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

Anti-apoptotic NF-κB and "gain of function" mutp53 in concert act pro-apoptotic in response to UVB+IL-1 via enhanced TNF production

In response to genotoxic stress, including UVB radiation, transcription factors NF-κB and p53 inevitably influence the cellular fate. Loss of p53 function has been attributed to malignant transformation and interferes with therapeutic interventions, whereas “gain of function” mutants even enhance tumor promotion. Constitutive NF-κB activation is linked to tumor maintenance and resistance against chemotherapy. The cross talk between p53 and NF-κB, however, is still under debate. Using the non-transformed keratinocyte cell line HaCaT, we shed light on the interplay between p53 and NF-κB by providing clear evidence that chronically activated NF-κB together with designated “gain of function” mutp53 promotes apoptosis via cooperative tumor necrosis factor (TNF) production in response to UVB+IL-1. Performing chromatin immunoprecipitation analysis we demonstrate that both transcription factors bind to the TNF promoter, whereas UVB-induced inhibition of Ser-Thr-phosphatase protein phosphatase 2A facilitates prolonged phosphorylation of NF-κB and the transcriptional cofactor cAMP response element–binding protein, both being required for extended TNF transcription. Thus, two major anti-apoptotic factors, NF-κB and mutp53, in concert may generate pro-apoptotic responses. As human skin is constantly exposed to UVB, causing IL-1 production as well, we hypothesize that the remarkable amount of hotspot p53 mutations within the epidermis (4%) may serve a protective function to eliminate precancerous cells at an early stage.

Mutant p53 stimulates chemoresistance of pancreatic adenocarcinoma cells to gemcitabine

Pancreatic adenocarcinoma (PDAC) is the fourth leading cause of cancer-related deaths worldwide; PDAC is characterized by poor prognosis, resistance to conventional chemotherapy and high mortality rate. TP53 tumor suppressor gene is frequently mutated in PDAC, resulting in the accumulation of mutated protein with potential gain-of-function (GOF) activities, such as genomic instability, hyperproliferation and chemoresistance. The purpose of this study was to assess the relevance of the p53 status on the PDAC cells response to the standard drug gemcitabine. We also examined the potential therapeutic effect of p53-reactivating molecules to restore the mutant p53 function in GEM treated PDAC cells. We showed that gemcitabine stabilized mutant p53 protein in the nuclei and induced chemoresistance, concurrent with the mutant p53-dependent expression of Cdk1 and CCNB1 genes, resulting in a hyperproliferation effect. Despite the adverse activation of mutant p53 by gemcitabine, simultaneous treatment of PDAC cells with gemcitabine and p53-reactivating molecules (CP-31398 and RITA) reduced growth rate and induced apoptosis. This synergistic effect was observed in both wild-type and mutant p53 cell lines and was absent in p53-null cells. The combination drug treatment induced p53 phosphorylation on Ser15, apoptosis and autophagosome formation. Furthermore, pharmacological inhibition of autophagy further increased apoptosis stimulated by gemcitabine/CP-31398 treatment. Together, our results show that gemcitabine aberrantly stimulates mutant p53 activity in PDAC cells identifying key processes with potential for therapeutic targeting. Our data also support an anti-tumoral strategy based on inhibition of autophagy combined with p53 activation and standard chemotherapy for both wild-type and mutant p53 expressing PDACs.

Caught in the cross fire: p53 in inflammation

The p53 transcription factor is a major tumor suppressor, whose diverse activities serve to ensure genome stability and inhibit neoplastic processes. In recent years, it is becoming increasingly clear that p53 also plays a broader role in maintaining cellular homeostasis, as well as contributing to tissue homeostasis in a non-cell-autonomous fashion. Chronic inflammation is a potential cancer-promoting condition, and as such is also within the radar of p53, which mounts a multifaceted attempt to prevent the escalation of chronic tissue imbalance into neoplasia. Recent understanding of the p53 pathway and other family members reveals a broad interaction with inflammatory elements such as reactive oxygen and nitrogen species, cytokines, infectious agents and major immune-regulatory pathways like nuclear factor-kappaB. This complex cross talk is highly dependent on p53 status, as different p53 isoforms and p53 mutants can mediate different responses and even promote chronic inflammation and associated cancer, acting in the tumor cells as well as in the stromal and immune compartments.

Mutant p53 gains new function in promoting inflammatory signals by repression of the secreted interleukin-1 receptor antagonist

The TP53 tumor-suppressor gene is frequently mutated in human cancer. Missense mutations can add novel functions (gain-of-function, GOF) that promote tumor malignancy. Here we report that mutant (mut) p53 promotes tumor malignancy by suppressing the expression of a natural occurring anti-inflammatory cytokine, the secreted interleukin-1 receptor antagonist (sIL-1Ra, IL1RN). We show that mutp53 but not wild-type (wt) p53 suppresses the sIL-1Ra production in conditioned media of cancer cells. Moreover, mutp53, but not wtp53, binds physically the sIL-1Ra promoter and the protein-protein interaction with the transcriptional co-repressor MAFF (v-MAF musculoaponeurotic fibrosarcoma oncogene family, protein F) is required for mutp53-induced sIL-1Ra suppression. Remarkably, when exposed to IL-1 beta (IL-1β) inflammatory stimuli, mutp53 sustains a ready-to-be-activated in vitro and in vivo cancer cells' response through the sIL-1Ra repression. Taken together, these results identify sIL-1Ra as a novel mutp53 target gene, whose suppression might be required to generate a chronic pro-inflammatory tumor microenvironment through which mutp53 promotes tumor malignancy.

The paradigm of mutant p53-expressing cancer stem cells and drug resistance

It is well accepted that expression of mutant p53 involves the gain of oncogenic-specific activities accentuating the malignant phenotype. Depending on the specific cancer type, mutant p53 can contribute to either the early or the late events of the multiphase process underlying the transformation of a normal cell into a cancerous one. This multifactorial system is evident in ~50% of human cancers. Mutant p53 was shown to interfere with a variety of cellular functions that lead to augmented cell survival, cellular plasticity, aberration of DNA repair machinery and other effects. All these effects culminate in the acquisition of drug resistance often seen in cancer cells. Interestingly, drug resistance has also been suggested to be associated with cancer stem cells (CSCs), which reside within growing tumors. The notion that p53 plays a regulatory role in the life of stem cells, coupled with the observations that p53 mutations may contribute to the evolvement of CSCs makes it challenging to speculate that drug resistance and cancer recurrence are mediated by CSCs expressing mutant p53.

Modulation of apoptosis-related cell signalling pathways by curcumin as a strategy to inhibit tumor progression

A hallmark of cancer is resistance to apoptosis, with both the loss of proapoptotic signals and the gain of anti-apoptotic mechanisms contributing to tumorigenesis. As inducing apoptosis in malignant cells is one of the most challenging tasks regarding cancer, researchers increasingly focus on natural products to regulate apoptotic signaling pathways. Curcumin, a polyphenolic derivative of turmeric, is a natural compound derived from Curcuma longa, has attracted great interest in the research of cancer during the last half century. Extensive studies revealed that curcumin has chemopreventive properties, which are mainly due to its ability to arrest cell cycle and to induce apoptosis in cancer cells either alone or in combination with chemotherapeutic agents or radiation. The underlying action mechanisms of curcumin are diverse and has not been elucidated so far. By regulating multiple important cellular signalling pathways including NF-κB, TRAIL, PI3 K/Akt, JAK/STAT, Notch-1, JNK, etc., curcumin are known to activate cell death signals and induce apoptosis in pre-cancerous or cancer cells without affecting normal cells, thereby inhibiting tumor progression. Several phase I and phase II clinical trials indicate that curcumin is quite safe and may exhibit therapeutic efficacy. This article reviews the main effects of curcumin on the different apoptotic signaling pathways involved in curcumin induced apoptosis in cancer cells via cellular transduction pathways and provides an in depth assessment of its pharmacological activity in the management of tumor progression.

