Genomic structure and analysis of transcriptional regulation of the mouse zinc-fingers and homeoboxes 1 (ZHX1) gene

Zinc Fingers and Homeobox Family in Cancer: A Double-Edged Sword

The zinc fingers and homeobox (ZHX) family includes ZHX1, ZHX2, and ZHX3, and their proteins have similar unique structures, containing two C2H2-type zinc finger motifs and four or five HOX-like homeodomains. The members of the ZHX family can form homodimers or heterodimers with each other or with a subunit of nuclear factor Y. Previous studies have suggested that ZHXs can function as positive or negative transcriptional regulators. Recent studies have further revealed their biological functions and underlying mechanisms in cancers. This review summarized the advances of ZHX-mediated functions, including tumor-suppressive and oncogenic functions in cancer formation and progression, the molecular mechanisms, and regulatory functions, such as cancer cell proliferation, migration, invasion, and metastasis. Moreover, the differential expression levels and their association with good or poor outcomes in patients with various malignancies and differential responses to chemotherapy exert opposite functions of oncogene or tumor suppressors. Therefore, the ZHXs act as a double-edged sword in cancers.

An insulin-inducible transcription factor, SHARP-1, represses transcription of the SIRT1 longevity gene

The rat enhancer of split- and hairy-related protein (SHARP)-1 genes encode insulin-inducible transcriptional repressors. A longevity gene, sirtuin 1 (SIRT1) encodes protein deacetylase. These play an important role in regulating hepatic glucose metabolism. In this study, to evaluate a correlation with these gene expressions, we examined whether SIRT1 effects on expression of the SHARP-1 gene by a treatment with a SIRT1 inhibitor or activator in rat H4IIE hepatoma cells. Whereas the SIRT1 inhibitor increased the level of SHARP-1 mRNA, the SIRT1 activator decreased it. Next, whether SHARP-1 effect on the transcriptional activity of the human SIRT1 gene using luciferase reporter assays was determined. Promoter activity of the SIRT1 gene was specifically repressed by SHARP-1. Further reporter analysis using 5'- deleted or mutated constructs revealed that an E box sequence (5'-CACGTG-3') of the SIRT1 gene promoter was required for the inhibitory effect of SHARP-1. Thus, we conclude that expressions between the SHARP-1 and the SIRT1 genes show a negative correlation and that SHARP-1 represses transcription of the SIRT1 gene.

Blocking lncRNA MALAT1/miR-199a/ZHX1 Axis Inhibits Glioblastoma Proliferation and Progression

Zinc fingers and homeoboxes 1 (ZHX1) is a transcription repressor that has been implicated in the tumorigenesis and progression of diverse tumors. The functional role and regulating mechanism of ZHX1 has not been elucidated in glioblastoma (GBM). Previous reports have suggested that a large number of non-coding RNAs play a vital role in glioma initiation and progression. This study aimed to investigate the functional role and co-regulatory mechanisms of the metastasis-associated lung adenocarcinoma transcript-1 (MALAT1)/ microRNA-199a (miR-199a)/ZHX1 axis in GBM. We analyzed the expression of the MALAT1/miR-199a/ZHX1 axis and its correlation with patients' overall survival using two different glioma gene-expression datasets. A series of in vitro and in vivo studies including dual luciferase reporter assay, fluorescence in situ hybridization (FISH), RNA immunoprecipitation, and pull-down experiments were completed to elucidate the biological significance of the MALAT1/miR-199a/ZHX1 axis in promoting glioma proliferation and progression. Elevated ZHX1 expression correlated with poor prognosis in GBM patients, and in vitro studies demonstrated that ZHX1 attenuated GBM cell apoptosis by downregulation of pro-apoptotic protein (Bax) and upregulation of anti-apoptotic protein (Bcl-2). Furthermore, knockdown of MALAT1 inhibited GBM proliferation and progression in vitro and reduced tumor volume and prolonged survival in an orthotopic GBM murine model. Finally, we demonstrated that MALAT1 promoted ZHX1 expression via acting as a competing endogenous RNA by sponging miR-199a. The MALAT1/miR-199a/ZHX1 axis promotes GBM cell proliferation and progression in vitro and in vivo, and its expression negatively correlates with GBM patient survival. Blocking the MALAT1/miR-199a/ZHX1 axis can serve as a novel therapeutic strategy for treating GBM.

