Expression of DeltaNp73 is a molecular marker for adverse outcome in neuroblastoma patients

The RUNX Family Defines Trk Phenotype and Aggressiveness of Human Neuroblastoma through Regulation of p53 and MYCN

The Runt-related transcription factor (RUNX) family, which is essential for the differentiation of cells of neural crest origin, also plays a potential role in neuroblastoma tumorigenesis. Consecutive studies in various tumor types have demonstrated that the RUNX family can play either pro-tumorigenic or anti-tumorigenic roles in a context-dependent manner, including in response to chemotherapeutic agents. However, in primary neuroblastomas, RUNX3 acts as a tumor-suppressor, whereas RUNX1 bifunctionally regulates cell proliferation according to the characterized genetic and epigenetic backgrounds, including MYCN oncogenesis. In this review, we first highlight the current knowledge regarding the mechanism through which the RUNX family regulates the neurotrophin receptors known as the tropomyosin-related kinase (Trk) family, which are significantly associated with neuroblastoma aggressiveness. We then focus on the possible involvement of the RUNX family in functional alterations of the p53 family members that execute either tumor-suppressive or dominant-negative functions in neuroblastoma tumorigenesis. By examining the tripartite relationship between the RUNX, Trk, and p53 families, in addition to the oncogene MYCN, we endeavor to elucidate the possible contribution of the RUNX family to neuroblastoma tumorigenesis for a better understanding of potential future molecular-based therapies.

Deciphering the Role of p53 and TAp73 in Neuroblastoma: From Pathogenesis to Treatment

Neuroblastoma (NB) is an embryonic cancer that develops from neural crest stem cells, being one of the most common malignancies in children. The clinical manifestation of this disease is highly variable, ranging from spontaneous regression to increased aggressiveness, which makes it a major therapeutic challenge in pediatric oncology. The p53 family proteins p53 and TAp73 play a key role in protecting cells against genomic instability and malignant transformation. However, in NB, their activities are commonly inhibited by interacting proteins such as murine double minute (MDM)2 and MDMX, mutant p53, ΔNp73, Itch, and Aurora kinase A. The interplay between the p53/TAp73 pathway and N-MYC, a known biomarker of poor prognosis and drug resistance in NB, also proves to be decisive in the pathogenesis of this tumor. More recently, a strong crosstalk between microRNAs (miRNAs) and p53/TAp73 has been established, which has been the focused of great attention because of its potential for developing new therapeutic strategies. Collectively, this review provides an updated overview about the critical role of the p53/TAp73 pathway in the pathogenesis of NB, highlighting encouraging clues for the advance of alternative NB targeted therapies.

Requirement for TP73 and genetic alterations originating from its intragenic super-enhancer in adult T-cell leukemia

Adult T-cell leukemia/lymphoma (ATL) is a genetically complex hematological malignancy derived from mature T cells. Using an integrative approach, we previously identified genes recurrently associated with super-enhancers in ATL. One of those genes was TP73, a TP53 family gene; however, the roles and function of TP73 and its super-enhancer in ATL pathogenesis are poorly understood. Our study demonstrates that TP73 is highly activated under the control of a super-enhancer in ATL cells but not in normal T cells or other hematological malignancies examined. Full-length TP73 is required for ATL cell maintenance in vitro and in vivo via the regulation of cell proliferation and DNA damage response pathways. Notably, recurrent deletions of TP73 exons 2-3 were observed in a fraction of primary ATL cases that harbored the super-enhancer, while induction of this deletion in cell lines further increased proliferation and mutational burden. Our study suggests that formation of the TP73 intragenic super-enhancer and genetic deletion are likely sequentially acquired in relation to intracellular state of ATL cells, which leads to functional alteration of TP73 that confers additional clonal advantage.

Anti-cancer therapy is associated with long-term epigenomic changes in childhood cancer survivors

BACKGROUND

Childhood cancer survivors (CCS) exhibit significantly increased chronic diseases and premature death. Abnormalities in DNA methylation are associated with development of chronic diseases and reduced life expectancy. We investigated the hypothesis that anti-cancer treatments are associated with long-term DNA methylation changes that could be key drivers of adverse late health effects.

METHODS

Genome-wide DNA methylation was assessed using MethylationEPIC arrays in paired samples (before/after therapy) from 32 childhood cancer patients. Separately, methylation was determined in 32 samples from different adult CCS (mean 22-years post-diagnosis) and compared with cancer-free controls (n = 284).

RESULTS

Widespread DNA methylation changes were identified post-treatment in childhood cancer patients, including 146 differentially methylated regions (DMRs), which were consistently altered in the 32 post-treatment samples. Analysis of adult CCS identified matching methylation changes at 107/146 of the DMRs, suggesting potential long-term retention of post-therapy changes. Adult survivors also exhibited epigenetic age acceleration, independent of DMR methylation. Furthermore, altered methylation at the DUSP6 DMR was significantly associated with early mortality, suggesting altered methylation may be prognostic for some late adverse health effects in CCS.

CONCLUSIONS

These novel methylation changes could serve as biomarkers for assessing normal cell toxicity in ongoing treatments and predicting long-term health outcomes in CCS.

Dual Role of p73 in Cancer Microenvironment and DNA Damage Response

Understanding the mechanisms that regulate cancer progression is pivotal for the development of new therapies. Although p53 is mutated in half of human cancers, its family member p73 is not. At the same time, isoforms of p73 are often overexpressed in cancers and p73 can overtake many p53 functions to kill abnormal cells. According to the latest studies, while p73 represses epithelial–mesenchymal transition and metastasis, it can also promote tumour growth by modulating crosstalk between cancer and immune cells in the tumor microenvironment, M2 macrophage polarisation, Th2 T-cell differentiation, and angiogenesis. Thus, p73 likely plays a dual role as a tumor suppressor by regulating apoptosis in response to genotoxic stress or as an oncoprotein by promoting the immunosuppressive environment and immune cell differentiation.

The p53 family member p73 in the regulation of cell stress response

During oncogenesis, cells become unrestrictedly proliferative thereby altering the tissue homeostasis and resulting in subsequent hyperplasia. This process is paralleled by resumption of cell cycle, aberrant DNA repair and blunting the apoptotic program in response to DNA damage. In most human cancers these processes are associated with malfunctioning of tumor suppressor p53. Intriguingly, in some cases two other members of the p53 family of proteins, transcription factors p63 and p73, can compensate for loss of p53. Although both p63 and p73 can bind the same DNA sequences as p53 and their transcriptionally active isoforms are able to regulate the expression of p53-dependent genes, the strongest overlap with p53 functions was detected for p73. Surprisingly, unlike p53, the p73 is rarely lost or mutated in cancers. On the contrary, its inactive isoforms are often overexpressed in cancer. In this review, we discuss several lines of evidence that cancer cells develop various mechanisms to repress p73-mediated cell death. Moreover, p73 isoforms may promote cancer growth by enhancing an anti-oxidative response, the Warburg effect and by repressing senescence. Thus, we speculate that the role of p73 in tumorigenesis can be ambivalent and hence, requires new therapeutic strategies that would specifically repress the oncogenic functions of p73, while keeping its tumor suppressive properties intact.

