Brn-3a transcription factor blocks p53-mediated activation of proapoptotic target genes Noxa and Bax in vitro and in vivo to determine cell fate

Synergistic activity of S63845 and parthenolide to overcome acquired resistance to MEK1/2 inhibitor in melanoma cells: Mechanisms and therapeutic potential

Melanoma remains a global health challenge. While targeted therapy with BRAFV600/MEK inhibitors largely improved the survival and quality of life for advanced melanoma patients, most of them progress due to acquired resistance. Dynamic heterogeneity and phenotypic plasticity of resistant melanoma prompted us to use parthenolide, an agent with an assorted bioactivity profile in combination with agents targeting enhanced pro-survival capacity of resistant melanoma cells. Parthenolide was used in combination with S63845, ABT-263 and ABT-199, BH3-mimetics targeting anti-/pro-apoptotic protein interactions. These drug combinations were investigated in patient-derived drug-naïve melanoma cell lines, their trametinib-resistant counterparts displaying either dedifferentiation neural-crest-like phenotype (MITFlow/NGFRhigh) or differentiation phenotype (MITFhigh/NGFRlow), and trametinib-resistant cell lines undergoing the phenotype transition after trametinib withdrawal. While parthenolide reduces proliferation and increases senescent cell fraction accompanied with reduction of NF-κB activity and MITF expression, it does not trigger apoptosis in high percentages of melanoma cells. Combination of parthenolide with BH3-mimetics induces externalization of phosphatidylserine, most efficiently with S63845, an inhibitor of pro-survival MCL-1. Parthenolide and S63845 synergize to cause massive apoptosis regardless of melanoma cell phenotypes, which is associated with caspase-3/7 activation, H2AX phosphorylation, and PARP cleavage. Mechanistically, parthenolide combined with S63845 reduces the protein level of MCL-1, upregulates pro-apoptotic NOXA, and prevents S63845-induced reduction of NOXA protein. Collectively, massive apoptosis induced synergistically by parthenolide combined with S63845 in trametinib-resistant melanoma cells displaying various phenotypes justifies exploring the potential of this strategy as a future treatment option for patients with melanoma resistant to therapies targeting MAPK signaling.

Strong activation of p53 by actinomycin D and nutlin-3a overcomes the resistance of cancer cells to the pro-apoptotic activity of the FAS ligand

The FAS ligand (FASLG) is expressed on lymphocytes, which employ it to activate death receptors on target cells. Cancer cells are generally resistant to apoptosis triggered by FASLG. In this work, we found a way to circumvent this resistance by treatment with actinomycin D (ActD) and nutlin-3a (Nut3a). We selected this drug combination based on our transcriptomic data showing strong activation of proapoptotic genes, including those for receptor-mediated apoptosis, in cells exposed to actinomycin D and nutlin-3a. To test our hypothesis, we pre-exposed cancer cell lines to this drug combination for 45 h and then treated them with recombinant FASLG. This almost instantaneously killed most cells. Actinomycin D and nutlin-3a strongly cooperated in the sensitization because the effect of the drugs acting solo was not as spectacular as the drug combination, which together with FASLG killed more than 99% of cells. Based on the caspase activation pattern (caspase-8, caspase-9, caspase-10), we conclude that both extrinsic and intrinsic pro-apoptotic pathways were engaged. In engineered p53-deficient cells, this pro-apoptotic effect was completely abrogated. Therefore, the combination of ActD + Nut3a activates p53 in an extraordinary way, which overcomes the resistance of cancer cells to apoptosis triggered by FASLG. Interestingly, other combinations of drugs, e.g., etoposide + nutlin-3a, actinomycin D + RG7112, and actinomycin D + idasanutlin had a similar effect. Moreover, normal human fibroblasts are less sensitive to death induced by ActD + Nut3a + FASLG. Our findings create the opportunity to revive the abandoned attempts of cancer immunotherapy employing the recombinant FAS ligand.

Multiple Actions of Telomerase Reverse Transcriptase in Cell Death Regulation

Telomerase reverse transcriptase (TERT), a core part of telomerase, has been known for a long time only for its telomere lengthening function by reverse transcription of RNA template. Currently, TERT is considered as an intriguing link between multiple signaling pathways. The diverse intracellular localization of TERT corresponds to a wide range of functional activities. In addition to the canonical function of protecting chromosome ends, TERT by itself or as a part of the telomerase complex participates in cell stress responses, gene regulation and mitochondria functioning. Upregulation of TERT expression and increased telomerase activity in cancer and somatic cells relate to improved survival and persistence of such cells. In this review, we summarize the data for a comprehensive understanding of the role of TERT in cell death regulation, with a focus on the interaction of TERT with signaling pathways involved in cell survival and stress response.

In vivo RNA-seq and ChIP-seq analyses show an obligatory role for the C terminus of p53 in conferring tissue-specific radiation sensitivity

Thymus and spleen, in contrast to liver, are radiosensitive tissues in which p53-dependent apoptosis is triggered after whole-body radiation in vivo. Combined RNA sequencing (RNA-seq) and chromatin immunoprecipitation sequencing (ChIP-seq) analyses of radiation-treated mouse organs identifies both shared and tissue-specific p53 transcriptional responses. As expected, the p53 targets shared among thymus and spleen are enriched in apoptotic targets. The inability to upregulate these genes in the liver is not due to reduced gene occupancy. Use of an engineered mouse model shows that deletion of the C terminus of p53 can confer radiation-induced expression of p53 apoptotic targets in the liver with concomitant increased cell death. Global RNA-seq analysis reveals that an additional role of the C terminus is also needed for transcriptional activation of liver-specific p53 targets. It is hypothesized that both suppression of apoptotic gene expression combined with enhanced activation of liver-specific targets confers tissue-specific radio-resistance.

Magnesium acetyltaurate prevents retinal damage and visual impairment in rats through suppression of NMDA-induced upregulation of NF-κB, p53 and AP-1 (c-Jun/c-Fos)

Magnesium acetyltaurate (MgAT) has been shown to have a protective effect against N-methyl-D-aspartate (NMDA)-induced retinal cell apoptosis. The current study investigated the involvement of nuclear factor kappa-B (NF-κB), p53 and AP-1 family members (c-Jun/c-Fos) in neuroprotection by MgAT against NMDA-induced retinal damage. In this study, Sprague-Dawley rats were randomized to undergo intravitreal injection of vehicle, NMDA or MgAT as pre-treatment to NMDA. Seven days after injections, retinal ganglion cells survival was detected using retrograde labelling with fluorogold and BRN3A immunostaining. Functional outcome of retinal damage was assessed using electroretinography, and the mechanisms underlying antiapoptotic effect of MgAT were investigated through assessment of retinal gene expression of NF-κB, p53 and AP-1 family members (c-Jun/c-Fos) using reverse transcription-polymerase chain reaction. Retinal phospho-NF-κB, phospho-p53 and AP-1 levels were evaluated using western blot assay. Rat visual functions were evaluated using visual object recognition tests. Both retrograde labelling and BRN3A immunostaining revealed a significant increase in the number of retinal ganglion cells in rats receiving intravitreal injection of MgAT compared with the rats receiving intravitreal injection of NMDA. Electroretinography indicated that pre-treatment with MgAT partially preserved the functional activity of NMDA-exposed retinas. MgAT abolished NMDA-induced increase of retinal phospho-NF-κB, phospho-p53 and AP-1 expression and suppressed NMDA-induced transcriptional activity of NF-κB, p53 and AP-1 family members (c-Jun/c-Fos). Visual object recognition tests showed that MgAT reduced difficulties in recognizing the visual cues (i.e. objects with different shapes) after NMDA exposure, suggesting that visual functions of rats were relatively preserved by pre-treatment with MgAT. In conclusion, pre-treatment with MgAT prevents NMDA induced retinal injury by inhibiting NMDA-induced neuronal apoptosis via downregulation of transcriptional activity of NF-κB, p53 and AP-1-mediated c-Jun/c-Fos. The experiments were approved by the Animal Ethics Committee of Universiti Teknologi MARA (UiTM), Malaysia, UiTM CARE No 118/2015 on December 4, 2015 and UiTM CARE No 220/7/2017 on December 8, 2017 and Ethics Committee of Belgorod State National Research University, Russia, No 02/20 on January 10, 2020.

