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Chakraborty AR, Vassilev A, Jaiswal SK, O'Connell CE, Ahrens JF, Mallon BS, Pera MF, DePamphilis ML. Selective elimination of pluripotent stem cells by PIKfyve specific inhibitors. Stem Cell Reports 2022; 17:397-412. [PMID: 35063131 PMCID: PMC8828683 DOI: 10.1016/j.stemcr.2021.12.013] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Revised: 12/15/2021] [Accepted: 12/16/2021] [Indexed: 01/05/2023] Open
Abstract
Inhibition of PIKfyve phosphoinositide kinase selectively kills autophagy-dependent cancer cells by disrupting lysosome homeostasis. Here, we show that PIKfyve inhibitors can also selectively eliminate pluripotent embryonal carcinoma cells (ECCs), embryonic stem cells, and induced pluripotent stem cells under conditions where differentiated cells remain viable. PIKfyve inhibitors prevented lysosome fission, induced autophagosome accumulation, and reduced cell proliferation in both pluripotent and differentiated cells, but they induced death only in pluripotent cells. The ability of PIKfyve inhibitors to distinguish between pluripotent and differentiated cells was confirmed with xenografts derived from ECCs. Pretreatment of ECCs with the PIKfyve specific inhibitor WX8 suppressed their ability to form teratocarcinomas in mice, and intraperitoneal injections of WX8 into mice harboring teratocarcinoma xenografts selectively eliminated pluripotent cells. Differentiated cells continued to proliferate, but at a reduced rate. These results provide a proof of principle that PIKfyve specific inhibitors can selectively eliminate pluripotent stem cells in vivo as well as in vitro.
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Affiliation(s)
- Arup R Chakraborty
- National Institute of Child Health & Human Development, National Institutes of Health, Bldg. 6A/3A15, 6 Center Drive, Bethesda, MD 20892-2790, USA
| | - Alex Vassilev
- National Institute of Child Health & Human Development, National Institutes of Health, Bldg. 6A/3A15, 6 Center Drive, Bethesda, MD 20892-2790, USA
| | - Sushil K Jaiswal
- National Institute of Child Health & Human Development, National Institutes of Health, Bldg. 6A/3A15, 6 Center Drive, Bethesda, MD 20892-2790, USA
| | - Constandina E O'Connell
- National Institute of Child Health & Human Development, National Institutes of Health, Bldg. 6A/3A15, 6 Center Drive, Bethesda, MD 20892-2790, USA
| | - John F Ahrens
- National Institute of Child Health & Human Development, National Institutes of Health, Bldg. 6A/3A15, 6 Center Drive, Bethesda, MD 20892-2790, USA
| | - Barbara S Mallon
- NIH Stem Cell Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | | | - Melvin L DePamphilis
- National Institute of Child Health & Human Development, National Institutes of Health, Bldg. 6A/3A15, 6 Center Drive, Bethesda, MD 20892-2790, USA.
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O'Connell CE, Vassilev A. Combined Inhibition of p38MAPK and PIKfyve Synergistically Disrupts Autophagy to Selectively Target Cancer Cells. Cancer Res 2021; 81:2903-2917. [PMID: 33685990 DOI: 10.1158/0008-5472.can-20-3371] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Revised: 01/29/2021] [Accepted: 03/01/2021] [Indexed: 12/09/2022]
Abstract
In nutrient-poor conditions, autophagy buffers metabolic stress and counteracts the effects of chemotherapy and radiation on cancer cells, which depend on autophagy for survival. However, clinical trials targeting autophagy have failed to produce successful anticancer treatments using currently available inhibitors. Recent studies have shown that PIKfyve kinase inhibitors disrupt lysosome function in autophagy and can selectively kill certain cancer cells. Analysis of biochemical changes caused by PIKfyve inhibition revealed that resistant cells contain significantly higher levels of cellular p38MAPK protein and phosphorylation. Expression of the lysosomal protein, lysosomal-associated membrane protein 2, carrying phosphomimetic mutations of the p38MAPK phosphorylation sites prevented all effects caused by PIKfyve inhibition-induced lysosome dysfunction. Thus, the activation of p38MAPK in response to PIKfyve inhibition revealed a novel compensatory role in maintaining lysosome function in autophagy. The functional cooperation between the cellular PIKfyve and p38MAPK pathways in regulating lysosome homeostasis was especially important in cancer cells. Combined inhibition of PIKfyve and p38MAPK activities synergistically blocked autophagy-mediated protein degradation, prevented cathepsin maturation, and markedly reduced the viability of multiple cancer cell types without affecting the viability of normal cells. Furthermore, combined PIKfyve and p38MAPK inhibitors synergistically reduced tumor growth in mice bearing xenografts of human colorectal adenocarcinoma, suggesting a novel way to target cancer cells by prolonged inhibition of autophagy using lower drug concentrations. SIGNIFICANCE: This study demonstrates that PIKfyve and p38MAPK cooperate to regulate lysosome homeostasis and their combined inhibition synergistically blocks autophagy to reduce cancer cell viability in vitro and in vivo.
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Affiliation(s)
| | - Alex Vassilev
- National Institute of Child Health and Human Development, NIH, Bethesda, Maryland.
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3
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Sharma G, Guardia CM, Roy A, Vassilev A, Saric A, Griner LN, Marugan J, Ferrer M, Bonifacino JS, DePamphilis ML. A family of PIKFYVE inhibitors with therapeutic potential against autophagy-dependent cancer cells disrupt multiple events in lysosome homeostasis. Autophagy 2019; 15:1694-1718. [PMID: 30806145 DOI: 10.1080/15548627.2019.1586257] [Citation(s) in RCA: 68] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
High-throughput screening identified 5 chemical analogs (termed the WX8-family) that disrupted 3 events in lysosome homeostasis: (1) lysosome fission via tubulation without preventing homotypic lysosome fusion; (2) trafficking of molecules into lysosomes without altering lysosomal acidity, and (3) heterotypic fusion between lysosomes and autophagosomes. Remarkably, these compounds did not prevent homotypic fusion between lysosomes, despite the fact that homotypic fusion required some of the same machinery essential for heterotypic fusion. These effects varied 400-fold among WX8-family members, were time and concentration dependent, reversible, and resulted primarily from their ability to bind specifically to the PIKFYVE phosphoinositide kinase. The ability of the WX8-family to prevent lysosomes from participating in macroautophagy/autophagy suggested they have therapeutic potential in treating autophagy-dependent diseases. In fact, the most potent family member (WX8) was 100-times more lethal to 'autophagy-addicted' melanoma A375 cells than the lysosomal inhibitors hydroxychloroquine and chloroquine. In contrast, cells that were insensitive to hydroxychloroquine and chloroquine were also insensitive to WX8. Therefore, the WX8-family of PIKFYVE inhibitors provides a basis for developing drugs that could selectively kill autophagy-dependent cancer cells, as well as increasing the effectiveness of established anti-cancer therapies through combinatorial treatments. Abbreviations: ACTB: actin beta; Baf: bafilomycin A1; BECN1: beclin 1; BODIPY: boron-dipyrromethene; BORC: BLOC-1 related complex; BRAF: B-Raf proto-oncogene, serine/threonine kinase; BSA: bovine serum albumin; CTSD: cathepsin D; CQ: chloroquine; DNA: deoxyribonucleic acid; EC50: half maximal effective concentration; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; HCQ: hydroxychloroquine; HOPS complex: homotypic fusion and protein sorting complex; Kd: equilibrium binding constant; IC50: half maximal inhibitory concentration; KO: knockout; LAMP1: lysosomal associated membrane protein 1; MAP1LC3A: microtubule associated protein 1 light chain 3 alpha; MES: 2-(N-morpholino)ethanesulphonic acid; MTOR: mechanistic target of rapamycin kinase; μM: micromolar; NDF: 3-methylbenzaldehyde (2,6-dimorpholin-4-ylpyrimidin-4-yl)hydrazine;NEM: N-ethylmaleimide; NSF: N-ethylmaleimide sensitive factor; PBS: phosphate-buffered saline; PIKFYVE: phosphoinositide kinase, FYVE-type zinc finger containing; PIP4K2C: phosphatidylinositol-5-phosphate 4-kinase type 2 gamma; PtdIns3P: phosphatidylinositol 3-phosphate; PtdIns(3,5)P2: phosphatidylinositol 3,5-biphosphate; RFP: red fluorescent protein; RPS6: ribosomal protein S6; RPS6KB1: ribosomal protein S6 kinase B1; SQSTM1: sequestosome 1; TWEEN 20: polysorbate 20; V-ATPase: vacuolar-type H+-translocating ATPase; VPS39: VPS39 subunit of HOPS complex; VPS41: VPS41 subunit of HOPS complex; WWL: benzaldehyde [2,6-di(4-morpholinyl)-4-pyrimidinyl]hydrazone; WX8: 1H-indole-3-carbaldehyde [4-anilino-6-(4-morpholinyl)-1,3,5-triazin-2-yl]hydrazine; XBA: N-(3-chloro-4-fluorophenyl)-4,6-dimorpholino-1,3,5-triazin-2-amine hydrochloride; XB6: N-(4-ethylphenyl)-4,6-dimorpholino-1,3,5-triazin-2-amine hydrochloride.
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Affiliation(s)
- Gaurav Sharma
- Division of Developmental Biology, National Institute of Child Health & Human Development, National Institutes of Health , Bethesda , MD , USA
| | - Carlos M Guardia
- Cell Biology and Neurobiology Branch, National Institute of Child Health & Human Development, National Institutes of Health , Bethesda , MD , USA
| | - Ajit Roy
- Division of Developmental Biology, National Institute of Child Health & Human Development, National Institutes of Health , Bethesda , MD , USA
| | - Alex Vassilev
- Division of Developmental Biology, National Institute of Child Health & Human Development, National Institutes of Health , Bethesda , MD , USA
| | - Amra Saric
- Cell Biology and Neurobiology Branch, National Institute of Child Health & Human Development, National Institutes of Health , Bethesda , MD , USA
| | - Lori N Griner
- Division of Developmental Biology, National Institute of Child Health & Human Development, National Institutes of Health , Bethesda , MD , USA
| | - Juan Marugan
- Division of Pre-Clinical Innovation, NIH Chemical Genomics Center, National Center for Advancing Translational Sciences, National Institutes of Health , Rockville , MD , USA
| | - Marc Ferrer
- Division of Pre-Clinical Innovation, NIH Chemical Genomics Center, National Center for Advancing Translational Sciences, National Institutes of Health , Rockville , MD , USA
| | - Juan S Bonifacino
- Cell Biology and Neurobiology Branch, National Institute of Child Health & Human Development, National Institutes of Health , Bethesda , MD , USA
| | - Melvin L DePamphilis
- Division of Developmental Biology, National Institute of Child Health & Human Development, National Institutes of Health , Bethesda , MD , USA
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Vassilev A, Lee CY, Vassilev B, Zhu W, Ormanoglu P, Martin SE, DePamphilis ML. Identification of genes that are essential to restrict genome duplication to once per cell division. Oncotarget 2018; 7:34956-76. [PMID: 27144335 PMCID: PMC5085202 DOI: 10.18632/oncotarget.9008] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 04/07/2016] [Indexed: 12/02/2022] Open
Abstract
Nuclear genome duplication is normally restricted to once per cell division, but aberrant events that allow excess DNA replication (EDR) promote genomic instability and aneuploidy, both of which are characteristics of cancer development. Here we provide the first comprehensive identification of genes that are essential to restrict genome duplication to once per cell division. An siRNA library of 21,584 human genes was screened for those that prevent EDR in cancer cells with undetectable chromosomal instability. Candidates were validated by testing multiple siRNAs and chemical inhibitors on both TP53+ and TP53- cells to reveal the relevance of this ubiquitous tumor suppressor to preventing EDR, and in the presence of an apoptosis inhibitor to reveal the full extent of EDR. The results revealed 42 genes that prevented either DNA re-replication or unscheduled endoreplication. All of them participate in one or more of eight cell cycle events. Seventeen of them have not been identified previously in this capacity. Remarkably, 14 of the 42 genes have been shown to prevent aneuploidy in mice. Moreover, suppressing a gene that prevents EDR increased the ability of the chemotherapeutic drug Paclitaxel to induce EDR, suggesting new opportunities for synthetic lethalities in the treatment of human cancers.
