Signal transducer and activator

Ihle, J. 1996. STATs signal transducers and activators of transcription. Cell 84, 331-334. 

JAKs and signal transducers and activators of transcription (STATs) are functionally analogous with IRS and PI3K. JAKs are physically associated with a cell surface receptor (e.g. for leptin, erythropoietin (EPO), growth factors or cytokines) STATs are free monomeric proteins within the cytosol but following phosphorylation by a JAK, individual proteins dimerize and then move into the nucleus of the cell where they control gene expression. 

Leptin signalling is via monomeric receptors in the brain. A short-form of the leptin receptor (Lep-R) is required to transport the hormone across the blood-brain barrier and a long-form Lep-R is located in the hypothalamus. The long-form is functionally linked with a particular type of receptor-associated tyrosine kinase called Janus kinase (JAK, see Section 4.7) whose function is to phosphorylate a STAT (signal transducer and activator of transcription) protein a similar mechanism to that often associated with signalling by inflammatory cytokines. 

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