Activation of c-myc gene expression by tumor-derived p53 mutants requires a discrete C-terminal domain

Machine Learning of Three-Dimensional Protein Structures to Predict the Functional Impacts of Genome Variation

Research in the human genome sciences generates a substantial amount of genetic data for hundreds of thousands of individuals, which concomitantly increases the number of variants of unknown significance (VUS). Bioinformatic analyses can successfully reveal rare variants and variants with clear associations with disease-related phenotypes. These studies have had a significant impact on how clinical genetic screens are interpreted and how patients are stratified for treatment. There are few, if any, computational methods for variants comparable to biological activity predictions. To address this gap, we developed a machine learning method that uses protein three-dimensional structures from AlphaFold to predict how a variant will influence changes to a gene's downstream biological pathways. We trained state-of-the-art machine learning classifiers to predict which protein regions will most likely impact transcriptional activities of two proto-oncogenes, nuclear factor erythroid 2 (NFE2L2)-related factor 2 (NRF2) and c-Myc. We have identified classifiers that attain accuracies higher than 80%, which have allowed us to identify a set of key protein regions that lead to significant perturbations in c-Myc or NRF2 transcriptional pathway activities.

Degradation of MYC by the mutant p53 reactivator drug, COTI-2 in breast cancer cells

TP53 (p53) and MYC are amongst the most frequently altered genes in cancer. Both are thus attractive targets for new anticancer therapies. Historically, however, both genes have proved challenging to target and currently there is no approved therapy against either. The aim of this study was to investigate the effect of the mutant p53 reactivating drug, COTI-2 on MYC. Total MYC, pSer62 MYC and pThr58 MYC were detected using Western blotting. Proteasome-mediated degradation was determined using the proteasome, inhibitor MG-132, while MYC half-life was measured using pulse chase experiments in the presence of cycloheximide. Cell proliferation was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Treatment of 5 mutant p53 breast cancer cell lines with COTI-2 resulted in dose-dependent MYC degradation. Addition of the proteasome inhibitor, MG132, rescued the degradation, suggesting that this proteolytic system was at least partly responsible for the inactivation of MYC. Using cycloheximide in pulse chase experiments, COTI-2 was found to reduce the half-life of MYC in 2 different mutant p53 breast cancer cell lines, i.e., from 34.8 to 18.6 min in MDA-MB-232 cells and from 29.6 to 20.3 min in MDA-MB-468 cells. Co-treatment with COTI-2 and the MYC inhibitor, MYCi975 resulted in synergistic growth inhibition in all 4 mutant p53 cell lines investigated. The dual ability of COTI-2 to reactivate mutant p53 and degrade MYC should enable this compound to have broad application as an anticancer drug.

Distinct clinicopathological characteristics, genomic alteration and prognosis in breast cancer with concurrent TP53 mutation and MYC amplification

BACKGROUND

Both TP53 mutation and MYC amplification indicate poor outcomes in breast cancer (BC), but the clinical values of concurrent TP53 and MYC alterations have not been well-characterized.

METHODS

A total of 494 BC patients diagnosed at Guangdong Provincial People's Hospital (GDPH) were retrospectively analyzed. Genomic alterations were determined using next-generation sequencing. Survival analysis was applied to assess the effects of genetic alterations on relapse-free survival. The prognosis was verified based on 1405 patients from METABRIC cohort. Additionally, we used logistic regression to identify the factors associated with pathological complete response (pCR) after neoadjuvant chemotherapy.

RESULTS

In GDPH cohort, patients with TP53/MYC co-alteration exhibited higher grade and stage, more positive HER2 status and higher Ki67 levels, but less luminal A subtypes. They also had more mutations in genes involved in ERBB and TGF-β signaling pathways, as well as exclusive FANCG/CDKN2B/QKI copy number amplifications and SUFU/HIST3H3/ERCC4/JUN/BCR mutations. Concurrent TP53 and MYC alterations independently increased hazards of relapse (HR, 5.425; 95% CI: 2.019-14.579; p < 0.001). They maintained independent significance for relapse-free (HR, 1.310; 95% CI: 1.012-1.697; p = 0.041) and overall survival (HR, 1.373; 95% CI: 1.093-1.725; p = 0.006) in METABRIC cohort. Among the 81 patients receiving chemotherapy, TP53 mutation (OR, 5.750; 95% CI: 1.553-25.776; p = 0.013) and earlier stage (OR, 0.275; 95% CI 0.088-0.788; p = 0.020) were associated with pCR, while the co-alteration did not serve as an independent predictor (p = 0.199).

CONCLUSIONS

TP53/MYC co-alteration was associated with distinct clinicopathological and genomic features. They also conferred unfavorable prognosis in BC patients, and did not improve pCR after neoadjuvant chemotherapy.

c-Myc Sustains Pancreatic Cancer Cell Survival and mutp53 Stability through the Mevalonate Pathway

It has been shown that wild-type (wt)p53 inhibits oncogene c-Myc while mutant (mut)p53 may transactivate it, with an opposite behavior that frequently occurs in the crosstalk of wt or mutp53 with molecules/pathways promoting carcinogenesis. Even if it has been reported that mutp53 sustains c-Myc, whether c-Myc could in turn influence mutp53 expression remains to be investigated. In this study, we found that pharmacological or genetic inhibition of c-Myc downregulated mutp53, impaired cell survival and increased DNA damage in pancreatic cancer cells. At the molecular level, we observed that c-Myc inhibition reduced the expression of mevalonate kinase (MVK), a molecule belonging to the mevalonate pathway that—according to previous findings—can control mutp53 stability, and thus contributes to cancer cell survival. In conclusion, this study unveils another criminal alliance between oncogenes, such as c-Myc and mutp53, that plays a key role in oncogenesis.

Identification and validation of the role of c-Myc in head and neck squamous cell carcinoma

Background

Many studies have shown that c-Myc plays a critical role in tumorigenesis. However, the molecular role of c-Myc in head and neck squamous cell carcinoma (HNSC) remains unclear.

Methods

Several biological databases, including UALCAN, TIMER2.0, TCGAportal, GEPIA, KM plotter, OncoLnc, LinkedOmics, GSCA, and TCIA, were used to analyze the molecular role of c-Myc in HNSC. The expression levels of c-Myc were validated by real-time PCR (RT–PCR) and Western blot in CAL-27 cells.

Results

The expression of c-Myc mRNA were significantly increased in HPV-negative HNSC tissues. The expression of c-Myc gene level was correlated with TP53 mutation status. HNSC also showed hypomethylated c-Myc compared with normal tissues. c-Myc was identified as an ominous prognostic factor for HNSC patients and correlated with immune infiltrating levels. Moreover, high c-Myc expression was associated with decreased expression of a series of immune checkpoints, resulting in a dampened immune response. c-Myc potentially mediated IL-17 signaling pathway and Th1 and Th2 cell differentiation. Inhibition of c-Myc expression increased apoptosis of CAL-27 cells.

Conclusions

These findings suggest a new mechanism of c-Myc in the prognosis of HNSC, implying the potential of c-Myc as a therapeutic target for HNSC patients.

Tumor suppressor p53: Biology, signaling pathways, and therapeutic targeting

TP53 is the most commonly mutated gene in human cancer with over 100,000 literature citations in PubMed. This is a heavily studied pathway in cancer biology and oncology with a history that dates back to 1979 when p53 was discovered. The p53 pathway is a complex cellular stress response network with multiple diverse inputs and downstream outputs relevant to its role as a tumor suppressor pathway. While inroads have been made in understanding the biology and signaling in the p53 pathway, the p53 family, transcriptional readouts, and effects of an array of mutants, the pathway remains challenging in the realm of clinical translation. While the role of mutant p53 as a prognostic factor is recognized, the therapeutic modulation of its wild-type or mutant activities remain a work-in-progress. This review covers current knowledge about the biology, signaling mechanisms in the p53 pathway and summarizes advances in therapeutic development.

Role of Dietary Antioxidants in p53-Mediated Cancer Chemoprevention and Tumor Suppression

Cancer arises through a complex interplay between genetic, behavioral, metabolic, and environmental factors that combined trigger cellular changes that over time promote malignancy. In terms of cancer prevention, behavioral interventions such as diet can promote genetic programs that may facilitate tumor suppression; and one of the key tumor suppressors responsible for initiating such programs is p53. The p53 protein is activated by various cellular events such as DNA damage, hypoxia, heat shock, and overexpression of oncogenes. Due to its role in cell fate decisions after DNA damage, regulatory pathways controlled by p53 help to maintain genome stability and thus “guard the genome” against mutations that cause cancer. Dietary intake of flavonoids, a C₁₅ group of polyphenols, is known to inhibit cancer progression and assist DNA repair through p53-mediated mechanisms in human cells via their antioxidant activities. For example, quercetin arrests human cervical cancer cell growth by blocking the G₂/M phase cell cycle and inducing mitochondrial apoptosis through a p53-dependent mechanism. Other polyphenols such as resveratrol upregulate p53 expression in several cancer cell lines by promoting p53 stability, which in colon cancer cells results in the activation of p53-mediated apoptosis. Finally, among vitamins, folic acid seems to play an important role in the chemoprevention of gastric carcinogenesis by enhancing gastric epithelial apoptosis in patients with premalignant lesions by significantly increased expression of p53. In this review, we discuss the role of these and other dietary antioxidants in p53-mediated cell signaling in relation to cancer chemoprevention and tumor suppression in normal and cancer cells.

Proteomic Profiling of BRAFV600E Mutant Colon Cancer Cells Reveals the Involvement of Nucleophosmin/c-Myc Axis in Modulating the Response and Resistance to BRAF Inhibition by Vemurafenib

BRAFV600E mutations are found in approximately 10% of colorectal cancer patients and are associated with worse prognosis and poor outcomes with systemic therapies. The aim of this study was to identify novel druggable features of BRAFV600E-mutated colon cancer (CC) cells associated with the response and resistance to BRAFV600E inhibitor vemurafenib. Towards this aim, we carried out global proteomic profiling of BRAFV600E mutant vs. KRAS mutant/BRAF wild-type and double wild-type KRAS/BRAF CC cells followed by bioinformatics analyses. Validation of selected proteomic features was performed by immunohistochemistry and in silico using the TCGA database. We reveal an increased abundance and activity of nucleophosmin (NPM1) in BRAFV600E-mutated CC in vitro, in silico and in tumor tissues from colon adenocarcinoma patients and demonstrate the roles of NPM1 and its interaction partner c-Myc in conveying the resistance to vemurafenib. Pharmacological inhibition of NPM1 effectively restored the sensitivity of vemurafenib-resistant BRAF-mutated CC cells by down-regulating c-Myc expression and activity and consequently suppressing its transcriptional targets RanBP1 and phosphoserine phosphatase that regulate centrosome duplication and serine biosynthesis, respectively. Altogether, findings from this study suggest that the NPM1/c-Myc axis could represent a promising therapeutic target to thwart resistance to vemurafenib in BRAF-mutated CC.

Transition and identification of pathological states in p53 dynamics for therapeutic intervention

We study a minimal model of the stress-driven p53 regulatory network that includes competition between active and mutant forms of the tumor-suppressor gene p53. Depending on the nature and level of the external stress signal, four distinct dynamical states of p53 are observed. These states can be distinguished by different dynamical properties which associate to active, apoptotic, pre-malignant and cancer states. Transitions between any two states, active, apoptotic, and cancer, are found to be unidirectional and irreversible if the stress signal is either oscillatory or constant. When the signal decays exponentially, the apoptotic state vanishes, and for low stress the pre-malignant state is bounded by two critical points, allowing the system to transition reversibly from the active to the pre-malignant state. For significantly large stress, the range of the pre-malignant state expands, and the system moves to irreversible cancerous state, which is a stable attractor. This suggests that identification of the pre-malignant state may be important both for therapeutic intervention as well as for drug delivery.

Cancer Stemness: p53 at the Wheel

The tumor suppressor p53 maintains an equilibrium between self-renewal and differentiation to sustain a limited repertoire of stem cells for proper development and maintenance of tissue homeostasis. Inactivation of p53 disrupts this balance and promotes pluripotency and somatic cell reprogramming. A few reports in recent years have indicated that prevalent TP53 oncogenic gain-of-function (GOF) mutations further boosts the stemness properties of cancer cells. In this review, we discuss the role of wild type p53 in regulating pluripotency of normal stem cells and various mechanisms that control the balance between self-renewal and differentiation in embryonic and adult stem cells. We also highlight how inactivating and GOF mutations in p53 stimulate stemness in cancer cells. Further, we have explored the various mechanisms of mutant p53-driven cancer stemness, particularly emphasizing on the non-coding RNA mediated epigenetic regulation. We have also analyzed the association of cancer stemness with other crucial gain-of-function properties of mutant p53 such as epithelial to mesenchymal transition phenotypes and chemoresistance to understand how activation of one affects the other. Given the critical role of cancer stem-like cells in tumor maintenance, cancer progression, and therapy resistance of mutant p53 tumors, targeting them might improve therapeutic efficacy in human cancers with TP53 mutations.

