The JAK-STAT pathway is one of the key signal transduction pathways in the cell. There are 4 JAK isoforms JAK1, JAK2, JAK3, and TYK2. In the cell the JAK isoforms bind to the intracellular domains of receptors. JAK activation occurs when 2 JAK isoforms are brought into close proximity while bound to the receptors and they phosphorylate each other. Once activated, the JAK isoforms phosphorylate STAT proteins, which are latent transcription factors that reside in the cytoplasm. After phosphorylation the STATs dimerize and travel to the nucleus where they activate transcription of target genes. When different cytokines bind their receptors this results in the binding and activation of the different JAKs, STATs, and ultimately the activation of different target genes.
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