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

We have examined the endocytosis of chimeric receptors consisting of the 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 also sufficient for normal receptor endocytosis. Chinese hamster ovary cells expressing the chimeric LDL-insulin receptor had internalization and degradation indices of 0.70 +/- 0.01 and 0.51 +/- 0.13 after 5 h at 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 for internalization are the same as those used by the native insulin receptor. The residues GPLY(950-953) serve as the predominant endocytosis signal: Mutation of these to APLA led to a 56% reduction in the internalization index. The sequence NPEY(957-960) is less important for endocytosis and when mutated to APEA led only to a 32% reduction of chimera internalization. We conclude that the juxtamembrane sequences of the insulin receptor are sufficient to cause internalization of the insulin receptor even in the absence of receptor tyrosine kinase activity. (C) 1995 Academic Press, Inc.