TP53 mutations in myelodysplastic syndromes and secondary AML confer an immunosuppressive phenotype

Somatic gene mutations are key determinants of outcome in patients with myelodysplastic syndromes (MDS) and secondary AML (sAML). In particular, patients with TP53 mutations represent a distinct molecular cohort with uniformly poor prognosis. The precise pathogenetic mechanisms underlying these inferior outcomes have not been delineated. In this study, we characterized the immunological features of the malignant clone and alterations in the immune microenvironment in patients with TP53-mutant and wild-type MDS or sAML. Notably, PDL1 expression is significantly increased in hematopoietic stem cells of patients with TP53 mutations, which is associated with MYC upregulation and marked downregulation of MYC's negative regulator miR-34a, a p53 transcription target. Notably, patients with TP53 mutations display significantly reduced numbers of bone marrow-infiltrating OX40+ cytotoxic T cells and helper T cells, as well as decreased ICOS+ and 4-1BB+ natural killer cells. Further, highly immunosuppressive regulatory T cells (Tregs) (ie, ICOShigh/PD-1-) and myeloid-derived suppressor cells (PD-1low) are expanded in cases with TP53 mutations. Finally, a higher proportion of bone marrow-infiltrating ICOShigh/PD-1- Treg cells is a highly significant independent predictor of overall survival. We conclude that the microenvironment of TP53 mutant MDS and sAML has an immune-privileged, evasive phenotype that may be a primary driver of poor outcomes and submit that immunomodulatory therapeutic strategies may offer a benefit for this molecularly defined subpopulation.

Transcription factors in epithelial ovarian cancer: histotype-specific drivers and novel therapeutic targets

Transcription factors (TFs) are major contributors to cancer risk and somatic development. In preclinical and clinical studies, direct or indirect inhibition of TF-mediated oncogenic gene expression profiles have proven to be effective in many tumor types, highlighting this group of proteins as valuable therapeutic targets. In spite of this, our understanding of TFs in epithelial ovarian cancer (EOC) is relatively limited. EOC is a heterogeneous disease composed of five major histologic subtypes; high-grade serous, low-grade serous, endometrioid, clear cell and mucinous. Each histology is associated with unique clinical etiologies, sensitivity to therapies, and molecular signatures - including diverse transcriptional regulatory programs. While some TFs are shared across EOC subtypes, a set of TFs are expressed in a histotype-specific manner and likely explain part of the histologic diversity of EOC subtypes. Targeting TFs present with unique opportunities for development of novel precision medicine strategies for ovarian cancer. This article reviews the critical TFs in EOC subtypes and highlights the potential of exploiting TFs as biomarkers and therapeutic targets.

Mast cell-based molecular subtypes and signature associated with clinical outcome in early-stage lung adenocarcinoma

Mast cells are a major component of the immune microenvironment in tumour tissues and modulate tumour progression by releasing pro‐tumorigenic and antitumorigenic molecules. Regarding the impact of mast cells on the outcomes of patients with lung adenocarcinoma (LUAD) patient, several published studies have shown contradictory results. Here, we aimed at elucidating the role of mast cells in early‐stage LUAD. We found that high mast cell abundance was correlated with prolonged survival in early‐stage LUAD patients. The mast cell‐related gene signature and gene mutation data sets were used to stratify early‐stage LUAD patients into two molecular subtypes (subtype 1 and subtype 2). The neural network‐based framework constructed with the mast cell‐related signature showed high accuracy in predicting response to immunotherapy. Importantly, the prognostic mast cell‐related signature predicted the survival probability and the potential relationship between TP53 mutation, c‐MYC activation and mast cell activities. The meta‐analysis confirmed the prognostic value of the mast cell‐related gene signature. In summary, this study might improve our understanding of the role of mast cells in early‐stage LUAD and aid in the development of immunotherapy and personalized treatments for early‐stage LUAD patients.

EZH2 expression is dependent on MYC and TP53 regulation in diffuse large B-cell lymphoma

EZH2 is an important epigenetic regulator, but its role in diffuse large B-cell lymphoma (DLBCL) pathogenesis and its relationship with MYC, BCL2, and TP53 expression, chromosomal rearrangements, and clinical features are still poorly understood. So, we investigated EZH2 expression and its associations with the immunophenotypic presentations, including MYC, BCL2, and TP53 expression, MYC, BCL2, and BCL6 translocation status, clinicopathological features, and therapeutic response to R-CHOP in a series of 139 DLBCL cases. EZH2 positivity was associated with MYC and TP53 expression (p = 0.0002 and p = 0.0000, respectively) and to high proliferative index (Ki67>70%, p = 0.0082). No associations were found among EZH2 expression and chromosomal translocation status. The non-germinal center (nGC) DLBCL presented most of associations observed in the general sample; however, only TP53 immunodetection showed associations with EZH2 expression in the germinal center (GC) DLBCL. EZH2 expression had no impact on therapeutic efficacy in R-CHOP-treated patients. In conclusion, EZH2 seems to be upregulated by MYC, to rely on TP53 alterations, and is associated with high proliferative tumors in DLBCL, which might be dependent on GC or nGC subclassifications. Furthermore, it is not a therapeutic efficacy marker to R-CHOP in our series.

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.

