Distinct pattern of oxidative DNA damage and DNA repair in follicular thyroid tumours.

Increased oxidative stress has been linked to thyroid carcinogenesis. In this paper, we investigate whether oxidative DNA damage and DNA repair differ in follicular adenoma (FA) and follicular thyroid carcinoma (FTC). 7,8-Dihydro-8-oxoguanine (8-OxoG) formation was analysed by immunohistochemistry in 46 FAs, 52 FTCs and 18 normal thyroid tissues (NTs). mRNA expression of DNA repair genes OGG1, Mut Y homologue (MUTYH) and endonuclease III (NTHL1) was analysed by real-time PCR in 19 FAs, 25 FTCs and 19 NTs. Induction and repair of oxidative DNA damage were studied in rat FRTL-5 cells after u.v. irradiation. Moreover, activation of DNA damage checkpoints (ataxia telangiectasia mutated (ATM) and H2A histone family, member X (H2AFX (H2AFX))) and proliferation index (MIB-1) were quantified in 28 non-oxyphilic and 24 oxyphilic FTCs. Increased nuclear and cytosolic 8-OxoG formation was detected in FTC compared with follicular adenoma, whereby cytosolic 8-OxoG formation was found to reflect RNA oxidation. Significant downregulation of DNA repair enzymes was detected in FTC compared with FA. In vitro experiments mirrored the findings in FTC with oxidative stress-induced DNA checkpoint activation and downregulation of OGG1, MUTYH and NTHL1 in FRTL-5 cells, an effect that, however, was reversible after 24  h. Further analysis of FTC variants showed decreased oxidative DNA damage, sustained checkpoint activation and decreased proliferation in oxyphilic vs non-oxyphilic FTC. Our data suggest a pathophysiological scenario of accumulating unrepaired DNA/RNA damage in FTC vs counterbalanced DNA/RNA damage and repair in FA. Furthermore, this study provides the first evidence for differences in oxidative stress defence in FTC variants with possible implications for therapeutic response and prognostic outcome.

TFF3-based candidate gene discrimination of benign and malignant thyroid tumors in a region with borderline iodine deficiency.

BACKGROUND: With the advent of microarray technology, increasing numbers of marker genes are proposed to distinguish benign and malignant thyroid lesions. However, most markers await confirmation through independent studies. In this paper, we re-evaluate the diagnostic potential of 10 proposed candidate genes in benign and malignant thyroid pathologies in a region with borderline iodine deficiency. METHODS: Quantitative real-time PCR was performed for CCND2, PLAB, PCSK2, HGD1, TFF3, B4GALT, LGALS3, ETS1, ADM3, and TG in 150 thyroid specimens, including 52 benign thyroid nodules (28 follicular adenoma and 24 adenomatous nodules), 52 corresponding normal thyroid tissues, 20 follicular carcinomas, 20 papillary carcinomas, and six undifferentiated carcinomas. RESULTS: On a single-gene basis, significant differences in mRNA expression were found for TFF3, PLAB, and ADM3 in benign thyroid nodules and thyroid malignancy. Using two-marker gene sets, we identified 11 combinations, which allowed both a distinction of benign and malignant thyroid nodules and a discrimination of follicular adenoma and carcinoma. However, for cancer prediction, analysis of a minimum of six genes per sample was necessary and allowed correct prediction of a benign thyroid lesion and thyroid cancer with 94% accuracy in the most discriminative set (TFF3/PLAB/TG/ADM3/HGD1/LGALS3). CONCLUSION: We confirm the applicability of a number of recently proposed marker genes for the distinction of benign and malignant thyroid tumor and suggest that their diagnostic usefulness is independent of the iodide supply. We propose that the most discriminative marker set identified in our validation study together with marker combinations proposed by other investigators should now be evaluated in multicenter trials.