m6A methylation-modified ETV1 drives multiple myeloma progression and M2 polarization of tumor-associated macrophage through transcriptional activation of RBMS1

Multiple myeloma (MM) is an incurable tumor characterized by the clonal expansion of malignant plasma cells in the bone marrow. Tumor-associated macrophages (TAMs) play a crucial role in the MM microenvironment by promoting plasma cell survival and conferring therapy resistance. ETV1 (E-twenty-six transformation-specific variant 1) is a transcription factor that has been proven to be an oncogenic driver in various cancers, but its functional role and the potential mechanisms in MM remain poorly understood. Gene expression profiles were analyzed in bone marrow plasma cells from three healthy and 45 MM samples obtained from the GSE125361 dataset. Cell growth was assessed using CCK-8 and colony formation assays. Macrophage phenotypes were characterized by flow cytometry, and TAM infiltration was evaluated via immunofluorescence double staining. Tumor development was detected by in vivo fluorescence imaging system. Transcriptional activity was examined using luciferase reporter and chromatin immunoprecipitation (ChIP) assays. The N6-Methyladenosine (m6A) modification levels of ETV1 in MM cells were detected by m6A RNA immunoprecipitation followed by qPCR (m6A RIP-qPCR), and the interaction between ETV1 mRNA and METTL3 (methyltransferase-like 3) was evaluated using RIP-PCR. Bioinformatics analysis revealed that ETV1 was significantly upregulated in MM and associated with poor prognosis of MM patients. Gain-of-function and loss-of-function experiments demonstrated that ETV1 overexpression enhanced MM cell proliferation and M2 polarization of TAMs both in vitro and in vivo, whereas ETV1 knockdown exerted the opposite effects. Mechanistically, we confirmed that METTL3 upregulated ETV1 expression by enhancing its m6A methylation modification. Furthermore, ETV1 transcriptionally activated RBMS1 (RNA-binding motif, single-stranded-interacting protein 1), and RBMS1 knockdown abrogated the pro-tumorigenic effects of ETV1 overexpression. These findings underscore the pivotal role of the ETV1/RBMS1 signaling axis in MM progression and M2 polarization of TAMs. Our results further suggest that ETV1 may represent a promising therapeutic target in MM, offering novel insights into its oncogenic function and underlying regulatory mechanisms.