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Früh K, Ahn K, Djaballah H, Sempé P, van Endert PM, Tampé R, Peterson PA, Yang Y. A viral inhibitor of peptide transporters for antigen presentation. Nature 1995; 375:415-8. [PMID: 7760936 DOI: 10.1038/375415a0] [Citation(s) in RCA: 465] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Cytotoxic T lymphocytes lyse target cells after T-cell-receptor-mediated recognition of class I major histocompatibility complex molecules presenting peptides. Antigenic peptides are generated in the cytoplasm by proteasomes and translocated into the lumen of the endoplasmic reticulum (ER) by peptide transporters (TAP). Herpes simplex virus (HSV) expresses a cytoplasmic protein, ICP47, which seems to interfere with such immune surveillance by mediating retention of 'empty' class I molecules in the ER. By expressing ICP47 in HeLa cells under an inducible promoter, we show that ICP47 efficiently inhibits peptide transport across the ER membrane such that nascent class I molecules fail to acquire antigenic peptides. This inhibition was overcome by transfecting murine TAP. Further, we demonstrate that ICP47 colocalizes and physically associates with TAP within the cell. Inhibition of peptide translocation by a viral protein indicates a previously undocumented potential mechanism for viral immune evasion.
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465 |
2
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Drapkin R, Reardon JT, Ansari A, Huang JC, Zawel L, Ahn K, Sancar A, Reinberg D. Dual role of TFIIH in DNA excision repair and in transcription by RNA polymerase II. Nature 1994; 368:769-72. [PMID: 8152490 DOI: 10.1038/368769a0] [Citation(s) in RCA: 382] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The RNA polymerase II general transcription factor TFIIH is composed of several polypeptides. The observation that the largest subunit of TFIIH is the excision-repair protein XPB/ERCC3 (ref. 1), a helicase implicated in the human DNA-repair disorders xeroderma pigmentosum (XP) and Cockayne's syndrome, suggests a functional link between transcription and DNA repair. To understand the connection between these two cellular processes, we have extensively purified and functionally analysed TFIIH. We find that TFIIH has a dual role, being required for basal transcription of class II genes and for participation in DNA-excision repair. TFIIH is shown to complement three different cell extracts deficient in excision repair: XPB/ERCC3, XPC and XPD/ERCC2. The complementation of XPB and XPD is a consequence of ERCC3 and ERCC2 being integral subunits of TFIIH, whereas complementation of XPC is due to an association of this polypeptide with TFIIH. We found that the general transcription factor IIE negatively modulates the helicase activity of TFIIH through a direct interaction between TFIIE and the ERCC3 subunit of TFIIH.
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382 |
3
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Ahn K, Gruhler A, Galocha B, Jones TR, Wiertz EJ, Ploegh HL, Peterson PA, Yang Y, Früh K. The ER-luminal domain of the HCMV glycoprotein US6 inhibits peptide translocation by TAP. Immunity 1997; 6:613-21. [PMID: 9175839 DOI: 10.1016/s1074-7613(00)80349-0] [Citation(s) in RCA: 359] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Human cytomegalovirus (HCMV) inhibits MHC class I antigen presentation by a sequential multistep process involving a family of unique short (US) region-encoded glycoproteins. US3 retains class I molecules, whereas US2 and US11 mediate the cytosolic degradation of heavy chains by the proteosomes. In US6-transfected cells, however, intracellular transport of class I molecules is impaired because of defective peptide translocation by transporters associated with antigen processing (TAP). Peptide transport is restored in HCMV mutants lacking US6. In contrast to the cytosolic herpes simplex virus protein ICP47, US6 interacts with TAP inside the endoplasmic reticulum lumen, as shown by US6 derivatives lacking the transmembrane and cytoplasmic domains and by the observation that US6 does not prevent peptides from binding to TAP. Thus, HCMV targets TAP for immune escape by a molecular mechanism different from that of herpes simplex virus.
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Andl T, Ahn K, Kairo A, Chu EY, Wine-Lee L, Reddy ST, Croft NJ, Cebra-Thomas JA, Metzger D, Chambon P, Lyons KM, Mishina Y, Seykora JT, Crenshaw EB, Millar SE. Epithelial Bmpr1a regulates differentiation and proliferation in postnatal hair follicles and is essential for tooth development. Development 2004; 131:2257-68. [PMID: 15102710 DOI: 10.1242/dev.01125] [Citation(s) in RCA: 296] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Bone morphogenetic protein (BMP) signaling is thought to perform multiple functions in the regulation of skin appendage morphogenesis and the postnatal growth of hair follicles. However, definitive genetic evidence for these roles has been lacking. Here, we show that Cre-mediated mutation of the gene encoding BMP receptor 1A in the surface epithelium and its derivatives causes arrest of tooth morphogenesis and lack of external hair. The hair shaft and hair follicle inner root sheath (IRS) fail to differentiate, and expression of the known transcriptional regulators of follicular differentiation Msx1, Msx2, Foxn1 and Gata3 is markedly downregulated or absent in mutant follicles. Lef1 expression is maintained, but nuclear beta-catenin is absent from the epithelium of severely affected mutant follicles, indicating that activation of the WNT pathway lies downstream of BMPR1A signaling in postnatal follicles. Mutant hair follicles fail to undergo programmed regression, and instead continue to proliferate, producing follicular cysts and matricomas. These results provide definitive genetic evidence that epithelial Bmpr1a is required for completion of tooth morphogenesis, and regulates terminal differentiation and proliferation in postnatal hair follicles.
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Research Support, U.S. Gov't, P.H.S. |
21 |
296 |
5
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Ahn K, Angulo A, Ghazal P, Peterson PA, Yang Y, Früh K. Human cytomegalovirus inhibits antigen presentation by a sequential multistep process. Proc Natl Acad Sci U S A 1996; 93:10990-5. [PMID: 8855296 PMCID: PMC38271 DOI: 10.1073/pnas.93.20.10990] [Citation(s) in RCA: 284] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The human cytomegalovirus (HCMV) genomic unique short (US) region encodes a family of homologous genes essential for the inhibition of major histocompatibility complex (MHC) class I-mediated antigen presentation during viral infection. Here we show that US3, the only immediate early (IE) gene within the US region, encodes an endoplasmic reticulum-resident glycoprotein that prevents intracellular transport of MHC class I molecules. In contrast to the rapid degradation of newly synthesized MHC class I heavy chains mediated by the early gene product US11, we found that US3 retains stable MHC class I heterodimers in the endoplasmic reticulum that are loaded with peptides while retained in the ER. Consistent with the expression pattern of US3 and US11, MHC class I molecules are retained but not degraded during the IE period of infection. Our data identify the first nonregulatory role of an IE protein of HCMV and suggest that HCMV uses different T-cell escape strategies at different times during the infectious cycle.
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research-article |
29 |
284 |
6
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Ahn K, Kornberg A. Polyphosphate kinase from Escherichia coli. Purification and demonstration of a phosphoenzyme intermediate. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)38459-5] [Citation(s) in RCA: 240] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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240 |
7
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Abstract
AIMS To evaluate the clinical significance of macular hole closure types assessed by optical coherence tomography (OCT). METHODS This study involved 34 eyes of 32 patients who had undergone anatomically successful idiopathic macular hole surgery. The closed macular holes were categorised into two patterns based on OCT; type 1 closure (closed without foveal neurosensory retinal defect) and type 2 closure (closed with foveal neurosensory retinal defect). Association between visual prognosis, type of hole closure, and possible prognostic factors were analysed. RESULTS 19 eyes (61.3%) were classified into the type 1 closure and 12 eyes (38.7%) into the type 2 closure. The extent of postoperative visual improvement of type 1 closure group was larger than that of type 2 closure group (p=0.002). The preoperative macular hole size of type 2 closure group was significantly larger than that of type 1 closure group (p=0.006). The duration of symptoms was positively correlated with the preoperative macular hole size (p=0.01). Recurrence of macular hole occurred only in the type 2 closure group. CONCLUSION The type of macular hole closure, which was influenced by the preoperative hole diameter, was associated with postoperative visual prognosis. Early detection and intervention in macular hole should be emphasised.
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research-article |
22 |
191 |
8
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Yang Y, Früh K, Ahn K, Peterson PA. In vivo assembly of the proteasomal complexes, implications for antigen processing. J Biol Chem 1995; 270:27687-94. [PMID: 7499235 DOI: 10.1074/jbc.270.46.27687] [Citation(s) in RCA: 156] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The multicatalytic and multisubunit proteasomal complexes have been implicated in the processing of antigens to peptides presented by class I major histocompatibility complex molecules. Two structural complexes of this proteinase, 20 S and 26 S proteasomes, have been isolated from cells. By analyzing in vivo assembly of the proteasomal complexes we show that the 20 S proteasomal complexes are irreversibly assembled via 15 S assembly intermediates containing unprocessed beta-type subunits. The 20 S proteasomes further associate reversibly with proteasome activators PA28 or pre-existing ATPase complexes to form 26 S proteasomal complexes. Our findings that not all of the 20 S proteasomal complexes are assembled into 26 S proteasomal complexes within cells and that all of PA28 and ATPase complexes are associated with 20 S proteasomes strongly suggest that all proteasomal complexes coexist within cells. We further demonstrate that 26 S proteasomal complexes are predominantly present in the cytoplasm and a significant portion of the 20 S proteasomal complexes is associated with the endoplasmic reticulum membrane. Taken together, our findings suggest that depending upon their associated regulatory components, 26 S and 20 S-PA28 proteasomal complexes serve different housekeeping functions within the cells, while they degrade antigens in a cooperative manner in antigen processing.
