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Jaks and cytokine receptors--an intimate relationship
Claude Haan1, Stephanie Kreis, Christiane Margue
1Laboratoire de Biologie et Physiologie Intégrée (LBPI), University of Luxembourg, 162a avenue de la Faïencerie, L-1511 Luxembourg, Luxembourg.
Abstract:
Most cytokine receptors lack intrinsic kinase activity and many of them signal via Janus kinases (Jaks). These tyrosine kinases are associated with cytokine receptor subunits, they become activated upon receptor triggering and subsequently activate downstream signalling events, e.g. the phosphorylation of STAT transcription factors. The successful interplay between cytokines, their receptors and the connected Jaks not only determines signalling competence but is also vital for intracellular traffic, stability, and fate of the cognate receptors. Here, we will discuss underlying mechanisms as well as some structural features with a focus on Jak1 and two of the signal transducing receptor subunits of interleukin (IL)-6 type cytokines, gp130 and OSMR. Regions that are critically involved in Jak-binding have been identified for many cytokine receptor subunits. In most cases the membrane-proximal parts comprising the box1 and box2 regions within the receptor are involved in this association while, within Jaks, the N-terminal FERM domain, possibly together with the SH2-like domain, are pivotal for binding to the relevant receptors. The exclusive membrane localisation of Jaks depends on their ability to associate with cytokine receptors. For gp130 and Jak1, it was shown that the cytokine receptor/Jak complex can be regarded as a receptor tyrosine kinase since both molecules have the same diffusion dynamics and are virtually undissociable. Furthermore, Jaks take an active role in the regulation of the surface expression of at least some cytokine receptors, including the OSMR and this may provide a quality control mechanism ensuring that only signalling-competent receptors (i.e. those with an associated Jak) would be enriched at the cell surface.
Insights
Cytokine receptors signal through Janus kinases (Jaks), which are essential for receptor function and stability. This study explores the structural basis of Jak-receptor interactions, focusing on Jak1, gp130, and OSMR.
Area of Science:
- Cellular signaling
- Molecular biology
- Immunology
Background:
- Most cytokine receptors lack intrinsic kinase activity and rely on associated Janus kinases (Jaks) for signal transduction.
- Jaks associate with receptor subunits, becoming activated upon cytokine binding to initiate downstream signaling pathways, such as STAT phosphorylation.
Purpose of the Study:
- To elucidate the mechanisms and structural features governing the interaction between Janus kinases (Jaks) and cytokine receptors.
- To focus on the specific interactions involving Jak1, gp130, and the Oncostatin M receptor (OSMR) in interleukin-6 (IL-6) type cytokine signaling.
Main Methods:
- Review of existing literature on cytokine receptor and Jak structure-function relationships.
- Analysis of identified binding regions (box1, box2 in receptors; FERM, SH2-like domains in Jaks).
- Discussion of experimental evidence regarding receptor-Jak complex dynamics and cellular localization.
Main Results:
- Specific regions, including box1 and box2 in receptors and the FERM/SH2-like domains in Jaks, are critical for Jak-receptor association.
- The association with cytokine receptors dictates the exclusive membrane localization of Jaks.
- The gp130/Jak1 complex exhibits characteristics of a receptor tyrosine kinase due to its stability and co-localization.
- Jaks play a role in regulating the surface expression of cytokine receptors like OSMR, potentially acting as a quality control mechanism.
Conclusions:
- The interaction between Jaks and cytokine receptors is crucial for signal transduction, receptor trafficking, and stability.
- Structural insights reveal specific domains responsible for Jak-receptor binding.
- Jaks are integral components of the functional cytokine receptor complex, influencing both signaling and cell surface expression.
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