CHIMERIC RECEPTORS EXPRESSING JUXTAMEMBRANE SEQUENCES OF THE INSULIN-RECEPTOR UNDERGO RAPID ENDOCYTOSIS IN THE ABSENCE OF RECEPTOR TYROSINEKINASE-ACTIVITY

We have examined the endocytosis of chimeric receptors consisting of t he extracellular domain of the low density lipoprotein (LDL) receptor linked to the juxtamembrane region of the human insulin receptor (hIR) . The latter domain contains amino acid motifs previously shown to be necessary for endocytosis. Here we demonstrate that these codes are al so sufficient for normal receptor endocytosis. Chinese hamster ovary c ells expressing the chimeric LDL-insulin receptor had internalization and degradation indices of 0.70 +/- 0.01 and 0.51 +/- 0.13 after 5 h a t 37 degrees C, compared to 0.62 +/- 0.03 and 0.33 +/- 0.09 for normal LDL receptors. The amino acid sequences that target these chimeras fo r internalization are the same as those used by the native insulin rec eptor. The residues GPLY(950-953) serve as the predominant endocytosis signal: Mutation of these to APLA led to a 56% reduction in the inter nalization index. The sequence NPEY(957-960) is less important for end ocytosis and when mutated to APEA led only to a 32% reduction of chime ra internalization. We conclude that the juxtamembrane sequences of th e insulin receptor are sufficient to cause internalization of the insu lin receptor even in the absence of receptor tyrosine kinase activity. (C) 1995 Academic Press, Inc.