Human telomerase catalyzes nucleolytic primer cleavage

Huard, Sylvain; Autexier, Chantal

doi:10.1093/nar/gkh546

Cited by 27 publications

(29 citation statements)

References 46 publications

(92 reference statements)

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“…This set of assays were repeated two more times, and the Mn 2ϩ -dependent doublet was reproducibly observed in the WT but absent in the reticulocyte lysate-alone and D868N reactions. The smaller than ϩ1 product is presumably due to the nucleolytic cleavage activity of human telomerase (49,50). Such products are also evident in some yeast telomerase reactions (e.g., lane 10 in Fig.…”

Section: Discussionmentioning

confidence: 81%

Telomerase can act as a template- and RNA-independent terminal transferase

Lue

Bosoy

Moriarty

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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Telomerase is a special reverse transcriptase that extends one strand of the telomere repeat by using a template embedded in an RNA subunit. Like other polymerases, telomerase is believed to use a pair of divalent metal ions (coordinated by a triad of aspartic acid residues) for catalyzing nucleotide addition. Here we show that, in the presence of manganese, both yeast and human telomerase can switch to a template-and RNA-independent mode of DNA synthesis, acting in effect as a terminal transferase. Even as a terminal transferase, yeast telomerase retains a species-dependent preference for GT-rich, telomere-like DNA on the 5 end of the substrate. The terminal transferase activity of telomerase may account for some of the hitherto unexplained effects of telomerase overexpression on cell physiology.reverse transcriptase ͉ telomere ͉ divalent metal ion T elomerase is a ribonucleoprotein responsible for the synthesis of one strand of the telomere terminal repeat. The catalytic core of telomerase consists minimally of two components: an RNA in which the template is embedded (named TLC1 in the budding yeast Saccharomyces cerevisiae), and a reverse transcriptase (RT)-like protein that mediates catalysis (named TERT in general and Est2p in yeast) (1-4). Telomerase RNAs from different organisms are divergent in sequence but share conserved secondary structural elements (5, 6). Many mutations in nontemplate regions of telomerase RNA reduced enzyme activity, suggesting that these regions contribute important catalytic functions [although the precise nature of the contribution(s) is not clear] (7-9). Other RNA structures act to define the boundary of the template segment that supports reverse transcription (10, 11). Thus, the RNA subunit serves multiple essential roles in the course of a normal telomerase reaction. The TERT protein is well conserved in evolution and comprises a central RT domain that is flanked on both the N-and C-terminal side by telomerase-specific motifs (4, 12, 13). Mutational analysis indicates that these motifs are likely to mediate binding to telomeric DNA and telomerase RNA. Direct recognition of telomeric DNA by TERT is believed to be sequence-dependent and to allow telomerase to catalyze the addition of multiple repeats without dissociation from the DNA (13,14).In unicellular organisms, telomerase is constitutively active and required for the long-term proliferation of cells. In some multicellular organisms, including humans, telomerase is repressed in normal somatic tissues but activated in cancer cells, and is believed to promote tumor growth (15). Although the two core components of telomerase are generally assumed to act in concert to replenish telomeres, there is increasing evidence that the TERT protein can have physiologic effects that are independent of telomere length and telomerase . For instance, in mice, TERT overexpression in the absence of telomerase RNA was reported to have an inhibitory effect on tumorigenesis and wound healing (20). The mechanisms for such effects are currently no...

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Section: Discussionmentioning

confidence: 81%

Telomerase can act as a template- and RNA-independent terminal transferase

Lue

Bosoy

Moriarty

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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“…However, previous studies suggest that a nuclease activity associated with the L1 RT domain may be important for TPRT (60). Similarly, although telomerase lacks an apparent EN domain, it is associated with a nuclease activity that can process telomeric adapter sequences before their use as substrates for telomere addition (69)(70)(71). It is tempting to speculate that the occult L1 nuclease activity may process dysfunctional telomeres in vivo before they can serve as substrates for ENi retrotransposition.…”

Section: Discussionmentioning

confidence: 98%

Similarities between long interspersed element-1 (LINE-1) reverse transcriptase and telomerase

