Human telomerase contains evolutionarily conserved catalytic and structural subunits

Abstract

We have cloned and characterized a human gene encoding TP2 (telomerase-associated protein 2), a protein with similarity to reverse transcriptases and the catalytic telomerase subunits from Saccharomyces cerevisiae and Euplotes aediculatus. Indirect immunofluorescence revealed that TP2 was localized to the nucleus. Using antibodies to endogenous and epitope-tagged TP2, we found that TP2 was associated specifically with human telomerase activity and the recently identified telomerase-associated protein TP1. Mutation of conserved residues within the reverse transcriptase domain of TP2 severely reduced associated telomerase activity. These results suggest that telomerase is an evolutionarily conserved multisubunit complex composed of both structural and catalytic subunits.

Telomerase reverse transcriptase gene is a direct target of c-Myc but is not functionally equivalent in cellular transformation

“…This notion is supported by the observation that TERT transcripts are low or undetectable in most human primary somatic cells and tissues, but readily observable in the same cell or tissue type following neoplastic transformation (Nakamura et al, 1997;Meyerson et al, 1997). Moreover, in approximately 90% of all tumors, telomerase activity (Kim et al, 1994) as well as TERT expression (Nakamura et al, 1997;Meyerson et al, 1997;Harrington et al, 1997;Kilian et al, 1997;Nakayama et al, 1998) are detected. Together, these ®ndings are consistent with the hypothesis that either activation of oncogene or loss of tumor suppressor function serves to override the strict repression of TERT in primary somatic cells.…”

“…Growth beyond the replicative senescence checkpoint (Hay¯ick limit) correlates well with genetic lesions that interfere with one or more key cellular mortality pathways, most prominently Myc, Rb and/or p53 Wright and Shay, 1995). Studies addressing the relationship between telomere length, telomerase regulation and replicative capacity have established a critical role for the telomerase catalytic protein component or TERT (for Telomerase Reverse Transcriptase) (Bodnar et al, 1998;Vaziri and Benchimol, 1998;Nakamura et al, 1997;Meyerson et al, 1997;Harrington et al, 1997;Kilian et al, 1997;Nakayama et al, 1998) in immortalization. Speci®cally, normal human somatic cells can acquire the ability to maintain telomeres and replicate well beyond the Hay¯ick limit by stable enforced expression of TERT (Bodnar et al, 1998;Vaziri and Benchimol, 1998).…”

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

“…Telomeres consist of lengthy G-rich simple repeat sequences that are synthesized de novo by a specialized reverse transcriptase known as telomerase (Greider and Blackburn, 1985;Yu et al, 1990;Singer and Gottschling, 1994). The telomerase core enzyme consists of an RNA component and a polypeptide that bears classical structural motifs and functional activities of a reverse transcriptase Nakamura et al, 1997Nakamura et al, , 1998Meyerson et al, 1997;Harrington et al, 1997;Kilian et al, 1997;. As conventional DNA-dependent DNA polymerases fail to fully replicate the ends of chromosomes, telomerase has evolved to serve as the primary means by which eukaryotic cells maintain telomere length with each cell division cycle.…”

“…The human telomerase reverse transcriptase protein (previously hTRT, now known as hTERT) has recently been cloned by Nakamura et al (1997) and by others under di erent names (hEST2, hTLP2, hTCS1, hTRT) (Meyerson et al, 1997;Harrington et al, 1997;Kilian et al, 1997;Nakayama et al, 1998). These studies, using primary and immortalized human cell lines, have established that an additional level of telomerase activity regulation is achieved through mechanisms governing expression of hTERT Nakamura et al, 1997Nakamura et al, , 1998Meyerson et al, 1997;Harrington et al, 1997;Kilian et al, 1997). In this study, we have isolated and characterized the mouse ortholog of hTERT with the goals of understanding the regulation of telomerase activity in normal and neoplastic processes in the mouse, providing insights into the immortalization behavior of mouse and human cells, and characterizing the catalytic activities of the mouse protein.…”

Molecular interactions between telomerase and the tumor suppressor protein p53 in vitro

“…The protein subunits of telomerase include telomerase reverse transcriptase (TERT) and telomerase associated protein 1 (TEP1). TERT is the catalytic subunit of telomerase Harrington et al, 1997b;Kilian et al, 1997;Lingner and Cech, 1996;Lingner et al, 1997;Meyerson et al, 1997;Nakamura et al, 1997;Nakayama et al, 1998), whereas TEP1 has been shown to co-purify with telomerase activity and bind to both telomerase RNA and TERT (Harrington et al, 1997a,b;Nakayama et al, 1997).…”