a surveillance program and a psychosocial evaluation of the surveillance. All known adult eligible carriers regardless of age are offered to take part of the surveillance program offering MRI yearly of the whole-body, breast, and brain as well as breast ultrasound. A special surveillance program is offered for individuals 15–18 years old with a 50% risk of being a mutation carrier or with a verified TP53 variation, includes ultrasound of the abdomen and urine corticosteroid profiles. Clinically motivated further examinations are performed upon need. The national inclusion is performed through the six clinical genetic units in Sweden at Umeå, Uppsala, Stockholm, Gothenburg, Linköping and Lund, and the surveillance is mainly performed through the oncology clinics.

Results

To date, a total of 41 adults and 11 children have been included in the study.

Conclusions

The SWEP53 is the first structured national surveillance program including radiological and clinical routines for TP53 mutation carriers in the Scandinavian setting. The aim of this publication is to present and describe the ongoing Swedish surveillance study to encourage the initiation of similar studies and to contribute to the knowledge of adequate clinical handling of these cancer prone families.

Trial registration

Trial registration number: ISRCTN13103571, retrospectively registered on 14/10/2019.

Small Molecules Targeting Mutant P53: A Promising Approach for Cancer Treatment

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More than half of all human tumors express mutant forms of p53, with the ovary, lung, pancreas, and colorectal cancers among the tumor types that display the highest prevalence of p53 mutations. In addition, the expression of mutant forms of p53 in tumors is associated with poor prognosis due to increased chemoresistance and invasiveness. Therefore, the pharmacological restoration of wild-type-like activity to mutant p53 arises as a promising therapeutic strategy against cancer. This review is focused on the most relevant mutant p53 small molecule reactivators described to date. Despite some of them have entered into clinical trials, none has reached the clinic, which emphasizes that new pharmacological alternatives, particularly with higher selectivity and lower adverse toxic side effects, are still required.

The Influence of Quadruplex Structure in Proximity to P53 Target Sequences on the Transactivation Potential of P53 Alpha Isoforms

p53 is one of the most studied tumor suppressor proteins that plays an important role in basic biological processes including cell cycle, DNA damage response, apoptosis, and senescence. The human TP53 gene contains alternative promoters that produce N-terminally truncated proteins and can produce several isoforms due to alternative splicing. p53 function is realized by binding to a specific DNA response element (RE), resulting in the transactivation of target genes. Here, we evaluated the influence of quadruplex DNA structure on the transactivation potential of full-length and N-terminal truncated p53α isoforms in a panel of S. cerevisiae luciferase reporter strains. Our results show that a G-quadruplex prone sequence is not sufficient for transcription activation by p53α isoforms, but the presence of this feature in proximity to a p53 RE leads to a significant reduction of transcriptional activity and changes the dynamics between co-expressed p53α isoforms.

Screening of Cellular Stress Responses Induced by Ambient Aerosol Ultrafine Particle Fraction PM0.5 in A549 Cells

Effects of airborne particles on the expression status of markers of cellular toxic stress and on the release of eicosanoids, linked with inflammation and oxidative damage, remain poorly characterized. Therefore, we proposed a set of various methodological approaches in order to address complexity of PM0.5-induced toxicity. For this purpose, we used a well-characterized model of A549 pulmonary epithelial cells exposed to a non-cytotoxic concentration of ambient aerosol particle fraction PM0.5 for 24 h. Electron microscopy confirmed accumulation of PM0.5 within A549 cells, yet, autophagy was not induced. Expression profiles of various cellular stress response genes that have been previously shown to be involved in early stress responses, namely unfolded protein response, DNA damage response, and in aryl hydrocarbon receptor (AhR) and p53 signaling, were analyzed. This analysis revealed induction of GREM1, EGR1, CYP1A1, CDK1A, PUMA, NOXA and GDF15 and suppression of SOX9 in response to PM0.5 exposure. Analysis of eicosanoids showed no oxidative damage and only a weak anti-inflammatory response. In conclusion, this study helps to identify novel gene markers, GREM1, EGR1, GDF15 and SOX9, that may represent a valuable tool for routine testing of PM0.5-induced in vitro toxicity in lung epithelial cells.

