Loss of Neuroligin 4X Induces An Intrinsic Innate Immune Response in TNBC

Abstract

Background Immune checkpoint blockade therapies, which act on T cell inhibitory receptors, including CTLA-4 and PD-1, induce durable responses across diverse cancers. However, most patients do not respond to these therapies, and initially responsive cancers may relapse. Identifying molecular mechanisms that influence therapeutic responses and resistance is critical to realize the full therapeutic potential of immune checkpoint inhibitors. The presence of immune infiltrates in the tumor microenvironment is associated with positive outcomes in breast cancer, specifically in triple-negative breast cancer (TNBC). The underlying mechanisms driving this response are unclear. We have previously identified Neuroligin 4X (NLGN4X) as a protein expressed in TNBC.Methods Bioinformatic analysis was used for pathway analysis of TCGA TNBC patient dataset. Immunohistochemistry was performed on breast cancer tissue microarray for NLGN4X protein expression. RNA-seq was performed on MDA-MB-231 breast cancer cells for differential gene expression upon gene knockdown. Cytokine array, western blot, cell adhesion array and Nanostring was performed to determine the role of NLGN4X in TNBC.Results In this study, we report that NLGN4X expression is lost in breast cancer with lymph node metastasis. Its expression negatively correlates with immune markers in vitro, The Cancer Genome Atlas (TCGA) TNBC patient dataset, and metastatic breast cancer tissues. RNA-seq analysis of the MDA-MB-231 breast cancer cell line, silenced for NLGN4X by siRNA showed more than 500 differentially regulated genes. GSEA analysis of these genes revealed upregulation of interferon signaling pathway, cytokine signaling, and downregulation of cholesterol metabolism and lipid metabolism pathways. NLGN4X knockdown induced loss of cell adhesion, epithelial to mesenchymal transition (EMT), and MAVS-IRF7 signaling in breast cancer cells. Interestingly, analysis of the TCGA dataset of 104 TNBC patients also showed interferon signaling (IFN) as one of the significant pathways downregulated in TNBC patients expressing NLGN4X.Conclusion Loss of NLGN4X leads to innate immune activation in breast cancer and coincides with an aggressive phenotype of cancer. This study identifies the role of NLGN4X in regulating interferon signaling and immune microenvironment in TNBC.