Mutant p53 enhances nuclear factor kappaB activation by tumor necrosis factor alpha in cancer cells

PI3K Inhibitors Curtail MYC-Dependent Mutant p53 Gain-of-Function in Head and Neck Squamous Cell Carcinoma

PURPOSE

Mutation of TP53 gene is a hallmark of head and neck squamous cell carcinoma (HNSCC) not yet exploited therapeutically. TP53 mutation frequently leads to the synthesis of mutant p53 proteins with gain-of-function activity, associated with radioresistance and high incidence of local recurrences in HNSCC.

EXPERIMENTAL DESIGN

Mutant p53-associated functions were investigated through gene set enrichment analysis in the Cancer Genome Atlas cohort of HNSCC and in a panel of 22 HNSCC cell lines. Mutant p53-dependent transcripts were analyzed in HNSCC cell line Cal27, carrying mutant p53H193L; FaDu, carrying p53R248L; and Detroit 562, carrying p53R175H. Drugs impinging on mutant p53-MYC-dependent signature were identified interrogating Connectivity Map (https://clue.io) derived from the Library of Integrated Network-based Cellular Signatures (LINCS) database (http://lincs.hms.harvard.edu/) and analyzed in HNSCC cell lines and patient-derived xenografts (PDX) models.

RESULTS

We identified a signature of transcripts directly controlled by gain-of-function mutant p53 protein and prognostic in HNSCC, which is highly enriched of MYC targets. Specifically, both in PDX and cell lines of HNSCC treated with the PI3Kα-selective inhibitor BYL719 (alpelisib) the downregulation of mutant p53/MYC-dependent signature correlates with response to this compound. Mechanistically, mutant p53 favors the binding of MYC to its target promoters and enhances MYC protein stability. Treatment with BYL719 disrupts the interaction of MYC, mutant p53, and YAP proteins with MYC target promoters. Of note, depletion of MYC, mutant p53, or YAP potentiates the effectiveness of BYL719 treatment.

CONCLUSIONS

Collectively, the blocking of this transcriptional network is an important determinant for the response to BYL719 in HNSCC.

Effect of new olivacine derivatives on p53 protein level

BACKGROUND

The p53 protein is a transcription factor for many genes, including genes involved in inhibiting cell proliferation and inducing apoptosis in genotoxically damaged and tumor-transformed cells. In more than 55% of cases of human cancers, loss of the essential function of p53 protein is found. In numerous reports, it has been shown that small molecules (chemical compounds) can restore the suppressor function of the mutant p53 protein in tumor cells. The aim of this study was to evaluate the potential anticancer activity of three newly synthesized olivacine derivatives.

METHODS

The study was performed using two cell lines-CCRF/CEM (containing the mutant p53 protein) and A549 (containing a non-mutant, wild-type p53 protein). The cells were incubated with olivacine derivatives for 18 h and then assays were carried out: measurement of the amount of p53 and p21 proteins, detection of apoptosis, cell cycle analysis, and rhodamine 123 accumulation assay (evaluation of P-glycoprotein inhibition). Multiple-criteria decision analysis was used to compare the anticancer activity of the tested compounds.

RESULTS

Each tested compound caused the reconstitution of suppressor activity of the p53 protein in cells with the mutant protein. In addition, one of the compounds showed significant antitumor activity in both wild-type and mutant cells. For all compounds, a stronger effect on the level of the p53 protein was observed than for the reference compound-ellipticine.

CONCLUSIONS

The observed effects of the tested new olivacine derivatives (pyridocarbazoles) suggest that they are good candidates for new anticancer drugs.

Gain-of-Function Mutant p53: All the Roads Lead to Tumorigenesis

The p53 protein is mutated in about 50% of human cancers. Aside from losing the tumor-suppressive functions of the wild-type form, mutant p53 proteins often acquire inherent, novel oncogenic functions, a phenomenon termed mutant p53 gain-of-function (GOF). A growing body of evidence suggests that these pro-oncogenic functions of mutant p53 proteins are mediated by affecting the transcription of various genes, as well as by protein-protein interactions with transcription factors and other effectors. In the current review, we discuss the various GOF effects of mutant p53, and how it may serve as a central node in a network of genes and proteins, which, altogether, promote the tumorigenic process. Finally, we discuss mechanisms by which "Mother Nature" tries to abrogate the pro-oncogenic functions of mutant p53. Thus, we suggest that targeting mutant p53, via its reactivation to the wild-type form, may serve as a promising therapeutic strategy for many cancers that harbor mutant p53. Not only will this strategy abrogate mutant p53 GOF, but it will also restore WT p53 tumor-suppressive functions.

Mutant p53 induces SIRT3/MnSOD axis to moderate ROS production in melanoma cells

The TP53 tumor suppressor gene is the most frequently altered gene in tumors and mutant p53 isoforms can acquire oncogenic properties referred to as gain-of-function (GOF). In this study, we used wild-type (A375) and mutant p53 (MeWo) melanoma cell lines to assess the regulation of the mitochondrial antioxidant manganese superoxide dismutase (MnSOD) by mutant p53. The effects of mutant p53 were evaluated by qPCR, immunoblotting, enzyme activity assay, cell proliferation assay, reactive oxygen species (ROS) assay after cellular transfection. We demonstrate that mutant p53 induces MnSOD expression, which is recovered by the ROS scavenger N-acetyl-l-cysteine. This suggests MnSOD induction as a defense mechanism of melanoma cells to counterbalance the pro-oxidant conditions induced by mutant p53. We also demonstrate that mutant p53 induces the expression of Sirtuin3 (SIRT3), a major mitochondrial NAD⁺-dependent deacetylase, stimulating MnSOD deacetylation and enzymatic activity. Indeed, the restoration of SIRT3 reverses MnSOD activity decrease by mutant p53 knock-down. Finally, MnSOD knock-down further enhances mutant p53-mediated ROS increase, counteracting mutp53-dependent cell hyperproliferation. This indicates that SIRT3 and MnSOD act to maintain ROS levels controlled to promote cell proliferation and survival, providing new therapeutic opportunities to be further considered for clinical studies in cancer patients bearing mutant TP53 gene.

Gain of function in somatic TP53 mutations is associated with immune-rich breast tumors and changes in tumor-associated macrophages

BACKGROUND

Somatic mutations in TP53 are present in 20%-30% of all breast tumors. While there are numerous population-based analyses of TP53, yet none have examined the relationship between somatic mutations in TP53 and tumor invasive immune cells.

METHODS

Clinical and genetic data from 601 women drawn from The Cancer Genome Atlas (TCGA) were used to test the association between somatic TP53 mutation and immune-rich or immune-poor tumor status; determined using the CIBERSORT-based gene expression signature of 22 immune cell types. Our validation dataset, the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC), used a pathologist-determined measure of lymphocyte infiltration.

