Activation of the Raf-1/MEK/ERK cascade by bile acids occurs via the epidermal growth factor receptor in primary rat hepatocytes.
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 p(74) Raf-1 in a time (5 to 20 minutes) and concentration-dependent (10 to 100 micromol/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 (approximately 81%) the activation of ERK by DCA. DCA rapidly (30 to 60 seconds) increased phosphorylation of the EGFR (approximately 2-fold) and Shc (approximately 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.
Rao
Yi-Ping
YP
Department of Microbiology and Immunology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, VA 23298-687, USA.
Studer
Elaine J
EJ
Stravitz
R Todd
RT
Gupta
Seema
S
Qiao
Liang
L
Dent
Paul
P
Hylemon
Phillip B
PB
D000818:Animals; D002478:Cells, Cultured; D003840:Deoxycholic Acid / Q000494:pharmacology*; D003902:Detergents / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D066246:ErbB Receptors / Q000187:drug effects / Q000378:metabolism; D005799:Genes, Dominant; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D051381:Rats; D013657:Taurodeoxycholic Acid / Q000494:pharmacology*; D018631:ras Proteins / Q000235:genetics / Q000494:pharmacology
D003902:Detergents; D003840:Deoxycholic Acid; D013657:Taurodeoxycholic Acid; D066246:ErbB Receptors; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins