The RNA Component of Human Telomerase

Abstract

Eukaryotic chromosomes are capped with repetitive telomere sequences that protect the ends from damage and rearrangements. Telomere repeats are synthesized by telomerase, a ribonucleic acid (RNA)-protein complex. Here, the cloning of the RNA component of human telomerase, termed hTR, is described. The template region of hTR encompasses 11 nucleotides (5'-CUAACCCUAAC) complementary to the human telomere sequence (TTAGGG)n. Germline tissues and tumor cell lines expressed more hTR than normal somatic cells and tissues, which have no detectable telomerase activity. Human cell lines that expressed hTR mutated in the template region generated the predicted mutant telomerase activity. HeLa cells transfected with an antisense hTR lost telomeric DNA and began to die after 23 to 26 doublings. Thus, human telomerase is a critical enzyme for the long-term proliferation of immortal tumor cells.

Expression of mouse telomerase reverse transcriptase during development, differentiation and proliferation

“…TRAP activity was not seen with the mTERT mutant, mTERT-T, which is a truncated version of the polypeptide containing the ®rst 738 amino acids of mTERT, but lacking motifs B', C, D and E. These in vitro reconstitution studies demonstrate that the mTERT cDNA encodes telomerase RNA-dependent catalytic activity. Furthermore, mTERT and hTR can form a functional ribonucleoprotein complex despite species di erences between the telomerase RNAs, including a longer template domain for hTR (Feng et al, 1995;Blasco et al, 1995).…”

“…mTERT transcripts were broadly distributed at varying levels in the panel of postnatal tissues assayed. Speci®cally, mTERT was expressed most prominently in (i) adult organs with detectable telomerase activity (thymus) (Feng et al, 1995), (ii) high renewal and proliferative pro®les (intestine and testes), or (iii) signi®cant regenerative capacity (liver). The lung which continues to develop postnatally also showed moderate levels of mTERT expression.…”

“…Previous studies have established that the telomerase RNA component in mouse (mTR) or humans (hTR) is invariably present in telomerase-positive cells and tissues and that RNA component levels and telomerase activity are coordinately down-regulated in most physiological settings and developing tissues (Feng et al, 1995;Blasco et al, 1995). However, this correlation is not absolute as evidenced by the detection of telomerase RNA in cells and tissues lacking detectable telomerase activity (Feng et al, 1995;Blasco et al, 1995Blasco et al, , 1996Avilion et al, 1996).…”

“…However, this correlation is not absolute as evidenced by the detection of telomerase RNA in cells and tissues lacking detectable telomerase activity (Feng et al, 1995;Blasco et al, 1995Blasco et al, , 1996Avilion et al, 1996). Such ®ndings have indicated that the regulation of telomerase activity in some cases must involve mechanisms other than those modulating telomerase RNA gene expression.…”

mRNA quantification and clinical evaluation of telomerase reverse transcriptase subunit (hTERT) in intracranial tumours of patients in the island of Crete

“…Telomeres shorten progressively with each round of cell division as a result of the inability of DNA polymerases to replicate the 5 0 end of linear DNA, and erosion of these sequences beyond a critical point is thought to signal cell cycle arrest and entry into cellular senescence (O'Reilly et al, 1999). Telomerase is a ribonucleoprotein polymerase composed of an integral RNA component (hTR) (Feng et al, 1995) and several protein components, including the reverse transcriptase subunit human telomerase reverse transcriptase (hTERT) (Kilian et al, 1997;Nakayama et al, 1998). The RNA component hTR contains the template for the reverse transcription of telomeres, and hTERT is the reverse transcriptase that catalyses this reaction.…”