Comparative analysis of the kinetics of binding and internalization of IL-5 in murine IL-5 receptors of high and low affinity.
The high affinity IL-5R consists of at least two chains, alpha and beta. IL-5R alpha binds IL-5 with low affinity. IL-5R beta is required to construct the high affinity IL-5R, although IL-5R beta does not bind IL-5 by itself. To characterize the roles of IL-5R alpha and IL-5R beta on the association, dissociation, and internalization of IL-5, we compared the binding kinetics and the internalization of 35S-labeled IL-5 by high affinity IL-5R (dissociation constant approximately 150 pM) bearing T88-M with those by low affinity IL-5R (dissociation constant approximately 30 nM) bearing MOPC104E. We found that association kinetics of IL-5 to either natural receptor were similar. The maximal binding of IL-5 to both high and low affinity IL-5R was rapid (within 10 min). The dissociation of IL-5 from low affinity IL-5R was rapid (t1/2 < 30 min), but that from the high affinity IL-5R was remarkably slower (t1/2 > 120 min). The internalization of IL-5 was observed only in T88-M, but not in MOPC104E, suggesting that IL-5 internalization is mediated via high affinity IL-5R. Association and dissociation kinetics observed in natural cell line were mostly reproduced by the kinetic analysis of reconstituted IL-5R on transfectants with either the IL-5R alpha or the IL-5R alpha and IL-5R beta genes. However, transfectants that expressed IL-5R alpha significantly internalized IL-5, although the level was much lower than observed with IL-5R alpha beta transfectants. These results suggest that IL-5R alpha may be involved in the internalization of IL-5, whereas IL-5R beta is responsible for slowing the dissociation and the efficient internalization of IL-5 by stabilizing the ligand-receptor complex.
Mita
S
S
Department of Surgery II, Kumamoto University Medical School, Japan.
Takaki
S
S
Tominaga
A
A
Takatsu
K
K
D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism; D002460:Cell Line; D018076:DNA, Complementary / Q000235:genetics; D015848:Interleukin-5 / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D018123:Receptors, Interleukin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D053649:Receptors, Interleukin-5; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D018076:DNA, Complementary; D015848:Interleukin-5; D018123:Receptors, Interleukin; D053649:Receptors, Interleukin-5; D011994:Recombinant Proteins