The SUMOylation of zinc-fingers and homeoboxes 1 (ZHX1) by Ubc9 regulates its stability and transcriptional repression activity

Zinc-fingers and homeoboxes protein 1 (ZHX1) belongs to the ZF (zinc-fingers) class of homeodomain transcription factors, and its function remains largely unknown. ZHX1 has been previously found to interact with the activation domain of the nuclear factor Y subunit A (NFYA) and to have a transcriptional repression activity. Here, we report that the SUMO-E2 conjugating enzyme Ubc9 was identified to interact with ZHX1 by an interaction screen using a yeast two-hybrid system. This interaction was confirmed by co-immunoprecipitation and co-localization assays. Further study showed that ZHX1 is SUMOylated by Ubc9 with SUMO1 at the sites K159, K454, and K626. Furthermore, we demonstrated that the SUMOylation of ZHX1 regulated the stability, ubiquitination and transcriptional activity of ZHX1.

SHARP-2 gene silencing by lentiviral-based short hairpin RNA interference prolonged rat kidney transplant recipients' survival time

Split- and hairy-related protein-2 (SHARP-2) controls the expression of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma), which both play a key role in transplant rejection. This study was designed to investigate whether SHARP-2 short hairpin RNA interference (shRNAi) could prolong the survival of rat kidney transplant recipients. A lentiviral-based shRNAi construct, LV-SHARP-2iC, showed a SHARP-2 gene silencing efficiency of 84% in normal rat kidney cells. In activated T-cells, SHARP-2 gene silencing with the LV-SHARP-2iC construct resulted in 61% and 69% down-regulation of IL-2 and IFN-gamma, respectively, compared with a scramble control construct. When donor kidney was perfused with 5 x 10(7) transforming units of the LV-SHARP-2iC construct, the median survival time of the transplant recipients was prolonged by 4 - 5 days compared with control groups. In conclusion, recombinant lentiviral LV-SHARP-2iC construct effectively silenced SHARP-2 gene expression, which reduced IL-2 and IFN-gamma mRNA expression and prolonged rat kidney transplant recipients' survival.

PI-3 kinase pathway can mediate the effect of TGF-beta1 in inducing the expression of SHARP-2 in LLC-PK1 cells

We aim to investigate the effect of transforming growth factor (TGF)-beta1 on the expression of enhancer of split- and hairy-related protein-2 (SHARP-2) messenger RNA (mRNA) and its signaling pathway. In this study, several cell lines including LLC-PK1 (a porcine kidney tubular epithelial cell line), MDCK (Madin-Darby canine kidney) and CTLL-2 (cytotoxic T-lymphocyte line) were treated with recombinant human TGF-beta1, and a series of experiments were carried out, involving Northern blot analysis of total RNA from these cells. Further, several specific chemical inhibitors were applied before TGF-beta1 treatment to probe the signaling pathway. The results showed that TGF-beta1 can significantly up-regulate SHARP-2 mRNA expression in the LLC-PK1 cell line. The peak level of induction was found 2 h after TGF-beta1 stimulation. While one phosphoinositide 3-kinases (PI-3) kinase inhibitor, LY294002, completely blocked the effect of TGF-beta1 on SHARP-2 mRNA expression in LLC-PK1 cells at a low concentration, other inhibitors, including PD98059, staurosporine, AG490, wortmannin, okadaic acid and rapamycin, had no effect. The effect of LY294002 was dose-dependent. We conclude that, in LLC-PK1 cells at least, TGF-beta1 can effectively induce the SHARP-2 mRNA expression and that the PI-3 kinase pathway can mediate this effect.

TDP-43: an emerging new player in neurodegenerative diseases

Until a couple of years ago, TAR-DNA-binding protein-43 (TDP-43) was a relatively unknown nuclear protein implicated in transcriptional repression and splicing. Since 2006, when the protein was reported to be present in inclusions in the neurons and/or glial cells of a range of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration with ubiquitin-positive, tau- and alpha-synuclein-negative inclusions (FTLD-U) and Alzheimer's disease (AD), many reports on the medical aspects of TDP-43 have been published. Here, we summarize the current literature on TDP-43, focusing on recent studies that provide clues to the function of TDP-43. Using this information and database analysis, we also suggest a molecular and cellular model for possible events in normal and diseased neurons in relation to the emerging importance of the function and dysfunction of this protein as a target for basic as well as translational research.

Regulation of Id2 expression by CCAAT/enhancer binding protein beta

Mice deficient for Id2, a negative regulator of basic helix–loop–helix (bHLH) transcription factors, exhibit a defect in lactation due to impaired lobuloalveolar development during pregnancy, similar to the mice lacking the CCAAT enhancer binding protein (C/EBP) β. Here, we show that Id2 is a direct target of C/EBPβ. Translocation of C/EBPβ into the nucleus, which was achieved by using a system utilizing the fusion protein between C/EBPβ and the ligand-binding domain of the human estrogen receptor (C/EBPβ-ERT), demonstrated the rapid induction of endogenous Id2 expression. In reporter assays, transactivation of the Id2 promoter by C/EBPβ was observed and, among three potential C/EBPβ binding sites found in the 2.3 kb Id2 promoter region, the most proximal element was responsible for the transactivation. Electrophoretic mobility shift assay (EMSA) identified this element as a core sequence to which C/EBPβ binds. Chromatin immunoprecipitation (ChIP) furthermore confirmed the presence of C/EBPβ in the Id2 promoter region. Northern blotting showed that Id2 expression in C/EBPβ-deficient mammary glands was reduced at 10 days post coitus (d.p.c.), compared with that in wild-type mammary glands. Thus, our data demonstrate that Id2 is a direct target of C/EBPβ and provide insight into molecular mechanisms underlying mammary gland development during pregnancy.

SHARP-2/Stra13/DEC1 as a potential repressor of phosphoenolpyruvate carboxykinase gene expression

The influence of the enhancer of split- and hairy-related protein-2 (SHARP-2) transcriptional repressor on the expression of rat phosphoenolpyruvate carboxykinase (PEPCK) gene was examined. When H4IIE cells were treated with epigallocatechin gallate, a green tea constituent, an increase in SHARP-2 mRNA levels and a decrease in PEPCK mRNA levels were observed. The adenovirus-mediated overexpression of SHARP-2 in H4IIE cells and primary cultured rat hepatocytes led to a decrease in the levels of PEPCK mRNA. Finally, when a SHARP-2 expression plasmid was transiently transfected with various reporter plasmids into MH1C1 cells, the promoter activity of a PEPCK reporter plasmid was specifically decreased. Based on these findings, we conclude that SHARP-2 is a potential repressor of PEPCK gene expression.

The G/G genotype of a resistin single-nucleotide polymorphism at -420 increases type 2 diabetes mellitus susceptibility by inducing promoter activity through specific binding of Sp1/3

Insulin resistance is a major cause of type 2 diabetes mellitus (T2DM). Resistin, an adipocyte-secreted hormone, antagonizes insulin. Transgenic mice that overexpress the resistin gene (Retn) in adipose tissue are insulin-resistant, whereas Retn (-/-) mice show lower fasting blood glucose, suggesting that the altered Retn promoter function could cause diabetes. To determine the role of RETN in human T2DM, we analyzed polymorphisms in its 5' flanking region. We found that the -420G/G genotype was associated with T2DM (397 cases and 406 controls) (P=.008; adjusted odds ratio = 1.97 [by logistic regression analysis]) and could accelerate the onset of disease by 4.9 years (P=.006 [by multiple regression analysis]). Meta-analysis of 1,888 cases and 1,648 controls confirmed this association (P=.013). Linkage disequilibrium analysis revealed that the -420G/G genotype itself was a primary variant determining T2DM susceptibility. Functionally, Sp1 and Sp3 transcription factors bound specifically to the susceptible DNA element that included -420G. Overexpression of Sp1 or Sp3 enhanced RETN promoter activity with -420G in Drosophila Schneider line 2 cells that lacked endogenous Sp family members. Consistent with these findings, fasting serum resistin levels were higher in subjects with T2DM who carried the -420G/G genotype. Therefore, the specific recognition of -420G by Sp1/3 increases RETN promoter activity, leading to enhanced serum resistin levels, thereby inducing human T2DM.

