A novel gene trapping for identifying genes expressed under the control of specific transcription factors

miR-139-5p Loss-Mediated WTAP Activation Contributes to Hepatocellular Carcinoma Progression by Promoting the Epithelial to Mesenchymal Transition

Background: Hepatocellular carcinoma (HCC) is a primary aggressive gastrointestinal neoplasm that affects patients worldwide. It has been shown that Wilms' tumor 1-associating protein (WTAP) is frequently upregulated in various cancers. However, the potential role of WTAP in HCC remains largely unknown.

Methods: The expression levels of WTAP in human HCC tissues were determined by the western blotting and immunohistochemical (IHC) staining. A correlation between the WTAP expression, clinicopathological features, and the HCC prognosis was analyzed. The WTAP expression was silenced by short hairpin RNA (shRNA), and effects of the knockdown of WTAP on the proliferation and invasion of HCC cells were assessed. The microRNAs (miRNAs) involved in the regulation of the WTAP expression were identified by a bioinformatics analysis and further confirmed by in vitro assays.

Results: The expression levels of WTAP in liver cancer tissues were significantly elevated and compared with those in the adjacent normal tissues and significantly correlated with the clinical stage and prognosis in patients with HCC. Further investigation revealed that the knockdown of WTAP drastically suppressed HCC cell proliferation and invasion abilities. Luciferase reporter assay and validation experiments confirmed that WTAP was a direct target of miR-139-5p. Moreover, the overexpression of WTAP could partly abolish the inhibitory effects of miR-139-5p on the HCC cell growth and invasion. Mechanistically, we revealed that the miR-139-5p/WTAP axis regulated the HCC progression by controlling the epithelial to mesenchymal transition (EMT).

Conclusions: In summary, the results indicate that WTAP is a potential oncogene in HCC and miR-139-5p negatively regulates the WTAP expression. MiR-139-5p/WTAP can be utilized as a potential therapeutic target for HCC.

Heterochromatin protein 1γ deficiency decreases histone H3K27 methylation in mouse neurosphere neuronal genes

Heterochromatin protein (HP) 1γ, a component of heterochromatin in eukaryotes, is involved in H3K9 methylation. Although HP1γ is expressed strongly in neural tissues and neural stem cells, its functions are unclear. To elucidate the roles of HP1γ, we analyzed HP1γ -deficient (HP1γ KO) mouse embryonic neurospheres and determined that HP1γ KO neurospheres tended to differentiate after quaternary culture. Several genes normally expressed in neuronal cells were upregulated in HP1γ KO undifferentiated neurospheres, but not in the wild type (WT). Compared to that in the control neurospheres, the occupancy of H3K27me3 was lower around the transcription start sites (TSSs) of these genes in HP1γ KO neurospheres, while H3K9me2/3, H3K4me3, and H3K27ac amounts remained unchanged. Moreover, amounts of the H3K27me2/3 demethylases, UTX, and JMJD3, were increased around the TSSs of these genes. Treatment with GSK-J4, an inhibitor of H3K27 demethylases, decreased the expression of genes upregulated in HP1γ KO neurospheres, along with an increase of H3K27me3 amounts. Therefore, in murine neurospheres, HP1γ protected the promoter sites of differentiated cell-specific genes against H3K27 demethylases to repress the expression of these genes. A better understanding of central cellular processes such as histone methylation will help elucidate critical events such as cell-specific gene expression, epigenetics, and differentiation.

Physiological functions of Wilms' tumor 1-associating protein and its role in tumourigenesis

The Wilms' tumor-associated gene WT1 encodes a tumor suppressor gene, which is implicated in renal differentiation and development of adult urogenital system. Wilms' tumor 1-associating protein (WTAP) is initially identified as a nuclear protein that specifically interacts with WT1 in both in vitro and in vivo assays. WTAP is ubiquitously expressed in different tissues and various growth periods, and its expression is involved in cell cycle, RNA splicing and stabilization, N6-methyladenosine RNA modification, cell proliferation, and apoptosis as well as embryonic development. In the present review, we aimed to summarize the functions of WTAP in various physiological and pathological processes, in particular with regard to the current knowledge about the role of WTAP in tumorigenesis of different cancers.

