Overexpression of the p73 gene is a novel finding in high-risk B-cell chronic lymphocytic leukemia

A novel TAp73-inhibitory compound counteracts stemness features of glioblastoma stem cells

Glioblastoma (GB) is the most common and fatal type of primary malignant brain tumor for which effective therapeutics are still lacking. GB stem cells, with tumor-initiating and self-renewal capacity, are mostly responsible for GB malignancy, representing a crucial target for therapies. The TP73 gene, which is highly expressed in GB, gives rise to the TAp73 isoform, a pleiotropic protein that regulates neural stem cell biology; however, its role in cancer has been highly controversial. We inactivated TP73 in human GB stem cells and revealed that TAp73 is required for their stemness potential, acting as a regulator of the transcriptional stemness signatures, highlighting TAp73 as a possible therapeutic target. As proof of concept, we identified a novel natural compound with TAp73-inhibitory capacity, which was highly effective against GB stem cells. The treatment reduced GB stem cell-invasion capacity and stem features, at least in part by TAp73 repression. Our data are consistent with a novel paradigm in which hijacking of p73-regulated neurodevelopmental programs, including neural stemness, might sustain tumor progression, pointing out TAp73 as a therapeutic strategy for GB.

The Role of Methylation in Chronic Lymphocytic Leukemia and Its Prognostic and Therapeutic Impacts in the Disease: A Systematic Review

Epigenetic regulation has been thoroughly investigated in recent years and has emerged as an important aspect of chronic lymphocytic leukemia (CLL) biology. Characteristic aberrant features such as methylation patterns and global DNA hypomethylation were the early findings of the research during the last decades. The investigation in this field led to the identification of a large number of genes where methylation features correlated with important clinical and laboratory parameters. Gene-specific analyses investigated methylation in the gene body enhancer regions as well as promoter regions. The findings included genes and proteins involved in key pathways that play central roles in the pathophysiology of the disease. Τhe application of these findings beyond the theoretical understanding can not only lead to the creation of prognostic and predictive models and scores but also to the design of novel therapeutic agents. The following is a review focusing on the present knowledge about single gene/gene promoter methylation or mRNA expression in CLL cases as well as records of older data that have been published in past papers.

Identification of the Potential Correlation between Tumor Protein 73 and Head and Neck Squamous Cell Carcinoma

Background

Head and neck squamous cell carcinomas (HNSC) are common malignant tumors with a high occurrence and poor prognosis. Tumor protein P73 (TP73) plays an integral role in a wide range of human malignancies, but its gene expression profile, prognostic value, and potential mechanisms in HNSC remain to be comprehensively explored.

Objective

This research aimed to elucidate the potential relationship between TP73 and HNSC through bioinformatics analysis.

Methods

The Cancer Genome Atlas (TCGA) database was queried to investigate the regulatory role of TP73 in HNSC. The survival probabilities linked to TP73 mRNA were determined via the Kaplan-Meier analysis using R packages. Subsequently, the association of TP73 with several clinical subgroups and immunological subtypes was studied using a cohort from the TCGA-HNSC. Functional analyses were used to identify the potential signaling pathways enriched by the correlated genes of TP73. The relationship between TP73 and immunological aspects, including immune cells, immune inhibitor genes, immune stimulator genes, and tumor immune microenvironment, were investigated.

Results

This study showed that the protein and mRNA levels of TP73 in HNSC patients were significantly higher than those in normal tissues. Elevated TP73 expression was related to a better survival outcome in HNSC patients. The TP73 gene was an independent prognostic factor for overall survival in HNSC samples. TP73 was mainly involved in DNA replication, ribosome, apoptosis, mismatch repair, and folate biosynthesis. TP73 was found to be positively correlated with the majority of tumor infiltrating immune cells and immunoinhibitory genes in HNSC.

Conclusions

Integrative bioinformatics and statistical analyses displayed that TP73 might serve as a novel marker for the diagnosis and prognosis of HNSC. TP73 modulates immune cells in the tumor microenvironment of HNSC patients, thereby bearing significance for HNSC immunotherapy.

BRD4 drives esophageal squamous cell carcinoma growth by promoting RCC2 expression

The low survival rate of esophageal squamous cell carcinoma patients is primarily attributed to technical limitations and a lack of insight regarding the molecular mechanisms contributing to its progression. Alterations in epigenetic modulators are critical to cancer development and prognosis. BRD4, a chromatin reader protein, plays an essential role in regulating oncogene expression. Here, we investigated the contributing role of BRD4 and its related mechanisms in the context of ESCC tumor progression. Our observations showed that BRD4 transcript and protein expression levels are significantly increased in ESCC patient tissues. Genetic or pharmacological inhibition of BRD4 suppressed ESCC cell proliferation in vitro and in vivo. Proteomic and transcriptomic analyses were subsequently used to deduce the potential targets of BRD4. Mechanistic studies showed that RCC2 is a downstream target of BRD4. Inhibition of either BRD4 or RCC2 resulted in decreased ESCC cell proliferation. The BRD4-TP73 interaction facilitated the binding of BRD4 complex to the promoter region of RCC2, and subsequently modulated RCC2 transcription. Furthermore, targeting BRD4 with inhibitors significantly decreased tumor volume in ESCC PDX models, indicating that BRD4 expression may contribute to tumor progression. Collectively, these findings suggest that BRD4 inhibition could be a promising strategy to treat ESCC by downregulating RCC2.

