Differential regulation of telomerase activity by six telomerase subunits.
Telomerase is a specialized reverse transcriptase responsible for synthesizing telomeric DNA at the ends of chromosomes. Six subunits composing the telomerase complex have been cloned: hTR (human telomerase RNA), TEP1 (telomerase-associated protein 1), hTERT (human telomerase reverse transcriptase), hsp90 (heat shock protein 90), p23, and dyskerin. In this study, we investigated the role of each the telomerase subunit on the activity of telomerase. Through down- or upregulation of telomerase, we found that only hTERT expression changed proportionally with the level of telomerase activity. The other components, TEP1, hTR, hsp90, p23, and dyskerin remained at high and unchanged levels throughout modulation. In vivo and in vitro experiments with antisense oligonucleotides against each telomerase component were also performed. Telomerase activity was decreased or abolished by antisense treatment. To correlate clinical sample status, four pairs of normal and malignant tissues from patients with oral cancer were examined. Except for the hTERT subunit, which showed differential expression in normal and cancer tissues, all other components were expressed in both normal and malignant tissues. We conclude that hTERT is a regulatable subunit, whereas the other components are expressed more constantly in cells. Although hTERT has a rate-limiting effect on enzyme activity, the other telomerase subunits (hTR, TEP1, hsp90, p23, dyskerin) participated in full enzyme activity. We hypothesize that once hTERT is expressed, all other telomerase subunits can be assembled to form a highly active holoenzyme.
Chang
Joseph Tung-Chieh
JT
Department of Radiation Oncology, Chang Gung Memorial Hospital, Taoyuan, Taiwan.
Chen
Yin-Ling
YL
Yang
Huei-Ting
HT
Chen
Chi-Yuan
CY
Cheng
Ann-Joy
AJ
D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D018797:Cell Cycle Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D004268:DNA-Binding Proteins; D004790:Enzyme Induction / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D018922:HL-60 Cells / Q000166:cytology / Q000201:enzymology; D018841:HSP90 Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D006367:HeLa Cells / Q000166:cytology / Q000201:enzymology; D020035:Holoenzymes / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D019746:Intramolecular Oxidoreductases; D007624:KB Cells / Q000166:cytology / Q000201:enzymology; D046911:Macromolecular Substances; D051379:Mice; D018832:Molecular Chaperones / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D009062:Mouth Neoplasms / Q000201:enzymology / Q000473:pathology; D009363:Neoplasm Proteins / Q000737:chemistry / Q000378:metabolism; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology; D010750:Phosphoproteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D000071876:Prostaglandin-E Synthases; D021122:Protein Subunits; D012313:RNA / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D016601:RNA-Binding Proteins; D019098:Telomerase / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000201:enzymology
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C112148:DKC1 protein, human; D004268:DNA-Binding Proteins; D018841:HSP90 Heat-Shock Proteins; D020035:Holoenzymes; D046911:Macromolecular Substances; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D020319:Oligodeoxyribonucleotides, Antisense; D010750:Phosphoproteins; D021122:Protein Subunits; D016601:RNA-Binding Proteins; C104342:TEP1 protein, human; C498415:Tep1 protein, mouse; C422952:telomerase RNA; D012313:RNA; D019098:Telomerase; D019746:Intramolecular Oxidoreductases; C490849:PTGES3 protein, human; D000071876:Prostaglandin-E Synthases