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30 |
156 |
9
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Ahn K, Mishina Y, Hanks MC, Behringer RR, Crenshaw EB. BMPR-IA signaling is required for the formation of the apical ectodermal ridge and dorsal-ventral patterning of the limb. Development 2001; 128:4449-61. [PMID: 11714671 DOI: 10.1242/dev.128.22.4449] [Citation(s) in RCA: 154] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We demonstrate that signaling via the bone morphogenetic protein receptor IA (BMPR-IA) is required to establish two of the three cardinal axes of the limb: the proximal-distal axis and the dorsal-ventral axis. We generated a conditional knockout of the gene encoding BMPR-IA (Bmpr) that disrupted BMP signaling in the limb ectoderm. In the most severely affected embryos, this conditional mutation resulted in gross malformations of the limbs with complete agenesis of the hindlimbs. The proximal-distal axis is specified by the apical ectodermal ridge (AER), which forms from limb ectoderm at the distal tip of the embryonic limb bud. Analyses of the expression of molecular markers, such as Fgf8, demonstrate that formation of the AER was disrupted in the Bmpr mutants. Along the dorsal/ventral axis, loss of engrailed 1 (En1) expression in the non-ridge ectoderm of the mutants resulted in a dorsal transformation of the ventral limb structures. The expression pattern of Bmp4 and Bmp7 suggest that these growth factors play an instructive role in specifying dorsoventral pattern in the limb. This study demonstrates that BMPR-IA signaling plays a crucial role in AER formation and in the establishment of the dorsal/ventral patterning during limb development.
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24 |
154 |
10
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Wine-Lee L, Ahn KJ, Richardson RD, Mishina Y, Lyons KM, Crenshaw EB. Signaling through BMP type 1 receptors is required for development of interneuron cell types in the dorsal spinal cord. Development 2004; 131:5393-403. [PMID: 15469980 DOI: 10.1242/dev.01379] [Citation(s) in RCA: 132] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
During spinal cord development, distinct classes of interneurons arise at stereotypical locations along the dorsoventral axis. In this paper, we demonstrate that signaling through bone morphogenetic protein (BMP) type 1 receptors is required for the formation of two populations of commissural neurons, DI1 and DI2, that arise within the dorsal neural tube. We have generated a double knockout of both BMP type 1 receptors, Bmpr1a and Bmpr1b, in the neural tube. These double knockout mice demonstrate a complete loss of D1 progenitor cells, as evidenced by loss of Math1expression, and the subsequent failure to form differentiated DI1 interneurons. Furthermore, the DI2 interneuron population is profoundly reduced. The loss of these populations of cells results in a dorsal shift of the dorsal cell populations, DI3 and DI4. Other dorsal interneuron populations, DI5 and DI6, and ventral neurons appear unaffected by the loss of BMP signaling. The Bmpr double knockout animals demonstrate a reduction in the expression of Wnt and Id family members, suggesting that BMP signaling regulates expression of these factors in spinal cord development. These results provide genetic evidence that BMP signaling is crucial for the development of dorsal neuronal cell types.
