title: Inhibition of RNA polymerase I transcription initiation by CX-5461 activates non-canonical ATM/ATR signaling.
abstract: 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.
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.|Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria, Australia.|Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden.
authors.forename: Jaclyn
authors.initials: J
authors.lastname: Quin
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.
authors.forename: Keefe T
authors.initials: KT
authors.lastname: Chan
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.|Institute for Molecular Medicine Finland, Biomedicum 2, Helsinki, Finland.
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Devlin
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.|Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Donald P
authors.initials: DP
authors.lastname: Cameron
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.|Josep Carreras Institute for Leukaemia Research (IJC), Campus ICO-HGTP, Badalona, Barcelona, Spain.
authors.forename: Jeannine
authors.initials: J
authors.lastname: Diesch
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.
authors.forename: Carleen
authors.initials: C
authors.lastname: Cullinane
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.
authors.forename: Jessica
authors.initials: J
authors.lastname: Ahern
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.
authors.forename: Amit
authors.initials: A
authors.lastname: Khot
authors.affiliation: The John Curtin School of Medical Research, Australian National University, Acton, ACT, Australia.
authors.forename: Nadine
authors.initials: N
authors.lastname: Hein
authors.affiliation: The John Curtin School of Medical Research, Australian National University, Acton, ACT, Australia.|Department of Pathology, University of Melbourne, Parkville, Victoria, Australia.|School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Amee J
authors.initials: AJ
authors.lastname: George
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria, Australia.|The John Curtin School of Medical Research, Australian National University, Acton, ACT, Australia.
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Hannan
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.|Department of Medicine, St Vincent's Hospital, University of Melbourne, Fitzroy, Victoria, Australia.
authors.forename: Gretchen
authors.initials: G
authors.lastname: Poortinga
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.|Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria, Australia.|Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Karen E
authors.initials: KE
authors.lastname: Sheppard
authors.affiliation: QIMR Berghofer Medical Research Institute, Brisbane City, Qld, Australia.
authors.forename: Kum Kum
authors.initials: KK
authors.lastname: Khanna
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.|Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria, Australia.|Department of Pathology, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Ricky W
authors.initials: RW
authors.lastname: Johnstone
authors.affiliation: Pimera Inc, San Diego, CA, USA.
authors.forename: Denis
authors.initials: D
authors.lastname: Drygin
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.|Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria, Australia.|Department of Pathology, University of Melbourne, Parkville, Victoria, Australia.|Department of Medicine, St Vincent's Hospital, University of Melbourne, Fitzroy, Victoria, Australia.
authors.forename: Grant A
authors.initials: GA
authors.lastname: McArthur
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.|Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria, Australia.|Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria, Australia.|Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Pearson
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.|Department of Pathology, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Elaine
authors.initials: E
authors.lastname: Sanij
authors.affiliation: Research Division, Peter MacCallum Cancer Centre, St. Andrews Place, East Melbourne, Victoria, Australia.|Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria, Australia.|Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria, Australia.|The John Curtin School of Medical Research, Australian National University, Acton, ACT, Australia.|School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia.|Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: Ross D
authors.initials: RD
authors.lastname: Hannan
mesh_terms: D000818:Animals; D017209:Apoptosis; D064007:Ataxia Telangiectasia Mutated Proteins / Q000378:metabolism*; D052160:Benzothiazoles / Q000494:pharmacology*; D049108:Cell Enlargement; D002466:Cell Nucleolus / Q000378:metabolism; D049109:Cell Proliferation; D002843:Chromatin / Q000378:metabolism; D020552:Comet Assay; D004249:DNA Damage; D004275:DNA, Ribosomal / Q000235:genetics; D005347:Fibroblasts / Q000378:metabolism; D019337:Hematologic Neoplasms / Q000378:metabolism; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D009287:Naphthyridines / Q000494:pharmacology*; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology*; D012318:RNA Polymerase I / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015398:Signal Transduction; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D052160:Benzothiazoles; C557717:CX 5461; D002843:Chromatin; D004275:DNA, Ribosomal; D009287:Naphthyridines; D019384:Nucleic Acid Synthesis Inhibitors; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D012318:RNA Polymerase I
keywords: CX-5461; DNA damage signaling; RNA polymerase I; nucleolar stress response; rDNA