Abstract 90: STING colocalizes with gamma-H2AX upon treatment of breast cancer cells with genotoxics: A new role in DNA repair
Authors: Cheredame Laura , Gaston Julie , Yvonnet Vanessa , Deas Olivier , Poupon Marie-Françe , Judde Jean-Gabriel , Goffin Vincent , Cairo Stefano 
Published: July 2017

Abstract
One of the current tumor immunotherapy strategies involves the use of STING agonist, a well-known inducer of interferon (IFN) signaling in the immune system, to promote tumor-rejection. However, recent evidence also indicates that constitutive activation of IFN signaling in the tumor may lead to a bad outcome. For instance, increased expression of IFN- stimulated genes (ISGs) at time of surgery was associated with early breast cancer recurrence, and an IFN-related DNA damage resistance signature (IRDS) was identified as a predictive marker of recurrence after radiotherapy. Thus, IFNs secreted into the tumor microenvironment may have complex opposite effects on tumor behavior and response to treatment.
Using patient-derived xenograft (PDX) models, we previously showed that the IFN/STAT1 pathway was activated within breast cancer cells in response to chemotherapy and that this pathway may be involved in treatment resistance and recurrence. The aim of this study was to elucidate the mechanisms by which IFN-signaling is triggered in breast cancer cells following chemotherapy and how its activation leads to tumor survival and recurrence. To this aim, the breast cancer cell line MCF7 was treated in vitro with mafosfamide and the activity of different IFN pathway effectors was monitored using western blot, immunofluorescence and cell fractionation techniques.
We found that in breast cancer cells, similarly to what is observed in immune cells, type I IFN expression is triggered in a STING-dependent manner. STING silencing abrogated chemotherapy-induced type I IFN production and signaling, while potentiating genotoxic treatment efficacy by promoting cell death and delaying cell colony regrowth. Surprisingly, while STING is described as an endoplasmic reticulum resident protein that relocalizes to perinuclear vesicles upon activation in immune cells, we showed that STING is constitutively present in the nucleus of breast cancer cells and, under activation, forms nuclear clusters that co-localize with gH2AX at DNA breaks.
This study provides the first demonstration of STING activation in breast cancer cells and describes a potential new role for the nuclear form of STING in DNA damage response. Our data suggest that genotoxic stress-induced STING activation is a cell-intrinsic mechanism of breast cancer cell survival and regrowth. Whether STING pro-survival role is IFN-dependent (through the activation of given ISGs), IFN-independent (through its involvement in the DNA damage response) or both is currently under investigation.
Citation Format: Laura Cheredame, Julie Gaston, Vanessa Yvonnet, Olivier Deas, Marie-Françe Poupon, Jean-Gabriel Judde, Vincent Goffin, Stefano Cairo. STING colocalizes with gamma-H2AX upon treatment of breast cancer cells with genotoxics: A new role in DNA repair [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 90. doi:10.1158/1538-7445.AM2017-90