Mita S, Takaki S, Tominaga A, Takatsu K
Department of Surgery II, Kumamoto University Medical School, Japan.
J Immunol. 1993 Dec 15;151(12):6924-32.
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.
高亲和力白细胞介素-5受体（IL-5R）至少由两条链组成，即α链和β链。IL-5Rα以低亲和力结合IL-5。构建高亲和力IL-5R需要IL-5Rβ，尽管IL-5Rβ自身并不结合IL-5。为了阐明IL-5Rα和IL-5Rβ在IL-5的结合、解离及内化过程中的作用，我们比较了携带T88-M的高亲和力IL-5R（解离常数约为150 pM）和携带MOPC104E的低亲和力IL-5R（解离常数约为30 nM）对35S标记的IL-5的结合动力学及内化情况。我们发现，IL-5与任一天然受体的结合动力学相似。IL-5与高亲和力和低亲和力IL-5R的最大结合都很快（在10分钟内）。IL-5从低亲和力IL-5R的解离很快（t1/2 < 30分钟），但从高亲和力IL-5R的解离则明显较慢（t1/2 > 120分钟）。仅在T88-M细胞中观察到了IL-5的内化，而在MOPC104E细胞中未观察到，这表明IL-5的内化是通过高亲和力IL-5R介导的。天然细胞系中观察到的结合和解离动力学在转染了IL-5Rα基因或IL-5Rα和IL-5Rβ基因的转染子上重组IL-5R的动力学分析中大多得以重现。然而，表达IL-5Rα的转染子也能显著内化IL-5，尽管其水平远低于IL-5Rαβ转染子所观察到的水平。这些结果表明，IL-5Rα可能参与IL-5的内化，而IL-5Rβ则通过稳定配体-受体复合物来减缓IL-5的解离并促进其有效内化。
