1
|
Roemer A, Mohammed L, Strickfaden H, Underhill DA, Hendzel MJ. Mechanisms governing the accessibility of DNA damage proteins to constitutive heterochromatin. Front Genet 2022; 13:876862. [PMID: 36092926 PMCID: PMC9458887 DOI: 10.3389/fgene.2022.876862] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Accepted: 07/18/2022] [Indexed: 12/05/2022] Open
Abstract
Chromatin is thought to regulate the accessibility of the underlying DNA sequence to machinery that transcribes and repairs the DNA. Heterochromatin is chromatin that maintains a sufficiently high density of DNA packing to be visible by light microscopy throughout the cell cycle and is thought to be most restrictive to transcription. Several studies have suggested that larger proteins and protein complexes are attenuated in their access to heterochromatin. In addition, heterochromatin domains may be associated with phase separated liquid condensates adding further complexity to the regulation of protein concentration within chromocenters. This provides a solvent environment distinct from the nucleoplasm, and proteins that are not size restricted in accessing this liquid environment may partition between the nucleoplasm and heterochromatin based on relative solubility. In this study, we assessed the accessibility of constitutive heterochromatin in mouse cells, which is organized into large and easily identifiable chromocenters, to fluorescently tagged DNA damage response proteins. We find that proteins larger than the expected 10 nm size limit can access the interior of heterochromatin. We find that the sensor proteins Ku70 and PARP1 enrich in mouse chromocenters. At the same time, MRE11 shows variability within an asynchronous population that ranges from depleted to enriched but is primarily homogeneously distribution between chromocenters and the nucleoplasm. While larger downstream proteins such as ATM, BRCA1, and 53BP1 are commonly depleted in chromocenters, they show a wide range of concentrations, with none being depleted beyond approximately 75%. Contradicting exclusively size-dependent accessibility, many smaller proteins, including EGFP, are also depleted in chromocenters. Our results are consistent with minimal size-dependent selectivity but a distinct solvent environment explaining reduced concentrations of diffusing nucleoplasmic proteins within the volume of the chromocenter.
Collapse
|
2
|
Abbasi S, Parmar G, Kelly RD, Balasuriya N, Schild-Poulter C. The Ku complex: recent advances and emerging roles outside of non-homologous end-joining. Cell Mol Life Sci 2021; 78:4589-4613. [PMID: 33855626 PMCID: PMC11071882 DOI: 10.1007/s00018-021-03801-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Revised: 01/29/2021] [Accepted: 02/24/2021] [Indexed: 12/15/2022]
Abstract
Since its discovery in 1981, the Ku complex has been extensively studied under multiple cellular contexts, with most work focusing on Ku in terms of its essential role in non-homologous end-joining (NHEJ). In this process, Ku is well-known as the DNA-binding subunit for DNA-PK, which is central to the NHEJ repair process. However, in addition to the extensive study of Ku's role in DNA repair, Ku has also been implicated in various other cellular processes including transcription, the DNA damage response, DNA replication, telomere maintenance, and has since been studied in multiple contexts, growing into a multidisciplinary point of research across various fields. Some advances have been driven by clarification of Ku's structure, including the original Ku crystal structure and the more recent Ku-DNA-PKcs crystallography, cryogenic electron microscopy (cryoEM) studies, and the identification of various post-translational modifications. Here, we focus on the advances made in understanding the Ku heterodimer outside of non-homologous end-joining, and across a variety of model organisms. We explore unique structural and functional aspects, detail Ku expression, conservation, and essentiality in different species, discuss the evidence for its involvement in a diverse range of cellular functions, highlight Ku protein interactions and recent work concerning Ku-binding motifs, and finally, we summarize the clinical Ku-related research to date.
Collapse
Affiliation(s)
- Sanna Abbasi
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Gursimran Parmar
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Rachel D Kelly
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Nileeka Balasuriya
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Caroline Schild-Poulter
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5B7, Canada.
| |
Collapse
|
3
|
Abbasi S, Schild-Poulter C. Identification of Ku70 Domain-Specific Interactors Using BioID2. Cells 2021; 10:cells10030646. [PMID: 33799447 PMCID: PMC8001828 DOI: 10.3390/cells10030646] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2021] [Revised: 03/04/2021] [Accepted: 03/10/2021] [Indexed: 11/23/2022] Open
Abstract
Since its inception, proximity-dependent biotin identification (BioID), an in vivo biochemical screening method to identify proximal protein interactors, has seen extensive developments. Improvements and variants of the original BioID technique are being reported regularly, each expanding upon the existing potential of the original technique. While this is advancing our capabilities to study protein interactions under different contexts, we have yet to explore the full potential of the existing BioID variants already at our disposal. Here, we used BioID2 in an innovative manner to identify and map domain-specific protein interactions for the human Ku70 protein. Four HEK293 cell lines were created, each stably expressing various BioID2-tagged Ku70 segments designed to collectively identify factors that interact with different regions of Ku70. Historically, although many interactions have been mapped to the C-terminus of the Ku70 protein, few have been mapped to the N-terminal von Willebrand A-like domain, a canonical protein-binding domain ideally situated as a site for protein interaction. Using this segmented approach, we were able to identify domain-specific interactors as well as evaluate advantages and drawbacks of the BioID2 technique. Our study identifies several potential new Ku70 interactors and validates RNF113A and Spindly as proteins that contact or co-localize with Ku in a Ku70 vWA domain-specific manner.
Collapse
|
4
|
Meyer-Nava S, Nieto-Caballero VE, Zurita M, Valadez-Graham V. Insights into HP1a-Chromatin Interactions. Cells 2020; 9:E1866. [PMID: 32784937 PMCID: PMC7465937 DOI: 10.3390/cells9081866] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 07/18/2020] [Accepted: 07/21/2020] [Indexed: 12/17/2022] Open
Abstract
Understanding the packaging of DNA into chromatin has become a crucial aspect in the study of gene regulatory mechanisms. Heterochromatin establishment and maintenance dynamics have emerged as some of the main features involved in genome stability, cellular development, and diseases. The most extensively studied heterochromatin protein is HP1a. This protein has two main domains, namely the chromoshadow and the chromodomain, separated by a hinge region. Over the years, several works have taken on the task of identifying HP1a partners using different strategies. In this review, we focus on describing these interactions and the possible complexes and subcomplexes associated with this critical protein. Characterization of these complexes will help us to clearly understand the implications of the interactions of HP1a in heterochromatin maintenance, heterochromatin dynamics, and heterochromatin's direct relationship to gene regulation and chromatin organization.
Collapse
Affiliation(s)
| | | | | | - Viviana Valadez-Graham
- Instituto de Biotecnología, Departamento de Genética del Desarrollo y Fisiología Molecular, Universidad Nacional Autónoma de México, Cuernavaca Morelos 62210, Mexico; (S.M.-N.); (V.E.N.-C.); (M.Z.)
| |
Collapse
|
5
|
Abbasi S, Schild-Poulter C. Mapping the Ku Interactome Using Proximity-Dependent Biotin Identification in Human Cells. J Proteome Res 2019; 18:1064-1077. [PMID: 30585729 DOI: 10.1021/acs.jproteome.8b00771] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The Ku heterodimer, composed of Ku70 and Ku80, is best characterized for its role in repairing double-stranded DNA breaks but is also known to participate in other regulatory processes. Despite our understanding of Ku protein interplay during DNA repair, the extent of Ku's protein interactions in other processes has never been fully determined. Using proximity-dependent biotin identification (BioID) and affinity purification coupled to mass spectrometry (AP-MS) with wild-type Ku70, we identified candidate proteins that interact with the Ku heterodimer in HEK293 cells, in the absence of exogenously induced DNA damage. BioID analysis identified approximately 250 nuclear proteins, appearing in at least two replicates, including known Ku-interacting factors such as MRE11A, WRN, and NCOA6. Meanwhile, AP-MS analysis identified approximately 50 candidate proteins. Of the novel protein interactors identified, many were involved in functions already suspected to involve Ku such as transcriptional regulation, DNA replication, and DNA repair, while several others suggest that Ku may be involved in additional functions such as RNA metabolism, chromatin-remodeling, and microtubule dynamics. Using a combination of BioID and AP-MS, this is the first report that comprehensively characterizes the Ku protein interaction landscape, revealing new cellular processes and protein complexes involving the Ku complex.
Collapse
Affiliation(s)
- Sanna Abbasi
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry , University of Western Ontario , London , Ontario N6A 5B7 , Canada
| | - Caroline Schild-Poulter
- Robarts Research Institute and Department of Biochemistry, Schulich School of Medicine and Dentistry , University of Western Ontario , London , Ontario N6A 5B7 , Canada
| |
Collapse
|
6
|
Hyun K, Jeon J, Park K, Kim J. Writing, erasing and reading histone lysine methylations. Exp Mol Med 2017; 49:e324. [PMID: 28450737 PMCID: PMC6130214 DOI: 10.1038/emm.2017.11] [Citation(s) in RCA: 688] [Impact Index Per Article: 98.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Accepted: 12/20/2016] [Indexed: 02/08/2023] Open
Abstract
Histone modifications are key epigenetic regulatory features that have important roles in many cellular events. Lysine methylations mark various sites on the tail and globular domains of histones and their levels are precisely balanced by the action of methyltransferases ('writers') and demethylases ('erasers'). In addition, distinct effector proteins ('readers') recognize specific methyl-lysines in a manner that depends on the neighboring amino-acid sequence and methylation state. Misregulation of histone lysine methylation has been implicated in several cancers and developmental defects. Therefore, histone lysine methylation has been considered a potential therapeutic target, and clinical trials of several inhibitors of this process have shown promising results. A more detailed understanding of histone lysine methylation is necessary for elucidating complex biological processes and, ultimately, for developing and improving disease treatments. This review summarizes enzymes responsible for histone lysine methylation and demethylation and how histone lysine methylation contributes to various biological processes.
