Another project currently being pursued is structure of the IL-4R on J774 murine macrophages by both metabolic labeling and cross-linking techniques. Preliminary experiments suggest that metabolically labeled cells express two major protein bands that are specifically precipitated by a monoclonal anti-IL4R antibody. Although one of these bands appears to be a lower molecular weight degradation project that has previously been described, a 200 kd band is precipitated that has not heretofore been characterized. Experiments using tunicamycin and endoglycosidases suggest that this 200 kd band is a highly glycosylated form of the 140 kd protein that has been recently cloned. By both pulse labeling and pulse chasing studies, it was determined that these cells rapidly synthesize new protein even in cells that had not been induced with IFN-gamma, but only in those cells exposed to IFN-gamma does membrane surface receptor expression increase. These results suggest that IL-4R expression on macrophages is under post-transcriptional regulation that is partially controlled by receptor protein stabilization.
