Molecular mechanism of mutant p53 stabilization: the role of HSP70 and MDM2

Knockout of Hsp70 genes significantly affects locomotion speed and gene expression in leg skeletal muscles of Drosophila melanogaster

The functions of the heat shock protein 70 (Hsp70) genes were studied using a line of Drosophila melanogaster with a knockout of 6 of these genes out of 13. Namely, the effect of knockout of Hsp70 genes on negative geotaxis climbing (locomotor) speed and the ability to adapt to climbing training (0.5-1.5 h/day, 7 days/wk, 19 days) were examined. Seven- and 23-day-old Hsp70- flies demonstrated a comparable reduction (twofold) in locomotor speed and widespread changes in leg skeletal muscle transcriptome (RNA sequencing) compared with w1118 flies. To identify the functions of genes related to decreased locomotor speed, the overlapped differentially expressed genes at both time points were analyzed: the upregulated genes encoded extracellular proteins, regulators of drug metabolism, and the antioxidant response, whereas downregulated genes encoded regulators of carbohydrate metabolism and transmembrane proteins. In addition, in Hsp70- flies, activation of transcription factors related to disruption of the fibril structure and heat shock response (Hsf) was predicted, using the position weight matrix approach. In control flies, adaptation to chronic exercise training was associated mainly with gene response to a single exercise bout, whereas the predicted transcription factors were related to stress/immune (Hsf, NF-κB, etc.) and early gene response. In contrast, Hsp70- flies demonstrated no adaptation to training as well as a significantly impaired gene response to a single exercise bout. In conclusion, the knockout of Hsp70 genes not only reduced physical performance but also disrupted adaptation to chronic physical training, which is associated with changes in the leg skeletal muscle transcriptome and impaired gene response to a single exercise bout.NEW & NOTEWORTHY Knockout of six heat shock protein 70 (Hsp70) genes in Drosophila melanogaster reduced locomotion (climbing) speed that is associated with genotype-specific differences in leg skeletal muscle gene expression. Disrupted adaptation of Hsp70- flies to chronic exercise training is associated with impaired gene response to a single exercise bout.

Recent Advances on Mutant p53: Unveiling Novel Oncogenic Roles, Degradation Pathways, and Therapeutic Interventions

The p53 protein is the master regulator of cellular integrity, primarily due to its tumor-suppressing functions. Approximately half of all human cancers carry mutations in the TP53 gene, which not only abrogate the tumor-suppressive functions but also confer p53 mutant proteins with oncogenic potential. The latter is achieved through so-called gain-of-function (GOF) mutations that promote cancer progression, metastasis, and therapy resistance by deregulating transcriptional networks, signaling pathways, metabolism, immune surveillance, and cellular compositions of the microenvironment. Despite recent progress in understanding the complexity of mutp53 in neoplastic development, the exact mechanisms of how mutp53 contributes to cancer development and how they escape proteasomal and lysosomal degradation remain only partially understood. In this review, we address recent findings in the field of oncogenic functions of mutp53 specifically regarding, but not limited to, its implications in metabolic pathways, the secretome of cancer cells, the cancer microenvironment, and the regulating scenarios of the aberrant proteasomal degradation. By analyzing proteasomal and lysosomal protein degradation, as well as its connection with autophagy, we propose new therapeutical approaches that aim to destabilize mutp53 proteins and deactivate its oncogenic functions, thereby providing a fundamental basis for further investigation and rational treatment approaches for TP53-mutated cancers.

A unique chaperoning mechanism in class A JDPs recognizes and stabilizes mutant p53

J-domain proteins (JDPs) constitute a large family of molecular chaperones that bind a broad spectrum of substrates, targeting them to Hsp70, thus determining the specificity of and activating the entire chaperone functional cycle. The malfunction of JDPs is therefore inextricably linked to myriad human disorders. Here, we uncover a unique mechanism by which chaperones recognize misfolded clients, present in human class A JDPs. Through a newly identified β-hairpin site, these chaperones detect changes in protein dynamics at the initial stages of misfolding, prior to exposure of hydrophobic regions or large structural rearrangements. The JDPs then sequester misfolding-prone proteins into large oligomeric assemblies, protecting them from aggregation. Through this mechanism, class A JDPs bind destabilized p53 mutants, preventing clearance of these oncoproteins by Hsp70-mediated degradation, thus promoting cancer progression. Removal of the β-hairpin abrogates this protective activity while minimally affecting other chaperoning functions. This suggests the class A JDP β-hairpin as a highly specific target for cancer therapeutics.

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

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

Novel insights into the post-translational modifications of Ydj1/DNAJA1 co-chaperones

The activity of the Hsp70 molecular chaperone is regulated by a suite of helper co-chaperones that include J-proteins. Studies on J-proteins have historically focused on their expression, localization, and activation of Hsp70. There is growing evidence that the post-translational modifications (PTMs) of chaperones (the chaperone code) fine-tune chaperone function. This mini-review summarizes the current understanding of the role and regulation of PTMs on the major J-proteins Ydj1 and DNAJA1. Understanding these PTMs may provide novel therapeutic avenues for targeting chaperone activity in cancer and neurodegenerative diseases.

Decoding the roles of heat shock proteins in liver cancer

Hepatocellular carcinoma (HCC) is one of the most common gastrointestinal malignancies, characterized by insidious onset and high propensity for metastasis and recurrence. Apart from surgical resection, there are no effective curative methods for HCC in recent years, due to resistance to radiotherapy and chemotherapy. Heat shock proteins (HSP) play a crucial role in maintaining cellular homeostasis and normal organism development as molecular chaperones for intracellular proteins. Both basic research and clinical data have shown that HSPs are crucial participants in the HCC microenvironment, as well as the occurrence, development, metastasis, and resistance to radiotherapy and chemotherapy in various malignancies, particularly liver cancer. This review aims to discuss the molecular mechanisms and potential clinical value of HSPs in HCC, which may provide new insights for HSP-based therapeutic interventions for HCC.

Amyloid-like p53 as prognostic biomarker in serous ovarian cancer-a study of the OVCAD consortium

TP53 is the most commonly mutated gene in cancer and has been shown to form amyloid-like aggregates, similar to key proteins in neurodegenerative diseases. Nonetheless, the clinical implications of p53 aggregation remain unclear. Here, we investigated the presence and clinical relevance of p53 aggregates in serous ovarian cancer (OC). Using the p53-Seprion-ELISA, p53 aggregates were detected in 46 out of 81 patients, with a detection rate of 84.3% in patients with missense mutations. High p53 aggregation was associated with prolonged progression-free survival. We found associations of overall survival with p53 aggregates, but they did not reach statistical significance. Interestingly, p53 aggregation was significantly associated with elevated levels of p53 autoantibodies and increased apoptosis, suggesting that high levels of p53 aggregates may trigger an immune response and/or exert a cytotoxic effect. To conclude, for the first time, we demonstrated that p53 aggregates are an independent prognostic marker in serous OC. P53-targeted therapies based on the amount of these aggregates may improve the patient's prognosis.

Targeting mutant p53 stabilization for cancer therapy

Over 50% cancer bears TP53 mutation, the highly stabilized mutant p53 protein drives the tumorigenesis and progression. Mutation of p53 not only cause loss-of-function and dominant-negative effects (DNE), but also results in the abnormal stability by the regulation of the ubiquitin-proteasome system and molecular chaperones that promote tumorigenesis through gain-of-function effects. The accumulation of mutant p53 is mainly regulated by molecular chaperones, including Hsp40, Hsp70, Hsp90 and other biomolecules such as TRIM21, BAG2 and Stat3. In addition, mutant p53 forms prion-like aggregates or complexes with other protein molecules and result in the accumulation of mutant p53 in tumor cells. Depleting mutant p53 has become one of the strategies to target mutant p53. This review will focus on the mechanism of mutant p53 stabilization and discuss how the strategies to manipulate these interconnected processes for cancer therapy.

How Driver Oncogenes Shape and Are Shaped by Alternative Splicing Mechanisms in Tumors

The development of RNA sequencing methods has allowed us to study and better understand the landscape of aberrant pre-mRNA splicing in tumors. Altered splicing patterns are observed in many different tumors and affect all hallmarks of cancer: growth signal independence, avoidance of apoptosis, unlimited proliferation, invasiveness, angiogenesis, and metabolism. In this review, we focus on the interplay between driver oncogenes and alternative splicing in cancer. On one hand, oncogenic proteins-mutant p53, CMYC, KRAS, or PI3K-modify the alternative splicing landscape by regulating expression, phosphorylation, and interaction of splicing factors with spliceosome components. Some splicing factors-SRSF1 and hnRNPA1-are also driver oncogenes. At the same time, aberrant splicing activates key oncogenes and oncogenic pathways: p53 oncogenic isoforms, the RAS-RAF-MAPK pathway, the PI3K-mTOR pathway, the EGF and FGF receptor families, and SRSF1 splicing factor. The ultimate goal of cancer research is a better diagnosis and treatment of cancer patients. In the final part of this review, we discuss present therapeutic opportunities and possible directions of further studies aiming to design therapies targeting alternative splicing mechanisms in the context of driver oncogenes.

p53 at the Crossroads between Doxorubicin-Induced Cardiotoxicity and Resistance: A Nutritional Balancing Act

Doxorubicin (DOX) is a highly effective chemotherapeutic drug, but its long-term use can cause cardiotoxicity and drug resistance. Accumulating evidence demonstrates that p53 is directly involved in DOX toxicity and resistance. One of the primary causes for DOX resistance is the mutation or inactivation of p53. Moreover, because the non-specific activation of p53 caused by DOX can kill non-cancerous cells, p53 is a popular target for reducing toxicity. However, the reduction in DOX-induced cardiotoxicity (DIC) via p53 suppression is often at odds with the antitumor advantages of p53 reactivation. Therefore, in order to increase the effectiveness of DOX, there is an urgent need to explore p53-targeted anticancer strategies owing to the complex regulatory network and polymorphisms of the p53 gene. In this review, we summarize the role and potential mechanisms of p53 in DIC and resistance. Furthermore, we focus on the advances and challenges in applying dietary nutrients, natural products, and other pharmacological strategies to overcome DOX-induced chemoresistance and cardiotoxicity. Lastly, we present potential therapeutic strategies to address key issues in order to provide new ideas for increasing the clinical use of DOX and improving its anticancer benefits.

Diverse rescue potencies of p53 mutations to ATO are predetermined by intrinsic mutational properties

Tumor suppressor p53 is inactivated by thousands of heterogeneous mutations in cancer, but their individual druggability remains largely elusive. Here, we evaluated 800 common p53 mutants for their rescue potencies by the representative generic rescue compound arsenic trioxide (ATO) in terms of transactivation activity, cell growth inhibition, and mouse tumor-suppressive activities. The rescue potencies were mainly determined by the solvent accessibility of the mutated residue, a key factor determining whether a mutation is a structural one, and the temperature sensitivity, the ability to reassemble the wild-type DNA binding surface at a low temperature, of the mutant protein. A total of 390 p53 mutants were rescued to varying degrees and thus were termed as type 1, type 2a, and type 2b mutations, depending on the degree to which they were rescued. The 33 type 1 mutations were rescued to amounts comparable to the wild type. In PDX mouse trials, ATO preferentially inhibited growth of tumors harboring type 1 and type 2a mutants. In an ATO clinical trial, we report the first-in-human mutant p53 reactivation in a patient harboring the type 1 V272M mutant. In 47 cell lines derived from 10 cancer types, ATO preferentially and effectively rescued type 1 and type 2a mutants, supporting the broad applicability of ATO in rescuing mutant p53. Our study provides the scientific and clinical communities with a resource of the druggabilities of numerous p53 mutations (www.rescuep53.net) and proposes a conceptual p53-targeting strategy based on individual mutant alleles rather than mutation type.

HSP70 Family in Cancer: Signaling Mechanisms and Therapeutic Advances

The 70 kDa heat shock proteins (HSP70s) are a group of highly conserved and inducible heat shock proteins. One of the main functions of HSP70s is to act as molecular chaperones that are involved in a large variety of cellular protein folding and remodeling processes. HSP70s are found to be over-expressed and may serve as prognostic markers in many types of cancers. HSP70s are also involved in most of the molecular processes of cancer hallmarks as well as the growth and survival of cancer cells. In fact, many effects of HSP70s on cancer cells are not only related to their chaperone activities but rather to their roles in regulating cancer cell signaling. Therefore, a number of drugs directly or indirectly targeting HSP70s, and their co-chaperones have been developed aiming to treat cancer. In this review, we summarized HSP70-related cancer signaling pathways and corresponding key proteins regulated by the family of HSP70s. In addition, we also summarized various treatment approaches and progress of anti-tumor therapy based on targeting HSP70 family proteins.

Association of Hsp90 with p53 and Fizzy related homolog (Fzr) synchronizing Anaphase Promoting Complex (APC/C): An unexplored ally towards oncogenic pathway

The intricate molecular interactions leading to the oncogenic pathway are the consequence of cell cycle modification controlled by a bunch of cell cycle regulatory proteins. The tumor suppressor and cell cycle regulatory proteins work in coordination to maintain a healthy cellular environment. The integrity of this cellular protein pool is perpetuated by heat shock proteins/chaperones, which assist in proper protein folding during normal and cellular stress conditions. Among these versatile groups of chaperone proteins, Hsp90 is one of the significant ATP-dependent chaperones that aid in stabilizing many tumor suppressors and cell cycle regulator protein targets. Recently, studies have revealed that in cancerous cell lines, Hsp90 stabilizes mutant p53, 'the guardian of the genome.' Hsp90 also has a significant impact on Fzr, an essential regulator of the cell cycle having an important role in the developmental process of various organisms, including Drosophila, yeast, Caenorhabditis elegans, and plants. During cell cycle progression, p53 and Fzr coordinately regulate the Anaphase Promoting Complex (APC/C) from metaphase to anaphase transition up to cell cycle exit. APC/C mediates proper centrosome function in the dividing cell. The centrosome acts as the microtubule organizing center for the correct segregation of the sister chromatids to ensure perfect cell division. This review examines the structure of Hsp90 and its co-chaperones, which work in synergy to stabilize proteins such as p53 and Fizzy-related homolog (Fzr) to synchronize the Anaphase Promoting Complex (APC/C). Dysfunction of this process activates the oncogenic pathway leading to the development of cancer. Additionally, an overview of current drugs targeting Hsp90 at various phases of clinical trials has been included.

Targeting p53 pathways: mechanisms, structures, and advances in therapy

The TP53 tumor suppressor is the most frequently altered gene in human cancers, and has been a major focus of oncology research. The p53 protein is a transcription factor that can activate the expression of multiple target genes and plays critical roles in regulating cell cycle, apoptosis, and genomic stability, and is widely regarded as the "guardian of the genome". Accumulating evidence has shown that p53 also regulates cell metabolism, ferroptosis, tumor microenvironment, autophagy and so on, all of which contribute to tumor suppression. Mutations in TP53 not only impair its tumor suppressor function, but also confer oncogenic properties to p53 mutants. Since p53 is mutated and inactivated in most malignant tumors, it has been a very attractive target for developing new anti-cancer drugs. However, until recently, p53 was considered an "undruggable" target and little progress has been made with p53-targeted therapies. Here, we provide a systematic review of the diverse molecular mechanisms of the p53 signaling pathway and how TP53 mutations impact tumor progression. We also discuss key structural features of the p53 protein and its inactivation by oncogenic mutations. In addition, we review the efforts that have been made in p53-targeted therapies, and discuss the challenges that have been encountered in clinical development.

Expression Levels of GHRH-Receptor, pAkt and Hsp90 Predict 10-Year Overall Survival in Patients with Locally Advanced Rectal Cancer

Background: Rectal cancer constitutes nearly one-third of all colorectal cancer diagnoses, and certain clinical and molecular markers have been studied as potential prognosticators of patient survival. The main objective of our study was to investigate the relationship between the expression intensities of certain proteins, including growth-hormone-releasing hormone receptor (GHRH-R), Hsp90, Hsp16.2, p-Akt and SOUL, in specimens of locally advanced rectal cancer patients, as well as the time to metastasis and 10-year overall survival (OS) rates. We also investigated whether these outcome measures were associated with the presence of other clinical parameters. Methods: In total, 109 patients were investigated retrospectively. Samples of pretreatment tumors were stained for the proteins GHRH-R, Hsp90, Hsp16.2, p-Akt and SOUL using immunhistochemistry methods. Kaplan–Meier curves were used to show the relationships between the intensity of expression of biomarkers, clinical parameters, the time to metastasis and the 10-year OS rate. Results: High levels of p-Akt, GHRH-R and Hsp90 were associated with a significantly decreased 10-year OS rate (p = 0.001, p = 0.000, p = 0.004, respectively) and high expression levels of p-Akt and GHRH-R were correlated with a significantly shorter time to metastasis. Tumors localized in the lower third of the rectum were linked to both a significantly longer time to metastasis and an improved 10-year OS rate. Conclusions: Hsp 90, pAkt and GHRH-R as well as the lower-third localization of the tumor were predictive of the 10-year OS rate in locally advanced rectal cancer patients. The GHRH-R and Hsp90 expression levels were independent prognosticators of OS. Our results imply that GHRH-R could play a particularly important role both as a molecular biomarker and as a target for the anticancer treatment of advanced rectal cancer.

Transition of amyloid/mutant p53 from tumor suppressor to an oncogene and therapeutic approaches to ameliorate metastasis and cancer stemness

The tumor suppressor p53 when undergoes amyloid formation confers several gain-of-function (GOF) activities that affect molecular pathways crucial for tumorigenesis and progression like some of the p53 mutants. Even after successful cancer treatment, metastasis and recurrence can result in poor survival rates. The major cause of recurrence is mainly the remnant cancer cells with stem cell-like properties, which are resistant to any chemotherapy treatment. Several studies have demonstrated the role of p53 mutants in exacerbating cancer stemness properties and epithelial-mesenchymal transition in these remnant cancer cells. Analyzing the amyloid/mutant p53-mediated signaling pathways that trigger metastasis, relapse or chemoresistance may be helpful for the development of novel or improved individualized treatment plans. In this review, we discuss the changes in the metabolic pathways such as mevalonate pathway and different signaling pathways such as TGF-β, PI3K/AKT/mTOR, NF-κB and Wnt due to p53 amyloid formation, or mutation. In addition to this, we have discussed the role of the regulatory microRNAs and lncRNAs linked with the mutant or amyloid p53 in human malignancies. Such changes promote tumor spread, potential recurrence, and stemness. Importantly, this review discusses the cancer therapies that target either mutant or amyloid p53, restore wild-type functions, and exploit the synthetic lethal interactions with mutant p53.

Computational Modeling of TP63-TP53 Interaction and Rational Design of Inhibitors: Implications for Therapeutics

Tumor protein p63 (TP63) is a member of the TP53 protein family that are important for development and in tumor suppression. Unlike TP53, TP63 is rarely mutated in cancer, but instead different TP63 isoforms regulate its activity. TA isoforms (TAp63) act as tumor suppressors, whereas ΔN isoforms are strong drivers of squamous or squamous-like cancers. Many of these tumors become addicted to ΔN isoforms and removal of ΔN isoforms result in cancer cell death. Furthermore, some TP53 conformational mutants (TP53CM) gain the ability to interact with TAp63 isoforms and inhibit their antitumorigenic function, while indirectly promoting tumorigenic function of ΔN isoforms, but the exact mechanism of TP63-TP53CM interaction is unclear. The changes in the balance of TP63 isoform activity are crucial to understanding the transition between normal and tumor cells. Here, we modeled TP63-TP53CM complex using computational approaches. We then used our models to design peptides to disrupt the TP63-TP53CM interaction and restore antitumorigenic TAp63 function. In addition, we studied ΔN isoform oligomerization and designed peptides to inhibit its oligomerization and reduce their tumorigenic activity. We show that some of our peptides promoted cell death in a TP63 highly expressed cancer cell line, but not in a TP63 lowly expressed cancer cell line. Furthermore, we performed kinetic-binding assays to validate binding of our peptides to their targets. Our computational and experimental analyses present a detailed model for the TP63-TP53CM interaction and provide a framework for potential therapeutic peptides for the elimination of TP53CM cancer cells.

p53 amyloid aggregation in cancer: function, mechanism, and therapy

Similar to neurodegenerative diseases, the concept that tumors are prion like diseases has been proposed in recent years. p53, the most well-known tumor suppressor, has been extensively studied for its expression, mutation, and function in various tumors. Currently, an interesting phenomenon of p53 prion-like aggregation has been found in several tumors, and studies have found that its pathological aggregation may lead to functional alterations and ultimately affect tumor progression. It has been demonstrated that the mechanism of p53 aggregation involves its mutation, domains, isoform, etc. In addition to p53 itself, some other factors, including Zn²⁺ concentration, pH, temperature and chaperone abnormalities, can also contribute to p53 aggregation. Although there are some studies about the mechanism and role of p53 aggregation and amyloidosis in tumors, there still exist some controversies. In this paper, we review the mechanism of p53 amyloid fibril structure and discuss the characteristics and effects of p53 amyloid aggregation, as well as the pathogenic mechanism leading to the occurrence of aggregation in tumors. Finally, we summarize the various inhibitors targeting p53 aggregation and prion-like behavior. In conclusion, a comprehensive understanding of p53 aggregation can expand our understanding of the causes leading its loss of physiological function and that targeting p53 aggregation might be a promising therapeutic strategy for tumor therapy.

A comparison of four technologies for detecting p53 aggregates in ovarian cancer

The tumor suppressor protein p53 is mutated in half of all cancers and has been described to form amyloid-like structures, commonly known from key proteins in neurodegenerative diseases. Still, the clinical relevance of p53 aggregates remains largely unknown, which may be due to the lack of sensitive and specific detection methods. The aim of the present study was to compare the suitability of four different methodologies to specifically detect p53 aggregates: co-immunofluorescence (co-IF), proximity ligation assay (PLA), co-immunoprecipitation (co-IP), and the p53-Seprion-ELISA in cancer cell lines and epithelial ovarian cancer tissue samples. In 7 out of 10 (70%) cell lines, all applied techniques showed concordance. For the analysis of the tissue samples co-IF, co-IP, and p53-Seprion-ELISA were compared, resulting in 100% concordance in 23 out of 30 (76.7%) tissue samples. However, Co-IF lacked specificity as there were samples, which did not show p53 staining but abundant staining of amyloid proteins, highlighting that this method demonstrates that proteins share the same subcellular space, but does not specifically detect p53 aggregates. Overall, the PLA and the p53-Seprion-ELISA are the only two methods that allow the quantitative measurement of p53 aggregates. On the one hand, the PLA represents the ideal method for p53 aggregate detection in FFPE tissue, which is the gold-standard preservation method of clinical samples. On the other hand, when fresh-frozen tissue is available the p53-Seprion-ELISA should be preferred because of the shorter turnaround time and the possibility for high-throughput analysis. These methods may add to the understanding of amyloid-like p53 in cancer and could help stratify patients in future clinical trials targeting p53 aggregation.

