COEXPRESSION OF THE HUMAN TNF RECEPTORS TR6O AND TR80 IN INSECT CELLS- ANALYSIS OF RECEPTOR COMPLEX-FORMATION

For investigation of a possible physical interaction between the two h uman tumor necrosis factor receptors, TR60 (type I) and TR80 (type II) , the baculovirus expression system was used. Each of the receptors wa s expressed as a membrane-integrated protein in insect cells, able to specifically bind the two ligands, tumor necrosis factor (TNF) and lym photoxin (LT(alpha)). Typically, about 150,000 membrane receptors per cell could be detected 40 h after infection, exerting high affinity li gand binding capacity with K-d values virtually identical to that of h uman cell lines. The baculovirus system allowed coexpression of both T NF membrane receptors at very high and about equal numbers to investig ate the existence of heteromultimeric receptor complexes, either forme d spontaneously or ligand induced. Neither saturation binding studies nor immunoprecipitation experiments gave an indication for the existen ce of TNF receptor heteromers. These data are in accordance with the c urrent view of TNF signaling, in which homomultimerization, rather tha n heteromer formation of TNF receptors is the initial activating event .