Basic Research
Copyright ©2005 Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Mar 7, 2005; 11(9): 1345-1350
Published online Mar 7, 2005. doi: 10.3748/wjg.v11.i9.1345
Differential phosphorylation of p38 induced by apoptotic and anti-apoptotic stimuli in murine hepatocytes
Li-Xia Guo, Hong Xie
Li-Xia Guo, Hong Xie, Laboratory of Biotherapy, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences; Graduate School of the Chinese Academy of Sciences
Author contributions: All authors contributed equally to the work.
Correspondence to: Professor Hong Xie, Laboratory of Biotherapy, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China. hxie@sibs.ac.cn
Telephone: +86-21-54921434 Fax: +86-21-34010138
Received: August 17, 2004
Revised: August 18, 2004
Accepted: September 8, 2004
Published online: March 7, 2005
Abstract

AIM: To investigate the differential phosphorylation and activation of p38 in hepatocytes by pro-apoptotic Transforming Growth Factor-β1 (TGF-β1), 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-β1-induced apoptosis was associated with the phosphorylation of p38, and SB202190, a specific inhibitor of p38, which was able to inhibit TGF-β1-induced caspase activation and apoptosis. TPA and EGF also blocked apoptosis induced by TGF-β1. Both of them induced the phosphorylation of p38. The results showed SB202190 had no effect on TGF-β1-induced phosphorylation of p38, but effectively inhibited both EGF and TPA-induced phosphorylation of p38.

CONCLUSION: Pro-apoptotic TGF-β1, 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-β1 plays an important role in caspase activation and apoptosis, TPA and EGF-induced p38 phosphorylation may not be requisite for their anti-apoptotic function.

Keywords: p38; Apoptosis; Hepatocytes