Abstract 4504: Androgen receptor aggregation is a key regulator of endoplasmic reticulum stress and cell survival in ETS-related gene driven prostate carcinogenesis
Authors: Sreenath Taduru L. , Mikhalkevich Natallia , Sharad Shashwat , Gupta Rishita , Diaro Oluwatosin , Babcock Kevin , Xavier Charles , Mohamed Ahmed , Jamal Muhammad , Tan Shyh-Han , Dobi Albert , Petrovics Gyorgy , Sesterhenn Isabell A. , McLeod David G. , Rosner Inger L. , Srivastava Shiv 
Published: July 2017

Introduction and Objectives: Deregulated androgen receptor (AR) signaling due to either mutations or altered expression of the AR and its cofactors (activators or suppressors) has been identified as critical in prostate cancer development and progression. AR regulated oncogenic activation of Ets Related Gene (ERG) represents one of the most common and validated prostate cancer driver gene. In our recent studies using prostate specific ERG transgenic mouse prostate glands, we observed novel morphological phenotypes of endoplasmic reticulum (ER) stress. Since AR was the critical regulator of ERG expression through TMPRSS2 promoter in human prostate cancer, the present study was aimed towards understanding the post-translational interactions between ERG and AR in ER stress and subsequent cell survival mechanisms in mouse and cell culture models. Understanding such mechanistic insights will potentially have major therapeutic implications.

Methods: Histological phenotype in the mouse prostate glands were examined by light and electron microscopy. Cell culture models of LNCaP, HEK293 and COS7 cells were utilized to examine the AR aggregations, Co-IP and Proximal Ligation Assay in the presence and absence of ERG. Various domain deletions of AR were utilized to identify specific AR domain interactions with ERG and its contribution in AR aggregation. Luminal cell surface markers on the isolated mouse prostate glands and spontaneously immortalized mouse prostate epithelial cells from ERG transgenic mouse (MoE1) were analyzed by FACS analysis.

Results: Co-expression of ERG and AR in LNCaP and COS-7 cells showed significant aggregation of AR in filter assays. Co-IP experiments and PLA assays in VCaP, LNCaP and HEK 293 cell revealed that ERG physically interacts with AR. Epithelial cells of ERG-Tg mouse prostates showed ~70% increase in CD49f (low) and Sca-1 (med) population with increased sphere formation capability and resistance to radiation induced cell death. Both epithelial cells grown into spheres and established MoE1 cells displayed increased CD49f (low) and significant increase in the EpCAM negative population.

Conclusions: Overall, our experiments demonstrate the mechanistic link that the physical interactions between ERG and AR initiate the ER stress in prostate epithelium through AR misfolding/aggregation. Our observation of ERG induced AR aggregation is one of the initial events that lead to ER stress to cell survival indicate a critical function for ERG in the etiology of prostate cancer initiation and progression.

Funding: This research in part was supported by the National Cancer Institute R01CA162383 (S. S.) and HU0001-10-2-0002 funds.

Citation Format: Taduru L. Sreenath, Natallia Mikhalkevich, Shashwat Sharad, Rishita Gupta, Oluwatosin Diaro, Kevin Babcock, Charles Xavier, Ahmed Mohamed, Muhammad Jamal, Shyh-Han Tan, Albert Dobi, Gyorgy Petrovics, Isabell A. Sesterhenn, David G. McLeod, Inger L. Rosner, Shiv Srivastava. Androgen receptor aggregation is a key regulator of endoplasmic reticulum stress and cell survival in ETS-related gene driven prostate carcinogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4504. doi:10.1158/1538-7445.AM2017-4504