Nucleophosmin acts as a novel AP2alpha-binding transcriptional corepressor during cell differentiation

Knockdown of dual-specificity phosphatase 3 drives differentiation and polarization of myeloid leukemia cells into macrophages with reduced proliferative and DNA repair fitness

Dual-specificity phosphatase 3 (DUSP3) regulates key cellular processes, including the cell cycle, proliferation, and differentiation. Recently, we demonstrated its crucial role in maintaining genomic stability by interacting with and dephosphorylating nucleophosmin (NPM), thereby modulating nuclear p53 activity under genotoxic stress. Given the frequent mutations in both p53 and NPM in acute myeloid leukemia (AML), this study aimed to investigate the impact of DUSP3 knockdown in two p53-deficient AML cell lines and explore potential correlations with NPM expression. THP-1 cells exhibited higher basal levels of DUSP3 and NPM compared to HL-60 cells, while DUSP3 knockdown reduced NPM expression in HL-60 cells. Upon phorbol 12-myristate 13-acetate (PMA)-induced differentiation into macrophage-like cells, only HL-60 cells displayed decreased levels of both DUSP3 and NPM. DUSP3 knockdown enhanced differentiation in THP-1 and HL-60 cells and promoted non-classical M2 macrophage polarization following additional PMA exposure, as indicated by increased expression of CD11b and CD206. Bioinformatics analysis revealed significant correlations between DUSP3 and NPM gene expression, AML patient survival, and the maturation stage of myeloid cells. Furthermore, DUSP3 knockdown in undifferentiated HL-60 cells impaired proliferation and compromised genomic stability under genotoxic stress induced by doxorubicin. These findings suggest that DUSP3 plays a regulatory role in the differentiation, polarization, and proliferation of myeloid cells. Through the modulation of NPM expression and activity, DUSP3 may contribute to a deeper understanding of leukemia pathophysiology and mechanisms of chemotherapy resistance.

Acute myeloid leukemia with NPM1, IDH2, and SETD2 mutations mimicking acute promyelocytic leukemia: A case report and literature review

RATIONALE

Acute myeloid leukemia with NPM1, IDH2, and SETD2 mutations can mimic acute promyelocytic leukemia (APL) and poses a challenge for the early and accurate differentiation and diagnosis of APL with PML::RARA.

PATIENT CONCERNS

A 70-year-old man was diagnosed with acute myeloid leukemia with NPM1, IDH2, and SETD2 mutations.

DIAGNOSIS

APL-like acute myeloid leukemia with NPM1, IDH2, and SETD2 mutations was made.

INTERVENTIONS

The patient received all-trans retinoic acid 20 mg 3 times a day for 22 days, azacitidine 100 mg subcutaneously once daily for 7 days, and venetoclax 100 mg once daily for 12 days.

OUTCOMES

Due to economical constraints, the patient stopped further treatment, and outcome was dismal.

LESSONS

The comprehensive evaluation of bone marrow morphology, immunology, cytogenetics, and molecular biology is essential for the accurate diagnosis of acute myeloid leukemia.

TFAP2 paralogs facilitate chromatin access for MITF at pigmentation and cell proliferation genes

In developing melanocytes and in melanoma cells, multiple paralogs of the Activating-enhancer-binding Protein 2 family of transcription factors (TFAP2) contribute to expression of genes encoding pigmentation regulators, but their interaction with Microphthalmia transcription factor (MITF), a master regulator of these cells, is unclear. Supporting the model that TFAP2 facilitates MITF's ability to activate expression of pigmentation genes, single-cell seq analysis of zebrafish embryos revealed that pigmentation genes are only expressed in the subset of mitfa-expressing cells that also express tfap2 paralogs. To test this model in SK-MEL-28 melanoma cells we deleted the two TFAP2 paralogs with highest expression, TFAP2A and TFAP2C, creating TFAP2 knockout (TFAP2-KO) cells. We then assessed gene expression, chromatin accessibility, binding of TFAP2A and of MITF, and the chromatin marks H3K27Ac and H3K27Me3 which are characteristic of active enhancers and silenced chromatin, respectively. Integrated analyses of these datasets indicate TFAP2 paralogs directly activate enhancers near genes enriched for roles in pigmentation and proliferation, and directly repress enhancers near genes enriched for roles in cell adhesion. Consistently, compared to WT cells, TFAP2-KO cells proliferate less and adhere to one another more. TFAP2 paralogs and MITF co-operatively activate a subset of enhancers, with the former necessary for MITF binding and chromatin accessibility. By contrast, TFAP2 paralogs and MITF do not appear to co-operatively inhibit enhancers. These studies reveal a mechanism by which TFAP2 profoundly influences the set of genes activated by MITF, and thereby the phenotype of pigment cells and melanoma cells.

Histone chaperone Nucleophosmin regulates transcription of key genes involved in oral tumorigenesis

Nucleophosmin (NPM1) is a multifunctional histone chaperone that can activate acetylation-dependent transcription from chromatin templates in vitro. Acetylation of NPM1 by p300 has been shown to further enhance its transcription activation potential. Moreover, its total and acetylated pools are increased in oral squamous cell carcinoma. However, the role of NPM1 or its acetylated form (AcNPM1) in transcriptional regulation in cells and oral tumorigenesis is not fully elucidated. Using ChIP-seq analyses, we provide the first genome-wide profile of AcNPM1 and show that AcNPM1 is enriched at transcriptional regulatory elements. AcNPM1 co-occupies marks of active transcription at promoters and DNase I hypersensitive sites at enhancers. In addition, using a high-throughput protein interaction profiling approach, we show that NPM1 interacts with RNA Pol II, general transcription factors, mediator subunits, histone acetyltransferase complexes, and chromatin remodelers. NPM1 histone chaperone activity also contributes to its transcription activation potential. Further, NPM1 depletion leads to decreased AcNPM1 occupancy and reduced expression of genes required for proliferative, migratory and invasive potential of oral cancer cells. NPM1 depletion also abrogates the growth of orthotopic tumors in mice. Collectively, these results establish that AcNPM1 functions as a coactivator during during RNA polymerase II-driven transcription and regulates the expression of genes that promote oral tumorigenesis.

Function and transcriptional regulation of TCTN1 in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is one of the most common types of head and neck squamous cell carcinoma (HNSCC) with a poor survival rate. In the present study, the involvement of tectonic 1 (TCTN1) in OSCC was explored. The relevance between TCTN1 and HNSCC clinicopathological features was first analyzed and it was revealed that TCTN1 was associated with the tumor clinical stage and grade. In in vitro experiments, it was demonstrated that the proliferative, migratory and invasive capacity of OSCC CAL27 cells and SCC15 cells was significantly suppressed due to TCTN1 knockdown. Additionally, the core promoter of TCTN1 was confirmed and transcription factor AP-2 alpha (TFAP2A) was suggested as a regulator of TCTN1 mRNA expression. On the whole, the present study elucidated the direct association between TCTN1 and OSCC for the first time, to the best of our knowledge, and the TFAP2A/TCTN1 axis was suggested as a potential novel therapeutic target for OSCC.

Epigenetic CRISPR Screens Identify Npm1 as a Therapeutic Vulnerability in Non-Small Cell Lung Cancer

Despite advancements in treatment options, the overall cure and survival rates for non-small cell lung cancers (NSCLC) remain low. While small-molecule inhibitors of epigenetic regulators have recently emerged as promising cancer therapeutics, their application in patients with NSCLC is limited. To exploit epigenetic regulators as novel therapeutic targets in NSCLC, we performed pooled epigenome-wide CRISPR knockout screens in vitro and in vivo and identified the histone chaperone nucleophosmin 1 (Npm1) as a potential therapeutic target. Genetic ablation of Npm1 significantly attenuated tumor progression in vitro and in vivo. Furthermore, KRAS-mutant cancer cells were more addicted to NPM1 expression. Genetic ablation of Npm1 rewired the balance of metabolism in cancer cells from predominant aerobic glycolysis to oxidative phosphorylation and reduced the population of tumor-propagating cells. Overall, our results support NPM1 as a therapeutic vulnerability in NSCLC. SIGNIFICANCE: Epigenome-wide CRISPR knockout screens identify NPM1 as a novel metabolic vulnerability and demonstrate that targeting NPM1 is a new therapeutic opportunity for patients with NSCLC.

Nucleophosmin contributes to vascular inflammation and endothelial dysfunction in atherosclerosis progression

OBJECTIVE

It is unclear whether nucleophosmin (NPM) participates in cardiovascular disease. The present study aimed to investigate the role and underlying mechanisms of NPM in atherosclerosis.

METHODS

Levels and location of NPM in human carotid atherosclerotic plaques and healthy controls were detected by real-time polymerase chain reaction, immunoblots, and immunofluorescence. Atherosclerotic prone ApoE^-/- mice were fed with a Western diet for 16 weeks as an in vivo model. Human primary umbilical vein endothelial cells (HUVECs) were cultured as an in vitro model.

RESULTS

Compared with controls, we found that NPM levels in human carotid atherosclerotic plaques were more than twice as high as in normal arteries, which mainly localized in endothelial cells. In vivo, adenovirus-containing NPM small hairpin RNA attenuated atherosclerotic lesion and promoted plaque stabilization in ApoE^-/- mice fed a Western diet by reducing vascular inflammation, maintaining endothelial function, and decreasing macrophage infiltration. Furthermore, NPM knockdown decreased nuclear factor-κB (NF-κB) p65 phosphorylation. In cultured HUVECs, palmitic acid increased the protein levels of NPM and induced the expression of inflammatory cytokines and monocyte adhesion, whereas NPM knockdown attenuated this effect. In HUVECs, NPM protein physically interacted with NF-κB p65 subunit and promoted its nuclear transposition. NPM also increased the transcriptional activity of NF-κB p65 promoter and enhance its binding to target genes, including interleukin-1β, interleukin-6, intercellular adhesion molecule-1, and E-selectin.

CONCLUSIONS

These data provide novel evidence that NPM promotes atherosclerosis by inducing vascular inflammation and endothelial dysfunction through the NF-κB signaling pathway and suggest that NPM may be a promising target for atherosclerosis prevention and treatment.

NPM and NPM-MLF1 interact with chromatin remodeling complexes and influence their recruitment to specific genes

Nucleophosmin (NPM1) is frequently mutated or subjected to chromosomal translocation in acute myeloid leukemia (AML). NPM protein is primarily located in the nucleus, but the recurrent NPMc+ mutation, which creates a nuclear export signal, is characterized by cytoplasmic localization and leukemogenic properties. Similarly, the NPM-MLF1 translocation product favors the partial cytoplasmic retention of NPM. Regardless of their common cellular distribution, NPM-MLF1 malignancies engender different effects on hematopoiesis compared to NPMc+ counterparts, highlighting possible aberrant nuclear function(s) of NPM in NPMc+ and NPM-MLF1 AML. We performed a proteomic analysis and found that NPM and NPM-MLF1 interact with various nuclear proteins including subunits of the chromatin remodeling complexes ISWI, NuRD and P/BAF. Accordingly, NPM and NPM-MLF1 are recruited to transcriptionally active or repressed genes along with NuRD subunits. Although the overall gene expression program in NPM knockdown cells is similar to that resulting from NPMc+, NPM-MLF1 expression differentially altered gene transcription regulated by NPM. The abnormal gene regulation imposed by NPM-MLF1 can be characterized by the enhanced recruitment of NuRD to gene regulatory regions. Thus, different mechanisms would orchestrate the dysregulation of NPM function in NPMc+- versus NPM1-MLF1-associated leukemia.

NPMc+ mutation is the most common mutation in acute myeloid leukemia (AML) with prevalence in one third of all AML cases. NPM can also be involved in leukemogenic translocation including the t(3;5)(q25;q34) NPM-MLF1 translocation, which is associated to bad clinical course but remains poorly defined. We are reporting that NPM and the leukemogenic NPM-MLF1 play central role in chromatin organization and gene regulation in hematopoietic cells. A proteomic analysis provided the evidence that NPM and NPM-MLF1 are interacting with the chromatin remodeling complexes NuRD, P/BAF and ISWI in hematopoietic cells. The NPM nuclear depletion, such as imposed by the leukemogenic NPMc+ mutation, or the expression of NPM-MLF1 favors the uncontrolled recruitment of the CHD4/NuRD to chromatin and the abnormal regulation of NPM-target genes. Our results suggest that the abnormal gene regulation forced by NPM-MLF1 is different than the loss of nuclear function imposed by NPMc+, and it can be characterized by the enhanced recruitment of CHD4/NuRD to genes. Thus, NPM-MLF1 is likely to promote hematopoietic malignancies by disruption of gene regulation imposed by the NuRD activity.

Chemotherapeutic Resistance in Egyptian Acute Myeloid Leukemia Patients

Background:

Acute Myeloid Leukemia (AML) is a heterogeneous disorder with variable genetic abnormalities and cytogenetic alterations which provide a significant disease prognosis and determine response to therapy.

Purpose:

We aim to investigate the expression of the MDR1 gene in 100 Egyptian AML patients, to identify their role on both the progression and chemotherapeutic refractoriness together with assessment of known prognostic molecular markers; FLT3-ITD and NPM1 mutations.

Methodology:

Quantitative assessment of MDR1 gene expression was performed by quantitative RT-PCR. Additional prognostic molecular markers were determined as internal tandem duplications of the FLT 3 gene and nucleophosmin gene mutation A.

Results:

MDR1 gene expression levels and FLT3/ITD mutations were significantly higher in AML patients with resistant disease with P value <0.001 and 0.002 respectively. However, NPM1 was insignificantly higher in patients with CR P-value 0.14. In MDR positive group, wild FLT3/ITD with or without NPM1 mutation was favorable in achieving CR with p value 0.02. MDR negative group, wild FLT3/ITD with or without NPM1 mutation showed insignificantly higher CR rates with p value (0.35). Kaplan-Meier curves revealed statistically significant difference between MDR1-negative and MDR1-positive patients regarding their DFS and OS between the two groups where DFS and OS were higher in MDR1-negative patients with p value 0.004 and 0.01, respectively.

Conclusion:

The results obtained by the current work together with the previous researches concerning the study of multidrug resistance genes in AML patients provide additional evidence of the role played by these genes as predictors of chemoresistance and poor treatment outcome.

Androgen upregulates NR4A1 via the TFAP2A and ETS signaling networks

Hyperandrogenism is one of the clinical and biochemical characteristics of polycystic ovary syndrome (PCOS). Our previous studies confirmed that nuclear receptor subfamily 4 group A member 1 (NR4A1), as a differentially expressed gene in the ovaries of PCOS patients, was upregulated by increased androgen. However, the potential mechanism of NR4A1 upregulation remains unknown. To elucidate the molecular mechanisms involved in NR4A1 regulation, we cloned and characterized the promoter regions of the NR4A1 gene using a series of truncated promoter plasmids in luciferase reporter assays. We identified two unique core promoters of NR4A1 located within the +1055/+1251 and +3183/+3233 regions relative to the transcription start site. TFAP2A downregulated NR4A1 expression, while five ETS transcription factors, ETS1, ELK1, ERG, FLI1 and SPI1, could upregulate NR4A1 promoter activity in HeLa cells. Of these transcription factors, ETS1 and ELK1 were the most effective ones. Moreover, all six transcription factors were confirmed to interact directly with the NR4A1 promoter. In conclusion, this study presents the first description that TFAP2A and ETS family signaling networks are involved in the androgen-mediated transcriptional regulation of NR4A1, which contributes to the understanding of the molecular mechanisms involved in the TFAP2A-NR4A1 and ETS-NR4A1 signaling networks in PCOS.

Nucleophosmin in leukemia: Consequences of anchor loss

Nucleophosmin (NPM), one of the most abundant nucleolar proteins, has crucial functions in ribosome biogenesis, cell cycle control, and DNA-damage repair. In human cells, NPM occurs mainly in oligomers. It functions as a chaperone, undergoes numerous interactions and forms part of many protein complexes. Although NPM role in carcinogenesis is not fully elucidated, a variety of tumor suppressor as well as oncogenic activities were described. NPM is overexpressed, fused with other proteins, or mutated in various tumor types. In the acute myeloid leukemia (AML), characteristic mutations in NPM1 gene, leading to modification of NPM C-terminus, are the most frequent genetic aberration. Although multiple mutation types of NPM are found in AML, they are all characterized by aberrant cytoplasmic localization of the mutated protein. In this review, current knowledge of the structure and function of NPM is presented in relation to its interaction network, in particular to the interaction with other nucleolar proteins and with proteins active in apoptosis. Possible molecular mechanisms of NPM mutation-driven leukemogenesis and NPM therapeutic targeting are discussed. Finally, recent findings concerning the immunogenicity of the mutated NPM and specific immunological features of AML patients with NPM mutation are summarized.

The biological characteristics of transcription factors AP-2α and AP-2γ and their importance in various types of cancers

The Activator Protein 2 (AP-2) transcription factor (TF) family is vital for the regulation of gene expression during early development as well as carcinogenesis process. The review focusses on the AP-2α and AP-2γ proteins and their dualistic regulation of gene expression in the process of carcinogenesis. Both AP-2α and AP-2γ influence a wide range of physiological or pathological processes by regulating different pathways and interacting with diverse molecules, i.e. other proteins, long non-coding RNAs (lncRNA) or miRNAs. This review summarizes the newest information about the biology of two, AP-2α and AP-2γ, TFs in the carcinogenesis process. We emphasize that these two proteins could have either oncogenic or suppressive characteristics depending on the type of cancer tissue or their interaction with specific molecules. They have also been found to contribute to resistance and sensitivity to chemotherapy in oncological patients. A better understanding of molecular network of AP-2 factors and other molecules may clarify the atypical molecular mechanisms occurring during carcinogenesis, and may assist in the recognition of new diagnostic biomarkers.

Nucleophosmin/B23 is a negative regulator of estrogen receptor α expression via AP2γ in endometrial cancer cells

Endometrial cancers expressing estrogen and progesterone receptors respond to hormonal therapy. The disappearance of steroid hormone receptor expression is common in patients with recurrent disease, ultimately hampering the clinical utility of hormonal therapy. Here, we demonstrate for the first time that nucleophosmin (NPM1/B23) suppression can restore the expression of estrogen receptor α (ESR1/ERα) in endometrial cancer cells. Mechanistically, B23 and activator protein-2γ (TFAP2C/AP2γ) form a complex that acts as a transcriptional repressor of ERα. Our results indicate that B23 or AP2γ knockdown can restore ERα levels and activate ERα-regulated genes (e.g., cathepsin D, EBAG9, and TFF1/pS2). Moreover, AP2γ knockdown in a xenograft model sensitizes endometrial cancer cells to megesterol acetate through the upregulation of ERα expression. An increased immunohistochemical expression of AP2γ is an adverse prognostic factor in endometrial cancer. In summary, B23 and AP2γ may act in combination to suppress ERα expression in endometrial cancer cells. The inhibition of B23 or AP2γ can restore ERα expression and can serve as a potential strategy for sensitizing hormone-refractory endometrial cancers to endocrine therapy.

DNMT3B modulates the expression of cancer-related genes and downregulates the expression of the gene VAV3 via methylation

Altered promoter DNA methylation is one of the most important epigenetic abnormalities in human cancer. DNMT3B, de novo methyltransferase, is clearly related to abnormal methylation of tumour suppressor genes, DNA repair genes and its overexpression contributes to oncogenic processes and tumorigenesis in vivo. The purpose of this study was to assess the effect of the overexpression of DNMT3B in HaCaT cells on global gene expression and on the methylation of selected genes to the identification of genes that can be target of DNMT3B. We found that the overexpression of DNMT3B in HaCaT cells, modulate the expression of genes related to cancer, downregulated the expression of 151 genes with CpG islands and downregulated the expression of the VAV3 gene via methylation of its promoter. These results highlight the importance of DNMT3B in gene expression and human cancer.

Interactomic analysis of REST/NRSF and implications of its functional links with the transcription suppressor TRIM28 during neuronal differentiation

RE-1 silencing transcription factor (REST) is a transcriptional repressor that regulates gene expression by binding to repressor element 1. However, despite its critical function in physiology, little is known about its interaction proteins. Here we identified 204 REST-interacting proteins using affinity purification and mass spectrometry. The interactome included proteins associated with mRNA processing/splicing, chromatin organization, and transcription. The interactions of these REST-interacting proteins, which included TRIM28, were confirmed by co-immunoprecipitation and immunocytochemistry, respectively. Gene Ontology (GO) analysis revealed that neuronal differentiation-related GO terms were enriched among target genes that were co-regulated by REST and TRIM28, while the level of CTNND2 was increased by the knockdown of REST and TRIM28. Consistently, the level of CTNND2 increased while those of REST and TRIM28 decreased during neuronal differentiation in the primary neurons, suggesting that CTNND2 expression may be co-regulated by both. Furthermore, neurite outgrowth was increased by depletion of REST or TRIM28, implying that reduction of both REST and TRIM28 could promote neuronal differentiation via induction of CTNND2 expression. In conclusion, our study of REST reveals novel interacting proteins which could be a valuable resource for investigating unidentified functions of REST and also suggested functional links between REST and TRIM28 during neuronal development.

Epigenetic programming of Dnmt3a mediated by AP2α is required for granting preadipocyte the ability to differentiate

Adipogenesis has an important role in regulating energy homeostasis in mammals. 3T3-L1 preadipocytes have been widely used as an in vitro model for analyzing the molecular mechanism of adipogenesis. Previous reports indicated that the stage of contact inhibition (CI), through which the proliferating cells exit from the cell cycle, was required for granting preadipocyte the ability to differentiate. While this kind of the granting mechanism remains elusive. In the present study, we showed that DNA (cytosine-5) methyltransferase 3a (Dnmt3a) was upregulated at both the mRNA and protein level during the CI stage, and resulted in increasing promoter methylation of adipogenic genes. We further identified that the expression of Activator protein 2α (AP2α), a member of the transcription factor activator protein 2 (AP2) family, was highly correlated with the expression of Dnmt3a during the CI stage. In addition, we showed that AP2α transcriptionally upregulated Dnmt3a by directly binding to its proximal promoter region. Importantly, treatment of 3T3-L1 preadipocytes with AP2α-specific siRNAs inhibited the preadipocyte differentiation in a stage-dependent manner, supporting the conclusion that AP2α has an important role during the CI stage. Furthermore, overexpression of Dnmt3a partially rescued the impairment of adipogenesis induced by AP2α knockdown. Collectively, our findings reveal that AP2α is an essential regulator for granting preadipocyte the ability to differentiate through the upregulation of Dnmt3a expression during the CI stage.

