7862 The Paradoxical Role Of ERFFI1 In Breast Cancer Progression Is Supported By Its Dynamic Protein Interactome

Abstract

Abstract Disclosure: A. Ocampo: None. P.D. Bagamasbad: None. In breast cancer (BCa), glucocorticoid (GC) therapy is used in anti-emetic and palliative care. However, the effects of GC therapy in BCa are conflicting as it is beneficial for hormone-responsive luminal subtypes while it promotes tumor progression in more aggressive triple-negative BCa (TNBCs). A factor implicated in this paradoxical shift is the feedback inhibitor of epidermal growth factor receptor (EGFR) signaling, ERBB receptor feedback inhibitor 1 (ERRFI1). In BCa cell lines, ERRFI1 expression is directly regulated by GC receptor (GR). More interestingly, ERRFI1 was found to restrict the GC-enhanced proliferation in normal breast epithelia but enhances the GC-mediated pro-tumorigenic effects in highly aggressive TNBC. To identify the mechanism behind the shift in ERFFI1 function through BCa progression, ERRFI1 protein interactions in the luminal, HER2, and TNBC subtypes were analyzed by identifying differentially expressed proteins from each subtype using available proteome and interactome datasets from Integrated Interactions Database and followed by network and clustering analyses through STRING. The ERRFI1 interactome varied across the subtypes, and gene ontology analysis of the protein networks revealed progressive tumorigenic effects from the least aggressive luminal subtype to the most aggressive TNBC. The luminal BCa-ERRFI1 interactome showed metastatic potential that is countered by negative regulation of receptor tyrosine kinase (RTK) signaling. The HER2-ERRFI1 interactome highlighted the amplification of RTK signaling and its possible modulation through SRC while the TNBC-ERRFI1 interactome presents pro-oncogenic proteins implicated in drug resistance, angiogenesis, and EMT. Interestingly, the interactome also revealed a link between EGFR signaling and GR signaling possibly through ERRFI1, EGFR, and SFN. To determine the function of ERFFI1 in EGFR signaling in BCa, we generated stable ERRFI1 knockdown in different breast epithelial cell models through lentiviral transduction. Cells were then treated with EGF followed by gene expression analysis of known EGF-upregulated genes such as MYC, GSK3B, MCL1, and MMP9. We found that ERRFI1 knockdown enhanced the EGF-dependent induction of MYC and MMP9 in normal MCF10A cells and this effect was not observed in the TNBC MDA-MB-468 line, suggesting the loss of ERRFI1-mediated inhibition of EGFR signaling with BCa tumorigenic potential. Taken together, our findings suggest that the progressive loss of anti-tumorigenic function of ERRFI1 may be explained by its changing interactome in BCa molecular subtypes. Presentation: 6/3/2024