Altered regulation of Src tyrosine kinase by transforming growth factor beta1 in a human hepatoma cell line.
Transforming growth factor betas (TGF-betas) are the potent growth inhibitors for various cell types. Certain transformed cells, however, show poor response to TGF-beta-induced growth inhibition, which contributes to their uncontrolled proliferation. Recently, we have reported that TGF-beta1 induces degradation of activated Src tyrosine kinase in rat fibroblasts. To elucidate the alteration in TGF-beta signaling pathway in tumor cells that cannot respond to the cytokine, we compared the effects of TGF-beta1 on Src kinase in two human hepatoma cell lines, TGF-beta1-insensitive Mahlavu cells and TGF-beta1-sensitive HepG2 cells. TGF-beta1 decreased Src kinase activity in HepG2 cells, but increased cellular Src levels and Src kinase activity in Mahlavu cells. Co-incubation of Mahlavu cells with TGF-beta1 and 12-O-tetradecanoyl phorbol 13-acetate (TPA) decreased Src protein levels and Src kinase activity, inducing TGF-beta1 sensitivity. TGF-beta1 induced tyrosine dephosphorylation of Ras guanosine triphosphatase-activating protein (Ras-GAP) and Ras inactivation in HepG2 cells, but induced Ras-GAP phosphorylation and Ras activation in Mahlavu cells. The Src kinase inhibitor abolished the increase of Src kinase activity in TGF-beta1-treated Mahlavu cells, and induced TGF-beta1 sensitivity. These findings suggest that regulation of Src kinase by TGF-beta1 is altered in Mahlavu cells. The altered regulation of Src may contribute to TGF-beta1 insensitivity in this cell line, at least in part through activation of Ras.
Fukuda
K
K
Second Department of Internal Medicine, Osaka University Medical School, Suita, Japan.
Kawata
S
S
Tamura
S
S
Matsuda
Y
Y
Inui
Y
Y
Igura
T
T
Inoue
S
S
Kudara
T
T
Matsuzawa
Y
Y
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000201:enzymology*; D015815:Cell Adhesion Molecules / Q000378:metabolism; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D020690:GTPase-Activating Proteins; D006801:Humans; D008113:Liver Neoplasms / Q000201:enzymology*; D051379:Mice; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism; D051381:Rats; D018125:Receptors, Transforming Growth Factor beta / Q000032:analysis; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism; D020703:ras GTPase-Activating Proteins; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D015815:Cell Adhesion Molecules; D020690:GTPase-Activating Proteins; D011506:Proteins; D018125:Receptors, Transforming Growth Factor beta; D016212:Transforming Growth Factor beta; D020703:ras GTPase-Activating Proteins; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; C496051:Ptk2 protein, mouse; C496052:Ptk2 protein, rat; D019061:src-Family Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)