A compensatory role of NF-κB to p53 in response to 5-FU-based chemotherapy for gastric cancer cell lines

Despite of remarkable improvement of postoperative 5-FU–based adjuvant chemotherapy, the relapse rate of gastric cancer patients who undergo curative resection followed by the adjuvant chemotherapy remains substantial. Therefore, it is important to identify prediction markers for the chemotherapeutic efficacy of 5-FU. We recently identified NF-κB as a candidate relapse prediction biomarker in gastric cancer. To evaluate the biological significance of NF-κB in the context of 5-FU–based chemotherapy, we analyzed the NF-κB-dependent biological response upon 5-FU treatment in gastric cancer cell lines. Seven genes induced by 5-FU treatment in an NF-κB-dependent manner were identified, five of which are known p53 targets. Knockdown of RELA, which encodes the p65 subunit of NF-κB, decreased both p53 and p53 target protein levels. In contrast, NF-κB was not affected by TP53 knockdown. We also demonstrated that cell lines bearing Pro/Pro homozygosity in codon72 of p53 exon4, which is important for NF-κB binding to p53, are more resistant to 5-FU than those with Arg/Arg homozygosity. We conclude that NF-κB plays an important role in the response to 5-FU treatment in gastric cancer cell lines, with a possible compensatory function of p53. These results suggest that NF-κB is a potential 5-FU-chemosensitivity prediction marker that may reflect 5-FU-induced stress-response pathways, including p53.

Interaction of mutant p53 with p73: a Surface Plasmon Resonance and Atomic Force Spectroscopy study

BACKGROUND

TP53 tumor suppressor gene is mutated in more than 50% of human tumors. Mutated p53 proteins could sequestrate and inactivate p73 reducing the apoptotic and anti-proliferative effects of the transcription factor, and yielding cancer cells more aggressive and chemoresistant. The possibility of using drugs to prevent the mutant p53/p73 complex formation preserving the p73 function, calls for a deeper insight into the molecular and biochemical mechanisms of mutant p53/p73 protein interaction.

METHODS

The kinetics of the mutant p53R175H/p73 complex was investigated with innovative and complementary techniques, operating in real time, in near physiological conditions and without any labeling. Specifically, Atomic Force Spectroscopy and Surface Plasmon Resonance working at single-molecule level and in bulk condition, respectively, were used.

RESULTS

The two techniques revealed that a stable complex is formed between mutant p53R175H and p73 proteins; the complex being characterized by a high interaction force and a dissociation equilibrium constant in the order of 10(-7)M, as expected for specific interactions. No binding was instead observed between p73 and wild type p53.

CONCLUSIONS

Mutant p53R175H protein, unlike wild type p53, can form a stable complex with p73. The mutant p53R175H/p73 protein complex could be a target for innovative pharmaceutical drugs that, by dissociating it or preventing biomolecule interaction thus preserving the p73 function, could enhance the response of cancerous cells carrying mutant p53R175H protein to common chemotherapeutic agents.

GENERAL SIGNIFICANCE

The kinetic information obtained in vitro may help to design specific pharmaceutical drugs directed against cancerous cells carrying mutant p53 proteins.

p53 mutation in the genesis of metastasis

Development of metastatic cancer is a complex series of events that includes genesis of tumor-related vascular and lymphatic systems, enhanced cellular motility, and the capacity to invade and survive at distant sites, as well as evasion of host defences. The wild-type p53 protein plays key roles in controlling these facets of tumor progression, and loss of normal p53 function can be sufficient to predispose tumor cells to gain metastatic properties. In contrast, dominant p53 mutants that have gained oncogenic functions can actively drive metastasis through a variety of mechanisms. This chapter aims to highlight these processes.

Cooperation of p53 mutations with other oncogenic alterations in cancer

Following the initial findings suggesting a pro-oncogenic role for p53 point mutants, more than 30 years of research have unveiled the critical role exerted by these mutants in human cancer. A growing body of evidence, including mouse models and clinical data, has clearly demonstrated a connection between mutant p53 and the development of aggressive and metastatic tumors. Even if the molecular mechanisms underlying mutant p53 activities are still the object of intense scrutiny, it seems evident that full activation of its oncogenic role requires the functional interaction with other oncogenic alterations. p53 point mutants, with their pleiotropic effects, simultaneously activating several mechanisms of aggressiveness, are engaged in multiple cross-talk with a variety of other cancer-related processes, thus depicting a complex molecular landscape for the mutant p53 network. In this chapter revealing evidence illustrating different ways through which this cooperation may be achieved will be discussed. Considering the proposed role for mutant p53 as a driver of cancer aggressiveness, disarming mutant p53 function by uncoupling the cooperation with other oncogenic alterations, stands out as an exciting possibility for the development of novel anti-cancer therapies.

p53: its mutations and their impact on transcription

p53 is a tumor suppressor protein whose key function is to maintain the integrity of the cell. Mutations in p53 have been found in up to 50 % of all human cancers and cause an increase in oncogenic phenotypes such as proliferation and tumorigenicity. Both wild-type and mutant p53 have been shown to transactivate their target genes, either through directly binding to DNA, or indirectly through protein-protein interactions. This review discusses possible mechanisms behind both wild-type and mutant p53-mediated transactivation and touches on the concept of addiction to mutant p53 of cancer cells and how that may be used for future therapies.

Disarming mutant p53 oncogenic function

In the last decade intensive research has confirmed the long standing hypothesis that some p53 point mutants acquire novel activities able to cooperate with oncogenic mechanisms. Particular attention has attracted the ability of several such mutants to actively promote the development of aggressive and metastatic tumors in vivo. This knowledge opens a new dimension on rational therapy design, suggesting novel strategies based on pharmacological manipulation of those neomorphic activities. P53 point mutants have several characteristics that make them attractive targets for anti-cancer therapies. Remarkably, mutant p53 has been found predominantly in tumor cells and may act pleiotropically by interfering with a variety of cellular processes. Therefore, drugs targeting mutant p53 may selectively affect tumor cells, inactivating simultaneously several mechanisms of tumor promotion. Moreover, the high frequency of missense mutations on the p53 gene suggests that interfering with mutant p53 function may provide a valuable approach for the development of efficient therapies able to target a wide range of tumor types.

Expression of galectin-7 is induced in breast cancer cells by mutant p53

Galectin-7 was initially described as a marker of epithelial differentiation expressed in the stratified epithelium of various tissues. Like other members of the galectin family, its expression level is often significantly altered in cancer cells. In breast cancer, its expression is significantly augmented in aggressive molecular subtypes, most notably in estrogen receptor-negative tumors and in cell lines with a basal-like phenotype. Studies using experimental mouse models have further shown high expression of galectin-7 was sufficient to increase the metastatic behavior of poorly metastatic breast cancer cells, rendering them more resistant to apoptosis. This expression pattern in breast cancer cells is unexpected because galectin-7 was originally identified as a p53-induced gene. To address this paradox, we have examined the molecular mechanisms regulating galectin-7 in breast cancer cells. Our results showed that transfection of breast cancer cells with expression vectors encoding mutant p53 was sufficient to induce galectin-7 at both mRNA and protein levels. Doxorubicin treatment of breast cancer cells harboring a mutant p53 also induced galectin-7. This induction was specific since knockdown of endogenous mutant p53 inhibited doxorubicin-induced galectin-7 expression. The p53-induced galectin-7 expression in breast cancer cells correlated with increased NF-κB activity and was inhibited by NF-κB inhibitors, indicating that the ability of mutant p53 to induce galectin-7 was dependent on NF-κB activity. The implication of NF-κB was further supported by data showing that NF-κB bound to the endogenous galectin-7 promoter and that TNFα-induced galectin-7 expression was abolished by NF-κB inhibitors. Taken together, our data provide an explanation to the observed high galectin-7 expression levels in cancer cells and suggest that galectin-7 could be part of a common pathway used by mutant p53 to promote cancer progression.