In silico study of cancer stage-specific DNA methylation pattern in White breast cancer patients based on TCGA dataset

BACKGROUND

Breast cancer is one of the most common types of cancer among women. As current breast cancer treatments are still ineffective, we assess the methylation pattern of White breast cancer patients across cancer stage based on The Cancer Genome Atlas (TCGA) dataset. Significant hypermethylation and hypomethylation can regulate the gene expression, thus becoming potential biomarkers in breast cancer tumorigenesis.

METHODS

DNA methylation data was downloaded using TCGA Assembler 2 based on race-specific metadata of TCGA - Breast Invasive Carcinoma (TCGA-BRCA) project from Genomic Data Commons (GDC) Data Portal. After the data was divided into each cancer stage, duplicated data of each patient was removed using OMICSBind, while differentially-expressed probes were identified using edgeR. The resulting probes were validated based on correlation and regression analysis with the gene expression, ANOVA between cancer stages, ROC curve per stage, as well as databases.

RESULTS

Based on the White dataset, we found 66 significant hypermethylated genes with logFC > 1.8 between Stage I-III. From this number, three epigenetic-regulated, stage-specific genes are proposed to be the detection biomarkers of breast cancer due to significant aberrant gene expression and/or low mutation ratio among breast cancer patients: ABCC9 (Stage III), SHISA3 (Stage II), and POU4F1 (Stage I-II).

CONCLUSIONS

Our study shows that ABCC9, SHISA3, and POU4F1 are potential stage-specific detection biomarkers of breast cancer for White individuals, whereas their roles in other races need to be studied further.

The Role of Polycomb Group Protein BMI1 in DNA Repair and Genomic Stability

The polycomb group (PcG) proteins are a class of transcriptional repressors that mediate gene silencing through histone post-translational modifications. They are involved in the maintenance of stem cell self-renewal and proliferation, processes that are often dysregulated in cancer. Apart from their canonical functions in epigenetic gene silencing, several studies have uncovered a function for PcG proteins in DNA damage signaling and repair. In particular, members of the poly-comb group complexes (PRC) 1 and 2 have been shown to recruit to sites of DNA damage and mediate DNA double-strand break repair. Here, we review current understanding of the PRCs and their roles in cancer development. We then focus on the PRC1 member BMI1, discussing the current state of knowledge of its role in DNA repair and genome integrity, and outline how it can be targeted pharmacologically.

Linking metabolic dysfunction with cardiovascular diseases: Brn-3b/POU4F2 transcription factor in cardiometabolic tissues in health and disease

Metabolic and cardiovascular diseases are highly prevalent and chronic conditions that are closely linked by complex molecular and pathological changes. Such adverse effects often arise from changes in the expression of genes that control essential cellular functions, but the factors that drive such effects are not fully understood. Since tissue-specific transcription factors control the expression of multiple genes, which affect cell fate under different conditions, then identifying such regulators can provide valuable insight into the molecular basis of such diseases. This review explores emerging evidence that supports novel and important roles for the POU4F2/Brn-3b transcription factor (TF) in controlling cellular genes that regulate cardiometabolic function. Brn-3b is expressed in insulin-responsive metabolic tissues (e.g. skeletal muscle and adipose tissue) and is important for normal function because constitutive Brn-3b-knockout (KO) mice develop profound metabolic dysfunction (hyperglycaemia; insulin resistance). Brn-3b is highly expressed in the developing hearts, with lower levels in adult hearts. However, Brn-3b is re-expressed in adult cardiomyocytes following haemodynamic stress or injury and is necessary for adaptive cardiac responses, particularly in male hearts, because male Brn-3b KO mice develop adverse remodelling and reduced cardiac function. As a TF, Brn-3b regulates the expression of multiple target genes, including GLUT4, GSK3β, sonic hedgehog (SHH), cyclin D1 and CDK4, which have known functions in controlling metabolic processes but also participate in cardiac responses to stress or injury. Therefore, loss of Brn-3b and the resultant alterations in the expression of such genes could potentially provide the link between metabolic dysfunctions with adverse cardiovascular responses, which is seen in Brn-3b KO mutants. Since the loss of Brn-3b is associated with obesity, type II diabetes (T2DM) and altered cardiac responses to stress, this regulator may provide a new and important link for understanding how pathological changes arise in such endemic diseases.

Multiple genetic programs contribute to CD4 T cell memory differentiation and longevity by maintaining T cell quiescence

While memory T-cells represent a hallmark of adaptive immunity, little is known about the genetic mechanisms regulating the longevity of memory CD4 T cells. Here, we studied the dynamics of gene expression in antigen specific CD4 T cells during infection, memory differentiation, and long-term survival up to nearly a year in mice. We observed that differentiation into long lived memory cells is associated with increased expression of genes inhibiting cell proliferation and apoptosis as well as genes promoting DNA repair response, lipid metabolism, and insulin resistance. We identified several transmembrane proteins in long-lived murine memory CD4 T cells, which co-localized exclusively within the responding antigen-specific memory CD4 T cells in human. The unique gene signatures of long-lived memory CD4 T cells, along with the new markers that we have defined, will enable a deeper understanding of memory CD4 T cell biology and allow for designing novel vaccines and therapeutics.

Brn3a/Pou4f1 Functions as a Tumor Suppressor by Targeting c-MET/STAT3 Signaling in Thyroid Cancer

BACKGROUND

Brn3a/Pou4f1 is a class IV POU domain-containing transcription factor and has been found to be expressed in a variety of cancers. However, the mechanism and action of Brn3a in thyroid cancer has not been investigated.

PURPOSE

To investigate the role of Brn3a in thyroid cancer progression and its clinical implication.

METHODS

We examined Brn3a expression status in patients with thyroid cancer and analyzed relationships between Brn3a expression and clinicopathological findings using The Cancer Genome Atlas (TCGA) database. For functional in vitro analysis, proliferation, migration, invasion assay, and Western blotting were performed after overexpression or suppression of Brn3a.

RESULTS

The promoter hypermethylation of Brn3a was found in patients with aggressive thyroid cancer and Brn3a was downregulated in tissues of patients with thyroid cancer. In TCGA database, the low-Brn3a-expression group revealed a more aggressive phenotype, including T stage and extrathyroid extension when compared with the high-Brn3a-expression group. Overexpression of Brn3a suppressed cell migration and invasion via regulation of epithelial-mesenchymal transition (EMT)-associated proteins in thyroid cancer cell lines. Brn3a overexpression also downregulated signal transducer and activator of transcription 3 (STAT3) signaling through suppression of tyrosine-protein kinase Met (c-MET). In contrast, knockdown of Brn3a by small interfering ribonucleic acid (siRNA) significantly increased cell migration and invasion through upregulation of c-MET/STAT3. These results imply that Brn3a suppresses tumor metastasis via c-MET/STAT3 inhibition and EMT suppression in thyroid cancer.

CONCLUSIONS

Our findings show that Brn3a is a potential tumor suppressor that leads to reduced cancer cell migration and invasion in thyroid cancer. Elucidation of the Brn3a-regulated cancer pathways may therefore provide novel therapeutic strategies to control thyroid cancer metastasis.