RNA-dependent disassembly of nuclear bodies

Nuclear bodies are membraneless organelles that play important roles in genome functioning. A specific type of nuclear bodies known as interphase prenucleolar bodies (iPNBs) are formed in the nucleoplasm after hypotonic stress from partially disassembled nucleoli. iPNBs are then disassembled, and the nucleoli are reformed simultaneously. Here, we show that diffusion of B23 molecules (also known as nucleophosmin, NPM1) from iPNBs, but not fusion of iPNBs with the nucleoli, contributes to the transfer of B23 from iPNBs to the nucleoli. Maturation of pre-ribosomal RNAs (rRNAs) and the subsequent outflow of mature rRNAs from iPNBs led to the disassembly of iPNBs. We found that B23 transfer was dependent on the synthesis of pre-rRNA molecules in nucleoli; these pre-rRNA molecules interacted with B23 and led to its accumulation within nucleoli. The transfer of B23 between iPNBs and nucleoli was accomplished through a nucleoplasmic pool of B23, and increased nucleoplasmic B23 content retarded disassembly, whereas B23 depletion accelerated disassembly. Our results suggest that iPNB disassembly and nucleolus assembly might be coupled through RNA-dependent exchange of nucleolar proteins, creating a highly dynamic system with long-distance correlations between spatially distinct processes.

TFAP2C promotes lung tumorigenesis and aggressiveness through miR-183- and miR-33a-mediated cell cycle regulation

Non-small cell lung cancer (NSCLC) remains one of the leading causes of death worldwide, and thus new molecular targets need to be identified to improve treatment efficacy. Although epidermal growth factor receptor (EGFR)/KRAS mutation-driven lung tumorigenesis is well understood, the mechanism of EGFR/KRAS-independent signal activation remains elusive. Enhanced TFAP2C (transcription factor activating enhancer-binding protein 2C) expression is associated with poor prognosis in some types of cancer patients, but little is known of its relation with the pathogenesis of lung cancer. In the present study, we found that TFAP2C overexpression was associated with cell cycle activation and NSCLC cell tumorigenesis. Interestingly, TFAP2C blocked AKAP12-mediated cyclin D1 inhibition by inducing the overexpression of oncogenic microRNA (miRNA)-183 and simultaneously activated cyclin-dependent kinase 6-mediated cell cycle progression by downregulating tumor-suppressive miRNA-33a. In a mouse xenograft model, TFAP2C promoted lung tumorigenesis and disease aggressiveness via the miR-183 and miR-33a pathways. The study provides a mechanism of mitogenic and oncogenic signaling via two functionally opposed miRNAs and suggests that TFAP2C-induced cell cycle hyperactivation contributes to lung tumorigenesis.

Activation of DNA Damage Response Induced by the Kaposi's Sarcoma-Associated Herpes Virus

The human herpes virus 8 (HHV-8), also known as Kaposi sarcoma-associated herpes virus (KSHV), can infect endothelial cells often leading to cell transformation and to the development of tumors, namely Kaposi’s sarcoma (KS), primary effusion lymphoma (PEL), and the plasmablastic variant of multicentric Castleman’s disease. KSHV is prevalent in areas such as sub-Saharan Africa and the Mediterranean region presenting distinct genotypes, which appear to be associated with differences in disease manifestation, according to geographical areas. In infected cells, KSHV persists in a latent episomal form. However, in a limited number of cells, it undergoes spontaneous lytic reactivation to ensure the production of new virions. During both the latent and the lytic cycle, KSHV is programmed to express genes which selectively modulate the DNA damage response (DDR) through the activation of the ataxia telangiectasia mutated (ATM) pathway and by phosphorylating factors associated with the DDR, including the major tumor suppressor protein p53 tumor suppressor p53. This review will focus on the interplay between the KSHV and the DDR response pathway throughout the viral lifecycle, exploring the putative molecular mechanism/s that may contribute to malignant transformation of host cells.

NPM and BRG1 Mediate Transcriptional Resistance to Retinoic Acid in Acute Promyelocytic Leukemia

Perturbation in the transcriptional control of genes driving differentiation is an established paradigm whereby oncogenic fusion proteins promote leukemia. From a retinoic acid (RA)-sensitive acute promyelocytic leukemia (APL) cell line, we derived an RA-resistant clone characterized by a block in transcription initiation, despite maintaining wild-type PML/RARA expression. We uncovered an aberrant interaction among PML/RARA, nucleophosmin (NPM), and topoisomerase II beta (TOP2B). Surprisingly, RA stimulation in these cells results in enhanced chromatin association of the nucleosome remodeler BRG1. Inhibition of NPM or TOP2B abrogated BRG1 recruitment. Furthermore, NPM inhibition and targeting BRG1 restored differentiation when combined with RA. Here, we demonstrate a role for NPM and BRG1 in obstructing RA differentiation and implicate chromatin remodeling in mediating therapeutic resistance in malignancies. NPM mutations are the most common genetic change in patients with acute leukemia (AML); therefore, our model may be applicable to other more common leukemias driven by NPM.

Insights into the regulation of neuronal viability by nucleophosmin/B23

The vastness of the neuronal network that constitutes the human brain proves challenging when trying to understand its complexity. Furthermore, due to the senescent state they enter into upon maturation, neurons lack the ability to regenerate in the face of insult, injury or death. Consequently, their excessive death can be detrimental to the proper functioning of the brain. Therefore, elucidating the mechanisms regulating neuronal survival is, while challenging, of great importance as the incidence of neurological disease is becoming more prevalent in today's society. Nucleophosmin/B23 (NPM) is an abundant and ubiquitously expressed protein that regulates vital cellular processes such as ribosome biogenesis, cell proliferation and genomic stability. As a result, it is necessary for proper embryonic development, but has also been implicated in many cancers. While highly studied in the context of proliferative cells, there is a lack of understanding NPM's role in post-mitotic neurons. By exploring its role in healthy neurons as well as its function in the regulation of cell death and neurodegeneration, there can be a better understanding of how these diseases initiate and progress. Owing to what is thus far known about its function in the cell, NPM could be an attractive therapeutic target in the treatment of neurodegenerative diseases.

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

Suv39h1 mediates AP-2α-dependent inhibition of C/EBPα expression during adipogenesis

Previous studies have shown that CCAAT/enhancer-binding protein α (C/EBPα) plays a very important role during adipocyte terminal differentiation and that AP-2α (activator protein 2α) acts as a repressor to delay the expression of C/EBPα. However, the mechanisms by which AP-2α prevents the expression of C/EBPα are not fully understood. Here, we present evidence that Suv39h1, a histone H3 lysine 9 (H3K9)-specific trimethyltransferase, and G9a, a euchromatic methyltransferase, both interact with AP-2α and enhance AP-2α-mediated transcriptional repression of C/EBPα. Interestingly, we discovered that G9a mediates dimethylation of H3K9, thus providing the substrate, which is methylated by Suv39h1, to H3K9me3 on the C/EBPα promoter. The expression level of AP-2α was consistent with enrichment of H3K9me2 and H3K9me3 on the C/EBPα promoter in 3T3-L1 preadipocytes. Knockdown of Suv39h markedly increased C/EBPα expression and promoted adipogenesis. Conversely, ectopic expression of Suv39h1 delayed C/EBPα expression and impaired the accumulation of triglyceride, while simultaneous knockdown of AP-2α or G9a partially rescued this process. These findings indicate that Suv39h1 enhances AP-2α-mediated transcriptional repression of C/EBPα in an epigenetic manner and further inhibits adipocyte differentiation.

AP2α transcriptional activity is essential for retinoid-induced neuronal differentiation of mesenchymal stem cells

Pre-activation of the retinoid signaling pathway by all-trans retinoic acid facilitates neuronal differentiation of mesenchymal stem cells. Using protein/DNA based screening assays, we identified activator protein 2α as an important downstream target of all-trans retinoic acid. Although all-trans retinoic acid treatment significantly increased activator protein 2α transcriptional activity, it did not affect its expression. Inhibition of activator protein 2α with dominant-negative mutants reduced ATRA-induced differentiation of mesenchymal stem cells into neurons and reversed its associated functional recovery of memory impairment in the cell-based treatment of a hypoxic-ischemic brain damage rat model. Dominant-negative mutants of activator protein 2α inhibited the expression of neuronal markers which were induced by retinoic acid receptor β activation. All-trans retinoic acid treatment increased phosphorylation of activator protein 2α and resulted in its nuclear translocation. This was blocked by siRNA-mediated knockdown of retinoic acid receptor β. Furthermore, we found that retinoic acid receptor β directly interacted with activator protein 2α. In summary, the regulation of all-trans retinoic acid on activator protein 2α transcriptional activity was mediated by activation of retinoic acid receptor β and subsequent phosphorylation and nuclear translocation of activator protein 2α. Our results strongly suggest that activator protein 2α transcriptional activity is essential for all-trans retinoic acid-induced neuronal differentiation of mesenchymal stem cells.

Inhibition of neural crest formation by Kctd15 involves regulation of transcription factor AP-2

The neural crest develops in vertebrate embryos within a discrete domain at the neural plate boundary and eventually gives rise to a migrating population of cells that differentiate into a multitude of derivatives. We have shown that the broad-complex, tramtrack and bric a brac (BTB) domain-containing factor potassium channel tetramerization domain containing 15 (Kctd15) inhibits neural crest formation, and we proposed that its function is to delimit the neural crest domain. Here we report that Kctd15 is a highly effective inhibitor of transcription factor activating enhancer binding protein 2 (AP-2) in zebrafish embryos and in human cells; AP-2 is known to be critical for several steps of neural crest development. Kctd15 interacts with AP-2α but does not interfere with its nuclear localization or binding to cognate sites in the genome. Kctd15 binds specifically to the activation domain of AP-2α and efficiently inhibits transcriptional activation by a hybrid protein composed of the regulatory protein Gal4 DNA binding and AP-2α activation domains. Mutation of one proline residue in the activation domain to an alanine (P59A) yields a protein that is highly active but largely insensitive to Kctd15. These results indicate that Kctd15 acts in the embryo at least in part by specifically binding to the activation domain of AP-2α, thereby blocking the function of this critical factor in the neural crest induction hierarchy.

Manganese superoxide dismutase regulation and cancer

Mitochondria are the power plants of the eukaryotic cell and the integrators of many metabolic activities and signaling pathways important for the life and death of a cell. Normal aerobic cells use oxidative phosphorylation to generate ATP, which supplies energy for metabolism. To drive ATP production, electrons are passed along the electron transport chain, with some leaking as superoxide during the process. It is estimated that, during normal respiration, intramitochondrial superoxide concentrations can reach 10⁻¹² M. This extremely high level of endogenous superoxide production dictates that mitochondria are equipped with antioxidant systems that prevent consequential oxidative injury to mitochondria and maintain normal mitochondrial functions. The major antioxidant enzyme that scavenges superoxide anion radical in mitochondria is manganese superoxide dismutase (MnSOD). Extensive studies on MnSOD have demonstrated that MnSOD plays a critical role in the development and progression of cancer. Many human cancer cells harbor low levels of MnSOD proteins and enzymatic activity, whereas some cancer cells possess high levels of MnSOD expression and activity. This apparent variation in MnSOD level among cancer cells suggests that differential regulation of MnSOD exists in cancer cells and that this regulation may be linked to the type and stage of cancer development. This review summarizes current knowledge of the relationship between MnSOD levels and cancer with a focus on the mechanisms regulating MnSOD expression.

Effects of PPARγ Ligands on Leukemia

Peroxisome proliferator-activated receptors (PPARs) and retinoic acid receptors (RARs), members of the nuclear receptor superfamily, are transcription factors that regulate a variety of important cellular functions. PPARs form heterodimers retinoid X receptor (RXR), an obligate heterodimeric partner for other nuclear receptors. Several novel links between retinoid metabolism and PPAR responses have been identified, and activation of PPAR/RXR expression has been shown to increase response to retinoids. PPARγ has emerged as a key regulator of cell growth and survival, whose activity is modulated by a number of synthetic and natural ligands. While clinical trials in cancer patients with thiazolidinediones (TZD) have been disappointing, novel structurally different PPARγ ligands, including triterpenoids, have entered clinical arena as therapeutic agents for epithelial and hematopoietic malignancies. Here we shall review the antitumor advances of PPARγ, alone and in combination with RARα ligands in control of cell proliferation, differentiation, and apoptosis and their potential therapeutic applications in hematological malignancies.

Prognostic implications of genetic aberrations in acute myelogenous leukemia with normal cytogenetics

Acute myelogenous leukemia (AML) is a genetically heterogeneous disease in which somatic mutations, that disturb cellular growth, proliferation, and differentiation, accumulate in hematopoietic progenitor cells. Cytogenetic findings, at diagnosis, have been proven to be one of the most important prognostic indicators in AML. About half of the patients with AML are found to have "normal" cytogenetic analysis by standard culture techniques. These patients are considered as an intermediate risk group. Cytogenetically normal AML (CN-AML) is the largest cytogenetic risk group, and the variation in clinical outcome of patients in this group is greater than in any other cytogenetic group. Besides mutation testing, age and presenting white blood cell count are important predictors of overall survival, suggesting that other factors independent of cytogenetic abnormalities, contribute to the outcome of patients with AML. The expanding knowledge at the genetic and molecular levels is helping define several subgroups of patients with CN-AML with variable prognosis. In this review, we describe the clinical and prognostic characteristics of CN-AML patients as a group, as well as the various molecular and genetic aberrations detected in these patients and their clinical and prognostic implications.

Prognostic and therapeutic implications of minimal residual disease detection in acute myeloid leukemia

The choice of either induction or postremission therapy for adults with acute myeloid leukemia is still largely based on the "one size fits all" principle. Moreover, pretreatment prognostic parameters, especially chromosome and gene abnormalities, may fail in predicting individual patient outcome. Measurement of minimal residual disease (MRD) is nowadays recognized as a potential critical tool to assess the quality of response after chemotherapy and to plan postremission strategies that are, therefore, driven by the individual risk of relapse. PCR and multiparametric flow cytometry have become the most popular methods to investigate MRD because they have been established as sensitive and specific enough to allow MRD to be studied serially. In the present review, we examine the evidence supporting the appropriateness of incorporating MRD detection into the AML risk assessment process. A comprehensive prognostic algorithm, generated by combining pretreatment cytogenetics/genetics and posttreatment MRD determination, should promote advances in development of personalized therapeutic approaches.

Fine-tuning nucleophosmin in macrophage differentiation and activation

M-CSF-driven differentiation of peripheral blood monocytes is one of the sources of tissue macrophages. In humans and mice, the differentiation process involves the activation of caspases that cleave a limited number of proteins. One of these proteins is nucleophosmin (NPM1), a multifunctional and ubiquitous protein. Here, we show that caspases activated in monocytes exposed to M-CSF cleave NPM1 at D213 to generate a 30-kDa N-terminal fragment. The protein is further cleaved into a 20-kDa fragment, which involves cathepsin B. NPM1 fragments contribute to the limited motility, migration, and phagocytosis capabilities of resting macrophages. Their activation with lipopolysaccharides inhibits proteolytic processes and restores expression of the full-length protein that negatively regulates the transcription of genes encoding inflammatory cytokines (eg, NPM1 is recruited with NF-κB on the MCP1 gene promoter to decrease its transcription). In mice with heterozygous npm gene deletion, cytokine production in response to lipopolysaccharides, including CXCL1 (KC), MCP1, and MIP2, is dramatically enhanced. These results indicate a dual function of NPM1 in M-CSF-differentiated macrophages. Proteolysis of the protein participates in the establishment of a mature macrophage phenotype. In response to inflammatory stimuli, the full-length protein negatively regulates inflammatory cytokine production.

