Protein kinase C and limited substrates for tyrosine kinase are involved in epidermal growth factor (EGF)-dependent growth of a human squamous cell carcinoma cell variant.
Human squamous cell carcinoma cells (NA cells) possess a large number of epidermal growth factor (EGF) receptors and their growth is inhibited by EGF. Recently, we isolated a series of variants which escaped EGF-mediated growth inhibition. The variant ER11 cells expressed a decreased level of EGF receptors and grew in an EGF-dependent fashion. Treatment of ER11 cells with EGF resulted in the activation of protein kinase C, which was followed by the enhancement of 80-kDa protein phosphorylation as observed in NA cells. Thus, EGF can activate not only tyrosine kinase but also protein kinase C in both NA and ER11 cells. The EGF-dependent growth stimulation in ER11 cells was inhibited by 12-O-tetradecanoylphorbol 13-acetate (TPA). Exposure of NA and ER11 cells to TPA for 30 h resulted in the down-regulation of protein kinase C. In these protein kinase C-deficient cells, EGF was able to activate autophosphorylation of the EGF receptor. The EGF-activated EGF receptor kinase phosphorylated numerous cellular proteins even in the protein kinase C-deficient cells. However, there were less tyrosine-phosphorylated proteins in ER11 cells than in NA cells. These results suggested that protein kinase C is necessary for the EGF-dependent growth stimulation of ER11 cells and that several tyrosine-phosphorylated proteins commonly observed in both NA and ER11 cells seem essential for cell proliferation.
Department of Molecular Biology, Keio University School of Medicine, Tokyo, Japan.
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Hirai
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Shimizu
D000596:Amino Acids / Q000378:metabolism; D002455:Cell Division / Q000502:physiology*; D015180:Electrophoresis, Gel, Two-Dimensional; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000502:physiology*; D066246:ErbB Receptors / Q000378:metabolism; D006801:Humans; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D019000:Phosphotyrosine; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000031:analogs & derivatives / Q000276:immunology / Q000378:metabolism
D000596:Amino Acids; D010750:Phosphoproteins; D019000:Phosphotyrosine; D014443:Tyrosine; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate