Functional Diversity of Human Protection of Telomeres 1 Isoforms in Telomere Protection and Cellular Senescence

Yang, Qin; Zhang, Ran; Horikawa, Izumi; Fujita, Kaori; Afshar, Yalda; Kokko, Antti; Laiho, Päivi; Aaltonen, Lauri A.; Harris, Curtis C.

doi:10.1158/0008-5472.can-07-1390

Cited by 32 publications

(40 citation statements)

References 46 publications

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“…In agreement, TIFs are reduced in murine fibroblasts in which both POT1 genes are disrupted upon expression of human POT1 and TPP1 (21), overexpression of a truncated TPP1 protein defective in POT1 binding (TPP1 ⌬RD ) can induce TIFs (17), and lastly, knockdown of the v5 splice version of POT1 that does not interact with TPP1 induced fewer DNA damage foci than did knockdown of the predominant splice form that binds TPP1 (54). Mechanistically, we show that knockdown of POT1 results in an accumulation of RPA at telomeres, as evidenced by an increased number of STAR-positive cells.…”

Section: Discussionmentioning

confidence: 82%

Distinct Functions of POT1 at Telomeres

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Freibaum

et al. 2008

Molecular and Cellular Biology

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The mammalian protein POT1 binds to telomeric single-stranded DNA (ssDNA), protecting chromosome ends from being detected as sites of DNA damage. POT1 is composed of an N-terminal ssDNA-binding domain and a C-terminal protein interaction domain. With regard to the latter, POT1 heterodimerizes with the protein TPP1 to foster binding to telomeric ssDNA in vitro and binds the telomeric double-stranded-DNA-binding protein TRF2. We sought to determine which of these functions-ssDNA, TPP1, or TRF2 binding-was required to protect chromosome ends from being detected as DNA damage. Using separation-of-function POT1 mutants deficient in one of these three activities, we found that binding to TRF2 is dispensable for protecting telomeres but fosters robust loading of POT1 onto telomeric chromatin. Furthermore, we found that the telomeric ssDNA-binding activity and binding to TPP1 are required in cis for POT1 to protect telomeres. Mechanistically, binding of POT1 to telomeric ssDNA and association with TPP1 inhibit the localization of RPA, which can function as a DNA damage sensor, to telomeres.Telomeres are DNA-protein complexes that protect the ends of linear eukaryotic chromosomes from illegitimate recombination, degradation, and recognition as DNA doublestrand breaks. The DNA portion of human telomeres is composed of tandem arrays of the short G-rich repetitive sequence TTAGGG in which the G-rich strand extends beyond the Crich strand, forming a 3Ј single-stranded DNA (ssDNA) overhang. Electron microscopic analysis suggests that the 3Ј overhang can loop back and invade telomeric double-stranded DNA (dsDNA) to form a large lariat structure, effectively hiding the end of the telomere (16). The protein portion of telomeres is composed of two telomeric dsDNA-binding proteins, TRF1 and TRF2 (6,25,42,46,47), and one telomeric ssDNA-binding protein, POT1 (4, 5), which form a large complex, mediated by proteins such as TIN2 and TPP1 (24,26,28,30,31,39,56,57), that maintains chromosome end stability (21,22,43,48).POT1 is a 634-amino-acid protein comprised of an N-terminal evolutionarily conserved pair of oligonucleotide/oligosaccharide (OB) folds responsible for telomeric ssDNA binding (4,5,33), with the remaining C terminus serving to bind TPP1 (31, 57) and TRF2 (55). With regard to TPP1, both recombinant (49) and purified (52) human TPP1 proteins form a heterodimer with POT1 in vitro, which enhances the association of POT1 with a G-strand telomere oligonucleotide. Moreover, in the lower eukaryote Oxytricha nova, the POT1 and TPP1 homologues TEBP␣ (4, 5) and TEBP␤ (49, 52) form a ternary complex with ssDNA (12, 23) that protects chromosome ends (15). Heterodimerization of POT1 with TPP1 thus appears to enhance POT1 function at telomeric ssDNA. With regard to TRF2, POT1 coimmunoprecipitates with TRF2 (55) and has been isolated by gel filtration in several protein subcomplexes containing TRF2 (27,30,39). POT1 thus interacts directly with telomeric ssDNA, in association with TPP1, and presumably indirectly with telomeric dsDNA, thr...

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Section: Discussionmentioning

confidence: 82%

Distinct Functions of POT1 at Telomeres

Barrientos

Kendellen

Freibaum

et al. 2008

Molecular and Cellular Biology

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“…Third, the POT1-TPP1 heterodimer recruits telomerase to telomeres and promotes its processivity (72,73). As an entrée to studying how POT1 regulates telomere length in telomerase-positive cells, we note that expression of POT1 ⌬OB , a mutant lacking the N-terminal OB folds responsible for telomeric ssDNA binding (3,50,51), is one of the most potent means of inducing elongation of telomeres (2,50,51,74). This mutant clearly disrupts at least one critical aspect of telomere length regulation.…”

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confidence: 89%

“…Telomeric ssDNA is bound directly by the protein POT1 (4, 5, 23, 52). POT1 acts in a heterodimer with the protein TPP1; this heterodimer promotes POT1 binding to telomeric ssDNA at least in vitro (72, 73), protects telomeres from being detected as sites of DNA damage (3,24,29,37,73,74), and inhibits replication protein A (RPA) localization to telomeres (3). In vitro-transcribed and -translated POT1 has also been shown to associate with recombinant glutathione S-transferase-TRF2 (75).…”

mentioning

confidence: 99%

“…Taken together, these data suggest that POT1 also associates with TRF2, potentially directly, and this interaction facilitates POT1 association with telomeric chromatin (3,37,53,75). All the aforementioned proteins are found in larger complexes containing other proteins involved in telomere length regulation, DNA damage response, and sister chromatid association (13,16,22,49,56,57,60,67).Inhibition of any of the proteins that directly bind telomeric DNA (TRF1, TRF2, or POT1) or many of their interacting partners (TPP1, TIN2, or RAP1) in telomerase-positive human cells results in telomere elongation (10,38,43,47,51,56,66,69,71,74,77). Such inhibition has also been reported to disrupt telomere protein complexes (57) and induce the mislocalization of other telomere-associated proteins (37,39,50,51,75,77).…”

mentioning

confidence: 99%

“…POT1 ⌬OB retains the protein interaction domain of the wildtype protein, which mediates its interaction with both TPP1 and TRF2 (3,39,50,74,75,77), and elongates telomeres in a dominant-negative fashion (2,50,51,74). This suggests that one of these protein interactions, when uncoupled from telomeric ssDNA binding, underlies the ability of POT1…”

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POT1 Association with TRF2 Regulates Telomere Length