The concomitant use of USP28 and p53 to predict the progression of urothelial carcinoma of the bladder

The Ubiquitin Specific Peptidase 28 (USP28) is a deubiquitinase involved in the DNA damage pathway. Recently, USP28 protein is reported to play roles in the mechanism of p53 action and could be a possible prognostic marker for bladder cancer (BCa). This study aims to explore the relation of USP28 with tumor growth and invasion, and also to investigate the interplay between USP28 and p53 in BCa. Expression levels of USP28 and p53 in human BCa (invasive and non-invasive, n = 43) and control tissues (n = 8) were evaluated by immunohistochemistry and quantitative real-time polymerase chain reaction (qPCR) profiling. The relationship between protein and gene expression levels, clinicopathologic features and prognosis were evaluated. Significant positive correlations were found between BCa tumor progression and the USP28 expression, and also between the USP28 and p53 scores (p all < 0.05). Immunohistochemistry staining percentages were strongly correlated between USP28 and p53, and also positive correlations between tumor progression and p53 expressions were determined (p all < 0.001). Interestingly, USP28 and p53 were highly expressed and correlated in BCa. Consequently, the immunohistochemistry and qPCR results reported in our study suggested the idea that USP28 in coordination with p53 could serve as a marker in BCa progression.

The Rich World of p53 DNA Binding Targets: The Role of DNA Structure

The tumor suppressor functions of p53 and its roles in regulating the cell cycle, apoptosis, senescence, and metabolism are accomplished mainly by its interactions with DNA. p53 works as a transcription factor for a significant number of genes. Most p53 target genes contain so-called p53 response elements in their promoters, consisting of 20 bp long canonical consensus sequences. Compared to other transcription factors, which usually bind to one concrete and clearly defined DNA target, the p53 consensus sequence is not strict, but contains two repeats of a 5′RRRCWWGYYY3′ sequence; therefore it varies remarkably among target genes. Moreover, p53 binds also to DNA fragments that at least partially and often completely lack this consensus sequence. p53 also binds with high affinity to a variety of non-B DNA structures including Holliday junctions, cruciform structures, quadruplex DNA, triplex DNA, DNA loops, bulged DNA, and hemicatenane DNA. In this review, we summarize information of the interactions of p53 with various DNA targets and discuss the functional consequences of the rich world of p53 DNA binding targets for its complex regulatory functions.

Functions of p53 in pluripotent stem cells

Pluripotent stem cells (PSCs) are capable of unlimited self-renewal in culture and differentiation into all functional cell types in the body, and thus hold great promise for regenerative medicine. To achieve their clinical potential, it is critical for PSCs to maintain genomic stability during the extended proliferation. The critical tumor suppressor p53 is required to maintain genomic stability of mammalian cells. In response to DNA damage or oncogenic stress, p53 plays multiple roles in maintaining genomic stability of somatic cells by inducing cell cycle arrest, apoptosis, and senescence to prevent the passage of genetic mutations to the daughter cells. p53 is also required to maintain the genomic stability of PSCs. However, in response to the genotoxic stresses, a primary role of p53 in PSCs is to induce the differentiation of PSCs and inhibit pluripotency, providing mechanisms to maintain the genomic stability of the self-renewing PSCs. In addition, the roles of p53 in cellular metabolism might also contribute to genomic stability of PSCs by limiting oxidative stress. In summary, the elucidation of the roles of p53 in PSCs will be a prerequisite for developing safe PSC-based cell therapy.

Construction and Validation of an Immune-Related Prognostic Model Based on TP53 Status in Colorectal Cancer

Growing evidence has indicated that prognostic biomarkers have a pivotal role in tumor and immunity biological processes. TP53 mutation can cause a range of changes in immune response, progression, and prognosis of colorectal cancer (CRC). Thus, we aim to build an immunoscore prognostic model that may enhance the prognosis of CRC from an immunological perspective. We estimated the proportion of immune cells in the GSE39582 public dataset using the CIBERSORT (Cell type identification by estimating relative subset of known RNA transcripts) algorithm. Prognostic genes that were used to establish the immunoscore model were generated by the LASSO (Least absolute shrinkage and selection operator) Cox regression model. We established and validated the immunoscore model in GEO (Gene Expression Omnibus) and TCGA (The Cancer Genome Atlas) cohorts, respectively; significant differences of overall survival analysis were found between the low and high immunoscore groups or TP53 subgroups. In the multivariable Cox analysis, we observed that the immunoscore was an independent prognostic factor both in the GEO cohort (HR (Hazard ratio) 1.76, 95% CI (confidence intervals): 1.26-2.46) and the TCGA cohort (HR 1.95, 95% CI: 1.20-3.18). Furthermore, we established a nomogram for clinical application, and the results suggest that the nomogram is a better predictive model for prognosis than immunoscore or TNM staging.

