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Sun H. COMPASS: An ab Initio Force-Field Optimized for Condensed-Phase ApplicationsOverview with Details on Alkane and Benzene Compounds. J Phys Chem B 1998. [DOI: 10.1021/jp980939v] [Citation(s) in RCA: 4118] [Impact Index Per Article: 152.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 11/30/2022]
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4118 |
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McClelland M, Sanderson KE, Spieth J, Clifton SW, Latreille P, Courtney L, Porwollik S, Ali J, Dante M, Du F, Hou S, Layman D, Leonard S, Nguyen C, Scott K, Holmes A, Grewal N, Mulvaney E, Ryan E, Sun H, Florea L, Miller W, Stoneking T, Nhan M, Waterston R, Wilson RK. Complete genome sequence of Salmonella enterica serovar Typhimurium LT2. Nature 2001; 413:852-6. [PMID: 11677609 DOI: 10.1038/35101614] [Citation(s) in RCA: 1425] [Impact Index Per Article: 59.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 11/08/2022]
Abstract
Salmonella enterica subspecies I, serovar Typhimurium (S. typhimurium), is a leading cause of human gastroenteritis, and is used as a mouse model of human typhoid fever. The incidence of non-typhoid salmonellosis is increasing worldwide, causing millions of infections and many deaths in the human population each year. Here we sequenced the 4,857-kilobase (kb) chromosome and 94-kb virulence plasmid of S. typhimurium strain LT2. The distribution of close homologues of S. typhimurium LT2 genes in eight related enterobacteria was determined using previously completed genomes of three related bacteria, sample sequencing of both S. enterica serovar Paratyphi A (S. paratyphi A) and Klebsiella pneumoniae, and hybridization of three unsequenced genomes to a microarray of S. typhimurium LT2 genes. Lateral transfer of genes is frequent, with 11% of the S. typhimurium LT2 genes missing from S. enterica serovar Typhi (S. typhi), and 29% missing from Escherichia coli K12. The 352 gene homologues of S. typhimurium LT2 confined to subspecies I of S. enterica-containing most mammalian and bird pathogens-are useful for studies of epidemiology, host specificity and pathogenesis. Most of these homologues were previously unknown, and 50 may be exported to the periplasm or outer membrane, rendering them accessible as therapeutic or vaccine targets.
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Sun H, Charles CH, Lau LF, Tonks NK. MKP-1 (3CH134), an immediate early gene product, is a dual specificity phosphatase that dephosphorylates MAP kinase in vivo. Cell 1993; 75:487-93. [PMID: 8221888 DOI: 10.1016/0092-8674(93)90383-2] [Citation(s) in RCA: 939] [Impact Index Per Article: 29.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 01/29/2023]
Abstract
Mitogenic stimulation of cells induces rapid and transient activation of MAP kinases. Here we report that a growth factor-inducible gene, 3CH134, encodes a dual specificity phosphatase that dephosphorylates and inactivates p42MAPK both in vitro and in vivo. In vitro, 3CH134 protein dephosphorylates both T183 and Y185 in p42MAPK. In serum-stimulated normal fibroblasts, the kinetics of inactivation of p42MAPK coincides with the appearance of newly synthesized 3CH134 protein, and the protein synthesis inhibitor cycloheximide leads to persistent activation of MAP kinase. Expression of 3CH134 in COS cells leads to selective dephosphorylation of p42MAPK from the spectrum of phosphotyrosyl proteins. 3CH134 blocks phosphorylation and activation of p42MAPK mediated by serum, oncogenic Ras, or activated Raf, whereas the catalytically inactive mutant of the phosphatase, Cys-258-->Ser, augments MAP kinase phosphorylation under similar conditions. The mutant 3CH134 protein also forms a physical complex with the phosphorylated form of p42MAPK. These findings suggest that 3CH134 is a physiological MAP kinase phosphatase; we propose the name MKP-1 for this phosphatase.