Collapse
Affiliation(s)
- Kwangbeom Hyun
- Laboratory of Eukaryotic Transcription, Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, South Korea
| | - Jongcheol Jeon
- Laboratory of Eukaryotic Transcription, Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, South Korea
| | - Kihyun Park
- Laboratory of Eukaryotic Transcription, Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, South Korea
| | - Jaehoon Kim
- Laboratory of Eukaryotic Transcription, Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon, South Korea
| |
Collapse
|
7
|
Zhao Y, Cheng N, Dai M, Pu H, Zheng T, Li H, He J, Bai Y. Dynamic variation of histone H3 trimethyl Lys4 (H3K4me3) and heterochromatin protein 1 (HP1) with employment length in nickel smelting workers. Biomarkers 2016; 22:420-428. [PMID: 27323841 DOI: 10.1080/1354750x.2016.1203996] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Affiliation(s)
- Yanhong Zhao
- Center for Cancer Prevent and Treatment, Institute of Epidemiology and Statistics, College of Public Health, Lanzhou University, Lanzhou, Gansu, China
| | - Ning Cheng
- Center of Medical Laboratory, College of Basic Medicine, Lanzhou University, Lanzhou, Gansu, China
| | - Min Dai
- Cancer Institute and Hospital, Chinese Academy of Medical Sciences, Beijing, China
| | - Hongquan Pu
- Workers’ Hospital of Jinchuan Company, Jinchuan Group Co, Ltd, Jinchang, Gansu, China
| | | | - Haiyan Li
- Workers’ Hospital of Jinchuan Company, Jinchuan Group Co, Ltd, Jinchang, Gansu, China
| | - Jie He
- Cancer Institute and Hospital, Chinese Academy of Medical Sciences, Beijing, China
| | - Yana Bai
- Center for Cancer Prevent and Treatment, Institute of Epidemiology and Statistics, College of Public Health, Lanzhou University, Lanzhou, Gansu, China
| |
Collapse
|
8
|
Hass EP, Zappulla DC. The Ku subunit of telomerase binds Sir4 to recruit telomerase to lengthen telomeres in S. cerevisiae. eLife 2015. [PMID: 26218225 PMCID: PMC4547093 DOI: 10.7554/elife.07750] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
In Saccharomyces cerevisiae and in humans, the telomerase RNA subunit is bound by Ku, a ring-shaped protein heterodimer best known for its function in DNA repair. Ku binding to yeast telomerase RNA promotes telomere lengthening and telomerase recruitment to telomeres, but how this is achieved remains unknown. Using telomere-length analysis and chromatin immunoprecipitation, we show that Sir4 – a previously identified Ku-binding protein that is a component of telomeric silent chromatin – is required for Ku-mediated telomere lengthening and telomerase recruitment. We also find that specifically tethering Sir4 directly to Ku-binding-defective telomerase RNA restores otherwise-shortened telomeres to wild-type length. These findings suggest that Sir4 is the telomere-bound target of Ku-mediated telomerase recruitment and provide one mechanism for how the Sir4-competing Rif1 and Rif2 proteins negatively regulate telomere length in yeast. DOI:http://dx.doi.org/10.7554/eLife.07750.001 Inside a cell's nucleus, DNA is packaged into structures called chromosomes. The ends of every chromosome are capped by repeating sequences of DNA known as telomeres, which protect the chromosomes from damage. Every time a cell divides, the telomeres shorten. If telomere length falls below a critical level, the cell can die or enter a state in which it can no longer divide. During cell division, an enzyme called telomerase normally restores telomeres to their original length. Telomerase is made up of several proteins and an RNA molecule. In yeast and humans, a protein called Ku is one part of the telomerase enzyme. Ku binds to the RNA subunit of telomerase and helps the enzyme find and interact with the telomeres. Previous research has shown that Ku is unable to work alone to recruit telomerase to the chromosome. A protein called Sir4 binds to telomeres and cells lacking it have short telomeres, but the reason behind this was not known. Hass and Zappulla confirmed previous reports that Ku binds to Sir4 using a biochemical approach. Additional experiments provided genetic evidence that this binding interaction is important for telomerase to lengthen telomeres appropriately. Cells in which the RNA subunit of telomerase is unable to bind effectively to Ku have short telomeres. Hass and Zappulla directly tethered Sir4 to this defective RNA and found this restored the shortened telomeres to a normal length, indicating that Sir4 normally binds Ku to recruit telomerase. Discovering this mode of recruitment also helps to explain how two other telomeric proteins (Rif1 and 2) limit telomere lengthening; they compete with Ku-Sir4 recruitment to form a length-regulating system. Taken together, Hass and Zappulla's results provide strong evidence that Sir4 cooperates with Ku to control the lengthening of chromosome ends. Future research will hopefully reveal the precise space and time requirements for this telomerase-controlling system in yeast. Additionally, because Ku has been reported to be a subunit of human telomerase, future studies could also explore whether human cells use a similar strategy. DOI:http://dx.doi.org/10.7554/eLife.07750.002
Collapse
Affiliation(s)
- Evan P Hass
- Department of Biology, Johns Hopkins University, Baltimore, United States
| | - David C Zappulla
- Department of Biology, Johns Hopkins University, Baltimore, United States
| |
Collapse
|
9
|
Chaudhary N, Nakka KK, Chavali PL, Bhat J, Chatterjee S, Chattopadhyay S. SMAR1 coordinates HDAC6-induced deacetylation of Ku70 and dictates cell fate upon irradiation. Cell Death Dis 2014; 5:e1447. [PMID: 25299772 PMCID: PMC4237237 DOI: 10.1038/cddis.2014.397] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Revised: 08/11/2014] [Accepted: 08/14/2014] [Indexed: 11/30/2022]
Abstract
Acetylation status of DNA end joining protein Ku70 dictates its function in DNA repair and Bax-mediated apoptosis. Despite the knowledge of HDACs and HATs that are reported to modulate the acetylation dynamics of Ku70, very little is known about proteins that critically coordinate these key modifications. Here, we demonstrate that nuclear matrix-associated protein scaffold/matrix-associated region-binding protein 1 (SMAR1) is a novel interacting partner of Ku70 and coordinates with HDAC6 to maintain Ku70 in a deacetylated state. Our studies revealed that knockdown of SMAR1 results in enhanced acetylation of Ku70, which leads to impaired recruitment of Ku70 in the chromatin fractions. Interestingly, ionizing radiation (IR) induces the expression of SMAR1 and its redistribution as distinct nuclear foci upon ATM-mediated phosphorylation at serine 370. Furthermore, SMAR1 regulates IR-induced G2/M cell cycle arrest by facilitating Chk2 phosphorylation. Alternatively, SMAR1 provides radioresistance by modulating the association of deacetylated Ku70 with Bax, abrogating the mitochondrial translocation of Bax. Thus, we provide mechanistic insights of SMAR1-mediated regulation of repair and apoptosis via a complex crosstalk involving Ku70, HDAC6 and Bax.
Collapse
Affiliation(s)
- N Chaudhary
- Chromatin and Disease Biology Laboratory, National Centre for Cell Science, Pune University Campus, Pune, India
| | - K K Nakka
- Chromatin and Disease Biology Laboratory, National Centre for Cell Science, Pune University Campus, Pune, India
| | - P L Chavali
- Chromatin and Disease Biology Laboratory, National Centre for Cell Science, Pune University Campus, Pune, India
| | - J Bhat
- Department of Biophysics, Bose Institute, Kolkata, India
| | - S Chatterjee
- Department of Biophysics, Bose Institute, Kolkata, India
| | - S Chattopadhyay
- Chromatin and Disease Biology Laboratory, National Centre for Cell Science, Pune University Campus, Pune, India
| |
Collapse
|
10
|
The Ku heterodimer: function in DNA repair and beyond. MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH 2014; 763:15-29. [PMID: 25795113 DOI: 10.1016/j.mrrev.2014.06.002] [Citation(s) in RCA: 185] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Revised: 06/07/2014] [Accepted: 06/25/2014] [Indexed: 01/11/2023]
Abstract
Ku is an abundant, highly conserved DNA binding protein found in both prokaryotes and eukaryotes that plays essential roles in the maintenance of genome integrity. In eukaryotes, Ku is a heterodimer comprised of two subunits, Ku70 and Ku80, that is best characterized for its central role as the initial DNA end binding factor in the "classical" non-homologous end joining (C-NHEJ) pathway, the main DNA double-strand break (DSB) repair pathway in mammals. Ku binds double-stranded DNA ends with high affinity in a sequence-independent manner through a central ring formed by the intertwined strands of the Ku70 and Ku80 subunits. At the break, Ku directly and indirectly interacts with several C-NHEJ factors and processing enzymes, serving as the scaffold for the entire DNA repair complex. There is also evidence that Ku is involved in signaling to the DNA damage response (DDR) machinery to modulate the activation of cell cycle checkpoints and the activation of apoptosis. Interestingly, Ku is also associated with telomeres, where, paradoxically to its DNA end-joining functions, it protects the telomere ends from being recognized as DSBs, thereby preventing their recombination and degradation. Ku, together with the silent information regulator (Sir) complex is also required for transcriptional silencing through telomere position effect (TPE). How Ku associates with telomeres, whether it is through direct DNA binding, or through protein-protein interactions with other telomere bound factors remains to be determined. Ku is central to the protection of organisms through its participation in C-NHEJ to repair DSBs generated during V(D)J recombination, a process that is indispensable for the establishment of the immune response. Ku also functions to prevent tumorigenesis and senescence since Ku-deficient mice show increased cancer incidence and early onset of aging. Overall, Ku function is critical to the maintenance of genomic integrity and to proper cellular and organismal development.
Collapse
|
11
|
Grundy GJ, Moulding HA, Caldecott KW, Rulten SL. One ring to bring them all--the role of Ku in mammalian non-homologous end joining. DNA Repair (Amst) 2014; 17:30-8. [PMID: 24680220 DOI: 10.1016/j.dnarep.2014.02.019] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Accepted: 02/25/2014] [Indexed: 12/26/2022]
Abstract
The repair of DNA double strand breaks is essential for cell survival and several conserved pathways have evolved to ensure their rapid and efficient repair. The non-homologous end joining pathway is initiated when Ku binds to the DNA break site. Ku is an abundant nuclear heterodimer of Ku70 and Ku80 with a toroidal structure that allows the protein to slide over the broken DNA end and bind with high affinity. Once locked into placed, Ku acts as a tool-belt to recruit multiple interacting proteins, forming one or more non-homologous end joining complexes that act in a regulated manner to ensure efficient repair of DNA ends. Here we review the structure and functions of Ku and the proteins with which it interacts during non-homologous end joining.
Collapse
Affiliation(s)
- Gabrielle J Grundy
- Genome Damage and Stability Centre, Science Park Road, Falmer, Brighton BN1 9RQ, UK.
| | - Hayley A Moulding
- School of Biochemistry, Medical Sciences, University Walk, Bristol BS8 1TD, UK
| | - Keith W Caldecott
- Genome Damage and Stability Centre, Science Park Road, Falmer, Brighton BN1 9RQ, UK.
| | - Stuart L Rulten
- Genome Damage and Stability Centre, Science Park Road, Falmer, Brighton BN1 9RQ, UK.
| |
Collapse
|
12
|
Deletion of individual Ku subunits in mice causes an NHEJ-independent phenotype potentially by altering apurinic/apyrimidinic site repair. PLoS One 2014; 9:e86358. [PMID: 24466051 PMCID: PMC3900520 DOI: 10.1371/journal.pone.0086358] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2013] [Accepted: 12/07/2013] [Indexed: 01/25/2023] Open
Abstract
Ku70 and Ku80 form a heterodimer called Ku that forms a holoenzyme with DNA dependent-protein kinase catalytic subunit (DNA-PKCS) to repair DNA double strand breaks (DSBs) through the nonhomologous end joining (NHEJ) pathway. As expected mutating these genes in mice caused a similar DSB repair-defective phenotype. However, ku70-/- cells and ku80-/- cells also appeared to have a defect in base excision repair (BER). BER corrects base lesions, apurinic/apyrimidinic (AP) sites and single stand breaks (SSBs) utilizing a variety of proteins including glycosylases, AP endonuclease 1 (APE1) and DNA Polymerase β (Pol β). In addition, deleting Ku70 was not equivalent to deleting Ku80 in cells and mice. Therefore, we hypothesized that free Ku70 (not bound to Ku80) and/or free Ku80 (not bound to Ku70) possessed activity that influenced BER. To further test this hypothesis we performed two general sets of experiments. The first set showed that deleting either Ku70 or Ku80 caused an NHEJ-independent defect. We found ku80-/- mice had a shorter life span than dna-pkcs-/- mice demonstrating a phenotype that was greater than deleting the holoenzyme. We also found Ku70-deletion induced a p53 response that reduced the level of small mutations in the brain suggesting defective BER. We further confirmed that Ku80-deletion impaired BER via a mechanism that was not epistatic to Pol β. The second set of experiments showed that free Ku70 and free Ku80 could influence BER. We observed that deletion of either Ku70 or Ku80, but not both, increased sensitivity of cells to CRT0044876 (CRT), an agent that interferes with APE1. In addition, free Ku70 and free Ku80 bound to AP sites and in the case of Ku70 inhibited APE1 activity. These observations support a novel role for free Ku70 and free Ku80 in altering BER.