RESULTS

Within TP53-mutated samples, a mutation at codon p.R175H was shown to be present at higher frequency in immune-rich tumors. In validation analysis, any somatic mutation in TP53 was associated with immune-rich status, and the mutation at p.R175H had a significant association with tumor-invasive lymphocytes. TCGA-only analysis of invasive immune cell type identified an increase in M0 macrophages associated with p.R175H.

CONCLUSIONS

These findings suggest that TP53 somatic mutations, particularly at codon p.R175H, are enriched in tumors with infiltrating immune cells. Our results confirm recent research showing inflammation-related gain of function in specific TP53 mutations.

The miR-205-5p/BRCA1/RAD17 Axis Promotes Genomic Instability in Head and Neck Squamous Cell Carcinomas

Defective DNA damage response (DDR) is frequently associated with tumorigenesis. Abrogation of DDR leads to genomic instability, which is one of the most common characteristics of human cancers. TP53 mutations with gain-of-function activity are associated with tumors under high replicative stress, high genomic instability, and reduced patient survival. The BRCA1 and RAD17 genes encode two pivotal DNA repair proteins required for proper cell-cycle regulation and maintenance of genomic stability. We initially evaluated whether miR-205-5p, a microRNA (miRNA) highly expressed in head and neck squamous cell carcinoma (HNSCC), targeted BRCA1 and RAD17 expression. We found that, in vitro and in vivo, BRCA1 and RAD17 are targets of miR-205-5p in HNSCC, leading to inefficient DNA repair and increased chromosomal instability. Conversely, miR-205-5p downregulation increased BRCA1 and RAD17 messenger RNA (mRNA) levels, leading to a reduction in in vivo tumor growth. Interestingly, miR-205-5p expression was significantly anti-correlated with BRCA1 and RAD17 targets. Furthermore, we documented that miR-205-5p expression was higher in tumoral and peritumoral HNSCC tissues than non-tumoral tissues in patients exhibiting reduced local recurrence-free survival. Collectively, these findings unveil miR-205-5p's notable role in determining genomic instability in HNSCC through its selective targeting of BRCA1 and RAD17 gene expression. High miR-205-5p levels in the peritumoral tissues might be relevant for the early detection of minimal residual disease and pre-cancer molecular alterations involved in tumor development.

Unfolded Protein Response supports endothelial barrier function

Ongoing efforts are oriented towards the development of novel therapeutic agents to repress lung hyperpermeability responses due to inflammation. The endothelial barrier dysfunction triggered by such events, may eventually lead to severe cardiovascular complications, such as the Acute Respiratory Distress Syndrome. Hsp90 inhibitors are anticancer compounds, associated with strong anti-inflammatory responses in the endothelium. Our latest observations in experimental models of Acute Lung Injury suggest that P53 orchestrates, at least in part, such activities. Remarkably, both Hsp90 inhibition and P53 induction are associated with the activation of the Unfolded Protein Response element. The purpose of the current manuscript, is to introduce the hypotheses that UPR induction protects the vasculature against inflammation.

β-arrestin1/YAP/mutant p53 complexes orchestrate the endothelin A receptor signaling in high-grade serous ovarian cancer

The limited clinical response observed in high-grade serous ovarian cancer (HG-SOC) with high frequency of TP53 mutations (mutp53) might be related to mutp53-driven oncogenic pathway network. Here we show that β-arrestin1 (β-arr1), interacts with YAP, triggering its cytoplasmic-nuclear shuttling. This interaction allows β-arr1 to recruit mutp53 to the YAP-TEAD transcriptional complex upon activation of endothelin-1 receptors (ET-1R) in patient-derived HG-SOC cells and in cell lines bearing mutp53. In parallel, β-arr1 mediates the ET-1R-induced Trio/RhoA-dependent YAP nuclear accumulation. In the nucleus, ET-1 through β-arr1 orchestrates the tethering of YAP and mutp53 to YAP/mutp53 target gene promoters, including EDN1 that ensures persistent signals. Treatment of patient-derived xenografts reveals synergistic antitumoral and antimetastatic effects of the dual ET-1R antagonist macitentan in combination with cisplatinum, shutting-down the β-arr1-mediated YAP/mutp53 transcriptional programme. Furthermore, ETAR/β-arr1/YAP gene signature correlates with a worst prognosis in HG-SOC. These findings support effective combinatorial treatment for repurposing the ET-1R antagonists in HG-SOC.

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.

Detection of a novel, primate-specific 'kill switch' tumor suppression mechanism that may fundamentally control cancer risk in humans: an unexpected twist in the basic biology of TP53

The activation of TP53 is well known to exert tumor suppressive effects. We have detected a primate-specific adrenal androgen-mediated tumor suppression system in which circulating DHEAS is converted to DHEA specifically in cells in which TP53 has been inactivated DHEA is an uncompetitive inhibitor of glucose-6-phosphate dehydrogenase (G6PD), an enzyme indispensable for maintaining reactive oxygen species within limits survivable by the cell. Uncompetitive inhibition is otherwise unknown in natural systems because it becomes irreversible in the presence of high concentrations of substrate and inhibitor. In addition to primate-specific circulating DHEAS, a unique, primate-specific sequence motif that disables an activating regulatory site in the glucose-6-phosphatase (G6PC) promoter was also required to enable function of this previously unrecognized tumor suppression system. In human somatic cells, loss of TP53 thus triggers activation of DHEAS transport proteins and steroid sulfatase, which converts circulating DHEAS into intracellular DHEA, and hexokinase which increases glucose-6-phosphate substrate concentration. The triggering of these enzymes in the TP53-affected cell combines with the primate-specific G6PC promoter sequence motif that enables G6P substrate accumulation, driving uncompetitive inhibition of G6PD to irreversibility and ROS-mediated cell death. By this catastrophic 'kill switch' mechanism, TP53 mutations are effectively prevented from initiating tumorigenesis in the somatic cells of humans, the primate with the highest peak levels of circulating DHEAS. TP53 mutations in human tumors therefore represent fossils of kill switch failure resulting from an age-related decline in circulating DHEAS, a potentially reversible artifact of hominid evolution.

Mutant p53 blocks SESN1/AMPK/PGC-1α/UCP2 axis increasing mitochondrial O2-· production in cancer cells

BACKGROUND

The TP53 tumor suppressor gene is the most frequently altered gene in tumors and mutant p53 gain-of-function isoforms actively promote cancer malignancy.

METHODS

A panel of wild-type and mutant p53 cancer cell lines of different tissues, including pancreas, breast, skin, and lung were used, as well as chronic lymphocytic leukemia (CLL) patients with different TP53 gene status. The effects of mutant p53 were evaluated by confocal microscopy, reactive oxygen species production assay, immunoblotting, and quantitative reverse transcription polymerase chain reaction after cellular transfection.

