MYC-mediated transcriptional control of splicing factors promotes RNA splicing in activated B lymphocytes.

Germinal center B cells play a pivotal role in the generation of long-lived plasma cells and high-affinity antibodies. Although RNA splicing and alternative splicing are known to regulate germinal center B cell responses, the upstream mechanisms controlling these splicing events remain poorly understood. RNA sequencing analysis revealed significant upregulation of alternative splicing factors and core spliceosome genes in germinal center B cells. Genome-wide binding analyses using CUT&RUN and ChIP-seq confirmed that MAX and MYC physically bind to the promoters of these splicing regulators. High MYC expression in B cells markedly upregulated multiple splicing factors, whereas MAX knockout substantially suppressed their expression. Through splicing event profiling, we demonstrated that MYC promotes the excision of introns and alternative exons by upregulating splicing factor expression. Additionally, we identified E2F1 as another transcriptional regulator that occupies splicing factor promoters. Genetic ablation of E2F1 disrupted germinal center B cell and follicular helper T cell populations; however, its deletion in activated B cells had minimal effect on global spliceosome gene expression. These findings establish MYC as an upstream regulator that controls both splicing factor expression and splicing event alterations in activated B cells.