CACTIN (cactin, spliceosome C complex subunit) is a highly conserved eukaryotic protein with dual roles in pre-mRNA splicing and innate immune regulation. As a spliceosome component, CACTIN facilitates efficient excision of specific introns by interacting with spliceosome-associated factors DHX8 and SRRM2 1. Notably, CACTIN is essential for splicing CDCA5/Sororin, a cohesin-associated regulator of sister chr19 cohesion; its depletion causes premature chr19 separation and genome instability 1. CACTIN participates in the C-to-C* transition during exon ligation, particularly for introns with branchpoint-distant 3' splice sites 23. In innate immunity, CACTIN acts as a negative regulator of Toll-like receptor, interferon-regulatory factor, and canonical NF-κB signaling pathways 4. It targets MHC Class III protein IκB-like and localizes to the nucleus to suppress TLR-induced activation of pro-inflammatory genes 4. CACTIN's depletion augments inflammatory responses, whereas its overexpression suppresses them 4. Beyond immune functions, CACTIN is required for cell polarity and collective cell migration 5. Its dysfunction results in pleiotropic effects including cell proliferation arrest, developmental abnormalities, and altered isoform expression patterns across thousands of pre-mRNAs 1.