RESULTS

We demonstrate that oncogenic mutant p53 isoforms are able to inhibit SESN1 expression and consequently the amount of SESN1/AMPK complex, resulting in the downregulation of the AMPK/PGC-1α/UCP2 axis and mitochondrial O₂-· production. We also show a correlation between the decrease of reduced thiols with a poorer clinical outcome of CLL patients bearing mutant TP53 gene. The restoration of the mitochondrial uncoupling protein 2 (UCP2) expression, as well as the addition of the radical scavenger N-acetyl-L-cysteine, reversed the oncogenic effects of mutant p53 as cellular hyper-proliferation, antiapoptotic effect, and resistance to drugs.

CONCLUSIONS

The inhibition of the SESN1/AMPK/PGC-1α/UCP2 axis contributes to the pro-oxidant and oncogenic effects of mutant p53, suggesting pro-oxidant drugs as a therapeutic approach for cancer patients bearing mutant TP53 gene.

Mutant p53 prevents GAPDH nuclear translocation in pancreatic cancer cells favoring glycolysis and 2-deoxyglucose sensitivity

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive and devastating human malignancies. In about 70% of PDACs the tumor suppressor gene TP53 is mutated generally resulting in conformational changes of mutant p53 (mutp53) proteins, which acquire oncogenic functions triggering aggressiveness of cancers and alteration of energetic metabolism. Here, we demonstrate that mutant p53 prevents the nuclear translocation of the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) stabilizing its cytoplasmic localization, thus supporting glycolysis of cancer cells and inhibiting cell death mechanisms mediated by nuclear GAPDH. We further show that the prevention of nuclear localization of GAPDH is mediated by both stimulation of AKT and repression of AMPK signaling, and is associated with the formation of the SIRT1:GAPDH complex. By using siRNA-GAPDH or an inhibitor of the enzyme, we functionally demonstrate that the maintenance of GAPDH in the cytosol has a critical impact on the anti-apoptotic and anti-autophagic effects driven by mutp53. Furthermore, the blockage of its mutp53-dependent cytoplasmic stabilization is able to restore the sensitivity of PDAC cells to the treatment with gemcitabine. Finally, our data suggest that mutp53-dependent enhanced glycolysis permits cancer cells to acquire sensitivity to anti-glycolytic drugs, such as 2-deoxyglucose, suggesting a potential personalized therapeutic approach in human cancers carrying mutant TP53 gene.

Role of p53 in the Regulation of the Inflammatory Tumor Microenvironment and Tumor Suppression

p53 has functional roles in tumor suppression as a guardian of the genome, surveillant of oncogenic cell transformation, and as recently demonstrated, a regulator of intracellular metabolism. Accumulating evidence has shown that the tumor microenvironment, accompanied by inflammation and tissue remodeling, is important for cancer proliferation, metastasis, and maintenance of cancer stem cells (CSCs) that self-renew and generate the diverse cells comprising the tumor. Furthermore, p53 has been demonstrated to inhibit inflammatory responses, and functional loss of p53 causes excessive inflammatory reactions. Moreover, the generation and maintenance of CSCs are supported by the inflammatory tumor microenvironment. Considering that the functions of p53 inhibit reprogramming of somatic cells to stem cells, p53 may have a major role in the inflammatory microenvironment as a tumor suppressor. Here, we review our current understanding of the mechanisms underlying the roles of p53 in regulation of the inflammatory microenvironment, tumor microenvironment, and tumor suppression.

How mutations shape p53 interactions with the genome to promote tumorigenesis and drug resistance

The tumor suppressive transcription factor p53 regulates a wide array of cellular processes that confer upon cells an essential protection against cancer development. Wild-type p53 regulates gene expression by directly binding to DNA in a sequence-specific manner. p53 missense mutations are the most common mutations in malignant cells and can be regarded as synonymous with anticancer drug resistance and poor prognosis. The current review provides an overview of how the extraordinary variety of more than 2000 different mutant p53 proteins, known as the p53 mutome, affect the interaction of p53 with DNA. We discuss how the classification of p53 mutations to loss of function (LOF), gain of function (GOF), and dominant-negative (DN) inhibition of a remaining wild-type allele, hides a complex p53 mutation spectrum that depends on the distinctive nature of each mutant protein, requiring different therapeutic strategies for each mutant p53 protein. We propose to regard the different mutant p53 categories as continuous variables, that may not be independent of each other. In particular, we suggest here to consider GOF mutations as a special subset of LOF mutations, especially when mutant p53 binds to DNA through cooperation with other transcription factors, and we present a model for GOF mechanism that consolidates many observations on the GOF phenomenon. We review how novel mutant p53 targeting approaches aim to restore a wild-type-like DNA interaction and to overcome resistance to cancer therapy.

Molecular Determinants of Sensitivity or Resistance of Cancer Cells Toward Sanguinarine

For decades, natural products represented a significant source of diverse and unique bioactive lead compounds in drug discovery field. In Clinical oncology, complete tumors remission is hampered by the development of drug-resistance. Therefore, development of cytotoxic agents that may overcome drug resistance is urgently needed. Here, the natural benzophenanthridine alkaloid sanguinarine has been studied for its cytotoxic activity against multidrug resistance (MDR) cancer cells. We investigated the role of the ATP-binding cassette (ABC) transporters BCRP/ABCG2, P-glycoprotein/ABCB1 and its close relative ABCB5 in drug resistance. Further drug resistance mechanisms analyzed in this study were the tumor suppressor TP53 and the epidermal growth factor receptor (EGFR). Multidrug resistant cells overexpressing BCRP, ABCB5 and mutated ΔEGFR were not cross-resistant toward sanguinarine. Interestingly, P-gp overexpressing cells were hypersensitive to sanguinarine. Doxorubicin uptake assay carried by flow cytometry revealed that sanguinarine is a potent inhibitor of the P-gp transporter. Moreover, immunoblotting analysis proved that P-gp was downregulated in a dose dependent manner after treating P-gp overexpressing cells with sanguinarine. It was surmised that The inhibition of NFκB activity might explain the collateral sensitivity in CEM/ADR5000 cells. The COMPARE and hierarchical cluster analyses of transcriptome-wide expression profiles of tumor cell lines of the National Cancer Institute identified genes involved in various cellular processes (immune response, inflammation signaling, cell migration and microtubule formation) significantly correlated with log₁₀IC₅₀ values for sanguinarine. In conclusion, sanguinarine may have therapeutic potential for treating multidrug resistant tumors.

