Gain-of-function mutant p53: history and speculation

Natural compound PEITC inhibits gain of function of p53 mutants in cancer cells by switching YAP-binding partners between p53 and p73

Phenethyl isothiocyanate (PEITC) derived from cruciferous vegetables has shown anticancer activities by modulating apoptosis, cell cycle arrest, drug-metabolizing enzymes and even preferentially restoring a 'WT-like' conformation to p53R175H. But its molecular anti-cancer mechanisms are not well understood. Evidence shows that switching YAP-binding partners from pro-tumorigenic to pro-apoptotic proteins might hold great potential for the treatment of human cancers harboring mtp53. In this study we investigated the impact of PEITC on mtp53-YAP-p73 interaction in cancers harboring a variety of p53 mutants, but not limited to structural mutations. We showed that breast cancer, colorectal and lung cancer cells harboring mtp53 (p53R280K, p53R273H) were more sensitive to PEITC than those cells harboring wtp53. We demonstrated that PEITC bound to YAP at its WW binding domain, and induced a conformational change, facilitated the dissociation of YAP-mtp53 complex and inhibited their pro-proliferative transcriptional activity in different cancer cells harboring mtp53. Concomitantly, PEITC acted as a molecular glue to enhance the association of YAP-p73 complex and induced apoptosis. These results provide insights into the anticancer activity of PEITC against a wide spectrum of cancers and highlight a unique mode of action for PEITC-based cancer therapy.

Mutant p53 confers chemoresistance by activating KMT5B-mediated DNA repair pathway in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC), a malignancy arising from the nasopharyngeal epithelium, is common in the east and southeast area of Asia. Treatments for locally advanced and recurrent NPC include chemotherapy (usually combined with 5-Fluorouracil, 5-FU) and radiotherapy, but response is limited due to chemo-resistance. p53 mutation is a critical factor for 5-FU resistance in some cancers, but its role in NPC chemo-resistance remains unclear. Here, we demonstrate that p53(R280T), a common p53 somatic mutation found in multiple NPC tumor samples, induces gain-of-function upregulation of DNA repair genes which leads to 5-FU resistance in NPC. p53(R280T) specifically upregulates the expression of DNA repair-associated gene KMT5B by binding to its promoter, which leads to 5-FU resistance. Depletion of KMT5B in NPCs restores 5-FU induced DNA damages and improve the efficacy of 5-FU. By screening compounds affecting KMT5B expression, we identify curcumin as an effective down-regulator of KMT5B in NPC cells. We therefore evaluate the therapeutic potential of a 5-FU/curcumin combination to treat NPC and discover that curcumin enhances the efficacy of 5-FU to suppress NPC tumor growth. In summary, our findings indicate that mutant p53 and its regulated DNA repair genes serve as potential therapeutic targets to reverse 5-FU resistance for NPC patients.

Comprehensive germline and somatic profiling of high-risk Thai breast cancer via next-generation sequencing

Breast cancer genomic landscapes differ across ethnic groups, yet the somatic profile of Thai breast tumours has remained uncharacterised. This study analysed 1676 high-hereditary-risk Thai breast cancer patients, identified according to National Comprehensive Cancer Network (NCCN) guideline. Germline alterations were assessed in 1370 cases using a custom 36-core cancer panel. Somatic mutations were characterised in formalin-fixed, paraffin-embedded tumour tissues from 180 of the 1676 patients using the 501-gene Oncomine Comprehensive Assay Plus panel. Pathogenic or likely pathogenic (P/LP) variants were detected in 13% of the 1370 germline analyses, with BRCA1 and BRCA2 being the most frequently altered genes. The prevalence of P/LP variants in BRCA1, BRCA2, and PALB2 differed from that observed in other ethnic cohorts. In somatic profiling, TP53 emerged as the most frequently mutated gene, especially in HER2 and TNBC tumours, whereas MAP3K1 and GATA3 were the most frequently mutated genes in the HR+/HER2- tumours. Moreover, hormone-receptor-positive (HR+) tumours showed distinct mutation patterns compared with other ethnicities. Notably, germline carriers exhibited lower PIK3CA mutation rates than non-carriers. These findings advance our understanding of Thai breast cancer genomics and underscore the importance of ethnic diversity in cancer research, offering insights into tailored screening and therapeutic approaches.

Phase Separation and Prion-Like Aggregation of p53 Family Tumor Suppressors: From Protein Evolution to Cancer Treatment

Biomolecular condensates, formed through phase separation (PS), are essential in various physiological processes, but they can also transition into amyloid-like structures, contributing to diseases like cancer and neurodegenerative disorders. This review centers on the tumor suppressor protein p53 and its paralogs, p63 and p73, which play significant roles in cancer biology. Mutations in the TP53 gene, present in over half of all malignant tumors, disrupt the function of p53 and contribute to cancer progression. Mutant p53 not only misfolds but also forms biomolecular condensates and amyloid-like aggregates, like the toxic amyloids seen in neurodegenerative diseases. These amyloid-like structures, characteristic of mutant p53, might be associated with its gain of function (GoF) in cancer. Recent in vitro and in cell studies demonstrate that mutant p53 can exert a prion-like effect on its paralogs, p63 and p73, which typically do not form amyloids under physiological conditions. Heparin inhibits the prion-like effect of mutant p53 on p63 and p73. These findings underscore the critical role of mutant p53 in promoting the aggregation of p63 and p73, and likely of other transcription factors, suggesting new therapeutic targets. The amyloid-like aggregation of mutant p53 is an excellent candidate target for cancer, as evidenced by recent studies. By understanding the phase transitions and amyloid formation of mutant p53, innovative diagnostic and treatment strategies have been explored to reveal and disrupt these processes, offering hope for improved cancer therapies.

Dysregulation of Iron Homeostasis Mediated by FTH Increases Ferroptosis Sensitivity in TP53-Mutant Glioblastoma

Iron metabolism is a critical factor in tumorigenesis and development. Although TP53 mutations are prevalent in glioblastoma (GBM), the mechanisms by which TP53 regulates iron metabolism remain elusive. We reveal an imbalance iron homeostasis in GBM via TCGA database analysis. TP53 mutations disrupted iron homeostasis in GBM, characterized by elevated total iron levels and reduced ferritin (FTH). The gain-of-function effect triggered by TP53 mutations upregulates itchy E3 ubiquitin-protein ligase (ITCH) protein expression in astrocytes, leading to FTH degradation and an increase in free iron levels. TP53-mut astrocytes were more tolerant to the high iron environment induced by exogenous ferric ammonium citrate (FAC), but the increase in intracellular free iron made them more sensitive to Erastin-induced ferroptosis. Interestingly, we found that Erastin combined with FAC treatment significantly increased ferroptosis. These findings provide new insights for drug development and therapeutic modalities for GBM patients with TP53 mutations from iron metabolism perspectives.

Morphogenesis and regeneration share a conserved core transition cell state program that controls lung epithelial cell fate

Transitional cell states are at the crossroads of crucial developmental and regenerative events, yet little is known about how these states emerge and influence outcomes. The alveolar and airway epithelia arise from distal lung multipotent progenitors, which undergo cell fate transitions to form these distinct compartments. The identification and impact of cell states in the developing lung are poorly understood. Here, we identified a population of Icam1/Nkx2-1 epithelial progenitors harboring a transitional state program remarkably conserved in humans and mice during lung morphogenesis and regeneration. Lineage-tracing and functional analyses reveal their role as progenitors to both airways and alveolar cells and the requirement of this transitional program to make distal lung progenitors competent to undergo airway cell fate specification. The identification of a common progenitor cell state in vastly distinct processes suggests a unified program reiteratively regulating outcomes in development and regeneration.

The Role of p53 Mutations in Early and Late Response to Mitotic Aberrations

Mutations in the TP53 gene and chromosomal instability (CIN) are two of the most common alterations in cancer. CIN, marked by changes in chromosome numbers and structure, drives tumor development, but is poorly tolerated in healthy cells, where developmental and tissue homeostasis mechanisms typically eliminate cells with chromosomal abnormalities. Mechanisms that allow cancer cells to acquire and adapt to CIN remain largely unknown. Tumor suppressor protein p53, often referred to as the "guardian of the genome", plays a critical role in maintaining genomic stability. In cancer, CIN strongly correlates with TP53 mutations, and recent studies suggest that p53 prevents the propagation of cells with abnormal karyotypes arising from mitotic errors. Furthermore, p53 dysfunction is frequent in cells that underwent whole-genome doubling (WGD), a process that facilitates CIN onset, promotes aneuploidy tolerance, and is associated with poor patient prognosis across multiple cancer types. This review summarizes current insights into p53's role in protecting cells from chromosome copy number alterations and discusses the implications of its dysfunction for the adaption and propagation of cancer cells.

