Tumor cell SPTBN1 inhibits M2 polarization of macrophages by suppressing CXCL1 expression.

Tumor-associated macrophages (TAMs) are the most abundant immune cells in the tumor microenvironment, and the M2-type TAMs can promote tumor growth, invasion and angiogenesis, and suppress antitumor immune responses. It has been reported that spectrin beta, non-erythrocytic 1 (SPTBN1) may inhibit the infiltration of macrophages in Sptbn1 +/-  mouse liver, but whether tumor SPTBN1 affects TAMs polarization remains unclear. This study investigated the effect and mechanism of tumor cell SPTBN1 on polarization and migration of TAMs in hepatoma and breast cancer. By analyzing tumor immune databases, we found a negative correlation between SPTBN1 and abundance of macrophages and myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment. By reverse transcription-quantitative real-time PCR assays and cell migration assays, the migration and M2 polarization of macrophages were enhanced by the culture medium from hepatocellular carcinoma cell line PLC/PRF/5, SNU449, and breast cancer cell line MDA-MB-231 with SPTBN1 suppression, which could be reversed by CXCL1 neutralizing antibody MAB275. Meanwhile, the ability of migration and colony formation of PLC/PRF/5, SNU449, and MDA-MB-231 cells were promoted when coculture with M2 macrophages. We also found that SPTBN1 regulated CXCL1 through p65 by cytoplasmic-nuclear protein isolation experiments and ChIP-qPCR. Our data suggest that tumor cell SPTBN1 inhibits migration and M2-type polarization of TAMs by reducing the expression and secretion of CXCL1 via inhibiting p65 nuclear localization.