Abstract
Alternative lengthening of telomeres (ALT) is mediated by break-induced replication (BIR), but how BIR is regulated at telomeres is poorly understood. Here, we show that telomeric BIR is a self-perpetuating process. By tethering PML-IV to telomeres, we induced telomere clustering in ALT-associated PML bodies (APBs) and a POLD3-dependent ATR response at telomeres, showing that BIR generates replication stress. Ablation of BLM helicase activity in APBs abolishes telomere synthesis but causes multiple chromosome bridges between telomeres, revealing a function of BLM in processing inter-telomere BIR intermediates. Interestingly, the accumulation of BLM in APBs requires its own helicase activity and POLD3, suggesting that BIR triggers a feedforward loop to further recruit BLM. Enhancing BIR induces PIAS4-mediated TRF2 SUMOylation, and PIAS4 loss deprives APBs of repair proteins and compromises ALT telomere synthesis. Thus, a BLM-driven and PIAS4-mediated feedforward loop operates in APBs to perpetuate BIR, providing a critical mechanism to extend ALT telomeres.
Keywords:
ALT; APB; BIR; BLM; PIAS4; PML; SUMO; phase separation; replication stress; telomere.
Copyright © 2020 Elsevier Inc. All rights reserved.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Cell Line
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Cell Line, Tumor
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DNA Polymerase III / genetics
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DNA Polymerase III / metabolism
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Epithelial Cells / cytology
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Epithelial Cells / metabolism
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Fanconi Anemia Complementation Group Proteins / antagonists & inhibitors
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Fanconi Anemia Complementation Group Proteins / genetics*
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Fanconi Anemia Complementation Group Proteins / metabolism
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Feedback, Physiological*
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Fibroblasts / cytology
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Fibroblasts / metabolism
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Gene Expression Regulation
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Gene Knockdown Techniques
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Humans
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Intranuclear Inclusion Bodies / genetics
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Intranuclear Inclusion Bodies / metabolism
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Poly-ADP-Ribose Binding Proteins / antagonists & inhibitors
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Poly-ADP-Ribose Binding Proteins / genetics*
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Poly-ADP-Ribose Binding Proteins / metabolism
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Protein Inhibitors of Activated STAT / antagonists & inhibitors
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Protein Inhibitors of Activated STAT / genetics*
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Protein Inhibitors of Activated STAT / metabolism
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RNA Helicases / antagonists & inhibitors
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RNA Helicases / genetics*
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RNA Helicases / metabolism
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RNA, Small Interfering / genetics
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RNA, Small Interfering / metabolism
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Rad52 DNA Repair and Recombination Protein / genetics
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Rad52 DNA Repair and Recombination Protein / metabolism
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RecQ Helicases / genetics
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RecQ Helicases / metabolism
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Signal Transduction
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Sumoylation
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Telomere / chemistry*
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Telomere / metabolism
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Telomere Homeostasis*
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Telomeric Repeat Binding Protein 2 / genetics
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Telomeric Repeat Binding Protein 2 / metabolism*
Substances
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Fanconi Anemia Complementation Group Proteins
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PIAS4 protein, human
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Poly-ADP-Ribose Binding Proteins
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Protein Inhibitors of Activated STAT
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RAD52 protein, human
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RNA, Small Interfering
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Rad52 DNA Repair and Recombination Protein
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TERF2 protein, human
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Telomeric Repeat Binding Protein 2
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POLD3 protein, human
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DNA Polymerase III
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Bloom syndrome protein
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RecQ Helicases
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BRIP1 protein, human
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RNA Helicases