Characterization of Rab21-positive tubular endosomes induced by PI3K inhibitors

Exp Cell Res. 2008 Feb 15;314(4):729-37. doi: 10.1016/j.yexcr.2007.11.018. Epub 2007 Dec 3.


We found that wortmannin, a potent phosphoinositide 3-kinase (PI3K) inhibitor, markedly induced the formation of Rab21-positive tubular compartments in A431 cells. By time-lapse fluorescence microscopy of live cells co-expressing fluorescent protein-fused Rab21 and other marker proteins, it was shown that the Rab21-positive tubules in wortmannin-treated cells were derived from Rab5-positive early endosomes, but not from late endosomes, recycling endosomes, lysosomes or the trans-Golgi network. The formation of Rab21-positive tubules was very dynamic and required microtubules. Rab21-positive tubules were also formed by the treatment of cells with 3-methyladenine (3-MA), which inhibits class III PI3K rather than class I PI3K. Furthermore, the loss of PI(3)P correlated with the tubulation of Rab21-positive endosomes in cells co-expressing fluorescent protein-fused Rab21 and a tandem FYVE domain. These results suggest that the lowering of PI(3)P as a result of class III PI3K inhibition may be an important cue for the morphological change of Rab21-positive early endosomes from vesicular to tubular form.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenine / analogs & derivatives
  • Adenine / pharmacology
  • Androstadienes / pharmacology*
  • Cell Line, Tumor
  • Endosomes / chemistry*
  • Endosomes / drug effects
  • Endosomes / ultrastructure
  • Enzyme Inhibitors / pharmacology*
  • Humans
  • Microscopy, Fluorescence
  • Microtubules / physiology
  • Phosphoinositide-3 Kinase Inhibitors*
  • Wortmannin
  • rab GTP-Binding Proteins / analysis*


  • Androstadienes
  • Enzyme Inhibitors
  • Phosphoinositide-3 Kinase Inhibitors
  • 3-methyladenine
  • RAB21 protein, human
  • rab GTP-Binding Proteins
  • Adenine
  • Wortmannin