Dr. Toru M. Nakamura
Professor

• 2005 Kimmel Scholar (Sidney Kimmel Foundation for Cancer Research)
• Postdoctoral Training, 1999 - 2004 The Scripps Res. Inst. (Russell Lab)
• Postdoc. Fellowship, 1999 - 2002 (Damon Runyon Cancer Research Foundation)
• Visiting Researcher, 1995 MRC Human Genetics Unit (Allshire Lab)
• Graduate School (Ph.D.), 1993 - 1999 Univ. Colorado Boulder (Cech Lab)

Research Interests:
Our laboratory is interested in understanding how checkpoint and DNA repair proteins contribute to maintenance of telomeres, the natural ends of linear eukaryotic chromosomes. Proper maintenance of telomeres is crucial for stable inheritance of the genome. Various checkpoint and DNA repair proteins, including evolutionarily highly conserved checkpoint kinases Tel1 (ATM) and Rad3 (ATR), play important roles in stable maintenance of telomeres. However, mechanistic roles for various checkpoint and DNA repair proteins in telomere maintenance have not been fully established. Deregulation of telomere maintenance mechanisms has been found to be a key event in tumorigenesis, thus mechanistic insights on how various proteins collaborate to generate functional telomeres might lead to effective methods for preventing cancer.

Tel1^ATM and Rad3^ATR promote telomere protection and telomerase recruitment.
(A) A model for telomere dysfunction caused by simultaneous loss of Tel1^ATM and Rad3^ATR in fission yeast. The "open" or accessible state of the telomere during late S-phase, which allows recruitment of Rad3-Rad26 and telomerase, is depicted.
(B) A proposed regulatory loop of Tel1^ATM/Rad3^ATR and the Pot1 sub-complex, required for telomere maintenance. The Pot1 sub-complex subunit Ccq1 is involved in telomere capping and telomerase recruitment, and its recruitment is redundantly promoted by Tel1^ATM and Rad3^ATR kinases. (Moser et al. 2009)

We use fission yeast Schizosaccharomyces pombe as a model system. Advantages of S. pombe include well-characterized DNA damage responses with high structural and functional conservation to mammalian cells, and amenability to genetic, biochemical and cytological studies. In addition, the ability of fission yeast to bypass the need for functional telomere maintenance mechanisms by circularizing all chromosomes provides flexibility, not available in any other organisms, in manipulating telomere related genes without being hindered by cell lethality. In fact, S. pombe cells lacking telomerase, as well as cells lacking both Tel1^ATM and Rad3^ATR kinases survive telomere maintenance defects by circularizing all three chromosomes.

We have demonstrated by quantitative chromatin immunoprecipitation assays that the leading strand DNA polymerase (Pol ε) arrives to replicating telomeres significantly earlier than the lagging strand DNA polymerases (Pol α and Pol δ), and replicating telomeres strongly recruit Replication Protein A (RPA) and Rad3-Rad26 (ATR-ATRIP) complexes in fission yeast. We have also established the cell-cycle-regulated recruitment timing for MCM, Mre11-Rad50-Nbs1 (MRN) complex, Trt1 (TERT, catalytic subunit of telomerase), and telomere capping proteins (Pot1 and Stn1). In addition, we have established that Tel1^ATM and Rad3^ATR kinases are redundantly required to promote telomere protection and telomerase recruitment by promoting efficient recruitment of the telomere capping complex subunit Ccq1 to telomeres.

A model of telomere length regulation in fission yeast. (Moser et al. 2011)

We have also discovered recently that Tel1^ATM/Rad3^ATR-dependent phosphorylation of Ccq1 on Thr93 is essential for telomerase association with telomeres, and that the 14-3-3-like domain of the telomerase regulatory subunit Est1 specifically recognizes and binds the phosphorylated Thr93 of Ccq1. Phosphorylation of Ccq1 is negatively regulated by the telomerase inhibitors Taz1, Rap1 and Poz1, and telomere elongation and increased telomerase association with telomeres found in rap1Δ cells are dependent on Ccq1 Thr93 phosphorylation. On the other hand, Ccq1 Thr93 phosphorylation is also increased as telomeres shorten in telomerase mutant cells. Taken together, we thus uncovered the Tel1^ATM/Rad3^ATR-dependent Ccq1-Est1 interaction as a critical regulatory mechanism that ensures stable maintenance of telomeres in fission yeast cells.

 

Selected Publications

Mennie, A.K., Moser, B.A., Hoyle, A., Low, R.S., Tanaka, K. and Nakamura, T.M. (2019) Tpz1^TPP1 prevents telomerase activation and protects telomeres by modulating the Stn1-Ten1 complex in fission yeast. Commun. Biol. 2:297.

Mennie, A.K., Moser, B.A. and Nakamura, T.M. (2018) LARP7-like protein Pof8 regulates telomerase assembly and poly(A)+TERRA expression in fission yeast. Nature Commun. 9(1): 586.

Moser, B.A., Raguimova, O.N. and Nakamura, T.M. (2015) Ccq1-Tpz1TPP1 interaction facilitates telomerase and SHREC association with telomeres in fission yeast. Mol. Biol. Cell 26(21): 3857-3866.

Miyagawa, K., Low, R.S., Santosa, V., Tsuji, H., Moser, B.A., Fujisawa, S., Harland, J., Raguimova, O.N., Go, A., Ueno, M., Matsuyama, A., Yoshida, M., Nakamura, T.M.* and Tanaka, K.* (2014) (*Co-corresponding authors) SUMOylation regulates telomere length by targeting Tpz1^TPP1 to modulate shelterin-Stn1 interaction in fission yeast. Proc. Natl. Acad. Sci. U.S.A. 111(16): 5950-5955.

Chang, Y.-T., Moser, B.A. and Nakamura, T.M. (2013) Fission yeast shelterin regulates DNA polymerases and Rad3^ATR kinase to limit telomere extension. PLoS Genet. 9(11): e1003936.

Moser, B.A., Chang, Y.-T., Kosti, J. and Nakamura, T.M. (2011) Tel1^ATM and Rad3^ATR kinases promote Ccq1-Est1 interaction to maintain telomeres in fission yeast. Nat. Struct. Mol. Biol. 18: 1408-1413.

Carneiro, T., Khair, L., Reis, C.C., Borges, V., Moser, B.A., Nakamura, T.M. and Ferreira, M.G. (2010) Telomeres avoid end detection by severing the checkpoint signal transduction pathway. Nature 467(7312): 228-232.