Novel BTB/POZ domain zinc-finger protein, LRF, is a potential target of the LAZ-3/BCL-6 oncogene

C2H2 Zinc Finger Transcription Factors Associated with Hemoglobinopathies

In humans, specific aberrations in β-globin results in sickle cell disease and β-thalassemia, symptoms of which can be ameliorated by increased expression of fetal globin (HbF). Two recent CRISPR-Cas9 screens, centered on ∼1500 annotated sequence-specific DNA binding proteins and performed in a human erythroid cell line that expresses adult hemoglobin, uncovered four groups of candidate regulators of HbF gene expression. They are (1) members of the nucleosome remodeling and deacetylase (NuRD) complex proteins that are already known for HbF control; (2) seven C2H2 zinc finger (ZF) proteins, including some (ZBTB7A and BCL11A) already known for directly silencing the fetal γ-globin genes in adult human erythroid cells; (3) a few other transcription factors of different structural classes that might indirectly influence HbF gene expression; and (4) DNA methyltransferase 1 (DNMT1) that maintains the DNA methylation marks that attract the MBD2-associated NuRD complex to DNA as well as associated histone H3 lysine 9 methylation. Here we briefly discuss the effects of these regulators, particularly C2H2 ZFs, in inducing HbF expression for treating β-hemoglobin disorders, together with recent advances in developing safe and effective small-molecule therapeutics for the regulation of this well-conserved hemoglobin switch.

Structural basis for transcription factor ZBTB7A recognition of DNA and effects of ZBTB7A somatic mutations that occur in human acute myeloid leukemia

ZBTB7A belongs to a small family of transcription factors having three members in humans (7A, 7B, and 7C). They share a BTB/POZ protein interaction domain at the amino end and a zinc-finger DNA-binding domain at the carboxyl end. They control the transcription of a wide range of genes, having varied functions in hematopoiesis, oncogenesis, and metabolism (in particular glycolysis). ZBTB7A-binding profiles at gene promoters contain a consensus G(a/c)CCC motif, followed by a CCCC sequence in some instances. Structural and mutational investigations suggest that DNA-specific contacts with the four-finger tandem array of ZBTB7A are formed sequentially, initiated from ZF1-ZF2 binding to G(a/c)CCC before spreading to ZF3-ZF4, which bind the DNA backbone and the 3' CCCC sequence, respectively. Here, we studied some mutations found in t(8;21)-positive acute myeloid leukemia patients that occur within the ZBTB7A DNA-binding domain. We determined that these mutations generally impair ZBTB7A DNA binding, with the most severe disruptions resulting from mutations in ZF1 and ZF2, and the least from a frameshift mutation in ZF3 that results in partial mislocalization. Information provided here on ZBTB7A-DNA interactions is likely applicable to ZBTB7B/C, which have overlapping functions with ZBTB7A in controlling primary metabolism.

Impact of SNPs, off-targets, and passive permeability on efficacy of BCL6 degrading drugs assigned by virtual screening and 3D-QSAR approach

B-cell lymphoma 6 (BCL6) regulates various genes and is reported to be overexpressed in lymphomas and other malignancies. Thus, BCL6 inhibition or its tagging for degradation would be an amenable therapeutic approach. A library of 2500 approved drugs was employed to find BCL6 inhibitory molecules via virtual screening. Moreover, the 3D core structure of 170 BCL6 inhibitors was used to build a 3D QSAR model and predict the biological activity. The SNP database was analyzed to study the impact on the destabilization of BCL6/drug interactions. Structural similarity search and molecular docking analyses were used to assess the interaction between possible off-targets and BCL6 inhibitors. The tendency of drugs for passive membrane permeability was also analyzed. Lifitegrast (DB11611) had favorable binding properties and biological activity compared to the BI-3802. Missense SNPs were located at the essential interaction sites of the BCL6. Structural similarity search resulted in five BTB-domain containing off-target proteins. BI-3802 and Lifitegrast had similar chemical behavior and binding properties against off-target candidates. More interestingly, the binding affinity of BI-3802 (against off-targets) was higher than Lifitegrast. Energetically, Lifitegrast was less favorable for passive membrane permeability. The interaction between BCL6 and BI-3802 is more prone to SNP-derived variations. On the other hand, higher nonspecific binding of BI-3802 to off-target proteins could bring about higher undesirable properties. It should also be noted that energetically less desirable passive membrane translocation of Lifitegrast would demand drug delivery vehicles. However, further empirical evaluation of Lifitegrast would unveil its true potential.

Energy Trade-Off and Four Extreme Human Body Types

BACKGROUND

Resource trade-off theory suggests that increased performance on a given trait comes at the cost of decreased performance on other traits.

METHODS

Growth data from 1889 subjects (996 girls) were used from the GrowUp1974 Gothenburg study. Energy Trade-Off (ETO) between height and weight for individuals with extreme body types was characterized using a novel ETO-Score (ETOS). Four extreme body types were defined based on height and ETOI at early adulthood: tall-slender, short-stout, short-slender, and tall-stout; their growth trajectories assessed from ages 0.5-17.5 years.A GWAS using UK BioBank data was conducted to identify gene variants associated with height, BMI, and for the first time with ETOS.

RESULTS

Height and ETOS trajectories show a two-hit pattern with profound changes during early infancy and at puberty for tall-slender and short-stout body types.Several loci (including FTO, ADCY3, GDF5, ) and pathways were identified by GWAS as being highly associated with ETOS. The most strongly associated pathways were related to 'extracellular matrix', 'signal transduction', 'chromatin organization', and 'energy metabolism'.

CONCLUSIONS

ETOS represents a novel anthropometric trait with utility in describing body types. We discovered the multiple genomic loci and pathways probably involved in energy trade-off.

The transcription factor LRF promotes integrin β7 expression by and gut homing of CD8αα+ intraepithelial lymphocyte precursors

While T cell receptor (TCR) αβ+CD8α+CD8β- intraepithelial lymphocytes (CD8αα+ IELs) differentiate from thymic IEL precursors (IELps) and contribute to gut homeostasis, the transcriptional control of their development remains poorly understood. In the present study we showed that mouse thymocytes deficient for the transcription factor leukemia/lymphoma-related factor (LRF) failed to generate TCRαβ+CD8αα+ IELs and their CD8β-expressing counterparts, despite giving rise to thymus and spleen CD8αβ+ T cells. LRF-deficient IELps failed to migrate to the intestine and to protect against T cell-induced colitis, and had impaired expression of the gut-homing integrin α4β7. Single-cell RNA-sequencing found that LRF was necessary for the expression of genes characteristic of the most mature IELps, including Itgb7, encoding the β7 subunit of α4β7. Chromatin immunoprecipitation and gene-regulatory network analyses both defined Itgb7 as an LRF target. Our study identifies LRF as an essential transcriptional regulator of IELp maturation in the thymus and subsequent migration to the intestinal epithelium.

