Title:	Functional Coupling of Janus Kinases with Cytokine Receptors at the Plasma Membrane
Authors:	Meyer, Thomas
Thesis advisor:	Piehler, Jacob
Thesis referee:	Holthuis, Joost
Abstract:	Cytokines and their corresponding receptors play crucial roles in regulating processes such as hematopoiesis, immunity, and inflammation. While being promising targets for therapeutic intervention, the high plasticity and pleiotropy of cellular responses to cytokines are currently obstructing medical applications. Class I and class II cytokine receptor (CR) signaling is propagated through Janus family tyrosine kinases (JAK), which bind non-covalently to specific motifs on the receptors' intracellular domains proximal to the plasma membrane (PM). These "Box" motifs, although exhibiting low conservation among different receptors, are essential for ensuring proper JAK activity. However, the precise understanding of mechanistic principles determining functional coupling of JAKs with CRs remain elusive. This thesis aimed to provide a molecular view on how JAKs bind class I and class II CRs in the context of the PM and to explore how the specificity and promiscuity of JAK recruitment contribute to the pleiotropy of CR signaling. We further sought to uncover the principles of membrane interaction and its impact on JAK association with CRs, downstream signal activation, and the significance of receptor juxtamembrane domain (JMD) in fine-tuning orientation and activity. Using live cell micropatterning, we obtained quantitative insights into the specificity and promiscuity of JAK family members in binding CRs. Our findings revealed that competitive JAK association with CRs enhances regulation of signaling activity. Moreover, we observed that the localization and stability of receptors on the cell surface depended strongly on the specific JAK involved, despite similar binding affinities. These results elucidated how different functional coupling in receptor-JAK complexes lead to distinct signaling patterns, contributing to their wide range of functions. Furthermore, we identified a membrane binding site of the JAK FERM-SH2 domains comprising conserved hydrophobic and positively charged residues, which controls receptor binding and formation of active signaling complexes at the PM. Interestingly, we find cooperation of the JAK membrane binding site with an amphipathic membrane-proximal helix of CRs. Correlation of binding and activity suggests that this cooperative membrane binding is required for productive orientations of JAKs to form active signaling complexes. Collectively, our results challenge the traditional understanding of JAK-receptor interactions and highlight the significance of PM interactions for effective signaling.
URL:	https://doi.org/10.48693/551 https://osnadocs.ub.uni-osnabrueck.de/handle/ds-2024060411268
Subject Keywords:	Janus Kinase; JAK/STAT signaling; Cytokine Receptor; Plasma Membrane
Issue Date:	4-Jun-2024
License name:	Attribution 3.0 Germany
License url:	http://creativecommons.org/licenses/by/3.0/de/
Type of publication:	Dissertation oder Habilitation [doctoralThesis]
Appears in Collections:	FB05 - E-Dissertationen

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