SMD2 reads pseudouridines to regulate mRNA splicing and promote tumorigenesis [RNA-seq]

Pseudouridines (Ψ) in mRNA are linked to alternative splicing, but their regulatory mechanisms remain unclear due to the lack of identified reader proteins. Here, we identify SMD2, a core spliceosomal component, as a direct Ψ reader. Using in vitro and ex vivo assays, we show that SMD2 preferentially binds Ψ over unmodified uridines. SMD2 collaborates with PUS family enzymes to regulate alternative splicing by binding Ψ near exon-intron boundaries, modulating the splicing of numerous pre-mRNAs. Notably, the gene encoding SMD2, SNRPD2, is overexpressed across multiple cancers and is essential for tumor cell proliferation through the maturation of key transcripts. These findings uncover a direct mechanistic link between Ψ and spliceosomal function, establishing SMD2 as a critical regulator of Ψ-mediated splicing and a potential cancer therapeutic target.