title: PDGF regulates the actin cytoskeleton through hnRNP-K-mediated activation of the ubiquitin E3-ligase MIR.
abstract: 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 E(3)-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.
authors.affiliation: Ludwig Institute for Cancer Research, Royal Free and University College London, Medical School, UK.
authors.forename: Kohji
authors.initials: K
authors.lastname: Nagano
authors.forename: Beat C
authors.initials: BC
authors.lastname: Bornhauser
authors.forename: Gayathri
authors.initials: G
authors.lastname: Warnasuriya
authors.forename: Alan
authors.initials: A
authors.lastname: Entwistle
authors.forename: Rainer
authors.initials: R
authors.lastname: Cramer
authors.forename: Dan
authors.initials: D
authors.lastname: Lindholm
authors.forename: Soren
authors.initials: S
authors.lastname: Naaby-Hansen
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D000199:Actins / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D002465:Cell Movement; D003599:Cytoskeleton / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D015536:Down-Regulation; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D034641:Heterogeneous-Nuclear Ribonucleoprotein K / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D051379:Mice; D018994:Myosin Light Chains / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex; D061988:Proteasome Inhibitors; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D041701:Swiss 3T3 Cells; D044767:Ubiquitin-Protein Ligases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D019061:src-Family Kinases / Q000037:antagonists & inhibitors
chemical_list: D000199:Actins; D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D018994:Myosin Light Chains; D010982:Platelet-Derived Growth Factor; D061988:Proteasome Inhibitors; D034741:RNA, Small Interfering; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; C559132:March8 protein, mouse; D044767:Ubiquitin-Protein Ligases; D019061:src-Family Kinases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease