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

Human telomeres are protected by TRF2. Inhibition of this telomeric protein results in partial loss of the telomeric 3' overhang and chromosome end fusions formed through nonhomologous end-joining (NHEJ). Here we report that ERCC1/XPF-deficient cells retained the telomeric overhang after TRF2 inhibition, identifying this nucleotide excision repair endonuclease as the culprit in overhang removal. Furthermore, these cells did not accumulate telomere fusions, suggesting that overhang processing is a prerequisite for NHEJ of telomeres. ERCC1/XPF was also identified as a component of the telomeric TRF2 complex. ERCC1/XPF-deficient mouse cells had a novel telomere phenotype, characterized by Telomeric DNA-containing Double Minute chromosomes (TDMs). We speculate that TDMs are formed through the recombination of telomeres with interstitial telomere-related sequences and that ERCC1/XPF functions to repress this process. Collectively, these data reveal an unanticipated involvement of the ERCC1/XPF NER endonuclease in the regulation of telomere integrity and establish that TRF2 prevents NHEJ at telomeres through protection of the telomeric overhang from ERCC1/XPF.
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PMID:ERCC1/XPF removes the 3' overhang from uncapped telomeres and represses formation of telomeric DNA-containing double minute chromosomes. 1469 Jun 2

TRF2, a telomere-binding protein, is a crucial player in telomere length maintenance. Overexpression of TRF2 results in telomere shortening in both normal primary fibroblasts and telomerase-positive cancer cells. TRF2 is found to be associated with XPF-ERCC1, a structure-specific endonuclease involved in nucleotide excision repair, crosslink repair and DNA recombination. XPF-ERCC1 is implicated in TRF2-dependent telomere loss in mouse keratinocytes, however, whether XPF-ERCC1 and its nuclease activity are required for TRF2-mediated telomere shortening in human cells is unknown. Here we report that TRF2-induced telomere shortening is abrogated in human cells deficient in XPF, demonstrating that XPF-ERCC1 is required for TRF2-promoted telomere shortening. To further understand the role of XPF in TRF2-dependent telomere shortening, we generated constructs containing either wild type XPF or mutant XPF proteins carrying amino acid substitutions in its conserved nuclease domain. We show that wild type XPF can complement XPF-deficient cells for repair of UV-induced DNA damage whereas the nuclease-inactive XPF proteins fail to do so, indicating that the nuclease activity of XPF is essential for nucleotide excision repair. In contrast, both wild type XPF and nuclease-inactive XPF proteins, when expressed in XPF-deficient cells, are able to rescue TRF2-mediated telomere shortening. Thus, our results suggest that the function of XPF in TRF2-mediated telomere shortening is conserved between mouse and human. Furthermore, our findings reveal an unanticipated nuclease-independent function of XPF in TRF2-mediated telomere shortening.
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PMID:XPF with mutations in its conserved nuclease domain is defective in DNA repair but functions in TRF2-mediated telomere shortening. 1705 45

Long interspersed element-1 (LINE-1 or L1) elements are abundant, non-long-terminal-repeat (non-LTR) retrotransposons that comprise approximately 17% of human DNA. The average human genome contains approximately 80-100 retrotransposition-competent L1s (ref. 2), and they mobilize by a process that uses both the L1 endonuclease and reverse transcriptase, termed target-site primed reverse transcription. We have previously reported an efficient, endonuclease-independent L1 retrotransposition pathway (EN(i)) in certain Chinese hamster ovary (CHO) cell lines that are defective in the non-homologous end-joining (NHEJ) pathway of DNA double-strand-break repair. Here we have characterized EN(i) retrotransposition events generated in V3 CHO cells, which are deficient in DNA-dependent protein kinase catalytic subunit (DNA-PKcs) activity and have both dysfunctional telomeres and an NHEJ defect. Notably, approximately 30% of EN(i) retrotransposition events insert in an orientation-specific manner adjacent to a perfect telomere repeat (5'-TTAGGG-3'). Similar insertions were not detected among EN(i) retrotransposition events generated in controls or in XR-1 CHO cells deficient for XRCC4, an NHEJ factor that is required for DNA ligation but has no known function in telomere maintenance. Furthermore, transient expression of a dominant-negative allele of human TRF2 (also called TERF2) in XRCC4-deficient XR-1 cells, which disrupts telomere capping, enables telomere-associated EN(i) retrotransposition events. These data indicate that L1s containing a disabled endonuclease can use dysfunctional telomeres as an integration substrate. The findings highlight similarities between the mechanism of EN(i) retrotransposition and the action of telomerase, because both processes can use a 3' OH for priming reverse transcription at either internal DNA lesions or chromosome ends. Thus, we propose that EN(i) retrotransposition is an ancestral mechanism of RNA-mediated DNA repair associated with non-LTR retrotransposons that may have been used before the acquisition of an endonuclease domain.
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PMID:Endonuclease-independent LINE-1 retrotransposition at mammalian telomeres. 1734 53

