Abstract 5290: Loss-of-Irf5 in mammary epithelial cells drives spontaneous mammary tumorigenesis by regulating EMT

Abstract

Abstract Interferon regulatory factor 5 (IRF5) is a member of the IRF family of transcription factors. In human breast cancer (BC), IRF5 expression is lost in ~ 60% of ductal carcinoma in situs (DCISs) and ~90% of invasive ductal carcinomas (IDCs). BCs expressing the lower quartile of IRF5 transcript expression were found to significantly correlate with poor prognosis for recurrence-free survival. To examine how loss-of-Irf5 promotes breast tumor initiation and progression, we generated Irf5 knockout (Irf5-/-) mice on a BALB/C background that are susceptible to spontaneous mammary tumorigenesis. At 1 year-old, female nulliparous Irf5-/- mice (n=21) had a >3-fold increase in the incidence of spontaneous mammary tumorigenesis as compared to Irf5+/+ littermate mice (WT, n=25). As early as 6 months old, we detected dramatic differences in the presence of atypical ductal hyperplasia, and at 9 months old, ~50% of Irf5-/- mice had ADH while only 17% of WT littermates had detectable ADH (n=12/group). Immunofluorescence (IF) staining showed expansion of the luminal epithelial compartment in Irf5-/- mice with ADH and/or mammary tumors. Further, proliferation of Irf5-/- luminal epithelial cells was significantly increased over WT mice (15 week-old, n=3/group, 2-way ANOVA, Genotype factor F (1, 4) = 0.04493), supporting a loss of cell growth control in this compartment. To identify the molecular mechanism(s) driving enhanced mammary tumorigenesis, we performed RNA-seq on FACS-sorted luminal and basal epithelial cells from 9 month-old Irf5-/- and Irf5+/+ littermate mice (n=3 mice/group). Gene Set Enrichment Analysis (GSEA) identified signatures that were either positively or negatively regulated in Irf5-/- luminal and basal epithelial cells as compared to WT littermates. We found that epithelial to mesenchymal transition (EMT)-transcription factors were significantly enriched in both Irf5-/- luminal (p=0.046) and basal (p=0.004) epithelial cells. A diverse array of signaling pathways and molecules that participate in EMT induction were also found enriched in Irf5-/- cells, including Wnt/β-catenin (Luminal p=0.021; basal p=0.294), Sonic hedgehog (Shh) (luminal p=0.849), Gli1 (Irf5-/- vs. WT, luminal 3.56 vs. 1.35; basal 10.04 vs. 8.88) and PI3K signaling (luminal p=0.941; basal p=0.970). Findings suggest that loss-of-Irf5 promotes EMT through one or more of these pathways, thus contributing to the striking increase in spontaneous mammary tumorigenesis that occurs in Irf5-/- mice. Results from this study are expected to identify mechanisms and pathways that may be therapeutically targeted in patients with IRF5-negative BC. Note: This abstract was not presented at the meeting. Citation Format: Su Song, Dan Li, Kyle Kampta, Betsy Barnes. Loss-of-Irf5 in mammary epithelial cells drives spontaneous mammary tumorigenesis by regulating EMT [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5290.