Selenium-dependent regulation of type I 5'-deiodinase expression

Area of Science:

• Biochemistry
• Cell Biology
• Endocrinology

Background:

• Type I 5'deiodinase (5'-D) is crucial for thyroid hormone metabolism.
• The p27 protein, a substrate-binding subunit of 5'-D, is regulated by selenium.
• The function of the p30 protein, also affected by selenium, remains unknown.

Purpose of the Study:

• To investigate the effect of selenite concentration on the activity and expression of the p27 substrate-binding subunit of type I 5'deiodinase (5'-D).
• To explore the role of selenite in regulating the expression of a protein labeled with bromoacetylthyroxin (BrAcT4), or p30.
• To understand the intracellular hierarchy of selenite utilization in porcine kidney epithelial cells (LLC-PK1).

Main Methods:

• Culturing porcine kidney epithelial cells (LLC-PK1) in a serum-free medium.
• Metabolic labeling of p27 using 75-selenite.
• Affinity labeling of p27 and p30 using bromoacetylthyroxin (BrAc[125I]T4).

Main Results:

• Selenite concentration directly regulates the activity and expression of the p27 subunit of type I 5'-D.
• Expression of the p27 5'-DI subunit is observed at 10-fold lower selenium concentrations compared to glutathione peroxidase.
• Selenium deficiency retards cell growth and inhibits 5'-DI expression.

Conclusions:

• Selenite plays a critical role in regulating thyroid hormone metabolism through its influence on type I 5'-deiodinase.
• There is an intracellular hierarchy for selenite utilization, with 5'-DI expression being more sensitive to selenium levels than glutathione peroxidase.
• Selenium deficiency may impair thyroid hormone action in vivo due to reduced 5'-DI expression.