A single mutant, A276S of p53, turns the switch to apoptosis

Robust p53 phenotypes and prospective downstream targets in telomerase-immortalized human cells

Cancers that retain wild type TP53 presumably harbor other clonal alterations that permitted their precursors to bypass p53-mediated growth suppression. Consequently, studies that employ TP53-wild type cancer cells and their isogenic derivatives may systematically fail to appreciate the full scope of p53 functionality. Several TP53 phenotypes are known to be absent in the widely used isogenic HCT116 colorectal cancer (CRC) model, which originated from a tumor that had retained wild type TP53. In contrast, we show that restoration of p53 in the TP53-mutant CRC cell line DLD-1 impeded cell proliferation, increased levels of senescence and sensitized cells to ionizing radiation (IR). To study p53 in a non-cancer context, we disrupted TP53 in hTERT-RPE1 cells. Derived from primary cells that were immortalized in vitro, hTERT-RPE1 expressed striking p53-dependent phenotypes and appeared to select for p53 loss during routine culture. hTERT-RPE1 expressed a p53-responsive transcriptome that was highly representative of diverse experimental systems. We discovered several novel downstream p53 targets of potential clinical relevance including ALDH3A1, which is involved in the detoxification of aldehydes and the metabolism of reactive oxygen species, and nectin cell adhesion molecule 4 (NECTIN4) which encodes a secreted surface protein that is overexpressed in many tumors.

Geometric deep learning of protein-DNA binding specificity

Predicting protein-DNA binding specificity is a challenging yet essential task for understanding gene regulation. Protein-DNA complexes usually exhibit binding to a selected DNA target site, whereas a protein binds, with varying degrees of binding specificity, to a wide range of DNA sequences. This information is not directly accessible in a single structure. Here, to access this information, we present Deep Predictor of Binding Specificity (DeepPBS), a geometric deep-learning model designed to predict binding specificity from protein-DNA structure. DeepPBS can be applied to experimental or predicted structures. Interpretable protein heavy atom importance scores for interface residues can be extracted. When aggregated at the protein residue level, these scores are validated through mutagenesis experiments. Applied to designed proteins targeting specific DNA sequences, DeepPBS was demonstrated to predict experimentally measured binding specificity. DeepPBS offers a foundation for machine-aided studies that advance our understanding of molecular interactions and guide experimental designs and synthetic biology.

DeepPBS: Geometric deep learning for interpretable prediction of protein-DNA binding specificity

Predicting specificity in protein-DNA interactions is a challenging yet essential task for understanding gene regulation. Here, we present Deep Predictor of Binding Specificity (DeepPBS), a geometric deep-learning model designed to predict binding specificity across protein families based on protein-DNA structures. The DeepPBS architecture allows investigation of different family-specific recognition patterns. DeepPBS can be applied to predicted structures, and can aid in the modeling of protein-DNA complexes. DeepPBS is interpretable and can be used to calculate protein heavy atom-level importance scores, demonstrated as a case-study on p53-DNA interface. When aggregated at the protein residue level, these scores conform well with alanine scanning mutagenesis experimental data. The inference time for DeepPBS is sufficiently fast for analyzing simulation trajectories, as demonstrated on a molecular-dynamics simulation of a Drosophila Hox-DNA tertiary complex with its cofactor. DeepPBS and its corresponding data resources offer a foundation for machine-aided protein-DNA interaction studies, guiding experimental choices and complex design, as well as advancing our understanding of molecular interactions.

p53-Bad: A Novel Tumor Suppressor/Proapoptotic Factor Hybrid Directed to the Mitochondria for Ovarian Cancer Gene Therapy

Clinical trials involving p53 gene therapy for ovarian cancer failed due to the dominant negative inhibition of wild-type p53 and multiple genetic aberrations in ovarian cancer. To overcome this problem, we have designed a more potent chimeric gene fusion, called p53-Bad, that combines p53 with the mitochondrial pro-apoptotic factor Bad. Unlike wild-type p53, which acts as a nuclear transcription factor, this novel p53-Bad construct has multiple unique mechanisms of action including a direct and rapid apoptotic effect at the mitochondria. The mitochondrial localization, transcription activity, and apoptotic activity of the constructs were tested. The results suggest that p53 can be effectively targeted to the mitochondria by controlling the phosphorylation of pro-apoptotic Bad, which can only localize to the mitochondria when Ser-112 and Ser-136 of Bad are unphosphorylated. By introducing S112A and S136A mutations, p53-Bad fusion cannot be phosphorylated at these two sites and always localizes to the mitochondria. p53-Bad constructs also have superior activity over p53 and Bad alone. The apoptotic activity is consistent in many ovarian cancer cell lines regardless of the endogenous p53 status. Both p53 and the BH3 domain of Bad contribute to the superior activity of p53-Bad. Our data suggests that p53-Bad fusions are capable of inducing apoptosis and should be further pursued for gene therapy for ovarian cancer.

Status quo of p53 in the treatment of tumors

The p53 gene is pivotal for oncogenesis in a combination of mutations in oncogenes and antioncogenes. The ubiquitous loss of the p53 pathway in human cancers has generated considerable interest in developing p53-targeted cancer therapies, but current ideas and approaches targeting p53 are conflicting. Current researches focus on cancer-selective drugs with therapeutic strategies that both activate and inhibit p53. As p53 is ubiquitously lost in human cancers, the strategy of exogenous p53 addition is reasonable. However, p53 acts not equally in all cell types; thus, individualized p53 therapy is the direction of future research. To clarify the controversies on p53 for improvement of future antitumor studies, the review focuses on the available technological protocols, including their advantages and limitations in terms of future therapeutic use of p53 in the management of tumors.

