Murine interleukin 7 (IL-7) receptor. Characterization on an IL-7-dependent cell line.
A murine cell line (IxN/2b) absolutely dependent upon exogenous IL-7 for continued growth has been obtained that expresses lymphoid precursor and class I MHC antigens and also contains a rearranged mu heavy chain. This cell line has been used to define the binding and structural characteristics of the murine IL-7 receptor using 125I-labeled recombinant murine IL-7. 125I-IL-7 binding to IxN/2b cell was rapid and saturable at both 4 degrees and 37 degrees C. Equilibrium binding studies produced curvilinear Scatchard plots at both temperatures with high and low affinity Ka values of approximately 1 x 10(10) M-1 and 4 x 10(8) M-1, respectively, and a total of 2,000-2,500 IL-7 binding sites expressed per cell. Experiments measuring inhibition of binding of 125I-IL-7 by unlabeled IL-7 also produced data consistent with the existence of two classes of IL-7 receptors. Evidence concerning the possible molecular nature of two classes of IL-7 receptors was provided by dissociation kinetics and affinity crosslinking experiments. The dissociation rate of 125I-IL-7 was markedly increased when measured in the presence of unlabeled IL-7 at both 37 degrees and 4 degrees C, which is diagnostic of a receptor population displaying negative cooperativity. Crosslinking studies showed that under both reducing and nonreducing conditions, the major crosslinked species observed corresponded to a receptor size of 75-79 kD while a less intense higher molecular mass crosslinked species was also seen which corresponded to a receptor size approximately twice as large (159-162 kD). Both types of experiments suggest that the IL-7 receptor may form noncovalently associated dimers in the membrane. The IL-7 receptor was expressed on pre-B cells, but not detected on several murine B cell lines or primary mature B cells. It was also expressed on murine thymocytes, some T lineage cell lines, and on bone marrow-derived macrophage. All cells binding 125I-IL-7 exhibited curvilinear Scatchard plots. No cytokines or growth factors tested were able to inhibit binding of 125I-IL-7 to its receptor. These results define the initial binding and structural characteristics, and the cellular distribution, of the murine IL-7 receptor.
Park
L S
LS
Immunex Corporation, Seattle, Washington 98101.
Friend
D J
DJ
Schmierer
A E
AE
Dower
S K
SK
Namen
A E
AE
D000818:Animals; D000954:Antigens, Surface / Q000032:analysis; D001667:Binding, Competitive; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology; D005434:Flow Cytometry; D006801:Humans; D015851:Interleukin-7 / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D007378:Interleukins / Q000494:pharmacology; D007700:Kinetics; D011971:Receptors, Immunologic / Q000187:drug effects / Q000502:physiology*; D020395:Receptors, Interleukin-7; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000276:immunology
D000954:Antigens, Surface; D015851:Interleukin-7; D007378:Interleukins; D011971:Receptors, Immunologic; D020395:Receptors, Interleukin-7; D011994:Recombinant Proteins