title: All-trans retinoic acid promotes TGF-β-induced Tregs via histone modification but not DNA demethylation on Foxp3 gene locus.
abstract: BACKGROUND
  It has been documented all-trans retinoic acid (atRA) promotes the development of TGF-β-induced CD4(+)Foxp3(+) regulatory T cells (iTreg) that play a vital role in the prevention of autoimmune responses, however, molecular mechanisms involved remain elusive. Our objective, therefore, was to determine how atRA promotes the differentiation of iTregs.
  
  
  RESULTS
  Addition of atRA to naïve CD4(+)CD25(-) cells stimulated with anti-CD3/CD28 antibodies in the presence of TGF-β not only increased Foxp3(+) iTreg differentiation, but maintained Foxp3 expression through apoptosis inhibition. atRA/TGF-β-treated CD4(+) cells developed complete anergy and displayed increased suppressive activity. Infusion of atRA/TGF-β-treated CD4(+) cells resulted in the greater effects on suppressing symptoms and protecting the survival of chronic GVHD mice with typical lupus-like syndromes than did CD4(+) cells treated with TGF-β alone. atRA did not significantly affect the phosphorylation levels of Smad2/3 and still promoted iTreg differentiation in CD4(+) cells isolated from Smad3 KO and Smad2 conditional KO mice. Conversely, atRA markedly increased ERK1/2 activation, and blockade of ERK1/2 signaling completely abolished the enhanced effects of atRA on Foxp3 expression. Moreover, atRA significantly increased histone methylation and acetylation within the promoter and conserved non-coding DNA sequence (CNS) elements at the Foxp3 gene locus and the recruitment of phosphor-RNA polymerase II, while DNA methylation in the CNS3 was not significantly altered.
  
  
  CONCLUSIONS
  We have identified the cellular and molecular mechanism(s) by which atRA promotes the development and maintenance of iTregs. These results will help to enhance the quantity and quality of development of iTregs and may provide novel insights into clinical cell therapy for patients with autoimmune diseases and those needing organ transplantation.
authors.affiliation: Division of Rheumatology, Department of Medicine, Saban Research Institute, Children's Hospital Los Angeles, Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America.
authors.forename: Ling
authors.initials: L
authors.lastname: Lu
authors.forename: Jilin
authors.initials: J
authors.lastname: Ma
authors.forename: Zhiyuan
authors.initials: Z
authors.lastname: Li
authors.forename: Qin
authors.initials: Q
authors.lastname: Lan
authors.forename: Maogen
authors.initials: M
authors.lastname: Chen
authors.forename: Ya
authors.initials: Y
authors.lastname: Liu
authors.forename: Zanxian
authors.initials: Z
authors.lastname: Xia
authors.forename: Julie
authors.initials: J
authors.lastname: Wang
authors.forename: Yuanping
authors.initials: Y
authors.lastname: Han
authors.forename: Wei
authors.initials: W
authors.lastname: Shi
authors.forename: Valerie
authors.initials: V
authors.lastname: Quesniaux
authors.forename: Bernhard
authors.initials: B
authors.lastname: Ryffel
authors.forename: David
authors.initials: D
authors.lastname: Brand
authors.forename: Bin
authors.initials: B
authors.lastname: Li
authors.forename: Zhongmin
authors.initials: Z
authors.lastname: Liu
authors.forename: Song Guo
authors.initials: SG
authors.lastname: Zheng
mesh_terms: D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology; D002454:Cell Differentiation; D004247:DNA / Q000235:genetics*; D019175:DNA Methylation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D051858:Forkhead Transcription Factors / Q000235:genetics* / Q000378:metabolism; D006657:Histones / Q000737:chemistry*; D053645:Interleukin-2 Receptor alpha Subunit / Q000096:biosynthesis; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010766:Phosphorylation; D050378:T-Lymphocytes, Regulatory / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D014212:Tretinoin / Q000378:metabolism*
chemical_list: D051858:Forkhead Transcription Factors; C498833:Foxp3 protein, mouse; D006657:Histones; D053645:Interleukin-2 Receptor alpha Subunit; D016212:Transforming Growth Factor beta; D014212:Tretinoin; D004247:DNA; D048049:Extracellular Signal-Regulated MAP Kinases