Addiction of lung cancer cells to GOF p53 is promoted by up-regulation of epidermal growth factor receptor through multiple contacts with p53 transactivation domain and promoter

Human lung cancers harboring gain-of-function (GOF) p53 alleles express higher levels of the epidermal growth factor receptor (EGFR). We demonstrate that a number of GOF p53 alleles directly upregulate EGFR. Knock-down of p53 in lung cancer cells lowers EGFR expression and reduces tumorigenicity and other GOF p53 properties. However, addiction of lung cancer cells to GOF p53 can be compensated by overexpressing EGFR, suggesting that EGFR plays a critical role in addiction. Chromatin immunoprecipitation (ChIP) using lung cancer cells expressing GOF p53 alleles showed that GOF p53 localized to the EGFR promoter. The sequence where GOF p53 is found to interact by ChIP seq can act as a GOF p53 response element. The presence of GOF p53 on the EGFR promoter increased histone H3 acetylation, indicating a mechanism whereby GOF p53 enhances chromatin opening for improved access to transcription factors (TFs). ChIP and ChIP-re-ChIP with p53, Sp1 and CBP histone acetylase (HAT) antibodies revealed docking of GOF p53 on Sp1, leading to increased binding of Sp1 and CBP to the EGFR promoter. Up-regulation of EGFR can occur via GOF p53 contact at other novel sites in the EGFR promoter even when TAD-I is inactivated; these sites are used by both intact and TAD-I mutated GOF p53 and might reflect redundancy in GOF p53 mechanisms for EGFR transactivation. Thus, the oncogenic action of GOF p53 in lung cancer is highly dependent on transactivation of the EGFR promoter via a novel transcriptional mechanism involving coordinated interactions of TFs, HATs and GOF p53.

Li-Fraumeni Syndrome Disease Model: A Platform to Develop Precision Cancer Therapy Targeting Oncogenic p53

Li-Fraumeni syndrome (LFS) is a rare hereditary autosomal dominant cancer disorder. Germline mutations in TP53, the gene encoding p53, are responsible for most cases of LFS. TP53 is also the most commonly mutated gene in human cancers. Because inhibition of mutant p53 is considered to be a promising therapeutic strategy to treat these diseases, LFS provides a perfect genetic model to study p53 mutation-associated malignancies as well as to screen potential compounds targeting oncogenic p53. In this review we briefly summarize the biology of LFS and current understanding of the oncogenic functions of mutant p53 in cancer development. We discuss the strengths and limitations of current LFS disease models, and touch on existing compounds targeting oncogenic p53 and in vitro clinical trials to develop new ones. Finally, we discuss how recently developed methodologies can be integrated into the LFS induced pluripotent stem cell (iPSC) platform to develop precision cancer therapy.

NF-κB Signalling in Glioblastoma

Nuclear factor-κB (NF-κB) is a transcription factor regulating a wide array of genes mediating numerous cellular processes such as proliferation, differentiation, motility and survival, to name a few. Aberrant activation of NF-κB is a frequent event in numerous cancers, including glioblastoma, the most common and lethal form of brain tumours of glial cell origin (collectively termed gliomas). Glioblastoma is characterized by high cellular heterogeneity, resistance to therapy and almost inevitable recurrence after surgery and treatment. NF-κB is aberrantly activated in response to a variety of stimuli in glioblastoma, where its activity has been implicated in processes ranging from maintenance of cancer stem-like cells, stimulation of cancer cell invasion, promotion of mesenchymal identity, and resistance to radiotherapy. This review examines the mechanisms of NF-κB activation in glioblastoma, the involvement of NF-κB in several mechanisms underlying glioblastoma propagation, and discusses some of the important questions of future research into the roles of NF-κB in glioblastoma.

Mutant p53 Protein and the Hippo Transducers YAP and TAZ: A Critical Oncogenic Node in Human Cancers

p53 protein is a well-known tumor suppressor factor that regulates cellular homeostasis. As it has several and key functions exerted, p53 is known as “the guardian of the genome” and either loss of function or gain of function mutations in the TP53 coding protein sequence are involved in cancer onset and progression. The Hippo pathway is a key regulator of developmental and regenerative physiological processes but if deregulated can induce cell transformation and cancer progression. The p53 and Hippo pathways exert a plethora of fine-tuned functions that can apparently be in contrast with each other. In this review, we propose that the p53 status can affect the Hippo pathway function by switching its outputs from tumor suppressor to oncogenic activities. In detail, we discuss: (a) the oncogenic role of the protein complex mutant p53/YAP; (b) TAZ oncogenic activation mediated by mutant p53; (c) the therapeutic potential of targeting mutant p53 to impair YAP and TAZ oncogenic functions in human cancers.

p53 and its mutants on the slippery road from stemness to carcinogenesis

Normal development, tissue homeostasis and regeneration following injury rely on the proper functions of wide repertoire of stem cells (SCs) persisting during embryonic period and throughout the adult life. Therefore, SCs employ robust mechanisms to preserve their genomic integrity and avoid heritage of mutations to their daughter cells. Importantly, propagation of SCs with faulty DNA as well as dedifferentiation of genomically altered somatic cells may result in derivation of cancer SCs, which are considered to be the driving force of the tumorigenic process. Multiple experimental evidence suggest that p53, the central tumor suppressor gene, plays a critical regulatory role in determination of SCs destiny, thereby eliminating damaged SCs from the general SC population. Notably, mutant p53 proteins do not only lose the tumor suppressive function, but rather gain new oncogenic function that markedly promotes various aspects of carcinogenesis. In this review, we elaborate on the role of wild type and mutant p53 proteins in the various SCs types that appear under homeostatic conditions as well as in cancer. It is plausible that the growing understanding of the mechanisms underlying cancer SC phenotype and p53 malfunction will allow future optimization of cancer therapeutics in the context of precision medicine.

Inhibition of the Nuclear Export Receptor XPO1 as a Therapeutic Target for Platinum-Resistant Ovarian Cancer

Purpose: The high fatality-to-case ratio of ovarian cancer is directly related to platinum resistance. Exportin-1 (XPO1) is a nuclear exporter that mediates nuclear export of multiple tumor suppressors. We investigated possible clinicopathologic correlations of XPO1 expression levels and evaluated the efficacy of XPO1 inhibition as a therapeutic strategy in platinum-sensitive and -resistant ovarian cancer.Experimental Design: XPO1 expression levels were analyzed to define clinicopathologic correlates using both TCGA/GEO datasets and tissue microarrays (TMA). The effect of XPO1 inhibition, using the small-molecule inhibitors KPT-185 and KPT-330 (selinexor) alone or in combination with a platinum agent on cell viability, apoptosis, and the transcriptome was tested in immortalized and patient-derived ovarian cancer cell lines (PDCL) and platinum-resistant mice (PDX). Seven patients with late-stage, recurrent, and heavily pretreated ovarian cancer were treated with an oral XPO1 inhibitor.Results: XPO1 RNA overexpression and protein nuclear localization were correlated with decreased survival and platinum resistance in ovarian cancer. Targeted XPO1 inhibition decreased cell viability and synergistically restored platinum sensitivity in both immortalized ovarian cancer cells and PDCL. The XPO1 inhibitor-mediated apoptosis occurred through both p53-dependent and p53-independent signaling pathways. Selinexor treatment, alone and in combination with platinum, markedly decreased tumor growth and prolonged survival in platinum-resistant PDX and mice. In selinexor-treated patients, tumor growth was halted in 3 of 5 patients, including one with a partial response, and was safely tolerated by all.Conclusions: Taken together, these results provide evidence that XPO1 inhibition represents a new therapeutic strategy for overcoming platinum resistance in women with ovarian cancer. Clin Cancer Res; 23(6); 1552-63. ©2016 AACR.

