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1.  Chromatin structure of two genomic sites for targeted transgene integration in induced pluripotent stem cells and hematopoietic stem cells 
Gene therapy  2012;20(2):201-214.
Achieving transgene integration into preselected genomic sites is currently one of the central tasks in stem cell gene therapy. A strategy to mediate such targeted integration involves site specific endonucleases. Two genomic sites within the MBS85 and CCR5 genes [AAVS1 and CCR5 zinc finger nuclease (CCR5-ZFN) site, respectively] have recently been suggested as potential target regions for integration as their disruption has no functional consequence. We hypothesized that efficient transgene integration maybe affected by DNA accessibility of endonucleases and therefore studied the transcriptional and chromatin status of the AAVS1 and CCR5 sites in eight human induced pluripotent stem (iPS) cell lines and pooled CD34+ hematopoietic stem cells. Matrixchromatin immunoprecipitation (ChIP) assays demonstrated that the CCR5 site and surrounding regions possessed a predominantly closed chromatin configuration consistent with its transcriptionally inactivity in these cell types. In contrast, the AAVS1 site was located within a transcriptionally active region and exhibited an open chromatin configuration in both iPS cells and hematopoietic stem cells. To show that the AAVS1 site is readily amendable to genome modification, we expressed Rep78, an AAV2-derived protein with AAVS1-specific endonuclease activity, in iPS cells after adenoviral gene transfer. We showed that Rep78 efficiently associated with the AAVS1 site and triggered genome modifications within this site. On the other hand, binding to and modification of the CCR5-ZFN site by a zinc-finger nuclease was relatively inefficient. Our data suggest a critical influence of chromatin structure on efficacy of site-specific endonucleases used for genome editing.
doi:10.1038/gt.2012.25
PMCID: PMC3661409  PMID: 22436965
2.  Synchronous Recruitment of Epigenetic Modifiers to Endotoxin Synergistically Activated Tnf-α Gene in Acute Kidney Injury 
PLoS ONE  2013;8(7):e70322.
Background
As a consequence of acute kidney injury (AKI), proximal tubular cells hyperrespond to endotoxin (lipopolysaccharide, LPS) by exaggerated renal Tnf-α Production. This LPS hyperresponsiveness is transcriptionally mediated. The epigenetic pathways that control these responses are unknown.
Methods/Findings
We applied multiplex chromatin immunoprecipitation platform (Matrix ChIP) to explore epigenetic pathways that underlie endotoxin hyperresponsiveness in the setting of preceding unilateral renal ischemia/reperfusion (I/R) in mouse AKI model. Endotoxin exposure after I/R resulted in enhanced transcription, manifested by hyperresponsive recruitment of RNA polymerase II (Pol II) at the Tnf-α gene. At this locus, LPS but not I/R increased levels of Pol II C-terminal domain (CTD) phosho-serine2 &5 and induced dephosphorylation of the transcription-repressive histone H4 phospho-serine-1. In contrast, I/R but not LPS increased the transcription-permissive histone phosphorylation (H3 phospho-serine-10, H3.3 phospho-serine-31) at the Tnf-α gene. In agreement with these observations, I/R but not LPS increased activity of cognate kinases (Erk1/2, Msk1/2 and Aurora A) at the Tnf-α locus. Cross-talk of histone phosphorylation and acetylation synergize to active gene expression. I/R and LPS increased histone acetylation. (H3K9/14Ac, H4K5/8/12/16Ac, H2KA5Ac, H2BK4/7Ac). Levels of some histone acetyltransferases at this gene (PCAF and MOF) were increased by I/R but not by LPS, while others were induced by either I/R or LPS and exhibited endotoxin hyperresponsive patterns (GCN5, CBP and p300). The adaptor protein 14-3-3 couples histone phosphorylation with acetylation, and tethers chromatin modifiers/transcription elongation factors to target genes. Both I/R and LPS increased levels of 14-3-3 and several chromatin/transcription modifiers (BRD4, BRG1, HP-1γ and IKKα) at the Tnf-α gene, all exhibiting endotoxin hyperresponsive recruitment patterns similar to Pol II.