Dominant-negative p53 mutant R248Q increases the motile and invasive activities of oral squamous cell carcinoma cells

The tumor suppressor gene TP53 (gene) codes for a transcription factor which transactivates its target genes responsible for cell cycle arrest, DNA repair, apoptosis, and senescence. TP53 is well known to be the most frequent target of genetic mutations in nearly half of human cancers including oral squamous cell carcinoma (OSCC). Many p53 mutants including R248Q and R248W not only lose its tumor-suppressor activities, but also interfere with the functions of wild-type p53; this is so-called dominant-negative (DN) mutation. The DN p53 mutation is a predictor of poor outcome in patients with various cancers, and also a risk factor for metastatic recurrence in patients with OSCC. Recently it has been reported that DN p53 mutants acquire new oncogenic activities, which is named gain-of-function (GOF). This study aimed at determining whether R248Q and R248W were involved in OSCC cells' acquiring aggressive phenotypes, using SAS, HSC4 and Ca9-22 cell lines. First, two mutants p53, R248Q and R248W, were respectively transfected into SAS cells harboring recessive-type p53 (E336X). As a result, SAS cells expressing R248Q showed highly spreading, motile and invasive activities compared to parent or mock-transfected cells whereas those expressing R248W did not increase those activities. Secondly, in HSC4 cells harboring R248Q and Ca9-22 cells harboring R248W, expressions of the mutants p53 were inhibited by the transfection with siRNAs targeting p53. The inhibition of the mutants p53 decreased spreading, motile and invasive activities of HSC4 cells whereas it did not affect those activities of Ca9-22 cells. These findings suggest that R248Q p53 mutation, but not R248W p53 mutation, induces more motile and invasive potentials in human OSCC cells.

Nonsteroidal Anti-inflammatory Drugs Sensitize CD44-Overexpressing Cancer Cells to Hsp90 Inhibitor Through Autophagy Activation

Recently, novel therapeutic strategies have been designed with the aim of killing cancer stem-like cells (CSCs), and considerable interest has been generated in the development of specific therapies that target stemness-related marker of CSCs. In this study, nonsteroidal anti-inflammatory drugs (NSAIDs) significantly potentiated Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG)-mediated cytotoxicity through apoptotic and autophagic cell death induction, but COX-2-inhibitory function was not required for NSAID-induced autophagy in CD44-overexpressing human chronic myeloid leukemia K562 (CD44^highK562) cells. Importantly, we found that treatment with NSAIDs resulted in a dose-dependent increase in LC3-II level and decrease in p62 level and simultaneous reduction in multiple stemness-related markers including CD44, Oct4, c-Myc, and mutant p53 (mutp53) in CD44^highK562 cells, suggesting that NSAIDs could induce autophagy, which might mediate degradation of stemness-related marker proteins. Activation of AMPK and inhibition of Akt/mTOR/p70S6K/4EBP1 participated in NSAID-induced autophagy in CD44^highK562 cells. In addition, treatment of CD44^highK562 cells with NSAIDs inhibited expression of HSF1/Hsps, which resulted in suppression of 17-AAG-induced activation of Hsp70, leading to reversal of 17-AAG resistance and sensitization of CD44^highK562 cells to 17-AAG by NSAIDs. In conclusion, combining NSAIDs with Hsp90 inhibitor may offer one of the most promising strategies for eradication of CD44-overexpressing CSCs.

Mutant p53 in cancer therapy-the barrier or the path

Since wild-type p53 is central for maintaining genomic stability and preventing oncogenesis, its coding gene TP53 is highly mutated in ~50% of human cancers, and its activity is almost abrogated in the rest of cancers. Approximately 80% of p53 mutations are single point mutations with several hotspot mutations. Besides loss of function and dominant-negative effect on the wild-type p53 activity, the hotspot p53 mutants also acquire new oncogenic functions, so-called 'gain-of-functions' (GOF). Because the GOF of mutant p53 is highly associated with late-stage malignance and drug resistance, these p53 mutants have become hot targets for developing novel cancer therapies. In this essay, we review some recent progresses in better understanding of the role of mutant p53 GOF in chemoresistance and the underlying mechanisms, and discuss the pros and cons of targeting mutant p53 for the development of anti-cancer therapies.

Cytarabine-Resistant FLT3-ITD Leukemia Cells are Associated with TP53 Mutation and Multiple Pathway Alterations-Possible Therapeutic Efficacy of Cabozantinib

Internal tandem duplication of FLT3 juxtamembrane domain (FLT3-ITD)-positive acute myeloid leukemia (AML) leads to poor clinical outcomes after chemotherapy. We aimed to establish a cytarabine-resistant line from FLT3-ITD-positive MV4-11 (MV4-11-P) cells and examine the development of resistance. The FLT3-ITD mutation was retained in MV4-11-R; however, the protein was underglycosylated and less phosphorylated in these cells. Moreover, the phosphorylation of ERK1/2, Akt, MEK1/2 and p53 increased in MV4-11-R. The levels of Mcl-1 and p53 proteins were also elevated in MV4-11-R. A p53 D281G mutant emerged in MV4-11-R, in addition to the pre-existing R248W mutation. MV4-11-P and MV4-11-R showed similar sensitivity to cabozantinib, sorafenib, and MK2206, whereas MV4-11-R showed resistance to CI-1040 and idarubicin. MV4-11-R resistance may be associated with inhibition of Akt phosphorylation, but not ERK phosphorylation, after exposure to these drugs. The multi-kinase inhibitor cabozantinib inhibited FLT3-ITD signaling in MV4-11-R cells and MV4-11-R-derived tumors in mice. Cabozantinib effectively inhibited tumor growth and prolonged survival time in mice bearing MV4-11-R-derived tumors. Together, our findings suggest that Mcl-1 and Akt phosphorylation are potential therapeutic targets for p53 mutants and that cabozantinib is an effective treatment in cytarabine-resistant FLT3-ITD-positive AML.

Dysregulation of Glucose Metabolism by Oncogenes and Tumor Suppressors in Cancer Cells

Cancers are complex diseases having several unique features, commonly described as ‘hallmarks of cancer’. Among them, altered signaling pathways are the common characteristic features that drive cancer progression; this is achieved due to mutations that lead to the activation of growth promoting(s) oncogenes and inactivation of tumor suppressors. As a result of which, cancer cells increase their glycolytic rate by consuming a large amount of glucose, and convert a majority of glucose to lactate even in the presence of oxygen known as the “Warburg effect”. Tumor cells like other cells are strictly dependent on energy for growth and survival; therefore, understanding energy metabolism will give us an idea to develop new effective anti-cancer therapies that target cancer energy production pathways. This review summarizes the roles of tumor suppressors and oncogenes and their products that provide metabolic advantages to cancer cells which in turn leads to the establishment of the “Warburg effect” and ultimately leads to cancer progression. Understanding cancer cell’s vulnerability will provide potential targets for its control.

