Research Paper Volume 13, Issue 7 pp 10490—10516

Nuclear envelope tethering inhibits the formation of ALT-associated PML bodies in ALT cells

Chia-Wei Yang1, , Meng-Hsun Hsieh1, , Hao-Jhe Sun1, , Shu-Chun Teng1,2, ,

  • 1 Department of Microbiology, College of Medicine, National Taiwan University, Taipei 10051, Taiwan
  • 2 Center of Precision Medicine, National Taiwan University, Taipei 10051, Taiwan

Received: August 29, 2020       Accepted: February 16, 2021       Published: April 4, 2021
How to Cite

Copyright: © 2021 Yang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


Telomere length homeostasis is essential for maintaining genomic stability and cancer proliferation. Telomerase-negative cancer cells undergo recombination-mediated alternative lengthening of telomeres. Telomeres associate with the nuclear envelope through the shelterin RAP1 and nuclear envelope SUN1 proteins. However, how the associations between telomeres and the nuclear envelope affect the progression of telomere recombination is not understood. Here, we show that telomere anchorage might inhibit telomere-telomere recombination. SUN1 depletion stimulates the formation of alternative lengthening of telomeres-associated promyelocytic leukemia bodies in ALT cells. In contrast, overexpression of a telomere-nuclear envelope-tethering chimera protein, RAP1-SUN1, suppresses APB formation. Moreover, inhibition of this nuclear envelope attachment alleviates the requirement of TOP3α for resolving the supercoiling pressure during telomere recombination. A coimmunoprecipitation assay revealed that the SUN1 N-terminal nucleoplasmic domain interacts with the RAP1 middle coil domain, and phosphorylation-mimetic mutations in RAP1 inhibit this interaction. However, abolishing the RAP1-SUN1 interaction does not hinder APB formation, which hints at the existence of another SUN1-dependent telomere anchorage pathway. In summary, our results reveal an inhibitory role of telomere-nuclear envelope association in telomere-telomere recombination and imply the presence of redundant pathways for the telomere-nuclear envelope association in ALT cells.


ALT: alternative lengthening of telomeres; PML: promyelocytic leukemia protein; APBs: ALT-associated PML bodies; T-SCE: telomeric sister chromatid exchange; MEF: mouse embryonic fibroblast; LINC: linkers of nucleoskeleton and cytoskeleton; shRNA: short hairpin RNA; SD: standard deviation; TRF: telomere restriction fragment; RCT: RAP1 C terminal; SUN1 N205: a truncated form of SUN1 that contains 205 N-terminal soluble amino acids; DSB: double-strand break; BIR: break-induced DNA replication.