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Affiliation(s)
- Alex Vassilev
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2753, USA
| | - Chrissie Y Lee
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2753, USA.,Current address: NantBioscience, Culver City, CA 90232, USA
| | - Boris Vassilev
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2753, USA
| | - Wenge Zhu
- Department of Biochemistry and Molecular Biology, George Washington University, Washington DC 20037, USA
| | - Pinar Ormanoglu
- National Center of Advancing Translational Sciences, National Institutes of Health, Rockville, MD 20850, USA
| | - Scott E Martin
- National Center of Advancing Translational Sciences, National Institutes of Health, Rockville, MD 20850, USA.,Current Address: Genentech, Inc., South San Francisco, CA 94080, USA
| | - Melvin L DePamphilis
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2753, USA
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Vercampt H, Koleva L, Vassilev A, Horemans N, Biermans G, Vangronsveld J, Cuypers A. The functional role of the photosynthetic apparatus in the recovery of Brassica napus plants from pre-emergent metazachlor exposure. J Plant Physiol 2016; 196-197:99-105. [PMID: 27135933 DOI: 10.1016/j.jplph.2016.04.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Revised: 03/10/2016] [Accepted: 04/01/2016] [Indexed: 06/05/2023]
Abstract
Metazachlor is a chloroacetamide herbicide, frequently used in Brassica napus cultivations around the world. Its primary target is the inhibition of very long chain fatty acid biosynthesis. This study included a morphological and physiological screening of hydroponically grown B. napus, exposed to a concentration range of 0, 0.25, 0.50, 0.75 and 1.0kg metazachlor per hectare. The results indicate that within a month after application, growth and development of B. napus are severely affected by low metazachlor doses. At intermediate metazachlor concentrations, loss of phosphorous and potassium from the plant tissues suggests destabilisation of cellular membranes, which may be a direct consequence of metazachlor application. This membrane instability could be indirectly linked with alterations of electron transport and a reduction of carbon assimilation. At increased metazachlor doses of 0.75kga.i.ha(-1), pigment concentrations are strongly reduced. However, chlorophyll fluorescence parameters seem to remain unaffected at metazachlor doses up to 0.75kga.i.ha(-1). At a metazachlor concentration of 1.0kga.i.ha(-1), negative effects are observed on all tested parameters, resulting in limited survival. The results indicate photosynthesis is assured at intermediate metazachlor concentrations for the cost of growth and development. It is clear that photosynthesis plays a key role in the survival strategy of young plants to overcome initially induced chemical stress.
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Affiliation(s)
- H Vercampt
- Hasselt University, Centre for Environmental Sciences, Agoralaan Building D, 3590 Diepenbeek, Belgium
| | - L Koleva
- Agricultural University of Plovdiv, 12 Mendeleev Street, 4000 Plovdiv, Bulgaria
| | - A Vassilev
- Agricultural University of Plovdiv, 12 Mendeleev Street, 4000 Plovdiv, Bulgaria
| | - N Horemans
- Belgian Nuclear Research Centre (SCK-CEN), Biosphere Impact Studies, Boeretang 200, 2400 Mol, Belgium
| | - G Biermans
- Federaal Agentschap voor Nucleaire Controle (FANC), Ravensteinstraat 36, 1000 Brussel, Belgium
| | - J Vangronsveld
- Hasselt University, Centre for Environmental Sciences, Agoralaan Building D, 3590 Diepenbeek, Belgium
| | - A Cuypers
- Hasselt University, Centre for Environmental Sciences, Agoralaan Building D, 3590 Diepenbeek, Belgium.
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Yarham JW, Lamichhane TN, Pyle A, Mattijssen S, Baruffini E, Bruni F, Donnini C, Vassilev A, He L, Blakely EL, Griffin H, Santibanez-Koref M, Bindoff LA, Ferrero I, Chinnery PF, McFarland R, Maraia RJ, Taylor RW. Defective i6A37 modification of mitochondrial and cytosolic tRNAs results from pathogenic mutations in TRIT1 and its substrate tRNA. PLoS Genet 2014; 10:e1004424. [PMID: 24901367 PMCID: PMC4046958 DOI: 10.1371/journal.pgen.1004424] [Citation(s) in RCA: 102] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2013] [Accepted: 04/20/2014] [Indexed: 01/10/2023] Open
Abstract
Identifying the genetic basis for mitochondrial diseases is technically challenging given the size of the mitochondrial proteome and the heterogeneity of disease presentations. Using next-generation exome sequencing, we identified in a patient with severe combined mitochondrial respiratory chain defects and corresponding perturbation in mitochondrial protein synthesis, a homozygous p.Arg323Gln mutation in TRIT1. This gene encodes human tRNA isopentenyltransferase, which is responsible for i6A37 modification of the anticodon loops of a small subset of cytosolic and mitochondrial tRNAs. Deficiency of i6A37 was previously shown in yeast to decrease translational efficiency and fidelity in a codon-specific manner. Modelling of the p.Arg323Gln mutation on the co-crystal structure of the homologous yeast isopentenyltransferase bound to a substrate tRNA, indicates that it is one of a series of adjacent basic side chains that interact with the tRNA backbone of the anticodon stem, somewhat removed from the catalytic center. We show that patient cells bearing the p.Arg323Gln TRIT1 mutation are severely deficient in i6A37 in both cytosolic and mitochondrial tRNAs. Complete complementation of the i6A37 deficiency of both cytosolic and mitochondrial tRNAs was achieved by transduction of patient fibroblasts with wild-type TRIT1. Moreover, we show that a previously-reported pathogenic m.7480A>G mt-tRNASer(UCN) mutation in the anticodon loop sequence A36A37A38 recognised by TRIT1 causes a loss of i6A37 modification. These data demonstrate that deficiencies of i6A37 tRNA modification should be considered a potential mechanism of human disease caused by both nuclear gene and mitochondrial DNA mutations while providing insight into the structure and function of TRIT1 in the modification of cytosolic and mitochondrial tRNAs. Mitochondrial disorders are clinically diverse, and identifying the underlying genetic mutations is technically challenging due to the large number of mitochondrial proteins. Using high-throughput sequencing technology, we identified a disease-causing mutation in the TRIT1 gene. This gene encodes an enzyme, tRNA isopentenyltransferase, that adds an N6-isopentenyl modification to adenosine-37 (i6A37) in a small number of tRNAs, enabling them to function correctly during the synthesis of essential mitochondrial proteins. We show that this mutation leads to severe deficiency of tRNA-i6A37 in the patient's cells that can be rescued by introduction of the wild-type TRIT1 protein. A deficiency in oxidative phosphorylation, the process by which energy (ATP) is generated in the mitochondria, leads to a mitochondrial disease presentation. Introducing the mutant protein into model yeast species and measuring the resulting impairment provided further evidence of the pathogenic effect of the mutation. Additional studies investigating a previously reported pathogenic mutation in a mitochondrial tRNA gene demonstrated that a mutation in a substrate of TRIT1 can also cause a loss of the modification, providing evidence of a new mechanism causing mitochondrial disease in humans.
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Affiliation(s)
- John W. Yarham
- Wellcome Trust Centre for Mitochondrial Research, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Tek N. Lamichhane
- Intramural Research Program, NICHD, NIH, Bethesda, Maryland, United States of America
| | - Angela Pyle
- Wellcome Trust Centre for Mitochondrial Research, Institute for Genetic Medicine, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Sandy Mattijssen
- Intramural Research Program, NICHD, NIH, Bethesda, Maryland, United States of America
| | | | - Francesco Bruni
- Wellcome Trust Centre for Mitochondrial Research, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Claudia Donnini
- Department of Life Sciences, University of Parma, Parma, Italy
| | - Alex Vassilev
- Intramural Research Program, NICHD, NIH, Bethesda, Maryland, United States of America
| | - Langping He
- Wellcome Trust Centre for Mitochondrial Research, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Emma L. Blakely
- Wellcome Trust Centre for Mitochondrial Research, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Helen Griffin
- Wellcome Trust Centre for Mitochondrial Research, Institute for Genetic Medicine, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Mauro Santibanez-Koref
- Wellcome Trust Centre for Mitochondrial Research, Institute for Genetic Medicine, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Laurence A. Bindoff
- Department of Neurology, Haukeland University Hospital, Bergen, Norway
- Department of Clinical Medicine, University of Bergen, Bergen, Norway
| | - Ileana Ferrero
- Department of Life Sciences, University of Parma, Parma, Italy
| | - Patrick F. Chinnery
- Wellcome Trust Centre for Mitochondrial Research, Institute for Genetic Medicine, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Robert McFarland
- Wellcome Trust Centre for Mitochondrial Research, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Richard J. Maraia
- Intramural Research Program, NICHD, NIH, Bethesda, Maryland, United States of America
- * E-mail: (RJM) (RM); (RWT) (RT)
| | - Robert W. Taylor
- Wellcome Trust Centre for Mitochondrial Research, Institute for Ageing and Health, The Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom
- * E-mail: (RJM) (RM); (RWT) (RT)
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Kofron M, Nadezdina E, Vassilev A, Matuliene J, Essner R, Kato J, Kuriyama R. Interaction of an Overexpressed gamma-Tubulin with Microtubules In Vivo and In Vitro. Zoolog Sci 2012; 15:477-87. [PMID: 18462027 DOI: 10.2108/0289-0003(1998)15[477:ioaotw]2.0.co;2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/1998] [Accepted: 05/06/1998] [Indexed: 11/17/2022]
Abstract
gamma-Tubulin is an ubiquitous MTOC (microtubule-organizing center) component essential for the regulation of microtubule functions. A 1.8 kb cDNA coding for gamma-tubulin was isolated from CHO cells. Analysis of nucleotide sequence predicts a protein of 451 amino acids, which is over 97% identical to human and Xenopus gamma-tubulin. When CHO cells were transiently transfected with the gamma-tubulin clone, epitope-tagged full-length, as well as truncated polypeptides (amino acids 1-398 and 1-340), resulted in the formation of cytoplasmic foci of various sizes. Although one of the foci was identified as the centrosome, the rest of the dots were not associated with any other centrosomal components tested so far. The pattern of microtubule organization was not affected by induction of such gamma-tubulin-containing dots in transfected cells. In addition, the cytoplasmic foci were unable to serve as the site for microtubule regrowth in nocodazole-treated cells upon removal of the drug, suggesting that gamma-tubulin-containing foci were not involved in the activity for microtubule formation and organization. Using the monomeric form of Chlamydomonas gamma-tubulin purified from insect Sf9 cells (), interaction between gamma-tubulin and microtubules was further investigated by immunoelectron microscopy. Microtubules incubated with gamma-tubulin monomers in vitro were associated with more gold particles conjugated with gamma-tubulin than in controls where no exogenous gamma-tubulin was added. However, binding of gamma-tubulin to microtubules was not extensive and was easily lost during sample preparation. Although gamma-tubulin was detected at the minus end of microtubules several times more frequently than the plus end, the majority of gold particles were seen along the microtubule length. These results contradict the previous reports (; ), which might be ascribed to the difference in the level of protein expression in transfected cells.