Targeting HSP90 as a Novel Therapy for Cancer: Mechanistic Insights and Translational Relevance

Heat shock protein (HSP90), a highly conserved molecular chaperon, is indispensable for the maturation of newly synthesized poly-peptides and provides a shelter for the turnover of misfolded or denatured proteins. In cancers, the client proteins of HSP90 extend to the entire process of oncogenesis that are associated with all hallmarks of cancer. Accumulating evidence has demonstrated that the client proteins are guided for proteasomal degradation when their complexes with HSP90 are disrupted. Accordingly, HSP90 and its co-chaperones have emerged as viable targets for the development of cancer therapeutics. Consequently, a number of natural products and their analogs targeting HSP90 have been identified. They have shown a strong inhibitory effect on various cancer types through different mechanisms. The inhibitors act by directly binding to either HSP90 or its co-chaperones/client proteins. Several HSP90 inhibitors—such as geldanamycin and its derivatives, gamitrinib and shepherdin—are under clinical evaluation with promising results. Here, we review the subcellular localization of HSP90, its corresponding mechanism of action in the malignant phenotypes, and the recent progress on the development of HSP90 inhibitors. Hopefully, this comprehensive review will shed light on the translational potential of HSP90 inhibitors as novel cancer therapeutics.

The role of heat shock proteins in metastatic colorectal cancer: A review

Heat shock proteins (HSPs) are a large molecular chaperone family classified by their molecular weights, including HSP27, HSP40, HSP60, HSP70, HSP90, and HSP110. HSPs are likely to have antiapoptotic properties and participate actively in various processes such as tumor cell proliferation, invasion, metastases, and death. In this review, we discuss comprehensively the functions of HSPs associated with the progression of colorectal cancer (CRC) and metastasis and resistance to cancer therapy. Taken together, HSPs have numerous clinical applications as biomarkers for cancer diagnosis and prognosis and potential therapeutic targets for CRC and its related metastases.

Mutations in DNA binding domain of p53 impede RSL1D1-p53 interaction to escape from degradation in human colorectal cancer cells

Different from the nucleolus-specific localization in some types of cancer cells, ribosomal L1 domain-containing protein 1 (RSL1D1) distributes throughout the nucleus in human colorectal cancer (CRC) cells. RSL1D1 directly interacts with DNA binding domain (aa 93-292) of wild-type p53 (p53-WT) and thereby recruits p53 to HDM2. The ensuing formation of RSL1D1/HDM2/p53 complex enhances p53 ubiquitination and decreases the protein level of p53 in CRC cells. In this study, we investigated the interaction between RSL1D1 and mutant p53 proteins. We first corroborated that aa 93-224 of p53 is a more precise domain for RSL1D1 binding and mutation in either aa 93-224 or aa 225-292 domain of p53 affects RSL1D1-p53 interaction. R175H mutated p53 does not interact with RSL1D1, whereas R273H mutated p53 still can bind to RSL1D1 but showing a remarkably decreased affinity than p53-WT. Although p53-R273H retained a weakened binding affinity with RSL1D1, it can hardly be recruited to HDM2 by RSL1D1 in HCT116 CRC cells. Accordingly, RSL1D1 lost its capacity to negatively regulate either R175H or R273H p53 mutant via directly interaction in HCT116 cells, thereby facilitating p53 mutants to accumulate and gain oncogenic function. Our findings help explain why mutant p53 proteins are more stable than p53-WT in CRC cells.

Mutual exclusivity of ESR1 and TP53 mutations in endocrine resistant metastatic breast cancer

Both TP53 and ESR1 mutations occur frequently in estrogen receptor positive (ER+) metastatic breast cancers (MBC) and their distinct roles in breast cancer tumorigenesis and progression are well appreciated. Recent clinical studies discovered mutual exclusivity between TP53 and ESR1 mutations in metastatic breast cancers; however, mechanisms underlying this intriguing clinical observation remain largely understudied and unknown. Here, we explored the interplay between TP53 and ESR1 mutations using publicly available clinical and experimental data sets. We first confirmed the robust mutational exclusivity using six independent cohorts with 1,056 ER+ MBC samples and found that the exclusivity broadly applies to all ER+ breast tumors regardless of their clinical and distinct mutational features. ESR1 mutant tumors do not exhibit differential p53 pathway activity, whereas we identified attenuated ER activity and expression in TP53 mutant tumors, driven by a p53-associated E2 response gene signature. Further, 81% of these p53-associated E2 response genes are either direct targets of wild-type (WT) p53-regulated transactivation or are mutant p53-associated microRNAs, representing bimodal mechanisms of ER suppression. Lastly, we analyzed the very rare cases with co-occurrences of TP53 and ESR1 mutations and found that their simultaneous presence was also associated with reduced ER activity. In addition, tumors with dual mutations showed higher levels of total and PD-L1 positive macrophages. In summary, our study utilized multiple publicly available sources to explore the mechanism underlying the mutual exclusivity between ESR1 and TP53 mutations, providing further insights and testable hypotheses of the molecular interplay between these two pivotal genes in ER+ MBC.

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.

VPA and TSA Interrupt the Interplay between mutp53 and HSP70, Leading to CHK1 and RAD51 Down-Regulation and Sensitizing Pancreatic Cancer Cells to AZD2461 PARP Inhibitor

HDAC inhibitors (HDACi) represent promising anti-cancer treatments, as the acetylation of histone and non-histone proteins is often dysregulated in cancer and contributes to cancer onset and progression. HDACi have been also reported to increase the cytotoxicity of DNA-damaging agents, such as radiation or cisplatin. In this study, we found that TSA and, even more effectively, VPA synergized with AZD2461, PARP1, 2 and 3 inhibitor (PARPi) to induce DNA damage and reduce pancreatic cancer cell survival. At a molecular level, VPA and TSA down-regulated CHK1 and RAD51, which is correlated with the interruption of the cross-talk between mutp53 and HSP70. Moreover, VPA and to a lesser extent TSA reactivated wtp53 in these cells, which contributed to CHK1 and RAD51 reduction. These findings suggest that the combination of HDACi and PARPi might improve the treatment of pancreatic cancer, which remains one of the most aggressive and therapy-resistant cancers.

Ergosterol Peroxide Inhibits Porcine Epidemic Diarrhea Virus Infection in Vero Cells by Suppressing ROS Generation and p53 Activation

Porcine epidemic diarrhea virus (PEDV) is an alphacoronavirus that causes severe watery diarrhea in piglets with high morbidity and mortality, resulting in serious economic losses to the farming industry. Ergosterol peroxide (EP) is a sterol with diverse biological activities including antiviral activity. In this study, we explored whether EP extracted from the fruiting body of the mushroom Cryptoporus volvatus had the potential to inhibit PEDV infection in Vero cells. The results revealed that EP had a remarkable inhibitory effect on PEDV infection. It could significantly inhibit multiple stages of the PEDV life cycle, including internalization, replication and release, and could directly inactivate PDCoV infectivity. However, it did not affect PEDV attachment. Furthermore, EP alleviated PEDV-induced apoptosis and mitigated the decrease in mitochondrial membrane potential caused by PEDV infection. It suppressed ROS generation and p53 activation caused by PEDV infection. The ROS scavenger N-acetyl-l-cysteine (NAC) and the p53 specific inhibitor Pifithrin-α (PFT-α) suppressed PEDV-induced apoptosis and impeded viral replication, suggesting that ROS and p53 play an important role in PEDV-induced apoptosis and viral replication. Collectively, EP can prevent PEDV internalization, replication and release, possesses the ability to directly inactivate PEDV, and can inhibit PEDV-induced apoptosis by interfering with PEDV-induced ROS production and p53 activation. These findings highlight the therapeutic potential of EP against PEDV infection.

