Type 2 inositol trisphosphate receptor gene expression in hepatocytes is regulated by cyclic AMP.
The type 2 inositol 1,4,5-trisphosphate receptor (IP3R2) is the principal intracellular Ca2+release channel in hepatocytes, and so is important for bile secretion and other functions. IP3R2 activity is regulated in part by post-translational modifications but little is known about transcriptional regulation of its expression. We found that both IP3R2 mRNA and protein levels in liver were increased during fasting. Treatment of hepatocytes with forskolin or 8-CPT-cAMP also increased IP3R2, and this was reduced by actinomycin D. Analysis of the IP3R2 promoter revealed five CREs, and CREB potently increased promoter activity. Mutation of CRE4 or CRE5 decreased induction by CREB, and ChIP assay showed recruitment of CREB to these sites. Adenylyl cyclase (AC) 6 and 9 were the principal AC isoforms detected in rat hepatocytes, and silencing either one decreased organic anion secretion, which depends on IP3R2. Secretion furthermore was increased by overnight but not acute treatment with forskolin or 8-CPT-cAMP. These findings provide evidence that IP3R2 expression is transcriptionally regulated by cAMP via CREB binding to CRE elements in its promoter. The findings furthermore suggest that this mechanism is relevant for hormonal regulation of bile secretion.
Digestive Diseases Section, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520-8019, USA.
Emma
E
Kruglov
Digestive Diseases Section, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520-8019, USA.
Meenakshisundaram
M
Ananthanarayanan
Digestive Diseases Section, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520-8019, USA.
Pedro
P
Sousa
Digestive Diseases Section, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520-8019, USA.
Jittima
J
Weerachayaphorn
Digestive Diseases Section, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520-8019, USA.
Mateus T
MT
Guerra
Digestive Diseases Section, Yale School of Medicine, 333 Cedar Street, New Haven, CT 06520-8019, USA. Electronic address: michael.nathanson@yale.edu.
Michael H
MH
Nathanson
D000262:Adenylyl Cyclases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D050882:CREB-Binding Protein / Q000235:genetics* / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D005215:Fasting; D005786:Gene Expression Regulation; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000235:genetics* / Q000378:metabolism; D008297:Male; D009154:Mutation; D061251:Primary Cell Culture; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020218:Response Elements; D015398:Signal Transduction; D013873:Thionucleotides / Q000494:pharmacology
D053496:Inositol 1,4,5-Trisphosphate Receptors; D012333:RNA, Messenger; D013873:Thionucleotides; D003609:Dactinomycin; D005576:Colforsin; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D000242:Cyclic AMP; D050882:CREB-Binding Protein; C494365:Crebbp protein, rat; D000262:Adenylyl Cyclases; C413923:adenylate cyclase 9; C121100:adenylyl cyclase 6
Bile secretion; Calcium signaling; Cyclic AMP; Hepatocytes; Type 2 inositol 1,4,5-trisphosphate receptor