O‐GlcNAc Regulates p53 in Ovarian Cancer

Abstract

O‐GlcNAcylation is a dynamic post‐translational modification (PTM) that consists of an addition of a single N‐acetylglucosamine sugar to serine and threonine residues in nuclear, cytoplasmic and mitochondrial proteins. The enzyme O‐linked β‐N‐acetylglucosamine transferase (OGT) adds the modification, while enzyme O‐GlcNAcase (OGA) removes the modification. O‐GlcNAc regulates enzymatic activity, localization, stability and protein‐protein interactions on a wide range of proteins such as transcription factors, structural proteins and kinases. In cancer, when comparing O‐GlcNAc levels in normal and tumor cells, tumor samples present higher O‐GlcNAcylation in vitro and in vivo. This aberrant O‐GlcNAc pattern contributes to changes in important signaling pathways and could contribute to the progression of the disease. Interestingly, the tumor suppressor p53 is modified by O‐GlcNAc. The transcription factor p53 regulates diverse cellular processes like cell survival and the cell cycle. Most solid tumors contain mutations in p53 leading to increased degradation or loss of p53 function, which promotes malignant tumor growth. Ovarian cancer has one of the highest frequencies of p53 mutation rates. The goal of this work is to understand the relationship between O‐GlcNAcylation and p53 function in ovarian cancer. First, O‐GlcNAcylation, OGT and OGA protein and mRNA levels were measured in a series of human ovarian cancer cell lines and no correlation was found between p53 genetic status and O‐GlcNAcylation. Overexpression or silencing of p53 in a p53 wild‐type cell line (A2780) had little effect on O‐GlcNAcylation. On the other hand, pharmacological inhibition of OGA with the inhibitor Thiamet‐G (TMG) leads to an increase in nuclear localization of p53 and increased mRNA levels of p53‐target genes (p21 and Bax). Overexpression of OGA or OGT leads to increased p53 protein but not mRNA levels and a concurrent increase in p53‐targets (Mdm‐2, p21 and Bax) expression. Also, p53 acetylation on lysine 382, a transcriptional activating modification, is higher in OGA/OGT overexpressing cells. In conclusion, O‐GlcNAcylation regulates p53 function through stabilization and activation.Support or Funding InformationSupport and funding: Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Science Without Borders Program, NIH NIDDK R01 DK 100595.