The two subunits of the interleukin-4 receptor mediate independent and distinct patterns of ligand endocytosis.
Interleukin-4 (IL-4) triggers cellular responses by interaction with the bipartite interleukin-4 receptor (IL-4R). IL-4-responsive cells specifically endocytose IL-4. We studied the ligand internalization properties of the human IL-4R and analyzed the specific functions of its two subunits IL-4Ralpha and gammac in this process. IL-4 mutant RY, which binds to IL-4Ralpha but does not recruit gammac into the receptor complex was used as a tool to show that IL-4Ralpha can promote independent ligand uptake in human T cells. Internalization was limited, however, by rapid IL-4 dissociation, suggesting that one important function of gammac in IL-4 endocytosis is to retain the ligand sufficiently long within the ternary receptor complex. We then measured IL-4 internalization by murine Ba/F3 cells that were stably transfected with various human IL-4R constructs. Efficient IL-4 uptake required the cytoplasmic section of the receptor. The intracellular domains of IL-4Ralpha and gammac were responsible for independent endocytosis processes with distinct kinetics. IL-4Ralpha-mediated internalization resulted in long-term intracellular maintainance of IL-4, whereas gammac directed the associated radioligand to intracellular breakdown and rapid release in the form of degraded protein. Mutants of either IL-4R subunit deficient in Janus kinase activation were not impaired in internalization, indicating that IL-4 endocytosis is not functionally connected to signal transduction.
Friedrich
K
K
Theodor-Boveri-Institut für Biowissenschaften (Biozentrum), Physiologische Chemie II, Am Hubland, Würzburg, Germany. khf@biozentrum.uni-wuerzburg.de
Kammer
W
W
Erhardt
I
I
Brändlein
S
S
Arnold
S
S
Sebald
W
W
D001692:Biological Transport; D016764:Cell Polarity; D003593:Cytoplasm; D019281:Dimerization; D004705:Endocytosis; D006801:Humans; D015847:Interleukin-4 / Q000378:metabolism*; D008024:Ligands; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D020836:Protein Structure, Quaternary; D019948:Receptors, Interleukin-4 / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction
D008024:Ligands; D010446:Peptide Fragments; D019948:Receptors, Interleukin-4; D011994:Recombinant Proteins; D015847:Interleukin-4