Poster Presentation 43rd Lorne Genome Conference 2022

Nuclear F-actin and the DNA damage response regulate telomerase recruitment (#162)

Ashley Harman 1 , Nohad Maroun 1 , Darren Nguyen 1 , Melissa Kartawinata 1 , Tracy Bryan 1
  1. Children's Medical Research Institute, Westmead, NSW, Australia

In germline, stem and ~85% of cancer cells, telomeres are elongated by the ribonucleoprotein telomerase, which allows these cells to replicate indefinitely. While the function of telomerase is reasonably well characterised, less is known about the processes which regulate its function, including its recruitment to telomeres. We have previously demonstrated that the DNA damage response is important in regulating telomerase recruitment to telomeres, specifically via the regulatory kinases ATR and ATM, which coordinate the cellular response to DNA damage, including replication stress1,2. Interestingly, it has also been identified that nuclear actin polymerisation is important for DNA replication dynamics following replication stress, in an ATR-dependent manner3. Given this, we hypothesise that there is controlled interplay between DNA replication, the DNA damage response, and telomere maintenance, which together result in cancer cell immortalisation.

In this work we have shown, using fixed and live cell fluorescence microscopy, that filamentous actin is important for telomerase recruitment, as inhibition of its polymerisation decreases the presence of telomerase at telomeres. This occurs in an ATR and mTOR-dependent manner, and also employs other regulators of actin structure and function (e.g. WASP and ARP2/3). We have previously demonstrated that the chemical induction of replication stress promotes telomerase recruitment1. Interestingly, the inhibition of actin polymerisation directly, or indirectly through its regulators, abrogates this stress-induced recruitment. Furthermore, we have found that cells undergoing mild replication stress possess a subset of telomeres on nuclear actin filaments which appear less mobile than other telomeres. These results together suggest that telomerase is recruited to telomeres by actin via activation of the DNA damage response. This supports a model of telomerase recruitment in which DNA replication and the DNA damage response are crucial factors which dictate the timing and occurrence of telomere maintenance.

 

  1. 1 Tong, A.S., Stern, J.L, Sfeir, A., Kartawinata, M., de Lange, T., Zhu, X.D. and Bryan, T.M. (2015) ATM and ATR Signaling Regulate the Recruitment of Human Telomerase to Telomeres. Cell Reports, 13(8):1633-46.
  2. 2 Lee, S.S., Bohrson, C., Pike, A.M., Wheelan, S.J. and Greider, C.W. (2015) ATM Kinase Is Required for Telomere Elongation in Mouse and Human Cells. Cell Reports, 13(8):1623-32.
  3. 3 Lamm, N., Read, M.N., Nobis, M., Van Ly, D., Page, S.G., Masamsetti, V.P., Timpson, P., Biro, M. and Cesare, A.J. (2020) Nuclear F-actin counteracts nuclear deformation and promotes fork repair during replication stress. Nature Cell Biology 22(12):1460-1470.