title: l-Tryptophan Activates Mammalian Target of Rapamycin and Enhances Expression of Tight Junction Proteins in Intestinal Porcine Epithelial Cells.
abstract: BACKGROUND
  Besides serving as a substrate for protein synthesis, L-tryptophan (L-Trp) is used via serotonin-, kynurenine-, and niacin-synthetic pathways to produce bioactive compounds crucial for whole-body homeostasis. It is unknown whether L-Trp itself can regulate metabolic pathways in animal cells.
  
  
  OBJECTIVE
  This study tested the hypothesis that L-Trp may activate mammalian target of rapamycin (mTOR) complex 1 and enhance expression of tight junction (TJ) proteins in intestinal porcine epithelial cells.
  
  
  METHODS
  Jejunal enterocytes, intestinal porcine epithelial cell line 1 (IPEC-1) isolated from newborn pigs, were cultured in customized Dulbecco's modified Eagle medium (DMEM) supplemented with or without L-Trp for the indicated time periods. Cell proliferation, L-Trp metabolism, protein turnover, mRNA abundance for L-Trp transporters [solute carrier family 3 member 1 (SLC3A1), solute carrier family 6 member 14 (SLC6A14), solute carrier family 6 member 19 (SLC6A19), and Na(+)/K(+) ATPase subunit-α1 (ATP1A1)], abundance of proteins involved in mTOR signaling, and TJ proteins were determined.
  
  
  RESULTS
  L-Trp was not degraded in IPEC-1 cells. Compared with basal medium containing 0.04 mmol/L L-Trp, 0.4 and 0.8 mmol/L L-Trp enhanced (P < 0.05) protein synthesis by 45-52% and cell growth by 17% and 25% on day 1 and 72% and 51% on day 2, respectively, while reducing (P < 0.05) protein degradation by 12% and 22%, respectively. These effects of L-Trp were associated with mTOR activation and increased (P < 0.05) mRNA abundance for L-Trp transporters (SLC6A19, SLC6A14, and SLC3A1) by 1.5-2.7 fold and ATP1A1 by 3 fold. L-Trp also upregulated (P < 0.05) the abundance of occludin, claudin-4, zonula occludens (ZO) 1 and 2 by 0.5-2 fold but did not affect expression of claudin-1 or ZO-3 in IPEC-1 cells.
  
  
  CONCLUSIONS
  L-Trp is not catabolized by pig small intestinal epithelial cells but can regulate intracellular protein turnover and expression of TJ proteins in these cells.
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
authors: Hao
authors: H
authors: Wang
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
authors: Yun
authors: Y
authors: Ji
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and Department of Animal Science, Texas A&M University, College Station, TX.
authors: Guoyao
authors: G
authors: Wu
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
authors: Kaiji
authors: K
authors: Sun
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
authors: Yuli
authors: Y
authors: Sun
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
authors: Wei
authors: W
authors: Li
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
authors: Bin
authors: B
authors: Wang
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
authors: Beibei
authors: B
authors: He
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
authors: Qing
authors: Q
authors: Zhang
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and.
authors: Zhaolai
authors: Z
authors: Dai
authors: State Key Laboratory of Animal Nutrition, China Agricultural University, Beijing, China; and bio2046@hotmail.com.
authors: Zhenlong
authors: Z
authors: Wu
mesh_terms: D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D062445:Claudin-1 / Q000235:genetics / Q000378:metabolism; D062506:Claudin-4 / Q000235:genetics / Q000378:metabolism; D020895:Enterocytes / Q000187:drug effects* / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism; D007421:Intestine, Small / Q000187:drug effects / Q000378:metabolism; D007422:Intestines / Q000166:cytology / Q000187:drug effects*; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D062793:Occludin / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013552:Swine; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D062725:Tight Junction Proteins / Q000235:genetics / Q000378:metabolism*; D019108:Tight Junctions / Q000187:drug effects / Q000378:metabolism; D014364:Tryptophan / Q000494:pharmacology*; D015854:Up-Regulation
chemical_list: D062445:Claudin-1; D062506:Claudin-4; D046912:Multiprotein Complexes; D062793:Occludin; D012333:RNA, Messenger; D062725:Tight Junction Proteins; D014364:Tryptophan; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases
keywords: cell proliferation; intestinal epithelial cells; mammalian target of rapamycin; pig; tight junction; tryptophan