Pevonedistat (MLN4924): mechanism of cell death induction and therapeutic potential in colorectal cancer

Pevonedistat (MLN4924), a selective inhibitor of the NEDD8-activating enzyme E1 regulatory subunit (NAE1), has demonstrated significant therapeutic potential in several malignancies. Although multiple mechanisms-of-action have been identified, how MLN4924 induces cell death and its potential as a combinatorial agent with standard-of-care (SoC) chemotherapy in colorectal cancer (CRC) remains largely undefined. In an effort to understand MLN4924-induced cell death in CRC, we identified p53 as an important mediator of the apoptotic response to MLN4924. We also identified roles for the extrinsic (TRAIL-R2/caspase-8) and intrinsic (BAX/BAK) apoptotic pathways in mediating the apoptotic effects of MLN4924 in CRC cells, as well as a role for BID, which modulates a cross-talk between these pathways. Depletion of the anti-apoptotic protein FLIP, which we identify as a novel mediator of resistance to MLN4924, enhanced apoptosis in a p53-, TRAIL-R2/DR5-, and caspase-8-dependent manner. Notably, TRAIL-R2 was involved in potentiating the apoptotic response to MLN4924 in the absence of FLIP, in a ligand-independent manner. Moreoever, when paired with SoC chemotherapies, MLN4924 demonstrated synergy with the irinotecan metabolite SN38. The cell death induced by MLN4924/SN38 combination was dependent on activation of mitochondria through BAX/BAK, but in a p53-independent manner, an important observation given the high frequency of TP53 mutation(s) in advanced CRC. These results uncover mechanisms of cell death induced by MLN4924 and suggest that this second-generation proteostasis-disrupting agent may have its most widespread activity in CRC, in combination with irinotecan-containing treatment regimens.

POU4F1 promotes the resistance of melanoma to BRAF inhibitors through MEK/ERK pathway activation and MITF up-regulation

BRAF inhibitors (BRAFi) have shown remarkable clinical efficacy in the treatment of melanoma with BRAF mutation. Nevertheless, most patients end up with the development of BRAFi resistance, which strongly limits the clinical application of these agents. POU4F1 is a stem cell-associated transcriptional factor that is highly expressed in melanoma cells and contributes to BRAF-activated malignant transformation. However, whether POU4F1 contributes to the resistance of melanoma to BRAFi remains poorly understood. Here, we report that over-expressed POU4F1 contributed to the acquired resistance of melanoma cells to Vemurafenib. Furthermore, POU4F1 promoted the activation of ERK signaling pathway via transcriptional regulation on MEK expression. In addition, POU4F1 could increase the expression of MITF to retain the resistance of melanoma cells to BRAFi. Collectively, our findings reveal that POU4F1 re-activates the MAPK pathway by transcriptional regulation on MEK expression and promotes MITF expression, which ultimately results in the resistance to BRAFi in melanoma. Our study supports that POU4F1 is a potential combined therapeutic target with BRAFi therapy for melanoma.

p60-katanin: a novel interacting partner for p53

Katanin, one of the best-characterized microtubule (MT) severing proteins, is composed of two subunits: catalytic p60-katanin, and regulatory p80-katanin. p60-katanin triggers MT reorganization by severing them. MT reorganization is essential for both mitotic cells and post-mitotic neurons in numerous vital processes such as intracellular transport, mitosis, cellular differentiation and apoptosis. Due to the deleterious effect of continuous severing for cells, p60-katanin requires a strategic regulation. However, there are only a few known regulators of p60-katanin. p53 functions in similar cellular processes as katanin such as cell cycle, differentiation, and apoptosis depending on its interacting partners. Considering this similarity, in this study we investigated p53 as a potential regulatory candidate of p60-katanin, and examined their interaction. Co-immunoprecipitation analyses revealed that p60-katanin interacts with p53. We were able to locate a potential interaction site for the two proteins by deleting different candidate regions We showed for the first time that p53 and p60-katanin interact. This interaction appears to occur via p53's DNA binding domain and p60-katanin's C-terminal. This study will pave the way for future studies regarding the functional outcomes of this interaction which is vital for understanding the regulation of cellular events such as cell cycle, differentiation, and apoptosis in disease and in health.

Pro-death signaling of cytoprotective heat shock factor 1: upregulation of NOXA leading to apoptosis in heat-sensitive cells

Heat shock can induce either cytoprotective mechanisms or cell death. We found that in certain human and mouse cells, including spermatocytes, activated heat shock factor 1 (HSF1) binds to sequences located in the intron(s) of the PMAIP1 (NOXA) gene and upregulates its expression which induces apoptosis. Such a mode of PMAIP1 activation is not dependent on p53. Therefore, HSF1 not only can activate the expression of genes encoding cytoprotective heat shock proteins, which prevents apoptosis, but it can also positively regulate the proapoptotic PMAIP1 gene, which facilitates cell death. This could be the primary cause of hyperthermia-induced elimination of heat-sensitive cells, yet other pro-death mechanisms might also be involved.

p53 regulates katanin-p60 promoter in HCT 116 cells

Tumor suppressor protein p53, which functions in the cell cycle, apoptosis and neuronal differentiation via transcriptional regulations of target genes or interactions with several proteins, has been associated with neurite outgrowth through microtubule re-organization. We previously demonstrated in neurons that upon p53 induction, the level of microtubule severing protein Katanin-p60 increases, indicating that p53 might be a transcriptional regulator of the KATNA1 gene encoding Katanin-p60. In this context, we firstly elucidated the activity of KATNA1 regulatory regions and endogenous KATNA1 mRNA levels in the presence or absence of p53 using HCT 116 WT and HCT 116 p53 (-/-) cells. Next, we demonstrated the binding of p53 to the KATNA1 promoter and then investigated the role of p53 on KATNA1 gene expression by ascertaining KATNA1 mRNA and Katanin-p60 protein levels upon p53 overexpression and activation in both cells. Moreover, we showed changes in microtubule network upon increased Katanin-p60 level due to p53 overexpression. Also, the changes in KATNA1 mRNA and Katanin-p60 protein levels upon p53 knockdown were investigated. Our results indicate that p53 is an activator of KATNA1 gene expression and we show that both p53 and Katanin-p60 expression have strict regulations and are maintained at balanced levels as they are vital proteins to orchestrate either survival and apoptosis or differentiation.

Expression of the type 3 InsP3 receptor is a final common event in the development of hepatocellular carcinoma

BACKGROUND & OBJECTIVES

Hepatocellular carcinoma (HCC) is the second leading cause of cancer death worldwide. Several types of chronic liver disease predispose to HCC, and several different signalling pathways have been implicated in its pathogenesis, but no common molecular event has been identified. Ca2+ signalling regulates the proliferation of both normal hepatocytes and liver cancer cells, so we investigated the role of intracellular Ca2+ release channels in HCC.

DESIGN

Expression analyses of the type 3 isoform of the inositol 1, 4, 5-trisphosphate receptor (ITPR3) in human liver samples, liver cancer cells and mouse liver were combined with an evaluation of DNA methylation profiles of ITPR3 promoter in HCC and characterisation of the effects of ITPR3 expression on cellular proliferation and apoptosis. The effects of de novo ITPR3 expression on hepatocyte calcium signalling and liver growth were evaluated in mice.

RESULTS

ITPR3 was absent or expressed in low amounts in hepatocytes from normal liver, but was expressed in HCC specimens from three independent patient cohorts, regardless of the underlying cause of chronic liver disease, and its increased expression level was associated with poorer survival. The ITPR3 gene was heavily methylated in control liver specimens but was demethylated at multiple sites in specimens of patient with HCC. Administration of a demethylating agent in a mouse model resulted in ITPR3 expression in discrete areas of the liver, and Ca2+ signalling was enhanced in these regions. In addition, cell proliferation and liver regeneration were enhanced in the mouse model, and deletion of ITPR3 from human HCC cells enhanced apoptosis.

CONCLUSIONS

These results provide evidence that de novo expression of ITPR3 typically occurs in HCC and may play a role in its pathogenesis.

Transcription factors Brn-3α and TRIM16 in cancers, association with hormone reception

Sex hormones, regulating normal physiological processes of most tissues and organs, are considered to be one of the key factors in the development of hormone-dependent cancer and formation of the hormone-resistant tumor phenotype. Recently, the importance of the system for control of hormone receptors expression mediated by nuclear peptides became evident. This system is involved in the regulation of normal physiological processes, in the pathogenesis of many diseases as well as oncogenesis. In the review, we discuss the relationships of the two regulatory peptides – Brn-3α, TRIM16 with hormone receptors. The transcription factor Brn-3α is able to affect the transcription activity of androgen and estrogen receptors. It is observed the participation of TRIM16 protein in the pathogenesis of hormone-dependent tumors due to its "anti-estrogenic effect". Additionally, they are involved in the key intracellular processes, such as proliferation, cell differentiation, and programmed death - apoptosis. Thus, Brn-3α and TRIM16 are associated with cancer development and progression. By understanding these alterations, we can identify potential markers and novel biochemical therapeutic targets. It makes clear the association between classical hormone-dependent tumors and less sensitive ones with the modification in the level of hormone receptors.

