Distinct mechanisms of alpha 5beta 1 integrin activation by Ha-Ras and R-Ras.
To investigate the possible roles of the Ras/Rho family members in the inside-out signals to activate integrins, we examined the ability of Ras/Rho small GTPases to stimulate avidity of alpha(5)beta(1) (VLA-5) to fibronectin in bone marrow-derived mast cells. We found that both Ha-Ras(Val-12) and R-Ras(Val-38) had strong stimulatory effects on adhesion and ligand binding activity of VLA-5 to fibronectin. However, only Ha-Ras(Val-12)-, but not R-Ras(Val-38)-induced adhesion was inhibited by wortmannin, which suggests that Ha-Ras(Val-12) is dependent on phosphatidylinositol (PI) 3-kinase on adhesion whereas R-Ras(Val-38) has another PI 3-kinase independent pathway to induce adhesion. The effector loop mutant Ha-Ras(Val-12)E37G, but not Y40C retained the ability to stimulate adhesion of mast cells to fibronectin. Consistently, PI 3-kinase p110delta, predominantly expressed in mast cells, interacted with Ha-Ras(Val-12) E37G, but not Y40C, which was also correlated with the levels of Akt phosphorylation in mast cells. Furthermore, marked adhesion was induced by a membrane-targeted version of p110delta. These results indicate that Ha-Ras(Val-12) activated VLA-5 through PI 3-kinase p110delta. The mutational effects of the R-Ras effector loop region on adhesion were not correlated with PI 3-kinase activities, consistent with our contention that R-Ras has a distinct pathway to modulate avidity of VLA-5.
Kinashi
T
T
Department of Immunology, Institute of Medical Science, University of Tokyo, Tokyo 108, Bayer-chair, Japan. tkinashi@mfour.med.kyoto-u.ac.jp
Katagiri
K
K
Watanabe
S
S
Vanhaesebroeck
B
B
Downward
J
J
Takatsu
K
K
D002448:Cell Adhesion; D002478:Cells, Cultured; D004789:Enzyme Activation; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006801:Humans; D008407:Mast Cells / Q000166:cytology / Q000378:metabolism; D017469:Receptors, Fibronectin / Q000378:metabolism*; D015398:Signal Transduction; D018631:ras Proteins / Q000378:metabolism*
D017469:Receptors, Fibronectin; D020558:GTP Phosphohydrolases; D018631:ras Proteins