PROTEIN-KINASE-B ACTIVATION AND LAMELLIPODIUM FORMATION ARE INDEPENDENT PHOSPHOINOSITIDE 3-KINASE-MEDIATED EVENTS DIFFERENTIALLY REGULATED BY ENDOGENOUS RAS
Dhj. Vanweering et al., PROTEIN-KINASE-B ACTIVATION AND LAMELLIPODIUM FORMATION ARE INDEPENDENT PHOSPHOINOSITIDE 3-KINASE-MEDIATED EVENTS DIFFERENTIALLY REGULATED BY ENDOGENOUS RAS, Molecular and cellular biology, 18(4), 1998, pp. 1802-1811
Regulation of phosphoinositide 3-kinase (PI 3-kinase) can occur by bin
ding of the regulatory p85 subunit to tyrosine-phosphorylated proteins
and by binding of the p110 catalytic subunit to activated Ras. Howeve
r, the way in which these regulatory mechanisms act to regulate PI 3-k
inase in vivo is unclear, Were we show that several growth factors (ba
sic fibroblast growth factor [bFGF], platelet-derived growth factor [P
DGF], and epidermal growth factor [EGF; to activate an EGF receptor-Re
t chimeric receptor]) all activate PI3-kinase in vivo in the neuroecto
derm-derived cell line SKF5. However, these growth factors differ in t
heir ability to activate PI 3-kinase-dependent signaling. PDGF and EGF
(Ret) treatment induced PI 3-kinase-dependent lamellipodium formation
and protein kinase B (PKB) activation. In contrast, bFGF did not induc
e lamelli-podium formation but activated PKB, albeit to a small extent
. PDGF and EGF(Ret) stimulation resulted in binding of p85 to tyrosine
-phosphorylated proteins and strong Ras activation, bFGF, however, ind
uced only strong activation of Ras, In addition, while Ras(Asn17) abol
ished bFGF activation of PKB, PDGF-and EGF(Rea)-induced PKB activation
was only partially, inhibited and lamelli-podium formation was unaffe
cted. Interestingly, in contrast to activation of only endogenous Ras
(bFGF), ectopic expression of activated Ras did result in lamelli-podi
um formation, From this we conclude that, in vivo, p85 and Ras synergi
ze to activate PI 3-kinase and that strong activation of only endogeno
us Bas exerts a small effect on PI 3-kinase activity, sufficient for P
KB activation but not lamelli-podium formation. This differential sens
itivity to PI3-kinase activation could be explained by our Ending that
PKB activation and lamelli-podium formation are independent PI 3-kina
se-induced events.