Collapse
|
13
|
Cabrero J, Bakkali M, Navarro-Domínguez B, Ruíz-Ruano FJ, Martín-Blázquez R, López-León MD, Camacho JPM. The Ku70 DNA-repair protein is involved in centromere function in a grasshopper species. Chromosome Res 2013; 21:393-406. [PMID: 23797468 DOI: 10.1007/s10577-013-9367-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2013] [Revised: 06/07/2013] [Accepted: 06/09/2013] [Indexed: 01/05/2023]
Abstract
The Ku70 protein is involved in numerous cell functions, the nonhomologous end joining (NHEJ) DNA repair pathway being the best known. Here, we report a novel function for this protein in the grasshopper Eyprepocnemis plorans. We observed the presence of large Ku70 foci on the centromeres of meiotic and mitotic chromosomes during the cell cycle stages showing the highest centromeric activity (i.e., metaphase and anaphase). The fact that colchicine treatment prevented centromeric location of Ku70, suggests a microtubule-dependent centromeric function for Ku70. Likewise, the absence of Ku70 at metaphase-anaphase centromeres from three males whose Ku70 gene had been knocked down using interference RNA, and the dramatic increase in the frequency of polyploid spermatids observed in these males, suggest that the centromeric presence of Ku70 is required for normal cytokinesis in this species. The centromeric function of Ku70 was not observed in 14 other grasshopper and locust species, or in the mouse, thus suggesting that it is an autapomorphy in E. plorans.
Collapse
Affiliation(s)
- Josefa Cabrero
- Departamento de Genética, Facultad de Ciencias, Universidad de Granada, Granada, Spain
| | | | | | | | | | | | | |
Collapse
|
14
|
Li H, Marple T, Hasty P. Ku80-deleted cells are defective at base excision repair. Mutat Res 2013; 745-746:16-25. [PMID: 23567907 DOI: 10.1016/j.mrfmmm.2013.03.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Revised: 03/18/2013] [Accepted: 03/29/2013] [Indexed: 11/27/2022]
Abstract
Ku80 forms a heterodimer with Ku70, called Ku, that repairs DNA double-strand breaks (DSBs) via the nonhomologous end joining (NHEJ) pathway. As a consequence of deleting NHEJ, Ku80-mutant cells are hypersensitive to agents that cause DNA DSBs like ionizing radiation. Here we show that Ku80 deletion also decreased resistance to ROS and alkylating agents that typically cause base lesions and single-strand breaks (SSBs). This is unusual since base excision repair (BER), not NHEJ, typically repairs these types of lesions. However, we show that deletion of another NHEJ protein, DNA ligase IV (Lig4), did not cause hypersensitivity to these agents. In addition, the ROS and alkylating agents did not induce γ-H2AX foci that are diagnostic of DSBs. Furthermore, deletion of Ku80, but not Lig4 or Ku70, reduced BER capacity. Ku80 deletion also impaired BER at the initial lesion recognition/strand scission step; thus, involvement of a DSB is unlikely. Therefore, our data suggests that Ku80 deletion impairs BER via a mechanism that does not repair DSBs.
Collapse
Affiliation(s)
- Han Li
- The Department of Molecular Medicine, The University of Texas Health Science Center, San Antonio, TX 78245-3207, USA
| | | | | |
Collapse
|
15
|
Jensik PJ, Huggenvik JI, Collard MW. Deformed epidermal autoregulatory factor-1 (DEAF1) interacts with the Ku70 subunit of the DNA-dependent protein kinase complex. PLoS One 2012; 7:e33404. [PMID: 22442688 PMCID: PMC3307728 DOI: 10.1371/journal.pone.0033404] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Accepted: 02/14/2012] [Indexed: 11/19/2022] Open
Abstract
Deformed Epidermal Autoregulatory Factor 1 (DEAF1) is a transcription factor linked to suicide, cancer, autoimmune disorders and neural tube defects. To better understand the role of DEAF1 in protein interaction networks, a GST-DEAF1 fusion protein was used to isolate interacting proteins in mammalian cell lysates, and the XRCC6 (Ku70) and the XRCC5 (Ku80) subunits of DNA dependent protein kinase (DNA-PK) complex were identified by mass spectrometry, and the DNA-PK catalytic subunit was identified by immunoblotting. Interaction of DEAF1 with Ku70 and Ku80 was confirmed to occur within cells by co-immunoprecipitation of epitope-tagged proteins, and was mediated through interaction with the Ku70 subunit. Using in vitro GST-pulldowns, interaction between DEAF1 and the Ku70 subunit was mapped to the DEAF1 DNA binding domain and the C-terminal Bax-binding region of Ku70. In transfected cells, DEAF1 and Ku70 colocalized to the nucleus, but Ku70 could not relocalize a mutant cytoplasmic form of DEAF1 to the nucleus. Using an in vitro kinase assay, DEAF1 was phosphorylated by DNA-PK in a DNA-independent manner. Electrophoretic mobility shift assays showed that DEAF1 or Ku70/Ku80 did not interfere with the DNA binding of each other, but DNA containing DEAF1 binding sites inhibited the DEAF1-Ku70 interaction. The data demonstrates that DEAF1 can interact with the DNA-PK complex through interactions of its DNA binding domain with the carboxy-terminal region of Ku70 that contains the Bax binding domain, and that DEAF1 is a potential substrate for DNA-PK.
Collapse
Affiliation(s)
| | | | - Michael W. Collard
- Department of Physiology, Southern Illinois University School of Medicine, Carbondale, Illinois, United States of America
- * E-mail:
| |
Collapse
|
16
|
Mitsunobu H, Izumi M, Mon H, Tatsuke T, Lee JM, Kusakabe T. Molecular characterization of heterochromatin proteins 1a and 1b from the silkworm, Bombyx mori. INSECT MOLECULAR BIOLOGY 2012; 21:9-20. [PMID: 22142192 DOI: 10.1111/j.1365-2583.2011.01115.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Heterochromatin protein 1s (HP1s) are nonhistone chromosomal proteins that play a direct role in the formation and maintenance of heterochromatin structure. Similarly to Caenorhabditis elegans, silkworms possess holocentric chromosomes, in which diffused kinetochores extend along the length of each chromosome. We have isolated two silkworm HP1 homologues, BmHP1a and BmHP1b. Cytological analysis showed a unique localization of BmHP1s during cell division, in which these proteins first appear to dissociate from the chromosomes, but then return to enclose the chromosomes during metaphase. BmHP1s formed homo- and hetero-dimers and interacted with BmSu(var)3-9, which is a methyltransferase for histone H3 lysine 9 (H3K9). We further showed, using a silkworm cell-based reporter system, that BmHP1b had higher transcriptional repression activity than BmHP1a, whereas BmHP1a interacted more strongly with BmSu(var)3-9 than did BmHP1b. These results suggest that silkworm HP1a and HP1b may play different roles in heterochromatin formation in holocentric silkworm chromosomes.
Collapse
Affiliation(s)
- H Mitsunobu
- Laboratory of Silkworm Science, Kyushu University Graduate School of Bioresource and Bioenvironmental Sciences, Fukuoka, Japan
| | | | | | | | | | | |
Collapse
|
17
|
Rosnoblet C, Vandamme J, Völkel P, Angrand PO. Analysis of the human HP1 interactome reveals novel binding partners. Biochem Biophys Res Commun 2011; 413:206-11. [PMID: 21888893 DOI: 10.1016/j.bbrc.2011.08.059] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2011] [Accepted: 08/12/2011] [Indexed: 10/17/2022]
Abstract
Heterochromatin protein 1 (HP1) has first been described in Drosophila as an essential component of constitutive heterochromatin required for stable epigenetic gene silencing. Less is known about the three mammalian HP1 isotypes CBX1, CBX3 and CBX5. Here, we applied a tandem affinity purification approach coupled with tandem mass spectrometry methodologies in order to identify interacting partners of the mammalian HP1 isotypes. Our analysis identified with high confidence about 30-40 proteins co-eluted with CBX1 and CBX3, and around 10 with CBX5 including a number of novel HP1-binding partners. Our data also suggest that HP1 family members are mainly associated with a single partner or within small protein complexes composed of limited numbers of components. Finally, we showed that slight binding preferences might exist between HP1 family members.
Collapse
Affiliation(s)
- Claire Rosnoblet
- Chromatinomics, Interdisciplinary Research Institute, Université de Lille Nord de France, Université de Lille 1 Sciences et Technologies/CNRS USR 3078, 50 Avenue Halley, Parc Scientifique de Haute Borne, F-59658 Villeneuve d'Ascq Cedex, France
| | | | | | | |
Collapse
|
18
|
Abstract
As a significant epigenetic regulation mechanism, histone methylation plays an important role in many biological processes. In cells, there are various histone methyltransferases and histone demethylases working cooperatively to regulate the histone methylation state. Upon histone modification, effector proteins recognize modification sites specifically, and affect gene transcriptional process. This review mainly focuses on recent advances in histone methylation effector protein's function mechanism.
Collapse
|
19
|
Kwon SH, Workman JL. The changing faces of HP1: From heterochromatin formation and gene silencing to euchromatic gene expression: HP1 acts as a positive regulator of transcription. Bioessays 2011; 33:280-9. [PMID: 21271610 DOI: 10.1002/bies.201000138] [Citation(s) in RCA: 120] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Heterochromatin protein 1 (HP1) is a positive regulator of active transcription in euchromatin. HP1 was first identified in Drosophila melanogaster as a major component of heterochromatin. Most eukaryotes have at least three isoforms of HP1, which are conserved in overall structure but localize differentially to heterochromatin and euchromatin. Although initial studies revealed a key role for HP1 in heterochromatin formation and gene silencing, recent progress has shed light on additional roles for HP1 in processes such as euchromatic gene expression. Recent studies have highlighted the importance of HP1-mediated gene regulation in euchromatin. Here, we focus on recent advances in understanding the role of HP1 in active transcription in euchromatin and how modification and localization of HP1 can regulate distinct functions for this protein in different contexts.