Mutant p53 regulates cancer cell invasion in complex three-dimensional environments through mevalonate pathway-dependent Rho/ROCK signaling

Certain mutations can confer neomorphic gain of function (GOF) activities to the p53 protein that affect cancer progression. Yet the concept of mutant p53 GOF has been challenged. Here, using various strategies to alter the status of mutant versions of p53 in different cell lines, we demonstrate that mutant p53 stimulates cancer cell invasion in three-dimensional environments. Mechanistically, mutant p53 enhances RhoA/ROCK-dependent cell contractility and cell-mediated extracellular matrix (ECM) re-organization via increasing mevalonate pathway-dependent RhoA localization to the membrane. In line with this, RhoA-dependent pro-invasive activity is also mediated by IDI-1, a mevalonate pathway product. Further, the invasion-enhancing effect of mutant p53 is dictated by the biomechanical properties of the surrounding ECM, thereby adding a cell-independent layer of regulation to mutant p53 GOF activity that is mediated by dynamic reciprocal cell-ECM interactions. Together our findings link mutant p53 metabolic GOF activity with an invasive cellular phenotype in physiologically relevant and context-dependent settings.

Significance

This study addresses the contribution of mutant p53 to the process of cancer cell dissemination in physiologically relevant three-dimensional environments - a key characteristic of metastatic disease. Several mutant p53 proteins display pro-oncogenic activity with respect to cancer cell invasion in 3D environments via mevalonate pathway-dependent Rho/ROCK signaling axis.

Targeting mutant p53: a key player in breast cancer pathogenesis and beyond

The p53 mutation is the most common genetic mutation associated with human neoplasia. TP53 missense mutations, which frequently arise early in breast cancer, are present in over thirty percent of breast tumors. In breast cancer, p53 mutations are linked to a more aggressive course of the disease and worse overall survival rates. TP53 mutations are mostly seen in triple-negative breast cancer, a very diverse kind of the disease. The majority of TP53 mutations originate in the replacement of individual amino acids within the p53 protein's core domain, giving rise to a variety of variations referred to as "mutant p53s." In addition to gaining carcinogenic qualities through gain-of-function pathways, these mutants lose the typical tumor-suppressive features of p53 to variable degrees. The gain-of-function impact of stabilized mutant p53 causes tumor-specific dependency and resistance to therapy. P53 is a prospective target for cancer therapy because of its tumor-suppressive qualities and the numerous alterations that it experiences in tumors. Phenotypic abnormalities in breast cancer, notably poorly differentiated basal-like tumors are frequently linked to high-grade tumors. By comparing data from cell and animal models with clinical outcomes in breast cancer, this study investigates the molecular mechanisms that convert gene alterations into the pathogenic consequences of mutant p53's tumorigenic activity. The study delves into current and novel treatment approaches aimed at targeting p53 mutations, taking into account the similarities and differences in p53 regulatory mechanisms between mutant and wild-type forms, as well.

FGFR3 alterations in bladder cancer: Sensitivity and resistance to targeted therapies

In this review, we revisit the pivotal role of fibroblast growth factor receptor 3 (FGFR3) in bladder cancer (BLCA), underscoring its prevalence in both non-muscle-invasive and muscle-invasive forms of the disease. FGFR3 mutations in up to half of BLCAs play a well-established role in tumorigenesis, shaping distinct tumor initiation patterns and impacting the tumor microenvironment (TME). Emphasizing the importance of considering epithelial-mesenchymal transition profile and TME status, we revisit their relevance in predicting responses to immune checkpoint inhibitors in FGFR3-mutated BLCAs. This writing highlights the initially promising yet transient efficacy of the FGFR inhibitor Erdafitinib on FGFR3-mutated BLCA, stressing the pressing need to unravel resistance mechanisms and identify co-targets for future combinatorial studies. A thorough analysis of recent preclinical and clinical evidence reveals resistance mechanisms, including secondary mutations, epigenetic alterations in pathway effectors, phenotypic heterogeneity, and population-specific variations within FGFR3 mutational status. Lastly, we discuss the potential of combinatorial treatments and concepts like synthetic lethality for discovering more effective targeted therapies against FGFR3-mutated BLCA.

Decoding the molecular symphony: interactions between the m6A and p53 signaling pathways in cancer

The p53 tumor suppressor gene governs a multitude of complex cellular processes that are essential for anti-cancer function and whose dysregulation leads to aberrant gene transcription, activation of oncogenic signaling and cancer development. Although mutations can occur at any point in the genetic sequence, missense mutations comprise the majority of observed p53 mutations in cancers regardless of whether the mutation is germline or somatic. One biological process involved in both mutant and wild-type p53 signaling is the N 6-methyladenosine (m6A) epitranscriptomic network, a type of post-transcriptional modification involved in over half of all eukaryotic mRNAs. Recently, a significant number of findings have demonstrated unique interactions between p53 and the m6A epitranscriptomic network in a variety of cancer types, shedding light on a previously uncharacterized connection that causes significant dysregulation. Cross-talk between wild-type or mutant p53 and the m6A readers, writers and erasers has been shown to impact cellular function and induce cancer formation by influencing various cancer hallmarks. Here, this review aims to summarize the complex interplay between the m6A epitranscriptome and p53 signaling pathway, highlighting its effects on tumorigenesis and other hallmarks of cancer, as well as identifying its therapeutic implications for the future.

A common druggable signature of oncogenic c-Myc, mutant KRAS and mutant p53 reveals functional redundancy and competition among oncogenes in cancer

The major driver oncogenes MYC, mutant KRAS, and mutant TP53 often coexist and cooperate to promote human neoplasia, which results in anticancer therapeutic opportunities within their downstream molecular programs. However, little research has been conducted on whether redundancy and competition among oncogenes affect their programs and ability to drive neoplasia. By CRISPR‒Cas9-mediated downregulation we evaluated the downstream proteomics and transcriptomics programs of MYC, mutant KRAS, and mutant TP53 in a panel of cell lines with either one or three of these oncogenes activated, in cancers of the lung, colon and pancreas. Using RNAi screening of the commonly activated molecular programs, we found a signature of three proteins - RUVBL1, HSPA9, and XPO1, which could be efficiently targeted by novel drug combinations in the studied cancer types. Interestingly, the signature was controlled by the oncoproteins in a redundant or competitive manner rather than by cooperation. Each oncoprotein individually upregulated the target genes, while upon oncogene co-expression each target was controlled preferably by a dominant oncoprotein which reduced the influence of the others. This interplay was mediated by redundant routes of target gene activation - as in the case of mutant KRAS signaling to c-Jun/GLI2 transcription factors bypassing c-Myc activation, and by competition - as in the case of mutant p53 and c-Myc competing for binding to target promoters. The global transcriptomics data from the cell lines and patient samples indicate that the redundancy and competition of oncogenic programs are broad phenomena, that may constitute even a majority of the genes dependent on oncoproteins, as shown for mutant p53 in colon and lung cancer cell lines. Nevertheless, we demonstrated that redundant oncogene programs harbor targets for efficient anticancer drug combinations, bypassing the limitations for direct oncoprotein inhibition.

Pyrimidine Triones as Potential Activators of p53 Mutants

p53 is a crucial tumor suppressor in vertebrates that is frequently mutated in human cancers. Most mutations are missense mutations that render p53 inactive in suppressing tumor initiation and progression. Developing small-molecule drugs to convert mutant p53 into an active, wild-type-like conformation is a significant focus for personalized cancer therapy. Prior research indicates that reactivating p53 suppresses cancer cell proliferation and tumor growth in animal models. Early clinical evidence with a compound selectively targeting p53 mutants with substitutions of tyrosine 220 suggests potential therapeutic benefits of reactivating p53 in patients. This study identifies and examines the UCI-1001 compound series as a potential corrector for several p53 mutations. The findings indicate that UCI-1001 treatment in p53 mutant cancer cell lines inhibits growth and reinstates wild-type p53 activities, including DNA binding, target gene activation, and induction of cell death. Cellular thermal shift assays, conformation-specific immunofluorescence staining, and differential scanning fluorometry suggest that UCI-1001 interacts with and alters the conformation of mutant p53 in cancer cells. These initial results identify pyrimidine trione derivatives of the UCI-1001 series as candidates for p53 corrector drug development.

p53 Genetics and Biology in Lung Carcinomas: Insights, Implications and Clinical Applications

The TP53 gene is renowned as a tumor suppressor, playing a pivotal role in overseeing the cell cycle, apoptosis, and maintaining genomic stability. Dysregulation of p53 often contributes to the initiation and progression of various cancers, including lung cancer (LC) subtypes. The review explores the intricate relationship between p53 and its role in the development and progression of LC. p53, a crucial tumor suppressor protein, exists in various isoforms, and understanding their distinct functions in LC is essential for advancing our knowledge of this deadly disease. This review aims to provide a comprehensive literature overview of p53, its relevance to LC, and potential clinical applications.