Mechanisms Underlying the Regulation of HP1γ by the NGF-PKA Signaling Pathway

Heterochromatin protein 1 γ (HP1γ) is a well-known chromatin protein, which regulates gene silencing during the execution of processes associated with embryogenesis, organ maturation, and cell differentiation. We find that, in vivo, the levels of HP1γ are downregulated during nervous system development. Similar results are recapitulated in vitro during nerve growth factor (NGF)-induced neuronal cell differentiation in PC12 cells. Mechanistically, our experiments demonstrate that in differentiating PC12 cells, NGF treatment decreases the association of HP1γ to silent heterochromatin, leads to phosphorylation of this protein at S83 via protein kinase A (PKA), and ultimately results in its degradation. Genome-wide experiments, using gain-of-function (overexpression) and loss-of-function (RNAi) paradigms, demonstrate that changing the level of HP1γ impacts on PC12 differentiation, at least in part, through gene networks involved in this process. Hence, inactivation of HP1γ by different post-translational mechanisms, including reduced heterochromatin association, phosphorylation, and degradation, is necessary for neuronal cell differentiation to occur. Indeed, we show that the increase of HP1γ levels has the reverse effect, namely antagonizing neuronal cell differentiation, supporting that this protein acts as a barrier for this process. Thus, these results describe the regulation and participation of HP1γ in a novel membrane-to-nucleus pathway, through NGF-PKA signaling, which is involved in NGF-induced neuronal cell differentiation.

Wilms' tumor 1-associating protein plays an aggressive role in diffuse large B-cell lymphoma and forms a complex with BCL6 via Hsp90

Background

Wilms’ tumor 1-associating protein (WTAP) is a nuclear protein, which is ubiquitously expressed in many tissues. Furthermore, in various types of malignancies WTAP is overexpressed and plays a role as an oncogene. The function of WTAP in diffuse large B-cell lymphoma (DLBCL), however, remains unclear.

Methods

Immunohistochemistry was applied to evaluate the levels of WTAP expression in DLBCL tissues and normal lymphoid tissues. Overexpression and knock-down of WTAP in DLBCL cell lines, verified on mRNA and protein level served to analyze cell proliferation and apoptosis in DLBCL cell lines by flow cytometry. Finally, co-immunoprecipitation (Co-IP), IP, and GST-pull down assessed the interaction of WTAP with Heat shock protein 90 (Hsp90) and B-cell lymphoma 6 (BCL6) as well as determined the extend of its ubiquitinylation.

Results

WTAP protein levels were consistently upregulated in DLBCL tissues. WTAP promoted DLBCL cell proliferation and improved the ability to confront apoptosis, while knockdown of WTAP in DLBCL cell lines allowed a significant higher apoptosis rate after treatment with Etoposide, an anti-tumor drug. The stable expression of WTAP was depended on Hsp90. In line, we demonstrated that WTAP could form a complex with BCL6 via Hsp90 in vivo and in vitro.

Conclusion

WTAP is highly expressed in DLBCL, promoting growth and anti-apoptosis in DLBCL cell lines. WTAP is a client protein of Hsp90 and can appear in a complex with BCL6 and Hsp90 in DLBCL. Down-regulation of WTAP could improve the chemotherapeutic treatments in DLBCL.

Electronic supplementary material

The online version of this article (10.1186/s12964-018-0258-6) contains supplementary material, which is available to authorized users.