Collapse
Affiliation(s)
- So Hee Kwon
- Stowers Institute for Medical Research, Kansas City, MO, USA
| | | |
Collapse
|
20
|
Zuccotti M, Merico V, Cecconi S, Redi CA, Garagna S. What does it take to make a developmentally competent mammalian egg? Hum Reprod Update 2011; 17:525-40. [DOI: 10.1093/humupd/dmr009] [Citation(s) in RCA: 122] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
|
21
|
Kubben N, Voncken JW, Demmers J, Calis C, van Almen G, Pinto Y, Misteli T. Identification of differential protein interactors of lamin A and progerin. Nucleus 2010; 1:513-25. [PMID: 21327095 PMCID: PMC3027055 DOI: 10.4161/nucl.1.6.13512] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2010] [Revised: 08/30/2010] [Accepted: 09/03/2010] [Indexed: 01/11/2023] Open
Abstract
The nuclear lamina is an interconnected meshwork of intermediate filament proteins underlying the nuclear envelope. The lamina is an important regulator of nuclear structural integrity as well as nuclear processes, including transcription, DNA replication and chromatin remodeling. The major components of the lamina are A- and B-type lamins. Mutations in lamins impair lamina functions and cause a set of highly tissue-specific diseases collectively referred to as laminopathies. The phenotypic diversity amongst laminopathies is hypothesized to be caused by mutations affecting specific protein interactions, possibly in a tissue-specific manner. Current technologies to identify interaction partners of lamin A and its mutants are hampered by the insoluble nature of lamina components. To overcome the limitations of current technologies, we developed and applied a novel, unbiased approach to identify lamin A-interacting proteins. This approach involves expression of the high-affinity OneSTrEP-tag, precipitation of lamin-protein complexes after reversible protein cross-linking and subsequent protein identification by mass spectrometry. We used this approach to identify in mouse embryonic fibroblasts and cardiac myocyte NklTAg cell lines proteins that interact with lamin A and its mutant isoform progerin, which causes the premature aging disorder Hutchinson-Gilford progeria syndrome (HGPS). We identified a total of 313 lamina-interacting proteins, including several novel lamin A interactors, and we characterize a set of 35 proteins which preferentially interact with lamin A or progerin.
Collapse
Affiliation(s)
- Nard Kubben
- Center for Heart Failure Research; Cardiovascular Research Institute Maastricht; Maastricht, The Netherlands
- National Cancer Institute; National Institutes of Health; Bethesda, MD USA
| | - Jan Willem Voncken
- Department of Molecular Genetics; GROW School for Oncology and Developmental Biology; Maastricht, The Netherlands
| | | | - Chantal Calis
- Department of Clinical Genetics; Maastricht University; Maastricht, The Netherlands
| | - Geert van Almen
- Center for Heart Failure Research; Cardiovascular Research Institute Maastricht; Maastricht, The Netherlands
| | - Yigal Pinto
- Heart Failure Research Center; Medical Center; Amsterdam, The Netherlands
| | - Tom Misteli
- National Cancer Institute; National Institutes of Health; Bethesda, MD USA
| |
Collapse
|
22
|
Telomere dysfunction-induced foci arise with the onset of telomeric deletions and complex chromosomal aberrations in resistant chronic lymphocytic leukemia cells. Blood 2010; 116:239-49. [PMID: 20424183 DOI: 10.1182/blood-2009-12-257618] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
In somatic cells, eroded telomeres can induce DNA double-strand break signaling, leading to a form of replicative senescence or apoptosis, both of which are barriers to tumorigenesis. However, cancer cells might display telomere dysfunctions which in conjunction with defects in DNA repair and apoptosis, enables them to circumvent these pathways. Chronic lymphocytic leukemia (CLL) cells exhibit telomere dysfunction, and a subset of these cells are resistant to DNA damage-induced apoptosis and display short telomeres. We show here that these cells exhibit significant resection of their protective telomeric 3' single-stranded overhangs and an increased number of telomere-induced foci containing gammaH2AX and 53BP1. Chromatin immunoprecipitation and immunofluorescence experiments demonstrated increased levels of telomeric Ku70 and phospho-S2056-DNA-PKcs, 2 essential components of the mammalian nonhomologous end-joining DNA repair system. Notably, these CLL cells display deletions of telomeric signals on one or 2 chromatids in parallel with 11q22 deletions, or with 13q14 deletions associated with another chromosomal aberration or with a complex karyotype. Taken together, our results indicate that a subset of CLL cells from patients with an unfavorable clinical outcome harbor a novel type of chromosomal aberration resulting from telomere dysfunction.
Collapse
|
23
|
Luijsterburg MS, Dinant C, Lans H, Stap J, Wiernasz E, Lagerwerf S, Warmerdam DO, Lindh M, Brink MC, Dobrucki JW, Aten JA, Fousteri MI, Jansen G, Dantuma NP, Vermeulen W, Mullenders LHF, Houtsmuller AB, Verschure PJ, van Driel R. Heterochromatin protein 1 is recruited to various types of DNA damage. ACTA ACUST UNITED AC 2009; 185:577-86. [PMID: 19451271 PMCID: PMC2711568 DOI: 10.1083/jcb.200810035] [Citation(s) in RCA: 204] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Heterochromatin protein 1 (HP1) family members are chromatin-associated proteins involved in transcription, replication, and chromatin organization. We show that HP1 isoforms HP1-α, HP1-β, and HP1-γ are recruited to ultraviolet (UV)-induced DNA damage and double-strand breaks (DSBs) in human cells. This response to DNA damage requires the chromo shadow domain of HP1 and is independent of H3K9 trimethylation and proteins that detect UV damage and DSBs. Loss of HP1 results in high sensitivity to UV light and ionizing radiation in the nematode Caenorhabditis elegans, indicating that HP1 proteins are essential components of DNA damage response (DDR) systems. Analysis of single and double HP1 mutants in nematodes suggests that HP1 homologues have both unique and overlapping functions in the DDR. Our results show that HP1 proteins are important for DNA repair and may function to reorganize chromatin in response to damage.
Collapse
Affiliation(s)
- Martijn S Luijsterburg
- Swammerdam Institute for Life Sciences, Department of Cell Biology and Histology, Academic Medical Center, University of Amsterdam, 1012 WX Amsterdam, Netherlands
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
24
|
Li H, Choi YJ, Hanes MA, Marple T, Vogel H, Hasty P. Deleting Ku70 is milder than deleting Ku80 in p53-mutant mice and cells. Oncogene 2009; 28:1875-8. [DOI: 10.1038/onc.2009.57] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
25
|
Motamedi MR, Hong EJE, Li X, Gerber S, Denison C, Gygi S, Moazed D. HP1 proteins form distinct complexes and mediate heterochromatic gene silencing by nonoverlapping mechanisms. Mol Cell 2009; 32:778-90. [PMID: 19111658 DOI: 10.1016/j.molcel.2008.10.026] [Citation(s) in RCA: 169] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2008] [Revised: 09/23/2008] [Accepted: 10/23/2008] [Indexed: 12/22/2022]
Abstract
HP1 proteins are a highly conserved family of eukaryotic proteins that bind to methylated histone H3 lysine 9 (H3K9) and are required for heterochromatic gene silencing. In fission yeast, two HP1 homologs, Swi6 and Chp2, function in heterochromatic gene silencing, but their relative contribution to silencing remains unknown. Here we show that Swi6 and Chp2 exist in nonoverlapping complexes and make distinct contributions to silencing. Chp2 associates with the SHREC histone deacetylase complex (SHREC2), is required for histone H3 lysine 14 (H3K14) deacetylation, and mediates transcriptional repression by limiting RNA polymerase II access to heterochromatin. In contrast, Swi6 associates with a different set of nuclear proteins and with noncoding centromeric transcripts and is required for efficient RNAi-dependent processing of these transcripts. Our findings reveal an unexpected role for Swi6 in RNAi-mediated gene silencing and suggest that different HP1 proteins ensure full heterochromatic gene silencing through largely nonoverlapping inhibitory mechanisms.
Collapse
Affiliation(s)
- Mohammad R Motamedi
- Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115, USA
| | | | | | | | | | | | | |
Collapse
|
26
|
Ida H, Suzusho N, Suyari O, Yoshida H, Ohno K, Hirose F, Itoh M, Yamaguchi M. Genetic screening for modifiers of the DREF pathway in Drosophila melanogaster: identification and characterization of HP6 as a novel target of DREF. Nucleic Acids Res 2009; 37:1423-37. [PMID: 19136464 PMCID: PMC2655671 DOI: 10.1093/nar/gkn1068] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The DNA replication-related element-binding factor (DREF) regulates cell proliferation-related gene expression in Drosophila. By genetic screening, taking advantage of the rough eye phenotype of transgenic flies that express DREF in the eye discs, we identified 24 genes that suppressed and 12 genes that enhanced the rough eye phenotype when heterozygous for mutations. Five genes, HP6, pigeon, lace, X box binding protein 1 and guftagu were found to carry replication-related element (DRE) sequences in their 5′-flanking regions. Of these, the HP6 gene carries two sequences that match seven out of eight nucleotides of DRE and two additional sequences that match six out of eight nucleotides of DRE in the 5′-flanking region. Band mobility shift assays using Drosophila Kc cell nuclear extracts demonstrated DREF binding to two of these sites and chromatin immunoprecipitation using anti-DREF antibodies confirmed that this occurs in vivo. Knockdown of DREF in Drosophila S2 cells decreased the HP6 mRNA level. The results, taken together, indicate that DREF directly regulates expression of the HP6 gene. HP6 mRNA was detected throughout development by RT-PCR with highest levels in adult males. In addition, immunostaining analyses revealed colocalization of HP6 and DREF in nuclei at the apical tips in the testes.
Collapse
Affiliation(s)
- Hiroyuki Ida
- Department of Applied Biology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
| | | | | | | | | | | | | | | |
Collapse
|
27
|
Spyridopoulos I, Erben Y, Brummendorf TH, Haendeler J, Dietz K, Seeger F, Kissel CK, Martin H, Hoffmann J, Assmus B, Zeiher AM, Dimmeler S. Telomere Gap Between Granulocytes and Lymphocytes Is a Determinant for Hematopoetic Progenitor Cell Impairment in Patients With Previous Myocardial Infarction. Arterioscler Thromb Vasc Biol 2008; 28:968-74. [DOI: 10.1161/atvbaha.107.160846] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Objective—
We have previously demonstrated that ischemic cardiomyopathy is associated with selective impairment of progenitor cell function in the bone marrow and in the peripheral blood, which may contribute to an unfavorable left ventricular remodeling process.
