Peroxisome proliferator-activated receptor alpha activates cyclooxygenase-2 gene transcription through bile acid transport in human colorectal cancer cell lines.
BACKGROUND
Evidence is accumulating that bile acids are involved in colon cancer development, but their molecular mechanisms remain unexplored. Bile acid has been reported to be associated with induction of the cyclooxygenase-2 (COX-2) gene. Because the human liver-specific organic anion transporter-2 (LST-2/OATP8/OATP1B3) is expressed in gastrointestinal cancers and might transport bile acids to the intracellular space, we studied the molecular mechanisms by which bile acids induce the transcription of COX-2, and the role of LST-2 in colonic cell lines.


METHODS
Transcriptional activity of COX-2 was measured using a human COX-2 promoter-luciferase assay under various concentrations of bile acids. Electrophoresis mobility shift assays (EMSAs) for peroxisome proliferators-activated receptor (PPAR) alpha and cyclic AMP responsive element (CRE) were performed.


RESULTS
The COX-2 promoter was induced by lithocholic acid (LCA), deoxycholic acid (DCA), and chenodeoxycholic acid (CDCA). Deletion and site-directed mutation analyses showed that CRE is the responsive element for LCA. An adenovirus expression system revealed that LST-2 is responsible for induction of COX-2. By EMSA using oligonucleotides of CRE, we observed formation of a specific protein-DNA complex, which was inhibited by a specific antibody against PPARalpha and CRE. A PPARalpha-specific agonist induced transcription of COX-2.


CONCLUSIONS
These results indicate that COX-2 is transcriptionally activated by the addition of LCA, CDCA, and DCA and that LST-2 plays an important role by transporting bile acid to the intracellular space. Moreover, LCA-dependent COX-2 gene activation consists of a transcriptional complex including PPARalpha and CRE-binding protein. Thus, this induction of COX-2 may participate in carcinogenesis and progression of colorectal cancer cells.
Oshio
Hiroshi
H
Division of Gastroenterological Surgery, Department of Surgery, Tohoku University Graduate School of Medical Science, 1-1 Seiryo-machi, Aoba, Sendai 980-8574, Japan.
Abe
Takaaki
T
Onogawa
Tohru
T
Ohtsuka
Hideo
H
Sato
Takeaki
T
Ii
Takayuki
T
Fukase
Kouji
K
Muto
Mitsuhisa
M
Katayose
Yu
Y
Oikawa
Masaya
M
Rikiyama
Toshiki
T
Egawa
Shinichi
S
Unno
Michiaki
M
D000256:Adenoviridae; D001647:Bile Acids and Salts / Q000494:pharmacology*; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein; D051546:Cyclooxygenase 2 / Q000235:genetics*; D024202:Electrophoretic Mobility Shift Assay; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D008095:Lithocholic Acid / Q000494:pharmacology; D029362:Organic Anion Transporters, Sodium-Independent / Q000378:metabolism / Q000494:pharmacology; D047493:PPAR alpha / Q000378:metabolism / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D000074542:Solute Carrier Organic Anion Transporter Family Member 1B3; D014158:Transcription, Genetic / Q000187:drug effects*; D015533:Transcriptional Activation; D014162:Transfection
D001647:Bile Acids and Salts; D017362:Cyclic AMP Response Element-Binding Protein; D029362:Organic Anion Transporters, Sodium-Independent; D047493:PPAR alpha; C421209:SLCO1B3 protein, human; D000074542:Solute Carrier Organic Anion Transporter Family Member 1B3; D008095:Lithocholic Acid; D051546:Cyclooxygenase 2