alphaPIX nucleotide exchange factor is activated by interaction with phosphatidylinositol 3-kinase.
p21-activated kinase (PAK) is a common effector protein of the small GTPases Cdc42 and Rac, leading to the activation of downstream mitogen activated protein kinases. PAK also mediates polarized cytoskeletal changes induced by these GTPases. The recently identified PAK-interacting exchange factor (PIX) acts as a guanine nucleotide exchange factor on Rac, and colocalizes with PAK in a focal complex, but little is known about the associated signaling cascades, including upstream activators of PIX. In this study, we show that one of the isoforms of PIX, alphaPIX, is activated by signaling cascades from the platelet-derived growth factor (PDGF) receptor and EphB2 receptor, and from integrin-induced signaling through phosphatidylinositol 3-kinase (PI3-kinase). alphaPIX is activated by forming a complex with these receptors either via association with PAK and Nck, or direct association with the p85 regulatory subunit of PI3-kinase. Synthetic phosphoinositide and membrane targeted PI3-kinase augmented the alphaPIX activity in vivo. In Xenopus, aggregates of mesodermal cells derived from embryos microinjected with alphaPIX significantly increased the peripheral spreading on fibronectin substrate in response to PDGF through PI3-kinase. These results indicate that alphaPIX is activated by PI3-kinase, and is involved in the receptor mediated signaling leading to the activation of the kinase activity of PAK, and the migration of mesodermal cells on extracellular matrix.
Yoshii
S
S
The First Department of Pathology, Hamamatsu University School of Medicine, 3600 Handa-cho, Hamamatsu, 431-3192 Japan.
Tanaka
M
M
Otsuki
Y
Y
Wang
D Y
DY
Guo
R J
RJ
Zhu
Y
Y
Takeda
R
R
Hanai
H
H
Kaneko
E
E
Sugimura
H
H
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D019556:COS Cells; D002448:Cell Adhesion; D018797:Cell Cycle Proteins / Q000502:physiology*; D002465:Cell Movement; D002522:Chlorocebus aethiops; D003599:Cytoskeleton / Q000648:ultrastructure; D005109:Extracellular Matrix; D005353:Fibronectins; D020558:GTP Phosphohydrolases / Q000502:physiology; D020662:Guanine Nucleotide Exchange Factors; D020935:MAP Kinase Signaling System; D046911:Macromolecular Substances; D008648:Mesoderm / Q000166:cytology; D008845:Microinjections; D008954:Models, Biological; D015513:Oncogene Proteins / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D010766:Phosphorylation; D020033:Protein Isoforms / Q000502:physiology*; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology; D036183:Receptor, EphB2; D017479:Receptors, Platelet-Derived Growth Factor / Q000502:physiology; D064067:Rho Guanine Nucleotide Exchange Factors; D015398:Signal Transduction / Q000502:physiology*; D014982:Xenopus laevis / Q000196:embryology; D054462:p21-Activated Kinases; D018909:src Homology Domains
D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; D005353:Fibronectins; D020558:GTP Phosphohydrolases; D020662:Guanine Nucleotide Exchange Factors; D046911:Macromolecular Substances; D015513:Oncogene Proteins; D019869:Phosphatidylinositol 3-Kinases; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases; D020794:Receptor Protein-Tyrosine Kinases; D036183:Receptor, EphB2; D017479:Receptors, Platelet-Derived Growth Factor; D064067:Rho Guanine Nucleotide Exchange Factors; D054462:p21-Activated Kinases; C078332:Nck protein