Untersuchungen zur Modulation der IL-6-Signaltransduktion und zur Funktion der feed back Inhibitoren SOCS1 und SOCS3

To avoid an uncontrolled activation of cells by extracellular stimuli there must exist mechanisms which regulate the signal transduction. Here, regulatory mechanisms of the IL-6 signal transduction pathway were analyzed. In the first part a desensitization of the IL-6 signal could be observed during the early stages of the differentiation of primary monocytes to macrophages. Interestingly the cells could not respond to IL-6 when they started to adhere, whereas the non-adherent cells as well as the adherent cells at later stages of differentiation did respond to IL-6. This effect seemed to be restricted to the IL-6 signal transduction since the cells did react to other stimuli like IFNg (STAT1 activation) and FMLP (migration). The desensitization was not due to down-regulation of the receptors gp130 and gp80 because the surface expression did not change during the differentiation of the monocytes. Further studies need to be done to solve the mechanisms of the observed effect. One possible explanation could be the constitutive expression of the feed back inhibitor SOCS3 in the early phase of differentiation. This would lead to the inhibition of IL-6 signalling. The second part of this thesis aimed at the characterization of the feed back inhibitors SOCS1 and SOCS3. It could be shown that endogenous SOCS3 is tyrosine phosphorylated upon stimulation of cells with IL-6 and other IL-6-type cytokines like OSM. Most interestingly, the recruitment of SOCS3 to the tyrosine motif pY759 of gp130, which is crucial for the inhibitory action of SOCS3, was not required for phosphorylation. In addition the function of the SOCS3-SH2 domain was not abrogated upon SOCS3 phosphorylation. It has been shown that SOCS proteins can be recruited to an E3-ubiquitin ligase complex through the interaction with ElonginC. This then leads to the degradation of SOCS binding proteins. In collaboration with the group of professor James A. Johnston at Queen´s University of Belfast we were able to show that the phosphorylation of SOCS3 disrupts the interaction with ElonginC. In this thesis it could be shown that phosphorylated SOCS3 has a shorter half-life than the non-phosphorylated protein. This suggests that the phosphorylation of SOCS3 affects the SOCS3-dependent degradation of binding partners by targetting SOCS3 itself for degradation. By combining mutagenesis studies with molecular modelling approaches a new mechanism for the inhibition of Janus kinases by SOCS proteins was proposed. A crucial amino acid within the ESS (Extended SH2 Subdomain) region of SOCS1 was identified that contributes to the stability of the SOCS1-SH2 domain. Based on this finding it can be postulated that the ESS region of SOCS1 forms a helical structure that stabilizes the SH2-domain and orientates the KIR (Kinase Inhibitory Region) towards the upper lobe of the Janus kinase. Furthermore mutations in this upper lobe showed that the binding of SOCS1 to the Janus kinase is reduced. It can thus be assumed that SOCS1 inhibits Janus kinases by contacting the upper lobe of the kinase domain through its KIR region.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2003

Author dc:creator

• Sommer, Ulrike

Contributors dc:contributor

• Heinrich, Peter C.

• info:eu-repo/classification/ddc/570
• Monozyt
• Zelldifferenzierung
• Makrophage
• Interleukin 6
• Signaltransduktion
• Inhibitor
• Cytokine
• Suppressorgen
• Biowissenschaften, Biologie
• IL-6
• SOCS3
• SOCS1

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-123582%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:61981