Tumor Environment Promotes Lnc57Rik-Mediated Suppressive Function of Myeloid-Derived Suppressor Cells

Myeloid-derived suppressor cells (MDSCs) are pathologically activated neutrophils and monocytes with potent immunosuppressive activity that regulate immune responses in the tumor microenvironment. We identified a novel long noncoding RNA (lncRNA), named as lnc57Rik, in the MDSCs that controls their immunosuppressive functions. Lnc57Rik was induced in in vitro and in vivo inflammatory settings and upregulated the genes related to MDSC-mediated immunosuppression, including Arg-1, NOS2, NOX2, and COX2. Furthermore, Lnc57Rik can not only bind with the C/EBPI3 isoform liver-enriched activator protein to activate C/EBPI3 but also with the methyltransferase WD repeat-containing protein 5 that enables the enrichment of histone H3 trimethylated lysine 4 marks on the promoter regions of Arg-1, NOS2, NOX2, and COX2, eventually resulting in their transcriptional activation. Furthermore, the conserved human lnc57Rik has a similar function as murine lnc57Rik. Taken together, upregulation of lnc57Rik in the tumor microenvironment promotes the immunosuppressive function of MDSCs.