Demonstration that the insulin receptor undergoes an early structural modification following insulin binding

Area of Science:

• Cell Biology
• Molecular Endocrinology
• Biochemistry

Background:

• The insulin receptor (IR) mediates insulin signaling.
• Understanding IR processing is crucial for metabolic research.
• Endocytosis plays a key role in receptor regulation.

Purpose of the Study:

• To investigate the structural modifications of the insulin receptor during endocytosis in hepatocytes.
• To analyze the fate of the insulin receptor within subcellular fractions after internalization.

Main Methods:

• Utilized a 125I-labeled photoreactive insulin derivative for covalent attachment to the insulin receptor.
• Employed SDS-polyacrylamide gel electrophoresis for structural analysis.
• Isolated subcellular fractions, including plasma membrane and endosomes, from hepatocytes.

Main Results:

• The intact insulin receptor (350 kDa) and alpha subunit (135 kDa) were identified in the plasma membrane.
• Internalized insulin receptor in endosomes showed a modified structure (140 kDa non-reduced), yielding 100 kDa and 68 kDa species upon reduction.
• These changes occurred rapidly during endocytosis and did not involve complete disulfide reduction.

Conclusions:

• The insulin receptor undergoes significant structural alterations during endocytosis.
• Endosomal processing of the insulin receptor may involve proteolytic events.
• These modifications suggest a dynamic regulation of receptor function post-internalization.