p53 alterations in human cancer: more questions than answers

Updates on Larynx Cancer: Risk Factors and Oncogenesis

Laryngeal cancer is a very common tumor in the upper aero-digestive tract. Understanding its biological mechanisms has garnered significant interest in recent years. The development of laryngeal squamous cell carcinoma (LSCC) follows a multistep process starting from precursor lesions in the epithelium. Various risk factors have been associated with laryngeal tumors, including smoking, alcohol consumption, opium use, as well as infections with HPV and EBV viruses, among others. Cancer development involves multiple steps, and genetic alterations play a crucial role. Tumor suppressor genes can be inactivated, and proto-oncogenes may become activated through mechanisms like deletions, point mutations, promoter methylation, and gene amplification. Epigenetic modifications, driven by miRNAs, have been proven to contribute to LSCC development. Despite advances in molecular medicine, there are still aspects of laryngeal cancer that remain poorly understood, and the underlying biological mechanisms have not been fully elucidated. In this narrative review, we examined the literature to analyze and summarize the main steps of carcinogenesis and the risk factors associated with laryngeal cancer.

miR-221/222 induce instability of p53 By downregulating deubiquitinase YOD1 in acute myeloid leukemia

Acute myeloid leukemia (AML) is a hematological malignancy characterized by the impaired differentiation and uncontrolled proliferation of myeloid blasts. Tumor suppressor p53 is often downregulated in AML cells via ubiquitination-mediated degradation. While the role of E3 ligase MDM2 in p53 ubiquitination is well-accepted, little is known about the involvement of deubiquitinases (DUBs). Herein, we found that the expression of YOD1, among several DUBs, is substantially reduced in blood cells from AML patients. We identified that YOD1 deubiqutinated and stabilized p53 through interaction via N-terminus of p53 and OTU domain of YOD1. In addition, expression levels of YOD1 were suppressed by elevated miR-221/222 in AML cells through binding to the 3' untranslated region of YOD1, as verified by reporter gene assays. Treatment of cells with miR-221/222 mimics and inhibitors yielded the expected effects on YOD1 expressions, in agreement with the negative correlation observed between the expression levels of miR-221/222 and YOD1 in AML cells. Finally, overexpression of YOD1 stabilized p53, upregulated pro-apoptotic p53 downstream genes, and increased the sensitivity of AML cells to FLT3 inhibitors remarkably. Collectively, our study identified a pathway connecting miR-221/222, YOD1, and p53 in AML. Targeting miR-221/222 and stimulating YOD1 activity may improve the therapeutic effects of FLT3 inhibitors in patients with AML.

A Brief Review on Chemoresistance; Targeting Cancer Stem Cells as an Alternative Approach

The acquisition of resistance to traditional chemotherapy and the chemoresistant metastatic relapse of minimal residual disease both play a key role in the treatment failure and poor prognosis of cancer. Understanding how cancer cells overcome chemotherapy-induced cell death is critical to improve patient survival rate. Here, we briefly describe the technical approach directed at obtaining chemoresistant cell lines and we will focus on the main defense mechanisms against common chemotherapy triggers by tumor cells. Such as, the alteration of drug influx/efflux, the enhancement of drug metabolic neutralization, the improvement of DNA-repair mechanisms, the inhibition of apoptosis-related cell death, and the role of p53 and reactive oxygen species (ROS) levels in chemoresistance. Furthermore, we will focus on cancer stem cells (CSCs), the cell population that subsists after chemotherapy, increasing drug resistance by different processes such as epithelial-mesenchymal transition (EMT), an enhanced DNA repair machinery, and the capacity to avoid apoptosis mediated by BCL2 family proteins, such as BCL-XL, and the flexibility of their metabolism. Finally, we will review the latest approaches aimed at decreasing CSCs. Nevertheless, the development of long-term therapies to manage and control CSCs populations within the tumors is still necessary.

Mutant P53 in the formation and progression of the tumor microenvironment: Friend or foe

TP53 is the most frequently mutated gene in human cancer. It encodes the tumor suppressor protein p53, which suppresses tumorigenesis by acting as a critical transcription factor that can induce the expression of many genes controlling a plethora of fundamental cellular processes, including cell cycle progression, survival, apoptosis, and DNA repair. Missense mutations are the most frequent type of mutations in the TP53 gene. While these can have variable effects, they typically impair p53 function in a dominant-negative manner, thereby altering intra-cellular signaling pathways and promoting cancer development. Additionally, it is becoming increasingly apparent that p53 mutations also have non-cell autonomous effects that influence the tumor microenvironment (TME). The TME is a complex and heterogeneous milieu composed of both malignant and non-malignant cells, including cancer-associated fibroblasts (CAFs), adipocytes, pericytes, different immune cell types, such as tumor-associated macrophages (TAMs) and T and B lymphocytes, as well as lymphatic and blood vessels and extracellular matrix (ECM). Recently, a large body of evidence has demonstrated that various types of p53 mutations directly affect TME. They fine-tune the inflammatory TME and cell fate reprogramming, which affect cancer progression. Notably, re-educating the p53 signaling pathway in the TME may be an effective therapeutic strategy in combating cancer. Therefore, it is timely to here review the recent advances in our understanding of how TP53 mutations impact the fate of cancer cells by reshaping the TME.

Analysis of Intrinsic Breast Cancer Subtypes: The Clinical Utility of Epigenetic Biomarkers and TP53 Mutation Status in Triple-Negative Cases

This study aimed at analyzing the DNA methylation pattern and TP53 mutation status of intrinsic breast cancer (BC) subtypes for improved characterization and survival prediction. DNA methylation of 17 genes was tested by methylation-specific PCR in 116 non-familial BRCA mutation-negative BC and 29 control noncancerous cases. At least one gene methylation was detected in all BC specimens and a 10-gene panel statistically significantly separated tumors from noncancerous breast tissues. Methylation of FILIP1L and MT1E was predominant in triple-negative (TN) BC, while other BC subtypes were characterized by RASSF1, PRKCB, MT1G, APC, and RUNX3 hypermethylation. TP53 mutation (TP53-mut) was found in 38% of sequenced samples and mainly affected TN BC cases (87%). Cox analysis revealed that TN status, age at diagnosis, and RUNX3 methylation are independent prognostic factors for overall survival (OS) in BC. The combinations of methylated biomarkers, RUNX3 with MT1E or FILIP1L, were also predictive for shorter OS, whereas methylated FILIP1L was predictive of a poor outcome in the TP53-mut subgroup. Therefore, DNA methylation patterns of specific genes significantly separate BC from noncancerous breast tissues and distinguishes TN cases from non-TN BC, whereas the combination of two-to-three epigenetic biomarkers can be an informative tool for BC outcome predictions.

Value of p53 sequencing in the prognostication of head and neck cancer: a systematic review and meta-analysis

This review aimed to examine the relationship between TP53 mutational status, as determined by genomic sequencing, and survival in squamous cell carcinoma of the head and neck. The databases Medline, Embase, Web of Science (core collection), Scopus and Cochrane Library were searched from inception to April 2021 for studies assessing P53 status and survival. Qualitative analysis was carried out using the REMARK criteria. A meta-analyses was performed and statistical analysis was carried out to test the stability and reliability of results. Twenty-five studies met the inclusion criteria, of which fifteen provided enough data for quantitative evaluation. TP53 mutation was associated with worse overall survival (HR 1.75 [95% CI 1.45-2.10], p < 0.001), disease-specific survival (HR 4.23 [95% CI 1.19-15.06], p = 0.03), and disease-free survival (HR 1.80 [95% CI 1.28-2.53], p < 0.001). Qualitative assessment identified room for improvement and the pooled analysis of all anatomical subsites leads to heterogeneity that may erode the validity of the observed overall effect and its subsequent extrapolation and application to individual patients. Our systematic review and meta-analysis supports the utility of TP53 mutational as a prognostic factor for survival in head and neck squamous cell carcinoma. A well designed prospective, multi-centre trial is needed to definitively answer this question.