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Chon H, Vassilev A, DePamphilis ML, Zhao Y, Zhang J, Burgers PM, Crouch RJ, Cerritelli SM. Contributions of the two accessory subunits, RNASEH2B and RNASEH2C, to the activity and properties of the human RNase H2 complex. Nucleic Acids Res 2008; 37:96-110. [PMID: 19015152 PMCID: PMC2615623 DOI: 10.1093/nar/gkn913] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Eukaryotic RNase H2 is a heterotrimeric enzyme. Here, we show that the biochemical composition and stoichiometry of the human RNase H2 complex is consistent with the properties previously deduced from genetic studies. The catalytic subunit of eukaryotic RNase H2, RNASEH2A, is well conserved and similar to the monomeric prokaryotic RNase HII. In contrast, the RNASEH2B and RNASEH2C subunits from human and Saccharomyces cerevisiae share very little homology, although they both form soluble B/C complexes that may serve as a nucleation site for the addition of RNASEH2A to form an active RNase H2, or for interactions with other proteins to support different functions. The RNASEH2B subunit has a PIP-box and confers PCNA binding to human RNase H2. Unlike Escherichia coli RNase HII, eukaryotic RNase H2 acts processively and hydrolyzes a variety of RNA/DNA hybrids with similar efficiencies, suggesting multiple cellular substrates. Moreover, of five analyzed mutations in human RNASEH2B and RNASEH2C linked to Aicardi-Goutières Syndrome (AGS), only one, R69W in the RNASEH2C protein, exhibits a significant reduction in specific activity, revealing a role for the C subunit in enzymatic activity. Near-normal activity of four AGS-related mutant enzymes was unexpected in light of their predicted impairment causing the AGS phenotype.
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Affiliation(s)
- Hyongi Chon
- Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda MD 20892, USA
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Noguchi K, Vassilev A, Ghosh S, Yates JL, DePamphilis ML. The BAH domain facilitates the ability of human Orc1 protein to activate replication origins in vivo. EMBO J 2006; 25:5372-82. [PMID: 17066079 PMCID: PMC1636626 DOI: 10.1038/sj.emboj.7601396] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2006] [Accepted: 09/21/2006] [Indexed: 11/09/2022] Open
Abstract
Selection of initiation sites for DNA replication in eukaryotes is determined by the interaction between the origin recognition complex (ORC) and genomic DNA. In mammalian cells, this interaction appears to be regulated by Orc1, the only ORC subunit that contains a bromo-adjacent homology (BAH) domain. Since BAH domains mediate protein-protein interactions, the human Orc1 BAH domain was mutated, and the mutant proteins expressed in human cells to determine their affects on ORC function. The BAH domain was not required for nuclear localization of Orc1, association of Orc1 with other ORC subunits, or selective degradation of Orc1 during S-phase. It did, however, facilitate reassociation of Orc1 with chromosomes during the M to G1-phase transition, and it was required for binding Orc1 to the Epstein-Barr virus oriP and stimulating oriP-dependent plasmid DNA replication. Moreover, the BAH domain affected Orc1's ability to promote binding of Orc2 to chromatin as cells exit mitosis. Thus, the BAH domain in human Orc1 facilitates its ability to activate replication origins in vivo by promoting association of ORC with chromatin.
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Affiliation(s)
- Kohji Noguchi
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Alex Vassilev
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Soma Ghosh
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - John L Yates
- Department of Cancer Genetics, Roswell Park Cancer Institute, Buffalo, NY, USA
| | - Melvin L DePamphilis
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
- National Institute of Child Health and Human Development, National Institutes of Health, Building 6/3A15, 9000 Rockville Pike, Bethesda, MD 20892-2753, USA. Tel.: +1 301 402 8234; Fax: +1 301 480 9354; E-mail:
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Kovalska VB, Tokar VP, Losytskyy MY, Deligeorgiev T, Vassilev A, Gadjev N, Drexhage KH, Yarmoluk SM. Studies of monomeric and homodimeric oxazolo[4,5-b]pyridinium cyanine dyes as fluorescent probes for nucleic acids visualization. ACTA ACUST UNITED AC 2006; 68:155-65. [PMID: 16828165 DOI: 10.1016/j.jbbm.2006.04.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2005] [Revised: 02/08/2006] [Accepted: 04/14/2006] [Indexed: 11/30/2022]
Abstract
The series of recently synthesized monomeric and homodimeric cyanine dyes based on monomethine cyanine chromophore with oxazolo[4,5-b]pyridinium and quinoline end groups [Vassilev A, Deligeorgiev T, Gadjev N, Drexhage K-H. Synthesis of novel monomeric and homodimeric cyanine dyes based on oxazolo[4,5-b]pyridinium and quinolinium end groups for nucleic acid detection, Dyes Pigm 2005;66:135-142] were studied as possible fluorescent probes for nucleic acids detection. Significant fluorescence enhancement and intensity level (quantum yield up to 0.75) was observed for all the dyes in the presence of DNA. The oxazolo[4,5-b]pyridinium cyanines demonstrated high sensitivity as fluorescent stains for post-electrophoretic visualization of nucleic acids in agarose gels upon both VIS and UV transillumination, and the visualized band contained 0.8 ng of dsDNA.
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Affiliation(s)
- V B Kovalska
- Institute of Molecular Biology and Genetics, National Academy of Science of Ukraine, 150 Zabolotnogo St., 03143 Kyiv, Ukraine
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11
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Radichev I, Kwon SW, Zhao Y, DePamphilis ML, Vassilev A. Genetic analysis of human Orc2 reveals specific domains that are required in vivo for assembly and nuclear localization of the origin recognition complex. J Biol Chem 2006; 281:23264-73. [PMID: 16762929 DOI: 10.1074/jbc.m603873200] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Eukaryotic DNA replication begins with the binding of a six subunit origin recognition complex (ORC) to DNA. To study the assembly and function of mammalian ORC proteins in their native environment, HeLa cells were constructed that constitutively expressed an epitope-tagged, recombinant human Orc2 subunit that had been genetically altered. Analysis of these cell lines revealed that Orc2 contains a single ORC assembly domain that is required in vivo for interaction with all other ORC subunits, as well as two nuclear localization signals (NLSs) that are required for ORC accumulation in the nucleus. The recombinant Orc2 existed in the nucleus either as an ORC-(2-5) or ORC-(1-5) complex; no other combinations of ORC subunits were detected. Moreover, only ORC-(1-5) was bound to the chromatin fraction, suggesting that Orc1 is required in vivo to load ORC-(2-5) onto chromatin. Surprisingly, recombinant Orc2 suppressed expression of endogenous Orc2, revealing that mammalian cells limit the intracellular level of Orc2, and thereby limit the amount of ORC-(2-5) in the nucleus. Because this suppression required only the ORC assembly and NLS domains, these domains appear to constitute the functional domain of Orc2.
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Affiliation(s)
- Ilian Radichev
- NICHD, National Institutes of Health, Bethesda, Maryland 20892-2753, USA
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12
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DePamphilis ML, Blow JJ, Ghosh S, Saha T, Noguchi K, Vassilev A. Regulating the licensing of DNA replication origins in metazoa. Curr Opin Cell Biol 2006; 18:231-9. [PMID: 16650748 DOI: 10.1016/j.ceb.2006.04.001] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2006] [Accepted: 04/04/2006] [Indexed: 01/19/2023]
Abstract
Eukaryotic DNA replication is a highly conserved process; the proteins and sequence of events that replicate animal genomes are remarkably similar to those that replicate yeast genomes. Moreover, the assembly of prereplication complexes at DNA replication origins ('DNA licensing') is regulated in all eukaryotes so that no origin fires more than once in a single cell cycle. And yet there are significant differences between species both in the selection of replication origins and in the way in which these origins are licensed to operate. Moreover, these differences impart advantages to multicellular animals and plants that facilitate their development, such as better control over endoreduplication, flexibility in origin selection, and discrimination between quiescent and proliferative states.
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Affiliation(s)
- Melvin L DePamphilis
- National Institute of Child Health and Human Development, National Institutes of Health, Building 6/3A-15, 9000 Rockville Pike, Bethesda, MD 20892-2753, USA.
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13
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Saha T, Ghosh S, Vassilev A, DePamphilis ML. Ubiquitylation, phosphorylation and Orc2 modulate the subcellular location of Orc1 and prevent it from inducing apoptosis. J Cell Sci 2006; 119:1371-82. [PMID: 16537645 PMCID: PMC2766536 DOI: 10.1242/jcs.02851] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Previous studies have suggested that the activity of the mammalian origin recognition complex (ORC) is regulated by cell-cycle-dependent changes in its Orc1 subunit. Here, we show that Orc1 modifications such as mono-ubiquitylation and hyperphosphorylation that occur normally during S and G2-M phases, respectively, can cause Orc1 to accumulate in the cytoplasm. This would suppress reassembly of pre-replication complexes until mitosis is complete. In the absence of these modifications, transient expression of Orc1 rapidly induced p53-independent apoptosis, and Orc1 accumulated perinuclearly rather than uniformly throughout the nucleus. This behavior mimicked the increased concentration and perinuclear accumulation of endogenous Orc1 in apoptotic cells that arise spontaneously in proliferating cell cultures. Remarkably, expression of Orc1 in the presence of an equivalent amount of Orc2, the only ORC subunit that did not induce apoptosis, prevented induction of apoptosis and restored uniform nuclear localization of Orc1. This would promote assembly of ORC-chromatin sites, such as occurs during the transition from M to G1 phase. These results provide direct evidence in support of the regulatory role proposed for Orc1, and suggest that aberrant DNA replication during mammalian development could result in apoptosis through the appearance of 'unmodified' Orc1.
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14
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Nakatani Y, Konishi H, Vassilev A, Kurooka H, Ishiguro K, Sawada JI, Ikura T, Korsmeyer SJ, Qin J, Herlitz AM. p600, a unique protein required for membrane morphogenesis and cell survival. Proc Natl Acad Sci U S A 2005; 102:15093-8. [PMID: 16214886 PMCID: PMC1247991 DOI: 10.1073/pnas.0507458102] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
In this article, we identify and characterize p600, a unique 600-kDa retinoblastoma protein- and calmodulin-binding protein. In the nucleus, p600 and retinoblastoma protein seem to act as a chromatin scaffold. In the cytoplasm, p600 and clathrin form a meshwork structure, which could contribute to cytoskeletal organization and membrane morphogenesis. Reduced expression of p600 with interference RNA abrogates integrin-mediated ruffled membrane formation and, furthermore, prevents activation of integrin-mediated survival pathways. Consequently, knockdown of p600 sensitizes cells to apoptosis induced by cell detachment. These findings provide mechanistic insight into the regulation of membrane-proximal events in tumorigenesis.
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Affiliation(s)
- Yoshihiro Nakatani
- Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02115, USA.
