Mutant p53 uses p63 as a molecular chaperone to alter gene expression and induce a pro-invasive secretome

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.

p63: a crucial player in epithelial stemness regulation

Epithelial tissue homeostasis is closely associated with the self-renewal and differentiation behaviors of epithelial stem cells (ESCs). p63, a well-known marker of ESCs, is an indispensable factor for their biological activities during epithelial development. The diversity of p63 isoforms expressed in distinct tissues allows this transcription factor to have a wide array of effects. p63 coordinates the transcription of genes involved in cell survival, stem cell self-renewal, migration, differentiation, and epithelial-to-mesenchymal transition. Through the regulation of these biological processes, p63 contributes to, not only normal epithelial development, but also epithelium-derived cancer pathogenesis. In this review, we provide an overview of the role of p63 in epithelial stemness regulation, including self-renewal, differentiation, proliferation, and senescence. We describe the differential expression of TAp63 and ΔNp63 isoforms and their distinct functional activities in normal epithelial tissues and in epithelium-derived tumors. Furthermore, we summarize the signaling cascades modulating the TAp63 and ΔNp63 isoforms as well as their downstream pathways in stemness regulation.

ΔNp63 overexpression promotes oral cancer cell migration through hyperactivated Activin A signaling

Oral cancer is a common malignant tumor of the oral cavity that affects many countries with a prevalent distribution in the Indian subcontinent, with poor prognosis rate on account of locoregional metastases. Gain-of-function mutations in p53 and overexpression of its related transcription factor, p63 are both widely reported events in oral cancers. However, targeting these alterations remains a far-achieved aim due to lack of knowledge on their downstream signaling pathways. In the present study, we characterize the isoforms of p63 and using knockdown strategy, decipher the functions and oncogenic signaling of p63 in oral cancers. Using Microarray and Chromatin Immunoprecipitation experiments, we decipher a novel transcriptional regulatory axis between p63 and Activin A and establish its functional significance in migration of oral cancer cells. Using an orally bioavailable inhibitor of the Activin A pathway to attenuate oral cancer cell migration and invasion, we further demonstrate the targetability of this signaling axis. Our study highlights the oncogenic role of ΔNp63 - Activin A - SMAD2/3 signaling and provides a basis for targeting this oncogenic pathway in oral cancers.

Mutant P53 in the formation and progression of the tumor microenvironment: Friend or foe

TP53 is the most frequently mutated gene in human cancer. It encodes the tumor suppressor protein p53, which suppresses tumorigenesis by acting as a critical transcription factor that can induce the expression of many genes controlling a plethora of fundamental cellular processes, including cell cycle progression, survival, apoptosis, and DNA repair. Missense mutations are the most frequent type of mutations in the TP53 gene. While these can have variable effects, they typically impair p53 function in a dominant-negative manner, thereby altering intra-cellular signaling pathways and promoting cancer development. Additionally, it is becoming increasingly apparent that p53 mutations also have non-cell autonomous effects that influence the tumor microenvironment (TME). The TME is a complex and heterogeneous milieu composed of both malignant and non-malignant cells, including cancer-associated fibroblasts (CAFs), adipocytes, pericytes, different immune cell types, such as tumor-associated macrophages (TAMs) and T and B lymphocytes, as well as lymphatic and blood vessels and extracellular matrix (ECM). Recently, a large body of evidence has demonstrated that various types of p53 mutations directly affect TME. They fine-tune the inflammatory TME and cell fate reprogramming, which affect cancer progression. Notably, re-educating the p53 signaling pathway in the TME may be an effective therapeutic strategy in combating cancer. Therefore, it is timely to here review the recent advances in our understanding of how TP53 mutations impact the fate of cancer cells by reshaping the TME.

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.

Knockout of mutant TP53 in the HaCaT cells enhances their migratory activity

The HaCaT cell line represents the spontaneously immortalized non-carcinogenic human keratinocytes that are used as a model for studying the function of normal human keratinocytes. There are two TP53 alleles in the HaCaT cell genome, which comprise two gain-of-function (GOF) mutations acquired through spontaneous immortalization (mutTP53). Mutations result in the increased proliferation rate and violation of the stratification program. The study was aimed to assess the effects of the mutTP53 gene knockout on the HaCaT keratinocytes capability of proliferation and migration in the in vitro model of epidermal injury and regeneration (scratch test), and on the ability to form stratified epithelium in the organotypic epidermal model. To perform the scratch-test, cells were cultured until monolayer was formed, then the standardized injury was created. The organotypic model was obtained by growing keratinocytes in the polycarbonate membrane inserts with the pore size of 0.4 μm at the interface between the phases (air-liquid). It has been shown that the mutant TP53 gene knockout results in the increased migration capability of the HaCaT keratinocytes: in the HaCaT with the mutTP53 knockout, the defect closure occurred faster than in the appropriate group of the WT HaCaT (p < 0.05), on day three the defect size was 12% ± 3% and 66% ± 5% of the initial size. There is evidence that mutant TP53 in the HaCaT cells is a negative regulator of the laminin 5 expression (LAMC2 expression was 9.96 ± 1.92 times higher in the cells with the mutTP53 knockout, p < 0.05), however, this does not promote normalization of the program of epithelial differentiation and stratification followed by formation of the stratum corneum in the organotypic model.

Impact of p53 knockdown on protein dataset of HaCaT cells

The HaCaT line of immortalized non-tumor cells is a popular model of keratinocytes used for dermatological studies, in the practice of toxicological tests, and in the study of skin allergic reactions. These cells maintain a stable keratinocyte phenotype, do not require specific growth factors during cultivation, and respond to keratinocyte differentiation stimuli. HaCaT cells bear two mutant p53 alleles - R282Q and H179Y. At least two mechanisms of GOF (gain-of-function) of mutant p53 are known: it affects functions of p63/p73 by inhibiting their binding to DNA; or it binds to new DNA sites by interacting with other transcription factors (NF-Y, E2F1, NF-KB, VDR, p63). Proteins of the P53 family play an important role in the regulation of proliferation and differentiation processes of human keratinocytes. Proteomic study of HaCaT cells with TP53 gene knockdown provides new data for understanding the limitations of HaCaT cells when using them as an experimental model of normal human keratinocytes.

