ZIA BC 011519 (ZIA) | |||
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Title | Telomere Biology | ||
Institution | NCI, Bethesda, MD | ||
Principal Investigator | Cooper, Julia | NCI Program Director | N/A |
Cancer Activity | N/A | Division | CCR |
Funded Amount | $1,183,392 | Project Dates | 00/00/0000 - 00/00/0000 |
Fiscal Year | 2016 | Project Type | Intramural |
Research Topics w/ Percent Relevance | Cancer Types w/ Percent Relevance | ||
Aging (45.0%) Ataxia Telangiectasia (2.0%) Cancer (100.0%) Gene Therapy (2.0%) |
N/A | ||
Research Type | |||
Normal Functioning Cancer Initiation: Alterations in Chromosomes |
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Abstract | |||
The termini of eukaryotic chromosomes are potentially dangerous sites, as their resemblance to damage-induced DNA breaks makes them vulnerable to degradation and end-joining pathways that provoke cancer. Telomeres protect chromosome ends from these hazards. On the other hand, we are increasingly recognizing that telomeres provide regulatory and choreography-related opportunities to the cell - for instance, their heterochromatic nature along with their tendency to cluster together allows telomeres to create subnuclear 'micro environments' that can be exploited to promote crucial nuclear activities like centromere assembly and the regulation of spindle formation. Fission yeast telomeres are remarkably similar to those of human but present substantial experimental benefits, like precise genetic manipulability. The components of human 'shelterin' are also found in fission yeast and we are building an integrated picture of how these proteins interact to protect chromosome ends. We have also identified unforeseen additional functions of telomeres that are likely to be widely conserved. Advances over the past year include: 1. Having shown previously that stalled telomeric replication forks trigger chromosome entanglement, we have now found a role for a widely conserved protein, Rif1, in controlling the final resolution of such entanglements at anaphase, thus uncovering an unanticipated facet (and time of action) of Rif1's activities and illuminating a final, regulated step of chromosome segregation. We find that this activity of Rif1 is separable from its described roles in controlling replication initiation and the resection of broken chromosome ends, being controlled independently of protein phosphatase binding. Moreover, we have defined several features of the chromosome 'bridges' whose resolution is blocked by Rif1 (e.g., the persistence of replicative DNA polymerases on these bridges), bringing us closer to defining the molecular mechanism of entanglement and its resolution. We have implicated these processes in the resolution of non-telomeric 'ultra-fine anaphase bridges' as well. 2. Survival without telomeres - Cells can occasionally survive the absence of telomerase, by maintaining telomeres via recombination or by circularizing their chromosomes. We had identified a third mode of telomerase-minus survival in which linear chromosomes are maintained using a strategy we dubbed 'HAATI' (heterochromatin amplification-mediated and telomerase independent). In HAATI cells, telomere repeats are absent but tracts of 'generic' heterochromatin jump to each chromosome end. This heterochromatin, along with a non-telomeric terminal 3'-overhang, recruits Pot1, which is essential for HAATI chromosome linearity. This discovery revealed an alternative mode by which cancer cells might survive without telomerase activation. We have now found that HAATI formation is limited only by the chromosome rearrangements that place generic heterochromatin at HAATI chromosome ends - once this 'jumping' of DNA sequences occurs, the cell has no problem in engaging chromosome end-protection at the non-telomeric chromosome termini. The details of this end-protection are under intense investigation. The sequence jumping is itself controlled by the RNAi pathway in both a canonical and a non-canonical capacity. We have also uncovered a role for the chromatin remodeling Ino80 complex in maintaining an unusual form of HAATI, providing the first foothold into understanding this genome-disrupting mode. 3. In a screen for factors required for HAATI maintenance, we uncovered a role for specific subnuclear domain positioning factor. We have characterized the role of this factor in wild type cells - it is required for tethering heterochromatic domains to the nuclear membrane specifically during the period in which these domains undergo DNA replication. In turn, this positioning delimits the reassembly of heterochromatin. We find that the nuclear membrane is not a homogene |