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21 |
132 |
11
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Johnson GD, Stevenson T, Ahn K. Hydrolysis of peptide hormones by endothelin-converting enzyme-1. A comparison with neprilysin. J Biol Chem 1999; 274:4053-8. [PMID: 9933597 DOI: 10.1074/jbc.274.7.4053] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Endothelins are peptide hormones with a potent vasoconstrictor activity that are also known to function as intercellular signaling molecules. The final step in the biosynthesis of endothelins is the proteolytic processing of precursor peptides by endothelin-converting enzymes (ECEs). ECE-1 is a zinc metalloendopeptidase related in amino acid sequence to neprilysin, a mammalian cell-surface peptidase involved in the metabolism of numerous biologically active peptides. Despite apparent structural similarities, ECE-1 and neprilysin have been considered to differ significantly in substrate specificity. In this study we have examined the activity of recombinant ECE-1 against a collection of biologically active peptides. ECE-1, unlike neprilysin, was found to have minimal activity against substrates smaller than hexapeptides, such as Leu-enkephalin. Larger peptides such as neurotensin, substance P, bradykinin, and the oxidized insulin B chain were hydrolyzed by ECE-1 as efficiently as big endothelin-1, a known in vivo substrate. Identification of the products of hydrolysis of six peptides indicates that ECE-1 has a substrate specificity similar to that of neprilysin, preferring to cleave substrates at the amino side of hydrophobic residues. The data indicate that ECE-1 possesses a surprisingly broad substrate specificity and is potentially involved in the metabolism of biologically active peptides distinct from the endothelins.
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Comparative Study |
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111 |
12
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Choi SP, Park HK, Park KN, Kim YM, Ahn KJ, Choi KH, Lee WJ, Jeong SK. The density ratio of grey to white matter on computed tomography as an early predictor of vegetative state or death after cardiac arrest. Emerg Med J 2008; 25:666-9. [DOI: 10.1136/emj.2007.053306] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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17 |
105 |
13
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Suzuki K, Bachiller D, Chen YP, Kamikawa M, Ogi H, Haraguchi R, Ogino Y, Minami Y, Mishina Y, Ahn K, Crenshaw EB, Yamada G. Regulation of outgrowth and apoptosis for the terminal appendage:external genitalia: development by concerted actions of BMP signaling. Development 2003; 130:6209-20. [PMID: 14602679 DOI: 10.1242/dev.00846] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Extra-corporal fertilization depends on the formation of copulatory organs:the external genitalia. Coordinated growth and differentiation of the genital tubercle (GT), an embryonic anlage of external genitalia, generates a proximodistally elongated structure suitable for copulation, erection, uresis and ejaculation. Despite recent progress in molecular embryology, few attempts have been made to elucidate the molecular developmental processes of external genitalia formation.Bone morphogenetic protein genes (Bmp genes) and their antagonists were spatiotemporally expressed during GT development. Exogenously applied BMP increased apoptosis of GT and inhibited its outgrowth. It has been shown that the distal urethral epithelium (DUE), distal epithelia marked by the Fgf8 expression, may control the initial GT outgrowth. Exogenously applied BMP4 downregulated the expression of Fgf8 and Wnt5a,concomitant with increased apoptosis and decreased cell proliferation of the GT mesenchyme. Furthermore, noggin mutants and Bmpr1a conditional mutant mice displayed hypoplasia and hyperplasia of the external genitalia respectively. noggin mutant mice exhibited downregulation of Wnt5aand Fgf8 expression with decreased cell proliferation. Consistent with such findings, Wnt5a mutant mice displayed GT agenesis with decreased cell proliferation. By contrast, Bmpr1a mutant mice displayed decreased apoptosis and augmented Fgf8 expression in the DUE associated with GT hyperplasia. These results suggest that some of the Bmp genes could negatively affect proximodistally oriented outgrowth of GT with regulatory functions on cell proliferation and apoptosis.The DUE region can be marked only until 14.0 dpc (days post coitum) in mouse development, while GT outgrowth continues thereafter. Possible signaling crosstalk among the whole distal GT regions were also investigated.
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22 |
104 |
14
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Park HS, Park E, Kim MS, Ahn K, Kim IY, Choi EJ. Selenite inhibits the c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) through a thiol redox mechanism. J Biol Chem 2000; 275:2527-31. [PMID: 10644709 DOI: 10.1074/jbc.275.4.2527] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Selenium, an essential biological trace element, has been shown to modulate functions of many regulatory proteins involved in signal transduction and to affect a variety of cellular activities including cell growth, survival, and death. The molecular mechanism by which selenium exerts its action on the cellular events, however, remains unclear. In our present study, we observed that selenite suppresses both the c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) and the p38 mitogen-activated protein kinase pathway in 293T cells. In contrast, selenite had little effect on the extracellular signal-regulated kinase pathway. Furthermore, selenite directly inhibited JNK/SAPK activity in vitro but not the p38 activity. The in vitro inhibition of JNK/SAPK by selenite was reversed by the addition of reducing agents such as dithiothreitol and beta-mercaptoethanol. Replacement of cysteine 116 in JNK1 by serine abolished the inhibitory effect of selenite on JNK1 activity both in vitro and in vivo. Selenite also suppressed a c-Jun-dependent luciferase reporter activity stimulated through the JNK signaling pathway. Taken together, our findings strongly suggest that selenite differentially modulates the mammalian mitogen-activated protein kinase pathways and that it can repress the JNK/SAPK signaling pathway by inhibiting JNK/SAPK through a thiol redox mechanism.