Delivery of drugs and macromolecules to the mitochondria for cancer therapy

Mitochondria are organelles that have pivotal functions in producing the energy necessary for life and executing the cell death pathway. Targeting drugs and macromolecules to the mitochondria may provide an effective means of inducing cell death for cancer therapy, and has been actively pursued in the last decade. This review will provide a brief overview of mitochondrial structure and function, how it relates to cancer, and importantly, will discuss different strategies of mitochondrial delivery including delivery using small molecules, peptides, genes encoding proteins and MTSs, and targeting polymers/nanoparticles with payloads to the mitochondria. The advantages and disadvantages for each strategy will be discussed. Specific examples using the latest strategies for mitochondrial targeting will be evaluated, as well as potential opportunities for specific mitochondrial compartment localization, which may lead to improvements in mitochondrial therapeutics. Future perspectives in mitochondrial targeting of drugs and macromolecules will be discussed. Currently this is an under-explored area that is prime for new discoveries in cancer therapeutics.

Re-engineered p53 activates apoptosis in vivo and causes primary tumor regression in a dominant negative breast cancer xenograft model

Inactivation of p53 pathway is reported in more than half of all human tumors and can be correlated to malignant development. Missense mutation in the DNA binding region (DBD) of p53 is the most common mechanism of p53 inactivation in cancer cells. The resulting tumor-derived p53 variants, similar to wild-type (wt) p53, retain their ability to oligomerize via the tetramerization domain (TD). Upon hetero-oligomerization, mutant p53 enforces a dominant negative effect over active wt-p53 in cancer cells. To overcome this barrier, we have previously designed a chimeric superactive p53 (p53-CC) with an alternative oligomerization domain capable of escaping transdominant inhibition by mutant p53 in vitro. In this report, we demonstrate the superior tumor suppressor activity of p53-CC and its ability to cause tumor regression of the MDA-MB-468 aggressive p53-dominant negative breast cancer tumor model in vivo. In addition, we illustrate the profound effects of the dominant negative effect of endogenous mutant p53 over wt-p53 in cancer cells. Finally, we investigate the underlying differential mechanisms of activity for p53-CC and wt-p53 delivered using viral-mediated gene therapy approach in the MDA-MB-468 tumor model.

Role of polymorphisms of PERP gene in the development of acantholysis in patients with pemphigus vulgaris

Goal. To determine the nucleotide protein-coding PERP gene sequence and assess the relation between the revealed mutations/polymorphisms and development of true acantholytic pemphigus as well as particular features of its course. Materials and methods. The protein-coding PERP gene DNA sequence was studied by the sequence analysis method in 18 patients with true acantholytic pemphigus. Results. Two polymorphisms were discovered in patients with true acantholytic pemphigus in Exon 3 of the PERP gene for the first time: rs648802 (non-synonymous) and rs648396 (synonymous). The incidence of wild type genotypes in the revealed polymorphisms (С/С genotype rs648802 and Т/Т genotype rs648396) in healthy volunteers reliably exceeded that in patients (p = 0.049). Patients with true acantholytic pemphigus are characterized by a higher incidence rate of mutant heterozygous genotypes С/G rs648802 and Т/C rs648396 (p = 0.09). Mutant heterozygous genotypes of the polymorphisms (G/G genotype rs648802 and С/С genotype rs648396) were revealed in patients with the earlier onset of the disease (41-60 years) (p = 0.025) more often while heterozygous genotypes (С/G genotype rs648802 and T/С genotype rs648396) were revealed when the disease developed at the age of 61 or older more often (p = 0.01). Conclusion. Identification of the polymorphous genotype by the sequence method or other molecular methods (e.g. PCR) can be used to forecast the terms when true acantholytic pemphigus can emerge in genetically inclined patients. However, it should be noted that it is necessary to specify the preliminary results obtained based on a greater sample of patients with true acantholytic pemphigus.

A chimeric p53 evades mutant p53 transdominant inhibition in cancer cells

Because of the dominant negative effect of mutant p53, there has been limited success with wild-type (wt) p53 cancer gene therapy. Therefore, an alternative oligomerization domain for p53 was investigated to enhance the utility of p53 for gene therapy. The tetramerization domain of p53 was substituted with the coiled-coil (CC) domain from Bcr (breakpoint cluster region). Our p53 variant (p53-CC) maintains proper nuclear localization in breast cancer cells detected via fluorescence microscopy and shows a similar expression profile of p53 target genes as wt-p53. Additionally, similar tumor suppressor activities of p53-CC and wt-p53 were detected by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), annexin-V, 7-aminoactinomycin D (7-AAD), and colony-forming assays. Furthermore, p53-CC was found to cause apoptosis in four different cancer cell lines, regardless of endogenous p53 status. Interestingly, the transcriptional activity of p53-CC was higher than wt-p53 in 3 different reporter gene assays. We hypothesized that the higher transcriptional activity of p53-CC over wt-p53 was due to the sequestration of wt-p53 by endogenous mutant p53 found in cancer cells. Co-immunoprecipitation revealed that wt-p53 does indeed interact with endogenous mutant p53 via its tetramerization domain, while p53-CC escapes this interaction. Therefore, we investigated the impact of the presence of a transdominant mutant p53 on tumor suppressor activities of wt-p53 and p53-CC. Overexpression of a potent mutant p53 along with wt-p53 or p53-CC revealed that, unlike wt-p53, p53-CC retains the same level of tumor suppressor activity. Finally, viral transduction of wt-p53 and p53-CC into a breast cancer cell line that harbors a tumor derived transdominant mutant p53 validated that p53-CC indeed evades sequestration and consequent transdominant inhibition by endogenous mutant p53.