The ligation between ERMAP, galectin-9 and dectin-2 promotes Kupffer cell phagocytosis and antitumor immunity
The innate immune system functions as the first line of defense against cancer cells, particularly the detection and clearance of cancer cells by phagocytosis. The liver resident macrophages, known as Kupffer cells, have the largest population of body's tissue resident macrophages and constitute the first line of defense against cancer cells invading the liver. However, the molecule mechanisms underlying the detection and phagocytosis of cancer cells by Kupffer cells are still unclear. Here, using in vivo genome-wide CRISPR-Cas9 knockout screening, we found that Ermap expressed on cancer cells delivered the pro-phagocytosis 'eat me' signal to promote Kupffer cells phagocytosis and control over liver metastasis of various cancer cells. Ermap ligated Galectin-9 expressed on Kupffer cells surface in a glycosylation dependent manner. Galectin-9 further formed a bridging complex with Ermap and transmembrane receptor Dectin-2 expressed on Kupffer cells to promote the detection and phagocytosis of cancer cells by Kupffer cells. Patients with tumors expressing low ERMAP had more liver metastases. Thus, our study identifies the Ermap–Galectin-9–Dectin-2 axis as an 'eat me' signal for Kupffer cells to engulf cancer cells and control liver metastasis. Overall design: CRISPR screen identifies novel targets regulating Hepa1-6 cells liver metastasis