Census and evaluation of p53 target genes

The tumor suppressor p53 functions primarily as a transcription factor. Mutation of the TP53 gene alters its response pathway, and is central to the development of many cancers. The discovery of a large number of p53 target genes, which confer p53's tumor suppressor function, has led to increasingly complex models of p53 function. Recent meta-analysis approaches, however, are simplifying our understanding of how p53 functions as a transcription factor. In the survey presented here, a total set of 3661 direct p53 target genes is identified that comprise 3509 potential targets from 13 high-throughput studies, and 346 target genes from individual gene analyses. Comparison of the p53 target genes reported in individual studies with those identified in 13 high-throughput studies reveals limited consistency. Here, p53 target genes have been evaluated based on the meta-analysis data, and the results show that high-confidence p53 target genes are involved in multiple cellular responses, including cell cycle arrest, DNA repair, apoptosis, metabolism, autophagy, mRNA translation and feedback mechanisms. However, many p53 target genes are identified only in a small number of studies and have a higher likelihood of being false positives. While numerous mechanisms have been proposed for mediating gene regulation in response to p53, recent advances in our understanding of p53 function show that p53 itself is solely an activator of transcription, and gene downregulation by p53 is indirect and requires p21. Taking into account the function of p53 as an activator of transcription, recent results point to an unsophisticated means of regulation.

Essential but partially redundant roles for POU4F1/Brn-3a and POU4F2/Brn-3b transcription factors in the developing heart

Congenital heart defects contribute to embryonic or neonatal lethality but due to the complexity of cardiac development, the molecular changes associated with such defects are not fully understood. Here, we report that transcription factors (TFs) Brn-3a (POU4F1) and Brn-3b (POU4F2) are important for normal cardiac development. Brn-3a directly represses Brn-3b promoter in cardiomyocytes and consequently Brn-3a knockout (KO) mutant hearts express increased Brn-3b mRNA during mid-gestation, which is linked to hyperplastic growth associated with elevated cyclin D1, a known Brn-3b target gene. However, during late gestation, Brn-3b can cooperate with p53 to enhance transcription of pro-apoptotic genes e.g. Bax, thereby increasing apoptosis and contribute to morphological defects such as non-compaction, ventricular wall/septal thinning and increased crypts/fissures, which may cause lethality of Brn-3a KO mutants soon after birth. Despite this, early embryonic lethality in e9.5 double KO (Brn-3a^-/- : Brn-3b^-/-) mutants indicate essential functions with partial redundancy during early embryogenesis. High conservation between mammals and zebrafish (ZF) Brn-3b (87%) or Brn-3a (76%) facilitated use of ZF embryos to study potential roles in developing heart. Double morphant embryos targeted with morpholino oligonucleotides to both TFs develop significant cardiac defects (looping abnormalities and valve defects) suggesting essential roles for Brn-3a and Brn-3b in developing hearts.

EGR-1/Bax pathway plays a role in vitamin E δ-tocotrienol-induced apoptosis in pancreatic cancer cells

The anticancer activity of δ-tocotrienol, a bioactive vitamin E present in whole grain cereals, annatto beans and palm fruit, is strongly dependent on its effect on the induction of apoptosis. δ-Tocotrienol-induced apoptosis is associated with consistent induction in the expression of the proapoptotic protein Bcl-2-associated X protein (Bax). The molecular mechanism by which δ-tocotrienol regulates Bax expression is unknown. We carried out a DNA microarray study that identified δ-tocotrienol induction of the zinc finger transcription factor EGR-1 in pancreatic cancer cells. Here, we provide evidence linking δ-tocotrienol-induced apoptosis in pancreatic cancer cells to EGR-1 regulation of Bax expression. Forced expression of EGR-1 induces Bax expression and apoptosis in pancreatic cancer cells. In contrast, knockdown of δ-tocotrienol-induced EGR-1 by small interfering RNA attenuated δ-tocotrienol-induced Bax expression and reduced δ-tocotrienol-induced apoptosis. Further analyses showed that de novo protein synthesis was not required for δ-tocotrienol-induced EGR-1 expression, suggesting a direct effect of δ-tocotrienol on EGR-1 expression. Furthermore, a chromatin immunoprecipitation assay demonstrated that EGR-1 binds to the Bax gene promoter. Finally, δ-tocotrienol treatment induced Bax expression and activated EGR-1 in the pancreatic neoplastic cells of the PDX-Cre Kras genetically engineered model of pancreatic cancer. Our study provides the first evidence for EGR-1 as a direct target of vitamin E δ-tocotrienol, suggesting that EGR-1 may act as a proapoptotic factor in pancreatic cancer cells via induction of Bax.

Co-expression of POU4F2/Brn-3b with p53 may be important for controlling expression of pro-apoptotic genes in cardiomyocytes following ischaemic/hypoxic insults

Cardiomyocyte death following ischaemic/hypoxic injury causes irreversible damage to cardiac function and contributes to chronic diseases such as heart failure. Understanding the mechanisms associated with myocyte loss under these conditions can help to identify strategies to minimise/abrogate such detrimental effects. The p53 protein can induce apoptosis or cell cycle arrest, but effects on cell fate depend on interactions with other regulators such as POU4F2/Brn-3b (Brn-3b), which co-operates with p53 to increase the expression of pro-apoptotic genes. In contrast, the related POU4F1/Brn-3a (Brn-3a) blocks p53-mediated apoptosis but co-operates with p53 to enhance cell cycle arrest. In this study, we showed that permanent coronary artery ligation in mouse hearts, which induced apoptotic markers, activated caspase-3 and -8 and necroptosis markers; RIP-1 and -3 also increased Brn-3b and Brn-3a expression. However, Brn-3a was only detected in uninjured myocardium but not at the site of injury, whereas Brn-3b showed generalised increase, including within the infarct zone. Conversely, p53 was detected in the infarct zone and in some cells adjacent to the site of injury but not in uninjured myocardium. Co-localisation studies showed Brn-3a co-expression with p53 in cardiomyocytes adjacent to the infarct zone, whereas Brn-3b was co-localised with p53 in the infarct zone only. Increased Brn-3b and p53 correlated with elevated expression of pro-apoptotic target genes, Bax, Noxa and PUMA, whereas cleaved caspase-3 confirmed the presence of apoptotic cells within this region of the injured heart. Similarly, simulated ischaemia/reoxygenation (sI/R) injury in neonatal rat ventricular cardiomyocytes (NRVM) and heart derived H9c2 myoblasts increased Brn-3b, p53 as well as apoptotic genes, and this was associated with enhanced apoptosis. Furthermore, targeted reduction of Brn-3b using shRNA caused reduction in pro-apoptotic Bax and Noxa proteins, even though p53 expression remained intact, suggesting that Brn-3b is important for controlling the fate of the myocardium in the injured heart.

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

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

Pou4f1 and pou4f2 are dispensable for the long-term survival of adult retinal ganglion cells in mice

PURPOSE

To investigate the role of Pou4f1 and Pou4f2 in the survival of adult retinal ganglion cells (RGCs).

METHODS

Conditional alleles of Pou4f1 and Pou4f2 were generated (Pou4f1loxP and Pou4f2loxP respectively) for the removal of Pou4f1 and Pou4f2 in adult retinas. A tamoxifen-inducible Cre was used to delete Pou4f1 and Pou4f2 in adult mice and retinal sections and flat mounts were subjected to immunohistochemistry to confirm the deletion of both alleles and to quantify the changes in the number of RGCs and other retinal neurons. To determine the effect of loss of Pou4f1 and Pou4f2 on RGC survival after axonal injury, controlled optic nerve crush (CONC) was performed and RGC death was assessed.

