Deciphering the PTM codes of the tumor suppressor p53

p53-Mediated Mitochondrial Translocation of EI24 Triggered by ER Stress Plays an Important Role in Arsenic-Induced Liver Damage via Activating Mitochondrial Apoptotic Pathway

Chronic arsenic poisoning is a public health problem worldwide. In addition to skin lesions, the detrimental effect of arsenic poisoning on liver damage is one of the major issues. Our previous studies demonstrated that endoplasmic reticulum (ER) stress and p53 were associated with arsenic-induced liver damage. Literature has shown that EI24 is involved in hepatocyte hypertrophy; however, the underlying role and mechanism in arsenic-induced liver damage have not been fully elucidated. In this study, we explored the role of ER stress, p53, and EI24 as well as the regulatory relationship in arsenic poisoning populations and L-02 cells treated with distinct concentration NaAsO2 (2.5, 5, 10, and 20 μM). Results showed that as with arsenic dose increment, expression levels of ER stress key proteins GRP78, ATF4, and CHOP were significantly enhanced. Additionally, p53 expression in nucleus, p53 phosphorylation at Ser15 and Ser1392, and p53 acetylation at lys382 were significantly increased in NaAsO2-treated L-02 cells. ER stress inhibitor 4-phenylbutyric acid (4-PBA) decreased the expression of p53 phosphorylation at Ser 392, p53 acetylation at lys382, and p53 expression in nucleus. Additionally, in 5 μM NaAsO2 condition, p53 inhibitor pifithrin-α (PFT-α) aggravated 5 μM NaAsO2-induced GRP78, ATF4, and CHOP expressions, cell apoptosis, and protein-SH consumption. But in 20 μM NaAsO2 condition, PFT-α attenuated NaAsO2-induced cell apoptosis. Further results showed that 20 μM NaAsO2 facilitated translocation of EI24 from ER to mitochondrion and interaction with VDAC2, leading to activate mitochondrial apoptotic pathway, but not observed in the 5-μM NaAsO2 group. Moreover, PFT-α and 4-PBA inhibited 20 μM NaAsO2-induced EI24 expression in mitochondrion. Collectively, our results indicated that arsenic induced p53 activation via ER stress, under relatively low NaAsO2 concentration, NaAsO2-triggered p53 activation protected cells from apoptosis by alleviating ER stress. Another finding was that under relatively high NaAsO2 concentration, NaAsO2-activated p53 facilitated EI24 mitochondrial translocation and caused mitochondrial permeability increase, which represented a switch of p53 from a benefit role to pro-apoptosis function in NaAsO2-treated cells. The study contributed to in-depth understanding the mechanism of arsenic-induced liver damage and providing potential clues for following study.

Inhibitors of the tyrosine kinases FMS-like tyrosine kinase-3 and WEE1 induce apoptosis and DNA damage synergistically in acute myeloid leukemia cells

Hyperactive FMS-like receptor tyrosine kinase-3 mutants with internal tandem duplications (FLT3-ITD) are frequent driver mutations of aggressive acute myeloid leukemia (AML). Inhibitors of FLT3 produce promising results in rationally designed cotreatment schemes. Since FLT3-ITD modulates DNA replication and DNA repair, valid anti-leukemia strategies could rely on a combined inhibition of FLT3-ITD and regulators of cell cycle progression and DNA integrity. These include the WEE1 kinase which controls cell cycle progression, nucleotide synthesis, and DNA replication origin firing. We investigated how pharmacological inhibition of FLT3 and WEE1 affected the survival and genomic integrity of AML cell lines and primary AML cells. We reveal that promising clinical grade and preclinical inhibitors of FLT3 and WEE1 synergistically trigger apoptosis in leukemic cells that express FLT3-ITD. An accumulation of single and double strand DNA damage precedes this process. Mass spectrometry-based proteomic analyses show that FLT3-ITD and WEE1 sustain the expression of the ribonucleotide reductase subunit RRM2, which provides dNTPs for DNA replication. Unlike their strong pro-apoptotic effects on leukemia cells with FLT3-ITD, inhibitors of FLT3 and WEE1 do not damage healthy human blood cells and murine hematopoietic stem cells. Thus, pharmacological inhibition of FLT3-ITD and WEE1 might become an improved, rationally designed therapeutic option.