The REGγ-Proteasome Regulates Spermatogenesis Partially by P53-PLZF Signaling

Development of spermatogonia and spermatocytes are the critical steps of spermatogenesis, impacting on male fertility. Investigation of the related regulators benefits the understanding of male reproduction. The proteasome system has been reported to regulate spermatogenesis, but the mechanisms and key contributing factors in vivo are poorly explored. Here we found that ablation of REGγ, a proteasome activator, resulted in male subfertility. Analysis of the mouse testes after birth showed there was a decreased number of PLZF⁺ spermatogonia and spermatocytes. Molecular analysis found that REGγ loss significantly increased the abundance of p53 protein in the testis, and directly repressed PLZF transcription in cell lines. Of note, allelic p53 haplodeficiency partially rescued the defects in spermatogenesis observed in REGγ-deficient mice. In summary, our results identify REGγ-p53-PLZF to be a critical pathway that regulates spermatogenesis and establishes a new molecular link between the proteasome system and male reproduction.

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REGγ loss results in male subfertility

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REGγ loss results in a decrease of spermatocytes and PLZF⁺ spermatogonial cells

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p53 protein, increased in REGγ^−/− mouse testes, represses PLZF expression

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Allelic p53 haplodeficiency partially rescues defects in REGγ^−/− mouse spermatogenesis

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.

Mutations in exon 8 of TP53 are associated with shorter survival in patients with advanced lung cancer

Currently, in clinical settings, all TP53 mutations have been considered equally. However, numerous studies have demonstrated that the position and type of mutation have differential effects on prognosis. Such discrepancy can be partially due to the lack of unifying classification system for TP53 mutations. In the present study, two of the most frequently used systems were compared, according to the location of the mutation or its functional effects on p53 protein and the impact of TP53 mutations on the overall survival (OS) time of 379 Chinese patients with advanced lung cancer was analyzed. Capture-based ultra-deep targeted sequencing on plasma samples of 379 patients with advanced lung cancer was performed. The present results suggested that mutations occurring in exon 8 may be associated with shorter OS in tyrosine kinase inhibitor-naïve patients (P=0.013) and in patients previously treated with one line of treatment (P=0.032). The results of the present study provided solid evidence that not all TP53 mutations were associated with a similar prognosis. Mutations in exon 8 were found in a subgroup of patients with unfavorable prognosis across various treatment histories. To the best of our knowledge, the present study is the first to compare different TP53 mutation classification systems in a large cohort of patients with advanced lung cancer.

Early Passage Mesenchymal Stem Cells Display Decreased Radiosensitivity and Increased DNA Repair Activity

Cell therapies using human mesenchymal stem cells (MSCs) have received much attention in the past decade. In pursuit of the therapeutic potential of MSCs, cell expansion is required to generate a great number of cells with desired phenotype and functionality. Long‐term expansion in vitro, however, can lead to altered functions. To explore the changes in DNA damage responses (DDR) in MSCs expanded, DDR pathways following irradiation were characterized in early‐ and late‐passage bone marrow MSCs. Seventy‐two hours after irradiation, the percentage of sub‐G1 cells in early‐passage MSCs did not change significantly. Reduced TUNEL staining was observed in early‐passage MSCs compared to late‐passage MSCs 4 h after irradiation. Comet assay also revealed that early‐passage MSCs were more resistant to irradiation or DNA damages induced by genotoxic agents than late‐passage MSCs. ATM phosphorylation and γ‐H2AX and phospho‐p53 increased in early‐passage MSCs while decreased in late‐passage MSCs. Through inhibition by KU55933, DDR pathway in early‐passage MSCs was shown to be ATM‐dependent. Higher levels of poly (ADP‐ribose) polymerase‐1 (PARP‐1) and PAR synthesis were observed in early‐passage MSCs than in late‐passage MSCs. Knockdown of PARP‐1 in early‐passage MSCs resulted in sensitization to irradiation‐induced apoptosis. Overexpression of PARP‐1 in late passage MSCs could render irradiation resistance. Lower activity of DDR in late‐passage MSCs was associated with rapid proteasomal degradation of PARP‐1. In conclusion, early‐passage MSCs are more irradiation‐resistant and have increased DDR activity involving PARP‐1, ATM and their downstream signals. Stem Cells Translational Medicine2017;6:1504–1514