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

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

The degradation of Rap1GAP via E6AP-mediated ubiquitin-proteasome pathway is associated with HPV16/18-infection in cervical cancer cells

BACKGROUND

Cervical cancers are closely associated with persistent high-risk human papillomaviruses (HR HPV) infection. The main mechanism involves the targeting of tumor suppressors, such as p53 and pRB, for degradation by HR HPV-encoded oncoproteins, thereby leading to tumorigenesis. Rap1GAP, a tumor suppressor gene, is down-regulated in many cancers. Previous studies have revealed that down-regulation of Rap1GAP is correlated with HPV16/18 infection in cervical cancer. However, the molecular mechanism remains unclear. In this study, we aimed to address the degradation pathway of Rap1GAP in HPV-positive cervical cancer cells.

METHODS

HPV-positive (HeLa and SiHa) and negative (C33A) cervical cancer cells were used to analyze the pathways of Rap1GAP degradation. MG132 (carbobenzoxy-leucyl-leucyl-leucine) was used to inhibit protein degradation by proteasome. Co-immunoprecipitation (co-IP) was used to detect the interaction between Rap1GAP and E6AP. siRNA for E6AP was used to silence the expression of E6AP. Rapamycin was used to induce cell autophagy. Western blotting was used to check the levels of proteins.

RESULTS

Following treatment with MG132, the levels of Rap1GAP were increased in the HR HPV-positive HeLa and SiHa cells, but not in the HPV-negative C33A cells. Co-immunoprecipitation assay revealed ubiquitinated Rap1GAP protein in HeLa and SiHa cells, but not in C33A cells. E6-associated protein (E6AP) mediated the ubiquitination of Rap1GAP by binding to it in HeLa and SiHa cells, but not in C33A cells. However, the levels of Rap1GAP were decreased in HeLa and SiHa cells after knocking down E6AP by siRNA. Silencing of E6AP did not affect the levels of Rap1GAP in C33A cells. Autophagy marker p62 was decreased and LC3 II/LC3 I was increased after knocking down E6AP in HeLa cells, but not in C33A cells. The levels of Rap1GAP were decreased after treating the cells with rapamycin to induce cell autophagy in HeLa and C33A cells.

CONCLUSION

Rap1GAP may be degraded by autophagy in cervical cancer cells, but HPV infection can switch the degradation pathway from autophagy to E6AP-mediated ubiquitin-proteasome degradation. E6AP may be a key component of the switch.

Attenuation Effect of Radiofrequency Irradiation on UV-B-Induced Skin Pigmentation by Decreasing Melanin Synthesis and through Upregulation of Heat Shock Protein 70

Excess melanin deposition in the skin causes cosmetic problems. HSP70 upregulation decreases microphthalmia-associated transcription factor (MITF) expression, which eventually decreases tyrosinase activity and melanogenesis. Ultraviolet (UV) radiation upregulates p53, which increases the melanocortin receptor (MC1R) and MITF. Furthermore, HSP70 decreases p53 and radiofrequency irradiation (RF) increases HSP70. We evaluated whether RF increased HSP70 and decreased p53, consequently decreasing the MITF/tyrosinase pathway and melanogenesis in UV-B radiated animal skin. Various RF combinations with 50, 100, and 150 ms and 5, 10, and 15 W were performed on the UV-B radiated mouse skin every 2 d for 28 d. When RF was performed with 100 ms/10 W, melanin deposition, evaluated by Fontana–Masson staining, decreased without skin crust formation in the UV-B radiated skin. Thus, we evaluated the effect of RF on decreasing melanogenesis in the HEMn and UV-B radiated skin at a setting of 100 ms/10 W. HSP70 expression was decreased in the UV-B radiated skin but was increased by RF. The expression of p53, MC1R, and MITF increased in the UV-B radiated skin but was decreased by RF. The expression of p53, MC1R, and MITF increased in the α-MSH treated HEMn but was decreased by RF. The decreasing effects of RF on p53, MC1R, CREB and MITF were higher than those of HSP70-overexpressed HEMn. The decreasing effect of RF on p53, MC1R, CREB, and MITF disappeared in the HSP70-silenced HEMn. MC1R, CREB, and MITF were not significantly decreased by the p53 inhibitor in α-MSH treated HEMn. RF induced a greater decrease in MC1R, CREB, and MITF than the p53 inhibitor. Therefore, RF may have decreased melanin synthesis by increasing HSP70 and decreasing p53, thus decreasing MC1R/CREB/MITF and tyrosinase activity.

Crosslink between p53 and metastasis: focus on epithelial-mesenchymal transition, cancer stem cell, angiogenesis, autophagy, and anoikis

INTRODUCTION

P53, as a tumor suppressor gene, is believed to be one of the most mutated genes in cancer cells. The mutant forms of this protein often play a tumorigenic role in cancer cells. Recent evidence shows that p53 plays a critical role in the migration, metastasis, and invasion of cancer cells. The present article aims to investigate the molecular mechanism that induces metastasis in cancer cells generated by the mutant P53, and to highlight the compounds targeting mutant-p53 together with their clinical applications.

METHODS

A detailed literature search was conducted to find information about the role of the mutant-p53 in the processes involved in metastasis in various databases.

RESULTS

A growing body of evidence suggests that Mutant-p53 enhances tumor metastasis affecting the Epithelial-mesenchymal transition (EMT) process, cancer stem cells, angiogenesis, autophagy, anoikis, and any other mechanisms regarding metastasis.

CONCLUSIONS

Taken together, targeting mutant-p53 by altering the processes involved in metastasis could be a potential therapeutic strategy in the treatment of metastatic cancer.

Selective functional inhibition of a tumor-derived p53 mutant by cytosolic chaperones identified using split-YFP in budding yeast

Life requires the oligomerization of individual proteins into higher-order assemblies. In order to form functional oligomers, monomers must adopt appropriate 3D structures. Molecular chaperones transiently bind nascent or misfolded proteins to promote proper folding. Single missense mutations frequently cause disease by perturbing folding despite chaperone engagement. A misfolded mutant capable of oligomerizing with wild-type proteins can dominantly poison oligomer function. We previously found evidence that human-disease-linked mutations in Saccharomyces cerevisiae septin proteins slow folding and attract chaperones, resulting in a kinetic delay in oligomerization that prevents the mutant from interfering with wild-type function. Here, we build upon our septin studies to develop a new approach for identifying chaperone interactions in living cells, and use it to expand our understanding of chaperone involvement, kinetic folding delays, and oligomerization in the recessive behavior of tumor-derived mutants of the tumor suppressor p53. We find evidence of increased binding of several cytosolic chaperones to a recessive, misfolding-prone mutant, p53(V272M). Similar to our septin results, chaperone overexpression inhibits the function of p53(V272M) with minimal effect on the wild type. Unlike mutant septins, p53(V272M) is not kinetically delayed under conditions in which it is functional. Instead, it interacts with wild-type p53 but this interaction is temperature sensitive. At high temperatures or upon chaperone overexpression, p53(V272M) is excluded from the nucleus and cannot function or perturb wild-type function. Hsp90 inhibition liberates mutant p53 to enter the nucleus. These findings provide new insights into the effects of missense mutations.

