ERK cascade by bile acids... : Hepatology (original) (raw)

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Activation of the Raf-1/MEK/ERK cascade by bile acids occurs via the epidermal growth factor receptor in primary rat hepatocytes

Rao, Yi-Ping1; Studer, Elaine J.1; Stravitz, Todd R.2; Gupta, Seema1; Qiao, Liang3; Dent, Paul3; Hylemon, Phillip B. Ph.D.*,1

1 Department of Microbiology and Immunology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, VA 23298

2 Department of Internal Medicine, McGuire Veterans Affairs Medical Center, Richmond, VA 23298

3 Department of Radiation Oncology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, VA 23298

E-mail:[email protected]

*Address reprint requests to: Department of Microbiology and Immunology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, VA 23298-0678. fax: 804-828-0676.

Received June 18, 2001; accepted November 19, 2001; previously published online December 30, 2003

Abstract

Bile acids have been reported to activate several different cell signaling cascades in rat hepatocytes. However, the mechanism(s) of activation of these pathways have not been determined. This study aims to determine which bile acids activate the Raf-1/MEK/ERK cascade and the mechanism of activation of this pathway. Taurodeoxycholic acid (TDCA) stimulated (+235%) the phosphorylation of p74 Raf-1 in a time (5 to 20 minutes) and concentration-dependent (10 to 100 μmol/L) manner. Raf-1 and ERK activities were both significantly increased by most bile acids tested. Deoxycholic acid (DCA) was the best activator of ERK (3.6-fold). A dominant negative Ras (N17) construct expressed in primary hepatocytes prevented the activation of ERK by DCA. The epidermal growth factor receptor (EGFR)-specific inhibitor (AG1478) significantly inhibited (˜81%) the activation of ERK by DCA. DCA rapidly (30 to 60 seconds) increased phosphorylation of the EGFR (˜2-fold) and Shc (˜4-fold). A dominant negative mutant of the EGFR (CD533) blocked the ability of DCA to activate ERK. In conclusion, these results show that DCA activates the Raf-1/MEK/ERK signaling cascade in primary hepatocytes primarily via an EGFR/Ras-dependent mechanism.