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Protection of telomeres 1 (POT1) is the 3' single-stranded overhang-binding telomeric protein that prevents an ataxia telangiectasia and Rad3-related (ATR) DNA damage response (DDR) at chromosome ends. What precludes the DDR machinery from accessing the telomeric double-stranded-single-stranded junction is unknown. We demonstrate that human POT1 binds this junction by recognizing the phosphorylated 5' end of the chromosome. High-resolution crystallographic structures reveal that the junction is capped by POT1 through a "POT-hole" surface, the mutation of which compromises junction protection in vitro and telomeric 5'-end definition and DDR suppression in human cells. Whereas both mouse POT1 paralogs bind the single-stranded overhang, POT1a, not POT1b, contains a POT-hole and binds the junction, which explains POT1a's sufficiency for end protection. Our study shifts the paradigm for DDR suppression at telomeres by highlighting the importance of protecting the double-stranded-single-stranded junction.
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http://dx.doi.org/10.1126/science.adi2436 | DOI Listing |
Front Immunol
September 2025
Laboratory of Molecular Oncology, Istituto Dermopatico dell'Immacolata IDI-IRCCS, Rome, Italy.
Background: Sézary syndrome (SS) is an aggressive and leukemic variant of Cutaneous T-cell Lymphoma (CTCL) with an incidence of 1 case per million people per year. It is characterized by a complex and heterogeneous profile of genetic alteration ns that has so far precluded the development of a specific and definitive therapeutic intervention.
Methods: Deep-RNA-sequencing (RNA-seq) data were used to analyze the single nucleotide variants (SNVs) carried by 128 putative CTCL-driver genes, previously identified as mutated in genomic studies, in longitudinal SS samples collected from 17 patients subjected to extracorporeal photopheresis (ECP) with Interferon-α.
Cancer Genet
August 2025
Cincinnati Children's Hospital Medical Center, Division of Oncology, Cincinnati, OH, USA; University of Cincinnati College of Medicine, Cincinnati, OH, USA. Electronic address:
Introduction: POT1 tumor predisposition (POT1-TPD) is associated with a spectrum of malignancies due to loss of function mutations in POT1 leading to telomere elongation and genomic instability. Osteosarcoma is the most common primary malignant bone tumor and has a poor prognosis when multifocal.
Case Presentation: A 15-year-old male was found to have a primary right distal femur osteosarcoma with multiple additional bony sites of disease.
Acta Oncol
August 2025
Department of Oncology and Pathology, Karolinska Institutet, Stockholm, Sweden; Theme Cancer, Karolinska University Hospital, Stockholm, Sweden.
Background And Purpose: Approximately 5-10% of cutaneous melanoma occurs in individuals with a family history of the disease. While known high-penetrance genes, such as CDKN2A, explain some cases, a substantial proportion of hereditary melanoma remains genetically undefined. Recently, germline variants in genes involved in telomere regulation, including POT1, TERT, ACD, and TERF2IP, have been identified in melanoma-prone families.
View Article and Find Full Text PDFCell Rep
August 2025
Institute for Quantitative Health Science and Engineering, Michigan State University, East Lansing, MI, USA; Department of Obstetrics, Gynecology, and Reproductive Biology, Michigan State University, East Lansing, MI, USA. Electronic address:
The shelterin complex protects chromosome ends from aberrant DNA repair and regulates telomerase access to telomeres. Shelterin is composed of six proteins (TRF1, TRF2, TIN2, TPP1, POT1, and RAP1) that can assemble into various subcomplexes in vitro, but their stoichiometry and dynamics in cells remain poorly understood. To quantitatively analyze shelterin function, we generated a panel of human cancer cell lines expressing HaloTagged shelterin proteins from their endogenous loci.
View Article and Find Full Text PDFElife
August 2025
Laboratory of Genome Integrity, National Cancer Institute, National Institutes of Health, Bethesda, United States.
A significant portion of human cancers utilize a recombination-based pathway, alternative lengthening of telomeres (ALT), to maintain telomere length. Targeting the ALT is of growing interest as a cancer therapy, yet a substantial knowledge gap remains regarding the basic features of telomeres in ALT-positive cells. To address this, we adopted END-seq, an unbiased sequencing-based approach, to define the identity and regulation of the terminal sequences of chromosomes in ALT cells.
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