= Cytokine receptor
A <cytokine receptor> recognizes a <cytokine> and couples its binding to changes in cellular behavior. Receptor identity, ligand recognition and the intracellular signaling machinery are distinct parts of the mechanism. The term covers receptors with different structures; the well-studied cytokine-receptor superfamily includes members that recruit associated kinases rather than supplying their own kinase domain.
The <erythropoietin receptor> provides a concrete example. <Erythropoietin> regulates the proliferation and differentiation of erythroid cells, yet its receptor lacks an intrinsic kinase domain. A 1993 study identified association with <JAK2> and activation-associated phosphorylation after erythropoietin stimulation. This connected extracellular recognition with a separate intracellular <protein kinase>.<JAK2 associates with the erythropoietin receptor and is tyrosine phosphorylated and activated following stimulation with erythropoietin by B. A. Witthuhn and others>[Abstract: receptor-superfamily membership, missing kinase domain and JAK2 response]{ref}
For an experimental reasoning example, compare receptor binding with a downstream phosphorylation measurement. Preserved binding but loss of signaling after disruption of an associated kinase would distinguish recognition from intracellular coupling. Reduced response alone would not identify which step failed: receptor abundance, ligand binding and kinase function require separate measurements.
This distinction also helps interpret other members, such as the <growth hormone receptor>, whose activation has been studied through receptor rearrangement and associated <JAK2> signaling.<Mechanism of activation of protein kinase JAK2 by the growth hormone receptor by Andrew J. Brooks and others>[2014 abstract: receptor rearrangement and JAK2 activation model]{ref} A mechanism established for one receptor should not be assumed for every receptor that recognizes a cytokine.
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