Heterozygous variants in ZBTB7A cause a neurodevelopmental disorder associated with symptomatic overgrowth of pharyngeal lymphoid tissue, macrocephaly, and elevated fetal hemoglobin

By clinical whole exome sequencing, we identified 12 individuals with ages 3 to 37 years, including three individuals from the same family, with a consistent phenotype of intellectual disability (ID), macrocephaly, and overgrowth of adenoid tissue. All 12 individuals harbored a rare heterozygous variant in ZBTB7A which encodes the transcription factor Zinc finger and BTB-domain containing protein 7A, known to play a role in lympho- and hematopoiesis. ID was generally mild. Fetal hemoglobin (HbF) fraction was elevated 2.2%-11.2% (reference value <2% in individuals > 6 months) in four of the five individuals for whom results were available. Ten of twelve individuals had undergone surgery at least once for lymphoid hypertrophy limited to the pharynx. In the most severely affected individual (individual 1), airway obstruction resulted in 17 surgical procedures before the age of 13 years. Sleep apnea was present in 8 of 10 individuals. In the nine unrelated individuals, ZBTB7A variants were novel and de novo. The six frameshift/nonsense and four missense variants were spread throughout the gene. This is the first report of a cohort of individuals with this novel syndromic neurodevelopmental disorder.

Physiological and Aberrant γ-Globin Transcription During Development

The expression of the fetal Gγ- and Aγ-globin genes in normal development is confined to the fetal period, where two γ-globin chains assemble with two α-globin chains to form α₂γ₂ tetramers (HbF). HbF sustains oxygen delivery to tissues until birth, when β-globin replaces γ-globin, leading to the formation of α₂β₂ tetramers (HbA). However, in different benign and pathological conditions, HbF is expressed in adult cells, as it happens in the hereditary persistence of fetal hemoglobin, in anemias and in some leukemias. The molecular basis of γ-globin differential expression in the fetus and of its inappropriate activation in adult cells is largely unknown, although in recent years, a few transcription factors involved in this process have been identified. The recent discovery that fetal cells can persist to adulthood and contribute to disease raises the possibility that postnatal γ-globin expression could, in some cases, represent the signature of the fetal cellular origin.

ZBTB7A functioned as an oncogene in colorectal cancer

Background

Despite zinc finger and BTB domain-containing 7A (ZBTB7A) documented importance in multiple tumors, the function and clinical value in Colorectal cancer (CRC) remain elusive. The aim of this study was to evaluate the functional roles and the clinical value of ZBTB7A in CRC progression.

Methods

The level of ZBTB7A was detected in a large cohort of CRC patients (n = 189) by immunohistochemistry (IHC), and we analyzed the diagnostic and prognostic value of the protein. In addition, the functional roles of ZBTB7A on CRC were explored in vitro and in vivo.

Results

Survival analyses indicated that patients with high ZBTB7A expression made the prognosis worse (P = 0.024). Functionally, knockdown of ZBTB7A could markedly inhibit tumor proliferation in vitro and in vivo, whereas ZBTB7A overexpression displayed the opposite results.

Conclusions

ZBTB7A was associated with poor survival outcomes and functioned as an oncogene in CRC patients, indicating that it is a potential prognostic biomarker and therapeutic target for CRC patients.

BTB/POZ zinc finger protein ZBTB16 inhibits breast cancer proliferation and metastasis through upregulating ZBTB28 and antagonizing BCL6/ZBTB27

Background

Breast cancer remains in urgent need of reliable diagnostic and prognostic markers. Zinc finger and BTB/POZ domain-containing family proteins (ZBTBs) are important transcription factors functioning as oncogenes or tumor suppressors. The role and regulation of ZBTB16 in breast cancer remain to be established.

Methods

Reverse-transcription PCR and methylation-specific PCR were applied to detect expression and methylation of ZBTB16 in breast cancer cell lines and tissues. The effects of ZBTB16 in breast cancer cells were examined via cell viability, CCK8, Transwell, colony formation, and flow cytometric assays. Xenografts and immunohistochemistry analyses were conducted to determine the effects of ZBTB16 on tumorigenesis in vivo. The specific mechanisms of ZBTB16 were further investigated using Western blot, qRT-PCR, luciferase assay, and co-IP.

Results

ZBTB16 was frequently downregulated in breast cancer cell lines in correlation with its promoter CpG methylation status. Restoration of ZBTB16 expression led to induction of G2/M phase arrest and apoptosis, inhibition of migration and invasion, reversal of EMT, and suppression of cell proliferation, both in vitro and in vivo. Furthermore, ectopically expressed ZBTB16 formed heterodimers with ZBTB28 or BCL6/ZBTB27 and exerted tumor suppressor effects through upregulation of ZBTB28 and antagonistic activity on BCL6.

Conclusions

Low expression of ZBTB16 is associated with its promoter hypermethylation and restoration of ZBTB16 inhibits tumorigenesis. ZBTB16 functions as a tumor suppressor through upregulating ZBTB28 and antagonizing BCL6. Our findings also support the possibility of ZBTB16 being a prognostic biomarker for breast cancer.

Emerging role of ZBTB7A as an oncogenic driver and transcriptional repressor

ZBTB7A is a member of the POK family of transcription factors that possesses a POZ-domain at the N-terminus and Krüppel-like zinc-finger at the c-terminus. ZBTB7A was initially isolated as a protein that binds to the inducer of the short transcript of HIV-1 virus TAT gene promoter. The protein forms a homodimer through protein-protein interaction via the N-terminus POZ-domains. ZBTB7A typically binds to the DNA elements through its zinc-finger domains and represses transcription both by modification of the chromatin organization and through the direct recruitment of transcription factors to gene regulatory regions. ZBTB7A is involved in several fundamental biological processes including cell proliferation, differentiation, and development. It also participates in hematopoiesis, adipogenesis, chondrogenesis, cellular metabolism and alternative splicing of BCLXL, DNA repair, development of oligodendrocytes, osteoclast and unfolded protein response. Aberrant ZBTB7A expression promotes oncogenic transformation and tumor progression, but also maintains a tumor suppressive role depending on the type and genetic context of cancer. In this comprehensive review we provide information about the structure, function, targets, and regulators of ZBTB7A and its role as an oncogenic driver and transcriptional repressor in various human diseases.

Knockdown of ZBTB7A inhibits cell proliferation of breast cancer through regulating the ubiquitination of estrogen receptor alpha

AIMS

ZBTB7A, a transcriptional repressor, accelerates the breast cancer progression. Over 70% of breast cancer samples are identified as ER-α positive. Due to the function of ZBTB7A in ER-α positive breast cancer incompletely known, we aimed to determine the role of ZBTB7A in ER-α positive cancer and explore the underlying mechanisms.

MAIN METHODS

In this study, the correlation between ZBTB7A and ER-α was confirmed by tissue microarray-based and TCGA database. Then, we explore if ZBTB7A maintains ER-α's level via targeting ER-α's expression or degradation. Finally, we examined the effect of ZBTB7A on the proliferation of breast cancer cells.

KEY FINDINGS

We further confirmed that ZBTB7A shows a significant positive correlation with ER-α in clinical breast cancer samples by tissue microarray-based analysis. Mechanically, we identified that the inhibition of ZBTB7A could upregulate E3 ligase TRIM25 leading to enhancement of ER-α ubiquitination and proteasomal degradation, which could partly explain the correlation between ZBTB7A and ER-α. Besides, we uncovered that ZBTB7A could also transcriptionally increase the expression of ER-α via indirectly binding to the region +146 to +461 bp downstream of the transcription start site of ESR1 (ERpro315) in breast cancer cells. Furthermore, ZBTB7A is found to stimulate the expression of ER-α's downstream genes, and promote the growth of estrogen receptor alpha (ER-α)-positive breast cancer cells.

