Phosphorylation of Ser-20 mediates stabilization of human p53 in response to DNA damage

Predicting p53-dependent cell transitions from thermodynamic models

A cell's fate involves transitions among its various states, each defined by a distinct gene expression profile governed by the topology of gene regulatory networks, which are affected by 3D genome organization. Here, we develop thermodynamic models to determine the fate of a malignant cell as governed by the tumor suppressor p53 signaling network, taking into account long-range chromatin interactions in the mean-field approximation. The tumor suppressor p53 responds to stress by selectively triggering one of the potential transcription programs that influence many layers of cell signaling. These range from p53 phosphorylation to modulation of its DNA binding affinity, phase separation phenomena, and internal connectivity among cell fate genes. We use the minimum free energy of the system as a fundamental property of biological networks that influences the connection between the gene network topology and the state of the cell. We constructed models based on network topology and equilibrium thermodynamics. Our modeling shows that the binding of phosphorylated p53 to promoters of target genes can have properties of a first order phase transition. We apply our model to cancer cell lines ranging from breast cancer (MCF-7), colon cancer (HCT116), and leukemia (K562), with each one characterized by a specific network topology that determines the cell fate. Our results clarify the biological relevance of these mechanisms and suggest that they represent flexible network designs for switching between developmental decisions.

DUSP3 modulates IRES-dependent translation of mRNAs through dephosphorylation of the HNRNPC protein in cells under genotoxic stimulus

BACKGROUND INFORMATION

The dual-specificity phosphatase 3 (DUSP3) regulates cell cycle progression, proliferation, senescence, and DNA repair pathways under genotoxic stress. This phosphatase interacts with HNRNPC protein suggesting an involvement in the regulation of HNRNPC-ribonucleoprotein complex stability. In this work, we investigate the impact of DUSP3 depletion on functions of HNRNPC aiming to suggest new roles for this enzyme.

RESULTS

The DUSP3 knockdown results in the tyrosine hyperphosphorylation state of HNRNPC increasing its RNA binding ability. HNRNPC is present in the cytoplasm where it interacts with IRES trans-acting factors (ITAF) complex, which recruits the 40S ribosome on mRNA during protein synthesis, thus facilitating the translation of mRNAs containing IRES sequence in response to specific stimuli. In accordance with that, we found that DUSP3 is present in the 40S, monosomes and polysomes interacting with HNRNPC, just like other previously identified DUSP3 substrates/interacting partners such as PABP and NCL proteins. By downregulating DUSP3, Tyr-phosphorylated HNRNPC preferentially binds to IRES-containing mRNAs within ITAF complexes preferentially in synchronized or stressed cells, as evidenced by the higher levels of proteins such as c-MYC and XIAP, but not their mRNAs such as measured by qPCR. Under DUSP3 absence, this increased phosphorylated-HNRNPC/RNA interaction reduces HNRNPC-p53 binding in presence of RNAs releasing p53 for specialized cellular responses. Similarly, to HNRNPC, PABP physically interacts with DUSP3 in an RNA-dependent manner.

CONCLUSIONS AND SIGNIFICANCE

Overall, DUSP3 can modulate cellular responses to genotoxic stimuli at the translational level by maintaining the stability of HNRNPC-ITAF complexes and regulating the intensity and specificity of RNA interactions with RRM-domain proteins.

Cell fate regulation governed by p53: Friends or reversible foes in cancer therapy

Cancer is a leading cause of death worldwide. Targeted therapies aimed at key oncogenic driver mutations in combination with chemotherapy and radiotherapy as well as immunotherapy have benefited cancer patients considerably. Tumor protein p53 (TP53), a crucial tumor suppressor gene encoding p53, regulates numerous downstream genes and cellular phenotypes in response to various stressors. The affected genes are involved in diverse processes, including cell cycle arrest, DNA repair, cellular senescence, metabolic homeostasis, apoptosis, and autophagy. However, accumulating recent studies have continued to reveal novel and unexpected functions of p53 in governing the fate of tumors, for example, functions in ferroptosis, immunity, the tumor microenvironment and microbiome metabolism. Among the possibilities, the evolutionary plasticity of p53 is the most controversial, partially due to the dizzying array of biological functions that have been attributed to different regulatory mechanisms of p53 signaling. Nearly 40 years after its discovery, this key tumor suppressor remains somewhat enigmatic. The intricate and diverse functions of p53 in regulating cell fate during cancer treatment are only the tip of the iceberg with respect to its equally complicated structural biology, which has been painstakingly revealed. Additionally, TP53 mutation is one of the most significant genetic alterations in cancer, contributing to rapid cancer cell growth and tumor progression. Here, we summarized recent advances that implicate altered p53 in modulating the response to various cancer therapies, including chemotherapy, radiotherapy, and immunotherapy. Furthermore, we also discussed potential strategies for targeting p53 as a therapeutic option for cancer.

Inorganic arsenic-mediated upregulation of TUG1 promotes apoptosis in human bronchial epithelial cells by activating the p53 signaling pathway

Exposure to arsenic, an environmental contaminant, is known to cause arsenicosis and cancer. Although considerable research has been conducted to understand the underlying mechanism responsible for arsenic-induced cancers, the precise molecular mechanisms remain unknown, especially at the epigenetic regulation level. Long non-coding RNAs (LncRNAs) that have been shown to mediate various biological processes, including proliferation, apoptosis, necrosis, and mutagenesis. There are few studies on LncRNAs and biological damage caused by environmental pollutants. The LncRNAs taurine upregulated gene 1 (TUG1) regulates cell growth both in vitro and in vivo, and contributes its oncogenic role. However, the precise roles and related mechanisms of arsenic-induced cell apoptosis are still not fully understood owing to controversial findings in the literature. In this study, quantitative real-time polymerase chain reaction (qRT-PCR) analysis revealed higher expression levels of TUG1 in people occupationally exposed to arsenic than in individuals living away from the source of arsenic exosure (N = 25). In addition, the results suggested that TUG1 was involved in arsenic-induced apoptosis. Furthermore, knockdown experiments showed that silencing of TUG1 markedly inhibited proliferation, whereas depletion of TUG1 led to increased apoptosis. The TUG1-small interfering RNA (siRNA) combination with arsenic (3 μM/L) slightly increased apoptosis compared with the TUG1-siRNA. Additionally, the knockdown experiments showed that the silencing of TUG1 by siRNA inhibited proliferation and promoted apoptosis by inducing p53, p-p53 (ser392), FAS, BCL2, MDM2, cleaved-caspase7 proteins in 16HBE cells. These results indicated that arsenic mediates the upregulation of TUG1 and induces cell apoptosis via activating the p53 signaling pathway.

Growing and dividing: how O-GlcNAcylation leads the way

Cell cycle errors can lead to mutations, chromosomal instability, or death; thus, the precise control of cell cycle progression is essential for viability. The nutrient-sensing posttranslational modification, O-GlcNAc, regulates the cell cycle allowing one central control point directing progression of the cell cycle. O-GlcNAc is a single N-acetylglucosamine sugar modification to intracellular proteins that is dynamically added and removed by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. These enzymes act as a rheostat to fine-tune protein function in response to a plethora of stimuli from nutrients to hormones. O-GlcNAc modulates mitogenic growth signaling, senses nutrient flux through the hexosamine biosynthetic pathway, and coordinates with other nutrient-sensing enzymes to progress cells through Gap phase 1 (G1). At the G1/S transition, O-GlcNAc modulates checkpoint control, while in S Phase, O-GlcNAcylation coordinates the replication fork. DNA replication errors activate O-GlcNAcylation to control the function of the tumor-suppressor p53 at Gap Phase 2 (G2). Finally, in mitosis (M phase), O-GlcNAc controls M phase progression and the organization of the mitotic spindle and midbody. Critical for M phase control is the interplay between OGT and OGA with mitotic kinases. Importantly, disruptions in OGT and OGA activity induce M phase defects and aneuploidy. These data point to an essential role for the O-GlcNAc rheostat in regulating cell division. In this review, we highlight O-GlcNAc nutrient sensing regulating G1, O-GlcNAc control of DNA replication and repair, and finally, O-GlcNAc organization of mitotic progression and spindle dynamics.

Experimental Insights into the Interplay between Histone Modifiers and p53 in Regulating Gene Expression

Chromatin structure plays a fundamental role in regulating gene expression, with histone modifiers shaping the structure of chromatin by adding or removing chemical changes to histone proteins. The p53 transcription factor controls gene expression, binds target genes, and regulates their activity. While p53 has been extensively studied in cancer research, specifically in relation to fundamental cellular processes, including gene transcription, apoptosis, and cell cycle progression, its association with histone modifiers has received limited attention. This review explores the interplay between histone modifiers and p53 in regulating gene expression. We discuss how histone modifications can influence how p53 binds to target genes and how this interplay can be disrupted in cancer cells. This review provides insights into the complex mechanisms underlying gene regulation and their implications for potential cancer therapy.

Medical Needs and Therapeutic Options for Melanoma Patients Resistant to Anti-PD-1-Directed Immune Checkpoint Inhibition

Available 4- and 5-year updates for progression-free and for overall survival demonstrate a lasting clinical benefit for melanoma patients receiving anti-PD-directed immune checkpoint inhibitor therapy. However, at least one-half of the patients either do not respond to therapy or relapse early or late following the initial response to therapy. Little is known about the reasons for primary and/or secondary resistance to immunotherapy and the patterns of relapse. This review, prepared by an interdisciplinary expert panel, describes the assessment of the response and classification of resistance to PD-1 therapy, briefly summarizes the potential mechanisms of resistance, and analyzes the medical needs of and therapeutic options for melanoma patients resistant to immune checkpoint inhibitors. We appraised clinical data from trials in the metastatic, adjuvant and neo-adjuvant settings to tabulate frequencies of resistance. For these three settings, the role of predictive biomarkers for resistance is critically discussed, as well as are multimodal therapeutic options or novel immunotherapeutic approaches which may help patients overcome resistance to immune checkpoint therapy. The lack of suitable biomarkers and the currently modest outcomes of novel therapeutic regimens for overcoming resistance, most of them with a PD-1 backbone, support our recommendation to include as many patients as possible in novel or ongoing clinical trials.

p53-Dependent Cytoprotective Mechanisms behind Resistance to Chemo-Radiotherapeutic Agents Used in Cancer Treatment

Resistance to chemoradiotherapy is the main cause of cancer treatment failure. Cancer cells, especially cancer stem cells, utilize innate cytoprotective mechanisms to protect themselves from the adverse effects of chemoradiotherapy. Here, we describe a few such mechanisms: DNA damage response (DDR), immediate early response gene 5 (IER5)/heat-shock factor 1 (HSF1) pathway, and p21/nuclear factor erythroid 2-related factor 2 (NRF2) pathway, which are regulated by the tumour suppressor p53. Upon DNA damage caused during chemoradiotherapy, p53 is recruited to the sites of DNA damage and activates various DNA repair enzymes including GADD45A, p53R2, DDB2 to repair damaged-DNA in cancer cells. In addition, the p53-IER5-HSF1 pathway protects cancer cells from proteomic stress and maintains cellular proteostasis. Further, the p53-p21-NRF2 pathway induces production of antioxidants and multidrug resistance-associated proteins to protect cancer cells from therapy-induced oxidative stress and to promote effusion of drugs from the cells. This review summarises possible roles of these p53-regulated cytoprotective mechanisms in the resistance to chemoradiotherapy.

Sting and p53 DNA repair pathways are compromised in Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia. A common finding in AD is DNA damage. Double-strand DNA breaks (DSBs) are particularly hazardous to neurons because their post-mitotic state forces neurons to rely on error-prone and potentially mutagenic mechanisms to repair DNA breaks. However, it remains unclear whether DNA damage results from increased DNA damage or failure of DNA repair. Oligomerization of the tumor suppressor protein p53 is an essential part of DSB repair, and p53 phosphorylated on S15 is an indicator of DNA damage. We report that the monomer:dimer ratio of phosphorylated (S15) p53 is increased by 2.86-fold in temporal lobes of AD patients compared to age-matched controls, indicating that p53 oligomerization is compromised in AD. In vitro oxidation of p53 with 100 nM H2O2 produced a similar shift in the monomer:dimer ratio. A COMET test showed a higher level of DNA degradation in AD consistent with double-strand DNA damage or inhibition of repair. Protein carbonylation was also elevated (190% of control), indicating elevated oxidative stress in AD patients. Levels of the DNA repair support protein 14-3-3σ, γ-H2AX, a phosphorylated histone marking double strand DNA breaks, and phosphorylated ataxia telangiectasia mutated (ATM) protein were all increased. cGAS-STING-interferon signaling was impaired in AD and was accompanied by a depletion of STING protein from Golgi and a failure to elevate interferon despite the presence of DSBs. The results suggest that oxidation of p53 by ROS could inhibit the DDR and decrease its ability to orchestrate DSB repair by altering the oligomerization state of p53. The failure of immune-stimulated DNA repair may contribute to cell loss in AD and suggests new therapeutic targets for AD.

Use of Arabidopsis thaliana as a model to understand specific carcinogenic events: Comparison of the molecular machinery associated with cancer-hallmarks in plants and humans

Model organisms are fundamental in cancer research given that they rise the possibility to characterize in a quantitative-objective fashion the organisms as a whole in ways that are infeasible in humans. From this perspective, model organisms with short generation times and established protocols for genetic manipulation allow the understanding of basic biology principles that might guide carcinogenic onset. The cancer-hallmarks (CHs) approach, a modular perspective for cancer understanding, stands that underlying the variability among different cancer types, critical events support the carcinogenic origin and progression. Thus, CHs as interconnected genetic circuitry, have a causal effect over cancer biogenesis and might represent a comparison scaffold among model organisms to identify and characterize evolutionarily conserved modules to understand cancer. Nevertheless, the identification of novel cancer regulators by comparative genomics approaches relies on selecting specific biological processes or related signaling cascades that limit the type of detected regulators, even more, holistic analysis from a systemic perspective is absent. Similarly, although the plant Arabidopsis thaliana has been used as a model organism to dissect specific disease-associated mechanisms, given the evolutionary distance between plants and humans, a general concern about the utility of using A. thaliana as a cancer model persists. In the present research, we take advantage of the CHs paradigm as a framework to establish a functional systemic comparison between plants and humans, that allowed the identification not only of specific novel key genetic regulators, but also, biological processes, metabolic systems, and genetic modules that might contribute to the neoplastic transformation. We propose five cancer-hallmarks that overlapped in conserved mechanisms and processes between Arabidopsis and human and thus, represent mechanisms which study can be prioritized in A. thaliana as an alternative model for cancer research. Additionally, derived from network analyses and machine learning strategies, a new set of potential candidate genes that might contribute to neoplastic transformation is described. These findings postulate A. thaliana as a suitable model to dissect, not all, but specific cancer properties, highlighting the importance of using alternative complementary models to understand carcinogenesis.

Toward a hypothesis-free understanding of how phosphorylation dynamically impacts protein turnover

The turnover measurement of proteins and proteoforms has been largely facilitated by workflows coupling metabolic labeling with mass spectrometry (MS), including dynamic stable isotope labeling by amino acids in cell culture (dynamic SILAC) or pulsed SILAC (pSILAC). Very recent studies including ours have integrated themeasurement of post-translational modifications (PTMs) at the proteome level (i.e., phosphoproteomics) with pSILAC experiments in steady state systems, exploring the link between PTMs and turnover at the proteome-scale. An open question in the field is how to exactly interpret these complex datasets in a biological perspective. Here, we present a novel pSILAC phosphoproteomic dataset which was obtained during a dynamic process of cell starvation using data-independent acquisition MS (DIA-MS). To provide an unbiased "hypothesis-free" analysis framework, we developed a strategy to interrogate how phosphorylation dynamically impacts protein turnover across the time series data. With this strategy, we discovered a complex relationship between phosphorylation and protein turnover that was previously underexplored. Our results further revealed a link between phosphorylation stoichiometry with the turnover of phosphorylated peptidoforms. Moreover, our results suggested that phosphoproteomic turnover diversity cannot directly explain the abundance regulation of phosphorylation during cell starvation, underscoring the importance of future studies addressing PTM site-resolved protein turnover.

Mechanism of apoptosis activation by Curcumin rescued mutant p53Y220C in human pancreatic cancer

The mutant p53Y220C (mutp53Y220C) is frequently observed in numerous tumors, including pancreatic cancer. The mutation creates a crevice in the DNA binding core domain and makes p53 a thermally unstable non-functional protein that assists tumor progression and confers resistance to chemotherapeutic drugs. Restoring mutp53 function to its wild type by selectively targeting this crevice with small molecules is a pivotal strategy to promote apoptosis. In this study, we have shown through different biophysical and cell-based studies that curcumin binds and rescues mutp53Y220C to an active wild-type conformation and restores its apoptotic transcription function in BxPC-3-pancreatic cancer cells. In addition, the curcumin-rescued-p53Y220C (CRp53) showed significant hyperphosphorylation at Ser15, Ser20, and acetylation at Lys382 with an 8-fold increase in transcription activity in the BxPC-3 cell lines. We also observed that the active CRp53 escapes Mdm2-mediated proteasomal degradation and the majority of the proteins were localized inside the nucleus with an increased half-life and transcription restoration compared to untreated BxPC-3 cells. By label-free proteomics analysis, we observed that upon curcumin treatment almost 227 proteins were dysregulated with the majority of them being transcriptional targets of p53. Based on our studies, it reflects that apoptosis in pancreatic cancer cells is mediated by curcumin-rescued mutant p53Y220C.

