Specificity and Stoichiometry of Subunit Interactions in the Human Telomerase Holoenzyme Assembled <i>In Vivo</i>

Egan, Emily D.; Collins, Kathleen

doi:10.1128/mcb.00151-10

Cited by 97 publications

(105 citation statements)

References 50 publications

(95 reference statements)

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“…5). This strongly supports a similar TR sno-/ scaRNA biogenesis pathway and 3 ′ -end processing mechanism between vertebrate and echinoderm TRs (Jády et al 2004;Egan and Collins 2010). Additionally, the presence of a CAB box in the apical loop of the P8 helix in the echinoderm H/ACA domain indicates binding by a homolog of the vertebrate TCAB1 protein for Cajal body localization (Venteicher et al 2009).…”

Section: Discussionsupporting

confidence: 62%

Structure and function of echinoderm telomerase RNA

Podlevsky

Chen

2015

RNA

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Telomerase is a ribonucleoprotein (RNP) enzyme that requires an integral telomerase RNA (TR) subunit, in addition to the catalytic telomerase reverse transcriptase (TERT), for enzymatic function. The secondary structures of TRs from the three major groups of species, ciliates, fungi, and vertebrates, have been studied extensively and demonstrate dramatic diversity. Herein, we report the first comprehensive secondary structure of TR from echinoderms-marine invertebrates closely related to vertebratesdetermined by phylogenetic comparative analysis of 16 TR sequences from three separate echinoderm classes. Similar to vertebrate TR, echinoderm TR contains the highly conserved template/pseudoknot and H/ACA domains. However, echinoderm TR lacks the ancestral CR4/5 structural domain found throughout vertebrate and fungal TRs. Instead, echinoderm TR contains a distinct simple helical region, termed eCR4/5, that is functionally equivalent to the CR4/5 domain. The urchin and brittle star eCR4/5 domains bind specifically to their respective TERT proteins and stimulate telomerase activity. Distinct from vertebrate telomerase, the echinoderm TR template/pseudoknot domain with the TERT protein is sufficient to reconstitute significant telomerase activity. This gain-of-function of the echinoderm template/pseudoknot domain for conferring telomerase activity presumably facilitated the rapid structural evolution of the eCR4/5 domain throughout the echinoderm lineage. Additionally, echinoderm TR utilizes the template-adjacent P1.1 helix as a physical template boundary element to prevent nontelomeric DNA synthesis, a mechanism used by ciliate and fungal TRs. Thus, the chimeric and eccentric structural features of echinoderm TR provide unparalleled insights into the rapid evolution of telomerase RNP structure and function.

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Section: Discussionsupporting

confidence: 62%

Structure and function of echinoderm telomerase RNA

Podlevsky

Chen

2015

RNA

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“…TCAB1 is an RNA chaperone that binds to RNA molecules via a 4-nucleotide motif termed the CAB box and targets these molecules to Cajal bodies. This protein was reported to interact with telomerase via the hTR CAB box but also through a direct interaction with dyskerin (11,34,35). TCAB1 has been shown to be necessary for the delivery of endogenous telomerase to telomeres in HeLa cells in S phase (35).…”

Section: Methodsmentioning

confidence: 99%

“…A mutation in the CAB box of hTR (G to C at nucleotide position 414) was reported to disrupt the ability of TCAB1 to interact with hTR (11). We constructed this mutant to determine whether TCAB1 localization to the telomere is dependent on its interaction with telomerase.…”

