Alternative glycosylation of the insulin receptor prevents oligomerization and acquisition of insulin-dependent tyrosine kinase activity.
Glucose deprivation leads to the synthesis of an aberrantly glycosylated ('alternative') and inefficiently processed form of the insulin proreceptor in 3T3-L1 adipocytes. To further explore the effect of aberrant (rather than absent) N-linked glycosylation of the insulin receptor, we examined the relationship of processing to function. Our studies show that the alternative form of the proreceptor does not oligomerize nor does it acquire the ability to undergo insulin-sensitive autophosphorylation. This along with an interaction with the glucose-regulated stress protein GRP78/BiP implies inappropriate folding/dimerization and retention in the ER. Glucose refeeding causes the post-translational modification of the alternative form of the proreceptor to a novel 'intermediate' form which is independent of new protein synthesis. As little as 100 microM glucose (or mannose) can induce this modification. In vitro digestion of the alternative and intermediate proreceptors with SPC1/furin shows that both the alpha- and beta-subunit domains are glycosylated, albeit aberrantly. This implies that the aberrantly glycosylated proreceptor could serve as a substrate for SPC1 in a physiological setting if the receptor was able to interact with the enzyme in the appropriate compartment (i.e., the trans-Golgi network). Based on inhibitor studies, however, both the alternative and intermediate forms of the proreceptor appear to be primarily targeted to the proteasome for degradation.
Hwang
J B
JB
Hernandez
J
J
Leduc
R
R
Frost
S C
SC
D016475:3T3 Cells; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002451:Cell Compartmentation; D003546:Cysteine Endopeptidases / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D000091342:Endoplasmic Reticulum Chaperone BiP; D005947:Glucose / Q000172:deficiency / Q000494:pharmacology; D006031:Glycosylation; D006360:Heat-Shock Proteins; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000737:chemistry; D018832:Molecular Chaperones / Q000378:metabolism; D009097:Multienzyme Complexes / Q000737:chemistry; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D017510:Protein Folding; D011498:Protein Precursors / Q000096:biosynthesis / Q000378:metabolism; D011972:Receptor, Insulin / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins; D015398:Signal Transduction
D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D018832:Molecular Chaperones; D009097:Multienzyme Complexes; D011498:Protein Precursors; D029702:Schizosaccharomyces pombe Proteins; C051512:insulin proreceptor; D011972:Receptor, Insulin; D020928:Mitogen-Activated Protein Kinases; C095409:sty1 protein, S pombe; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D005947:Glucose