In this article we present datasets obtained through the high-throughput shotgun proteomics analysis of human immortalized HaCaT keratinocytes and p53 knockdown HaCaT keratinocytes. As a protocol for proteomic profiling of cells, we used the approach of obtaining LC-MS/MS measurements followed by their processing with MaxQuant software (version 1.6.3.4). The “RAW” files were deposited to the ProteomeXchange with identifier PXD033538.

Impact of p53 Knockout on Protein Data Set of HaCaT Cells in Confluent and Subconfluent Conditions

The immortalized keratinocytes, HaCaT, are a popular model for skin research (toxicity, irritation, allergic reactions, or interaction of cells). They maintain a stable keratinocyte phenotype and respond to keratinocyte differentiation stimuli. However, programs of stratification and expression of differentiation markers in HaCaT keratinocytes are aberrant. In HaCaT cells, there are two mutant p53 alleles (i.e., R282Q and H179Y) that contain gain-of-function (GOF) mutations resulting from spontaneous immortalization (mutp53). At the same time, mutp53 acts as a transcription factor and also affects the interaction of p63 protein with its transcription targets. Proteins of the p53 family are crucial for regulation of proliferation and differentiation processes in human keratinocytes, although the involvement of mutp53 in these processes is not fully clear. We present data sets obtained as a result of high-performance proteomic analysis of immortalized HaCaT keratinocytes with p53 knockout in two different states, subconfluent and confluent, which are characterized by different intensites of cell differentiation processes. To obtain the proteomic profiles of the cells, we applied LC-MS/MS measurements processed with MaxQuant software (version 1.6.3.4).

p53 signaling in cancer progression and therapy

The p53 protein is a transcription factor known as the "guardian of the genome" because of its critical function in preserving genomic integrity. The TP53 gene is mutated in approximately half of all human malignancies, including those of the breast, colon, lung, liver, prostate, bladder, and skin. When DNA damage occurs, the TP53 gene on human chromosome 17 stops the cell cycle. If p53 protein is mutated, the cell cycle is unrestricted and the damaged DNA is replicated, resulting in uncontrolled cell proliferation and cancer tumours. Tumor-associated p53 mutations are usually associated with phenotypes distinct from those caused by the loss of the tumor-suppressing function exerted by wild-type p53protein. Many of these mutant p53 proteins have oncogenic characteristics, and therefore modulate the ability of cancer cells to proliferate, escape apoptosis, invade and metastasize. Because p53 deficiency is so common in human cancer, this protein is an excellent option for cancer treatment. In this review, we will discuss some of the molecular pathways by which mutant p53 proteins might perform their oncogenic activities, as well as prospective treatment methods based on restoring tumor suppressive p53 functions.

Characterization of METTL7B to Evaluate TME and Predict Prognosis by Integrative Analysis of Multi-Omics Data in Glioma

Glioma is the most common and aggressive type of primary brain malignant tumor with limited treatment approaches. Methyltransferase-like 7B (METTL7B) is associated with the pathogenesis of several diseases but is rarely studied in glioma. In this study, 1,493 glioma samples (data from our cohort, TCGA, and CGGA) expressing METTL7B were used to explore its prognostic value and mechanism in the immune microenvironment. Results showed that high expression of METTL7B is associated with poor prognosis and abundant immunosuppressive cells. Further, functional enrichment showed that METTL7B is involved in the negative regulation of immunity and carcinogenic signaling pathways. Moreover, a METTL7B-related prognostic signature constructed based on multi-omics showed a good prediction of the overall survival (OS) time of glioma patients. In conclusion, METTL7B is a potential prognostic biomarker. In addition, the prognostic prediction model constructed in this study can be used in clinical setups for the development of novel effective therapeutic strategies for glioma patients and improving overall survival.

Δ133p53β isoform pro-invasive activity is regulated through an aggregation-dependent mechanism in cancer cells

The p53 isoform, Δ133p53β, is critical in promoting cancer. Here we report that Δ133p53β activity is regulated through an aggregation-dependent mechanism. Δ133p53β aggregates were observed in cancer cells and tumour biopsies. The Δ133p53β aggregation depends on association with interacting partners including p63 family members or the CCT chaperone complex. Depletion of the CCT complex promotes accumulation of Δ133p53β aggregates and loss of Δ133p53β dependent cancer cell invasion. In contrast, association with p63 family members recruits Δ133p53β from aggregates increasing its intracellular mobility. Our study reveals novel mechanisms of cancer progression for p53 isoforms which are regulated through sequestration in aggregates and recruitment upon association with specific partners like p63 isoforms or CCT chaperone complex, that critically influence cancer cell features like EMT, migration and invasion.

The Role of p53 in Progression of Cutaneous Squamous Cell Carcinoma

Skin cancers are the most common types of cancer worldwide, and their incidence is increasing. Melanoma, basal cell carcinoma (BCC), and cutaneous squamous cell carcinoma (cSCC) are the three major types of skin cancer. Melanoma originates from melanocytes, whereas BCC and cSCC originate from epidermal keratinocytes and are therefore called keratinocyte carcinomas. Chronic exposure to ultraviolet radiation (UVR) is a common risk factor for skin cancers, but they differ with respect to oncogenic mutational profiles and alterations in cellular signaling pathways. cSCC is the most common metastatic skin cancer, and it is associated with poor prognosis in the advanced stage. An important early event in cSCC development is mutation of the TP53 gene and inactivation of the tumor suppressor function of the tumor protein 53 gene (TP53) in epidermal keratinocytes, which then leads to accumulation of additional oncogenic mutations. Additional genomic and proteomic alterations are required for the progression of premalignant lesion, actinic keratosis, to invasive and metastatic cSCC. Recently, the role of p53 in the invasion of cSCC has also been elucidated. In this review, the role of p53 in the progression of cSCC and as potential new therapeutic target for cSCC will be discussed.

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.

Targeting the mutant p53 secretome

While p53 is the most highly mutated and perhaps best studied tumor suppressor protein related to cancer, it remains refractory to targeted therapeutic strategies. In this issue of the JCI, Tan and colleagues investigated the mechanistic basis of the mutant p53 secretome in preclinical models of lung adenocarcinoma. The authors uncovered miR-34a as a regulator of a conventional protein secretion axis, which is mediated by three proteins: the Golgi reassembly and stacking protein 55 kDa (GRASP55), basic leucine zipper nuclear factor 1, and myosin IIA. Inhibition of GRASP55 in TP53-deficient lung adenocarcinoma suppressed protumorigenic secretion of osteopontin/secreted phosphoprotein 1 and insulin-like growth factor binding protein 2 and reduced tumor growth and metastases in mice as well as in patient-derived xenografts. These results provide a therapeutic opportunity to target downstream effects of p53 loss.

