TRIM59: A membrane protein expressed on Bacillus Calmette-Guérin-activated macrophages that induces apoptosis of fibrosarcoma cells by direct contact

Abstract Bacillus Calmette-Guerin (BCG)-activated macrophages (BAMs) have anti-tumor effects, especially on fibrosarcoma cells. However, the mechanism governing this process has not been elucidated to date. TRIM59 is an up-regulated membrane protein expressed on the surface of BAMs. In this study, we found that up-regulated TRIM59 macrophages exhibited excellent growth inhibition on MCA207 fibrosarcoma and induced tumor apoptosis. Moreover, TRIM59 enhanced macrophage infiltration and increased the M1 phenotype macrophages inside the tumor. Furthermore, the cytotoxic T cells and B cells in the spleen and lymphnode have not been affected by TRIM59. These results showed that macrophages expressing TRIM59 exhibited the main cytotoxic effect on tumors. In vitro, we co-cultured TRIM59 up-regulated macrophages fixed with 1% paraformaldehyde or cell culture supernatant and tumor cells. We found that the killing activities of macrophages decreased after treatment with anti-TRIM59 antibody, and the supernatant of TRIM59 up-regulated macrophages had no tumoricidal effect on fibrosarcoma cells, which demonstrated that TRIM59 may be involved in tumoricidal effects via cell-cell contact. In addition, the PI3K-Akt pathway of MCA207 co-cultured with macrophages highly expressing TRIM59 was significantly inhibited, whereas the activation of the PI3K-Akt pathway in MCA207 was not affected after co-culture with TRIM59-CKO macrophages. These results define a vital role of TRIM59 as an anti-tumor effector molecule of BAMs and suggest a new therapeutic target for the treatment of fibrosarcoma.