Activation of phosphoinositide 3-kinase is required for PDGF-stimulated membrane ruffling.
BACKGROUND
There is substantial evidence that phosphoinositide 3-kinase (PI 3-kinase) is a critical component of signalling pathways used by the cell-surface receptors for a variety of mammalian growth factors and other hormones. The physiological product of this enzyme is a highly polar membrane lipid called phosphatidylinositol (3,4,5)-trisphosphate This lipid has been postulated to act as a second-messenger in cells but its putative targets are still unknown.


RESULTS
A particular rearrangement of actin filaments, which results in membrane ruffling, is elicited by the activation of PDGF beta-receptors expressed in cultured porcine aortic endothelial cells. We have found that this consequence of PDGF beta-receptor activation is inhibited by three independent manipulations of PI 3-kinase activity: firstly, by the deletion of tyrosine residues in the PDGF beta-receptor to which PI 3-kinase binds; secondly, by the overexpression of a mutant 85 kD PI 3-kinase regulatory subunit to which the catalytic kinase subunit cannot bind; and thirdly, by the addition of the fungal metabolite wortmannin, which is a potent inhibitor of the catalytic activity of PI 3-kinase.


CONCLUSIONS
These results argue strongly that phosphatidylinositol (3,4,5)-trisphosphate synthesis is required for growth-factor-stimulated membrane ruffling in porcine aortic endothelial cells, and suggest that synthesis of this lipid may be part of a signalling pathway leading to direct or indirect activation of the small GTP-binding protein Rac.
Wennström
S
S
Ludwig Institute for Cancer Research, Uppsala Branch, Sweden.
Hawkins
P
P
Cooke
F
F
Hara
K
K
Yonezawa
K
K
Kasuga
M
M
Jackson
T
T
Claesson-Welsh
L
L
Stephens
L
L
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D004789:Enzyme Activation; D008954:Models, Biological; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases; D018129:Phosphatidylinositol Phosphates / Q000096:biosynthesis; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D017479:Receptors, Platelet-Derived Growth Factor / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013552:Swine; D000077191:Wortmannin
D000730:Androstadienes; D018129:Phosphatidylinositol Phosphates; D010982:Platelet-Derived Growth Factor; C060974:phosphatidylinositol 3,4,5-triphosphate; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D017479:Receptors, Platelet-Derived Growth Factor; D000077191:Wortmannin