Inhibitory Effects of a Novel PPAR-γ Agonist MEKT1 on Pomc Expression/ACTH Secretion in AtT20 Cells.

Rehana Parvin,Kyoko Shimizu,Hiroyuki Miyachi,Hiroki Shimada,Erika Noro,Atsushi Yokoyama,Akira Sugawara,Susumu Suzuki,Akiko Saito-Hakoda

doi:10.1155/2018/5346272

Abstract

Although therapeutic effects of the peroxisome proliferator-activated receptor gamma (PPAR-γ) agonists rosiglitazone and pioglitazone against Cushing's disease have been reported, their effects are still controversial and inconsistent. We therefore examined the effects of a novel PPAR-γ agonist, MEKT1, on Pomc expression/ACTH secretion using murine corticotroph-derived AtT20 cells and compared its effects with those of rosiglitazone and pioglitazone. AtT20 cells were treated with either 1 nM~10 μM MEKT1, rosiglitazone, or pioglitazone for 24 hours. Thereafter, their effects on proopiomelanocortin gene (Pomc) mRNA expression were studied by qPCR and the Pomc promoter (−703/+58) activity was demonstrated by luciferase assay. Pomc mRNA expression and promoter activity were significantly inhibited by MEKT1 at 10 μM compared to rosiglitazone and pioglitazone. SiRNA-mediated PPAR-γ knockdown significantly abrogated MEKT1-mediated Pomc mRNA suppression. ACTH secretion from AtT20 cells was also significantly inhibited by MEKT1. Deletion/point mutant analyses of Pomc promoter indicated that the MEKT1-mediated suppression was mediated via NurRE, TpitRE, and NBRE at −404/−383, −316/−309, and −69/−63, respectively. Moreover, MEKT1 significantly suppressed Nur77, Nurr1, and Tpit mRNA expression. MEKT1 also was demonstrated to inhibit the protein-DNA interaction of Nur77/Nurr1-NurRE, Tpit-TpitRE, and Nur77-NBRE by ChIP assay. Taken together, it is suggested that MEKT1 could be a novel therapeutic medication for Cushing's disease.

Highlights

Peroxisome proliferator-activated receptor gamma (PPARγ) is a member of the nuclear receptor superfamily known as ligand-inducible transcription factors [1]
We examined the effects of a novel PPAR-γ agonist, MEKT1, on proopiomelanocortin gene (Pomc) expression/ACTH secretion using murine pituitary corticotroph tumor-derived AtT20 cells and compared them with rosiglitazone and pioglitazone
We first analyzed the effects of rosiglitazone, pioglitazone, and MEKT1 on mRNA expression of Pomc at various concentrations in AtT20 cells

Summary

Introduction

Peroxisome proliferator-activated receptor gamma (PPARγ) is a member of the nuclear receptor superfamily known as ligand-inducible transcription factors [1]. Ligand binding with PPAR-γ receptor acts as a switch leading to the transcription complexes mediating repression or activation of transcription on specific target genes [2]. PPAR-γ is expressed in normal human anterior pituitary as well as in adrenocorticotropic hormone- (ACTH-) secreting pituitary adenomas. PPAR-γ expression was significantly higher in pituitary adenomas than normal pituitary tissues, and its expression in ACTH-secreting adenomas was significantly higher than any other types of pituitary adenomas [10,11,12,13]. ACTH, the product of proopiomelanocortin gene (Pomc), is secreted from the corticotroph cells of the anterior pituitary. Pomc is exhibited in various tissues including pituitary (anterior and intermediate), hypothalamus, and skin [14]

Methods

Results

Conclusion