Binding of insulin to isolated nuclei

Area of Science:

• Endocrinology
• Molecular Biology
• Cell Biology

Background:

• Insulin is a key metabolic hormone primarily acting through cell surface receptors.
• The intracellular mechanisms and potential nuclear actions of insulin remain incompletely understood.

Purpose of the Study:

• To investigate the presence and characteristics of specific insulin binding sites within purified rat liver cell nuclei.
• To explore the potential for the nucleus as an intracellular site of insulin action.

Main Methods:

• Isolation of purified nuclei from rat liver.
• Incubation of nuclei with 125I-labeled insulin to assess binding.
• Competition assays using unlabeled native insulin, proinsulin, desoctapeptide insulin, glucagon, thyrotropin, growth hormone, and prolactin.
• Comparison of insulin binding to nuclei versus glucagon binding to liver plasma membranes.

Main Results:

• Specific binding sites for 125I-labeled insulin were identified in purified rat liver nuclei.
• Insulin binding was rapid, reversible, and dose-dependent.
• Native insulin effectively inhibited labeled insulin binding, while proinsulin and desoctapeptide insulin showed reduced potency.
• Glucagon, thyrotropin, growth hormone, and prolactin did not compete for nuclear insulin binding.
• Glucagon bound strongly to liver plasma membranes but not to liver nuclei.

Conclusions:

• Purified rat liver nuclei possess specific binding sites for insulin.
• These findings indicate that the cell nucleus may represent an intracellular site for insulin action, distinct from its known plasma membrane receptor signaling.