Activation of the small GTP-binding proteins rho and rac by growth factor receptors

1995 ◽  
Vol 108 (1) ◽  
pp. 225-233 ◽  
Author(s):  
C.D. Nobes ◽  
P. Hawkins ◽  
L. Stephens ◽  
A. Hall
Keyword(s):  
Plasma Membrane ◽  
Growth Factor ◽  
Tyrosine Kinase ◽  
Phorbol Ester ◽  
Lysophosphatidic Acid ◽  
Actin Polymerization ◽  
Binding Proteins ◽  
Platelet Derived Growth Factor ◽  
Gtp Binding ◽  
Rho Protein

The small GTP-binding proteins, rho and rac, control signal transduction pathways that link growth factor receptors to the activation of actin polymerization. In Swiss 3T3 cells, rho proteins mediate the lysophosphatidic acid and bombesin-induced formation of focal adhesions and actin stress fibres, whilst rac proteins are required for the platelet-derived growth factor-, insulin-, bombesin- and phorbol ester (phorbol 12-myristate 13-acetate)-stimulated actin polymerization at the plasma membrane that results in membrane ruffling. To investigate the role of p85/p110 phosphatidylinositol 3-kinase in the rho and rac signalling pathways, we have used a potent inhibitor of this activity, wortmannin. Wortmannin has no effect on focal adhesion or actin stress fibre formation induced by lysophosphatidic acid, bombesin or microinjected recombinant rho protein. In contrast, it totally inhibits plasma membrane edge-ruffling induced by platelet-derived growth factor and insulin though not by bombesin, phorbol ester or microinjected recombinant rac protein. We conclude that phosphatidylinositol 3,4,5 trisphosphate mediates activation of rac by the platelet-derived growth factor and insulin receptors. The effects of lysophosphatidic acid on the Swiss 3T3 actin cytoskeleton can be blocked by the tyrosine kinase inhibitor, tyrphostin. Since tyrphostin does not inhibit the effects of microinjected rho protein, we conclude that lysophosphatidic acid activation of rho is mediated by a tyrosine kinase.

scholarly journals Rac GTPase interacts specifically with phosphatidylinositol 3-kinase

1996 ◽  
Vol 315 (3) ◽  
pp. 775-779 ◽  
Author(s):  
Gary M. BOKOCH ◽  
Chris J. VLAHOS ◽  
Yan WANG ◽  
Ulla G. KNAUS ◽  
Alexis E. TRAYNOR-KAPLAN
Keyword(s):  
Growth Factor ◽  
Actin Polymerization ◽  
Binding Proteins ◽  
Specific Interaction ◽  
Bound State ◽  
Rac Gtpase ◽  
Gtp Binding Proteins ◽  
Gtp Binding ◽  
Rho Family

The Rac GTP-binding proteins are members of the Rho family and regulate growth factor-stimulated actin assembly in a variety of cells. The formation of phosphorylated inositol lipids has been implicated in control of the processes initiating and regulating such actin polymerization. Associations of Rho family GTP-binding proteins with enzymes involved in lipid metabolism have been described. Here we demonstrate a direct and specific interaction of Rac proteins with phosphatidylinositol (PI) 3-kinase. This interaction is dependent upon Rac being in a GTP-bound state and requires an intact Rac effector domain. In contrast, direct binding of RhoA to PI 3-kinase could not be detected. Rac–GTP also bound to PI 3-kinase in Swiss 3T3 fibroblast and human neutrophil lysates, and increased PI 3-kinase activity became associated with Rac–GTP in platelet-derived growth factor-stimulated cells. Interaction of Rac–GTP with PI 3-kinase in vitro stimulated the activity of the enzyme by 2–9-fold. A specific interaction of active Rac with PI 3-kinase might be important in regulation of the actin cytoskeleton.

Molecular Targeting of Platelet-Derived Growth Factor B by Imatinib Mesylate in a Patient With Metastatic Dermatofibrosarcoma Protuberans

2002 ◽  
Vol 20 (17) ◽  
pp. 3586-3591 ◽  
Author(s):  
Brian P. Rubin ◽  
Scott M. Schuetze ◽  
Janet F. Eary ◽  
Thomas H. Norwood ◽  
Sohail Mirza ◽  
...  
Keyword(s):  
Growth Factor ◽  
Tyrosine Kinase ◽  
Imatinib Mesylate ◽  
Kinase Inhibitor ◽  
Dermatofibrosarcoma Protuberans ◽  
Response To Therapy ◽  
Platelet Derived Growth Factor ◽  
Response To Treatment ◽  
Resected Specimen ◽  
Factor B

PURPOSE: Dermatofibrosarcoma protuberans is caused by activation of the platelet-derived growth factor B (PDGFB) receptor, a transmembrane tyrosine kinase. We investigated the response of dermatofibrosarcoma protuberans to the tyrosine kinase inhibitor imatinib mesylate. PATIENTS AND METHODS: A patient with unresectable, metastatic dermatofibrosarcoma protuberans received imatinib mesylate (400 mg bid). Response to therapy was assessed by [18F]fluorodeoxyglucose (FDG) positron emission tomography, magnetic resonance imaging, and histopathologic and immunohistochemical evaluation. RESULTS: The patient was treated for 4 months with imatinib mesylate. The hypermetabolic uptake of FDG fell to background levels within 2 weeks of treatment, and the tumor volume shrank by over 75% during the 4 months of therapy, allowing for resection of the mass. There was no residual viable tumor in the resected specimen, indicating a complete histologic response to treatment with imatinib mesylate. CONCLUSION: Imatinib mesylate is highly active in dermatofibrosarcoma protuberans. The dramatic response seen in this patient demonstrates that inhibition of PDGFB receptor tyrosine kinase activity can significantly impact viability of at least one type of solid tumor.

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