OLIGOMERIZATION OF IL-2Rα

Interleukin (IL) 2 receptor subunit alpha (IL-2Rα) increases the affinity of the IL-2 receptor complex while hetero-association of IL-2Rβ and γc chains initiates a proliferative signal. We show here that IL-2Rα is necessary for receptor clustering required for augmentation of IL-2 signalling. Cells expressing chimeras incorporating the extracellular domain of IL-2Rα demonstrated IL-2 independent homo-association of the IL-2Rα chimera. Singly or co-transfected IL-2Rβ and γc chimeras showed no spontaneous or IL-2-inducible oligomerization. Co-transfection of IL-2Rα and IL-2Rβ (±γc) chimeras diminished spontaneous IL-2Rα chimera oligomerization and permitted IL-2-inducible hetero-oligomerization of receptor components. Homo-association of IL-2Rα was also demonstrated by fluorescence resonance energy transfer (FRET). The spontaneous homo-oligomerization property of IL-2Rα required the membrane proximal region of the receptor (exon 6) by deletion analysis; the IL-2 inducible oligomerization property of IL-2Rα required the second “sushi” domain (exon 4). This work provides insight into the mechanics of this complex receptor system and to other receptor complexes in the immune system that send signals by clustering receptor subunits.