Selective glucocorticoid receptor translational isoforms reveal glucocorticoid-induced apoptotic transcriptomes

I Wu,R P Schleimer,N Jafari,G Feng,S Lin,Y Cao,N Z Lu,I K Bender,J A Cidlowski,S C Shin

doi:10.1038/cddis.2012.193

Abstract

Induction of T-cell apoptosis contributes to the anti-inflammatory and antineoplastic benefits of glucocorticoids. The glucocorticoid receptor (GR) translational isoforms have distinct proapoptotic activities in osteosarcoma cells. Here we determined whether GR isoforms selectively induce apoptosis in Jurkat T lymphoblastic leukemia cells. Jurkat cells stably expressing individual GR isoforms were generated and treated with vehicle or dexamethasone (DEX). DEX induced apoptosis in cells expressing the GR-A, -B, or -C, but not the GR-D, isoform. cDNA microarray analyses of cells sensitive (GR-C3) and insensitive (GR-D3) to DEX revealed glucocorticoid-induced proapoptotic transcriptomes. Genes that were regulated by the proapoptotic GR-C3, but not by the GR-D3, isoform likely contributed to glucocorticoid-induced apoptosis. The identified genes include those that are directly involved in apoptosis and those that facilitate cell killing. Chromatin immunoprecipitation assays demonstrated that distinct chromatin modification abilities may underlie the distinct functions of GR isoforms. Interestingly, all GR isoforms, including the GR-D3 isoform, suppressed mitogen-stimulated cytokines. Furthermore, the GR-C isoforms were selectively upregulated in mitogen-activated primary T cells and DEX treatment induced GR-C target genes in activated T cells. Cell-specific expressions and functions of GR isoforms may help to explain the tissue- and individual-selective actions of glucocorticoids and may provide a basis for developing improved glucocorticoids.

Highlights

Despite the wide range of gene targets of the glucocorticoid receptor (GR), only one single GR gene has been discovered to date
The GR-C3 isoform has enhanced activity as demonstrated by the earlier onset and higher percentage of cell death in GR-C3 isoformexpressing cells compared with cells expressing other GR isoforms, whereas GR-D3 isoform-expressing cells are insensitive to glucocorticoid killing
Using chromatin immunoprecipitation (ChIP) analyses of the MYC gene regulatory region, we found that all GR isoforms bound to the inverse repeat negative glucocorticoid response elements (IR-GRE)[17] in the presence of DEX (Figures 2d and e)

Summary

Introduction

Despite the wide range of gene targets of the GR, only one single GR gene has been discovered to date This single GR gene generates several GR isoforms, including GRa and b via alternative splicing, with GRa being expressed at relatively higher levels in the majority of tissues examined.[10] We have reported that each GR transcript generates additional isoforms via alternative translation initiation. Activated primary T cells selectively increased the expression of the GR-C isoforms and certain GR-C target genes These studies improve our understanding of the role of GR isoforms in apoptosis and in regulation of Jurkat and primary T cells and may provide a basis for the development of new anti-inflammatory and antineoplastic glucocorticoids

Methods

Results

Conclusion