Conclusions
Our results suggest that I/R and LPS differentially trigger phosphorylation (Pol II and histone) and acetylation (histone) epigenetic pathways that interact at the Tnf-α gene to generate endotoxin hyperresponse in AKI.
doi:10.1371/journal.pone.0070322
PMCID: PMC3728219  PMID: 23936185
3.  Activation of Wnt/β-Catenin Signaling Increases Apoptosis in Melanoma Cells Treated with Trail 
PLoS ONE  2013;8(7):e69593.
While the TRAIL pathway represents a promising therapeutic target in melanoma, resistance to TRAIL-mediated apoptosis remains a barrier to its successful adoption. Since the Wnt/β-catenin pathway has been implicated in facilitating melanoma cell apoptosis, we investigated the effect of Wnt/β-catenin signaling on regulating the responses of melanoma cells to TRAIL. Co-treatment of melanoma cell lines with WNT3A-conditioned media and recombinant TRAIL significantly enhanced apoptosis compared to treatment with TRAIL alone. This apoptosis correlates with increased abundance of the pro-apoptotic proteins BCL2L11 and BBC3, and with decreased abundance of the anti-apoptotic regulator Mcl1. We then confirmed the involvement of the Wnt/β-catenin signaling pathway by demonstrating that siRNA-mediated knockdown of an intracellular β-catenin antagonist, AXIN1, or treating cells with an inhibitor of GSK-3 also enhanced melanoma cell sensitivity to TRAIL. These studies describe a novel regulation of TRAIL sensitivity in melanoma by Wnt/β-catenin signaling, and suggest that strategies to enhance Wnt/β-catenin signaling in combination with TRAIL agonists warrant further investigation.
doi:10.1371/journal.pone.0069593
PMCID: PMC3711908  PMID: 23869245
4.  Direct Recruitment of Insulin Receptor and ERK Signaling Cascade to Insulin-Inducible Gene Loci 
Diabetes  2010;60(1):127-137.
OBJECTIVE
Insulin receptor (IR) translocates to the nucleus, but its recruitment to gene loci has not been demonstrated. Here, we tested the hypothesis that IR and its downstream mitogenic transducers are corecruited to two prototypic insulin-inducible genes: early growth response 1 (egr-1), involved in mitogenic response, and glucokinase (Gck), encoding a key metabolic enzyme.
RESEARCH DESIGN AND METHODS
We used RNA and chromatin from insulin-treated rat hepatic tumor cell line expressing human insulin receptor (HTC-IR) and livers from lean and insulin-resistant ob/ob glucose-fed mice in quantitative RT-PCR and chromatin immunoprecipitation studies to determine gene expression levels and associated recruitment of RNA polymerase II (Pol II), insulin receptor, and cognate signaling proteins to gene loci, respectively.
RESULTS
Insulin-induced egr-1 mRNA in HTC-IR cells was associated with corecruitment of IR signaling cascade (IR, SOS, Grb2, B-Raf, MEK, and ERK) to this gene. Recruitment profiles of phosphorylated IR, B-Raf, MEK, and Erk along egr-1 transcribed region were similar to those of elongating Pol II. Glucose-feeding increased Gck mRNA expression in livers of lean but not ob/ob mice. In lean mice, there was glucose feeding-induced recruitment of IR and its transducers to Gck gene synchronized with elongating Pol II. In sharp contrast, in glucose-fed ob/ob mice, the Gck recruitment patterns of active MEK/Erk, IR, and Pol II were asynchronous.
CONCLUSIONS
IR and its signal transducers recruited to genes coupled to elongating Pol II may play a role in maintaining productive mRNA synthesis of target genes. These studies suggest a possibility that impaired Pol II processivity along genes bearing aberrant levels of IR/signal transducers is a previously unrecognized facet of insulin resistance.
doi:10.2337/db09-1806
PMCID: PMC3012164  PMID: 20929976
5.  Microplate-based platform for combined chromatin and DNA methylation immunoprecipitation assays 
BMC Molecular Biology  2011;12:49.
