Fig. 1.
Signaling between breast cancer cells (BCCs), mesenchymal stem cells (MSCs), myeloid-derived suppressor cells (MDSCs), and tumor associated macrophages (TAMs) stimulates metastasis. Large colored arrows indicate intercellular signaling through interaction of ligand with its cognate receptor. Thin black arrows indicate intracellular signaling activated by ligand-receptor interaction. Hypoxia-inducible factors directly activate transcription of the genes encoding the three ligands (CXCL16, PGF, CSF1) and two receptors (CCR5, CXCR3) in hypoxic BCCs.