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Allikmets R, Singh N, Sun H, Shroyer NF, Hutchinson A, Chidambaram A, Gerrard B, Baird L, Stauffer D, Peiffer A, Rattner A, Smallwood P, Li Y, Anderson KL, Lewis RA, Nathans J, Leppert M, Dean M, Lupski JR. A photoreceptor cell-specific ATP-binding transporter gene (ABCR) is mutated in recessive Stargardt macular dystrophy. Nat Genet 1997; 15:236-46. [PMID: 9054934 DOI: 10.1038/ng0397-236] [Citation(s) in RCA: 889] [Impact Index Per Article: 31.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 02/03/2023]
Abstract
Stargardt disease (STGD, also known as fundus flavimaculatus; FFM) is an autosomal recessive retinal disorder characterized by a juvenile-onset macular dystrophy, alterations of the peripheral retina, and subretinal deposition of lipofuscin-like material. A gene encoding an ATP-binding cassette (ABC) transporter was mapped to the 2-cM (centiMorgan) interval at 1p13-p21 previously shown by linkage analysis to harbour the STGD gene. This gene, ABCR, is expressed exclusively and at high levels in the retina, in rod but not cone photoreceptors, as detected by in situ hybridization. Mutational analysis of ABCR in STGD families revealed a total of 19 different mutations including homozygous mutations in two families with consanguineous parentage. These data indicate that ABCR is the causal gene of STGD/FFM.
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Tsvetkov LM, Yeh KH, Lee SJ, Sun H, Zhang H. p27(Kip1) ubiquitination and degradation is regulated by the SCF(Skp2) complex through phosphorylated Thr187 in p27. Curr Biol 1999; 9:661-4. [PMID: 10375532 DOI: 10.1016/s0960-9822(99)80290-5] [Citation(s) in RCA: 611] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 12/13/2022]
Abstract
Many tumorigenic processes affect cell-cycle progression by their effects on the levels of the cyclin-dependent kinase inhibitor p27(Kip1) [1,2]. The phosphorylation- and ubiquitination-dependent proteolysis of p27 is implicated in control of the G1-S transition in the cell cycle [3-6]. To determine the factors that control p27 stability, we established a cell-free extract assay that recapitulates the degradation of p27. Phosphorylation of p27 at Thr187 was essential for its degradation. Degradation was also dependent on SCF(Skp2), a protein complex implicated in targeting phosphorylated proteins for ubiquitination [7-10]. Immunodepletion of components of the complex - Cul-1, Skp1, or Skp2 - from the extract abolished p27 degradation, while addition of purified SCF(Skp2) to Skp2- depleted extract restored the capacity to degrade p27. A specific association was observed between Skp2 and a p27 carboxy-terminal peptide containing phosphorylated Thr187, but not between Skp2 and the non-phosphorylated peptide. Skp2-dependent associations between Skp1 or Cul-1 and the p27 phosphopeptide were also detected. Isolated SCF(Skp2) contained an E3 ubiquitin ligase activity towards p27. Our data thus suggest that SCF(Skp2) specifically targets p27 for degradation during cell-cycle progression.
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611 |
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Sun H, Lesche R, Li DM, Liliental J, Zhang H, Gao J, Gavrilova N, Mueller B, Liu X, Wu H. PTEN modulates cell cycle progression and cell survival by regulating phosphatidylinositol 3,4,5,-trisphosphate and Akt/protein kinase B signaling pathway. Proc Natl Acad Sci U S A 1999; 96:6199-204. [PMID: 10339565 PMCID: PMC26859 DOI: 10.1073/pnas.96.11.6199] [Citation(s) in RCA: 595] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Received: 10/26/1998] [Accepted: 03/29/1999] [Indexed: 11/18/2022] Open
Abstract
To investigate the molecular basis of PTEN-mediated tumor suppression, we introduced a null mutation into the mouse Pten gene by homologous recombination in embryonic stem (ES) cells. Pten-/- ES cells exhibited an increased growth rate and proliferated even in the absence of serum. ES cells lacking PTEN function also displayed advanced entry into S phase. This accelerated G1/S transition was accompanied by down-regulation of p27(KIP1), a major inhibitor for G1 cyclin-dependent kinases. Inactivation of PTEN in ES cells and in embryonic fibroblasts resulted in elevated levels of phosphatidylinositol 3,4,5,-trisphosphate, a product of phosphatidylinositol 3 kinase. Consequently, PTEN deficiency led to dosage-dependent increases in phosphorylation and activation of Akt/protein kinase B, a well-characterized target of the phosphatidylinositol 3 kinase signaling pathway. Akt activation increased Bad phosphorylation and promoted Pten-/- cell survival. Our studies suggest that PTEN regulates the phosphatidylinositol 3,4, 5,-trisphosphate and Akt signaling pathway and consequently modulates two critical cellular processes: cell cycle progression and cell survival.