Depletion of R270C Mutant p53 in Osteosarcoma Attenuates Cell Growth but Does Not Prevent Invasion and Metastasis In Vivo

Novel therapeutic targets are needed to better treat osteosarcoma, which is the most common bone malignancy. We previously developed mouse osteosarcoma cells, designated AX (accelerated bone formation) cells from bone marrow stromal cells. AX cells harbor both wild-type and mutant forms of p53 (R270C in the DNA-binding domain, which is equivalent to human R273C). In this study, we showed that mutant p53 did not suppress the transcriptional activation function of wild-type p53 in AX cells. Notably, AXT cells, which are cells derived from tumors originating from AX cells, lost wild-type p53 expression, were devoid of the intact transcription activation function, and were resistant to doxorubicin. ChIP-seq analyses revealed that this mutant form of p53 bound to chromatin in the vicinity of the transcription start sites of various genes but exhibited a different binding profile from wild-type p53. The knockout of mutant p53 in AX and AXT cells by CRISPR-Cas9 attenuated tumor growth but did not affect the invasion of these cells. In addition, depletion of mutant p53 did not prevent metastasis in vivo. Therefore, the therapeutic potency targeting R270C (equivalent to human R273C) mutant p53 is limited in osteosarcoma. However, considering the heterogeneous nature of osteosarcoma, it is important to further evaluate the biological and clinical significance of mutant p53 in various cases.

Molecular Targeting of the Most Functionally Complex Gene in Precision Oncology: p53

While chemotherapy is a key treatment strategy for many solid tumors, it is rarely curative, and most tumor cells eventually become resistant. Because of this, there is an unmet need to develop systemic treatments that capitalize on the unique mutational landscape of each patient's tumor. The most frequently mutated protein in cancer, p53, has a role in nearly all cancer subtypes and tumorigenesis stages and therefore is one of the most promising molecular targets for cancer treatment. Unfortunately, drugs targeting p53 have seen little clinical success despite promising preclinical data. Most of these drug compounds target specific aspects of p53 inactivation, such as through inhibiting negative regulation by the mouse double minute (MDM) family of proteins. These treatment strategies fail to address cancer cells' adaptation mechanisms and ignore the impact that p53 loss has on the entire p53 network. However, recent gene therapy successes show that targeting the p53 network and cellular dysfunction caused by p53 inactivation is now possible and may soon translate into successful clinical responses. In this review, we discuss p53 signaling complexities in cancer that have hindered the development and use of p53-targeted drugs. We also describe several current therapeutics reporting promising preclinical and clinical results.

Immunosuppression and apoptosis activation mediated by p53-Bcl2/Bax signaling pathway -The potential mechanism of goldfish (Carassius auratus Linnaeus) gill disease caused by Myxobolus ampullicapsulatus

Myxobolus, a major harmful type of myxospora, is one of the main parasitic pathogens of freshwater fish. Once myxoboliosis occurs, treatment can be extremely difficult. Therefore, clear understandings of the etiology of myxoboliosis and its pathological mechanism are keys for prevention and control. Here, histology, transmission electron microscopy, transcriptome study, tunel assay, and immunohistochemistry were carried out, revealing the morphology, pathological effects as well as host response mechanism of goldfish gill to Myxobolus ampullicapsulatus. Histological studies showed that the mature spores of Myxobolus ampullicapsulatus were composed of three parts, the spore shell, sporoplasm and bottle shaped polar capsule containing double S-shaped polar filaments. Transcriptome analysis revealed that Myxobolus ampullicapsulatus -infected (Myx) goldfish gills were characterized by apoptosis activation mediated by "p53 signaling pathway" with significantly up-regulated apoptosis-related differential genes dominated by p53-Bcl2/Bax signaling pathway. In addition, tunel assay revealed severe gill apoptosis in the Myx group. Transcriptome analysis also revealed that Myx group showed changes in immune response and significantly down-regulated immune-related differential genes. Beyond that, immunohistochemistry showed that there was no significant increase in the number of gill lymphocyte after parasite infection. These results suggest that the pathological mechanism of Myxobolus ampullicapsulatus infection on gills of goldfish may be related to apoptosis and immunosuppression. Subsequent qRT-PCR showed that apoptosis-related genes (Caspase3,Bad, Bax) and anti-inflammatory gene IL-10 were significantly increased, while immune-related pro-inflammatory genes (IL-1β, IL-8) were markedly down-regulated, further verifying the transcriptome results. Based on the above results, we concluded that p53-Bcl2/Bax related networks that dominant the expression of apoptosis genes were activated while immunity was suppressed in the gills of Myxobolus ampullicapsulatus infected goldfish. Our study is not only of benefit to enrich the taxonomy of Myxobolus but also clarifies its pathogenic mechanism, thus providing targets for prevention and control of myxoboliosis.

Inhibition of PLK3 Attenuates Tubular Epithelial Cell Apoptosis after Renal Ischemia–Reperfusion Injury by Blocking the ATM/P53-Mediated DNA Damage Response

Objective

Renal ischemia–reperfusion (I/R) injury is a major cause of acute kidney injury (AKI) in transplanted kidneys. This study was aimed at exploring the role of PLK3 (polo-like kinase 3) in renal I/R injury, focusing on its relationship with oxidative stress-induced DNA damage and renal tubular epithelial cell (TEC) apoptosis.

Methods

TRAP-seq data from the development dataset GSE52004 and the validation dataset GSE121191 were analyzed using GEO2R. PLK3 overexpression plasmids and targeted silencing siRNAs were used in a model of hypoxia/reoxygenation (H/R) injury, and rAAV-9-PLK3-KD were administered to C57BL/6J mice exposed to I/R injury. The ATM-specific inhibitor KU-60019 was used to block the DNA damage response (DDR). Western blotting was performed to measure DDR- and apoptosis-associated protein expression. Cell viability was measured by CCK-8 reagent, and apoptosis was examined by flow cytometry and TUNEL assay. Furthermore, the fluorescent probes H₂DCFH-DA and DHE were used to measure ROS production in vitro. The MDA level and SOD activity were measured to assess oxidative stress in vivo. KIM-1 staining and Scr and BUN were used to evaluate kidney injury.

Results

The mRNA and protein levels of PLK3 were markedly increased in the H/R injury and I/R injury models. GO terms showed that PLK3 was mainly involved in oxidative stress and DNA damage after renal I/R injury. Overexpression of PLK3 decreased cell viability and increased apoptosis. In contrast, targeted silencing of PLK3 expression decreased the Bax/Bcl-2 ratio by decreasing P53 phosphorylation, thereby reducing TEC apoptosis. Furthermore, KU-60019 reduced PLK3 activation and DDR-induced apoptosis, while overexpression of PLK3 reversed the mitigating effect of KU-60019 on TEC apoptosis. Similarly, rAAV-9-PLK3 KD mice exhibited a lower rate of TEC apoptosis and milder renal damage after I/R injury.

Conclusion

We demonstrate for the first time that PLK3 is involved in oxidative stress-induced DNA damage and TEC apoptosis in renal I/R injury. Inhibition of PLK3 attenuates TEC apoptosis after I/R injury by blocking the ATM/P53-mediated DDR. Therefore, PLK3 may serve as a potential therapeutic target for ischemic AKI.

Post-Translational Modifications of p53 in Ferroptosis: Novel Pharmacological Targets for Cancer Therapy

The tumor suppressor p53 is a well-known cellular guardian of genomic integrity that blocks cell cycle progression or induces apoptosis upon exposure to cellular stresses. However, it is unclear how the remaining activities of p53 are regulated after the abrogation of these routine activities. Ferroptosis is a form of iron- and lipid-peroxide-mediated cell death; it is particularly important in p53-mediated carcinogenesis and corresponding cancer prevention. Post-translational modifications have clear impacts on the tumor suppressor function of p53. Here, we review the roles of post-translational modifications in p53-mediated ferroptosis, which promotes the elimination of tumor cells. A thorough understanding of the p53 functional network will be extremely useful in future strategies to identify pharmacological targets for cancer therapy.

Exosome-transmitted miR-769-5p confers cisplatin resistance and progression in gastric cancer by targeting CASP9 and promoting the ubiquitination degradation of p53

Background

Cisplatin resistance is the main cause of poor clinical prognosis in patients with gastric cancer (GC). Yet, the exact mechanism underlying cisplatin resistance remains unclear. Recent studies have suggested that exocrine miRNAs found in the tumor microenvironment participate in tumor metastasis and drug resistance.

Methods

Exosomes isolated from BGC823 and BGC823/DDP culture medium were characterized by transmission electron microscopy and differential ultracentrifugation, and miRNA expression profiles of BGC823 and BGC823/DDP cells derived exosomes were analyzed using miRNA microarray. In vivo and in vitro assays were used to identify roles of exosomal miR‐769‐5p and clarify the mechanism of exosomal miR‐769‐5p regulated the crosstalk between sensitive and resistant GC cells.

Results

In this study, we found that cisplatin‐resistant GC cells communicated with the tumor microenvironment by secreting microvesicles. MiR‐769‐5p was upregulated in GC tissues and enriched in the serum exosomes of cisplatin‐resistant patients. The biologically active miR‐769‐5p could be integrated into exosomes and delivered to sensitive cells, spreading cisplatin resistance. Underlying cellular and molecular mechanism was miR‐769‐5p targeting CASP9, thus inhibiting the downstream caspase pathway and promoting the degradation of the apoptosis‐related protein p53 through the ubiquitin‐proteasome pathway. Targeting miR‐769‐5p with its antagonist to treat cisplatin‐resistant GC cells can restore the cisplatin response, confirming that exosomal miR‐769‐5p can act as a key regulator of cisplatin resistance in GC.