TAp73 and ΔNp73 relative expression in Egyptian patients with lymphoid neoplasms

BACKGROUND AND AIMS

The p73 gene has different isoforms with opposing anti- and pro-apoptotic functions. The pro-apoptotic activities are inhibited by overexpression of the dominant ΔNp73 isoform. The aim of this study was to detect the expression of the TAp73 and ΔNp73 isoforms in Egyptian patients with malignant lymphoid neoplasms. Their expression was analyzed by quantitative RT-PCR.

PATIENTS AND METHODS

The study included 30 B-NHL patients, 24 T-NHL patients, 16 ALL patients, 18 CLL patients, 22 patients with reactive lymphoid hyperplasia, and 6 healthy control subjects.

RESULTS

ALL and CLL patients expressed both isoforms at higher levels compared to lymphoma patients. Higher expression of TAp73 was found in both B-NHL and T-NHL (around 4-fold and 16-fold, respectively) in comparison to ΔNp73 (2-fold and 14-fold, respectively). In CLL patients both isoforms showed higher expression levels in comparison to normal peripheral blood lymphocytes controls: nearly 27-fold for TAp73 and 233-fold for ΔNp73. All ALL patients showed higher expression of both studied isoforms than controls (9-fold for TAp73 and 386-fold for ΔNp73). The highest ΔNp73 expression along with a higher ΔNp73/TAp73 ratio (67-fold) was found in ALL patients compared with CLL patients (21-fold).

CONCLUSIONS

A considerable number of lymphoma patients lacked the expression of either or both isoforms, while all lymphoid leukemia patients expressed both isoforms. The expression pattern differences of p73 isoforms may reflect differences in the biology of these malignancies.

Interplay between TAp73 Protein and Selected Activator Protein-1 (AP-1) Family Members Promotes AP-1 Target Gene Activation and Cellular Growth

Unlike p53, which is mutated at a high rate in human cancers, its homologue p73 is not mutated but is often overexpressed, suggesting a possible context-dependent role in growth promotion. Previously, we have shown that co-expression of TAp73 with the proto-oncogene c-Jun can augment cellular growth and potentiate transactivation of activator protein (AP)-1 target genes such as cyclin D1. Here, we provide further mechanistic insights into the cooperative activity between these two transcription factors. Our data show that TAp73-mediated AP-1 target gene transactivation relies on c-Jun dimerization and requires the canonical AP-1 sites on target gene promoters. Interestingly, only selected members of the Fos family of proteins such as c-Fos and Fra1 were found to cooperate with TAp73 in a c-Jun-dependent manner to transactivate AP-1 target promoters. Inducible expression of TAp73 led to the recruitment of these Fos family members to the AP-1 target promoters on which TAp73 was found to be bound near the AP-1 site. Consistent with the binding of TAp73 and AP-1 members on the target promoters in a c-Jun-dependent manner, TAp73 was observed to physically interact with c-Jun specifically at the chromatin via its carboxyl-terminal region. Furthermore, co-expression of c-Fos or Fra1 was able to cooperate with TAp73 in potentiating cellular growth, similarly to c-Jun. These data together suggest that TAp73 plays a vital role in activation of AP-1 target genes via direct binding to c-Jun at the target promoters, leading to enhanced loading of other AP-1 family members, thereby leading to cellular growth.

TAp73β-mediated suppression of cell migration requires p57Kip2 control of actin cytoskeleton dynamics

The TP73 gene, a member of the p53 family, due to the use of different promoters and alternative splicing, is transcribed into different isoforms with contrasting attributes and which contribute to its functional diversity. Considerable efforts are made to identify the functional diversity of the p73 splicing variants during tumorigenesis.TAp73α and TAp73β isoforms have been shown to differentially regulate cell cycle progression, differentiation and apoptosis. Interestingly, a particular increase in expression of the TAp73 isoform, in favor of the α splicing variant, has been reported in multiple tumour types. Here, we report a distinctive role for TAp73β isoform in the control of cell migration and invasion. In fact, TAp73β-dependent induction of p57^Kip2 expression accounted for inhibitory effects on the actin cytoskeleton dynamics and thereby cancer cell motility. In contrast, TAp73α is not able to induce p57^Kip2 expression, and exhibits a positive effect on actin cytoskeleton dynamics as well as cell migration and invasion. In conclusion, the inhibitory effect on cell migration and invasion of TAp73β would qualify this distinct p73 isoform as tumor suppressor gene. In contrast, the promoting effect of TAp73α on cell motility and invasion strengthens the potential oncogenic activities of this p73 isoform.

