Endogenous Transactivation of PPARγ1 in breast Cancer

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SUN 338-365-Metabolic & Stress Receptors in Energy Homeostasis
Sunday, June 16, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SUN-359
Natalie Wallis1, Linah Al-Alem2, R Chase Southard3 and Michael Kilgore*4
1University of Kentucky Coll of Medicine, Lexington, KY, 2Univeristy of Kentucky, Lexington, KY, 3Univ of Kentucky, Lexington, KY, 4Univ of Kentucky Coll of Med, Lexington, KY
A growing body of evidence demonstrates that the peroxisome proliferator-activated receptor gamma 1 (PPARγ1) plays a critical role in breast cancer progression yet very little is known regarding the mechanisms of its actions.  We have shown that PPARγ1 is highly overexpressed in human breast cancer, including triple negative breast cancer, a process driven by the recruitment of a tumor specific promoter.  While synthetic ligands have been widely reported to be antiproliferative in breast cancer cells, it is unclear whether these actions are mediated through PPARγ1.  By contrast, genetic models clearly demonstrate that a constitutively activated PPARγ1 drives promotion, increase metastasis and greatly reduce survival.  This supports our observations that intrinsic activation of PPARγ1 accompanies the increase in expression seen in malignant transformation.  Both expression and endogenous transactivation are necessary for the survival as the knockdown of PPARγ1 is lethal in breast cancer cells.  While these studies clearly demonstrate that intrinsic transactivation is critical to breast cancer progression the mechanism(s) controlling its activity remain poorly understood.  Neither the identity of the endogenous ligand(s) nor the contributions that post-translational modifications (PTMs) play in tumor progression are known.  To begin to define the mechanisms that control PPARγ1 activity during tumor progression we have constructed both HA- and FLAG-tagged expression vectors of wild type PPARg1 and proteomic approaches are underway to compare the PTMs seen between normal mammary epithelial cells (HMEC), non-transformed cell lines (MCF10A) and metastatic breast cancer (MDA-MB-231) cells.  Additionally, site directed mutations to putative phosphorylation (S84A) and sumoylation sites (K79R and K367R) have also been constructed.  The ability of these to control transcription demonstrates an interdependence of the PTM and the response to the exogenous ligand pioglitazone.  To explore the role of intrinsic activation by endogenous ligands we have also constructed a mutation in the ligand-binding domain (Q286P) that prevents ligand activation of transcription.  The fact that Q286P does not act as dominant negative suggest that an endogenous ligand may not be present although additional studies are underway to verify this observation.  Together, these studies could explain the “Janus Faced” actions of PPARg1 in cancer progression and reveal novel therapeutic strategies for treatment.

Nothing to Disclose: NW, LA, RCS, MK

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

Sources of Research Support: NIH Grants CA95609, AG029268 and  RR15592 to MK.