Distinct p53 isoforms code for opposing transcriptional outcomes

p53 genes are conserved transcriptional activators that respond to stress. These proteins can also downregulate genes, but the mechanisms are not understood and are generally assumed to be indirect. Here, we investigate synthetic and native cis-regulatory elements in Drosophila to examine opposing features of p53-mediated transcriptional control in vivo. We show that transcriptional repression by p53 operates continuously through canonical DNA binding sites that confer p53-dependent transactivation at earlier developmental stages. p53 transrepression is correlated with local H3K9me3 chromatin marks and occurs without the need for stress or Chk2. In sufficiency tests, two p53 isoforms qualify as transrepressors and a third qualifies as a transcriptional activator. Targeted isoform-specific knockouts dissociate these opposing transcriptional activities, highlighting features that are dispensable for transactivation but critical for repression and for proper germ cell formation. Together, these results demonstrate that certain p53 isoforms function as constitutive tissue-specific repressors, raising important implications for tumor suppression by the human counterpart.

p53-Mediated Indirect Regulation on Cellular Metabolism: From the Mechanism of Pathogenesis to the Development of Cancer Therapeutics

The transcription factor p53 is the most well-characterized tumor suppressor involved in multiple cellular processes, which has expanded to the regulation of metabolism in recent decades. Accumulating evidence reinforces the link between the disturbance of p53-relevant metabolic activities and tumor development. However, a full-fledged understanding of the metabolic roles of p53 and the underlying detailed molecular mechanisms in human normal and cancer cells remain elusive, and persistent endeavor is required to foster the entry of drugs targeting p53 into clinical use. This mini-review summarizes the indirect regulation of cellular metabolism by wild-type p53 as well as mutant p53, in which mechanisms are categorized into three major groups: through modulating downstream transcriptional targets, protein-protein interaction with other transcription factors, and affecting signaling pathways. Indirect mechanisms expand the p53 regulatory networks of cellular metabolism, making p53 a master regulator of metabolism and a key metabolic sensor. Moreover, we provide a brief overview of recent achievements and potential developments in the therapeutic strategies targeting mutant p53, emphasizing synthetic lethal methods targeting mutant p53 with metabolism. Then, we delineate synthetic lethality targeting mutant p53 with its indirect regulation on metabolism, which expands the synthetic lethal networks of mutant p53 and broadens the horizon of developing novel therapeutic strategies for p53 mutated cancers, providing more opportunities for cancer patients with mutant p53. Finally, the limitations and current research gaps in studies of metabolic networks controlled by p53 and challenges of research on p53-mediated indirect regulation on metabolism are further discussed.

Importance of p53 gene polymorphisms in myelodysplastic syndrome disease

Aim: Myelodysplastic syndrome (MDS) is a clonal disease with a high risk of conversion to acute myeloid leukemia, characterized by increased apoptosis and decreased hematopoiesis. The pathogenesis of MDS has not been fully explained. ~50% of cases have abnormal karyotype and this rate is around 80% in secondary MDS. The p53 protein is an important regulator of stem cell homeostasis and is involved in a range of cellular events such as cell cycle regulation, apoptotic and inflammatory response. The TP53 gene, which has important roles in maintaining genomic integrity, is frequently mutated in cancers; however, some gene polymorphisms are known to be associated with cancer, as well as mutations. Our aim in the study is to determine the prevalence of four common p53 single nucleotide polymorphisms in MDS and their effects on disease development. For this reason, 100 cases followed up with the diagnosis of MDS or newly diagnosed in Ege University Faculty of Medicine, Department of Internal Medicine, Department of Hematology were included in the study. Materials and Methods: DNAs isolated from peripheral blood leukocytes of MDS cases were studied by real-time PCR method, p53 polymorphisms (rs35163653, rs35993958, rs1800371, rs1042522) were determined by using appropriate probes and melting curve analysis. Results: Among the four common p53 polymorphisms examined, especially the non-ancestral G allele in the rs1042522 polymorphism was observed to be increased in MDS cases (C: 30.3%; G: 69.7%). In this polymorphism, which is known to be functional, that is, affecting the function of the synthesized protein, the transition of the C nucleotide at position 417 to G (C>G) causes the coding of the amino acid proline at position 72 of the protein to arginine (P72R). Conclusion: Our study is the first to investigate the p53 polymorphisms of rs35163653, rs35993958, rs1800371 and rs1042522 in the MDS disease group. Of these, rs1042522 polymorphism has been shown to be associated with cancer susceptibility and susceptibility, and it is thought that it may pose a high risk for MDS disease as well. In conclusion, rs1042522 polymorphism may be used as a marker in the diagnosis of MDS in the future by repeating this study for MDS disease with a larger case group.

Generation of a uniform thymic malignant lymphoma model with C57BL/6J p53 gene deficient mice

Lymphoma is the third most common cancer diagnosed in children, and T-cell lymphoma has the worst prognosis based on clinical observations. To date, a lymphoma model with uniform penetrance has not yet been developed. In this study, we generated a p53 deficient mouse model by targeting embryonic stem cells derived from a C57BL/6J mouse strain. Homozygous p53 deficient mice exhibited a higher rate of spontaneous tumorigenesis, with a high spontaneous occurrence rate (93.3%) of malignant lymphoma. Because tumor models with high phenotypic consistency are currently needed, we generated a lymphoma model by a single intraperitoneal injection of 37.5 or 75 mg/kg N-methyl-N-nitrosourea to p53 deficient mice. Lymphoma and retinal degeneration occurred in 100% of p53^+/− mice administered with higher concentrations of N-methyl-N-nitrosourea, a much greater response than those of previously reported models. The main anatomic sites of lymphoma were the thymus, spleen, bone marrow, and lymph nodes. Both induced and spontaneous lymphomas in the thymus and spleen stained positive for CD3 antigen, and flow cytometry detected positive CD4 and/or CD8 cells. Based on our observations and previous data, we hypothesize that mice with a B6 background are prone to lymphomagenesis.

Sphingolipid metabolism in the development and progression of cancer: one cancer's help is another's hindrance

Cancer development is a multistep process in which cells must overcome a series of obstacles before they can become fully developed tumors. First, cells must develop the ability to proliferate unchecked. Once this is accomplished, they must be able to invade the neighboring tissue, as well as provide themselves with oxygen and nutrients. Finally, they must acquire the ability to detach from the newly formed mass in order to spread to other tissues, all the while evading an immune system that is primed for their destruction. Furthermore, increased levels of inflammation have been shown to be linked to the development of cancer, with sites of chronic inflammation being a common component of tumorigenic microenvironments. In this Review, we give an overview of the impact of sphingolipid metabolism in cancers, from initiation to metastatic dissemination, as well as discussing immune responses and resistance to treatments. We explore how sphingolipids can either help or hinder the progression of cells from a healthy phenotype to a cancerous one.

