Clarifying functions of the p53 protein is a crucial aspect of cancer research. We analyzed the binding sites of p53 wild-type (WT) protein and its oncologically significant mutants and evaluated their transactivation properties using a functional yeast assay. Unlike the binding sites as determined in myeloid leukemia cell lines by chromatin immunoprecipitation of p53-R175H, p53-Y220C, p53-M237I, p53-R248Q, and p53-R273H mutants, the target sites of p53-WT and p53-R282W were significantly associated with putative G-quadruplex sequences (PQSs). Guanine-quadruplex (G-quadruplex or G4) formation in these sequences was evaluated by using a set of biophysical methods. G4s can modulate gene expression induced by p53. At low p53 expression level, PQS upstream of the p53-response element (RE) leads to greater gene expression induced by p53-R282W compared to that for the RE without PQS. Meanwhile, p53-WT protein expression is decreased by the PQS presence. At a high p53 expression level, the presence of PQS leads to a decreased expression of the reporter regardless of the distance and localization of the G4 from the RE.

• Publication type
• Journal Article MeSH

The transcription factor p53 is the most frequently impaired tumor suppressor in human cancers. In response to various stress stimuli, p53 activates transcription of genes that mediate its tumor-suppressive functions. Distinctive characteristics of p53 outlined here enable a well-defined program of genes involved in cell cycle arrest, apoptosis, senescence, differentiation, metabolism, autophagy, DNA repair, anti-viral response, and anti-metastatic functions, as well as facilitating autoregulation within the p53 network. This versatile, anti-cancer network governed chiefly by a single protein represents an immense opportunity for targeted cancer treatment, since about half of human tumors retain unmutated p53. During the last two decades, numerous compounds have been developed to block the interaction of p53 with the main negative regulator MDM2. However, small molecule inhibitors of MDM2 only induce a therapeutically desirable apoptotic response in a limited number of cancer types. Moreover, clinical trials of the MDM2 inhibitors as monotherapies have not met expectations and have revealed hematological toxicity as a characteristic adverse effect across this drug class. Currently, combination treatments are the leading strategy for enhancing efficacy and reducing adverse effects of MDM2 inhibitors. This review summarizes efforts to identify and test therapeutics that work synergistically with MDM2 inhibitors. Two main types of drugs have emerged among compounds used in the following combination treatments: first, modulators of the p53-regulated transcriptome (including chromatin modifiers), translatome, and proteome, and second, drugs targeting the downstream pathways such as apoptosis, cell cycle arrest, DNA repair, metabolic stress response, immune response, ferroptosis, and growth factor signaling. Here, we review the current literature in this field, while also highlighting overarching principles that could guide target selection in future combination treatments.

• Keywords
• combination therapy, integrated stress response, nelfinavir, nutlin, p53, polytherapy,
• MeSH
• Molecular Targeted Therapy * MeSH
• Humans MeSH
• Tumor Suppressor Protein p53 * metabolism   genetics   antagonists & inhibitors   MeSH
• Neoplasms * drug therapy   metabolism   genetics   MeSH
• Antineoplastic Agents * therapeutic use   pharmacology   MeSH
• Proto-Oncogene Proteins c-mdm2 antagonists & inhibitors   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Tumor Suppressor Protein p53 * MeSH
• Antineoplastic Agents * MeSH
• Proto-Oncogene Proteins c-mdm2 MeSH

Cruciforms occur when inverted repeat sequences in double-stranded DNA adopt intra-strand hairpins on opposing strands. Biophysical and molecular studies of these structures confirm their characterization as four-way junctions and have demonstrated that several factors influence their stability, including overall chromatin structure and DNA supercoiling. Here, we review our understanding of processes that influence the formation and stability of cruciforms in genomes, covering the range of sequences shown to have biological significance. It is challenging to accurately sequence repetitive DNA sequences, but recent advances in sequencing methods have deepened understanding about the amounts of inverted repeats in genomes from all forms of life. We highlight that, in the majority of genomes, inverted repeats are present in higher numbers than is expected from a random occurrence. It is, therefore, becoming clear that inverted repeats play important roles in regulating many aspects of DNA metabolism, including replication, gene expression, and recombination. Cruciforms are targets for many architectural and regulatory proteins, including topoisomerases, p53, Rif1, and others. Notably, some of these proteins can induce the formation of cruciform structures when they bind to DNA. Inverted repeat sequences also influence the evolution of genomes, and growing evidence highlights their significance in several human diseases, suggesting that the inverted repeat sequences and/or DNA cruciforms could be useful therapeutic targets in some cases.

• Keywords
• DNA base sequence, DNA structure, DNA supercoiling, cruciform, epigenetics, genome stability, inverted repeat, replication, transcription,
• MeSH
• DNA genetics   MeSH
• Nucleic Acid Conformation MeSH
• DNA, Cruciform MeSH
• Humans MeSH
• Nucleic Acids * MeSH
• Inverted Repeat Sequences MeSH
• Repetitive Sequences, Nucleic Acid genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• DNA MeSH
• DNA, Cruciform MeSH
• Nucleic Acids * MeSH

Recently, the quest for the mythical fountain of youth has produced extensive research programs that aim to extend the healthy lifespan of humans. Despite advances in our understanding of the aging process, the surprisingly extended lifespan and cancer resistance of some animal species remain unexplained. The p53 protein plays a crucial role in tumor suppression, tissue homeostasis, and aging. Long-lived, cancer-free African elephants have 20 copies of the TP53 gene, including 19 retrogenes (38 alleles), which are partially active, whereas humans possess only one copy of TP53 and have an estimated cancer mortality rate of 11-25%. The mechanism through which p53 contributes to the resolution of the Peto's paradox in Animalia remains vague. Thus, in this work, we took advantage of the available datasets and inspected the p53 amino acid sequence of phylogenetically related organisms that show variations in their lifespans. We discovered new correlations between specific amino acid deviations in p53 and the lifespans across different animal species. We found that species with extended lifespans have certain characteristic amino acid substitutions in the p53 DNA-binding domain that alter its function, as depicted from the Phenotypic Annotation of p53 Mutations, using the PROVEAN tool or SWISS-MODEL workflow. In addition, the loop 2 region of the human p53 DNA-binding domain was identified as the longest region that was associated with longevity. The 3D model revealed variations in the loop 2 structure in long-lived species when compared with human p53. Our findings show a direct association between specific amino acid residues in p53 protein, changes in p53 functionality, and the extended animal lifespan, and further highlight the importance of p53 protein in aging.

