CD74 regulates the tumor immunosuppressive microenvironment in triple-negative brest cancer
CD74 is a cell-surface receptor for the cytokine macrophage migration inhibitory factor (MIF). MIF binding to CD74 induces a signaling cascade resulting in the release of its cytosolic intracellular domain (CD74-ICD), which regulates transcription in naive B and chronic lymphocytic leukemia (CLL) cells. In the current study, we investigated the role of CD74 in the regulation of the immunosuppressive tumor microenvironment (TME) in triple-negative breast cancer (TNBC). TNBC is the most aggressive breast cancer subtype, in which there is a massive infiltration of immune cells to the tumor microenvironment, making this tumor a good candidate for immunotherapy. The tumor and immune cells in TNBC express high levels of CD74, however, the function of this receptor in this environment was not fully characterized. Regulatory B cells (Bregs) and tolerogenic dendritic cells )tol-DCs( were previously shown to attenuate the antitumor immune response in TNBC. Here, we demonstrate that CD74 enhances tumor growth by inducing the expansion of tumor-infiltrating tol-DCs and Bregs. Utilizing CD74-KO mice, conditionally CD74 -/- Cre-flox mice lacking CD74 in CD23+ mature B cells and mice lacking CD74 in the CD11c+ population and a CD74 inhibitor (DRQ), revealed that MIF secreted from the tumor cells activate CD74 expressed on DCs. This activation induces the binding of CD74-ICD to the SP1 promotor, resulting in the upregulation of SP1 expression. SP1 binds the IL-1ß promotor, leading to the downregulation of its transcription. The reduced levels of IL-1ß lead to decreased anti-tumor activity by allowing expansion of the tol-DC, which induce the expansion of the Breg population, suggesting the cross-talk between these two populations. Taken together, these results suggest that CD74+ CD11c+ DCs are the dominant cell type involved in the regulation of the TNBC progression. These findings indicate that CD74 might serve as a novel therapeutic target in triple-negative breast cancer. Overall design: we wanted to investigate the role of CD74 in DCs. To this purpose WT mice were injected with E0771 cancer cell line and divided in two group. One  treated with PBS and one treated with DRQ, a CD74 inhibitor, starting from day 10. 3 weeks post-injection, mice were sacrificed and DCs were sorted from the tumor microenvironment of the PBS/DRQ -treated mice and RNA-seq was performed. ?