Telomeres, the nucleoprotein structures that cap chromosome ends, are maintained by telomerase, a multi-subunit enzyme complex. In settings of insufficient telomerase, including in aging human tissues, telomeres shorten with cell division. Telomerase subunits are mutated in certain human genetic diseases, such as dyskeratosis congenita, in which telomere shortening is accelerated and tissue progenitor cells are dysfunctional. The profound impairment of tissue progenitor cell function caused by telomere shortening in both human genetic syndromes and in knockout mouse models provides strong support for the hypothesis that telomere shortening in aging humans contributes to aspects of the aging phenotype. However, the precise mechanisms that underlie telomere shortening with aging and the specific approaches for blunting or reversing telomere shortening as a therapeutic strategy remain very poorly understood. Defining why telomeres shorten with advancing age and developing therapeutics to prevent such telomere shortening will require a much more complete understanding of telomerase. Although telomerase enzyme extracted from human cancer cells behaves as a very large complex, only three components of the telomerase holoenzyme were identified until recently: TERT, the telomerase reverse transcriptase, TERC, the telomerase RNA component, and dyskerin, a TERC-binding protein. To address this critical area in aging research, we have purified telomerase complexes from human cells and identified new telomerase-associated proteins by mass spectrometry. Through this approach, we identified a new component of the telomerase holoenzyme, termed TCAB1, for Telomerase Cajal Body Protein 1. TCAB1 associates with all active telomerase enzyme and associates with all TERC in human cell extracts. Importantly, TCAB1 is specifically found in Cajal bodies, subnuclear foci that serve as sites of ribonucleoprotein complex modification or assembly. Cajal Bodies were recently shown to be sites of telomerase localization and TCAB1 is the first Cajal body-specific protein component of the holoenzyme. Depletion of TCAB1 in human cells using RNA interference prevents telomerase from localizing in Cajal bodies and leads to profound telomere shortening. Thus, TCAB1 is a unique and essential telomerase component required for telomerase trafficking and telomere synthesis. We plan the following: (1) To study the biochemistry of TCAB1 in the telomerase complex and in scaRNA complexes (2) To study the requirement for TCAB1 in telomerase function through genetic approaches in cultured cells and through analysis of the TCAB1 protein complex (3) To understand the role of TCAB1 in telomerase function and stem cell regulation in vivo.

Public Health Relevance

Aging is a process during which fitness diminishes over time, resulting in impaired tissue function and reduced responses to stress. Aging, and the diseases to which aged individuals succumb, represent an enormous public health problem, particularly with the aging of the population in the United States and in other industrialized nations. The molecular changes that characterize and cause aging and aging-related disease are just being unraveled. One such change is the shortening of telomeres, the caps that protect the ends of our chromosomes. This proposal will study a new component of the enzyme telomerase that is required for maintaining telomeres. An improved understanding of telomerase is crucial for designing therapies that will delay or reverse certain aspects of aging.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Research Project (R01)
Project #
5R01AG033747-03
Application #
8220800
Study Section
Cellular Mechanisms in Aging and Development Study Section (CMAD)
Program Officer
Guo, Max
Project Start
2010-02-01
Project End
2015-01-31
Budget Start
2012-02-01
Budget End
2013-01-31
Support Year
3
Fiscal Year
2012
Total Cost
$322,448
Indirect Cost
$125,402
Name
Stanford University
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
009214214
City
Stanford
State
CA
Country
United States
Zip Code
94305
Batista, Luis F Z; Artandi, Steven E (2013) Understanding telomere diseases through analysis of patient-derived iPS cells. Curr Opin Genet Dev 23:526-33
Shkreli, Marina; Sarin, Kavita Y; Pech, Matthew F et al. (2012) Reversible cell-cycle entry in adult kidney podocytes through regulated control of telomerase and Wnt signaling. Nat Med 18:111-9
Zhong, Franklin; Savage, Sharon A; Shkreli, Marina et al. (2011) Disruption of telomerase trafficking by TCAB1 mutation causes dyskeratosis congenita. Genes Dev 25:11-6
Batista, Luis F Z; Pech, Matthew F; Zhong, Franklin L et al. (2011) Telomere shortening and loss of self-renewal in dyskeratosis congenita induced pluripotent stem cells. Nature 474:399-402