Kopera¹,

Moldovan²,

Morrish³

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Long interspersed element-1 (LINE-1 or L1) retrotransposons encode two proteins (ORF1p and ORF2p) that contain activities required for conventional retrotransposition by a mechanism termed target-site primed reverse transcription. Previous experiments in XRCC4 or DNA protein kinase catalytic subunit-deficient CHO cell lines, which are defective for the nonhomologous endjoining DNA repair pathway, revealed an alternative endonuclease-independent (ENi) pathway for L1 retrotransposition. Interestingly, some ENi retrotransposition events in DNA protein kinase catalytic subunit-deficient cells are targeted to dysfunctional telomeres. Here we used an in vitro assay to detect L1 reverse transcriptase activity to demonstrate that wild-type or endonuclease-defective L1 ribonucleoprotein particles can use oligonucleotide adapters that mimic telomeric ends as primers to initiate the reverse transcription of L1 mRNA. Importantly, these ribonucleoprotein particles also contain a nuclease activity that can process the oligonucleotide adapters before the initiation of reverse transcription. Finally, we demonstrate that ORF1p is not strictly required for ENi retrotransposition at dysfunctional telomeres. Thus, these data further highlight similarities between the mechanism of ENi L1 retrotransposition and telomerase.L ong interspersed element-1 sequences (LINE-1s or L1s) are abundant non-long terminal repeat (non-LTR) retrotransposons that constitute approximately one-sixth (i.e., ≈17%) of human nuclear DNA (1). An estimated 80-100 full-length, retrotransposition competent L1s (RC-L1s) are present in a typical diploid human genome, and a small number, termed "hot L1s" exhibit high retrotransposition efficiencies in cultured human cells (2). Human RC-L1s are ≈6 kb (3, 4) and encode two proteins (ORF1p and ORF2p) required for retrotransposition (5). ORF1p is a 40-kDa protein (6) with RNA binding (7-12) and nucleic acid chaperone activities (13-15). ORF2p is a 150-kDa protein (16, 17) with endonuclease (EN) (18,19) and reverse transcriptase (RT) (20, 21) activities.The mobilization of RC-L1s can be mutagenic (22); germ line and, less often, somatic L1 insertions have led to ≈65 sporadic cases of disease in humans (reviewed in ref. 23). ORF1p and/or ORF2p also can act in trans to mobilize short interspersed elements [e.g., Alu (24) and SINE-VNTR-Alu (25) elements], certain noncoding RNAs [e.g., U6 snRNA and small nucleolar RNAs (24, 26-29)], and some cellular mRNAs, which leads to the formation of processed pseudogenes (30-32). In total, these trans retrotransposition events account for at least an additional 10% of human DNA (1). Moreover, several recent studies have further demonstrated that L1-mediated retrotransposition events are responsible for a significant proportion of interindividual genetic variation in the human population (33-39) and may cause intraindividual variation in the mammalian nervous system (40, 41). L1 retrotransposition likely occurs by a mechanism termed target-site primed reverse transcription (TPRT) (42)...

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“…ALT cells can efficiently maintain telomere length in the absence of telomerase; however, little is known about the maintenance of telomere end structures by the ALT mechanism. Telomerase is reported to associate with specific exonuclease activities (Huard and Autexier, 2004;Oulton and Harrington, 2004); following telomere repeat synthesis, this nuclease activity could contribute to the correct and efficient generation of telomeric DNA end structure. The ensured timely resolution and reformation of the higher-order telomere loop structures predict the efficient progression of the cell cycle through G2 and mitosis phases of the cell cycle, illustrated by our cell cycle analysis data.…”

Section: Discussionmentioning

confidence: 99%

Telomerase promotes efficient cell cycle kinetics and confers growth advantage to telomerase-negative transformed human cells

Fleisig

Wong

2011

Oncogene

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Constitutive telomerase activity maintains telomere length and confers immortal phenotypes to human cancers. The prevalence of telomerase, rather than a homologous recombination-based mechanism, in telomere length maintenance suggests that telomerase also has auxiliary roles in tumorigenesis. Here, we investigate growth advantages provided by the telomerase enzyme in oncogene-transformed human cells that do not require telomerase activity for telomere length control. Our data suggest that in oncogene-transformed cells, telomerase activity accelerates cell growth kinetics in a cell cycle phase-specific manner and promotes anchorage-independent growth. Coculture experiments demonstrated that this growth advantage conferred by telomerase activity is not due to increased cellular cross-talk. Growth advantages provided by telomerase required all functional aspects of the enzyme. Dissociation-of-activity-in-telomerase mutants and other functionally defective versions of telomerase were unable to promote oncogene-transformed cell growth, suggesting that canonical telomerase activities may be involved. We conclude that telomerase provides advantages to oncogene-transformed human cells, thereby supporting the development of telomerasebased anticancer chemotherapies targeting these growthpromoting effects.

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Human telomerase catalyzes nucleolytic primer cleavage

Cited by 27 publications

References 46 publications

Telomerase can act as a template- and RNA-independent terminal transferase

Telomerase can act as a template- and RNA-independent terminal transferase

Similarities between long interspersed element-1 (LINE-1) reverse transcriptase and telomerase

Telomerase promotes efficient cell cycle kinetics and confers growth advantage to telomerase-negative transformed human cells

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