Oncogene c-fos and mutant R175H p53 regulate expression of Nucleophosmin implicating cancer manifestation

Nucleophosmin (NPM1) is a nucleolar protein that is frequently overexpressed in various types of solid tumors. NPM1 is involved in several cellular processes that might contribute significantly to the increased proliferation potential of cancers. Previous reports suggest that NPM1 expression is highly increased in response to mitogenic and oncogenic signals, the mechanisms of which have not been elucidated extensively. Using constructs incorporating different fragments of the NPM1 promoter upstream to a Luciferase reporter gene, we have identified the minimal promoter of NPM1 and candidate transcription factors regulating NPM1 promoter activity by luciferase reporter assays. We have validated the roles of a few candidate factors at the transcriptional and protein level by quantitative reverse transcriptase PCR, immunoblotting and immunohistochemistry, and explored the mechanism of regulation of NPM1 expression using immunoprecipitation and chromatin immunoprecipitation assays. We show here that the expression of NPM1 is regulated by transcription factor c-fos, a protein that is strongly activated by growth factor signals. In addition, mutant p53 (R175H) overexpression also enhances NPM1 expression possibly through c-myc and c-fos. Moreover, both c-fos and mutant p53 are overexpressed in oral tumor tissues that showed NPM1 overexpression. Collectively, our results suggest that c-fos and mutant p53 R175H positively regulate NPM1 expression, possibly in synergism, that might lead to oncogenic manifestation.

Aberrant expression of ETS1 and ETS2 proteins in cancer

The ETS transcription factors regulate expression of genes involved in normal cell development, proliferation, differentiation, angiogenesis, and apoptosis, consisting of 28 family members in humans. Dysregulation of these transcription factors facilitates cell proliferation in cancers, and several members participate in invasion and metastasis by activating gene transcription. ETS1 and ETS2 are the founding members of the ETS family and regulate transcription by binding to ETS sequences. They are both involved in oncogenesis and tumor suppression depending on the biological situations used. The essential roles of ETS proteins in human telomere maintenance have been suggested, which have been linked to creation of new Ets binding sites. Recently, preferential binding of ETS2 to gain-of-function mutant p53 and ETS1 to wild type p53 (WTp53) has been suggested, raising the tumor promoting role for the former and tumor suppressive role for the latter. The oncogenic and tumor suppressive functions of ETS1 and 2 proteins have been discussed.

Control of Nucleotide Metabolism Enables Mutant p53's Oncogenic Gain-of-Function Activity

Since its discovery as an oncoprotein in 1979, investigation into p53's many identities has completed a full circle and today it is inarguably the most extensively studied tumor suppressor (wild-type p53 form or WTp53) and oncogene (mutant p53 form or mtp53) in cancer research. After the p53 protein was declared "Molecule of the Year" by Science in 1993, the p53 field exploded and a plethora of excellent reviews is now available on every aspect of p53 genetics and functional repertoire in a cell. Nevertheless, new functions of p53 continue to emerge. Here, we discuss a novel mechanism that contributes to mtp53's Gain of Functions GOF (gain-of-function) activities and involves the upregulation of both nucleotide de novo synthesis and nucleoside salvage pathways.

Transcriptional repression of Aurora-A gene by wild-type p53 through directly binding to its promoter with histone deacetylase 1 and mSin3a

In this study, we firstly showed that p53 transcriptionally represses Aurora-A gene expression through directly binding to its promoter. DNA affinity precipitation assay and chromatin immunoprecipitation assay indicated that p53 physically bound to the Aurora-A promoter. Moreover, the in vitro and in vivo assays showed that p53 directly bound to the Aurora-A promoter together with histone deacetylase 1 (HDAC1) and mSin3a as corepressors. Furthermore, we identified that the nucleotides -360 to -354 (CCTGCCC), upstream of the Aurora-A transcriptional start site, was responsible for the p53-mediated repression. Mutation within this site disrupted its interaction with p53, mSin3a and HDAC1, as well as attenuated the repressive effect of p53 on Aurora-A promoter activity. Treatment with trichostatin A (TSA), a HDAC1 inhibitor, disrupted the interaction of p53-HDAC1-mSin3a complex with the nucleotides -365∼-345 region, and enhanced the Aurora-A promoter activity and gene expression. Additionally, knockdown of p53 or mSin3a also drastically blocked the formation of p53-HDAC1-mSin3a repressive complex onto this promoter region and elevated the Aurora-A promoter activity and gene expression. Moreover, the p53-HDAC1-mSin3a repressive complex also involved in the inhibition of Aurora-A gene expression upon cisplatin treatment. Finally, the clinical investigation showed that Aurora-A and p53 exhibited an inverse correlation in both the expression level and prognostic status, and the low p53/high Aurora-A showed the poorest prognosis of NSCLC patients. Our findings showed novel regulatory mechanisms of p53 in regulating Aurora-A gene expression in NSCLC cells.

Mutant p53 stimulates cell invasion through an interaction with Rad21 in human ovarian cancer cells

Missense mutations of TP53 are extremely common, and mutant p53 accumulation and gain-of-function play crucial roles in human ovarian cancer. Here, we investigated the role of mutant p53 in cell migration and invasion as well as its underlying molecular mechanisms in human ovarian cancer cells. Overexpression of mutant p53 significantly increased migration and invasion in p53-null SKOV3 cells. In contrast, knockdown of mutant p53 significantly compromised mutant p53-induced cell migration and invasion. Microarray analysis revealed that several migration/invasion-related genes, including S1PR1 (Sphingosine-1-phosphate receptor 1) and THBS1 (Thrombospodin 1), were significantly upregulated in SKOV3 cells that overexpressed mutant p53-R248 (SKOV3^R248). We found that Rad21 is involved in the transcriptional regulation of the migration/invasion-related genes induced by mutant p53-R248. Knockdown of Rad21 significantly attenuated the mutant p53-R248-induced invasion and the expressions of S1PR1 and THBS1. Moreover, co-immunoprecipitation and chromatin immunoprecipitation assays revealed that mutant p53 interacts with Rad21 and binds to the Rad21-binding elements in the S1PR1 and THBS1 genes. Finally, downregulation of S1PR1 significantly attenuated the invasion driven by mutant p53-R248. These novel findings reveal that mutant p53-R248 maintains gain-of-function activity to stimulate cell invasion and induces the related gene expressions through an interaction with Rad21 in human ovarian cancer cells.