Background
The processes that compose expression of a given gene are far more complex than previously thought presenting unprecedented conceptual and mechanistic challenges that require development of new tools. Chromatin structure, which is regulated by DNA methylation and histone modification, is at the center of gene regulation. Immunoprecipitations of chromatin (ChIP) and methylated DNA (MeDIP) represent a major achievement in this area that allow researchers to probe chromatin modifications as well as specific protein-DNA interactions in vivo and to estimate the density of proteins at specific sites genome-wide. Although a critical component of chromatin structure, DNA methylation has often been studied independently of other chromatin events and transcription.
Results
To allow simultaneous measurements of DNA methylation with other genomic processes, we developed and validated a simple and easy-to-use high throughput microplate-based platform for analysis of DNA methylation. Compared to the traditional beads-based MeDIP the microplate MeDIP was more sensitive and had lower non-specific binding. We integrated the MeDIP method with a microplate ChIP assay which allows measurements of both DNA methylation and histone marks at the same time, Matrix ChIP-MeDIP platform. We illustrated several applications of this platform to relate DNA methylation, with chromatin and transcription events at selected genes in cultured cells, human cancer and in a model of diabetic kidney disease.
Conclusion
The high throughput capacity of Matrix ChIP-MeDIP to profile tens and potentially hundreds of different genomic events at the same time as DNA methylation represents a powerful platform to explore complex genomic mechanism at selected genes in cultured cells and in whole tissues. In this regard, Matrix ChIP-MeDIP should be useful to complement genome-wide studies where the rich chromatin and transcription database resources provide fruitful foundation to pursue mechanistic, functional and diagnostic information at genes of interest in health and disease.
doi:10.1186/1471-2199-12-49
PMCID: PMC3247195  PMID: 22098709
6.  Allele-specific transcriptional elongation regulates monoallelic expression of the IGF2BP1 gene 
Background
Random monoallelic expression contributes to phenotypic variation of cells and organisms. However, the epigenetic mechanisms by which individual alleles are randomly selected for expression are not known. Taking cues from chromatin signatures at imprinted gene loci such as the insulin-like growth factor 2 gene 2 (IGF2), we evaluated the contribution of CTCF, a zinc finger protein required for parent-of-origin-specific expression of the IGF2 gene, as well as a role for allele-specific association with DNA methylation, histone modification and RNA polymerase II.
Results
Using array-based chromatin immunoprecipitation, we identified 293 genomic loci that are associated with both CTCF and histone H3 trimethylated at lysine 9 (H3K9me3). A comparison of their genomic positions with those of previously published monoallelically expressed genes revealed no significant overlap between allele-specifically expressed genes and colocalized CTCF/H3K9me3. To analyze the contributions of CTCF and H3K9me3 to gene regulation in more detail, we focused on the monoallelically expressed IGF2BP1 gene. In vitro binding assays using the CTCF target motif at the IGF2BP1 gene, as well as allele-specific analysis of cytosine methylation and CTCF binding, revealed that CTCF does not regulate mono- or biallelic IGF2BP1 expression. Surprisingly, we found that RNA polymerase II is detected on both the maternal and paternal alleles in B lymphoblasts that express IGF2BP1 primarily from one allele. Thus, allele-specific control of RNA polymerase II elongation regulates the allelic bias of IGF2BP1 gene expression.
Conclusions
Colocalization of CTCF and H3K9me3 does not represent a reliable chromatin signature indicative of monoallelic expression. Moreover, association of individual alleles with both active (H3K4me3) and silent (H3K27me3) chromatin modifications (allelic bivalent chromatin) or with RNA polymerase II also fails to identify monoallelically expressed gene loci. The selection of individual alleles for expression occurs in part during transcription elongation.
doi:10.1186/1756-8935-4-14
PMCID: PMC3174113  PMID: 21812971
7.  Halogenated imidazole derivatives block RNA polymerase II elongation along mitogen inducible genes 
Background
Aberrant activation of protein kinases is one of the essential oncogenic driving forces inherent to the process of tumorigenesis. The protein kinase CK2 plays an important role in diverse biological processes, including cell growth and proliferation as well as in the governing and transduction of prosurvival signals. Increased expression of CK2 is a hallmark of some cancers, hence its antiapoptotic properties may be relevant to cancer onset. Thus, the designing and synthesis of the CK2 inhibitors has become an important pursuit in the search for cancer therapies.