Conclusions

These findings indicate that exosome‐transmitted miR‐769‐5p confers cisplatin resistance and progression in gastric cancer by targeting CASP9 and promoting the ubiquitination degradation of p53. These findings reveal exosomal miR‐769‐5p derived from drug‐resistant cells can be used as a potential therapeutic predictor of anti‐tumor chemotherapy to enhance the effect of anti‐cancer chemotherapy, which provides a new treatment option for GC.

Intra Q-body: an antibody-based fluorogenic probe for intracellular proteins that allows live cell imaging and sorting

Although intracellular biomarkers can be imaged with fluorescent dye(s)-labeled antibodies, the use of such probes for precise imaging of intracellular biomarkers in living cells remains challenging due to background noise from unbound probes. Herein, we describe the development of a conditionally active Fab-type Quenchbody (Q-body) probe derived from a monoclonal antibody (DO-1) with the ability to both target and spatiotemporally visualize intracellular p53 in living cells with low background signal. p53 is a key tumor suppressor and validated biomarker for cancer diagnostics and therapeutics. The Q-body displayed up to 27-fold p53 level-dependent fluorescence enhancement in vitro with a limit of detection of 0.72 nM. In fixed and live cells, 8.3- and 8.4-fold enhancement was respectively observed. Furthermore, we demonstrate live-cell sorting based on p53 expression. This study provides the first evidence of the feasibility and applicability of Q-body probes for the live-cell imaging of intrinsically intracellular proteins and opens a novel avenue for research and diagnostic applications on intracellular target-based live-cell sorting.

A fluorescent immunosensor that lights up tumor biomarker p53 in living cells was developed based on the Q-body technology. The technology was further applied to the live cell monitoring of p53 levels, and live cell sorting based on p53 expression.

p53 signaling in cancer progression and therapy

The p53 protein is a transcription factor known as the "guardian of the genome" because of its critical function in preserving genomic integrity. The TP53 gene is mutated in approximately half of all human malignancies, including those of the breast, colon, lung, liver, prostate, bladder, and skin. When DNA damage occurs, the TP53 gene on human chromosome 17 stops the cell cycle. If p53 protein is mutated, the cell cycle is unrestricted and the damaged DNA is replicated, resulting in uncontrolled cell proliferation and cancer tumours. Tumor-associated p53 mutations are usually associated with phenotypes distinct from those caused by the loss of the tumor-suppressing function exerted by wild-type p53protein. Many of these mutant p53 proteins have oncogenic characteristics, and therefore modulate the ability of cancer cells to proliferate, escape apoptosis, invade and metastasize. Because p53 deficiency is so common in human cancer, this protein is an excellent option for cancer treatment. In this review, we will discuss some of the molecular pathways by which mutant p53 proteins might perform their oncogenic activities, as well as prospective treatment methods based on restoring tumor suppressive p53 functions.

Dual roles of SIRT1 in the BAX switch through the P53 module: A mathematical modeling study

SIRT1 is a multifunctional deacetylase that participates in a variety of cellular physiological processes to cope with stress. The anticancer protein P53 is an important target of SIRT1. It has been found that SIRT1 is involved in apoptosis by regulating the activity and intracellular location of P53. Moreover, P53-dependent apoptosis is inseparable from the BCL-2 protein family. Among the members of this family, BAX’s switching dynamics may play a key role in apoptosis. Therefore, a challenging question arises: what effect does SIRT1 have on the BAX switch? To answer this question, we built a small-scale protein network model. Through computer simulation, the properties of SIRT1 that on the one hand promote and on the other inhibit apoptosis are revealed. We found that the opening time of the BAX switch will be delayed in the case of either SIRT1 excess or deficiency. Similarly, the stimulus threshold required for apoptosis will also increase in the above two scenarios. Thereby, we proposed that SIRT1 has an optimal content at which the probability of apoptosis is greatest. In addition, P53 oscillation requires the concentration of SIRT1 to be higher than the optimal value. This work may be helpful both experimentally and clinically.

Increased H2O2 levels and p53 stabilization lead to mitochondrial dysfunction in XPC-deficient cells

XPC deficiency is associated with mitochondrial dysfunction, increased mitochondrial H2O2 production and sensitivity to the Complex III inhibitor antimycin A (AA), through a yet unclear mechanism. We found an imbalanced expression of several proteins that participate in important mitochondrial function and increased expression and phosphorylation of the tumor suppressor p53 in Xeroderma pigmentosum complementation group C (XP-C) (XPC-null) cells compared with an isogenic line corrected in locus with wild-type XPC (XPC-wt). Interestingly, inhibition of p53 nuclear import reversed the overexpression of mitochondrial proteins, whereas AA treatment increased p53 expression more strongly in the XP-C cells. However, inhibition of p53 substantially increased XP-C cellular sensitivity to AA treatment, suggesting that p53 is a critical factor mediating the cellular response to mitochondrial stress. On the other hand, treatment with the antioxidant N-acetylcysteine increased glutathione concentration and decreased basal H2O2 production, p53 levels and sensitivity to AA treatment in the XPC-null back to the levels found in XPC-wt cells. Thus, the results suggest a critical role for mitochondrially generated H2O2 in the regulation of p53 expression, which in turn modulates XP-C sensitivity to agents that cause mitochondrial stress.

Frequent Epigenetic Inactivation of DIRAS-1 and DIRAS-2 Contributes to Chemo-Resistance in Gliomas

Simple Summary

We investigated the genes DIRAS-1 and DIRAS-2 in terms of their regulation and functional relevance in brain tumors (gliomas). We found that in a majority of patients the expression of both genes is strongly downregulated on the mRNA level when comparing tumors with healthy brain tissue. We could show that epigenetic mechanisms account for this downregulation. Both promoter methylation and histone modifications are accountable. We performed experiments in tumor tissues (direct bisulfite sequencing and chromatin-immunoprecipitation) and we treated glioblastoma cell lines in a way to overcome epigenetic inactivation of both genes. When genes were re-expressed, the tumor cells turned out more sensitive to alkylating chemotherapeutic agents such as Lomustin. Changes in intracellular pathways related to p53-mediated DNA damage response may explain for this observation.

Abstract

We previously reported that DIRAS-3 is frequently inactivated in oligodendrogliomas due to promoter hypermethylation and loss of the chromosomal arm 1p. DIRAS-3 inactivation was associated with better overall survival. Consequently, we now investigated regulation and function of its family members DIRAS-1 and DIRAS-2. We found that DIRAS-1 was strongly downregulated in 65% and DIRAS-2 in 100% of analyzed glioma samples compared to non-neoplastic brain tissue (NNB). Moreover, a significant down-regulation of DIRAS-1 and -2 was detected in glioma data obtained from the TCGA database. Mutational analyses did not reveal any inactivating mutations in the DIRAS-1 and -2 coding regions. Analysis of the DIRAS-1 and -2 promoter methylation status showed significantly higher methylation in IDH-mutant astrocytic and IDH-mutant and 1p/19q-codeleted oligodendroglial tumors compared to NNB. Treatment of U251MG and Hs683 glioblastoma cells lines with 5-azacytidine led to significant re-expression of DIRAS-1 and -2. For IDH-wild-type primary gliomas, however, we did not observe significantly elevated DIRAS-1 and -2 promoter methylation levels, but still detected strong downregulation of both DIRAS family members. Additional analyses revealed that DIRAS-1 and -2 expression was also regulated by histone modifications. We observed a shift towards promoter heterochromatinization for DIRAS-1 and less promoter euchromatinization for DIRAS-2 in IDH-wild-type glioblastomas compared to controls. Treatment of the two glioblastoma cell lines with a histone deacetylase inhibitor led to significant re-expression of DIRAS-1 and -2. Functionally, overexpression of DIRAS-1 and -2 in glioblastoma cells translated into significantly higher sensitivity to lomustine treatment. Analyses of DNA damage markers revealed that DIRAS-1 and -2 may play a role in p53-dependent response to alkylating chemotherapy.

Viral targeting of glioblastoma stem cells with patient-specific genetic and post-translational p53 deregulations

Cancer therapy urges targeting of malignant subsets within self-renewing heterogeneous stem cell populations. We dissect the genetic and functional heterogeneity of human glioblastoma stem cells (GSCs) within patients by their innate responses to non-pathogenic mouse parvoviruses that are tightly restrained by cellular physiology. GSC neurospheres accumulate assembled capsids but restrict viral NS1 cytotoxic protein expression by an innate PKR/eIF2α-P response counteractable by electric pulses. NS1 triggers a comprehensive DNA damage response involving cell-cycle arrest, neurosphere disorganization, and bystander disruption of GSC-derived brain tumor architecture in rodent models. GSCs and cancer cell lines permissive to parvovirus genome replication require p53-Ser15 phosphorylation (Pp53S15). NS1 expression is enhanced by exogeneous Pp53S15 induction but repressed by wtp53. Consistently, patient-specific GSC subpopulations harboring p53 gain-of-function mutants and/or Pp53S15 are selective viral targets. This study provides a molecular foundation for personalized biosafe viral therapies against devastating glioblastoma and other cancers with deregulated p53 signaling.

