The IL-2 receptor beta-chain (p70). Ligand binding ability of the cDNA-encoding membrane and secreted forms.
The high affinity IL-2R is composed of at least two distinct subunits; alpha (p55 or Tac)- and beta (p70)-chains. Recent cDNA expression studies with lymphoid cells unequivocally demonstrated that the IL-2R beta is an indispensable component for the ligand internalization and the signal transduction via the high affinity IL-2R. Furthermore, these studies confirmed that the IL-2R beta singly expressed on T lymphoid cells represents the intermediate affinity IL-2R. In the present study, however, we show 1) the IL-2R beta expressed on a mouse fibroblast line, NIH-3T3, did not bind IL-2 under the intermediate affinity conditions, 2) nevertheless, the IL-2R beta coexpressed with the IL-2R alpha not only formed the high affinity receptor but also internalized IL-2. By the use of competitive sandwich ELISA to study the IL-2 binding ability of the IL-2R beta molecule itself, we also show that the IL-2R beta present in the detergent-solubilized cell extracts and the secreted IL-2R beta (p37) produced by the truncated cDNA are actually capable of binding IL-2, but with a much reduced affinity compared with the intact IL-2R beta expressed on the lymphoid cells. These findings lead us to postulate a more complex feature of the IL-2R than ever speculated; the IL-2R beta molecule having on its own minimal IL-2 binding ability requires a putative gamma-chain specifically present on lymphoid cells to generate the functional intermediate affinity IL-2R. The gamma-chain, however, seems not to be required as far as the formation of the high affinity IL-2R by the alpha- and beta-chains and the ligand internalization through it are concerned.
Tsudo
M
M
Department of Immunology, Tokyo Metropolitan Institute of Medical Science, Japan.
Karasuyama
H
H
Kitamura
F
F
Tanaka
T
T
Kubo
S
S
Yamamura
Y
Y
Tamatani
T
T
Hatakeyama
M
M
Taniguchi
T
T
Miyasaka
M
M
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D004247:DNA / Q000235:genetics; D005347:Fibroblasts; D005434:Flow Cytometry; D006801:Humans; D007376:Interleukin-2 / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000648:ultrastructure; D051379:Mice; D008969:Molecular Sequence Data; D015375:Receptors, Interleukin-2 / Q000378:metabolism* / Q000648:ultrastructure; D012995:Solubility; D013329:Structure-Activity Relationship; D014162:Transfection
D007376:Interleukin-2; D008562:Membrane Glycoproteins; D015375:Receptors, Interleukin-2; D004247:DNA