The Role of p53 Dysfunction in Colorectal Cancer and Its Implication for Therapy

Colorectal cancer (CRC) is one of the most common and fatal cancers worldwide. The carcinogenesis of CRC is based on a stepwise accumulation of mutations, leading either to an activation of oncogenes or a deactivation of suppressor genes. The loss of genetic stability triggers activation of proto-oncogenes (e.g., KRAS) and inactivation of tumor suppression genes, namely TP53 and APC, which together drive the transition from adenoma to adenocarcinoma. On the one hand, p53 mutations confer resistance to classical chemotherapy but, on the other hand, they open the door for immunotherapy, as p53-mutated tumors are rich in neoantigens. Aberrant function of the TP53 gene product, p53, also affects stromal and non-stromal cells in the tumor microenvironment. Cancer-associated fibroblasts together with other immunosuppressive cells become valuable assets for the tumor by p53-mediated tumor signaling. In this review, we address the manifold implications of p53 mutations in CRC regarding therapy, treatment response and personalized medicine.

circ-PSD3 promoted proliferation and invasion of papillary thyroid cancer cells via regulating the miR-7-5p/METTL7B axis

Papillary thyroid cancer (PTC) is a common tumor malignancy of the endocrine system worldwide. Recently, circular RNAs (circRNAs) have been reported to participate in diverse pathological processes, especially in tumorigenesis. However, the functional role and mechanism of circRNA pleckstrin and Sec7 domain containing 3 (circ-PSD3) in PTC are still unclear. In this study, qRT-PCR results showed that circ-PSD3 was significantly upregulated in PTC tissues and cell lines. Meanwhile, circ-PSD3 overexpression was positively associated with larger tumor size, TNM stage, and lymph node metastasis. Knockdown of circ-PSD3 suppressed the proliferation and invasion of PTC cells. Besides, circ-PSD3 interacted with miR-7-5p to reduce its expression, and methyltransferase like 7B (METTL7B) was verified as a target gene of miR-7-5p. Functionally, inhibition of circ-PSD3 impeded PTC cell proliferation and invasion via targeting miR-7-5p to downregulate METTL7B expression. Taken together, silencing of circ-PSD3 hampered the proliferation and invasion of PTC cells via upregulating the inhibitory effect of miR-7-5p on METTL7B expression. Therefore, circ-PSD3 could be a potential diagnostic biomarker or molecular treatment target for PTC.

Mutant p53 in cell-cell interactions

In this review, Pilley et al. examine the impact of different p53 mutations and focus on how heterogeneity of p53 status can affect relationships between cells within a tumor.

p53 is an important tumor suppressor, and the complexities of p53 function in regulating cancer cell behaviour are well established. Many cancers lose or express mutant forms of p53, with evidence that the type of alteration affecting p53 may differentially impact cancer development and progression. It is also clear that in addition to cell-autonomous functions, p53 status also affects the way cancer cells interact with each other. In this review, we briefly examine the impact of different p53 mutations and focus on how heterogeneity of p53 status can affect relationships between cells within a tumor.

Amplifying Tumor-Stroma Communication: An Emerging Oncogenic Function of Mutant p53

TP53 mutations are widespread in human cancers. An expanding body of evidence highlights that, in addition to their manifold cell-intrinsic activities boosting tumor progression, missense p53 mutants enhance the ability of tumor cells to communicate amongst themselves and with the tumor stroma, by affecting both the quality and the quantity of the cancer secretome. In this review, we summarize recent literature demonstrating that mutant p53 enhances the production of growth and angiogenic factors, inflammatory cytokines and chemokines, modulates biochemical and biomechanical properties of the extracellular matrix, reprograms the cell trafficking machinery to enhance secretion and promote recycling of membrane proteins, and affects exosome composition. All these activities contribute to the release of a promalignant secretome with both local and systemic effects, that is key to the ability of mutant p53 to fuel tumor growth and enable metastatic competence. A precise knowledge of the molecular mechanisms underlying the interplay between mutant p53 and the microenvironment is expected to unveil non-invasive biomarkers and actionable targets to blunt tumor aggressiveness.

Low OCEL1 expression is associated with poor prognosis in human non-small cell lung cancer

BACKGROUND

Occludin/ELL domain containing 1 (OCEL1) is a novel discovered protein with its molecular functions remaining unknown and its role in lung cancer has not been directly explored.

OBJECTIVES

This study focused on the role of OCEL1 in the progression and prognosis of non-small cell lung cancer (NSCLC).

METHODS

A public database and tissue samples (80 NSCLC tissue samples and paired normal lung samples) were used to compare differences in OCEL1 expression and investigate its relationship with clinical characteristics and prognosis.

RESULTS

Compared to adjacent normal lung tissue samples, OCEL1 expression was significantly down-regulated in tumor tissues. In addition, there was a negative correlation between OCEL1 and Ki67 expression levels. Low OCEL1 expression was significantly associated with lymph node metastasis, higher TNM stage, and poor prognosis. Importantly, multivariate analysis identified OCEL1 expression as an independent predictor for unfavorable NSCLC prognosis.

CONCLUSIONS

These results indicated that OCEL1 protein may serve as a novel prognostic biomarker in NSCLC.

Disruption of TP63-miR-27a* Feedback Loop by Mutant TP53 in Head and Neck Cancer

BACKGROUND

Alterations in the epidermal growth factor receptor and PI3K pathways in head and neck squamous cell carcinomas (HNSCCs) are frequent events that promote tumor progression. Ectopic expression of the epidermal growth factor receptor-targeting microRNA (miR), miR-27a* (miR-27a-5p), inhibits tumor growth. We sought to identify mechanisms mediating repression of miR-27a* in HNSCC, which have not been previously identified.

METHODS

We quantified miR-27a* in 47 oral cavity squamous cell carcinoma patient samples along with analysis of miR-27a* in 73 oropharyngeal and 66 human papillomavirus-positive (HPV+) samples from The Cancer Genome Atlas. In vivo and in vitro TP53 models engineered to express mutant TP53, along with promoter analysis using chromatin immunoprecipitation and luciferase assays, were used to identify the role of TP53 and TP63 in miR-27a* transcription. An HNSCC cell line engineered to conditionally express miR-27a* was used in vitro to determine effects of miR-27a* on target genes and tumor cells.