Methods and Results—
With this study, we intended to identify the influence of telomere length on bone marrow functionality in 50 patients with coronary artery disease (CAD) and previous myocardial infarction. Mean telomere length (mTL) was measured simultaneously in peripheral blood leukocytes and mononuclear bone marrow cells (BMC), using the flow-FISH method. Telomere erosion already occurred at the bone marrow level, whereby age (39 bp/yr,
P
=0.025) and the number of affected vessels (434 bp/vessel,
P
=0.029) were the only independent predictors. Lymphocytes demonstrated significant TL shortening between BMCs and peripheral blood in CAD patients (−1011±897 bp) as opposed to an increase in a young control group (+235±459 bp,
P
<0.001). SDF- and VEGF-specific migration of BMCs correlated with mTL of lymphocytes (
r
=0.42,
P
<0.001) and was significantly reduced in CAD patients. Finally, the telomere length difference between granulocytes and lymphocytes was the most determinant for telomere-associated bone marrow impairment (
P
<0.001).
Conclusion—
In patients with CAD, telomere shortening of BMCs is dependent on both age and the extent of CAD and correlates with bone marrow cell functionality.
Collapse
Affiliation(s)
- Ioakim Spyridopoulos
- From the Departments of Cardiology and Molecular Cardiology (I.S., Y.E., J.H., F.S., C.K., J.H., B.A., A.M.Z., S.D.), Johann Wolfgang Goethe University of Frankfurt, Germany; the Department of Oncology and Hematology (T.H.B.), University Medical Center Hamburg-Eppendorf, Hamburg, Germany; the Department of Medical Biometry (K.D.), University of Tübingen, Germany; and the Department of Hematology (H.M.), Johann Wolfgang Goethe University of Frankfurt, Germany
| | - Young Erben
- From the Departments of Cardiology and Molecular Cardiology (I.S., Y.E., J.H., F.S., C.K., J.H., B.A., A.M.Z., S.D.), Johann Wolfgang Goethe University of Frankfurt, Germany; the Department of Oncology and Hematology (T.H.B.), University Medical Center Hamburg-Eppendorf, Hamburg, Germany; the Department of Medical Biometry (K.D.), University of Tübingen, Germany; and the Department of Hematology (H.M.), Johann Wolfgang Goethe University of Frankfurt, Germany
| | - Tim H. Brummendorf
- From the Departments of Cardiology and Molecular Cardiology (I.S., Y.E., J.H., F.S., C.K., J.H., B.A., A.M.Z., S.D.), Johann Wolfgang Goethe University of Frankfurt, Germany; the Department of Oncology and Hematology (T.H.B.), University Medical Center Hamburg-Eppendorf, Hamburg, Germany; the Department of Medical Biometry (K.D.), University of Tübingen, Germany; and the Department of Hematology (H.M.), Johann Wolfgang Goethe University of Frankfurt, Germany
| | - Judith Haendeler
- From the Departments of Cardiology and Molecular Cardiology (I.S., Y.E., J.H., F.S., C.K., J.H., B.A., A.M.Z., S.D.), Johann Wolfgang Goethe University of Frankfurt, Germany; the Department of Oncology and Hematology (T.H.B.), University Medical Center Hamburg-Eppendorf, Hamburg, Germany; the Department of Medical Biometry (K.D.), University of Tübingen, Germany; and the Department of Hematology (H.M.), Johann Wolfgang Goethe University of Frankfurt, Germany
| | - Klaus Dietz
- From the Departments of Cardiology and Molecular Cardiology (I.S., Y.E., J.H., F.S., C.K., J.H., B.A., A.M.Z., S.D.), Johann Wolfgang Goethe University of Frankfurt, Germany; the Department of Oncology and Hematology (T.H.B.), University Medical Center Hamburg-Eppendorf, Hamburg, Germany; the Department of Medical Biometry (K.D.), University of Tübingen, Germany; and the Department of Hematology (H.M.), Johann Wolfgang Goethe University of Frankfurt, Germany
| | - Florian Seeger
- From the Departments of Cardiology and Molecular Cardiology (I.S., Y.E., J.H., F.S., C.K., J.H., B.A., A.M.Z., S.D.), Johann Wolfgang Goethe University of Frankfurt, Germany; the Department of Oncology and Hematology (T.H.B.), University Medical Center Hamburg-Eppendorf, Hamburg, Germany; the Department of Medical Biometry (K.D.), University of Tübingen, Germany; and the Department of Hematology (H.M.), Johann Wolfgang Goethe University of Frankfurt, Germany
| | - Christine K. Kissel
- From the Departments of Cardiology and Molecular Cardiology (I.S., Y.E., J.H., F.S., C.K., J.H., B.A., A.M.Z., S.D.), Johann Wolfgang Goethe University of Frankfurt, Germany; the Department of Oncology and Hematology (T.H.B.), University Medical Center Hamburg-Eppendorf, Hamburg, Germany; the Department of Medical Biometry (K.D.), University of Tübingen, Germany; and the Department of Hematology (H.M.), Johann Wolfgang Goethe University of Frankfurt, Germany
| | - Hans Martin
- From the Departments of Cardiology and Molecular Cardiology (I.S., Y.E., J.H., F.S., C.K., J.H., B.A., A.M.Z., S.D.), Johann Wolfgang Goethe University of Frankfurt, Germany; the Department of Oncology and Hematology (T.H.B.), University Medical Center Hamburg-Eppendorf, Hamburg, Germany; the Department of Medical Biometry (K.D.), University of Tübingen, Germany; and the Department of Hematology (H.M.), Johann Wolfgang Goethe University of Frankfurt, Germany
| | - Jedrzej Hoffmann
- From the Departments of Cardiology and Molecular Cardiology (I.S., Y.E., J.H., F.S., C.K., J.H., B.A., A.M.Z., S.D.), Johann Wolfgang Goethe University of Frankfurt, Germany; the Department of Oncology and Hematology (T.H.B.), University Medical Center Hamburg-Eppendorf, Hamburg, Germany; the Department of Medical Biometry (K.D.), University of Tübingen, Germany; and the Department of Hematology (H.M.), Johann Wolfgang Goethe University of Frankfurt, Germany
| | - Birgit Assmus
- From the Departments of Cardiology and Molecular Cardiology (I.S., Y.E., J.H., F.S., C.K., J.H., B.A., A.M.Z., S.D.), Johann Wolfgang Goethe University of Frankfurt, Germany; the Department of Oncology and Hematology (T.H.B.), University Medical Center Hamburg-Eppendorf, Hamburg, Germany; the Department of Medical Biometry (K.D.), University of Tübingen, Germany; and the Department of Hematology (H.M.), Johann Wolfgang Goethe University of Frankfurt, Germany
| | - Andreas M. Zeiher
- From the Departments of Cardiology and Molecular Cardiology (I.S., Y.E., J.H., F.S., C.K., J.H., B.A., A.M.Z., S.D.), Johann Wolfgang Goethe University of Frankfurt, Germany; the Department of Oncology and Hematology (T.H.B.), University Medical Center Hamburg-Eppendorf, Hamburg, Germany; the Department of Medical Biometry (K.D.), University of Tübingen, Germany; and the Department of Hematology (H.M.), Johann Wolfgang Goethe University of Frankfurt, Germany
| | - Stefanie Dimmeler
- From the Departments of Cardiology and Molecular Cardiology (I.S., Y.E., J.H., F.S., C.K., J.H., B.A., A.M.Z., S.D.), Johann Wolfgang Goethe University of Frankfurt, Germany; the Department of Oncology and Hematology (T.H.B.), University Medical Center Hamburg-Eppendorf, Hamburg, Germany; the Department of Medical Biometry (K.D.), University of Tübingen, Germany; and the Department of Hematology (H.M.), Johann Wolfgang Goethe University of Frankfurt, Germany
| |
Collapse
|
28
|
Fanti L, Pimpinelli S. HP1: a functionally multifaceted protein. Curr Opin Genet Dev 2008; 18:169-74. [PMID: 18329871 DOI: 10.1016/j.gde.2008.01.009] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2007] [Revised: 01/18/2008] [Accepted: 01/18/2008] [Indexed: 12/27/2022]
Abstract
HP1 (heterochromatin protein 1) is a nonhistone chromosomal protein first discovered in Drosophila melanogaster because of its association with heterochromatin. Numerous studies have shown that such a protein plays a role in heterochromatin formation and gene silencing in many organisms, including fungi and animals. Cytogenetic and molecular studies, performed in Drosophila and other organisms, have revealed that HP1 associates with heterochromatin, telomeres and multiple euchromatic sites. There is increasing evidence that the different locations of HP1 are related to multiple different functions. In fact, recent work has shown that HP1 has a role not only in heterochromatin formation and gene silencing, but also in telomere stability and in positive regulation of gene expression.
Collapse
Affiliation(s)
- Laura Fanti
- Istituto Pasteur, Fondazione Cenci Bolognetti, Dipartimento di Genetica e Biologia molecolare, Università La Sapienza, 00185 Roma, Italy
| | | |
Collapse
|
29
|
Raynaud CM, Sabatier L, Philipot O, Olaussen KA, Soria JC. Telomere length, telomeric proteins and genomic instability during the multistep carcinogenic process. Crit Rev Oncol Hematol 2008; 66:99-117. [PMID: 18243729 DOI: 10.1016/j.critrevonc.2007.11.006] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2007] [Revised: 11/08/2007] [Accepted: 11/30/2007] [Indexed: 12/29/2022] Open
Abstract
Telomeres form specialized structures at the ends of eukaryotic chromosomes, preventing them from being wrongly recognized as DNA damage. The human telomere DNA sequence is a tandem repetition of the sequence TTAGGG. In normal cells, the DNA replication machinery is unable to completely duplicate the telomeric DNA; thus, telomeres are shortened after every cell division. Having reached a critical length, telomeres may be recognized as double strand break DNA lesions, and cells eventually enter senescence. Carcinogenesis is a multistep process involving multiple mutations and chromosomal aberrations. One of the most prevalent aberrations in pre-cancerous lesions is telomere shortening and telomerase activation. We discuss the role and homeostasis of telomeres in normal cells and their implication in the early steps of carcinogenesis. We also discuss various techniques used, and their limitations, in the study of telomeres and genome instability and their role in carcinogenesis and related genomic modifications.