Acute myeloid leukemia with mutated nucleophosmin (NPM1): any hope for a targeted therapy?

Acute myeloid leukemia (AML) carrying nucleophosmin (NPM1) mutations displays distinct molecular and clinical-pathological features that led to its inclusion as provisional entity in 2008 WHO classification of myeloid neoplasms. Since NPM1 mutations behave as a founder genetic lesion in AML, they could be an attractive target for therapeutic intervention. Here, we discuss the potential for developing targeted therapies for NPM1-mutated AML with focus on: (i) interfering with the abnormal traffic of the NPM1 leukemic mutant, i.e., its cytoplasmic dislocation; (ii) disrupting the nucleolar structure/function by interfering with residual wild-type nucleophosmin and other nucleolar components acting as hub proteins; and (iii) evaluating the activity of epigenetic drugs (e.g., 5-azacytidine) or agents acting on differentiation and apoptosis. As quantitative assessment of NPM1 mutated transcript copies now provides the means to measure minimal residual disease, we also discuss the potential for intervening in NPM1-mutated AML before overt hematological relapse occurs (so-called pre-emptive therapy).

Nucleophosmin and its complex network: a possible therapeutic target in hematological diseases

Nucleophosmin (NPM, also known as B23, numatrin or NO38) is a ubiquitously expressed phosphoprotein belonging to the nucleoplasmin family of chaperones. NPM is mainly localized in the nucleolus where it exerts many of its functions, but a proportion of the protein continuously shuttles between the nucleus and the cytoplasm. A growing number of cellular proteins have been described as physical interactors of NPM, and consequently, NPM is thought to have a relevant role in diverse cellular functions, including ribosome biogenesis, centrosome duplication, DNA repair and response to stress. NPM has been implicated in the pathogenesis of several human malignancies and intriguingly, it has been described both as an activating oncogene and a tumor suppressor, depending on cell type and protein levels. In fact, increased NPM expression is associated with different types of solid tumors whereas an impairment of NPM function is characteristic of a subgroup of hematolologic malignancies. A large body of experimental evidence links the deregulation of specific NPM functions to cellular transformation, yet the molecular mechanisms through which NPM contributes to tumorigenesis remain elusive. In this review, we have summarized current knowledge concerning NPM functions, and attempted to interpret its multifaceted and sometimes apparently contradictory activities in the context of both normal cellular homeostasis and neoplastic transformation.

WDHD1 modulates the post-transcriptional step of the centromeric silencing pathway

The centromere is a highly specialized chromosomal element that is essential for chromosome segregation during mitosis. Centromere integrity must therefore be properly preserved and is strictly dependent upon the establishment and maintenance of surrounding chromatin structure. Here we identify WDHD1, a WD40-domain and HMG-domain containing protein, as a key regulator of centromere function. We show that WDHD1 associates with centromeres in a cell cycle-dependent manner, coinciding with mid-to-late S phase. WDHD1 down-regulation compromises HP1α localization to pericentric heterochromatin and leads to altered expression of epigenetic markers associated with this chromatin region. As a consequence, such reduced epigenetic silencing is manifested in disrupted heterochromatic state of the centromere and a defective mitosis. Moreover, we demonstrate that a possible underlying mechanism of WDHD1's involvement lies in the proper generation of the small non-coding RNAs encoded by the centromeric satellite repeats. This role is mediated at the post-transcriptional level and likely through stabilizing Dicer association with centromeric RNA. Collectively, these findings suggest that WDHD1 may be a critical component of the RNA-dependent epigenetic control mechanism that sustains centromere integrity and genomic stability.

The Multifunctional Nucleolar Protein Nucleophosmin/NPM/B23 and the Nucleoplasmin Family of Proteins

The nucleophosmin (NPM)/nucleoplasmin family of nuclear chaperones has three members: NPM1, NPM2, and NPM3. Nuclear chaperones serve to ensure proper assembly of nucleosomes and proper formation of higher order structures of chromatin. In fact, this family of proteins has such diverse functions in cellular processes such as chromatin remodeling, ribosome biogenesis, genome stability, centrosome replication, cell cycle, transcriptional regulation, apoptosis, and tumor suppression. Of the members of this family, NPM1 is the most studied and is the main focus of this review. NPM2 and NPM3 are less well characterized, and are also discussed wherever appropriate. The structure–function relationship of NPM proteins has largely been worked out. Other than the many processes in which NPM1 takes part, the major interest comes from its involvement in human cancers, particularly acute myeloid leukemia (AML). Its significance stems from the fact that AML with mutated NPM1 accounts for ∼30% of all AML cases and usually has good prognosis. Its clinical importance also comes from its involvement in virus replication, particularly in the era of outbreaks of infectious diseases.

Dephosphorylation of nucleophosmin by PP1β facilitates pRB binding and consequent E2F1-dependent DNA repair

We report a new pathway through which PP1β signals to nucleophosmin (NPM) in response to DNA damage. UV induces dephosphorylation of NPM at multiple sites, leading to enhancement of complex formation between NPM and retinoblastoma tumor suppressor protein and the subsequent upregulation of E2F1. Consequently, such signaling pathway potentiates the cellular DNA repair capacity.

Nucleophosmin (NPM) is an important phosphoprotein with pleiotropic functions in various cellular processes. Although phosphorylation has been postulated as an important functional determinant, possible regulatory roles of this modification on NPM are not fully characterized. Here, we find that NPM is dephosphorylated on various threonine residues (Thr199 and Thr234/237) in response to UV-induced DNA damage. Further experiments indicate that the serine/threonine protein phosphatase PP1β is a physiological NPM phosphatase under both the genotoxic stress and growth conditions. As a consequence, NPM in its hypophosphorylated state facilitates DNA repair. Finally, our results suggest that one possible mechanism of this protective response lies in enhanced NPM-retinoblastoma tumor suppressor protein (pRB) interaction, leading to the relief of the repressive pRB–E2F1 circuitry and the consequent transcriptional activation of E2F1 and several downstream DNA repair genes. Thus, this study unveils a key phosphatase of NPM and highlights a novel mechanism by which the PP1β–NPM pathway contributes to cellular DNA damage response.

NPM1/B23: A Multifunctional Chaperone in Ribosome Biogenesis and Chromatin Remodeling

At a first glance, ribosome biogenesis and chromatin remodeling are quite different processes, but they share a common problem involving interactions between charged nucleic acids and small basic proteins that may result in unwanted intracellular aggregations. The multifunctional nuclear acidic chaperone NPM1 (B23/nucleophosmin) is active in several stages of ribosome biogenesis, chromatin remodeling, and mitosis as well as in DNA repair, replication and transcription. In addition, NPM1 plays an important role in the Myc-ARF-p53 pathway as well as in SUMO regulation. However, the relative importance of NPM1 in these processes remains unclear. Provided herein is an update on the expanding list of the diverse activities and interacting partners of NPM1. Mechanisms of NPM1 nuclear export functions of NPM1 in the nucleolus and at the mitotic spindle are discussed in relation to tumor development. It is argued that the suggested function of NPM1 as a histone chaperone could explain several, but not all, of the effects observed in cells following changes in NPM1 expression. A future challenge is to understand how NPM1 is activated, recruited, and controlled to carry out its functions.

