Deoxycholic acid activates the c-Jun N-terminal kinase pathway via FAS receptor activation in primary hepatocytes. Role of acidic sphingomyelinase-mediated ceramide generation in FAS receptor activation.
We have shown previously that bile acids can activate the JNK pathway and down-regulate cholesterol 7alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in the neutral pathway of bile acid biosynthesis. In this study, the mechanism(s) by which deoxycholic acid (DCA) activates the JNK pathway were examined. FAS receptor (FAS-R) and acidic sphingomyelinase (ASM)-deficient hepatocytes were resistant to DCA-induced activation of the JNK pathway. Activation of the JNK pathway (2-3-fold) in response to tumor necrosis factor-alpha was similar in both wild-type and FAS-R(-/-) hepatocytes. In wild-type and FAS-R(-/-) hepatocytes, ceramide elevation was detected as early as 2 min and peaked at 10 min after DCA treatment. In contrast, ASM(-/-) hepatocytes were defective in DCA-induced ceramide generation. Treatment with DCA resulted in movement of FAS-R to the cell surface, which was blocked upon treatment with brefeldin A. However, brefeldin A failed to block DCA-mediated JNK activation in wild-type hepatocytes. DCA-induced JNK activation was independent of either the epidermal growth factor receptor activation or free radical generation. Addition of ASM to rat hepatocytes activated JNK and down-regulated CYP7A1 mRNA levels. In conclusion, these results show that DCA activates JNK and represses CYP7A1 mRNA levels in primary hepatocytes via an ASM/FAS-R-dependent mechanism that is independent of either the epidermal growth factor receptor or free radical generation.
Gupta
Seema
S
Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond 23298, USA.
Natarajan
Ramesh
R
Payne
Shawn G
SG
Studer
Elaine J
EJ
Spiegel
Sarah
S
Dent
Paul
P
Hylemon
Phillip B
PB
D000483:Alleles; D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism; D020126:Brefeldin A / Q000494:pharmacology; D002478:Cells, Cultured; D002518:Ceramides / Q000378:metabolism; D002790:Cholesterol 7-alpha-Hydroxylase / Q000096:biosynthesis / Q000378:metabolism; D003840:Deoxycholic Acid / Q000378:metabolism*; D015536:Down-Regulation; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism; D005609:Free Radicals; D022781:Hepatocytes / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases; D008024:Ligands; D048670:MAP Kinase Kinase 4; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D019014:fas Receptor / Q000378:metabolism*
D001647:Bile Acids and Salts; D002518:Ceramides; D004791:Enzyme Inhibitors; D005609:Free Radicals; D008024:Ligands; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D019014:fas Receptor; D003840:Deoxycholic Acid; D020126:Brefeldin A; D002790:Cholesterol 7-alpha-Hydroxylase; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D013108:Sphingomyelin Phosphodiesterase