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The Jak-STAT pathway: cytokine signalling from the receptor to the nucleus
1Department of Research, University Hospital Basel, Switzerland.
Abstract:
The Jak-STAT pathway was originally discovered through the study of interferon induced intracellular signal transduction. Meanwhile, a large number of cytokines, hormones and growth factors have been found to activate Jaks and STATs. Jaks (Janus Kinases) are a unique class of tyrosine kinases that associate with cytokine receptors. Upon ligand binding, they activate members of the Signal Transducers and Activators of Transcription (STAT) family through phosphorylation on a single tyrosine. Activated STATs form dimers, translocate to the nucleus, bind to specific response elements in promotors of target genes, and transcriptionally activate these genes. Both positive and negative regulations of the Jak-STAT pathway have been identified. In a positive feedback loop, interferons transcriptionally activate the genes for components of the interferon stimulated gene factor 3 (ISGF3). A number of cytokines that activate the Jak-STAT pathway, e.g. IL-6, IL-4, LIF, G-CSF, have been shown to upregulate the expression of SOCS-JABs-SSIs, a recently discovered class of STAT inhibitors. Targeted disruption of genes for a number of Jaks and STATs in mice have revealed specific biological functions for many of them. Although most of the STATs are activated in cell culture by many different ligands, STAT knockout mice mostly show defects in a single or a few cytokine dependent processes. STAT1 knockout mice have an impaired interferon signalling, STAT4 knockouts impaired IL-12 signalling, STAT5a knockouts impaired prolactin signalling, STAT5b knockouts impaired growth hormone signalling, and STAT6 knockout impaired IL-4 and IL-13 signalling. Defects in the Jak-STAT pathway have already been identified in a number of human diseases. Prominent amongst them are leukaemias, lymphomas and inherited immunodeficiency syndromes. It can be expected that additional Jak-STAT related diseases will be identified over the next years. To date, specific STAT inhibitory drugs are not known, but a number of specific protein-protein interactions in the Jak-STAT pathway are potential targets for pharmaceutical interventions.
Insights
The Janus Kinase-Signal Transducer and Activator of Transcription (Jak-STAT) pathway regulates cell signaling. Genetic studies in mice reveal specific roles for Jaks and STATs in cytokine responses and disease.
Area of Science:
- Cellular Biology
- Molecular Biology
- Immunology
Background:
- The Jak-STAT pathway is crucial for intracellular signal transduction initiated by cytokines, hormones, and growth factors.
- Janus Kinases (Jaks) are tyrosine kinases that associate with cytokine receptors, phosphorylating Signal Transducers and Activators of Transcription (STATs).
- Activated STATs dimerize, translocate to the nucleus, and regulate gene expression.
Purpose of the Study:
- To elucidate the functions of Jaks and STATs through gene knockout studies in mice.
- To identify the roles of specific Jak-STAT pathway components in cytokine signaling.
- To explore the involvement of the Jak-STAT pathway in human diseases.
Main Methods:
- Gene targeting and disruption in mice to create knockout models for Jaks and STATs.
- Analysis of cytokine signaling pathways in knockout mice.
- Investigation of human diseases associated with Jak-STAT pathway defects.
Main Results:
- STAT knockout mice exhibit defects in specific cytokine-dependent processes (e.g., STAT1 in interferon signaling, STAT6 in IL-4/IL-13 signaling).
- The Jak-STAT pathway is implicated in various human diseases, including leukemias, lymphomas, and immunodeficiency syndromes.
- Positive and negative regulatory mechanisms, including STAT inhibitors (SOCS-JABs-SSIs), modulate pathway activity.
Conclusions:
- Jak-STAT pathway components have distinct biological functions, primarily revealed through knockout mouse models.
- Dysregulation of the Jak-STAT pathway is linked to significant human pathologies.
- Protein-protein interactions within the Jak-STAT pathway represent potential therapeutic targets.