Nucleophosmin phosphorylation by v-cyclin-CDK6 controls KSHV latency

Nucleophosmin (NPM) is a multifunctional nuclear phosphoprotein and a histone chaperone implicated in chromatin organization and transcription control. Oncogenic Kaposi's sarcoma herpesvirus (KSHV) is the etiological agent of Kaposi's sarcoma, primary effusion lymphoma (PEL) and multicentric Castleman disease (MCD). In the infected host cell KSHV displays two modes of infection, the latency and productive viral replication phases, involving extensive viral DNA replication and gene expression. A sustained balance between latency and reactivation to the productive infection state is essential for viral persistence and KSHV pathogenesis. Our study demonstrates that the KSHV v-cyclin and cellular CDK6 kinase phosphorylate NPM on threonine 199 (Thr199) in de novo and naturally KSHV-infected cells and that NPM is phosphorylated to the same site in primary KS tumors. Furthermore, v-cyclin-mediated phosphorylation of NPM engages the interaction between NPM and the latency-associated nuclear antigen LANA, a KSHV-encoded repressor of viral lytic replication. Strikingly, depletion of NPM in PEL cells leads to viral reactivation, and production of new infectious virus particles. Moreover, the phosphorylation of NPM negatively correlates with the level of spontaneous viral reactivation in PEL cells. This work demonstrates that NPM is a critical regulator of KSHV latency via functional interactions with v-cyclin and LANA.

Latency is the predominant mode of viral persistence in KS and PEL tumors, and has a fundamental impact on KSHV tumorigenesis. Establishment and maintenance of latency involves a number of viral and cellular factors. This study provides a novel functional link between LANA and v-cyclin by showing that phosphorylation of nucleophosmin (NPM) by the v-cyclin-CDK6 kinase complex supports its interaction with LANA, and thus enables the transcriptional silencing of KSHV lytic genes needed for latency. These findings indicate that KSHV has evolved mechanisms to utilize host proteins for maintaining the latency, and underscores the role of NPM as a regulator of not only mammalian transcription but also of viral transcription. Taken together, our data suggests that a cellular protein, NPM, is a critical factor for the latency of this oncogenic human virus, and may thus represent an attractive novel target for intervention.

Tumor suppressor HLJ1 binds and functionally alters nucleophosmin via activating enhancer binding protein 2alpha complex formation

HLJ1, a member of the heat shock protein 40 chaperone family, is a newly identified tumor suppressor that has been implicated in tumorigenesis and metastasis in non-small cell lung cancer. However, the mechanism of HLJ1 action is presently obscure. In this study, we report that HLJ1 specifically interacts with the nuclear protein nucleophosmin (NPM1), forming a multiprotein complex that alters the nucleolar distribution and oligomerization state of NPM1. Enforced accumulation of NPM1 oligomers by overexpression in weakly invasive but high HLJ1-expressing cells induced the activity of signal transducer and activator of transcription 3 (STAT3) and increased cellular migration, invasiveness, and colony formation. Furthermore, silencing HLJ1 accelerated NPM1 oligomerization, inhibited the activity of transcription corepressor activating enhancer binding protein 2alpha (AP-2alpha), and increased the activities of matrix metalloproteinase-2 (MMP-2) and STAT3. Our findings suggest that HLJ1 switches the role of NPM1, which can act as tumor suppressor or oncogene, by modulating the oligomerization of NPM1 via HLJ1-NPM1 heterodimer formation and recruiting AP-2alpha to the MMP-2 promoter.

Regulation of E2F1-induced apoptosis by the nucleolar protein RRP1B

Regulation of the E2F family of transcription factors is important in control of cellular proliferation; dysregulation of the E2Fs is a hallmark of many cancers. One member of the E2F family, E2F1, also has the paradoxical ability to induce apoptosis; however, the mechanisms underlying this selectivity are not fully understood. We now identify a nucleolar protein, RRP1B, as an E2F1-specific transcriptional target. We characterize the RRP1B promoter and demonstrate its selective response to E2F1. Consistent with the activation of E2F1 activity upon DNA damage, RRP1B is induced by several DNA-damaging agents. Importantly, RRP1B is required for the expression of certain E2F1 proapoptotic target genes and the induction of apoptosis by DNA-damaging agents. This activity is mediated in part by complex formation between RRP1B and E2F1 on selective E2F1 target gene promoters. Interaction between RRP1B and E2F1 can be found inside the nucleolus and diffuse nucleoplasmic punctates. Thus, E2F1 makes use of its transcriptional target RRP1B to activate other genes directly involved in apoptosis. Our data also suggest an underappreciated role for nucleolar proteins in transcriptional regulation.

Induction of dystrophin Dp71 expression during neuronal differentiation: opposite roles of Sp1 and AP2alpha in Dp71 promoter activity

In this study, we delineated the molecular mechanisms that modulate Dp71 expression during neuronal differentiation, using the N1E-115 cell line. We demonstrated that Dp71 expression is up-regulated in response to cAMP-mediated neuronal differentiation of these cells, and that this induction is controlled at promoter level. Functional deletion analysis of the Dp71 promoter revealed that a 5'-flanking 159-bp DNA fragment that contains Sp1 and AP2 binding sites is necessary and sufficient for basal expression of this TATA-less promoter, as well as for its induction during neuronal differentiation. Electrophoretic mobility shift and chromatin immunoprecipitation assays revealed that Sp1 and AP2alpha bind to their respective DNA elements within the Dp71 basal promoter. Overall, mutagenesis assays on the Sp1 and AP2 binding sites, over-expression of Sp1 and AP2alpha, as well as knock-down experiments on Sp1 and AP2alpha gene expression established that Dp71 basal expression is controlled by the combined action of Sp1 and AP2alpha, which act as activator and repressor, respectively. Furthermore, we demonstrated that induction of Dp71 expression in differentiated cells is the result of the maintenance of positive regulation exerted by Sp1, as well as of the loss of AP2alpha binding, which ultimately releases the promoter from repression.

Role of nucleophosmin in acute myeloid leukemia

Nucleophosmin (NPM) is a nucleolar phosphoprotein implicated in the regulation of multiple cellular functions, which possesses both oncogenic and tumor-suppressor properties. Mutations of the NPM1 gene leading to the expression of a cytoplasmic mutant protein, NPMc+, are the most frequent genetic abnormalities found in acute myeloid leukemias. Acute myeloid leukemias with mutated NPM1 have distinct characteristics, including a significant association with a normal karyotype, involvement of different hematopoietic lineages, a specific gene-expression profile and clinically, a better response to induction therapy and a favorable prognosis. NPMc+ maintains the capacity of wild-type NPM to interact with a variety of cellular proteins, and impairs their activity by delocalizing them to the cytoplasm. In this review we summarize recent discoveries concerning NPM function, and discuss their possible impact on the pathogenesis of acute myeloid leukemias with mutated NPM1.

AP-2gamma promotes proliferation in breast tumour cells by direct repression of the CDKN1A gene

Overexpression of the activator protein (AP)-2gamma transcription factor in breast tumours has been identified as an independent predictor of poor outcome and failure of hormone therapy. To understand further the function of AP-2gamma in breast carcinoma, we have used an RNA interference and gene expression profiling strategy with the MCF-7 cell line as a model. Gene expression changes between control and silenced cells implicate AP-2gamma in the control of cell cycle progression and developmental signalling. A function for AP-2gamma in cell cycle control was verified using flow cytometry: AP-2gamma silencing led to a partial G1/S arrest and induction of the cyclin-dependent kinase inhibitor, p21cip/CDKN1A. Reporter and chromatin immunoprecipitation assays demonstrated a direct, functional interaction by AP-2gamma at the CDKN1A proximal promoter. AP-2gamma silencing coincided with acquisition of an active chromatin conformation at the CDKN1A locus and increased gene expression. These data provide a mechanism whereby AP-2gamma overexpression can promote breast epithelial proliferation and, coupled with previously published data, suggest how loss of oestrogen regulation of AP-2gamma may contribute to the failure of hormone therapy in patients.

