Tim-3 promotes tumor-promoting M2 macrophage polarization by binding to STAT1 and suppressing the STAT1-miR-155 signaling axis

Abstract

T cell Ig mucin-3 (Tim-3), an immune checkpoint inhibitor, shows therapeutic potential. However, the molecular mechanism by which Tim-3 regulates immune responses remains to be determined. In particular, very little is known about how Tim-3 works in innate immune cells. Here, we demonstrated that Tim-3 is involved in the development of tumor-promoting M2 macrophages in colon cancer. Manipulation of the Tim-3 pathway significantly affected the polarization status of intestinal macrophages and the progression of colon cancer. The Tim-3 signaling pathway in macrophages was explored using microarray, co-immunoprecipitation, gene mutation, and high-content analysis. For the first time, we demonstrated that Tim-3 polarizes macrophages by directly binding to STAT1 via residue Y256 and Y263 in its intracellular tail and inhibiting the STAT1-miR-155-SOCS1 signaling axis. We also identified a new signaling adaptor of Tim-3 in macrophages, and, by modulating the Tim-3 pathway, demonstrated the feasibility of altering macrophage polarization as a potential tool for treating this kind of disease.

Monoclonal antibody against human Tim‐3 enhances antiviral immune response

“…Thus, the expression (transfection) of Tim‐3 alone reduces STAT1 phosphorylation, while blocking Tim‐3 signalling using the antibody enhances STAT1 phosphorylation and promotes the expression of cytokines in Jurkat and/or monocytes/macrophages. We previously found that Tim‐3 binds to STAT1 on its intracellular tail and inhibits the phosphorylation and nuclear translocation of STAT1 in macrophages, which suggested a direct effect of Tim‐3 on STAT1 . Here, we demonstrated that Tim‐3 also inhibits STAT1 phosphorylation in T cells.…”

“…Subsequently, we investigated the mechanisms by which L3G induces cytokine expression in immune cells. STAT1 phosphorylation is an important signalling event that triggers the production of many cytokines, including interferons and interleukins . We previously found that Tim‐3 signalling inhibits STAT1 phosphorylation .…”

“…STAT1 phosphorylation is an important signalling event that triggers the production of many cytokines, including interferons and interleukins . We previously found that Tim‐3 signalling inhibits STAT1 phosphorylation . Here, we assessed whether L3G administration enhances cell activity by preventing the Tim‐3‐mediated inhibition of STAT1.…”

“…Recently, the significance of Tim‐3‐induced innate immune tolerance has attracted considerable attention in the field of immunotherapy. Our previous report revealed that Tim‐3 can induce infection and tumour tolerance by inhibiting macrophage activation . Therefore, the effects of Tim‐3 antibodies on innate immunity should also be investigated.…”

“…However, studies investigating Tim‐3 signalling in innate immune cells are scarce. We found that Tim‐3 promoted M2 macrophage polarization by binding STAT1 via its SH2‐binding domain to inhibit the phosphorylation and nuclear translocation of STAT1 . As STAT1 is involved in many signalling cascades against infection, investigating whether Tim‐3 antibody treatment promotes the STAT1 signalling pathway and, therefore, enhances immune cell‐mediated immunity against infection is highly important.…”