Results
Using a high-throughput microarray approach, we demonstrate that two potent inhibitors of CK2, 4,5,6,7-tetrabromo-benzimidazole (TBBz) and 2-Dimethyloamino-4,5,6,7-tetrabromo-1H-benzimidazole (DMAT), blocked mitogen induced mRNA expression of immediate early genes. Given the impact of these inhibitors on the process of transcription, we investigated their effects on RNA Polymerase II (RNAPII) elongation along the mitogen inducible gene, EGR1 (early growth response 1), using chromatin immunoprecipitation (ChIP) assay. ChIP analysis demonstrated that both drugs arrest RNAPII elongation. Finally, we show that CDK9 kinase activity, essential for the triggering of RNAPII elongation, was blocked by TBBz and to lesser degree by DMAT.
Conclusions
Our approach revealed that small molecules derived from halogenated imidazole compounds may decrease cell proliferation, in part, by inhibiting pathways that regulate transcription elongation.
doi:10.1186/1471-2199-11-4
PMCID: PMC2824761  PMID: 20078881
8.  The Rapid Growth Phase in Mice is Associated with Increasing Susceptibility to Acute Renal Failure 
Kidney international  2008;74(5):674-678.
In recent years, experimental studies of acute renal failure (ARF) have been most widely conducted in young mice that are in a rapid growth phase. However, the impact of early growth and development on renal susceptibility to ARF has not been defined. The present study has begun to address this issue by testing the severity of endotoxemic-, glycerol-, and maleate-induced ARF in male CD-1 mice ranging from 3-16 weeks of age (17-45 gm). The potential for age to alter the expression of at least one injury modifier, cellular cholesterol, was also assessed. The severity of each ARF model (BUN / histology) directly correlated with mouse wt. and age (p <0.001). Progressive age- dependent reductions in renal cholesterol content were also observed. The latter were paralleled by stepwise decrements in mRNA levels of two key cholesterol homeostatic genes (HMG CoA reductase, HMGCR, and low density lipoprotein receptor, LDL-R). The mRNA reductions were paralleled by falling RNA polymerase II and transcription factor (SREBP 1 / 2) densities at the HMGCR and LDL-R genes. Hence, we conclude that: 1) the early phase of mouse growth can profoundly alter renal susceptibility to diverse forms of ARF; 2) these changes can reflect fundamental fluxes in select, and likely protean, biochemical and molecular changes at the whole tissue and genomic levels (cholesterol being one such example); 3) ChIP is a powerful tool for studying such changes; and 4) the early growth period needs to be carefully controlled for when conducting studies of experimental ARF.
doi:10.1038/ki.2008.251
PMCID: PMC2744310  PMID: 18563055
9.  High Ambient Glucose Augments Angiotensin II-Induced Proinflammatory Gene mRNA Expression in Human Mesangial Cells: Effects of Valsartan and Simvastatin 
American Journal of Nephrology  2009;30(2):99-111.
Background
Hyperglycemia may potentiate the adverse renal effects of angiotensin II (AII). In the kidney, the major target of AII action is the glomerular mesangial cell, where its hemodynamic and proinflammatory action contributes to renal injury. AII action is mediated by several types of cell receptors. Among those, the AT1 receptor has been best studied using specific AII receptor blockers (ARBs). These agents have emerged as major new modalities in the prevention and amelioration of renal disease where the ARB renoprotective anti-inflammatory properties could be more important than previously appreciated. Like the ARBs, statins may also modulate inflammatory responses that are renoprotective and complement their cholesterol-lowering effects.
Aim
The aim of this project was to (i) identify a repertoire of proinflammatory mesangial cell AII-inducible mRNAs; (ii) determine if the AII-induced proinflammatory mRNA responses depend on ambient glucose, and (iii) test the anti-inflammatory effectiveness of an ARB, valsartan, either alone or in combination with a statin, simvastatin.
Results/Conclusions
Using high-density microarrays and real-time PCR we identified several AII-inducible proinflammatory mesangial genes that exhibited augmented mRNA responses in high-glucose milieu. Valsartan blocked the AII-induced mRNA expression of proinflammatory genes (i.e. MCP-1, LIF and COX-2) maintained in normal and high glucose. These observations add to the mounting evidence that ARBs have anti-inflammatory effects in the kidney, a beneficial effect that may be more important in protecting renal function in diabetic patients. While simvastatin inhibited expression of some mRNAs encoding chemokines/cytokines, it enhanced expression of mRNA encoding COX-2, a key mediator of inflammation. Thus, the non-cholesterol effects of statins on inflammatory responses appear complex.
doi:10.1159/000203619
PMCID: PMC2786028  PMID: 19225232
Angiotensin II; Hyperglycemia; Glomerular mesangial cell; Proinflammatory action
10.  Epistatic Interaction Between the K-Homology Domain Protein HEK2 and SIR1 at HMR and Telomeres in Yeast 
Journal of molecular biology  2007;375(4):1178-1187.
In budding yeast, telomeres, the ribosomal DNA array, and HM loci are transcriptionally silenced by chromatin complexes containing Sir proteins. Hek2, a protein containing three evolutionary conserved RNA-binding K-homology domains, was identified as a suppressor of telomeric silencing [telomeric position effect (TPE)]. To explore the mechanisms of Hek2p action in gene silencing, we examined its relationship with Sir proteins. This search revealed an epistatic interaction between HEK2 and SIR1 at telomeres. Both single mutations, sir1Δ and hek2Δ, enhanced TPE, whereas the effect of double mutation, sir1Δ hek2Δ, did not exceed that of the single mutations. The results of chromatin immunoprecipitation analysis demonstrate that the TPE enhancement observed in these mutants is associated with increased binding of Sir2 protein to telomeres. At the HMR locus, hek2Δ rescues the silencing defect caused by sir1Δ mutation and reverses the loss of Sir2p and Sir3p. These data suggest that the epistatic interaction of HEK2 and SIR1 reflects competition between telomeres and HMR for Sir2/3 factors where HEK2 acts to suppress silencing. Because chromatin immunoprecipitation analysis reveals the presence of Hek2p at a subtelomeric region and HMR, its silencing effects at these loci are likely direct. These observations suggest that HEK2 regulates the composition of Sir complexes at HMR and telomeres.
doi:10.1016/j.jmb.2007.11.001
PMCID: PMC2367324  PMID: 18067921
Hek2; Gene silencing; Sir proteins; Telomeres; HMR
11.  Microplate-based chromatin immunoprecipitation method, Matrix ChIP: a platform to study signaling of complex genomic events 
Nucleic Acids Research  2008;36(3):e17.
The chromatin immunoprecipitation (ChIP) assay is a major tool in the study of genomic processes in vivo. This and other methods are revealing that control of gene expression, cell division and DNA repair involves multiple proteins and great number of their modifications. ChIP assay is traditionally done in test tubes limiting the ability to study signaling of the complex genomic events. To increase the throughput and to simplify the assay we have developed a microplate-based ChIP (Matrix ChIP) method, where all steps from immunoprecipitation to DNA purification are done in microplate wells without sample transfers. This platform has several important advantages over the tube-based assay including very simple sample handling, high throughput, improved sensitivity and reproducibility, and potential for automation. 96 ChIP measurements including PCR can be done by one researcher in one day. We illustrate the power of Matrix ChIP by parallel profiling 80 different chromatin and transcription time-course events along an inducible gene including transient recruitment of kinases.
doi:10.1093/nar/gkn001
PMCID: PMC2241906  PMID: 18203739
12.  Fast chromatin immunoprecipitation assay 
Nucleic Acids Research  2006;34(1):e2.