Evaluation of growth inhibitory response of Resveratrol and Salinomycin combinations against triple negative breast cancer cells

Resveratrol (RSVL) a dietary phytochemical showed to enhance the efficacy of chemotherapeutic drugs. Recently, Salinomycin (SAL) has gained importance as cancer therapeutic value for breast cancer (BC), however, its superfluxious toxicity delimits the utility. Taking the advantage of RSVL, the therapeutic efficacy of RSVL and SAL combination was studied in vitro and in vivo system. Firstly, the synergistic combination dose of RSVL and SAL was calculated and further, the efficacy was examined by wound healing, and Western blots analysis. Further, in vivo study was performed to confirm the effect of colony formation and apoptosis detection by flow cytometry based assays. Further, the molecular mode of action was determined at both transcript and translational level by quantitative Real Time PCR combination in Ehrlich ascitic carcinoma model.The combination of IC20 (R20) of RSVL and IC10 (S10) dose of SAL showed best synergism (CI<1) with ∼5 fold dose advantage of SAL. Gene expression results at mRNA and protein level revealed that the unique combination of RSVL and SAL significantly inhibited epithelial mesenchymal transition (Fibronectin, Vimentin, N-Cadherin, and Slug); chronic inflammation (Cox2, NF-kB, p53), autophagy (Beclin and LC3) and apoptotic (Bax, Bcl-2) markers. Further, i n vivo study showed that low dose of SAL in combination with RSVL increased life span of Ehrlich ascitic mice. Overall, our study revealed that RSVL synergistically potentiated the anticancer potential of SAL against triple negative BC.

Transcriptional Regulation by Wild-Type and Cancer-Related Mutant Forms of p53

TP53 missense mutations produce a mutant p53 protein that cannot activate the p53 tumor suppressive transcriptional response, which is the primary selective pressure for TP53 mutation. Specific codons of TP53, termed hotspot mutants, are mutated at elevated frequency. Hotspot forms of mutant p53 possess oncogenic properties in addition to being deficient in tumor suppression. Such p53 mutants accumulate to high levels in the cells they inhabit, causing transcriptional alterations that produce pro-oncogenic activities, such as increased pro-growth signaling, invasiveness, and metastases. These forms of mutant p53 very likely use features of wild-type p53, such as interactions with the transcriptional machinery, to produce oncogenic effects. In this review, we discuss commonalities between wild-type and mutant p53 proteins with an emphasis on transcriptional processes.

Novel targets and interaction partners of mutant p53 Gain-Of-Function

In many human cancers p53 expression is lost or a mutant p53 protein is expressed. Over the past 15 years it has become apparent that a large number of these mutant p53 proteins have lost wild type function, but more importantly have gained functions that promote tumorigenesis and drive chemo-resistance, invasion and metastasis. Many researchers have investigated the underlying mechanisms of these Gain-Of-Functions (GOFs) and it has become apparent that many of these functions are the result of mutant p53 hijacking other transcription factors. In this review, we summarize the latest research on p53 GOF and categorize these in light of the hallmarks of cancer as presented by Hannahan and Weinberg.

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.

Double gene siRNA knockdown of mutant p53 and TNF induces apoptosis in triple-negative breast cancer cells

Apoptosis is the major downregulated pathway in cancer. Simultaneous inhibition using specific small interfering RNA (siRNA) of two key player genes, p53 and TNF, is an interesting and feasible strategy when it comes to investigating various molecular pathways and biological processes in triple-negative breast cancer (TNBC), which is one of the most aggressive and therapeutically unresponsive forms of breast cancers. Our present research focuses on evaluating the impact of double p53-siRNA and TNF-siRNA knockdown at a cellular level, and also evaluating cell proliferation, apoptosis, induction of autophagy, and gene expression by using reverse transcription polymerase chain reaction array approaches. Simultaneous inhibition of p53 and TNF in Hs578T TNBC human cell line revealed a panel of up- and downregulated genes involved in apoptosis. Furthermore, the effects of double gene knockdown were validated in a second TNBC cell line, MDA-MB-231, by using reverse transcription polymerase chain reaction TaqMan assay. All our findings help in understanding the functional mechanisms of extrinsic apoptosis, cell signaling pathways, and the mechanisms involved in tumor cell survival, growth, and death in TNBC.

p53 and the Carcinogenicity of Chronic Inflammation

Chronic inflammation is a major cancer predisposition factor. Constitutive activation of the inflammation-driving NF-κB pathway commonly observed in cancer or developed in normal tissues because of persistent infections or endogenous tissue irritating factors, including products of secretion by senescent cells accumulating with age, markedly represses p53 functions. In its turn, p53 acts as a suppressor of inflammation helping to keep it within safe limits. The antagonistic relationship between p53 and NF-κB is controlled by multiple mechanisms and reflects cardinal differences in organismal responses to intrinsic and extrinsic cell stresses driven by these two transcription factors, respectively. This provides an opportunity for developing drugs to treat diseases associated with inappropriate activity of either p53 or NF-κB through targeting the opposing pathway. Several drug candidates of this kind are currently in clinical testing. These include anticancer small molecules capable of simultaneous suppression of p53 and activation of NF-κB and NF-κB-activating biologics that counteract p53-mediated pathologies associated with systemic genotoxic stresses such as acute radiation syndrome and side effects of cancer treatment.

Oncogenic Mutant p53 Gain of Function Nourishes the Vicious Cycle of Tumor Development and Cancer Stem-Cell Formation

More than half of human tumors harbor an inactivated p53 tumor-suppressor gene. It is well accepted that mutant p53 shows an oncogenic gain-of-function (GOF) activity that facilitates the transformed phenotype of cancer cells. In addition, a growing body of evidence supports the notion that cancer stem cells comprise a seminal constituent in the initiation and progression of cancer development. Here, we elaborate on the mutant p53 oncogenic GOF leading toward the acquisition of a transformed phenotype, as well as placing mutant p53 as a major component in the establishment of cancer stem cell entity. Therefore, therapy targeted toward cancer stem cells harboring mutant p53 is expected to pave the way to eradicate tumor growth and recurrence.