TAp73alpha protects small cell lung carcinoma cells from caspase-2 induced mitochondrial mediated apoptotic cell death

Caspase-2 is ubiquitously expressed and the most evolutionarily conserved mammalian caspase. It can be activated by a range of death stimuli prior to Bax activation and the occurrence of apoptotic mitochondrial dysfunctions. Caspase-2 has also been reported to exert tumour suppressor function in vivo. The full length TAp73alpha isoform is found up-regulated in various tumour types, and is reported in a cell-type specific manner to repress drug-induced apoptosis. Here, we report that TAp73alpha represses caspase-2 enzymatic activity and by this means reduce caspase-2 induced Bax activation, loss of mitochondrial transmembrane potential and resulting apoptosis. The inhibitory effect on caspase-2 requires the presence of the DNA binding domain and SAM domain region of TAp73alpha. In conclusion, the ability of TAp73alpha to act as an inhibitor of caspase-2-induced cell death together with its up-regulation in certain tumour types strengthen the potential oncogenic activities for this protein.

Role of p53 family members p73 and p63 in human hematological malignancies

p53, mutated in over half of human cancers and about 13% of all hematological malignancies, maintains genomic integrity and triggers cellular senescence and apoptosis of damaged cells. In contrast to p53, the homologs p73 and p63 play critical roles in development of the central nervous system and skin/limbs, respectively. Moreover, dependent on the context they can exert tumor suppressor activities that cooperate with p53. Unlike p53, p73 and p63 are rarely mutated in cancers. Instead, up-regulation of the anti-apoptotic dominant-negative ΔNp73 and ΔNp63 isoforms is the most frequent abnormality in solid cancers. In hematological malignancies the most frequent p73 defect is promoter methylation and loss of expression, associated with unfavorable clinical outcomes. This suggests an essential tumor suppressor role of p73 in blood cells, also supported by genetic mouse models. Many therapeutic approaches aiming to restore p73 activity are currently being investigated. In contrast, the most frequent p63 abnormality is protein overexpression, associated with higher disease grade and poorer prognosis. Surprisingly, although available data are still scarce, the emerging picture is up-regulation of transactivation-competent TAp63 isoforms, suggesting a tumor-promoting role in this context.

Transferrin-conjugated curcumin-loaded superparamagnetic iron oxide nanoparticles induce augmented cellular uptake and apoptosis in K562 cells

Superparamagnetic iron oxide nanoparticles are currently used for precise drug delivery and as an image contrast agent. In the present study, the potentiality of curcumin-loaded magnetic nanoparticles (Cur-MNPs) for the treatment of chronic myeloid leukemia (CML) was investigated. For active therapy, transferrin (Tf) ligand was further conjugated to Cur-MNPs, which demonstrated enhanced uptake compared to Cur-MNPs in p210bcr/abl-positive cell line (K562). Cur-MNPs demonstrated greater and sustained anti-proliferative activity in a dose- and time-dependent manner; however, with the advent of a magnetic field the anti-proliferative activity of Cur-MNPs as well as Tf-Cur-MNPs was enhanced due to higher cellular uptake with enhanced cytotoxicity activity. Down-regulation of Bcr-Abl protein activates intrinsic apoptotic pathways for promoting anti-leukemic responses. Our in vitro results advocate potential clinical applications of Cur-MNPs by activating multiple signaling pathways for provoking the anti-leukemic activity.

Hsp72 mediates TAp73α anti-apoptotic effects in small cell lung carcinoma cells

The transcription factor p73, a member of the p53 family of proteins, is involved in the regulation of cell cycle progression and apoptosis. Due to alternative promoters and carboxy-terminal splicing, the P73 gene gives rise to a range of different isoforms. Interestingly, a particular increase in expression of the TAp73α isoform has been reported in various tumours. In addition, TAp73α has been shown to inhibit Bax activation and mitochondrial dysfunctions and thereby to confer small cell lung carcinoma (SCLC) cells resistance to drug-induced apoptosis. However, the precise mechanism by which TAp73α exerts its pro-survival effect is yet unclear. Here we report that TAp73α, but not TAp73β, regulates the expression of inducible Hsp72/HSPA1A. Hsp72 proved to be required for the survival effects of TAp73α as antisense knockdown of Hsp72 resulted in an abolishment of the anti-apoptotic effect of TAp73α in SCLC cells upon Etoposide treatment. Importantly, depletion of Hsp72 allowed activation of Bax, loss of mitochondrial membrane potential and lysosomal membrane permeabilization in SCLC cells even in the presence of TAp73α. Finally, we revealed that TAp73β counteracts the anti-apoptotic effect of TAp73α by preventing Hsp72 induction. Our results thus provide additional evidence for the potential oncogenic role of TAp73α, and extend the understanding of the mechanism for its anti-apoptotic effect.