Chemical proteomics approaches for protein post-translational modification studies

The diversity and dynamics of proteins play essential roles in maintaining the basic constructions and functions of cells. The abundance of functional proteins is regulated by the transcription and translation processes, while the alternative splicing enables the same gene to generate distinct protein isoforms of different lengths. Beyond the transcriptional and translational regulations, post-translational modifications (PTMs) are able to further expand the diversity and functional scope of proteins. PTMs have been shown to make significant changes in the surface charges, structures, activation states, and interactome of proteins. Due to the functional complexity, highly dynamic nature, and low presence percentage, the study of protein PTMs remains challenging. Here we summarize and discuss the major chemical biology tools and chemical proteomics approaches to enrich and investigate the protein PTM of interest.

The next decade of SET: from an oncoprotein to beyond

This year marks the fourth decade of research into the protein SET, which was discovered in 1992. SET was initially identified as an oncoprotein but later shown to be a multifaceted protein involved in regulating numerous biological processes under both physiological and pathophysiological conditions. SET dysfunction is closely associated with diseases, such as cancer and Alzheimer's disease. With the increasing understanding of how SET works and how it is regulated in cells, targeting aberrant SET has emerged as a potential strategy for disease intervention. In this review, we present a comprehensive overview of the advancements in SET studies, encompassing its biological functions, regulatory networks, clinical implications, and pharmacological inhibitors. Furthermore, we provide insights into the future prospects of SET research, with a particular emphasis on its promising potential in the realm of immune modulation.

The Strong Activation of p53 Tumor Suppressor Drives the Synthesis of the Enigmatic Isoform of DUSP13 Protein

The p53 tumor suppressor protein activates various sets of genes depending on its covalent modifications, which are controlled by the nature and intensity of cellular stress. We observed that actinomycin D and nutlin-3a (A + N) collaborate in inducing activating phosphorylation of p53. Our recent transcriptomic data demonstrated that these substances strongly synergize in the upregulation of DUSP13, a gene with an unusual pattern of expression, coding for obscure phosphatase having two isoforms, one expressed in the testes and the other in skeletal muscles. In cancer cells exposed to A + N, DUSP13 is expressed from an alternative promoter in the intron, resulting in the expression of an isoform named TMDP-L1. Luciferase reporter tests demonstrated that this promoter is activated by both endogenous and ectopically expressed p53. We demonstrated for the first time that mRNA expressed from this promoter actually produces the protein, which can be detected with Western blotting, in all examined cancer cell lines with wild-type p53 exposed to A + N. In some cell lines, it is also induced by clinically relevant camptothecin, by nutlin-3a acting alone, or by a combination of actinomycin D and other antagonists of p53-MDM2 interaction-idasanutlin or RG7112. This isoform, fused with green fluorescent protein, localizes in the perinuclear region of cells.

Cellular and epigenetic perspective of protein stability and its implications in the biological system

Protein stability is a fundamental prerequisite in both experimental and therapeutic applications. Current advancements in high throughput experimental techniques and functional ontology approaches have elucidated that impairment in the structure and stability of proteins is intricately associated with the cause and cure of several diseases. Therefore, it is paramount to deeply understand the physical and molecular confounding factors governing the stability of proteins. In this review article, we comprehensively investigated the evolution of protein stability, examining its emergence over time, its relationship with organizational aspects and the experimental methods used to understand it. Furthermore, we have also emphasized the role of Epigenetics and its interplay with post-translational modifications (PTMs) in regulating the stability of proteins.

Interplay between posttranslational modifications and liquid‒liquid phase separation in tumors

Liquid‒liquid phase separation (LLPS) is a general phenomenon recently recognized to be critically involved in the regulation of a variety of cellular biological processes, such as transcriptional regulation, heterochromatin formation and signal transduction, through the compartmentalization of proteins or nucleic acids into droplet-like condensates. These processes are directly or indirectly related to tumor initiation and treatment. Posttranslational modifications (PTMs), which represent a rapid and reversible mechanism involved in the functional regulation of proteins, have emerged as key events in modulating LLPS under physiological or pathophysiological conditions, including tumorigenesis and antitumor therapy. In this review, we introduce the biological functions participated in cancer-associated LLPS, discuss the potential roles of LLPS during tumor onset or therapy, and emphasize the mechanistic characteristics of LLPS regulated by PTMs and its effects on tumor progression. We then provide a perspective on further studies on LLPS and its regulation by PTMs in cancer research. This review aims to broaden the understanding of the functions of LLPS and its regulation by PTMs under normal or aberrant cellular conditions.