RESULTS

Pou4f1 and Pou4f2 were ablated two weeks after tamoxifen treatment. Retinal interneurons and Müller glial cells are not affected by the ablation of Pou4f1 or Pou4f2 or both. Although the deletion of both Pou4f1 and Pou4f2 slightly delays the death of RGCs at 3 days post-CONC in adult mice, it does not affect the cell death progress afterwards. Moreoever, deletion of Pou4f1 or Pou4f2 or both has no impact on the long-term viability of RGCs at up to 6 months post-tamoxifen treatment.

CONCLUSION

Pou4f1 and Pou4f2 are involved in the acute response to damage to RGCs but are dispensable for the long-term survival of adult RGC in mice.

The transcription factor p53: not a repressor, solely an activator

The predominant function of the tumor suppressor p53 is transcriptional regulation. It is generally accepted that p53-dependent transcriptional activation occurs by binding to a specific recognition site in promoters of target genes. Additionally, several models for p53-dependent transcriptional repression have been postulated. Here, we evaluate these models based on a computational meta-analysis of genome-wide data. Surprisingly, several major models of p53-dependent gene regulation are implausible. Meta-analysis of large-scale data is unable to confirm reports on directly repressed p53 target genes and falsifies models of direct repression. This notion is supported by experimental re-analysis of representative genes reported as directly repressed by p53. Therefore, p53 is not a direct repressor of transcription, but solely activates its target genes. Moreover, models based on interference of p53 with activating transcription factors as well as models based on the function of ncRNAs are also not supported by the meta-analysis. As an alternative to models of direct repression, the meta-analysis leads to the conclusion that p53 represses transcription indirectly by activation of the p53-p21-DREAM/RB pathway.

The neural crest transcription factor Brn3a is expressed in melanoma and required for cell cycle progression and survival

Pigment cells and neuronal cells both are derived from the neural crest. Here, we describe the Pit-Oct-Unc (POU) domain transcription factor Brn3a, normally involved in neuronal development, to be frequently expressed in melanoma, but not in melanocytes and nevi. RNAi-mediated silencing of Brn3a strongly reduced the viability of melanoma cell lines and decreased tumour growth in vivo. In melanoma cell lines, inhibition of Brn3a caused DNA double-strand breaks as evidenced by Mre11/Rad50-containing nuclear foci. Activated DNA damage signalling caused stabilization of the tumour suppressor p53, which resulted in cell cycle arrest and apoptosis. When Brn3a was ectopically expressed in primary melanocytes and fibroblasts, anchorage-independent growth was increased. In tumourigenic melanocytes and fibroblasts, Brn3a accelerated tumour growth in vivo. Furthermore, Brn3a cooperated with proliferation pathways such as oncogenic BRAF, by reducing oncogene-induced senescence in non-malignant melanocytes. Together, these results identify Brn3a as a new factor in melanoma that is essential for melanoma cell survival and that promotes melanocytic transformation and tumourigenesis.

Protein kinase C activation causes neurite retraction via cyclinD1 and p60-katanin increase in rat hippocampal neurons

Neurons are differentiated postmitotic cells residing in G0 phase of the cell cycle and are unable to proceed through G1 phase, in which cyclinD1 needs to be up-regulated for initiation. Yet, a growing body of evidence has shown that cell cycle re-activation via cyclinD1 up-regulation drives neurons into apoptosis. By contrast, there is also evidence demonstrating cell cycle proteins playing roles in neuronal differentiation. cyclinD1 has been shown to be differently regulated by protein kinase C alpha (PKC-α) in various mitotic cells. Based on these different effects, we investigated the role of PKC-α on cyclinD1 regulation in hippocampal neurons. Neurons were treated with PKC activator, PMA, and analysed for subcellular distributions of PKC-α and cyclinD1. Remarkably, PMA treatment increased nuclear PKC-α and cyclinD1, but not PKC-ε in hippocampal neurons. Increases in nuclear PKC-α and cyclinD1 were accompanied by microtubule re-organisation via increases in tau and retinoblastoma protein phosphorylation levels. Increased p60-katanin and p53 changed the neuronal morphology into neurons with shorter, but increased number of side branches. Since up-regulation of cell cycle is associated with apoptosis in neurons, we also analysed changes in Bax, Bcl-2 early and PARP (poly(ADP-ribose)polymerase), caspase3 late apoptotic markers. However, we did not observe any indication of apoptosis. These data suggest that in addition to their previously known roles in mitotic cells on cell cycle regulation, PKC-α and cyclinD1 seem to be important for differentiation, and nuclear PKC-α and cyclinD1 interfere with differentiation by promoting microtubule re-organisation through PKC signaling without triggering apoptosis.

Whole number, distribution and co-expression of brn3 transcription factors in retinal ganglion cells of adult albino and pigmented rats

The three members of the Pou4f family of transcription factors: Pou4f1, Pou4f2, Pou4f3 (Brn3a, Brn3b and Brn3c, respectively) play, during development, essential roles in the differentiation and survival of sensory neurons. The purpose of this work is to study the expression of the three Brn3 factors in the albino and pigmented adult rat. Animals were divided into these groups: i) untouched; ii) fluorogold (FG) tracing from both superior colliculli; iii) FG-tracing from one superior colliculus; iv) intraorbital optic nerve transection or crush. All retinas were dissected as flat-mounts and subjected to single, double or triple immunohistofluorescence The total number of FG-traced, Brn3a, Brn3b, Brn3c or Brn3 expressing RGCs was automatically quantified and their spatial distribution assessed using specific routines. Brn3 factors were studied in the general RGC population, and in the intrinsically photosensitive (ip-RGCs) and ipsilateral RGC sub-populations. Our results show that: i) 70% of RGCs co- express two or three Brn3s and the remaining 30% express only Brn3a (26%) or Brn3b; ii) the most abundant Brn3 member is Brn3a followed by Brn3b and finally Brn3c; iii) Brn3 a-, b- or c- expressing RGCs are similarly distributed in the retina; iv) The vast majority of ip-RGCs do not express Brn3; v) The main difference between both rat strains was found in the population of ipsilateral-RGCs, which accounts for 4.2% and 2.5% of the total RGC population in the pigmented and albino strain, respectively. However, more ipsilateral-RGCs express Brn3 factors in the albino than in the pigmented rat; vi) RGCs that express only Brn3b and RGCs that co-express the three Brn3 members have the biggest nuclei; vii) After axonal injury the level of Brn3a expression in the surviving RGCs decreases compared to control retinas. Finally, this work strengthens the validity of Brn3a as a marker to identify and quantify rat RGCs.

The RNA helicase p68 (DDX5) is selectively required for the induction of p53-dependent p21 expression and cell-cycle arrest after DNA damage

The RNA helicase p68 (DDX5) is an established co-activator of the p53 tumour suppressor that itself has a pivotal role in orchestrating the cellular response to DNA damage. Although several factors influence the biological outcome of p53 activation, the mechanisms governing the choice between cell-cycle arrest and apoptosis remain to be elucidated. In the present study, we show that, while p68 is critical for p53-mediated transactivation of the cell-cycle arrest gene p21(WAF1/CIP1), it is dispensable for induction of several pro-apoptotic genes in response to DNA damage. Moreover, p68 depletion results in a striking inhibition of recruitment of p53 and RNA Pol II to the p21 promoter but not to the Bax or PUMA promoters, providing an explanation for the selective effect on p21 induction. Importantly, these findings are mirrored in a novel inducible p68 knockout mouse model in which p68 depletion results in a selective inhibition of p21 induction in several tissues. Moreover, in the bone marrow, p68 depletion results in an increased sensitivity to γ-irradiation, consistent with an increased level of apoptosis. These data highlight a novel function of p68 as a modulator of the decision between p53-mediated growth arrest and apoptosis in vitro and in vivo.

Driving apoptosis-relevant proteins toward neural differentiation

Emerging evidence suggests that apoptosis regulators and executioners may control cell fate, without involving cell death per se. Indeed, several conserved elements of apoptosis are integral components of terminal differentiation, which must be restrictively activated to assure differentiation efficiency, and carefully regulated to avoid cell loss. A better understanding of the molecular mechanisms underlying key checkpoints responsible for neural differentiation, as an alternative to cell death will surely make stem cells more suitable for neuro-replacement therapies. In this review, we summarize recent studies on the mechanisms underlying the non-apoptotic function of p53, caspases, and Bcl-2 family members during neural differentiation. In addition, we discuss how apoptosis-regulatory proteins control the decision between differentiation, self-renewal, and cell death in neural stem cells, and how activity is restrained to prevent cell loss.

