O-Linked β-N-Acetylglucosamine Glycosylation Is Involved in Glucocorticoid Receptor-Mediated Gene Repression in AtT-20 Cells

Presentation Number: MON 378
Date of Presentation: April 3rd, 2017

Koshi Makita*1, Shinobu Takayasu1, Kazunori Kageyama2 and Makoto Daimon2
1Hirosaki University Graduate School of Medicine and Hospital, Hirosaki Aomori, Japan, 2Hirosaki University Graduate School of Medicine, Hirosaki Aomori, Japan

Abstract

The pituitary pro-opiomelanocortin (POMC) gene is under multi hormonal control of transcription. In particular, the hypothalamic hormone CRH activates its transcription through the orphan nuclear receptor NGFI-B and Nurr1 whereas the glucocorticoid receptor (GR) represses it. We have reported that the involvement of NF-κB and Nurr1 in cytokine-induced transcription of POMC gene (1). O-linked β-N-acetylglucosamine (O-GlcNAc) glycosylation of nuclear and cytosolic proteins plays an important role in gene repression. Recent analyses have shown that O-GlcNAc transferase (OGT) modified RNA polymerase II (Pol II) C-teriminal domain (CTD), and is involved in glucocorticoid receptor (GR) -mediated transrepression (2, 3). Enhanced O-GlcNAc modification of proteins has been shown to regulate gene expression on high concentration of glucose (4). Here we report that OGT represses POMC gene and transcription activity of NF-κB in a pituitary corticotroph model cell line, the AtT-20 cells. Overexpression of OGT decreased POMC promoter activity and NF-κB dependent transcription. Overexpression of OGT also potentiated dexamethasone-dependent repression of POMC gene and NF-κB under high glucose concentration. Knockdown of OGT attenuates the glucocorticoid-mediated reduction of POMC expression and the effect was increased on high glucose. The peak of Pol II was observed at POMC transcription start site. However, glucose concentration did not alter the recruitment of Pol II. In summary, the present work supports that OGT is an essential cofactor for GR-mediated gene repression in AtT-20 cells under high glucose condition. OGT may affect the stability of Pol II. Therefore further investigation is needed to determine whether OGT causes transcriptional pausing or arrest by preventing phosphorylation at Pol II CTD leading to elongation.

 

Nothing to Disclose: KM, ST, KK, MD