miR-150 orchestrates immune activation and lymphocyte trafficking in breast cancer

Background: Tumor-infiltrating lymphocytes (TILs) are known to relate with response to treatments followed by better survival; however, majority of breast cancer (BC) hardly have any TILs. Thus, discovery of targetable novel mechanism of TIL infiltration is expected to have a major clinical implication. MiR-150 has been reported to promote cell proliferation and migration, but its role in TIL infiltration is not known. The aim of this study is to investigate the role and clinical relevance of tumor miR-150 expression and attraction of TILs in BC patients. Methods: In silico analyses was conducted on total of 1,961 breast cancer patients from large independent cohorts, The Cancer Genome Atlas (TCGA) and the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC). In Vitro experiments using MDA-MB231 and BT-549 BC cell lines and Jurkart lymphocyte cell line, were repeated three times to ensure rigor and reproducibility. Results: As expected, miR-150 expression correlated with Nottingham grade and was higher in triple negative subtype in both cohorts (all p<0.001). On the other hand, miR-150 expression not only enriched MTORC1 and KRAS signaling, but also multiple immune-related Hallmark gene sets including IFN-ϒ, TNF-alpha, IL-2, IL-6, IFN-alpha, allograft rejection, and inflammatory response by gene set variant analysis (all Spearman's coefficient r>0.50 and p<0.01). High miR-150 expression significantly correlated with lymphocyte infiltration and TCR-Shannon in TCGA cohort. High miR-150 expression was associated with high infiltration of CD8+, CD4+ memory T cells and dendritic cells, and was strongly correlated with cytolytic activity consistently in both cohorts (r=0.824 and 0.786, both p<0.01), all suggesting strong relationship with immune cell infiltration and immune response. In agreement, high MiR-150 expression was associated with improved overall survival (p<0.001, p=0.030), particularly in ER-positive/HER2-negative patients. Surprisingly, mimic overexpression of miR-150 did not promote cell proliferation, migration nor invasion neither in MDA-MB231 or BT-549 BC cell lines. However, mimic overexpression of miR-150 in either MB231 or BT-549 cells significantly increased the migration intensity of Jurkart cells demonstrated by Transwell invasion assay. Further, mimic overexpression of miR-150 in MDA-MB231 cells enriched cell proliferation-related gene sets; E2F Targets, G2M checkpoint, as well as multiple immune-related gene sets including IFN-ϒ, TNF-alpha, IL-2, IL-6, allograft rejection and inflammatory response. Conclusions: MiR-150 expression in patients' breast cancer evoke immune response, attracts lymphocytes to tumor microenvironment and is associated with overall survival.