Working title: Molecular involvement of p53-MDM2 interactome in gastrointestinal cancers

The interaction between murine double minute 2 (MDM2) and p53, marked by transcriptional induction and feedback inhibition, orchestrates a functional loop dictating cellular fate. The functional loop comprising p53-MDM2 axis is made up of an interactome consisting of approximately 81 proteins, which are spatio-temporally regulated and involved in DNA repair mechanisms. Biochemical and genetic alterations of the interactome result in dysregulation of the p53-mdm2 axis that leads to gastrointestinal (GI) cancers. A large subset of interactome is well known and it consists of proteins that either stabilize p53 or MDM2 and proteins that target the p53-MDM2 complex for ubiquitin-mediated destruction. Upstream signaling events brought about by growth factors and chemical messengers invoke a wide variety of posttranslational modifications in p53-MDM2 axis. Biochemical changes in the transactivation domain of p53 impact the energy landscape, induce conformational switching, alter interaction potential and could change solubility of p53 to redefine its co-localization, translocation and activity. A diverse set of chemical compounds mimic physiological effectors and simulate biochemical modifications of the p53-MDM2 interactome. p53-MDM2 interactome plays a crucial role in DNA damage and repair process. Genetic aberrations in the interactome, have resulted in cancers of GI tract (pancreas, liver, colorectal, gastric, biliary, and esophageal). We present in this article a review of the overall changes in the p53-MDM2 interactors and the effectors that form an epicenter for the development of next-generation molecules for understanding and targeting GI cancers.

STK11/LKB1 alterations worsen the poor prognosis of KRAS mutated early-stage non-squamous non-small cell lung carcinoma, results based on the phase 2 IFCT TASTE trial

BACKGROUND

STK11/LKB1 mutations have been associated with primary resistance to PD-1 axis inhibitors and poor prognosis in advanced KRAS-mutant lung adenocarcinoma. This study aimed to assess the prognostic significance of STK11/LKB1 alterations in localized non-squamous non-small cell lung carcinoma (non-sq NSCLC).

PATIENTS AND METHODS

Surgical samples from patients undergoing complete resection for stage IIa, IIb, or IIIa (N2 excluded) non-sq NSCLC in the randomized adjuvant phase II trial (NCT00775385 IFCT-1801 TASTE trial) were examined. Patients received either standard chemotherapy (Pemetrexed Cisplatin) or personalized treatment based on EGFR mutation (Erlotinib) and ERCC1 expression. Tumor molecular profiles were analyzed using targeted NGS and correlated with overall survival (OS) and disease-free survival (DFS), adjusting for relevant clinical variables. Additionally, interactions between treatment groups and molecular alterations on OS, PD-L1 expression, and tumor-circulating DNA in post-operative plasma samples were evaluated.

RESULTS

Among 134 patients (predominantly male smokers with adenocarcinoma), KRAS mutations were associated with shorter DFS (HR: 1.95, 95 % CI: 1.1-3.4, p = 0.02) and OS (HR: 2.32, 95 % CI: 1.2-4.6, p = 0.014). Isolated STK11/LKB1 mutations (n = 18) did not significantly impact DFS or OS. However, within KRAS-mutated samples (n = 53), patients with concurrent STK11/LKB1 mutations (n = 10) exhibited significantly shorter DFS (HR: 3.85, CI: 1.5-10.2, p = 0.006) and a trend towards shorter OS (HR: 1.80, CI: 0.6-5.3, p = 0.28). No associations were found between PD-L1 expression, other gene mutations, progression-free survival (PFS), or OS.

CONCLUSION

This analysis reinforces KRAS mutations as predictive factors for relapse and poor survival in localized non-sq NSCLC. Furthermore, the presence of concomitant STK11/LKB1 mutations exacerbated the prognosis within the KRAS-mutated subset. These findings emphasize the clinical relevance of these molecular markers and their potential impact on treatment strategies in non-sq NSCLC.

An overview of the functions of p53 and drugs acting either on wild- or mutant-type p53

TP53, also known as the "guardian of the genome," is an important tumor suppressor gene. It is encoded by the human genome and is associated with the development of diverse cancers. The p53 protein, encoded by TP53, functions in the cell to monitor DNA damage and prompts the cell to respond appropriately. When DNA is damaged, p53 halts the cell cycle, allowing cells to enter the repair state. If the repair is ineffective, p53 induces cell death via apoptosis. This prevents DNA damage transmission during cell division and reduces cancer risk. However, the p53 gene mutation compromises its function. This leads to the inability of cells to respond properly to DNA damage, which may result in cancer development. Mutations in p53 are widespread in diverse cancers, especially highly prevalent cancers, including breast, colon, and lung cancers. Despite the association between p53 mutations and cancer, researchers have discovered drugs and treatments that may reactivate mutated p53 function. Therefore, p53 remains an important area of research in cancer treatment and holds promise as a new direction for cancer therapy. In summary, TP53 is a vital tumor suppressor gene responsible for monitoring DNA damage and prompting cells to respond appropriately. This article summarizes drugs related to p53 and diverse strategies for discovering drugs that act on either wide or mutant p53. Herein, p53 is categorized into two types: wild and mutant type. Drugs are also classified according to diverse treatment strategies, enabling readers to differentiate between the two types of p53 and aiding in selecting the appropriate research direction. Additionally, this review offers a valuable reference for drug design.

A CANCER PERSISTENT DNA REPAIR CIRCUIT DRIVEN BY MDM2, MDM4 (MDMX), AND MUTANT P53 FOR RECRUITMENT OF MDC1 AND 53BP1 TO CHROMATIN

The influence of the metastasis promoting proteins mutant p53 (mtp53) and MDM2 on Cancer Persistent Repair (CPR) to promote cancer cell survival is understudied. Interactions between the DNA repair choice protein 53BP1 and wild type tumor suppressor protein p53 (wtp53) regulates cell cycle control. Cancer cells often express elevated levels of transcriptionally inactive missense mutant p53 (mtp53) that interacts with MDM2 and MDM4/MDMX (herein called MDMX). The ability of mtp53 to maintain a 53BP1 interaction while in the context of interactions with MDM2 and MDMX has not been described. We asked if MDM2 regulates chromatin-based phosphorylation events in the context of mtp53 by comparing the chromatin of T47D breast cancer cells with and without MDM2 in a phospho-peptide stable isotope labeling in cell culture (SILAC) screen. We found reduced phospho-53BP1 chromatin association, which we confirmed by chromatin fractionation and immunofluorescence in multiple breast cancer cell lines. We used the Proximity Ligation Assay (PLA) in breast cancer cell lines and detected 53BP1 in close proximity to mtp53, MDM2, and the DNA repair protein MDC1. Through disruption of the mtp53-MDM2 interaction, by either Nutlin 3a or a mtp53 R273H C-terminal deletion, we uncovered that mtp53 was required for MDM2-53BP1 interaction foci. Our data suggests that mtp53 works with MDM2 and 53BP1 to promote CPR and cell survival.

Hepatitis C virus may accelerate breast cancer progression by increasing mutant p53 and c-Myc oncoproteins circulating levels

BACKGROUND

Hepatitis C virus (HCV) was reported to relate to polymorphous and frequent extrahepatic manifestation. Despite the limited studies, HCV viral oncoproteins may be implicated in breast cancer (BC) tumor aggressiveness. In a trial to elucidate a mechanistic link, this study aimed to investigate a mutant p53 and c-Myc oncoprotein expression levels in BC patients with and without HCV infection.

METHODS

A total of 215 BC patients (119 infected and 96 non-infected with HCV) were collected. ELISA was used for detection of anti-HCV antibodies, mutant p53, c-Myc, HCV-NS4, CEA, CA 125, and CA-15.3.

RESULTS

HCV infection was related to BC late stages, lymph-node invasion, distant metastasis, high grades, and large size. HCV-infected patients had a significantly (P < 0.05) higher WBCs, ALT and AST activity, bilirubin CEA, CA125 and CA15.3 levels, and reduced hemoglobin, albumin, and RBCs count. Regardless of tumor severity, HCV infection was associated with significant elevated levels of mutant p53 (22.5 ± 3.5 µg/mL; 1.9-fold increase) and c-Myc (21.4 ± 1.8 µg/mL; 1.5-fold increase). Among HCV-infected patients, elevated levels of p53 and c-Myc were significantly correlated with elevated tumor markers (CEA, CA 125, and CA15.3) and HCV-NS4 levels.

