Untersuchungen zum Aktivierungsmechanismus des Signalübermittlers gp130 und Bedeutung seiner juxtamembranären Region
The glycoprotein 130 (gp130) is the common signal transducing receptor chain of the interleukin-6 family of cytokines. Here requirements for transfer of the information given by ligand binding to the cytoplasmic domain of gp130 were investigated. Mutagenesis studies of the transmembrane domain (TMD) were performed in a chimeric receptor system. The TMD of gp130 was replaced by the TMD of the IL-5 receptor a and b chains. The resulting chimeras show no altered response to ligand binding in a homodimeric setting. In the heterodimeric state signal transduction was impaired, suggesting transmembrane interactions. Binding of overexpressed Janus kinases to the chimeras is equal in both systems. Interestingly the IL-5 receptor TMD leads to a slight constitutive signaling, which is not seen in the chimera with the TMD of the gp130 chain. These results suggest that the gp130 TMD is stabilizing the inactive state of the receptor. It is demonstrated that the box1/2 region has to be located membrane-proximally in order to bind and activate Janus kinases. To test the possible requirement of an a-helical orientation one to four alanine residues were inserted into the juxtamembrane intracellular region. The insertion of one alanine results in a strongly reduced activation of STAT1 and STAT3, while insertion of three alanine residues leads to a stronger STAT activation. These results suggest that gp130-mediated activation of STATs is sensitive to rotational changes around the receptor axis perpendicular to the membrane. Surprisingly, insertion of 1, 2, 3 or 4 alanine residues into this juxtamembrane region leads to successive impairment but not abolishment of Jak and receptor phosphorylation supporting the finding of sensitivity of Janus kinases towards changes in distance of box1/2 from the plasma membrane. We suggest a new model concerning the gp130 activation mode in which the relative orientation of the cytoplasmic regions seems to be critical for further signal transduction.
info:eu-repo/classification/ddc/610, Medizin, Rezeptororientierung, gp130, IL-6, Aktivierungsmechnanismus, Zytokine, JAK
Networked Digital Library of Theses and Dissertations
Publikationsserver der RWTH Aachen University