SIRT6-Autophagy-Warburg Effect Axis in Papillary Thyroid Cancer

Background: Our previous study has demonstrated SIRT6 promotes aggression and epithelial-mesenchymal transition (EMT) in papillary thyroid cancer (PTC). In this study, we focused on the regulatory axis between SIRT6-Autophagy-Warburg effect. Methods: Autophagy activation was confirmed by Western Blotting, quantitative PCR, immunofluorescence and transmission electron microscopy. Warburg effect was examined by Seahorse XF96 analysis and PET imaging. Regulation of SIRT6 in negatively regulates reactive oxygen species (NRROS) was confirmed by chromatin immunoprecipitation. Findings: We innovatively confirmed overexpression of SIRT6 depleted histone H3 lysine 56 acetylation (H3K56ac) of NRROS in vitro, thus increased reactive oxygen species (ROS). Then, accumulated ROS activated endoplasmic reticulum stress (ER stress), and subsequently induced autophagy. Furthermore, the overexpression of SIRT6 inhibited Glucose Transporter 1 (Glut1) via autophagic degradation, thus ulteriorly suppressed Warburg effect. Treatment of ROS scavenger N-acetyl-L-cysteine (NAC, 5mM) or autophagy inhibitor chloroquine (CQ) both rescued the inhibition of Warburg effect. In addition, higher concentration of NAC (15mM) deepened the inhibited Warburg effect. This concentration-dependent bilateral effects of NAC in this process had been confirmed owe to regulation of AMPK signaling pathway. Finally, we further determined above mechanism in vivo via subcutaneous xenografts in nude mice applied with 18F-FDG PET/CT. Interpretation: We identified a SIRT6-ROS-ERstress-Autophagy-Glut1-Warburg effect axis in PTC, which may provide new target for therapy. In addition, NAC (low concentration) and CQ which previously been considered as tumor inhibitors, have been shown to promote tumorigenesis in PTC with high SIRT6 expression via activation of Warburg effect. Funding Statement: This study was funded by Specialty Feature Construction Project of Pudong Health and Family Planning Commission of Shanghai (Min Ye, Grant No.PWZzb2017-21). Declaration of Interests: The authors declare that they have no competing interests. Ethics Approval Statement: All participating patients gave their written informed consent. This study was approved by the Ethical Committee of Shanghai Pudong Hospital.