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25 |
97 |
15
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Ahn KJ, You WJ, Jeong SL, Lee JW, Kim BS, Lee JH, Yang DW, Son YM, Hahn ST. Atypical manifestations of reversible posterior leukoencephalopathy syndrome: findings on diffusion imaging and ADC mapping. Neuroradiology 2004; 46:978-83. [PMID: 15536557 DOI: 10.1007/s00234-004-1276-1] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2004] [Revised: 08/03/2004] [Accepted: 08/17/2004] [Indexed: 11/24/2022]
Abstract
Typically, reversible posterior leukoencephalopathy syndrome (RPLS) involves the parieto-occipital lobes. When regions of the brain other than the parieto-occipital lobes are predominantly involved, the syndrome can be called atypical RPLS. The purpose of this study is to find radiological and pathophysiological features of atypical RPLS by using diffusion-weighted imaging (D-WI). We retrospectively reviewed seven patients (two with eclampsia, one with cyclosporine neurotoxicity, and four with hypertensive encephalopathy) with atypical MR manifestations of RPLS. Changes in signal intensity on T2-weighted imaging (T2-WI) and D-WI, and ADC ratio, were analyzed. In patients with atypical manifestation of RPLS, high signal intensities on T2-WI were noted in the frontal lobe, basal ganglia, thalamus, brainstem, and subcortical white matter in regions other than the parieto-occipital lobes. These areas of increased signal intensities on T2-WI showed increased ADC values, representing vasogenic edema in all seven patients. This result should be very useful in differentiating atypical RPLS from other metabolic brain disorders that affect the same sites with cytotoxic edema.
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21 |
92 |
16
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Jun Y, Kim E, Jin M, Sung HC, Han H, Geraghty DE, Ahn K. Human cytomegalovirus gene products US3 and US6 down-regulate trophoblast class I MHC molecules. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2000; 164:805-11. [PMID: 10623826 DOI: 10.4049/jimmunol.164.2.805] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The epidemiological correlation between human CMV (HCMV) infection and spontaneous fetal loss has been suggested, but the underlying mechanism is not well understood. Fetal cytotrophoblasts, which are in direct contact with the maternal immune system in the uterus during pregnancy, do not express HLA-A and HLA-B, but express the nonclassical class I HLA-G and HLA-C. It has been shown that both HLA-G and HLA-C are capable of inhibiting NK-mediated cell lysis. In our present study, using human trophoblast cell lines as well as other cell lines stably transfected with the human class I genes, we have demonstrated that HCMV US3 and US6 down-regulate the cell-surface expression of both HLA-G and HLA-C by two different mechanisms. HCMV US3 physically associates with both trophoblast class I MHC species, retaining them in the endoplasmic reticulum. In contrast, HCMV US6 inhibits peptide transport by TAP and thus specifically the intracellular trafficking of class I molecules. Therefore, these findings suggest for the first time a possible molecular mechanism underlying HCMV-related spontaneous pregnancy loss.
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25 |
87 |
17
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Park B, Lee S, Kim E, Chang S, Jin M, Ahn K. The truncated cytoplasmic tail of HLA-G serves a quality-control function in post-ER compartments. Immunity 2001; 15:213-24. [PMID: 11520457 DOI: 10.1016/s1074-7613(01)00179-0] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In contrast to the current model of MHC class I trafficking, which predicts that once a MHC class I molecule leaves the ER, it moves to the cell surface by bulk flow, we show that HLA-G that is loaded with suboptimal peptides is retrieved from post-ER compartments to the ER. Loading of HLA-G with high-affinity peptides abrogates this retrieval due to the lack of binding affinity to coatomer. Moreover, the loss of the endocytosis motif in the truncated cytoplasmic tail results in the prolonged half-life of HLA-G on the cell surface. Our findings reveal that surface expression of HLA-G can be further regulated in post-ER compartments and that the truncated cytoplasmic tail plays a critical role in such quality-control mechanisms.