Chromosome Region Maintenance 1 (XPO1/CRM1) as an Anticancer Target and Discovery of Its Inhibitor

Chromosome region maintenance 1 (CRM1) is a major nuclear export receptor protein and contributes to cell homeostasis by mediating the transport of cargo from the nucleus to the cytoplasm. CRM1 is a therapeutic target comprised of several tumor types, including osteosarcoma, multiple myeloma, gliomas, and pancreatic cancer. In the past decade, dozens of CRM1 inhibitors have been discovered and developed, including KPT-330, which received FDA approval for multiple myeloma (MM) and diffuse large B-cell lymphoma (DLBCL) in 2019 and 2020, respectively. This review summarizes the biological functions of CRM1, the current understanding of the role CRM1 plays in cancer, the discovery of CRM1 small-molecule inhibitors, preclinical and clinical studies on KPT-330, and other recently developed inhibitors. A new CRM1 inhibition mechanism and structural dynamics are discussed. Through this review, we hope to guide the future design and optimization of CRM1 inhibitors.

Clinical Characteristics, Prognosis, and Treatment Strategies of TP53 Mutations in Myelodysplastic Syndromes

TP53 gene mutations are common in myelodysplastic syndromes (MDS). Previous studies have reported their detrimental effects on patient survival. However, current treatment strategies mainly based on hypomethylating agent therapy (HMA) and hematopoietic stem cell transplantation (HSCT) still leave a lot to be desired. And there is also a lack of studies on large sample with a view to the refinement of specific characteristics and disease progression. So we performed a meta-analysis including 20 studies compromising 5067 patients to assess the prognostic impact and clinical characteristics of TP53 mutations in MDS patients. The overall hazard ratio for overall survival (OS) was 2.14 (95% confidence interval 1.94-2.37, P < .00001) compared with patients with MDS without TP53 mutations. Lower progression-free survival and leukemia-free survival were associated with TP53 mutations. Subgroup analysis revealed that TP53 mutations were significantly associated with high levels of blast cells and karyotypic aberrations. And among Asian population, the adverse impact on OS of TP53 mutations seemed worse than those in Western countries. (HR 2.87 vs. 2.02, P = .01). In addition, TP53 mutations had no effect on response to HMA therapy, and HSCT improved OS in patients carrying TP53 mutations.

KLF5 regulates epithelial-mesenchymal transition of liver cancer cells in the context of p53 loss through miR-192 targeting of ZEB2

Krüppel-like factor 5 (KLF5) can both promote and suppress cell migration, but the underlying mechanisms have not been elucidated. In this study, we show that the function of KLF5 in epithelial-mesenchymal transition (EMT) and migration of liver cancer cells depends on the status of the cellular tumor antigen p53 (p53). Furthermore, zinc finger E-box-binding homeobox 2 (ZEB2) is the main regulator of KLF5 in EMT in liver cancer cells in the context of p53 loss. Most importantly, the regulation of ZEB2 by p53 and KLF5 is indirect and that miR-192 mediates this regulation. Finally, we find that in invasive liver cancer, KLF5 is absent in the context of p53 loss or mutation.

Biomarkers of laryngeal squamous cell carcinoma: a review

Laryngeal carcinoma is the second common malignancy of the upper aerodigestive tract after lung cancer; in most cases is a squamous cell carcinoma, whose risk factors include tobacco smoking and alcohol consumption. Despite therapeutic progress, the five-year overall survival rate for this malignancy has remained nearly 50% and many patients already present metastasis at the time of diagnosis. To date, there are no tools that predict the evolution of laryngeal carcinoma: in this light, during the last years, many studies were planned with the aim to investigate the role played by different biomarkers expressed by larynx cancer, which can help make an early diagnosis, predict disease evolution and direct therapeutic choice. This review aims to summarize these markers and correlating them with disease evolution.

Regulation of miR-186-YY1 axis by the p53 translational isoform ∆40p53: implications in cell proliferation

We have earlier shown that p53-FL and its translational isoform ∆40p53 are differentially regulated. In this study, we have investigated the cellular effect of ∆40p53 regulation on downstream gene expression, specifically miRNAs. Interestingly, ∆40p53 showed antagonistic regulation of miR-186-5p as compared to either p53 alone or a combination of both the isoforms. We have elucidated the miR-186-5p mediated effect of ∆40p53 in cell proliferation. Upon expression of ∆40p53, we observed a significant decrease in YY1 levels, an established target of miR-186-5p, which is involved in cell proliferation. Further assays with anti-miR-186 established the interdependence of ∆40p53- miR-186-5p-YY1- cell proliferation. The results unravel a new dimension toward the understanding of ∆40p53 functions, which seems to regulate cellular fate independent of p53FL.

An Overview of Promising Biomarkers in Cancer Screening and Detection

Applications of biomarkers have been proved in oncology screening, diagnosis, predicting response to treatment as well as monitoring the progress of the disease. Considering the crucial role played by them during different disease stages, it is extremely important to evaluate, validate, and assess them to incorporate them into routine clinical care. In this review, the role of few most promising and successfully used biomarkers in cancer detection, i.e. PD-L1, E-Cadherin, TP53, Exosomes, cfDNA, EGFR, mTOR with regard to their structure, mode of action, and reports signifying their pathological significance, are addressed. Also, an overview of some successfully used biomarkers for cancer medicine has been presented. The study also summarizes biomarker-driven personalized cancer therapy i.e., approved targets and indications, as per the US FDA. The review also highlights the increasingly prominent role of biomarkers in drug development at all stages, with particular reference to clinical trials. The increasing utility of biomarkers in clinical trials is clearly evident from the trend shown, wherein ~55 percent of all oncology clinical trials in 2019 were seen to involve biomarkers, as opposed to ~ 15 percent in 2001, which clearly proves the essence and applicability of biomarkers for synergizing clinical information with tumor progression. Still, there are significant challenges in the implementation of these possibilities with strong evidence in cost-- effective manner.

The p53/miR-193a/EGFR feedback loop function as a driving force for non-small cell lung carcinoma tumorigenesis

Background

Non-small cell lung carcinoma (NSCLC) is a major worldwide health threat due to its low cure rate and high lethality. Emerging evidence suggests that epidermal growth factor receptor (EGFR) plays vital roles in cancer initiation and progression, and is considered an important cancer-driving protein. However, how EGFR expression is regulated during NSCLC development remains to be fully elucidated.

Methods

In NSCLC clinical samples, EGFR protein levels were measured by western blotting and qRT-PCR, respectively. Combining microRNA (miRNA) target prediction software and the pulldown assay, we predicted microRNAs (miRNAs) that targeted EGFR. Next, three NSCLC cell lines, A549 (p53 WT), H322 (p53 mutant), and H1299 (p53 null), were used to demonstrate the direct targeting of EGFR by miR-193a. In addition, we investigated the biological effects of EGFR inhibition by miR-193a in vitro using Cell Counting Kit-8, 5-Ethynyl-2'-deoxyuridine (EdU), transwell, and apoptosis assays. Then, using ChIP and luciferase assays, we demonstrated that miR-193a was directly activated by p53 at the transcriptional level and that p53-induced-miR-193a and EGFR form a double-negative feedback loop.

Results

We found that EGFR mRNA and protein were upregulated in NSCLC. We predicted that EGFR was a target of miR-193a and validated that miR-193a bound directly to the 3'-UTR of the EGFR mRNA. Moreover, miR-193a inhibited NSCLC proliferation and invasion, and promotes NSCLC apoptosis by directly downregulating EGFR. Then, we demonstrated that p53 directly activated miR-193a transcription, whereas EGFR functioned as a transcriptional repressor to negatively control miR-193a expression, forming a feedback loop. The loop promoted NSCLC cell proliferation and migration and accelerated tumor growth in xenograft mice.

