METTL3-dependent m6A-modified circ_0026652 facilitates immune evasion of diffuse large B-cell lymphoma cells by inhibiting CD8+ T-cell responses

Diffuse large B-cell lymphoma (DLBCL) is the most common non-Hodgkin lymphoma, characterized by high heterogeneity that leads to treatment resistance and relapse in up to 40% of patients. Circular RNAs (circRNAs) primarily function as miRNA sponges to modulate gene expression involved in DLBCL tumorigenesis, resistance, and relapse. Lymph node tissues were collected from patients with reactive lymph node hyperplasia or DLBCL for gene expression analysis. DLBCL cells harboring the indicated genetic modification were co-cultured with CD8+ T cells to analyze cytokine secretion, CD8+ T cell cytotoxicity, ratio and apoptosis. DLBCL cell proliferation and apoptosis were evaluated by CCK-8, EdU incorporation, and Annexin V-APC and PI staining assays. m6A modification was assessed by MeRIP assays. Luciferase, ChIP and RIP assays were conducted to analyze gene interaction in DLBCL cells. Mice were inoculated with DLBCL cells to evaluate the effects of circ_0026652 and miR-1287-5p on DLBCL progression in vivo. METTL3-mediated m6A modification drove circ_0026652 upregulation, and YTHDC1 promoted the nuclear export of m6A-modifed circ_0026652 in DLBCL cells. Functioning as a miR-1287-5p sponge, circ_0026652 inhibited miR-1287-5p, thereby enhancing DLBCL cell proliferation and inhibiting apoptosis. Importantly, circ_0026652 suppressed T-cell cytokine production, was associated with resistance to T-cell cytotoxicity, and correlated with impaired CD8+ T-cell activity dependent on miR-1287-5p. Furthermore, miR-1287-5p-mediated regulation of DLBCL cell proliferation and apoptosis was dependent on USP22. USP22 stabilized β-catenin by reducing its ubiquitination and facilitating its nuclear translocation, which correlated with PD-L1 expression in DLBCL cells. The USP22/PD-L1 axis appear to mediate miR-1287-5p-dependent effects on DLBCL immune evasion in vitro. Circ_0026652 promoted tumor growth and was associated with inhibited CD8+ T-cell activity through the miR-1287-5p/USP22/β-catenin/PD-L1 signaling axis in vivo. METTL3-dependent m6A-modified circ_0026652 functions as a miR-1287-5p sponge to reduce miR-1287-5p expression, which in turn upregulates USP22 to stabilize β-catenin and enhance β-catenin nuclear localization. This pathway may contribute to promoting PD-L1 expression in DLBCL cells, with potential implications for inhibiting CD8+ T cell responses and facilitating DLBCL immune evasion.