Subunit structure of the high and low affinity human interleukin-15 receptors.
Radio-iodinated cytokines and monoclonal antibodies directed at the IL-2R beta- and gamma-chains were used to analyze the structure of the cell-surface IL-15 and IL-2 receptors expressed by the human lymphoma cell clone YT-2C2. YT-2C2 cells are IL-2R alpha negative and express IL-2R gamma (15,000 molecules/cell) in excess of IL-2R beta (11,000 molecules/cell). Accordingly, they display a number of beta/gamma complexes of intermediate affinity for IL-2 and IL-15 which is equivalent to the number of beta-chains. Both cytokines compete for binding to this beta/gamma complex. There are about 800 high affinity IL-15 receptors, suggesting the presence of a similar number of IL-15R alpha-chains. Within the common intermediate affinity beta/gamma-complex, the anti-beta-chain A41 mAb defines an epitope which is similarly engaged in IL-2 and IL-15 binding, whereas the anti-beta-chain 284 mAb defines an epitope which does not display similar interaction with either cytokines. Thus, although IL-2 and IL-15 compete for binding to this beta/gamma-complex, they do not use similar binding areas. Cross-linking and immunoprecipitation experiments have shown that the high affinity IL-15 receptors comprises IL-2R beta/gamma, in association with IL-15R alpha and that the three chains can be efficiently cross-linked to IL-15 and co-immunoprecipitated. Contrary to the intermediate affinity situation, high affinity IL-15 binding and subunit cross-linking were not affected by excess amounts of IL-2, A41 or 284 mAb, suggesting that when engaged in the IL-15 high affinity complex, the beta- and gamma-chains adopt different conformations, at least with respect to IL-15 binding. Finally, we provide evidence for the participation of a novel 35 kDa component within the high affinity structure. This component is immunoprecipitated with anti-IL-2R gamma mAb but not with anti-IL-2R beta mAb and might correspond to a truncated form of IL-2R gamma-chain.
Lehours
P
P
Groupe de Recherche Cytokines/Récepteurs et Transduction, Unité INSERM 463, Institut de Biologie, 9, Quai Moncousu, 44035 Nantes Cedex 01, France.
Raher
S
S
Dubois
S
S
Guo
J
J
Godard
A
A
Jacques
Y
Y
D000911:Antibodies, Monoclonal; D001667:Binding, Competitive; D002999:Clone Cells; D003432:Cross-Linking Reagents; D006801:Humans; D019409:Interleukin-15 / Q000378:metabolism; D007376:Interleukin-2 / Q000378:metabolism; D011233:Precipitin Tests; D020836:Protein Structure, Quaternary; D053647:Receptors, Interleukin-15; D015375:Receptors, Interleukin-2 / Q000737:chemistry* / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D003432:Cross-Linking Reagents; C508024:IL15RA protein, human; D019409:Interleukin-15; D007376:Interleukin-2; D053647:Receptors, Interleukin-15; D015375:Receptors, Interleukin-2