Mutant p53 prolongs NF-κB activation and promotes chronic inflammation and inflammation-associated colorectal cancer

The tumor suppressor p53 is frequently mutated in human cancer. Common mutant p53 (mutp53) isoforms can actively promote cancer through gain-of-function (GOF) mechanisms. We report that mutp53 prolongs TNF-α-induced NF-κB activation in cultured cells and intestinal organoid cultures. Remarkably, when exposed to dextran sulfate sodium, mice harboring a germline p53 mutation develop severe chronic inflammation and persistent tissue damage, and are highly prone to inflammation-associated colon cancer. This mutp53 GOF is manifested by rapid onset of flat dysplastic lesions that progress to invasive carcinoma with mutp53 accumulation and augmented NF-κB activation, faithfully recapitulating features frequently observed in human colitis-associated colorectal cancer (CAC). These findings might explain the early appearance of p53 mutations in human CAC.

Pharmacological Importance of Simple Phenolic Compounds on Inflammation, Cell Proliferation and Apoptosis with a Special Reference to β-D-Salicin and Hydroxybenzoic Acid

Simple phenolic (SP) compounds are natural products that exhibit multiple pharmacological functions. The best known of these compounds is β-D-salicin, the first discovered phenolic glycoside and salicylic acid, or 2-hydroxybenzoic acid (2-HBA). Both of these compounds have attracted the interest of scientists in various interdisciplinary fields, including chemistry, pharmacology and medicine. Although β-D-salicin is found in various plants, it is often associated with willow, as it was first discovered in this species of plant. While the presence of glucose in β-D-salicin improves the physicochemical properties of the benzyl moiety, β-D-salicin itself does not have anti-inflammatory or anti-proliferative activity until it is metabolised into 2-HBA in the gastrointestinal tract and blood stream. Likewise, the majority of 2-acetoxybenzoic acid (2-ABA), or acetoxysalicylic acid also undergoes metabolic hydrolysis into 2-HBA. 2-HBA has been shown to play a role in modulating both inflammation and cancer partly through the inhibition of cyclooxygenase-2 (COX-2). It is now clear that 2-HBA most likely acts on the transcription factor NF-κB, which regulates the transcription of COX-2 thereby suppressing inflammation and cell proliferation and promoting apoptosis. Other phenolates, also exhibit anti-inflammation and anti-proliferation activities like the 4-hydroxybenzoate zinc (4-HBZn) complex, which was previously shown to preferentially inhibit COX-2 compared to 2-HBA and ASA. This review aims to collect all the available information related to β-D-salicin and other SP compounds in order to promote a new perspective of this interesting class of compounds and encourage further research into their pharmacological and clinical properties.

Mutant p53 in cell adhesion and motility

Pro-oncogenic properties of mutant p53 were investigated with the aid of migration assays, adhesion assays, and soft agar growth assays using cells stably expressing gain-of-function p53 mutants. To determine cell migration, "wound-healing" (scratch) assays and haptotactic (chamber) assays were used. H1299 cells expressing mutant p53 were found to migrate more rapidly than cells transfected with empty vector alone. Results from both types of migration assay were broadly similar. Migratory ability differed for different p53 mutants, suggesting allele-specific effects. Cells expressing p53 mutants also showed enhanced adhesion to extracellular matrix compare to controls. Furthermore, stable transfection of mutant p53-H179L into NIH3T3 fibroblasts was sufficient to allow anchorage-independent growth in soft agar.

The importance of oncogenic transcription factors for oral cancer pathogenesis and treatment

Oral squamous cell carcinoma is a major cause of morbidity and mortality worldwide. Current experimental evidence shows that most important risk factors for oral cancer include tobacco use and excessive alcohol consumption and less well-defined risks include viral infection and a diet deficient in antioxidants. The positive correlation between various risk/etiologic factors of oral cancer and the activation of various transcription factors (TFs) has been reported in the literature. Although initially, TFs were considered to be very difficult targets for use in clinical treatment, recent technological advances have provided the ability to control these factors of cancer progression. This review focuses on the role of oncogenic transcription factors in oral cancer, their modes of activation through various biological pathways, the promises and pitfalls in viewing them as potent oncotargets, the way they can be controlled based on the current understanding, and the future research to be done in this area.

Mollugin inhibits proliferation and induces apoptosis by suppressing fatty acid synthase in HER2-overexpressing cancer cells

Mollugin is a naphthohydroquine found in the roots of Rubia cordifolia, and has been reported to have a variety of biological activities, including anti-inflammatory and apoptotic effects. In the present study, we investigated the molecular mechanisms by which mollugin exerts anti-tumor effect in HER2-overexpressing cancer cells. Our results showed that mollugin exhibited potent inhibitory effects on cancer cell proliferation, especially in HER2-overexpressing SK-BR-3 human breast cancer cells and SK-OV-3 human ovarian cancer cells in a dose- and time-dependent manner without affecting immortalized normal mammary epithelial cell line MCF-10A. Furthermore, we found that a blockade of Akt/SREBP-1c signaling through mollugin treatment significantly reduced FAS expression and subsequently suppressed cell proliferation and induced apoptosis in HER2-overexpressing cancer cells. Mollugin treatment caused a dose-dependent inhibition of HER2 gene expression at the transcriptional level, potentially in part through suppression of NF-κB activation. The combination of mollugin with a MEK1/2 inhibitor may be required in order to achieve optimal efficacy in HER2-overexpressing cancers. These data provide evidence that mollugin inhibits proliferation and induces apoptosis in HER2-overexpressing cancer cells by blocking expression of the FAS gene through modulation of a HER2/Akt/SREBP-1c signaling pathway. Our findings suggest that mollugin is a novel modulator of the HER2 pathway in HER2-overexpressing cancer cells with a potential role in the treatment and prevention of human breast and ovarian cancer with HER2 overexpression.

Gain-of-Function Activity of Mutant p53 in Lung Cancer through Up-Regulation of Receptor Protein Tyrosine Kinase Axl

p53 mutations are present in up to 70% of lung cancer. Cancer cells with p53 mutations, in general, grow more aggressively than those with wild-type p53 or no p53. Expression of tumor-derived mutant p53 in cells leads to up-regulated expression of genes that may affect cell growth and oncogenesis. In our study of this aggressive phenotype, we have investigated the receptor protein tyrosine kinase Axl, which is up-regulated by p53 mutants at both RNA and protein levels in H1299 lung cancer cells expressing mutants p53-R175H, -R273H, and -D281G. Knockdown of endogenous mutant p53 levels in human lung cancer cells H1048 (p53-R273C) and H1437 (p53-R267P) led to a reduction in the level of Axl as well. This effect on Axl expression is refractory to the mutations at positions 22 and 23 of p53, suggesting that p53's transactivation domain may not play a critical role in the up-regulation of Axl gene expression. Chromatin immunoprecipitation (ChIP) assays carried out with acetylated histone antibodies demonstrated induced histone acetylation on the Axl promoter region by mutant p53. Direct mutant p53 nucleation on the Axl promoter was demonstrated by ChIP assays using antibodies against p53. The Axl promoter has a p53/p63 binding site, which however is not required for mutant p53-mediated transactivation. Knockdown of Axl by Axl-specific RNAi caused a reduction of gain-of-function (GOF) activities, reducing the cell growth rate and motility rate in lung cancer cells expressing mutant p53. This indicates that for lung cancer cell lines with mutant p53, GOF activities are mediated in part through Axl.

