Protein kinase C-dependent, CCAAT/enhancer-binding protein beta-mediated expression of insulin-like growth factor I gene.
The possible involvement of the protein kinase C (PKC) pathway in transcriptional regulation of the human insulin-like growth factor-I (IGF-I) gene has been suggested. In this study, we sought to determine whether a PKC-dependent pathway is implicated in the transcriptional control, and if it is, how this occurs. Treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA) caused an increase in the activity of the human IGF-I gene major promoter in HepG2 cells. A CCAAT/enhancer-binding protein (C/EBP) binding site located at +22 to +30 was bound by C/EBP beta in a TPA-dependent manner and was solely responsible for the TPA responsiveness. This increase in C/EBP beta activity occurs through transcriptional and posttranslational regulation, and the latter is mediated by activation of p90 ribosomal S6 kinase (RSK): co-expression of dominant negative RSK abolished the TPA-responsive and C/EBP beta-dependent transactivation. Also, TPA-responsive activation of GAL4-C/EBP beta chimera required the Ser residue known as the RSK target. In SK-N-MC cells, which display constitutive, high expression of IGF-I on use of the major promoter, a large amount of C/EBP beta binding was observed with the C/EBP site in the basal state. Treatment with PKC inhibitors substantially reduced the promoter activity and mRNA amounts of IGF-I, with the binding of C/EBP beta to the C/EBP site also being reduced. When the C/EBP site was disrupted, the basal promoter activity was reduced, but the reduction by the PKC inhibitor was no longer observed. These observations suggest that the increase of C/EBP beta binding to the C/EBP site, which is in part mediated via activation of RSK, can primarily explain the TPA responsiveness of the IGF-I gene promoter. The intrinsic PKC activity in SK-N-MC cells should play a major role in the constitutive, high expression of IGF-I and may therefore contribute in part to the maintenance of the tumor phenotype of the cells.
Umayahara
Yutaka
Y
Department of Internal Medicine and Therapeutics (A8), Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita City, Osaka Pref. 565-0871, Japan.
Kajimoto
Yoshitaka
Y
Fujitani
Yoshio
Y
Gorogawa
Shin-Ichi
S
Yasuda
Tetsuyuki
T
Kuroda
Akio
A
Ohtoshi
Kentaro
K
Yoshida
Shigeru
S
Kawamori
Dan
D
Yamasaki
Yoshimitsu
Y
Hori
Masatsugu
M
D001483:Base Sequence; D001665:Binding Sites; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000378:metabolism*; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D008301:Maleimides / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012694:Serine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D022763:CCAAT-Enhancer-Binding Protein-alpha; D022782:CCAAT-Enhancer-Binding Protein-beta; D004791:Enzyme Inhibitors; D007211:Indoles; D008301:Maleimides; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D012694:Serine; D007334:Insulin-Like Growth Factor I; D011493:Protein Kinase C; C070515:bisindolylmaleimide I; D013755:Tetradecanoylphorbol Acetate