Conclusions

This study highlights a double-negative feedback loop in NSCLC. The feedback loop is crucial because overexpressing EGFR strongly accelerated tumor growth, while miR-193a restoration blocked tumor growth in vivo. Our findings are in line with the emerging opinion that miRNAs and protein regulators form regulatory networks in critical biological processes and that their dysregulation can lead to cellular dysfunction. In conclusion, this study provides important insights into the molecular mechanisms of NSCLC progression and may help inform the development of new therapeutics for managing NSCLC.

Characterization of Exosomes in Plasma of Patients with Breast, Ovarian, Prostate, Hepatic, Gastric, Colon, and Pancreatic Cancers

Detection of circulating tumor-specific DNA, RNA or proteins can be difficult due to relative scarcity. Exosomes are extracellular vesicles, 30 - 150 nm in diameter derived from fusion of multivesicular bodies with the plasma membrane. They are composed of a lipid bilayer membrane and contain proteins, mRNA and miRNA. Exosomes are secreted by multiple cell types, including cancer cells. However, there is a relative lack of information concerning the contents of exosomes secreted by various tumor cell types. To examine exosomes in cancer, we collected blood plasma samples from patients with breast, ovarian, prostate, hepatic, gastric, colon, and pancreatic cancers. Exosomes were isolated from plasma and confirmed by AchE assay, transmission electron microscopy and expression of the CD63 exosomal marker. Expression of AFP, CA724, CA153, CEA, CA125, CA199 and PSA antigens were determined using an automated electro-chemiluminescence assay. Expression of the tumor-related chaperone protein, mortalin, was determined by Western blot analysis. Levels of exosome secretion were variable among the different tumor types. Both exosome levels and mortalin expression within tumor cell exosomes were higher than in healthy donors, except in pancreatic carcinoma, where exosomes were elevated but mortalin expression was not significantly different from healthy donors. Exosomes provide unique opportunities for the enrichment of tumor-specific materials and may be useful as biomarkers and possibly as tools of cancer therapies. Mortalin, which has been linked to cell proliferation and induction of epithelial-mesenchymal transition of cancer cells, may be useful as a prognostic bio-marker and as a possible therapeutic target.

Oxidation Chemistry of DNA and p53 Tumor Suppressor Gene

The chemistry of DNA and its repair selectivity control the influence of genomic oxidative stress on the development of serious disorders such as cancer and heart diseases. DNA is oxidized by endogenous reactive oxygen species (ROS) in vivo or in vitro as a result of high energy radiation, non-radiative metabolic processes, and other consequences of oxidative stress. Some oxidations of DNA and tumor suppressor gene p53 are thought to be mutagenic when not repaired. For example, site-specific oxidations of p53 tumor suppressor gene may lead to cancer-related mutations at the oxidation site codon. This review summarizes the research on the primary products of the most easily oxidized nucleobase guanine (G) when different oxidation methods are used. Guanine is by far the most oxidized DNA base. The primary initial oxidation product of guanine for most, but not all, pathways is 8-oxoguanine (8-oxoG). With an oxidation potential much lower than G, 8-oxoG is readily susceptible to further oxidation, and the products often depend on the oxidants. Specific products may control the types of subsequent mutations, but mediated by gene repair success. Site-specific oxidations of p53 tumor suppressor gene have been reported at known mutation hot spots, and the codon sites also depend on the type of oxidants. Modern methodologies using LC-MS/MS for codon specific detection and identification of oxidation sites are summarized. Future work aimed at understanding DNA oxidation in nucleosomes and interactions between DNA damage and repair is needed to provide a better picture of how cancer-related mutations arise.

Pathways of Metabolite-Related Damage to a Synthetic p53 Gene Exon 7 Oligonucleotide Using Magnetic Enzyme Bioreactor Beads and LC-MS/MS Sequencing

Reactive metabolites of environmental chemicals and drugs can cause site specific damage to the p53 tumor suppressor gene in a major pathway for genotoxicity. We report here a high-throughput, cell-free, 96-well plate magnetic bead-enzyme system interfaced with LC-MS/MS sequencing for bioactivating test chemicals and identifying resulting adduction sites on genes. Bioactivated aflatoxin B1 was reacted with a 32 bp exon 7 fragment of the p53 gene using eight microsomal cytochrome (cyt) P450 enzymes from different organs coated on magnetic beads. All cyt P450s converted aflatoxin B1 to aflatoxin B1-8,9-epoxide that adducts guanine (G) in codon 249, with subsequent depurination to give abasic sites and then strand breaks. This is the first demonstration in a cell-free medium that the aflatoxin B1 metabolite selectively causes abasic site formation and strand breaks at codon 249 of the p53 probe, corresponding to the chemical pathway and mutations of p53 in human liver cells and tumors. Molecular modeling supports the view that binding of aflatoxin B1-8,9-epoxide to G in codon 249 precedes the S_N2 adduction reaction. Among a range of metabolic enzymes characteristic of different organs, human liver microsomes and cyt P450 3A5 supersomes showed the highest bioactivation rate for p53 exon 7 damage. This method of identifying metabolite-related gene damage sites may facilitate predictions of organ specific cancers for test chemicals via correlations with mutation sites.

Relevance of DNA repair gene polymorphisms to gastric cancer risk and phenotype

Variations in DNA repair genes have been reported as key factors in gastric cancer (GC) susceptibility but results among studies are inconsistent. We aimed to assess the relevance of DNA repair gene polymorphisms and environmental factors to GC risk and phenotype in a Caucasian population in Spain. Genomic DNA from 603 patients with primary GC and 603 healthy controls was typed for 123 single nucleotide polymorphisms in DNA repair genes using the Illumina platform. Helicobacter pylori infection with CagA strains (odds ratio (OR): 1.99; 95% confidence interval (CI): 1.55–2.54), tobacco smoking (OR: 1.77; 95% CI: 1.22–2.57), and family history of GC (OR: 2.87; 95% CI: 1.85–4.45) were identified as independent risk factors for GC. By contrast, the TP53 rs9894946A (OR: 0.73; 95% CI: 0.56–0.96), TP53 rs1042522C (OR: 0.76; 95% CI: 0.56–0.96), and BRIP1 rs4986764T (OR: 0.55; 95% CI: 0.38–0.78) variants were associated with lower GC risk. Significant associations with specific anatomopathological GC subtypes were also observed, most notably in the ERCC4 gene with the rs1799801C, rs2238463G, and rs3136038T variants being inversely associated with cardia GC risk. Moreover, the XRCC3 rs861528 allele A was significantly increased in the patient subgroup with diffuse GC (OR: 1.75; 95% CI: 1.30–2.37). Our data show that specific TP53, BRIP1, ERCC4, and XRCC3 polymorphisms are relevant in susceptibility to GC risk and specific subtypes in Caucasians.

Potential therapeutic targets of TP53 gene in the context of its classically canonical functions and its latest non-canonical functions in human cancer

In normal tissue, p53 protein has a wide range of functions involving cell homeostasis; its mutation, however, permits a carcinogenic acquisition of function. TP53 gene mutation is a major genomic aberration in various human cancers and is a critical event in the multi-step carcinogenesis process. TP53 mutation is clinically relevant for the molecular classification of carcinogenesis, as most recently described rigorously by the Cancer Genome Atlas Research Network. TP53 gene mutation has been considered to work as a tumor suppressor gene through the loss of its transcriptional activity, which is designated as a canonical function. However, in cancer patients with mutant TP53, mutated p53 protein is frequently overexpressed, suggesting the activation of an oncogenic process through a gain of function (GOF). As part of this GOF, molecular mechanisms explaining the non-canonical function of TP53 gene abnormality have been reported, in which mutant p53 unconventionally binds with various critical molecules suppressing oncogenic properties, such as p63 and p73. Moreover, mutant TP53 gene-targeted therapy has been rigorously developed, and promising clinical trials have been started. In this study, we summarize the novel aspects of mutant p53 and describe its prominent therapeutic potentials in human cancer.