Mutant TP53 enhances the resistance of glioblastoma cells to temozolomide by up-regulating O(6)-methylguanine DNA-methyltransferase

The "gain of function" of mutant TP53 is an important determinant in human tumor development and progression. This study aimed to investigate the possible mechanism of mutant TP53 inducing temozolomide resistance in glioblastoma cells. Three established human glioma cell lines, T98G, U87, and U138, were chemoresistant cells. The mRNA of cells was sequenced to confirm the status of TP53. Synthetic small interfering RNA (siRNA) was used to knock down TP53 in cells. TP53 mRNA was detected "silenced" by reverse transcriptase-polymerase chain reaction (RT-PCR) in five consecutive days. Viable cell survival was measured when these cells were exposed to temozolomide or semustine in step-up concentrations. The expression of O(6)-methylguanine DNA-methyltransferase (MGMT) at mRNA level was also determined. T98G, U87, and U138 cells were resistant to temozolomide. T98G and U138 cells expressed mutant-type TP53 with positive MGMT, while U87 cell expressed wild-type TP53 with negative MGMT. TP53-siRNA knocked down TP53 effectively (P = 0.021) in five consecutive days. Knockdown of mutant TP53 in T98G and U138 cells led to a fivefold increase in chemosensitivity to temozolomide, but not semustine. Knockdown of wild TP53 in U87 cell did not affect the chemoresistance. In addition, mutant TP53 knockdown induced a dramatic decrease of MGMT expression (P = 0.0000034). TP53 mutation decreases the chemosensitivity of malignant gliomas to temozolomide. This "gain of function" in drug resistance may be obtained by increasing MGMT expression.

Advances in research of signaling pathways in cholangiocarcinoma

Epidemiological data indicate that the incidence and mortality of cholangiocarcinoma (CC) show an increasing trend worldwide over the past several years. Many pathophysiologic aspects of this neoplasia are still unknown and need to be fully discovered. However, progress has been recently made in understanding molecular mechanisms involved in the transformation and growth of malignant cholangiocytes. It is found that cholangiocarcinogenesis is a multistep cellular process evolving from a normal condition of the epithelial biliary cells and ending with malignant transformation through a chronic inflammation status. The bad prognosis related to CC justifies why a better identification of the molecular mechanisms involved in the growth and progression of this cancer is required for the development of effective preventive measures and valid treatment regimens. Signaling pathways can regulate substance and energy metabolism in organisms and are closely related to biological growth and development. This paper mainly introduces signaling pathways which occur in cholangiocarcinoma and their roles in cholangiocarcinoma cells.

Allele specific gain-of-function activity of p53 mutants in lung cancer cells

p53 mutations are mostly single amino acid changes resulting in expression of a stable mutant protein with "gain of function" (GOF) activity having a dominant oncogenic role rather than simple loss of function of wild-type p53. Knock-down of mutant p53 in human lung cancer cell lines with different endogenous p53 mutants results in loss of GOF activity as shown by lowering of cell growth rate. Two lung cancer cell lines, ABC1 and H1437, carrying endogenous mutants p53-P278S and -R267P, show reduction in growth rate on knock-down on p53 levels. However, whereas reduction of the p53 level induces loss of tumorigenicity in nude mice for ABC1 cells, it escalates tumorigenicity for H1437 cells. We have tested their transactivation potential on p53 target gene promoters by performing transient transcriptional assays in the p53-null H1299 lung cancer cell line. Interestingly, while the mutant p53 target promoter Axl was activated by both the mutants, the p21 promoter was activated by p53-R267P and wild-type p53 but not by p53-P278S; showing a clear difference in transcriptional activity between the two mutants. Our results demonstrate allele specificity between GOF p53 mutants and attempt to show that the specificity is dependent on the transactivation property of GOF p53; it also suggests importance of p21 activation in tumor suppression by p53.

Mutant p53: one name, many proteins

There is now strong evidence that mutation not only abrogates p53 tumor-suppressive functions, but in some instances can also endow mutant proteins with novel activities. Such neomorphic p53 proteins are capable of dramatically altering tumor cell behavior, primarily through their interactions with other cellular proteins and regulation of cancer cell transcriptional programs. Different missense mutations in p53 may confer unique activities and thereby offer insight into the mutagenic events that drive tumor progression. Here we review mechanisms by which mutant p53 exerts its cellular effects, with a particular focus on the burgeoning mutant p53 transcriptome, and discuss the biological and clinical consequences of mutant p53 gain of function.

Mutant p53 is a transcriptional co-factor that binds to G-rich regulatory regions of active genes and generates transcriptional plasticity

The molecular mechanisms underlying mutant p53 (mutp53) "gain-of-function" (GOF) are still insufficiently understood, but there is evidence that mutp53 is a transcriptional regulator that is recruited by specialized transcription factors. Here we analyzed the binding sites of mutp53 and the epigenetic status of mutp53-regulated genes that had been identified by global expression profiling upon depletion of endogenous mutp53 (R273H) expression in U251 glioblastoma cells. We found that mutp53 preferentially and autonomously binds to G/C-rich DNA around transcription start sites (TSS) of many genes characterized by active chromatin marks (H3K4me3) and frequently associated with transcription-competent RNA polymerase II. Mutp53-bound regions overlap predominantly with CpG islands and are enriched in G4-motifs that are prone to form G-quadruplex structures. In line, mutp53 binds and stabilizes a well-characterized G-quadruplex structure in vitro. Hence, we assume that binding of mutp53 to G/C-rich DNA regions associated with a large set of cancer-relevant genes is an initial step in their regulation by mutp53. Using GAS1 and HTR2A as model genes, we show that mutp53 affects several parameters of active transcription. Finally, we discuss a dual mode model of mutp53 GOF, which includes both stochastic and deterministic components.

The gain of function of p53 cancer mutant in promoting mammary tumorigenesis

Tumor suppressor p53 is critical for suppressing all types of human cancers, including breast cancer. The p53 gene is somatically mutated in over half of all human cancers. The majority of the p53 mutations are missense mutations, leading to the expression of the full-length p53 mutants. Several hotspot mutations, including R175H, are frequently detected in human breast cancer. P53 cancer mutants not only lose tumor suppression activity but, more problematically, also gain new oncogenic activities. Despite correlation of the expression of p53 cancer mutants and the poor prognosis of human breast cancer patients, the roles of p53 cancer mutants in promoting breast cancer remain unclear. We used the humanized p53 cancer mutant knock-in (R175H) mice and mouse mammary tumor virus (MMTV)-Wnt-1 transgenic (mWnt-1) mice to specifically address the gain of function of R175H in promoting breast cancer. Although both R175H/R175HmWnt-1(R175HmWnt-1) and p53(-/-)mWnt-1 mice died from mammary tumor at the same kinetics, which was much earlier than mWnt-1 mice, most of the R175HmWnt-1 mice developed multiple mammary tumors per mouse, whereas p53(-/-)mWnt-1 and mWnt-1 mice mostly developed one tumor per mouse. The multiple mammary tumors arose in the same R175HmWnt-1 mouse exhibited different histological characters. Moreover, R175H gain-of-function mutant expands the mammary epithelial stem cells (MESCs) that give rise to the mammary tumors. As ATM suppresses the expansion of MESCs, the inactivation of ATM by R175H in mammary epithelial cells (MECs) could contribute to the expansion of MESCs in R175HmWnt-1 mice. These findings provide the basis for R175H to promote the initiation of breast cancer by expanding MESCs.

The rebel angel: mutant p53 as the driving oncogene in breast cancer

Breast cancer is the most frequent invasive tumor diagnosed in women, causing over 400 000 deaths yearly worldwide. Like other tumors, it is a disease with a complex, heterogeneous genetic and biochemical background. No single genomic or metabolic condition can be regarded as decisive for its formation and progression. However, a few key players can be pointed out and among them is the TP53 tumor suppressor gene, commonly mutated in breast cancer. In particular, TP53 mutations are exceptionally frequent and apparently among the key driving factors in triple negative breast cancer -the most aggressive breast cancer subgroup-whose management still represents a clinical challenge. The majority of TP53 mutations result in the substitution of single aminoacids in the central region of the p53 protein, generating a spectrum of variants ('mutant p53s', for short). These mutants lose the normal p53 oncosuppressive functions to various extents but can also acquire oncogenic properties by gain-of-function mechanisms. This review discusses the molecular processes translating gene mutations to the pathologic consequences of mutant p53 tumorigenic activity, reconciling cell and animal models with clinical outcomes in breast cancer. Existing and speculative therapeutic methods targeting mutant p53 are also discussed, taking into account the overlap of mutant and wild-type p53 regulatory mechanisms and the crosstalk between mutant p53 and other oncogenic pathways in breast cancer. The studies described here concern breast cancer models and patients-unless it is indicated otherwise and justified by the importance of data obtained in other models.

