Constitutive internalization and association with adaptor protein-2 of theinterleukin-6 signal transducer gp130

The transmembrane protein gp130 is the common signalling receptor subunit f or the interleukin-6 (IL-6)-type cytokines, It has recently been shown that the cytoplasmic domain of gp130 contains a dileucine internalization motif and that endocytosis of gp130 occurs signal-independent. Here, we have stu died whether gp130 itself undergoes constitutive internalization or whether its endocytosis is stimulated by formation of the IL-6/IL-6R/gp130 complex . Using two different assays, we found that gp130 is internalized independe nt from lL-6/IL-6R stimulation. In addition, we show that gp130 is constitu tively associated with the cell surface adaptor complex AP-2. Our findings strongly suggest endocytosis of gp130 to be constitutive. (C) 1998 Federati on of European Biochemical Societies.