Sphingosine-1-phosphate promotes ovarian cancer cell proliferation by disrupting Hippo signaling

Epithelial ovarian carcinomas account for more than 90% of human ovarian cancers and have become the primary cause of death for gynecological malignancies. Unlimited cell proliferation and resistance to cell apoptosis contribute to the development of ovarian cancers. However, the underlying mechanisms involved in these processes in epithelial ovarian carcinomas are yet poorly understood. In the present study, we examined the Hippo signaling gene expression and investigated the effects of Sphingosine 1-phosphate (S1P) on cell proliferation and the underlying mechanisms in human ovarian cancer cell lines, OVCAR3 and SKOV3. Our results demonstrate that S1P disrupts Hippo signaling by reducing YAP phosphorylation and increasing the expression of CCN1 and CCN2 in both ovarian cancer cells. Furthermore, the increase in CCN1/CCN2 expression contributes to the S1P-induced increase in cancer cell proliferation.

Cadherin-6 type 2, K-cadherin (CDH6) is regulated by mutant p53 in the fallopian tube but is not expressed in the ovarian surface

High-grade serous ovarian cancer (HGSOC) is the most lethal gynecological malignancy and may arise in either the fallopian tube epithelium (FTE) or ovarian surface epithelium (OSE). A mutation in p53 is reported in 96% of HGSOC, most frequently at R273 and R248. The goal of this study was to identify specific gene targets in the FTE that are altered by mutant p53, but not in the OSE. Gene analysis revealed that both R273 and R248 mutant p53 reduces CDH6 expression in the oviduct, but CDH6 was not detected in murine OSE cells. p53^R273H induced SLUG and FOXM1 while p53^R248W did not induce SLUG and only modestly increased FOXM1, which correlated with less migration as compared to p53^R273H. An oviduct specific PAX8^Cre/+/p53^R270H/+ mouse model was created and confirmed that in vivo mutant p53 repressed CDH6 but was not sufficient to stabilize p53 expression alone. Overexpression of mutant p53 in the p53 null OVCAR5 cells decreased CDH6 levels indicating this was a gain-of-function. SLUG knockdown in murine oviductal cells with p53^R273H restored CDH6 repression and a ChIP analysis revealed direct binding of mutant p53 on the CDH6 promoter. NSC59984, a small molecule that degrades mutant p53^R273H, rescued CDH6 expression. In summary, CDH6 is expressed in the oviduct, but not the ovary, and is repressed by mutant p53. CDH6 expression with further validations may aide in establishing markers that inform upon the cell of origin of high grade serous tumors.

Clinical implications of TP53 mutations in myelodysplastic syndromes treated with hypomethylating agents

We screened TP53 mutations in 168 MDS patients who were treated with HMA and evaluated predictive and prognostic value of TP53 mutations. Overall response to HMA was not different based on TP53 mutation status (45% vs. 32% in TP53-mutated and wild type [WT], respectively, P = 0.13). However, response duration was significantly shorter in TP53-mutated patients compared to WT patients (5.7 months vs. 28.5 months, P = 0.003). Longitudinal analysis of TP53 mutations after HMA showed that TP53 mutations almost always persisted at times of disease progression. TP53-mutated patients showed significantly worse overall survival (OS) compared to WT patients (9.4 months vs. 20.7 months, P <0.001). Further, TP53 mutations distinguished prognosis in the subgroup of patients with complex karyotype and Revised International Prognostic Scoring System (IPSS-R) defined very high-risk disease. Multivariate analysis showed that TP53 mutation status is significantly prognostic for OS after adjusting prognostic effect from other factors. The current study provides evidence that TP53 mutations are independently prognostic in MDS patients treated with HMA. While TP53-mutated MDS patients initially respond well to HMA, their duration of response is significantly shorter than WT patients. Novel strategies to improve duration of response in TP53-mutated MDS are urgently needed.

Direct LC-MS/MS Detection of Guanine Oxidations in Exon 7 of the p53 Tumor Suppressor Gene

Oxidation of DNA by reactive oxygen species (ROS) yields 8-oxo-7,8-dihydroguanosine (8-oxodG) as primary oxidation product, which can lead to downstream G to T transversion mutations. DNA mutations are nonrandom, and mutations at specific codons are associated with specific cancers, as widely documented for the p53 tumor suppressor gene. Here, we present the first direct LC-MS/MS study (without isotopic labeling or hydrolysis) of primary oxidation sites of p53 exon 7. We oxidized a 32 base pair (bp) double-stranded (ds) oligonucleotide representing exon 7 of the p53 gene. Oxidized oligonucleotides were cut by a restriction endonuclease to provide small strands and enable positions and amounts of 8-oxodG to be determined directly by LC-MS/MS. Oxidation sites on the oligonucleotide generated by two oxidants, catechol/Cu2+/NADPH and Fenton's reagent, were located and compared. Guanines in codons 243, 244, 245, and 248 were most frequently oxidized by catechol/Cu2+/NADPH with relative oxidation of 5.6, 7.2, 2.6, and 10.7%, respectively. Fenton's reagent oxidations were more specific for guanines in codons 243 (20.3%) and 248 (10.4%). Modeling of docking of oxidizing species on the ds-oligonucleotide were consistent with the experimental codon oxidation sites. Significantly, codons 244 and 248 are mutational "hotspots" in nonsmall cell and small cell lung cancers, supporting a possible role of oxidation in p53 mutations leading to lung cancer.

Can adnexal torsion be predicted by measuring plasma heat shock protein 70 level? An experimental study

OBJECTIVE

To investigate the effect of adnexal torsion on the plasma heat shock protein 70 level and to determine whether plasma heat shock protein 70 can be used in the adnexal torsion diagnosis.

MATERIALS AND METHODS

Twenty-one nulligravid 3-month-old female Wistar albino rats were randomly and equally allocated into three groups: study group (ovarian torsion) (n = 7), laparotomy group (sham operation) (n = 7) and control group (received no special treatment) (n = 7). Ovarian torsion model was created by twisting the right adnexa two times around its pedicle and fixing over the lateral pelvis with 6.0 polyglactin absorbable surgical suture. Blood was sampled before and 12 h after operation to assess plasma heat shock protein 70 level.

RESULTS

In the study group, the mean plasma heat shock protein 70 level was significantly higher than that in the laparotomy and control groups (1.75 ± 0.25), (1.16 ± 0.99), (1.19 ± 0.11) ng/ml, respectively, P = 0.001), following 12 h of ovarian torsion.

CONCLUSION

A significant increase in plasma heat shock protein 70 level in the study group indicates that plasma heat shock protein 70 level could be used as a serum marker in the early detection of adnexal torsion. However, further clinical and experimental studies of a larger size are required.