NOBILETIN AMELIORATES HEATSTROKE-INDUCED ACUTE LUNG INJURY BY INHIBITING FERROPTOSIS VIA P53/SLC7A11 PATHWAY

ABSTRACT

The molecular mechanism for nobiletin's protective effect against heatstroke-induced acute lung injury (HS-ALI) remains largely unknown. Previous research has demonstrated that ferroptosis is an important pathogenic event in HS-ALI. Nobiletin is a natural polymethoxylated flavonoid. Herein, we investigated the potential contribution of nobiletin to HS-ALI by inhibiting ferroptosis. Heat stress was used to induce HS-ALI in mice, and mouse lung epithelial-12 (MLE-12) cells were stimulated by heat stress in vitro . Nobiletin was administrated by gavage for 2 h before HS induction. Biochemical kits, immunofluorescence staining, and western blotting were performed on the markers of ferroptosis. Our results showed that nobiletin administration significantly attenuated HS-induced lung injury and ferroptosis. Moreover, nobiletin pretreatment significantly reversed HS-induced p53 upregulation in vivo and in vitro . Pretreatment with a p53 agonist, tenovin-6, partly abolished the protective effect of nobiletin in mice with HS-ALI. Meanwhile, p53 knockdown significantly increased GPX4 and SLC7A11 expression levels compared with the HS group in HS-induced MLE-12 cells. Subsequently, nobiletin ameliorated HS-induced MLE-12 cells ferroptosis by activating the SLC7A11/GPX4 pathway, whereas p53 overexpression effectively abolished the protective effect of nobiletin. Taken together, our findings reveal that nobiletin attenuates HS-ALI by inhibiting ferroptosis through the p53/SLC7A11 pathway, indicating it to be a potential therapeutic agent for HS-ALI prevention and treatment.

UBE1C is upregulated and promotes neddylation of p53 in lung cancer

NEDDylation is a type of protein post-translational modification that has high similarity to ubiquitination. UBE1C encodes NEDDylation E1 enzyme, locates at chromatin region 3p14.1 and shows high gene dosage amplification frequency in both Asian and Caucasian lung cancer patients. However, its NEDDylation substrates and roles in tumorigenesis remain elucidated. In this study, we aim to investigate the oncogenic role of UBE1C and its involvement in how NEDDylation regulates p53 in lung cancer. We found that UBE1C mRNA overexpression and DNA amplification in most of the lung cell lines and cancer patients. Patients with UBE1C overexpression showed poor prognosis. Moreover, we demonstrated that overexpression of UBE1C and NEDD8, a NEDDylation moiety, resulted in the p53 NEDDylation with inhibition of p53 acetylation at K373 residue. Importantly, UBE1C-mediated NEDDylation downregulated the transcriptional activity of p53 by inhibiting p53 ability to target promoter regions of its downstream transcription targets, consequently inhibiting the promoter activities and the expression of mRNA and protein of the p53 downstream genes including p21 and PTEN. In addition, UBE1C and NEDD8 overexpression promoted migration, invasion, and proliferation of lung cancer cells. Our findings suggest that UBE1C acts as an oncogene with prognostic potential and highlight a potential role of UBE1C-mediated NEDDylation in downregulation of p53 transcriptional activity in lung cancer.

Alternatively mechanistic insights into acetylation in p53-mediated transcriptional regulation of cancer cell-intrinsic PD-1

Since the recent discovery of cancer cell-intrinsic programmed cell death protein-1 (PD-1), the mechanisms that manipulate PD-1 functions in tumor development beyond its immune checkpoint roles have become attractive research topics in oncology. Our previous study validated that PD-1 exists in lung cancer cells and is directly transactivated by p53 in a DNA-binding domain (DBD) acetylation-dependent manner. Here, we report that the carboxyl-terminal domain (CTD) of p53 likewise participates in PD-1 transcriptional regulation in cancer cells under different regulatory mechanisms. By mutating the lysine residues within the CTD to mimic either acetylation-deficient or fully acetylated status, we proved that acetylated CTD dramatically impeded p53-mediated transactivation of PD-1. Furthermore, we identified bromodomain-containing protein 4 (BRD4) as a transcriptional coactivator of p53 that facilitates p53-mediated PD-1 transcription. Mechanistically, BRD4 specifically bound to the unacetylated CTD of p53, while CTD acetylation almost completely destroyed the BRD4-p53 interaction and thus led to compromised PD-1 expression. Collectively, this study unveils an alternative mechanism of p53 acetylation-directed PD-1 transcriptional regulation, which would broaden our current understanding of the molecular regulatory network of cancer cell-intrinsic PD-1.