Depletion of runt-related transcription factor 2 (RUNX2) enhances SAHA sensitivity of p53-mutated pancreatic cancer cells through the regulation of mutant p53 and TAp63

Suberoylanilide hydroxamic acid (SAHA) represents one of the new class of anti-cancer drugs. However, multiple lines of clinical evidence indicate that SAHA might be sometimes ineffective on certain solid tumors including pancreatic cancer. In this study, we have found for the first time that RUNX2/mutant p53/TAp63-regulatory axis has a pivotal role in the determination of SAHA sensitivity of p53-mutated pancreatic cancer MiaPaCa-2 cells. According to our present results, MiaPaCa-2 cells responded poorly to SAHA. Forced depletion of mutant p53 stimulated SAHA-mediated cell death of MiaPaCa-2 cells, which was accomapanied by a further accumulation of γH2AX and cleaved PARP. Under these experimental conditions, pro-oncogenic RUNX2 was strongly down-regulated in mutant p53-depleted MiaPaCa-2 cells. Surprisingly, RUNX2 silencing augmented SAHA-dependent cell death of MiaPaCa-2 cells and caused a significant reduction of mutant p53. Consistent with these observations, overexpression of RUNX2 in MiaPaCa-2 cells restored SAHA-mediated decrease in cell viability and increased the amount of mutant p53. Thus, it is suggestive that there exists a positive auto-regulatory loop between RUNX2 and mutant p53, which might amplify their pro-oncogenic signals. Intriguingly, knockdown of mutant p53 or RUNX2 potentiated SAHA-induced up-regulation of TAp63. Indeed, SAHA-stimulated cell death of MiaPaCa-2 cells was partially attenuated by p63 depletion. Collectively, our present observations strongly suggest that RUNX2/mutant p53/TAp63-regulatory axis is one of the key determinants of SAHA sensitivity of p53-mutated pancreatic cancer cells.

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.

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.

Emerging Non-Canonical Functions and Regulation by p53: p53 and Stemness

Since its discovery nearly 40 years ago, p53 has ascended to the forefront of investigated genes and proteins across diverse research disciplines and is recognized most exclusively for its role in cancer as a tumor suppressor. Levine and Oren (2009) reviewed the evolution of p53 detailing the significant discoveries of each decade since its first report in 1979. In this review, we will highlight the emerging non-canonical functions and regulation of p53 in stem cells. We will focus on general themes shared among p53's functions in non-malignant stem cells and cancer stem-like cells (CSCs) and the influence of p53 on the microenvironment and CSC niche. We will also examine p53 gain of function (GOF) roles in stemness. Mutant p53 (mutp53) GOFs that lead to survival, drug resistance and colonization are reviewed in the context of the acquisition of advantageous transformation processes, such as differentiation and dedifferentiation, epithelial-to-mesenchymal transition (EMT) and stem cell senescence and quiescence. Finally, we will conclude with therapeutic strategies that restore wild-type p53 (wtp53) function in cancer and CSCs, including RING finger E3 ligases and CSC maintenance. The mechanisms by which wtp53 and mutp53 influence stemness in non-malignant stem cells and CSCs or tumor-initiating cells (TICs) are poorly understood thus far. Further elucidation of p53's effects on stemness could lead to novel therapeutic strategies in cancer research.

Wild-type p53 binds to MYC promoter G-quadruplex

G-quadruplexes are four-stranded nucleic acid structures that are implicated in the regulation of transcription, translation and replication. Genome regions enriched in putative G-quadruplex motifs include telomeres and gene promoters. Tumour suppressor p53 plays a critical role in regulatory pathways leading to cell cycle arrest, DNA repair and apoptosis. In addition to transcriptional regulation mediated via sequence-specific DNA binding, p53 can selectively bind various non-B DNA structures. In the present study, wild-type p53 (wtp53) binding to G-quadruplex formed by MYC promoter nuclease hypersensitive element (NHE) III₁ region was investigated. Wtp53 binding to MYC G-quadruplex is comparable to interaction with specific p53 consensus sequence (p53CON). Apart from the full-length wtp53, its isolated C-terminal region (aa 320-393) as well, is capable of high-affinity MYC G-quadruplex binding, suggesting its critical role in this type of interaction. Moreover, wtp53 binds to MYC promoter region containing putative G-quadruplex motif in two wtp53-expressing cell lines. The results suggest that wtp53 binding to G-quadruplexes can take part in transcriptional regulation of its target genes.

Barasertib (AZD1152), a Small Molecule Aurora B Inhibitor, Inhibits the Growth of SCLC Cell Lines In Vitro and In Vivo

Small-cell lung cancer (SCLC) cells have rapid proliferation, universal Rb inactivation, and high rates of MYC family amplification, making aurora kinase inhibition a natural target. Preclinical studies have demonstrated activity for Aurora A and pan-Aurora inhibitors with some relationship to MYC family expression. A clinical trial showed activity for an Aurora kinase A inhibitor, but no biomarkers were evaluated. We screened a panel of 23 SCLC lines with and without MYC family gene amplification or high MYC family gene expression for growth inhibition by the highly potent, selective aurora kinase B inhibitor barasertib. Nine of the SCLC lines were very sensitive to growth inhibition by barasertib, with IC₅₀ values of <50 nmol/L and >75% growth inhibition at 100 nmol/L. Growth inhibition correlated with cMYC amplification (P = 0.018) and cMYC gene expression (P = 0.026). Sensitive cell lines were also enriched in a published MYC gene signature (P = 0.042). In vivo, barasertib inhibited the growth of xenografts established from an SCLC line that had high cMYC gene expression, no cMYC amplification, and was positive for the core MYC gene signature. Our studies suggest that SCLC tumors with cMYC amplification/high gene expression will frequently respond to Aurora B inhibitors and that clinical studies coupled with predictive biomarkers are indicated. Mol Cancer Ther; 15(10); 2314-22. ©2016 AACR.

Mutant p53 Gain of Function and Chemoresistance: The Role of Mutant p53 in Response to Clinical Chemotherapy

PURPOSE

To review mechanisms underlying mutant p53 (mutp53) gain of function (GOF) and mutp53-induced chemoresistance, and to investigate the role of mutp53 in response to clinical chemotherapy.

METHODS

We searched the PubMed database for clinical studies from the past decade, including data evaluating the impact of mutp53 in clinical chemotherapy response.