XPF-ERCC1, a structure-specific endonuclease, is involved in nucleotide excision repair, crosslink repair and homologous recombination. XPF-ERCC1 is also found to interact with TRF2, a duplex telomeric DNA binding protein. We have previously shown that XPF-ERCC1 is required for TRF2-promoted telomere shortening. However, whether XPF-ERCC1 by itself has a role in telomere length maintenance has not been determined. Here we report that overexpression of XPF induces telomere shortening in XPF-proficient cells whereas XPF complementation suppresses telomere lengthening in XPF-deficient cells. These results suggest that XPF-ERCC1 can function as a negative mediator of telomere length maintenance. In addition, we find that introduction of wild type XPF into XPF-deficient cells leads to over 40% reduction in TRF2 association with telomeric DNA, indicating that XPF-ERCC1 negatively regulates TRF2 binding to telomeric DNA. Furthermore, we show that XPF carrying mutations in the conserved nuclease domain fails to control TRF2 association with telomeric DNA but it is competent for modulating telomere length maintenance. These results imply that XPF-ERCC1 controls TRF2 and telomere length maintenance through two distinctive mechanisms, with the former requiring its nuclease activity. Our results further imply that TRF2 association with telomeres may be deregulated in cells derived from XPF patients.
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PMID:Human XPF controls TRF2 and telomere length maintenance through distinctive mechanisms. 1881 85

Telomerase-negative cancer cells maintain their telomeres through the alternative lengthening of telomeres (ALT) pathway. Although a growing body of evidence demonstrates that the ALT mechanism is a post-replicative telomere recombination process, molecular details of this pathway are largely unknown. Here we demonstrate that MUS81, a DNA structure specific recombination endonuclease, has a key role in the maintenance of telomeres in human ALT cells. We find that MUS81 specifically localizes to ALT-associated promyelocytic leukaemia (PML) nuclear bodies (APBs) and associates with telomeric DNA in ALT cells, which is enriched during the G2 phase of the cell cycle. Depletion of MUS81 results in the reduction of ALT-specific telomere recombination and leads to proliferation arrest of ALT cells. In addition, the endonuclease activity of MUS81 is required for recombination-based ALT cell survival, and the interaction of MUS81 with the telomeric repeat-binding factor TRF2 regulates this enzymatic activity, thereby maintaining telomere recombination. Thus, our results suggest that MUS81 is involved in the maintenance of ALT cell survival at least in part by homologous recombination of telomeres.
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PMID:Telomere recombination requires the MUS81 endonuclease. 1936 87

A substantial number of human tumors (approximately 10%) are telomerase negative, and cells in such tumors have been proposed to maintain telomere length by the alternative lengthening of telomeres (ALT) pathway. Although details of the molecular mechanism of ALT are largely unknown, previous studies have shown that telomere homologous recombination (HR) is implicated in the ALT pathway. MUS81 is a DNA structure-specific recombination endonuclease and functions on aberrant DNA replication and recombination. Recently, we demonstrate that MUS81 plays a key role in the maintenance of telomeres in ALT cells (Zeng, et al. Nature Cell Biology, 2009). The MUS81 endonuclease specifically localizes to ALT-associated promyelocytic leukemia nuclear bodies (APBs) and interacts with telomeres in ALT cells. Depletion of MUS81 leads to reduced telomere recombination resulting in the growth arrest of ALT cells. The endonuclease activity of MUS81, regulated by its binding partner TRF2, is found to be essential for telomere post-replicative recombination. This study provides the first direct evidence that MUS81 specifically functions on ALT recombination-based cell survival. The specific function of MUS81 on the ALT pathway provides a potential powerful diagnostic marker and a therapeutic target for ALT tumors.
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PMID:The MUS81 endonuclease is essential for telomerase negative cell proliferation. 1961 16

SLX4 interacts with several endonucleases to resolve structural barriers in DNA metabolism. SLX4 also interacts with telomeric protein TRF2 in human cells. The molecular mechanism of these interactions at telomeres remains unknown. Here, we report the crystal structure of the TRF2-binding motif of SLX4 (SLX4TBM) in complex with the TRFH domain of TRF2 (TRF2TRFH) and map the interactions of SLX4 with endonucleases SLX1, XPF, and MUS81. TRF2 recognizes a unique HxLxP motif on SLX4 via the peptide-binding site in its TRFH domain. Telomeric localization of SLX4 and associated nucleases depend on the SLX4-endonuclease and SLX4-TRF2 interactions and the protein levels of SLX4 and TRF2. SLX4 assembles an endonuclease toolkit that negatively regulates telomere length via SLX1-catalyzed nucleolytic resolution of telomere DNA structures. We propose that the SLX4-TRF2 complex serves as a double-layer scaffold bridging multiple endonucleases with telomeres for recombination-based telomere maintenance.
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PMID:SLX4 assembles a telomere maintenance toolkit by bridging multiple endonucleases with telomeres. 2401 55

A delay in the completion of metaphase induces a stress response that inhibits further cell proliferation or induces apoptosis. This response is thought to protect against genomic instability and is important for the effects of anti-mitotic cancer drugs. Here, we show that mitotic arrest induces a caspase-dependent DNA damage response (DDR) at telomeres in non-apoptotic cells. This pathway is under the control of Mcl-1 and other Bcl-2 family proteins and requires caspase-9, caspase-3/7 and the endonuclease CAD/DFF40. The gradual caspase-dependent loss of the shelterin complex protein TRF2 from telomeres promotes a DDR that involves DNA-dependent protein kinase (DNA-PK). Suppression of mitotic telomere damage by enhanced expression of TRF2, or the inhibition of either caspase-3/7 or DNA-PK during mitotic arrest, promotes subsequent cell survival. Thus, we demonstrate that mitotic stress is characterised by the sub-apoptotic activation of a classical caspase pathway, which promotes telomere deprotection, activates DNA damage signalling, and determines cell fate in response to a prolonged delay in mitosis.
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PMID:Prolonged mitotic arrest induces a caspase-dependent DNA damage response at telomeres that determines cell survival. 2723 Jun 93