SIGNIFICANCE

Our data revealed the novel mechanisms through which ZBTB7A manipulates ER-α level and might provide a new avenue for endocrine therapy in breast cancer.

Tumor suppressive BTB/POZ zinc-finger protein ZBTB28 inhibits oncogenic BCL6/ZBTB27 signaling to maintain p53 transcription in multiple carcinogenesis

Zinc-finger and BTB/POZ domain-containing family proteins (ZBTB) are important transcription factors functioning as tumor suppressors or oncogenes, such as BCL6/ZBTB27 as a key oncoprotein for anti-cancer therapy. Through epigenome study, we identified ZBTB28/BCL6B/BAZF, a BTB/POZ domain protein highly homologous to BCL6, as a methylated target in multiple tumors. However, the functions and mechanism of ZBTB28 in carcinogenesis remain unclear. Methods: ZBTB28 expression and methylation were examined by reverse-transcription PCR and methylation-specific PCR. The effects and mechanisms of ectopic ZBTB28 expression on tumor cells were assessed with molecular biological and cellular approaches in vitro and in vivo. Results: Albeit broadly expressed in multiple normal tissues, ZBTB28 is frequently downregulated in aero- and digestive carcinoma cell lines and primary tumors, and correlated with its promoter CpG methylation status. Further gain-of-function study showed that ZBTB28 functions as a tumor suppressor inhibiting carcinoma cell growth in vitro and in vivo, through inducing cell cycle arrest and apoptosis of tumor cells. ZBTB28 suppresses cell migration and invasion by reversing EMT and cell stemness. ZBTB28 transactivates TP53 expression, through binding to the p53 promoter in competition with BCL6, while BCL6 itself was also found to be a direct target repressed by ZBTB28. Conclusion: Our results demonstrate that ZBTB28 functions as a tumor suppressor through competing with BCL6 for targeting p53 regulation. This newly identified ZBTB28/BCL6/p53 regulatory axis provides further molecular insight into carcinogenesis mechanisms and has implications in further improving BCL6-based anticancer therapy.

ZBTB7 evokes 5-fluorouracil resistance in colorectal cancer through the NF‑κB signaling pathway

Zinc finger and BTB domain containing 7A (ZBTB7), a POZ/BTB and Krüppel erythroid myeloid oncogenic factor, is critical for the tumorigenicity and progression of various cancer types. ZBTB7 has been reported to promote the cell proliferation of colorectal cancers (CRC). However, the function of ZBTB7 to 5-fluorouracil (5‑FU) resistance has not yet been studied. In the current study, ZBTB7 expression and function in 5‑FU resistance in CRC were investigated using with multidisciplinary approaches, including western blot analysis, Transwell assay, CCK8 and a tumor xenograft model. Overexpression of ZBTB7 was increased the level of proteins associated with cell invasion and epithelial-mesenchymal transition. ZBTB7 inhibition attenuated the invasion and enhanced the apoptosis of CRC cells. IC50 values and cell viability were significantly reduced in cells with short hairpin RNA (shRNA)-mediated ZBTB7 depletion compared with the control group. 5‑FU administration decreased viability to a greater extent in the ZBTB7-shRNA group compared with the control, which was dose- and time-dependent. Analysis of gene expression omnibus data demonstrated that ZBTB7 mediated 5‑FU resistance, potentially through nuclear factor (NF)-κB signaling. NF‑κB inhibitor SN50 reversed ZBTB7-induced resistance in CRC. Collectively, the findings demonstrated that ZBTB7 mediated 5‑FU resistance in CRC cells through NF‑κB signaling. Thus, targeting ZBTB7 and NF‑κB signaling may be an effective strategy to reverse 5‑FU resistance in CRC.

Zbtb7a is a transducer for the control of promoter accessibility by NF-kappa B and multiple other transcription factors

Gene expression in eukaryotes is controlled by DNA sequences at promoter and enhancer regions, whose accessibility for binding by regulatory proteins dictates their specific patterns of activity. Here, we identify the protein Zbtb7a as a factor required for inducible changes in accessibility driven by transcription factors (TFs). We show that Zbtb7a binds to a significant fraction of genomic promoters and enhancers, encompassing many target genes of nuclear factor kappa B (NFκB) p65 and a variety of other TFs. While Zbtb7a binding is not alone sufficient to directly activate promoters, it is required to enable TF-dependent control of accessibility and normal gene expression. Using p65 as a model TF, we show that Zbtb7a associates with promoters independently of client TF binding. Moreover, the presence of prebound Zbtb7a can specify promoters that are amenable to TF-induced changes in accessibility. Therefore, Zbtb7a represents a widely used promoter factor that transduces signals from other TFs to enable control of accessibility and regulation of gene expression.

Gene activation is driven by the binding of regulatory proteins to the specific DNA sequences that control each gene. However, these sequences are not always accessible for binding in every type of cell, and so differences in their accessibility can underlie the range of cell types in which particular genes can be activated. Although several cellular processes can alter the accessibilities of these sequences, it is still often unclear how these processes are directed to act at specific genes. We have discovered that the protein Zbtb7a binds near numerous gene-regulatory sequences throughout the genome and that it enables other DNA-binding proteins to trigger changes in their accessibility and to activate nearby genes. However, unlike many other factors that control gene activation, the binding of Zbtb7a alone does not seem to be sufficient to switch on gene expression; instead, its function is required for activation of genes that are independently bound by a specific set of transcription factors (TFs), and it could therefore be considered to “transduce” their gene-regulatory activities. The implication of this is that the presence or absence of Zbtb7a at any gene in a particular cell type may represent one of the aspects that can determine whether that gene is able to be activated or not.

Zbtb7a induction in alveolar macrophages is implicated in anti-HLA-mediated lung allograft rejection

Chronic rejection significantly limits long-term success of solid organ transplantation. De novo donor-specific antibodies (DSAs) to mismatched donor human leukocyte antigen after human lung transplantation predispose lung grafts to chronic rejection. We sought to delineate mediators and mechanisms of DSA pathogenesis and to define early inflammatory events that trigger chronic rejection in lung transplant recipients and obliterative airway disease, a correlate of human chronic rejection, in mouse. Induction of transcription factor zinc finger and BTB domain containing protein 7a (Zbtb7a) was an early response critical in the DSA-induced chronic rejection. A cohort of human lung transplant recipients who developed DSA and chronic rejection demonstrated greater Zbtb7a expression long before clinical diagnosis of chronic rejection compared to nonrejecting lung transplant recipients with stable pulmonary function. Expression of DSA-induced Zbtb7a was restricted to alveolar macrophages (AMs), and selective disruption of Zbtb7a in AMs resulted in less bronchiolar occlusion, low immune responses to lung-restricted self-antigens, and high protection from chronic rejection in mice. Additionally, in an allogeneic cell transfer protocol, antigen presentation by AMs was Zbtb7a-dependent where AMs deficient in Zbtb7a failed to induce antibody and T cell responses. Collectively, we demonstrate that AMs play an essential role in antibody-induced pathogenesis of chronic rejection by regulating early inflammation and lung-restricted humoral and cellular autoimmunity.