P53 deregulation in Epstein-Barr virus-associated gastric cancer

TP53 is a tumour suppressor gene frequently mutated in human cancers; nevertheless, in EBV-associated malignancies mutations are uncommon despite frequent deregulation of the p53 pathway. In this study, we aimed to investigate p53 expression, TP53 mRNA levels and TP53 mutations in EBV-associated gastric carcinoma (EBVaGC). A case-control study was performed using 46 patients: 15 EBVaGC and 31 EBV-negative GC (EBVnGC) cases. p53 expression was detected by immunohistochemistry (IHC), the evaluation of p53 mRNA levels was performed by RT-qPCR and TP53 mutations were investigated only in EBVaGC cases using the DNA sanger sequencing method. p53 expression was found in 97.8% (45/46) of all gastric cancer cases (including EBVaGC and EBVnGC groups). Despite the high frequency of p53 expression in both groups, the percentages of cells are significantly higher among EBVaGC cases (p = 0.027). Regarding the mRNA levels, we found a significantly increased expression of p53 mRNA in EBVnGC (2^-ΔΔCt = 13.4 ± 2.4; p = 0.0029) when compared with EBVaGC. Furthermore, the sequencing analysis of TP53 gene revealed that only one of the 15 EBVaGC cases presented a missense mutation. Our results demonstrated that EBV-associated gastric carcinomas are characterized by a significant decrease of TP53 mRNA levels with a strong p53 expression and rare TP53 mutations when compared with EBV-negative cancers. Considering these results, EBV seems to induce a stabilization of p53 in the EBVaGC independently of the presence of mutations, which remains to be explained.

Downregulation of PRRX1 via the p53-dependent signaling pathway predicts poor prognosis in hepatocellular carcinoma

Paired-related homeobox 1 (PRRX1) has been identified as a novel molecule associated with induction of epithelial-mesenchymal transition (EMT), acquisition of cancer stem cell like properties and poor prognosis in tumors. However, the function of PRRX1 in hepatocellular carcinoma has not been elucidated. In the present study, we observed that PRRX1 expression levels were downregulated and positively correlated with the downregulated expression of p53 in hepatocellular carcinoma specimens. Decreased expression of PRRX1 and/or p53 by siRNA induced both the migration and the invasion features of HCC cells in vitro. Furthermore, the loss of PRRX1 inhibits hepatocellular carcinoma (HCC) cell apoptosis, an anti-apoptotic expression profile was upregulated accompanied by downregulated expression of p53. HCC patients with low-expression of both PRRX1 and p53 had a significantly shorter overall and disease-free survival. These findings demonstrate that PRRX1 plays an important role in metastasis and apoptosis of HCC cells through the p53-dependent signaling pathway and is expected to become a novel biomarker associated with patient prognosis and survival.

Regulation of Metabolic Activity by p53

Metabolic reprogramming in cancer cells is controlled by the activation of multiple oncogenic signalling pathways in order to promote macromolecule biosynthesis during rapid proliferation. Cancer cells also need to adapt their metabolism to survive and multiply under the metabolically compromised conditions provided by the tumour microenvironment. The tumour suppressor p53 interacts with the metabolic network at multiple nodes, mostly to reduce anabolic metabolism and promote preservation of cellular energy under conditions of nutrient restriction. Inactivation of this tumour suppressor by deletion or mutation is a frequent event in human cancer. While loss of p53 function lifts an important barrier to cancer development by deleting cell cycle and apoptosis checkpoints, it also removes a crucial regulatory mechanism and can render cancer cells highly sensitive to metabolic perturbation. In this review, we will summarise the major concepts of metabolic regulation by p53 and explore how this knowledge can be used to selectively target p53 deficient cancer cells in the context of the tumour microenvironment.

Loss of LZAP inactivates p53 and regulates sensitivity of cells to DNA damage in a p53-dependent manner

Chemotherapy and radiation, the two most common cancer therapies, exert their anticancer effects by causing damage to cellular DNA. However, systemic treatment damages DNA not only in cancer, but also in healthy cells, resulting in the progression of serious side effects and limiting efficacy of the treatment. Interestingly, in response to DNA damage, p53 seems to play an opposite role in normal and in the majority of cancer cells—wild-type p53 mediates apoptosis in healthy tissues, attributing to the side effects, whereas mutant p53 often is responsible for acquired cancer resistance to the treatment. Here, we show that leucine zipper-containing ARF-binding protein (LZAP) binds and stabilizes p53. LZAP depletion eliminates p53 protein independently of its mutation status, subsequently protecting wild-type p53 cells from DNA damage-induced cell death, while rendering cells expressing mutant p53 more sensitive to the treatment. In human non-small-cell lung cancer, LZAP levels correlated with p53 levels, suggesting that loss of LZAP may represent a novel mechanism of p53 inactivation in human cancer. Our studies establish LZAP as a p53 regulator and p53-dependent determinative of cell fate in response to DNA damaging treatment.

Evaluation of the use of therapeutic peptides for cancer treatment

Cancer along with cardiovascular disease are the main causes of death in the industrialised countries around the World. Conventional cancer treatments are losing their therapeutic uses due to drug resistance, lack of tumour selectivity and solubility and as such there is a need to develop new therapeutic agents. Therapeutic peptides are a promising and a novel approach to treat many diseases including cancer. They have several advantages over proteins or antibodies: as they are (a) easy to synthesise, (b) have a high target specificity and selectivity and (c) have low toxicity. Therapeutic peptides do have some significant drawbacks related to their stability and short half-life. In this review, strategies used to overcome peptide limitations and to enhance their therapeutic effect will be compared. The use of short cell permeable peptides that interfere and inhibit protein-protein interactions will also be evaluated.

Noncoding RNAs and immune checkpoints-clinical implications as cancer therapeutics

A major mechanism of tumor development and progression is silencing of the patient's immune response to cancer-specific antigens. Defects in the so-called cancer immunity cycle may occur at any stage of tumor development. Within the tumor microenvironment, aberrant expression of immune checkpoint molecules with activating or inhibitory effects on T lymphocytes induces immune tolerance and cellular immune escape. Targeting immune checkpoint molecules such as programmed cell death protein 1 (PD-1) and its ligand PD-L1 with specific antibodies has proven to be a major advance in the treatment of several types of cancer. Another way to therapeutically influence the tumor microenvironment is by modulating the levels of microRNAs (miRNAs), small noncoding RNAs that shuttle bidirectionally between malignant and tumor microenvironmental cells. These small RNA transcripts have two features: (a) their expression is quite specific to distinct tumors, and (b) they are involved in early regulation of immune responses. Consequently, miRNAs may be ideal molecules for use in cancer therapy. Many miRNAs are aberrantly expressed in human cancer cells, opening new opportunities for cancer therapy, but the exact functions of these miRNAs and their interactions with immune checkpoint molecules have yet to be investigated. This review summarizes recently reported findings about miRNAs as modulators of immune checkpoint molecules and their potential application as cancer therapeutics in clinical practice.

The p53 isoform delta133p53ß regulates cancer cell apoptosis in a RhoB-dependent manner

The TP53 gene plays essential roles in cancer. Conventionally, wild type (WT) p53 is thought to prevent cancer development and metastasis formation, while mutant p53 has transforming abilities. However, clinical studies failed to establish p53 mutation status as an unequivocal predictive or prognostic factor of cancer progression. The recent discovery of p53 isoforms that can differentially regulate cell cycle arrest and apoptosis suggests that their expression, rather than p53 mutations, could be a more clinically relevant biomarker in patients with cancer. In this study, we show that the p53 isoform delta133p53ß is involved in regulating the apoptotic response in colorectal cancer cell lines. We first demonstrate delta133p53ß association with the small GTPase RhoB, a well-described anti-apoptotic protein. We then show that, by inhibiting RhoB activity, delta133p53ß protects cells from camptothecin-induced apoptosis. Moreover, we found that high delta133p53 mRNA expression levels are correlated with higher risk of recurrence in a series of patients with locally advanced rectal cancer (n = 36). Our findings describe how a WT TP53 isoform can act as an oncogene and add a new layer to the already complex p53 signaling network.