Gain-of-function mutant p53 in cancer progression and therapy

p53 is a key tumor suppressor, and loss of p53 function is frequently a prerequisite for cancer development. The p53 gene is the most frequently mutated gene in human cancers; p53 mutations occur in >50% of all human cancers and in almost every type of human cancers. Most of p53 mutations in cancers are missense mutations, which produce the full-length mutant p53 (mutp53) protein with only one amino acid difference from wild-type p53 protein. In addition to loss of the tumor-suppressive function of wild-type p53, many mutp53 proteins acquire new oncogenic activities independently of wild-type p53 to promote cancer progression, termed gain-of-function (GOF). Mutp53 protein often accumulates to very high levels in cancer cells, which is critical for its GOF. Given the high mutation frequency of the p53 gene and the GOF activities of mutp53 in cancer, therapies targeting mutp53 have attracted great interest. Further understanding the mechanisms underlying mutp53 protein accumulation and GOF will help develop effective therapies treating human cancers containing mutp53. In this review, we summarize the recent advances in the studies on mutp53 regulation and GOF as well as therapies targeting mutp53 in human cancers.

The Gain-of-Function p53 R248W Mutant Promotes Migration by STAT3 Deregulation in Human Pancreatic Cancer Cells

Missense p53 mutations (mutp53) occur in approx. 70% of pancreatic ductal adenocarcinomas (PDAC). Typically, mutp53 proteins are aberrantly stabilized by Hsp90/Hsp70/Hsp40 chaperone complexes. Notably, stabilization is a precondition for specific mutp53 alleles to acquire powerful neomorphic oncogenic gain-of-functions (GOFs) that promote tumor progression in solid cancers mainly by increasing invasion and metastasis. In colorectal cancer (CRC), we recently established that the common hotspot mutants mutp53^R248Q and mutp53^R248W exert GOF activities by constitutively binding to and hyperactivating STAT3. This results in increased proliferation and invasion in an autochthonous CRC mouse model and correlates with poor survival in patients. Comparing a panel of p53 missense mutations in a series of homozygous human PDAC cell lines, we show here that, similar to CRC, the mutp53^R248W protein again undergoes a strong Hsp90-mediated stabilization and selectively promotes migration. Highly stabilized mutp53 is degradable by the Hsp90 inhibitors Onalespib and Ganetespib, and correlates with growth suppression, possibly suggesting therapeutic vulnerabilities to target GOF mutp53 proteins in PDAC. In response to mutp53 depletion, only mutp53^R248W harboring PDAC cells show STAT3 de-phosphorylation and reduced migration, again suggesting an allele-specific GOF in this cancer entity, similar to CRC. Moreover, mutp53^R248W also exhibits the strongest constitutive complex formation with phosphorylated STAT3. The selective mutp53^R248W GOF signals through enhancing the STAT3 axis, which was confirmed since targeting STAT3 by knockdown or pharmacological inhibition phenocopied mutp53 depletion and reduced cell viability and migration preferentially in mutp53^R248W-containing PDAC cells. Our results confirm that mutp53 GOF activities are allele specific and can span across tumor entities.

Gain-of-function p53 protein transferred via small extracellular vesicles promotes conversion of fibroblasts to a cancer-associated phenotype

Tumor and stromal interactions consist of reciprocal signaling through cytokines, growth factors, direct cell-cell interactions, and extracellular vesicles (EVs). Small EVs (≤200 nm) have been considered critical messengers of cellular communication during tumor development. Here, we demonstrate that gain-of-function (GOF) p53 protein can be packaged into small EVs and transferred to fibroblasts. GOF p53 protein is selectively bound by heat shock protein 90 (HSP90), a chaperone protein, and packaged into small EVs. Inhibition of HSP90 activity blocks packaging of GOF, but not wild-type, p53 in small EVs. GOF p53-containing small EVs result in their conversion to cancer-associated fibroblasts. In vivo studies reveal that GOF p53-containing small EVs can enhance tumor growth and promote fibroblast transformation into a cancer-associated phenotype. These findings provide a better understanding of the complex interactions between cancer and stromal cells and may have therapeutic implications.

Ma et al. report that gain-of-function (GOF) p53 protein can be packaged into small EVs and transferred to stromal fibroblasts. The packaging of GOF p53 into small EVs is regulated by HSP90. Small EVs with GOF p53 activate Nrf2-mediated pathways in fibroblasts and induce their conversion to a cancer-associated phenotype.

p53, A Victim of the Prion Fashion

Identified in the late 1970s as an oncogene, a driving force leading to tumor development, p53 turned out to be a key tumor suppressor gene. Now p53 is considered a master gene regulating the transcription of over 3000 target genes and controlling a remarkable number of cellular functions. The elevated prevalence of p53 mutations in human cancers has led to a recurring questioning about the roles of mutant p53 proteins and their functional consequences. Both mutants and isoforms of p53 have been attributed dominant-negative and gain of function properties among which is the ability to form amyloid aggregates and behave in a prion-like manner. This report challenges the ongoing "prion p53" hypothesis by reviewing evidence of p53 behavior in light of our current knowledge regarding amyloid proteins, prionoids and prions.

Deferasirox-Dependent Iron Chelation Enhances Mitochondrial Dysfunction and Restores p53 Signaling by Stabilization of p53 Family Members in Leukemic Cells

Iron is crucial to satisfy several mitochondrial functions including energy metabolism and oxidative phosphorylation. Patients affected by Myelodysplastic Syndromes (MDS) and acute myeloid leukemia (AML) are frequently characterized by iron overload (IOL), due to continuous red blood cell (RBC) transfusions. This event impacts the overall survival (OS) and it is associated with increased mortality in lower-risk MDS patients. Accordingly, the oral iron chelator Deferasirox (DFX) has been reported to improve the OS and delay leukemic transformation. However, the molecular players and the biological mechanisms laying behind remain currently mostly undefined. The aim of this study has been to investigate the potential anti-leukemic effect of DFX, by functionally and molecularly analyzing its effects in three different leukemia cell lines, harboring or not p53 mutations, and in human primary cells derived from 15 MDS/AML patients. Our findings indicated that DFX can lead to apoptosis, impairment of cell growth only in a context of IOL, and can induce a significant alteration of mitochondria network, with a sharp reduction in mitochondrial activity. Moreover, through a remarkable reduction of Murine Double Minute 2 (MDM2), known to regulate the stability of p53 and p73 proteins, we observed an enhancement of p53 transcriptional activity after DFX. Interestingly, this iron depletion-triggered signaling is enabled by p73, in the absence of p53, or in the presence of a p53 mutant form. In conclusion, we propose a mechanism by which the increased p53 family transcriptional activity and protein stability could explain the potential benefits of iron chelation therapy in terms of improving OS and delaying leukemic transformation.

Identification of Small Molecules that Modulate Mutant p53 Condensation

Structural mutants of p53 induce global p53 protein destabilization and misfolding, followed by p53 protein aggregation. First evidence indicates that p53 can be part of protein condensates and that p53 aggregation potentially transitions through a condensate-like state. We show condensate-like states of fluorescently labeled structural mutant p53 in the nucleus of living cancer cells. We furthermore identified small molecule compounds that interact with the p53 protein and lead to dissolution of p53 structural mutant condensates. The same compounds lead to condensation of a fluorescently tagged p53 DNA-binding mutant, indicating that the identified compounds differentially alter p53 condensation behavior depending on the type of p53 mutation. In contrast to p53 aggregation inhibitors, these compounds are active on p53 condensates and do not lead to mutant p53 reactivation. Taken together our study provides evidence for structural mutant p53 condensation in living cells and tools to modulate this process.

