RING1 Inhibition Has a Cell-Specific Antitumoral Role by Promoting Autophagy in Endometrial Cancer Cells

Background/Aims: Factors influencing gene expression through chemical modifications of histones may play an important role in the regulation of the autophagy process in cancers. RING1A or RING1B are responsible for the catalytical activity of Polycomb repressive complex 1 (PRC1) which monoubiquitylate histone H2A. The aim of the study was to determine the effect of the RING1A/B protein inhibition on the autophagy process in endometrial cancer cells and the anticancer effectiveness of RING1 inhibitor PRT4165 in combination with autophagy inhibitors. Methods: The expression of autophagy genes and proteins were analyzed in endometrial cancer cells HEC-1A and Ishikawa grown in different glucose concentrations and treated with PRT4165. To assess the effectiveness of PRT4165 used alone or in combination with HCQ or Lys05, IC50 and the combination index (CI) were calculated. Flow cytometry method was used to estimate apoptotic cells after treatment. Results: The results confirm the impact of RINGs on autophagy and apoptosis in endometrial cancer cells. PRT4165 inhibitor causes changes in the expression of ATG genes and autophagy markers and the effect depends on glucose concentration and cell types. However, the anticancer effectiveness of PRT4165 was lower when it was used in combination with autophagy inhibitors, suggesting that such a combination is not a promising anticancer strategy. Conclusion: The results indicate the importance of the RINGs in the process of autophagy and apoptosis. Further potentially more effective combinations of PRT4165 with autophagy modulators should be sought.