Inhibition of tumor suppressor p73 by nerve growth factor receptor via chaperone-mediated autophagy

The tumor suppressr p73 is a homolog of p53 and is capable of inducing cell cycle arrest and apoptosis. Here, we identify nerve growth factor receptor (NGFR, p75NTR, or CD271) as a novel negative p73 regulator. p73 activates NGFR transcription, which, in turn, promotes p73 degradation in a negative feedback loop. NGFR directly binds to p73 central DNA-binding domain and suppresses p73 transcriptional activity as well as p73-mediated apoptosis in cancer cells. Surprisingly, we uncover a previously unknown mechanism of NGFR-facilitated p73 degradation through the chaperone-mediated autophagy (CMA) pathway. Collectively, our studies demonstrate a new oncogenic function for NGFR in inactivating p73 activity by promoting its degradation through the CMA.

ΔNp73, TAp73 and Δ133p53 Extracellular Vesicle Cargo as Early Diagnosis Markers in Colorectal Cancer

Simple Summary

The survival of colorectal cancer patients largely relies on the stage at diagnosis. The identification of early and non-invasive biomarkers to be used in screening programs for the diagnosis of the disease at the premalignant stage is mandatory. The aim of this study is to validate in plasma-derived extracellular vesicles secreted by malignant cells the diagnostic potential of well-known tumor-associated genes, ΔNp73, TAp73, and Δ133p53, in healthy subjects (n = 29), individuals with premalignant lesions (n = 49), and colorectal cancer patients (n = 42). Our data support ΔNp73 levels contained in extracellular vesicles as such a non-invasive and premature biomarker for the early diagnosis of colorectal cancer.

Abstract

The early diagnosis of colorectal cancer is a key factor in the overall survival of the patients. The actual screening programs include different approaches with significant limitations such as unspecificity, high invasiveness, and detection at late stages of the disease. The specific content of extracellular vesicles derived from malignant cells may represent a non-invasive technique for the early detection of colorectal cancer. Here, we studied the mRNA levels of ΔNp73, TAp73, and Δ133p53 in plasma-derived extracellular vesicles from healthy subjects (n = 29), individuals with premalignant lesions (n = 49), and colorectal cancer patients (n = 42). Extracellular vesicles’ ΔNp73 levels were already significantly high in subjects with premalignant lesions. Δ133p53 levels were statistically increased in colorectal cancer patients compared to the other two groups and were associated with patients’ survival. Remarkably, TAp73 mRNA was not detected in any of the individuals. The evaluation of ΔNp73, Δ133p53 and CEA sensitivity, specificity and AUC values supports ΔNp73 as a better early diagnosis biomarker and CEA as the best to identify advanced stages. Thus, low levels of CEA and a high content of ΔNp73 may identify in screening programs those individuals at higher risk of presenting a premalignant lesion. In addition, Δ133p53 emerges as a potential prognosis biomarker in colorectal cancer.

New inhibitor of the TAp73 interaction with MDM2 and mutant p53 with promising antitumor activity against neuroblastoma

TAp73 is a key tumor suppressor protein, regulating the transcription of unique and shared p53 target genes with crucial roles in tumorigenesis and therapeutic response. As such, in tumors with impaired p53 signaling, like neuroblastoma, TAp73 activation represents an encouraging strategy, alternative to p53 activation, to suppress tumor growth and chemoresistance. In this work, we report a new TAp73-activating agent, the 1-carbaldehyde-3,4-dimethoxyxanthone (LEM2), with potent antitumor activity. Notably, LEM2 was able to release TAp73 from its interaction with both MDM2 and mutant p53, enhancing TAp73 transcriptional activity, cell cycle arrest, and apoptosis in p53-null and mutant p53-expressing tumor cells. Importantly, LEM2 displayed potent antitumor activity against patient-derived neuroblastoma cells, consistent with an activation of the TAp73 pathway. Additionally, potent synergistic effects were obtained for the combination of LEM2 with doxorubicin and cisplatin in patient-derived neuroblastoma cells. Collectively, besides its relevant contribution to the advance of TAp73 pharmacology, LEM2 may pave the way to improved therapeutic alternatives against neuroblastoma.

Tumor promoter role of miR‑647 in gastric cancer via repression of TP73

It has previously been demonstrated that miRNA (miR)‑647 exhibits an important role in various cancers, and is aberrantly expressed in gastric cancer (GC). However, the exact role of miR‑647 in GC still remains unclear. The present study aimed to investigate the functional significance of miR‑647 and its target gene in GC. TargetScan and Miranda databases were used to predict the putative targets, and the prediction was validated by Dual‑luciferase Reporter Assays. To investigate whether miR‑647 affects GC cell behavior, a stable miR‑647‑overexpression/low‑expression cell line was generated by transfection with miR‑647 mimic/inhibitor. MTT, Flow Cytometry and Transwell invasion assays were performed to investigate the proliferation, cell apoptosis, migration and invasion properties of MGC‑803 cells. Additionally, reverse transcription‑quantitative polymerase chain reaction and western blot analysis were performed to detect the mRNA and protein expression levels of the apoptosis‑associated genes. The results suggested that tumor protein P73 (TP73) is a target gene of miR‑647. TP73 was markedly decreased following miR‑647 overexpression and significantly increased following miR‑647 inhibition. Following overexpression of miR‑647, the proliferation, migration and invasion of MGC‑803 cells were significantly increased, whereas the percentage of apoptotic cells decreased. Conversely, the proliferation, migration and invasion of MGC‑803 cells were significantly declined, and the percentage of apoptotic cells increased following miR‑647 inhibition. In addition, the B cell lymphoma (Bcl)‑2 Associated X, Apoptosis Regulator/Bcl‑2 ratio was markedly decreased when miR‑647 was overexpressed by miRNA mimics, and significantly increased when miR‑647 expression was inhibited via an miRNA inhibitor. Overall, miR‑647 functions as a tumor promoter in GC by repressing TP73.

MicroRNA‑663b mediates TAM resistance in breast cancer by modulating TP73 expression

Breast cancer is the second leading cause of cancer‑associated mortalities in women. Tamoxifen (TAM) is an endocrine therapy commonly used in the treatment of patients with breast cancer expressing estrogen receptor α. However, treatment often ends in failure due to the emergence of drug resistance. MicroRNAs (miRNAs), a family of small non‑coding RNAs, serve critical roles in the regulation of gene expression and cell events. To date, whether miRNA‑663b could mediate TAM resistance in breast cancer remains unknown. Therefore, the aim of the present study was to investigate the role of miRNA‑663b in TAM resistance in breast cancer. The results demonstrated that miRNA‑663b was upregulated in breast cancer with TAM resistance. Tumor protein 73 (TP73) was a direct target of miRNA‑663b, and was negatively regulated by miRNA‑663b in MCF‑7 cells. Furthermore, it was identified that downregulation of miRNA‑663b inhibited cell proliferation ability and promoted cell apoptosis, resulting in enhanced TAM sensitivity. In addition, these findings suggested that TP73 silencing may have eliminated the effects of miRNA‑663b inhibitor on breast cancer cells. In conclusion, the present study verified a novel molecular link between miRNA‑663b and TP73, and indicated that miRNA‑663b may be a critical therapeutic target in breast cancer.