Regulation of the Development and Function of B Cells by ZBTB Transcription Factors

The large ZBTB family comprises a diverse group of transcriptional factors. Several ZBTB proteins have emerged as critical factors that regulate the lineage commitment, differentiation, and function of lymphoid cells as well as many other developmental events. For instance, dysfunctions of ZBTB20 or ZBTB24 have been linked to multisystem failures in humans. Within the B-cell lineage, BCL6, ZBTB7A, ZBTB17, and ZBTB1 regulate the development/differentiation of B cells in both bone marrow and peripheral lymphoid organs, while ZBTB20 and ZBTB32 seem to mainly impact the maintenance of terminal plasma cells. Given the importance of B cells in the prevention and treatment of infectious or autoimmune disorders, we herein summarize the roles of seven ZBTB family members (BCL6, ZBTB7A, ZBTB17, ZBTB20, ZBTB32, ZBTB1, and ZBTB24) in the development, differentiation, and function of B cells as well as the underlying molecular mechanisms.

Recent progress in understanding and manipulating haemoglobin switching for the haemoglobinopathies

The major β-haemoglobinopathies, sickle cell disease and β-thalassaemia, represent the most common monogenic disorders worldwide and a steadily increasing global disease burden. Allogeneic haematopoietic stem cell transplantation, the only curative therapy, is only applied to a small minority of patients. Common clinical management strategies act mainly downstream of the root causes of disease. The observation that elevated fetal haemoglobin expression ameliorates these disorders has motivated longstanding investigations into the mechanisms of haemoglobin switching. Landmark studies over the last decade have led to the identification of two potent transcriptional repressors of γ-globin, BCL11A and ZBTB7A. These regulators act with additional trans-acting epigenetic repressive complexes, lineage-defining factors and developmental programs to silence fetal haemoglobin by working on cis-acting sequences at the globin gene loci. Rapidly advancing genetic technology is enabling researchers to probe deeply the interplay between the molecular players required for γ-globin (HBG1/HBG2) silencing. Gene therapies may enable permanent cures with autologous modified haematopoietic stem cells that generate persistent fetal haemoglobin expression. Ultimately rational small molecule pharmacotherapies to reactivate HbF could extend benefits widely to patients.

Upregulation of ZBTB7A exhibits a tumor suppressive role in gastric cancer cells

Gastric cancer presents as a complex solid tumor and is the third leading cause of global cancer‑associated mortality. The genetic alterations in gastric cancer remain unclear and deserve further investigation. Mining The Cancer Genome Atlas gastric adenocarcinoma dataset identified a frequent loss of the zinc finger and BTB domain containing 7A (ZBTB7A) gene locus and a significant correlation between low ZBTB7A expression and poor patient survival. ZBTB7A belongs to the POZ/BTB and Kruppel transcription factor family. In the present study, overexpression of ZBTB7A in a gastric cancer cell line induced cell cycle arrest at the S phase. Upregulation of ZBTB7A also promoted apoptosis and repressed cell migration. The results of the present study indicated that ZBTB7A functions as a tumor suppressor in gastric cancer cells. Understanding the role of ZBTB7A in gastric cancer may provide important clinical insight for treatment.

MicroRNA-137 represses FBI-1 to inhibit proliferation and in vitro invasion and migration of hepatocellular carcinoma cells

The pro-oncogene factor that binds to inducer of short transcripts-1 (FBI-1), which is encoded by ZBTB7A gene and belongs to POK (POZ/BTB and KrÜppel) protein family, has been shown to enhance hepatocellular carcinoma (HCC) cells proliferation and multi-drug resistance (MDR) process. However, the possibility that FBI-1 is a therapeutic target for further HCC treatment remains poorly determined. In the current study, two microRNA (miRNA) target prediction programs (TargetScan and MiRanda) were used to identify miR-137 as a potential regulator of FBI-1. Our results showed that expression of miR-137 was downregulated, while FBI-1 was upregulated in clinical HCC specimens, compared with paired non-tumor specimens. Overexpression of miR-137 via adenoviral vector inhibited the proliferation and anchorage-independent growth of HCC cells, HepG2 and MHCC-97H. Our data also showed that miR-137 repressed endogenous expression level of FBI-1, as well as Notch-1 and Survivin. MiR-137 also inhibited in vitro invasion and migration of HCC cells and attenuated their epithelial-mesenchymal transition (EMT) process. Moreover, miR-137 suppressed the growth rate of HepG2 cells in nude mice model. Overexpression of miR-137 via its adenoviral vector enhanced the sensitivity of HepG2 cells to anti-tumor drugs and attenuated the MDR process of a resistance cell line HepG2/adriamycin (ADR). Thus, FBI-1 downregulation mediated by miR-137 overexpression may be a potential strategy for HCC treatment.

Regulation of hematopoietic development by ZBTB transcription factors

Hematopoietic development is governed by the coordinated expression of lineage- and differentiation stage-specific genes. Transcription factors play major roles in this process and their perturbation may underlie hematologic and immunologic disorders. Nearly 1900 transcription factors are encoded in the human genome: of these, 49 BTB (for broad-complex, tram-track and bric à brac)-zinc finger transcription factors referred to as ZBTB or POK proteins have been identified. ZBTB proteins, including BCL6, PLZF, ThPOK and LRF, exhibit a broad spectrum of functions in normal and malignant hematopoiesis. This review summarizes developmental and molecular functions of ZBTB proteins relevant to hematology.

LRF maintains genome integrity by regulating the non-homologous end joining pathway of DNA repair

Leukemia/lymphoma-related factor (LRF) is a POZ/BTB and Krüppel (POK) transcriptional repressor characterized by context-dependent key roles in cell fate decision and tumorigenesis. Here we demonstrate an unexpected transcription-independent function for LRF in the classical non-homologous end joining (cNHEJ) pathway of double-strand break (DSB) repair. We find that LRF loss in cell lines and mouse tissues results in defective cNHEJ, genomic instability and hypersensitivity to ionizing radiation. Mechanistically, we show that LRF binds and stabilizes DNA-PKcs on DSBs, in turn favouring DNA-PK activity. Importantly, LRF loss restores ionizing radiation sensitivity to p53 null cells, making LRF an attractive biomarker to direct p53-null LRF-deficient tumours towards therapeutic treatments based on genotoxic agents or PARP inhibitors following a synthetic lethal strategy.

LRF maintains genome integrity by regulating the non-homologous end joining pathway of DNA repair

Leukemia/lymphoma-related factor (LRF) is a POZ/BTB and Krüppel (POK) transcriptional repressor characterized by context-dependent key roles in cell fate decision and tumorigenesis. Here we demonstrate an unexpected transcription-independent function for LRF in the classical non-homologous end joining (cNHEJ) pathway of double-strand break (DSB) repair. We find that LRF loss in cell lines and mouse tissues results in defective cNHEJ, genomic instability and hypersensitivity to ionizing radiation. Mechanistically, we show that LRF binds and stabilizes DNA-PKcs on DSBs, in turn favouring DNA-PK activity. Importantly, LRF loss restores ionizing radiation sensitivity to p53 null cells, making LRF an attractive biomarker to direct p53-null LRF-deficient tumours towards therapeutic treatments based on genotoxic agents or PARP inhibitors following a synthetic lethal strategy.

