Abstract 3457: Chemotherapy enables Brk/PTK6-dependent survival of triple-negative breast cancer cells via induction of an AhR/GR/HIF signaling axis
Authors: Anderson Tarah M. Regan , Ma Shihong , Kerkvliet Carlos J. Perez , Helle Taylor M. , Krutilina Raisa , Raj Ganesh V. , Cidlowski John A. , Schwertfeger Kathryn L. , Seagroves Tiffany N. , Lange Carol A. 
Published: August 2018

The metastatic cascade is a complex process that requires cancer cells to survive despite exposure to conditions of high physiologic stress. We previously showed that breast tumor kinase (Brk; also known as PTK6), a mediator of aggressive breast cancer phenotypes, is induced in breast cancer cells in response to a convergence of cellular and hormonal stress signals mediated by cross talk between hypoxia-inducible factors (HIFs) and glucocorticoid receptors (GR). Specifically, p38-MAPK dependent phosphorylation of GR-Ser134 (p-GR) and p-GR/HIF transcriptional complexes mediated heightened Brk gene expression in response to multiple inputs to stress pathway activation. Following studies in mice to demonstrate that Brk is a GR target gene in the mammary gland, immunohistochemistry (IHC) was performed on human primary breast tumor tissues using total and p-GR antibodies. To model stress-induced p-GR action relevant to tumor progression, molecular markers of stress signaling were measured in triple negative breast cancer (TNBC) cell lines treated with chemotherapy (Taxol and 5-flourouricil) and following growth in suspension (ultra-low attachment (ULA)). Co-immunoprecipitation and ChIP assays were used to demonstrate association of p-GR with novel co-regulatory factors in transcription complexes at the Brk promoter. Cell viability and migration assays were performed following Brk knock-out using CRISPR/Cas9 gene editing. Systemic Dex administration in mice confirmed that Brk is a GR target gene in vivo. In human breast tumor samples, phospho-GR was significantly associated with TNBC relative to luminal cancers. Chemotherapy and ULA induced activation of p38 MAPK, phosphorylation of GR, and upregulation of HIFs as well as the Aryl hydrocarbon receptor (AhR), a known mediator of cancer cell survival under cellular stress. Moreover, AhR and GR co-purified constitutively, and following chemotherapy or ULA culture, these factors assembled at the Brk promoter in a HIF-dependent manner. Brk induction was critical for TNBC cell survival during Taxol treatment or during ULA culture and for cancer cell migration, acquired biological phenotypes that enable cancer cells to successfully complete the metastatic cascade.These studies define AhR as a novel p-GR binding partner and show that increased p-GR/AhR and Brk expression drive a migratory phenotype relevant to TNBC progression. Strategies to target p-GR signaling may ameliorate stress-induced acquisition of aggressive cancer phenotypes required for metastatic cancer spread that are linked to high breast cancer patient mortality.

Citation Format: Tarah M. Regan Anderson, Shihong Ma, Carlos J. Perez Kerkvliet, Taylor M. Helle, Raisa Krutilina, Ganesh V. Raj, John A. Cidlowski, Kathryn L. Schwertfeger, Tiffany N. Seagroves, Carol A. Lange. Chemotherapy enables Brk/PTK6-dependent survival of triple-negative breast cancer cells via induction of an AhR/GR/HIF signaling axis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3457.