Sensitization strategies in lung cancer

The commonly used treatment avenues employed by cancer physicians include surgery, radiotherapy (RT) and chemotherapy in addition to rapid developmental and confirmatory studies on the efficacy of targeted therapies. However, the success rate in these commonly used treatments remains relatively low due to associated side effects, such as normal cell targeting/toxicity and resistance. In addition, investigators are continuing their efforts to enhance the efficacy of RT and chemotherapy to prevent associated side effects and improve the survival rate of the affected patient in order to increase patient survival. In the present study, we have reviewed the sensitization approaches used to improve chemotherapy and RT sensitivity in tumors.

Immunomodulatory Function of the Tumor Suppressor p53 in Host Immune Response and the Tumor Microenvironment

The tumor suppressor p53 is the most frequently mutated gene in human cancers. Most of the mutations are missense leading to loss of p53 function in inducing apoptosis and senescence. In addition to these autonomous effects of p53 inactivation/dysfunction on tumorigenesis, compelling evidence suggests that p53 mutation/inactivation also leads to gain-of-function or activation of non-autonomous pathways, which either directly or indirectly promote tumorigenesis. Experimental and clinical results suggest that p53 dysfunction fuels pro-tumor inflammation and serves as an immunological gain-of-function driver of tumorigenesis via skewing immune landscape of the tumor microenvironment (TME). It is now increasingly appreciated that p53 dysfunction in various cellular compartments of the TME leads to immunosuppression and immune evasion. Although our understanding of the cellular and molecular processes that link p53 activity to host immune regulation is still incomplete, it is clear that activating/reactivating the p53 pathway in the TME also represents a compelling immunological strategy to reverse immunosuppression and enhance antitumor immunity. Here, we review our current understanding of the potential cellular and molecular mechanisms by which p53 participates in immune regulation and discuss how targeting the p53 pathway can be exploited to alter the immunological landscape of tumors for maximizing therapeutic outcome.

TP53 and 53BP1 Reunited

Identified as a TP53-binding protein, 53BP1 is a key regulator of the cellular response to double-strand breaks, a TP53-independent activity. Recent data have established a new TP53-dependent function for 53BP1 in mitotic surveillance after centrosome loss.

TP53 drives invasion through expression of its Δ133p53β variant

TP53 is conventionally thought to prevent cancer formation and progression to metastasis, while mutant TP53 has transforming activities. However, in the clinic, TP53 mutation status does not accurately predict cancer progression. Here we report, based on clinical analysis corroborated with experimental data, that the p53 isoform Δ133p53β promotes cancer cell invasion, regardless of TP53 mutation status. Δ133p53β increases risk of cancer recurrence and death in breast cancer patients. Furthermore Δ133p53β is critical to define invasiveness in a panel of breast and colon cell lines, expressing WT or mutant TP53. Endogenous mutant Δ133p53β depletion prevents invasiveness without affecting mutant full-length p53 protein expression. Mechanistically WT and mutant Δ133p53β induces EMT. Our findings provide explanations to 2 long-lasting and important clinical conundrums: how WT TP53 can promote cancer cell invasion and reciprocally why mutant TP53 gene does not systematically induce cancer progression.

DOI:http://dx.doi.org/10.7554/eLife.14734.001

Most cancers are caused by a build-up of mutations that are acquired throughout life. One gene in particular, called TP53, is the most commonly mutated gene in many types of human cancers. This suggests that TP53 mutations play an important role in cancer development.

It is widely considered that the TP53 gene normally stops tumors from forming, while mutant forms of the gene somehow promote cancer growth. Evidence from patients with cancer has shown, however, that the relationship between TP53 mutations and cancer is not that simple. Some very aggressive cancers that resist treatment and spread have a normal TP53 gene. Some cancers with a mutated gene do not spread and respond well to cancer treatments. Recent studies have shown that the normal TP53 gene produces many different versions of its protein, and that some of these naturally occurring forms are found more often in tumors that others. However, it was not clear if certain versions of TP53’s proteins contributed to the development of cancer.

Now, Gadea, Arsic, Fernandes et al. show that Δ133p53β, one version of the protein produced by the TP53 gene in human cells, helps tumor cells to spread to other organs. Tests of 273 tumors taken from patients with breast cancer revealed that tumors with the Δ133p53β protein were more likely to spread. Patients with these Δ133p53β-containing tumors were also more likely to develop secondary tumors at other sites in the body and to die within five years.

Next, a series of experiments showed that removing Δ133p53β from breast cancer cells grown in the laboratory made them less likely to invade, while adding it back had the opposite effect. The same thing happened in colon cancer cells grown in the laboratory. The experiments showed that Δ133p53β causes tumor cells with the normal TP53 gene or a mutated TP53 gene to spread to other organs.

Together the new findings help explain why some aggressive cancers develop even with a normal version of the tumor-suppressing TP53 gene. They also help explain why not all cancers with a mutant version of the TP53 gene go on to spread. Future studies will be needed to determine whether drugs that prevent the production of the Δ133p53β protein can help to treat aggressive cancers.

DOI:http://dx.doi.org/10.7554/eLife.14734.002

A platform for interrogating cancer-associated p53 alleles

p53 is the most frequently mutated gene in human cancer. Compelling evidence argues that full transformation involves loss of growth suppression encoded by wild-type p53 together with poorly understood oncogenic activity encoded by missense mutations. Furthermore, distinguishing disease alleles from natural polymorphisms is an important clinical challenge. To interrogate the genetic activity of human p53 variants, we leveraged the Drosophila model as an in vivo platform. We engineered strains that replace the fly p53 gene with human alleles, producing a collection of stocks that are, in effect, ‘humanized’ for p53 variants. Like the fly counterpart, human p53 transcriptionally activated a biosensor and induced apoptosis after DNA damage. However, all humanized strains representing common alleles found in cancer patients failed to complement in these assays. Surprisingly, stimulus-dependent activation of hp53 occurred without stabilization, demonstrating that these two processes can be uncoupled. Like its fly counterpart, hp53 formed prominent nuclear foci in germline cells but cancer-associated p53 variants did not. Moreover, these same mutant alleles disrupted hp53 foci and inhibited biosensor activity, suggesting that these properties are functionally linked. Together these findings establish a functional platform for interrogating human p53 alleles and suggest that simple phenotypes could be used to stratify disease variants.

p53 determines prognostic significance of the carbohydrate stem cell marker TF1 (CD176) in ovarian cancer

INTRODUCTION

The oncofoetal Thomsen-Friedenreich (TF1, CD176) epitope is a carbohydrate cancer stem cell (CSC) antigen, and TF1-mediated cancer progression can be widely reversed by anti-TF1 antibodies. Particularly, CSC-like cells are regarded to be tumorigenic and chemoresistant. Aberrant p53 is probably the factor most closely associated with chemoresistance and tumour aggressiveness in ovarian tumours. We thus questioned whether TF1 in combination with p53 or as a single marker may be related to clinico-pathological features and survival of ovarian cancer patients.

PATIENTS AND METHODS

Both markers were quantified in ovarian cancer tissue (n = 151) by immunohistochemistry. p53 staining was subdivided into three subgroups [n (completely negative) = 57, n (moderately stained) = 28, n (overexpressing) = 66]. TF1 was scored as positive (n = 30) versus negative (n = 121).

RESULTS

Only in those cancers classified with moderate p53 staining-and thus most likely displaying with wild-type TP53-TF1 positivity turned out to be a predictor for shortened overall survival (univariate: p < 0.001, multivariate: p = 0.001). By screening 17 different protein markers for correlation with TF1, only mucin-1 emerged as a potential TF1 carrier protein.

