Biochemical Identity and Characterization of the Mouse Interleukin-2 Receptor β and γ_c Subunits

Although the mouse IL-2 receptor (IL-2R) β and γ_c subunits have been identified by molecular cloning, the biochemical identity of these subunits has not yet been established. In the present study, the mouse IL-2R was biochemically characterized from cell lines expressing normal and aberrant IL-2R. Using novel monoclonal antibodies specific for the β or γ_c subunits, we established that the M_r of the β chain is 90,000–100,000 and that of the γ_c subunit is 75,000–80,000. Analysis of transfected EL4 cells that expressed α, γ_c, and truncated β subunits or mutant EL4 cells, which selectively lacked cell surface γ_c, revealed that no other material migrated to a position on SDS-PAGE characteristic of IL-2/IL-2Rβ and IL-2/IL-2Rγ_c cross-linked complexes, respectively. Thus, the β and γ_c subunits appear to be the sole IL-2R constituents of these IL-2 cross-linked complexes. The IL-2/IL-2Rγ_c, but not the IL-2/IL-2Rβ, complex exhibited enhanced mobility after SDS-polyacrylamide gel electrophoresis under nonreducing conditions, suggesting a more compact structure for γ_c as a result of intrachain disulfide bonds. The primary posttranslational modification of the mouse β and γ_c subunits is N-linked glycosylation. These biochemical studies reconcile past uncertainties concerning the subunit composition of the mouse IL-2R and are consistent with a model of the IL-2R containing only three subunits.