ΔNp73 overexpression promotes resistance to apoptosis but does not cooperate with PML/RARA in the induction of an APL-leukemic phenotype

Here, we evaluated whether the overexpression of transcriptionally inactive ΔNp73 cooperates with PML/RARA fusion protein in the induction of an APL-leukemic phenotype, as well as its role in vitro in proliferation, myeloid differentiation, and drug-induced apoptosis. Using lentiviral gene transfer, we showed in vitro that ΔNp73 overexpression resulted in increased proliferation in murine bone marrow (BM) cells from hCG-PML/RARA transgenic mice and their wild-type (WT) counterpart, with no accumulation of cells at G2/M or S phases; instead, ΔNp73-expressing cells had a lower rate of induced apoptosis. Next, we evaluated the effect of ΔNp73 on stem-cell self-renewal and myeloid differentiation. Primary BM cells lentivirally infected with human ΔNp73 were not immortalized in culture and did not present significant changes in the percentage of CD11b. Finally, we assessed the impact of ΔNp73 on leukemogenesis or its possible cooperation with PML/RARA fusion protein in the induction of an APL-leukemic phenotype. After 120 days of follow-up, all transplanted mice were clinically healthy and, no evidence of leukemia/myelodysplasia was apparent. Taken together, our data suggest that ΔNp73 had no leukemic transformation capacity by itself and apparently did not cooperate with the PML/RARA fusion protein to induce a leukemic phenotype in a murine BM transplantation model. In addition, the forced expression of ΔNp73 in murine BM progenitors did not alter the ATRA-induced differentiation rate in vitro or induce aberrant cell proliferation, but exerted an important role in cell survival, providing resistance to drug-induced apoptosis.

Clinical implications of the deregulated TP73 isoforms expression in cancer

TP73 is a member of the TP53 family whose expression has been observed altered in most human cancers and associated with the prognosis. TP73 translates into a complex number of isoforms with both oncogenic and tumour-suppressor functions and presents a complex cross-talk with other members of the family (TP53 and TP63). In this revision, we focus on the evidence that may support TP73 variants as prognostic markers in cancer. Nowadays, most publications in this topic highlight the association between overexpression of the oncogenic variants and failure to respond to chemotherapy and/or shorter survival. In addition, we comment on the putative possibilities that the detection through a liquid biopsy of TP73 variants may provide, and finally, the significance of determining the value of the combined alteration of the TP53 family members in the clinical setting.

TP73 DNA methylation and upregulation of ΔNp73 are associated with an adverse prognosis in breast cancer

AIM

Accumulated evidence suggests that aberrant methylation of the TP73 gene and increased levels of ΔNp73 in primary tumours correlate with poor prognosis. However, little is known regarding the transcriptional and functional regulation of the TP73 gene in breast cancer. The aim of the present study was to determine the expression of the ΔNp73 isoform, its relationship with DNA methylation of TP73 and their clinical prognostic significance in breast cancer patients.

METHODS

TP73 gene methylation was studied in TCGA datasets and in 70 invasive ductal breast carcinomas (IDCs). The expression of p73 isoforms was evaluated by immunohistochemistry (IHC) and Western blot and correlated with clinicopathological variables and clinical outcome.

RESULTS

We observed that the methylation of diverse CpG islands of TP73 differed significantly between molecular subtypes. An inverse correlation was found between p73 protein expression and the methylation status of the TP73 gene. The expression of exon 3' of p73 (only expressed in ΔNp73) was significantly higher in patients with wild-type p53. Immunohistochemical analysis revealed that all p73 isoforms were localised in both the nuclear and cytoplasmic compartments. We confirmed a positive association between the expression of ∆Np73 and high histological grade.

CONCLUSIONS

Our findings suggest that high expression of ΔNp73 could be used to determine the aggressiveness of IDCs and could be incorporated in the pathologist's report.

Effect of low doses of actinomycin D on neuroblastoma cell lines

BACKGROUND

Neuroblastoma is a malignant embryonal tumor occurring in young children, consisting of undifferentiated neuroectodermal cells derived from the neural crest. Current therapies for high-risk neuroblastoma are insufficient, resulting in high mortality rates and high incidence of relapse. With the intent to find new therapies for neuroblastomas, we investigated the efficacy of low-doses of actinomycin D, which at low concentrations preferentially inhibit RNA polymerase I-dependent rRNA trasncription and therefore, ribosome biogenesis.

METHODS

Neuroblastoma cell lines with different p53 genetic background were employed to determine the response on cell viability and apoptosis of low-dose of actinomycin D. Subcutaneously-implanted SK-N-JD derived neuroblastoma tumors were used to assess the effect of low-doses of actinomycin D on tumor formation.

RESULTS

Low-dose actinomycin D treatment causes a reduction of cell viability in neuroblastoma cell lines and that this effect is stronger in cells that are wild-type for p53. MYCN overexpression contributes to enhance this effect, confirming the importance of this oncogene in ribosome biogenesis. In the wild-type SK-N-JD cell line, apoptosis was the major mechanism responsible for the reduction in viability and we demonstrate that treatment with the MDM2 inhibitor Nutlin-3, had a similar effect to that of actinomycin D. Apoptosis was also detected in p53(-/-)deficient LA1-55n cells treated with actinomycin D, however, only a small recovery of cell viability was found when apoptosis was inhibited by a pan-caspase inhibitor, suggesting that the treatment could activate an apoptosis-independent cell death pathway in these cells. We also determined whether actinomycin D could increase the efficacy of the histone deacetylase inhibitor, SAHA, which is in being used in neuroblastoma clinical trials. We show that actinomycin D synergizes with SAHA in neuroblastoma cell lines. Moreover, on subcutaneously-implanted neuroblastoma tumors derived from SK-N-JD cells, actinomycin D led to tumor regression, an effect enhanced in combination with SAHA.

CONCLUSIONS

The results presented in this work demonstrate that actinomycin D, at low concentrations, inhibits proliferation and induces cell death in vitro, as well as tumor regression in vivo. From this study, we propose that use of ribosome biogenesis inhibitors should be clinically considered as a potential therapy to treat neuroblastomas.

Neuroblastoma: oncogenic mechanisms and therapeutic exploitation of necroptosis

Neuroblastoma (NB) is the most common extracranial childhood tumor classified in five stages (1, 2, 3, 4 and 4S), two of which (3 and 4) identify chemotherapy-resistant, highly aggressive disease. High-risk NB frequently displays MYCN amplification, mutations in ALK and ATRX, and genomic rearrangements in TERT genes. These NB subtypes are also characterized by reduced susceptibility to programmed cell death induced by chemotherapeutic drugs. The latter feature is a major cause of failure in the treatment of advanced NB patients. Thus, proper reactivation of apoptosis or of other types of programmed cell death pathways in response to treatment is relevant for the clinical management of aggressive forms of NB. In this short review, we will discuss the most relevant genomic rearrangements that define high-risk NB and the role that destabilization of p53 and p73 can have in NB aggressiveness. In addition, we will propose a strategy to stabilize p53 and p73 by using specific inhibitors of their ubiquitin-dependent degradation. Finally, we will introduce necroptosis as an alternative strategy to kill NB cells and increase tumor immunogenicity.

Structure and apoptotic function of p73

p73 is a structural and functional homologue of the p53 tumor suppressor protein. Like p53, p73 induces apoptosis and cell cycle arrest and transactivates p53-responsive genes, conferring its tumor suppressive activity. In addition, p73 has unique roles in neuronal development and differentiation. The importance of p73-induced apoptosis lies in its capability to substitute the pro-apoptotic activity of p53 in various human cancer cells in which p53 is mutated or inactive. Despite the great importance of p73-induced apoptosis in cancer therapy, little is known about the molecular basis of p73-induced apoptosis. In this review, we discuss the p73 structures reported to date, detailed structural comparisons between p73 and p53, and current understanding of the transcription-dependent and -independent mechanisms of p73-induced apoptosis. [BMB Reports 2015; 48(2): 81-90]

Environmental Epigenetics: Crossroad between Public Health, Lifestyle, and Cancer Prevention

Epigenetics provides the key to transform the genetic information into phenotype and because of its reversibility it is considered an ideal target for therapeutic interventions. This paper reviews the basic mechanisms of epigenetic control: DNA methylation, histone modifications, chromatin remodeling, and ncRNA expression and their role in disease development. We describe also the influence of the environment, lifestyle, nutritional habits, and the psychological influence on epigenetic marks and how these factors are related to cancer and other diseases development. Finally we discuss the potential use of natural epigenetic modifiers in the chemoprevention of cancer to link together public health, environment, and lifestyle.