Chromatin immunoprecipitation (ChIP) is a widely used method to explore in vivo interactions between proteins and DNA. The ChIP assay takes several days to complete, involves several tube transfers and uses either phenol–chlorophorm or spin columns to purify DNA. The traditional ChIP method becomes a challenge when handling multiple samples. We have developed an efficient and rapid Chelex resin-based ChIP procedure that dramatically reduces time of the assay and uses only a single tube to isolate PCR-ready DNA. This method greatly facilitates the probing of chromatin changes over many time points with several antibodies in one experiment.
doi:10.1093/nar/gnj004
PMCID: PMC1325209  PMID: 16397291
13.  Transient recruitment of the hnRNP K protein to inducibly transcribed gene loci 
Nucleic Acids Research  2003;31(14):3954-3962.
The heterogeneous nuclear ribonucleoprotein K protein is an RNA- and DNA-binding protein implicated in the regulation of multiple processes that comprise gene expression. We used chromatin immunoprecipitation (ChIP) assays to explore K protein interactions with serum-inducible, constitutively expressed and untranscribed gene loci in vivo. In the rat HTC-IR hepatoma cell line, serum treatment induced transient increases in the mRNA levels of two immediate-early genes, egr-1 and c-myc. ChIP analysis showed that the induction of egr-1 and c-myc genes was associated with a transient recruitment of K protein to multiple sites within each of these loci, including the promoter and transcribed regions. In contrast, recruitment of K protein to the constitutively transcribed β-actin locus and to randomly chosen non-transcribed loci was far weaker. In rat mesangial cells, c-myc was constitutively expressed while egr-1 remained serum responsive. In these cells, ChIP analysis showed serum-induced recruitment to the inducible egr-1 but not to the c-myc locus. Pre-treatment with the transcription inhibitor actinomycin D blocked the inducible but not the constitutive binding of K protein to these loci. Taken together, the results of this study suggest that the transient recruitment of K protein to serum-responsive loci depends on the inducible transcription of these immediate-early genes.
PMCID: PMC165967  PMID: 12853611
14.  c-Src-Mediated Phosphorylation of hnRNP K Drives Translational Activation of Specifically Silenced mRNAs 
Molecular and Cellular Biology  2002;22(13):4535-4543.
hnRNPK and hnRNP E1/E2 mediate translational silencing of cellular and viral mRNAs in a differentiation-dependent way by binding to specific regulatory sequences. The translation of 15-lipoxygenase (LOX) mRNA in erythroid precursor cells and of the L2 mRNA of human papilloma virus type 16 (HPV-16) in squamous epithelial cells is silenced when either of these cells is immature and is activated in maturing cells by unknown mechanisms. Here we address the question of how the silenced mRNA can be translationally activated. We show that hnRNP K and the c-Src kinase specifically interact with each other, leading to c-Src activation and tyrosine phosphorylation of hnRNP K in vivo and in vitro. c-Src-mediated phosphorylation reversibly inhibits the binding of hnRNP K to the differentiation control element (DICE) of the LOX mRNA 3′ untranslated region in vitro and specifically derepresses the translation of DICE-bearing mRNAs in vivo. Our results establish a novel role of c-Src kinase in translational gene regulation and reveal a mechanism by which silenced mRNAs can be translationally activated.
doi:10.1128/MCB.22.13.4535-4543.2002
PMCID: PMC133888  PMID: 12052863
15.  Synergistic activation of the rat laminin γ1 chain promoter by the gut-enriched Kruppel-like factor (GKLF/KLF4) and Sp1 
Nucleic Acids Research  2002;30(11):2270-2279.
