Thyroid oxidase (THOX2) gene expression in the rat thyroid cell line FRTL-5

Area of Science:

• Biochemistry
• Molecular Biology
• Endocrinology

Background:

• NADPH oxidase (NOX) flavoproteins are crucial enzymes involved in reactive oxygen species generation.
• Previous studies identified THOX1 and THOX2 (also known as DUOX1 and DUOX2) in humans, but their homologs and functions in other species, like rats, require further elucidation.

Purpose of the Study:

• To isolate and characterize a novel NADPH oxidase flavoprotein from rat thyroid tissue.
• To investigate the expression and regulation of this flavoprotein in cultured rat thyroid cells and in vivo.

Main Methods:

• cDNA isolation and sequencing from rat thyroid gland.
• Bioinformatic analysis to compare the rat sequence with known human homologs.
• Messenger RNA (mRNA) expression analysis in cultured FRTL-5 cells and rat thyroid tissue using quantitative methods.
• Investigation of regulatory effects of cyclic adenosine monophosphate (cAMP) and methimazole on mRNA levels.

Main Results:

• A cDNA encoding a 1517-residue polypeptide, highly similar to human THOX2/DUOX2 and THOX1/DUOX1, was isolated.
• Rat THOX2 exhibited a distinct feature: a 30-residue deletion absent in human sequences.
• THOX2 mRNA was detected in FRTL-5 cells, upregulated by cAMP, and downregulated by methimazole, contrasting with TPO and NIS mRNA regulation.
• The flavoprotein was also found in the intestine, duodenum, and colon.

Conclusions:

• The identified rat NADPH oxidase flavoprotein shares significant homology with human DUOX proteins.
• The distinct sequence and broader tissue distribution (thyroid and intestine) suggest a new classification: Long-chain NOX (LNOX) flavoproteins, rather than THOX/DUOX.
• This finding broadens the understanding of NOX flavoprotein family diversity and function across species and tissues.