10 - The Internalization and Intracellular Processing of Insulin Receptors

Abstract

This chapter reviews the studies that provide evidence for the internalization and cellular processing of insulin receptors in various target cells. It focuses on the studies carried out on isolated adipocytes using in vitro insulin binding assays and photoaffinity labeling procedures. Receptor-mediated endocytosis is a process by which cells internalize a variety of molecules, including polypeptide hormones, nutrients, plasma transport proteins, and antibodies. The intracellular pathway taken by these different ligands is similar and involves sequestration within smooth or coated vesicles followed by fusion with smooth membrane vesicles and eventual delivery of the ligand to the lysosomes. The ligand and receptor enter the cell together. The chapter discusses the internalization of insulin receptors, recycling of internalized receptors back to the plasma membrane, intracellular degradation of insulin receptors, and the speculations about the functional significance of these processes in target cells. Internalization of insulin–receptor complexes may have roles in the overall action of insulin. Internalized insulin accumulates in Golgi and nuclear compartments. Therefore, it is possible that the following internalization, insulin would be transported to intracellular organelles where it binds to intracellular receptors on these structures and regulates Golgi function or nuclear activities.