How Do Cancer-Related Mutations Affect the Oligomerisation State of the p53 Tetramerisation Domain?

Tumour suppressor p53 plays a key role in the development of cancer and has therefore been widely studied in recent decades. While it is well known that p53 is biologically active as a tetramer, the tetramerisation mechanism is still not completely understood. p53 is mutated in nearly 50% of cancers, and mutations can alter the oligomeric state of the protein, having an impact on the biological function of the protein and on cell fate decisions. Here, we describe the effects of a number of representative cancer-related mutations on tetramerisation domain (TD) oligomerisation defining a peptide length that permits having a folded and structured domain, thus avoiding the effect of the flanking regions and the net charges at the N- and C-terminus. These peptides have been studied under different experimental conditions. We have applied a variety of techniques, including circular dichroism (CD), native mass spectrometry (MS) and high-field solution NMR. Native MS allows us to detect the native state of complexes maintaining the peptide complexes intact in the gas phase; the secondary and quaternary structures were analysed in solution by NMR, and the oligomeric forms were assigned by diffusion NMR experiments. A significant destabilising effect and a variable monomer population were observed for all the mutants studied.

RNA Modifications Meet Tumors

RNA modifications occur through the whole process of gene expression regulation, including transcription, translation, and post-translational processes. They are closely associated with gene expression, RNA stability, and cell cycle. RNA modifications in tumor cells play a vital role in tumor development and metastasis, changes in the tumor microenvironment, drug resistance in tumors, construction of tumor cell-cell "internet", etc. Several types of RNA modifications have been identified to date and have various effects on the biological characteristics of different tumors. In this review, we discussed the function of RNA modifications, including N 6-methyladenine (m6A), 5-methylcytosine (m5C), N 7-methyladenosine (m7G), N 1-methyladenosine (m1A), pseudouridine (Ψ), and adenosine-to-inosine (A-to-I), in the microenvironment and therapy of solid and liquid tumors.

The chameleonic behavior of p53 in health and disease: the transition from a client to an aberrant condensate scaffold in cancer

In 1972, the Weber statement, “The multiplicity of interactions and the variety of effects that follow from them show that multimer proteins are unlikely to be limited to a minimal number of allowed conformations,” first addressed the dynamic nature of proteins. This idea serves as a foundation for understanding why several macromolecules, such as p53, exhibit the properties of a molecular chameleon. Functionally competent states comprise a myriad of p53 three-dimensional arrangements depending on the stimuli. For instance, the interaction of p53 with nuclear components could induce liquid–liquid phase separation (LLPS) and the formation of membraneless organelles. The functional or deleterious role of p53 in liquid droplets is still unclear. Functional aspects display p53 interconverting between droplets and tetramer with its functional abilities maintained. In contrast, the aberrant phase separation is likely to fuel the aggregation path, usually associated with the onset and progression of age-related neurodegenerative diseases and cancer. Here, we gathered the most relevant aspects that lead p53 to phase separation and the resulting structural effects, attempting to understand p53’s functional and disease-relevant processes. Aberrant phase separation and aggregation of mutant p53 have become important therapeutic targets against cancer.

Porcine Circovirus 2 Activates the PERK-Reactive Oxygen Species Axis To Induce p53 Phosphorylation with Subsequent Cell Cycle Arrest at S Phase in Favor of Its Replication

Coinfections or noninfectious triggers have long been considered to potentiate PCV2 infection, leading to manifestation of PCVAD. The triggering mechanisms remain largely unknown.

