Differential shedding of the two subunits of the interleukin-6 receptor

cDNAs coding for the two receptor subunits of the interleukin-6 receptor have been stably expressed in Madine Darby canine kidney (MDCK) cells. The fate of the IL-6 binding protein (IL-6R) and of the signal transducing protein gp130 was studied independently. Both proteins were proteolytically cleaved from cells metabolically labeled with [35S]methionine/cysteine leading to the release of soluble receptor proteins of 55 kDa and 100 kDa, respectively. In contrast to the shedding of the IL-6R gp130 was inefficiently released from the cells and the process was not significantly stimulated by the phorbolester PMA. In addition we show that the soluble forms of the IL-6R and gp130 released by transfected cells can form a ternary complex with interleukin-6 indicating that such complexes also may occur in vivo.