RESULTS

miR-27a* expression was repressed in 47 oral cavity tumor samples vs matched normal tissue (mean log2 difference = -0.023, 95% confidence interval = -0.044 to -0.002; two-sided paired t test, P = .03), and low miR-27a* levels were associated with poor survival in HPV+ and oropharyngeal HNSCC samples. Binding of ΔNp63α to the promoter led to an upregulation of miR-27a*. In vitro and in vivo findings showed that mutant TP53 represses the miR-27a* promoter, downregulating miR-27a* levels. ΔNp63α and nucleoporin 62, a protein involved in ΔNP63α transport, were validated as novel targets of miR-27a*.

CONCLUSION

Our results characterize a negative feedback loop between TP63 and miR-27a*. Genetic alterations in TP53, a frequent event in HNSCC, disrupt this regulatory loop by repressing miR-27a* expression, promoting tumor survival.

Mutant p53 induces Golgi tubulo-vesiculation driving a prometastatic secretome

TP53 missense mutations leading to the expression of mutant p53 oncoproteins are frequent driver events during tumorigenesis. p53 mutants promote tumor growth, metastasis and chemoresistance by affecting fundamental cellular pathways and functions. Here, we demonstrate that p53 mutants modify structure and function of the Golgi apparatus, culminating in the increased release of a pro-malignant secretome by tumor cells and primary fibroblasts from patients with Li-Fraumeni cancer predisposition syndrome. Mechanistically, interacting with the hypoxia responsive factor HIF1α, mutant p53 induces the expression of miR-30d, which in turn causes tubulo-vesiculation of the Golgi apparatus, leading to enhanced vesicular trafficking and secretion. The mut-p53/HIF1α/miR-30d axis potentiates the release of soluble factors and the deposition and remodeling of the ECM, affecting mechano-signaling and stromal cells activation within the tumor microenvironment, thereby enhancing tumor growth and metastatic colonization.

Mutant p53-a potential player in shaping the tumor-stroma crosstalk

A plethora of studies suggest that the non-transformed cellular and non-cellular components of the tumor, collectively known as the tumor microenvironment, have a significant impact on the tumorigenic process. It was suggested that the microenvironment, which initially restricts tumor development, is recruited by the tumor and maintains a crosstalk that further promotes cancer progression. Indeed, many of the molecules that participate in the tumor–stroma crosstalk have been characterized. However, the crucial factors that are responsible for the initiation of this crosstalk or the ‘recruitment’ process remain poorly understood. We propose that oncogenes themselves may influence the ‘recruitment’ of the stromal cells, while focusing on mutant p53. Apart from losing its tumor-suppressing properties, mutant p53 gains novel oncogenic functions, a phenomenon dubbed mutant p53 gain of function (GOF). Here, we discuss possible ways in which mutant p53 may modulate the microenvironment in order to promote tumorigenesis. We thus propose that mutant p53 may serve as a key player in the modulation of the tumor–stroma crosstalk in a way that benefits the tumor. Further elucidation of these ‘recruitment’ processes, dictated by mutant p53, may be utilized for tailoring personalized therapeutic approaches for patients with tumors that harbor p53 mutation.

METTL7B Is Required for Cancer Cell Proliferation and Tumorigenesis in Non-Small Cell Lung Cancer

Lung cancer remains a leading cause of cancer-associated mortality worldwide, however, molecular mechanisms underlying lung cancer tumorigenesis and progression remain unknown. Here, we report evidence showing that one member of the mammalian methyltransferase-like family (METTL), METTL7B, is a potential molecular target for treatment of non-small cell lung cancer (NSCLC). METTL7B expression was elevated in the majority of NSCLC comparing to normal tissues. Increased expression of METTL7B contributed to advanced stages of tumor development and poor survival in NSCLC patients. Lentivirus-mediated shRNA silencing of METTL7B suppressed proliferation and tumorigenesis of cancer cells in vitro and in vivo. Investigation on gene expression profiles of NSCLC cells revealed that abundant cell cycle related genes were downregulated in the absence of METTL7B. Pathway enrichment analysis indicated that METTL7B participated in cell cycle regulation. Notably, CCND1, a key regulator for G1/S transition, was significantly decreased with the depletion of METTL7B, resulting in G0/G1 arrest, indicating that METTL7B is critical for cell cycle progression. Taken together, our findings implicate that METTL7B is essential for NSCLC development and progression. METTL7B might serve as a potential therapeutic target for NSCLC.

p53's Extended Reach: The Mutant p53 Secretome

p53 suppresses tumorigenesis by activating a plethora of effector pathways. While most of these operate primarily inside of cells to limit proliferation and survival of incipient cancer cells, many extend to the extracellular space. In particular, p53 controls expression and secretion of numerous extracellular factors that are either soluble or contained within extracellular vesicles such as exosomes. As part of the cellular secretome, they execute key roles in cell-cell communication and extracellular matrix remodeling. Mutations in the p53-encoding TP53 gene are the most frequent genetic alterations in cancer cells, and therefore, have profound impact on the composition of the tumor cell secretome. In this review, we discuss how the loss or dominant-negative inhibition of wild-type p53 in concert with a gain of neomorphic properties observed for many mutant p53 proteins, shapes a tumor cell secretome that creates a supportive microenvironment at the primary tumor site and primes niches in distant organs for future metastatic colonization.

Mutant p53 Gain-of-Function: Role in Cancer Development, Progression, and Therapeutic Approaches

Frequent p53 mutations (mutp53) not only abolish tumor suppressor capacities but confer various gain-of-function (GOF) activities that impacts molecules and pathways now regarded as central for tumor development and progression. Although the complete impact of GOF is still far from being fully understood, the effects on proliferation, migration, metabolic reprogramming, and immune evasion, among others, certainly constitute major driving forces for human tumors harboring them. In this review we discuss major molecular mechanisms driven by mutp53 GOF. We present novel mechanistic insights on their effects over key functional molecules and processes involved in cancer. We analyze new mechanistic insights impacting processes such as immune system evasion, metabolic reprogramming, and stemness. In particular, the increased lipogenic activity through the mevalonate pathway (MVA) and the alteration of metabolic homeostasis due to interactions between mutp53 and AMP-activated protein kinase (AMPK) and Sterol regulatory element-binding protein 1 (SREBP1) that impact anabolic pathways and favor metabolic reprograming. We address, in detail, the impact of mutp53 over metabolic reprogramming and the Warburg effect observed in cancer cells as a consequence, not only of loss-of-function of p53, but rather as an effect of GOF that is crucial for the imbalance between glycolysis and oxidative phosphorylation. Additionally, transcriptional activation of new targets, resulting from interaction of mutp53 with NF-kB, HIF-1α, or SREBP1, are presented and discussed. Finally, we discuss perspectives for targeting molecules and pathways involved in chemo-resistance of tumor cells resulting from mutp53 GOF. We discuss and stress the fact that the status of p53 currently constitutes one of the most relevant criteria to understand the role of autophagy as a survival mechanism in cancer, and propose new therapeutic approaches that could promote the reduction of GOF effects exercised by mutp53 in cancer.

ΔNp63α Suppresses TGFB2 Expression and RHOA Activity to Drive Cell Proliferation in Squamous Cell Carcinomas

The transcriptional repressor ΔNp63α is a potent oncogene widely overexpressed in squamous cell carcinomas (SCCs) of diverse tissue origins, where it promotes malignant cell proliferation and survival. We report here the results of a genome-wide CRISPR screen to identify pathways controlling ΔNp63α-dependent cell proliferation, which revealed that the small GTPase RHOA blocks cell division upon ΔNp63α knockdown. After ΔNp63α depletion, RHOA activity is increased, and cells undergo RHOA-dependent proliferation arrest along with transcriptome changes indicative of increased TGF-β signaling. Mechanistically, ΔNp63α represses transcription of TGFB2, which induces a cell cycle arrest that is partially dependent on RHOA. Ectopic TGFB2 activates RHOA and impairs SCC proliferation, and TGFB2 neutralization restores cell proliferation during ΔNp63α depletion. Genomic data from tumors demonstrate inactivation of RHOA and the TGFBR2 receptor and ΔNp63α overexpression in more than 80% of lung SCCs. These results reveal a signaling pathway controlling SCC proliferation that is potentially amenable to pharmacological intervention.

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.

Genome-Wide Small RNA Sequencing Identifies MicroRNAs Deregulated in Non-Small Cell Lung Carcinoma Harboring Gain-of-Function Mutant p53

Mutations in the TP53 gene are one of the most frequent events in cancers. Certain missense mutant p53 proteins gain oncogenic functions (gain-of-functions) and drive tumorigenesis. Apart from the coding genes, a few non-coding microRNAs (miRNAs) are implicated in mediating mutant p53-driven cancer phenotypes. Here, we identified miRNAs in mutant p53^R273H bearing non-small cell lung carcinoma (NSCLC) cells while using small RNA deep sequencing. Differentially regulated miRNAs were validated in the TCGA lung adenocarcinoma patients with p53 mutations and, subsequently, we identified specific miRNA signatures that are associated with lymph node metastasis and poor survival of the patients. Pathway analyses with integrated miRNA-mRNA expressions further revealed potential regulatory molecular networks in mutant p53 cancer cells. A possible contribution of putative mutant p53-regulated miRNAs in epithelial-to-mesenchymal transition (EMT) is also predicted. Most importantly, we identified a novel miRNA from the unmapped sequencing reads through a systematic computational approach. The newly identified miRNA promotes proliferation, colony-forming ability, and migration of NSCLC cells. Overall, the present study provides an altered miRNA expression profile that might be useful in biomarker discovery for non-small cell lung cancers with TP53 mutations and discovers a hitherto unknown miRNA with oncogenic potential.

ΔNp63 in squamous cell carcinoma: defining the oncogenic routes affecting epigenetic landscape and tumour microenvironment

Squamous cell carcinoma (SCC) is a treatment‐refractory tumour which arises from the epithelium of diverse anatomical sites such as oesophagus, head and neck, lung and skin. Accumulating evidence has revealed a number of genomic, clinical and molecular features commonly observed in SCC of distinct origins. Some of these genetic events culminate in fostering the activity of ΔNp63, a potent oncogene which exerts its pro‐tumourigenic effects by regulating specific transcriptional programmes to sustain malignant cell proliferation and survival. In this review, we will describe the genetic and epigenetic determinants underlying ΔNp63 oncogenic activities in SCC, and discuss some relevant transcriptional effectors of ΔNp63, emphasizing their impact in modulating the crosstalk between tumour cells and tumour microenvironment (TME).

Mutant p53 as a guardian of the cancer cell

Forty years of research have established that the p53 tumor suppressor provides a major barrier to neoplastic transformation and tumor progression by its unique ability to act as an extremely sensitive collector of stress inputs, and to coordinate a complex framework of diverse effector pathways and processes that protect cellular homeostasis and genome stability. Missense mutations in the TP53 gene are extremely widespread in human cancers and give rise to mutant p53 proteins that lose tumor suppressive activities, and some of which exert trans-dominant repression over the wild-type counterpart. Cancer cells acquire selective advantages by retaining mutant forms of the protein, which radically subvert the nature of the p53 pathway by promoting invasion, metastasis and chemoresistance. In this review, we consider available evidence suggesting that mutant p53 proteins can favor cancer cell survival and tumor progression by acting as homeostatic factors that sense and protect cancer cells from transformation-related stress stimuli, including DNA lesions, oxidative and proteotoxic stress, metabolic inbalance, interaction with the tumor microenvironment, and the immune system. These activities of mutant p53 may explain cancer cell addiction to this particular oncogene, and their study may disclose tumor vulnerabilities and synthetic lethalities that could be exploited for hitting tumors bearing missense TP53 mutations.

Regulation of the interferon-gamma (IFN-γ) pathway by p63 and Δ133p53 isoform in different breast cancer subtypes

The TP53 family consists of three sets of transcription factor genes, TP53, TP63 and TP73, each of which expresses multiple RNA variants and protein isoforms. Of these, TP53 is mutated in 25-30% of breast cancers. How TP53 mutations affect the interaction of TP53 family members and their isoforms in breast cancer is unknown. To investigate this, 3 independent breast cancer cohorts were stratified into 4 groups based on oestrogen receptor (ER) and TP53 mutation status. Using bioinformatic methodologies, principal signalling pathways associated with the expression of TP53 family members were identified. Results show an enrichment of IFN-γ signalling associated with TP63 RNA in wild type TP53 (wtTP53), ER negative (ER-) tumours and with Δ133TP53 RNA in mutant TP53 (mTP53) ER positive (ER+) tumours. Moreover, tumours with low IFN-γ signalling were associated with significantly poorer patient outcome. The predicted changes in expression of a subset of RNAs involved in IFN-γ signalling were confirmed in vitro. Our data show that different members of the TP53 family can drive transcription of genes involved in IFN-γ signalling in different breast cancer subgroups.

MiR-766 induces p53 accumulation and G2/M arrest by directly targeting MDM4

p53, a transcription factor that participates in multiple cellular functions, is considered the most important tumor suppressor. Previous evidence suggests that post-transcriptional deregulation of p53 by microRNAs contributes to tumorigenesis, tumor progression and therapeutic resistance. In the present study, we found that the microRNA miR-766 was aberrantly expressed in breast cancer, and that over-expression of miR-766 caused accumulation of wild-type p53 protein in multiple cancer cell lines. Supporting its role in the p53 signalling pathway, miR-766 decreased cell proliferation and colony formation in several cancer cell lines, and cell cycle analyses revealed that miR-766 causes G2 arrest. At a mechanistic level, we demonstrate that miR-766 enhances p53 signalling by directly targeting MDM4, an oncogene and negative regulator of p53. Analysis of clinical genomic data from multiple cancer types supports the relevance of miR-766 in p53 signalling. Collectively, our study demonstrates that miR-766 can function as a novel tumor suppressor by enhancing p53 signalling.

TP53 mutations and protein immunopositivity may predict for poor outcome but also for trastuzumab benefit in patients with early breast cancer treated in the adjuvant setting

BACKGROUND

We investigated the impact of PIK3CA and TP53 mutations and p53 protein status on the outcome of patients who had been treated with adjuvant anthracycline-taxane chemotherapy within clinical trials in the pre- and post-trastuzumab era.

RESULTS

TP53 and PIK3CA mutations were found in 380 (21.5%) and 458 (25.9%) cases, respectively, including 104 (5.9%) co-mutated tumors; p53 immunopositivity was observed in 848 tumors (53.5%). TP53 mutations (p < 0.001) and p53 protein positivity (p = 0.001) were more frequent in HER2-positive and triple negative (TNBC) tumors, while PIK3CA mutations were more frequent in Luminal A/B tumors (p < 0.001). TP53 mutation status and p53 protein expression but not PIK3CA mutation status interacted with trastuzumab treatment for disease-free survival; patients with tumors bearing TP53 mutations or immunopositive for p53 protein fared better when treated with trastuzumab, while among patients treated with trastuzumab those with the above characteristics fared best (interaction p = 0.017 for mutations; p = 0.015 for IHC). Upon multivariate analysis the above interactions remained significant in HER2-positive patients; in the entire cohort, TP53 mutations were unfavorable in patients with Luminal A/B (p = 0.003) and TNBC (p = 0.025); p53 immunopositivity was strongly favorable in patients treated with trastuzumab (p = 0.009).

MATERIALS AND METHODS

TP53 and PIK3CA mutation status was examined in 1766 paraffin tumor DNA samples with informative semiconductor sequencing results. Among these, 1585 cases were also informative for p53 protein status assessed by immunohistochemistry (IHC; 10% positivity cut-off).

CONCLUSIONS

TP53 mutations confer unfavorable prognosis in patients with Luminal A/B and TNBC tumors, while p53 immunopositivity may predict for trastuzumab benefit in the adjuvant setting.

ERβ decreases the invasiveness of triple-negative breast cancer cells by regulating mutant p53 oncogenic function

Most (80%) of the triple-negative breast cancers (TNBCs) express mutant p53 proteins that acquire oncogenic activities including promoting metastasis. We previously showed that wild-type ERβ (ERβ1) impedes epithelial to mesenchymal transition (EMT) and decreases the invasiveness of TNBC cells. In the present study we searched for signaling pathways that ERβ1 uses to inhibit EMT and invasion in TNBC cells. We show that ERβ1 binds to and opposes the transcriptional activity of mutant p53 at the promoters of genes that regulate metastasis. p63 that transcriptionally cooperates with mutant p53 also binds to ERβ1. Downregulation of p63 represses the epithelial phenotype of ERβ1-expressing cells and alters the expression of mutant p53 target genes. These results describe a novel mechanism through which ERβ1 can disturb oncogenic signals to inhibit aggressiveness in TNBCs.

Proteomic profiling of the cancer cell secretome: informing clinical research

INTRODUCTION

Cancer represents one of the major causes of human deaths. Identification of proteins as biomarkers for early detection of cancer and therapeutic targets for cancer treatment are important issues in precision medicine. Secretome of cancer cells represents the collection of proteins secreted or shed from cancer cells. Proteomic profiling of the cancer cell secretome has been proven to be a convenient and efficient way to discover cancer biomarker and/or therapeutic targets. Areas covered: There have been numerous reviews describing the history and application of secretome analysis in cancer biomarker/therapeutic target research. The present review focuses on the technological advancement for profiling low-molecular-mass proteins in secretome, the latest information regarding the new candidate biomarkers and molecular mechanisms discovered on the basis of cancer cell secretome analysis, as well as the previously discovered candidate biomarkers that enter into clinical trials. Expert commentary: Current technologies for protein sample preparation/separation and MS-based protein identification have allowed in-depth analysis of cancer cell secretome. Future efforts should focus on the comprehensiveness of cancer cell secretome, meta-analysis of different secretome datasets and integrated analysis via combining other omics datasets, as well as the incorporation of MS-based biomarker verification pipeline into both preclinical studies and clinical trials.