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2009

Molecular and Cellular Biology

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Deleting the OB folds encoding the telomeric single-stranded DNA (ssDNA)-binding activity of the human telomeric protein POT1 induces significant telomere elongation, suggesting that at least one critical aspect of the regulation of telomere length is disrupted by this POT1 ⌬OB mutant protein. POT1 is known to associate with two proteins through the protein interaction domain retained in POT1⌬OB -the telomeric doublestranded DNA-binding protein TRF2 and the telomere-associated protein TPP1. We report that introducing a mutation that reduces association of POT1 with TRF2, but not a mutation that reduces the association with TPP1, abrogates the ability of POT1 ⌬OB to promote telomere elongation. Mechanistically, expression of POT1 ⌬OB reduced the association of TRF2 with POT1, RAP1, and TIN2; however, of these proteins, only ectopic expression of POT1 suppressed the telomere elongation induced by POT1 ⌬OB . Lastly, replacing endogenous POT1 with a full-length POT1 mutant defective in the association with TRF2 induced telomere elongation. Thus, we conclude that the association of POT1 with both ssDNA and TRF2 is critical for telomere length homeostasis.Telomeres are DNA-protein complexes that protect the ends of eukaryotic chromosomes from degradation and detection as sites of DNA damage (reviewed in reference 23). Telomeric DNA is composed of tandem arrays of repetitive double-stranded DNA (dsDNA), wherein the G-rich strand extends beyond the C-rich strand. The resultant 3Ј singlestranded DNA (ssDNA) overhang can invade the dsDNA, forming a lariat structure termed the t-loop (28).The regulation of telomere length affects mammalian biology at both the cellular and organismal levels. In normal human somatic cells, telomeres progressively shorten (32, 33) to a critical length before entering a state of permanent growth arrest termed senescence (1,12,21,34,35). Abnormally short telomeres in humans and mice are associated with various anemias, cirrhosis of the liver, and other disorders due to the premature induction of senescence, particularly in highly proliferative tissues (7,11,61). Conversely, de novo elongation of the telomere by the reverse transcriptase telomerase (27, 54) ensures maintenance of telomere length in the germ line and endows cultured cells with an immortal life span (8,17,18,20,30,36,70,78). Moreover, telomerase activation and subsequent stabilization of telomere length occur in the vast majority of cancer cells (41, 62) and are required for cellular immortalization and the tumorigenic conversion of normal human cells (19,30,31,36,78).The dsDNA portion of telomeres is bound directly by two proteins, TRF1 and TRF2 (9, 23). In turn, TRF1 and TRF2 are bridged by the protein TIN2 (23, 43, 76) and bind other telomere-associated proteins such as tankyrase 1 (23, 63, 64) and RAP1 (48, 56). Telomeric ssDNA is bound directly by the protein POT1 (4, 5, 23, 52). POT1 acts in a heterodimer with the protein TPP1; this heterodimer promotes POT1 binding to telomeric ssDNA at least in vitro (72, 73), protects tel...

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MicroRNA‐340‐5p increases telomere length by targeting telomere protein POT1 to improve Alzheimer's disease in mice

Zhang

Yang

et al. 2021

Cell Biology International

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Alzheimer′s disease (AD) is a chronic neurodegenerative disorder which is the primary cause of dementia in the elderly. Telomere attrition has been proposed as a hallmark of aging. Our study aimed to explore the mechanism of the protection of telomere 1 (POT1) in regulating telomere length and affecting cellular senescence in AD. The AD mouse model was established by d‐galactose and aluminum chloride, and the water maze test and dark avoidance test were used to detect the behaviors of mice and confirm the success of AD mouse model. AD cell model was established with HT22 cells induced by Aβ42 oligomers. POT1 expression in the AD model was detected by quantitative real‐time polymerase chain reaction. Cellular telomere length in hippocampal tissue was analyzed by telomere restriction fragment. Localization of intracellular POT1, telomerase, and telomeres was analyzed by immunofluorescence and fluorescence in situ hybridization. Dual‐luciferase assay was used to validate the targeted binding relationship between microRNA‐340‐5p (miR‐340‐5p) and POT1. After inhibiting POT1 expression, the symptoms of AD in mice were improved. Aβ1–42 deposition was reduced, whereas telomere length and telomerase activity was increased. Dual‐luciferase assay verified the binding relationship between miR‐340‐5p and POT1. An increase in miR‐340‐5p expression could alleviate cellular senescence and AD symptoms. miR‐340‐5p increased cellular telomere length and delayed cell senescence by inhibiting POT1 expression to improve AD symptoms. This study made a conclusion that miR‐340‐5p increased cellular telomere length and delayed cell senescence by inhibiting POT1 expression to improve AD symptoms in mice.

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Functional Diversity of Human Protection of Telomeres 1 Isoforms in Telomere Protection and Cellular Senescence

Cited by 32 publications

References 46 publications

Distinct Functions of POT1 at Telomeres

Distinct Functions of POT1 at Telomeres

POT1 Association with TRF2 Regulates Telomere Length

MicroRNA‐340‐5p increases telomere length by targeting telomere protein POT1 to improve Alzheimer's disease in mice

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