Glucocorticoid Receptor and Sequential P53 Activation by Dexamethasone Mediates Apoptosis and Cell Cycle Arrest of Osteoblastic MC3T3-E1 Cells

Hui Li,Wenwei Qian,Huihua Li,Xisheng Weng,Zhihong Wu,Yanyan Bian,Bin Feng,Qianyu Zhuang,Carl G Maki

doi:10.1371/journal.pone.0037030

Abstract

Glucocorticoids play a pivotal role in the proliferation of osteoblasts, but the underlying mechanism has not been successfully elucidated. In this report, we have investigated the molecular mechanism which elucidates the inhibitory effects of dexamethasone on murine osteoblastic MC3T3-E1 cells. It was found that the inhibitory effects were largely attributed to apoptosis and G1 phase arrest. Both the cell cycle arrest and apoptosis were dependent on glucocorticoid receptor (GR), as they were abolished by GR blocker RU486 pre-treatment and GR interference. G1 phase arrest and apoptosis were accompanied with a p53-dependent up-regulation of p21 and pro-apoptotic genes NOXA and PUMA. We also proved that dexamethasone can’t induce apoptosis and cell cycle arrest when p53 was inhibited by p53 RNA interference. These data demonstrate that proliferation of MC3T3-E1 cell was significantly and directly inhibited by dexamethasone treatment via aberrant GR activation and subsequently P53 activation.

Highlights

Glucocorticoids (GCs) are the most frequently used antiinammatory and immunosuppressive drugs in clinic to treat a variety of diseases including inflammation, cancer, and autoimmune disorders [1]
To determine whether the inhibitory effect can be attributed to apoptosis and cell cycle arrest, and whether the effect results from glucocorticoid receptor (GR) activation, we treated MC3T3-E1 cells with PBS, 1 mmol/L dexamethasone (DEX group), RU486 (RU486 group), and 1 mmol/L dexamethasone plus 10 mmol/L RU486 (DEX+RU group) respectively
By adding RU486 2 hours prior to dexamethasone treatment, we blocked the GR and the apoptosis effect associated with GR activation

Summary

Introduction

Glucocorticoids (GCs) are the most frequently used antiinammatory and immunosuppressive drugs in clinic to treat a variety of diseases including inflammation, cancer, and autoimmune disorders [1]. It has been reported that GCs could induce apoptosis of osteoblasts and inhibit its proliferation, leading to osteoporosis and osteonecrosis [4]. Previous studies have reported that GCs treatment induce osteoblast apoptosis by enhancing the expression of BH3-only protein Bim [6], down-regulation of TIMP-1 [7], and activation of glycogen synthase kinase 3 beta (GSK-3b) [8]. We reviewed previous studies in terms of the relationship between GR activation and apoptosis, and these studies has reported that p53 [9], granzyme A [10,11] or Glucocorticoid-induced leucine zipper (GILZ) [12,13] may be the downstream molecules of GR activation

Methods

Results

Conclusion