SMD2 reads pseudouridines to regulate mRNA splicing and promote tumorigenesis

Pseudouridines (ψ) in mRNA are linked to alternative splicing, but their regulatory mechanisms remain unclear due to the lack of known reader proteins. Here, we identify SMD2, a core spliceosomal component, as a direct ψ reader. Through in vitro and ex vivo assays, we show that SMD2 preferentially binds to ψ-modified RNA over unmodified uridines in human cells. Specifically, SMD2 collaborates with ψ synthase (PUS) family enzymes to regulate alternative splicing by recognizing ψ residues near exon-intron junctions. Notably, SNRPD2, the gene encoding SMD2, is overexpressed in multiple cancers and is essential for tumor cell proliferation through modulating mRNA maturation. These findings establish a direct mechanistic link between ψ and spliceosomal function, which positions SMD2 as a key regulator of ψ-mediated splicing and a promising therapeutic target in cancer.