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24 |
76 |
18
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Ahn K, Erlander M, Leturcq D, Peterson PA, Früh K, Yang Y. In vivo characterization of the proteasome regulator PA28. J Biol Chem 1996; 271:18237-42. [PMID: 8663520 DOI: 10.1074/jbc.271.30.18237] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
A proteasome regulator, termed PA28, has been shown to modulate peptidase activities of the proteasomes in vitro. Two different but homologous PA28 molecules, designated as PA28alpha and PA28beta, have been cloned. Both alpha and beta polypeptides of PA28 are found in PA28 complexes isolated from cells, indicating that both are constituents of functional PA28 complexes. Using antisera specific to PA28alpha, PA28beta, and epitope-tagged PA28 molecules, we show that expression of PA28alpha and PA28beta is coordinately induced by various cytokines in different cell lines and that PA28 subunits and proteasomes have almost identical half-lives. In addition, we show that PA28 complexes are associated with 20 S but not 26 S proteasomes in vivo. Moreover, we demonstrate that PA28 complex is a heterohexamer composed of both alpha and beta subunits with a stoichiometry of alpha3beta3 in an alternating order.
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Comparative Study |
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68 |
19
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Ahn K, Bardina L, Grishina G, Beyer K, Sampson HA. Identification of two pistachio allergens, Pis v 1 and Pis v 2, belonging to the 2S albumin and 11S globulin family. Clin Exp Allergy 2009; 39:926-34. [PMID: 19522997 DOI: 10.1111/j.1365-2222.2009.03259.x] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND IgE-mediated allergic reactions to pistachio appear to be occurring more frequently; however, little is known about its allergenic proteins. OBJECTIVE We attempted to identify pistachio allergens and to clone the encoding genes. METHODS Pistachio proteins were extracted and separated by SDS-PAGE. Immunolabelling was performed with sera from 28 pistachio-allergic individuals. Proteins of interest were further analysed by Edman sequencing and mass spectrometry/mass spectrometry (MS/MS). In parallel, a cDNA library was generated from immature pistachios and screened with primers designed on the basis of internal sequences and peptide spectra. Full-length cDNA clones were isolated from the library and sequenced. Recombinant proteins were expressed and tested with sera from pistachio-allergic patients. RESULTS Nineteen out of 28 patients (68%) showed IgE binding to a 7 kDa protein fraction, while 14 (50%) showed specific IgE to a 32 kDa protein fraction. Analysis by Edman sequencing and MS/MS revealed that these proteins were homologue to the cashew nut allergens Ana o 3 and Ana o 2, respectively. Screening of the pistachio cDNA library resulted in isolation of novel protein cDNAs. Open-reading frame translation provided the complete amino acid sequences of two new allergenic pistachio proteins. Recombinant proteins were recognized by six out of six selected patients. Therefore, these new allergens were named Pis v 1 and Pis v 2 by the Allergen Nomenclature Subcommittee. CONCLUSION Novel allergens in pistachio, Pis v 1 and Pis v 2, which belong to 2S albumin and 11S globulin family, respectively, were isolated and the genes encoding these allergens were identified.
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Research Support, Non-U.S. Gov't |
16 |
67 |
20
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See J, Mamontov P, Ahn K, Wine-Lee L, Crenshaw EB, Grinspan JB. BMP signaling mutant mice exhibit glial cell maturation defects. Mol Cell Neurosci 2007; 35:171-82. [PMID: 17391983 PMCID: PMC1950488 DOI: 10.1016/j.mcn.2007.02.012] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2006] [Revised: 01/16/2007] [Accepted: 02/13/2007] [Indexed: 10/23/2022] Open
Abstract
Bone morphogenetic proteins have been implicated in the development of oligodendrocytes and astrocytes, however, a role for endogenous BMP signaling in glial development has not been demonstrated in a genetic model. Using mice in which signaling via type I BMP receptors Bmpr1a and Bmpr1b have been inactivated in the neural tube, we demonstrate that BMP signaling contributes to the maturation of glial cells in vivo. At P0, mutant mice exhibited a 25-40% decrease in GFAP+ or S100beta+ astrocytes in the cervical spinal cord. The number of oligodendrocyte precursors and the timing of their emergence was unchanged in the mutant mice compared to the normals, however myelin protein expression and mature oligodendrocyte numbers were significantly reduced. These data indicate that BMP signaling promotes the generation of astrocytes and mature, myelinating oligodendrocytes in vivo but does not affect oligodendrocyte precursor development, thus suggesting tight regulation of BMP signaling to ensure proper gliogenesis.
