Telomerase elongates chromosome ends by addition of tandem telomeric repeats. This new DNA synthesis is required to balance the loss of DNA that is inherent in the incomplete replication of chromosome ends by conventional DNA polymerases. Single-celled eukaryotes constitutively activate telomerase and maintain a homeostasis of telomere length. Surprisingly, human somatic cells do not: they show progressive shortening of the telomeric repeat array with proliferation. Some human cells in the embryo, germline, epithelial tissues, and hematopoietic system have detectable levels of telomerase catalytic activity in cell lysates, but this level of activation is insufficient to prevent an overall loss of telomere length in all human tissues with age. Cumulative loss eventually produces a repeat array that is too short to protect the chromosome end, resulting in a forced exit from the cell cycle. Cancer cells dramatically up-regulate telomerase to permit indefinite growth. For this reason, telomerase inhibitors have great promise as broadly effective anti-cancer therapeutics. Telomerase activators may have equally significant application for expanding the renewal capacity of normal somatic cells with critically short telomeres arising from genetics, disease, age, or environment. The telomerase RNA subunit (TER) is expressed as a precursor that must be processed, folded, and assembled as a stable ribonucleoprotein (RNP) complex in order to accumulate to detectable level in vivo. This RNP then recruits telomerase reverse transcriptase (TERT) to generate the active enzyme. Collins lab efforts in previous funding periods have contributed pioneering insights about the endogenous pathway of human TER precursor processing and RNP assembly and discovered defects in the accumulation of mature telomerase RNP that underlie X-linked and autosomal dominant forms of the bone marrow failure syndrome dyskeratosis congenita.
The Specific Aims of the next funding period address remaining gaps in knowledge about human telomerase RNP accumulation and catalytic activation in vivo.
Aim 1 exploits methods of transient and stable TER expression in human cells to discover and characterize additional RNA motifs and proteins required for TER maturation and biological stability.
Aim 2 applies Collins lab expertise in RNA-protein interaction assays and affinity purification to define the biochemical defects that underlie inherited human diseases of telomerase deficiency.
Aim 3 investigates the assembly and activity of telomerase RNP with TERT. In vivo reconstitution methods will be combined with in vitro and in vivo activity assays to define TER motif functions in the catalytic cycle. The physiological specificity of RNA and protein domain interactions within the active RNP will be established. The long-term goal of these studies is to understand telomerase RNP assembly, catalytic activation, and cellular regulation in normal cells and disease and to exploit this understanding for improvement of human health.

Public Health Relevance

Understanding the biochemical specificity of telomerase biogenesis and catalytic activation in human somatic cells and cancer cells will generate opportunities for clinical manipulation of telomerase to reduce cancer growth or enhance tissue renewal. In addition, therapies can be designed for patients with bone marrow failure syndromes arising from telomerase deficiency.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL079585-08
Application #
8463827
Study Section
Cellular Mechanisms in Aging and Development Study Section (CMAD)
Program Officer
Qasba, Pankaj
Project Start
2004-09-30
Project End
2014-04-30
Budget Start
2013-05-01
Budget End
2014-04-30
Support Year
8
Fiscal Year
2013
Total Cost
$361,677
Indirect Cost
$126,057
Name
University of California Berkeley
Department
Biochemistry
Type
Schools of Arts and Sciences
DUNS #
124726725
City
Berkeley
State
CA
Country
United States
Zip Code
94704
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Katibah, George E; Lee, Ho Jun; Huizar, John P et al. (2013) tRNA binding, structure, and localization of the human interferon-induced protein IFIT5. Mol Cell 49:743-50
Robart, Aaron R; Collins, Kathleen (2011) Human telomerase domain interactions capture DNA for TEN domain-dependent processive elongation. Mol Cell 42:308-18
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Collins, Kathleen (2008) Physiological assembly and activity of human telomerase complexes. Mech Ageing Dev 129:91-8
Fu, Dragony; Collins, Kathleen (2007) Purification of human telomerase complexes identifies factors involved in telomerase biogenesis and telomere length regulation. Mol Cell 28:773-85
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Fu, Dragony; Collins, Kathleen (2006) Human telomerase and Cajal body ribonucleoproteins share a unique specificity of Sm protein association. Genes Dev 20:531-6