Separate roles for H-Ras and Rac in signaling by transforming growth factor (TGF)-beta. H-Ras is essential for activation of MAP kinase, partially required for transcriptional activation by TGF-beta, but not required for signaling of growth suppression by TGF-beta.
The signaling components located downstream of the transforming growth factor (TGF)-beta receptor are poorly understood. We constructed adenoviral vectors expressing a dominant-negative form of either H-Ras (AdCARasY57) or Rac (AdCARacN17), and used them to examine the roles of H-Ras and Rac in TGF-beta signaling using arterial endothelial cells in primary culture, and several established cells including a mink lung epithelial cell line (Mv1Lu). The rapid activation of p42/44 MAP kinase (MAPK) by TGF-beta1 was eliminated completely, and transcriptional activation by TGF-beta1 of the plasminogen activator inhibitor-1 gene was reduced by 50% in both endothelial cells and Mv1Lu when they were infected with AdCARasY57. However, the antiproliferative effect of TGF-beta, as assessed by the induction of the mRNA for Cdk4/6-specific inhibitor p15INK4B and by DNA synthesis, was not affected in AdCARasY57-infected cells. A MAPK kinase (MEK)1/2 inhibitor, U0126 also abolished MAPK activation and partially inhibited transcriptional activation by TGF-beta, suggesting that MAPK may be partially involved in this pathway. MAPK activation, transcriptional activation and growth suppression by TGF-beta were all unaffected in cells infected with AdCARacN17, although the DNA synthesis elicited by serum mitogens was suppressed completely in the infected cells. Our data indicate that H-Ras is essential for mitogen-activated protein kinase activation, partly required for transcriptional activation by TGF-beta, but not critically involved in the signaling that exerts the antiproliferative effect of TGF-beta. The results also suggest that Rac may not serve as an essential molecule in signaling by TGF-beta in the cells tested.
Yamamoto
H
H
Molecular Cardiology Unit, Research Institute of Angiocardiology and Cardiology Clinic, Kyushu University School of Medicine, Fukuoka, Japan.
Atsuchi
N
N
Tanaka
H
H
Ogawa
W
W
Abe
M
M
Takeshita
A
A
Ueno
H
H
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002455:Cell Division; D002460:Cell Line; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D008907:Mink; D015689:Oncogene Protein p21(ras) / Q000378:metabolism*; D015398:Signal Transduction; D015533:Transcriptional Activation; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D020744:rac GTP-Binding Proteins
D016212:Transforming Growth Factor beta; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D015689:Oncogene Protein p21(ras); D020744:rac GTP-Binding Proteins