View the Current Issue

Article

  • The EMBO Journal (2006) 25, 1871 - 1882
  • doi:10.1038/sj.emboj.7601059

Published online: 13 April 2006

PDGF regulates the actin cytoskeleton through hnRNP-K-mediated activation of the ubiquitin E3-ligase MIR

Kohji Nagano1,ab, Beat C Bornhauser2,ac, Gayathri Warnasuriya1, Alan Entwistle1, Rainer Cramer1,3,d, Dan Lindholm2,4 and Soren Naaby-Hansen1,3

  1. Ludwig Institute for Cancer Research, Royal Free and University College London, Medical School, London, UK
  2. Department of Neuroscience, University of Uppsala, Uppsala, Sweden
  3. Department of Biochemistry and Molecular Biology, University College London, London, UK
  4. Minerva Research Institute, Biomedicum Helsinki, Helsinki, Finland

Correspondence to:

Soren Naaby-Hansen, Ludwig Institute for Cancer Research, Royal Free and University College London Medical School, Courtauld Building, 91 Riding House Street, London W1W 7BS, UK. Tel.: +44 208 346 4948; Fax: +44 207 878 4040; E-mail: soren@ludwig.ucl.ac.uk

aThese authors contributed equally to this work

bPresent address: Department of Proteomics Research, Institute of Medical Sciences, University of Tokyo, Tokyo, Japan

cPresent address: Department of Oncology, Childrens Hospital, University of Zyrich, Zyrich, Switzerland

dPresent address: The BioCentre and School of Chemistry, University of Reading, Reading, UK

Received 14 March 2005; Accepted 1 March 2006

PDGF is a potent chemotactic mitogen and a strong inductor of fibroblast motility. In Swiss 3T3 fibroblasts, exposure to PDGF but not EGF or IGF-1 causes a rapid loss of actin stress fibers (SFs) and focal adhesions (FAs), which is followed by the development of retractile dendritic protrusions and induction of motility. The PDGF-specific actin reorganization was blocked by inhibition of Src-kinase and the 26S proteasome. PDGF induced Src-dependent association between the multifunctional transcription/translation regulator hnRNP-K and the mRNA-encoding myosin regulatory light-chain (MRLC)-interacting protein (MIR), a E3-ubiquitin ligase that is MRLC specific. This in turn rapidly increased MIR expression, and led to ubiquitination and proteasome-mediated degradation of MRLC. Downregulation of MIR by RNA muting prevented the reorganization of actin structures and severely reduced the migratory and wound-healing potential of PDGF-treated cells. The results show that activation of MIR and the resulting removal of diphosphorylated MRLC are essential for PDGF to instigate and maintain control over the actin–myosin-based contractile system in Swiss 3T3 fibroblasts. The PDGF induced protein destabilization through the regulation of hnRNP-K controlled ubiquitin -ligase translation identifies a novel pathway by which external stimuli can regulate phenotypic development through rapid, organelle-specific changes in the activity and stability of cytoskeletal regulators.

  • Keywords:

    • focal adhesions,
    • hnRNP-K,
    • MIR,
    • PDGF,
    • ubiquitin