Evaluation of promoter hypomethylation and expression of p73 as a diagnostic and prognostic biomarker in Wilms' tumour

AIMS

A member of the p53 family, the p73 gene is essential for the maintenance of genomic stability, DNA repair and apoptosis regulation. This study was designed to evaluate the utility of expression and DNA methylation patterns of the p73 gene in the early diagnosis and prognosis of Wilms' tumour (WT).

METHODS

Methylation-specific PCR, semi-quantitative (sq-PCR), real-time quantitative PCR (qRT-PCR), receiver operating characteristic (ROC), and survival and hazard function curve analyses were utilised to measure the expression and DNA methylation patterns of p73 in WT tissue samples with a view to assessing diagnostic and prognostic value.

RESULTS

The relative expression of p73 mRNA was higher, while the promoter methylation level was lower in the WT than the control group (p<0.05) and closely associated with poor survival prognosis in children with WT (p<0.05). Increased expression and decreased methylation of p73 were correlated with increasing tumour size, clinical stage and unfavourable histological differentiation (p<0.05). ROC curve analysis showed areas under the curve of 0.544 for methylation and 0.939 for expression in WT venous blood, indicating the higher diagnostic yield of preoperative p73 expression.

CONCLUSIONS

Preoperative venous blood p73 level serves as an underlying biomarker for the early diagnosis of WT. p73 overexpression and concomitantly decreased promoter methylation are significantly associated with poor survival in children with WT.

∆Np73 is capable of inducing apoptosis by co-ordinately activating several BH3-only proteins

Inactivation of p53 is one of the most relevant events in human cancer, since it allows transformed cells to escape their own proliferation control and leave them irresponsive to drugs that aim to damage their DNA. When p53 falls, other members of its family may become targets to attack tumoural cells. p73 has shown capacity to mediate these attacks. However, its N-terminal truncated isoforms have been associated with oncogenesis due to their capacity to act as dominant negatives of p53 and the transactivation (TA) isoforms of p73. We previously found a relationship between the overexpression of N-terminus-truncated p73 isoform (∆Np73) and that of the proapoptotic gene Bcl-2-interacting killer (BIK). In the present report we demonstrate that ∆Np73-α has the capacity to induce apoptosis through the co-ordinated activation of a group of genes harbouring GC-rich elements in their regulatory regions. ∆Np73-α synergizes with specificity protein (Sp1) on these elements but the overall response of these genes probably depends on the additional presence of consensus p53 elements. We explore the domains of ∆Np73-α involved in this transactivation capacity and found divergences with the previously described functions for them. Moreover, we found that the transforming mutation V12 of HRas impairs this transactivation capacity of ∆Np73-α, further supporting the anti-tumoural function of this later. Our data add complexity to the action of p73 on the induction of apoptosis and tumourogenesis, opening new interpretations to the expression profile of p73 isoforms in different human neoplasias.

Overexpression of the ∆Np73 isoform is associated with centrosome amplification in brain tumor cell lines

The p73 protein is a member of the p53 family, and this protein is known to be essential for the maintenance of genomic stability, DNA repair, and apoptosis regulation. Transcription from two promoters leads to two main N-terminal isoforms: the TAp73 isoform is reported to have tumor suppressor function, whereas the ΔNp73 isoform likely has oncogenic potential. The present study is focused on the investigation of a possible role of both these p73 N-terminal isoforms in the process of centrosome amplification. HGG-02 and GM7 glioblastoma cell lines and the Daoy medulloblastoma cell line were used in this study. The cells were analyzed using indirect immunofluorescence to determine TAp73 and ΔNp73 expression patterns and possible co-localization with the BubR1 protein, as well as the number of centrosomes. A transiently transfected GM7 cell line was used to verify the results concerning the N-terminal isoforms in relation to centrosome amplification. We found that increased immunoreactivity for the ΔNp73 isoform is associated with the occurrence of an abnormal number of centrosomes in particular cells. Using the transiently transfected GM7 cell line, we confirmed that centrosome amplification is present in cells with overexpression of the ΔNp73 isoform. In contrast, the immunoreactivity for the TAp73 isoform was weak or medium in most of the cells with an aberrant number of centrosomes. To determine the putative counterpart of the p73 N-terminal isoforms among spindle assembly checkpoint (SAC) proteins, we also evaluated possible interactions between the N-terminal isoforms and BubR1 protein, but no co-localization of these proteins was observed.

Preclinical activity of combined HDAC and KDM1A inhibition in glioblastoma

BACKGROUND

Glioblastoma (GBM) is the most common and aggressive form of brain cancer. Our previous studies demonstrated that combined inhibition of HDAC and KDM1A increases apoptotic cell death in vitro. However, whether this combination also increases death of the glioma stem cell (GSC) population or has an effect in vivo is yet to be determined. Therefore, we evaluated the translational potential of combined HDAC and KDM1A inhibition on patient-derived GSCs and xenograft GBM mouse models. We also investigated the changes in transcriptional programing induced by the combination in an effort to understand the induced molecular mechanisms of GBM cell death.

METHODS

Patient-derived GSCs were treated with the combination of vorinostat, a pan-HDAC inhibitor, and tranylcypromine, a KDM1A inhibitor, and viability was measured. To characterize transcriptional profiles associated with cell death, we used RNA-Seq and validated gene changes by RT-qPCR and protein expression via Western blot. Apoptosis was measured using DNA fragmentation assays. Orthotopic xenograft studies were conducted to evaluate the effects of the combination on tumorigenesis and to validate gene changes in vivo.

RESULTS

The combination of vorinostat and tranylcypromine reduced GSC viability and displayed efficacy in the U87 xenograft model. Additionally, the combination led to changes in apoptosis-related genes, particularly TP53 and TP73 in vitro and in vivo.

CONCLUSIONS

These data support targeting HDACs and KDM1A in combination as a strategy for GBM and identifies TP53 and TP73 as being altered in response to treatment.

A balancing act: orchestrating amino-truncated and full-length p73 variants as decisive factors in cancer progression

p73 is the older sibling of p53 and mimics most of its tumor-suppressor functions. Through alternative promoter usage and splicing, the TP73 gene generates more than two dozen isoforms of which N-terminal truncated DNp73 variants have a decisive role in cancer pathogenesis as they outweigh the positive effects of full-length TAp73 and p53 in acting as a barrier to tumor development. Beyond the prevailing view that DNp73 predominantly counteract cell cycle arrest and apoptosis, latest progress indicates that these isoforms acquire novel functions in epithelial-to-mesenchymal transition, metastasis and therapy resistance. New insight into the mechanisms underlying this behavior reinforced the expectation that DNp73 variants contribute to aggressive cellular traits through both loss of wild-type tumor-suppressor activity and gain-of-function, suggesting an equally important role in cancer progression as mutant p53. In this review, we describe the novel properties of DNp73 in the invasion metastasis cascade and outline the comprehensive p73 regulatome with an emphasis on molecular processes putting TAp73 out of action in advanced tumors. These intriguing insights provoke a new understanding of the acquisition of aggressive traits by cancer cells and may help to set novel therapies for a broad range of metastatic tumors.

