Genomic mapping of glucocorticoid receptor binding in myeloma

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SAT 1-25-Glucocorticoid Actions & HPA Axis
Basic
Saturday, June 15, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SAT-20
Nancy L Krett*1, Jun Qian1, Weimin Xiao2, Cristian Coarfa3, Preethi Gunaratne2 and Steven T. Rosen1
1Northwestern University, Chicago, IL, 2University of Houston, Houston, TX, 3Baylor College of Medicine, Houston, TX
Glucocorticoids (GC) are a cornerstone of treatment for myeloma, a hematologic malignancy of B cells.  However, patients develop resistance to this therapy in part due to loss of glucocorticoid receptor (GR) expression.  Despite the long term clinical use of GCs, little is known about mechanisms which induce cell death or post-receptor mechanisms to obviate resistance to GCs. Our overall goal is to define the direct targets of GC actions which induce cell death and identify druggable targets of GC signaling pathways that can be used to overcome resistance to GC in the absence of a functional GR. The induction of apoptosis by GCs primarily involves trans-repression of growth inducing genes but may also involve trans-activation.  Mechanisms of trans-activation involve binding to glucocorticoid response elements (GRE) as dimers leading to transcription.  Mechanisms for GR-mediated trans-repression include GR tethering to and inhibiting growth inducing transcription factors (TFs) through protein-protein interactions; by interactions with growth inducing TFs at composite GREs or by direct DNA binding to newly described negative GREs (nGRE).  The TFs which interact with GR have not been identified in myeloma and are likely cell specific.  In addition, global GR-chromatin interactions have not been investigated in myeloma. Chromatin immunoprecipitation combined with massively parallel sequencing (ChIP-seq) of GR in conjunction with bioinformatics platforms to integrate ChIP-seq data with GR-induced changes in gene expression have been used to globally elucidate the primary targets of GC actions in myeloma cell lines.  GC sensitive MM.1S myeloma cell line was treated with 1 micromolar GC for 2 hours prior to ChIP of GR.  As negative controls we performed GR ChIP on MM.1S cells with no drug treatment as well as GR negative MM.1RL cells with and without GC treatment.  In the massively parallel sequencing, we observed 8,689 GR peaks in the GC-treated MM.1S cells compared to 177 peaks in the untreated MM.1S cells and less than 26 peaks in either of the MM.1RL treatments indicating specific binding with GC treatment.  We identified GR binding sites in 44 of 503 genes repressed by GCs including genes for growth inducing kinases, cytokines and inhibitors of apoptosis.  We identified GR binding sites in 118 of 310 genes up-regulated by GC treatment including GILZ, inducers of apoptosis and tumor suppressors.  These data will provide the basis of downstream target identification for drug development.

Disclosure: STR: Speaker, Alios Therapeutics, Inc., Speaker Bureau Member, Celgene, , Hunt Suedhoff & Kalamaros, LLP, , Flubrite & Jawarski LLP, Speaker, The Medal Group Corporation, Scientific Board Member, Cephalon, Inc., Speaker, Studio ER Congresi - The Triumph Group, Advisory Group Member, Millennium Pharmaceutical, Inc, Consultant, Prostraken, Inc., Advisory Group Member, Seattle Genetics, , The CM Group. Nothing to Disclose: NLK, JQ, WX, CC, PG

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: International Myeloma Foundation Brian D. Novis Research Grant awarded to NLK