ID4-dependent reprogramming of tumor associated macrophages in triple negative breast cancer

Breast cancer is one of the most common cancer affecting especially women worldwide and it shows a particularly aggressive behavior in the triple negative (TNBC) and basal-like breast cancer (BLBC) subtypes that are characterized by poor prognosis and by the lack of targeted therapies. Moreover, it is well established that the presence of a massive leukocyte infiltrate, is involved in the promotion of tumor progression, contributing in particular to the angiogenic switch that occurs in the early phases of tumor progression. Among the variety of cells infiltrating breast tumors, macrophages have been extensively shown to tightly control the angiogenic onset and progression to malignancy. Here, we investigated whether ID4 protein, previously reported to enhance the angiogenic potential of breast cancer cells, exerts its function also modulating the activity of tumor-associated macrophages. We first assessed the significant association between the expression of ID4 and the macrophages marker CD68 in series of triple negative breast tumors. Of note, high ID4 mRNA expression in presence of a high macrophage infiltrate (determined as the expression of 8 macrophage markers) in BLBC is a strong predictor of poor survival. In vitro and in vivo migration assays evidenced that expression of ID4 in breast cancer cells is able to influence macrophages motility. At gene expression level we observed induction of ID4 itself, in macrophages co-cultured with breast cancer cells, induction that was impaired when breast cancer cells were depleted of ID4 expression. The same ID4-dependent behavior was observed for HIF-1A and for an angiogenesis-related signature in macrophages. Expression of angiogenesis-related genes was further controlled by miR-107, down-regulated in macrophages in ID4-dependent manner. Altogether our results highlight a key role for ID4 in dictating the angiogenic behavior of tumor-associated macrophages in breast cancer.