C-Myc Induces Chromosomal Rearrangements Through Telomere and Chromosome Remodeling in the Interphase Nucleus
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c-Myc induces chromosomal rearrangements through telomere and chromosome remodeling in the interphase nucleus Sherif F. Louis*†, Bart J. Vermolen†‡, Yuval Garini†‡, Ian T. Young‡, Amanda Guffei*, Zelda Lichtensztejn*, Fabien Kuttler*, Tony C. Y. Chuang*§¶, Sharareh Moshir*ʈ, Virginie Mougey**, Alice Y. C. Chuang*, Paul Donald Kerr§, Thierry Fest**††, Petra Boukampʈ, and Sabine Mai*‡‡ *Manitoba Institute of Cell Biology, University of Manitoba, 675 McDermot Avenue, Winnipeg, MB, Canada R3E 0V9; ‡Department of Imaging Science and Technology, Faculty of Applied Sciences, Quantitative Imaging Group, Delft University of Technology, 2628 CJ Delft, The Netherlands; §Department of Otolaryngology Head and Neck Surgery, Health Sciences Centre, GB421-820 Sherbrook Street, Winnipeg, MB, Canada R3A 1R9; ʈDivision of Genetics of Skin Carcinogenesis, German Cancer Research Centre, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany; **Hematology Department, IETG Laboratory, University Hospital Jean Minjoz, 25030 Besanc¸on, France; and ††Hematology Department, EA 3889, IFR140 GFAS, University Hospital Pontchaillou, 35033 Rennes, France Edited by George Klein, Karolinska Institutet, Stockholm, Sweden, and approved May 9, 2005 (received for review October 11, 2004) In previous work, we showed that telomeres of normal cells are promotes tumorigenesis (26–30). When c-Myc deregulation is organized within the 3D space of the interphase nucleus in a abolished, in vivo tumorigenesis is reversible, provided that no nonoverlapping and cell cycle-dependent manner. This order is additional mutations had occurred (29–34). distorted in tumor cell nuclei where telomeres are found in close Prompted by the complexity of downstream genetic alterations association forming aggregates of various numbers and sizes. Here that result from c-Myc deregulation, we investigated whether c-Myc we show that c-Myc overexpression induces telomeric aggrega- affected the 3D organization of the mammalian interphase nucleus tions in the interphase nucleus. Directly proportional to the dura- and whether this remodeling had an impact on genomic stability. tion of c-Myc deregulation, we observe three or five cycles of We show that c-Myc deregulation causes remodeling of the 3D telomeric aggregate formation in interphase nuclei. These cycles nuclear organization of telomeres and chromosomes, thus creating reflect the onset and propagation of breakage-bridge-fusion cycles the topological conditions that initiate genomic instability. MEDICAL SCIENCES that are initiated by end-to-end telomeric fusions of chromosomes. Subsequent to initial chromosomal breakages, new fusions follow Materials and Methods and the breakage-bridge-fusion cycles continue. During this time, Cells and Conditional Myc Activation. Culture conditions have been nonreciprocal translocations are generated. c-Myc-dependent re- described for Ba͞F3 (35) and PreB (36) cells. The plasmacytoma modeling of the organization of telomeres thus precedes the onset cell line MOPC460D was a gift of J. Mushinski (National Institutes of genomic instability and subsequently leads to chromosomal of Health, Bethesda). Cell viability was determined by hemocy- rearrangements. Our findings reveal that c-Myc possesses the tometer counts by using trypan blue. The primary mouse plasma- ͞ ͞ ability to structurally modify chromosomes through telomeric cytoma DCPC21 was isolated from a BALB c mouse (37). v-abl fusions, thereby reorganizing the genetic information. myc-induced plasmacytomas (38) and primary lymphocytes were collected from BALB͞c mice (Central Animal Care protocol genomic instability ͉ 3D nucleus ͉ breakage-bridge-fusion 02-039). To activate MycER (39) in Ba͞F3 or PreB cells, 105 cells per ml were treated with 100 nM 4-hydroxytamoxifen (4HT). Cells were ultiple alterations accompany tumor initiation and progres- split 24 h before 4HT treatment. Non-4HT treated control cells Msion resulting in the modulation of gene expression and in were cultivated in ethanol, which is used to dissolve 4HT (25, 26, genomic instability. These interconnected changes occur within 39). Two different MycER activation schemes were performed. nuclei that harbor an altered 3D organization (1–3). In agreement First, analyses of c-Myc-induced changes in 3D telomere organi- with this concept, recent reports suggest tumor-associated changes zation were carried out after a single addition of 4HT that was left of chromosomal organization in an altered 3D nucleus (3–8). in the culture medium until its biological effects subsided (40– 42). However, mechanisms leading to structural changes of telomeres Nuclei were examined every 24 h over a 10-day period. A second and