A role for the immunoglobulin-like domain of the human IL-6 receptor. Intracellular protein transport and shedding.
Interleukin (IL)-6, IL-11 and cililary neurotrophic factor (CNTF) belong to the same family of hematopoietic and neurotrophic cytokines. Their receptor complexes contain a cytokine-binding alpha receptor and the common glycoprotein (gp)130 subunit for signal transduction. The extracellular parts of the alpha-receptor subunits consist of a membrane-proximal cytokine-binding domain and an N-terminal immunoglobulin (Ig)-like domain with unknown function. We examined the role of the Ig-like domain of IL-6R by constructing deletion mutants lacking the Ig domain (IL-6RDeltaIg and soluble IL-6RDeltaIg). IL-6RDeltaIg was shed as effectively as wild-type IL-6R from transfected COS-7 cells upon 4beta-phorbol 12-myristate 13-acetate (PMA) treatment, whereas nonstimulated shedding of IL-6RDeltaIg was not observed. The shed sIL-6RDeltaIg from PMA-treated cells, as well as the transmembrane IL-6RDeltaIg, had the same biological activity as wild-type sIL-6R, as measured by the induction of haptoglobin secretion in HepG2-IL-6 cells and IL-6-dependent proliferation of IL-6RDeltaIg transfected BAF/gp130 cells. In COS-7 cells transfected with IL-6RDeltaIg or soluble IL-6RDeltaIg cDNA, transport of the deletion mutants through the secretory pathway appeared to be delayed because a sizeable proportion of the mutants was detected as an endo-beta-N-acetylglucosaminidase-sensitive intermediate, suggesting that transport and processing of the DeltaIg mutants on the secretory pathway were impaired. These experiments suggest that the Ig-like domain of the IL-6R is important for intracellular transport of IL-6R through the secretory pathway. Furthermore, the Ig-like domain is necessary for noninduced shedding of the IL-6R, whereas it has no function in PKC-dependent shedding of the IL-6R.
Vollmer
P
P
I. Medical Clinic-Section Pathophysiology, Johannes Gutenberg-University of Mainz, Mainz, Germany.
Oppmann
B
B
Voltz
N
N
Fischer
M
M
Rose-John
S
S
D000818:Animals; D019556:COS Cells; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D006031:Glycosylation; D006801:Humans; D015850:Interleukin-6 / Q000494:pharmacology; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D019947:Receptors, Interleukin-6 / Q000737:chemistry*; D011994:Recombinant Proteins; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection; D052118:Lysosomal-Associated Membrane Protein 1
D015850:Interleukin-6; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D019947:Receptors, Interleukin-6; D011994:Recombinant Proteins; D013755:Tetradecanoylphorbol Acetate; C489116:LAMP1 protein, human; D052118:Lysosomal-Associated Membrane Protein 1; C052255:Lamp1 protein, mouse