Structural Basis of Mutation-Dependent p53 Tetramerization Deficiency

The formation of a tetrameric assembly is essential for the ability of the tumor suppressor protein p53 to act as a transcription factor. Such a quaternary conformation is driven by a specific tetramerization domain, separated from the central DNA-binding domain by a flexible linker. Despite the distance, functional crosstalk between the two domains has been reported. This phenomenon can explain the pathogenicity of some inherited or somatically acquired mutations in the tetramerization domain, including the widespread R337H missense mutation present in the population in south Brazil. In this work, we combined computational predictions through extended all-atom molecular dynamics simulations with functional assays in a genetically defined yeast-based model system to reveal structural features of p53 tetramerization domains and their transactivation capacity and specificity. In addition to the germline and cancer-associated R337H and R337C, other rationally designed missense mutations targeting a significant salt-bridge interaction that stabilizes the p53 tetramerization domain were studied (i.e., R337D, D352R, and the double-mutation R337D plus D352R). The simulations revealed a destabilizing effect of the pathogenic mutations within the p53 tetramerization domain and highlighted the importance of electrostatic interactions between residues 337 and 352. The transactivation assay, performed in yeast by tuning the expression of wild-type and mutant p53 proteins, revealed that p53 tetramerization mutations could decrease the transactivation potential and alter transactivation specificity, in particular by better tolerating negative features in weak DNA-binding sites. These results establish the effect of naturally occurring variations at positions 337 and 352 on p53’s conformational stability and function.

Mechanisms of carcinogenic activity triggered by lysine-specific demethylase 1A

Epigenetics has emerged as a prime focus area in the field of cancer research. Lysine-specific demethylase 1A (LSD1), the first discovered histone demethylase, is mainly responsible for catalysing demethylation of histone 3 lysine 4 (H3K4) and H3K9 to activate or inhibit gene transcription. LSD1 is abnormally expressed in various cancers and participates in cancer proliferation, apoptosis, metastasis, invasion, drug resistance and other processes by interacting with regulatory factors. Therefore, it may serve as a potential therapeutic target for cancer. This review summarises the major oncogenic mechanisms mediated by LSD1 and provides a reference for developing novel and efficient anticancer strategies targeting LSD1.

Identification of a reciprocal negative feedback loop between tau-modifying proteins MARK2 kinase and CBP acetyltransferase

The posttranslational regulation of the neuronal proteome is critical for brain homeostasis but becomes dysregulated in the aged or diseased brain, in which abnormal posttranslational modifications (PTMs) are frequently observed. While the full extent of modified substrates that comprise the "PTM-ome" are slowly emerging, how the upstream enzymes catalyzing these processes are regulated themselves is not well understood, particularly in the context of neurodegeneration. Here, we describe the reciprocal regulation of a kinase, the microtubule affinity-regulating kinase 2 (MARK2), and an acetyltransferase, CREB-binding protein (CBP), two enzymes known to extensively modify tau proteins in the progression of Alzheimer's disease. We found that MARK2 negatively regulates CBP and, conversely, CBP directly acetylates and inhibits MARK2 kinase activity. These findings highlight a reciprocal negative feedback loop between a kinase and an acetyltransferase, which has implications for how PTM interplay is coordinated on substrates including tau. Our study suggests that PTM profiles occur through the posttranslational control of the master PTM remodeling enzymes themselves.

Deciphering the acetylation code of p53 in transcription regulation and tumor suppression

Although it is well established that p53-mediated tumor suppression mainly acts through its ability in transcriptional regulation, the molecular mechanisms of this regulation are not completely understood. Among a number of regulatory modes, acetylation of p53 attracts great interests. p53 was one of the first non-histone proteins found to be functionally regulated by acetylation and deacetylation, and subsequent work has established that reversible acetylation is a general mechanism for regulation of non-histone proteins. Unlike other types of post-translational modifications occurred during stress responses, the role of p53 acetylation has been recently validated in vivo by using the knockin mice with both acetylation-defective and acetylation-mimicking p53 mutants. Here, we review the role of acetylation in p53-mediated activities, with a focus on which specific acetylation sites are critical for p53-dependent transcription regulation during tumor suppression and how acetylation of p53 recruits specific “readers” to execute its promoter-specific regulation of different targets. We also discuss the role of p53 acetylation in differentially regulating its classic activities in cell cycle arrest, senescence and apoptosis as well as newly identified unconventional functions such as cell metabolism and ferroptosis.

