Learning Objective

Understand the structure, signaling mechanism, and functional outcomes of cytokine receptors, including the JAK-STAT pathway.

Cytokine Receptors

Examples:

• • Erythropoietin receptor
  • Somatotropin (growth hormone) receptor
  • Interferon receptors

Structure:

• • Membrane-spanning receptors
  • No intrinsic kinase activity; instead, they activate cytoplasmic tyrosine kinases (JAKs)

JAK-STAT Signaling Pathway

• Ligand Binding: Cytokine binds to its receptor.
• JAK Activation: Associated Janus kinases (JAKs) are activated.
• STAT Phosphorylation: JAKs phosphorylate STAT (Signal Transducers and Activators of Transcription) proteins.
• Dimerization: Phosphorylated STATs dimerize.
• Nuclear Translocation: STAT dimers cross the nuclear membrane.
• Gene Transcription: STAT dimers modulate transcription of target genes → physiological responses like cell proliferation, differentiation, or immune modulation.

Quick Tip:

• Remember “Cytokine → JAK → STAT → Nucleus → Gene transcription” as the flow of signaling.

Activity