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15
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Uckun FM, Venkatachalam TK, Erbeck D, Chen CL, Petkevich AS, Vassilev A. Zidampidine, an aryl phosphate derivative of AZT: in vivo pharmacokinetics, metabolism, toxicity, and anti-viral efficacy against hemorrhagic fever caused by Lassa virus. Bioorg Med Chem 2005; 13:3279-88. [PMID: 15809163 DOI: 10.1016/j.bmc.2005.02.031] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2004] [Accepted: 02/14/2005] [Indexed: 01/23/2023]
Abstract
The pharmacokinetics, metabolism, and toxicity of Zidampidine, an aryl phosphate derivative of AZT, 3'-azidothymidine-5'-[p-bromophenyl methoxyalaninyl phosphate] were investigated in CD-1 mice. Following iv injection, Zidampidine was rapidly converted to its metabolites Ala-AZT-MP and AZT. Zidampidine was not toxic to mice at doses up to 250mg/kg. We next examined the therapeutic effect of Zidampidine in CBA mice challenged with intracerebral injections of the Josiah strain of Lassa virus. Mice were treated either with vehicle or non-toxic doses of Zidampidine administered intraperitoneally 24h prior, 1h prior, and 24, 48, 72, and 96h after virus inoculation. The probability of survival following the Lassa challenge was significantly improved for Zidampidine-treated mice (Kaplan Meier, Log-Rank p value<0.0001). This pilot study provides the basis for future preclinical evaluation of Zidampidine and its potential as a new agent for the treatment of viral hemorrhagic fevers caused by Lassa virus.
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Affiliation(s)
- F M Uckun
- Drug Discovery Program, Parker Hughes Center for Clinical Immunology, 2699 Patton Road, St. Paul, MN 55113, USA.
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16
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Intine RV, Dundr M, Vassilev A, Schwartz E, Zhao Y, Zhao Y, Depamphilis ML, Maraia RJ. Nonphosphorylated human La antigen interacts with nucleolin at nucleolar sites involved in rRNA biogenesis. Mol Cell Biol 2004; 24:10894-904. [PMID: 15572691 PMCID: PMC533991 DOI: 10.1128/mcb.24.24.10894-10904.2004] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2004] [Revised: 08/20/2004] [Accepted: 09/17/2004] [Indexed: 02/07/2023] Open
Abstract
La is a RNA-binding protein implicated in multiple pathways related to the production of tRNAs, ribosomal proteins, and other components of the translational machinery (D. J. Kenan and J. D. Keene, Nat. Struct. Mol. Biol. 11:303-305, 2004). While most La is phosphorylated and resides in the nucleoplasm, a fraction is in the nucleolus, the site of ribosome production, although the determinants of this localization are incompletely known. In addition to its conserved N-terminal domain, human La harbors a C-terminal domain that contains an atypical RNA recognition motif and a short basic motif (SBM) adjacent to phosphoserine-366. We report that nonphosphorylated La (npLa) is concentrated in nucleolar sites that correspond to the dense fibrillar component that harbors nascent pol I transcripts as well as fibrillarin and nucleolin, which function in early phases of rRNA maturation. Affinity purification and native immunoprecipitation of La and fluorescence resonance energy transfer in the nucleolus reveal close association with nucleolin. Moreover, La lacking the SBM does not localize to nucleoli. Lastly, La exhibits SBM-dependent, phosphorylation-sensitive interaction with nucleolin in a yeast two-hybrid assay. The data suggest that interaction with nucleolin is, at least in part, responsible for nucleolar accumulation of La and that npLa may be involved in ribosome biogenesis.
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Affiliation(s)
- Robert V Intine
- Laboratory of Molecular Growth Regulation, National Institute of Child Health & Human Development, 6 Center Dr., Rm. 416, Bethesda, MD 20892-2753, USA
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17
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Uckun F, Tibbles H, Vassilev A, Waurzyniak B, Liu X. 344 JANEX-1, a novel anti-cancer agent with anti-thrombotic properties. EJC Suppl 2004. [DOI: 10.1016/s1359-6349(04)80351-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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18
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Vassilev A, Zheng Y, Grigoriants O, Qazi S, Uckun F. 229 Activation of caspases in human t-lineage leukemia cells treated with analogs of leflunomide metabolite. EJC Suppl 2004. [DOI: 10.1016/s1359-6349(04)80237-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
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19
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Li CJ, Vassilev A, DePamphilis ML. Role for Cdk1 (Cdc2)/cyclin A in preventing the mammalian origin recognition complex's largest subunit (Orc1) from binding to chromatin during mitosis. Mol Cell Biol 2004; 24:5875-86. [PMID: 15199143 PMCID: PMC480893 DOI: 10.1128/mcb.24.13.5875-5886.2004] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The eukaryotic origin recognition complex (ORC) selects the genomic sites where prereplication complexes are assembled and DNA replication begins. In proliferating mammalian cells, ORC activity appears to be regulated by reducing the affinity of the Orc1 subunit for chromatin during S phase and then preventing reformation of a stable ORC-chromatin complex until mitosis is completed and a nuclear membrane is assembled. Here we show that part of the mechanism by which this is accomplished is the selective association of Orc1 with Cdk1 (Cdc2)/cyclin A during the G(2)/M phase of cell division. This association accounted for the appearance in M-phase cells of hyperphosphorylated Orc1 that was subsequently dephosphorylated during the M-to-G(1) transition. Moreover, inhibition of Cdk activity in metaphase cells resulted in rapid binding of Orc1 to chromatin. However, chromatin binding was not mediated through increased affinity of Orc1 for Orc2, suggesting that additional events are involved in the assembly of functional ORC-chromatin sites. These results reveal that the same cyclin-dependent protein kinase that initiates mitosis in mammalian cells also concomitantly inhibits assembly of functional ORC-chromatin sites.
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Affiliation(s)
- Cong-jun Li
- Growth Biology Laboratory, Animal and Natural Resources Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland 20705, USA
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20
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Abstract
Histone deacetylases are required for transcriptional repression in eukaryotes. Saccharomyces cerevisiae has several histone deacetylases, of which ySir2p is the most conserved throughout evolution. Currently, there is no report on the interacting protein partner of a human Sir2 homolog, SIRT2. Here we show for the first time that SIRT2 interacts with the homeobox transcription factor, HOXA10, which was identified in a two-hybrid screen. Interactions were confirmed by co-immunoprecipitation from in vitro translations as well as in human cell-free extracts. Taken together with mouse knockout studies, our results raise the intriguing possibility that SIRT2 plays a role in mammalian development.
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Affiliation(s)
- Nancy S Bae
- Laboratory of Molecular and Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
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21
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Kossev K, Vassilev A, Popova Y, Ivanov I, Troev K. Functionalization of poly(oxyethylene phosphonate) under phase-transfer catalyst conditions. POLYMER 2003. [DOI: 10.1016/s0032-3861(03)00081-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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22
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Abstract
The authors investigated the effects of 2,4,6-trihydroxy-alpha-p-methoxyphenylacetophenone (compound D-58), a potent inhibitor of protein tyrosine kinases SYK and Bruton's tyrosine kinase (BTK), on IgE receptor/FcepsilonRI-triggered mast cell-mediated acute allergic responses in vitro and in vivo. Compound D-58 abrogated IgE receptor/FcepsilonRI-mediated SYK and BTK activation as well as calcium mobilization in mast cells. Mast-cell degranulation and leukotriene (LT) C(4) release was inhibited by compound D-58 in a concentration-dependent fashion. Notably, compound D-58 prevented the mast cell mediator-induced vascular hyperpermeability in an in vivo murine model of passive cutaneous anaphylaxis as measured by the prevention of extravasation of systemically administered Evans blue dye. The results uniquely indicate that compound D-58 has potent antiallergic properties. Therefore, further development of compound D-58 may provide the basis for new and effective treatment programs for severe allergic disorders.
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Affiliation(s)
- R Malaviya
- Department of Allergy and Inflammatory Diseases, Parker Hughes Institute, 2665 Long Lake Road, St. Paul, MN 55113, USA.
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23
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Abstract
STAT5A is a molecular regulator of proliferation, differentiation, and apoptosis in lymphohematopoietic cells. Here we show that STAT5A can serve as a functional substrate of Bruton's tyrosine kinase (BTK). Purified recombinant BTK was capable of directly binding purified recombinant STAT5A with high affinity (K(d) = 44 nm), as determined by surface plasmon resonance using a BIAcore biosensor system. BTK was also capable of tyrosine-phosphorylating ectopically expressed recombinant STAT5A on Tyr(694) both in vitro and in vivo in a Janus kinase 3-independent fashion. BTK phosphorylated the Y665F, Y668F, and Y682F,Y683F mutants but not the Y694F mutant of STAT5A. STAT5A mutations in the Src homology 2 (SH2) and SH3 domains did not alter the BTK-mediated tyrosine phosphorylation. Recombinant BTK proteins with mutant pleckstrin homology, SH2, or SH3 domains were capable of phosphorylating STAT5A, whereas recombinant BTK proteins with SH1/kinase domain mutations were not. In pull-down experiments, only full-length BTK and its SH1/kinase domain (but not the pleckstrin homology, SH2, or SH3 domains) were capable of binding STAT5A. Ectopically expressed BTK kinase domain was capable of tyrosine-phosphorylating STAT5A both in vitro and in vivo. BTK-mediated tyrosine phosphorylation of ectopically expressed wild type (but not Tyr(694) mutant) STAT5A enhanced its DNA binding activity. In BTK-competent chicken B cells, anti-IgM-stimulated tyrosine phosphorylation of STAT5 protein was prevented by pretreatment with the BTK inhibitor LFM-A13 but not by pretreatment with the JAK3 inhibitor HI-P131. B cell antigen receptor ligation resulted in enhanced tyrosine phosphorylation of STAT5 in BTK-deficient chicken B cells reconstituted with wild type human BTK but not in BTK-deficient chicken B cells reconstituted with kinase-inactive mutant BTK. Similarly, anti-IgM stimulation resulted in enhanced tyrosine phosphorylation of STAT5A in BTK-competent B cells from wild type mice but not in BTK-deficient B cells from XID mice. In contrast to B cells from XID mice, B cells from JAK3 knockout mice showed a normal STAT5A phosphorylation response to anti-IgM stimulation. These findings provide unprecedented experimental evidence that BTK plays a nonredundant and pivotal role in B cell antigen receptor-mediated STAT5A activation in B cells.
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Affiliation(s)
- S Mahajan
- Molecular Signal Transduction Laboratory, Parker Hughes Cancer Center and the Department of Biochemistry, Parker Hughes Institute, St. Paul, Minnesota 55113, USA
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24
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Vassilev A, Kaneko KJ, Shu H, Zhao Y, DePamphilis ML. TEAD/TEF transcription factors utilize the activation domain of YAP65, a Src/Yes-associated protein localized in the cytoplasm. Genes Dev 2001; 15:1229-41. [PMID: 11358867 PMCID: PMC313800 DOI: 10.1101/gad.888601] [Citation(s) in RCA: 540] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Mammals express four highly conserved TEAD/TEF transcription factors that bind the same DNA sequence, but serve different functions during development. TEAD-2/TEF-4 protein purified from mouse cells was associated predominantly with a novel TEAD-binding domain at the amino terminus of YAP65, a powerful transcriptional coactivator. YAP65 interacted specifically with the carboxyl terminus of all four TEAD proteins. Both this interaction and sequence-specific DNA binding by TEAD were required for transcriptional activation in mouse cells. Expression of YAP in lymphocytic cells that normally do not support TEAD-dependent transcription (e.g., MPC11) resulted in up to 300-fold induction of TEAD activity. Conversely, TEAD overexpression squelched YAP activity. Therefore, the carboxy-terminal acidic activation domain in YAP is the transcriptional activation domain for TEAD transcription factors. However, whereas TEAD was concentrated in the nucleus, excess YAP65 accumulated in the cytoplasm as a complex with the cytoplasmic localization protein, 14-3-3. Because TEAD-dependent transcription was limited by YAP65, and YAP65 also binds Src/Yes protein tyrosine kinases, we propose that YAP65 regulates TEAD-dependent transcription in response to mitogenic signals.
