title: Metformin suppresses expression of the selenoprotein P gene via an AMP-activated kinase (AMPK)/FoxO3a pathway in H4IIEC3 hepatocytes.
abstract: Selenoprotein P (SeP; encoded by SEPP1 in humans) is a liver-derived secretory protein that induces insulin resistance in type 2 diabetes. Suppression of SeP might provide a novel therapeutic approach to treating type 2 diabetes, but few drugs that inhibit SEPP1 expression in hepatocytes have been identified to date. The present findings demonstrate that metformin suppresses SEPP1 expression by activating AMP-activated kinase (AMPK) and subsequently inactivating FoxO3a in H4IIEC3 hepatocytes. Treatment with metformin reduced SEPP1 promoter activity in a concentration- and time-dependent manner; this effect was cancelled by co-administration of an AMPK inhibitor. Metformin also suppressed Sepp1 gene expression in the liver of mice. Computational analysis of transcription factor binding sites conserved among the species resulted in identification of the FoxO-binding site in the metformin-response element of the SEPP1 promoter. A luciferase reporter assay showed that metformin suppresses Forkhead-response element activity, and a ChIP assay revealed that metformin decreases binding of FoxO3a, a direct target of AMPK, to the SEPP1 promoter. Transfection with siRNAs for Foxo3a, but not for Foxo1, cancelled metformin-induced luciferase activity suppression of the metformin-response element of the SEPP1 promoter. The overexpression of FoxO3a stimulated SEPP1 promoter activity and rescued the suppressive effect of metformin. Metformin did not affect FoxO3a expression, but it increased its phosphorylation and decreased its nuclear localization. These data provide a novel mechanism of action for metformin involving improvement of systemic insulin sensitivity through the regulation of SeP production and suggest an additional approach to the development of anti-diabetic drugs.
authors.affiliation: From the Department of Disease Control and Homeostasis, Kanazawa University Graduate School of Medical Sciences, 13-1 Takara-machi, Kanazawa, Ishikawa 920-8641, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Takayama
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Misu
authors.forename: Hisakazu
authors.initials: H
authors.lastname: Iwama
authors.forename: Keita
authors.initials: K
authors.lastname: Chikamoto
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Saito
authors.forename: Koji
authors.initials: K
authors.lastname: Murao
authors.forename: Atsushi
authors.initials: A
authors.lastname: Teraguchi
authors.forename: Fei
authors.initials: F
authors.lastname: Lan
authors.forename: Akihiro
authors.initials: A
authors.lastname: Kikuchi
authors.forename: Reina
authors.initials: R
authors.lastname: Saito
authors.forename: Natsumi
authors.initials: N
authors.lastname: Tajima
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Shirasaki
authors.forename: Seiichi
authors.initials: S
authors.lastname: Matsugo
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Miyamoto
authors.forename: Shuichi
authors.initials: S
authors.lastname: Kaneko
authors.forename: Toshinari
authors.initials: T
authors.lastname: Takamura
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D021581:Active Transport, Cell Nucleus / Q000187:drug effects / Q000235:genetics; D000818:Animals; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D008687:Metformin / Q000494:pharmacology*; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D051381:Rats; D020218:Response Elements / Q000187:drug effects / Q000235:genetics; D051149:Selenoprotein P / Q000096:biosynthesis* / Q000235:genetics
chemical_list: C499517:FOXO3 protein, human; C499515:FOXO3 protein, rat; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; C474033:FoxO3 protein, mouse; D007004:Hypoglycemic Agents; D051149:Selenoprotein P; D008687:Metformin; D055372:AMP-Activated Protein Kinases
keywords: AMP-activated Kinase (AMPK); FoxO3a; Gene Expression; Hepatocyte; Hepatokine; Insulin Resistance; Metformin; Selenoprotein P; Transcription Promoter