Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Triggering of the T cell receptor of T cell hybridomas leads to interleukin (IL) 2 secretion, inhibition of spontaneous growth, degradation of genomic DNA and cell death. We have investigated the relationship between the ability of mitochondria to convert 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), DNA fragmentation and growth arrest in hybridomas stimulated with anti-CD3/T cell receptor antibodies. We describe a variant T hybridoma whose mitochondrial function remains unaffected upon stimulation with anti-CD3 antibody, although it does undergo DNA fragmentation. By contrast, treatment of another anti-CD3-stimulated T hybridoma with endonuclease inhibitor completely inhibits the DNA fragmentation response but not mitochondrial failure induced by anti-CD3 antibody. Thus, we have been able to dissociate anti-CD3-induced mitochondrial failure and DNA fragmentation, suggesting that they are separate events. Although both undoubtedly contribute to cell death induced by activation the primary cause of death may be mitochondrial failure rather than DNA fragmentation.
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PMID:Anti-CD3-induced cell death in T cell hybridomas: mitochondrial failure and DNA fragmentation are distinct events. 182 34

We have analyzed the origin and development of unusual CD4-CD8- alpha/beta T cell receptor-positive peripheral T cells produced in large numbers by mice homozygous for the gld mutation (C3H-gld/gld). These mice may be an important model for investigating processes controlling T cell development. Bone marrow transfers demonstrated that the gld defect was intrinsic to bone marrow-derived cells. Clonal deletion of potentially autoreactive cells was observed in peripheral gld CD4-CD8-, CD4+CD8-, and CD4-CD8+ T cells, as well as mature thymocytes. This suggests that gld CD4-CD8- T cells have passed through the thymus in ontogeny and that gld autoimmunity does not result from a general defect in elimination of self-reactive thymocytes. These observations, combined with demethylation of the CD8 gene in the CD4-CD8- population, support prior expression of CD4 and/or CD8 in gld CD4-CD8- T cell ontogeny, perhaps at a CD4+CD8+ stage. Steroid sensitivity of gld thymocytes and CD4-CD8- T cells was normal. Therefore, we found no gross abnormalities in two major mechanisms of inducible cell death in the gld thymus, the clonal deletion process associated with tolerance and the steroid-inducible endogenous endonuclease thought to be involved in apoptosis of unselected thymocytes. The data suggest that if gld CD4-CD8- T cells arise via escape from normal elimination in the thymus, they must do so by a novel defect in thymic selection (perhaps related to aberrant positive signals) and/or are expanded by an extrathymic process which allows clonal deletion to occur.
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PMID:Origin and selection of peripheral CD4-CD8- T cells bearing alpha/beta T cell antigen receptors in autoimmune gld mice. 197 89

We investigated the T cell receptor constant beta chain (TCR C beta) genes of patients with insulin dependent diabetes mellitus (IDDM) using DNA restriction fragment length polymorphism (RFLP) analysis. Genomic DNA from patients and controls was digested with the restriction endonuclease Bg1 II and transferred to nylon filters using the Southern blot procedure. This enzyme identifies a polymorphic site between the two TCR C beta chain genes. We have found a highly significant increase in the frequency of the 10.0; 9.2 kilobase heterozygous phenotype in patients with IDDM (62.7% versus 42.0% in normal controls; P = 0.0006). In identical twin pairs, this association was most striking in those concordant for IDDM (79.2% versus 42.0% in controls; P = 0.0006).
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PMID:T cell receptor beta chain polymorphisms are associated with insulin-dependent diabetes. 289 59

One of the hallmarks of apoptosis is the digestion of genomic DNA by an endonuclease, generating a ladder of small fragments of double-stranded DNA. We have examined the nature of the DNA breaks produced in mouse thymocytes triggered to undergo apoptosis by steroids or by stimulation of the T cell receptor. Whereas the typical ladder pattern of oligonucleosomal fragments was observed after agarose gel electrophoresis, numerous single-strand cuts were detected after electrophoresis under denaturing conditions. Single-strand nicks were found to be very frequent in the internucleosomal regions, but also to occur in the core particle-associated DNA. An identical pattern of single-strand nicks was obtained when chromatin DNA was exposed to the single-strand cleaving deoxyribonuclease I. The nicked DNA fragments, extracted from apoptotic thymocytes, were sensitive to the action of S1-nuclease. We propose that DNA fragmentation induced during apoptosis is not due to a double-strand cutting enzyme as previously postulated, but rather is the result of single-strand breaks. This ensures the dissociation of the DNA molecule at sites where cuts are found within close proximity.
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PMID:DNA fragmentation during apoptosis is caused by frequent single-strand cuts. 841 75

Programmed cell death (PCD), also known as apoptosis, is a genetically controlled cellular response, manifested in morphologically distinct non-necrotic cellular destruction: cell shrinkage, cytoplasmic "boiling", condensation of chromatin, loss of nuclear membrane followed by DNA fragmentation and cell membrane blebbing, all of which initiate the formation of apoptotic bodies. During the early stages of PCD, cell membrane phospholipid asymmetry is altered, resulting in the dislocation of phosphatidylserine (PS) to the cell surface. During apoptosis, DNA is cut by endonucleases at DNA-linked sites between nucleosomes, producing a number of multimers of nucleosomal DNA units in the cell nuclei. The mechanism of apoptosis and the cellular signals involved in its induction have been studied during thymic prenatal ontogenesis and postnatal development, mainly in immature thymocytes and in the cells of the reticulo-epithelial (RE) network. In thymocytes or resting T lymphocytes, p53 tumor suppressor protein was identified to be a critical mediator of apoptosis in response to DNA damage. The cellular interaction of immature, cortical thymocytes (characterized by a double positive CD4+CD8+TCRlow immunophenotype) with thymic RE cells induces positive selection of T lymphocytes that recognize, but are not activated by self-MHC molecules (tolerance induction). Double positive CD4+CD8+CD3- thymocytes undergo Fas-mediated apoptosis, while CD4+CD8+CD3+ cells use the CD3 mediated pathway of PCD. Two step, apoptotic cell death is mainly restricted to the CD4+CD8+TCRdull thymocyte subpopulation. T-lymphocytes which do not undergo positive selection are killed by apoptosis in response to a number of intrinsic and extrinsic factors, such as chemical toxins, viral infections, X- and UV irradiation, mild hyperthermia, the actions of various hormones, extracellular survival factors, calcium ionophores (such as A23187), various chemotherapeutic drugs (adriamycin, actinomycin D, etc) and antibodies directed to the CD3-TCR (T cell receptor) complex. Immature thymocytes also undergo a second selective process, so-called negative selection, when thymic stromal cells eliminate autoreactive T lymphocytes. This process has been termed clonal deletion and also involves apoptosis. In addition to the two intrathymic T lymphocyte selection mechanisms, Immunocompetent, but autoreactive T lymphocytes which have already reached the periphery are also eliminated by apoptosis. All the divers stimuli of PCD are associated with an increase in the concentration of cytosolic calcium ions (Ca+2), which activate an endogenous endonuclease. This trigger for PCD results in rapid cleavage of DNA, a hallmark of apoptosis. Despite the diversity of the signals that can trigger apoptosis, the changes in cellular morphology characteristic of PCD are very similar. The uniformity of the morphological changes suggests the existence of a predetermined, final and common cell suicide pathway. Apoptosis requires energy in the form of ATP, indicating that PCD, as opposed to necrosis, is an energy dependent, active physiological and pathophysiological phenomenon.
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PMID:Apoptosis in the mammalian thymus during normal histogenesis and under various in vitro and in vivo experimental conditions. 957 34

During B and T lymphocyte development, immunoglobulin and T cell receptor genes are assembled from the germline V, (D) and J gene segments (Lewis, S.M., 1994. The mechanism of V(D)J joining: lessons from molecular, immunological and comparative analyses. Adv. Immunol. 56, 27-150). These DNA rearrangements, responsible for immune system diversity, are mediated by a site specific recombination machinery via recognition signal sequences (RSSs) composed of conserved heptamers and nonamers separated by spacers of 12 or 23 nucleotides (Lewis, S.M., 1994. The mechanism of V(D)J joining: lessons from molecular, immunological and comparative analyses. Adv. Immunol. 56, 27-150). Recombination occurs only between a RSS with a 12mer spacer and a RSS with a 23mer spacer (Lewis, S.M., 1994. The mechanism of V(D)J joining: lessons from molecular, immunological and comparative analyses. Adv. Immunol. 56, 27-150). RAG1 and RAG2 proteins cleave precisely at the RSS-coding sequence border leading to flush signal ends and coding ends with a hairpin structure (Eastman, M., Leu, T., Schatz, D., 1996. Initiation of V(D)J recombination in vitro obeying the 12/23 rule. Nature 380, 85-88; Roth, D.B., Menetski, J.P., Nakajima, P.B., Bosma, M.J., Gellert, M., 1992. V(D)J recombination: broken DNA molecules with covalently sealed (hairpin) coding ends in scid mouse thymocytes. Cell 983-991: Roth, D.B., Zhu, C., Gellert. M., 1993. Characterization of broken DNA molecules associated with V(D)J recombination. Proc. Natl. Acad. Sci. USA 90, 10,788-10,792; van Gent, D., McBlane, J.. Sadofsky, M., Hesse, J., Gellert, M., 1995. Initiation of V(D)J recombination in a cell-free system. Cell 81, 925-934). Signal ends join, forming a signal joint. The hairpin coding ends are opened by a yet unknown endonuclease, and are further processed to form the coding joint (Lewis, S.M., 1994. The mechanism of V(D)J joining: lessons from molecular, immunological and comparative analyses. Ad. Immunol. 56, 27-150.) The murine scid mutation has been shown to affect coding joints, but much less signal joint formation. In this study we demonstrate that the murine scid mutation inhibits correct signal joint formation when both coding ends contain homopolymeric sequences. We suggest that this finding may be due to the function of the SCID protein as an assembly component in V(D)J recombination.
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PMID:Signal joint formation is inhibited in murine scid preB cells and fibroblasts in substrates with homopolymeric coding ends. 1047 10

