EGFR and BER pathways in human thyroid goiter: role of oxidative stress

Background: Thyroid nodules occur in over 50% of the Italian population. In thyroid, H2O2 is largely produced and DNA lesions, generated by ROS excess, are physiologically removed by the BER system. Since EGF is a physiological regulator of thyroid functions, this study investigated the effect of oxidative stress on EGFR and BER signaling in goiter. Methods: Normal human thyroid cells, Nthy-ori3-1, were treated with H2O2, EGF, LY294002, and PD98059 alone and in combination. Goiter tissues were obtained from patients undergoing thyroidectomy. EGFR and BER pathways were analyzed by Western blot and RT-qPCR. Results: A time-dependent increase of OGG1 and MUTYH gene expression was observed after H2O2 treatment and was reversed by EGF and LY294002 alone or combined with H2O2. EGF and LY294002 induced EGFR overexpression, alone and combined with H2O2. H2O2 treatment, alone or combined with EGF, LY294002, and PD98059 resulted in increased EGFR and MAPK activation. In addition, H2O2, alone and combined with EGF, induced a rapid increase of ErbB2 gene expression, while LY294002, alone and combined with H2O2, reduced its expression. Surprisingly, PD98059 enhanced ErbB2 expression compared to H2O2- treated and control cells. Tissue analysis showed a strong individual variability among patients. Preliminary data displayed a downregulation of OGG1 in pathologic tissue compared to control. The opposite trend was observed with the Nrf2 gene. Conclusions: These results indicate that EGFR and ErbB2 are upregulated in response to oxidative stress, suggesting an Akt-dependent mechanism. Our observations present the first evidence that pronounced H2O2 tress may directly interact with ErbB2 and BER downstream signaling.