Regulation of cell death and autophagy by IKK and NF-κB: critical mechanisms in immune function and cancer

The cellular response to survive or to undergo death is fundamental to the benefit of the organism, and errors in this process can lead to autoimmunity and cancer. The transcription factor nuclear factor κB (NF-κB) functions to block cell death through transcriptional induction of genes encoding anti-apoptotic and antioxidant proteins. This is essential for survival of activated cells of the immune system and for cells undergoing a DNA damage response. In Ras-transformed cells and tumors as well as other cancers, NF-κB functions to suppress apoptosis--a hallmark of cancer. Critical prosurvival roles for inhibitor of NF-κB kinase (IKK) family members, including IKKε and TBK1, have been reported, which are both NF-κB-dependent and -independent. While the roles of NF-κB in promoting cell survival in lymphocytes and in cancers is relatively clear, evidence has been presented that NF-κB can promote cell death in particular contexts. Recently, IKK was shown to play a critical role in the induction of autophagy, a metabolic response typically associated with cell survival but which can lead to cell death. This review provides an historical perspective, along with new findings, regarding the roles of the IKK and NF-κB pathways in regulating cell survival.

Attenuation of soft-tissue sarcomas resistance to the cytotoxic action of TNF-α by restoring p53 function

Background

Isolated limb perfusion with TNF-α and melphalan is used with remarkable efficiency to treat unresectable limb sarcomas. Here we tested the ability of TNF-α to directly induce apoptosis of sarcoma cells. In addition, we investigated the impact of p53 in the regulation of such effect.

Methodology/Principal Findings

We first analysed the ability of TNF-α to induce apoptosis in freshly isolated tumour cells. For this purpose, sarcoma tumours (n = 8) treated ex vivo with TNF-α were processed for TUNEL staining. It revealed substantial endothelial cell apoptosis and levels of tumour cell apoptosis that varied from low to high. In order to investigate the role of p53 in TNF-α-induced cell death, human sarcoma cell lines (n = 9) with different TP53 and MDM2 status were studied for their sensitivity to TNF-α. TP53^Wt cell lines were sensitive to TNF-α unless MDM2 was over-expressed. However, TP53^Mut and TP53^Null cell lines were resistant. TP53 suppression in TP53^Wt cell lines abrogated TNF-α sensitivity and TP53 overexpression in TP53^Null cell lines restored it. The use of small molecules that restore p53 activity, such as CP-31398 or Nutlin-3a, in association with TNF-α, potentiated the cell death of respectively TP53^Mut and TP53^Wt/MDM2^Ampl. In particular, CP-31398 was able to induce p53 as well as some of its apoptotic target genes in TP53^Mut cells. In TP53^Wt/MDM2^Ampl cells, Nutlin-3a effects were associated with a decrease of TNF-α-induced NF-κB-DNA binding and correlated with a differential regulation of pro- and anti-apoptotic genes such as TP53BP2, GADD45, TGF-β1 and FAIM.

Conclusion/Significance

More effective therapeutic approaches are critically needed for the treatment of unresectable limb sarcomas. Our results show that restoring p53 activity in sarcoma cells correlated with increased sensitivity to TNF-α, suggesting that this strategy may be an important determinant of TNF-α-based sarcomas treatment.

Inhibition of specific NF-κB activity contributes to the tumor suppressor function of 14-3-3σ in breast cancer

14-3-3σ is frequently lost in human breast cancers by genetic deletion or promoter methylation. We have now investigated the involvement of 14-3-3σ in the termination of NF-κB signal in mammary cells and its putative role in cancer relapse and metastasis. Our results show that 14-3-3σ regulates nuclear export of p65-NF-κB following chronic TNFα stimulation. Restoration of 14-3-3σ in breast cancer cells reduces migration capacity and metastatic abilities in vivo. By microarray analysis, we have identified a genetic signature that responds to TNFα in a 14-3-3σ-dependent manner and significantly associates with different breast and other types of cancer. By interrogating public databases, we have found that over-expression of this signature correlates with poor relapse-free survival in breast cancer patients. Finally, screening of 96 human breast tumors showed that NF-κB activation strictly correlates with the absence of 14-3-3σ and it is significantly associated with worse prognosis in the multivariate analysis. Our findings identify a genetic signature that is important for breast cancer prognosis and for future personalized treatments based on NF-κB targeting.

CCN5/WISP-2: A micromanager of breast cancer progression

The gain of plasticity by a subset of cancer cells is a unique but common sequence of cancer progression from epithelial phenotype to mesenchymal phenotype (EMT) that is followed by migration, invasion and metastasis to a distant organ, and drug resistance. Despite multiple studies, it is still unclear how cancer cells regulate plasticity. Recent studies from our laboratory and others' proposed that CCN5/WISP-2, which is found intracellularly (in the nucleus and cytoplasm) and extracellularly, plays a negative regulator of plasticity. It prevents the EMT process in breast cancer cells as well as pancreatic cancer cells. Multiple genetic insults, including the gain of p53 mutations that accumulate over the time, may perturb CCN5 expression in non-invasive breast cancer cells, which ultimately helps cells to gain invasive phenotypes. Moreover, emerging evidence indicates that several oncogenic lesions such as miR-10b upregulation and activation of TGF-β-signaling can accumulate during CCN5 crisis in breast cancer cells. Collectively, these studies indicate that loss of CCN5 activity may promote breast cancer progression; application of CCN5 protein may represent a novel therapeutic intervention in breast cancer and possibly pancreatic cancer.

Various p53 mutant proteins differently regulate the Ras circuit to induce a cancer-related gene signature

Concomitant expression of mutant p53 and oncogenic Ras, leading to cellular transformation, is well documented. However, the mechanisms by which the various mutant p53 categories cooperate with Ras remain largely obscure. From this study we suggest that different mutant p53 categories cooperate with H-Ras in different ways to induce a unique expression pattern of a cancer-related gene signature (CGS). The DNA-contact p53 mutants (p53(R248Q) and p53(R273H)) exhibited the highest level of CGS expression by cooperating with NFκB. Furthermore, the Zn(+2) region conformational p53 mutants (p53(R175H) and p53(H179R)) induced the CGS by elevating H-Ras activity. This elevation in H-Ras activity stemmed from a perturbed function of the p53 transcription target gene, BTG2. By contrast, the L3 loop region conformational mutant (p53(G245S)) did not affect CGS expression. Our findings were further corroborated in human tumor-derived cell lines expressing Ras and the aforementioned mutated p53 proteins. These data might assist in future tailor-made therapy targeting the mutant p53-Ras axis in cancer.

Ubiquitination and the Ubiquitin-Proteasome System as regulators of transcription and transcription factors in epithelial mesenchymal transition of cancer

Epithelial to Mesenchymal Transition (EMT) in cancer is a process that allows cancer cells to detach from neighboring cells, become mobile and metastasize and shares many signaling pathways with development. Several molecular mechanisms which regulate oncogenic properties in neoplastic cells such as proliferation, resistance to apoptosis and angiogenesis through transcription factors or other mediators are also regulators of EMT. These pathways and downstream transcription factors are, in their turn, regulated by ubiquitination and the Ubiquitin-Proteasome System (UPS). Ubiquitination, the covalent link of the small 76-amino acid protein ubiquitin to target proteins, serves as a signal for protein degradation by the proteasome or for other outcomes such as endocytosis, degradation by the lysosome or directing these proteins to specific cellular compartments. This review discusses aspects of the regulation of EMT by ubiquitination and the UPS and underlines its complexity focusing on transcription and transcription factors regulating EMT and are being regulated by ubiquitination.