CONCLUSIONS

This study concluded that HCV infection may be accompanied with BC severity behavior and this may be owing to elevated expression of mutant p53 and c-Myc oncoproteins.

p53 deficient breast cancer cells reprogram preadipocytes toward tumor-protective immunomodulatory cells

The TP53 gene is mutated in approximately 30% of all breast cancer cases. Adipocytes and preadipocytes, which constitute a substantial fraction of the stroma of normal mammary tissue and breast tumors, undergo transcriptional, metabolic, and phenotypic reprogramming during breast cancer development and play an important role in tumor progression. We report here that p53 loss in breast cancer cells facilitates the reprogramming of preadipocytes, inducing them to acquire a unique transcriptional and metabolic program that combines impaired adipocytic differentiation with augmented cytokine expression. This, in turn, promotes the establishment of an inflammatory tumor microenvironment, including increased abundance of Ly6C+ and Ly6G+ myeloid cells and elevated expression of the immune checkpoint ligand PD-L1. We also describe a potential gain-of-function effect of common p53 missense mutations on the inflammatory reprogramming of preadipocytes. Altogether, our study implicates p53 deregulation in breast cancer cells as a driver of tumor-supportive adipose tissue reprogramming, expanding the network of non-cell autonomous mechanisms whereby p53 dysfunction may promote cancer. Further elucidation of the interplay between p53 and adipocytes within the tumor microenvironment may suggest effective therapeutic targets for the treatment of breast cancer patients.

From cultivation to cancer: formation of N-nitrosamines and other carcinogens in smokeless tobacco and their mutagenic implications

Tobacco use is a major cause of preventable morbidity and mortality globally. Tobacco products, including smokeless tobacco (ST), generally contain tobacco-specific N-nitrosamines (TSNAs), such as N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-butanone (NNK), which are potent carcinogens that cause mutations in critical genes in human DNA. This review covers the series of biochemical and chemical transformations, related to TSNAs, leading from tobacco cultivation to cancer initiation. A key aim of this review is to provide a greater understanding of TSNAs: their precursors, the microbial and chemical mechanisms that contribute to their formation in ST, their mutagenicity leading to cancer due to ST use, and potential means of lowering TSNA levels in tobacco products. TSNAs are not present in harvested tobacco but can form due to nitrosating agents reacting with tobacco alkaloids present in tobacco during certain types of curing. TSNAs can also form during or following ST production when certain microorganisms perform nitrate metabolism, with dissimilatory nitrate reductases converting nitrate to nitrite that is then released into tobacco and reacts chemically with tobacco alkaloids. When ST usage occurs, TSNAs are absorbed and metabolized to reactive compounds that form DNA adducts leading to mutations in critical target genes, including the RAS oncogenes and the p53 tumor suppressor gene. DNA repair mechanisms remove most adducts induced by carcinogens, thus preventing many but not all mutations. Lastly, because TSNAs and other agents cause cancer, previously documented strategies for lowering their levels in ST products are discussed, including using tobacco with lower nornicotine levels, pasteurization and other means of eliminating microorganisms, omitting fermentation and fire-curing, refrigerating ST products, and including nitrite scavenging chemicals as ST ingredients.

p53 at the crossroad between mitochondrial reactive oxygen species and necroptosis

p53 is a redox-sensitive transcription factor that can regulate multiple cell death programs through different signaling pathways. In this review, we assess the role of p53 in the regulation of necroptosis, a programmed form of lytic cell death highly involved in the pathophysiology of multiple diseases. In particular, we focus on the role of mitochondrial reactive oxygen species (mtROS) as essential contributors to modulate necroptosis execution through p53. The enhanced generation of mtROS during necroptosis is critical for the correct interaction between receptor-interacting serine/threonine-protein kinase 1 (RIPK1) and 3 (RIPK3), two key components of the functional necrosome. p53 controls the occurrence of necroptosis by modulating the levels of mitochondrial H2O2 via peroxiredoxin 3 and sulfiredoxin. Furthermore, in response to increased levels of H2O2, p53 upregulates the long non-coding RNA necrosis-related factor, favoring the translation of RIPK1 and RIPK3. In parallel, a fraction of cytosolic p53 migrates into mitochondria, a process notably involved in necroptosis execution via its interaction with the mitochondrial permeability transition pore. In conclusion, p53 is located at the intersection between mtROS and the necroptosis machinery, making it a key protein to orchestrate redox signaling during necroptosis.

Small-molecule correctors and stabilizers to target p53

The tumor suppressor p53 is the most frequently mutated protein in human cancer and tops the list of high-value precision oncology targets. p53 prevents initiation and progression of cancer by inducing cell-cycle arrest and various forms of cell death. Tumors have thus evolved ways to inactivate p53, mainly by TP53 mutations or by hyperactive p53 degradation. This review focuses on two types of p53 targeting compounds, MDM2 antagonists and mutant p53 correctors. MDM2 inhibitors prevent p53 protein degradation, while correctors restore tumor suppressor activity of p53 mutants by enhancing thermodynamic stability. Herein we explore both novel and repurposed p53 targeting compounds, discuss their mode of action, and examine the challenges in advancing them to the clinic.

Domain-specific p53 mutants activate EGFR by distinct mechanisms exposing tissue-independent therapeutic vulnerabilities

Mis-sense mutations affecting TP53 promote carcinogenesis both by inactivating tumor suppression, and by conferring pro-carcinogenic activities. We report here that p53 DNA-binding domain (DBD) and transactivation domain (TAD) mis-sense mutants unexpectedly activate pro-carcinogenic epidermal growth factor receptor (EGFR) signaling via distinct, previously unrecognized molecular mechanisms. DBD- and TAD-specific TP53 mutants exhibited different cellular localization and induced distinct gene expression profiles. In multiple tissues, EGFR is stabilized by TAD and DBD mutants in the cytosolic and nuclear compartments respectively. TAD mutants promote EGFR-mediated signaling by enhancing EGFR interaction with AKT via DDX31 in the cytosol. Conversely, DBD mutants maintain EGFR activity in the nucleus, by blocking EGFR interaction with the phosphatase SHP1, triggering c-Myc and Cyclin D1 upregulation. Our findings suggest that p53 mutants carrying gain-of-function, mis-sense mutations affecting two different domains form new protein complexes that promote carcinogenesis by enhancing EGFR signaling via distinctive mechanisms, exposing clinically relevant therapeutic vulnerabilities.

Rewired m6A epitranscriptomic networks link mutant p53 to neoplastic transformation

N6-methyladenosine (m6A), one of the most prevalent mRNA modifications in eukaryotes, plays a critical role in modulating both biological and pathological processes. However, it is unknown whether mutant p53 neomorphic oncogenic functions exploit dysregulation of m6A epitranscriptomic networks. Here, we investigate Li-Fraumeni syndrome (LFS)-associated neoplastic transformation driven by mutant p53 in iPSC-derived astrocytes, the cell-of-origin of gliomas. We find that mutant p53 but not wild-type (WT) p53 physically interacts with SVIL to recruit the H3K4me3 methyltransferase MLL1 to activate the expression of m6A reader YTHDF2, culminating in an oncogenic phenotype. Aberrant YTHDF2 upregulation markedly hampers expression of multiple m6A-marked tumor-suppressing transcripts, including CDKN2B and SPOCK2, and induces oncogenic reprogramming. Mutant p53 neoplastic behaviors are significantly impaired by genetic depletion of YTHDF2 or by pharmacological inhibition using MLL1 complex inhibitors. Our study reveals how mutant p53 hijacks epigenetic and epitranscriptomic machinery to initiate gliomagenesis and suggests potential treatment strategies for LFS gliomas.

Common activities and predictive gene signature identified for genetic hypomorphs of TP53

Missense mutations that inactivate p53 occur commonly in cancer, and germline mutations in TP53 cause Li Fraumeni syndrome, which is associated with early-onset cancer. In addition, there are over two hundred germline missense variants of p53 that remain uncharacterized. In some cases, these germline variants have been shown to encode lesser-functioning, or hypomorphic, p53 protein, and these alleles are associated with increased cancer risk in humans and mouse models. However, most hypomorphic p53 variants remain un- or mis-classified in clinical genetics databases. There thus exists a significant need to better understand the behavior of p53 hypomorphs and to develop a functional assay that can distinguish hypomorphs from wild-type p53 or benign variants. We report the surprising finding that two different African-centric genetic hypomorphs of p53 that occur in distinct functional domains of the protein share common activities. Specifically, the Pro47Ser variant, located in the transactivation domain, and the Tyr107His variant, located in the DNA binding domain, both share increased propensity to misfold into a conformation specific for mutant, misfolded p53. Additionally, cells and tissues containing these hypomorphic variants show increased NF-κB activity. We identify a common gene expression signature from unstressed lymphocyte cell lines that is shared between multiple germline hypomorphic variants of TP53, and which successfully distinguishes wild-type p53 and a benign variant from lesser-functioning hypomorphic p53 variants. Our findings will allow us to better understand the contribution of p53 hypomorphs to disease risk and should help better inform cancer risk in the carriers of p53 variants.

