Differential phosphorylation of p38 induced by apoptotic and anti-apoptotic stimuli in murine hepatocytes.
OBJECTIVE
To investigate the differential phosphorylation and activation of p38 in hepatocytes by pro-apoptotic Transforming Growth Factor-beta1 (TGF-beta1), pro-survival factors Epidermal Growth Factor (EGF) and 12-O-tetradecanoylphorbol-13-acetate (TPA) and the potential mechanisms.


METHODS
The phosphorylation and activation of p38 were determined by immunoblotting. Apoptosis was analyzed by morphological staining and observation, FACS analysis of sub-G1 content and DNA fragmentation assay. To quantitatively determine caspase activation, caspase activity assay was performed in vitro.


RESULTS
TGF-beta1-induced apoptosis was associated with the phosphorylation of p38, and SB202190, a specific inhibitor of p38, which was able to inhibit TGF-beta1-induced caspase activation and apoptosis. TPA and EGF also blocked apoptosis induced by TGF-beta1. Both of them induced the phosphorylation of p38. The results showed SB202190 had no effect on TGF-beta1-induced phosphorylation of p38, but effectively inhibited both EGF and TPA-induced phosphorylation of p38.


CONCLUSIONS
Pro-apoptotic TGF-beta1, anti-apoptotic TPA and EGF induce the phosphorylation of p38 through different mechanisms that can be distinguished by SB202190. The data suggest that TPA and EGF-induced p38 phosphorylation is through an autophosphorylation-dependent mechanism. Since p38 phosphorylation induced by TGF-beta1 plays an important role in caspase activation and apoptosis, TPA and EGF-induced p38 phosphorylation may not be requisite for their anti-apoptotic function.
Guo
Li-Xia
LX
Laboratory of Biotherapy, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
Xie
Hong
H
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002273:Carcinogens / Q000494:pharmacology; D020169:Caspases / Q000378:metabolism; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D022781:Hepatocytes / Q000166:cytology* / Q000201:enzymology*; D007093:Imidazoles / Q000494:pharmacology; D051379:Mice; D010766:Phosphorylation; D011725:Pyridines / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D053773:Transforming Growth Factor beta1; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D002273:Carcinogens; D004791:Enzyme Inhibitors; D007093:Imidazoles; D011725:Pyridines; C508961:Tgfb1 protein, mouse; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D004815:Epidermal Growth Factor; D048051:p38 Mitogen-Activated Protein Kinases; D020169:Caspases; D013755:Tetradecanoylphorbol Acetate; C090942:4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)imidazole