The diverse and complex roles of NF-κB subunits in cancer

It is only recently that the full importance of nuclear factor-κB (NF-κB) signalling to cancer development has been understood. Although much attention has focused on the upstream pathways leading to NF-κB activation, it is now becoming clear that the inhibitor of NF-κB kinases (IKKs), which regulate NF-κB activation, have many independent functions in tissue homeostasis and normal immune function that could compromise the clinical utility of IKK inhibitors. Therefore, if the NF-κB pathway is to be properly exploited as a target for both anticancer and anti-inflammatory drugs, it is appropriate to reconsider the complex roles of the individual NF-κB subunits.

p53 mutants induce transcription of NF-κB2 in H1299 cells through CBP and STAT binding on the NF-κB2 promoter and gain of function activity

Cancer cells with p53 mutations, in general, grow more aggressively than those with wild-type p53 and show "gain of function" (GOF) phenotypes such as increased growth rate, enhanced resistance to chemotherapeutic drugs, increased cell motility and tumorigenicity; although the mechanism for this function remains unknown. In this communication we report that p53-mediated NF-κB2 up-regulation significantly contributes to the aggressive oncogenic behavior of cancer cells. Lowering the level of mutant p53 in a number of cancer cell lines resulted in a loss of GOF phenotypes directly implicating p53 mutants in the process. RNAi against NF-κB2 in naturally occurring cancer cell lines also lowers GOF activities. In H1299 cells expressing mutant p53, chromatin immunoprecipitation (ChIP) assays indicate that mutant p53 induces histone acetylation at specific sites on the regulatory regions of its target genes. ChIP assays using antibodies against transcription factors putatively capable of interacting with the NF-κB2 promoter show increased interaction of CBP and STAT2 in the presence of mutant p53. Thus, we propose that in H1299 cells, mutant p53 elevates expression of genes capable of enhancing cell proliferation, motility, and tumorigenicity by inducing acetylation of histones via recruitment of CBP and STAT2 on the promoters causing CBP-mediated histone acetylation.

Mutant p53 gain of function is interwoven into the hallmarks of cancer

Cancer is viewed as being governed by several aberrant biological events defined by Weinberg and Hanahan as 'hallmarks'. In most human cancers the tumour suppressor p53 is mutated, leading to its malfunction and to the acquirement of oncogenic activities, termed 'gain of function'. This commentary links mutant p53 activities to the hallmarks of cancer, describing its involvement in resistance to apoptosis, genomic instability, aberrant cell cycle, invasion and metastasis, tumour microenvironment, and inflammation. Recent work published in The Journal of Pathology by Acin and colleagues, summarized here, reveals an interesting mechanism by which mutant p53 accelerates mitosis entry. Collectively, the growing body of evidence relating mutant p53 and the hallmarks of cancer reinforces the notion that targeting mutant p53 pathways might be beneficial for anti-cancer therapy.

Inflammation and p53: A Tale of Two Stresses

Numerous observations indicate a strong link between chronic inflammation and cancer. This link is supported by substantial experimental evidence indicating mutual negative regulation of NF-κB, the major regulator of inflammation, and p53, the major tumor suppressor. This antagonistic relationship reflects the opposite principles of the physiological responses driven by these transcription factors, which act as sensors and mediators of intrinsic and extrinsic cell stresses, respectively. Constitutive activation of NF-κB, the underlying cause of chronic inflammation, is a common acquired characteristic of tumors. A variety of experimental methods have been used to demonstrate that constitutive activation of NF-κB reduces the tumor suppressor activity of p53, thereby creating permissive conditions for dominant oncogene-mediated transformation. Loss of p53 activity is also a characteristic of the majority of tumors and results in unleashed inflammatory responses due to loss of p53-mediated NF-κB suppression. On the other hand, in natural or pharmacological situations of enforced p53 activation, NF-κB activity, inflammation, and immune responses are reduced, resulting in different pathologies. It is likely that the chronic inflammation that is commonly acquired in various tissues of older mammals leads to general suppression of p53 function, which would explain the increased risk of cancer observed in aging animals and humans. Although the molecular mechanisms underlying reciprocal negative regulation of p53 and NF-κB remain to be deciphered, this phenomenon has important implications for pharmacological prevention of cancer and aging and for new approaches to control inflammation.

Mutant p53 drives multinucleation and invasion through a process that is suppressed by ANKRD11

Mutations of p53 in cancer can result in a gain of function associated with tumour progression and metastasis. We show that inducible expression of several p53 'hotspot' mutants promote a range of centrosome abnormalities, including centrosome amplification, increased centrosome size and loss of cohesion, which lead to mitotic defects and multinucleation. These mutant p53-expressing cells also show a change in morphology and enhanced invasive capabilities. Consequently, we sought for a means to specifically target the function of mutant p53 in cancer cells. This study has identified ANKRD11 as a key regulator of the oncogenic potential of mutant p53. Loss of ANKRD11 expression with p53 mutation defines breast cancer patients with poor prognosis. ANKRD11 alleviates the mitotic defects driven by mutant p53 and suppresses mutant p53-mediated mesenchymal-like transformation and invasion. Mechanistically, we show that ANKRD11 restores a native conformation to the mutant p53 protein and causes dissociation of the mutant p53-p63 complex. This represents the first evidence of an endogenous protein with the capacity to suppress the oncogenic properties of mutant p53.

Caffeic acid phenethyl ester (CAPE), derived from a honeybee product propolis, exhibits a diversity of anti-tumor effects in pre-clinical models of human breast cancer

Breast cancer (BC) patients use alternative and natural remedies more than patients with other malignancies. Specifically, 63-83% use at least one type of alternative medicine and 25-63% use herbals and vitamins. Propolis is a naturopathic honeybee product, and CAPE (caffeic acid phenethyl ester), is a major medicinal component of propolis. CAPE, in a concentration dependent fashion, inhibits MCF-7 (hormone receptor positive, HR+) and MDA-231 (a model of triple negative BC (TNBC) tumor growth, both in vitro and in vivo without much effect on normal mammary cells and strongly influences gene and protein expression. It induces cell cycle arrest, apoptosis and reduces expression of growth and transcription factors, including NF-κB. Notably, CAPE down-regulates mdr-1 gene, considered responsible for the resistance of cancer cells to chemotherapeutic agents. Further, CAPE dose-dependently suppresses VEGF formation by MDA-231 cells and formation of capillary-like tubes by endothelial cells, implicating inhibitory effects on angiogenesis. In conclusion, our results strongly suggest that CAPE inhibits MDA-231 and MCF-7 human breast cancer growth via its apoptotic effects, and modulation of NF-κB, the cell cycle, and angiogenesis.

Curcumin suppresses proliferation and induces apoptosis in human biliary cancer cells through modulation of multiple cell signaling pathways

Cholangiocarcinoma (CCA) is a tumor with poor prognosis that is resistant to all currently available treatments. Whether curcumin, a nutraceutical derived from turmeric (Curcuma longa), has potential therapeutic activity against human CCA was investigated using three CCA cell lines (KKU100, KKU-M156 and KKU-M213). Examination of mitochondrial dehydrogenase activity, phosphatidylserine externalization, esterase staining, caspase activation and poly-adenosine diphosphate ribose polymerase cleavage demonstrated that curcumin inhibited proliferation of and induced apoptosis in these biliary cancer cells. Colony-formation assay confirmed the growth-inhibitory effect of curcumin on CCA cells. When examined for the mechanism, curcumin was found to activate multiple cell signaling pathways in these cells. First, all CCA cells exhibited constitutively active nuclear factor (NF)-κB, and treatment with curcumin abolished this activation as indicated by DNA binding, nuclear translocation and p65 phosphorylation. Second, curcumin suppressed activation of signal transducer and activator of transcription-3 as indicated by decreased phosphorylation at both tyrosine(705) and serine(727) and inhibition of janus kinase-1 phosphorylation. Third, curcumin induced expression of peroxisome proliferator-activated receptor gamma. Fourth, curcumin upregulated death receptors, DR4 and DR5. Fifth, curcumin suppressed the Akt activation pathway. Sixth, curcumin inhibited expression of cell survival proteins such as B-cell lymphoma-2, B-cell leukemia protein xL, X-linked inhibitor of apoptosis protein, c-FLIP, cellular inhibitor of apoptosis protein (cIAP)-1, cIAP-2 and survivin and proteins linked to cell proliferation, such as cyclin D1 and c-Myc. Seventh, the growth inhibitory effect of curcumin was enhanced in the IκB kinase-deficient cells, the enzyme required for nuclear factor-kappaB activation. Overall, our results indicate that curcumin mediates its antiproliferative and apoptotic effects through activation of multiple cell signaling pathways, and thus, its activity against CCA should be further investigated.

Upregulation of the mitochondrial transport protein, Tim50, by mutant p53 contributes to cell growth and chemoresistance

The p53 gene is one of the most frequently mutated genes in human cancer. Some p53 mutations impart additional functions that promote oncogenesis. To investigate how these p53 mutants function, a proteomic analysis was performed. The protein, translocator of the inner mitochondrial membrane 50 (Tim50), was upregulated in a non-small cell lung carcinoma cell line (H1299) that expressed the p53 mutants R175H and R273H compared to cells lacking p53. Tim50 was also elevated in the breast cancer cell lines MDA-MB-468 and SK-BR-3, that endogenously express the p53 mutants R175H and R273H, respectively, compared to MCF-10A. The p53 mutants R175H and R273H, but not WT p53, upregulated the expression of a Tim50 promoter construct and chromatin immunoprecipitation (ChIP) analysis indicated increased histone acetylation and increased interaction of the transcription factors Ets-1, CREB and CREB-binding protein (CBP) with the Tim50 promoter in the presence of mutant p53. Finally, reduction of Tim50 expression reduced the growth rate and chemoresistance of cells harboring mutant p53 but had no effect upon cells lacking p53. Taken together, these findings identify the Tim50 gene as a transcriptional target of mutant p53 and suggest a novel mechanism by which p53 mutants enhance cell growth and chemoresistance.

Forced expression of heat shock protein 27 (Hsp27) reverses P-glycoprotein (ABCB1)-mediated drug efflux and MDR1 gene expression in Adriamycin-resistant human breast cancer cells

Mutant p53 accumulation has been shown to induce the multidrug resistance gene (MDR1) and ATP binding cassette (ABC)-based drug efflux in human breast cancer cells. In the present work, we have found that transcriptional activation of the oxidative stress-responsive heat shock factor 1 (HSF-1) and expression of heat shock proteins, including Hsp27, which is normally known to augment proteasomal p53 degradation, are inhibited in Adriamycin (doxorubicin)-resistant MCF-7 cells (MCF-7/adr). Such an endogenous inhibition of HSF-1 and Hsp27 in turn results in p53 mutation with gain of function in its transcriptional activity and accumulation in MCF-7/adr. Also, lack of HSF-1 enhances nuclear factor κB (NF-κB) DNA binding activity together with mutant p53 and induces MDR1 gene and P-glycoprotein (P-gp, ABCB1), resulting in a multidrug-resistant phenotype. Ectopic expression of Hsp27, however, significantly depleted both mutant p53 and NF-κB (p65), reversed the drug resistance by inhibiting MDR1/P-gp expression in MCF-7/adr cells, and induced cell death by increased G(2)/M population and apoptosis. We conclude from these results that HSF-1 inhibition and depletion of Hsp27 is a trigger, at least in part, for the accumulation of transcriptionally active mutant p53, which can either directly or NF-κB-dependently induce an MDR1/P-gp phenotype in MCF-7 cells. Upon Hsp27 overexpression, this pathway is abrogated, and the acquired multidrug resistance is significantly abolished so that MCF-7/adr cells are sensitized to Dox. Thus, clinical alteration in Hsp27 or NF-κB level will be a potential approach to circumvent drug resistance in breast cancer.

High-level expression of wild-type p53 in melanoma cells is frequently associated with inactivity in p53 reporter gene assays

BACKGROUND

Inactivation of the p53 pathway that controls cell cycle progression, apoptosis and senescence, has been proposed to occur in virtually all human tumors and p53 is the protein most frequently mutated in human cancer. However, the mutational status of p53 in melanoma is still controversial; to clarify this notion we analysed the largest series of melanoma samples reported to date.

METHODOLOGY/PRINCIPAL FINDINGS

Immunohistochemical analysis of more than 180 melanoma specimens demonstrated that high levels of p53 are expressed in the vast majority of cases. Subsequent sequencing of the p53 exons 5-8, however, revealed only in one case the presence of a mutation. Nevertheless, by means of two different p53 reporter constructs we demonstrate transcriptional inactivity of wild type p53 in 6 out of 10 melanoma cell lines; the 4 other p53 wild type melanoma cell lines exhibit p53 reporter gene activity, which can be blocked by shRNA knock down of p53.

CONCLUSIONS/SIGNIFICANCE

In melanomas expressing high levels of wild type p53 this tumor suppressor is frequently inactivated at transcriptional level.

Missense mutations located in structural p53 DNA-binding motifs are associated with extremely poor survival in chronic lymphocytic leukemia

PURPOSE

There is a distinct connection between TP53 defects and poor prognosis in chronic lymphocytic leukemia (CLL). It remains unclear whether patients harboring TP53 mutations represent a homogenous prognostic group.

PATIENTS AND METHODS

We evaluated the survival of patients with CLL and p53 defects identified at our institution by p53 yeast functional assay and complementary interphase fluorescence in situ hybridization analysis detecting del(17p) from 2003 to 2010.

RESULTS

A defect of the TP53 gene was identified in 100 of 550 patients. p53 mutations were strongly associated with the deletion of 17p and the unmutated IgVH locus (both P < .001). Survival assessed from the time of abnormality detection was significantly reduced in patients with both missense (P < .001) and nonmissense p53 mutations (P = .004). In addition, patients harboring missense mutation located in p53 DNA-binding motifs (DBMs), structurally well-defined parts of the DNA-binding domain, manifested a clearly shorter median survival (12 months) compared with patients having missense mutations outside DBMs (41 months; P = .002) or nonmissense alterations (36 months; P = .005). The difference in survival was similar in the analysis limited to patients harboring mutation accompanied by del(17p) and was also confirmed in a subgroup harboring TP53 defect at diagnosis. The patients with p53 DBMs mutation (at diagnosis) also manifested a short median time to first therapy (TTFT; 1 month).

CONCLUSION

The substantially worse survival and the short TTFT suggest a strong mutated p53 gain-of-function phenotype in patients with CLL with DBMs mutations. The impact of p53 DBMs mutations on prognosis and response to therapy should be analyzed in investigative clinical trials.

ChIP-on-chip analysis of in vivo mutant p53 binding to selected gene promoters

Growing evidence shows that mutant p53 proteins, which are present in many human tumors, gain oncogenic activities that can actively contribute to tumorigenesis. Mutant p53 proteins have been extensively shown to affect the expression of several genes involved in various aspects of cancer biology. We show here the ChIP-on-chip analysis of mutant p53 binding to a set of 154 promoters, composed of both validated and putative mutant p53 target genes. By using the chromatin obtained from mutant p53R175H-immunoprecipitation in proliferating SKBr3 breast cancer cells, we found that mutant p53 binds to 40 of the 154 promoters analyzed. siRNA-mediated mutant p53 knock-down modulates the transcript abundance of some of these target genes. Two-thirds of the mutant p53-bound promoters were also engaged by either p300 or PCAF acetyl-transferases, strongly indicating the presence of transcriptionally active complexes. We also found that NF-kB binding sites are overrepresented among the mutant p53-bound promoters; a ChIP-on-chip analysis confirmed that NF-kB p65 binds to 27 of the mutant p53-bound promoters, indicating that mutant p53 could influence the transcriptional output of these NF-kB target genes.

The estrogen receptor alpha-derived peptide ERα17p (P(295)-T(311)) exerts pro-apoptotic actions in breast cancer cells in vitro and in vivo, independently from their ERα status

In recent years, our knowledge on estrogen receptors (ER) has been modified profoundly with the identification and the deciphering of the role of its protein effectors, as well as with the deeper insight of its molecular structure/function dynamics, characteristics associated with its nucleo-cytoplasmic-membrane shuttling properties. Also, significant progress has been made concerning its turn-over and associated final proteasomal degradation processes. These advances could lead in the near future to the design and the synthesis of novel receptor-interacting drugs. Recently, a number of receptor-related peptides acting as specific ER ligands have been identified and extensively studied with respect to their estrogenic/antiestrogenic activities. Among them, ERα17p, a synthetic analog of the P(295)-T(311) sequence of ERα, has been shown to exert pseudo-estrogenic effects by interacting in the close vicinity of its hinge region (BF3 domain). Remarkably, this sequence appears as the epicenter of a number of post-transcriptional modifications as well as of the recruitment of co-regulators, suggesting that it would play a key role in ERα functions. Here, we provide evidence that ERα17p induces apoptosis in ERα-positive (MCF-7, T47D) and -negative (MDA-MB-231, SK-BR-3) breast cancer cells by an ERα-independent membrane mechanism, triggering major pro-apoptotic signaling cascades. Finally, ERα17p induces the regression of breast ERα-negative cancer tumor xenografts, without apparent toxicity, suggesting that it could represent a new attractive tool for the development of future promising therapeutic approaches, and providing a novel insight to ER regulation of cell fate.

Methylation profiling with a panel of cancer related genes: association with estrogen receptor, TP53 mutation status and expression subtypes in sporadic breast cancer

Breast cancer is a heterogeneous disease that can be divided in subtypes based on histology, gene expression profiles as well as differences in genomic aberrations. Distinct global DNA methylation profiles have been reported in normal breast epithelial cells as well as in breast tumors. However, the influence of the tumor methylome on the previously described subgroups of breast cancer is not fully understood. Here we report the DNA methylation profiles of 80 breast tumors using a panel of 807 cancer related genes interrogating 1505 CpG sites. We identified three major clusters based on the methylation profiles; one consisting of mainly tumors of myoepithelial origin and two other clusters with tumors of predominantly luminal epithelial origin. The clusters were different with respect to estrogen receptor status, TP53 status, ErbB2 status and grade. The most significantly differentially methylated genes including HDAC1, TFF1, OGG1, BMP3, FZD9 and HOXA11 were confirmed by pyrosequencing. Gene Ontology analysis revealed enrichment for genes involved in developmental processes including homeobox domain genes (HOXA9, HOXA11, PAX6, MYBL2, ISL1 and IPF1) and (ETS1, HDAC1, CREBBP, GAS7, SPI1 and TBX1). Extensive correlation to mRNA expression was observed. Pathway analyses identified a significant association with canonical (curated) pathways such as hepatic fibrosis including genes like EGF, NGFR and TNF, dendritic cell maturation and the NF-κB signaling pathway. Our results show that breast tumor expression subtypes harbor major epigenetic differences and tumors with similar gene expression profiles might belong to epigenetically different subtypes. Some of the transcription factors identified, with key roles in differentiation and development might play a role in inducing and maintaining the different phenotypes.

TNFalpha up-regulates SLUG via the NF-kappaB/HIF1alpha axis, which imparts breast cancer cells with a stem cell-like phenotype

Extracellular and intracellular mediators of inflammation, such as tumor necrosis factor alpha (TNFα) and NF-kappaB (NF-κB), play major roles in breast cancer pathogenesis, progression and relapse. SLUG, a mediator of the epithelial-mesenchymal transition process, is over-expressed in CD44(+)/CD24(-) tumor initiating breast cancer cells and in basal-like carcinoma, a subtype of aggressive breast cancer endowed with a stem cell-like gene expression profile. Cancer stem cells also over-express members of the pro-inflammatory NF-κB network, but their functional relationship with SLUG expression in breast cancer cells remains unclear. Here, we show that TNFα treatment of human breast cancer cells up-regulates SLUG with a dependency on canonical NF-κB/HIF1α signaling, which is strongly enhanced by p53 inactivation. Moreover, SLUG up-regulation engenders breast cancer cells with stem cell-like properties including enhanced expression of CD44 and Jagged-1 in conjunction with estrogen receptor alpha down-regulation, growth as mammospheres, and extracellular matrix invasiveness. Our results reveal a molecular mechanism whereby TNFα, a major pro-inflammatory cytokine, imparts breast cancer cells with stem cell-like features, which are connected to increased tumor aggressiveness.

Understanding wild-type and mutant p53 activities in human cancer: new landmarks on the way to targeted therapies

Three decades of p53 research have led to many advances in understanding the basic biology of normal and cancer cells. Nonetheless, the detailed functions of p53 in normal cells, and even more so in cancer cells, remain obscure. A major breakthrough is the realization that mutant p53 has a life of its own: it contributes to cancer not only through loss of activity, but also through gain of specific 'mutant functions'. This new focus on mutant p53 is the rationale behind the meeting series dedicated to advances on mutant p53 biology. This review provides an overview of results presented at the Fourth International Workshop on Mutant p53, held in Akko, Israel in March 2009. New roles and functions of p53 relevant for tumor suppressions were presented, including the regulation of microRNAs networks, the modulation of cell-stroma interactions and the induction of senescence. A main focus of the meeting was the rapidly growing body of knowledge on autonomous properties of mutant p53 and on their oncogenic 'gain of function' impact. Importantly, the meeting highlighted that, 30 years after p53 discovery, research on mutant p53 is entering the clinical and translational era. Two major steps forward in this respect are a better understanding of the active mechanism of small drugs targeting mutant p53 in tumor cells and an improved definition of the prognostic and predictive value of mutant p53 in human cancer.

NFκB/p53 crosstalk-a promising new therapeutic target

The transcription factors p53 and NFκB determine cellular fate and are involved in the pathogenesis of most-if not all-cancers. The crosstalk between these transcription factors becomes increasingly appreciated as an important mechanism operative during all stages of tumorigenesis, metastasis, and immunological surveillance. In this review, we summarize molecular mechanisms regulating cross-signaling between p53 and NFκB proteins and how dysregulated interactions between p53 and NFκB family members contribute to oncogenesis. We furthermore analyze how such signaling modules represent targets for the design of novel intervention strategies using established compounds and powerful combination therapies.

Mutant p53 gain-of-function in cancer

In its wild-type form, p53 is a major tumor suppressor whose function is critical for protection against cancer. Many human tumors carry missense mutations in the TP53 gene, encoding p53. Typically, the affected tumor cells accumulate excessive amounts of the mutant p53 protein. Various lines of evidence indicate that, in addition to abrogating the tumor suppressor functions of wild-type p53, the common types of cancer-associated p53 mutations also endow the mutant protein with new activities that can contribute actively to various stages of tumor progression and to increased resistance to anticancer treatments. Collectively, these activities are referred to as mutant p53 gain-of-function. This article addresses the biological manifestations of mutant p53 gain-of-function, the underlying molecular mechanisms, and their possible clinical implications.