Interaction of IL-15 with the shared IL-2 receptor beta and gamma c subunits. The IL-15/beta/gamma c receptor-ligand complex is less stable than the IL-2/beta/gamma c receptor-ligand complex.
This study was designed to compare the interactions of IL-2 and IL-15 with the IL-2R beta and IL-2R gamma c subunits, as differences in receptor interactions between IL-2 and IL-15 might contribute to the functional differences between these two cytokines. The results suggest the existence of a human IL-15R alpha subunit, although physical evidence of this molecule was not obtained. Proliferation of anti-CD3 (OKT3)-stimulated human PBL was compared for responsiveness to IL-2, IL-15, and F42K, and IL-2 mutant that does not bind the IL-2R alpha chain. F42K was more potent than IL-15 in activating a dose-dependent response. This fact, along with Scatchard binding analyses of IL-15 on OKT3 blasts and YT cells revealing both high and intermediate affinity receptors, supports the existence of IL-15R alpha on these cells. Additional characterization of the IL-15R utilized covalent cross-linking to affinity label IL-2R and IL-15R on YT cells and OKT3 blasts. Consistent with previously reported functional data, IL-2R alpha was not co-precipitated from the [125I]IL-15 receptor-ligand complex, demonstrating that IL-15 does not interact physically with the IL-2R alpha subunit. While IL-2R alpha did co-precipitate with IL-2R beta and IL-2R gamma c in the presence of IL-2, IL-15R alpha did not co-precipitate with the IL-2R beta/gamma c complex. Finally, YT cells equilibrated with IL-2 and then precipitated through IL-2R beta showed that IL-2R beta and IL-2R gamma c co-precipitate in a 1:1 ratio, while only IL-2R beta was found in the immunoprecipitates of YT cells equilibrated with IL-15. This indicates that IL-15 creates a less stable bridge between the IL-2R beta and IL-2R gamma c chains than does IL-2 on YT cells. This result was identical for both surface-iodinated YT cells and immunoprecipitates that were probed for IL-2R beta and IL-2R gamma c on Western blots.
de Jong
J L
JL
Department of Human Oncology, University of Wisconsin, Madison 53792, USA.
Farner
N L
NL
Widmer
M B
MB
Giri
J G
JG
Sondel
P M
PM
D006801:Humans; D019409:Interleukin-15; D007378:Interleukins / Q000378:metabolism*; D007694:Killer Cells, Natural; D008213:Lymphocyte Activation; D046911:Macromolecular Substances; D011485:Protein Binding; D011940:Receptor Aggregation; D053647:Receptors, Interleukin-15; D015375:Receptors, Interleukin-2 / Q000737:chemistry* / Q000378:metabolism*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000378:metabolism*; D014407:Tumor Cells, Cultured
C508024:IL15RA protein, human; D019409:Interleukin-15; D007378:Interleukins; D046911:Macromolecular Substances; D053647:Receptors, Interleukin-15; D015375:Receptors, Interleukin-2