Cbx3/HP1γ deficiency confers enhanced tumor-killing capacity on CD8+ T cells

Cbx3/HP1γ is a histone reader whose function in the immune system is not completely understood. Here, we demonstrate that in CD8⁺ T cells, Cbx3/HP1γ insufficiency leads to chromatin remodeling accompanied by enhanced Prf1, Gzmb and Ifng expression. In tumors obtained from Cbx3/HP1γ-insufficient mice or wild type mice treated with Cbx3/HP1γ-insufficient CD8⁺ T cells, there is an increase of CD8⁺ effector T cells expressing the stimulatory receptor Klrk1/NKG2D, a decrease in CD4⁺ CD25⁺ FOXP3⁺ regulatory T cells (Treg cells) as well as CD25⁺ CD4⁺ T cells expressing the inhibitory receptor CTLA4. Together these changes in the tumor immune environment may have mitigated tumor burden in Cbx3/HP1γ-insufficient mice or wild type mice treated with Cbx3/HP1γ-insufficient CD8⁺ T cells. These findings suggest that targeting Cbx3/HP1γ can represent a rational therapeutic approach to control growth of solid tumors.

Identifying the role of Wilms tumor 1 associated protein in cancer prediction using integrative genomic analyses

The Wilms tumor suppressor, WT1 was first identified due to its essential role in the normal development of the human genitourinary system. Wilms tumor 1 associated protein (WTAP) was subsequently revealed to interact with WT1 using yeast two-hybrid screening. The present study identified 44 complete WTAP genes in the genomes of vertebrates, including fish, amphibians, birds and mammals. The vertebrate WTAP proteins clustered into the primate, rodent and teleost lineages using phylogenetic tree analysis. From 1,347 available SNPs in the human WTAP gene, 19 were identified to cause missense mutations. WTAP was expressed in bladder, blood, brain, breast, colorectal, esophagus, eye, head and neck, lung, ovarian, prostate, skin and soft tissue cancers. A total of 17 out of 328 microarrays demonstrated an association between WTAP gene expression and cancer prognosis. However, the association between WTAP gene expression and prognosis varied in distinct types of cancer, and even in identical types of cancer from separate microarray databases. By searching the Catalogue of Somatic Mutations in Cancer database, 65 somatic mutations were identified in the human WTAP gene from the cancer tissue samples. These results suggest that the function of WTAP in tumor formation may be multidimensional. Furthermore, signal transducer and activator of transcription 1, forkhead box protein O1, interferon regulatory factor 1, glucocorticoid receptor and peroxisome proliferator-activated receptor γ transcription factor binding sites were identified in the upstream (promoter) region of the human WTAP gene, suggesting that these transcription factors may be involved in WTAP functions in tumor formation.

The Aurora A-HP1γ pathway regulates gene expression and mitosis in cells from the sperm lineage

BACKGROUND

HP1γ, a well-known regulator of gene expression, has been recently identified to be a target of Aurora A, a mitotic kinase which is important for both gametogenesis and embryogenesis. The purpose of this study was to define whether the Aurora A-HP1γ pathway supports cell division of gametes and/or early embryos, using western blot, immunofluorescence, immunohistochemistry, electron microscopy, shRNA-based knockdown, site-directed mutagenesis, and Affymetrix-based genome-wide expression profiles.

RESULTS

We find that the form of HP1γ phosphorylated by Aurora A, P-Ser83 HP1γ, is a passenger protein, which localizes to the spermatozoa centriole and axoneme. In addition, disruption in this pathway causes centrosomal abnormalities and aberrations in cell division. Expression profiling of male germ cell lines demonstrates that HP1γ phosphorylation is critical for the regulation of mitosis-associated gene expression networks. In female gametes, we observe that P-Ser83-HP1γ is not present in meiotic centrosomes of M2 oocytes, but after syngamy, it becomes detectable during cleavage divisions, coinciding with early embryonic genome activation.

CONCLUSIONS

These results support the idea that phosphorylation of HP1γ by Aurora A plays a role in the regulation of gene expression and mitotic cell division in cells from the sperm lineage and in early embryos. Combined, this data is relevant to better understanding the function of HP1γ in reproductive biology.