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Research Support, Non-U.S. Gov't |
18 |
67 |
21
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Szczesna-Skorupa E, Ahn K, Chen CD, Doray B, Kemper B. The cytoplasmic and N-terminal transmembrane domains of cytochrome P450 contain independent signals for retention in the endoplasmic reticulum. J Biol Chem 1995; 270:24327-33. [PMID: 7592644 DOI: 10.1074/jbc.270.41.24327] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Microsomal cytochrome P450 is inserted into the membrane of the endoplasmic reticulum (ER) by its N-terminal signal/anchor sequence which also functions as an ER retention signal. To analyze further potential retention signals of cytochrome P450, topological domains of cytochrome P450 2C1 or 2C2, epidermal growth factor receptor, a plasma membrane protein, and bacterial alkaline phosphatase, a secreted protein were exchanged. The N-terminal signal/anchor of cytochrome P450 2C1 functioned as an ER retention signal when placed at the N terminus of several reporter proteins but not when fused at the C terminus of the extracellular domain of epidermal growth factor receptor, with or without a heterologous cytoplasmic domain. Chimeric proteins in which the cytoplasmic domain of cytochrome P450 2C2 was substituted for that of epidermal growth factor receptor were retained in the ER indicating that an independent retention signal is present in the cytoplasmic part of cytochrome P450 2C2. These chimeras were enzymatically active which argues against misfolding as the primary cause of retention. The ER retention signal of the cytoplasmic domain could not be localized to a single amino acid segment by deletion analysis. These results show that cytochrome P450 2C2 contains redundant, complex ER retention signals in its cytoplasmic and N-terminal hydrophobic domains and that the function of the N-terminal signal is context-dependent.
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Park K, Ahn K, Lee S, Ryu S, Park Y, Azadzoi KM. Decreased circulating levels of estrogen alter vaginal and clitoral blood flow and structure in the rabbit. Int J Impot Res 2001; 13:116-24. [PMID: 11426351 DOI: 10.1038/sj.ijir.3900655] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2000] [Revised: 10/16/2000] [Accepted: 12/04/2000] [Indexed: 12/20/2022]
Abstract
Aging and menopause related decline in circulating levels of estrogen has been shown to adversely affect female sexual arousal function. Our aim was to study the effects of circulating levels of estrogen on the hemodynamic mechanism of vaginal and clitoral engorgement and on the structure of the vaginal and clitoral cavernosal tissue in the rabbit. New Zealand White female rabbits (3.5-4 kg) were randomly divided into three groups with five rabbits in each group: control; bilateral oophorectomy; bilateral oophorectomy undergoing subcutaneous injection of estrogen (40 microg/kg/day). After 6 weeks, the serum levels of 17 beta-estradiol were measured and systemic blood pressure was monitored. Vaginal and clitoral cavernosal blood flows were measured with laser Doppler flowmeter before and after pelvic nerve stimulation. Cross sections of the clitoris and vagina were processed for histologic examination and histomorphometric image analysis. Serum level of 17 beta-estradiol (pg/ml; mean+/-s.d.) revealed a significant decrease in the oophorectomy group (25.4+/-5.1) compared with the control (38.5+/-7.6) and estrogen replacement (115.9+/-57.3) groups (P<0.05). Nerve stimulation-induced peak vaginal and clitoral intracavernosal blood flows in the oophorectomy group (28.9+/-16.3 and 6.1+/-1.4, respectively) were significantly less than those recorded in the control (48.9+/-6.5 and 11.0+/-2.4, respectively) or estrogen replacement (48.7+/-12.2 and 10.1+/-2.8, respectively) group (P<0.05). In histology, marked thinning of the vaginal epithelial layers, decreased vaginal submucosal microvasculature, and diffuse clitoral cavernosal fibrosis were evident in the oophorectomy group but not in the estrogen supplement and control groups. In histomorphometry, the percentage of clitoral cavernosal smooth muscle in the oophorectomy group (49.6+/-6.2) was significantly decreased compared with the control (56.8+/-2.6) and estrogen replacement (58+/-3.0) groups (P<0.05). Our studies show that decline in circulating levels of estrogen impairs the hemodynamic mechanism of vaginal and clitoral engorgement and leads to histopathologic changes in the vagina and clitoral cavernosal tissue. These observations suggest that decreased circulating levels of estrogen, a physiologic change in the menopausal state, may play a role in the development of female sexual arousal dysfunction.
