Send to

Choose Destination
Mol Cell Biol. 2017 Sep 26;37(20). pii: e00226-17. doi: 10.1128/MCB.00226-17. Print 2017 Oct 15.

Alternative Lengthening of Telomeres Mediated by Mitotic DNA Synthesis Engages Break-Induced Replication Processes.

Author information

Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, Texas, USA


Alternative lengthening of telomeres (ALT) is a telomerase-independent telomere maintenance mechanism that occurs in a subset of cancers. By analyzing telomerase-positive cells and their human TERC knockout-derived ALT human cell lines, we show that ALT cells harbor more fragile telomeres representing telomere replication problems. ALT-associated replication defects trigger mitotic DNA synthesis (MiDAS) at telomeres in a RAD52-dependent, but RAD51-independent, manner. Telomeric MiDAS is a conservative DNA synthesis process, potentially mediated by break-induced replication, similar to type II ALT survivors in Saccharomyces cerevisiae Replication stresses induced by ectopic oncogenic expression of cyclin E, G-quadruplexes, or R-loop formation facilitate the ALT pathway and lead to telomere clustering, a hallmark of ALT cancers. The TIMELESS/TIPIN complex suppresses telomere clustering and telomeric MiDAS, whereas the SMC5/6 complex promotes them. In summary, ALT cells exhibit more telomere replication defects that result in persistent DNA damage responses at telomeres, leading to the engagement of telomeric MiDAS (spontaneous mitotic telomere synthesis) that is triggered by DNA replication stress, a potential driver of genomic duplications in cancer.


ALT; G quadruplex; MiDAS; R-loop; RAD51; RAD52; SMC5/6; TIMELESS; cyclin E; telomerase; telomere

[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center