NRG1 and cancer: In another study, it was found that TNBC cells expressed neuregulin 1 (NRG1) that activated macrophage-expressed ErbB3, leading to increased expression of Jag1 by the macrophages; then, when the two cells interacted in co-culture, Jag1 was necessary for induction of tumor cell trans-endothelial migration (presumably by binding to cancer cell-expressed Notch) [89].