Differential regulation of TP73 isoforms by 1α,25-dihydroxyvitamin D3 and survivin in human colon and breast carcinomas

We evaluate whether 1,25(OH)(2)D(3) downregulates TP73 variants in colon and breast carcinomas, the role of survivin in this context, and the significance of this network in the clinic. Tumor cells were treated/untreated with 1,25(OH)(2)D(3) and transiently transfected with survivin. Levels of survivin and TP73 variants were evaluated by quantitative RT-PCR and Western blotting. In 75 colon and 60 breast cancer patients, the expressions of survivin and TP73 isoforms were determined. Tumor characteristics were examined in each patient. Survivin protein levels were also evaluated in a subgroup of patients and cell lines. Decrease in survivin and TAp73 transcripts and protein and ΔNp73 mRNA was detected after 1,25(OH)(2)D(3) treatment. Ectopic survivin expression led to an increase in the TAp73, ΔNp73, ΔEx2p73, and ΔEx2-3p73 transcripts. In cancer patients, direct correlations were observed between TP73 variants and survivin levels. 1,25(OH)(2)D(3) negatively regulate survivin and TP73 variants in colon and breast cancer cells. Positive regulation of TP73 isoforms by survivin may exist, which reinforces the possibility that the downregulation of TP73 forms by 1,25(OH)(2)D(3) is survivin-dependent.

CpG island methylation patterns in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most common leukemia in Western countries. In CLL, a large number of genes affecting cancer-related pathways may be dysregulated by epigenetic silencing. We analysed by methylation-specific polymerase chain reaction the CpG island methylation status of 15 well-characterised cancer-related genes in 32 patients with CLL. Aberrant methylation in the sample of patients with CLL was shown for secreted frizzled-related protein 1 (68.8%), secreted frizzled-related protein 2 (65.6%), death-associated protein kinase 1 (50.0%), E-cadherin (21.9%), secreted frizzled-related protein 4 (15.6%), p15 (9.4%), p16 (6.3%), retinoic acid receptor beta2 (3.1%), secreted frizzled-related protein 5 (3.1%) and tissue inhibitor of matrix metalloproteinases 3 (3.1%). For human Mut-L homolog 1, O(6)-methylguanine DNA methyltransferase, p73, suppressor of cytokine signalling 1 and tissue inhibitor of matrix metalloproteinases 2 no hypermethylation was detected. Hypermethylation of at least one gene was observed in 87.5% of the samples. Our results show that aberrant CpG island methylation affecting cancer-related pathways such as Wnt signalling, regulation of apoptosis, cell cycle control and tissue invasion is a common phenomenon in CLL. Epigenetic disturbances may be involved in the pathogenesis of CLL and thus may provide a molecular rationale for therapeutic approaches.

Expression of p63 in anaplastic large cell lymphoma but not in classical Hodgkin's lymphoma

Immunohistochemical determination of p63 protein is frequently used in the pathologic diagnosis of nonhematological solid tumors. In malignant hematological disease, p63 expression has been reported in 22% of follicular lymphoma, about 35% of diffuse large B-cell lymphoma, 23% of chronic lymphocytic leukemia, and in some cases of blast crisis of chronic myelogenous leukemia. Anaplastic large cell lymphoma is a rare disease that accounts for less than 5% of all cases of non-Hodgkin's lymphoma. There is little information concerning p63 expression in this specific type of lymphoma. In some cases, the morphological and phenotypic features between anaplastic large cell lymphoma and classical Hodgkin's lymphoma are similar, making this differential diagnosis challenging. We studied p63 expression using a tissue microarray approach in 154 cases of anaplastic large cell lymphoma, including 38% anaplastic large cell kinase positive and 62% anaplastic large cell kinase negative, and 58 Hodgkin's lymphoma cases. Sixty-eight cases of anaplastic large cell lymphoma (44%) showed p63 nuclear positivity (41% of anaplastic large cell kinase positive and 47% of anaplastic large cell kinase negative). Of 130 cases of systemic-anaplastic large cell lymphoma, 42% showed p63 positivity. The neoplastic cells expressed p63 in 38% of the cases of CD45-negative/anaplastic large cell kinase-negative null cell-type anaplastic large cell lymphoma, a subgroup that offers the most difficulties in the differential diagnosis with classical Hodgkin's lymphoma. In contrast, none of the cases of classical Hodgkin's lymphoma demonstrated any p63 expression. These results demonstrate that p63 protein expression is frequently expressed in a subset of anaplastic large cell lymphoma cases and may be used as a potential tool in the differential diagnosis between anaplastic large cell lymphoma and classical Hodgkin's lymphoma.

