FAM114A1 Promotes Immune Evasion of Triple-negative Breast Cancer by Simultaneously Activating PI3K/AKT Signaling and Disrupting E2F4-condensate Formation

Immune checkpoint blockade (ICB) therapy, which revolutionized cancer treatment, has been approved for triple-negative breast cancer (TNBC) treatment. Unfortunately, the majority of TNBC patients are either not eligible for the treatment or exhibit resistance. Understanding the underlying mechanisms and enhancing treatment efficacy are urgently needed. Here, utilizing CRISPR activation screening, we identified FAM114A1 as a key mediator of immune evasion and ICB therapy resistance in TNBC patients. Mechanistically, FAM114A1 binds to p85a to activate PI3K/AKT pathway, and simultaneously, prevents E2F4-condensate formation to promote E2F4-driven MTDH expression. Elevation of these FAM114A1-mediated pathways inhibit tumor antigen presentation and consequently suppress anti-tumor immunity in TNBC. Moreover, FAM114A1-targeting boosts anti-PD-1 treatment in mouse models and the FAM114A1 signature shows strong predictive performance in recognizing TNBC patients who may benefit from ICB therapy. Collectively, our study provides new insights into the mechanisms underlying TNBC immune evasion and a potential avenue to improve ICB treatment effectiveness. Overall design: To study the role FAM114A1 in tumorigenesis, Py8119 murine breast cancer cells, either transduced with control shRNA (shCOO2) or engineered with Fam114a1 knocdown (Fam114a1 KD), were orthotopically injected into the mammary fat pads of 4–6-week-old female C57BL/6 OT-I mice. After tumor formation, mice were sacrificed at the defined endpoint, and tumor tissues were collected and processed into formalin-fixed, paraffin-embedded (FFPE) blocks for downstream analyses.