CONCLUSION

It is hypothesized that TF1 may confer tumour-promoting features, especially in a TP53 wild-type genetic background. In addition, TF1 is an attractive immunotherapeutic target. Whether those cases classified as TF1 positive and at the same time as moderately stained for p53 might particularly benefit from a future anti-TF1 antibody treatment or from TF1 vaccination therapy remains to be determined.

Autophagy in hepatocellular carcinomas: from pathophysiology to therapeutic response

Autophagy is an intracellular lysosomal degradation process performed by the cells to maintain energy balance. The autophagy response plays an important role in the progression of liver disease due to hepatitis virus infection, alcoholic liver disease, nonalcoholic fatty liver disease, liver cirrhosis, and hepatocellular carcinoma (HCC). An increased autophagy response also contributes to the pathogenesis of liver disease through modulation of innate and adaptive immune responses; a defective cellular autophagy response leads to the development of HCC. Recent progress in the field indicates that autophagy modulation provides a novel targeted therapy for human liver cancer. The purpose of this review is to update our understanding of how the cellular autophagy response impacts the pathophysiology of liver disease and HCC treatment.

Integrated analysis of DNA methylation and mutations in esophageal squamous cell carcinoma

The recent development of next-generation sequencing technology for extensive mutation analysis, and beadarray technology for genome-wide DNA methylation analysis has made it possible to obtain integrated pictures of genetic and epigenetic alterations, using the same cancer samples. In this study, we aimed to characterize such a picture in esophageal squamous cell carcinomas (ESCCs). Base substitutions of 55 cancer-related genes and copy number alterations (CNAs) of 28 cancer-related genes were analyzed by targeted sequencing. Forty-four of 57 ESCCs (77%) had 64 non-synonymous somatic mutations, and 24 ESCCs (42%) had 35 CNAs. A genome-wide DNA methylation analysis using an Infinium HumanMethylation450 BeadChip array showed that the CpG island methylator phenotype was unlikely to be present in ESCCs, a different situation from gastric and colon cancers. Regarding individual pathways affected in ESCCs, the WNT pathway was activated potentially by aberrant methylation of its negative regulators, such as SFRP1, SFRP2, SFRP4, SFRP5, SOX17, and WIF1 (33%). The p53 pathway was inactivated by TP53 mutations (70%), and potentially by aberrant methylation of its downstream genes. The cell cycle was deregulated by mutations of CDKN2A (9%), deletions of CDKN2A and RB1 (32%), and by aberrant methylation of CDKN2A and CHFR (9%). In conclusion, ESCCs had unique methylation profiles different from gastric and colon cancers. The genes involved in the WNT pathway were affected mainly by epigenetic alterations, and those involved in the p53 pathway and cell cycle regulation were affected mainly by genetic alterations. © 2016 Wiley Periodicals, Inc.

p53 genes function to restrain mobile elements

Wylie et al. show that p53 restricts retrotransposon activity and genetically interacts with components of the piRNA pathway. In gene complementation studies, normal human p53 alleles restrained these mobile elements, but mutant p53 alleles from cancer patients could not. Consistent with these observations, they also found patterns of unrestrained retrotransposons in p53-driven mouse and human cancers.

Throughout the animal kingdom, p53 genes govern stress response networks by specifying adaptive transcriptional responses. The human member of this gene family is mutated in most cancers, but precisely how p53 functions to mediate tumor suppression is not well understood. Using Drosophila and zebrafish models, we show that p53 restricts retrotransposon activity and genetically interacts with components of the piRNA (piwi-interacting RNA) pathway. Furthermore, transposon eruptions occurring in the p53⁻ germline were incited by meiotic recombination, and transcripts produced from these mobile elements accumulated in the germ plasm. In gene complementation studies, normal human p53 alleles suppressed transposons, but mutant p53 alleles from cancer patients could not. Consistent with these observations, we also found patterns of unrestrained retrotransposons in p53-driven mouse and human cancers. Furthermore, p53 status correlated with repressive chromatin marks in the 5′ sequence of a synthetic LINE-1 element. Together, these observations indicate that ancestral functions of p53 operate through conserved mechanisms to contain retrotransposons. Since human p53 mutants are disabled for this activity, our findings raise the possibility that p53 mitigates oncogenic disease in part by restricting transposon mobility.

Damage-inducible intragenic demethylation of the human TP53 tumor suppressor gene is associated with transcription from an alternative intronic promoter

Wild-type TP53 exons 5-8 contain CpG dinucleotides that are prone to methylation-dependent mutation during carcinogenesis, but the regulatory effects of methylation affecting these CpG sites are unclear. To clarify this, we first assessed site-specific TP53 CpG methylation in normal and transformed cells. Both DNA damage and cell ageing were associated with site-specific CpG demethylation in exon 5 accompanied by induction of a truncated TP53 isoform regulated by an adjacent intronic promoter (P2). We then synthesized novel synonymous TP53 alleles with divergent CpG content but stable encodement of the wild-type polypeptide. Expression of CpG-enriched TP53 constructs selectively reduced production of the full-length transcript (P1), consistent with a causal relationship between intragenic demethylation and transcription. 450K methylation comparison of normal (TP53-wildtype) and cancerous (TP53-mutant) human cells and tissues revealed focal cancer-associated declines in CpG methylation near the P1 transcription start site, accompanied by rises near the alternate exon 5 start site. These data confirm that site-specific changes of intragenic TP53 CpG methylation are extrinsically inducible, and suggest that human cancer progression is mediated in part by dysregulation of damage-inducible intragenic CpG demethylation that alters TP53 P1/P2 isoform expression. © 2015 The Authors. Molecular Carcinogenesis Published by Wiley Periodicals, Inc.

p53 regulates cytoskeleton remodeling to suppress tumor progression

Cancer cells possess unique characteristics such as invasiveness, the ability to undergo epithelial-mesenchymal transition, and an inherent stemness. Cell morphology is altered during these processes and this is highly dependent on actin cytoskeleton remodeling. Regulation of the actin cytoskeleton is, therefore, important for determination of cell fate. Mutations within the TP53 (tumor suppressor p53) gene leading to loss or gain of function (GOF) of the protein are often observed in aggressive cancer cells. Here, we highlight the roles of p53 and its GOF mutants in cancer cell invasion from the perspective of the actin cytoskeleton; in particular its reorganization and regulation by cell adhesion molecules such as integrins and cadherins. We emphasize the multiple functions of p53 in the regulation of actin cytoskeleton remodeling in response to the extracellular microenvironment, and oncogene activation. Such an approach provides a new perspective in the consideration of novel targets for anti-cancer therapy.

Enhanced antigen detection in immunohistochemical staining using a 'digitized' chimeric antibody

The immunohistochemical (IHC) staining of mouse tissue sections using antibodies of mouse origin can result in high nonspecific background due to the staining of endogenous immunoglobulins (Igs) by enzyme-conjugated secondary antibodies. In order to obviate this issue, we developed a chimeric mouse-human anti-p53 monoclonal antibody (MH242) by grafting the variable regions of a known mouse antibody into a human Ig scaffold. This facilitated use of an anti-human secondary antibody, and resulted in near-zero background when compared with its parental mouse monoclonal antibody (PAb242). Furthermore, the chimeric antibody enabled reproducible detection of mutant p53 (homozygous R172H) expression in mouse tissue, an observation hitherto largely equivocal based on the use of existing antibodies. The approach we describe leads to the generation of tractable antibody reagents, whose integrity can be readily verified through DNA sequencing of expressor plasmids. The wide-spread adoption of such 'digitized' antibodies should reduce experimental disparities that can commonly arise through variations in antibody quality.