AP-2alpha induces epigenetic silencing of tumor suppressive genes and microsatellite instability in head and neck squamous cell carcinoma

BACKGROUND

Activator protein 2 alpha (AP-2alpha) is involved in a variety of physiological processes. Increased AP-2alpha expression correlates with progression in various squamous cell carcinomas, and a recent publication found AP-2alpha to be overexpressed in approximately 70% of Head and Neck Squamous Cell Carcinoma (HNSCC) patient samples. It was found to repress transcription of the tumor suppressor gene C/CAAT Enhancer Binding Protein alpha (C/EBPalpha), and its binding site correlated with upstream methylation of the C/EBPalpha promoter. Therefore, we investigated the potential for AP-2alpha to target methylation to additional genes that would be relevant to HNSCC pathogenesis.

PRINCIPAL FINDINGS

Stable downregulation of AP-2alpha stable by shRNA in HNSCC cell lines correlated with decreased methylation of its target genes' regulatory regions. Furthermore, methylation of MLH1 in HNSCC with and without AP-2alpha downregulation revealed a correlation with microsatellite instability (MSI). ChIP analysis was used to confirm binding of AP-2alpha and HDAC1/2 to the targets. The effects of HDAC inhibition was assessed using Trichostatin A in a HNSCC cell line, which revealed that AP-2alpha targets methylation through HDAC recruitment.

CONCLUSIONS

These findings are significant because they suggest AP-2alpha plays a role not only in epigenetic silencing, but also in genomic instability. This intensifies the potential level of regulation AP-2alpha has through transcriptional regulation. Furthermore, these findings have the potential to revolutionize the field of HNSCC therapy, and more generally the field of epigenetic therapy, by targeting a single gene that is involved in the malignant transformation via disrupting DNA repair and cell cycle control.

The Myc-nucleophosmin-ARF network: a complex web unveiled

The multifunctional nucleolar proteins, nucleophosmin (NPM) and the tumor suppressor ARF, have been assigned numerous roles in diverse cellular processes impacting cellular proliferation, tumorigenesis and apoptosis. In addition, both proteins have been linked to the oncogenic function of c-Myc, a transcription factor that drives the majority of human cancers. Both proteins are induced by oncogenic c-Myc, but have opposing outcomes. Whereas loss of ARF accelerates c-Myc-induced tumorigenesis, NPM overexpression enhances c-Myc transformation. Accordingly, ARF expression is lost in many tumors, while NPM expression is elevated. Previously, we demonstrated that ARF interacts directly with c-Myc, leading to inhibition of its transforming activity while enhancing its apoptotic activity, independently of p53. We have recently shown that NPM also binds directly to c-Myc, but with opposite effects compared to ARF. NPM dramatically enhances the oncogenic activity of c-Myc, independently of ARF and p53. In tumor cells, the ARF-p53 pathway is often inactivated while NPM is elevated. However, when NPM and ARF are both expressed with oncogenic c-Myc the outcome of the interactions becomes more complex, since NPM and ARF also interact directly and NPM controls ARF localization. In this report we demonstrate that in the presence of ARF, NPM overexpression dramatically inhibits c-Myc-induced p53-independent apoptosis, while enhancing proliferation and transformation. We find that NPM sequesters ARF in nucleoli, blocking the relocalization of ARF to the nucleoplasm caused by activation of c-Myc. Therefore, the fate of a cell to undergo apoptosis or become transformed is dependent on this complex interacting network of oncogenic and tumor suppressor proteins.

Impact of new prognostic markers in treatment decisions in acute myeloid leukemia

PURPOSE OF REVIEW

In recent years, new molecular markers have emerged as significant prognostic parameters and as potential targets for molecularly targeted therapy in acute myeloid leukemia (AML). However, prognostic markers cannot guide the decision for a specific treatment, as they are associated with a differential outcome regardless of the given treatment. In contrast, predictive markers indicate a treatment benefit in patients that are characterized through these markers. Thus, predictive markers can guide clinical decision-making.

RECENT FINDINGS

In young adults, mutations of the nucleophosmin (gene 9NPM1) in the absence of concurrent FLT3-internal tandem duplication (ITD) (FLT3-ITD) have impressive prognostic and, beyond prognostication, predictive properties. This NPM1/FLT3-ITD genotype predicts equivalent favorable outcome after intensive chemotherapy and allogeneic stem cell transplantation, whereas in the absence of this marker clinical outcome was significantly improved after an allogeneic transplantation. In addition, within a retrospective study performed on older adults, the same genotype predicted a significantly improved outcome if all-trans retinoic acid was added to intensive chemotherapy.

SUMMARY

The discovery of new prognostic and predictive markers has increased our understanding of leukemogenesis and this may lead to improved prognostication and, more important, to novel genotype-specific treatment strategies.

Activator protein 2 alpha (AP2alpha) suppresses 42 kDa C/CAAT enhancer binding protein alpha (p42(C/EBPalpha)) in head and neck squamous cell carcinoma

The tumor suppressor C/CAAT enhancer binding protein alpha (C/EBPalpha) is a transcription factor involved in cell cycle control and cellular differentiation. A recent study showed that C/EBPalpha is frequently downregulated in head and neck squamous cell carcinoma (HNSCC) by DNA methylation in an upstream regulatory region. Here, we investigated how DNA methylation in the upstream regulatory region disrupts the transcriptional regulation of C/EBPalpha in HNSCC. The results reveal that aberrant methylation correlates with methyl binding domain protein binding and repressive histone modifications. This methylated region contains previously uninvestigated AP2alpha binding sites. AP2alpha suppresses C/EBPalpha promoter activity and protein expression. Interestingly, silencing AP2alpha by shRNA increases the antiproliferative isoform of C/EBPalpha (p42(C/EBPalpha)). Furthermore, growth analysis revealed that these 2 isoforms yield very different proliferative properties in HNSCC.

Gene mutations and response to treatment with all-trans retinoic acid in elderly patients with acute myeloid leukemia. Results from the AMLSG Trial AML HD98B

BACKGROUND

In a previous randomized trial, AML HD98B, we showed that administration of all-trans retinoic acid in addition to intensive chemotherapy improved the outcome of older patients with acute myeloid leukemia. The objectives of this study were to evaluate the prognostic impact of gene mutations and to identify predictive genetic factors for the all-trans retinoic acid treatment effect.

DESIGN AND METHODS

Data from mutation analyses of the NPM1, CEBPA, FLT3, and MLL genes were correlated with outcome in patients 61 years and older treated within the AML HD98B trial.

RESULTS

The frequencies of mutations were: NPM1, 23%; CEBPA, 8.5% (analysis restricted to patients with a normal karyotype); FLT3 internal tandem duplications (ITD), 17%; FLT3 tyrosine kinase domain mutations, 5%; and MLL partial tandem duplications, 4.5%. The genotype mutant NPM1 was positively and adverse cytogenetics as well as higher white blood cell count negatively correlated with achievement of complete remission. In Cox regression analysis, a significant interaction between the genotype mutant NPM1 without FLT3-ITD and treatment with all-trans retinoic acid was identified, in that the beneficial effect of all-trans retinoic acid on relapse-free and overall survival was restricted to this subgroup of patients. Other significant factors for survival were age, adverse cytogenetics, and logarithm of white cell count.

CONCLUSIONS

In elderly patients with acute myeloid leukemia, NPM1 mutations are associated with achievement of complete remission, and the genotype 'mutant NPM1 without FLT3-ITD' appears to be a predictive marker for response to all-trans retinoic acid given as an adjunct to intensive chemotherapy (ClinicalTrials.gov Identifier: NCT00151242).