Abstract 4047: Loss of IFN-γ pathway gene expression in tumor cells as mechanism of immune escape of colorectal carcinoma
Authors: Britzen-Laurent Nathalie , Straube Julia , Waldner Maximilian , Becker Christoph , Croner Roland , Pilarsky Christian , Merkel Susanne , Stürzl Michael 
Published: August 2018

Abstract
In colorectal carcinoma (CRC), the infiltration of tumor tissue by cytotoxic and T-helper 1 (Th1) T cells has been associated with an improved clinical outcome. This antitumor immune response is characterized by an elevated expression of interferon (IFN)-γ and IFN-stimulated genes such as IRF-1, CXCL-9, CXCL-10, caspase-1 or guanylate-binding protein 1 (GBP-1). Using GBP-1 as a marker of cellular response to IFN-γ in human CRC specimens, we observed that tumor cells, but not stroma cells, frequently lose GBP-1 expression in the context of a Th-1-dominated immune response. Similarly, 6 out of 11 colorectal carcinoma cell lines failed to express GBP-1 or other IFN-stimulated genes after treatment with IFN-γ, and were resistant to IFN-γ-induced apoptosis. This indicated that the loss of responsiveness to IFN-γ might represent a mechanism of immune escape in CRC tumor cells. We then investigated whether defects in RNA and protein expression of IFN-γ pathway genes (IFNGR1, IFNGR2, JAK1, JAK2, STAT1) might account for the loss of responsiveness to the cytokine. The most frequent deregulation observed was the downregulation of IFNGR1 expression at the RNA and protein level in 4 out of 6 resistant cell lines, where treatment with 5-Aza-deoxycytidine, a DNA methylation inhibitor, could restore IFNGR1 expression. In the two remaining resistant cell lines, IFNGR1 was expressed but the protein (IFNγRα) was mis-glycosylated and failed to locate at the plasma membrane. In addition, STAT1 protein expression was downregulated in two resistant cell lines. Using a Crispr/Cas9 silencing approach, we showed that the downregulation of IFNGR1 expression is sufficient to inhibit IFN-γ signaling in CRC cell lines. Moreover, long-term treatment of a sensitive cell line with IFN-γ resulted in the downregulation of IFNGR1, but not STAT1 expression. In human CRC samples, mRNA expression of IFNGR1 was decreased compared to normal tissue. Furthermore, low tumor expression of IFNGR1, but not STAT1, correlated with a reduced cancer-related survival in patients with CRC. Finally, mice harboring a specific knockout of the IFN-γ receptor in intestinal epithelial cells developed more tumors than control mice in a carcinogen-induced colon tumorigenesis model, indicating that the absence of IFN-γ receptor expression in intestinal epithelial cells fosters tumor growth. Altogether, our data suggest that the loss of IFN-γ pathway gene expression is a common event in CRC and represents an intrinsic mechanism of immune escape.
Citation Format: Nathalie Britzen-Laurent, Julia Straube, Maximilian Waldner, Christoph Becker, Roland Croner, Christian Pilarsky, Susanne Merkel, Michael Stürzl. Loss of IFN-γ pathway gene expression in tumor cells as mechanism of immune escape of colorectal carcinoma [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 4047.