Role of p53 in breast cancer progression: An insight into p53 targeted therapy

The transcription factor p53 is an important regulator of a multitude of cellular processes. In the presence of genotoxic stress, p53 is activated to facilitate DNA repair, cell cycle arrest, and apoptosis. In breast cancer, the tumor suppressive activities of p53 are frequently inactivated by either the overexpression of its negative regulator MDM2, or mutation which is present in 30-35% of all breast cancer cases. Notably, the frequency of p53 mutation is highly subtype dependent in breast cancers, with majority of hormone receptor-positive or luminal subtypes retaining the wild-type p53 status while hormone receptor-negative patients predominantly carry p53 mutations with gain-of-function oncogenic activities that contribute to poorer prognosis. Thus, a two-pronged strategy of targeting wild-type and mutant p53 in different subtypes of breast cancer can have clinical relevance. The development of p53-based therapies has rapidly progressed in recent years, and include unique small molecule chemical inhibitors, stapled peptides, PROTACs, as well as several genetic-based approaches using vectors and engineered antibodies. In this review, we highlight the therapeutic strategies that are in pre-clinical and clinical development to overcome p53 inactivation in both wild-type and mutant p53-bearing breast tumors, and discuss their efficacies and limitations in pre-clinical and clinical settings.

The C-terminus of Gain-of-Function Mutant p53 R273H Is Required for Association with PARP1 and Poly-ADP-Ribose

The TP53 gene is mutated in 80% of triple-negative breast cancers. Cells that harbor the hot-spot p53 gene mutation R273H produce an oncogenic mutant p53 (mtp53) that enhances cell proliferative and metastatic properties. The enhanced activities of mtp53 are collectively referred to as gain-of-function (GOF), and may include transcription-independent chromatin-based activities shared with wild-type p53 (wtp53) such as association with replicating DNA and DNA replication associated proteins like PARP1. However, how mtp53 upregulates cell proliferation is not well understood. wtp53 interacts with PARP1 using a portion of its C-terminus. The wtp53 oligomerization and far C-terminal domain (CTD) located within the C-terminus constitute putative GOF-associated domains, because mtp53 R273H expressing breast cancer cells lacking both domains manifest slow proliferation phenotypes. We addressed if the C-terminal region of mtp53 R273H is important for chromatin interaction and breast cancer cell proliferation using CRISPR-Cas9 mutated MDA-MB-468 cells endogenously expressing mtp53 R273H C-terminal deleted isoforms (R273HΔ381-388 and R273HΔ347-393). The mtp53 R273HΔ347-393 lacks the CTD and a portion of the oligomerization domain. We observed that cells harboring mtp53 R273HΔ347-393 (compared with mtp53 R273H full-length) manifest a significant reduction in chromatin, PARP1, poly-ADP-ribose (PAR), and replicating DNA binding. These cells also exhibited impaired response to hydroxyurea replicative stress, decreased sensitivity to the PARP-trapping drug combination temozolomide-talazoparib, and increased phosphorylated 53BP1 foci, suggesting reduced Okazaki fragment processing.

IMPLICATIONS

The C-terminal region of mtp53 confers GOF activity that mediates mtp53-PARP1 and PAR interactions assisting DNA replication, thus implicating new biomarkers for PARP inhibitor therapy.

Elevated NRAS expression during DCIS is a potential driver for progression to basal-like properties and local invasiveness

BACKGROUND

Ductal carcinoma in situ (DCIS) is the most common type of in situ premalignant breast cancers. What drives DCIS to invasive breast cancer is unclear. Basal-like invasive breast cancers are aggressive. We have previously shown that NRAS is highly expressed selectively in basal-like subtypes of invasive breast cancers and can promote their growth and progression. In this study, we investigated whether NRAS expression at the DCIS stage can control transition from luminal DCIS to basal-like invasive breast cancers.

METHODS

Wilcoxon rank-sum test was performed to assess expression of NRAS in DCIS compared to invasive breast tumors in patients. NRAS mRNA levels were also determined by fluorescence in situ hybridization in patient tumor microarrays (TMAs) with concurrent normal, DCIS, and invasive breast cancer, and association of NRAS mRNA levels with DCIS and invasive breast cancer was assessed by paired Wilcoxon signed-rank test. Pearson's correlation was calculated between NRAS mRNA levels and basal biomarkers in the TMAs, as well as in patient datasets. RNA-seq data were generated in cell lines, and unsupervised hierarchical clustering was performed after combining with RNA-seq data from a previously published patient cohort.

RESULTS

Invasive breast cancers showed higher NRAS mRNA levels compared to DCIS samples. These NRAShigh lesions were also enriched with basal-like features, such as basal gene expression signatures, lower ER, and higher p53 protein and Ki67 levels. We have shown previously that NRAS drives aggressive features in DCIS-like and basal-like SUM102PT cells. Here, we found that NRAS-silencing induced a shift to a luminal gene expression pattern. Conversely, NRAS overexpression in the luminal DCIS SUM225 cells induced a basal-like gene expression pattern, as well as an epithelial-to-mesenchymal transition signature. Furthermore, these cells formed disorganized mammospheres containing cell masses with an apparent reduction in adhesion.

CONCLUSIONS

These data suggest that elevated NRAS levels in DCIS are not only a marker but can also control the emergence of basal-like features leading to more aggressive tumor activity, thus supporting the therapeutic hypothesis that targeting NRAS and/or downstream pathways may block disease progression for a subset of DCIS patients with high NRAS.

Discovery of compounds that reactivate p53 mutants in vitro and in vivo

The tumor suppressor p53 is the most frequently mutated protein in human cancer. The majority of these mutations are missense mutations in the DNA binding domain of p53. Restoring p53 tumor suppressor function could have a major impact on the therapy for a wide range of cancers. Here we report a virtual screening approach that identified several small molecules with p53 reactivation activities. The UCI-LC0023 compound series was studied in detail and was shown to bind p53, induce a conformational change in mutant p53, restore the ability of p53 hotspot mutants to associate with chromatin, reestablish sequence-specific DNA binding of a p53 mutant in a reconstituted in vitro system, induce p53-dependent transcription programs, and prevent progression of tumors carrying mutant p53, but not p53null or p53WT alleles. Our study demonstrates feasibility of a computation-guided approach to identify small molecule corrector drugs for p53 hotspot mutations.

DAXX-ATRX regulation of p53 chromatin binding and DNA damage response

DAXX and ATRX are tumor suppressor proteins that form a histone H3.3 chaperone complex and are frequently mutated in cancers with the alternative lengthening of telomeres (ALT). Here, we show that DAXX and ATRX knock-out (KO) U87-T cells that have acquired ALT-like features have defects in p53 chromatin binding and DNA damage response. RNA-seq analysis revealed that p53 pathway is among the most perturbed. ChIP-seq and ATAC-seq revealed a genome-wide reduction in p53 DNA-binding and corresponding loss of chromatin accessibility at many p53 response elements across the genome. Both DAXX and ATRX null cells showed a depletion of histone H3.3 and accumulation of γH2AX at many p53 sites, including subtelomeres. These findings indicate that loss of DAXX or ATRX can compromise p53 chromatin binding and p53 DNA damage response in ALT-like cells, providing a link between histone composition, chromatin accessibility and tumor suppressor function of p53.

Predictors of Long-Term Survival in Pancreatic Ductal Adenocarcinoma after Pancreatectomy: TP53 and SMAD4 Mutation Scoring in Combination with CA19-9

BACKGROUND

Pancreatic ductal adenocarcinoma (PDA) is a fatal cancer for which even unfavorable clinicopathological factors occasionally fail to preclude long-term survival. We sought to establish a scoring system that utilizes measurable pre-intervention factors for predicting survival following surgical resection.

METHODS

We retrospectively analyzed 34 patients who died from short-term recurrences and 32 long-term survivors among 310 consecutively resected patients with PDA. A logistic regression model was used to define factors related to clinical parameters, molecular profiles of 18 pancreatic cancer-associated genes, and aberrant expression of major tumor suppressors.

RESULTS

Carbohydrate antigen 19-9 (CA19-9) had the best ability to classify patients with short-term recurrence and long-term survivors [odds ratio 21.04, 95% confidence interval (CI) 4.612-96.019], followed by SMAD4 and TP53 mutation scoring (odds ratio 41.322, 95% CI 3.156-541.035). Missense TP53 mutations were strongly associated with the nuclear expression of p53, whereas truncating mutations were associated with the absence of nuclear p53. The former subset was associated with a worse prognosis. The combination of aberrant SMAD4 and mutation types of TP53 exhibited a better resolution for distinguishing patients with short-term recurrences from long-term survivors (compared with the assessment of the number of mutated KRAS, CDKN2A, TP53, and SMAD4 genes). Calibration of mutation scores combined with CA19-9 in a logistic regression model setting demonstrated a practical effect in classifying long survivors and patients with early recurrence (c-statistic = 0.876).

