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  • The EMBO Journal (2005) 24, 1696 - 1705
  • doi:10.1038/sj.emboj.7600648

Published online: 14 April 2005

The tRNA methylase METTL1 is phosphorylated and inactivated by PKB and RSK in vitro and in cells

Robert A Cartlidge1, Axel Knebel1, Mark Peggie2, Andrei Alexandrov3, Eric M Phizicky3 and Philip Cohen1,2

  1. MRC Protein Phosphorylation Unit, School of Life Sciences, MSI/WTB complex, University of Dundee, Dundee, UK
  2. Division of Signal Transduction Therapy, School of Life Sciences, MSI/WTB complex, University of Dundee, Dundee, UK
  3. Department of Biochemistry and Biophysics, University of Rochester School of Medicine, Rochester, NY, USA

Correspondence to:

Philip Cohen, MRC Protein Phosphorylation Unit, School of Life Sciences, MSI/WTB complex, University of Dundee, Dow Street, Dundee DD1 5EH, UK. Tel.: +44 1382 344238; Fax: 44 1382 223778; E-mail: p.cohen@dundee.ac.uk

Received 9 February 2005; Accepted 23 March 2005

A substrate for protein kinase B (PKB)alpha in HeLa cell extracts was identified as methyltransferase-like protein-1 (METTL1), the orthologue of trm8, which catalyses the 7-methylguanosine modification of tRNA in Saccharomyces cerevisiae. PKB and ribosomal S6 kinase (RSK) both phosphorylated METTL1 at Ser27 in vitro. Ser27 became phosphorylated when HEK293 cells were stimulated with insulin-like growth factor-1 (IGF-1) and this was prevented by inhibition of phosphatidyinositol 3-kinase. The IGF-1-induced Ser27 phosphorylation did not occur in 3-phosphoinositide-dependent protein kinase-1 (PDK1)-deficient embryonic stem cells, but occurred normally in PDK1[L155E] cells, indicating that the effect of IGF-1 is mediated by PKB. METTL1 also became phosphorylated at Ser27 in response to phorbol-12-myristate 13-acetate and this was prevented by PD 184352 or pharmacological inhibition of RSK. Phosphorylation of METTL1 by PKB or RSK inactivated METTL1 in vitro, as did mutation of Ser27 to Asp or Glu. Expression of METTL1[S27D] or METTL1[S27E] did not rescue the growth phenotype of yeast lacking trm8. In contrast, expression of METTL1 or METTL1[S27A] partially rescued growth. These results demonstrate that METTL1 is inactivated by PKB and RSK in cells, and the potential implications of this finding are discussed.

  • Keywords:

    • METTL1,
    • PKB,
    • protein synthesis,
    • RSK,
    • tRNA methylation