HP-1γ Controls High-Affinity Antibody Response to T-Dependent Antigens

In vitro observations suggest a role for the mouse heterochromatin protein 1γ (HP-1γ) in the immune system. However, it has not been shown if and how HP-1γ contributes to immunity in vivo. Here we show that in mice, HP-1γ positively regulates the germinal center reaction and high-affinity antibody response to thymus (T)-dependent antigens by limiting the size of CD8⁺ regulatory T-cell (T_reg) compartment without affecting progenitor B- or T-cell-development. Moreover, HP-1γ does not control cell proliferation or class switch recombination. Haploinsufficiency of cbx-3 (gene encoding HP-1γ) is sufficient to expand the CD8⁺ T_reg population and impair the immune response in mice despite the presence of wild-type HP-1α and HP-1β. This is the first in vivo evidence demonstrating the non-redundant role of HP-1γ in immunity.

The Drosophila Wilms׳ Tumor 1-Associating Protein (WTAP) homolog is required for eye development

Sine Oculis (So), the founding member of the SIX family of homeobox transcription factors, binds to sequence specific DNA elements and regulates transcription of downstream target genes. It does so, in part, through the formation of distinct biochemical complexes with Eyes Absent (Eya) and Groucho (Gro). While these complexes play significant roles during development, they do not account for all So-dependent activities in Drosophila. It is thought that additional So-containing complexes make important contributions as well. This contention is supported by the identification of nearly two-dozen additional proteins that complex with So. However, very little is known about the roles that these additional complexes play in development. In this report we have used yeast two-hybrid screens and co-immunoprecipitation assays from Kc167 cells to identify a biochemical complex consisting of So and Fl(2)d, the Drosophila homolog of human Wilms׳ Tumor 1-Associating Protein (WTAP). We show that Fl(2)d protein is distributed throughout the entire eye-antennal imaginal disc and that loss-of-function mutations lead to perturbations in retinal development. The eye defects are manifested behind the morphogenetic furrow and result in part from increased levels of the pan-neuronal RNA binding protein Embryonic Lethal Abnormal Vision (Elav) and the RUNX class transcription factor Lozenge (Lz). We also provide evidence that So and Fl(2)d interact genetically in the developing eye. Wilms׳ tumor-1 (WT1), a binding partner of WTAP, is required for normal eye formation in mammals and loss-of-function mutations are associated with some versions of retinoblastoma. In contrast, WTAP and its homologs have not been implicated in eye development. To our knowledge, the results presented in this report are the first description of a role for WTAP in the retina of any seeing animal.

WTAP regulates migration and invasion of cholangiocarcinoma cells

BACKGROUND

Wilms' tumor 1-associating protein (WTAP) is a nuclear protein that has been associated with the regulation of proliferation and apoptosis. Although its dynamic expression and physiological functions in vascular cells have been reported, its expression and roles in cholangiocarcinoma cells are poorly characterized.

METHODS

To examine the expression of WTAP in patient tissues, we performed immunohistochemistry. To examine motility of cholangiocarcinoma cells, we employed Boyden chamber, wound healing and Matrigel invasion assays, and a liver xenograft model.

RESULTS

Immunohistochemistry in patient tissues showed WTAP overexpression in cholangiocarcinoma tissues and correlation of WTAP expression with metastasis of cholangiocarcinoma cells. Overexpression or knockdown of WTAP significantly increased or decreased the motility of cholangiocarcinoma cells. Moreover, WTAP overexpression or knockdown significantly increased or decreased tumorigenicity of cholangiocarcinoma cells in an orthotopic xenograft model. Furthermore, microarray study showed that WTAP induce the expressions of MMP7, MMP28, cathepsin H and Muc1.

CONCLUSION

WTAP is overexpressed in cholangiocarcinoma and regulates motility of cholangiocarcinoma cells.

