title: Saturated fatty acids induce post-transcriptional regulation of HAMP mRNA via AU-rich element-binding protein, human antigen R (HuR).
abstract: Iron is implicated in fatty liver disease pathogenesis. The human hepcidin gene, HAMP, is the master switch of iron metabolism. The aim of this study is to investigate the regulation of HAMP expression by fatty acids in HepG2 cells. For these studies, both saturated fatty acids (palmitic acid (PA) and stearic acid (SA)) and unsaturated fatty acid (oleic acid (OA)) were used. PA and, to a lesser extent, SA, but not OA, up-regulated HAMP mRNA levels, as determined by real-time PCR. To understand whether PA regulates HAMP mRNA at the transcriptional or post-transcriptional level, the transcription inhibitor actinomycin D was employed. PA-mediated induction of HAMP mRNA expression was not blocked by actinomycin D. Furthermore, PA activated HAMP 3'-UTR, but not promoter, activity, as shown by reporter assays. HAMP 3'-UTR harbors a single AU-rich element (ARE). Mutation of this ARE abolished the effect of PA, suggesting the involvement of ARE-binding proteins. The ARE-binding protein human antigen R (HuR) stabilizes mRNA through direct interaction with AREs on 3'-UTR. HuR is regulated by phosphorylation-mediated nucleo-cytoplasmic shuttling. PA activated this process. The binding of HuR to HAMP mRNA was also induced by PA in HepG2 cells. Silencing of HuR by siRNA abolished PA-mediated up-regulation of HAMP mRNA levels. PKC is known to phosphorylate HuR. Staurosporine, a broad-spectrum PKC inhibitor, inhibited both PA-mediated translocation of HuR and induction of HAMP expression. Similarly, rottlerin, a novel class PKC inhibitor, abrogated PA-mediated up-regulation of HAMP expression. In conclusion, lipids mediate post-transcriptional regulation of HAMP throughPKC- and HuR-dependent mechanisms.
authors: From the Department of Biochemistry and Molecular Biology and.
authors: Sizhao
authors: S
authors: Lu
authors: From the Department of Biochemistry and Molecular Biology and.
authors: Justin L
authors: JL
authors: Mott
authors: the Division of Gastroenterology and Hepatology, Department of Internal Medicine, University of Nebraska Medical Center, Omaha, Nebraska 68198-5820 dharrisonfindik@unmc.edu.
authors: Duygu Dee
authors: DD
authors: Harrison-Findik
mesh_terms: D020413:3' Untranslated Regions; D000818:Animals; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D000067780:ELAV-Like Protein 1 / Q000378:metabolism*; D005227:Fatty Acids / Q000737:chemistry*; D005234:Fatty Liver / Q000378:metabolism*; D056945:Hep G2 Cells; D064451:Hepcidins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007501:Iron / Q000737:chemistry; D051379:Mice; D016296:Mutagenesis; D009154:Mutation; D019308:Palmitic Acid / Q000737:chemistry*; D010766:Phosphorylation; D011485:Protein Binding; D021381:Protein Transport; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D020413:3' Untranslated Regions; D000067780:ELAV-Like Protein 1; C098770:ELAVL1 protein, human; D005227:Fatty Acids; C578702:HAMP protein, human; D064451:Hepcidins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D019308:Palmitic Acid; D007501:Iron
keywords: AU-rich element; HuR; fatty acid; fatty liver disease; hepcidin; iron; mRNA decay; microRNA (miRNA); post-transcriptional regulation; protein kinase C (PKC)