Sema3F downregulates p53 expression leading to axonal growth cone collapse in primary hippocampal neurons

Hippocampal nerve growth is regulated by the coordinated action of numerous external stimuli, including positively acting neurotrophin-derived growth cues and restrictive semaphorin cues, however the underlying cellular mechanisms remain largely unclear. We examined the potential cellular mechanism of Semaphorin3F (Sema3F) in cultured primary hippocampal neurons. We show that Sema3F can down-regulate p53 expression in primary hippocampal neurons, thereby contributing to growth cone collapse. Sema3F suppressed p53-induced pathways, which we show to be required to maintain growth cone structure. Sema3F-induced growth cone collapse was partially reversed by overexpression of p53, which promoted growth cone extension. Inhibition of p53 function by inhibitor, siRNAs, induced axonal growth cone collapse, whereas p53 over-expression led to larger growth cones in cultured primary hippocampal neurons.These data reveal a novel mechanism by which Sema3F can induce hippocampal neuron growth cone collapse and provide evidence for an intracellular mechanism for cross talk between positive and negative axon growth cues.

Molecular analysis of oncogenicity of the transcription factor, BRN3A, in cervical cancer cells

OBJECTIVE

The host cellular transcription factor, BRN3A, has been observed to play a vital role in cancer of the uterine cervix. BRN3A possesses multipartite functions, which include transcription of the genes of the high-risk HPVs and mediation of cellular changes in the host. In this study, we made an effort to decipher the regulation of BRN3A in cervical cancer cells by studying its interaction with different components of the cell.

METHODS

In cervical cancer cells, the endogenous HIPK2 was induced through cisplatin treatment, and then, its subsequent effect on BRN3A was primarily investigated through co-immunostaining and western blotting as HIPK2 has been observed to act as a co-repressor of Brn3a. The physical interaction of the two proteins was analyzed through co-immunoprecipitation. We resorted to chromatin immunoprecipitation in order to testify the autoregulatory pathway of BRN3A in cervical cancer cells. Interaction of BRN3A with cellular components, p73 and active form of JNK, was also studied through co-immunostaining.

RESULTS

We observed that BRN3A is independent of the regulative activity of HIPK2 and undergoes positive autoregulation in cervical cancer cells. Interestingly, during the study, it was revealed that BRN3A is unaffected by the treatment of cisplatin. Interaction of BRN3A with p73 and phosphorylated JNK in cervical cancer cells, observed in the present study, would help in understanding the molecular mechanism directed by BRN3A.

CONCLUSIONS

BRN3A possesses anti-apoptotic property, and considering the above results, it may be regarded as the key component in promoting tumorigenic growth in the uterine cervical cells.

Axotomy-induced retinal ganglion cell death in adult mice: quantitative and topographic time course analyses

The fate of retinal ganglion cells after optic nerve injury has been thoroughly described in rat, but not in mice, despite the fact that this species is amply used as a model to study different experimental paradigms that affect retinal ganglion cell population. Here we have analyzed, quantitatively and topographically, the course of mice retinal ganglion cells loss induced by intraorbital nerve transection. To do this, we have doubly identified retinal ganglion cells in all retinas by tracing them from their main retinorecipient area, the superior colliculi, and by their expression of BRN3A (product of Pou4f1 gene). In rat, this transcription factor is expressed by a majority of retinal ganglion cells; however in mice it is not known how many out of the whole population of these neurons express it. Thus, in this work we have assessed, as well, the total population of BRN3A positive retinal ganglion cells. These were automatically quantified in all whole-mounted retinas using a newly developed routine. In control retinas, traced-retinal ganglion cells were automatically quantified, using the previously reported method (Salinas-Navarro et al., 2009b). After optic nerve injury, though, traced-retinal ganglion cells had to be manually quantified by retinal sampling and their total population was afterwards inferred. In naïve whole-mounts, the mean (±standard deviation) total number of traced-retinal ganglion cells was 40,437(±3196) and of BRN3A positive ones was 34,697(±1821). Retinal ganglion cell loss was first significant for both markers 5 days post-axotomy and by day 21, the last time point analyzed, only 15% or 12% of traced or BRN3A positive retinal ganglion cells respectively, survived. Isodensity maps showed that, in control retinas, BRN3A and traced-retinal ganglion cells were distributed similarly, being densest in the dorsal retina along the naso-temporal axis. After axotomy the progressive loss of BRN3A positive retinal ganglion cells was diffuse and affected the entire retina. In conclusion, this is the first study assessing the values, in terms of total number and density, of the retinal ganglion cells surviving axotomy from 2 till 21 days post-lesion. Besides, we have demonstrated that BRN3A is expressed by 85.6% of the total retinal ganglion cell population, and because BRN3A positive retinal ganglion cells show the same spatial distribution and temporal course of degeneration than traced ones, BRN3A is a reliable marker to identify, quantify and assess, ex-vivo, retinal ganglion cell loss in this species.

Expression of inhibitor of apoptosis family proteins in human oral squamous cell carcinogenesis

BACKGROUND

The purpose of this study was to determine inhibitor of apoptosis (IAP) expression, its relationship with p53, and epigenetic change in oral carcinogenesis that remain to be elucidated.

METHODS

We measured IAP and p53 expression in 44 oral potentially malignant disorders and their corresponding malignant-transformed oral squamous cell carcinomas (OSCCs), and in 44 other non-transformed oral potentially malignant disorders. IAP and p53 expression in 10 fresh OSCCs, together with epigenetic change of their mutation, were also determined.

RESULTS

Normal mucosa did not express IAP/mutated p53. Oral potentially malignant disorders that underwent transformation exhibited high IAPs (>90%) and less-consistent mutated-p53 (34%) expression, whereas transformed OSCCs exhibited high IAP and mutated-p53 expression. Fresh OSCCs exhibited 80% to 100% IAP mRNA expression and 50% protein, mRNA, and p53 mutation expression. Normal tissues revealed DNA methylation of IAP, whereas cancerous tissues overexpressing IAP exhibited hypomethylation.

CONCLUSION

This study showed that IAP expression is an early event in oral carcinogenesis and that epigenetic and genetic pathways are associated with IAP expression in OSCC.

Life or death: p53-induced apoptosis requires DNA binding cooperativity

The tumor suppressor p53 provides exquisite protection from cancer by balancing cell survival and death in response to stress. Sustained stress or irreparable damage trigger p53's killer functions to permanently eliminate genetically-altered cells as a potential source of cancer. To prevent the unnecessary loss of cells that could cause premature aging as a result of stem cell attrition, the killer functions of p53 are tightly regulated and balanced against protector functions that promote damage repair and support survival in response to low stress or mild damage. In molecular terms these p53-based cell fate decisions involve protein interactions with cofactors and modifying enzymes, which modulate the activation of distinct sets of p53 target genes. In addition, we demonstrate that part of this regulation occurs at the level of DNA binding. We show that the killer function of p53 requires the four DNA binding domains within the p53 tetramer to interact with one another. These intermolecular interactions enable cooperative binding of p53 to less perfect response elements in the genome, which are present in many target genes essential for apoptosis. Modulating p53 interactions within the tetramer could therefore present a novel promising strategy to fine-tune p53-based cell fate decisions.

Neuronal transcription factor Brn-3a(l) is over expressed in high-grade ovarian carcinomas and tumor cells from ascites of patients with advanced-stage ovarian cancer

Objectives

In view of the recent association of Brn-3 transcription factors with neuroblastomas, cervical, breast, and prostate cancers we examined the expression of Brn-3a(l) in normal ovaries and in different histological grades of ovarian tumors. The expression of Brn-3a(l) was also evaluated in normal ovarian and cancer cell lines and tumor cells isolated from the ascites of advanced-stage ovarian cancer patients.

