AIC2A is a component of the purified high affinity mouse IL-3 receptor: temperature-dependent modulation of AIC2A structure

Abstract

IL-3, a potent hemopoietic growth factor, interacts with distinct classes of receptor, one of high affinity and the other of low affinity. The gene for a 115 kDa, low affinity IL-3 binding protein (AIC2A) was recently cloned. Ligand affinity purification was used to show that the AIC2A gene product participates in the formation of a high affinity IL-3 receptor (IL-3R). Cells were incubated with biotin-IL-3 at 4 degrees C and IL-3 bound to the low affinity site was removed by washing, cells were detergent extracted, and then streptavidin - agarose was used to purify proteins bound to biotin-IL-3. A 115 kDa phosphotyrosine (Ptyr)-containing protein was specifically purified and its identity as AIC2A was shown in Western assays using polyclonal anti-AIC2A antibodies. A brief temperature shift of the intact, biotin-IL-3-treated cells from 4 to 37 degrees C, prior to receptor purification, results in structural and compositional changes in the IL-3R, including: (i) a 10-20 kDa increase in the apparent Mr of both the AIC2A and the Ptyr antigens, and (ii) the association of a serine/threonine kinase. These observations indicate that in its native environment, the low affinity IL-3 binding protein, AIC2A, participates to form the high affinity IL-3R and is a substrate for a tyrosine kinase. Moreover, a ligand-induced, temperature-regulatable structural change in the IL-3R may be of importance in the transduction of information through the receptor, as suggested by the enhanced association of the IL-3R with a serine/threonine kinase.