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Affiliation(s)
- A Vassilev
- National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-2753, USA
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25
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Goodman PA, Wood CM, Vassilev A, Mao C, Uckun FM. Spleen tyrosine kinase (Syk) deficiency in childhood pro-B cell acute lymphoblastic leukemia. Oncogene 2001; 20:3969-78. [PMID: 11494125 DOI: 10.1038/sj.onc.1204515] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2001] [Revised: 04/03/2001] [Accepted: 04/09/2001] [Indexed: 01/27/2023]
Abstract
The cytoplasmic spleen tyrosine kinase (SYK) is a key regulator of signal transduction events, apoptosis and orderly cell cycle progression in B-lineage lymphoid cells. Although SYK has not been linked to a human disease, defective expression of the closely related T-cell tyrosine kinase ZAP-70 has been associated with severe combined immunodeficiency. Childhood CD19(+)CD10(-) pro-B cell acute lymphoblastic leukemia (ALL) is thought to originate from B-cell precursors with a maturational arrest at the pro-B cell stage and it is associated with poor prognosis. Since lethally irradiated mice reconstituted with SYK-deficient fetal liver-derived lymphohematopoietic progenitor cells show a block in B-cell ontogeny at the pro-B to pre-B cell transition, we examined the SYK expression profiles of primary leukemic cells from children with pro-B cell ALL. Here we report that leukemic cells from pediatric CD19(+)CD10(-) pro-B cell ALL patients (but not leukemic cells from patients with CD19(+)CD10(+) common pre-pre-B cell ALL) have markedly reduced SYK activity. Sequencing of the reverse transcriptase-polymerase chain reaction (RT-PCR) products of the Syk mRNA in these pro-B leukemia cells revealed profoundly aberrant coding sequences with deletions or insertions. These mRNA species encode abnormal SYK proteins with a missing or truncated catalytic kinase domain. In contrast to pro-B leukemia cells, pre-pre-B leukemia cells from children with CD19(+)CD10(+) common B-lineage ALL and EBV-transformed B-cell lines from healthy volunteers expressed wild-type Syk coding sequences. Examination of the genomic structure of the Syk gene by inter-exonic PCR and genomic cloning demonstrated that the deletions and insertions in the abnormal mRNA species of pro-B leukemia cells are caused by aberrant splicing resulting in either mis-splicing, exon skipping or inclusion of alternative exons, consistent with an abnormal posttranscriptional regulation of alternative splicing of Syk pre-mRNA. Our findings link for the first time specific molecular defects involving the Syk gene to an immunophenotypically distinct category of childhood ALL. To our knowledge, this is the first discovery of a specific tyrosine kinase deficiency in a human hematologic malignancy.
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Affiliation(s)
- P A Goodman
- Department of Molecular Genetics, Parker Hughes Institute & Parker Hughes Cancer Center, St Paul, Minnesota, MN 55113, USA
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26
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Tibbles HE, Vassilev A, Wendorf H, Schonhoff D, Zhu D, Lorenz D, Waurzyniak B, Liu XP, Uckun FM. Role of a JAK3-dependent biochemical signaling pathway in platelet activation and aggregation. J Biol Chem 2001; 276:17815-22. [PMID: 11278899 DOI: 10.1074/jbc.m011405200] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Here we provide experimental evidence that identifies JAK3 as one of the regulators of platelet function. Treatment of platelets with thrombin induced tyrosine phosphorylation of the JAK3 target substrates STAT1 and STAT3. Platelets from JAK3-deficient mice displayed a decrease in tyrosine phosphorylation of STAT1 and STAT3. In accordance with these data, pretreatment of human platelets with the JAK3 inhibitor WHI-P131 markedly decreased the base-line enzymatic activity of constitutively active JAK3 and abolished the thrombin-induced tyrosine phosphorylation of STAT1 and STAT3. Following thrombin stimulation, WHI-P131-treated platelets did not undergo shape changes indicative of activation such as pseudopod formation. WHI-P131 inhibited thrombin-induced degranulation/serotonin release as well as platelet aggregation. Highly effective platelet inhibitory plasma concentrations of WHI-P131 were achieved in mice without toxicity. WHI-P131 prolonged the bleeding time of mice in a dose-dependent manner and improved event-free survival in a mouse model of thromboplastin-induced generalized and invariably fatal thromboembolism. To our knowledge, WHI-P131 is the first anti-thrombotic agent that prevents platelet aggregation by inhibiting JAK3.
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Affiliation(s)
- H E Tibbles
- Parker Hughes Cancer Center, Departments of Hematology, Parker Hughes Institute, St. Paul, Minnesota, 55113, USA
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27
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Mizuguchi G, Vassilev A, Tsukiyama T, Nakatani Y, Wu C. ATP-dependent nucleosome remodeling and histone hyperacetylation synergistically facilitate transcription of chromatin. J Biol Chem 2001; 276:14773-83. [PMID: 11279013 DOI: 10.1074/jbc.m100125200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Drosophila nucleosome remodeling factor (NURF) is an ISWI-containing protein complex that facilitates nucleosome mobility and transcriptional activation in an ATP-dependent manner. Numerous studies have implicated histone acetylation in transcriptional activation. We investigated the relative contributions of these two chromatin modifications to transcription in vitro of a chromatinized adenovirus E4 minimal promoter that contains binding sites for the GAL4-VP16 activator. We found that NURF could remodel chromatin and stimulate transcription irrespective of the acetylation status of histones. In contrast, hyperacetylation of histones in the absence of NURF was unable to stimulate transcription, suggesting that NURF-dependent chromatin remodeling is an obligatory step in E4 promoter activation. When chromatin templates were first hyperacetylated and then incubated with NURF, significantly greater transcription stimulation was observed. The results suggest that changes in chromatin induced by acetylation of histones and the mobilization of nucleosomes by NURF combine synergistically to facilitate transcription. Experiments using single and multiple rounds of transcription indicate that these chromatin modifications stimulate transcription preinitiation as well as reinitiation.
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Affiliation(s)
- G Mizuguchi
- Laboratory of Molecular Cell Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA
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28
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Navara CS, Benyumov A, Vassilev A, Narla RK, Ghosh P, Uckun FM. Vanadocenes as potent anti-proliferative agents disrupting mitotic spindle formation in cancer cells. Anticancer Drugs 2001; 12:369-76. [PMID: 11335794 DOI: 10.1097/00001813-200104000-00010] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
We present experimental data which establish the organometallic compounds vanadocene dichloride (VDC) and vanadocene acetylacetonate (VDacac) as potent anti-proliferative agents. We first examined the effects of VDC and VDacac on the rapid embryonic cell division and development of Zebrafish. Both compounds were capable of causing cell division block at the 8-16 cell stage of embryonic development followed by total cell fusion and developmental arrest. We next examined the effect of VDC and VDacac on proliferation of human breast cancer and glioblastoma cell lines using MTT assays. VDC inhibited the proliferation of the breast cancer cell line BT-20 as well as the glioblastoma cell line U373 in a concentration-dependent fashion with IC50 values of 11.0, 14.9 and 18.6 microM, respectively. VDacac inhibited cellular proliferation with IC50 values of 9.1, 26.9 and 35.5 microM, respectively. Whereas in vehicle-treated control cancer cells mitotic spindles were organized as a bipolar microtubule array and the DNA was organized on a metaphase plate, vanadocene-treated cancer cells had aberrant monopolar mitotic structures where microtubules were detected only on one side of the chromosomes and the chromosomes were arranged in a circular pattern. In contrast to control cells which showed a single focus of gamma-tubulin at each pole of the bipolar mitotic spindle, VDC- or VDacac-treated cells had two foci of gamma-tubulin on the same side of the chromosomes resulting in a broad centrosome at one pole. All monopolar spindles examined had two foci of gamma-tubulin labeling consistent with a mechanism in which the centrosomes duplicate but do not separate properly to form a bipolar spindle. These results provide unprecedented evidence that organometallic compounds can block cell division in human cancer cells by disrupting bipolar spindle formation. In accordance with these results vanadocene treatment caused an arrest at the G2/M phase of the cell cycle. This unique mechanism of anti-mitotic function warrants further development of vanadocene complexes as anti-cancer drugs.
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Affiliation(s)
- C S Navara
- Parker Hughes Cancer Center, Departments of Cell Biology, Oncology, Chemistry and Drug Discovery Program, Parker Hughes Institute, St Paul, MN 55113, USA.
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Mihaylova M, Vassilev A. Effect of stimulus contrast uncertainty on simple reaction time. Acta Physiol Pharmacol Bulg 2001; 24:81-90. [PMID: 11098294] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Abstract
Both reaction time (RT) and the latency of the visually evoked potentials (VEP) to grating onset increase with increasing stimulus spatial frequency (SF). At SF higher than 5 c/deg RT increases faster than VEP latency, the difference resulting in a "central delay" (Mihaylova et al., 1999). Due to the equipment limitations, RT and VEP experiments of Mihaylova et al. (1999) differed in constancy of stimulus contrast within a sequence of trials. The present experiments were aimed at testing the assumption that the central delay is a result of contrast uncertainty effect on RT. To this end, RT were measured in condition of both constant and variable grating contrast. The stimuli were sinusoidal gratings ranging in SF from 0.5 to 16 c/deg and in contrast from 2.5 to 50%. In addition, VEP were recorded to the same stimuli in blocks of fixed contrast and the latencies of the early VEP wave were subtracted from RT. Contrast uncertainty did not affect RT at low SF, 0.5 and 2 c/deg, while increasing RT at SF higher than 5 c/deg both at low and high stimulus contrast. The results showed that the central component of RT increase at high SF is reduced but not eliminated under constant contrast condition. The uncertainty effect at high SF might be due to contrast sensitivity reduction, reduced subjective stimulus probability and differences in response strategy adopted by the subjects when contrast was constant or variable. An alternative explanation is a larger ability of low SF stimuli compared to high SF stimuli to attract visual attention.
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Affiliation(s)
- M Mihaylova
- Institute of Physiology, Bulgarian Academy of Sciences, Sofia, Bulgaria.
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30
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Abstract
In the primate retina, blue-OFF cells are less numerous than blue-ON cells but no psychophysical equivalent of this asymmetry has been found so far. The hypothesis put forward in the present study is that the ON-OFF asymmetry should manifest itself in the size and effectiveness of spatial summation of S-cone signals of opposite polarity. To test this hypothesis upon selective stimulation of the S-cones in man, a 3 cd/m(2) blue light was superimposed on a 300 cd/m(2) yellow background and the test stimulus consisted in a luminance increment or decrement of the blue light from its steady level over a circular area of variable size. The test stimuli were presented at 12.5 degrees retinal eccentricity. Within the test-stimulus spectral band, sensitivity was that of Stiles' pi(1) mechanism. Increasing stimulus area reduced more the decrement threshold than the increment threshold, and Ricco's area was larger for luminance decrements (0.8-2 degrees ) than for increments (0.6-0.9 degrees ). Experiments with red-on-red stimuli confirmed that the large summation area and stimulus-polarity-dependent spatial summation are specific for the isolated S-cone signals. The sign-dependency of spatial summation is probably a psychophysical correlate of the asymmetry of the ON- and OFF- visual pathways receiving S-cone input.
