TGFbeta1-induced aortic endothelial morphogenesis requires signaling by small GTPases Rac1 and RhoA.
TGFbeta is a potent regulator of cell differentiation in many cell types. On aortic endothelial cells, TGFbeta1 displays angiogenic properties in inducing capillary-like tube formation in collagen I gels, in vitro. We investigated cytoskeletal changes that precede tube formation and related these alterations to the effects of TGFbeta1 on the activation state of members of the RhoGTPase family. TGFbeta1 promotes cell elongation and stress fiber formation in aortic endothelial cells. Using cell lines with inducible expression of Rac1 mutants, we show that these events are mimicked by expression of dominant-negative Rac1 whereas the constitutively active mutant prevents the TGFbeta1-mediated change of phenotype. Although TGFbeta1 induces an initial rise in the Rac1-GTP content, this phase is followed by a prolonged loss of the active form. In contrast, RhoA activity increases progressively and reaches a plateau when Rac1-GTP is no longer detectable. Prolonged inhibition of Rac1 appears necessary and sufficient for the increase in RhoA-GTP. In situ examination of Rho activity in TGFbeta1-treated cells provides evidence that active RhoA relocalizes to the tips of elongated cells. Inhibiting the Rho effector ROCK abrogates tube formation. Thus, Rac1 and RhoA are regulated by TGFbeta1 in the process of endothelial tube formation in collagen I gels.
Varon
Christine
C
European Institute of Chemistry and Biology, University of Bordeaux I and Unité INSERM 441, Université Victor Segalen Bordeaux 2, Bordeaux, 2, rue Robert Escarpit, 33 600 Pessac, France.
Basoni
Caroline
C
Reuzeau
Edith
E
Moreau
Violaine
V
Kramer
I Jsbrand
IJ
Génot
Elisabeth
E
D000199:Actins / Q000378:metabolism; D000818:Animals; D001011:Aorta / Q000033:anatomy & histology* / Q000196:embryology; D002417:Cattle; D048430:Cell Shape; D002478:Cells, Cultured; D024042:Collagen Type I / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D042783:Endothelial Cells / Q000166:cytology / Q000502:physiology; D004730:Endothelium, Vascular / Q000033:anatomy & histology / Q000196:embryology* / Q000502:physiology; D004789:Enzyme Activation; D006160:Guanosine Triphosphate / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D009024:Morphogenesis; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013552:Swine; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
D000199:Actins; D024042:Collagen Type I; D047908:Intracellular Signaling Peptides and Proteins; D053773:Transforming Growth Factor beta1; D006160:Guanosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein