Alternative Lengthening of Telomeres through Two Distinct Break-Induced Replication Pathways.
Alternative lengthening of telomeres (ALT) is a telomerase-independent but recombination-dependent pathway that maintains telomeres. Here, we describe an assay to visualize ALT-mediated telomeric DNA synthesis in ALT-associated PML bodies (APBs) without DNA-damaging agents or replication inhibitors. Using this assay, we find that ALT occurs through two distinct mechanisms. One of the ALT mechanisms requires RAD52, a protein implicated in break-induced DNA replication (BIR). We demonstrate that RAD52 directly promotes telomeric D-loop formation in vitro and is required for maintaining telomeres in ALT-positive cells. Unexpectedly, however, RAD52 is dispensable for C-circle formation, a hallmark of ALT. In RAD52-knockout ALT cells, C-circle formation and RAD52-independent ALT DNA synthesis gradually increase as telomeres are shortened, and these activities are dependent on BLM and BIR proteins POLD3 and POLD4. These results suggest that ALT occurs through a RAD52-dependent and a RAD52-independent BIR pathway, revealing the bifurcated framework and dynamic nature of this process.
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- Telomere Homeostasis
- Rad52 DNA Repair and Recombination Protein
- Humans
- DNA Replication
- DNA Polymerase III
- DNA Breaks
- Cell Line, Tumor
- 31 Biological sciences
- 1116 Medical Physiology
- 0601 Biochemistry and Cell Biology
Citation
Published In
DOI
EISSN
Publication Date
Volume
Issue
Start / End Page
Location
Related Subject Headings
- Telomere Homeostasis
- Rad52 DNA Repair and Recombination Protein
- Humans
- DNA Replication
- DNA Polymerase III
- DNA Breaks
- Cell Line, Tumor
- 31 Biological sciences
- 1116 Medical Physiology
- 0601 Biochemistry and Cell Biology