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Affiliation(s)
- A Vassilev
- Institute of Physiology, Bulgarian Academy of Sciences, Acad G Bonchev St Bl 23, 1113, Sofia, Bulgaria.
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31
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Lau OD, Courtney AD, Vassilev A, Marzilli LA, Cotter RJ, Nakatani Y, Cole PA. p300/CBP-associated factor histone acetyltransferase processing of a peptide substrate. Kinetic analysis of the catalytic mechanism. J Biol Chem 2000; 275:21953-9. [PMID: 10777508 DOI: 10.1074/jbc.m003219200] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
p300/CBP-associated factor (PCAF) is a histone acetyltransferase that plays an important role in the remodeling of chromatin and the regulation of gene expression. It has been shown to catalyze preferentially acetylation of the epsilon-amino group of lysine 14 in histone H3. In this study, the kinetic mechanism of PCAF was evaluated with a 20-amino acid peptide substrate derived from the amino terminus of histone H3 (H3-20) and recombinant bacterially expressed PCAF catalytic domain (PCAF(cat)). The enzymologic behavior of full-length PCAF and PCAF(cat) were shown to be similar. PCAF-catalyzed acetylation of the substrate H3-20 was shown to be specific for Lys-14, analogous to its behavior with the full-length histone H3 protein. Two-substrate kinetic analysis displayed an intersecting line pattern, consistent with a ternary complex mechanism for PCAF. The dead-end inhibitor analog desulfo-CoA was competitive versus acetyl-CoA and noncompetitive versus H3-20. The dead-end analog inhibitor H3-20 K14A was competitive versus H3-20 and uncompetitive versus acetyl-CoA. The potent bisubstrate analog inhibitor H3-CoA-20 was competitive versus acetyl-CoA and noncompetitive versus H3-20. Taken together, these inhibition patterns support an ordered BiBi kinetic mechanism for PCAF in which acetyl-CoA binding precedes H3-20 binding. Viscosity experiments suggest that diffusional release of product is not rate-determining for PCAF catalysis. These results provide a mechanistic framework for understanding the detailed catalytic behavior of an important subset of the histone acetyltransferases and have significant implications for molecular regulation of and inhibitor design for these enzymes.
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Affiliation(s)
- O D Lau
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Abstract
The hypothesis that identification of line orientation is based on different mechanisms--a detector mechanism at large orientation differences and a computational one at small orientation differences--was tested in three experiments. The first two experiments compared reaction time and time of complete temporal summation (tc) in two tasks, line detection and line orientation identification. Identification at orientation differences 15 degrees or more was similar to detection in several respects, suggesting that it was accomplished according to the principle of "labeled lines." In agreement with the initial hypothesis, identification at differences smaller than 15 degrees had a slower time course and could not be explained by the "labeled lines" principle. Experiment 3 explored the orientation acuity as a function of exposure duration and stimulus energy. Energy could not completely substitute for time in providing high orientation acuity, a result suggesting the involvement of neurophysiological mechanisms of large time constants.
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Affiliation(s)
- M Zlatkova
- Institute of Physiology, Bulgarian Academy of Sciences, Sofia, Bulgaria.
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D'Cruz OJ, Vassilev A, Uckun FM. Evaluation of boar sperm as a model system to study the mechanism of spermicidal activity of vanadocenes. Biochem Biophys Res Commun 2000; 270:826-30. [PMID: 10772910 DOI: 10.1006/bbrc.2000.2517] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
bis-cyclopentadienyl [Cp] complexes of vanadium(IV) or vanadocenes are rapid and potent inhibitors of human sperm motility with potential as a new class of contraceptive agents. We investigated the utility of boar sperm as a model system to study the mechanisms of drug action because boar sperm lacks phosphocreatine and creatine kinase activity, the essential components of the "phosphagen shuttle" system for human sperm motility. Two representative vanadocenes, vanadocene dichloride [VDC] and bis[pentamethylcyclopentadienyl] vanadium dichloride [VPMDC], in which the bis-Cp rings were substituted with five electron-donating methyl groups were evaluated. The concentration-dependent effects of VDC and VPMDC on spermicidal activity, axonemal dynein adenosine triphosphatase (ATPase) activity, and tyrosine phosphorylation of global sperm proteins were assessed by computer-assisted sperm analysis, spectrophotometry, and immunoblotting, respectively. Both the unsubstituted and the pentamethyl-substituted vanadocene induced rapid sperm immobilization (T(1/2) < 15 s). Substitution of the bis-Cp rings by five methyl groups augmented the SIA of VDC threefold. The EC(50) values for VDC and VPMDC were 2.1 and 0.76 microM, respectively. Spermicidal activity of vanadocenes was not associated with the inhibition of dynein ATPase(s) or increase in tyrosine phosphorylation of sperm proteins. These results suggest that the potent spermicidal activity of vanadocenes against boar sperm is mediated by a unique mechanism that is independent of dynein ATPase activity, phosphatase activity, and phosphocreatine/creatine kinase system. Therefore, boar sperm is a suitable model for further investigating the molecular mechanism of spermicidal action of vanadocenes.
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Affiliation(s)
- O J D'Cruz
- Drug Discovery Program, Department of Reproductive Biology, Department of Biochemistry, Parker Hughes Institute, 2665 Long Lake Road, St. Paul, Minnesota 55113, USA.
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Harrod R, Kuo YL, Tang Y, Yao Y, Vassilev A, Nakatani Y, Giam CZ. p300 and p300/cAMP-responsive element-binding protein associated factor interact with human T-cell lymphotropic virus type-1 Tax in a multi-histone acetyltransferase/activator-enhancer complex. J Biol Chem 2000; 275:11852-7. [PMID: 10766811 DOI: 10.1074/jbc.275.16.11852] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human T-cell lymphotropic virus, type (HTLV)-1 trans-activator, Tax, coordinates with cAMP-responsive element-binding protein (CREB) and the transcriptional co-activators p300/CBP on three 21-base pair repeat elements in the proviral long terminal repeat (LTR) to promote viral mRNA transcription. Recruitment of p300/CBP to the activator-enhancer complex, however, is insufficient to support Tax-dependent LTR trans-activation. Here, we report that the p300/CBP-associated factor (P/CAF) is a critical and integral component of the functional HTLV-1 activator-enhancer complex. The HTLV-1 Tax protein directly binds P/CAF in vitro and co-immunoprecipitates with this co-activator in vivo. The Tax mutants (K88A and V89A) defective for p300/CBP-binding and LTR trans-activation, retained their abilities to interact with P/CAF. The M47 mutant (L319R, L320S) protein, which has previously been shown to interact with p300/CBP, by contrast, failed to form complexes with P/CAF and is impaired in LTR trans-activation. Furthermore, LTR trans-activation by Tax is competitively inhibited by the adenoviral E1A 12S gene product, which displaces P/CAF from p300/CBP and inhibits the histone acetyltransferase activities of both P/CAF and p300/CBP. This inhibition is partially reversed by exogenously added P/CAF. These results imply that simultaneous recruitment of two distinct co-activators (p300/CBP and P/CAF) by Tax is essential for the assembly of a trans-activation competent, nucleoprotein complex.
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Affiliation(s)
- R Harrod
- Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814, USA
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Bergel M, Herrera JE, Thatcher BJ, Prymakowska-Bosak M, Vassilev A, Nakatani Y, Martin B, Bustin M. Acetylation of novel sites in the nucleosomal binding domain of chromosomal protein HMG-14 by p300 alters its interaction with nucleosomes. J Biol Chem 2000; 275:11514-20. [PMID: 10753971 DOI: 10.1074/jbc.275.15.11514] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The reversible acetylation of histones is associated with structural alterations in the chromatin fiber that affect various DNA-related activities. Here we show that the histone acetyltransferase p300 specifically acetylates HMG-14, a nonhistone structural protein that binds to nucleosomes and reduces the compactness of the chromatin fiber. We identify 7 major acetylation sites, 6 of which are novel and have not been known to be acetylated in either HMG-14 or the closely related HMG-17 protein. All the acetylation sites involve evolutionarily conserved residues: 3 within the HMG-14/-17 nucleosomal binding domain and 4 in or near the bipartite nuclear localization domains of the proteins. In tissue culture cells the acetylation pattern is indicative of a selective process in which a subfraction of HMG-14 is preferentially acetylated. We find that the nucleosomal binding domain is a major target for acetylation in vivo and that the specific acetylation of HMG-14 by p300 weakens its interaction with nucleosome cores. Our results suggest that p300 modulates the interaction of HMG-14 with nucleosomes. Thus, p300 may affect chromatin-related activities not only by modifying histones or transcription factors but also by targeting structural nonhistone proteins.
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Affiliation(s)
- M Bergel
- Protein Section, Division of Basic Science, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA.
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D'Cruz OJ, Vassilev A, Uckun FM. Studies in humans on the mechanism of potent spermicidal and apoptosis-inducing activities of vanadocene complexes. Biol Reprod 2000; 62:939-49. [PMID: 10727263 DOI: 10.1095/biolreprod62.4.939] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
We previously demonstrated that bis-cyclopentadienyl (Cp) complexes of vanadium(IV) (vanadocenes) are potent spermicidal and apoptosis-inducing agents. To gain further insight into the structure-function relationships controlling these two properties of vanadocenes, we have synthesized analogues in which the bis-Cp rings were substituted with one or five electron-donating methyl groups. The three complexes included vanadocene dichloride (VDC), bis(methylcyclopentadienyl) vanadium dichloride (VMDC), and bis(pentamethylcyclopentadienyl) vanadium dichloride (VPMDC). The concentration-dependent effect of these vanadocenes on sperm-immobilizing activity (SIA), mitochondrial membrane potential (DeltaPsim), axonemal dynein ATPase activity, and tyrosine phosphorylation of global and axoneme-specific sperm proteins was assessed by computer-assisted sperm analysis, flow cytometry, colorimetry, and immunoblotting, respectively. Apoptosis-inducing ability was quantitated by the two-color flow cytometric terminal dideoxynucleotidyl transferase-based assay that labels 3'-hydroxyl ends of fragmented DNA. All three vanadocenes induced rapid sperm immobilization (T(1/2) < 15 sec). Substitution of the bis-Cp rings by five methyl groups augmented the SIA of VDC by 10-fold. The EC(50) values (50% inhibitory concentration) for VDC, VMDC, and VPMDC were 7.5 microM, 4.3 microM, and 0.7 microM, respectively. Whereas SIA of vanadocenes was apparent at low micromolar concentrations, the apoptosis-inducing property was evident only at higher micromolar concentrations. The concentrations of VDC, VMDC, and VPMDC required for 50% apoptosis were 49 microM, 67 microM, and 153 microM, and for 50% reduction in sperm DeltaPsim were 435 microM, 173 microM, and 124 microM, respectively. Spermicidal activity of vanadocenes was not dependent on the inhibition of ATPase or tyrosine phosphorylation of global and sperm axonemal proteins. Due to the ability of these vanadocene complexes to rapidly generate hydroxyl radicals in the presence of oxidant, our findings provide unprecedented evidence for a novel mechanism of action for spermicidal vanadocenes. The differential concentration-dependent spermicidal and apoptosis-inducing properties of vanadocenes gives them particular utility as a new class of vaginal contraceptives.