• Keywords
• aging, comparative analysis, longevity, p53, protein sequence,
• MeSH
• Databases, Genetic * MeSH
• Longevity * MeSH
• Species Specificity MeSH
• Gene Dosage * MeSH
• Models, Molecular * MeSH
• Tumor Suppressor Protein p53 chemistry   genetics   metabolism   MeSH
• Protein Domains MeSH
• Protein Structure, Secondary MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Tumor Suppressor Protein p53 MeSH

P53, P63, and P73 proteins belong to the P53 family of transcription factors, sharing a common gene organization that, from the P1 and P2 promoters, produces two groups of mRNAs encoding proteins with different N-terminal regions; moreover, alternative splicing events at C-terminus further contribute to the generation of multiple isoforms. P53 family proteins can influence a plethora of cellular pathways mainly through the direct binding to specific DNA sequences known as response elements (REs), and the transactivation of the corresponding target genes. However, the transcriptional activation by P53 family members can be regulated at multiple levels, including the DNA topology at responsive promoters. Here, by using a yeast-based functional assay, we evaluated the influence that a G-quadruplex (G4) prone sequence adjacent to the p53 RE derived from the apoptotic PUMA target gene can exert on the transactivation potential of full-length and N-terminal truncated P53 family α isoforms (wild-type and mutant). Our results show that the presence of a G4 prone sequence upstream or downstream of the P53 RE leads to significant changes in the relative activity of P53 family proteins, emphasizing the potential role of structural DNA features as modifiers of P53 family functions at target promoter sites.

• Keywords
• G-quadruplex (G4) prone sequence, P53 family, transactivation potential, wild-type and mutant P53/P63 proteins, yeast,
• MeSH
• Apoptosis genetics   MeSH
• DNA genetics   ultrastructure   MeSH
• G-Quadruplexes * MeSH
• Nucleic Acid Conformation MeSH
• Humans MeSH
• Membrane Proteins genetics   ultrastructure   MeSH
• Tumor Suppressor Protein p53 genetics   ultrastructure   MeSH
• Promoter Regions, Genetic genetics   MeSH
• Tumor Protein p73 genetics   ultrastructure   MeSH
• Apoptosis Regulatory Proteins genetics   MeSH
• Proto-Oncogene Proteins genetics   MeSH
• Response Elements genetics   MeSH
• Saccharomyces cerevisiae genetics   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• BBC3 protein, human MeSH Browser
• CKAP4 protein, human MeSH Browser
• DNA MeSH
• Membrane Proteins MeSH
• Tumor Suppressor Protein p53 MeSH
• Tumor Protein p73 MeSH
• Apoptosis Regulatory Proteins MeSH
• Proto-Oncogene Proteins MeSH
• TP73 protein, human MeSH Browser

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

• Keywords
• p53 protein, protein-DNA interaction, transactivation potential,
• MeSH
• G-Quadruplexes * MeSH
• Humans MeSH
• Tumor Suppressor Protein p53 genetics   metabolism   MeSH
• Promoter Regions, Genetic genetics   MeSH
• Protein Isoforms genetics   metabolism   MeSH
• Apoptosis Regulatory Proteins genetics   metabolism   MeSH
• Proto-Oncogene Proteins genetics   metabolism   MeSH
• Response Elements genetics   MeSH
• Protein Binding MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• BBC3 protein, human MeSH Browser
• Tumor Suppressor Protein p53 MeSH
• Protein Isoforms MeSH
• Apoptosis Regulatory Proteins MeSH
• Proto-Oncogene Proteins MeSH

The p53 family of transcription factors plays key roles in development, genome stability, senescence and tumor development, and p53 is the most important tumor suppressor protein in humans. Although intensively investigated for many years, its initial evolutionary history is not yet fully elucidated. Using bioinformatic and structure prediction methods on current databases containing newly-sequenced genomes and transcriptomes, we present a detailed characterization of p53 family homologs in remote members of the Holozoa group, in the unicellular clades Filasterea, Ichthyosporea and Corallochytrea. Moreover, we show that these newly characterized homologous sequences contain domains that can form structures with high similarity to the human p53 family DNA-binding domain, and some also show similarities to the oligomerization and SAM domains. The presence of these remote homologs demonstrates an ancient origin of the p53 protein family.

• Keywords
• Holozoa, evolution, p53, p63, p73,
• MeSH
• Databases, Genetic MeSH
• Eukaryota classification   genetics   MeSH
• Exons MeSH
• Phylogeny MeSH
• Protein Interaction Domains and Motifs MeSH
• Introns MeSH
• Protein Conformation MeSH
• Evolution, Molecular * MeSH
• Models, Molecular MeSH
• Multigene Family * MeSH
• Tumor Suppressor Protein p53 chemistry   genetics   metabolism   MeSH
• Amino Acid Sequence MeSH
• Sequence Homology, Amino Acid * MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Tumor Suppressor Protein p53 MeSH