CONCLUSIONS

Genetic information, i.e., TP53 mutation types and SMAD4 abnormalities, combined with CA19-9, will be a valuable tool for improving surgical strategies for pancreatic cancer.

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.

Novel protein contact points among TP53 and minichromosome maintenance complex proteins 2, 3, and 5

OBJECTIVE

Identify protein contact points between TP53 and minichromosome maintenance (MCM) complex proteins 2, 3, and 5 with high resolution allowing for potential novel Cancer drug design.

METHODS

A next-generation sequencing-based protein-protein interaction method developed in our laboratory called AVA-Seq was applied to a gold-standard human protein interaction set. Proteins including TP53, MCM2, MCM3, MCM5, HSP90AA1, PCNA, NOD1, and others were sheared and ligated into the AVA-Seq system. Protein-protein interactions were then identified in both mild and stringent selective conditions.

RESULTS

Known interactions among MCM2, MCM3, and MCM5 were identified with the AVA-Seq system. The interacting regions detected between these three proteins overlap with the structural data of the MCM complex, and novel domains were identified with high resolution determined by multiple overlapping fragments. Fragments of wild type TP53 were shown to interact with MCM2, MCM3, and MCM5, and details on the location of the interactions were provided. Finally, a mini-network of known and novel cancer protein interactions was provided, which could have implications for fundamental changes in multiple cancers.

CONCLUSION

We provide a high-resolution mini-interactome that could direct novel drug targets and implicate possible effects of specific cancer mutations.

Mutant p53: it's not all one and the same

Mutation of the TP53 tumor suppressor gene is the most common genetic alteration in cancer, and almost 1000 alleles have been identified in human tumors. While virtually all TP53 mutations are thought to compromise wild type p53 activity, the prevalence and recurrence of missense TP53 alleles has motivated countless research studies aimed at understanding the function of the resulting mutant p53 protein. The data from these studies support three distinct, but perhaps not necessarily mutually exclusive, mechanisms for how different p53 mutants impact cancer: first, they lose the ability to execute wild type p53 functions to varying degrees; second, they act as a dominant negative (DN) inhibitor of wild type p53 tumor-suppressive programs; and third, they may gain oncogenic functions that go beyond mere p53 inactivation. Of these possibilities, the gain of function (GOF) hypothesis is the most controversial, in part due to the dizzying array of biological functions that have been attributed to different mutant p53 proteins. Herein we discuss the current state of understanding of TP53 allele variation in cancer and recent reports that both support and challenge the p53 GOF model. In these studies and others, researchers are turning to more systematic approaches to profile TP53 mutations, which may ultimately determine once and for all how different TP53 mutations act as cancer drivers and whether tumors harboring distinct mutations are phenotypically unique. From a clinical perspective, such information could lead to new therapeutic approaches targeting the effects of different TP53 alleles and/or better sub-stratification of patients harboring TP53 mutant cancers.

Endometrial Carcinoma as the Presenting Malignancy in a Teenager With a Pathogenic TP53 Germline Mutation: A Case Report and Literature Review

Patients with germline TP53 mutations are characterized by the occurrence of multiple early-onset malignancies. The characteristic syndrome is Li-Fraumeni syndrome (OMIM # 151623), an autosomal dominant disorder typified by premenopausal breast carcinoma, adrenal cortical tumors, bone and soft tissue sarcomas, leukemias, and tumors of the brain and spinal cord. Gynecologic malignancies are uncommonly reported in families harboring TP53 mutations, and the predominant tumor type reported is ovarian. Uterine carcinoma has been reported only a handful of times in patients with germline TP53 mutations, none as a presenting tumor in a teenager. We report on an 18-year-old patient who presented with grade 3, high-stage endometrioid endometrial carcinoma. Sequencing detected a single-nucleotide substitution in the TP53 gene (NM_000546.6:c.818G>A), encoding the missense substitution p.Arg273His (R273H) in both the tumor and normal tissue, consistent with a germline mutation. We discuss the biology of the TP53 gene and p53 protein, with emphasis on the R273H mutation. We also review the literature on endometrial carcinoma in patients with germline TP53 mutations.

Cross-talk between mutant p53 and p62/SQSTM1 augments cancer cell migration by promoting the degradation of cell adhesion proteins

Missense mutations in the TP53 gene, encoding the p53 tumor suppressor, are very frequent in human cancer. Some of those mutations, particularly the more common (“hotspot”) ones, not only abrogate p53’s tumor suppressor activities but also endow the mutant protein with oncogenic gain of function (GOF). We report that p53^R273H, the most common p53 mutant in pancreatic cancer, interacts with the SQSTM1/p62 protein to accelerate the degradation of cell adhesion proteins. This enables pancreatic cancer cells to detach from the epithelial sheet and engage in individualized cell migration, probably augmenting metastatic spread. By providing insights into mechanisms that underpin mutant p53 GOF, this study may suggest ways to interfere with the progression of cancers bearing particular p53 mutants.

Missense mutations in the p53 tumor suppressor abound in human cancer. Common (“hotspot”) mutations endow mutant p53 (mutp53) proteins with oncogenic gain of function (GOF), including enhanced cell migration and invasiveness, favoring cancer progression. GOF is usually attributed to transcriptional effects of mutp53. To elucidate transcription-independent effects of mutp53, we characterized the protein interactome of the p53^R273H mutant in cells derived from pancreatic ductal adenocarcinoma (PDAC), where p53^R273H is the most frequent p53 mutant. We now report that p53^R273H, but not the p53^R175H hotspot mutant, interacts with SQSTM1/p62 and promotes cancer cell migration and invasion in a p62-dependent manner. Mechanistically, the p53^R273H-p62 axis drives the proteasomal degradation of several cell junction–associated proteins, including the gap junction protein Connexin 43, facilitating scattered cell migration. Concordantly, down-regulation of Connexin 43 augments PDAC cell migration, while its forced overexpression blunts the promigratory effect of the p53^R273H-p62 axis. These findings define a mechanism of mutp53 GOF.

p53 and Zinc: A Malleable Relationship

A large percentage of transcription factors require zinc to bind DNA. In this review, we discuss what makes p53 unique among zinc-dependent transcription factors. The conformation of p53 is unusually malleable: p53 binds zinc extremely tightly when folded, but is intrinsically unstable in the absence of zinc at 37°C. Whether the wild-type protein folds in the cell is largely determined by the concentration of available zinc. Consequently, zinc dysregulation in the cell as well as a large percentage of tumorigenic p53 mutations can cause p53 to lose zinc, misfold, and forfeit its tumor suppressing activity. We highlight p53’s noteworthy biophysical properties that give rise to its malleability and how proper zinc binding can be restored by synthetic metallochaperones to reactivate mutant p53. The activity and mechanism of metallochaperones are compared to those of other mutant p53-targeted drugs with an emphasis on those that have reached the clinical trial stage.

Mutant p53 achieved Gain-of-Function by promoting tumor growth and immune escape through PHLPP2/AKT/PD-L1 pathway

The most frequent genetic alterations of the TP53 gene in human cancer were reported. TP53 mutation gains new function as a target of genetic instability, which is associated with increased tumor progression and poor survival rate in patients. In this study, more than three hundred colorectal cancer patients' samples were firstly analyzed, and the results showed that patients with mutant p53 had higher levels of AKT phosphorylation and PD-L1 expression, which were next verified both in cell lines in vitro and patients' samples in vivo. Further studies demonstrated that the hotspot of mutant p53 directly binds to the promoter of PHLPP2 to inhibit its transcription, and resulting in down-regulating its protein expressional level. Subsequently, AKT was released and activated, promoting tumor proliferation and metastasis. In parallel, 4EBP1/eIF4E was identified as downstream executors of AKT to enhance the translational level of PD-L1, which decreased the activation of T cells. Besides, inhibiting AKT/mTOR pathway significantly suppressed PD-L1 expression, tumor growth, and immune escape in p53 mutated cells. In conclusion, mutant p53 achieved its Gain-of-Function by transcriptionally inhibiting PHLPP2 and activating AKT, which suppresses immune response and advances tumor growth. Thus, this study provides an excellent basis for a further understanding of the clinical treatment of neoplastic diseases for patients with mutant p53, with an emphasis on immunotherapy.

Mutational Characteristics of Primary Mucosal Melanoma: A Systematic Review

BACKGROUND

Primary mucosal melanomas (PMMs) are rare and clinically heterogeneous, including head and neck (HNMs), vulvovaginal (VVMs), conjunctival (CjMs), anorectal (ARMs) and penile (PMs) melanomas. While the prognosis of advanced cutaneous melanoma has noticeably improved using treatments with immune checkpoint inhibitors (ICIs) and molecules targeting BRAF and MEK, few advances have been made for PMMs because of their poorer response to ICIs and their different genetic profile. This prompted us to conduct a systematic review of molecular studies of PMMs to clarify their pathogenesis and potential therapeutic targets.