LRF maintains genome integrity by regulating the non-homologous end joining pathway of DNA repair

Leukemia/lymphoma-related factor (LRF) is a POZ/BTB and Krüppel (POK) transcriptional repressor characterized by context-dependent key roles in cell fate decision and tumorigenesis. Here we demonstrate an unexpected transcription-independent function for LRF in the classical non-homologous end joining (cNHEJ) pathway of double-strand break (DSB) repair. We find that LRF loss in cell lines and mouse tissues results in defective cNHEJ, genomic instability and hypersensitivity to ionizing radiation. Mechanistically, we show that LRF binds and stabilizes DNA-PKcs on DSBs, in turn favouring DNA-PK activity. Importantly, LRF loss restores ionizing radiation sensitivity to p53 null cells, making LRF an attractive biomarker to direct p53-null LRF-deficient tumours towards therapeutic treatments based on genotoxic agents or PARP inhibitors following a synthetic lethal strategy.

LRF maintains genome integrity by regulating the non-homologous end joining pathway of DNA repair

Leukemia/lymphoma-related factor (LRF) is a POZ/BTB and Krüppel (POK) transcriptional repressor characterized by context-dependent key roles in cell fate decision and tumorigenesis. Here we demonstrate an unexpected transcription-independent function for LRF in the classical non-homologous end joining (cNHEJ) pathway of double-strand break (DSB) repair. We find that LRF loss in cell lines and mouse tissues results in defective cNHEJ, genomic instability and hypersensitivity to ionizing radiation. Mechanistically, we show that LRF binds and stabilizes DNA-PKcs on DSBs, in turn favouring DNA-PK activity. Importantly, LRF loss restores ionizing radiation sensitivity to p53 null cells, making LRF an attractive biomarker to direct p53-null LRF-deficient tumours towards therapeutic treatments based on genotoxic agents or PARP inhibitors following a synthetic lethal strategy.

LRF maintains genome integrity by regulating the non-homologous end joining pathway of DNA repair

Leukemia/lymphoma-related factor (LRF) is a POZ/BTB and Krüppel (POK) transcriptional repressor characterized by context-dependent key roles in cell fate decision and tumorigenesis. Here we demonstrate an unexpected transcription-independent function for LRF in the classical non-homologous end joining (cNHEJ) pathway of double-strand break (DSB) repair. We find that LRF loss in cell lines and mouse tissues results in defective cNHEJ, genomic instability and hypersensitivity to ionizing radiation. Mechanistically, we show that LRF binds and stabilizes DNA-PKcs on DSBs, in turn favouring DNA-PK activity. Importantly, LRF loss restores ionizing radiation sensitivity to p53 null cells, making LRF an attractive biomarker to direct p53-null LRF-deficient tumours towards therapeutic treatments based on genotoxic agents or PARP inhibitors following a synthetic lethal strategy.

LRF maintains genome integrity by regulating the non-homologous end joining pathway of DNA repair

Leukemia/lymphoma-related factor (LRF) is a POZ/BTB and Krüppel (POK) transcriptional repressor characterized by context-dependent key roles in cell fate decision and tumorigenesis. Here we demonstrate an unexpected transcription-independent function for LRF in the classical non-homologous end joining (cNHEJ) pathway of double-strand break (DSB) repair. We find that LRF loss in cell lines and mouse tissues results in defective cNHEJ, genomic instability and hypersensitivity to ionizing radiation. Mechanistically, we show that LRF binds and stabilizes DNA-PKcs on DSBs, in turn favouring DNA-PK activity. Importantly, LRF loss restores ionizing radiation sensitivity to p53 null cells, making LRF an attractive biomarker to direct p53-null LRF-deficient tumours towards therapeutic treatments based on genotoxic agents or PARP inhibitors following a synthetic lethal strategy.

LRF maintains genome integrity by regulating the non-homologous end joining pathway of DNA repair

Leukemia/lymphoma-related factor (LRF) is a POZ/BTB and Krüppel (POK) transcriptional repressor characterized by context-dependent key roles in cell fate decision and tumorigenesis. Here we demonstrate an unexpected transcription-independent function for LRF in the classical non-homologous end joining (cNHEJ) pathway of double-strand break (DSB) repair. We find that LRF loss in cell lines and mouse tissues results in defective cNHEJ, genomic instability and hypersensitivity to ionizing radiation. Mechanistically, we show that LRF binds and stabilizes DNA-PKcs on DSBs, in turn favouring DNA-PK activity. Importantly, LRF loss restores ionizing radiation sensitivity to p53 null cells, making LRF an attractive biomarker to direct p53-null LRF-deficient tumours towards therapeutic treatments based on genotoxic agents or PARP inhibitors following a synthetic lethal strategy.

LRF maintains genome integrity by regulating the non-homologous end joining pathway of DNA repair

Leukemia/lymphoma-related factor (LRF) is a POZ/BTB and Krüppel (POK) transcriptional repressor characterized by context-dependent key roles in cell fate decision and tumorigenesis. Here we demonstrate an unexpected transcription-independent function for LRF in the classical non-homologous end joining (cNHEJ) pathway of double-strand break (DSB) repair. We find that LRF loss in cell lines and mouse tissues results in defective cNHEJ, genomic instability and hypersensitivity to ionizing radiation. Mechanistically, we show that LRF binds and stabilizes DNA-PKcs on DSBs, in turn favouring DNA-PK activity. Importantly, LRF loss restores ionizing radiation sensitivity to p53 null cells, making LRF an attractive biomarker to direct p53-null LRF-deficient tumours towards therapeutic treatments based on genotoxic agents or PARP inhibitors following a synthetic lethal strategy.

Expression of the Pokemon proto-oncogene in nasopharyngeal carcinoma cell lines and tissues

To study the differentiated expression of the proto-oncogene Pokemon in nasopharyngeal carcinoma (NPC) cell lines and tissues, mRNA and protein expression levels of CNE1, CNE2, CNE3 and C666-1 were detected separately by reverse transcription polymerase chain reaction (RT-PCR), real-time PCR and Western-blotting. The immortalized nasopharyngeal epithelial cell line NP69 was used as a control. The Pokemon protein expression level in biopsy specimens from chronic rhinitis patients and undifferentiated non keratinizing NPC patients was determined by Western-blotting and arranged from high to low: C666-1>CNE1>CNE2> CNE3>NP69. The Pokemon mRNA expression level was also arranged from high to low: CNE1>CNE2>NP69>C666-1>CNE3. Pokemon expression of NP69 and C666-1 obviously varied from mRNA to protein. The Pokemon protein level of NPC biopsy specimens was obviously higher than in chronic rhinitis. The data suggest that high Pokemon protein expression is closely associated with undifferentiated non-keratinizing NPC and may provide useful information for NPC molecular target therapy.

A ThPOK-LRF transcriptional node maintains the integrity and effector potential of post-thymic CD4+ T cells

The transcription factor ThPOK promotes CD4⁺ T cell differentiation in the thymus. Here, using a mouse strain that allows post-thymic gene deletion, we show that ThPOK maintains CD4⁺ T lineage integrity and couples effector differentiation to environmental cues after antigenic stimulation. ThPOK preserved the integrity and amplitude of effector responses, and was required for proper T_H1 and T_H2 differentiation in vivo by restraining the expression and function of the transcriptional regulator of cytotoxic T cell differentiation, Runx3. The transcription factor LRF contributed in a redundant manner with ThPOK to prevent the trans-differentiation of mature CD4⁺ T cells into CD8⁺ T cells. As such, the ThPOK-LRF transcriptional module was essential for CD4⁺ T cell integrity and responses.