RESULTS

Interactions between mutp53 and transcriptional factors, proteins or DNA structures, as well as epigenetic regulation, contribute to mutp53 GOF. Major mechanisms of mutp53-induced chemoresistance include enhanced drug efflux and metabolism, promoting survival, inhibiting apoptosis, upregulating DNA repair, suppressing autophagy, elevating microenvironmental resistance and inducing a stem-like phenotype. Clinically, mutp53 predicted resistance to chemotherapy in diffuse large B-cell lymphoma, and esophageal and oropharyngeal cancers, but its impact on chronic lymphocytic leukemia was unclear. In bladder cancer, mutp53 did not predict resistance, whereas in some breast and ovarian cancers, it was associated with sensitivity to certain chemotherapeutic agents.

CONCLUSION

mutp53 has an intricate role in the response to clinical chemotherapy and should not be interpreted in isolation. Furthermore, when predicting tumor response to chemotherapy based on the p53 status, the drugs used should also be taken into consideration. These concepts require further investigation.

A rare DNA contact mutation in cancer confers p53 gain-of-function and tumor cell survival via TNFAIP8 induction

The p53 tumor suppressor gene encodes a sequence-specific transcription factor. Mutations in the coding sequence of p53 occur frequently in human cancer and often result in single amino acid substitutions (missense mutations) in the DNA binding domain (DBD), blocking normal tumor suppressive functions. In addition to the loss of canonical functions, some missense mutations in p53 confer gain-of-function (GOF) activities to tumor cells. While many missense mutations in p53 cluster at six "hotspot" amino acids, the majority of mutations in human cancer occur elsewhere in the DBD and at a much lower frequency. We report here that mutations at K120, a non-hotspot DNA contact residue, confer p53 with the previously unrecognized ability to bind and activate the transcription of the pro-survival TNFAIP8 gene. Mutant K120 p53 binds the TNFAIP8 locus at a cryptic p53 response element that is not occupied by wild-type p53. Furthermore, induction of TNFAIP8 is critical for the evasion of apoptosis by tumor cells expressing the K120R variant of p53. These findings identify induction of pro-survival targets as a mechanism of gain-of-function activity for mutant p53 and will likely broaden our understanding of this phenomenon beyond the limited number of GOF activities currently reported for hotspot mutants.

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.

TP53 mutation, mitochondria and cancer

Under normal conditions, basal levels of wild-type p53 promote mitochondrial function through multiple mechanisms. Remarkably, some missense mutations of p53, in contrast to the null state, can result in the retention of its metabolic activities. These effects are particularly prominent in the mitochondria and demonstrate a functional role for mutant p53 in cancer metabolism. This review summarizes accumulating data on the mechanisms by which p53 missense mutations can regulate mitochondrial metabolism and promote the viability and survival of both normal and cancer cells, thus acting as a double edged sword for the host. Greater understanding of these mechanisms may provide insights for developing new treatment or preventive strategies against cancer.

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.

Expression of CDK8 and CDK8-interacting Genes as Potential Biomarkers in Breast Cancer

CDK8 and its paralog CDK19, in complex with CCNC, MED12 and MED13, are transcriptional regulators that mediate several carcinogenic pathways and the chemotherapy-induced tumor-supporting paracrine network. Following up on our previous observation that CDK8, CDK19 and CCNC RNA expression is associated with shorter relapse-free survival (RFS) in breast cancer, we now found by immunohistochemical analysis that CDK8/19 protein is overexpressed in invasive ductal carcinomas relative to non-malignant mammary tissues. Meta-analysis of transcriptomic data revealed that higher CDK8 expression is associated with shorter RFS in all molecular subtypes of breast cancer. These correlations were much stronger in patients who underwent systemic adjuvant therapy, suggesting that CDK8 impacts the failure of systemic therapy. The same associations were found for CDK19, CCNC and MED13. In contrast, MED12 showed the opposite association with a longer RFS. The expression levels of CDK8 in breast cancer samples were directly correlated with the expression of MYC, as well as CDK19, CCNC and MED13 but inversely correlated with MED12. CDK8, CDK19 and CCNC expression was strongly increased and MED12 expression was decreased in tumors with mutant p53. Gene amplification is the most frequent type of genetic alterations of CDK8, CDK19, CCNC and MED13 in breast cancers (9.7% of which have amplified MED13), whereas point mutations are more common in MED12. These results suggest that the expression of CDK8 and its interactive genes has a profound impact on the response to adjuvant therapy in breast cancer in accordance with the role of CDK8 in chemotherapy-induced tumor-supporting paracrine activities.

Arsenic trioxide reactivates proteasome-dependent degradation of mutant p53 protein in cancer cells in part via enhanced expression of Pirh2 E3 ligase

The p53 gene is mutated in more than 50% of human tumors. Mutant p53 exerts an oncogenic function and is often highly expressed in cancer cells due to evasion of proteasome-dependent degradation. Thus, reactivating proteasome-dependent degradation of mutant p53 protein is an attractive strategy for cancer management. Previously, we found that arsenic trioxide (ATO), a drug for acute promyelocytic leukemia, degrades mutant p53 protein through a proteasome pathway. However, it remains unclear what is the E3 ligase that targets mutant p53 for degradation. In current study, we sought to identify an E3 ligase necessary for ATO-mediated degradation of mutant p53. We found that ATO induces expression of Pirh2 E3 ligase at the transcriptional level. We also found that knockdown of Pirh2 inhibits, whereas ectopic expression of Pirh2 enhances, ATO-induced degradation of mutant p53 protein. Furthermore, we found that Pirh2 E3 ligase physically interacts with and targets mutant p53 for polyubiquitination and subsequently proteasomal degradation. Interestingly, we found that ATO cooperates with HSP90 or HDAC inhibitor to promote mutant p53 degradation and growth suppression in tumor cells. Together, these data suggest that ATO promotes mutant p53 degradation in part via induction of the Pirh2-dependent proteasome pathway.

Cancer cell metabolism and developmental homeodomain/POU domain transcription factors: a connecting link

The human race is afflicted with more than 100 types of cancer with diversified underlying genetic events. Still, altered metabolism (known as 'Warburg effect') and unrestrained cellular proliferation are precise traits of all cancers, being governed by the expression of genes. The obligatory energy for the proliferating neoplastic cells is endowed through the glycolytic pathway, albeit, lesser ATP is generated in this metabolic process. So, some perceptible cancer cell specific signalling is at the base of the transformed metabolism. Concurrently, the regulators of gene expression, transcription factors, have been observed to be one of the driving forces for tumourigenesis through transcriptional activation of genes involved not only in proliferation, growth and survival signalling, but also in glycolysis. This may be exemplified by the extensively studied metabolic functions of the transcriptional regulator, hypoxia inducible factor 1 (HIF1), which transactivates genes of the major enzymes of glycolysis. Preliminary investigation of a vital group of transcription factors, homeodomain transcription factors, revealed association with the process of development of an organism. The homeodomain transcription factors are, however, also found to be involved in the tumourigenesis process, with little or no information on their involvement in cancer cell metabolism. So, this is a review of the existing knowledge on homeodomain transcription factor/s for deciphering their involvement in neoplastic metabolism and it emerges that homeodomain transcription factors influence the transformed metabolic pathway in a circuitous manner.

