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Sodium‐coupled neutral amino acid transporter 4 functions as a regulator of protein synthesis during liver development
Author(s) -
Kondou Hiroki,
Kawai Masanobu,
Tachikawa Kanako,
Kimoto Akihito,
Yamagata Masayo,
Koinuma Tomoko,
Yamazaki Miwa,
Nakayama Masahiro,
Mushiake Sotaro,
Ozono Keiichi,
Michigami Toshimi
Publication year - 2013
Publication title -
hepatology research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.123
H-Index - 75
eISSN - 1872-034X
pISSN - 1386-6346
DOI - 10.1111/hepr.12069
Subject(s) - ap 1 transcription factor , transactivation , hepatocyte nuclear factors , hepatocyte nuclear factor 4 , microbiology and biotechnology , biology , transporter , amino acid transporter , electrophoretic mobility shift assay , amino acid , transcription factor , chemistry , biochemistry , gene , nuclear receptor
Aim The molecular mechanisms by which hepatocyte nuclear factor ( HNF )4α regulates fetal liver development have not been fully elucidated. We screened the downstream molecules of HNF4 α during liver development and identified sodium‐coupled neutral amino acid transporter ( SNAT )4. The aim of this study is to investigate the regulation of SNAT4 by HNF4 α and to clarify its roles in differentiating hepatocytes. Methods HNF4 α was overexpressed in cultured liver buds using adenovirus, and suppression subtractive hybridization screening was performed. Temporal and spatial expression of SNAT4 during liver development was investigated. Regulation of SNAT4 by HNF4 α was examined by promoter analyses and electrophoretic mobility shift assays ( EMSA ). Metabolic labeling and western blotting were carried out using primary hepatoblasts with SNAT4 overexpression. Results The expression of S lc38a4 encoding SNAT4 showed a marked perinatal increase, and was predominant among system A amino acid transporters. It was first detected in embryonic day 18.5 liver, and found in most hepatocytes after birth. Three alternative first exons were found in the SNAT4 gene. Promoter analyses using approximately 3‐kb fragments corresponding to each first exon ( AP1 , AP2 , AP3 ) revealed that AP1 and AP2 exhibited strong promoter activity in mouse hepatoblasts with endogenous HNF4 α. Transactivation of AP2 was upregulated by HNF4 α in H e L a cells without endogenous HNF4 α. EMSA has demonstrated that HNF4 α directly binds to cis ‐elements in AP2 . Overexpression of SNAT4 facilitated amino acid uptake and de novo protein synthesis in primary hepatoblasts. Conclusion SNAT4 functions downstream of HNF4 α and plays significant roles in liver development through mechanisms of amino acid uptake and protein synthesis.