Details

Autor(en) / Beteiligte

• Hwang, J B
• Frost, S C

Titel

Effect of Alternative Glycosylation on Insulin Receptor Processing

Ist Teil von

• The Journal of biological chemistry, 1999-08, Vol.274 (32), p.22813-22820

Ort / Verlag

United States: American Society for Biochemistry and Molecular Biology

Erscheinungsjahr

1999

Quelle

Free E-Journal (出版社公開部分のみ）

Beschreibungen/Notizen

• The mature insulin receptor is a cell surface heterotetrameric glycoprotein composed of two α- and two β-subunits. In 3T3-L1 adipocytes as in other cell types, the receptor is synthesized as a single polypeptide consisting of uncleaved α- and β-subunits, migrating as a 190-kDa glycoprotein. To examine the importance of N -linked glycosylation on insulin receptor processing, we have used glucose deprivation as a tool to alter protein glycosylation. Western blot analysis shows that glucose deprivation led to a time-dependent accumulation of an alternative proreceptor of 170 kDa in a subcellular fraction consistent with endoplasmic reticulum localization. Co-precipitation assays provide evidence that the alternative proreceptor bound GRP78, an endoplasmic reticulum molecular chaperone. N -Glycosidase F treatment shows that the alternative proreceptor contained N -linked oligosaccharides. Yet, endoglycosidase H insensitivity indicates an aberrant oligosaccharide structure. Using pulse-chase methodology, we show that the synthetic rate was similar between the normal and alternative proreceptor. However, the normal proreceptor was processed into α- and β-subunits ( t = 1.3 ± 0.6 h), while the alternative proreceptor was degraded ( t = 5.1 ± 0.6 h). Upon refeeding cells that were initially deprived of glucose, the alternative proreceptor was processed to a higher molecular weight form and gained sensitivity to endoglycosidase H. This “intermediate” form of the proreceptor was also degraded, although a small fraction escaped degradation, resulting in cleavage to the α- and β-subunits. These data provide evidence for the first time that glucose deprivation leads to the accumulation of an alternative proreceptor, which can be post-translationally glycosylated with the readdition of glucose inducing both accelerated degradation and maturation.