The role of p73 in hematological malignancies

The P73 gene is a homologue of the P53 tumor suppressor. Owing to its structural similarity with p53, p73 was originally considered to have tumor suppressor function. However, the discovery of N-terminal truncated isoforms with oncogenic properties showed a 'two in one' structure of its product, p73 protein. The full-length variants are strong inducers of apoptosis, whereas the truncated isoforms inhibit proapoptotic activity of p53 and the full-length p73. Thus, p73 is involved in the regulation of cell cycle, cell death and development. Moreover, it plays a role in carcinogenesis and controls tumor sensitivity to treatment. p73 is commonly expressed in tumor cells in hematological malignancies. Overexpression of p73 protein and aberrant expression of its particular isoforms, with very low frequency of P73 hypermethylation or mutations, were found in malignant myeloproliferations, including acute myeloblastic leukemia. In contrast, hypermethylation and subsequent inactivation of the P73 gene are the most common findings in malignant lymphoproliferative disorders, especially acute lymphoblastic leukemia (ALL) and non-Hodgkin's lymphomas. Assessment of P73 methylation may provide important prognostic information, as was confirmed in patients with ALL. This review summarizes some aspects of p73 biology with particular reference to its possible pathogenetic role and prognostic significance in hematological malignancies.

Differential expression of p73 isoforms in relation to drug resistance in childhood T-lineage acute lymphoblastic leukaemia

The T-lineage phenotype of childhood acute lymphoblastic leukaemia (ALL) is associated with an increased relapse-risk and in vitro resistance to drugs as compared to a precursor B phenotype. Antiapoptotic isoforms of p73 that lack part of the transactivation (TA) domain (DeltaTA-p73, i.e. p73Deltaex2, p73Deltaex3, p73Deltaex2/3 and DeltaN-p73) may cause resistance to anticancer agents through inhibition of p53 and/or proapoptotic p73 family members (TA-p73). We demonstrate in our study that the expression of total p73 mRNA was higher in childhood T-ALL compared to controls (P=0.004). In T-ALL, the relative contribution of antiapoptotic DeltaTA-p73 (88%) was larger than of proapoptotic TA-p73 (12%). Leukaemic cells of T-ALL patients expressing higher levels of antiapoptotic p73 were more resistant to the DNA-damaging drug daunorubicin compared to cells of patients with low or negative expression or these isoforms (P(trend)=0.045). Interestingly, p73Deltaex2 was the most abundantly expressed antiapoptotic isoform in daunorubicin-resistant patient cells (44% of total p73). No association was found between high expression of proapoptotic TA-p73 or antiapoptotic DeltaTA-p73 and relapse-risk. Our results suggest that childhood T-ALL is associated with a high expression of DeltaTA-p73. These isoforms may play a role in cellular resistance to DNA-damaging drugs in children at initial diagnosis of T-ALL.

CD154 induces p73 to overcome the resistance to apoptosis of chronic lymphocytic leukemia cells lacking functional p53

Intravenous infusion of autologous chronic lymphocytic leukemia (CLL) cells transduced with an adenovirus encoding CD40-ligand (CD154) caused rapid reductions in leukemia-cell counts and lymphnode size. We hypothesized that CD40-ligation via CD154 sensitized CLL cells to death-receptor-mediated apoptosis. We found that CD154-expressing cells induced expression of CD95 and the BH3-interacting-domain death agonist (Bid) in CLL, regardless of whether the leukemia cells had functional p53. Such treatment also induced p73, a p53-related transcription factor regulated by c-Abl kinase, and enhanced the sensitivity to fludarabine (F-ara-A) of CLL cells lacking functional p53. Transduction of CLL cells with an adenovirus encoding p73 also induced Bid and CD95 and enhanced the sensitivity to F-ara-A of p53-deficient CLL cells. However, inhibition of c-Abl with imatinib suppressed CD154-induced expression of p73, p73-induced expression of Bid and CD95, and blocked the sensitization of p53-deficient CLL cells to CD95-mediated or F-ara-A-induced apoptosis. Conversely, CLL cells transduced with an imatinib-resistant c-Abl mutant could be induced by CD154 to express p73 and Bid even when treated with imatinib. These results indicate that CD154 can sensitize leukemia cells to apoptosis via the c-Abl-dependent activation of p73 and mitigate the resistance of p53-deficient CLL cells to anticancer drug therapy.

RNA interference: a potential therapeutic tool for silencing splice isoforms linked to human diseases

Alternative splicing of precursor messenger RNAs (pre-mRNAs) is one of the most important sources of protein diversity in vertebrates. An estimated 35%-70% of human genes generate transcripts that are alternatively spliced, and defects in this process are linked to numerous human genetic diseases and various forms of cancer. The discovery that 21-23 nucleotide RNA duplexes, known as small interfering RNAs (siRNAs), can knockdown the homologous mRNAs in mammalian cells has revolutionized many aspects of drug discovery including down-regulation of disease-associated splicing isoforms. In addition, RNA interference (RNAi)-mediated silencing of splicing regulators has the potential to define the complex network of alternative splicing regulation and to analyze gene function. In this review, I first provide a brief introduction to mRNA splicing and its relationship to human diseases. This is followed by a brief overview of RNAi. Finally I discuss the therapeutic potential of RNAi in targeting disease-linked splicing isoforms.

