Effect And Mechanism Of GPX3Reactivation On The Progrssion Of Papillary Thyroid Carcinoma

BackgroundFor thyroid gland, the main physiologic function is the synthesis of thyroidhormones (TH) whose catalysis essentially need thyroid peroxidase(TPO).H2O2,anessential co-substrate for TPO, can freely diffuse into the cytoplasm and nucleus athigh concentration and then trigger apoptosis and induce DNA damage. As aconsequence, the gland is continuously exposed to relevant concentrations of H2O2and to H2O2-derived ROS. Glutathione peroxidase3(GPX3) is an extracellularantioxidant enzyme abundant in plasma, kidney, thyroid and so on and can reduceH2O2and ROS using glutathione as reductant and therefore protect the glands againstoxidative damage.However,GPX3was observed down-regulated in thyroid cancercells with a more oxidized state. Han C et al demonstrated an epigenetic regulation ofGPX3by aberrant methylation in thyroid cancer cell line (TPC-1).However, theclinical significance of GPX3methylation need further investigation. Moreover, apaper on colorectal carcinoma showed that GPX3-deficient mice exhibited anincreased tumor number, increased proliferation and hyperactive WNT signaling.These findings demonstrated that GPX3can act as a tumor suppressor in colorectalcarcinoma and its function was associated with Wnt/β-catenin signaling pathway.However, the function and its molecular pathways of GPX3in thyroid cancer remainunclear.Objective1．To evaluate if GPX3acted as a tumor suppressor in thyroid cancer throughanalyzing the effect of GPX3on thyroid cancer cell proliferation, invasion and migration.2．To investagate if GPX3was correlated with the progression of thyroid cancervia Wnt/β-catenin signaling pathway.3．To analyze how GPX3expression or methylation associated with clinicalfeatures so that we can discuss the possibility of GPX3as a diagnosis symbol ofpapillary thyroid carcinoma.MethodsLentiviral expression vector of GPX3or empty vector was constructed andtransfected into the thyroid cancer cell line where GPX3was silenced through DNAmethylation to reexpress GPX3. Then cell proliferation assay and transwell assaywere adopted to analyze the effect of GPX3on thyroid cell viability, invasion andmigration. And western blot was applied to detect the expression of Matrixmetalloproteinase2(MMP-2) and key factors (β-catenin, p-β-catenin, c-Myc andcyclinD1) in Wnt/β-catenin signaling pathway. Immunohistochemistry andmethylation specific PCR (MSP) were employed to measure the expression andmethylation status of GPX3in94cases of primary PTC tissues.Results1．Restoration of GPX3expression exhibited reduced cell viability (p<0.01),decreased number of invasive and migratory cells (p<0.001) and reduced expressionof MMP-2.2．Expression of β-catenin, c-Myc and cyclinD1were reduced whereas p-β-catenin was increased after re-expression of GPX3.3．GPX3expression was significantly decreased in PTC tissues (p<0.001) whichwas inversely associated its promoter methylation (46.8%methylated)(p=0.037).Positive correlations were found between regional lymph node metastasis andreduced expression as well as hypermethylation of GPX3(p=0.033and p=0.001respectively). ConclusionGPX3can inhibit thyroid cancer progression via Wnt/β-catenin signalingpathway and therefore act as a tumor suppressor. GPX3hypermethylation correlateswith the progression of papillary thyroid carcinoma and possibly serves as a potentialdetection marker in thyroid cancer.