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Affiliation(s)
- O J D'Cruz
- Drug Discovery Program, Departments of Reproductive Biology and Biochemistry, Parker Hughes Institute, St. Paul, Minnesota 55113, USA.
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Lau OD, Kundu TK, Soccio RE, Ait-Si-Ali S, Khalil EM, Vassilev A, Wolffe AP, Nakatani Y, Roeder RG, Cole PA. HATs off: selective synthetic inhibitors of the histone acetyltransferases p300 and PCAF. Mol Cell 2000; 5:589-95. [PMID: 10882143 DOI: 10.1016/s1097-2765(00)80452-9] [Citation(s) in RCA: 307] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Histone acetyltransferases (HATs) play important roles in the regulation of gene expression. In this report, we describe the design, synthesis, and application of peptide CoA conjugates as selective HAT inhibitors for the transcriptional coactivators p300 and PCAF. Two inhibitors (Lys-CoA for p300 and H3-CoA-20 for PCAF) were found to be potent (IC(50) approximately = 0.5 microM) and selective (approximately 200-fold) in blocking p300 and PCAF HAT activities. These inhibitors were used to probe enzymatic and transcriptional features of HAT function in several assay systems. These compounds should be broadly useful as biological tools for evaluating the roles of HATs in transcriptional studies and may serve as lead agents for the development of novel antineoplastic therapeutics.
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Affiliation(s)
- O D Lau
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Sun L, Goodman PA, Wood CM, Crotty ML, Sensel M, Sather H, Navara C, Nachman J, Steinherz PG, Gaynon PS, Seibel N, Vassilev A, Juran BD, Reaman GH, Uckun FM. Expression of aberrantly spliced oncogenic ikaros isoforms in childhood acute lymphoblastic leukemia. J Clin Oncol 1999; 17:3753-66. [PMID: 10577847 DOI: 10.1200/jco.1999.17.12.3753] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
PURPOSE We sought to determine if molecular abnormalities involving the Ikaros gene could contribute to the development of acute lymphoblastic leukemia (ALL) in children. PATIENTS AND METHODS We studied Ikaros gene expression in normal human bone marrow, normal thymocytes, normal fetal liver-derived immature lymphocyte precursor cell lines, eight different ALL cell lines, and leukemic cells from 69 children with ALL (T-lineage ALL, n = 18; B-lineage ALL, n = 51). Expression of Ikaros protein and its subcellular localization were examined by immunoblotting and confocal laser-scanning microscopy, respectively. Polymerase chain reaction (PCR) and nucleotide sequencing were used to identify the specific Ikaros isoforms expressed in these cells. Genomic sequencing of splice junction regions of the Ikaros gene was performed in search for mutations. RESULTS In each of the ALL cases, we found high-level expression of a non-DNA-binding or aberrant DNA-binding isoform of Ikaros with abnormal subcellular compartmentalization patterns. In contrast, only wild-type Ik-1 and Ik-2 isoforms with normal subcellular localization were found in normal bone marrow cells and thymus-derived or fetal liver-derived normal lymphocyte precursors. In leukemic cells expressing the aberrant Ikaros coding sequences with the 30-base-pair deletion, genomic sequence analysis of the intron-exon junctions between exons 6 and 7 yielded the wild-type sequence. We identified a single nucleotide polymorphism (SNP) affecting the third base of the triplet codon for a proline (CCC or CCA) in the highly conserved bipartite activation region (viz, A or C at position 1002 numbering from the translation start site of Ik-1) within our Ikaros clones. Bi-allelic expression of truncated and/or non-DNA-binding isoforms along with wild-type isoforms was observed in leukemic cells, which implicates trans-acting factor(s) affecting splice site recognition. CONCLUSION Our findings link specific molecular defects involving the Ikaros gene to childhood ALL. Posttranscriptional regulation of alternative splicing of Ikaros RNA seems to be defective in leukemic lymphocyte precursors from most children with ALL. Consequently, leukemic cells from ALL patients, in contrast to normal lymphocyte precursors, express high levels of non-DNA-binding Ikaros isoforms that are reminiscent of the non-DNA-binding Ikaros isoforms that lead to lymphoblastic leukemia in mice.
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Affiliation(s)
- L Sun
- Parker Hughes Cancer Center and Children's Cancer Group ALL Biology Reference Laboratory, Hughes Institute, St Paul, MN 55113, USA
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Sun L, Crotty ML, Sensel M, Sather H, Navara C, Nachman J, Steinherz PG, Gaynon PS, Seibel N, Mao C, Vassilev A, Reaman GH, Uckun FM. Expression of dominant-negative Ikaros isoforms in T-cell acute lymphoblastic leukemia. Clin Cancer Res 1999; 5:2112-20. [PMID: 10473095] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
Ikaros, a zinc finger-containing DNA-binding protein, is required for normal lymphocyte development. Germ-line mutant mice that express only non-DNA binding dominant-negative "leukemogenic" Ikaros isoforms lacking critical NH2-terminal zinc fingers develop an aggressive form of T-cell leukemia. We studied Ikaros gene expression in leukemic cells from 18 children with T-cell acute lymphoblastic leukemia (T-ALL). In each of the 18 T-ALL cases as well as JK-E6-1 and MOLT-3 cell lines, we found high-level expression of dominant-negative isoforms of Ikaros with abnormal subcellular compartmentalization patterns. Nuclear extracts from these cells failed to bind to the IKAROS-specific binding sequence in DNA. PCR cloning and sequencing confirmed that JK-E6-1 and MOLT-3 cell lines as well as leukemic cells from 9 of 10 patients with T-ALL expressed dominant-negative Ikaros isoforms Ik-4, Ik-7, and Ik-8 that lack critical NH2-terminal zinc fingers. In 6 of 10 patients, we detected a specific mutation leading to an in-frame deletion of 10 amino acids (delta KSSMPQKFLG) upstream to the transcription activation domain and adjacent to the COOH-terminal zinc fingers of Ik-2, Ik-4, Ik-7, and Ik-8. Thus, children with T-ALL express high levels of dysfunctional dominant-negative Ikaros isoforms.
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Affiliation(s)
- L Sun
- Parker Hughes Cancer Center and Children's Cancer Group ALL Biology Reference Laboratory, Hughes Institute, St. Paul, Minnesota 55113, USA
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Kotani T, Zhang X, Schiltz RL, Ogryzko VV, Howard T, Swanson MJ, Vassilev A, Zhang H, Yamauchi J, Howard BH, Qin J, Nakatani Y. TBP-associated factors in the PCAF histone acetylase complex. Cold Spring Harb Symp Quant Biol 1999; 63:493-9. [PMID: 10384313 DOI: 10.1101/sqb.1998.63.493] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Affiliation(s)
- T Kotani
- Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA
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Abstract
Visually evoked potentials (VEP) and reaction time (RT) were recorded under stimulation with sinusoidal gratings. Grating spatial frequency (SF) was 0.5, 5 or 12 cd and grating contrast was varied. Consistent with previous findings, both VEP latency and RT increased with the increase of grating SF and with the decrease of grating contrast. It was found, in addition, that RT and VEP latency increased by approximately the same amount when SF increased from 0.5 to 5 cd, thus suggesting that the main source of the RT delay at 5 cd in comparison with RT at 0.5 cd is of peripheral origin. However, in comparison with the data at 0.5 and 5 cd, RT at 12 cd increased much more than VEP latency. We conclude that the RT delay at high SF involves a substantial central component in addition to the peripheral delay.
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Affiliation(s)
- M Mihaylova
- Institute of Physiology, Bulgarian Academy of Sciences, Sofia, Bulgaria
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42
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Sun L, Heerema N, Crotty L, Wu X, Navara C, Vassilev A, Sensel M, Reaman GH, Uckun FM. Expression of dominant-negative and mutant isoforms of the antileukemic transcription factor Ikaros in infant acute lymphoblastic leukemia. Proc Natl Acad Sci U S A 1999; 96:680-5. [PMID: 9892693 PMCID: PMC15196 DOI: 10.1073/pnas.96.2.680] [Citation(s) in RCA: 162] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ikaros, a zinc finger-containing DNA-binding protein, is required for normal lymphocyte development, and germline mutant mice that express only non-DNA binding dominant-negative "leukemogenic" Ikaros isoforms lacking critical N-terminal zinc fingers develop an aggressive form of lymphoblastic leukemia 3-6 months after birth. Therefore, we sought to determine whether molecular abnormalities involving the Ikaros gene could contribute to the development of acute lymphoblastic leukemia (ALL) in infants. Primary leukemic cells were freshly obtained from 12 infants (<1 year of age) with newly diagnosed ALL. In leukemic cells from each of the 12 infants with ALL, we found high level expression of dominant-negative isoforms of Ikaros with abnormal subcellular compartmentalization patterns. PCR cloning and nucleotide sequencing were used to identify the specific Ikaros isoforms and detect Ikaros gene mutations in these cells. Leukemic cells from seven of seven infants with ALL, including five of five MLL-AF4(+) infants, expressed dominant-negative Ikaros isoforms Ik-4, Ik-7, and Ik-8 that lack critical N-terminal zinc fingers. In six of seven patients, we detected a specific mutation leading to an in-frame deletion of 10 amino acids (Delta KSSMPQKFLG) upstream of the transcription activation domain adjacent to the C-terminal zinc fingers of Ik-2, Ik-4, Ik-7, and Ik-8. In contrast, only wild-type Ik-1 and Ik-2 isoforms with normal nuclear localization were found in normal infant bone marrow cells and infant thymocytes. These results implicate the expression of dominant-negative Ikaros isoforms and the disruption of normal Ikaros function in the leukemogenesis of ALL in infants.
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Affiliation(s)
- L Sun
- Parker Hughes Cancer Center, Children's Cancer Group ALL Biology Reference Laboratory, Departments of Genetics, Hughes Institute, St. Paul, MN 55113, USA
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Abstract
Bruton's tyrosine kinase (BTK) is a member of the Src-related Tec family of protein tyrosine kinases. Mutations in the btk gene have been linked to severe developmental blocks in human B-cell ontogeny leading to X-linked agammaglobulinemia. Here, we provide unique biochemical and genetic evidence that BTK is an inhibitor of the Fas/APO-1 death-inducing signaling complex in B-lineage lymphoid cells. The Src homology 2, pleckstrin homology (PH), and kinase domains of BTK are all individually important and apparently indispensable, but not sufficient, for its function as a negative regulator of Fas-mediated apoptosis. BTK associates with Fas via its kinase and PH domains and prevents the FAS-FADD interaction, which is essential for the recruitment and activation of FLICE by Fas during the apoptotic signal. Fas-resistant DT-40 lymphoma B-cells rendered BTK-deficient through targeted disruption of the btk gene by homologous recombination knockout underwent apoptosis after Fas ligation, but wild-type DT-40 cells or BTK-deficient DT-40 cells reconstituted with wild-type human btk gene did not. Introduction of an Src homology 2 domain, a PH domain, or a kinase domain mutant human btk gene into BTK-deficient cells did not restore the resistance to Fas-mediated apoptosis. Introduction of wild-type BTK protein by electroporation rendered BTK-deficient DT-40 cells resistant to the apoptotic effects of Fas ligation. BTK-deficient RAMOS-1 human Burkitt's leukemia cells underwent apoptosis after Fas ligation, whereas BTK-positive NALM-6-UM1 human B-cell precursor leukemia cells expressing similar levels of Fas did not. Treatment of the anti-Fas-resistant NALM-6-UM1 cells with the leflunomide metabolite analog alpha-cyano-beta-methyl-beta-hydroxy-N-(2, 5-dibromophenyl)propenamide, a potent inhibitor of BTK, abrogated the BTK-Fas association without affecting the expression levels of BTK or Fas and rendered them sensitive to Fas-mediated apoptosis. The ability of BTK to inhibit the pro-apoptotic effects of Fas ligation prompts the hypothesis that apoptosis of developing B-cell precursors during normal B-cell ontogeny may be reciprocally regulated by Fas and BTK.