Collapse
|
30
|
Kavi HH, Fernandez H, Xie W, Birchler JA. Genetics and biochemistry of RNAi in Drosophila. Curr Top Microbiol Immunol 2008; 320:37-75. [PMID: 18268839 DOI: 10.1007/978-3-540-75157-1_3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
RNA interference (RNAi) is the technique employing double-stranded RNA to target the destruction of homologous messenger RNAs. It has gained wide usage in genetics. While having the potential for many practical applications, it is a reflection of a much broader spectrum of small RNA-mediated processes in the cell. The RNAi machinery was originally perceived as a defense mechanism against viruses and transposons. While this is certainly true, small RNAs have now been implicated in many other aspects of cell biology. Here we review the current knowledge of the biochemistry of RNAi in Drosophila and the involvement of small RNAs in RNAi, transposon silencing, virus defense, transgene silencing, pairing-sensitive silencing, telomere function, chromatin insulator activity, nucleolar stability, and heterochromatin formation. The discovery of the role of RNA molecules in the degradation of mRNA transcripts leading to decreased gene expression resulted in a paradigm shift in the field of molecular biology. Transgene silencing was first discovered in plant cells (Matzke et al. 1989; van der Krol et al. 1990; Napoli et al. 1990) and can occur on both the transcriptional and posttranscriptional levels, but both involve short RNA moieties in their mechanism. RNA interference (RNAi) is a type of gene silencing mechanism in which a double-stranded RNA (dsRNA) molecule directs the specific degradation of the corresponding mRNA (target RNA). The technique of RNAi was first discovered in Caenorhabditis elegans in 1994 (Guo and Kemphues 1994). Later the active component was found to be a dsRNA (Fire et al. 1998). In subsequent years, it has been found to occur in diverse eukaryotes
Collapse
Affiliation(s)
- Harsh H Kavi
- Division of Biological Sciences, University of Missouri, Tucker Hall, Columbia, MO 65211, USA
| | | | | | | |
Collapse
|
31
|
Li H, Vogel H, Holcomb VB, Gu Y, Hasty P. Deletion of Ku70, Ku80, or both causes early aging without substantially increased cancer. Mol Cell Biol 2007; 27:8205-14. [PMID: 17875923 PMCID: PMC2169178 DOI: 10.1128/mcb.00785-07] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2007] [Revised: 07/13/2007] [Accepted: 09/07/2007] [Indexed: 11/20/2022] Open
Abstract
Ku70 forms a heterodimer with Ku80, called Ku, that is critical for repairing DNA double-stand breaks by nonhomologous end joining and for maintaining telomeres. Mice with either gene mutated exhibit similar phenotypes that include increased sensitivity to ionizing radiation and severe combined immunodeficiency. However, there are also differences in the reported phenotypes. For example, only Ku70 mutants are reported to exhibit a high incidence of thymic lymphomas while only Ku80 mutants are reported to exhibit early aging with very low cancer levels. There are two explanations for these differences. First, either Ku70 or Ku80 functions outside the Ku heterodimer such that deletion of one is not identical to deletion of the other. Second, divergent genetic backgrounds or environments influence the phenotype. To distinguish between these possibilities, the Ku70 and Ku80 mutations were crossed together to generate Ku70, Ku80, and double-mutant mice in the same genetic background raised in the same environment. We show that these three cohorts have similar phenotypes that most resemble the previous report for Ku80 mutant mice, i.e., early aging without substantially increased cancer levels. Thus, our observations suggest that the Ku heterodimer is important for longevity assurance in mice since divergent genetic backgrounds and/or environments likely account for these previously reported differences.
Collapse
Affiliation(s)
- Han Li
- Department of Molecular Medicine and Institute of Biotechnology, The University of Texas Health Science Center, San Antonio, Texas 78245, USA
| | | | | | | | | |
Collapse
|
32
|
Kim B, Koo H, Yang S, Bang S, Jung Y, Kim Y, Kim J, Park J, Moon RT, Song K, Lee I. TC1(C8orf4) correlates with Wnt/beta-catenin target genes and aggressive biological behavior in gastric cancer. Clin Cancer Res 2007; 12:3541-8. [PMID: 16740781 DOI: 10.1158/1078-0432.ccr-05-2440] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
PURPOSE We have recently reported that TC1(C8orf4), a small protein present in vertebrates, functions as a novel regulator of the Wnt/beta-catenin pathway. TC1 up-regulates beta-catenin target genes that are implicated in the aggressive behavior of cancers. Our aim was to investigate the clinical and pathobiological relevance of TC1 in gastric cancer. EXPERIMENTAL DESIGN The expression of TC1 was analyzed using tissue microarray in correlation with clinicopathologic variables and beta-catenin target genes in 299 gastric cancers. The biological effects of TC1 on Matrigel invasiveness and the proliferation of cancer cells were analyzed. TC1 expression was analyzed in gastric cancer cells after serial peritoneal implantation in nude mice. RESULTS TC1 expression was present in 111 carcinomas (37.1%), correlating with tumor stage (P < 0.002), poor differentiation (P < 0.001), lymphatic infiltration (P < 0.005), and lymph node metastasis (P < 0.006). TC1 also correlated with poor survival in diffuse type carcinomas (P < 0.0001), and even in patients with lymph node metastasis (P < 0.0014). TC1 also correlated with the expression of beta-catenin target genes including laminin gamma2, metalloproteinase-7 and metalloproteinase-14, cyclin D1, c-Met, and CD44. TC1 enhanced Matrigel invasiveness and proliferation, supporting its role in the aggressive biological behavior of cancers. The expression of TC1 increased in MKN45 cells after serial peritoneal seeding in nude mice. CONCLUSIONS Our data suggests that TC1 coordinates the up-regulation of Wnt/beta-catenin target genes that are implicated in the aggressive biological behavior of cancers. The strong clinical relevance, even in patients with lymph node metastasis, suggested that TC1 could be a potential therapeutic target of advanced gastric cancers.
Collapse
Affiliation(s)
- Byungsik Kim
- Department of General Surgery, University of Ulsan College of Medicine, Seoul, Korea
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
33
|
The DNA-repair Ku70 protein is located in the nucleus and tail of elongating spermatids in grasshoppers. Chromosome Res 2007; 15:1093-100. [DOI: 10.1007/s10577-007-1183-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2007] [Revised: 10/18/2007] [Accepted: 10/18/2007] [Indexed: 01/10/2023]
|
34
|
Moss TJ, Wallrath LL. Connections between epigenetic gene silencing and human disease. Mutat Res 2007; 618:163-74. [PMID: 17306846 PMCID: PMC1892579 DOI: 10.1016/j.mrfmmm.2006.05.038] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2006] [Accepted: 05/25/2006] [Indexed: 04/15/2023]
Abstract
Alterations in epigenetic gene regulation are associated with human disease. Here, we discuss connections between DNA methylation and histone methylation, providing examples in which defects in these processes are linked with disease. Mutations in genes encoding DNA methyltransferases and proteins that bind methylated cytosine residues cause changes in gene expression and alterations in the patterns of DNA methylation. These changes are associated with cancer and congenital diseases due to defects in imprinting. Gene expression is also controlled through histone methylation. Altered levels of methyltransferases that modify lysine 27 of histone H3 (K27H3) and lysine 9 of histone H3 (K9H3) correlate with changes in Rb signaling and disruption of the cell cycle in cancer cells. The K27H3 mark recruits a Polycomb complex involved in regulating stem cell pluripotency, silencing of developmentally regulated genes, and controlling cancer progression. The K9H3 methyl mark recruits HP1, a structural protein that plays a role in heterochromatin formation, gene silencing, and viral latency. Cells exhibiting altered levels of HP1 are predicted to show a loss of silencing at genes regulating cancer progression. Gene silencing through K27H3 and K9H3 can involve histone deacetylation and DNA methylation, suggesting cross talk between epigenetic silencing systems through direct interactions among the various players. The reversible nature of these epigenetic modifications offers therapeutic possibilities for a wide spectrum of disease.
Collapse
Affiliation(s)
- Timothy J Moss
- Department of Biochemistry, 3136 MERF, University of Iowa, Iowa City, IA 52242, USA
| | | |
Collapse
|
35
|
Terada Y. Aurora-B/AIM-1 regulates the dynamic behavior of HP1alpha at the G2-M transition. Mol Biol Cell 2006; 17:3232-41. [PMID: 16687578 PMCID: PMC1483052 DOI: 10.1091/mbc.e05-09-0906] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Heterochromatin protein 1 (HP1) plays an important role in heterochromatin formation and undergoes large-scale, progressive dissociation from heterochromatin in prophase cells. However, the mechanisms regulating the dynamic behavior of HP1 are poorly understood. In this study, the role of Aurora-B was investigated with respect to the dynamic behavior of HP1alpha. Mammalian Aurora-B, AIM-1, colocalizes with HP1alpha to the heterochromatin in G2. Depletion of Aurora-B/AIM-1 inhibited dissociation of HP1alpha from the chromosome arms at the G2-M transition. In addition, depletion of INCENP led to aberrant cellular localization of Aurora-B/AIM-1, but it did not affect heterochromatin targeting of HP1alpha. It was proposed in the binary switch hypothesis that phosphorylation of histone H3 at Ser-10 negatively regulates the binding of HP1alpha to the adjacent methylated Lys-9. However, Aurora-B/AIM-1-mediated phosphorylation of H3 induced dissociation of the HP1alpha chromodomain but not of the intact protein in vitro, indicating that the center and/or C-terminal domain of HP1alpha interferes with the effect of H3 phosphorylation on HP1alpha dissociation. Interestingly, Lys-9 methyltransferase SUV39H1 is abnormally localized together along the metaphase chromosome arms in Aurora-B/AIM-1-depleted cells. In conclusion, these results showed that Aurora-B/AIM-1 is necessary for regulated histone modifications involved in binding of HP1alpha by the N terminus of histone H3 during mitosis.
Collapse
Affiliation(s)
- Yasuhiko Terada
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455, USA.
| |
Collapse
|
36
|
Lomberk G, Bensi D, Fernandez-Zapico ME, Urrutia R. Evidence for the existence of an HP1-mediated subcode within the histone code. Nat Cell Biol 2006; 8:407-15. [PMID: 16531993 DOI: 10.1038/ncb1383] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2005] [Accepted: 01/11/2006] [Indexed: 11/08/2022]
Abstract
Currently, the mammalian heterochromatic proteins HP1alpha, HP1beta and the pan-nuclear HP1gamma are considered 'gatekeepers' of methyl-K9-H3-mediated silencing. Understanding how the binding of these proteins to post-translationally modified histones is switched on and off will further our knowledge of how the histone code is modulated. Here, we report that all three HP1 isoforms can be extensively modified, similar to histones, suggesting that the silencing of gene expression may be further regulated beyond the histone code. To assess the potential impact of these modifications, we analysed the phosphorylation of HP1gamma at Ser 83 as a 'model modification'. We demonstrate that P-Ser 83-HP1gamma has an exclusively euchromatic localization, interacts with Ku70 (a regulatory protein involved in multiple nuclear procesess), has impaired silencing activity and serves as a marker for transcription elongation. These observations predict that regulation of silencing by methyl-K9-H3 through modification of mammalian HP1 proteins may be more complex than previously thought and suggests the existence of an HP1-mediated 'silencing subcode' that underlies the instructions of the histone code.
