The interleukin-4/interleukin-13 receptor of human synovial fibroblasts: overexpression of the nonsignaling interleukin-13 receptor alpha2.
Interleukin (IL)-4 and IL-13 are known to bind to shared heteromultimeric receptor complexes of variable composition. Given the many regulatory effects of IL-4 and IL-13 on synovial cells, we aimed to characterize their IL-4/IL-13 receptor (R). Cultivated synovial fibroblasts expressed transcripts for IL-4Ralpha and IL-13Ralpha1, the human homolog of the recently cloned mouse IL-13R, but not the common gamma-chain of the IL-2R. In particular, IL-13Ralpha2 mRNA, encoding a different IL-13R recently cloned from human renal carcinoma cells, was expressed at a strikingly high level. Correspondingly, a predominant protein migrating at 65 to 75 kd was cross-linked by iodinated IL-13 and was not cross-competed by an excess of unlabeled IL-4. However, by flow cytofluorometry, IL-13Ralpha1 (detected by the anti-lL-13Ralpha1 mAb 65) and IL-4Ralpha (detected by the mAb S697) were expressed at similar low density. Radioligand binding studies revealed for both cytokines approximately 300 receptors/cell with similar high affinity. An additional class of IL-13Rs was identified after occupation of the shared high-affinity receptors by the nonsignaling, double-mutant IL-4121R-->D, 124Y-->D (RY-IL-4). In these experiments, 1251-IL-13 bound to a single receptor population with a Kd of approximately 300 pM and approximately 5000 sites/cell, matching the published affinity of monomeric IL-13Ralpha2 when expressed in COS7 cells. RY-IL-4 blocked the IL-4- and IL-13-mediated vascular cell adhesion molecule (VCAM)-1 expression and Stat6 activation, suggesting that the large number of high-affinity IL-13Ralpha2 monomers are silent receptors, likely representing a decoy target for IL-13.
Feng
N
N
Institute of Clinical Chemistry, University Hospital, Zurich, Switzerland.
Lugli
S M
SM
Schnyder
B
B
Gauchat
J F
JF
Graber
P
P
Schlagenhauf
E
E
Schnarr
B
B
Wiederkehr-Adam
M
M
Duschl
A
A
Heim
M H
MH
Lutz
R A
RA
Moser
R
R
D002352:Carrier Proteins / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D018793:Interleukin-13 / Q000378:metabolism / Q000494:pharmacology; D053661:Interleukin-13 Receptor alpha1 Subunit; D015847:Interleukin-4 / Q000378:metabolism / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D018123:Receptors, Interleukin / Q000235:genetics / Q000378:metabolism*; D053660:Receptors, Interleukin-13; D019948:Receptors, Interleukin-4 / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013583:Synovial Membrane / Q000166:cytology / Q000378:metabolism*; D019010:Vascular Cell Adhesion Molecule-1 / Q000378:metabolism
D002352:Carrier Proteins; C508181:IL13RA1 protein, human; C508183:Il13ra1 protein, mouse; D018793:Interleukin-13; D053661:Interleukin-13 Receptor alpha1 Subunit; D012333:RNA, Messenger; D018123:Receptors, Interleukin; D053660:Receptors, Interleukin-13; D019948:Receptors, Interleukin-4; D019010:Vascular Cell Adhesion Molecule-1; D015847:Interleukin-4