Mutant p53 proteins counteract autophagic mechanism sensitizing cancer cells to mTOR inhibition

Mutations in TP53 gene play a pivotal role in tumorigenesis and cancer development. Here, we report that gain-of-function mutant p53 proteins inhibit the autophagic pathway favoring antiapoptotic effects as well as proliferation of pancreas and breast cancer cells. We found that mutant p53 significantly counteracts the formation of autophagic vesicles and their fusion with lysosomes throughout the repression of some key autophagy-related proteins and enzymes as BECN1 (and P-BECN1), DRAM1, ATG12, SESN1/2 and P-AMPK with the concomitant stimulation of mTOR signaling. As a paradigm of this mechanism, we show that atg12 gene repression was mediated by the recruitment of the p50 NF-κB/mutant p53 protein complex onto the atg12 promoter. Either mutant p53 or p50 NF-κB depletion downregulates atg12 gene expression. We further correlated the low expression levels of autophagic genes (atg12, becn1, sesn1, and dram1) with a reduced relapse free survival (RFS) and distant metastasis free survival (DMFS) of breast cancer patients carrying TP53 gene mutations conferring a prognostic value to this mutant p53-and autophagy-related signature. Interestingly, the mutant p53-driven mTOR stimulation sensitized cancer cells to the treatment with the mTOR inhibitor everolimus. All these results reveal a novel mechanism through which mutant p53 proteins promote cancer cell proliferation with the concomitant inhibition of autophagy.

Proteasome machinery is instrumental in a common gain-of-function program of the p53 missense mutants in cancer

In cancer, the tumour suppressor gene TP53 undergoes frequent missense mutations that endow mutant p53 proteins with oncogenic properties. Until now, a universal mutant p53 gain-of-function program has not been defined. By means of multi-omics: proteome, DNA interactome (chromatin immunoprecipitation followed by sequencing) and transcriptome (RNA sequencing/microarray) analyses, we identified the proteasome machinery as a common target of p53 missense mutants. The mutant p53-proteasome axis globally affects protein homeostasis, inhibiting multiple tumour-suppressive pathways, including the anti-oncogenic KSRP-microRNA pathway. In cancer cells, p53 missense mutants cooperate with Nrf2 (NFE2L2) to activate proteasome gene transcription, resulting in resistance to the proteasome inhibitor carfilzomib. Combining the mutant p53-inactivating agent APR-246 (PRIMA-1MET) with the proteasome inhibitor carfilzomib is effective in overcoming chemoresistance in triple-negative breast cancer cells, creating a therapeutic opportunity for treatment of solid tumours and metastasis with mutant p53.

Increased mitochondrial fission promotes autophagy and hepatocellular carcinoma cell survival through the ROS-modulated coordinated regulation of the NFKB and TP53 pathways

Mitochondrial morphology is dynamically remodeled by fusion and fission in cells, and dysregulation of this process is closely implicated in tumorigenesis. However, the mechanism by which mitochondrial dynamics influence cancer cell survival is considerably less clear, especially in hepatocellular carcinoma (HCC). In this study, we systematically investigated the alteration of mitochondrial dynamics and its functional role in the regulation of autophagy and HCC cell survival. Furthermore, the underlying molecular mechanisms and therapeutic application were explored in depth. Mitochondrial fission was frequently upregulated in HCC tissues mainly due to an elevated expression ratio of DNM1L to MFN1, which significantly contributed to poor prognosis of HCC patients. Increased mitochondrial fission by forced expression of DNM1L or knockdown of MFN1 promoted the survival of HCC cells both in vitro and in vivo mainly by facilitating autophagy and inhibiting mitochondria-dependent apoptosis. We further demonstrated that the survival-promoting role of increased mitochondrial fission was mediated via elevated ROS production and subsequent activation of AKT, which facilitated MDM2-mediated TP53 degradation, and NFKBIA- and IKK-mediated transcriptional activity of NFKB in HCC cells. Also, a crosstalk between TP53 and NFKB pathways was involved in the regulation of mitochondrial fission-mediated cell survival. Moreover, treatment with mitochondrial division inhibitor-1 significantly suppressed tumor growth in an in vivo xenograft nude mice model. Our findings demonstrate that increased mitochondrial fission plays a critical role in regulation of HCC cell survival, which provides a strong evidence for this process as drug target in HCC treatment.

The NF-κB Pathway and Cancer Stem Cells

The NF-κB transcription factor pathway is a crucial regulator of inflammation and immune responses. Additionally, aberrant NF-κB signaling has been identified in many types of cancer. Downstream of key oncogenic pathways, such as RAS, BCR-ABL, and Her2, NF-κB regulates transcription of target genes that promote cell survival and proliferation, inhibit apoptosis, and mediate invasion and metastasis. The cancer stem cell model posits that a subset of tumor cells (cancer stem cells) drive tumor initiation, exhibit resistance to treatment, and promote recurrence and metastasis. This review examines the evidence for a role for NF-κB signaling in cancer stem cell biology.

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 mutant p53 proteins cooperate with E2F4 to transcriptionally downregulate RAD17 and BRCA1 gene expression

Genomic instability (IN) is a common feature of many human cancers. The TP53 tumour suppressor gene is mutated in approximately half of human cancers. Here, we show that BRCA1 and RAD17 genes, whose derived proteins play a pivotal role in DNA damage repair, are transcriptional targets of gain-of-function mutant p53 proteins. Indeed, high levels of mutp53 protein facilitate DNA damage accumulation and severely impair BRCA1 and RAD17 expression in proliferating cancer cells. The recruitment of mutp53/E2F4 complex onto specific regions of BRCA1 and RAD17 promoters leads to the inhibition of their expression. BRCA1 and RAD17 mRNA expression is reduced in HNSCC patients carrying TP53 mutations when compared to those bearing wt-p53 gene. Furthermore, the analysis of gene expression databases for breast cancer patients reveals that low expression of DNA repair genes correlates significantly with reduced relapse free survival of patients carrying TP53 gene mutations. Collectively, these findings highlight the direct involvement of transcriptionally active gain of function mutant p53 proteins in genomic instability through the impairment of DNA repair mechanisms.

Mutant p53 in concert with an interleukin-27 receptor alpha deficiency causes spontaneous liver inflammation, fibrosis, and steatosis in mice

The cellular and molecular etiology of unresolved chronic liver inflammation remains obscure. Whereas mutant p53 has gain-of-function properties in tumors, the role of this protein in liver inflammation is unknown. Herein, mutant p53(R172H) is mechanistically linked to spontaneous and sustained liver inflammation and steatosis when combined with the absence of interleukin-27 (IL27) signaling (IL27RA), resembling the phenotype observed in nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) patients. Indeed, these mice develop, with age, hepatocyte necrosis, immune cell infiltration, fibrosis, and micro- and macrosteatosis; however, these phenotypes are absent in mutant p53(R172H) or IL27RA(-/-) mice. Mechanistically, endothelin A receptor (ETAR)-positive macrophages are highly accumulated in the inflamed liver, and chemical inhibition of ETAR signaling reverses the observed phenotype and negatively regulates mutant p53 levels in macrophages.

