POLIE suppresses telomerase-mediated telomere G-strand extension and helps ensure proper telomere C-strand synthesis in trypanosomes

Rabbani, M A G; Tonini, Maiko Luis; Afrin, Marjia; Li, Bibo

doi:10.1093/nar/gkac023

Cited by 7 publications

(36 citation statements)

References 87 publications

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“…DNA double strand breaks (DSBs) at the active VSG vicinity has been shown to be a potent trigger for VSG switching (Alsford et al, 2009;Boothroyd et al, 2009;Glover et al, 2013;Li, 2021), as homology directed DNA recombination (HDR) repairs DSBs most accurately (Jasin and Rothstein, 2013;Haber, 2018;Wright et al, 2018), and HDR is very active in T. brucei (McCulloch and Barry, 1999;Robinson et al, 1999;Conway et al, 2002a;Barnes and McCulloch, 2007;Glover et al, 2008;Marin et al, 2018). Consistently, for known essential T. brucei telomere proteins, a transient depletion of the protein leads to an increased amount of DNA breaks at the telomere and subtelomere and more frequent VSG switching, indicating that these telomere proteins help maintain the telomere stability and suppress VSG switching (Jehi et al, 2014a;Jehi et al, 2014b;Jehi et al, 2016;Nanavaty et al, 2017;Afrin et al, 2020a;Afrin et al, 2020b;Saha et al, 2021;Rabbani et al, 2022;Gaurav et al, 2023). Furthermore, in telomerase null cells where the active ES-adjacent telomere is extremely short, a significant increase in the VSG switching rate is observed (Hovel-Miner et al, 2012).…”

Section: Introductionmentioning

confidence: 80%

Telomere maintenance in African trypanosomes

2023

Front. Mol. Biosci.

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Telomere maintenance is essential for genome integrity and chromosome stability in eukaryotic cells harboring linear chromosomes, as telomere forms a specialized structure to mask the natural chromosome ends from DNA damage repair machineries and to prevent nucleolytic degradation of the telomeric DNA. In Trypanosoma brucei and several other microbial pathogens, virulence genes involved in antigenic variation, a key pathogenesis mechanism essential for host immune evasion and long-term infections, are located at subtelomeres, and expression and switching of these major surface antigens are regulated by telomere proteins and the telomere structure. Therefore, understanding telomere maintenance mechanisms and how these pathogens achieve a balance between stability and plasticity at telomere/subtelomere will help develop better means to eradicate human diseases caused by these pathogens. Telomere replication faces several challenges, and the “end replication problem” is a key obstacle that can cause progressive telomere shortening in proliferating cells. To overcome this challenge, most eukaryotes use telomerase to extend the G-rich telomere strand. In addition, a number of telomere proteins use sophisticated mechanisms to coordinate the telomerase-mediated de novo telomere G-strand synthesis and the telomere C-strand fill-in, which has been extensively studied in mammalian cells. However, we recently discovered that trypanosomes lack many telomere proteins identified in its mammalian host that are critical for telomere end processing. Rather, T. brucei uses a unique DNA polymerase, PolIE that belongs to the DNA polymerase A family (E. coli DNA PolI family), to coordinate the telomere G- and C-strand syntheses. In this review, I will first briefly summarize current understanding of telomere end processing in mammals. Subsequently, I will describe PolIE-mediated coordination of telomere G- and C-strand synthesis in T. brucei and implication of this recent discovery.

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Section: Introductionmentioning

confidence: 80%

Telomere maintenance in African trypanosomes

2023

Front. Mol. Biosci.

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“…The RNA component of T. brucei telomerase (TbTR) has a unique structure and sequence composition compared to higher eukaryotes (Sandhu et al, 2013;Podlevsky et al, 2016;Dey et al, 2021). Our recent study on TbTR suggests mechanistic differences in telomere maintenance between T. brucei and higher eukaryotes (Dey et al, 2021;Rabbani et al, 2022, underscoring the importance of investigating the functional interactome of T. brucei telomerase. Previous proteomic studies on ciliated single-cell protozoan Tetrahymena identified several RNA binding proteins, including p65 that copurifies with TR and TERT and promotes proper folding of TR for telomerase holoenzyme assembly and activity (Witkin and Collins, 2004;Berman et al, 2010;Singh et al, 2012;Upton et al, 2017;He et al, 2021).…”

Section: Introductionmentioning

confidence: 98%

“…In cells where the TERT protein has been deleted ( Tb TERT −/− ), extremely short telomeres adjacent to the active ES leads to an increase in VSG switching frequency ( Dreesen and Cross, 2006 ; Hovel-Miner et al, 2012 ). Telomeric binding proteins have also been shown to affect VSG silencing and switching ( Yang et al, 2009 ; Benmerzouga et al, 2013 ; Jehi et al, 2014 ; Jehi et al, 2016 ; Nanavaty et al, 2017 ; Afrin et al, 2020 ; Rabbani et al, 2022 ). Telomerase mediated telomere maintenance in T. brucei is required for the maintenance of subtelomeric VSG genes.…”

Section: Introductionmentioning

confidence: 99%

Proteomic analysis defines the interactome of telomerase in the protozoan parasite, Trypanosoma brucei

Davis

Reyes

Nitika

et al. 2023

Front. Cell Dev. Biol.

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Telomerase is a ribonucleoprotein enzyme responsible for maintaining the telomeric end of the chromosome. The telomerase enzyme requires two main components to function: the telomerase reverse transcriptase (TERT) and the telomerase RNA (TR), which provides the template for telomeric DNA synthesis. TR is a long non-coding RNA, which forms the basis of a large structural scaffold upon which many accessory proteins can bind and form the complete telomerase holoenzyme. These accessory protein interactions are required for telomerase activity and regulation inside cells. The interacting partners of TERT have been well studied in yeast, human, and Tetrahymena models, but not in parasitic protozoa, including clinically relevant human parasites. Here, using the protozoan parasite, Trypanosoma brucei (T. brucei) as a model, we have identified the interactome of T. brucei TERT (TbTERT) using a mass spectrometry-based approach. We identified previously known and unknown interacting factors of TbTERT, highlighting unique features of T. brucei telomerase biology. These unique interactions with TbTERT, suggest mechanistic differences in telomere maintenance between T. brucei and other eukaryotes.

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“…PolIE is a putative translesion polymerase localized at the nuclear periphery, and its depletion leads to deregulation of VSG expression and aberrant chromosome segregation. Furthermore, cells depleted of PolIE have longer 3’ overhangs, suggesting that PolIE is also involved in telomerase regulation (34).…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, cells depleted of PolIE have longer 3' overhangs, suggesting that PolIE is also involved in telomerase regulation (34).…”

Section: Introductionmentioning

confidence: 99%

TelAP2 links TelAP1 to the telomere complex inTrypanosoma brucei

Weisert,

Majewski,

Hartleb

et al. 2024

Preprint

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The extracellular parasite Trypanosoma brucei evades the immune system of the mammalian host by periodically exchanging its variant surface glycoprotein (VSG) coat. Hereby, only one VSG gene is transcribed from one of 15 subtelomeric so-called bloodstream form expression sites (BES) at any given timepoint, while all other BESs are silenced. VSG gene expression is altered by homologous recombination using a large VSG gene repertoire or by a so-called in situ switch, which activates a previously silent BES. Transcriptional activation, VSG switching and VSG silencing during developmental differentiation from the bloodstream form to the procyclic form present in the tsetse fly vector are tightly regulated. Due to their subtelomeric position, telomere-associated proteins are involved in the regulation of VSG expression. Three functional homologs of mammalian telomere complex proteins have been characterized thus far, and novel telomere-interacting proteins, such as telomere-associated protein 1 (TelAP1), have recently been identified. Here, we used mass spectrometry-based proteomics and interactomics approaches, telomere pull-down assays with recombinant material and immunofluorescence analysis to elucidate the interactions of 21 other putative TelAPs. We investigated the influence on VSG expression and showed that depletion of TelAPs does not ultimately lead to changes in VSG expression. Additionally, we examined the interaction patterns of four TelAPs with the TbTRF/TbTIF2/TbRAP1 telomere complex by reciprocal affinity purification. We further propose that TelAP1 interacts with Tb927.6.4330, now called TelAP2, and that TelAP1 depends on this interaction to form a complex with the telomeric proteins TbTRF, TbTIF2 and TbRAP1.

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POLIE suppresses telomerase-mediated telomere G-strand extension and helps ensure proper telomere C-strand synthesis in trypanosomes

Cited by 7 publications

References 87 publications

Telomere maintenance in African trypanosomes

Telomere maintenance in African trypanosomes

Proteomic analysis defines the interactome of telomerase in the protozoan parasite, Trypanosoma brucei

TelAP2 links TelAP1 to the telomere complex inTrypanosoma brucei

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