Molecular mechanisms of telomerase regulation in human T lymphocytes

博士 === 長庚大學 === 基礎醫學研究所 === 95 === Telomerase, a specialized reverse transcriptase that directs the synthesis of telomeric repeats at the ends of chromosome, plays an important role in the maintenance of telomere length and replicative senescence. Human telomerase is known to consist of an RNA compo...

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Bibliographic Details
Main Authors: Wei-Yun Sheng, 盛瑋芸
Other Authors: Tzu-Chien Van Wang
Format: Others
Language:zh-TW
Published: 2007
Online Access:http://ndltd.ncl.edu.tw/handle/21013271185826144451
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Summary:博士 === 長庚大學 === 基礎醫學研究所 === 95 === Telomerase, a specialized reverse transcriptase that directs the synthesis of telomeric repeats at the ends of chromosome, plays an important role in the maintenance of telomere length and replicative senescence. Human telomerase is known to consist of an RNA component (hTR), a reverse transcriptase (hTERT) and several associated proteins. Among these components, hTERT represents the key regulator of telomerase expression in human cells. Telomerase activity is repressed in most human somatic cells, but is activated in germ cells and in cells with high proliferative capacity, such as stem cells, active lymphocytes, and cancer cells. Exactly how telomerase is controlled in different types of human cells remains largely unknown. In this study, the mechanism of telomerase regulation in activated T cells was examined by stimulation with phytohemagglutinin (PHA). Here, we present evidence that the essential role of protein kinase C (PKC) in the activation of telomerase activity is attributed both to its role in the transcriptional upregulation of hTERT expression and also to its participation of post-transcriptional phosphorylation of telomerase proteins, demonstrating for the first time for an involvement of PKC in the transcriptional regulation of hTERT expression. Of the several PKC-mediated singalings, we show that the upregulation of hTERT expression is mediated through NF-κB pathway, but not through MAPK pathway. Studies of promoter occupancy in vivo, however, revealed that NF-κB did not function by direct binding to the hTERT promoter. Rather, NF-κB appears to transactivate the expression of cMyc, which in turn upregulates the expression of hTERT. Evidences supporting for such a postulate are presented. Additionally, we have employed proteomic approach to search for the regulators that participate in the control of telomerase activity in T cells. Of the differentially expressed proteins identified in activated T cells, 26 proteins were down-regulated while 20 proteins were up-regulated. One of the upregulated proteins, GAPDH, was further investigated for its potential role in controlling telomerase activity, since this house keeping gene, in addition to its role in glycolysis, is also known to function in apoptosis, proliferation, telomere protection, transcription, and DNA repair. Here, we show that several modified forms of GAPDH were detected only in the activated T cells and they were preferentially localized in the nucleus. Preliminary promoter occupancy studies have revealed that GAPDH could bind to both the hTERT and cMyc promoters. However, the significance of this GAPDH binding in the regulation of hTERT expression remains to be explored.