Utility of LRF/Pokemon and NOTCH1 protein expression in the distinction between nodular lymphocyte-predominant Hodgkin lymphoma and classical Hodgkin lymphoma

Classical Hodgkin lymphoma (CHL) and nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) are considered separate entities with different prognosis and treatment. However, morphologic features can be similar and immunohistochemical studies are essential in the distinction; thus, determination of additional biomarkers is of utmost importance. LRF/Pokemon is a proto-oncogene, an interacting partner co-expressed with BCL6 in germinal centers and highly expressed in diffuse large B-cell lymphoma and follicular lymphoma. Conversely, loss of the LRF gene in mouse hematopoietic stem cells results in complete block of early B cell development with concomitant Notch de-repression, indicating its critical role in B versus T cell fate decision at the hematopoietic stem cell stage. For the first time, we show that LRF/Pokemon is predominantly expressed in NLPHL cases as is BCL6 with low to absent NOTCH1 protein expression; while Hodgkin Reed-Sternberg (HRS) cells in CHL show low to absent BCL6 and LRF/Pokemon expression with higher NOTCH1 expression. We illustrate a potential functional interaction between LRF and BCL6 in NLPHL pathogenesis, and differential expression of LRF/Pokemon and NOTCH1 proteins in CHL thus showing differential expression, making for an additional diagnostic marker and therapeutic target.

microRNA 21-mediated suppression of Sprouty1 by Pokemon affects liver cancer cell growth and proliferation

Transcriptional repressor Pokemon is a critical factor in embryogenesis, development, cell proliferation, differentiation, and oncogenesis, thus behaving as an oncogene. Oncomine database suggests a potential correlation between the expressions of Pokemon and Sprouty1. This study investigated the regulatory role of Pokemon in Sprouty1 expression and the effect on liver cancer cell growth and proliferation, revealing a novel miR-21-mediated regulatory circuit. In normal (HL-7702) and cancer (QGY-7703) liver cell lines, Sprouty1 expression is inversely correlated with Pokemon levels. Targeted expression or siRNA-mediated silencing showed that Pokemon is a repressor of Sprouty1 expression at both mRNA and protein levels, but Pokemon cannot affect the promoter activity of Sprouty1. Sprouty1 is a target of miR-21 and interestingly, we found that miR-21 is up-regulated by Pokemon in liver cancer cells. Luciferase reporter assays showed that Pokemon up-regulated miR-21 transcription in a dose-dependent manner, and ChIP assay exhibited a direct binding of Pokemon to the miR-21 promoter at -747 to -399 bp. Site-directed mutagenesis of the GC boxes at -684 to -679 bp and -652 to -647 bp of miR-21 promoter abolished the regulatory activity by Pokemon. Furthermore, we found that the modulation of Pokemon and miR-21 expression affected the growth and proliferation of liver cancer cells QGY-7703. In summary, our findings demonstrate that Pokemon suppresses Sprouty1 expression through a miR-21-mediated mechanism, affecting the growth and proliferation of liver cancer cells. This study recognized miR-21 and Sprouty1 as novel targets of the Pokemon regulatory network.

The Oncogene LRF Stimulates Proliferation of Mesenchymal Stem Cells and Inhibits Their Chondrogenic Differentiation

OBJECTIVE

The oncogene leukemia/lymphoma-related factor (LRF) enhances chondrosarcoma proliferation and malignancy. This study aimed to investigate the roles of LRF in chondrogenic differentiation of primary human bone marrow-derived mesenchymal stem cells (BMSCs).

DESIGN

LRF was overexpressed in BMSC by lentiviral transduction. Chondrogenic differentiation of BMSC was induced by high-density pellet culture. Western blotting and real-time polymerase chain reaction were used to investigate changes in protein and mRNA levels, respectively, during chondrogenesis. Safranin-O staining, immunohistochemistry, and glycoaminoglycan contents were used to assess cartilage matrix deposition. BMSC proliferation was determined by mitochondrial dehydrogenase activity and cell counting. Cell cycle profiling was performed by flow cytometry.

RESULTS

LRF overexpression effectively inhibited protein and mRNA expression of chondrocyte markers and cartilage matrix deposition during chondrogenesis of BMSC. Endogenous LRF expression was constitutively high in undifferentiated BMSC but remained low in primary articular chondrocytes. Endogenous LRF protein was downregulated in a time-dependent manner during chondrogenesis. BMSCs overexpressing LRF had higher proliferation rates and cell population in the S phase. LRF suppressed p53 expression during chondrogenesis and this might prevent differentiating chondrocytes from entering a quiescent state.

CONCLUSION

Our data showed that LRF is important for stimulating stem cell proliferation and cell cycle progression. It is known that LRF is highly expressed in the mouse limb buds prior to overt chondrogenesis; thus, LRF might function to prevent premature chondrogenic differentiation of stem cells.

Knockdown of Pokemon protein expression inhibits hepatocellular carcinoma cell proliferation by suppression of AKT activity

Overexpression of Pokemon, which is an erythroid myeloid ontogenic factor protein, occurs in different cancers, including hepatocellular carcinoma (HCC). Pokemon is also reported to have an oncogenic activity in various human cancers. This study investigated the effect of Pokemon knockdown on the regulation of HCC growth. POK shRNA suppressed the expression of Pokemon protein in HepG2 cells compared to the negative control vector-transfected HCC cells. Pokemon knockdown also reduced HCC cell viability and enhanced cisplatin-induced apoptosis in HCC cells. AKT activation and the expression of various cell cycle-related genes were inhibited following Pokemon knockdown. These data demonstrate that Pokemon may play a role in HCC progression, suggesting that inhibition of Pokemon expression using Pokemon shRNA should be further evaluated as a novel target for the control of HCC.

Silencing of Pokemon enhances caspase-dependent apoptosis via fas- and mitochondria-mediated pathways in hepatocellular carcinoma cells

The role of Pokemon (POK erythroid myeloid ontogenic actor), a recently identified POK transcription factor with proto-oncogenic activity, in hepatocellular carcinogenesis has only been assessed by a few studies. Our previous study revealed that Pokemon is overexpressed in hepatocellular carcinomas (HCC) and promotes HCC cell proliferation and migration via an AKT- and ERK- dependent manner. In the present study, we used the TUNEL assay and FACS analysis to demonstrate that oxaliplatin induced apoptosis was significantly increased in cells with silenced Pokemon. Western blots showed that p53 expression and phosphorylation were significantly increased in Pokemon defective cells, thereby initiating the mitochondria-mediated and death receptor-mediated apoptotic pathways. In the mitochondria-mediated pathway, expression of pro-apoptotic Bcl-2 family members (including Bad, Bid, Bim and Puma) as well as AIF was increased and decreasing the mitochondrial membrane potential resulted in cytochrome C released from mitochondrial in HepG2 si-Pokemon cells. In addition, upon oxaliplatin treatment of Pokemon-silenced cells, the FAS receptor, FADD and their downstream targets caspase-10 and caspase-8 were activated, causing increased release of caspase-8 active fragments p18 and p10. Increased activated caspase-8-mediated cleavage and activation of downstream effector caspases such as caspase-9 and caspase-3 was observed in HepG2 si-Pokemon cells as compared to control. Therefore, Pokemon might serve as an important mediator of crosstalk between intrinsic and extrinsic apoptotic pathways in HCC cells. Moreover, our findings suggest that Pokemon could be an attractive therapeutic target gene for human cancer therapy.