Gene targeting studies have shown that T cell receptor (TCR)-beta gene expression and recombination are inhibited after deletion of an enhancer (Ebeta) located at the 3' end of the approximately 500-kb TCR-beta locus. Using knockout mouse models, we have measured, at different regions throughout the TCR-beta locus, the effects of Ebeta deletion on molecular parameters believed to reflect epigenetic changes associated with the control of gene activation, including restriction endonuclease access to chromosomal DNA, germline transcription, DNA methylation, and histone H3 acetylation. Our results demonstrate that, in early developing thymocytes, Ebeta contributes to major chromatin remodeling directed to an approximately 25-kb upstream domain comprised of the Dbeta-Jbeta locus regions. Accordingly, treatment of Ebeta-deleted thymocytes with the histone deacetylase inhibitor trichostatin A relieved the block in TCR-beta gene expression and promoted recombination within the Dbeta-Jbeta loci. Unexpectedly, however, epigenetic processes at distal Vbeta genes on the 5' side of the locus and at the 3' proximal Vbeta14 gene appear to be less dependent on Ebeta, suggesting that Ebeta activity is confined to a discrete region of the TCR-beta locus. These findings have implications with respect to the developmental control of TCR-beta gene recombination, and the process of allelic exclusion at this locus.
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PMID:Chromatin remodeling by the T cell receptor (TCR)-beta gene enhancer during early T cell development: Implications for the control of TCR-beta locus recombination. 1097 29

The recombination activating gene (RAG) is a lymphoid-specific endonuclease involved in the V(D)J recombination. It has long been proposed that mis-targeting of RAG proteins is one of the factors contributing to lymphoid chromosomal translocation bearing authentic recombination signal sequences (RSSs) in immunoglobulin (Ig) and T cell receptor (TCR) gene loci or cryptic RSSs (cRSSs). However, it is unclear whether primary sequence-dependent targeting mistake involved in the chromosomal translocation bearing no Ig/TCR gene loci is mediated by RAG proteins. Using an extrachromosomal recombination assay, we found RAG-dependent recombination in the regions dense in breakpoints within TEL and AML1 gene loci related to acute lymphoid leukemia-associated t(12;21)(p13;q22) chromosomal translocation. Sequence analyses revealed several heptamer-like sequences located in the vicinity of RAG-dependent recombination sites. By chromatin immunoprecipitation (ChIP) and ligation-mediated PCR (LM-PCR) assays, we have shown that RAG proteins bind to and cleave the TEL translocation region dense in breakpoints. These results suggest that mis-targeting of RAG proteins to cRSSs within TEL and AML1 translocation regions might be responsible for the t(12;21)(p13;q22) chromosomal translocation not bearing Ig/TCR regions.
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PMID:RAG-dependent recombination at cryptic RSSs within TEL-AML1 t(12;21)(p13;q22) chromosomal translocation region. 2102 24

An effective adaptive immune system depends on the ability of developing B and T cells to generate diverse immunoglobulin (Ig) and T cell receptor repertoires, respectively. Such diversity is achieved through a programmed somatic recombination process whereby germline V, D, and J segments of antigen receptor loci are assembled to form the variable region V(D)J exons of Ig and TCRs. Studies of this process, termed V(D)J recombination, have provided key insights into our understanding of a variety of general gene regulatory and DNA repair processes over the last several decades. V(D)J recombination is initiated by the RAG endonuclease which generates DNA double-stranded breaks at the borders of V, D, and J segments. In this review, we cover recent work that has elucidated RAG structure and work that revealed that RAG has a novel chromatin scanning activity, likely mediated by chromatin loop extrusion, that contributes to its ability to locate V, D, J gene segment substrates within large chromosomal loop domains bounded by CTCF-binding elements (CBEs). This latter function, coupled with the role CBE-based chromatin loop domains and subdomains within them play in focusing V(D)J recombination activity within antigen receptor loci, provide mechanistic explanations for long-standing questions regarding V(D)J segment usage diversification and in limiting potentially deleterious off-target RAG-initiated recombination events genome-wide. This review will focus mainly on studies of the mouse Ig heavy chain locus, but the principles described also apply to other Ig loci and to TCR loci in mice and humans.
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PMID:RAG Chromatin Scanning During V(D)J Recombination and Chromatin Loop Extrusion are Related Processes. 3024 35