title: Regulation of intestinal serotonin transporter expression via epigenetic mechanisms: role of HDAC2.
abstract: The serotonin (5-HT) transporter (SERT) facilitates clearance of extracellular 5-HT by its uptake and internalization. Decreased expression of SERT and consequent high 5-HT levels have been implicated in various diarrheal disorders. Thus, appropriate regulation of SERT is critical for maintenance of 5-HT homeostasis in health and disease. Previous studies demonstrated that SERT is regulated via posttranslational and transcriptional mechanisms. However, the role of epigenetic mechanisms in SERT regulation is not known. Current studies investigated the effects of histone deacetylase (HDAC) inhibition on SERT expression and delineated the mechanisms. Treatment of Caco-2 cells with the pan-HDAC inhibitors butyrate (5 mM) and trichostatin (TSA, 1 μM) decreased SERT mRNA and protein levels. Butyrate- or TSA-induced decrease in SERT was associated with decreased activity of human SERT (hSERT) promoter 1 (upstream of exon 1a), but not hSERT promoter 2 (upstream of exon 2). Butyrate + TSA did not show an additive effect on SERT expression, indicating that mechanisms involving histone hyperacetylation may be involved. Chromatin immunoprecipitation assays demonstrated enrichment of the hSERT promoter 1 (flanking nt -250/+2) with tetra-acetylated histone H3 or H4, which was increased (~3-fold) by butyrate. Interestingly, specific inhibition of HDAC2 (but not HDAC1) utilizing small interfering RNA decreased SERT mRNA and protein levels. The decrease in SERT expression by HDAC inhibition was recapitulated in an in vivo model. SERT mRNA levels were decreased in the ileum and colon of mice fed pectin (increased availability of butyrate) compared with controls fed a fiber-free diet (~50-60%). Our results identify a novel role of HDAC2 as a regulator of SERT gene expression in intestinal epithelial cells.
authors.affiliation: Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA. rgill@uic.edu
authors.forename: Ravinder K
authors.initials: RK
authors.lastname: Gill
authors.forename: Anoop
authors.initials: A
authors.lastname: Kumar
authors.forename: Pooja
authors.initials: P
authors.lastname: Malhotra
authors.forename: Daniel
authors.initials: D
authors.lastname: Maher
authors.forename: Varsha
authors.initials: V
authors.lastname: Singh
authors.forename: Pradeep K
authors.initials: PK
authors.lastname: Dudeja
authors.forename: Waddah
authors.initials: W
authors.lastname: Alrefai
authors.forename: Seema
authors.initials: S
authors.lastname: Saksena
mesh_terms: D000107:Acetylation; D000818:Animals; D002087:Butyrates / Q000494:pharmacology; D018938:Caco-2 Cells; D044127:Epigenesis, Genetic; D055785:Gene Knockdown Techniques; D056284:Histone Deacetylase 1 / Q000235:genetics / Q000378:metabolism; D056464:Histone Deacetylase 2 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology; D006657:Histones / Q000378:metabolism; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010368:Pectins / Q000008:administration & dosage; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D034741:RNA, Small Interfering / Q000235:genetics; D050486:Serotonin Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D002087:Butyrates; D056572:Histone Deacetylase Inhibitors; D006657:Histones; D006877:Hydroxamic Acids; D034741:RNA, Small Interfering; C493230:SLC6A4 protein, human; D050486:Serotonin Plasma Membrane Transport Proteins; C012589:trichostatin A; D010368:Pectins; C110550:HDAC1 protein, human; C533423:HDAC2 protein, human; D056284:Histone Deacetylase 1; D056464:Histone Deacetylase 2