METHODS

All articles that examined gene mutations in PMMs were identified from the databases and selected based on predefined inclusion criteria. Mutation rate was calculated for all PMMs and each location group by relating the number of mutations identified to the total number of samples analysed.

RESULTS

Among 1,581 studies identified, 88 were selected. Overall, the frequency of KIT, BRAF and NRAS mutation was 13.5%, 12.9% and 12.1%, respectively. KIT mutation ranged from 6.4% for CjMs to 16.6% for ARMs, BRAF mutation from 8.6% for ARMs to 31.1% for CjMs, and NRAS mutation from 6.2% for ARMs to 18.5% for CjMs. Among 101 other genes analysed, 33 had mutation rates over 10%, including TTN, TSC1, POM121, NF1, MTOR and SF3B1.

CONCLUSION

In addition to BRAF, NRAS and KIT genes commonly studied, our systematic review identified significantly mutated genes that have already been associated (e.g., TSC1, mTOR, POLE or ATRX) or could be associated with (future) targeted therapies.

PROSPERO ID

CRD42020185552.

Etoposide-induced DNA damage is increased in p53 mutants: identification of ATR and other genes that influence effects of p53 mutations on Top2-induced cytotoxicity

The functional status of the tumor suppressor p53 is a critical component in determining the sensitivity of cancer cells to many chemotherapeutic agents. DNA topoisomerase II (Top2) plays essential roles in DNA metabolism and is the target of FDA approved chemotherapeutic agents. Topoisomerase targeting drugs convert the enzyme into a DNA damaging agent and p53 influences cellular responses to these agents. We assessed the impact of the loss of p53 function on the formation of DNA damage induced by the Top2 poison etoposide. Using human HCT116 cells, we found resistance to etoposide in cell growth assays upon the functional loss of p53. Nonetheless, cells lacking fully functional p53 were etoposide hypersensitive in clonogenic survival assays. This complex role of p53 led us to directly examine the effects of p53 status on topoisomerase-induced DNA damage. A deficiency in functional p53 resulted in elevated levels of the Top2 covalent complexes (Top2cc) in multiple cell lines. Employing genome-wide siRNA screens, we identified a set of genes for which reduced expression resulted in enhanced synthetic lethality upon etoposide treatment of p53 defective cells. We focused on one hit from this screen, ATR, and showed that decreased expression sensitized the p53-defective cells to etoposide in all assays and generated elevated levels of Top2cc in both p53 proficient and deficient cells. Our findings suggest that a combination of etoposide treatment with functional inactivation of DNA repair in p53 defective cells could be used to enhance the therapeutic efficacy of Top2 targeting agents.

The dominant TP53 hotspot mutation in -mutant astrocytoma, R273C, has distinctive pathologic features and sex-specific prognostic implications

BACKGROUND

Infiltrative astrocytic tumors with and without isocitrate dehydrogenase (IDH) mutation frequently contain mutations in the TP53 tumor suppressor gene. Disruption of normal p53 protein activity confers neoplastic cells with a number of oncogenic properties and is a common feature of aggressive malignancies. However, the high prevalence of TP53 mutation and its pathogenic role in IDH-mutant (IDHmut) astrocytoma is not well understood.

METHODS

We performed a retrospective analysis of molecular and clinical data from patients with IDHmut astrocytoma at the University of Pittsburgh Medical Center between 2015 and 2019 as our initial cohort. We validated and expanded our findings using molecular and clinical data from The Cancer Genome Atlas.

RESULTS

We show that the TP53 mutational spectrum in IDHmut astrocytomas is dominated by a single hotspot mutation that codes for the R273C amino acid change. This mutation is not enriched in IDH-wildtype astrocytomas. The high prevalence of TP53 R273C mutation is not readily explained by known mutagenic mechanisms, and TP53 R273C mutant tumors have lower transcriptional levels of proliferation-related genes compared to IDHmut astrocytomas harboring other forms of mutant p53. Despite lower proliferation, TP53 R273C mutant tumors tend to progress more quickly and have a shorter overall survival than those with other TP53 mutations, particularly in male patients.

CONCLUSIONS

Our findings suggest that compared to other TP53 mutations, IDHmut astrocytomas may select for TP53 R273C mutations during tumorigenesis. The genotype, sex, and mutation-specific findings are clinically relevant and should prompt further investigation of TP53 R273C.

Oligomerization of Mutant p53 R273H is not Required for Gain-of-Function Chromatin Associated Activities

The TP53 gene is often mutated in cancer, with missense mutations found in the central DNA binding domain, and less often in the C-terminal oligomerization domain (OD). These types of mutations are found in patients with the rare inherited cancer predisposition disorder called Li-Fraumeni syndrome. We previously found that mutant p53 (mtp53) R273H associates with replicating DNA and promotes the chromatin association of replication-associated proteins mini-chromosome maintenance 2 (MCM2), and poly ADP-ribose polymerase 1(PARP1). Herein, we created dual mutants in order to test if the oligomerization state of mtp53 R273H played a role in chromatin binding oncogenic gain-of-function (GOF) activities. We used site-directed mutagenesis to introduce point mutations in the OD in wild-type p53 (wtp53), and mtp53 R273H expressing plasmids. The glutaraldehyde crosslinking assay revealed that both wtp53 and mtp53 R273H formed predominantly tetramers, while the single OD mutant A347D, and the dual mtp53 R273H-A347D, formed predominantly dimers. The R337C, L344P, mtp53 R273H-R337C, and mtp53 R273H-L344P proteins formed predominantly monomers. Wtp53 was able to activate the cyclin-dependent kinase gene p21/waf and the p53 feedback regulator MDM2. As expected, the transactivation activity was lost for all the single mutants, as well as the mtp53 R273H-dual mutants. Importantly, mtp53 R273H and the dual oligomerization mutants, R273H-A347D, R273H-R337C, and R273H-L344P were able to interact with chromatin. Additionally, the dual oligomerization mutants, R273H-A347D, R273H-R337C, and R273H-L344P, maintained strong interactions with MCM2 and PARP1. Our findings suggest that while mtp53 R273H can form tetramers, tetramer formation is not required for the GOF associated chromatin interactions.

Targeting the DIO3 enzyme using first-in-class inhibitors effectively suppresses tumor growth: a new paradigm in ovarian cancer treatment

The enzyme iodothyronine deiodinase type 3 (DIO3) contributes to cancer proliferation by inactivating the tumor-suppressive actions of thyroid hormone (T3). We recently established DIO3 involvement in the progression of high-grade serous ovarian cancer (HGSOC). Here we provide a link between high DIO3 expression and lower survival in patients, similar to common disease markers such as Ki67, PAX8, CA-125, and CCNE1. These observations suggest that DIO3 is a logical target for inhibition. Using a DIO3 mimic, we developed original DIO3 inhibitors that contain a core of dibromomaleic anhydride (DBRMD) as scaffold. Two compounds, PBENZ-DBRMD and ITYR-DBRMD, demonstrated attenuated cell counts, induction in apoptosis, and a reduction in cell proliferation in DIO3-positive HGSOC cells (OVCAR3 and KURAMOCHI), but not in DIO3-negative normal ovary cells (CHOK1) and OVCAR3 depleted for DIO3 or its substrate, T3. Potent tumor inhibition with a high safety profile was further established in HGSOC xenograft model, with no effect in DIO3-depleted tumors. The antitumor effects are mediated by downregulation in an array of pro-cancerous proteins, the majority of which known to be repressed by T3. To conclude, using small molecules that specifically target the DIO3 enzyme we present a new treatment paradigm for ovarian cancer and potentially other DIO3-dependent malignancies.

p53 isoforms differentially impact on the POLι dependent DNA damage tolerance pathway

The recently discovered p53-dependent DNA damage tolerance (DDT) pathway relies on its biochemical activities in DNA-binding, oligomerization, as well as complex formation with the translesion synthesis (TLS) polymerase iota (POLι). These p53-POLι complexes slow down nascent DNA synthesis for safe, homology-directed bypass of DNA replication barriers. In this study, we demonstrate that the alternative p53-isoforms p53β, p53γ, Δ40p53α, Δ133p53α, and Δ160p53α differentially affect this p53-POLι-dependent DDT pathway originally described for canonical p53α. We show that the C-terminal isoforms p53β and p53γ, comprising a truncated oligomerization domain (OD), bind PCNA. Conversely, N-terminally truncated isoforms have a reduced capacity to engage in this interaction. Regardless of the specific loss of biochemical activities required for this DDT pathway, all alternative isoforms were impaired in promoting POLι recruitment to PCNA in the chromatin and in decelerating DNA replication under conditions of enforced replication stress after Mitomycin C (MMC) treatment. Consistent with this, all alternative p53-isoforms no longer stimulated recombination, i.e., bypass of endogenous replication barriers. Different from the other isoforms, Δ133p53α and Δ160p53α caused a severe DNA replication problem, namely fork stalling even in untreated cells. Co-expression of each alternative p53-isoform together with p53α exacerbated the DDT pathway defects, unveiling impaired POLι recruitment and replication deceleration already under unperturbed conditions. Such an inhibitory effect on p53α was particularly pronounced in cells co-expressing Δ133p53α or Δ160p53α. Notably, this effect became evident after the expression of the isoforms in tumor cells, as well as after the knockdown of endogenous isoforms in human hematopoietic stem and progenitor cells. In summary, mimicking the situation found to be associated with many cancer types and stem cells, i.e., co-expression of alternative p53-isoforms with p53α, carved out interference with p53α functions in the p53-POLι-dependent DDT pathway.