A review on cullin neddylation and strategies to identify its inhibitors for cancer therapy

The cullin-RING E3 ligases (CRLs) are the biggest components of the E3 ubiquitin ligase protein family, and they represent an essential role in various diseases that occur because of abnormal activation, particularly in tumors development. Regulation of CRLs needs neddylation, a post-translational modification involving an enzymatic cascade that transfers small, ubiquitin-like NEDD8 protein to CRLs. Many previous studies have confirmed neddylation as an enticing target for anticancer drug discoveries, and few recent studies have also found a significant increase in advancement in protein neddylation, including preclinical and clinical target validation to discover the neddylation inhibitor compound. In the present review, we first presented briefly the essence of CRLs' neddylation and its control, systematic analysis of CRLs, followed by the description of a few recorded chemical inhibitors of CRLs neddylation enzymes with recent examples of preclinical and clinical targets. We have also listed various structure-based pointing of protein-protein dealings in the CRLs' neddylation reaction, and last, the methods available to discover new inhibitors of neddylation are elaborated. This review will offer a concentrated, up-to-date, and detailed description of the discovery of neddylation inhibitors.

p53 Modulation of Autophagy Signaling in Cancer Therapies: Perspectives Mechanism and Therapeutic Targets

The key tumor suppressor protein p53, additionally known as p53, represents an attractive target for the development and management of anti-cancer therapies. p53 has been implicated as a tumor suppressor protein that has multiple aspects of biological function comprising energy metabolism, cell cycle arrest, apoptosis, growth and differentiation, senescence, oxidative stress, angiogenesis, and cancer biology. Autophagy, a cellular self-defense system, is an evolutionarily conserved catabolic process involved in various physiological processes that maintain cellular homeostasis. Numerous studies have found that p53 modulates autophagy, although the relationship between p53 and autophagy is relatively complex and not well understood. Recently, several experimental studies have been reported that p53 can act both an inhibitor and an activator of autophagy which depend on its cellular localization as well as its mode of action. Emerging evidences have been suggested that the dual role of p53 which suppresses and stimulates autophagy in various cencer cells. It has been found that p53 suppression and activation are important to modulate autophagy for tumor promotion and cancer treatment. On the other hand, activation of autophagy by p53 has been recommended as a protective function of p53. Therefore, elucidation of the new functions of p53 and autophagy could contribute to the development of novel therapeutic approaches in cancer biology. However, the underlying molecular mechanisms of p53 and autophagy shows reciprocal functional interaction that is a major importance for cancer treatment and manegement. Additionally, several synthetic drugs and phytochemicals have been targeted to modulate p53 signaling via regulation of autophagy pathway in cancer cells. This review emphasizes the current perspectives and the role of p53 as the main regulator of autophagy-mediated novel therapeutic approaches against cancer treatment and managements.

Protein of a thousand faces: The tumor-suppressive and oncogenic responses of p53

The p53 protein is a pleiotropic regulator working as a tumor suppressor and as an oncogene. Depending on the cellular insult and the mutational status, p53 may trigger opposing activities such as cell death or survival, senescence and cell cycle arrest or proliferative signals, antioxidant or prooxidant activation, glycolysis, or oxidative phosphorylation, among others. By augmenting or repressing specific target genes or directly interacting with cellular partners, p53 accomplishes a particular set of activities. The mechanism in which p53 is activated depends on increased stability through post-translational modifications (PTMs) and the formation of higher-order structures (HOS). The intricate cell death and metabolic p53 response are reviewed in light of gaining stability via PTM and HOS formation in health and disease.

At a Crossroads to Cancer: How p53-Induced Cell Fate Decisions Secure Genome Integrity

P53 is known as the most critical tumor suppressor and is often referred to as the guardian of our genome. More than 40 years after its discovery, we are still struggling to understand all molecular details on how this transcription factor prevents oncogenesis or how to leverage current knowledge about its function to improve cancer treatment. Multiple cues, including DNA-damage or mitotic errors, can lead to the stabilization and nuclear translocation of p53, initiating the expression of multiple target genes. These transcriptional programs may be cell-type- and stimulus-specific, as is their outcome that ultimately imposes a barrier to cellular transformation. Cell cycle arrest and cell death are two well-studied consequences of p53 activation, but, while being considered critical, they do not fully explain the consequences of p53 loss-of-function phenotypes in cancer. Here, we discuss how mitotic errors alert the p53 network and give an overview of multiple ways that p53 can trigger cell death. We argue that a comparative analysis of different types of p53 responses, elicited by different triggers in a time-resolved manner in well-defined model systems, is critical to understand the cell-type-specific cell fate induced by p53 upon its activation in order to resolve the remaining mystery of its tumor-suppressive function.