Crosstalk among p53 family members in cutaneous carcinoma

Cutaneous squamous cell carcinoma (cSCC) is the second most common human cancer with a frequency increasing worldwide. The risk of developing cSCC has been strongly associated with chronic sun exposure, especially in light skin people. The aim of this viewpoint is to discuss the contribution of the tumor suppressor p53 and its homologues p63 and p73 in the formation and progression of cSCC. Mutations in the p53 gene are early and frequent events in skin carcinogenesis mainly as a consequence of UV light exposure, often followed by loss of function of the second allele. Although rarely mutated in cancer, p63 and p73 play key roles in human cancers, with their truncated isoforms lacking the N-terminal transactivating domain (∆N) being often upregulated as compared to normal tissues. ∆Np63 is abundantly expressed in cSCC, and it is likely to favour tumor initiation and progression. The function of p73 in cSCC is more enigmatic and awaits further studies. Interestingly, an intimate interplay exists between both p53 and p63, and the Notch signalling pathway, often inactivated in cSCC. Here, we summarize our current knowledge about the biological activities of p53 family members in cSCC and propose that integration of their signalling with Notch is key to cSCC formation and progression.

Histone deacetylase 2 controls p53 and is a critical factor in tumorigenesis

Histone deacetylase 2 (HDAC2) regulates biological processes by deacetylation of histones and non-histone proteins. HDAC2 is overexpressed in numerous cancer types, suggesting general cancer-relevant functions of HDAC2. In human tumors the TP53 gene encoding p53 is frequently mutated and wild-type p53 is often disarmed. Molecular pathways inactivating wild-type p53 often remain to be defined and understood. Remarkably, current data link HDAC2 to the regulation of the tumor suppressor p53 by deacetylation and to the maintenance of genomic stability. Here, we summarize recent findings on HDAC2 overexpression in solid and hematopoietic cancers with a focus on mechanisms connecting HDAC2 and p53 in vitro and in vivo. In addition, we present an evidence-based model that integrates molecular pathways and feedback loops by which p53 and further transcription factors govern the expression and the ubiquitin-dependent proteasomal degradation of HDAC2 and of p53 itself. Understanding the interactions between p53 and HDAC2 might aid in the development of new therapeutic approaches against cancer.

TP63 and TP73 in cancer, an unresolved "family" puzzle of complexity, redundancy and hierarchy

TP53 belongs to a small gene family that includes, in mammals, two additional paralogs, TP63 and TP73. The p63 and p73 proteins are structurally and functionally similar to p53 and their activity as transcription factors is regulated by a wide repertoire of shared and unique post-translational modifications and interactions with regulatory cofactors. p63 and p73 have important functions in embryonic development and differentiation but are also involved in tumor suppression. The biology of p63 and p73 is complex since both TP63 and TP73 genes are transcribed into a variety of different isoforms that give rise to proteins with antagonistic properties, the TA-isoforms that act as tumor-suppressors and DN-isoforms that behave as proto-oncogenes. The p53 family as a whole behaves as a signaling "network" that integrates developmental, metabolic and stress signals to control cell metabolism, differentiation, longevity, proliferation and death. Despite the progress of our knowledge, the unresolved puzzle of complexity, redundancy and hierarchy in the p53 family continues to represent a formidable challenge.

Expression level of quiescin sulfhydryl oxidase 1 (QSOX1) in neuroblastomas

Neuroblastoma is the most common extracranial solid malignant tumor observed during childhood. Although these tumors can sometimes regress spontaneously or respond well to treatment in infants, genetic alterations that influence apoptosis can, in some cases, confer resistance to chemotherapy or result in relapses and adversely affect prognosis for these patients. The aim of this study was to correlate immunohistochemical expression of the protein quiescin sulfhydryl oxidase 1 (QSOX1) in samples obtained from untreated neuroblastomas with the patients’ clinical and pathological prognostic factors and clinical course. Neuroblastoma samples (n=23) obtained from histology blocks were arrayed into tissue microarrays and analysed by immunohistochemistry. The cases were classified according to the following clinical and pathological prognostic factors: age at diagnosis greater or less than/equal to 18 months; location of the lesion at diagnosis (abdominal or extra-abdominal); presence or absence of bone-marrow infiltration; tumor differentiation (well or poorly differentiated); Shimada histopathologic classification (favourable or unfavourable); state of the tumor extracellular matrix (Schwannian-stroma rich or poor); amplification of the MYCN oncogene; and clinical course (dead or alive with or without relapses/residual lesions). Twelve of the cases were female, 9 children were over 18 months old, 9 cases presented with extra-abdominal tumors and 9 cases exhibited tumors with unfavourable histologies. Fifteen patients underwent bone-marrow biopsy, and 4 of these were positive for metastasis. Nine patients died. The higher immunohistochemical expression of QSOX1 was more common in well-differentiated samples (P=0.029), in stroma-rich samples (P=0.029) and in samples from patients with a high prevalence of relapses/residual disease. The functions of QSOX1 include extracellular matrix maturation and the induction of apoptosis. Therefore, QSOX1 may be involved in neuroblastoma differentiation and regression and may thus function as a biomarker for identifying risk groups for this neoplasm.

The TP73 complex network: ready for clinical translation in cancer?

TP73 is a member of the TP53 family, whose deregulated expression has been reported in a wide variety of cancers and linked to patients' outcome. The fact that TP73 encodes a complex number of isoforms (TAp73 and ΔTAp73) with opposing functions and the cross-talk with other members of the family (TP53 and TP63) make it difficult to determine its clinical relevance. Here, we review the molecular mechanisms driving TAp73 and ΔTAp73 expression and how these variants inhibit or promote carcinogenesis. We also highlight the intricate interplay between TP53 family members. In addition, we comment on current pharmacological approaches targeting the TP73 pathway and those affecting the TAp73/ΔTAp73 ratio. Finally, we discuss the current data available in the literature that provide evidence on the role of TP73 variants in predicting prognosis. To date, most of the studies that evaluate the status levels of TP73 isoforms have been based on limited-size series. Despite this limitation, these publications highlight the correlation between high levels of the oncogenic forms and failure to respond to chemotherapy and/or shorter survival. Finally, we emphasize the need for studies to evaluate the significance of combining the deregulation of various members of the TP53 family in order to define patient outcome or their responsiveness to specific therapies.

Apoptotic cell death in neuroblastoma

Neuroblastoma (NB) is one of the most common malignant solid tumors in childhood, which derives from the sympathoadrenal lineage of the neural crest and exhibits extremely heterogeneous biological and clinical behaviors. The infant patients frequently undergo spontaneous regression even with metastatic disease, whereas the patients of more than one year of age who suffer from disseminated disease have a poor outcome despite intensive multimodal treatment. Spontaneous regression in favorable NBs has been proposed to be triggered by nerve growth factor (NGF) deficiency in the tumor with NGF dependency for survival, while aggressive NBs have defective apoptotic machinery which enables the tumor cells to evade apoptosis and confers the resistance to treatment. This paper reviews the molecules and pathways that have been recently identified to be involved in apoptotic cell death in NB and discusses their potential prospects for developing more effective therapeutic strategies against aggressive NB.

Mechanisms, function and clinical applications of DNp73

p73, has two distinct promoters, which allow the formation of two protein isoforms: full-length transactivating (TA) p73 and an N-terminally truncated p73 species (referred to as DNp73) that lacks the N-terminal transactivating domain. Although the exact cellular function of DNp73 is unclear, the high expression levels of the genes have been observed in a variety of human cancers and cancer cell lines and have been connected to pro-tumor activities. Hence the aim of this review is to summarize DNp73 expression status in cancer in the current literature. Furthermore, we also focused on recent findings of DNp73 related to the biological functions from apoptosis, chemosensitivity, radiosensitibity, differentiation, development, etc. Thus this review highlights the significance of DNp73 as a marker for disease severity in patients and as target for cancer therapy.

Effects of carbon-ion beam or X-ray irradiation on anti-apoptosis ΔNp73 expression in HeLa cells

ΔNp73 has emerged as an interesting novel factor in cancer research. Here, we report the effect of carbon-ion beams on ΔNp73 expression in human cervix carcinoma HeLa cells in contrast to the effect of X-rays. Cellular sensitivities were determined by colony formation. Radiation-induced cell cycle arrest was investigated with flow cytometry. Additionally, radiation-induced apoptosis was analyzed with flow cytometry and Hoechst staining. Furthermore, ΔNp73 expression was examined by semi-quantitative reverse transcription-PCR (semi-quantitative RT-PCR) as well as by Western blot analysis. Following irradiation, stronger G2/M phase arrest, more significant increase in apoptosis and more pronounced ΔNp73 degradation were observed after exposure to high-LET carbon beams in comparison with X-rays at 4 Gy doses. These observations indicate that there is a differential ΔNp73 expression in response to different LET radiations, and down-regulated ΔNp73 expression might play a critical role in promoting cycle arrest and apoptosis in cancer cells. This study highlights the potential of ΔNp73 in radiotherapy.

Apoptin induces apoptosis by changing the equilibrium between the stability of TAp73 and ΔNp73 isoforms through ubiquitin ligase PIR2

Apoptin, a protein derived from the chicken anaemia virus, induces cell death in various cancer cells but shows little or no cytotoxicity in normal cells. The mechanism of apoptin-induced cell death is currently unknown but it appears to induce apoptosis independent of p53 status. Here we show that p73, a p53 family member, is important in apoptin-induced apoptosis. In p53 deficient and/or mutated cells, apoptin induced the expression of TAp73 leading to the induction of apoptosis. Knockdown of p73 using siRNA resulted in a significant reduction in apoptin-induced cytotoxicity. The p53 and p73 pro-apoptotic target PUMA plays an important role in apoptin-induced cell death as knockdown of PUMA significantly reduced cell sensitivity to apoptin. Importantly, apoptin expression resulted in a marked increase in TAp73 protein stability. Investigation into the mechanisms of TAp73 stability showed that apoptin induced the expression of the ring finger domain ubiquitin ligase PIR2 which is involved in the degradation of the anti-apoptotic ∆Np73 isoform. Collectively, our results suggest a novel mechanism of apoptin-induced apoptosis through increased TAp73 stability and induction of PIR2 resulting in the degradation of ∆Np73 and activation of pro-apoptotic targets such as PUMA causing cancer cell death.

p73 expression is regulated by RNPC1, a target of the p53 family, via mRNA stability

p73, a p53 family tumor suppressor, is expressed as TA and ΔN isoforms. Due to the role of p73 in tumor suppression and neural development, its expression and activity are tightly regulated by multiple mechanisms, including transcription and posttranslational modifications. Here, we found that p73 mRNA stability is regulated by RNPC1, an RNA binding protein and a target of the p53 family. We also showed that a CU-rich element in the 3' untranslated region of p73 is recognized by and responsive to RNPC1. To explore the physiological significance of RNPC1-regulated p73 expression, we showed that the loss of RNPC1 in p53-null mouse embryonic fibroblasts leads to reduced expression of p73, along with decreased expression of p21, p130, and γ-H2A.X, and consequently a decreased number of senescent cells. Furthermore, we observed that knockdown of TAp73 or p21, another target of RNPC1, attenuates the inhibitory effect of RNPC1 on cell proliferation and premature senescence, whereas combined knockdown of TAp73 and p21 completely abolishes it. Due to the fact that RNPC1 is a target of p73, the mutual regulation between p73 and RNPC1 constitutes a novel feed-forward loop, which might be explored as a target for tumors without a functional p53.

TAp63γ enhances nucleotide excision repair through transcriptional regulation of DNA repair genes

p63 and p73, two p53 family members, play crucial roles in development and tumor suppression. p63 and p73 have multiple isoforms, which have similar or distinct biological functions. Transactivation (TA) isoforms of p63 and p73 have high similarity with p53 and often have biological functions similar to p53. p53 plays an important role in nucleotide excision repair (NER) through transcriptional regulation of target genes involved in NER, including DDB2, XPC and GADD45. To investigate whether TAp63 and TAp73 play a similar role in NER, Saos2 cells with inducible expression of specific isoforms of TAp63 and TAp73, including TAp63α/β/γ and TAp73α/β/γ isoforms, were employed. Overexpression of TAp63γ significantly enhances NER of ultraviolet (UV)-induced DNA damage, including cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts, and enhances cell survival after UV irradiation in Soas2 cells. The enhancement of NER of UV-induced DNA damage by TAp63γ was also confirmed in H1299 cells with overexpression of TAp63γ. Consistently, knockdown of endogenous TAp63 decreases NER of UV-induced DNA damage in H1299 cells. TAp63α/β and TAp73α/β/γ isoforms do not have a clear effect on NER in Saos2 or H1299 cells. TAp63γ overexpression clearly induces the expression of DDB2, XPC and GADD45 at both RNA and protein levels. Furthermore, luciferase reporter assays show that TAp63γ transcriptionally activates DDB2, XPC and GADD45 genes through the regulation of the p53 binding elements in these genes. These results demonstrate that TAp63γ enhances NER to remove UV-induced DNA damage and maintain genomic stability through transcriptional induction of a set of NER proteins, which provides an additional important mechanism that contributes to the function of TAp63 in tumor suppression.

p73 in Cancer

p73 is a tumor suppressor belonging to the p53 family of transcription factors. Distinct isoforms are transcribed from the p73 locus. The use of 2 promoters at the N-terminus allows the expression of an isoform containing (TAp73) or not containing (ΔNp73) a complete N-terminal transactivation domain, with the latter isoform capable of a dominant negative effect over the former. In addition, both N-terminal variants are alternatively spliced at the C-terminus. TAp73 is a bona fide tumor suppressor, being able to induce cell death and cell cycle arrest; conversely, ΔNp73 shows oncogenic properties, inhibiting TAp73 and p53 functions. Here, we discuss the latest findings linking p73 to cancer. The generation of isoform specific null mice has helped in dissecting the contribution of TA versus ΔNp73 isoforms to tumorigenesis. The activity of both isoforms is regulated transcriptionally and by posttranslational modification. p73 dysfunction, particularly of TAp73, has been associated with mitotic abnormalities, which may lead to polyploidy and aneuploidy and thus contribute to tumorigenesis. Although p73 is only rarely mutated in cancer, the tumor suppressor actions of TAp73 are inhibited by mutant p53, a finding that has important implications for cancer therapy. Finally, we discuss the expression and role of p73 isoforms in human cancer, with a particular emphasis on the neuroblastoma cancer model. Broadly, the data support the hypothesis that the ratio between TAp73 and ΔNp73 is crucial for tumor progression and therapeutic response.

