Interchromosomal Homology Searches Drive Directional ALT Telomere Movement and Synapsis

Abstract

Summary Telomere length maintenance is a requisite feature of cellular immortalization and a hallmark of human cancer. While most human cancers express telomerase activity, approximately 10-15% employ a recombination-dependent telomere maintenance pathway known as Alternative Lengthening of Telomeres (ALT) that is characterized by multi-telomere clusters and associated promyelocytic leukemia protein bodies. Here, we show that a DNA double-strand break (DSB) response at ALT telomeres triggers long-range movement and clustering between chromosome termini, resulting in homology-directed telomere synthesis. Damaged telomeres initiate increased random surveillance of nuclear space before displaying rapid directional movement and association with recipient telomeres over micron-range distances. This phenomenon required Rad51 and the Hop2-Mnd1 heterodimer, which are essential for homologous chromosome synapsis during meiosis. These findings implicate a specialized homology searching mechanism in ALT dependent telomere maintenance and provide a molecular basis underlying the preference for recombination between non- sister telomeres during ALT.

PML induces compaction, TRF2 depletion and DNA damage signaling at telomeres and promotes their alternative lengthening

“…We found here that APB assembly in U2OS cells was inhibited by an 'open' telomeric chromatin state, as the knockdown of several repressive chromatin modifiers, as well as chromatin decondensation initiated by HDAC inhibition or HMGN5 recruitment, resulted in a The formation of a PML subcompartment at telomeres induces telomeric chromatin compaction and clustering of telomeres, and possibly also ECTRs, as proposed previously (Cho et al, 2014;Draskovic et al, 2009). As a result of APB formation, TRF2 becomes partly depleted at associated telomeres.…”

“…5). First, formation of a PML subcompartment at telomeres induces telomeric chromatin compaction and clustering of telomeres, and possibly also ECTRs, as proposed previously (Cho et al, 2014;Draskovic et al, 2009). Second, as a result of APB formation, TRF2 becomes partly depleted at associated telomeres.…”

“…artificially enlarged APBs (Draskovic et al, 2009) and that damaged telomeres preferentially cluster with telomeres that are associated with PML in ALT-positive cells (Cho et al, 2014). Notably, long-term PML knockdown induced telomere shortening and significantly increased the number of chromosomal ends where a telomere repeat signal was absent.…”

Mitotic progression following DNA damage enables pattern recognition within micronuclei

“…The mCherry fragement was isolated from the pHFUW-mCherry-TRF-FOKI plasmid 31 with Q5 polymerase and primers (5’-agaggatctatttaaataccggatccATGGTGAGCAAGGGCGAG-3’, 5’-ccatcttcatctcgagCTTGTACAGCTCGTCCATGC-3’). These two fragments were joined by Gibson assembly (New England Biolabs) and digested with XhoI/NotI (New England Biolabs).…”

Germline/meiotic genes in cancer: new dimensions

“…This changed when it was discovered that the ALT telomere maintenance pathway used by some telomerease deficient cancer cells to maintain their telomeres was dependent upon 2 meiosis-specific factors, Hop2 and Mnd1, both of which normally drive the mechanism that biases meiotic recombination to establish the inter homolog connections required for correct reductional chromosome segregation during meiosis I. 6 This discovery adds a new class of factors to the complex mix of genes that become activated during oncogenesis and highlights the need to explore the functional activity of other human meiotic genes that may contribute to cancer formation, maintenance and evolution. 4,5 In addition, it places further importance on the study of basic molecular mechanisms of the meiotic program.…”