Methods

Normal ovaries, benign, borderline, grades 1, 2 and 3 ovarian tumors were analyzed by immunohistochemistry for Brn-3a(l) expression. A total of 46 ovarian specimens were included in the study. Immunofluorescence was used to investigate the expression of Brn-3a in normal ovarian and cancer cell lines. Brn-3a(l) expression was also evaluated by Western blot in tumor cells isolated from ascites of advanced-stage ovarian cancer patients and also in ovarian cancer cell lines.

Results

Nearly 12% of normal and benign ovarian tissues and 57% of borderline ovarian tumors were positive for epithelial Brn-3a(l) expression. Stromal staining was higher and it constituted 40% of normal non-cancerous ovaries compared to 50 and 86% in benign and borderline tumors. On the other hand, 85-100% of grades 1, 2 & 3 ovarian tumors demonstrated nuclear and cytoplasmic Brn-3a(l) staining in the epithelium. Stromal staining in grades1, 2 and 3 tumors constituted 71-88% of total staining. Overall, immunoreactive Brn-3a was present in all grades of ovarian tumors. The extent of epithelial and stromal Brn-3a staining was significantly different between the normal and histological grades of tumors (epithelial-χ² = 41.01, df = 20, P = 0.004, stromal-χ² = 24.66. df = 15, P = 0.05). The extent of epithelial staining was significantly higher in grades 1 and 2 ovarian tumors compared to normal ovaries and benign ovarian tumors (p < 0.05). In parallel, stromal staining was significantly higher in grade 3 tumors compared to normal ovaries (p < 0.05). In addition, cytoplasmic and nuclear Brn-3a expression was evident in ovarian cancer cell lines while no such expression was observed in SV40 antigen immortalized normal ovarian cell lines.

Conclusion

These data suggest that like other cancers, Brn-3a(l) expression is enhanced in ovarian tumors and its expression is consistent with its known role in inhibiting apoptosis and enhancing tumorigenesis. Specific targeting of Brn-3a may provide a useful strategy for regulating multiple tumor related genes involved with ovarian carcinomas.

p53-dependent induction of prostate cancer cell senescence by the PIM1 protein kinase

The PIM family of serine threonine protein kinases plays an important role in regulating both the growth and transformation of malignant cells. However, in a cell line-dependent manner, overexpression of PIM1 can inhibit cell and tumor growth. In 22Rv1 human prostate cells, but not in Du145 or RWPE-2, PIM1 overexpression was associated with marked increases in cellular senescence, as shown by changes in the levels of beta-galactosidase (SA-beta-Gal), p21, interleukin (IL)-6 and IL-8 mRNA and protein. During early cell passages, PIM1 induced cellular polyploidy. As the passage number increased, markers of DNA damage, including the level of gammaH2AX and CHK2 phosphorylation, were seen. Coincident with these DNA damage markers, the level of p53 protein and genes transcriptionally activated by p53, such as p21, TP53INP1, and DDIT4, increased. In these 22Rv1 cells, the induction of p53 protein was associated not only with senescence but also with a significant level of apoptosis. The importance of the p53 pathway to PIM1-driven cellular senescence was further shown by the observation that expression of dominant-negative p53 or shRNA targeting p21 blocked the PIM1-induced changes in the DNA damage response and increases in SA-beta-Gal activity. Likewise, in a subcutaneous tumor model, PIM1-induced senescence was rescued when the p53-p21 pathways are inactivated. Based on these results, PIM1 will have its most profound effects on tumorigenesis in situations where the senescence response is inactivated.

A simple technique for the prediction of interacting proteins reveals a direct Brn-3a-androgen receptor interaction

The formation of multiprotein complexes constitutes a key step in determining the function of any translated gene product. Thus, the elucidation of interacting partners for a protein of interest is of fundamental importance to cell biology. Here we describe a simple methodology for the prediction of novel interactors. We have applied this to the developmental transcription factor Brn-3a to predict and verify a novel interaction between Brn-3a and the androgen receptor (AR). We demonstrate that these transcription factors form complexes within the nucleus of ND7 neuroblastoma cells, while in vitro pull-down assays show direct association. As a functional consequence of the Brn-3a-AR interaction, the factors bind cooperatively to multiple elements within the promoter of the voltage-gated sodium channel, Nav1.7, leading to a synergistic increase in its expression. Thus, these data define AR as a direct Brn-3a interactor and verify a simple interacting protein prediction methodology that is likely to be useful for many other proteins.

Anti-apoptotic factor z-Val-Ala-Asp-fluoromethylketone promotes the survival of cochlear hair cells in a mouse model for human deafness

A major challenge in the inner ear research field is to restore hearing loss of both non-genetic and genetic origin. A large effort is being made to protect hair cells from cell death after exposure to noise or drugs that can cause hearing loss. Our research focused on protecting hair cells from cell death occurring in a genetic model for human deafness. POU4F3 is a transcription factor associated with human hearing impairment. Pou4f3 knockout mice (Pou4f3(-/-)) have no cochlear hair cells, resulting in complete deafness. Although the hair cells appear to form properly, they progressively degenerate via apoptosis. In order to rescue the hair cells in the knockout mice, we produced explant cultures from mouse cochleae at an early embryonic stage and treated the cells with z-Val-Ala-Asp-fluoromethylketone (z-VAD-fmk), a general caspase inhibitor. Hair cell numbers in the knockout mice treated with z-VAD-fmk were significantly higher than in the untreated mice. We found that the time window that z-VAD-fmk has a protective effect is between E14.5 (P=0.001) to E16.5 (P=0.03), but not after E18.5. The source of the surviving hair cells is not due to proliferation, as measured by 5-bromo-2-deoxyuridine (BrdU) labeling, or to supporting cell transdifferentiation to hair cells, since there was no change in supporting cell numbers. Instead, the survival appears to be a direct effect of the anti-apoptotic agent on the dying hair cells with an early developmental window. These results help towards providing a comprehensive understanding of the molecular mechanisms of hair cell death, which might lead to the development of new therapeutic anti-apoptotic agents to alleviate hereditary hearing loss (HL).

The expanding universe of p53 targets

The p53 tumour suppressor is modified through mutation or changes in expression in most cancers, leading to the altered regulation of hundreds of genes that are directly influenced by this sequence-specific transcription factor. Central to the p53 master regulatory network are the target response element (RE) sequences. The extent of p53 transactivation and transcriptional repression is influenced by many factors, including p53 levels, cofactors and the specific RE sequences, all of which contribute to the role that p53 has in the aetiology of cancer. This Review describes the identification and functionality of REs and highlights the inclusion of non-canonical REs that expand the universe of genes and regulation mechanisms in the p53 tumour suppressor network.

NGFI-B nuclear orphan receptor Nurr1 interacts with p53 and suppresses its transcriptional activity

Nurr1 is a member of the NGFI-B nuclear orphan receptor family which includes two other members, Nur77 and Nor-1. Nurr1 is essential for the development and survival of dopaminergic neurons. It was reported that Nurr1 has antiapoptotic functions, however, the mechanisms by which Nurr1 mediates these effects remain unknown. Here, we show that overexpression of Nurr1 decreases Bax expression whereas knockdown of Nurr1 increases Bax expression. Nurr1 also interacts with p53 and represses its assembly. Furthermore, Nurr1 represses p53 transcriptional activity in interaction-dependent and dose-dependent manners. Moreover, Nurr1 protects cells from doxorubicin-induced apoptosis. These findings provide evidence that Nurr1 promotes cell survival through its interacting with and repressing p53, thus implicating that Nurr1 may play an important role in carcinogenesis and other diseases.

Blinded by the Light: The Growing Complexity of p53

While the tumor suppressor functions of p53 have long been recognized, the contribution of p53 to numerous other aspects of disease and normal life is only now being appreciated. This burgeoning range of responses to p53 is reflected by an increasing variety of mechanisms through which p53 can function, although the ability to activate transcription remains key to p53's modus operandi. Control of p53's transcriptional activity is crucial for determining which p53 response is activated, a decision we must understand if we are to exploit efficiently the next generation of drugs that selectively activate or inhibit p53.