Aberrant expression of DeltaNp73 in benign and malignant tumours of the prostate: correlation with Gleason score

BACKGROUND

The p73 gene is a p53 homologue that induces apoptosis and inhibits cell proliferation. N-terminal truncated isoforms of p73 (DeltaNp73) act as dominant-negative inhibitors of wild-type p53 and TAp73 and result in tumour growth in nude mice.

AIMS

To detect DeltaNp73 expression in 24 benign prostatic hyperplasia samples, 33 prostate carcinomas, and five normal samples and to evaluate the relation between DeltaNp73, TAp73 concentrations, and the clinicopathological characteristics of patients with prostate cancer.

METHODS

TAp73 was determined by real time polymerase chain reaction (PCR); DeltaNp73 and DeltaN'p73 were assessed using reverse transcription PCR. western blotting was used to analyse protein expression. p53 mutation was determined by immunohistochemistry.

RESULTS

A significant increase of DeltaNp73 was seen in 20 of 33 carcinomas and 17 of 24 benign prostate hyperplasia tissues, but in none of the normal samples. None of the specimens expressed DeltaN'p73. No significant relation was found between TAp73 expression and clinical parameters. The incidence of positive expression of DeltaNp73 correlated with the Gleason score in prostate carcinomas. Cancer samples with wild-type p53 had significantly higher expression of DeltaNp73 than p53 mutant cancers.

CONCLUSION

These data suggest a potential role for DeltaNp73 in prostate cancer progression.

Full-length p73α Represses Drug-induced Apoptosis in Small Cell Lung Carcinoma Cells

The p73 gene, a member of the p53 family, encodes several variants through differential splicing and use of alternative promoters. At the NH2 terminus, two different promoters generate the full-length and the DeltaN isoforms, with or without the transactivating domain. At the COOH terminus, seven isoforms generated through alternative splicing have been cloned. Previous studies have demonstrated that DeltaNp73 isoforms exert a dominant-negative effect on p73 by blocking their transactivation activity and hence the ability to induce apoptosis. Considerable efforts are made to identify the functional diversity of the COOH-terminal p73 variants. In this study, we found that p73alpha inhibited drug-induced apoptosis in small cell lung carcinoma cells, whereas p73beta promoted it. p73alpha prevented Bax activation, mitochondrial dysfunction, and caspase activation. In addition, p73alpha was also able to reduce apoptosis induced by the BH3-only protein PUMA (p53 up-regulated modulator of apoptosis). Furthermore, we discovered that p73alpha is able to inhibit the pro-apoptotic effect of p73beta, demonstrating the existence of equilibrium between these two p73 isoforms. In conclusion, the reported overexpression of p73alpha in certain tumor types, and our findings that p73alpha exerts anti-apoptotic functions, indicate a potential oncogenic activity for p73.

Expression of p63 in Diffuse Large B-Cell Lymphoma

The p63 gene, a homolog of the tumor suppressor gene TP53, maps to chromosome 3q27-28, a region frequently displaying genomic amplification in squamous cell carcinomas. p63 is expressed in a variety of epithelial tissues and has been reported to be critical for the normal development of stratified epithelia, including skin epidermis. In a previous study, the authors reported the expression of p63 in occasional cells in the germinal center of lymph nodes and also observed p63 expression in B-cell lymphomas, among other tumor types surveyed in that analysis. The present study was conducted to further analyze the potential clinical significance of identifying p63 expression, assessing a larger cohort of well-characterized patients with diffuse large B-cell lymphoma (DLBCL) (n = 172 cases) and a panel of established lymphoma cell lines. p63 expression at the microanatomic detail was examined by immunohistochemistry using a monoclonal antibody (clone 4A4), while distinction of p63 isoforms was analyzed by Western blotting and reverse transcription-polymerase chain reaction using isoform-specific primers. The authors found that a subset of DLBCL (32% of cases) expressed p63 in the nuclei of neoplastic lymphocytes. Examination of the different p63 isoforms revealed that the DeltaNp63 species was expressed by only one cell line, while the other p63 isoforms were found in most cell lines analyzed. The authors also observed that p63 expression correlated with high proliferative index, as assessed by Ki-67 immunostaining. Even though in univariate analysis p63 expression did not correlate with overall survival, the association of p63 with increased proliferative index suggests its involvement in DLBCL tumor progression.