Section: If/fish Experiments On Cells Treated With Control or Tcab1mentioning

confidence: 99%

Telomerase Recruitment Requires both TCAB1 and Cajal Bodies Independently

Stern

Zyner

Pickett

et al. 2012

Molecular and Cellular Biology

107

123

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The ability of most cancer cells to grow indefinitely relies on the enzyme telomerase and its recruitment to telomeres. In human cells, recruitment depends on the Cajal body RNA chaperone TCAB1 binding to the RNA subunit of telomerase (hTR) and is also thought to rely on an N-terminal domain of the catalytic subunit, hTERT. We demonstrate that coilin, an essential structural component of Cajal bodies, is required for endogenous telomerase recruitment to telomeres but that overexpression of telomerase can compensate for Cajal body absence. In contrast, recruitment of telomerase was sensitive to levels of TCAB1, and this was not rescued by overexpression of telomerase. Thus, although Cajal bodies are important for recruitment, TCAB1 has an additional role in this process that is independent of these structures. TCAB1 itself localizes to telomeres in a telomerase-dependent but Cajal body-independent manner. We identify a point mutation in hTERT that largely abolishes recruitment yet does not affect association of telomerase with TCAB1, suggesting that this region mediates recruitment by an independent mechanism. Our results demonstrate that telomerase has multiple independent requirements for recruitment to telomeres and that the function of TCAB1 is to directly transport telomerase to telomeres.T elomeres are protein-nucleic acid structures at the ends of linear chromosomes, which protect the DNA termini from degradation and inappropriate processing as damaged DNA. Despite this protective role, telomere shortening still occurs in most normal human somatic cells during DNA replication due to inherent limitations in the replication machinery, and this shortening is the basis of cellular senescence (5,14,28). Approximately 85 to 90% of human cancers counteract this shortening and avoid senescence by activating the ribonucleoprotein telomerase to extend telomeres (13,30). Active telomerase consists of three core components essential for activity (7): hTERT, the reverse transcriptase catalytic subunit (26); hTR, the RNA subunit, used as a cognate template for reverse transcription of telomeric DNA (12); and the protein dyskerin, which is essential for hTR stability (23). The extension of telomeres by telomerase is preceded by a complex series of events involving enzyme biogenesis, transport from sites of enzyme assembly, and trafficking of telomerase in the nucleus at the appropriate phase in the cell cycle. The factors involved in these steps and how these stages are integrated are not fully understood.Regions of hTERT have been identified that are essential for the enzyme to extend the life span of untransformed cells but which are dispensable for enzyme function ex vivo (2, 4). These regions, which separate the in vivo functionality of the enzyme from ex vivo telomerase activity, were termed DAT for "dissociates the activities of telomerase." A potential explanation for this observation is a failure of the enzyme to be transported or recruited to telomeres. Fusion of the single-stranded telomeric DNA binding protein...

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“…In the mature telomerase RNP, each H/ACA RNA hairpin assembles with a set of four proteins: the pseudouridylase dyskerin, NOP10, NHP2, and GAR1 (Fig. 5;Collins 2008;Egan and Collins 2010). As in a canonical H/ACA RNA, the hTR H/ ACA motif is required for hTR accumulation in vivo as a biologically stable RNP (Mitchell et al 1999;Mitchell and Collins 2000;Fu and Collins 2003).…”

Section: Human Telomerase Human Telomerase Rna Structurementioning

confidence: 99%

“…Cellular depletion of TCAB1/WDR79 does not affect hTR accumulation but does reduce RNP association with Cajal bodies and telomeres and results in telomere shortening (Venteicher et al 2009;Zhong et al 2011). TCAB1/WDR79 associates with overexpressed hTR partly independent of the CAB box, and, unlike the CAB box, is essential for telomere elongation (Cristofari et al 2007;Fu and Collins 2007;Egan and Collins 2010;Stern et al 2012). The significance of TCAB1/WDR79 for telomere maintenance is highlighted by the discovery of TCAB1/WDR79 gene mutations that cause dyskeratosis congenita (Zhong et al 2011), a human disease of telomerase deficiency (Armanios 2009;Savage and Bertuch 2010).…”

Section: Human Telomerase Rnp Maturationmentioning

confidence: 99%

Biogenesis of telomerase ribonucleoproteins

Egan

Collins

2012

RNA

Self Cite

157

168

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Telomerase adds simple-sequence repeats to the ends of linear chromosomes to counteract the loss of end sequence inherent in conventional DNA replication. Catalytic activity for repeat synthesis results from the cooperation of the telomerase reverse transcriptase protein (TERT) and the template-containing telomerase RNA (TER). TERs vary widely in sequence and structure but share a set of motifs required for TERT binding and catalytic activity. Species-specific TER motifs play essential roles in RNP biogenesis, stability, trafficking, and regulation. Remarkably, the biogenesis pathways that generate mature TER differ across eukaryotes. Furthermore, the cellular processes that direct the assembly of a biologically functional telomerase holoenzyme and its engagement with telomeres are evolutionarily varied and regulated. This review highlights the diversity of strategies for telomerase RNP biogenesis, RNP assembly, and telomere recruitment among ciliates, yeasts, and vertebrates and suggests common themes in these pathways and their regulation.

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Specificity and Stoichiometry of Subunit Interactions in the Human Telomerase Holoenzyme Assembled In Vivo

Cited by 97 publications

References 50 publications

Structure and function of echinoderm telomerase RNA

Structure and function of echinoderm telomerase RNA

Telomerase Recruitment Requires both TCAB1 and Cajal Bodies Independently

Biogenesis of telomerase ribonucleoproteins

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