| Modification Notes |
Interleukin-3, or IL-3, is a pleiotropic cytokine that is primarily secreted by activated T lymphocytes and stimulates the proliferation and differentiation of hematopoietic cells. IL-3 exerts its biological effects through a receptor which consists of a ligand-specific å subunit (IL-3Rå) and a signal transducing ∫ subunit (IL-3R∫) common to the IL-3/IL-5/GM-CSF receptors. The å subunits are low-affinity ligand-binding proteins while the ∫ subunits do not themselves bind ligand, but are required for high affinity binding by the å subunits. The mouse IL-3 receptor has two distinct ∫ subunits, one that functions only in IL-3-mediated cell signaling and a second that is shared with IL-5 and GM-CSF. The murine ∫ subunits are 91% homologous at the amino acid level but only 56% homologous to the human ∫ subunit. The carboxy-terminus of the ∫ subunit has been shown to be necessary for activation of the MAP kinase signaling pathway. Although the IL-3 receptor has no intrinsic kinase activity, stimulation with IL-3 leads to tyrosine phosphorylation of the JAK/Tyk 2 family member, JAK2, which in turn activates and causes nuclear translocation of Stat5a and Stat5b. |