DNA damage and oxidant stress activate p53 through differential upstream signaling pathways

Stabilization and activation of the p53 tumor suppressor are triggered in response to various cellular stresses, including DNA damaging agents and elevated Reactive Oxygen Species (ROS) like H₂O₂. When cells are exposed to exogenously added H₂O₂, ATR/CHK1 and ATM/CHK2 dependent DNA damage signaling is switched on, suggesting that H₂O₂ induces both single and double strand breaks. These collective observations have resulted in the widely accepted model that oxidizing conditions lead to DNA damage that subsequently mediates a p53-dependent response like cell cycle arrest and apoptosis. However, H₂O₂ also induces signaling through stress-activated kinases (SAPK, e.g., JNK and p38 MAPK) that can activate p53. Here we dissect to what extent these pathways contribute to functional activation of p53 in response to oxidizing conditions. Collectively, our data suggest that p53 can be activated both by SAPK signaling and the DDR independently of each other, and which of these pathways is activated depends on the type of oxidant used. This implies that it could in principle be possible to modulate oxidative signaling to stimulate p53 without inducing collateral DNA damage, thereby limiting mutation accumulation in both healthy and tumor tissues.

Tumor suppressor p53: Biology, signaling pathways, and therapeutic targeting

TP53 is the most commonly mutated gene in human cancer with over 100,000 literature citations in PubMed. This is a heavily studied pathway in cancer biology and oncology with a history that dates back to 1979 when p53 was discovered. The p53 pathway is a complex cellular stress response network with multiple diverse inputs and downstream outputs relevant to its role as a tumor suppressor pathway. While inroads have been made in understanding the biology and signaling in the p53 pathway, the p53 family, transcriptional readouts, and effects of an array of mutants, the pathway remains challenging in the realm of clinical translation. While the role of mutant p53 as a prognostic factor is recognized, the therapeutic modulation of its wild-type or mutant activities remain a work-in-progress. This review covers current knowledge about the biology, signaling mechanisms in the p53 pathway and summarizes advances in therapeutic development.

Stability of p53 oligomers: Tetramerization of p53 impinges on its stability

The p53 protein has been known to exist structurally in three different forms inside the cells. Earlier studies have reported the predominance of the lower oligomeric forms of p53 over its tetrameric form inside the cells, although only the tetrameric p53 contributes to its transcriptional activity. However, it remains unclear the functional relevance of the existence of other p53 oligomers inside the cells. In this study, we characterize the stability and conformational state of tetrameric, dimeric and monomeric p53 that spans both DNA Binding Domain (DBD) and Tetramerization Domain (TD) of human p53 (94-360 amino acid residues). Intriguingly, our studies reveal an unexpected drastic reduction in tetrameric p53 thermal stability in comparison to its dimeric and monomeric form with a higher propensity to aggregate at physiological temperature. Our EMSA study suggests that tetrameric p53, not their lower oligomeric counterpart, exhibit rapid loss of binding to their consensus DNA elements at the physiological temperature. This detrimental effect of destabilization is imparted due to the tetramerization of p53 that drives the DBDs to misfold at a faster pace when compared to its lower oligomeric form. This crosstalk between DBDs is achieved when it exists as a tetramer but not as dimer or monomer. Our findings throw light on the plausible reason for the predominant existence of p53 in dimer and monomer forms inside the cells with a lesser population of tetramer form. Therefore, the transient disruption of tetramerization between TDs could be a potential cue for the stabilization of p53 inside the cells.

Novel function of PERP-428 variants impacts lung cancer risk through the differential regulation of PTEN/MDM2/p53-mediated antioxidant activity

Lung cancer is the leading cause of cancer-related deaths worldwide. Identifying genetic risk factors and understanding their mechanisms will help reduce lung cancer incidence. The p53 apoptosis effect is related to PMP-22 (PERP), a tetraspan membrane protein, and an apoptotic effector protein downstream of p53. Although historically considered a tumor suppressor, PERP is highly expressed in lung cancers. Stable knockdown of PERP expression induces CL1-5 and A549 lung cancer cell death, but transient knockdown has no effect. Interestingly, relative to the PERP-428GG genotype, PERP-428CC was associated with the highest lung cancer risk (OR = 5.38; 95% CI = 2.12-13.65, p < 0.001), followed by the PERP-428CG genotype (OR = 2.34; 95% CI = 1.55-3.55, p < 0.001). Ectopic expression of PERP-428G, but not PERP-428C, protects lung cancer cells against ROS-induced DNA damage. Mechanistically, PERP-428 SNPs differentially regulate p53 protein stability. p53 negatively regulates the expression of the antioxidant enzymes catalase (CAT) and glutathione reductase (GR), thereby modulating redox status. p53 protein stability is higher in PERP-428C-expressing cells than in PERP-428G-expressing cells because MDM2 expression is decreased and p53 Ser20 phosphorylation is enhanced in PERP-428C-expressing cells. The MDM2 mRNA level is decreased in PERP-428C-expressing cells via PTEN-mediated downregulation of the MDM2 constitutive p1 promoter. This study reveals that in individuals with PERP-428CC, CAT/GR expression is decreased via the PTEN/MDM2/p53 pathway. These individuals have an increased lung cancer risk. Preventive antioxidants and avoidance of ROS stressors are recommended to prevent lung cancer or other ROS-related chronic diseases.

Theabrownin Induces Cell Apoptosis and Cell Cycle Arrest of Oligodendroglioma and Astrocytoma in Different Pathways

Theabrownin (TB), a natural compound present in the fresh leaves of green tea, is a potential antitumor agent. However, so far whether and how TB affects glioma is unclear. In this study, we investigated the effect of TB on astroglioma and oligodendroglioma cells. Surprisingly, TB significantly reduced the viabilities of HOG and U251 cells in a dose-dependent manner, which was accompanied by the upregulation of active-Casp-3, Bax, and PTEN; meanwhile, the antiapoptotic gene Bcl-2 was downregulated. In addition, TB treatment induced cell cycle arrest at the G1 and G2/M phases in HOG and U251 cells, respectively. TB treatment caused the downregulating of c-myc, cyclin D, CDK2, and CDK4 and upregulating of p21 and p27 in the HOG cell, while TB increased P53, p21, and p27 levels and decreased the levels of cell cycle regulator proteins such as CDK and cyclin A/B in the U251 cells. Therefore, the c-myc- and P53-related mechanisms were proposed for cell cycle arrest in these two glioma cell lines, respectively. Overall, our findings indicated that TB could be a novel candidate drug for the treatment of gliomas.

Role of FOXO protein's abnormal activation through PI3K/AKT pathway in platinum resistance of ovarian cancer

AIM

Platinum-based chemotherapy is the standard treatment for ovarian cancer. However, tumor cells' resistance to platinum drugs often occurs. This paper provides a review of Forkhead box O (FOXO) protein's role in platinum resistance of ovarian cancer which hopefully may provide some further guidance for the treatment of platinum-resistant ovarian cancer.

METHODS

We reviewed a 128 published papers from authoritative and professional journals on FOXO and platinum-resistant ovarian cancer, and adopts qualitative analyses and interpretation based on the literature.

RESULTS

Ovarian cancer often has abnormal activation of cellular pathways, the most important of which is the PI3K/AKT pathway. FOXOs act as crucial downstream factor of the PI3K/Akt pathway and are negatively regulated by it. DNA damage response and apoptosis including the relationship between FOXOs and ATM-Chk2-p53 are essential for platinum resistance of ovarian cancer. Through gene expression analysis in platinum-resistant ovarian cancer cell model, it was found that FoxO-1 is decreased in platinum-resistant ovarian cancer, so studying the role of FOXO in the pathway on platinum-induced apoptosis may further guide the treatment of platinum-resistant ovarian cancer.

CONCLUSIONS

There are many drug resistance mechanisms in ovarian cancer, wherein the decrease in cancer cells apoptosis is one of the important causes. Constituted by a series of transcription factors evolving conservatively and mainly working in inhibiting cancer, FOXO proteins play various roles in cells' antitumor response. More and more evidence suggests that we need to re-understand the role that FOXOs have played in cancer development and treatment.

Mechanisms of Cellular Senescence: Cell Cycle Arrest and Senescence Associated Secretory Phenotype

Cellular senescence is a stable cell cycle arrest that can be triggered in normal cells in response to various intrinsic and extrinsic stimuli, as well as developmental signals. Senescence is considered to be a highly dynamic, multi-step process, during which the properties of senescent cells continuously evolve and diversify in a context dependent manner. It is associated with multiple cellular and molecular changes and distinct phenotypic alterations, including a stable proliferation arrest unresponsive to mitogenic stimuli. Senescent cells remain viable, have alterations in metabolic activity and undergo dramatic changes in gene expression and develop a complex senescence-associated secretory phenotype. Cellular senescence can compromise tissue repair and regeneration, thereby contributing toward aging. Removal of senescent cells can attenuate age-related tissue dysfunction and extend health span. Senescence can also act as a potent anti-tumor mechanism, by preventing proliferation of potentially cancerous cells. It is a cellular program which acts as a double-edged sword, with both beneficial and detrimental effects on the health of the organism, and considered to be an example of evolutionary antagonistic pleiotropy. Activation of the p53/p21^WAF1/CIP1 and p16^INK4A/pRB tumor suppressor pathways play a central role in regulating senescence. Several other pathways have recently been implicated in mediating senescence and the senescent phenotype. Herein we review the molecular mechanisms that underlie cellular senescence and the senescence associated growth arrest with a particular focus on why cells stop dividing, the stability of the growth arrest, the hypersecretory phenotype and how the different pathways are all integrated.