PARP-Targeted Auger Therapy in p53 Mutant Colon Cancer Xenograft Mouse Models

Despite Auger electrons being highly appealing due to their short-range and high linear energy transfer to surrounding tissues, the progress in the field has been limited due to the challenge in delivering a therapeutic dose within the close proximity of cancer cell's DNA. Here, we demonstrate that the PARP inhibitor 123I-MAPi is a viable agent for the systemic administration and treatment of p53 mutant cancers. Significantly, minimal off-site toxicity was observed in mice administered with up to 74 MBq of 127I-PARPi. Taken together, these results lay the foundation for future clinical evaluation and broader preclinical investigations. By harnessing the scaffold of the PARP inhibitor Olaparib, we were able to deliver therapeutic levels of Auger radiation to the site of human colorectal cancer xenograft tumors after systemic administration. In-depth toxicity studies analyzed blood chemistry levels and markers associated with specific organ toxicity. Finally, p53+/+ and p53-/- human colorectal cancer cell lines were evaluated for the ability of 123I-MAPi to induce tumor growth delay. Toxicity studies demonstrate that both 123I-MAPi and its stable isotopologue, 127I-PARPi, have no significant off-site toxicity when administered systemically. Analysis following 123I-MAPi treatment confirmed its ability to induce DNA damage at the site of xenograft tumors when administered systemically. Finally, we demonstrate that 123I-MAPi generates a therapeutic response in p53-/-, but not p53+/+, subcutaneous xenograft tumors in mouse models. Taken together, these results represent the first example of a PARP Auger theranostic agent capable of delivering a therapeutic dose to xenograft human colorectal cancer tumors upon systemic administration without causing significant toxicity to surrounding mouse organs. Moreover, it suggests that a PARP Auger theranostic can act as a targeted therapeutic for cancers with mutated p53 pathways. This landmark goal paves the way for clinical evaluation of 123I-MAPi for pan cancer therapeutics.

Gain-of-function p53R172H mutation drives accumulation of neutrophils in pancreatic tumors, promoting resistance to immunotherapy

Tumor genotype can influence the immune microenvironment, which plays a critical role in cancer development and therapy resistance. However, the immune effects of gain-of-function Trp53 mutations have not been defined in pancreatic cancer. We compare the immune profiles generated by KrasG12D-mutated mouse pancreatic ductal epithelial cells (PDECs) engineered genetically to express the Trp53R172H mutation with their p53 wild-type control. KrasG12D/+;Trp53R172H/+ tumors have a distinct immune profile characterized by an influx of CD11b+Ly6G+ neutrophils and concomitant decreases in CD3+ T cells, CD8+ T cells, and CD4+ T helper 1 cells. Knockdown of CXCL2, a neutrophil chemokine, in the tumor epithelial compartment of CRISPR KrasG12D/+;Trp53R172H/+ PDEC tumors reverses the neutrophil phenotype. Neutrophil depletion of mice bearing CRISPR KrasG12D/+;Trp53R172H/+ tumors augments sensitivity to combined CD40 immunotherapy and chemotherapy. These data link Trp53R172H to the presence of intratumoral neutrophils in pancreatic cancer and suggest that tumor genotypes could inform selection of affected individuals for immunotherapy.

Induction of Apoptosis and Autophagy by Ternary Copper Complex Towards Breast Cancer Cells

BACKGROUND

Copper complex has been gaining much attention in anticancer research as targeted agent since cancer cells uptake more copper than non-cancerous cells. Our group has synthesised a ternary copper complex which is composed of 1,10-phenanthroline and tyrosine [Cu(phen)(L-tyr)Cl].3H₂0. These two payloads are designed to cleave DNA and inhibit protein degradation system (proteasome) concurrently in cancer cells, making this copper complex a dual-target compound.

OBJECTIVE

Current study was carried out to investigate the mode of cell death and role of autophagy induced by [Cu(phen)(L-tyr)Cl].3H₂0 in MCF-7 and MDA-MB-231 breast cancer cells.

METHODS

Growth inhibition of [Cu(phen)(L-tyr)Cl].3H₂0 towards MDA-MB-231 and human non-cancerous MCF10A breast cells was determined by MTT assay. Annexin-V-FITC/PI and cell cycle analysis were evaluated by flow cytometry. The expression of p53, Bax, caspase-9, caspase-7, caspase-3 and LC3 were determined using western blot analysis. The cells were then co-treated with hydroxychloroquine to ascertain the role of autophagy induced by [Cu(phen)(L-tyr)Cl].3H₂0.

RESULTS

[Cu(phen)(L-tyr)Cl].3H20 inhibited the growth of cancer cells dose-dependently with less toxicity towards MCF10A cells. Additionally, [Cu(phen)(L-tyr)Cl].3H20 induced apoptosis and cell cycle arrest towards MCF-7 and MDA-MB-231 breast cancer cells possibly via regulation of p53, Bax, caspase-9, caspase-3 and capase-7. The expression of LC3II was upregulated in both cancer cell lines upon treatment with [Cu(phen)(L-tyr) Cl].3H₂0, indicating the induction of autophagy. Co-treatment with autophagy inhibitor hydroxychloroquine significantly enhanced growth inhibition of both cell lines, suggesting that the autophagy induced by [Cu(phen)(L-tyr) Cl].3H₂0 in both breast cancer cells was promoting cell survival.

CONCLUSION

[Cu(phen)(L-tyr)Cl].3H20 holds great potential to be developed for breast cancer treatment.

Frame-shift mediated reduction of gain-of-function p53 R273H and deletion of the R273H C-terminus in breast cancer cells result in replication-stress sensitivity

We recently documented that gain-of-function (GOF) mutant p53 (mtp53) R273H in triple negative breast cancer (TNBC) cells interacts with replicating DNA and PARP1. The missense R273H GOF mtp53 has a mutated central DNA binding domain that renders it unable to bind specifically to DNA, but maintains the capacity to interact tightly with chromatin. Both the C-terminal domain (CTD) and oligomerization domain (OD) of GOF mtp53 proteins are intact and it is unclear whether these regions of mtp53 are responsible for chromatin-based DNA replication activities. We generated MDA-MB-468 cells with CRISPR-Cas9 edited versions of the CTD and OD regions of mtp53 R273H. These included a frame-shift mtp53 R273Hfs387, which depleted mtp53 protein expression; mtp53 R273HΔ381-388, which had a small deletion within the CTD; and mtp53 R273HΔ347-393, which had both the OD and CTD regions truncated. The mtp53 R273HΔ347-393 existed exclusively as monomers and disrupted the chromatin interaction of mtp53 R273H. The CRISPR variants proliferated more slowly than the parental cells and mt53 R273Hfs387 showed the most extreme phenotype. We uncovered that after thymidine-induced G1/S synchronization, but not hydroxyurea or aphidicholin, R273Hfs387 cells displayed impairment of S-phase progression while both R273HΔ347-393 and R273HΔ381-388 displayed only moderate impairment. Moreover, reduced chromatin interaction of MCM2 and PCNA in mtp53 depleted R273Hfs387 cells post thymidine-synchronization revealed delayed kinetics of replisome assembly underscoring the slow S-phase progression. Taken together our findings show that the CTD and OD domains of mtp53 R273H play critical roles in mutant p53 GOF that pertain to processes associated with DNA replication.

Tumor suppressor p53 regulates intestinal type 2 immunity

The role of p53 in tumor suppression has been extensively studied and well-established. However, the role of p53 in parasitic infections and the intestinal type 2 immunity is unclear. Here, we report that p53 is crucial for intestinal type 2 immunity in response to the infection of parasites, such as Tritrichomonas muris and Nippostrongylus brasiliensis. Mechanistically, p53 plays a critical role in the activation of the tuft cell-IL-25-type 2 innate lymphoid cell circuit, partly via transcriptional regulation of Lrmp in tuft cells. Lrmp modulates Ca2+ influx and IL-25 release, which are critical triggers of type 2 innate lymphoid cell response. Our results thus reveal a previously unrecognized function of p53 in regulating intestinal type 2 immunity to protect against parasitic infections, highlighting the role of p53 as a guardian of immune integrity.