title: Ileal apical sodium-dependent bile acid transporter protein levels are down-regulated through ubiquitin-dependent protein degradation induced by bile acids.
abstract: The ileal apical sodium-dependent bile acid transporter (ASBT or SLC10A2) has a crucial role in intestinal bile acid absorption. We previously reported that enterobacteria-mediated bile acid conversion was involved in the alteration of ileal ASBT expression levels. In the present study, to investigate the hypothesis that ileal ASBT protein levels are post-translationally regulated by enterobacteria-associated bile acids, alteration of ileal ASBT protein levels was analysed in mice 12 h and 24 h after anti-bacterial drug ampicillin (ABPC) treatment (100 mg/kg, single shot) that altered bile acid composition in the intestinal lumen. In ABPC-treated mice, enterobacteria-biotransformed bile acid, taurodeoxycholic acid (TDCA) and cholic acid (CA) levels were decreased, whereas taurocholic acid (TCA) and tauro-β-muricholic acid levels were increased in the intestinal lumen. Ileal ASBT protein levels in brush-border membrane vesicles (BBMVs), but not ileal Asbt mRNA levels, were significantly increased in the ABPC-treated mice, and the extent of ubiquitination of the ileal ASBT protein was reduced in the ABPC-treated mice. Treatment of ABPC-pretreated mice with CA or TDCA, but not TCA, significantly decreased ileal ASBT protein levels and increased the extent of ubiquitination of ileal ASBT protein. Treatment of mice with the lysosome inhibitor, chloroquine, or the proteasome inhibitor, MG132, increased ileal ASBT protein levels in BBMVs. CA-mediated reduction of ASBT protein levels in the ABPC-pretreated mice was attenuated by co-treatment with chloroquine or MG132. These results suggest that ileal ASBT protein is degraded by a ubiquitin-dependent pathway in response to enterobacteria-associated bile acids.
authors.affiliation: Division of Drug Metabolism and Molecular Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3, Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan. mmiyata@fish-u.ac.jp
authors.forename: Masaaki
authors.initials: M
authors.lastname: Miyata
authors.forename: Hiroki
authors.initials: H
authors.lastname: Yamakawa
authors.forename: Kenjiro
authors.initials: K
authors.lastname: Hayashi
authors.forename: Hideaki
authors.initials: H
authors.lastname: Kuribayashi
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Yamazoe
authors.forename: Kouichi
authors.initials: K
authors.lastname: Yoshinari
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects; D007082:Ileum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D029363:Organic Anion Transporters, Sodium-Dependent / Q000378:metabolism*; D059748:Proteolysis / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D027981:Symporters / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D054875:Ubiquitination / Q000187:drug effects
chemical_list: D001647:Bile Acids and Salts; D029363:Organic Anion Transporters, Sodium-Dependent; D027981:Symporters; D025801:Ubiquitin; C071908:sodium-bile acid cotransporter; D000667:Ampicillin
keywords: ASBT; Antibiotics; Bile acid; Enterobacteria; MG132; Ubiquitination