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26 |
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Lecuit T, Brook WJ, Ng M, Calleja M, Sun H, Cohen SM. Two distinct mechanisms for long-range patterning by Decapentaplegic in the Drosophila wing. Nature 1996; 381:387-93. [PMID: 8632795 DOI: 10.1038/381387a0] [Citation(s) in RCA: 554] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 02/01/2023]
Abstract
Secreted signalling molecules provide cells with positional information that organizes long-range pattern during the development of multicellular animals. Evidence is presented that localized expression of Decapentaplegic instructs cells about their position along the anterior-posterior axis of the Drosophila wing in two distinct ways. One mechanism is based on the local concentration of the secreted protein; the other is based on the ability of the cells to retain an instruction received at an earlier time when their progenitors were in close proximity to the signal. Both mechanisms are involved in axis formation.
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554 |
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23 |
533 |
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Chen S, Wang QL, Nie Z, Sun H, Lennon G, Copeland NG, Gilbert DJ, Jenkins NA, Zack DJ. Crx, a novel Otx-like paired-homeodomain protein, binds to and transactivates photoreceptor cell-specific genes. Neuron 1997; 19:1017-30. [PMID: 9390516 DOI: 10.1016/s0896-6273(00)80394-3] [Citation(s) in RCA: 504] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 02/05/2023]
Abstract
The otd/Otx gene family encodes paired-like homeodomain proteins that are involved in the regulation of anterior head structure and sensory organ development. Using the yeast one-hybrid screen with a bait containing the Ret 4 site from the bovine rhodopsin promoter, we have cloned a new member of the family, Crx (Cone rod homeobox). Crx encodes a 299 amino acid residue protein with a paired-like homeodomain near its N terminus. In the adult, it is expressed predominantly in photoreceptors and pinealocytes. In the developing mouse retina, it is expressed by embryonic day 12.5 (E12.5). Recombinant Crx binds in vitro not only to the Ret 4 site but also to the Ret 1 and BAT-1 sites. In transient transfection studies, Crx transactivates rhodopsin promoter-reporter constructs. Its activity is synergistic with that of Nrl. Crx also binds to and transactivates the genes for several other photoreceptor cell-specific proteins (interphotoreceptor retinoid-binding protein, beta-phosphodiesterase, and arrestin). Human Crx maps to chromosome 19q13.3, the site of a cone rod dystrophy (CORDII). These studies implicate Crx as a potentially important regulator of photoreceptor cell development and gene expression and also identify it as a candidate gene for CORDII and other retinal diseases.
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Xin G, Yao T, Sun H, Scott SM, Shao D, Wang G, Lian J. Highly thermally conductive and mechanically strong graphene fibers. Science 2015; 349:1083-7. [DOI: 10.1126/science.aaa6502] [Citation(s) in RCA: 471] [Impact Index Per Article: 47.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 01/18/2023]
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471 |
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Sun H, Treco D, Szostak JW. Extensive 3'-overhanging, single-stranded DNA associated with the meiosis-specific double-strand breaks at the ARG4 recombination initiation site. Cell 1991; 64:1155-61. [PMID: 2004421 DOI: 10.1016/0092-8674(91)90270-9] [Citation(s) in RCA: 417] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 12/29/2022]
Abstract
Meiosis-specific double-strand breaks occur at the initiation site for meiotic gene conversion in the yeast ARG4 gene. Here we show that the break fragments end in extensive 3'-overhanging, single-stranded tails. The single-stranded tails very in length, generating a gradient of single-strandedness that parallels the gradient of gene conversion frequencies in ARG4. In strains carrying a rad50S mutation, which blocks meiotic recombination, the extensive single-stranded tails do not form, suggesting that their generation is an obligatory step in meiotic recombination. Using the rad50S mutant, we have mapped the site of the ARG4 break to a small region within the genetically defined recombination initiation site. These results strongly support the double-strand break model of meiotic recombination.
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Abstract
BLM, the gene that is defective in Bloom's syndrome, encodes a protein homologous to RecQ subfamily helicases that functions as a 3'-5' DNA helicase in vitro. We now report that the BLM helicase can unwind G4 DNA. The BLM G4 DNA unwinding activity is ATP-dependent and requires a short 3' region of single-stranded DNA. Strikingly, G4 DNA is a preferred substrate of the BLM helicase, as measured both by efficiency of unwinding and by competition. These results suggest that G4 DNA may be a natural substrate of BLM in vivo and that the failure to unwind G4 DNA may cause the genomic instability and increased frequency of sister chromatid exchange characteristic of Bloom's syndrome.
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Comparative Study |
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408 |
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Nagueh SF, Sun H, Kopelen HA, Middleton KJ, Khoury DS. Hemodynamic determinants of the mitral annulus diastolic velocities by tissue Doppler. J Am Coll Cardiol 2001; 37:278-85. [PMID: 11153752 DOI: 10.1016/s0735-1097(00)01056-1] [Citation(s) in RCA: 386] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Academic Contribution Register] [Indexed: 01/09/2023]
Abstract
OBJECTIVES Our goal was to identify the hemodynamic determinants of the mitral annulus (MA) diastolic velocities by tissue Doppler. BACKGROUND The MA diastolic velocities are promising indexes of left ventricular (LV) diastolic function. However, their hemodynamic determinants have not yet been evaluated. METHODS Ten adult mongrel dogs underwent left atrial (LA) and LV pressure measurements by Millar catheters while tissue Doppler was applied to record the MA diastolic velocities at the septal and lateral comers. Conventional transmitral flow was also obtained. Left atrial and LV pressures were modified utilizing fluid administration and caval occlusion, whereas dobutamine and esmolol were used to change LV and LA relaxation. Left ventricular filling pressures were altered during different lusitropic states to evaluate for the possible interaction of preload and LV relaxation on the early diastolic velocity (Ea). RESULTS In the majority of dogs, a positive significant relation was observed between Ea and the transmitral pressure gradient (r = 0.57, p = 0.04). The Ea had strong correlations with tau (r = -0.83, p < 0.001), LV -dP/dt (r = 0.8, p < 0.001) and minimal LV pressure (r = -0.76, p < 0.01). However, there was no relation between Ea and the transmitral pressure gradient in experimental stages where tau >50 ms. Furthermore, the late diastolic velocity at both corners of the MA had significant positive relations with LA dP/dt (r = 0.67, p < 0.01) and LA relaxation (r = 0.73, p < 0.01) but an inverse correlation with LV end-diastolic pressure (r = -0.53, p = 0.01). CONCLUSIONS Left ventricular relaxation, minimal pressure and preload determine Ea while late diastolic velocity determinants include LA dP/dt, LA relaxation and LV end-diastolic pressure.
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386 |
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Sun H, Treco D, Schultes NP, Szostak JW. Double-strand breaks at an initiation site for meiotic gene conversion. Nature 1989; 338:87-90. [PMID: 2645528 DOI: 10.1038/338087a0] [Citation(s) in RCA: 384] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 01/01/2023]
Abstract
It has been proposed that the initiation of meiotic recombination involves either single-strand or double-strand breaks in DNA. It is difficult to distinguish between these on the basis of genetic evidence because they give rise to similar predictions. All models invoke initiation at specific sites to explain polarity, which is a gradient in gene conversion frequency from one end of a gene to the other. In the accompanying paper we describe the localization of an initiation site for gene conversion to the promoter region of the ARG4 gene of the yeast Saccharomyces cerevisiae. Here, we show that a double-strand break appears at the ARG4 recombination initiation site at the time of recombination, and that the broken DNA molecules end in long single-stranded tails.
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384 |
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Li DM, Sun H. PTEN/MMAC1/TEP1 suppresses the tumorigenicity and induces G1 cell cycle arrest in human glioblastoma cells. Proc Natl Acad Sci U S A 1998; 95:15406-11. [PMID: 9860981 PMCID: PMC28055 DOI: 10.1073/pnas.95.26.15406] [Citation(s) in RCA: 372] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 01/08/2023] Open
Abstract
PTEN/MMAC1/TEP1 is a tumor suppressor that possesses intrinsic phosphatase activity. Deletions or mutations of its encoding gene are associated with a variety of human cancers. However, very little is known about the molecular mechanisms by which this important tumor suppressor regulates cell growth. Here, we show that PTEN expression potently suppressed the growth and tumorigenicity of human glioblastoma U87MG cells. The growth suppression activity of PTEN was mediated by its ability to block cell cycle progression in the G1 phase. Such an arrest correlated with a significant increase of the cell cycle kinase inhibitor p27(KIP1) and a concomitant decrease in the activities of the G1 cyclin-dependent kinases. PTEN expression also led to the inhibition of Akt/protein kinase B, a serine-threonine kinase activated by the phosphatidylinositol 3-kinase (PI 3-kinase) signaling pathway. In addition, the effect of PTEN on p27(KIP1) and the cell cycle can be mimicked by treatment of U87MG cells with LY294002, a selective inhibitor of PI 3-kinase. Taken together, our studies suggest that the PTEN tumor suppressor modulates G1 cell cycle progression through negatively regulating the PI 3-kinase/Akt signaling pathway, and one critical target of this signaling process is the cyclin-dependent kinase inhibitor p27(KIP1).
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research-article |
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372 |
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Bunte SW, Sun H. Molecular Modeling of Energetic Materials: The Parameterization and Validation of Nitrate Esters in the COMPASS Force Field. J Phys Chem B 2000. [DOI: 10.1021/jp991786u] [Citation(s) in RCA: 354] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 11/29/2022]
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25 |
354 |
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King AJ, Sun H, Diaz B, Barnard D, Miao W, Bagrodia S, Marshall MS. The protein kinase Pak3 positively regulates Raf-1 activity through phosphorylation of serine 338. Nature 1998; 396:180-3. [PMID: 9823899 DOI: 10.1038/24184] [Citation(s) in RCA: 341] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 11/09/2022]
Abstract
The pathway involving the signalling protein p21Ras propagates a range of extracellular signals from receptors on the cell membrane to the cytoplasm and nucleus. The Ras proteins regulate many effectors, including members of the Raf family of protein kinases. Ras-dependent activation of Raf-1 at the plasma membrane involves phosphorylation events, protein-protein interactions and structural changes. Phosphorylation of serine residues 338 or 339 in the catalytic domain of Raf-1 regulates its activation in response to Ras, Src and epidermal growth factor. Here we show that the p21-activated protein kinase Pak3 phosphorylates Raf-1 on serine 338 in vitro and in vivo. The p21-activated protein kinases are regulated by the Rho-family GTPases Rac and Cdc42. Our results indicate that signal transduction through Raf-1 depends on both Ras and the activation of the Pak pathway. As guanine-nucleotide-exchange activity on Rac can be stimulated by a Ras-dependent phosphatidylinositol-3-OH kinase, a mechanism could exist through which one Ras effector pathway can be influenced by another.