Laminin is a multifunctional heterotrimeric protein present in extracellular matrix where it regulates processes that compose tissue architecture including cell differentiation. Laminin γ1 is the most widely expressed laminin chain and its absence causes early lethality in mouse embryos. Laminin γ1 chain gene (LAMC1) promoter contains several GC/GT-rich motifs including the bcn-1 element. Using the bcn-1 element as a bait in the yeast one-hybrid screen, we cloned the gut-enriched Kruppel-like factor (GKLF or KLF4) from a rat mesangial cell library. We show that GKLF binds bcn-1, but this binding is not required for the GKLF-mediated activation of the LAMC1 promoter. The activity of GKLF is dependent on a synergism with another Kruppel-like factor, Sp1. The LAMC1 promoter appears to have multiple GKLF- and Sp1-responsive elements which may account for the synergistic activation. We provide evidence that the synergistic action of GKLF and Sp1 is dependent on the promoter context and the integrity of GKLF activation and DNA-binding domain. GKLF is thought to participate in the switch from cell proliferation to differentiation. Thus, the Sp1–GKLF synergistic activation of the LAMC1 promoter may be one of the avenues for expression of laminin γ1 chain when laminin is needed to regulate cell differentiation.
PMCID: PMC117209  PMID: 12034813
16.  Yeast hnRNP K-Like Genes Are Involved in Regulation of the Telomeric Position Effect and Telomere Length 
Molecular and Cellular Biology  2002;22(1):286-297.
Mammalian heterogeneous nuclear ribonucleoprotein K (hnRNP K) is an RNA- and DNA-binding protein implicated in the regulation of gene expression processes. To better understand its function, we studied two Saccharomyces cerevisiae homologues of the human hnRNP K, PBP2 and HEK2 (heterogeneous nuclear RNP K-like gene). pbp2Δ and hek2Δ mutations inhibited expression of a marker gene that was inserted near telomere but not at internal chromosomal locations. The telomere proximal to the ectopic marker gene became longer, while most of the other telomeres were not altered in the double mutant cells. We provide evidence that telomere elongation might be the primary event that causes enhanced silencing of an adjacent reporter gene. The telomere lengthening could, in part, be explained by the inhibitory effect of hek2Δ mutation on the telomeric rapid deletion pathway. Hek2p was detected in a complex with chromosome regions proximal to the affected telomere, suggesting a direct involvement of this protein in telomere maintenance. These results identify a role for hnRNP K-like genes in the structural and functional organization of telomeric chromatin in yeast.
doi:10.1128/MCB.22.1.286-297.2002
PMCID: PMC134203  PMID: 11739741
17.  Point Mutations in the WD40 Domain of Eed Block Its Interaction with Ezh2 
Molecular and Cellular Biology  1998;18(10):5634-5642.
The Polycomb group proteins are involved in maintenance of the silenced state of several developmentally regulated genes. These proteins form large aggregates with different subunit compositions. To explore the nature of these complexes and their function, we used the full-length Eed (embryonic ectoderm development) protein, a mammalian homolog of the Drosophila Polycomb group protein Esc, as a bait in the yeast two-hybrid screen. Several strongly interacting cDNA clones were isolated. The cloned cDNAs all encoded the 150- to 200-amino-acid N-terminal fragment of the mammalian homolog of the Drosophila Enhancer of zeste [E(z)] protein, Ezh2. The full-length Ezh2 bound strongly to Eed in vitro, and Eed coimmunoprecipitated with Ezh2 from murine 70Z/3 cell extracts, confirming the interaction between these proteins observed in yeast. Mutations T1031A and T1040C in one of the WD40 repeats of Eed, which account for the hypomorphic and lethal phenotype of eed in mouse development, blocked binding of Ezh2 to Eed in a two-hybrid interaction in yeast and in mammalian cells. These mutations also blocked the interaction between these proteins in vitro. In mammalian cells, the Gal4-Eed fusion protein represses the activity of a promoter bearing Gal4 DNA elements. The N-terminal fragment of the Ezh2 protein abolished the transcriptional repressor activity of Gal4-Eed protein when they were coexpressed in mammalian cells. Eed and Ezh2 were also found to bind RNA in vitro, and RNA altered the interaction between these proteins. These findings suggest that Polycomb group proteins Eed and Ezh2 functionally interact in mammalian cells, an interaction that is mediated by the WD40-containing domain of Eed protein.
PMCID: PMC109149  PMID: 9742080

Results 1-17 (17)