Poster Presentation 26th Lorne Cancer Conference 2014

Mechanisms regulating ribosome biogenesis by AKT and c-MYC  (#284)

Simone Woods 1 , Colin House 1 , Gretchen Poortinga 1 , Ross Hannan 1 2 3 4 5 , Richard Pearson 1 2 3 4 5 , Katherine Hannan 1 3
  1. Peter MacCallum Cancer Centre, Melbourne, VIC, Australia
  2. Sir Peter MacCallum Department of Oncology, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia
  3. Department of Biochemistry and Molecular Biology, University of Melbourne, Melbourne, Victoria, Australia
  4. Department of Biochemistry, Monash University, Melbourne, Victoria , Australia
  5. School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia

Ribosome biogenesis is an energy consuming process essential for cell growth and proliferation, thereby requiring tight regulation. Recently it has become evident that deregulated ribosome biogenesis can underlie cancer susceptibility, and be specifically targeted in cancer cells [1]. The transcription factor c-MYC is a master regulator of ribosome biogenesis. We have reported that c-MYC can selectively transcribe a RNA Polymerase I (Pol I) specific regulon [2]. We recently demonstrated that the kinase AKT also mediates Pol I-driven rDNA transcription to a similar extent as c-MYC [3]. Importantly, maximal activation of rDNA transcription and thus cell growth was achieved through the cooperative activities of both c-MYC and AKT [3].1 2 3 

The mechanism by which AKT alone and in cooperation with c-MYC regulates Pol I transcription remains unknown. We hypothesise that AKT may phosphorylate and subsequently activate c-MYC-regulated Pol I regulon components. We have identified nine out of sixty-six of these components and associated factors as putative AKT substrates based on a high stringency bioinformatics analysis using Motif scan. To test this hypothesis, we immunopreciptated the Pol I complex and associated proteins and used high sensitivity LC-MS/MS to characterise the members of the complex and to identify phosphorylated peptides. We find that endogenous nucleolar protein treacle is present in the Pol I complex and phosphorylated at one of the putative AKT phosphorylation sites identified by Motif Scan. Furthermore, immunoprecipitated treacle can be phosphorylated by purified AKT in vitro demonstrating that treacle is a direct AKT substrate. Consistent with our hypothesis, the treacle gene (TCOF1) is also a c-MYC target [2]. We are currently further validating treacle as a target of c-MYC and AKT and assessing the contribution of increased treacle expression and AKT-dependent phosphorylation to the cooperation of AKT and c-MYC in driving Pol I transcription and ribosome biogenesis.

  1. Bywater, M.J., et al., Inhibition of RNA polymerase I as a therapeutic strategy to promote cancer-specific activation of p53. Cancer Cell, 2012. 22(1): p. 51-65.
  2. Poortinga, G., et al., c-MYC coordinately regulates ribosomal gene chromatin remodeling and Pol I availability during granulocyte differentiation. Nucleic Acids Res, 2010. 39(8): p. 3267-81.
  3. Chan, J.C., et al., AKT promotes rRNA synthesis and cooperates with c-MYC to stimulate ribosome biogenesis in cancer. Sci Signal, 2011. 4(188): p. ra56.