Mechanisms and dynamics of heterochromatin formation during mammalian development: closed paths and open questions

Early embryonic development in mammals is characterized by major changes in the components of the chromatin and its remodeling. The embryonic chromatin and the nuclear organization in the mouse preimplantation embryo display particular features that are dramatically different from somatic cells. These include the highly specific organization of the pericentromeric heterochromatin within the nucleus and the suggested lack of conventional heterochromatin. We postulate that the plasticity of the cells in the early embryo relies on the distinctive heterochromatin features that prevail during early embryogenesis. Here, we review some of these features and discuss recent findings on the mechanisms driving heterochromatin formation after fertilization, in particular, the emerging role of RNA as a regulator of heterochromatic loci also in mammals. Finally, we believe that there are at least three major avenues that should be addressed in the coming years: (i) Is heterochromatin a driving force in development? (ii) Does it have a role in lineage allocation? (iii) How can heterochromatin "regulate" epigenetic reprogramming?

Expression and roles of Wilms' tumor 1-associating protein in glioblastoma

Glioblastoma is a diffusely growing malignant brain tumor and among the most aggressive of all tumors. Wilms' tumor 1-associating protein (WTAP) is a nuclear protein that has been associated with regulation of proliferation and apoptosis. Although its dynamic expression and physiological functions in vascular cells have been reported, those in other cells are largely unknown. Here, we show for the first time that WTAP is overexpressed in glioblastoma. Moreover we found that WTAP regulates migration and invasion of glioblatoma cells. Specific knockdown by siRNA or overexpression by cDNA regulated migration and invasion of cancer cells. In xenograft study, WTAP overexpression made cancer cells more tumorigenic. In the investigation for its underlying mechanism, we found that the activity of epidermal growth factor receptor can be regulated by WTAP. These results reveal a novel function of WTAP and suggest its clinical application.

HP1γ links histone methylation marks to meiotic synapsis in mice

During meiosis, specific histone modifications at pericentric heterochromatin (PCH), especially histone H3 tri- and dimethylation at lysine 9 (H3K9me3 and H3K9me2, respectively), are required for proper chromosome interactions. However, the molecular mechanism by which H3K9 methylation mediates the synapsis is not yet understood. We have generated a Cbx3-deficient mouse line and performed comparative analysis on Suv39h1/h2-, G9a- and Cbx3-deficient spermatocytes. This study revealed that H3K9me2 at PCH depended on Suv39h1/h2-mediated H3K9me3 and its recognition by the Cbx3 gene product HP1γ. We further found that centromere clustering and synapsis were commonly affected in G9a- and Cbx3-deficient spermatocytes. These genetic observations suggest that HP1γ/G9a-dependent PCH-mediated centromere clustering is an axis for proper chromosome interactions during meiotic prophase. We propose that the role of the HP1γ/G9a axis is to retain centromeric regions of unpaired homologous chromosomes in close alignment and facilitate progression of their pairing in early meiotic prophase. This study also reveals considerable plasticity in the interplay between different histone modifications and suggests that such stepwise and dynamic epigenetic modifications may play a pivotal role in meiosis.

Loss of heterochromatin protein 1 gamma reduces the number of primordial germ cells via impaired cell cycle progression in mice

Signals from extraembryonic tissues in mice determine which proximal epiblast cells become primordial germ cells (PGCs). After their specification, approximately 40 PGCs appear at the base of the allantoic bud and migrate to the genital ridges, where they expand to about 25 000 cells by Embryonic Day (E)13.5. The heterochromatin protein 1 (HP1) family members HP1alpha, HP1beta, and HP1gamma (CBX5, CBX1, and CBX3, respectively) are thought to induce heterochromatin structure and to regulate gene expression by binding methylated histone H3 lysine 9. We found a dramatic loss of germ cells before meiosis in HP1gamma mutant (HP1gamma(-/-)) mice that we generated previously. The reduction in PGCs in HP1gamma(-/-) embryos was detectable from the early bud stage (E7.25), and the number of HP1gamma(-/-) PGCs was gradually reduced thereafter. Bromodeoxyuridine incorporation into PGCs was significantly reduced in E7.25 and E12.5 HP1gamma(-/-) embryos. Furthermore, a lower proportion of HP1gamma(-/-) PGCs than wild-type PGCs was in S phase, and a higher proportion, respectively, was in G1 phase at E12.5. Moreover, the proportion of p21 (Cip, official symbol CDKN1A)-positive HP1gamma(-/-) PGCs was increased, suggesting that the G1/S phase transition was inhibited. However, no differences were detected between fate determination, migration, apoptosis, or histone modification of PGCs of control embryos and those of HP1gamma(-/-) embryos. Therefore, the reduction in PGCs in HP1gamma(-/-) embryos could be caused by impaired cell cycle in PGCs. These results suggest that HP1gamma plays an important role in keeping enough germ cells by regulating the PGC cell cycle.