Salvation of the fallen angel: Reactivating mutant p53

The transcription factor p53 is known as the guardian of the genome for its powerful anti-tumour capacity. However, mutations of p53 that undermine their protein structure, resulting in loss of tumour suppressor function and gain of oncogenic function, have been implicated in more than half of human cancers. The crucial role of mutant forms of p53 in cancer makes it an attractive therapeutic target. A large number of candidates, including low MW compounds, peptides, and nucleic acids, have been identified or designed to rescue p53 mutants and reactivate their anti-tumour capacity through a variety of mechanisms. In this review, we summarize the progress made in the reactivation of mutant forms of p53, focusing on the pharmacological mechanisms of the reactivators of p53 mutants.

Comparison of genotoxic versus nongenotoxic stabilization of p53 provides insight into parallel stress-responsive transcriptional networks

The tumor suppressor protein p53 is activated in response to diverse intrinsic and extrinsic cellular stresses and controls a broad cell-protective gene network. Whether p53:DNA binding and subsequent transcriptional activation differs downstream of these diverse intrinsic and extrinsic activators is controversial. Using primary human fibroblasts, we assessed the genome-wide profile of p53 binding, chromatin structure, and transcriptional dynamics after either genotoxic or nongenotoxic activation of p53. Activation of p53 by treatment with either etoposide or the small-molecule MDM2 inhibitor nutlin 3A yields strikingly similar genome-wide binding of p53 and concomitant changes to local chromatin modifications and structure. DNA damage, but not p53 activation per se, leads to increased expression of genes in an inflammatory cytokine pathway. The NF-κB pathway inhibitor Bay 11-7082 abrogates etoposide-mediated activation of the inflammation gene signature but does not affect expression of canonical p53 target genes. Our data demonstrate that differential activation of p53 within the same cell type leads to highly similar genome-wide binding, chromatin dynamics, and gene expression dynamics and that DNA damage-mediated signaling through NF-κB likely controls the observed pro-inflammatory cytokine gene expression pattern.

Association between TP53 rs1042522 gene polymorphism and the risk of malignant bone tumors: a meta-analysis

TP53 is a tumor suppressor gene which is essential for regulating cell division and preventing tumor formation. Several studies have assessed the associations of TP53 single-nucleotide polymorphisms (SNP) with susceptibility of malignant bone tumors, including osteosarcoma and Ewing sarcoma, but the results are inconsistent. In the present meta-analysis, we aimed to elucidate the associations of TP53 rs1042522 genetic polymorphism with the risk of osteosarcoma or Ewing sarcoma. We systematically searched Medline, PubMed, Web of Science, Embase, and the Cochrane Library databases. Eligible studies assessing the polymorphisms in the TP53 rs1042522 gene and risk of malignant bone tumors were incorporated. The pooled odds ratio (OR) with its 95% confidence intervals (95% CIs) were used to assess these possible associations. Five studies with a total of 567 cases and 935 controls were finally included the meta-analysis. Meta-analysis of TP53 rs1042522 polymorphism was significantly associated with an increased risk of malignant bone tumors (G versus C: OR = 1.27, 95% CI 1.08–1.50, P=0.005; GG versus GC/CC: OR = 1.55, 95% CI 1.21–2.00, P=0.001). Moreover, in a stratified analysis, a statistically significant correlation between this SNP and osteosarcoma risk was also observed. Our results suggest that there are significant associations of TP53 rs1042522 polymorphism with malignant bone tumors risk. More studies based on larger sample sizes and homogeneous samples are warranted to confirm these findings.

