Activation of protein kinase C alpha is required for TPA-triggered ERK (MAPK) signaling and growth inhibition of human hepatoma cell HepG2.
The signaling mechanisms for most of the antiproliferative processes are not fully understood. We have demonstrated that ERK(MAPK) signaling was involved in the induction of both p15(INK4b)and p16(INK4a) CDK inhibitors and growth inhibition of hepatoma cell HepG2 triggered by the tumor promoter tetradecanoyl phorbol acetate (TPA). In this study, the upstream signal mechanism for TPA-induced ERK(MAPK) activation was investigated. In HepG2 cells only one of the cPKC isozymes, PKCalpha, but not cPKCbetaII, nPKCepsilon or aPKCzeta was activated by TPA as demonstrated by its membrane translocation within 10-30 min and down-regulation at 24 h after TPA treatment. Pretreatment of 0.2-2.0 microM Bisindolylmaleimides, an inhibitor of PKC, attenuated the TPA-induced phosphorylation of ERK, gene expressions of p15(INK4b) and p16(INK4a), and growth inhibition of HepG2 cell in a dose-dependent manner. Consistently, transfection of HepG2 with 1.0-3.0 microM antisense (AS) PKCalpha, but not (AS) PKCbetaII, or nPKCepsilon oligonucleotides (ODN), for 36 h prior to TPA treatment also prevented the TPA-induced molecular and cellular effects described above. Taken together, we concluded that PKCalpha is specifically required for TPA-induced ERK(MAPK) signaling to trigger gene expressions of p15(INK4b) and p16(INK4a) leading to HepG2 growth inhibition.
Wen-Sheng
Wu
W
Department of Medical Technology, TZU CHI University, Taiwan. wuws@mail.tcu.edu.tw
Jun-Ming
Huang
H
D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000201:enzymology*; D018797:Cell Cycle Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D020935:MAP Kinase Signaling System; D008301:Maleimides / Q000494:pharmacology; D009841:Oligonucleotides / Q000737:chemistry; D016376:Oligonucleotides, Antisense / Q000737:chemistry / Q000494:pharmacology; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D020033:Protein Isoforms; D011493:Protein Kinase C / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate; D013997:Time Factors; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000378:metabolism
C493966:CDKN2B protein, human; D018797:Cell Cycle Proteins; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D007211:Indoles; D008301:Maleimides; D009841:Oligonucleotides; D016376:Oligonucleotides, Antisense; D020033:Protein Isoforms; D025521:Tumor Suppressor Proteins; C496628:PRKCA protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D048049:Extracellular Signal-Regulated MAP Kinases; C088060:bisindolylmaleimide; D013755:Tetradecanoylphorbol Acetate