title: IL-6 activates STAT5 in T cells.
abstract: BACKGROUND
  IL-6 is a pleiotropic cytokine which emerged recently as a key regulator of CD4 T cell function. IL-6 alone or in combination with other cytokines promotes T helper 1, T helper 17 and T follicular helper cell differentiation whilst inhibiting the induction of regulatory T cell generation. IL-6 activates multiple pathways among which JAK/STAT3 is the most clearly validated in the control of CD4 T helper differentiation. Activation of STAT5 by cytokines such as IL-2 can counteract IL-6-induced T helper 17 and T follicular helper cell differentiation and promote the induction of regulatory T cell generation. STAT5 and STAT3 are known to compete for promoter binding sites in CD4 T cells and the two transcription factors are believed to have opposite functions in the control of CD4 T cell differentiation.
  
  
  METHODS
  We analyzed IL-6-induced STAT1, 3 and 5 activation by flow cytometry (phosflow) in mouse mononuclear cells and its effect on the level of the mRNA coding for cytokine-inducible SH2-containing protein (CIS).
  
  
  RESULTS
  The results show that IL-6 also induces STAT5 activation in both CD4 and CD8 T as well as NK cells. Analysis of STAT5 phosphorylation in CD4 T cells indicates that it is transient and requires higher cytokine concentrations than that of STAT3. CD4 T cell stimulation with IL-6 induces the synthesis of CIS, which is encoded by a gene known to be regulated by STAT5.
  
  
  CONCLUSIONS
  Thus, IL-6 at concentrations corresponding to levels observed in the serum during inflammation may activate, in CD4 T cells, a STAT5-negative feedback loop which alters the balance between STAT3-dependent pro-inflammatory helper T cells and STAT5-induced T regulatory cells. STAT5 activation may modulate the differentiation of T helper cells through attenuation of TGF-β stability and production. Since STAT5 is directly activated by Janus kinases, therapeutic approaches designed to inhibit STAT3 activation or to recruit STAT3 phosphatases may be useful in altering the balance of activated STAT3 and STAT5 in favor a profile that would be beneficial in pathologies involving IL-6.
authors.affiliation: Département de Pharmacologie, Université de Montréal, Montreal QC, Canada.
authors.forename: Aurélie Jeanne
authors.initials: AJ
authors.lastname: Tormo
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Letellier
authors.forename: Mukut
authors.initials: M
authors.lastname: Sharma
authors.forename: Greg
authors.initials: G
authors.lastname: Elson
authors.forename: Sandrine
authors.initials: S
authors.lastname: Crabé
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Gauchat
mesh_terms: D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D005260:Female; D015850:Interleukin-6 / Q000378:metabolism* / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects*; D051379:Mice; D008810:Mice, Inbred C57BL; D010766:Phosphorylation / Q000187:drug effects; D050794:STAT1 Transcription Factor / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism; D050799:STAT5 Transcription Factor / Q000378:metabolism*; D050826:Suppressor of Cytokine Signaling Proteins / Q000378:metabolism; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism*
chemical_list: D015850:Interleukin-6; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; D050826:Suppressor of Cytokine Signaling Proteins