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Kumble KD, Ahn K, Kornberg A. Phosphohistidyl active sites in polyphosphate kinase of Escherichia coli. Proc Natl Acad Sci U S A 1996; 93:14391-5. [PMID: 8962061 PMCID: PMC26142 DOI: 10.1073/pnas.93.25.14391] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/23/1996] [Indexed: 02/03/2023] Open
Abstract
In the synthesis of inorganic polyphosphate (polyP) from ATP by polyphosphate kinase (PPK; EC 2.7.4.1) of Escherichia coli, an N-P-linked phosphoenzyme was previously identified as the intermediate. The phosphate is presumed to be linked to N3 of the histidine residue because of its chemical stabilities and its resemblance to other enzymes known to contain N3-phosphohistidine. Tryptic digests of [32P]PPK contain a predominant 32P-labeled peptide that includes His-441. Of the 16 histidine residues in PPK of E. coli, 4 are conserved among several bacterial species. Mutagenesis of these 4 histidines shows that two (His-430 and His-598) are unaffected in function when mutated to glutamine, whereas two others (His-441 and His-460) mutated to glutamine or alanine fail to be phosphorylated, show no enzymatic activities, and fail to support polyP accumulation in cells bearing these mutant enzymes.
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Ahn K, Takai S, Pawankar R, Kuramasu A, Ohtsu H, Kempuraj D, Tomita H, Iida M, Matsumoto K, Akasawa A, Miyazaki M, Saito H. Regulation of chymase production in human mast cell progenitors. J Allergy Clin Immunol 2000; 106:321-8. [PMID: 10932077 DOI: 10.1067/mai.2000.108107] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
BACKGROUND Although mature tryptase-positive mast cells (MCs) and tryptase and chymase double-positive MCs are recognized using in situ staining and are preferentially distributed in different tissues, recent findings suggest that tryptase-positive MCs can give rise to tryptase and chymase double-positive MCs. OBJECTIVE We investigated the regulation of chymase production in developing MCs. METHODS Human cord blood or peripheral blood cells were cultured in the presence of stem cell factor and IL-6 with or without IL-4 in methylcellulose or liquid medium. Intracellular chymase and tryptase were determined with immunocytochemistry, flow cytometry, and ELISA. Chymase messenger RNA expression was examined with 3 different methods, such as Northern blotting. RESULTS Flow cytometric analysis always showed a unimodal histogram of chymase-positive, as well as tryptase-positive, cells in the presence of various cytokines, even when chymase was not detected in some MCs with immunocytochemistry. The chymase protein expression increased by culture duration and was enhanced by cytokines, such as a high concentration of stem cell factor or IL-4. Chymase messenger RNA was expressed higher in immature MCs than mature chymase protein-rich MCs. We generated macroscopic MC colonies in methylcellulose by culturing CD34(+) cells for 10 weeks and measured cellular chymase, tryptase, and histamine. The chymase/histamine ratio widely varied (0.07-1.01) depending on MC colony, even under the same culture conditions, including IL-4, whereas the tryptase/histamine ratio was relatively constant (1.02-1.89). CONCLUSION All human MCs in culture are capable of producing chymase, and the production is clonally regulated at their progenitors by cytokine-independent mechanisms, as well as being totally controlled by cytokine-dependent mechanisms accompanied by maturation.
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Sohn HW, Shin YK, Lee IS, Bae YM, Suh YH, Kim MK, Kim TJ, Jung KC, Park WS, Park CS, Chung DH, Ahn K, Kim IS, Ko YH, Bang YJ, Kim CW, Park SH. CD99 regulates the transport of MHC class I molecules from the Golgi complex to the cell surface. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2001; 166:787-794. [PMID: 11145651 DOI: 10.4049/jimmunol.166.2.787] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The down-regulation of surface expression of MHC class I molecules has recently been reported in the CD99-deficient lymphoblastoid B cell line displaying the characteristics of Hodgkin's and Reed-Sternberg phenotype. Here, we demonstrate that the reduction of MHC class I molecules on the cell surface is primarily due to a defect in the transport from the Golgi complex to the plasma membrane. Loss of CD99 did not affect the steady-state expression levels of mRNA and protein of MHC class I molecules. In addition, the assembly of MHC class I molecules and the transport from the endoplasmic reticulum to the cis-Golgi occurred normally in the CD99-deficient cells, and no difference was detected between the CD99-deficient and the control cells in the pattern and degree of endocytosis. Instead, the CD99-deficient cells displayed the delayed transport of newly synthesized MHC class I molecules to the plasma membrane, thus causing accumulation of the molecules within the cells. The accumulated MHC class I molecules in the CD99-deficient cells were colocalized with alpha-mannosidase II and gamma-adaptin in the Golgi compartment. These results suggest that CD99 may be associated with the post-Golgi trafficking machinery by regulating the transport to the plasma membrane rather than the endocytosis of surface MHC class I molecules, providing a novel mechanism of MHC class I down-regulation for immune escape.
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