Molecular chaperones in the acquisition of cancer cell chemoresistance with mutated TP53 and MDM2 up-regulation

Utilizing the TCGA PANCAN12 dataset we discovered that cancer patients with mutations in TP53 tumor suppressor and overexpression of MDM2 oncogene exhibited decreased survival post treatment. Interestingly, in the case of breast cancer patients, this phenomenon correlated with high expression level of several molecular chaperones belonging to the HSPA, DNAJB and HSPC families. To verify the hypothesis that such a genetic background may promote chaperone-mediated chemoresistance, we employed breast and lung cancer cell lines that constitutively overexpressed heat shock proteins and have shown that HSPA1A/HSP70 and DNAJB1/HSP40 facilitated the binding of mutated p53 to the TAp73α protein. This chaperone-mediated mutated p53–TAp73α complex induced chemoresistance to DNA damaging reagents, like Cisplatin, Doxorubicin, Etoposide or Camptothecin. Importantly, when the MDM2 oncogene was overexpressed, heat shock proteins were displaced and a stable multiprotein complex comprising of mutated p53-TAp73α-MDM2 was formed, additionally amplifying cancer cells chemoresistance. Our findings demonstrate that molecular chaperones aid cancer cells in surviving the cytotoxic effect of chemotherapeutics and may have therapeutic implications.

DNA damage induces expression of WWP1 to target ΔNp63α to degradation

ΔNp63αplays key roles in cell survival and proliferation. So its expression is always tightly controlled in cells. We previously reported that DNA damage down-regulates transcription of ΔNp63αin FaDu and HaCat cells, which contributes to cell apoptosis. In the present study, we found that DNA damage induces down-regulation of ΔNp63αvia facilitating its proteasomal degradation in cell lines such as MDA-MB-231 and MCF10A. Further investigation revealed that transcription of WWP1 is stimulated by DNA damage in these cells. Knock-down of WWP1 abrogates DNA damage-induced down-regulation of ΔNp63αand partially rescues cell apoptosis. Interestingly, DNA damage may stimulate WWP1 through different mechanisms in different cell types: it up-regulates transcription of WWP1 in a p53-dependent manner in MCF10A and HEK293 cells, while miR-452 may be involved in DNA damage-induced up-regulation of WWP1 in MDA-MB-231 cells. Our study demonstrates a novel pathway which regulates ΔNp63αupon cellular response to chemotherapeutic agents.

Mutant p53 upregulates alpha-1 antitrypsin expression and promotes invasion in lung cancer

Missense mutations in the TP53 tumor-suppressor gene inactivate its antitumorigenic properties and endow the incipient cells with newly acquired oncogenic properties that drive invasion and metastasis. Although the oncogenic effect of mutant p53 transcriptome has been widely acknowledged, the global influence of mutant p53 on cancer cell proteome remains to be fully elucidated. Here, we show that mutant p53 drives the release of invasive extracellular factors (the 'secretome') that facilitates the invasion of lung cancer cell lines. Proteomic characterization of the secretome from mutant p53-inducible H1299 human non-small cell lung cancer cell line discovered that the mutant p53 drives its oncogenic pathways through modulating the gene expression of numerous targets that are subsequently secreted from the cells. Of these genes, alpha-1 antitrypsin (A1AT) was identified as a critical effector of mutant p53 that drives invasion in vitro and in vivo, together with induction of epithelial-mesenchymal transition markers expression. Mutant p53 upregulated A1AT transcriptionally through the involvement with its family member p63. Conditioned medium containing secreted A1AT enhanced cell invasion, while an A1AT-blocking antibody attenuated the mutant p53-driven migration and invasion. Importantly, high A1AT expression correlated with increased tumor stage, elevated p53 staining and shorter overall survival in lung adenocarcinoma patients. Collectively, these findings suggest that A1AT is an indispensable target of mutant p53 with prognostic and therapeutic potential in mutant p53-expressing tumors.

Targeting mutant p53 in cancer: a long road to precision therapy

The TP53 tumor suppressor is the most frequently mutated gene in human cancers. In recent years, a blooming of research efforts based on both cell lines and mouse models have highlighted how deeply mutant p53 proteins affect fundamental cellular pathways with cancer-promoting outcomes. Neomorphic mutant p53 activities spread over multiple levels, impinging on chromatin structure, transcriptional regulation and microRNA maturation, shaping the proteome and the cell's metabolic pathways, and also exerting cytoplasmic functions and displaying cell-extrinsic effects. These tumorigenic activities are inextricably linked with the blend of highly corrupted processes that characterize the tumor context. Recent studies indicate that successful strategies to extract core aspects of mutant p53 oncogenic potential and to identify unique tumor dependencies entail the superimposition of large-scale analyses performed in multiple experimental systems, together with a mindful use of animal models. This will hopefully soon lead to the long-awaited inclusion of mutant p53 as an actionable target of clinical antitumor therapies.

CerS6 Is a Novel Transcriptional Target of p53 Protein Activated by Non-genotoxic Stress

Our previous study suggested that ceramide synthase 6 (CerS6), an enzyme in sphingolipid biosynthesis, is regulated by p53: CerS6 was elevated in several cell lines in response to transient expression of p53 or in response to folate stress, which is known to activate p53. It was not clear, however, whether CerS6 gene is a direct transcriptional target of p53 or whether this was an indirect effect through additional regulatory factors. In the present study, we have shown that the CerS6 promoter is activated by p53 in luciferase assays, whereas transcriptionally inactive R175H p53 mutant failed to induce the luciferase expression from this promoter. In vitro immunoprecipitation assays and gel shift analyses have further demonstrated that purified p53 binds within the CerS6 promoter sequence spanning 91 bp upstream and 60 bp downstream of the transcription start site. The Promo 3.0.2 online tool for the prediction of transcription factor binding sites indicated the presence of numerous putative non-canonical p53 binding motifs in the CerS6 promoter. Luciferase assays and gel shift analysis have identified a single motif upstream of the transcription start as a key p53 response element. Treatment of cells with Nutlin-3 or low concentrations of actinomycin D resulted in a strong elevation of CerS6 mRNA and protein, thus demonstrating that CerS6 is a component of the non-genotoxic p53-dependent cellular stress response. This study has shown that by direct transcriptional activation of CerS6, p53 can regulate specific ceramide biosynthesis, which contributes to the pro-apoptotic cellular response.