chromosomes remain elusive. time course was performed every 6 h for 120 h (Fig. 1). To enable We recently reported that the normal interphase nucleus has a a time-dependent analysis of Myc activation, 4HT was given for 2 unique 3D telomeric organization that is cell cycle dependent (9, or 12 h and was removed. Alternatively, 4HT was added every 12 h 10). Telomeres are organized in a nonoverlapping manner and align or was given once but left in the culture. MycER activation was into a central telomeric disk during the late G2 phase of the cell cycle determined by fluorescent immunohistochemistry. (9). In contrast, tumor cells display an aberrant organization of telomeres that can be objectively measured in nuclei showing Immunohistochemistry (IHC). Fluorescent IHC of Myc protein was telomeric aggregates of various complexity and sizes (9). performed as described in ref. 43 by using a polyclonal anti-c-Myc Constitutive expression of c-Myc due to chromosomal translo- antibody (N262; Santa Cruz Biotechnology) and a goat anti-rabbit cations, mutation, or amplification contributes to the development IgG FITC antibody, each at a dilution of 1:100. Analysis was and progression of many cancers (11, 12). c-Myc deregulation directly promotes genomic instability (13), causing locus-specific and karyotypic instability (14–18). Additionally, c-Myc induces This paper was submitted directly (Track II) to the PNAS office. illegitimate replication initiation (19, 20), DNA breakage (21), Abbreviations: 4HT, 4-hydroxytamoxifen; SKY, spectral karyotyping; TA, telomeric aggregate. alterations of DNA repair (22, 23), and a low level of point †S.F.L., B.J.V., and Y.G. contributed equally to this work. mutations (24, 25). Effects of c-Myc on genomic instability are ¶Present address: Department of Otolaryngology Head and Neck Surgery, Head and Neck reversible after a transient experimental activation of c-Myc (15). Division, The Johns Hopkins University School of Medicine, Baltimore, MD 21205. However, c-Myc continues to generate instability after constitutive ‡‡To whom correspondence should be addressed. E-mail: [email protected]. deregulation (16). In vivo, c-Myc deregulation directly initiates and © 2005 by The National Academy of Sciences of the USA www.pnas.org͞cgi͞doi͞10.1073͞pnas.0407512102 PNAS ͉ July 5, 2005 ͉ vol. 102 ͉ no. 27 ͉ 9613–9618 Downloaded by guest on October 1, 2021 nuclei was performed as described above. Measurements of chro- mosomal overlaps were performed after 3D image acquisition and constrained iterative deconvolution as follows: (i) based on the DAPI counterstain image, we determined the 3D boundary of the nuclear volume. Data outside that volume were ignored. (ii) For each one of the chromosomes, we determined an intensity threshold and referred only to voxels that were above the threshold that belonged to the specific chromosomes. The total volume occupied by each one of the chromosome pairs is measured (V1 and V2). (iii) Fig. 1. MycER activation scheme. The effects of 4HT last 15–24 h in cell lines The volume occupied by both chromosome pairs is measured, Vo. (40–42), as indicated by dashed lines. Cells were harvested every 6 h over a By dividing this value by V1 and by V2, the level of overlap relative time period of 120 h. Mock-treated control cells were processed in parallel. to the total volume of each chromosome pair was measured, V0͞V1, V0͞V2 (for details, see Fig. 8 which is published as supporting information on the PNAS web site). performed by using a Zeiss Axiophot 2 microscope. Images were acquired with a Cooke CCD SensiCam Camera. Spectral Karyotyping (SKY). Mouse SKY was performed by using a SKY system (Applied Spectral Imaging) (37). Twenty metaphases Cell Death. Apoptotic bodies for control and MycER-activated cells were examined per time point. Significant values for chromosomal were assessed by two independent observers who scored 300 rearrangements were determined after MycER activation. Mean DAPI-stained nuclei per time point in the presence or absence of total chromosomes and numbers of each chromosome observed for MycER activation. control and Myc-activated cells were compared over time by two-way ANOVA. In addition, statistical analyses were performed Telomere FISH. Ba͞F3, PreB, and plasmacytoma cells were collected for the occurrence of translocations, breakages, and fusions over the (200 ϫ g for 10 min) and resuspended in PBS containing 3.7% experimental period of 120 h. P values of Ͻ0.05 were considered formaldehyde (Fluka) and incubated for 20 min. Thereafter, the significant. Only the frequency procedure was used, followed by telomere FISH protocol was performed (9, 44) by using Cy3- or Fisher’s exact test. The P value of the overall study was Ͻ0.0001. FITC-labeled PNA probes (DAKO). Three independent experi- ments were performed. At least 30 nuclei and 20 metaphases