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Affiliation(s)
- A Vassilev
- Parker Hughes Cancer Center, Molecular Signal Transduction Laboratory, Departments of Immunology, Molecular Biology, and Biochemistry, Hughes Institute, St. Paul, Minnesota 55113, USA
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44
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Schiltz RL, Mizzen CA, Vassilev A, Cook RG, Allis CD, Nakatani Y. Overlapping but distinct patterns of histone acetylation by the human coactivators p300 and PCAF within nucleosomal substrates. J Biol Chem 1999; 274:1189-92. [PMID: 9880483 DOI: 10.1074/jbc.274.3.1189] [Citation(s) in RCA: 324] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A number of transcriptional coactivators possess intrinsic histone acetylase activity, providing a direct link between hyperacetylated chromatin and transcriptional activation. We have determined the core histone residues acetylated in vitro by recombinant p300 and PCAF within mononucleosomes. p300 specifically acetylates all sites of histones H2A and H2B known to be acetylated in bulk chromatin in vivo but preferentially acetylates lysines 14 and 18 of histone H3 and lysines 5 and 8 of histone H4. PCAF primarily acetylates lysine 14 of H3 but also less efficiently acetylates lysine 8 of H4. PCAF in its native form, which is present in a stable multimeric protein complex lacking p300/CBP, primarily acetylates H3 to a monoacetylated form, suggesting that PCAF-associated polypeptides do not alter the substrate specificity. These distinct patterns of acetylation by the p300 and PCAF may contribute to their differential roles in transcriptional regulation.
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Affiliation(s)
- R L Schiltz
- Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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Vassilev A, Yamauchi J, Kotani T, Prives C, Avantaggiati ML, Qin J, Nakatani Y. The 400 kDa subunit of the PCAF histone acetylase complex belongs to the ATM superfamily. Mol Cell 1998; 2:869-75. [PMID: 9885574 DOI: 10.1016/s1097-2765(00)80301-9] [Citation(s) in RCA: 140] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
PCAF histone acetylase is found in a complex with more than 20 associated polypeptides. Here we report cloning and characterization of the 400 kDa PCAF-associated factor referred to as PAF400. PAF400 is almost identical to TRRAP, which binds to c-Myc and E2F, and has significant sequence similarities to the ATM superfamily including FRAP, ATM, ATR, and the catalytic subunit of DNA-PK. Remarkably, PAF400 and FRAP share sequence similarity in broad regions that cover 80% of the entire PAF400 sequence. However, unlike the other members of the ATM superfamily, PAF400 is not a protein kinase as judged from the lack of kinase motif and autophosphorylation activity. We discuss the possibility that PAF400 may play a role in signaling of DNA damage to p53 by stimulation of p53 acetylation.
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Affiliation(s)
- A Vassilev
- Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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Sakaguchi K, Herrera JE, Saito S, Miki T, Bustin M, Vassilev A, Anderson CW, Appella E. DNA damage activates p53 through a phosphorylation-acetylation cascade. Genes Dev 1998; 12:2831-41. [PMID: 9744860 PMCID: PMC317174 DOI: 10.1101/gad.12.18.2831] [Citation(s) in RCA: 915] [Impact Index Per Article: 35.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Activation of p53-mediated transcription is a critical cellular response to DNA damage. p53 stability and site-specific DNA-binding activity and, therefore, transcriptional activity, are modulated by post-translational modifications including phosphorylation and acetylation. Here we show that p53 is acetylated in vitro at separate sites by two different histone acetyltransferases (HATs), the coactivators p300 and PCAF. p300 acetylates Lys-382 in the carboxy-terminal region of p53, whereas PCAF acetylates Lys-320 in the nuclear localization signal. Acetylations at either site enhance sequence-specific DNA binding. Using a polyclonal antisera specific for p53 that is phosphorylated or acetylated at specific residues, we show that Lys-382 of human p53 becomes acetylated and Ser-33 and Ser-37 become phosphorylated in vivo after exposing cells to UV light or ionizing radiation. In vitro, amino-terminal p53 peptides phosphorylated at Ser-33 and/or at Ser-37 differentially inhibited p53 acetylation by each HAT. These results suggest that DNA damage enhances p53 activity as a transcription factor in part through carboxy-terminal acetylation that, in turn, is directed by amino-terminal phosphorylation.
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Affiliation(s)
- K Sakaguchi
- Laboratory of Cell Biology, National Cancer Institute (NCI), National Institutes of Health, Bethesda, Maryland 20892, USA
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47
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Harrod R, Tang Y, Nicot C, Lu HS, Vassilev A, Nakatani Y, Giam CZ. An exposed KID-like domain in human T-cell lymphotropic virus type 1 Tax is responsible for the recruitment of coactivators CBP/p300. Mol Cell Biol 1998; 18:5052-61. [PMID: 9710589 PMCID: PMC109090 DOI: 10.1128/mcb.18.9.5052] [Citation(s) in RCA: 150] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/1998] [Accepted: 06/09/1998] [Indexed: 11/20/2022] Open
Abstract
Human T-cell lymphotropic virus type 1 (HTLV-1) transcriptional activation is mediated by the viral transactivator, Tax, and three 21-bp repeats (Tax response element [TxRE]) located in the U3 region of the viral long terminal repeat (LTR). Each TxRE contains a core cyclic AMP response element (CRE) flanked by 5' G-rich and 3' C-rich sequences. The TxRE binds CREB (CRE-binding protein) and Tax to form a ternary complex and confers Tax-dependent transactivation. Recent data indicate that Tax functions as a specific link to connect CREB-binding protein (CBP)/p300 in a phosphorylation-independent manner to CREB/ATF-1 assembled on the viral 21-bp repeats. Glutathione S-transferase pull-down performed with Tax deletion mutants and peptide competition have localized the site in Tax critical for binding CBP/p300 to a highly protease-sensitive region around amino acid residues 81 to 95 (81QRTSKTLKVLTPPIT95) which lies between the domains previously proposed to be important for CREB binding and Tax subunit dimerization. Amino acid residues around the trypsin- and chymotrypsin-sensitive sites (88KVL90) of Tax bear resemblance to those in the kinase-inducible domain of CREB (129SRRPSYRKILNE140) surrounding Ser-133, which undergoes signal-induced phosphorylation to recruit CBP/p300. Site-directed mutagenesis of residues in this domain (R82A, K85A, K88A, and V89A) resulted in proteins which failed to transactivate from the HTLV-1 LTR in vivo. These mutants (K85A, K88A, and V89A) bind CREB with similar affinities as wild-type Tax, yet interaction with CBP/p300 is abrogated in various biochemical assays, indicating that the recruitment of CBP/p300 is crucial for Tax transactivation. A Tax mutant, M47, defective in the COOH-terminal transactivation domain, continued to interact with CBP/p300, suggesting that interactions with additional cellular factors are required for proper Tax function.
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Affiliation(s)
- R Harrod
- Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814, USA
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48
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Wolf E, Vassilev A, Makino Y, Sali A, Nakatani Y, Burley SK. Crystal structure of a GCN5-related N-acetyltransferase: Serratia marcescens aminoglycoside 3-N-acetyltransferase. Cell 1998; 94:439-49. [PMID: 9727487 DOI: 10.1016/s0092-8674(00)81585-8] [Citation(s) in RCA: 188] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The X-ray structure of a canonical GCN5-related N-acetyltransferase (GNAT), Serratia marcescens aminoglycoside 3-N-acetyltransferase, bound to coenzyme A (CoA) has been determined at 2.3 A resolution. The single domain alpha/beta protein resembles a cupped right hand wrapped around a cylinder and consists of a highly curved, six-stranded beta sheet of mixed polarity that is sandwiched between four alpha helices. The structure includes all four conserved GNAT motifs (C, D, A, and B) and represents the catalytic core of this large enzyme superfamily. Acetyl CoA recognition is mediated by a betaalpha structure derived from GNAT motif A, which presents an invariant Arg/Gln-X-X-Gly-X-Gly/Ala segment for hydrogen bonding with the cofactor. Motif B contributes acidic residues to the binding site for the positively charged antibiotic substrate.
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Affiliation(s)
- E Wolf
- Laboratories of Molecular Biophysics, The Rockefeller University, New York, New York 10021, USA
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49
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Kristupaitis D, Dibirdik I, Vassilev A, Mahajan S, Kurosaki T, Chu A, Tuel-Ahlgren L, Tuong D, Pond D, Luben R, Uckun FM. Electromagnetic field-induced stimulation of Bruton's tyrosine kinase. J Biol Chem 1998; 273:12397-401. [PMID: 9575194 DOI: 10.1074/jbc.273.20.12397] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Here we present evidence that exposure of DT40 lymphoma B-cells to low energy electromagnetic fields (EMF) results in activation of phospholipase C-gamma 2 (PLC-gamma2), leading to increased inositol phospholipid turnover. PLC-gamma2 activation in EMF-stimulated cells is mediated by stimulation of the Bruton's tyrosine kinase (BTK), a member of the Src-related TEC family of protein tyrosine kinases, which acts downstream of LYN kinase and upstream of PLC-gamma2. B-cells rendered BTK-deficient by targeted disruption of the btk gene did not show enhanced PLC-gamma2 activation in response to EMF exposure. Introduction of the wild-type (but not a kinase domain mutant) human btk gene into BTK-deficient B-cells restored their EMF responsiveness. Thus, BTK exerts a pivotal and mandatory function in initiation of EMF-induced signaling cascades in B-cells.
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Affiliation(s)
- D Kristupaitis
- Biotherapy Program, University of Minnesota, Minneapolis, Minnesota 55455, USA
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50
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Stomonyakov V, Krumov A, Vassilev A, Yankova T. An apparatus for measuring the optical density of human ocular media to blue light. Acta Physiol Pharmacol Bulg 1998; 23:101-5. [PMID: 10672336] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 04/14/2023]
Abstract
The paper describes an apparatus constructed by the authors and aimed at evaluating the optical density of human ocular media by a non-invasive psychophysical method described previously (Sample et al. 1988). The device has two light sources within the wavelength bands of 437 +/- 6 nm and 557 +/- 6 nm, respectively. They are a square-wave alternated at 1 Hz. The radiance of each can be controlled by the subject and adjusted at visibility threshold or at subjective equiluminance. Upon scotopic vision, the ratio between the two thresholds (or ratio of radiances at equiluminance) is a function of the ocular optical density at the short wavelength. The psychophysical procedures of adjustment of the 437 nm source at the absolute threshold and at equality with the 557 nm source had been tested with volunteers aged between 24 and 67 years. The dependence of blue-light sensitivities on age, obtained with the two procedures, suggests, in agreement with the literature, two main sources of sensitivity decline with age: senile myosis and ocular-media density increase at the short wavelength end of the visible spectrum.
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Affiliation(s)
- V Stomonyakov
- Institute of Physiology, Bulgarian Academy of Sciences, Sofia, Bulgaria
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