The MDM2 ligand Nutlin-3 differentially alters expression of the immune blockade receptors PD-L1 and CD276

BACKGROUND

The links between the p53/MDM2 pathway and the expression of pro-oncogenic immune inhibitory receptors in tumor cells are undefined. In this report, we evaluate whether there is p53 and/or MDM2 dependence in the expression of two key immune receptors, CD276 and PD-L1.

METHODS

Proximity ligation assays were used to quantify protein-protein interactions in situ in response to Nutlin-3. A panel of p53-null melanoma cells was created using CRISPR-Cas9 guide RNA mediated genetic ablation. Flow cytometric analyses were used to assess the impact of TP53 or ATG5 gene ablation, as well as the effects of Nutlin-3 and an ATM inhibitor on cell surface PD-L1 and CD276. Targeted siRNA was used to deplete CD276 to assess changes in cell cycle parameters by flow cytometry. A T-cell proliferation assay was used to assess activity of CD4+ T-cells as a function of ATG5 genotype.

RESULTS

CD276 forms protein-protein interactions with MDM2 in response to Nutlin-3, similar to the known MDM2 interactors p53 and HSP70. Isogenic HCT116 p53-wt/null cancer cells demonstrated that CD276 is induced on the cell surface by Nutlin-3 in a p53-dependent manner. PD-L1 was also unexpectedly induced by Nutlin-3, but PD-L1 does not bind MDM2. The ATM inhibitor KU55993 reduced the levels of PD-L1 under conditions where Nutlin-3 induces PD-L1, indicating that MDM2 and ATM have opposing effects on PD-L1 steady-state levels. PD-L1 is also up-regulated in response to genetic ablation of TP53 in A375 melanoma cell clones under conditions in which CD276 remains unaffected. A549 cells with a deletion in the ATG5 gene up-regulated only PD-L1, further indicating that PD-L1 and CD276 are under distinct genetic control.

CONCLUSION

Genetic inactivation of TP53, or the use of the MDM2 ligand Nutlin-3, alters the expression of the immune blockade receptors PD-L1 and CD276. The biological function of elevated CD276 is to promote altered cell cycle progression in response to Nutlin-3, whilst the major effect of elevated PD-L1 is T-cell suppression. These data indicate that TP53 gene status, ATM and MDM2 influence PD-L1 and CD276 paralogs on the cell surface. These data have implications for the use of drugs that target the p53 pathway as modifiers of immune checkpoint receptor expression.

P53 aggregation, interactions with tau, and impaired DNA damage response in Alzheimer's disease

The transcription factor, p53, is critical for many important cellular functions involved in genome integrity, including cell cycle control, DNA damage response, and apoptosis. Disruption of p53 results in a wide range of disorders including cancer, metabolic diseases, and neurodegenerative diseases. Alzheimer's disease (AD) is a neurodegenerative disorder characterized by protein aggregates that contribute to disease pathology. Although p53 is known to aggregate, its propensity to aggregate in AD has never been assessed. Moreover, AD neuropathology includes lethal cell cycle re-entry, excessive DNA damage, and abnormal cell death which are all controlled by p53. Here, we show p53 forms oligomers and fibrils in human AD brain, but not control brain. p53 oligomers can also be detected in htau and P301L mouse models. Additionally, we demonstrate that p53 interacts with tau, specifically tau oligomers, in AD brain and can be recapitulated by in vitro exogenous tau oligomer treatment in C57BL/6 primary neurons. p53 oligomers also colocalize, potentially seeding, endogenous p53 in primary neurons. Lastly, we demonstrate that in the presence of DNA damage, phosphorylated p53 is mislocalized outside the nucleus and p53-mediated DNA damage responders are significantly decreased in AD brain. Control brain shows a healthy DNA damage response, indicating a loss of nuclear p53 function in AD may be due to p53 aggregation and/or interactions with tau oligomers. Given the critical role of p53 in cellular physiology, the disruption of this crucial transcription factor may set an irreversible course towards neurodegeneration in AD and potentially other tauopathies, warranting further investigation.

A Driver Never Works Alone-Interplay Networks of Mutant p53, MYC, RAS, and Other Universal Oncogenic Drivers in Human Cancer

The knowledge accumulating on the occurrence and mechanisms of the activation of oncogenes in human neoplasia necessitates an increasingly detailed understanding of their systemic interactions. None of the known oncogenic drivers work in isolation from the other oncogenic pathways. The cooperation between these pathways is an indispensable element of a multistep carcinogenesis, which apart from inactivation of tumor suppressors, always includes the activation of two or more proto-oncogenes. In this review we focus on representative examples of the interaction of major oncogenic drivers with one another. The drivers are selected according to the following criteria: (1) the highest frequency of known activation in human neoplasia (by mutations or otherwise), (2) activation in a wide range of neoplasia types (universality) and (3) as a part of a distinguishable pathway, (4) being a known cause of phenotypic addiction of neoplastic cells and thus a promising therapeutic target. Each of these universal oncogenic factors—mutant p53, KRAS and CMYC proteins, telomerase ribonucleoprotein, proteasome machinery, HSP molecular chaperones, NF-κB and WNT pathways, AP-1 and YAP/TAZ transcription factors and non-coding RNAs—has a vast network of molecular interrelations and common partners. Understanding this network allows for the hunt for novel therapeutic targets and protocols to counteract drug resistance in a clinical neoplasia treatment.

Heat Shock Proteins: Agents of Cancer Development and Therapeutic Targets in Anti-Cancer Therapy

Heat shock proteins (HSPs) constitute a large family of molecular chaperones classified by their molecular weights, and they include HSP27, HSP40, HSP60, HSP70, and HSP90. HSPs function in diverse physiological and protective processes to assist in maintaining cellular homeostasis. In particular, HSPs participate in protein folding and maturation processes under diverse stressors such as heat shock, hypoxia, and degradation. Notably, HSPs also play essential roles across cancers as they are implicated in a variety of cancer-related activities such as cell proliferation, metastasis, and anti-cancer drug resistance. In this review, we comprehensively discuss the functions of HSPs in association with cancer initiation, progression, and metastasis and anti-cancer therapy resistance. Moreover, the potential utilization of HSPs to enhance the effects of chemo-, radio-, and immunotherapy is explored. Taken together, HSPs have multiple clinical usages as biomarkers for cancer diagnosis and prognosis as well as the potential therapeutic targets for anti-cancer treatment.

The Diverse Functions of Mutant 53, Its Family Members and Isoforms in Cancer

The p53 family of proteins has grown substantially over the last 40 years. It started with p53, then p63, p73, isoforms and mutants of these proteins. The function of p53 as a tumour suppressor has been thoroughly investigated, but the functions of all isoforms and mutants and the interplay between them are still poorly understood. Mutant p53 proteins lose p53 function, display dominant-negative (DN) activity and display gain-of-function (GOF) to varying degrees. GOF was originally attributed to mutant p53′s inhibitory function over the p53 family members p63 and p73. It has become apparent that this is not the only way in which mutant p53 operates as a large number of transcription factors that are not related to p53 are activated on mutant p53 binding. This raises the question to what extent mutant p53 binding to p63 and p73 plays a role in mutant p53 GOF. In this review, we discuss the literature around the interaction between mutant p53 and family members, including other binding partners, the functional consequences and potential therapeutics.

Heat Shock Proteins in Glioblastoma Biology: Where Do We Stand?