Sustained CHK2 activity, but not ATM activity, is critical to maintain a G1 arrest after DNA damage in untransformed cells

BACKGROUND

The G1 checkpoint is a critical regulator of genomic stability in untransformed cells, preventing cell cycle progression after DNA damage. DNA double-strand breaks (DSBs) recruit and activate ATM, a kinase which in turn activates the CHK2 kinase to establish G1 arrest. While the onset of G1 arrest is well understood, the specific role that ATM and CHK2 play in regulating G1 checkpoint maintenance remains poorly characterized.

RESULTS

Here we examine the impact of ATM and CHK2 activities on G1 checkpoint maintenance in untransformed cells after DNA damage caused by DSBs. We show that ATM becomes dispensable for G1 checkpoint maintenance as early as 1 h after DSB induction. In contrast, CHK2 kinase activity is necessary to maintain the G1 arrest, independently of ATM, ATR, and DNA-PKcs, implying that the G1 arrest is maintained in a lesion-independent manner. Sustained CHK2 activity is achieved through auto-activation and its acute inhibition enables cells to abrogate the G1-checkpoint and enter into S-phase. Accordingly, we show that CHK2 activity is lost in cells that recover from the G1 arrest, pointing to the involvement of a phosphatase with fast turnover.

CONCLUSION

Our data indicate that G1 checkpoint maintenance relies on CHK2 and that its negative regulation is crucial for G1 checkpoint recovery after DSB induction.

Role of inhibiting Chk1-p53 pathway in hepatotoxicity caused by chronic arsenic exposure from coal-burning

Arsenic is a naturally occurring environmental toxicant, chronic exposure to arsenic can cause multiorgan damage, except for typical skin lesions, liver damage is the main problem for health concern in population with arsenic poisoning. Abnormal apoptosis is closely related to liver-related diseases, and p53 is one of the important hallmark proteins in apoptosis progression. This study was to investigate whether arsenic poisoning-induced hepatocyte apoptosis and the underlying role of p53 signaling pathway. A rat model of arsenic poisoning was established by feeding corn powder for 90 days, which was baked with high arsenic coal, then were treated with Ginkgo biloba extract (GBE) for 45 days by gavage. The results showed that arsenic induced liver damage, increased hepatocyte apoptosis and elevated the expression level of Chk1 and the ratios of p-p53/p53 and Bax/Bcl-2 in liver tissues, which were significantly attenuated by GBE. Additionally, to further demonstrate the potential apoptosis-associated mechanism, L-02 cells were pre-incubated with p53 inhibitor pifithrin-α (PFTα), ataxia telangiectasia-mutated (ATM)/ataxia telangiectasia-mutated and Rad3-related (ATR) inhibitor (CGK733) or GBE, then treated with sodium arsenite (NaAsO₂) for 24 h. The results showed that GBE, PFTα or CGK733 significantly reduced arsenic-induced Chk1 expression and the ratios of p-p53/p53 and Bax/Bcl-2. In conclusion, Chk1-p53 pathway was involved in arsenic poisoning-induced hepatotoxicity, and inhibiting of Chk1-p53 pathway ameliorated hepatocyte apoptosis caused by coal-burning arsenic poisoning. The study provides a pivotal clue for understanding of the mechanism of arsenic poisoning-induced liver damage, and possible intervention strategies.

Emerging roles of DYRK2 in cancer

Over the last decade, the CMGC kinase DYRK2 has been reported as a tumor suppressor across various cancers triggering major antitumor and proapoptotic signals in breast, colon, liver, ovary, brain, and lung cancers, with lower DYRK2 expression correlated with poorer prognosis in patients. Contrary to this, various medicinal chemistry studies reported robust antiproliferative properties of DYRK2 inhibitors, whereas unbiased 'omics' and genome-wide association study-based studies identified DYRK2 as a highly overexpressed kinase in various patient tumor samples. A major paradigm shift occurred in the last 4 years when DYRK2 was found to regulate proteostasis in cancer via a two-pronged mechanism. DYRK2 phosphorylated and activated the 26S proteasome to enhance degradation of misfolded/tumor-suppressor proteins while also promoting the nuclear stability and transcriptional activity of its substrate, heat-shock factor 1 triggering protein folding. Together, DYRK2 regulates proteostasis and promotes protumorigenic survival for specific cancers. Indeed, potent and selective small-molecule inhibitors of DYRK2 exhibit in vitro and in vivo anti-tumor activity in triple-negative breast cancer and myeloma models. However, with conflicting and contradictory reports across different cancers, the overarching role of DYRK2 remains enigmatic. Specific cancer (sub)types coupled to spatiotemporal interactions with substrates could decide the procancer or anticancer role of DYRK2. The current review aims to provide a balanced and critical appreciation of the literature to date, highlighting top substrates such as p53, c-Myc, c-Jun, heat-shock factor 1, proteasome, or NOTCH1, to discuss DYRK2 inhibitors available to the scientific community and to shed light on this duality of protumorigenic and antitumorigenic roles of DYRK2.

Therapeutic potential of p53 reactivation in cervical cancer

Cervical cancer (CC) is one of most common malignancies affecting women worldwide. To date, surgical resection is the only effective radical remedy for CC at its early stages, while the prognosis of metastatic or recurrent CC is very poor. Dysfunction of the tumor suppressor p53 due to aberrant expression, post-translational modification, mutations, SNPs, and LOH as well as sequestration by viral antigens and MDM2/HDM2-mediated degradation is closely associated with the therapeutic insensitivity and relapse of many malignancies, including CC. Accumulating studies have demonstrated that restoration of p53 activity can induce cell cycle arrest and apoptosis, eliminate radio- and chemotherapy resistance, and inhibit tumor growth in CC cells. Therefore, activation of wild-type p53 as well as restoration of p53 function seems appealing as a therapeutic strategy. In this review, we focus on the potential roles of p53 reactivation in CC treatment and their underlying molecular mechanisms towards the development of novel therapies.

Ubiquitin Modification of the Epstein-Barr Virus Immediate Early Transactivator Zta

The Epstein-Barr virus (EBV) immediate early transactivator Zta plays a key role in regulating the transition from latency to the lytic replication stages of EBV infection. Regulation of Zta is known to be controlled through a number of transcriptional and posttranscriptional events. Here, we show that Zta is targeted for ubiquitin modification and that this can occur in EBV-negative and in EBV-infected cells. Genetic studies show critical roles for both an amino-terminal region of Zta and the basic DNA binding domain of Zta in regulating Zta ubiquitination. Pulse-chase experiments demonstrate that the bulk population of Zta is relatively stable but that at least a subset of ubiquitinated Zta molecules are targeted for degradation in the cell. Mutation of four out of a total of nine lysine residues in Zta largely abrogates its ubiquitination, indicating that these are primary ubiquitination target sites. A Zta mutant carrying mutations at these four lysine residues (lysine 12, lysine 188, lysine 207, and lysine 219) cannot induce latently infected cells to produce and/or release infectious virions. Nevertheless, this mutant can induce early gene expression, suggesting a possible defect at the level of viral replication or later in the lytic cascade. As far as we know, this is the first study that has investigated the targeting of Zta by ubiquitination or its role in Zta function.IMPORTANCE Epstein-Barr virus (EBV) is a ubiquitous human pathogen and associated with various human diseases. EBV undergoes latency and lytic replication stages in its life cycle. The transition into the lytic replication stage, at which virus is produced, is mainly regulated by the viral gene product, Zta. Therefore, the regulation of Zta function becomes a central issue regarding viral biology and pathogenesis. Known modifications of Zta include phosphorylation and sumoylation. Here, we report the role of ubiquitination in regulating Zta function. We found that Zta is subjected to ubiquitination in both EBV-infected and EBV-negative cells. The ubiquitin modification targets 4 lysine residues on Zta, leading to both mono- and polyubiquitination of Zta. Ubiquitination of Zta affects the protein's stability and likely contributes to the progression of viral lytic replication. The function and fate of Zta may be determined by the specific lysine residue being modified.