Survivin regulates the p53 tumor suppressor gene family

Survivin regulates cell division and inhibits apoptosis by blocking caspase activation. The tumor suppressor p53 inhibits cell cycle progression and induces apoptosis. Since Survivin overexpression and loss of wild-type p53 expression/function occur in most cancers, we investigated whether Survivin regulates p53. Stable overexpression of Survivin protects BaF3 cells from Adriamycin-induced apoptosis, while dominant-negative (T34A) and antisense (AS) Survivin accelerate apoptosis. In BaF3 cells and transiently transfected MCF7 breast cancer cells, elevation of total and phospho-Ser15-p53 in response to Adriamycin is blocked by Survivin and enhanced by Survivin disruption. Furthermore, in Adriamycin-treated MCF7 cells, ectopic Survivin decreased p53 mRNA and increased mRNA and protein of the p53 homologues DeltaNp63 and TAp73 and mRNA for DeltaNp73, suggesting that Survivin may differentially regulate p53 family transcription. Concomitant with decreasing p53 mRNA, Survivin decreased Mdm2 mRNA. Survivin disruption by T34A or AS Survivin resulted in reduced Mdm2 protein. The caspase inhibitor, Z-VAD-FMK, blocked the decrease in Mdm2 as well as the increase in p53 resulting from Survivin disruption, indicating that Survivin regulates Mdm2 at the post-translational level. Proteosome inhibition confirmed that reduced p53 protein observed in cells overexpressing Survivin is due to enhanced p53 degradation resulting from Survivin-mediated inhibition of Mdm2 cleavage by caspases. In summary, our results identify regulatory interactions between Survivin and p53 at the mRNA and protein levels, and suggest that the p53 homologues DeltaNp63, TAp73 and DeltaNp73 may also be regulated by Survivin.

Quantitative TP73 transcript analysis in hepatocellular carcinomas

PURPOSE

The p53 family member p73 displays significant homology to p53, but data from primary tumors demonstrating increased expression levels of p73 in the absence of any gene mutations argue against a classical tumor suppressor function. A detailed analysis of the p73 protein in tumor tissues has revealed expression of two classes of p73 isoforms. Whereas the proapoptotic, full-length, transactivation-competent p73 protein (TA-p73) has a putative tumor suppressor activity similar to p53, the antiapoptotic, NH(2)-terminally truncated, transactivation-deficient p73 protein (DeltaTA-p73) has been shown to possess oncogenic activity. The oncogenic proteins can be generated by the following two different mechanisms: (a) aberrant splicing (p73Deltaex2, p73Deltaex2/3, DeltaN'-p73) and (b) alternative promoter usage of a second intronic promoter (DeltaN-p73). The purpose of our study was to elucidate the origin of DeltaTA-p73 isoforms in hepatocellular carcinomas.

EXPERIMENTAL DESIGN

We analyzed the underlying mechanisms of p73 overexpression in cancer cells by quantification of p73 transcripts from 10 hepatocellular carcinoma patients using isoform-specific real-time reverse transcription-PCR.

RESULTS

Our data demonstrate that only aberrantly spliced DeltaTA-p73 transcripts from the TA promoter show significantly increased expression levels in the tumor whereas the DeltaN-p73 transcript generated from the second promoter is not significantly up-regulated.

CONCLUSIONS

Although we only analyzed 10 patient samples the results strongly suggest that the elevated activity of the first promoter (TA promoter) accounts for high-level expression of both full-length TA-p73 and aberrantly spliced DeltaTA-p73 isoforms in hepatocellular carcinoma tissues.

p63 and p73: Roles in Development and Tumor Formation

The tumor suppressor p53 is critically important in the cellular damage response and is the founding member of a family of proteins. All three genes regulate cell cycle and apoptosis after DNA damage. However, despite a remarkable structural and partly functional similarity among p53, p63, and p73, mouse knockout studies revealed an unexpected functional diversity among them. p63 and p73 knockouts exhibit severe developmental abnormalities but no increased cancer susceptibility, whereas this picture is reversed for p53 knockouts. Neither p63 nor p73 is the target of inactivating mutations in human cancers. Genomic organization is more complex in p63 and p73, largely the result of an alternative internal promoter generating NH2-terminally deleted dominant-negative proteins that engage in inhibitory circuits within the family. Deregulated dominant-negative p73 isoforms might play an active oncogenic role in some human cancers. Moreover, COOH-terminal extensions specific for p63 and p73 enable further unique protein-protein interactions with regulatory pathways involved in development, differentiation, proliferation, and damage response. Thus, p53 family proteins take on functions within a wide biological spectrum stretching from development (p63 and p73), DNA damage response via apoptosis and cell cycle arrest (p53, TAp63, and TAp73), chemosensitivity of tumors (p53 and TAp73), and immortalization and oncogenesis (ΔNp73).

Alterations of DeltaTA-p 73 splice transcripts during melanoma development and progression

In the last 2 years, it has become apparent that the p53-family members p53 and p73 play fundamentally different roles in human malignancies. In contrast to p53, many studies on cancer patients failed to detect mutational inactivation of p73 and reported overexpression of wild-type p73 instead. A possible explanation was provided by the recent discovery of N-terminal truncated isoforms of p73 (DeltaTA-p73) that act as dominant-negative inhibitors of wild-type p53 and TA-p73 and result in tumor growth in nude mice. We investigated the role of DeltaTA-p73 in the development and progression of human melanomas, which lack p53 mutations. We analyzed 8 benign melanocytic nevi, 8 primary melanomas and 19 melanoma metastases for alterations of TA-p73 and DeltaTA-p73 expression using isoform-specific real-time RT-PCR. Based on our results, p73Deltaex2 and Deltaex2/3 spliced transcripts derived from the first promoter were significantly up-regulated in melanoma metastases, whereas DeltaN-p73 generated from the second promoter was the predominant isoform in benign nevi. Moreover, increased expression of p73Deltaex2 and p73Deltaex2/3 correlated with high-levels of both TA-p73 and E2F1. Our data suggest a potential function of DeltaTA-p73 splice isoforms in melanoma progression.

