Importance of the membrane-proximal extracellular domains for activation of the signal transducer glycoprotein 130.
The transmembrane glycoprotein gp130 is the common signal transducing receptor subunit of the IL-6-type cytokines. The gp130 extracellular part is predicted to consist of six individual domains. Whereas the role of the three membrane-distal domains (D1-D3) in binding of IL-6 and IL-11 is well established, the function of the membrane-proximal domains (D4-D6) is unclear. Mapping of a neutralizing mAb to the membrane-proximal part of gp130 suggests a functional role of D4-D6 in receptor activation. Individual deletion of these three domains differentially interferes with ligand binding of the soluble and membrane-bound receptors. All deletion mutants do not signal in response to IL-6 and IL-11. The deletion mutants Delta4 and, to a lesser extent, Delta6 are still activated by agonistic monoclonal gp130 Abs, whereas the deletion mutant Delta5 does not respond. Because membrane-bound Delta5 binds IL-6/soluble IL-6R as does wild-type gp130, but does not transduce a signal in response to various stimuli, this domain plays a prominent role in coupling of ligand binding and signal transduction. Replacement of the fifth domain of gp130 by the corresponding domain of the homologous G-CSF receptor leads to constitutive activation of the chimera upon overexpression in COS-7 cells. In HepG2 cells this mutant responds to IL-6 comparable to wild-type gp130. Our findings suggest a functional role of the membrane-proximal domains of gp130 in receptor activation. Thus, within the hematopoietic receptor family the mechanism of receptor activation critically depends on the architecture of the receptor ectodomain.
Kurth
I
I
Institut für Biochemie, Rheinisch-Westfälische Technische Hochschule Aachen, Germany.
Horsten
U
U
Pflanz
S
S
Timmermann
A
A
Küster
A
A
Dahmen
H
H
Tacken
I
I
Heinrich
P C
PC
Müller-Newen
G
G
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D015703:Antigens, CD / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D019556:COS Cells; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D050822:Cytokine Receptor gp130; D005110:Extracellular Space / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D017370:Interleukin-11 / Q000037:antagonists & inhibitors / Q000502:physiology; D015850:Interleukin-6 / Q000502:physiology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D010449:Peptide Mapping; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D017434:Protein Structure, Tertiary / Q000235:genetics; D016188:Receptors, Granulocyte Colony-Stimulating Factor / Q000235:genetics; D017384:Sequence Deletion; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D012995:Solubility; D000093242:Interleukin-6 Inhibitors
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D050822:Cytokine Receptor gp130; D017370:Interleukin-11; D015850:Interleukin-6; D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D016188:Receptors, Granulocyte Colony-Stimulating Factor; D000093242:Interleukin-6 Inhibitors; C494199:IL6ST protein, human; C494200:Il6st protein, mouse