Expression of reduced nicotinamide adenine dinucleotide phosphate oxidase (ThoX, LNOX, Duox) genes and proteins in human thyroid tissues

The large homolog of NADPH oxidase flavoprotein LNOX2, and probably LNOX1, are flavoproteins involved in the thyroid H2O2 generator. Western blot anal ysis of membrane proteins from normal human thyroid, using antipeptide anti bodies, indicated that LNOX1,2 are 164-kDa glycoproteins and that N-glycosy lated motifs account for at least 10-20 kDa of their total apparent molecul ar mass. Northern blot analysis of 23 different human tissues demonstrated that LNOX2 messenger RNA (mRNA) is strongly expressed only in the thyroid g land, although blast analysis of expressed sequence tags databases indicate d that LNOX genes are also expressed in some nonthyroid cells. We investigated LNOX1, 2 gene and protein expressions in normal and patholo gical human thyroid tissues using real-time kinetic quantitative PCR and an tipeptide antibodies, respectively. In normal tissue, LNOX1,2 are localized at the apical pole of thyrocytes. Immunostaining for LNOX1,2 was heterogen eous, inside a given follicle, with 40-60% of positive follicular cells. Am ong normal and pathological tissues, variations of LNOX1 and LNOX2 mRNA lev els were parallel, suggesting a similar regulation of both gene expressions . Whereas LNOX mRNAs seemed slightly affected in benign disease, the expres sion of protein was highly variable. In multinodular goiters, 40-60% of cel ls were stained. In hypofunctioning adenomas, LNOX immunostaining was highl y variable among follicles, whereas sodium/iodide (Na +/I-) symporter immun ostaining was decreased. In hyperfunctioning thyroid tissues, only few cell s (0-10%) were weakly stained, whereas sodium/iodide symporter staining was found in the majority of follicular cells. In conclusion, LNOX proteins are new apical glycoproteins with a regulation of expression that differs from other thyroid markers.