CONCLUSION

The combination of mutant p53 and IL27RA(-/-) causes spontaneous liver inflammation, steatosis, and fibrosis in vivo, whereas either gene alone in vivo has no effects on the liver.

Increased expression of bFGF is associated with carotid atherosclerotic plaques instability engaging the NF-κB pathway

Unstable atherosclerotic plaques of the carotid arteries are at great risk for the development of ischemic cerebrovascular events. The degradation of the extracellular matrix by matrix metalloproteinases (MMPs) and NO-induced apoptosis of vascular smooth muscle cells (VSMCs) contribute to the vulnerability of the atherosclerotic plaques. Basic fibroblast growth factor (bFGF) through its mitogenic and angiogenic properties has already been implicated in the pathogenesis of atherosclerosis. However, its role in plaque stability remains elusive. To address this issue, a panel of human carotid atherosclerotic plaques was analyzed for bFGF, FGF-receptors-1 and -2 (FGFR-1/-2), inducible nitric oxide synthase (iNOS) and MMP-9 expression. Our data revealed increased expression of bFGF and FGFR-1 in VSMCs of unstable plaques, implying the existence of an autocrine loop, which significantly correlated with high iNOS and MMP-9 levels. These results were recapitulated in vitro by treatment of VSMCs with bFGF. bFGF administration led to up-regulation of both iNOS and MMP-9 that was specifically mediated by nuclear factor-kappaB (NF-kappaB) activation. Collectively, our data demonstrate a novel NF-kappaB-mediated pathway linking bFGF with iNOS and MMP-9 expression that is associated with carotid plaque vulnerability.

Nuclear factor-κB in glioblastoma: insights into regulators and targeted therapy

Nuclear factor-κB (NF-κB) is a ubiquitous transcription factor that regulates multiple aspects of cancer formation, growth, and treatment response. Glioblastoma (GBM), the most common primary malignant tumor of the central nervous system, is characterized by molecular heterogeneity, resistance to therapy, and high NF-κB activity. In this review, we examine the mechanisms by which oncogenic pathways active in GBM impinge on the NF-κB system, discuss the role of NF-κB signaling in regulating the phenotypic properties that promote GBM and, finally, review the components of the NF-κB pathway that have been targeted for treatment in both preclinical studies and clinical trials. While a direct role for NF-κB in gliomagenesis has not been reported, the importance of this transcription factor in the overall malignant phenotype suggests that more rational and specific targeting of NF-κB-dependent pathways can make a significant contribution to the management of GBM.

The Expression and Correlation of iNOS and p53 in Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is the most prevalent form of oral cancer. Inducible nitric oxide synthase (iNOS) and p53 are associated with a variety of human cancers, but their expression and interaction in OSCC have not been fully explored. In this study, we investigated the expression of iNOS and p53 in OSCC and their correlation with tumor development and prognosis. In addition, we explored the interaction of iNOS and p53 in OSCC. The expression of iNOS and p53 in OSCC was investigated using immunohistochemical method and their interaction was studied using RNAi technique. Our results showed that the expression of both iNOS and p53 was significantly correlated with tumor stages and pathological grade of OSCC (P < 0.05). In contrast, there was no correlation between iNOS and p53 expression and lymph node metastasis (P < 0.05). The OSCC survival rate was negatively associated with iNOS expression, but not with p53. A significant increase in the expression of the p53 was observed when iNOS expression was knocked down. The immunoexpression of iNOS is correlated with tumorigenesis and prognosis of OSCC and may serve as a prognostic marker.

The network of pluripotency, epithelial-mesenchymal transition, and prognosis of breast cancer

Breast cancer is the leading female cancer in terms of prevalence. Progress in molecular biology has brought forward a better understanding of its pathogenesis that has led to better prognostication and treatment. Subtypes of breast cancer have been identified at the genomic level and guide therapeutic decisions based on their biology and the expected benefit from various interventions. Despite this progress, a significant percentage of patients die from their disease and further improvements are needed. The cancer stem cell theory and the epithelial-mesenchymal transition are two comparatively novel concepts that have been introduced in the area of cancer research and are actively investigated. Both processes have their physiologic roots in normal development and common mediators have begun to surface. This review discusses the associations of these networks as a prognostic framework in breast cancer.

p53 modulates NF-κB mediated epithelial-to-mesenchymal transition in head and neck squamous cell carcinoma

OBJECTIVES

To investigate the role of p53 in NF-κB mediated epithelial-to-mesenchymal (EMT) in head and neck squamous cell carcinoma (HNSCC).

MATERIALS AND METHODS

We utilized HNSCC and normal oral epithelial cell lines as our model system. We used a lentiviral shRNA system to silence the expression of p65 and p53 in these cell lines. Mutant and wild-type (WT) p53 background genotypes were analyzed. The expression of epithelial and mesenchymal markers was determined using western blotting and quantitative PCR assays. Cell morphology, growth, and invasion were determined using a 3-dimensional spheroid culture and anchorage independent growth (AIG) assays.

RESULTS

In HNSCC cells with mutant p53 we found that silencing p65 expression promoted EMT. In contrast, in the context of WT p53, ectopic p65 over-expression promoted EMT. Ablation of WT p53 in normal oral epithelial cells blocked EMT induced by p65 over-expression. We demonstrate that AIG and apoptosis induced by NF-κB activation is regulated by p53.

CONCLUSION

Our data demonstrates that p53 mutational status is critical in determining the outcome of NF-κB activation in HNSCC. In the presence of WT p53, excess p65 signal can promote EMT. Conversely, ablation of p65 in the context of mutant p53 drives EMT. These results demonstrate that p53 mutational status alters the outcome of NF-κB signaling. These results, though preliminary, demonstrate the critical role of p53 mutational status in determining the outcome of NF-κB signaling and suggest that monitoring p53 status may inform the utility of NF-κB inhibitor treatment in HNSCC.