A mutant p53/let-7i-axis-regulated gene network drives cell migration, invasion and metastasis

Most p53 mutations in human cancers are missense mutations resulting in a full-length mutant p53 protein. Besides losing tumor suppressor activity, some hotspot p53 mutants gain oncogenic functions. This effect is mediated in part, through gene expression changes due to inhibition of p63 and p73 by mutant p53 at their target gene promoters. Here, we report that the tumor suppressor microRNA let-7i is downregulated by mutant p53 in multiple cell lines expressing endogenous mutant p53. In breast cancer patients, significantly decreased let-7i levels were associated with missense mutations in p53. Chromatin immunoprecipitation and promoter luciferase assays established let-7i as a transcriptional target of mutant p53 through p63. Introduction of let-7i to mutant p53 cells significantly inhibited migration, invasion and metastasis by repressing a network of oncogenes including E2F5, LIN28B, MYC and NRAS. Our findings demonstrate that repression of let-7i expression by mutant p53 has a key role in enhancing migration, invasion and metastasis.

Transcriptional regulation by mutant p53 and oncogenesis

More than half of all human cancers carry p53 gene mutations whose resulting proteins are mostly full-length with a single amino acid change, abundantly present in cancer cells and unable to exert oncosuppressor activities. Frequently, mutant p53 proteins gain oncogenic functions through which they actively contribute to the establishment, the maintenance and the spreading of a given cancer cell. Intense research effort has been devoted to the deciphering of the molecular mechanisms underlying the gain of function of mutant p53 proteins. Here we mainly review the oncogenic transcriptional activity of mutant p53 proteins that mainly occurs through the aberrant cooperation with bona-fide transcription factors and leads to either aberrant up-regulation or down-regulation of selected target genes. Thus, mutant p53 proteins are critical components of oncogenic transcriptional networks that have a profound impact in human cancers.

APE1/Ref-1 enhances DNA binding activity of mutant p53 in a redox-dependent manner

Apurinic/apyrimidinic endonuclease 1/redox factor-1 (APE1/Ref-1) is a dual function protein; in addition to its DNA repair activity, it can stimulate DNA binding activity of numerous transcription factors as a reduction-oxidation (redox) factor. APE1/Ref-1 has been found to be a potent activator of wild-type p53 (wtp53) DNA binding in vitro and in vivo. Although p53 is mutated in most types of human cancer including hepatocellular carcinoma (HCC), little is known about whether APE1/Ref-1 can regulate mutant p53 (mutp53). Herein, we reported the increased APE1/Ref-1 protein and accumulation of mutp53 in HCC by immunohistochemistry. Of note, it was observed that APE1/Ref-1 high-expression and mutp53 expression were associated with carcinogenesis and progression of HCC. To determine whether APE1/Ref-1 regulates DNA binding of mutp53, we performed electromobility shift assays (EMSAs) and quantitative chromatin immunoprecipitation (ChIP) assays in HCC cell lines. In contrast to sequence-specific and DNA structure-dependent binding of wtp53, reduced mutp53 efficiently bound to nonlinear DNA, but not to linear DNA. Notably, overexpression of APE1/Ref-1 resulted in increased DNA binding activity of mutp53, while downregulation of APE1/Ref-1 caused a marked decrease of mutp53 DNA binding. In addition, APE1/Ref-1 could not potentiate the accumulation of p21 mRNA and protein in mutp53 cells. These data indicate that APE1/Ref-1 can stimulate mutp53 DNA binding in a redox-dependent manner.

HDAC inhibitor DWP0016 activates p53 transcription and acetylation to inhibit cell growth in U251 glioblastoma cells

Here we report a hydroacid named DWP0016, which exhibited HDAC inhibition and induced p53 acetylation in U251 glioblastoma cells. DWP0016 effectively inhibited the cell growth of U251 cells and other four carcinoma cell lines but did not affect the normal cells. Cell cycle distribution analysis showed DWP0016 arrested at G1 phase cell cycle dose-dependently in U251 cells. DWP0016 induced caspase-dependent and independent apoptosis in U251 cells, which was identified by flow cytometry analysis, caspases activity analysis, Western blotting assay, and caspases inhibition. Mechanisms research suggested that DWP0016 activated transcription and acetylation of tumor suppressor p53. DWP0016 regulated p300, CBP, and PCAF to facilitate p53 acetylation at lys382 in U251 cells. In addition, activation of p53 by DWP0016 promoted PUMA to catalyze mitochondrial pathway. Besides, siRNA assay indicated p53 was the key gene to induce growth inhibition, cell cycle arrest, and apoptosis in DWP0016 treated U251 cells. Conclusively, our results show DWP0016 is a potent HDAC inhibitor and the anti-tumor activity is consistent with its intended p53 activation mechanisms. These findings indicate the promising antitumor potential of DWP0016 for further glioblastoma treatment applications.

The consequence of oncomorphic TP53 mutations in ovarian cancer

Ovarian cancer is the most lethal gynecological malignancy, with an alarmingly poor prognosis attributed to late detection and chemoresistance. Initially, most tumors respond to chemotherapy but eventually relapse due to the development of drug resistance. Currently, there are no biological markers that can be used to predict patient response to chemotherapy. However, it is clear that mutations in the tumor suppressor gene TP53, which occur in 96% of serous ovarian tumors, alter the core molecular pathways involved in drug response. One subtype of TP53 mutations, widely termed gain-of-function (GOF) mutations, surprisingly converts this protein from a tumor suppressor to an oncogene. We term the resulting change an oncomorphism. In this review, we discuss particular TP53 mutations, including known oncomorphic properties of the resulting mutant p53 proteins. For example, several different oncomorphic mutations have been reported, but each mutation acts in a distinct manner and has a different effect on tumor progression and chemoresistance. An understanding of the pathological pathways altered by each mutation is necessary in order to design appropriate drug interventions for patients suffering from this deadly disease.