Zbtb7a suppresses prostate cancer through repression of a Sox9-dependent pathway for cellular senescence bypass and tumor invasion

Lrf has been previously described as a powerful proto-oncogene. Here we surprisingly demonstrate that Lrf plays a critical oncosuppressive role in the prostate. Prostate specific inactivation of Lrf leads to a dramatic acceleration of Pten-loss-driven prostate tumorigenesis through a bypass of Pten-loss-induced senescence (PICS). We show that LRF physically interacts with and functionally antagonizes SOX9 transcriptional activity on key target genes such as MIA, which is involved in tumor cell invasion, and H19, a long non-coding RNA precursor for an Rb-targeting miRNA. Inactivation of Lrf in vivo leads to Rb down-regulation, PICS bypass and invasive prostate cancer. Importantly, we found that LRF is genetically lost, as well as down-regulated at both the mRNA and protein levels in a subset of human advanced prostate cancers. Thus, we identify LRF as a context-dependent cancer gene that can act as an oncogene in some contexts but also displays oncosuppressive-like activity in Pten^−/− tumors.

The proto-oncoprotein FBI-1 interacts with MBD3 to recruit the Mi-2/NuRD-HDAC complex and BCoR and to silence p21WAF/CDKN1A by DNA methylation

The tumour-suppressor gene CDKN1A (encoding p21Waf/Cip1) is thought to be epigenetically repressed in cancer cells. FBI-1 (ZBTB7A) is a proto-oncogenic transcription factor repressing the alternative reading frame and p21WAF/CDKN1A genes of the p53 pathway. FBI-1 interacts directly with MBD3 (methyl-CpG–binding domain protein 3) in the nucleus. We demonstrated that FBI-1 binds both non-methylated and methylated DNA and that MBD3 is recruited to the CDKN1A promoter through its interaction with FBI-1, where it enhances transcriptional repression by FBI-1. FBI-1 also interacts with the co-repressors nuclear receptor corepressor (NCoR), silencing mediator for retinoid and thyroid receptors (SMRT) and BCL-6 corepressor (BCoR) to repress transcription. MBD3 regulates a molecular interaction between the co-repressor and FBI-1. MBD3 decreases the interaction between FBI-1 and NCoR/SMRT but increases the interaction between FBI-1 and BCoR. Because MBD3 is a subunit of the Mi-2 autoantigen (Mi-2)/nucleosome remodelling and histone deacetylase (NuRD)-HDAC complex, FBI-1 recruits the Mi-2/NuRD-HDAC complex via MBD3. BCoR interacts with the Mi-2/NuRD-HDAC complex, DNMTs and HP1. MBD3 and BCoR play a significant role in the recruitment of the Mi-2/NuRD-HDAC complex– and the NuRD complex–associated proteins, DNMTs and HP. By recruiting DNMTs and HP1, Mi-2/NuRD-HDAC complex appears to play key roles in epigenetic repression of CDKN1A by DNA methylation.

Role of LRF/Pokemon in lineage fate decisions

In the human genome, 43 different genes are found that encode proteins belonging to the family of the POK (poxvirus and zinc finger and Krüppel)/ZBTB (zinc finger and broad complex, tramtrack, and bric à brac) factors. Generally considered transcriptional repressors, several of these genes play fundamental roles in cell lineage fate decision in various tissues, programming specific tasks throughout the life of the organism. Here, we focus on functions of leukemia/lymphoma-related factor/POK erythroid myeloid ontogenic factor, which is probably one of the most exciting and yet enigmatic members of the POK/ZBTB family.

Investigation of Pokemon-regulated proteins in hepatocellular carcinoma using mass spectrometry-based multiplex quantitative proteomics

Pokemon is a transcription regulator involved in embryonic development, cellular differentiation and oncogenesis. It is aberrantly overexpressed in multiple human cancers including Hepatocellular carcinoma (HCC) and is considered as a promising biomarker for HCC. In this work, the isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomics strategy was used to investigate the proteomic profile associated with Pokemon in human HCC cell line QGY7703 and human hepatocyte line HL7702. Samples were labeled with four-plex iTRAQ reagents followed by two-dimensional liquid chromatography coupled with tandem mass spectrometry analysis. A total of 24 differentially expressed proteins were selected as significant. Nine proteins were potentially up-regulated by Pokemon while 15 proteins were potentially down-regulated and many proteins were previously identified as potential biomarkers for HCC. Gene ontology (GO) term enrichment revealed that the listed proteins were mainly involved in DNA metabolism and biosynthesis process. The changes of glucose-6-phosphate 1-dehydrogenase (G6PD, up-regulated) and ribonucleoside-diphosphate reductase large sub-unit (RIM1, down-regulated) were validated by Western blotting analysis and denoted as Pokemon's function of oncogenesis. We also found that Pokemon potentially repressed the expression of highly clustered proteins (MCM3, MCM5, MCM6, MCM7) which played key roles in promoting DNA replication. Altogether, our results may help better understand the role of Pokemon in HCC and promote the clinical applications.

Homeostatic regulatory role of Pokemon in NF-κB signaling: stimulating both p65 and IκBα expression in human hepatocellular carcinoma cells

NF-κB consists of p50, p65 (RelA), p52, c-Rel, and RelB, and among them p65 is a representative protein to investigate the regulation and function of this signaling. NF-κB integrates inflammation and carcinogenesis and regulates the expression of a variety of genes in response to immunity, inflammation, and apoptosis. IκBα acts as an inhibitor of NF-κB through forming an inactive NF-κB/IκBα complex. Pokemon is a ubiquitous transcription factor involved in different signaling pathways, playing a pivotal role in cell proliferation, anti-apoptosis, embryonic development, and maintenance. In this study, we found that p65 and IκBα are both novel regulatory targets of Pokemon. Ectopic expression of Pokemon in immortalized liver cells HL7702 enhanced p65 and IκBα expression, whereas silencing of Pokemon in hepatocellular carcinoma cells QGY7703 reduced cellular p65 levels. ChIP assay and targeted mutagenesis revealed that Pokemon directly binds to the element of -434 to -430 bp in p65 promoter and of -453 to -448 bp in IκBα promoter and stimulates luciferase reporter gene expression. Co-transfection of Pokemon with p65 or IκBα promoter-reporter notably enhanced their promoter activity. These data suggest that Pokemon activates the expression of both p65 and IκBα by sequence-specific binding to their promoters and plays a dual role in regulating NF-κB signaling.

The transcription factors Thpok and LRF are necessary and partly redundant for T helper cell differentiation

T helper (Th) cells are critical for defenses against infection and recognize peptides bound to class II major histocompatibility complex (MHC II) molecules. Although transcription factors have been identified that direct Th cells into specific effector fates, whether a "master" regulator controls the developmental program common to all Th cells remains unclear. Here, we showed that the two transcription factors Thpok and LRF share this function. Although disruption of both factors did not prevent the generation of MHC II-specific T cells, these cells failed to express Th cell genes or undergo Th cell differentiation in vivo. In contrast, T cells lacking Thpok, which only displayed LRF-dependent functions, contributed to multiple effector responses, both in vitro and in vivo, with the notable exception of Th2 cell responses that control extracellular parasites. These findings identify the Thpok-LRF pair as a core node of Th cell differentiation and function.