Cloning and characterization of a novel gene with alternative splicing in murine mesenchymal stem cell line C3H/10T1/2 by gene trap screening

A novel gene, designated mgt-6, containing four splicing variants, was isolated from a gene trap clone library of C3H/10T1/2 cells transfected with retroviral promoterless gene-trap vector, ROSAFARY. The transcript variants were differentially expressed in murine tissues and cell lines and differentially responded to diverse stimuli including TGF-β1 and mitogen-activated protein kinase (MAPK) inhibitors. The mgt-6 gene encoded a protein of 37 or 11 amino acid residuals with cytoplasmic distribution. However, when C3H/10T1/2 cells were treated with 5-azacytidine, the protein translocated into cell nucleus as indicated by fused LacZ or C-terminally tagged EGFP. Our preliminary results suggest that further study on the role of mgt-6 gene in cell transformation and differentiation may be of significance.

Wtap is required for differentiation of endoderm and mesoderm in the mouse embryo

Wilms' tumor 1-associating protein (WTAP) was previously identified as a protein associated with Wilms' tumor-1 (WT-1) protein that is essential for the development of the genitourinary system. Although WTAP has been suggested to function in alternative splicing, stabilization of mRNA, and cell growth, its in vivo function is still unclear. We generated Wtap mutant mice using a novel gene-trap approach and showed that Wtap mutant embryos exhibited defective egg-cylinder formation at the gastrulation stage and died by embryonic day 10.5. Although they could form extraembryonic tissues and anterior visceral endoderm, Wtap mutant embryos and embryonic stem cells failed to differentiate into endoderm and mesoderm. The chimera analysis showed that Wtap in extraembryonic tissues was required for the formation of mesoderm and endoderm in embryonic tissues. Taken together, our findings indicate that Wtap is indispensable for differentiation of mesoderm and endoderm in the mouse embryo.

Vascular biology and the sex of flies: regulation of vascular smooth muscle cell proliferation by wilms' tumor 1-associating protein

Smooth muscle cells (SMCs) are called on to proliferate during vascular repair but must return to a nonproliferative state if remodeling is to terminate appropriately. One gene that has recently been implicated in the acquisition of SMC replicative quiescence is Wilms' tumor 1-associating protein (WTAP). Wilms' tumor 1-associating protein is a nuclear constituent of uncertain function that, as the name implies, interacts with the Wilms' tumor 1 tumor suppressor gene product (WT1). Wilms' tumor 1-associating protein is essential for embryonic development, and recent data suggest that WTAP regulates the proliferation of both SMCs and endothelial cells. In SMCs, WTAP appears to be antiproliferative, inhibiting G(1)-to-S phase cell cycle transition and also promoting apoptosis. These effects could be the result of WTAP suppressing the transcriptional activity of WT1 in SMCs. Interestingly, the Drosophila homologue of WTAP, fl(2)d, is a protein essential for alternative splicing regulation and sexual determination in this species. Wilms' tumor 1-associating protein may thus also play a role in messenger RNA processing in mammalian cells, either dependent on or independent of its interaction with WT1. The putative actions of WTAP as a regulator of transcriptional and posttranscriptional events and emerging evidence for a WTAP-WT1 axis in vascular cells suggest that WTAP is a vital and multifaceted regulator of vascular remodeling.