Evidence for a low-affinity interleukin-3 receptor.
Interleukin-3 (IL-3) regulates the proliferation of myeloid, erythroid, and lymphoid cells. Previous reports showed IL-3 binding restricted to a single high-affinity (Kd = 50-200 pM) site. Here, we demonstrate by equilibrium studies an additional binding site for IL-3 with lower apparent affinity (Kd = 5-20 nM). Furthermore, kinetic analysis shows that two binding sites for IL-3 exist: IL-3 dissociates slowly from the first site (T1/2 = 4 hr; k-1 = 2.7 x 10(-3) min-1), whereas it dissociates rapidly (T1/2 = 4.0 min; k-1 = 0.116 min-1) from the second site. Cross-linking showed that [125I]IL-3 binding to the 115- and 140-kD proteins was not saturable at concentrations commensurate with high-affinity binding and IL-3 dissociated rapidly from these same molecules. Thus, the low affinity IL-3 receptor is a molecule(s) of 115- to 140-kD.
Department of Molecular Biology, DNAX Research Institute of Molecular and Cellular Biology, Palo Alto, CA 94304-1104.
J
J
Schreurs
K
K
Arai
A
A
Miyajima
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002460:Cell Line; D003432:Cross-Linking Reagents; D007377:Interleukin-3 / Q000378:metabolism*; D007700:Kinetics; D008970:Molecular Weight; D011971:Receptors, Immunologic / Q000145:classification / Q000302:isolation & purification / Q000378:metabolism*; D016185:Receptors, Interleukin-3
D003432:Cross-Linking Reagents; D007377:Interleukin-3; D011971:Receptors, Immunologic; D016185:Receptors, Interleukin-3