Collapse
Affiliation(s)
- Gwen Lomberk
- Gastroenterology Research Unit, Department of Medicine, and Mayo Clinic Cancer Center, Rochester, MN 55605, USA
| | | | | | | |
Collapse
|
37
|
Jung Y, Bang S, Choi K, Kim E, Kim Y, Kim J, Park J, Koo H, Moon RT, Song K, Lee I. TC1 (C8orf4) enhances the Wnt/beta-catenin pathway by relieving antagonistic activity of Chibby. Cancer Res 2006; 66:723-8. [PMID: 16424001 DOI: 10.1158/0008-5472.can-05-3124] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The Wnt/beta-catenin pathway has been implicated in human cancers. Here, we show that TC1 (C8orf4), a small protein present in vertebrates, functions as a positive regulator of the pathway. TC1 interacts with Chibby (Cby) and thereby enhances the signaling pathway by relieving the antagonistic function of Cby on the beta-catenin-mediated transcription. Upon coexpression in mammalian cells, TC1 redistributes from nucleolus to nuclear speckles, where it colocalizes with Cby. TC1 up-regulates the expression of beta-catenin target genes that are implicated in invasiveness and aggressive behavior of cancers, such as metalloproteinases, laminin gamma2, and others. Our data indicate that TC1 is a novel upstream regulator of the Wnt/beta-catenin pathway that enhances aggressive behavior of cancers.
Collapse
Affiliation(s)
- Yusun Jung
- Asan Institute for Life Sciences, Asan Medical Center, University of Ulsan College of Medicine, 388-1 Poongnap-Dong, Songpa-Gu, Seoul 138-736, Korea
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
38
|
Abstract
Heterochromatin Protein 1 (HP1) was first discovered in Drosophila as a dominant suppressor of position-effect variegation and a major component of heterochromatin. The HP1 family is evolutionarily conserved, with members in fungi, plants and animals but not prokaryotes, and there are multiple members within the same species. The amino-terminal chromodomain binds methylated lysine 9 of histone H3, causing transcriptional repression. The highly conserved carboxy-terminal chromoshadow domain enables dimerization and also serves as a docking site for proteins involved in a wide variety of nuclear functions, from transcription to nuclear architecture. In addition to heterochromatin packaging, it is becoming increasingly clear that HP1 proteins have diverse roles in the nucleus, including the regulation of euchromatic genes. HP1 proteins are amenable to posttranslational modifications that probably regulate these distinct functions, thereby creating a subcode within the context of the 'histone code' of histone posttranslational modifications.
Collapse
Affiliation(s)
- Gwen Lomberk
- Gastroenterology Research Unit, Saint Mary's Hospital, Mayo Clinic, Rochester, MN 55905, USA
| | - Lori Wallrath
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
| | - Raul Urrutia
- Gastroenterology Research Unit, Saint Mary's Hospital, Mayo Clinic, Rochester, MN 55905, USA
| |
Collapse
|
39
|
Abstract
In most eukaryotes, telomeres are composed of simple repetitive sequences renewable by telomerase. By contrast, Drosophila telomeres comprise arrays of non-LTR retrotransposons HeT-A, TART, and TAHRE belonging to three different families. However, closer inspection reveals that the two quite different telomere systems share quite a few components and regulatory circuits. Here we present the current knowledge on Drosophila telomeres and discuss the possible mechanisms of telomere length control.
Collapse
Affiliation(s)
- Larisa Melnikova
- Institute of Gene Biology, Russian Academy of Sciences, 34/5 Vavilov St., Moscow 119334, Russia
| | | |
Collapse
|
40
|
Slijepcevic P, Al-Wahiby S. Telomere biology: integrating chromosomal end protection with DNA damage response. Chromosoma 2005; 114:275-85. [PMID: 15843951 DOI: 10.1007/s00412-005-0338-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2005] [Revised: 02/12/2005] [Accepted: 02/28/2005] [Indexed: 01/01/2023]
Abstract
Telomeres play the key protective role at chromosomes. Many studies indicate that loss of telomere function causes activation of DNA damage response. Here, we review evidence supporting interdependence between telomere maintenance and DNA damage response and present a model in which these two pathways are combined into a single mechanism for protecting chromosomal integrity. Proteins directly involved in telomere maintenance and DNA damage response include Ku, DNA-PKcs, RAD51D, PARP-2, WRN and RAD50/MRE11/NBS1 complex. Since most of these proteins participate in the repair of DNA double-strand breaks (DSBs), this was perceived by many authors as a paradox, given that telomeres function to conceal natural DNA ends from mechanisms that detect and repair DSBs. However, we argue here that the key function of one particular DSB protein, Ku, is to prevent or control access of telomerase, the enzyme that synthesises telomeric sequences, to both internal DSBs and natural chromosomal ends. This view is supported by observations that Ku has a high affinity for DNA ends; it acts as a negative regulator of telomerase and that telomerase itself can target internal DSBs. Ku then directs other DSB repair/telomere maintenance proteins to either repair DSBs at internal chromosomal sites or prevent uncontrolled elongation of telomeres by telomerase. This model eliminates the above paradox and provides a testable scenario in which the role of DSB repair proteins is to protect chromosomal integrity by balancing repair activities and telomere maintenance. In our model, a close association between telomeres and different DNA damage response factors is not an unexpected event, but rather a logical result of chromosomal integrity maintenance activities.
Collapse
Affiliation(s)
- Predrag Slijepcevic
- Brunel Institute of Cancer Genetics and Pharmacogenomics, Division of Biosciences, School of Health Sciences and Social Care, Brunel University, Uxbridge, Middlesex UB8 3PH, UK.
| | | |
Collapse
|
41
|
Wang Q, Zhang Z, Blackwell K, Carmichael GG. Vigilins bind to promiscuously A-to-I-edited RNAs and are involved in the formation of heterochromatin. Curr Biol 2005; 15:384-91. [PMID: 15723802 DOI: 10.1016/j.cub.2005.01.046] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2004] [Revised: 11/27/2004] [Accepted: 11/30/2004] [Indexed: 01/09/2023]
Abstract
The fate of double-stranded RNA (dsRNA) in the cell depends on both its length and location . The expression of dsRNA in the nucleus leads to several distinct consequences. First, the promiscuous deamination of adenosines to inosines by dsRNA-specific adenosine deaminase (ADAR) can lead to the nuclear retention of edited transcripts . Second, dsRNAs might induce heterochromatic gene silencing through an RNAi-related mechanism . Is RNA editing also connected to heterochromatin? We report that members of the conserved Vigilin class of proteins have a high affinity for inosine-containing RNAs. In agreement with other work , we find that these proteins localize to heterochromatin and that mutation or depletion of the Drosophila Vigilin, DDP1, leads to altered nuclear morphology and defects in heterochromatin and chromosome segregation. Furthermore, nuclear Vigilin is found in complexes containing not only the editing enzyme ADAR1 but also RNA helicase A and Ku86/70. In the presence of RNA, the Vigilin complex recruits the DNA-PKcs enzyme, which appears to phosphorylate a discrete set of targets, some or all of which are known to participate in chromatin silencing. These results are consistent with a mechanistic link between components of the DNA-repair machinery and RNA-mediated gene silencing.
Collapse
Affiliation(s)
- Qiaoqiao Wang
- Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, CT 06030 USA
| | | | | | | |
Collapse
|
42
|
Kaminker P, Plachot C, Kim SH, Chung P, Crippen D, Petersen OW, Bissell MJ, Campisi J, Lelièvre SA. Higher-order nuclear organization in growth arrest of human mammary epithelial cells: a novel role for telomere-associated protein TIN2. J Cell Sci 2005; 118:1321-30. [PMID: 15741234 PMCID: PMC2933191 DOI: 10.1242/jcs.01709] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Nuclear organization, such as the formation of specific nuclear subdomains, is generally thought to be involved in the control of cellular phenotype; however, there are relatively few specific examples of how mammalian nuclei organize during radical changes in phenotype, such as those occurring during differentiation and growth arrest. Using human mammary epithelial cells in which growth arrest is essential for morphological differentiation, we show that the arrest of cell proliferation is accompanied by a reorganization of the telomere-associated protein, TIN2, into one to three large nuclear subdomains. The large TIN2 domains do not contain telomeres and occur concomitant with the continued presence of TIN2 at telomeres. The TIN2 domains were sensitive to DNase, but not RNase, occurred frequently, but not exclusively near nucleoli, and overlapped often with dense domains containing heterochromatin protein 1gamma. Expression of truncated forms of TIN2 simultaneously prevented the formation of TIN2 domains and relaxed the stringent morphogenesis-induced growth arrest in human mammary epithelial cells. Here we show that a novel extra-telomeric organization of TIN2 is associated with the control of cell proliferation and identify TIN2 as an important regulator of mammary epithelial differentiation.
Collapse
Affiliation(s)
- Patrick Kaminker
- Buck Institute for Age Research, 8001 Redwood Boulevard, Novato, California 94945, USA
| | - Cedric Plachot
- Department of Basic Medical Sciences and Cancer Center, Purdue University, 625 Harrison Street, West Lafayette, Indiana 47907-2026, USA
| | - Sahn-Ho Kim
- Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California, 94720, USA
| | - Peter Chung
- Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California, 94720, USA
| | - Danielle Crippen
- Buck Institute for Age Research, 8001 Redwood Boulevard, Novato, California 94945, USA
| | - Ole W. Petersen
- Structural Cell Biology Unit, The Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200, Copenhagen, Denmark
| | - Mina J. Bissell
- Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California, 94720, USA
| | - Judith Campisi
- Buck Institute for Age Research, 8001 Redwood Boulevard, Novato, California 94945, USA
- Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California, 94720, USA
| | - Sophie A. Lelièvre
- Department of Basic Medical Sciences and Cancer Center, Purdue University, 625 Harrison Street, West Lafayette, Indiana 47907-2026, USA
- Author for correspondence ()
| |
Collapse
|
43
|
Abstract
Vigilin proteins, the absence of which is known to cause abnormalities in heterochromatin, have been found to bind edited RNAs. Molecular complexes including vigilin comprise proteins involved with RNA editing and with DNA repair, making connections between these processes and RNA-based silencing mechanisms.
Collapse
Affiliation(s)
- H R Fernandez
- Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211, USA
| | | | | | | |
Collapse
|
44
|
Ma H, Thibault J, Lu Y, Whiting C, Long S, Lindwall G, Bennett K, Truong L, Aimes RT, Wong-Staal F. The development and applications of nonradioactive plate-formatted DNA-binding assay for Ku70/80, a multifunctional DNA-binding protein complex. Assay Drug Dev Technol 2005; 2:483-95. [PMID: 15671646 DOI: 10.1089/adt.2004.2.483] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Ku is a heterodimer composed of p70 and p80, and is the regulatory subunit of DNA-dependent protein kinase. As a multifunctional DNA-binding protein complex, Ku plays important roles in DNA damage repair through non-homologous end joining and in V(D)J recombination. In addition, Ku has also been implicated in various biological functions including growth control, cell proliferation, cell cycle, chromosome maintenance, transcriptional regulation, apoptosis, and viral infection. In particular, using our Inverse Genomics (Immusol, Inc., San Diego, CA) platform technology, we recently identified Ku80 as an essential co-factor for human immunodeficiency virus replication. Although Ku has been studied extensively in the past years, its in-depth study as well as development as a drug target has been limited by conventional DNA-binding activity assay. Here we describe the development and applications of a nonradioactive DNA binding assay in the 96-well format. We show that this plate-formatted assay is more sensitive and allows for direct quantification when compared with an electrophoretic mobility shift assay. The establishment of this assay will not only facilitate structure and function studies on Ku, but also help the development of Ku protein or its DNA repair enzyme complex as a drug target.