The non-apoptotic role of p53 in neuronal biology: enlightening the dark side of the moon

The transcription factor p53 protects neurons from transformation and DNA damage through the induction of cell-cycle arrest, DNA repair and apoptosis in a range of in vitro and in vivo conditions. Indeed, p53 has a crucial role in eliciting neuronal cell death during development and in adult organisms after exposure to a range of stressors and/or DNA damage. Nevertheless, accumulating evidence challenges this one-sided view of the role of p53 in the nervous system. Here, we discuss how-unexpectedly-p53 can regulate the proliferation and differentiation of neural progenitor cells independently of its role in apoptosis, and p53 post-translational modifications might promote neuronal maturation, as well as axon outgrowth and regeneration, following neuronal injury. We hope to encourage a more comprehensive view of the non-apoptotic functions of p53 during neural development, and to warn against oversimplifications regarding its role in neurons. In addition, we discuss how further insight into the p53-dependent modulation of these mechanisms is necessary to elucidate the decision-making processes between neuronal cell death and differentiation during development, and between neuronal degeneration and axonal regeneration after injury.

Regulation of Brn-3a N-terminal transcriptional activity by MEK1/2-ERK1/2 signalling in neural differentiation

The POU family transcription factor Brn-3a is required for the differentiation and survival of sensory neurones, and is phosphorylated in neuroblastoma cells following treatment with all-trans retinoic acid (RA). Mutation of serines-121 and -122 of Brn-3a to alanine blocks its phosphorylation and impairs RA-mediated neurite outgrowth. Here we show that this deficit in differentiation is mimicked by a single mutation at serine-122, and demonstrate a similar requirement for a second residue, threonine-39. Like Brn-3a, the neuropeptide Galanin has been implicated in the development of sensory neurones. We show that Brn-3a over-expression acts synergistically with RA treatment to up-regulate Galanin promoter activity; that the activity of the N-terminal transcriptional activation domain of Brn-3a is increased following RA treatment; and that both these effects require threonine-39 and serine-122. In addition, we demonstrate that the RA-mediated activation of Galanin promoter activity and Brn-3a N-terminal transcriptional activity are both blocked by pan-MEK inhibitors, and show that the expression of a constitutively-active mutant of MEK1, but not MEK5, is sufficient to increase Brn-3a activity. These results reveal an important role for the ERK1/2 pathway in Brn-3a regulation during RA-mediated neuronal differentiation and define the neuropeptide Galanin as a novel target of this transcription factor.

The p53 family and programmed cell death

The p53 tumor suppressor continues to hold distinction as the most frequently mutated gene in human cancer. The ability of p53 to induce programmed cell death, or apoptosis, of cells exposed to environmental or oncogenic stress constitutes a major pathway whereby p53 exerts its tumor suppressor function. In the past decade, we have discovered that p53 is not alone in its mission to destroy damaged or aberrantly proliferating cells: it has two homologs, p63 and p73, that in various cellular contexts and stresses contribute to this process. In this review, the mechanisms whereby p53, and in some cases p63 and p73, induce apoptosis are discussed. Other reviews have focused more extensively on the contribution of individual p53-regulated genes to apoptosis induction by this protein, whereas in this review, we focus more on those factors that mediate the decision between growth arrest and apoptosis by p53, p63 and p73, and on the post-translational modifications and protein-protein interactions that influence this decision.

Wild-type p53 in cancer cells: when a guardian turns into a blackguard

The tumor suppressor p53 controls a broad range of cellular responses. Induction of a transient (cell cycle arrest) or a permanent (senescence) block of cell proliferation, or the activation of cell death pathways in response to genotoxic stress comprise the major arms of the survival-death axis governed by p53. Due to these biological properties, inactivation of p53 is a crucial step in tumor development and progression, reflected by the high incidence of TP53 mutations in different types of human cancers. The remarkable potency of p53 in suppressing tumorigenic outgrowth has promoted the expectation that tumor cells expressing wild-type p53 (wtp53) should be more prone to elimination by cytotoxic treatments than tumor cells expressing mutant p53 (mutp53) with defunct wtp53 activities. However, recent findings yielded somewhat unexpected insights concerning the preponderance of the survival-promoting effects of wtp53 in cancer cells, a rather undesired property from the therapeutic point of view. In this commentary we will discuss the possibility that the developmentally established distinct patterns of wtp53 mediated responses in different tissues are an important factor in determining the ultimate outcome of cellular responses mediated by wtp53 in different types of tumor cells, with a particular focus on the divergent impact of wtp53 in malignant tumors of the central nervous system. We infer that a selective gain of pro-survival functions of wtp53 in cancer cells will confer a survival advantage that counteracts tumor therapy.

Cardiac expression of Brn-3a and Brn-3b POU transcription factors and regulation of Hsp27 gene expression

The Brn-3 family of transcription factors play a critical role in regulating expression of genes that control cell fate, including the small heat shock protein Hsp27. The aim of this study was to investigate the relationship between Brn-3a and Brn-3b and Hsp27 expression in the developing rodent heart. Brn-3a and Brn-3b were detected from embryonic days 9.5-10.5 (E9.5-E10.5) in the mouse heart, with significant increases seen later during development. Two isoforms (long and short) of each protein were detected during embryogenesis and postnatally. Brn-3a messenger RNA (mRNA) and protein were localized by E13.0 to the atrio-ventricular (AV) valve cushions and leaflets, outflow tract (OFT), epicardium and cardiac ganglia. By E14.5, Brn-3a was also localised to the septa and compact ventricular myocardium. An increase in expression of the long Brn-3a(l) isoform between E17 and adult coincided with a decrease in expression of Brn-3b(l) and a marked increase in expression of Hsp27. Hearts from Brn-3a-/- mice displayed a partially penetrant phenotype marked by thickening of the endocardial cushions and AV valve leaflets and hypoplastic ventricular myocardium. Loss of Brn-3a was correlated with a compensatory increase in Brn-3b and GATA3 mRNA but no change in Hsp27 mRNA. Reporter assays in isolated cardiomyocytes demonstrated that both Brn-3a and Brn-3b activate the hsp27 promoter via a consensus Brn-3-binding site. Therefore, Brn-3 POU factors may play an important role in the development and maintenance of critical cell types and structures within the heart, in part via developmental regulation of myocardial Hsp27 expression. Furthermore, Brn-3a may be necessary for correct valve and myocardial remodelling and maturation.

Brn-3a/POU4F1 interacts with and differentially affects p73-mediated transcription

The Brn-3a/POU4F1 POU transcription factor is critical for the survival and differentiation of specific sensory neurons during development or upon injury; by regulating expression of target genes, either directly or indirectly upon interaction with other proteins. In this study, we demonstrated the physical interaction of Brn-3a with different p73 isoforms and showed co-localization in sensory neurons arising from the neural crest. The biological effects of p73/ Brn-3a interaction depend on the particular p73 isoform, because co-expression of Brn-3a with TAp73 enhanced cell cycle arrest, whereas Brn-3a and DeltaNp73 cooperated to increase protection from apoptosis. Brn-3a antagonized TAp73 transactivation of pro-apoptotic Bax, but co-operated to increase transcription of the cell cycle regulator p21 CIP1/Waf1. The region 425-494 amino acids within the TAp73 C terminus were critical for Brn-3a to repress Bax transactivation, but not for cooperation on the p21 CIP1/Waf1 promoter. Our results suggest that co-factors binding to the p73 C terminus facilitate maximal activation on the Bax but not p21 CIP1/Waf1 promoter and that Brn-3a modulates this interaction. Thus, the physical interaction of Brn-3a with specific p73 isoforms will be critical for determining cell fate during neuronal development or in injured neurons expressing both factors.

HIPK2: a multitalented partner for transcription factors in DNA damage response and development

Protein phosphorylation is a widely diffuse and versatile post-translational modification that controls many cellular processes, from signal transduction to gene transcription. The homeodomain-interacting protein kinases (HIPKs) belong to a new family of serine-threonine kinases first identified as corepressors for homeodomain transcription factors. Different screenings for the identification of new partners of transcription factors have indicated that HIPK2, the best characterized member of the HIPK family, is a multitalented coregulator of an increasing number of transcription factors and cofactors. The aim of this review is to describe the different mechanisms through which HIPK2 regulates gene transcription.