FOXM1 derived from Triple negative breast cancer exosomes promotes cancer progression by activating IDO1 transcription in macrophages to suppress ferroptosis and induce M2 polarization of Tumor-associated macrophages.

To explore the oncogenic mechanism of FOXM1 in the tumor microenvironment (TME) regarding triple negative breast cancer (TNBC) promotion. The mRNA and protein levels of target genes in TNBC cells and their exosomes were detected by RT-qPCR and western blot. Co-culture models of TNBC cells and THP-1/M0 macrophages was established to detect the impact of co-culture on FOXM1 expression and macrophage polarization direction. The bioinformatics website was used to predict the binding sites between the FOXM1 and IDO1 promoter, which were further validated using dual-luciferase reporter assay and chromatin immunoprecipitation (ChIP) assay. Finally, after erastin-induced ferroptosis, Cell Counting Kit-8 (CCK-8), terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), and other experiments were conducted to investigate whether the FOXM1/IDO1 axis regulates M2 macrophage polarization through ferroptosis. It was found that FOXM1 was highly expressed in exosomes derived from TNBC cells, and TNBC cells upregulated FOXM1 expression in THP-1 cells through exosomes to promote M2 macrophage polarization. Furthermore, FOXM1 upregulated IDO1 in M2-type TAMs by regulating transcription. Lastly, FOXM1/IDO1 inhibited ferroptosis, promoting M2 macrophage polarization, thereby advancing TNBC progression. In conclusions, FOXM1 derived from TNBC cell-derived exosomes activated IDO1 transcription in TAMs to inhibit ferroptosis, promoting TAMs' M2 polarization and exerting carcinogenic effects.