Mutant p53-R273H mediates cancer cell survival and anoikis resistance through AKT-dependent suppression of BCL2-modifying factor (BMF)

p53 is the most frequently mutated tumor-suppressor gene in human cancers. Unlike other tumor-suppressor genes, p53 mutations mainly occur as missense mutations within the DNA-binding domain, leading to the expression of full-length mutant p53 protein. Mutant p53 proteins not only lose their tumor-suppressor function, but may also gain new oncogenic functions and promote tumorigenesis. Here, we showed that silencing of endogenous p53-R273H contact mutant, but not p53-R175H conformational mutant, reduced AKT phosphorylation, induced BCL2-modifying factor (BMF) expression, sensitized BIM dissociation from BCL-X_L and induced mitochondria-dependent apoptosis in cancer cells. Importantly, cancer cells harboring endogenous p53-R273H mutant were also found to be inherently resistant to anoikis and lack BMF induction following culture in suspension. Underlying these activities is the ability of p53-R273H mutant to suppress BMF expression that is dependent on constitutively active PI3K/AKT signaling. Collectively, these findings suggest that p53-R273H can specifically drive AKT signaling and suppress BMF expression, resulting in enhanced cell survivability and anoikis resistance. These findings open the possibility that blocking of PI3K/AKT will have therapeutic benefit in mutant p53-R273H expressing cancers.

Targeting HER (ERBB) signaling in head and neck cancer: An essential update

HNC (head and neck cancer) remains the 6th most common carcinoma worldwide. The suboptimal survival and toxicities observed with conventional approaches warrant exploration of novel therapeutic strategies such as targeted therapies. Although targeting EGFR (epidermal growth factor receptor) with cetuximab demonstrated clinical promise, HER (human epidermal growth factor receptor) or ERBB (erythroblastic leukemia viral oncogene homolog) targeted therapy in HNC has overall been suboptimal to date in clinical settings. Overcoming the resistance as well as identifying new strategies therefore remains a significant challenge. In this review, we will discuss the emerging roles of HER members besides EGFR. A comprehensive "three-dimensional" view of HER signaling pathway from the importance of EGFR nuclear translocation to our maturing concept of receptors' "spatial regulation", as well as the interdependence and interaction among different HER members will also be addressed to complete an essential update of HER signaling in HNC.

Cytoplasmic gain-of-function mutant p53 contributes to inflammation-associated cancer

Inflammation and mutation of the tumor suppressor p53 are two apparently unrelated conditions that are strongly associated with cancer initiation and progression. We recently reported that gain-of-function mutant p53 modifies the response of cancer cells to inflammatory signals by binding a cytoplasmic tumor suppressor protein involved in TNFα signaling.

Preferred binding of gain-of-function mutant p53 to bidirectional promoters with coordinated binding of ETS1 and GABPA to multiple binding sites

Gain-of-function mutant p53 is thought to induce gene expression in part by binding transcription factors bound to promoters for genes that mediate oncogenesis. We investigated the mechanism of mutant p53 binding by mapping the human genomic binding sites for p53 R273H using ChIP-Seq and showed them to localize to ETS DNA sequence motifs and locations with ETS1 and GABPA binding, both within promoters and distal to promoters. Strikingly, p53 R273H showed statistically significant and substantial binding to bidirectional promoters, which are enriched for inverted repeated ETS DNA sequence motifs. p53 R273H exhibited an exponential increase in probability of binding promoters with a higher number of ETS motifs. Both ETS1 and GABPA also showed an increase in the probability of binding to promoters with a higher number of ETS motifs. However, despite this increase in probability of binding by p53 R273H and ETS1, there was no increase in the binding signal, suggesting that the number of ETS1 and p53 R273H proteins bound per promoter is being limited. In contrast, GABPA did exhibit an increase in binding signal with higher numbers of ETS motifs per promoter. Analysis of the distance between inverted pairs of ETS motifs within promoters and binding by p53 R273H, ETS1 and GABPA, showed a novel coordination of binding for the three proteins. Both ETS1 and p53 R273H exhibited preference for binding promoters with distantly spaced ETS motifs in face-to-face and back-to-back orientations, and low binding preference to promoters with closely spaced ETS motifs. GABPA exhibited the inverse pattern of binding by preferring to bind promoters with closely spaced ETS motifs. Analysis of the helical phase between ETS motifs showed that ETS1 and p53 R273H exhibited a low preference for binding promoters with ETS motifs on the same face of the DNA helix. We propose a model for the binding of ETS1 and p53 R273H in which two inverted ETS motifs on a looped DNA helix are juxtaposed for ETS1 binding as a homodimer, with p53 R273H bound to ETS1. We propose that the formation of this DNA loop and protein-bound complex prevents additional binding of ETS1 and p53 R273H proteins to other proximal binding sites.

Methotrexate-mediated inhibition of nuclear factor κB activation by distinct pathways in T cells and fibroblast-like synoviocytes

OBJECTIVES

Nuclear factor κB (NF-κB) is a critical activator of inflammatory processes and MTX is one of the most commonly prescribed DMARDs for treatment of RA. We sought to determine whether MTX inhibited NF-κB activity in RA and in lymphocytes and fibroblast-like synoviocytes (FLSs) and to define underlying mechanisms of action.

METHODS

An NF-κB luciferase reporter plasmid was used to measure NF-κB activation across experimental stimuli. Flow cytometry was used to quantify changes in intracellular protein levels, measure levels of reactive oxygen species and determine apoptosis. Quantitative RT-PCR was used to identify changes in MTX target genes.

RESULTS

In T cell lines, MTX (0.1 μM) inhibited activation of NF-κB via depletion of tetrahydrobiopterin (BH4) and increased Jun-N-terminal kinase (JNK)-dependent p53 activity. Inhibitors of BH4 activity or synthesis also inhibited NF-κB activation and, similar to MTX, increased JNK, p53, p21 and JUN activity. Patients with RA expressed increased levels of phosphorylated or active RelA (p65) compared with controls. Levels of phosphorylated RelA were reduced in patients receiving low-dose MTX therapy. In contrast, inhibition of NF-κB activation by MTX was not mediated via BH4 depletion and JNK activation in FLSs, but rather was completely prevented by adenosine receptor antagonists.

CONCLUSION

Our findings support a model whereby distinct pathways are activated by MTX in T cells and FLSs to inhibit NF-κB activation.

Mutant p53 reprograms TNF signaling in cancer cells through interaction with the tumor suppressor DAB2IP

Inflammation is a significant factor in cancer development, and a molecular understanding of the parameters dictating the impact of inflammation on cancers could significantly improve treatment. The tumor suppressor p53 is frequently mutated in cancer, and p53 missense mutants (mutp53) can acquire oncogenic properties. We report that cancer cells with mutp53 respond to inflammatory cytokines increasing their invasive behavior. Notably, this action is coupled to expression of chemokines that can expose the tumor to host immunity, potentially affecting response to therapy. Mechanistically, mutp53 fuels NF-κB activation while it dampens activation of ASK1/JNK by TNFα, and this action depends on mutp53 binding and inhibiting the tumor suppressor DAB2IP in the cytoplasm. Interfering with such interaction reduced aggressiveness of cancer cells in xenografts. This interaction is an unexplored mechanism by which mutant p53 can influence tumor evolution, with implications for our understanding of the complex role of inflammation in cancer.