Importance of cholesterol-rich microdomains in the regulation of Nox isoforms and redox signaling in human vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) function is regulated by Nox-derived reactive oxygen species (ROS) and redox-dependent signaling in discrete cellular compartments. Whether cholesterol-rich microdomains (lipid rafts/caveolae) are involved in these processes is unclear. Here we examined the sub-cellular compartmentalization of Nox isoforms in lipid rafts/caveolae and assessed the role of these microdomains in VSMC ROS production and pro-contractile and growth signaling. Intact small arteries and primary VSMCs from humans were studied. Vessels from Cav-1^-/- mice were used to test proof of concept. Human VSMCs express Nox1, Nox4, Nox5 and Cav-1. Cell fractionation studies showed that Nox1 and Nox5 but not Nox4, localize in cholesterol-rich fractions in VSMCs. Angiotensin II (Ang II) stimulation induced trafficking into and out of lipid rafts/caveolae for Nox1 and Nox5 respectively. Co-immunoprecipitation studies showed interactions between Cav-1/Nox1 but not Cav-1/Nox5. Lipid raft/caveolae disruptors (methyl-β-cyclodextrin (MCD) and Nystatin) and Ang II stimulation variably increased O₂^- generation and phosphorylation of MLC20, Ezrin-Radixin-Moesin (ERM) and p53 but not ERK1/2, effects recapitulated in Cav-1 silenced (siRNA) VSMCs. Nox inhibition prevented Ang II-induced phosphorylation of signaling molecules, specifically, ERK1/2 phosphorylation was attenuated by mellitin (Nox5 inhibitor) and Nox5 siRNA, while p53 phosphorylation was inhibited by NoxA1ds (Nox1 inhibitor). Ang II increased oxidation of DJ1, dual anti-oxidant and signaling molecule, through lipid raft/caveolae-dependent processes. Vessels from Cav-1^-/- mice exhibited increased O₂^- generation and phosphorylation of ERM. We identify an important role for lipid rafts/caveolae that act as signaling platforms for Nox1 and Nox5 but not Nox4, in human VSMCs. Disruption of these microdomains promotes oxidative stress and Nox isoform-specific redox signalling important in vascular dysfunction associated with cardiovascular diseases.

Oscillatory Dynamics of p53-Mdm2 Circuit in Response to DNA Damage Caused by Ionizing Radiation

Although the dynamical behavior of the p53-Mdm2 loop has been extensively studied, the understanding of the mechanism underlying the regulation of this pathway still remains limited. Herein, we developed an integrated model with five basic components and three ubiquitous time delays for the p53-Mdm2 interaction in response to DNA damage following ionizing radiation (IR). We showed that a sufficient amount of activated ATM level can initiate the p53 oscillations with nearly the same amplitude over a wide range of the ATM level; a proper range of p53 level is also required for generating the oscillations, for too high or too low levels it would fail to generate the oscillations; and increased Mdm2 level leads to decreased amplitude of the p53 oscillation and reduced expression of the p53 activity. Moreover, we found that the negative feedback loop formed between p53 and nuclear Mdm2 plays a dominant role in determining the p53 dynamics, whereas when interaction strength of the negative feedback loop becomes weaker, the positive feedback loop formed between p53 and cytoplasmatic Mdm2 can induce different types of dynamics. Furthermore, we demonstrated that the total time delay required for protein production and nuclear translocation of Mdm2 can induce p53 oscillations even when the p53 level is at a certain stable high steady state or at a certain stable low steady state. In addition, the two important features of the oscillatory dynamics-amplitude and period-can be controlled by such time delay. These results are in agreement with multiple experimental observations and may enrich our understanding of the dynamics of the p53 network.

Allosteric changes in HDM2 by the ATM phosphomimetic S395D mutation: implications on HDM2 function

Allosteric changes imposed by post-translational modifications regulate and differentiate the functions of proteins with intrinsic disorder regions. HDM2 is a hub protein with a large interactome and with different cellular functions. It is best known for its regulation of the p53 tumour suppressor. Under normal cellular conditions, HDM2 ubiquitinates and degrades p53 by the 26S proteasome but after DNA damage, HDM2 switches from a negative to a positive regulator of p53 by binding to p53 mRNA to promote translation of the p53 mRNA. This change in activity is governed by the ataxia telangiectasia mutated kinase via phosphorylation on serine 395 and is mimicked by the S395D phosphomimetic mutant. Here we have used different approaches to show that this event is accompanied by a specific change in the HDM2 structure that affects the HDM2 interactome, such as the N-termini HDM2–p53 protein–protein interaction. These data will give a better understanding of how HDM2 switches from a negative to a positive regulator of p53 and gain new insights into the control of the HDM2 structure and its interactome under different cellular conditions and help identify interphases as potential targets for new drug developments.

Regulating tumor suppressor genes: post-translational modifications

Tumor suppressor genes cooperate with each other in tumors. Three important tumor suppressor proteins, retinoblastoma (Rb), p53, phosphatase, and tensin homolog deleted on chromosome ten (PTEN) are functionally associated and they regulated by post-translational modification (PTMs) as well. PTMs include phosphorylation, SUMOylation, acetylation, and other novel modifications becoming growing appreciated. Because most of PTMs are reversible, normal cells use them as a switch to control the state of cells being the resting or proliferating, and PTMs also involve in cell survival and cell cycle, which may lead to abnormal proliferation and tumorigenesis. Although a lot of studies focus on the importance of each kind of PTM, further discoveries shows that tumor suppressor genes (TSGs) form a complex "network" by the interaction of modification. Recently, there are several promising strategies for TSGs for they change more frequently than carcinogenic genes in cancers. We here review the necessity, characteristics, and mechanisms of each kind of post-translational modification on Rb, p53, PTEN, and its influence on the precise and selective function. We also discuss the current antitumoral therapies of Rb, p53 and PTEN as predictive, prognostic, and therapeutic target in cancer.

p53-PHLDA3-Akt Network: The Key Regulators of Neuroendocrine Tumorigenesis

p53 is a well-known tumor suppressor gene and one of the most extensively studied genes in cancer research. p53 functions largely as a transcription factor and can trigger a variety of antiproliferative programs via induction of its target genes. We identified PHLDA3 as a p53 target gene and found that its protein product is a suppressor of pancreatic neuroendocrine tumors (PanNETs) and a repressor of Akt function. PHLDA3 is frequently inactivated by loss of heterozygosity (LOH) and methylation in human PanNETs, and LOH at the PHLDA3 gene locus correlates with PanNET progression and poor prognosis. In addition, in PHLDA3-deficient mice, pancreatic islet cells proliferate abnormally and acquire resistance to apoptosis. In this article, we briefly review the roles of p53 and Akt in human neuroendocrine tumors (NETs) and describe the relationship between the p53-PHLDA3 and Akt pathways. We also discuss the role of PHLDA3 as a tumor suppressor in various NETs and speculate on the possibility that loss of PHLDA3 function may be a useful prognostic marker for NET patients indicating particular drug therapies. These results suggest that targeting the downstream PHLDA3-Akt pathway might provide new therapies to treat NETs.

Less-well known functions of cyclin/CDK complexes

Cyclin-dependent kinases (CDKs) are activated by cyclins, which play important roles in dictating the actions of CDK/cyclin complexes. Cyclin binding influences the substrate specificity of these complexes in addition to their susceptibility to inhibition or degradation. CDK/cyclin complexes are best known to promote cell cycle progression in the mitotic cell cycle but are also crucial for important cellular processes not strictly associated with cellular division. This chapter primarily explores the understudied topic of CDK/cyclin complex functionality during the DNA damage response. We detail how CDK/cyclin complexes perform dual roles both as targets of DNA damage checkpoint signaling as well as effectors of DNA repair. Additionally, we discuss the potential CDK-independent roles of cyclins in these processes and the impact of such roles in human diseases such as cancer. Our goal is to place the spotlight on these important functions of cyclins either acting as independent entities or within CDK/cyclin complexes which have attracted less attention in the past. We consider that this will be important for a more complete understanding of the intricate functions of cell cycle proteins in the DNA damage response.

Structural basis for DNA damage-induced phosphoregulation of MDM2 RING domain

Phosphorylation of MDM2 by ATM upon DNA damage is an important mechanism for deregulating MDM2, thereby leading to p53 activation. ATM phosphorylates multiple residues near the RING domain of MDM2, but the underlying molecular basis for deregulation remains elusive. Here we show that Ser429 phosphorylation selectively enhances the ubiquitin ligase activity of MDM2 homodimer but not MDM2-MDMX heterodimer. A crystal structure of phospho-Ser429 (pS429)-MDM2 bound to E2-ubiquitin reveals a unique 310-helical feature present in MDM2 homodimer that allows pS429 to stabilize the closed E2-ubiquitin conformation and thereby enhancing ubiquitin transfer. In cells Ser429 phosphorylation increases MDM2 autoubiquitination and degradation upon DNA damage, whereas S429A substitution protects MDM2 from auto-degradation. Our results demonstrate that Ser429 phosphorylation serves as a switch to boost the activity of MDM2 homodimer and promote its self-destruction to enable rapid p53 stabilization and resolve a long-standing controversy surrounding MDM2 auto-degradation in response to DNA damage.

Harnessing the vulnerabilities of p53 mutants in lung cancer - Focusing on the proteasome: a new trick for an old foe?

