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Cellular and Molecular Life Sciences CMLS

, Volume 60, Issue 12, pp 2710–2720 | Cite as

Targeting of the Akt/PKB kinase to the actin skeleton

  • V. Cenni
  • A. Sirri
  • M. Riccio
  • G. Lattanzi
  • S. Santi
  • A. de Pol
  • N. M. Maraldi
  • S. MarmiroliEmail author
Research Article

Abstract

Serine/threonine kinase Akt/PKB intracellular distribution undergoes rapid changes in response to agonists such as Platelet-derived growth factor (PDGF) or Insulin-like growth factor (IGF). The concept has recently emerged that Akt subcellular movements are facilitated by interaction with nonsubstrate ligands. Here we show that Akt is bound to the actin skeleton in in situ cytoskeletal matrix preparations from PDGF-treated Saos2 cells, suggesting an interaction between the two proteins. Indeed, by immunoprecipitation and subcellular fractioning, we demonstrate that endogenous Akt and actin physically interact. Using recombinant proteins in in vitro binding and overlay assays, we further demonstrate that Akt interacts with actin directly. Expression of Akt mutants strongly indicates that the N-terminal PH domain of Akt mediates this interaction. More important, we show that the partition between actin bound and unbound Akt is not constant, but is modulated by growth factor stimulation. In fact, PDGF treatment of serum-starved cells triggers an increase in the amount of Akt associated with the actin skeleton, concomitant with an increase in Akt phosphorylation. Conversely, expression of an Akt mutant in which both Ser473 and Thr308 have been mutated to alanine completely abrogates PDGF-induced binding. The small GTPases Rac1 and Cdc42 seem to facilitate actin binding, possibly increasing Akt phosphorylation.

Akt cytoskeleton PDGF Rac Cdc42 GFP-actin 

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Copyright information

© Birkhäuser-Verlag Basel 2003

Authors and Affiliations

  • V. Cenni
    • 1
  • A. Sirri
    • 1
    • 4
  • M. Riccio
    • 1
  • G. Lattanzi
    • 2
  • S. Santi
    • 2
  • A. de Pol
    • 3
  • N. M. Maraldi
    • 1
    • 2
  • S. Marmiroli
    • 2
    • 3
    Email author
  1. 1.Laboratory of Cell Biology and Electron MicroscopyRizzoli Orthopedic InstituteBolognaItaly
  2. 2.ITOI, CNRRizzoli Orthopedic InstituteBolognaItaly
  3. 3.Department of Anatomy and HistologyUniversity of Modena and Reggio EmiliaModenaItaly
  4. 4.Laboratory of Immunology, Scientific Institute San Raffaele-DibitVita-Salute University, School of MedicineMilanoItaly

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