Translocation of Akt/PKB to the nucleus of osteoblast-like MC3T3-E1 cells exposed to proliferative growth factors

FEBS Lett. 2000 Jul 14;477(1-2):27-32. doi: 10.1016/s0014-5793(00)01758-0.

Abstract

An active phosphatidylinositol 3-kinase (PI3K) has been shown in nuclei of different cell types. The products of this enzyme, i.e. inositides phosphorylated in the D3 position of the inositol ring, may act as second messengers themselves. Nuclear PI3K translocation has been demonstrated to be related to an analogous translocation of a PtdIns(3,4,5)P(3) activated PKC, the zeta isozyme. We have examined the issue of whether or not in the osteoblast-like clonal cell line MC3T3-E1 there may be observed an insulin-like growth factor-I- (IGF-I) and platelet-derived growth factor- (PDGF) dependent nuclear translocation of an active Akt/PKB. Western blot analysis showed a maximal nuclear translocation after 20 min of IGF-I stimulation or after 30 min of PDGF treatment. Both growth factors increased rapidly and transiently the enzyme activity of immunoprecipitable nuclear Akt/PKB on a similar time scale and after 60 min the values were slightly higher than the basal levels. Enzyme translocation was blocked by the specific PI3K inhibitor, LY294002, as well as cell entry into S-phase. Confocal microscopy showed an evident increase in immunostaining intensity in the nuclear interior after growth factor treatment but no changes in the subcellular distribution of Akt/PKB when a LY294002 pre-treatment was administered to the cells. These findings strongly suggest that the intranuclear translocation of Akt/PKB is an important step in signalling pathways that mediate cell proliferation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Transport / drug effects
  • Cell Division / drug effects
  • Cell Line
  • Cell Nucleus / drug effects
  • Cell Nucleus / enzymology
  • Cell Nucleus / metabolism*
  • Chromones / pharmacology
  • Enzyme Activation / drug effects
  • Fibroblasts
  • Fluorescent Antibody Technique
  • Insulin-Like Growth Factor I / pharmacology*
  • Kinetics
  • Mice
  • Morpholines / pharmacology
  • Osteoblasts / cytology
  • Osteoblasts / drug effects*
  • Osteoblasts / enzymology
  • Osteoblasts / metabolism*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphoinositide-3 Kinase Inhibitors
  • Platelet-Derived Growth Factor / pharmacology*
  • Protein-Serine-Threonine Kinases / metabolism
  • Protein-Tyrosine Kinases / metabolism
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-akt
  • S Phase / drug effects
  • Signal Transduction / drug effects
  • Skull

Substances

  • Chromones
  • Morpholines
  • Phosphoinositide-3 Kinase Inhibitors
  • Platelet-Derived Growth Factor
  • Proto-Oncogene Proteins
  • 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
  • Insulin-Like Growth Factor I
  • Protein-Tyrosine Kinases
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt