The RNA-Binding Protein RBMX Mediates the Immunosuppressive Microenvironment of Osteosarcoma by Regulating CD8+T Cells

Background: The progression of osteosarcoma is closely related to the immune microenvironment. Related studies have found that the RNA-binding motif protein, X-linked (RBMX), plays a regulatory role in modulating the biological characteristics of the tumor microenvironment (TME). However, its regulatory mechanism in osteosarcoma remains unclear. Methods: In this study, the expression of RBMX in osteosarcoma was analyzed using the results of bulk and single-cell transcriptome sequencing of human osteosarcoma. The RBMX knockout cell line was constructed via lentivirus transfection. The mouse subcutaneous implantable tumor model and single-cell transcriptome sequencing analysis revealed the effects of RBMX on the osteosarcoma microenvironment, as verified via multiplex immunofluorescence, flow cytometry, and PCR experiments. Results: Using the TARGET database and multiplex immunofluorescence, we found that RBMX is highly expressed in human osteosarcoma and is associated with poor prognosis. The high expression of RBMX may mediate the immunosuppressive microenvironment of human osteosarcoma. In vitro cell experiments showed that knockout of RBMX significantly inhibited the proliferation of mouse osteosarcoma cells. Through single-cell transcriptome sequencing analysis of subcutaneous implantable tumors in mice, we determined that RBMX deletion substantially elevated the recruitment of cytotoxic CD8+T cells within the mouse TME, which was further verified through flow cytometry analysis. Cell coculture assay confirmed that knockout of RBMX significantly enhanced the cytotoxic activity of CD8+T cells. Finally, cell communication and in vitro experimental verification revealed that knocking out RBMX might enhance the infiltration of CD8+T cells by upregulating histocompatibility 2, K1, and K region (H2-K1) and downregulating thrombospondin 1 (THBS1). Conclusions: This study may provide potential targets for reshaping the immune microenvironment of osteosarcoma and improving its therapeutic efficacy.