A mechanism of induction of the mouse zinc-fingers and homeoboxes 1 (ZHX1) gene expression by interleukin-2

The effect of IL-2 on the expression of the mouse zinc-fingers and homeoboxes 1 (ZHX1) gene was investigated in a mouse cytotoxic T cell line, CTLL-2 cells. IL-2 specifically induced the expression of ZHX1 mRNA. The level of ZHX1 mRNA was decreased in the absence of IL-2. These alterations were in parallel with the status of cell proliferation. The signaling pathways involved in the induction were examined. AG-490, wortmannin, and LY294002 blocked the induction by IL-2. Nuclear run-on assays and a mRNA stability analysis revealed that the half-life of ZHX1 mRNA but not the transcription rate of the gene was increased by IL-2. Thus, we conclude that IL-2 induces the expression of the mouse ZHX1 gene in CTLL-2 cells, that both Janus kinase 3/signal transducer and activator of transcription 5 and phosphoinositide 3-kinase pathways are involved in the induction, and that the increased mRNA stability results in the induction.

The rat enhancer of split- and hairy-related protein-2 gene: hepatic expression, genomic structure, and promoter analysis

The rat enhancer of split- and hairy-related protein-2 (SHARP-2) is a basic helix-loop-helix transcription factor. The hepatic expression of SHARP-2 mRNA was investigated under various conditions. The level was decreased in the regenerating rat liver and malignant hepatoma cells. In contrast, the expression of SHARP-2 mRNA was induced in rat livers by feeding a high-carbohydrate diet. To analyze the molecular mechanism involved in the regulation of the rat SHARP-2 gene expression, the gene was cloned. It was approximately 6-kb in length and consists of five exons and four introns. To investigate the transcriptional regulatory region of this gene, SHARP-2/firefly luciferase reporter plasmids were transfected into hepatoma cells. A functional analysis of 5(')-deletion constructs revealed that two E box sequences between -160 and -144 are mainly responsible for promoter activity. Although upstream stimulatory factors (USFs) bound to the element in vitro, USF2 failed to stimulate promoter activity from the element using the co-transfection experiment. Therefore, other E box-binding transcription factors differing from USF proteins or USF-associated proteins are necessary for transcriptional stimulation of the rat SHARP-2 gene.

The mouse zinc-fingers and homeoboxes (ZHX) family; ZHX2 forms a heterodimer with ZHX3

Human zinc-fingers and homeoboxes (ZHX) 1, ZHX2 and ZHX3, members of the ZHX family, contain two Cys(2)-His(2)-type zinc-finger motifs and five homeodomains (HDs). These proteins not only form homodimers but heterodimers with ZHX1 as well and act as ubiquitous transcriptional repressors. The cloning of mouse ZHX2 and ZHX3 cDNAs and the corresponding genes from a 129 mouse genomic library are reported, along with an analysis of the heterodimerization of ZHX2 with ZHX3. The mouse ZHX2 and ZHX3 proteins consist of 836 and 951 amino acid residues, respectively. The similarity of amino acid sequences of each protein with those of human orthologue is 87.0% and 85.2%, respectively. An analysis of genomic clones revealed that an entire coding sequence and a portion of the 5'- and 3'-noncoding sequence of mouse ZHX2 cDNA are encoded by a single exon of the mouse ZHX2 gene as well as the mouse ZHX1 gene. In contrast, in the case of the mouse ZHX3 gene, the coding sequences of ZHX3 cDNA are separated by an intron. A 4.5-kb ZHX2 transcript, and three ZHX3 transcripts, 9.5-, 6.5- and 4.4-kb, are ubiquitously expressed, although their levels vary. Lastly, in vitro and in vivo protein-protein interaction assays revealed that ZHX2 is able to form a heterodimer with ZHX3 via a region containing each HD1.

Gene expression of basic helix-loop-helix transcription factor, SHARP-2, is regulated by gonadotropins in the rat ovary and MA-10 cells