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341 |
19
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Sun H. Force field for computation of conformational energies, structures, and vibrational frequencies of aromatic polyesters. J Comput Chem 1994. [DOI: 10.1002/jcc.540150708] [Citation(s) in RCA: 330] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 11/06/2022]
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330 |
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Abstract
Like early Xenopus embryos, extracts made from Xenopus eggs lack the cell cycle checkpoint that keeps anaphase from occurring before spindle assembly is complete. At very high densities of sperm nuclei, however, microtubule depolymerization arrests the extracts in mitosis. The arrested extracts have high levels of maturation-promoting factor activity, fail to degrade cyclin B, and contain activated ERK2/mitogen-activated protein (MAP) kinase. The addition of the purified MAP kinase-specific phosphatase MKP-1 demonstrates that MAP kinase activity is required for both the establishment and maintenance of the mitotic arrest induced by spindle depolymerization. Increased calcium concentrations, which release unfertilized frog eggs from their natural arrest in metaphase of meiosis II, have no effect on the mitotic arrest.
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Zhang Z, Han Y, Xiao FS, Qiu S, Zhu L, Wang R, Yu Y, Zhang Z, Zou B, Wang Y, Sun H, Zhao D, Wei Y. Mesoporous aluminosilicates with ordered hexagonal structure, strong acidity, and extraordinary hydrothermal stability at high temperatures. J Am Chem Soc 2001; 123:5014-21. [PMID: 11457329 DOI: 10.1021/ja004138t] [Citation(s) in RCA: 311] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 11/30/2022]
Abstract
Highly ordered hexagonal mesoporous aluminosilicates (MAS-5) with uniform pore sizes have been successfully synthesized from assembly of preformed aluminosilcate precursors with cetyltrimethylammonium bromide (CTAB) surfactant. The aluminosilicate precursors were obtained by heating, at 100--140 degrees C for 2--10 h, aluminasilica gels at the Al(2)O(3)/SiO(2)/TEAOH/H(2)O molar ratios of 1.0/7.0--350/10.0--33.0/500--2000. Mesoporous MAS-5 shows extraordinary stability both in boiling water (over 300 h) and in steam (800 degrees C for 2 h). Temperature-programmed desorption of ammonia shows that the acidic strength of MAS-5 is much higher than that of MCM-41 and is comparable to that of microporous Beta zeolite. In catalytic cracking of 1,3,5-triisopropylbenzene and alkylation of isobutane with butene, MAS-5 exhibits greater catalytic activity and selectivity, as compared with MCM-41 and HZSM-5. The MAS-5 samples were characterized with infrared, UV--Raman, and NMR spectroscopy and numerous other techniques. The results suggest that MAS-5 consists of both mesopores and micropores and that the pore walls of MAS-5 contain primary and secondary structural building units, similar to those of microporous zeolites. Such unique structural features might be responsible for the observed strong acidity and high thermal stability of the mesoporous aluminosilicates with well-ordered hexagonal symmetry.
