c-Myc-Induced Extrachromosomal Elements Carry Active Chromatin

Manitoba Institute of Cell Biology, CancerCare Manitoba, the Genomic Center for Cancer Research and Diagnosis, Winnipeg, Manitoba, Canada.
Neoplasia (Impact Factor: 4.25). 03/2003; 5(2):110-20. DOI: 10.1016/S1476-5586(03)80002-7
Source: PubMed


Murine Pre-B lymphocytes with experimentally activated MycER show both chromosomal and extrachromosomal gene amplification. In this report, we have elucidated the size, structure, and functional components of c-Myc-induced extrachromosomal elements (EEs). Scanning electron microscopy revealed that EEs isolated from MycER-activated Pre-B+ cells are an average of 10 times larger than EEs isolated from non-MycER-activated control Pre-B- cells. We demonstrate that these large c-Myc-induced EEs are associated with histone proteins, whereas EEs of non-MycER-activated Pre B- cells are not. Immunohistochemistry and Western blot analyses using pan-histone-specific, histone H3 phosphorylation-specific, and histone H4 acetylation-specific antibodies indicate that a significant proportion of EEs analyzed from MycER-activated cells harbors transcriptionally competent and/or active chromatin. Moreover, these large, c-Myc-induced EEs carry genes. Whereas the total genetic make-up of these c-Myc-induced EEs is unknown, we found that 30.2% of them contain the dihydrofolate reductase (DHFR) gene, whereas cyclin C (CCNC) was absent. In addition, 50% of these c-Myc-activated Pre-B+ EEs incorporated bromodeoxyuridine (BrdU), identifying them as genetic structures that self-propagate. In contrast, EEs isolated from non-Myc-activated cells neither carry the DHFR gene nor incorporate BrdU, suggesting that c-Myc deregulation generates a new class of EEs.

Download full-text


Available from: Stephen Symons,
19 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: c-myc is one of a small family of proto-oncogenes that do not require mutation to contribute to neoplastic transformation. Instead, the deregulated expression of the oncoprotein at even modest levels is sufficient to initiate this process. The transforming activity of c-Myc is generally thought to lie in its ability to modulate the expression of a series of genes, among them certain proliferation-promoting genes. In reality, c-Myc is a multifunctional protein that also affects the stability of the genome. In this review, we summarize the growing evidence that deregulated c-myc expression generates genomic instability by initiating gene amplification (both intra- and extra-chromosomally), gene rearrangements, and karyotypic instability. Cancer is a disease of impaired genomic stability, to which c-Myc contributes during its initiation and progression through the induction of genomic instability in critical genes. Myc thus acts as a structural modifier of the genome and as a promoter of neoplastic transformation.
    Journal of Environmental Pathology Toxicology and Oncology 02/2003; 22(3):179-99. DOI:10.1615/JEnvPathToxOncol.v22.i3.30 · 1.15 Impact Factor
  • Source
    Neoplasia (New York, N.Y.) 11/2004; 4(6). DOI:10.1593/neo.6-6ED · 4.25 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In previous work, we showed that telomeres of normal cells are organized within the 3D space of the interphase nucleus in a nonoverlapping and cell cycle-dependent manner. This order is distorted in tumor cell nuclei where telomeres are found in close association forming aggregates of various numbers and sizes. Here we show that c-Myc overexpression induces telomeric aggregations in the interphase nucleus. Directly proportional to the duration of c-Myc deregulation, we observe three or five cycles of telomeric aggregate formation in interphase nuclei. These cycles reflect the onset and propagation of breakage-bridge-fusion cycles that are initiated by end-to-end telomeric fusions of chromosomes. Subsequent to initial chromosomal breakages, new fusions follow and the breakage-bridge-fusion cycles continue. During this time, nonreciprocal translocations are generated. c-Myc-dependent remodeling of the organization of telomeres thus precedes the onset of genomic instability and subsequently leads to chromosomal rearrangements. Our findings reveal that c-Myc possesses the ability to structurally modify chromosomes through telomeric fusions, thereby reorganizing the genetic information.
    Proceedings of the National Academy of Sciences 08/2005; 102(27):9613-8. DOI:10.1073/pnas.0407512102 · 9.67 Impact Factor
Show more