Insulin upregulates the expression of zinc finger and BTB domain-containing 7A in HepG2 cells

Zinc finger and BTB domain-containing 7A (Zbtb7A) is a proto-oncogene overexpressed in numerous cancers. In this study, we explored the mechanism of insulin-induced Zbtb7A expression. Real-time PCR and western blotting were used to detect Zbtb7A expression. Zbtb7A promoter activity was monitored by Luciferase reporter assay. It was shown that insulin elevates the mRNA and protein levels of the Zbtb7A gene in HepG2 cells. Using chemical inhibitors of insulin downstream pathways, we demonstrated that the insulin-induced Zbtb7A gene expression was completely blocked by LY294002, a PI3K/AKT inhibitor, and partially attenuated by the MAPK inhibitor PD98059. Transfection of HepG2 cells with a 1 kb Zbtb7A promoter-luciferase reporter construct revealed a dose-dependent activation of the Zbtb7A promoter by insulin, while mutation of the Sp1 binding site within the Zbtb7A promoter resulted in the failure of insulin-induced promoter activation, suggesting that insulin increases Zbtb7A expression through transcriptional regulation mediated by Sp1 in HepG2 cells.

The BTB-ZF transcription factors

The BTB-ZF (broad-complex, tramtrack and bric-à-brac--zinc finger) proteins are encoded by at least 49 genes in mouse and man and commonly serve as sequence-specific silencers of gene expression. This review will focus on the known physiological functions of mammalian BTB-ZF proteins, which include essential roles in the development of the immune system. We discuss their function in terminally differentiated lymphocytes and the progenitors that give rise to them, their action in hematopoietic malignancy and roles beyond the immune system.

High levels of IL-7 cause dysregulation of thymocyte development

IL-7 signaling is required for thymocyte development and its loss has a severe deleterious effect on thymus function. Thymocyte-stromal cell interactions and other mechanisms tightly regulate IL-7 expression. We show that disruption of that regulation by over-expression of IL-7 inhibits T-cell development and promotes extensive B-cell lymphopoiesis in the thymus. Our data reveal that high levels of IL-7 negate Notch-1 function in thymocytes found in IL-7 transgenic mice and in co-culture with OP9-DL1 cells. While high levels of IL-7R are present on thymocytes, increased suppressor of cytokine signaling-1 expression blunts IL-7 downstream signaling, resulting in hypo-phosphorylation of proteins in the PI3K-Akt pathway. Consequently, GSK3β remains active and inhibits Notch-1 signaling as observed by decreased Hes-1 and Deltex expression in thymic progenitors. This is the first demonstration that high levels of IL-7 antagonize Notch-1 signaling and suggest that IL-7 may affect T- versus B-lineage choice in the thymus.

The Drosophila BCL6 homolog Ken and Barbie promotes somatic stem cell self-renewal in the testis niche

Stem cells sustain tissue regeneration by their remarkable ability to replenish the stem cell pool and to generate differentiating progeny. Signals from local microenvironments, or niches, control stem cell behavior. In the Drosophila testis, a group of somatic support cells called the hub creates a stem cell niche by locally activating the Janus Kinase-Signal Transducer and Activator of Transcription (JAK-STAT) pathway in two adjacent types of stem cells: germline stem cells (GSCs) and somatic cyst stem cells (CySCs). Here, we find that ken and barbie (ken) is autonomously required for the self-renewal of CySCs but not GSCs. Furthermore, Ken misexpression in the CySC lineage induces the cell-autonomous self-renewal of somatic cells as well as the nonautonomous self-renewal of germ cells outside the niche. Thus, Ken, like Stat92E and its targets ZFH1 (Leatherman and Dinardo, 2008) and Chinmo (Flaherty et al., 2010), is necessary and sufficient for CySC renewal. However, ken is not a JAK-STAT target in the testis, but instead acts in parallel to Stat92E to ensure CySC self-renewal. Ken represses a subset of Stat92E targets in the embryo (Arbouzova et al., 2006) suggesting that Ken maintains CySCs by repressing differentiation factors. In support of this hypothesis, we find that the global JAK-STAT inhibitor Protein tyrosine phosphatase 61F (Ptp61F) is a JAK-STAT target in the testis that is repressed by Ken. Together, our work demonstrates that Ken has an important role in the inhibition of CySC differentiation. Studies of ken may inform our understanding of its vertebrate orthologue B-Cell Lymphoma 6 (BCL6) and how misregulation of this oncogene leads to human lymphomas.

POK/ZBTB proteins: an emerging family of proteins that regulate lymphoid development and function

The germinal center (GC) is a unique histological structure found in peripheral lymphoid organs. GCs provide an important source of humoral immunity by generating high affinity antibodies against a pathogen. The GC response is tightly regulated during clonal expansion, immunoglobulin modification, and affinity maturation, whereas its deregulation has a detrimental effect on immune function, leading to development of diseases, such as lymphoma and autoimmunity. LRF (lymphoma/leukemia-related factor), encoded by the ZBTB7A gene, is a transcriptional repressor belonging to the POK (POZ and Krüppel)/ZBTB (zing finger and BTB) protein family. LRF was originally identified as a PLZF (promyelocytic leukemia zinc finger) homolog that physically interacts with BCL6 (B-cell lymphoma 6), whose expression is required for GC formation and associated with non-Hodgkin's lymphoma. Recently, our group demonstrated that LRF plays critical roles in regulating lymphoid lineage commitment, mature B-cell development, and the GC response via distinct mechanisms. Herein, we review POK/ZBTB protein function in lymphoid development, with particular emphasis on the role of LRF in GC B cells.

POZ-, AT-hook-, and zinc finger-containing protein (PATZ) interacts with human oncogene B cell lymphoma 6 (BCL6) and is required for its negative autoregulation

The PATZ1 gene encoding a POZ/AT-hook/Kruppel zinc finger (PATZ) transcription factor, is considered a cancer-related gene because of its loss or misexpression in human neoplasias. As for other POZ/domain and Kruppel zinc finger (POK) family members, the transcriptional activity of PATZ is due to the POZ-mediated oligomer formation, suggesting that it might be not a typical transactivator but an architectural transcription factor, thus functioning either as activator or as repressor depending on the presence of proteins able to interact with it. Therefore, to better elucidate PATZ function, we searched for its molecular partners. By yeast two-hybrid screenings, we found a specific interaction between PATZ and BCL6, a human oncogene that plays a key role in germinal center (GC) derived neoplasias. We demonstrate that PATZ and BCL6 interact in germinal center-derived B lymphoma cells, through the POZ domain of PATZ. Moreover, we show that PATZ is able to bind the BCL6 regulatory region, where BCL6 itself acts as a negative regulator, and to contribute to negatively modulate its activity. Consistently, disruption of one or both Patz1 alleles in mice causes focal expansion of thymus B cells, in which BCL6 is up-regulated. This phenotype was almost completely rescued by crossing Patz1(+/-) with Bcl6(+/-) mice, indicating a key role for Bcl6 expression in its development. Finally, a significant number of Patz1 knock-out mice (both heterozygous and homozygous) also develop BCL6-expressing lymphomas. Therefore, the disruption of one or both Patz1 alleles may favor lymphomagenesis by activating the BCL6 pathway.