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Garzon R, Pichiorri F, Palumbo T, Visentini M, Aqeilan R, Cimmino A, Wang H, Sun H, Volinia S, Alder H, Calin GA, Liu CG, Andreeff M, Croce CM. MicroRNA gene expression during retinoic acid-induced differentiation of human acute promyelocytic leukemia. Oncogene 2007; 26:4148-57. [PMID: 17260024 DOI: 10.1038/sj.onc.1210186] [Citation(s) in RCA: 299] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 02/06/2023]
Abstract
MicroRNAs (miRNAs) are small non-coding RNAs of 19-25 nucleotides that are involved in the regulation of critical cell processes such as apoptosis, cell proliferation and differentiation. However, little is known about the role of miRNAs in granulopoiesis. Here, we report the expression of miRNAs in acute promyelocytic leukemia patients and cell lines during all-trans-retinoic acid (ATRA) treatment by using a miRNA microarrays platform and quantitative real time-polymerase chain reaction (qRT-PCR). We found upregulation of miR-15a, miR-15b, miR-16-1, let-7a-3, let-7c, let-7d, miR-223, miR-342 and miR-107, whereas miR-181b was downregulated. Among the upregulated miRNAs, miR-107 is predicted to target NFI-A, a gene that has been involved in a regulatory loop involving miR-223 and C/EBPa during granulocytic differentiation. Indeed, we have confirmed that miR-107 targets NF1-A. To get insights about ATRA regulation of miRNAs, we searched for ATRA-modulated transcription factors binding sites in the upstream genomic region of the let-7a-3/let-7b cluster and identified several putative nuclear factor-kappa B (NF-kappaB) consensus elements. The use of reporter gene assays, chromatin immunoprecipitation and site-directed mutagenesis revealed that one proximal NF-kappaB binding site is essential for the transactivation of the let-7a-3/let-7b cluster. Finally, we show that ATRA downregulation of RAS and Bcl2 correlate with the activation of known miRNA regulators of those proteins, let-7a and miR-15a/miR-16-1, respectively.
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Research Support, Non-U.S. Gov't |
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Abstract
The levels of tyrosine phosphorylation required for cell growth and differentiation are achieved through the coordinated action of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). Depending upon the cellular context, these two types of enzymes may either antagonize or cooperate with each other during the signal transmission process. An imbalance between these enzymes may impair normal cell growth, leading to cellular transformation. Both PTKs and PTPs have evolved to a level of structural diversity that allows them to regulate many cellular processes. This review will focus on several specific examples that highlight the interplay between PTPs and PTKs in cell signaling.
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Review |
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Sun H, Molday RS, Nathans J. Retinal stimulates ATP hydrolysis by purified and reconstituted ABCR, the photoreceptor-specific ATP-binding cassette transporter responsible for Stargardt disease. J Biol Chem 1999; 274:8269-81. [PMID: 10075733 DOI: 10.1074/jbc.274.12.8269] [Citation(s) in RCA: 279] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Academic Contribution Register] [Indexed: 11/06/2022] Open
Abstract
Many substrates for P-glycoprotein, an ABC transporter that mediates multidrug resistance in mammalian cells, have been shown to stimulate its ATPase activity in vitro. In the present study, we used this property as a criterion to search for natural and artificial substrates and/or allosteric regulators of ABCR, the rod photoreceptor-specific ABC transporter responsible for Stargardt disease, an early onset macular degeneration. ABCR was immunoaffinity purified to apparent homogeneity from bovine rod outer segments and reconstituted into liposomes. All-trans-retinal, a candidate ligand, stimulates the ATPase activity of ABCR 3-4-fold, with a half-maximal effect at 10-15 microM. 11-cis- and 13-cis-retinal show similar activity. All-trans-retinal stimulates the ATPase activity of ABCR with Michaelis-Menten behavior indicative of simple noncooperative binding that is associated with a rate-limiting enzyme-substrate intermediate in the pathway of ATP hydrolysis. Among 37 structurally diverse non-retinoid compounds, including nine previously characterized substrates or sensitizers of P-glycoprotein, only four show significant ATPase stimulation when tested at 20 microM. The dose-response curves of these four compounds are indicative of multiple binding sites and/or modes of interaction with ABCR. Two of these compounds, amiodarone and digitonin, can act synergistically with all-trans-retinal, implying that they interact with a site or sites on ABCR different from the one with which all-trans-retinal interacts. Unlike retinal, amiodarone appears to interact with both free and ATP-bound ABCR. Together with clinical observations on Stargardt disease and the localization of ABCR to rod outer segment disc membranes, these data suggest that retinoids, and most likely retinal, are the natural substrates for transport by ABCR in rod outer segments. These observations have significant implications for understanding the visual cycle and the pathogenesis of Stargardt disease and for the identification of compounds that could modify the natural history of Stargardt disease or other retinopathies associated with impaired ABCR function.
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