Collapse
Affiliation(s)
- Hongwen Ma
- Immusol, Inc., 10790 Roselle Street, San Diego, CA 92121, USA.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
45
|
Sharma GG, Hwang KK, Pandita RK, Gupta A, Dhar S, Parenteau J, Agarwal M, Worman HJ, Wellinger RJ, Pandita TK. Human heterochromatin protein 1 isoforms HP1(Hsalpha) and HP1(Hsbeta) interfere with hTERT-telomere interactions and correlate with changes in cell growth and response to ionizing radiation. Mol Cell Biol 2003; 23:8363-76. [PMID: 14585993 PMCID: PMC262350 DOI: 10.1128/mcb.23.22.8363-8376.2003] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Telomeres are associated with the nuclear matrix and are thought to be heterochromatic. We show here that in human cells the overexpression of green fluorescent protein-tagged heterochromatin protein 1 (GFP-HP1) or nontagged HP1 isoforms HP1(Hsalpha) or HP1(Hsbeta), but not HP1(Hsgamma), results in decreased association of a catalytic unit of telomerase (hTERT) with telomeres. However, reduction of the G overhangs and overall telomere sizes was found in cells overexpressing any of these three proteins. Cells overexpressing HP1(Hsalpha) or HP1(Hsbeta) also display a higher frequency of chromosome end-to-end associations and spontaneous chromosomal damage than the parental cells. None of these effects were observed in cells expressing mutants of GFP-DeltaHP1(Hsalpha), GFP-DeltaHP1(Hsbeta), or GFP-DeltaHP1(Hsgamma) that had their chromodomains deleted. An increase in the cell population doubling time and higher sensitivity to cell killing by ionizing radiation (IR) treatment was also observed for cells overexpressing HP1(Hsalpha) or HP1(Hsbeta). In contrast, cells expressing mutant GFP-DeltaHP1(Hsalpha) or GFP-DeltaHP1(Hsbeta) showed a decrease in population doubling time and decreased sensitivity to IR compared to the parental cells. The effects on cell doubling times were paralleled by effects on tumorigenicity in mice: overexpression of HP1(Hsalpha) or HP1(Hsbeta) suppressed tumorigenicity, whereas expression of mutant HP1(Hsalpha) or HP1(Hsbeta) did not. Collectively, the results show that human cells are exquisitely sensitive to the amount of HP1(Hsalpha) or HP1(Hsbeta) present, as their overexpression influences telomere stability, population doubling time, radioresistance, and tumorigenicity in a mouse xenograft model. In addition, the isoform-specific effects on telomeres reinforce the notion that telomeres are in a heterochromatinized state.
Collapse
Affiliation(s)
- Girdhar G Sharma
- Radiation and Cancer Biology Division, Washington University School of Medicine, 4511 Forest Park, St Louis, MO 63108, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
46
|
Hayakawa T, Haraguchi T, Masumoto H, Hiraoka Y. Cell cycle behavior of human HP1 subtypes: distinct molecular domains of HP1 are required for their centromeric localization during interphase and metaphase. J Cell Sci 2003; 116:3327-38. [PMID: 12840071 DOI: 10.1242/jcs.00635] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Heterochromatin protein 1 (HP1) plays an important role in heterochromatin formation. Three subtypes of HP1, namely HP1alpha, beta, and gamma, have been identified in humans. In this study, using yellow fluorescent protein (YFP) fusion constructs, we examined the intracellular localization of human HP1 subtypes during the cell cycle. During interphase, all three HP1 subtypes were localized to centromeric heterochromatin and to promyelocytic leukemia (PML) nuclear bodies. Different preferences, however, were observed among the subtypes: during interphase HP1beta localized most preferentially to centromeric heterochromatin, whereas HP1alpha and gamma were more preferentially localized to PML nuclear bodies. During metaphase, only HP1alpha, was localized to the centromere. We thus determined which molecular domains of HP1 were necessary for their intracellular localization. Our results showed that the C-terminal fragment (amino acid residues 101-180) of HP1alpha was necessary for localization to the metaphase centromere and the N-terminal fragment (amino acid residues 1-76) of HP1beta was necessary for localization to the interphase centromere. Interestingly, simultaneous observations of residues 101-180 of HP1alpha and residues 1-76 of HP1beta in living HeLa cells revealed that during late prophase, the HP1beta fragment dissociated from centromeric regions and the HP1alpha fragment accumulated in centromeric regions. These results indicate that different specific regions of human HP1alpha and HP1beta mediate localization to metaphase and interphase centromeric regions resulting in association of different subtypes of HP1 with the centromere at different times during the cell cycle.
Collapse
Affiliation(s)
- Tomohiro Hayakawa
- CREST Research Project, Kansai Advanced Research Center, Communications Research Laboratory, 588-2 Iwaoka, Iwaoka-cho, Nishi-ku, Kobe 651-2492, Japan
| | | | | | | |
Collapse
|
47
|
Abstract
Since its discovery almost two decades ago, heterochromatin protein 1 (HP1) has emerged as a major player in the transcriptional regulation of both heterochromatic and euchromatic genes as well as the mechanics of chromosome segregation and the functional and structural organization of the interphase nucleus. Recent years have brought the identification of a myriad of HP1-interacting proteins. Each of these is discussed in relationship to its role in heterochromatin assembly and HP1 function. The breadth of functions represented by HP1-interacting proteins testifies to its pivotal role in the daily operations of the nucleus.
Collapse
Affiliation(s)
- R Kellum
- School of Biological Sciences, 101 T. H. Morgan Building, University of Kentucky, Lexington, KY 40506-0225, USA.
| |
Collapse
|
48
|
Przewloka MR, Pardington PE, Yannone SM, Chen DJ, Cary RB. In vitro and in vivo interactions of DNA ligase IV with a subunit of the condensin complex. Mol Biol Cell 2003; 14:685-97. [PMID: 12589063 PMCID: PMC150001 DOI: 10.1091/mbc.e01-11-0117] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Several findings have revealed a likely role for DNA ligase IV, and interacting protein XRCC4, in the final steps of mammalian DNA double-strand break repair. Recent evidence suggests that the human DNA ligase IV protein plays a critical role in the maintenance of genomic stability. To identify protein-protein interactions that may shed further light on the molecular mechanisms of DSB repair and the biological roles of human DNA ligase IV, we have used the yeast two-hybrid system in conjunction with traditional biochemical methods. These efforts have resulted in the identification of a physical association between the DNA ligase IV polypeptide and the human condensin subunit known as hCAP-E. The hCAP-E polypeptide, a member of the Structural Maintenance of Chromosomes (SMC) super-family of proteins, coimmunoprecipitates from cell extracts with DNA ligase IV. Immunofluorescence studies reveal colocalization of DNA ligase IV and hCAP-E in the interphase nucleus, whereas mitotic cells display colocalization of both polypeptides on mitotic chromosomes. Strikingly, the XRCC4 protein is excluded from the area of mitotic chromosomes, suggesting the formation of specialized DNA ligase IV complexes subject to cell cycle regulation. We discuss our findings in light of known and hypothesized roles for ligase IV and the condensin complex.
Collapse
Affiliation(s)
- Marcin R Przewloka
- Los Alamos National Laboratory, Biosciences Division, New Mexico 87545, USA
| | | | | | | | | |
Collapse
|
49
|
Hibino H, Pironkova R, Onwumere O, Rousset M, Charnet P, Hudspeth AJ, Lesage F. Direct interaction with a nuclear protein and regulation of gene silencing by a variant of the Ca2+-channel beta 4 subunit. Proc Natl Acad Sci U S A 2003; 100:307-12. [PMID: 12518067 PMCID: PMC140959 DOI: 10.1073/pnas.0136791100] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The beta subunits of voltage-gated Ca(2+) channels are known to be regulators of the channels' gating properties. Here we report a striking additional function of a beta subunit. Screening of chicken cochlear and brain cDNA libraries identified beta(4c), a short splice variant of the beta(4) subunit. Although beta(4c) occurs together with the longer isoforms beta(4a) or beta(4b) in the brain, eye, heart, and lung, the cochlea expresses exclusively beta(4c). The association of beta(4c) with the Ca(2+)-channel alpha(1) subunit has slight but significant effects on the kinetics of channel activation and inactivation. Yeast two-hybrid and biochemical assays revealed that beta(4c) interacts directly with the chromo shadow domain of chromobox protein 2heterochromatin protein 1gamma (CHCB2HP1gamma), a nuclear protein involved in gene silencing and transcriptional regulation. Coexpression of this protein specifically recruits beta(4c) to the nuclei of mammalian cells. Furthermore, beta(4c) but not beta(4a) dramatically attenuates the gene-silencing activity of chromobox protein 2heterochromatin protein 1gamma. The beta(4c) subunit is therefore a multifunctional protein that not only constitutes a portion of the Ca(2+) channel but also regulates gene transcription.
Collapse
Affiliation(s)
- H Hibino
- The Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
| | | | | | | | | | | | | |
Collapse
|
50
|
Li Y, Kirschmann DA, Wallrath LL. Does heterochromatin protein 1 always follow code? Proc Natl Acad Sci U S A 2002; 99 Suppl 4:16462-9. [PMID: 12151603 PMCID: PMC139909 DOI: 10.1073/pnas.162371699] [Citation(s) in RCA: 154] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Heterochromatin protein 1 (HP1) is a conserved chromosomal protein that participates in chromatin packaging and gene silencing. A loss of HP1 leads to lethality in Drosophila and correlates with metastasis in human breast cancer cells. On Drosophila polytene chromosomes HP1 is localized to centric regions, telomeric regions, in a banded pattern along the fourth chromosome, and at many sites scattered throughout the euchromatic arms. Recently, one mechanism of HP1 chromosome association was revealed; the amino-terminal chromo domain of HP1 interacts with methylated lysine nine of histone H3, consistent with the histone code hypothesis. Compelling data support this mechanism of HP1 association at centric regions. Is this the only mechanism by which HP1 associates with chromosomes? Interest is now shifting toward the role of HP1 within euchromatic domains. Accumulating evidence in Drosophila and mammals suggests that HP1 associates with chromosomes through interactions with nonhistone chromosomal proteins at locations other than centric heterochromatin. Does HP1 play a similar role in chromatin packaging and gene regulation at these sites as it does in centric heterochromatin? Does HP1 associate with the same proteins at these sites as it does in centric heterochromatin? A first step toward answering these questions is the identification of sequences associated with HP1 within euchromatic domains. Such sequences are likely to include HP1 "target genes" whose discovery will aid in our understanding of HP1 lethality in Drosophila and metastasis of breast cancer cells.
Collapse
Affiliation(s)
- Yuhong Li
- Department of Biochemistry, University of Iowa, Iowa City 52242, USA
| | | | | |
Collapse
|