TI  -  <prot>Stat3</prot>  recruitment by two distinct ligand-induced, tyrosine-phosphorylated
      docking sites in the  <prot><prot>interleukin-10</prot>  receptor</prot> intracellular domain.
PG  - 27954-61
AB  - Recent work has shown that <prot>IL-10</prot> induces activation of the JAK-STAT
      signaling pathway. To define the mechanism underlying signal transducer
      and activator of transcription (STAT) protein recruitment to the
      <prot><prot>interleukin 10</prot> (<prot>IL-10</prot>) receptor</prot>, the STAT proteins activated by <prot>IL-10</prot> in
      different cell populations were first defined using electrophoretic
      mobility shift assays. In all cells tested,   <prot>IL-10</prot>   activated  <prot>Stat1</prot>  and
       <prot>Stat3</prot>  and induced the formation of three distinct DNA binding complexes
      that contained different combinations of these two transcription factors.
       <prot>IL-10</prot>  also activated  <prot>Stat5</prot>  in Ba/F3 cells that stably expressed the murine
      <prot><prot>IL-10</prot> receptor</prot>. Using a structure-function mutagenesis approach, two
      tyrosine residues (Tyr427 and Tyr477) in the intracellular domain of the
      murine  <prot><prot>IL-10</prot> receptor</prot>  were found to be redundantly required for receptor
      function and for activation of  <prot>Stat3</prot>  but not for <prot>Stat1</prot> or Stat5. Twelve
      amino acid peptides encompassing either of these two tyrosine residues in
      phosphorylated form coprecipitated <prot>Stat3</prot> but not <prot>Stat1</prot> and blocked
      <prot>IL-10</prot>-induced <prot>Stat3</prot> phosphorylation in a cell-free system. In contrast,
      tyrosine-phosphorylated peptides containing Tyr374 or Tyr396 did not
      interact with <prot>Stat3</prot> or block <prot>Stat3</prot> activation. These data demonstrate that
       <prot>Stat3</prot>  but not <prot>Stat1</prot> or <prot>Stat5</prot> is directly recruited to the ligand-activated
       <prot><prot>IL-10</prot> receptor</prot>  by binding to specific but redundant receptor intracellular
      domain sequences containing phosphotyrosine. This study thus supports the
      concept that utilization of distinct STAT proteins by different cytokine
      receptors is dependent on the expression of particular ligand-activatable,
      tyrosine-containing STAT docking sites in receptor intracellular domains.
AD  - Center for Immunology, Department of Pathology, Washington University