The application of ApcMin/+ mouse model in colorectal tumor researches

PURPOSE

Apc^Min/+ mouse is an excellent animal model bearing multiple intestinal neoplasia, used to simulate human familial adenomatous polyposis and colorectal tumors. The key point of this model is the mutation of Apc gene, which is a significant tumor-suppressor gene in the Wnt signaling pathway. There are also some other possible mechanisms responsible for the development of colorectal tumors in the Apc^Min/+ mouse model, such as tumor-associated signaling pathways activation, the changes of tumor-related genes, and the involvement of some related proteins or molecules.

METHODS

The relevant literatures about Apc^Min/+ mouse model from PUBMED databases are reviewed in this study.

RESULTS

In recent years, increasing studies have focused on the application of Apc^Min/+ mouse model in colorectal tumor, trying to find effective therapeutic targets for further use.

CONCLUSION

This article will give a brief review on the related molecular mechanisms of the Apc^Min/+ mouse model and its application in colorectal tumor researches.

Relevance of TP53 for CLL diagnostics

TP53 disruption in chronic lymphocytic leukaemia (CLL) is a well-established prognostic marker and informs on the appropriate course of treatment for patients. TP53 status is commonly assessed by fluorescence in situ hybridisation for del(17 p) and Sanger sequencing for TP53 mutations. At present, current screening methods for TP53 mutations fail to detect diagnostically relevant mutations potentially leading to inappropriate treatment decisions. In addition, low levels of mutations that are proving to be clinically relevant may not be discovered with current less sensitive techniques. This review describes the structure, function and regulation of the TP53 protein, the mutations found in cancer and CLL, the relevance of TP53 disruption in CLL and the current screening methods for TP53 mutations including next-generation sequencing.

ADP-ribosylation and intracellular traffic: an emerging role for PARP enzymes

ADP-ribosylation is an ancient and reversible post-translational modification (PTM) of proteins, in which the ADP-ribose moiety is transferred from NAD+ to target proteins by members of poly-ADP-ribosyl polymerase (PARP) family. The 17 members of this family have been involved in a variety of cellular functions, where their regulatory roles are exerted through the modification of specific substrates, whose identification is crucial to fully define the contribution of this PTM. Evidence of the role of the PARPs is now available both in the context of physiological processes and of cell responses to stress or starvation. An emerging role of the PARPs is their control of intracellular transport, as it is the case for tankyrases/PARP5 and PARP12. Here, we discuss the evidence pointing at this novel aspect of PARPs-dependent cell regulation.

Apoptosis and apoptotic body: disease message and therapeutic target potentials

Apoptosis is widely known as programmed cell death eliciting no inflammatory responses. The intricacy of apoptosis has been a focus of an array of researches, accumulating a wealth of knowledge which led to not only a better understanding of the fundamental process, but also potent therapies of diseases. The classic intrinsic and extrinsic signaling pathways of apoptosis, along with regulatory factors have been well delineated. Drugs and therapeutic measures designed based on current understanding of apoptosis have long been employed. Small-molecule apoptosis inducers have been clinically used for eliminating morbid cells and therefore treating diseases, such as cancer. Biologics with improved apoptotic efficacy and selectivity, such as recombinant proteins and antibodies, are being extensively researched and some have been approved by the FDA. Apoptosis also produces membrane-bound vesicles derived from disassembly of apoptotic cells, now known as apoptotic bodies (ApoBDs). These little sealed sacs containing information as well as substances from dying cells were previously regarded as garbage bags until they were discovered to be capable of delivering useful materials to healthy recipient cells (e.g., autoantigens). In this review, current understandings and knowledge of apoptosis were summarized and discussed with a focus on apoptosis-related therapeutic applications and ApoBDs.

Erythropoietin inhibits chemotherapy-induced cell death and promotes a senescence-like state in leukemia cells

There are conflicting reports on the adverse effects of erythropoietin (EPO) for the management of cancer-associated anemia. The recognition that erythropoietin receptors (EPORs) are expressed outside the erythroid lineage and concerns that erythropoiesis-stimulating agents (ESAs) may cause tumors to grow and increase the risk of venous thromboembolism have resulted in substantially fewer cancer patients receiving ESA therapy to manage myelosuppressive chemotherapy. In this study, we found that EPO suppresses p53-dependent apoptosis induced by genotoxic (daunorubicin, doxorubicin, and γ-radiation) and non-genotoxic (nutlin-3a) agents and induces a senescence-like state in myeloid leukemia cells. EPO interferes with stress-dependent Mdm2 downregulation and leads to the destabilization of p53 protein. EPO selectively modulates the expression of p53 target genes in response to DNA damage preventing the induction of a number of noncoding RNAs (ncRNAs) previously associated with p53-dependent apoptosis. EPO also enhances the expression of the cyclin-dependent kinase inhibitor p21^WAF1 and promotes recruitment of p53 to the p21 promoter. In addition, EPO antagonizes Mcl-1 protein degradation in daunorubicin-treated cells. Hence, EPO signaling targets Mcl-1 expression and the p53-Mdm2 network to promote tumor cell survival.

Progesterone up-regulates p27 through an increased binding of the progesterone receptor-A-p53 protein complex onto the non-canonical p53 binding motif in HUVEC

We previously demonstrated that progesterone (P4) up-regulated p53 expression, which in turn increased p21 and p27 expression, and finally resulted in proliferation inhibition in human umbilical vein endothelial cells (HUVEC). While a direct transcriptional activation of p21 by p53 protein has been clearly elucidated, the mechanism by which p53 induces p27 expression has not been documented. In this study, we identified three putative p53 protein binding domains at the p27 promoter. Luciferase assay showed that the activity of ectopically introduced p27 promoter constructs containing the potential p53 protein binding region was significantly increased by P4. Immunoblotting analysis indicated that P4 increased the level of p53 protein. Treatment with pifithrin-α-HBr (PFTα), a specific blocker of p53-responsive gene transactivation, reduced the P4-increased p27 promoter activity and p27 protein expression. Transfection with dominant-negative mutants of p53 (C135Y, R175H and R248 W) abolished the P4-increased p27 promoter activity. Moreover, deletion or TCCT nucleotide sequence fill-in at the core site of any of p53 protein binding domains led to the irresponsiveness of the p27 promoter to P4 treatment. Interestingly, immunoprecipitation and chromatin-immunoprecipitation analyses demonstrated that P4 increased the complex of p53-P4 receptor (PR) protein in the nucleus and the assembly of PR protein to the p53 protein binding region of the p27 promoter. Ectopic co-overexpression of p53 and PR-A constructs further augmented the P4-increased p27 promoter activity. Taken together, the results from the present study suggest that P4-increased p53 expression might directly up-regulate p27 transactivation, and PR-A protein might promote this effect by forming complex with p53 protein.

P53 and Apoptosis in the Drosophila Model

Human P53 (HsP53) is the most frequently mutated gene associated with cancers. Despite heightened research interest over the last four decades, a clear picture of how wild type HsP53 functions as the guardian against malignant transformation remains elusive. Studying the ortholog of P53 in the genetic model organism Drosophila melanogaster (DmP53) has revealed many interesting insights. This chapter focuses on recent findings that have shed light on how DmP53 -mediated apoptosis plays an important role in maintaining genome integrity, and how the immediate output of activated DmP53 is determined by the epigenetic landscape of individual cells.

SIRT2-mediated inactivation of p73 is required for glioblastoma tumorigenicity

Glioblastoma is one of the most aggressive forms of cancers and has a poor prognosis. Genomewide analyses have revealed that a set of core signaling pathways, the p53, RB, and RTK pathways, are commonly deregulated in glioblastomas. However, the molecular mechanisms underlying the tumorigenicity of glioblastoma are not fully understood. Here, we show that the lysine deacetylase SIRT2 is required for the proliferation and tumorigenicity of glioblastoma cells, including glioblastoma stem cells. Furthermore, we demonstrate that SIRT2 regulates p73 transcriptional activity by deacetylation of its C-terminal lysine residues. Our results suggest that SIRT2-mediated inactivation of p73 is critical for the proliferation and tumorigenicity of glioblastoma cells and that SIRT2 may be a promising molecular target for the therapy of glioblastoma.

Awakening the "guardian of genome": reactivation of mutant p53

The role of tumor suppressor protein p53 is undeniable in the suppression of cancer upon oncogenic stress. It induces diverse conditions such as cell-cycle arrest, cell death, and senescence to protect the cell from carcinogenesis. The rate of mutations in p53 gene nearly accounts for 50% of the human cancers. Upon mutations, the conformation gets altered and becomes non-native. Mutant p53 displays long half-life and accumulates in the nucleus and interacts with oncoproteins to promote carcinogenesis and these interactions present a formidable challenge for clinicians in therapy of the disease. Variety of approaches have been developed, through which native-like function of p53 can be restored, such as restoration of the native-like structure of p53, activating the p53 family members, etc. Modern scientific techniques have led to the discovery of a variety of molecules to reactivate mutant p53 and restore its transcriptional activity. These compounds include small molecules, various peptides, and phytochemicals. In this review article, we comprehensively discuss these molecules to reactivate mutant p53 to restore the normal function with a particular focus on molecular mechanisms.

Antitumor activity of RT2 peptide derived from crocodile leukocyte peptide on human colon cancer xenografts in nude mice

RT2, derived from the leukocyte peptide of Crocodylus siamensis, can kill human cervical cancer cells via apoptosis induction, but no evidence has shown in vivo. In this study, we investigated the antitumor effect of RT2 on human colon cancer xenografts in nude mice. Twenty-four mice were injected subcutaneously with human colon cancer HCT 116 cells. Eleven days after cancer cell implantation, the mice were treated with intratumoral injections of phosphate buffered saline (PBS) or RT2 (0.01, 0.1, and 1 mg/mouse) once every 2 days for a total of 5 times. The effect of a 10-day intratumoral injection of RT2 on body weight, biochemical, and hematological parameters in BALB/c mice showed no significant difference between the groups. Tumor volume showed a significant decrease only in the treatment group with RT2 (1 mg/mouse) at day 6 (P < .05), day 8 (P < .01), and day 10 (P < .01) after the first treatment. The protein expression levels of cleaved poly (ADP-ribose) polymerase (PARP), apoptosis-inducing factor (AIF), and the p53 tumor suppressor protein (p53) in xenograft tumors increased after treatment with RT2 (1 mg/mouse) compared to those in the PBS-injected group. Moreover, RT2 increased the expression of Endo G and Bcl-2 family proteins. Therefore, the peptide RT2 can inhibit tumor growth via the induction of apoptosis in an in vivo xenograft model.

Gallid Herpesvirus 1 Initiates Apoptosis in Uninfected Cells through Paracrine Repression of p53

Apoptosis is a common innate defense mechanism of host cells against viral infection and is therefore suppressed by many viruses, including herpes simplex virus (HSV), via various strategies. A recent in vivo study reported the apoptosis of remote uninfected cells during Gallid herpesvirus 1 (GaHV-1) infection, yet little is known about this previously unknown aspect of herpesvirus-host interactions. The aim of the present study was to investigate the apoptosis of uninfected host cells during GaHV-1 infection. The present study used in vitro and in ovo models, which avoided potential interference by host antiviral immunity, and demonstrated that this GaHV-1-host interaction is independent of host immune responses and important for both the pathological effect of viral infection and early viral dissemination from the primary infection site to distant tissues. Further, we revealed that GaHV-1 infection triggers this process in a paracrine-regulated manner. Using genome-wide transcriptome analyses in combination with a set of functional studies, we found that this paracrine-regulated effect requires the repression of p53 activity in uninfected cells. In contrast, the activation of p53 not only prevented the apoptosis of remote uninfected cells and subsequent pathological damage induced by GaHV-1 infection but also delayed viral dissemination significantly. Moreover, p53 activation repressed viral replication both in vitro and in ovo, suggesting that dual cell-intrinsic mechanisms underlie the suppression of GaHV-1 infection by p53 activation. This study uncovers the mechanism underlying the herpesvirus-triggered apoptosis of remote host cells and extends our understanding of both herpesvirus-host interactions and the roles of p53 in viral infection.IMPORTANCE It is well accepted that herpesviruses suppress the apoptosis of host cells via various strategies to ensure sustained viral replication during infection. However, a recent in vivo study reported the apoptosis of remote uninfected cells during GaHV-1 infection. The mechanism and the biological meaning of this unexpected herpesvirus-host interaction are unclear. This study uncovers the mechanisms of herpesvirus-triggered apoptosis in uninfected cells and may also contribute to a mechanistic illustration of paracrine-regulated apoptosis induced by other viruses in uninfected host cells.