Our long-term goal is to determine the mechanisms of telomerase regulation during development. The hTERT gene, which encodes the limiting subunit of human telomerase, is primarily regulated at the level of transcription. It is highly expressed in pluripotent stem cells, but stringently repressed in most adult somatic cells. Despite intensive investigation in the past decade, mechanisms of its repression, including cis-regulatory elements and trans-acting factors remain to be elucidated. We previously reported that the endogenous hTERT locus was embedded in a condensed chromatin domain in many somatic cells, while such a domain did not exist in the less repressed mouse TERT gene. Consistent with the vital role of chromatin in its tight regulation, we also found that an episomal hTERT locus in human fibroblasts was not subjected to repression, whereas a chromosomally integrated hTERT locus recapitulated its native regulation. Thus, we hypothesize that 1) the interplay between distal elements and core promoter in their native chromatin context is important for hTERT repression;and 2) partial loss of this repression leads to hTERT transcription during cellular immortalization. To study the mechanisms of hTERT repression, we developed a novel technical platform, the recombinase-mediated BAC targeting or RMBT method, for targeted integration of single-copy BAC reporters into specified chromosomal sites. Using this technique, we demonstrated that chromosomal integration of a BAC construct containing the hTERT locus resulted in the establishment of a surrogate chromatin setting in which the hTERT promoter was tightly repressed and recapitulated its endogenous gene in human fibroblasts. In this application, we plan to pursue the following specific aims: 1) Delineate cis elements involved in hTERT repression in human fibroblasts. 2) Identify and characterize protein factors involved in hTERT repression in human fibroblasts. 3) Determine cis elements that confer humanized regulation of the mTERT gene in mESCs.

Public Health Relevance

Telomeres are ends of linear chromosomes and essential for long-term cell proliferation and survival. Telomerase, the enzyme that elongates telomeres, plays an important role in cancers and aging-related diseases. This grant application is proposed to determine the mechanisms of telomerase regulation in human somatic cells.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Cellular Mechanisms in Aging and Development Study Section (CMAD)
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Carter, Anthony D
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Pennsylvania State University
Schools of Medicine
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Zhang, Fan; Cheng, De; Wang, Shuwen et al. (2016) Human Specific Regulation of the Telomerase Reverse Transcriptase Gene. Genes (Basel) 7:
Yaswen, Paul; MacKenzie, Karen L; Keith, W Nicol et al. (2015) Therapeutic targeting of replicative immortality. Semin Cancer Biol 35 Suppl:S104-28
Ma, Yanchun; Hao, Sijie; Wang, Shuwen et al. (2015) A Combinatory Strategy for Detection of Live CTCs Using Microfiltration and a New Telomerase-Selective Adenovirus. Mol Cancer Ther 14:835-43
Cheng, De; Zhao, Yuanjun; Wang, Shuwen et al. (2015) Human Telomerase Reverse Transcriptase (hTERT) Transcription Requires Sp1/Sp3 Binding to the Promoter and a Permissive Chromatin Environment. J Biol Chem 290:30193-203
Block, Keith I; Gyllenhaal, Charlotte; Lowe, Leroy et al. (2015) Designing a broad-spectrum integrative approach for cancer prevention and treatment. Semin Cancer Biol 35 Suppl:S276-304
Zhao, Yuanjun; Cheng, De; Wang, Shuwen et al. (2014) Dual roles of c-Myc in the regulation of hTERT gene. Nucleic Acids Res 42:10385-98
Zhao, Yuanjun; Wang, Shuwen; Zhu, Jiyue (2011) A multi-step strategy for BAC recombineering of large DNA fragments. Int J Biochem Mol Biol 2:199-206
Jia, Wenwen; Wang, Shuwen; Horner, James W et al. (2011) A BAC transgenic reporter recapitulates in vivo regulation of human telomerase reverse transcriptase in development and tumorigenesis. FASEB J 25:979-89
Zhu, Jiyue; Zhao, Yuanjun; Wang, Shuwen (2010) Chromatin and epigenetic regulation of the telomerase reverse transcriptase gene. Protein Cell 1:22-32
Wang, Shuwen; Hu, Chunguang; Zhu, Jiyue (2010) Distinct and temporal roles of nucleosomal remodeling and histone deacetylation in the repression of the hTERT gene. Mol Biol Cell 21:821-32

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