Related Experiment Videos
Megalin (gp330): a putative endocytic receptor for thyroglobulin (Tg)
1Pathology Research Laboratory, Massachusetts General Hospital, Harvard Medical School, Charlestown 02129, USA.
Endocrinology
|March 10, 1998
Summary
Megalin, a receptor on thyroid cells, binds thyroglobulin. This suggests megalin may play a role in thyroid hormone release by endocytosing thyroglobulin from the colloid.
Area of Science:
- Cell Biology
- Endocrinology
- Molecular Biology
Background:
- Megalin (gp330) is a glycoprotein receptor found on absorptive epithelial cells, including thyroid cells.
- Megalin binds multiple ligands in vitro, but its physiological ligands are largely unknown.
- Thyroglobulin (Tg) is essential for thyroid hormone synthesis and release.
Purpose of the Study:
- To investigate the interaction between megalin and thyroglobulin (Tg).
- To determine if megalin binds Tg and to characterize the binding interaction.
- To explore the potential role of megalin in Tg endocytosis in thyroid cells.
Main Methods:
- Solid-phase binding assays using purified rat megalin and rat thyroglobulin (Tg).
- Inhibition studies using excess Tg, known megalin ligands, receptor-associated protein (RAP), and anti-megalin antibodies.
- Analysis of Tg binding to megalin using SDS-PAGE, autoradiography, and immunoblotting after release from megalin.
- Measurement of binding affinity (Kd) and calcium dependence.
Main Results:
- Purified rat megalin binds rat Tg with an estimated Kd of 9.2+/-0.6 nM.
- Tg binding to megalin is calcium-dependent and inhibited by excess Tg, lactoferrin, lipoprotein lipase, apolipoprotein J, and RAP.
- Megalin binds both monomeric (330 kD) and dimeric (660 kD) Tg.
Conclusions:
- Megalin directly binds thyroglobulin.
- Megalin's interaction with Tg is specific and characterized.
- Megalin may mediate the endocytosis of Tg from the thyroid colloid, contributing to thyroid hormone release.