Does cyclic guanosine monophosphate induce autophagy in thyroid malignant carcinoma through down-regulation of cyclic guanosine monophosphate phosphodiesterase?

The aim of this study was to evaluate whether or not the expression of cGMP- phosphodiesterases (cGMP-PDE) varies in different thyroid pathologies and to elucidate the relationship between the expression of cGMP-PDE, cGMP, and autophagy. Fifty-four thyroid biopsy samples, excised to perform the biopsy, were split into two parts and randomly assigned: one part was microscopically examined and histological classified, and the other was frozen and analysed in order to evaluate the cGMP-PDE activity. Intracellular cGMP was also measured. A strong expression of intracellular cGMP and cGMP-PDE activity was observed in carcinoma in respect to controls and benign pathologies. The level of cGMP-PDE in papillary carcinoma without lymph node involvement (N-) was approximately four-fold higher compared to those with lymph node invasion (N±). On the contrary, the cGMP was one and a half times higher in N± than N-. Our results are promising, although further epigenetical studies are needed to confirm this association. A correlation between the cGMP-degrading activity and the severity of thyroid pathology has been shown. The decrease of cGMP-PDE and the increase of cGMP in N± papillar carcinoma could be an autophagic stimulus, a defence mechanism of the body, against the cancer that is expanding and invading other tissues and organs.