Basic helix-loop-helix (bHLH) proteins regulate transcription from the E box sequence (5'-CANNTG-3') located in the regulatory region of most gene promoters. The rat enhancer of split- and hairy-related protein 2 (SHARP-2) is a member of the bHLH protein family. To analyze the possible role of SHARP-2 in the rat ovary, the regulation of the expression of the SHARP-2 gene was examined, and the SHARP-2 protein was characterized. Northern blot analysis revealed that the level of SHARP-2 mRNA abruptly and temporarily increases as the result of the action of LH, i.e., eCG or hCG treatment alone or hCG after eCG treatment, in the rat ovary, as indicated by the treatment of primary cultured rat granulosa cells with hCG after FSH treatment or of mouse Leydig MA-10 cells with hCG or 8-bromoadenosine 3',5'-cyclic monophosphate. An in situ hybridization analysis showed that eCG treatment increases the level of the SHARP-2 transcript in theca interna cells and that hCG treatment, after the administration of eCG, increases the level of the SHARP-2 transcript in granulosa cells. Furthermore, transfection experiments with green fluorescence protein (GFP) expression vectors into primary cultured granulosa cells and MA-10 cells revealed that the entire coding sequence of SHARP-2 fused to the GFP is localized in the nucleus. The transcriptional activity of SHARP-2 also was examined using transient DNA transfection experiments. When an expression vector encoding the full length of SHARP-2 was cotransfected with thymidine kinase promoter-luciferase reporter plasmids, with or without E box sequences, into MA-10 cells, the luciferase activity was decreased in an E box-dependent manner. We conclude that the level of SHARP-2 mRNA is regulated by gonadotropins and that SHARP-2 functions as a transcriptional repressor localized in the nucleus.

Insulin induces the expression of the SHARP-2/Stra13/DEC1 gene via a phosphoinositide 3-kinase pathway

Transcription of the rat fatty acid synthase (FAS) gene in the rat liver can be regulated by feeding a high carbohydrate diet. A carbohydrate response element (ChoRE) located on the rat FAS gene promoter has been identified. Using multiple copies of the ChoRE as the bait in a yeast one-hybrid system, a rat liver cDNA library was screened, and the cDNA of ChoRE-binding proteins was cloned. A positive clone that encodes a basic helix-loop-helix protein, enhancer of split- and hairy-related protein-2 (SHARP-2), was obtained. Northern blot analysis revealed that the levels of SHARP-2 mRNA increase when a high carbohydrate diet is fed to normal rats or when insulin is administered to diabetic rats. In primary cultured rat hepatocytes, insulin rapidly induced an accumulation of SHARP-2 mRNA even in the absence of glucose. A time course for the increase in SHARP-2 mRNA levels indicated that it followed by those of FAS and L-type pyruvate kinase mRNAs and that the initial time course of SHARP-2 mRNA was similar to changes in the levels of glucokinase mRNA and phosphoenolpyruvate carboxykinase mRNA. Although wortmannin, LY294002, and actinomycin D blocked the increase in SHARP-2 mRNA levels by insulin, rapamycin, staurosporine, PD98059, okadaic acid, and 8-bromocyclic AMP had no effect. In addition, nuclear run-on assay revealed that transcription of the rat SHARP-2 gene was induced by insulin. Thus, we conclude that insulin induces the transcription of the rat SHARP-2 gene via a phosphoinositide 3-kinase pathway.

Zinc-fingers and homeoboxes (ZHX) 2, a novel member of the ZHX family, functions as a transcriptional repressor

Zinc-fingers and homeoboxes (ZHX) 1 is a transcription factor that interacts with the activation domain of the A subunit of nuclear factor-Y (NF-YA). Using a yeast two-hybrid system, a novel ubiquitous transcription factor ZHX2 as a ZHX1-interacting protein was cloned. ZHX2 consists of 837 amino acid residues and contains two zinc-finger motifs and five homeodomains (HDs) as well as ZHX1. The mRNA is expressed among various tissues. ZHX2 not only forms a heterodimer with ZHX1, but also forms a homodimer. Moreover, ZHX2 interacts with the activation domain of NF-YA. Further analysis revealed that ZHX2 is a transcriptional repressor that is localized in the nuclei. Since ZHX2 shares a number of properties in common with ZHX1, we conclude that all these come under the ZHX family. The minimal functional domains of ZHX2 were then characterized. The dimerization domain with both ZHX1 and ZHX2 is the region containing HD1, the domain that interacts with NF-YA is the HD1 to HD2 region, the repressor domain is the HD1 to a proline-rich region. Lastly, using an immunoprecipitation assay, we showed that ZHX2 intrinsically interacts with NF-YA in HEK-293 cells and that ZHX2 represses the promoter activity of the cdc25C gene stimulated by NF-Y in Drosophila Schneider line 2 cells. Thus the ZHX family of proteins may participate in the expression of a number of NF-Y-regulated genes via a more organized transcription network.