Research Papers:

Inhibition of RNA polymerase I transcription initiation by CX-5461 activates non-canonical ATM/ATR signaling

Jaclyn Quin, Keefe T. Chan, Jennifer R. Devlin, Donald P. Cameron, Jeannine Diesch, Carleen Cullinane, Jessica Ahern, Amit Khot, Nadine Hein, Amee J. George, Katherine M Hannan, Gretchen Poortinga, Karen E. Sheppard, Kum Kum Khanna, Ricky W. Johnstone, Denis Drygin, Grant A. McArthur, Richard B. Pearson, Elaine Sanij and Ross D. Hannan _

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Oncotarget. 2016; 7:49800-49818. https://doi.org/10.18632/oncotarget.10452

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Jaclyn Quin1,2,11, Keefe T. Chan1, Jennifer R. Devlin1,12, Donald P. Cameron1,3, Jeannine Diesch1,13, Carleen Cullinane1, Jessica Ahern1, Amit Khot1, Nadine Hein4, Amee J. George4,5,6, Katherine M Hannan2,4, Gretchen Poortinga1,7, Karen E. Sheppard1,2,3, Kum Kum Khanna8, Ricky W. Johnstone1,3,5, Denis Drygin9, Grant A. McArthur1,3,5,7, Richard B. Pearson1,2,3,10, Elaine Sanij1,5,*, Ross D. Hannan1,2,3,4,6,10,*

1Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia

2Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria, Australia

3Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria, Australia

4The John Curtin School of Medical Research, Australian National University, Acton, ACT, Australia

5Department of Pathology, University of Melbourne, Parkville, Victoria, Australia

6School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia

7Department of Medicine, St Vincent’s Hospital, University of Melbourne, Fitzroy, Victoria, Australia

8QIMR Berghofer Medical Research Institute, Brisbane City, Qld, Australia

9Pimera Inc, San Diego, CA, USA

10Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia

11Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden

12Institute for Molecular Medicine Finland, Biomedicum 2, Helsinki, Finland

13Josep Carreras Institute for Leukaemia Research (IJC), Campus ICO-HGTP, Badalona, Barcelona, Spain

*These authors contributed equally to this work

Correspondence to:

Elaine Sanij, email: [email protected]

Ross D. Hannan, email: [email protected]

Keywords: RNA polymerase I, rDNA, CX-5461, nucleolar stress response, DNA damage signaling

Received: March 17, 2016     Accepted: June 13, 2016     Published: July 06, 2016


RNA polymerase I (Pol I)-mediated transcription of the ribosomal RNA genes (rDNA) is confined to the nucleolus and is a rate-limiting step for cell growth and proliferation. Inhibition of Pol I by CX-5461 can selectively induce p53-mediated apoptosis of tumour cells in vivo. Currently, CX-5461 is in clinical trial for patients with advanced haematological malignancies (Peter Mac, Melbourne).

Here we demonstrate that CX-5461 also induces p53-independent cell cycle checkpoints mediated by ATM/ATR signaling in the absence of DNA damage. Further, our data demonstrate that the combination of drugs targeting ATM/ATR signaling and CX-5461 leads to enhanced therapeutic benefit in treating p53-null tumours in vivo, which are normally refractory to each drug alone. Mechanistically, we show that CX-5461 induces an unusual chromatin structure in which transcriptionally competent relaxed rDNA repeats are devoid of transcribing Pol I leading to activation of ATM signaling within the nucleoli. Thus, we propose that acute inhibition of Pol transcription initiation by CX-5461 induces a novel nucleolar stress response that can be targeted to improve therapeutic efficacy.

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