Heat shock proteins (HSPs) are evolutionary conserved proteins that work as molecular chaperones and perform broad and crucial roles in proteostasis, an important process to preserve the integrity of proteins in different cell types, in health and disease. Their function in cancer is an important aspect to be considered for a better understanding of disease development and progression. Glioblastoma (GBM) is the most frequent and lethal brain cancer, with no effective therapies. In recent years, HSPs have been considered as possible targets for GBM therapy due their importance in different mechanisms that govern GBM malignance. In this review, we address current evidence on the role of several HSPs in the biology of GBMs, and how these molecules have been considered in different treatments in the context of this disease, including their activities in glioblastoma stem-like cells (GSCs), a small subpopulation able to drive GBM growth. Additionally, we highlight recent works that approach other classes of chaperones, such as histone and mitochondrial chaperones, as important molecules for GBM aggressiveness. Herein, we provide new insights into how HSPs and their partners play pivotal roles in GBM biology and may open new therapeutic avenues for GBM based on proteostasis machinery.

Intratumour heterogeneity of p53 expression; causes and consequences

Genomic alterations in different types of cancer have been identified by comprehensive sequencing methodologies, revealing TP53 as the most frequently mutated gene across the majority of human cancer types. Cytotoxic treatments are still major cancer therapy strategies but cancer recurrence due to therapy resistance is a major challenge. Resistant cell populations may be associated with TP53 mutant clones exhibiting abnormal p53 expression patterns in tumours. Given data that levels of mutant p53 influence cancer cell growth and survival, understanding the mechanisms underlying intratumour heterogeneity of p53 can be exploited to design strategies that improve patient survival. The patterns of p53 protein examined by immunohistochemistry of both premalignant and malignant tissues are complex, ranging from intense staining of all tumour cell nuclei to complete absence of staining and with many intermediate phenotypes. Animal models that express only mutant proteins and adoption of international standards for terminology have brought greater clarity to understanding the causes of variation and are at the same time demonstrating the utility of p53 in oncology. In addition to p53 mutation, MDM2 and chaperone activities, gene copy number and TP53 mRNA levels linked to proliferative activity and differentiation are all now established as causes of variation in p53 staining, with clinical implications. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Mutant p53 and Cellular Stress Pathways: A Criminal Alliance That Promotes Cancer Progression

The capability of cancer cells to manage stress induced by hypoxia, nutrient shortage, acidosis, redox imbalance, loss of calcium homeostasis and exposure to drugs is a key factor to ensure cancer survival and chemoresistance. Among the protective mechanisms utilized by cancer cells to cope with stress a pivotal role is played by the activation of heat shock proteins (HSP) response, anti-oxidant response induced by nuclear factor erythroid 2-related factor 2 (NRF2), the hypoxia-inducible factor-1 (HIF-1), the unfolded protein response (UPR) and autophagy, cellular processes strictly interconnected. However, depending on the type, intensity or duration of cellular stress, the balance between pro-survival and pro-death pathways may change, and cell survival may be shifted into cell death. Mutations of p53 (mutp53), occurring in more than 50% of human cancers, may confer oncogenic gain-of-function (GOF) to the protein, mainly due to its stabilization and interaction with the above reported cellular pathways that help cancer cells to adapt to stress. This review will focus on the interplay of mutp53 with HSPs, NRF2, UPR, and autophagy and discuss how the manipulation of these interconnected processes may tip the balance towards cell death or survival, particularly in response to therapies.

A nuclear phosphoinositide kinase complex regulates p53

The tumour suppressor p53 (encoded by TP53) protects the genome against cellular stress and is frequently mutated in cancer. Mutant p53 acquires gain-of-function oncogenic activities that are dependent on its enhanced stability. However, the mechanisms by which nuclear p53 is stabilized are poorly understood. Here, we demonstrate that the stability of stress-induced wild-type and mutant p53 is regulated by the type I phosphatidylinositol phosphate kinase (PIPKI-α (also known as PIP5K1A)) and its product phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P₂). Nuclear PIPKI-α binds to p53 upon stress, resulting in the production and association of PtdIns(4,5)P₂ with p53. PtdIns(4,5)P₂ binding promotes the interaction between p53 and the small heat shock proteins HSP27 (also known as HSPB1) and αB-crystallin (also known as HSPB5), which stabilize nuclear p53. Moreover, inhibition of PIPKI-α or PtdIns(4,5)P₂ association results in p53 destabilization. Our results point to a previously unrecognized role of nuclear phosphoinositide signalling in regulating p53 stability and implicate this pathway as a promising therapeutic target in cancer.

Diverse and cancer type‑specific roles of the p53 R248Q gain‑of‑function mutation in cancer migration and invasiveness

Gain‑of‑function (GOF) mutations in the TP53 gene lead to acquisition of new functions by the mutated tumor suppressor p53 protein. A number of the over‑represented 'hot spot' mutations, including the ones in codons 175, 248 or 273, convey GOF phenotypes. Such phenotypes may include resistance to chemotherapeutics or changes in motility and invasiveness. Whereas the prevalent notion is that the acquisition of the p53 GOF phenotype translates into poorer prognosis for the patient, the analysis of a human somatic p53 mutations dataset demonstrated earlier tumor onset, but decreased frequency and altered location of metastases in patients with the p53‑R248Q allele. Therefore, the GOF activities of p53‑R248Q and p53‑D281G were analyzed in triple negative breast cancer MDA‑MB‑231 and lung adenocarcinoma H1299 cell lines with regard to invasive and metastatic traits. The expression of p53‑D281G increased the motility and invasiveness of the lung cancer cells, but not those of the breast cancer cells. In contrast, the expression of p53‑R248Q decreased the motility and invasiveness of the breast and lung cancer cells in a p53 transactivation‑dependent manner. The intravenous xenotransplantation of MDA‑MB‑231 cells expressing p53‑R248Q into zebrafish embryos resulted in an alteration of the distribution of cancer cells in the body of the fish. In p53‑R248Q‑expressing H1299 cells a decrease in the expression of TCF8/ZEB1 and N‑cadherin was observed, suggesting partial mesenchymal‑to‑epithelial transition. In the two cell lines expressing p53‑R248Q a decrease was noted in the expression of myosin light chain 2, a protein involved in actomyosin‑based motility. To the best of our knowledge, the present study is one of only few reports demonstrating the mutated p53 GOF activity resulting in a decrease of a malignant trait in human cancer.

p53 reactivation with induction of massive apoptosis-1 (PRIMA-1) inhibits amyloid aggregation of mutant p53 in cancer cells

p53 mutants can form amyloid-like structures that accumulate in cells. p53 reactivation with induction of massive apoptosis-1 (PRIMA-1) and its primary active metabolite, 2-methylene-3-quinuclidinone (MQ), can restore unfolded p53 mutants to a native conformation that induces apoptosis and activates several p53 target genes. However, whether PRIMA-1 can clear p53 aggregates is unclear. In this study, we investigated whether PRIMA-1 can restore aggregated mutant p53 to a native form. We observed that the p53 mutant protein is more sensitive to both PRIMA-1 and MQ aggregation inhibition than WT p53. The results of anti-amyloid oligomer antibody assays revealed that PRIMA-1 reverses mutant p53 aggregate accumulation in cancer cells. Size-exclusion chromatography of the lysates from mutant p53-containing breast cancer and ovarian cell lines confirmed that PRIMA-1 substantially decreases p53 aggregates. We also show that MDA-MB-231 cell lysates can "seed" aggregation of the central core domain of recombinant WT p53, corroborating the prion-like behavior of mutant p53. We also noted that this aggregation effect was inhibited by MQ and PRIMA-1. This study provides the first demonstration that PRIMA-1 can rescue amyloid-state p53 mutants, a strategy that could be further explored as a cancer treatment.