title: Mechanisms of Intestinal Serotonin Transporter (SERT) Upregulation by TGF-β1 Induced Non-Smad Pathways.
abstract: TGF-β1 is an important multifunctional cytokine with numerous protective effects on intestinal mucosa. The influence of TGF-β1 on serotonin transporter (SERT) activity, the critical mechanism regulating the extracellular availability of serotonin (5-HT), is not known. Current studies were designed to examine acute effects of TGF-β1 on SERT. Model human intestinal Caco-2 cells grown as monolayer's or as cysts in 3D culture and ex vivo mouse model were utilized. Treatment of Caco-2 cells with TGF-β1 (10 ng/ml, 60 min) stimulated SERT activity (~2 fold, P<0.005). This stimulation of SERT function was dependent upon activation of TGF-β1 receptor (TGFRI) as SB-431542, a specific TGF-βRI inhibitor blocked the SERT stimulation. SERT activation in response to TGF-β1 was attenuated by inhibition of PI3K and occurred via enhanced recruitment of SERT-GFP to apical surface in a PI3K dependent manner. The exocytosis inhibitor brefeldin A (2.5 μM) attenuated the TGF-β1-mediated increase in SERT function. TGF-β1 increased the association of SERT with the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) syntaxin 3 (STX3) and promoted exocytosis of SERT. Caco-2 cells grown as cysts in 3D culture recapitulated the effects of TGF-β1 showing increased luminal staining of SERT. Ussing chamber studies revealed increase in 3H-5-HT uptake in mouse ileum treated ex vivo with TGF-β1 (10 ng/ml, 1h). These data demonstrate a novel mechanism rapidly regulating intestinal SERT via PI3K and STX3. Since decreased SERT is implicated in various gastro-intestinal disorders e.g IBD, IBS and diarrhea, understanding mechanisms stimulating SERT function by TGF-β1 offers a novel therapeutic strategy to treat GI disorders.
authors.affiliation: Division of Gastroenterology & Hepatology, Dept. of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America.
authors.forename: Saad
authors.initials: S
authors.lastname: Nazir
authors.affiliation: Division of Gastroenterology & Hepatology, Dept. of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America.
authors.forename: Anoop
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Division of Gastroenterology & Hepatology, Dept. of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America.
authors.forename: Ishita
authors.initials: I
authors.lastname: Chatterjee
authors.affiliation: Division of Gastroenterology & Hepatology, Dept. of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America.
authors.forename: Arivarasu N
authors.initials: AN
authors.lastname: Anbazhagan
authors.affiliation: Division of Gastroenterology & Hepatology, Dept. of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America.
authors.forename: Tarunmeet
authors.initials: T
authors.lastname: Gujral
authors.affiliation: Division of Gastroenterology & Hepatology, Dept. of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America.
authors.forename: Shubha
authors.initials: S
authors.lastname: Priyamvada
authors.affiliation: Division of Gastroenterology & Hepatology, Dept. of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America.
authors.forename: Seema
authors.initials: S
authors.lastname: Saksena
authors.affiliation: Division of Gastroenterology & Hepatology, Dept. of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America; Jesse Brown VA Medical Center, Chicago, Illinois, United States of America.
authors.forename: Waddah A
authors.initials: WA
authors.lastname: Alrefai
authors.affiliation: Division of Gastroenterology & Hepatology, Dept. of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America; Jesse Brown VA Medical Center, Chicago, Illinois, United States of America.
authors.forename: Pradeep K
authors.initials: PK
authors.lastname: Dudeja
authors.affiliation: Division of Gastroenterology & Hepatology, Dept. of Medicine, University of Illinois at Chicago, Chicago, Illinois, United States of America.
authors.forename: Ravinder K
authors.initials: RK
authors.lastname: Gill
mesh_terms: D000818:Animals; D018938:Caco-2 Cells; D005089:Exocytosis; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D008810:Mice, Inbred C57BL; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D060066:Protein Interaction Maps; D021381:Protein Transport; D050765:Qa-SNARE Proteins / Q000378:metabolism; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D050765:Qa-SNARE Proteins; D018125:Receptors, Transforming Growth Factor beta; D050486:Serotonin Plasma Membrane Transport Proteins; D053773:Transforming Growth Factor beta1; D012701:Serotonin; D019869:Phosphatidylinositol 3-Kinases