Regulation of Fertility by the p53 Family Members

The p53 family members, which consist of 3 transcription factors-p53, p63, and p73-are conserved during evolution. The p53 family proteins are involved in many important cellular functions, including tumor suppression (p53 and p73), the development of epithelial cell layers (p63), and the development of central nervous system and immune system (p73). Studies on p53-like proteins in low organisms have demonstrated that their primordial functions are to maintain the genomic integrity of germ cells and ensure faithful development and reproduction. In vertebrates, the p53 family proteins retain these functions in reproduction and at the same time have developed additional important functions in reproduction, such as the regulation of embryonic implantation (p53). p53 regulates embryonic implantation through transcriptional regulation of leukemia inhibitory factor (LIF). p63, in particular TAp63, is a main regulator to protect the fidelity of female germ cells during meiotic arrest. p73, in particular TAp73, regulates the ovary function and the quality of oocytes. Loss of p53, p63, or p73 genes in female mice leads to a significant decrease in fertility. These functions of the p53 family proteins in reproduction provide a plausible explanation for positive evolutionary selection observed in a group of single nucleotide polymorphisms and haplotypes in the p53 family genes. A better understanding of the functions of the p53 family proteins in reproduction may lead to new strategies for fertility treatment.

p73 as a pharmaceutical target for cancer therapy

About half of all human tumors contain an inactivating mutation of p53, while in the remaining tumors, the p53 pathway is frequently abrogated by alterations of other components of its signaling pathway. In humans, the p53 tumor suppressor is part of a small gene family that includes two other members, p73 and p63, structurally and functionally related to p53. Accumulating evidences indicate that all p53-family proteins function as molecular hubs of a highly interconnected signaling network that coordinates cell proliferation, differentiation and death in response to physiological inputs and oncogenic stress. Therefore, not only the p53-pathway but the entire “p53-family pathway” is a primary target for cancer drug development. In particular, the p53-related protein p73 has a crucial role in determining cellular responses to chemotherapy, and can vicariate p53 functions in triggering cell death after DNA damage in multiple experimental models. The biology and regulation of p73 is complex, since the TP73 gene incorporates both tumor-suppressive and proto-oncogenic functions. However, the p73 gene is rarely mutated in tumors, so appropriate pharmacological manipulation of the p73 pathway is a very promising approach for cancer therapy. Here we provide an overview of the principal mechanism of p73 regulation, and describe several examples of pharmacological tools that can induce p73 accumulation and function by acting on upstream p73 modulators or displacing inhibitory p73 interactors. A better understanding of how the p73 pathway works is mandatory to discover additional players intervening in this pathway and has important implications for the improvement of cancer treatment with the development of new molecules or with the reposition of currently available drugs.

p73 protein regulates DNA damage repair

Although the p53 tumor suppressor is relatively well characterized, much less is known about the functions of other members of the p53 family, p73 and p63. Here, we present evidence that in specific pathological conditions caused by exposure of normal cells to bile acids in acidic conditions, p73 protein plays the predominant role in the DNA damage response. These pathological conditions frequently occur during gastric reflux in the human esophagus and are associated with progression to esophageal adenocarcinoma. We found that despite strong DNA damage induced by bile acid exposure, only p73 (but not p53 and p63) is selectively activated in a c-Abl kinase-dependent manner. The activated p73 protein induces DNA damage repair. Using a human DNA repair PCR array, we identified multiple DNA repair genes affected by p73. Two glycosylases involved in base excision repair, SMUG1 and MUTYH, were characterized and found to be transcriptionally regulated by p73 in DNA damage conditions. Using a surgical procedure in mice, which recapitulates bile acid exposure, we found that p73 deficiency is associated with increased DNA damage. These findings were further investigated with organotypic and traditional cell cultures. Collectively our studies demonstrate that p73 plays an important role in the regulation of DNA damage repair.

Effects of ΔNp73β on cisplatin treatment in colon cancer cells

p73 can activate transcription of p53-responsive genes, thereby inhibiting cell growth. An alternative promoter in the TP73 gene gives rise to an N-terminally truncated isoform of p73, ΔNp73, which lacks the transactivation domain of the full length TAp73 protein. TAp73 is considered pro-apoptotic, and ΔNp73 anti-apoptotic. In this study, we overexpressed ΔNp73β in p53 wild type and p53 mutant colon cancer cell lines and further exposed the cells to cancer therapeutic drug cisplatin. The results showed that cisplatin decreased the protein expression levels of ΔNp73β in a dose-dependent manner, and both TAp73 and p53 were upregulated after cisplatin treatment. Further, clonogenic potential and cell viability were decreased, and apoptotic cells increased, in p53 mutant and in p53 wild type cells. Cellular viability was significantly higher in ΔNp73β-cells than mock-transfected cells. However, ΔNp73β overexpression did not affect the cellular susceptibility to cisplatin. In conclusion, the overexpression of ΔNp73β increases viability in p53 wild type and p53 mutant colon cancer cells, and cisplatin induces the degradation of ΔNp73β in a dose-dependent manner.

The MYCN oncogene and differentiation in neuroblastoma

Childhood neuroblastoma exhibits a heterogeneous clinical behavior ranging from low-risk tumors with the ability to spontaneously differentiate and regress, to high-risk tumors causing the highest number of cancer related deaths in infants. Amplification of the MYCN oncogene is one of the few prediction markers for adverse outcome. This gene encodes the MYCN transcriptional regulator predominantly expressed in the developing peripheral neural crest. MYCN is vital for proliferation, migration and stem cell homeostasis while decreased levels are associated with terminal neuronal differentiation. Interestingly, high-risk tumors without MYCN amplification frequently display increased c-MYC expression and/or activation of MYC signaling pathways. On the other hand, downregulation of MYCN leads to decreased proliferation and differentiation, emphasizing the importance of MYC signaling in neuroblastoma biology. Furthermore, expression of the neurotrophin receptor TrkA is associated with good prognosis, the ability to differentiate and spontaneous regression while expression of the related TrkB receptor is correlated with bad prognosis and MYCN amplification. Here we discuss the role of MYCN in neuroblastoma with a special focus on the contribution of elevated MYCN signaling for an aggressive and undifferentiated phenotype as well as the potential of using MYCN as a therapeutic target.

Prognostic impact of ΔTAp73 isoform levels and their target genes in colon cancer patients

PURPOSE

Cumulative data support the role of ΔTAp73 variants in tumorigenic processes such as drug resistance. We evaluate the impact of TP73 isoforms and their putative target genes ABCB1, HMGB1, and CASP1 on the survival of colon cancer patients and the correlation between their expressions.

EXPERIMENTAL DESIGN

We determined in 77 colon cancer patients the expression of ΔEx2p73, ΔEx2/3p73, ΔNp73, TAp73, ABCB1, HMGB1, and CASP1 by quantitative real-time reverse transcriptase-PCR. Tumor characteristics, disease-free survival, and overall survival (OS) were examined in each patient. Functional experiments were carried out to check whether ectopic expression of ΔNp73 modifies the proliferation, drug resistance, migration, and invasion properties of colon tumor cells and the expression of ABCB1, HMGB1, and CASP1.

RESULTS

Positive correlations were observed between the expression levels of ΔTAp73 variants and HMGB1. Furthermore, a trend was observed for ABCB1. Overexpression of ΔEx2/3p73 and ΔNp73 isoforms was significantly associated with advanced stages (P = 0.04 and P = 0.03, respectively) and predicted shortened OS (P = 0.04 and P = 0.05, respectively). High levels of ABCB1 and HMGB1 were associated with shorter OS (P = 0.04 and P = 0.05, respectively). Multivariate analysis showed that, in addition to the tumor stage, ABCB1 and HMGB1 had independent relationships with OS (P = 0.008). Ectopic expression of ΔNp73 was associated with an increase in proliferation and drug resistance.

CONCLUSIONS

The positive correlation between ΔTAp73 variants and HMGB1 and ABCB1 expression supports them as TP73 targets. The fact that upregulation of ΔTAp73 isoforms was associated with shortened OS, increase in proliferation, and drug resistance confirms their oncogenic role and plausible value as prognostic markers. ABCB1 and HMGB1, putative ΔTAp73 target genes, strongly predict OS in an independent manner, making clear the importance of studying downstream TP73 targets that could predict the outcome of colon cancer patients better than ΔTAp73 variants themselves do.

Inhibition of the nicotinic acetylcholine receptors by cobra venom α-neurotoxins: is there a perspective in lung cancer treatment?

Nicotine exerts its oncogenic effects through the binding to nicotinic acetylcholine receptors (nAChRs) and the activation of downstream pathways that block apoptosis and promote neo-angiogenesis. The nAChRs of the α7 subtype are present on a wide variety of cancer cells and their inhibition by cobra venom neurotoxins has been proposed in several articles and reviews as a potential innovative lung cancer therapy. However, since part of the published results was recently retracted, we believe that the antitumoral activity of cobra venom neurotoxins needs to be independently re-evaluated.

We determined the activity of α-neurotoxins from Naja atra (short-chain neurotoxin, α-cobrotoxin) and Naja kaouthia (long-chain neurotoxin, α-cobratoxin) in vitro by cytotoxicity measurements in 5 lung cancer cell lines, by colony formation assay with α7nAChRs expressing and non-expressing cell lines and in vivo by assessing tumor growth in an orthotopic Non-Obese Diabetic/Severe Combined Immunodeficient (NOD/SCID) mouse model system utilizing different treatment schedules and dosages.

No statistically significant reduction in tumor growth was observed in the treatment arms in comparison to the control for both toxins. Paradoxically α-cobrotoxin from Naja atra showed the tendency to enhance tumor growth although, even in this case, the statistical significance was not reached.

In conclusion our results show that, in contrast with other reports, the nAChR inhibitors α-cobratoxin from N. kaouthia and α-cobrotoxin from N. atra neither suppressed tumor growth nor prolonged the survival of the treated animals.

DeltaNp63alpha confers tumor cell resistance to cisplatin through the AKT1 transcriptional regulation

Strategies to address resistance to platin drugs are greatly needed in human epithelial cancers (e.g., ovarian, head/neck, and lung) where platins are used widely and resistance occurs commonly. We found that upon ΔNp63α overexpression, AKT1 and phospho-AKT1 levels are upregulated in cancer cells. Investigations using gel-shift, chromatin immunoprecipitation and functional reporter assays implicated ΔNp63α in positive regulation of AKT1 transcription. Importantly, we found that ΔNp63α, AKT1, and phospho-AKT levels are greater in 2008CI3 CDDP-resistant ovarian cancer cells than in 2008 CDDP-sensitive cells. siRNA-mediated knockdown of ΔNp63α expression dramatically decreased AKT1 expression, whereas knockdown of either ΔNp63α or AKT1 decreased cell proliferation and increased death of ovarian and head/neck cancer cells. Conversely, enforced expression of ΔNp63α increased cancer cell proliferation and reduced apoptosis. Together, our findings define a novel ΔNp63α-dependent regulatory mechanism for AKT1 expression and its role in chemotherapeutic resistance of ovarian and head/neck cancer cells.

p73-Binding Partners and Their Functional Significance

p73 is one of the tumor-suppressor p53 family of nuclear transcription factor. As expected from the structural similarity between p53 and p73, p73 has a tumor-suppressive function. However, p73 was rarely mutated in human primary tumors. Under normal physiological conditions, p73 is kept at an extremely low level to allow cells normal growth. In response to a certain subset of DNA damages, p73 is induced dramatically and transactivates an overlapping set of p53-target genes implicated in the promotion of cell cycle arrest and/or apoptotic cell death. Cells undergo cell cycle arrest and/or apoptotic cell death depending on the type and strength of DNA damages. p73 is regulated largely through the posttranslational modifications such as phosphorylation and acetylation. These chemical modifications are tightly linked to direct protein-protein interactions. In the present paper, the authors describe the functional significance of the protein-protein interactions in the regulation of proapoptotic p73.

Oncomodulation by human cytomegalovirus: novel clinical findings open new roads

The question whether human cytomegalovirus may affect cancer diseases has been discussed (very controversially) for decades. There are convinced believers and strict opponents of the idea that HCMV might be able to play a role in the course of cancer diseases. In parallel, the number of published reports on the topic is growing. Recently published and presented (Ranganathan P, Clark P, Kuo JS, Salamat S, Kalejta RF. A Survey of Human Cytomegalovirus Genomic Loci Present in Glioblastoma Multiforme Tissue Samples. 35th Annual International Herpes Workshop, Salt Lake City, 2010) data on HCMV detection in glioblastoma tissues and colocalisation of HCMV proteins with cellular proteins known to be relevant for glioblastoma progression motivated us to recapitulate the current state of evidence.

Characterization of ΔNp73 expression and regulation in gastric and esophageal tumors

p73 is a member of the p53 protein family. Although the tumor suppressor function of p53 is clearly defined, the role of p73 in tumorigenesis is still a matter of debate. A complex pattern of expression of p73 isoforms makes it difficult to unambiguously interpret the experimental results. Previously, we along with others have found that the N-terminally truncated isoform of p73, ΔNp73, has potent anti-apoptotic and oncogenic properties in vitro and in vivo. In this study, we analyzed, for the first time, the regulation of ΔNp73 in a large number of gastric, gastroesophageal junction and esophageal tumors. We found that expression of ΔNp73 mRNA and protein is increased in these neoplasms. Furthermore, the upregulation of the ΔNp73 protein is significantly associated with poor patient survival. Oncogenic properties of ΔNp73 were further confirmed by finding that ΔNp73 facilitates anchorage-independent growth of gastric epithelial cells in soft agar. As little is currently known about the regulation of ΔNp73 transcription, we investigated the alternative p73 gene promoter that mediates the ΔNp73 expression. Analyzing the ΔNp73 promoter in silico as well as by using chromatin immunoprecipitation, site-directed mutagenesis and deletion analyses, we identified the evolutionary conserved region within the ΔNp73 promoter that contains binding sites for HIC1 (hypermethylated in cancer) protein. We found that HIC1 negatively regulates ΔNp73 transcription in mucosal epithelial cells. This leads to a decrease in ΔNp73 protein levels and may normally control the oncogenic potential of the ΔNp73 isoform.

p53 family: Therapeutic targets in neuroblastoma

Survival rates for metastatic neuroblastoma remain poor, despite significant increase in the intensity of therapy. Although it represents approximately 7% of pediatric cancer, neuroblastoma accounts for approximately 15% of childhood cancer deaths. Thus, novel approaches to enhance neuroblastoma chemotherapy sensitivity and prevent or bypass chemoresistance are required. Disruption of the p53 pathway is a common mechanism leading to defects in apoptosis in cancer cells. Increasing evidence suggests that the p53 pathway may be inactivated in neuroblastoma. Inactivation of the p53 pathway occurs most commonly at the time of relapse, and probably contributes to chemoresistance. The p53 family proteins, p73 and p63, can also induce apoptosis, and early studies suggest that p73 may be important in neuroblastoma pathogenesis and response to treatment. This article focuses on current therapies and novel drugs targeting p53 and p73 signaling pathways in neuroblastoma. Understanding the balance between the p53 family proteins in neuroblastoma and how their expression and activity are regulated will hopefully lead to the discovery of agents that target these pathways to induce neuroblastoma cell death, alone or in combination with chemotherapies.