Replacement of the human insulin receptor transmembrane and cytoplasmic domains by corresponding domains of the oncogene product v-ros leads to accelerated internalization, degradation, and down-regulation.
Internalization, degradation, and insulin-induced down-regulation of insulin receptors were studied comparatively in transformed Chinese hamster ovary (CHO) cell lines, CHO.T and CHO.IR.ros, respectively expressing either the wild-type human insulin receptor (hIR) or a mutated hybrid receptor in which the transmembrane and cytoplasmic domains of hIR were replaced by corresponding domains of the transforming protein p68gag-ros (v-ros) of avian sarcoma virus UR2. At 37 degrees C, degradation of insulin receptors photoaffinity labeled on the cell surface (440 kDa) was most rapid for the hybrid hIR.ros (t1/2 1.0 +/- 0.1 h), intermediate for the wild-type hIR (t1/2 2.7 +/- 0.5 h), and slowest for the endogenous CHO insulin receptors (t1/2 3.7 +/- 0.7 h). Initial intracellular accumulation of the hIR.ros hybrid was also most rapid, reaching maximal amounts in 20 min following which the receptors disappeared rapidly from the intracellular compartment. In contrast, intracellular accumulation of the receptors in the CHO.T and CHO cells was slower, reaching maximal amounts in 60 min, and rapid disappearance of the receptors from the intracellular compartment did not occur. Chloroquine, a lysosomotropic agent, inhibited degradation of both the wild-type hIR and the chimeric hIR.ros and increased their intracellular accumulation. However, the chloroquine effect was much more marked for the hIR.ros receptors whose intracellular accumulation was increased by greater than 300% (in comparison with approximately 60% increase for the wild-type hIR), demonstrating marked intracellular degradation of the hybrid hIR.ros at chloroquine-sensitive sites. Insulin-induced down-regulation of the cell surface hIR.ros (52% loss in 3 h) was also more marked than the wild-type hIR (approximately 30% loss in 3 h). Thus, in the hybrid hIR.ros receptor, which was shown previously to exhibit insulin-stimulated autophosphorylation and kinase activity but not insulin-stimulated metabolic function, the capacity for internalization and down-regulation is not only preserved but is also markedly accelerated. These findings suggest that 1) the postreceptor coupling mechanisms mediating insulin-induced receptor internalization, degradation, and down-regulation are different from those mediating metabolic functions; and 2) v-ros may contain the structural information directing accelerated receptor catabolism.
Berhanu
P
P
Department of Medicine, University of Colorado Health Sciences Center, Denver 80262.
Rohilla
A M
AM
Rutter
W J
WJ
D000345:Affinity Labels; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002738:Chloroquine / Q000494:pharmacology; D006224:Cricetinae; D003593:Cytoplasm / Q000378:metabolism; D015536:Down-Regulation; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D007700:Kinetics; D009154:Mutation; D009856:Oncogene Proteins, Viral / Q000378:metabolism; D010777:Photochemistry; D020794:Receptor Protein-Tyrosine Kinases; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism
D000345:Affinity Labels; D007328:Insulin; D009856:Oncogene Proteins, Viral; D011993:Recombinant Fusion Proteins; D002738:Chloroquine; D020794:Receptor Protein-Tyrosine Kinases; D011972:Receptor, Insulin; C058682:v-ros protein, Avian sarcoma virus UR2