IFITM1 Influences Natural Killer Cell-Mediated Cytotoxicity by Modulation of HLA class I Expression in Triple-Negative Breast Cancer Cells

Purpose Interferon-induced transmembrane protein 1 (IFITM1) is associated with a poor prognosis in triple-negative breast cancer (TNBC); however, the mechanisms by which IFITM1 contributes to oncogenesis in TNBC are unclear. Materials and Methods We established two stable cell lines: IFITM1-overexpressing cell line (MB-231-IFITM1-OE) and IFITM1 knockdown cell line (BT-20-IFITM1-KD). The transcriptional activity of β-catenin and the cytotoxic activity of natural killer (NK) cells were evaluated using the luciferase assay and the lactate dehydrogenase cytotoxicity assay. The expression of IFITM1, β-catenin, and HLA class I was assessed by immunohistochemistry in patients with TNBC. Results Knockdown of IFITM1 in BT-20 cells reduced cell proliferation and ectopically expressed IFITM1 in MB-231 cells increased cell proliferation. RNA sequencing analysis revealed that IFITM1 expression positively correlated with the Wnt/β-catenin signaling pathway and NK cell-mediated cytotoxicity. MB-231-IFITM1-OE cells showed increased β-catenin transcriptional activity and NK cell cytotoxic activity compared with controls, while transient knockdown of IFITM1 in MB-231-IFITM1-OE cells led to a decrease in β-catenin transcriptional activity and NK cell cytotoxic activity. MB-231-IFITM1-OE cells exhibited decreased HLA class I expression, which may have contributed to their increased susceptibility to NK cell-mediated lysis. β-catenin or JAK inhibitor reduced NK cell-mediated cytotoxicity via upregulation of HLA class I. Patients with IFITM1 overexpression showed a trend toward increased β-catenin positivity and HLA class I negativity. Conclusion IFITM1 overexpression was associated with Wnt/β-catenin signaling and NK cell-mediated cytotoxicity via downregulation of HLA class I in TNBC cells, suggesting that IFITM1 might have immunoregulatory effects on the tumor microenvironment.