The expression of p73, p21 and MDM2 proteins in gliomas

p73 protein, a member of the p53 family protein, induce p21 and MDM2 transcription. In some carcinomas, the expression of p73 was higher in carcinoma than in normal tissue, and the overexpression was correlated to grade, stage or prognosis. However, either the expression of p73 protein or the relationship among p73, p21 and MDM2 proteins was not known well in glioma. In this study, we examined the expression of p73, p21 and MDM2 proteins immunohistochemically and analyzed the relationship among these three proteins in sixty surgical specimens of gliomas including 10 glioblastomas, 10 anaplastic astrocytomas, 6 diffuse astrocytomas, 8 pilocytic astrocytomas, 1 anaplastic ependymoma, 8 ependymomas, 9 anaplastic oligodendroglial tumors and 8 low grade oligodendroglial tumors. The p73 labelling index (LI)s and p21 LIs differed among the tumor types, but there was no difference in the MDM2 LIs among all of the tumor types. The mean p73 LI of ependymomas was significantly higher than in any other tumor type. The mean p2I LIs of ependymomas and pilocytic astrocytomas were significantly higher than in any other tumor type. There were no significant correlations among p73 LIs, p21 LIs, MDM2 LIs and MIB-1 LIs in all p73 immunopositive tumors. The present results suggest that p73 and p21 overexpression of ependymomas and p21 overexpression of pilocytic astrocytomas are one of the features of these tumors, and that p73 overexpression does not influence the expression manners of either p21 or MDM2 in gliomas.

Novel cell-specific and dominant negative anti-apoptotic roles of p73 in transformed leukemia cells

Although extensive homology exists between related genes p53 and p73, recent data suggest that the family members have divergent roles. We demonstrate that the differential regulatory roles of p53 family member p73 are highly cell-context and promoter-specific. Full-length p73 expressed in the transformed leukemia cell line Jurkat behaves as a specific dominant negative transcriptional repressor of the cell cycle inhibitor gene p21 and blocks p53-mediated apoptosis. These findings provide evidence for a new mechanism in oncogenesis through which the functional properties of p73 can be altered in an inheritable and cell-specific fashion independent of transcriptional coding.

Transactivation-deficient Delta TA-p73 inhibits p53 by direct competition for DNA binding: implications for tumorigenesis

The p53 family member p73 displays significant structural and functional homology to p53. However, instead of mutational inactivation, overexpression of wild-type p73 has been reported in various tumor types compared with normal tissues, arguing against a classical tumor suppressor function. Recently, N-terminally truncated, transactivation-deficient p73 isoforms (DeltaTA-p73) have been identified as a second class of p73 proteins. Because overexpression of p73 in tumors includes DeltaTA-p73, we further characterized these novel p73 isoforms. We show that DeltaTA-p73 retains DNA-binding competence but lacks transactivation functions, resulting in an inability to induce growth arrest and apoptosis. Importantly, DeltaTA-p73 acts as a dominant-negative inhibitor of p53 and full-length p73 (TA-p73). We demonstrate that inhibition of p53 involves competition for DNA binding, whereas TA-p73 can be inhibited by direct protein-protein interaction. Further, we show that up-regulation of endogenous p73 just like ectopic overexpression of DeltaTA-p73 confers resistance to p53-mediated apoptosis induced by the chemotherapeutic agent H-7. Because inhibition of p53 is a common theme in human cancer, our data strongly support a role of DeltaTA-p73 expression for tumor formation.

Role of p73 in malignancy: tumor suppressor or oncogene?

The recently identified p53 family member, p73, shows substantial structural and functional homology with p53. However, despite the established role of p53 as a proto-type tumor suppressor, a similar function of p73 in malignancy is questionable. Overexpression of p73 can activate typical p53-responsive genes, and activation of p73 has been implicated in apoptotic cell death induced by aberrant cell proliferation and some forms of DNA-damage. These data together with the localization of TP73 on chromosome 1p36, a region frequently deleted in a variety of human tumors, led to the hypothesis that p73 has tumor suppressor activity just like p53. However, unlike p53-/- mice, p73 knockout mice do not develop tumors. Extensive studies on primary tumor tissues have revealed overexpression of wild-type p73 in the absence of p73 mutations instead, suggesting that p73 may augment, rather than inhibit tumor development. In contrast to p53, differential splicing of the TP73 gene locus gives rise to a complex pattern of interacting p73 isoforms with antagonistic functions. In fact, induction of apoptosis by increased levels of p73 can be blocked by both p53 mutants and the N-terminally truncated p73 isoforms, which were recently shown to possess oncogenic potential. In the light of these new findings the contradictory role of p73 in malignancy will be discussed.