Investigation of conformational dynamics of Tyr89Cys mutation in protection of telomeres 1 gene associated with familial melanoma.

Protection of telomeres 1 (POT1) is a component of the shelterin complex which is crucial for the regulation of telomere length and maintenance. Many naturally occurring mutations in the POT1 gene have been found to be associated with cardiac angiosarcoma, glioma, familial melanoma, and chronic lymphocytic leukemia. In particular, Y89C is a naturally occurring mutation of POT1, responsible for familial melanoma, and the molecular basis of this mutation is unexplored. In this study, we have extensively analyzed the structure of WT and Y89C mutant of POT1 to see the change in the conformational dynamics, free energy landscape, molecular motions and configurational frustration using molecular dynamics (MD) and other bioinformatics approaches. Y89C mutation shows a significant change in the backbone orientation, compactness, residual fluctuation, solvent accessibility, and hydrogen bonding, suggesting an overall destabilization of the protein structure. Besides, essential dynamics, conformation, magnitude, direction of motion and frustration analysis further suggesting the structural loss in POT1 due to Y89C mutation. Free energy landscape analysis also indicates the presence of a single well-defined free-energy minima in case of WT compared to multiple wells defined free energy minima observed in Y89C, clearly suggesting that this mutation leads to reduce the stability of POT1. This study possibly provides a valuable path to understand the molecular basis of Y89C-mediated development of familial melanoma.Communicated by Ramaswamy H. Sarma.

POT1-TPP1 telomere length regulation and disease.

Telomeres are DNA repeats at the ends of linear chromosomes and are replicated by telomerase, a ribonucleoprotein reverse transcriptase. Telomere length regulation and chromosome end capping are essential for genome stability and are mediated primarily by the shelterin and CST complexes. POT1-TPP1, a subunit of shelterin, binds the telomeric overhang, suppresses ATR-dependent DNA damage response, and recruits telomerase to telomeres for DNA replication. POT1 localization to telomeres and chromosome end protection requires its interaction with TPP1. Therefore, the POT1-TPP1 complex is critical to telomere maintenance and full telomerase processivity. The aim of this mini-review is to summarize recent POT1-TPP1 structural studies and discuss how the complex contributes to telomere length regulation. In addition, we review how disruption of POT1-TPP1 function leads to human disease.

MiR-185 targets POT1 to induce telomere dysfunction and cellular senescence.

Protection of telomere 1 (POT1), the telomeric single-stranded DNA (ssDNA)-binding protein in the shelterin complex, has been implicated in the DNA damage response, tumorigenesis and aging. Telomere dysfunction induced by telomere deprotection could accelerate cellular senescence in primary human cells. While previous work demonstrated the biological mechanism of POT1 in aging and cancer, how POT1 is posttranscriptionally regulated remains largely unknown. To better understand the POT1 regulatory axis, we performed bioinformatic prediction, and selected candidates were further confirmed by dual-luciferase reporter assay. Collectively, our results revealed that miR-185 can significantly reduce POT1 mRNA and protein levels by directly targeting the POT1 3'-untranslated region (3'-UTR). Overexpression of miR-185 increased telomere dysfunction-induced foci (TIF) signals in both cancer cells and primary human fibroblasts. Elevated miR-185 led to telomere elongation in the telomerase-positive cell line HTC75, which was phenotypically consistent with POT1 knocking down. Moreover, miR-185 accelerated the replicative senescence process in primary human fibroblasts in a POT1-dependent manner. Interestingly, increased serum miR-185 could represent a potential aging-related biomarker. Taken together, our findings reveal miR-185 as a novel aging-related miRNA that targets POT1 and provide insight into the telomere and senescence regulatory network at both the intracellular and extracellular levels.

Impact of Gln94Glu mutation on the structure and function of protection of telomere 1, a cause of cutaneous familial melanoma.

Protection of telomere 1 (POT1) is a key component of shelterin complex, essential for maintaining telomere length and its regulation. It consists of N-terminal domain (residues 1-299), which interacts with telomeric ssDNA, and the C-terminal domain (residues 320-634) that binds to the tripeptidyl-peptidase I (TPP1). A large number of naturally occurring mutations in the POT1 gene are associated with glioma, cardiac angiosarcoma and cutaneous familial melanoma (FM). In particular, Q94E mutation disrupts the interaction of POT1 with telomeric DNA which subsequently enhances telomere uncapping and elongation and promotes the development of cutaneous familial melanoma. To understand the underlying mechanism of familial melanoma developed by Q94E-mutation, we have performed extensive structure analysis of WT and mutant protein followed by molecular dynamics simulations. Q94E mutation causes a dramatic change in the structure and stability of POT1 protein. A considerable decrease in the flexibility, fluctuation and solvent accessibility of Q94E was observed in comparison to the WT, indicating overall destabilization of protein. Essential dynamics and Anisotropic Network Mode analysis have quantified a significant change in direction and magnitude of conformational motion in Q94E mutant compared to WT. A significant loss of frustration due to Q94E mutation was also observed. Our findings indicate the loss of protein stability and dynamics of POT1 protein by Q94E mutation may be associated with the familial melanoma. AbbreviationsANManisotropic network modeEDessential dynamicsFMfamilial melanomaMDmolecular dynamicsPOT1protection of telomere 1Rgradius of gyrationRMSDroot-mean-square deviationRMSFroot-mean-square fluctuationsSASAsolvent accessible surface areaSIFTsorting Intolerant from TolerantTPP1tripeptidyl-peptidase IWTwild typeCommunicated by Ramaswamy H. Sarma.

Investigation of deleterious effects of nsSNPs in the POT1 gene: a structural genomics-based approach to understand the mechanism of cancer development.

Protection of telomere 1 (POT1) is one of the key components of shelterin complex, implicated in maintaining the telomere homeostasis, and thus stability of the eukaryotic genome. A large number of non-synonymous single nucleotide polymorphisms (nsSNPs) in the POT1 gene have been reported to cause varieties of human diseases, including cancer. In recent years, a number of mutations in POT1 has been markedly increased, and interpreting the effect of these large numbers of mutations to understand the mechanism of associated diseases seems impossible using experimental approaches. Herein, we employ varieties of computational methods such as PROVEAN, PolyPhen-2, SIFT, PoPMuSiC, SDM2, STRUM, and MAESTRO to identify the effects of 387 nsSNPs on the structure and function of POT1 protein. We have identified about 183 nsSNPs as deleterious and termed them as "high-confidence nsSNPs." Distribution of these high-confidence nsSNPs demonstrates that the mutation in oligonucleotide binding domain 1 is highly deleterious (one in every three nsSNPs), and high-confidence nsSNPs show a strong correlation with residue conservation. The structure analysis provides a detailed insights into the structural changes occurred in consequence of conserved mutations which lead to the cancer progression. This study, for the first time, offers a newer prospective on the role of POT1 mutations on the structure, function, and their relation to associated diseases.