Obatoclax kills anaplastic thyroid cancer cells by inducing lysosome neutralization and necrosis

Poorly differentiated and anaplastic thyroid carcinomas are very aggressive, almost invariably lethal neoplasms for which no effective treatment exists. These tumors are intrinsically resistant to cell death, even when their driver oncogenic signaling pathways are inhibited.We have undertaken a detailed analysis, in mouse and human thyroid cancer cells, of the mechanism through which Obatoclax, a pan-inhibitor of the anti-apoptotic proteins of the BCL2 family, effectively reduces tumor growth in vitro and in vivo.We demonstrate that Obatoclax does not induce apoptosis, but rather necrosis of thyroid cancer cells, and that non-transformed thyroid cells are significantly less affected by this compound. Surprisingly, we show that Obatoclax rapidly localizes to the lysosomes and induces loss of acidification, block of lysosomal fusion with autophagic vacuoles, and subsequent lysosomal permeabilization. Notably, prior lysosome neutralization using different V-ATPase inhibitors partially protects cancer cells from the toxic effects of Obatoclax. Although inhibition of autophagy does not affect Obatoclax-induced cell death, selective down-regulation of ATG7, but not of ATG5, partially impairs Obatoclax effects, suggesting the existence of autophagy-independent functions for ATG7. Strikingly, Obatoclax killing activity depends only on its accumulation in the lysosomes, and not on its interaction with BCL2 family members.Finally, we show that also other lysosome-targeting compounds, Mefloquine and LLOMe, readily induce necrosis in thyroid cancer cells, and that Mefloquine significantly impairs tumor growth in vivo, highlighting a clear vulnerability of these aggressive, apoptosis-resistant tumors that can be therapeutically exploited.

Oncogenic Intra-p53 Family Member Interactions in Human Cancers

The p53 gene family members p53, p73, and p63 display several isoforms derived from the presence of internal promoters and alternative splicing events. They are structural homologs but hold peculiar functional properties. p53, p73, and p63 are tumor suppressor genes that promote differentiation, senescence, and apoptosis. p53, unlike p73 and p63, is frequently mutated in cancer often displaying oncogenic “gain of function” activities correlated with the induction of proliferation, invasion, chemoresistance, and genomic instability in cancer cells. These oncogenic functions are promoted either by the aberrant transcriptional cooperation of mutant p53 (mutp53) with transcription cofactors (e.g., NF-Y, E2F1, Vitamin D Receptor, Ets-1, NF-kB and YAP) or by the interaction with the p53 family members, p73 and p63, determining their functional inactivation. The instauration of these aberrant transcriptional networks leads to increased cell growth, low activation of DNA damage response pathways (DNA damage response and DNA double-strand breaks response), enhanced invasion, and high chemoresistance to different conventional chemotherapeutic treatments. Several studies have clearly shown that different cancers harboring mutant p53 proteins exhibit a poor prognosis when compared to those carrying wild-type p53 (wt-p53) protein. The interference of mutantp53/p73 and/or mutantp53/p63 interactions, thereby restoring p53, p73, and p63 tumor suppression functions, could be among the potential therapeutic strategies for the treatment of mutant p53 human cancers.

Gain of function of mutant p53: R282W on the peak?

Mutant p53 proteins commonly lose their tumor suppression function and gain novel oncogenic functions (gain of function (GOF)). Different p53 mutations are often considered in one class in biological and clinical studies. However, recent studies have revealed that p53 mutations are biologically and clinically distinct. The R282W mutant associates with earlier onset of familial cancers and poorer outcome of cancer patients, suggesting a more prominent GOF effect of this specific mutant. Here we discuss our current understanding on the multifaceted effects of R282W mutation, including its structural features, signaling pathways and clinical implications. The destabilizing nature, aggregation proneness, altered transcriptome and interactome may collaboratively contribute to the unique phenotype of R282W mutation. The quest for mechanistic insights into the unique GOF effects of R282W mutation would further our understanding of the biology of mutant proteins in cancers, and enforce the development of more effective targeted therapies.

p53 family interactions and yeast: together in anticancer therapy

The p53 family proteins are among the most appealing targets for cancer therapy. A deeper understanding of the complex interplay that these proteins establish with murine double minute (MDM)2, MDMX, and mutant p53 could reveal new exciting therapeutic opportunities in cancer treatment. Here, we summarize the most relevant advances in the biology of p53 family protein-protein interactions (PPIs), and the latest pharmacological developments achieved from targeting these interactions. We also highlight the remarkable contributions of yeast-based assays to this research. Collectively, we emphasize promising strategies, based on the inhibition of p53 family PPIs, which have expedited anticancer drug development.

Mutant p53: One, No One, and One Hundred Thousand

Encoded by the mutated variants of the TP53 tumor suppressor gene, mutant p53 proteins are getting an increased experimental support as active oncoproteins promoting tumor growth and metastasis. p53 missense mutant proteins are losing their wild-type tumor suppressor activity and acquire oncogenic potential, possessing diverse transforming abilities in cell and mouse models. Whether various mutant p53s differ in their oncogenic potential has been a matter of debate. Recent discoveries are starting to uncover the existence of mutant p53 downstream programs that are common to different mutant p53 variants. In this review, we discuss a number of studies on mutant p53, underlining the advantages and disadvantages of alternative experimental approaches that have been used to describe the numerous mutant p53 gain-of-function activities. Therapeutic possibilities are also discussed, taking into account targeting either individual or multiple mutant p53 proteins in human cancer.

TAp73 promotes anabolism

Metabolic adaptation has emerged as a hallmark of cancer and a promising therapeutic target, as rapidly proliferating cancer cells adapt their metabolism increasing nutrient uptake and reorganizing metabolic fluxes to support biosynthesis. The transcription factor p73 belongs to the p53-family and regulates tumorigenesis via its two N-terminal isoforms, with (TAp73) or without (ΔNp73) a transactivation domain. TAp73 acts as tumor suppressor, at least partially through induction of cell cycle arrest and apoptosis and through regulation of genomic stability. Here, we sought to investigate whether TAp73 also affects metabolic profiling of cancer cells. Using high throughput metabolomics, we unveil a thorough and unexpected role for TAp73 in promoting Warburg effect and cellular metabolism. TAp73-expressing cells show increased rate of glycolysis, higher amino acid uptake and increased levels and biosynthesis of acetyl-CoA. Moreover, we report an extensive TAp73-mediated upregulation of several anabolic pathways including polyamine and synthesis of membrane phospholipids. TAp73 expression also increases cellular methyl-donor S-adenosylmethionine (SAM), possibly influencing methylation and epigenetics, and promotes arginine metabolism, suggestive of a role in extracellular matrix (ECM) modeling. In summary, our data indicate that TAp73 regulates multiple metabolic pathways that impinge on numerous cellular functions, but that, overall, converge to sustain cell growth and proliferation.