Proteomics reveals alterations in thyroglobulin expression and in the H2O2 detoxifying system in cold thyroid nodules

Szintigraphically cold thyroid nodules (CTN) are frequent findings in regions with iodine deficiency. While the presence of a CTN raises the possibility of thyroid cancer probably less than 3% of CTNs acutally represent malignancy. The molecular etiology of benign CTNs is still unresolved. We applied 2 D-gel electrophoresis in combination with MS analysis to define a protein fingerprint of CTNs as a pre-requiste to get further insights into their pathogenesis. 10 benign CTNs (colloid nodules and follicular adenoma) and corresponding normal thyroid tissue (ST) of the same patient were studied. The proteomics approach resulted in a protein resolution of ~ 1.500 spots/gel. Differential regulation of protein expression in CTN vs. ST was observed for 250 spots, which were subsequently identified by ESI-MS or FTICR. Proteins consistenly upregulated (>2fold) in CTNs fell into three major categories: 1. Cellular proliferation (amyloid precursor protein), 2. Tg trafficking (cathepsin B, PDI, HSP90, calreticulin, Tg fragments) and 3. H2O2 detoxifying system (peroxiredoxin 2 and 6, Glutathione S-transferase π, DJ-1). Western blot analysis for selective proteins e.g. APP, Cathepsin B and Tg was performed and verified the 2D-gel results.

In summary we report the first characterization of the proteome of benign CTNs. Our results suggest specific alterations in Tg expression and upregulation of the peroxide detoxification system in CTNs possibly due to a failure in the processing and iodination of thyroglobulin (Tg). In fact, in a follow-up study, the complete absence of iodinated Tg in the follicular lumina of CTNs was shown, which reinforces the hypothesis of an inherent functional or molecular Tg defect in CTNs.