Gain-of-function (GOF) p53 mutations occur commonly in human cancer and lead to both loss of p53 tumor suppressor function and acquisition of aggressive cancer phenotypes. The oncogenicity of GOF mutant p53 is highly related to its abnormal protein stability relative to wild type p53, and overall stoichiometric excess. We provide an overview of the mechanisms of dysfunction and abnormal stability of GOF p53 specifically in lung cancer, the leading cause of cancer-related mortality, where, depending on histologic subtype, 33-90% of tumors exhibit GOF p53 mutations. As a distinguishing feature and oncogenic mechanism in lung and many other cancers, GOF p53 represents an appealing and cancer-specific therapeutic target. We review preclinical evidence demonstrating paradoxical depletion of GOF p53 by proteasome inhibitors, as well as preclinical and clinical studies of proteasome inhibition in lung cancer. Finally, we provide a rationale for a reexamination of proteasome inhibition in lung cancer, focusing on tumors expressing GOF p53 alleles.

The Antiproliferative Activity of Oxypeucedanin via Induction of G2/M Phase Cell Cycle Arrest and p53-Dependent MDM2/p21 Expression in Human Hepatoma Cells

Oxypeucedanin (OPD), a furocoumarin compound from Angelica dahurica (Umbelliferae), exhibits potential antiproliferative activities in human cancer cells. However, the underlying molecular mechanisms of OPD as an anticancer agent in human hepatocellular cancer cells have not been fully elucidated. Therefore, the present study investigated the antiproliferative effect of OPD in SK-Hep-1 human hepatoma cells. OPD effectively inhibited the growth of SK-Hep-1 cells. Flow cytometric analysis revealed that OPD was able to induce G₂/M phase cell cycle arrest in cells. The G₂/M phase cell cycle arrest by OPD was associated with the downregulation of the checkpoint proteins cyclin B1, cyclin E, cdc2, and cdc25c, and the up-regulation of p-chk1 (Ser345) expression. The growth-inhibitory activity of OPD against hepatoma cells was found to be p53-dependent. The p53-expressing cells (SK-Hep-1 and HepG2) were sensitive, but p53-null cells (Hep3B) were insensitive to the antiproliferative activity of OPD. OPD also activated the expression of p53, and thus leading to the induction of MDM2 and p21, which indicates that the antiproliferative activity of OPD is in part correlated with the modulation of p53 in cancer cells. In addition, the combination of OPD with gemcitabine showed synergistic growth-inhibitory activity in SK-Hep-1 cells. These findings suggest that the anti-proliferative activity of OPD may be highly associated with the induction of G₂/M phase cell cycle arrest and upregulation of the p53/MDM2/p21 axis in SK-HEP-1 hepatoma cells.

Adipose Tissue-Derived Mesenchymal Stem Cells Suppress Growth of Huh7 Hepatocellular Carcinoma Cells via Interferon (IFN)-β-Mediated JAK/STAT1 Pathway in vitro

Interferon (IFN)-β and/or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) secreted by adipose tissue-derived mesenchymal stem cells (ASCs) have been proposed as key mechanistic factors in anti-cancer efficacy in lung cancer and breast cancer cells, where they act through paracrine signaling. We hypothesized that IFN-β and TRAIL produced by ASCs suppress proliferation of hepatocellular carcinoma cells (HCCs). The present study evaluated the anti-cancer effects of ASCs on HCCs in vitro. We found that indirect co-culture with ASCs diminished growth of Huh7 hepatocellular carcinoma cells with increased protein levels of p53/p21 and phosphorylated STAT1 (pSTAT1), without apoptosis. Treatment with ASC-conditioned medium (ASC-CM) also decreased growth of Huh7 cells through elevated p53/p21 and pSTAT1 signaling. ASC-CM-mediated inhibition of cell growth was neutralized in Huh7 cells treated with anti-IFN-β antibody compared to that in ASC-CM-treated Huh7 cells incubated with an anti-TRAIL antibody. Treatment with JAK1/JAK2 inhibitors recovered inhibition of growth in Huh7 cells incubated in ASC-CM or IFN-β via down-regulation of pSTAT1/p53/p21. However, treatment of IFN-β resulted in no alterations in resistance of Huh7 cells to TRAIL. Our findings suggest that ASCs decrease growth through activated STAT1-mediated p53/p21 by IFN-β, but not TRAIL, in Huh7 cells.

Synergism Through WEE1 and CHK1 Inhibition in Acute Lymphoblastic Leukemia

Introduction: Screening for synthetic lethality markers has demonstrated that the inhibition of the cell cycle checkpoint kinases WEE1 together with CHK1 drastically affects stability of the cell cycle and induces cell death in rapidly proliferating cells. Exploiting this finding for a possible therapeutic approach has showed efficacy in various solid and hematologic tumors, though not specifically tested in acute lymphoblastic leukemia. Methods: The efficacy of the combination between WEE1 and CHK1 inhibitors in B and T cell precursor acute lymphoblastic leukemia (B/T-ALL) was evaluated in vitro and ex vivo studies. The efficacy of the therapeutic strategy was tested in terms of cytotoxicity, induction of apoptosis, and changes in cell cycle profile and protein expression using B/T-ALL cell lines. In addition, the efficacy of the drug combination was studied in primary B-ALL blasts using clonogenic assays. Results: This study reports, for the first time, the efficacy of the concomitant inhibition of CHK1/CHK2 and WEE1 in ALL cell lines and primary leukemic B-ALL cells using two selective inhibitors: PF-0047736 (CHK1/CHK2 inhibitor) and AZD-1775 (WEE1 inhibitor). We showed strong synergism in the reduction of cell viability, proliferation and induction of apoptosis. The efficacy of the combination was related to the induction of early S-phase arrest and to the induction of DNA damage, ultimately triggering cell death. We reported evidence that the efficacy of the combination treatment is independent from the activation of the p53-p21 pathway. Moreover, gene expression analysis on B-ALL primary samples showed that Chek1 and Wee1 are significantly co-expressed in samples at diagnosis (Pearson r = 0.5770, p = 0.0001) and relapse (Pearson r= 0.8919; p = 0.0001). Finally, the efficacy of the combination was confirmed by the reduction in clonogenic survival of primary leukemic B-ALL cells. Conclusion: Our findings suggest that the combination of CHK1 and WEE1 inhibitors may be a promising therapeutic strategy to be tested in clinical trials for adult ALL.

Decoding the link between WWOX and p53 in aggressive breast cancer

Basal-like breast cancer (BLBC) and triple-negative breast cancer (TNBC) are aggressive forms of human breast cancer with poor prognosis and limited treatment response. Molecular understanding of BLBC and TNBC biology is instrumental to improve detection and management of these deadly diseases. Tumor suppressors WW domain-containing oxidoreductase (WWOX) and TP53 are altered in BLBC and in TNBC. Nevertheless, the functional interplay between WWOX and p53 is poorly understood. In a recent study by Abdeen and colleagues, it has been demonstrated that WWOX loss drives BLBC formation via deregulating p53 functions. In this review, we highlight important signaling pathways regulated by WWOX and p53 that are related to estrogen receptor signaling, epithelial-to-mesenchymal transition, and genomic instability and how they impact BLBC and TNBC development.

Protein Kinase C Quality Control by Phosphatase PHLPP1 Unveils Loss-of-Function Mechanism in Cancer

Protein kinase C (PKC) isozymes function as tumor suppressors in increasing contexts. In contrast to oncogenic kinases, whose function is acutely regulated by transient phosphorylation, PKC is constitutively phosphorylated following biosynthesis to yield a stable, autoinhibited enzyme that is reversibly activated by second messengers. Here, we report that the phosphatase PHLPP1 opposes PKC phosphorylation during maturation, leading to the degradation of aberrantly active species that do not become autoinhibited. Cancer-associated hotspot mutations in the pseudosubstrate of PKCβ that impair autoinhibition result in dephosphorylated and unstable enzymes. Protein-level analysis reveals that PKCα is fully phosphorylated at the PHLPP site in over 5,000 patient tumors, with higher PKC levels correlating (1) inversely with PHLPP1 levels and (2) positively with improved survival in pancreatic adenocarcinoma. Thus, PHLPP1 provides a proofreading step that maintains the fidelity of PKC autoinhibition and reveals a prominent loss-of-function mechanism in cancer by suppressing the steady-state levels of PKC.

Effects of ammonia on apoptosis and oxidative stress in bovine mammary epithelial cells

Ammonia, produced mainly from the deamination of amino acids and glutamine, is one of the major toxic components in blood and tissues that may affect bovine health. However, the physiological and pathological roles of ammonia in the mammary glands are not understood clearly. In the present study, the bovine mammary epithelial cell line (MAC-T) was utilised as an in vitro model to determine the effects of ammonia on bovine mammary gland. We demonstrated that ammonia stimulated the production of intracellular reactive oxygen species, decreased mitochondrial membrane potential, interrupted intracellular calcium ion (Ca2+) homeostasis and induced cell apoptosis. Ammonia also significantly reduced cell viability and increased the proportion of apoptotic cells through enhancing the level of p53 phosphorylation and increasing the expressions of BAX, caspase 8, caspase 9, caspase 3. Interestingly, bumetanide, a specific Na+ K+ 2Cl--cotransporter inhibitor, dramatically abolished the damaging effects of ammonia on the cells. These data suggest that ammonia exposure induces apoptosis in bovine mammary epithelial cells via activation of the p53 pathway and the mitochondrial apoptotic pathway, and that these effects involved the Na+ K+ 2Cl--cotransporter.