CLNS1A (chloride nucleotide-sensitive channel 1A) is a multifunctional protein serving dual roles in spliceosomal assembly and methylosome function. Primarily, CLNS1A acts as a chaperone regulating assembly of spliceosomal U1, U2, U4, and U5 snRNPs by sequestering Sm proteins in an inactive 6S pICln-Sm complex in the cytosol until the SMN complex triggers their transfer to form core snRNPs 12. Beyond splicing, CLNS1A interacts with protein arginine methyltransferase 5 (PRMT5) as an adaptor protein enabling substrate recruitment to the methylosome complex 3. This PRMT5-CLNS1A axis regulates symmetric histone and Sm protein dimethylation, critical for proper spliceosome function and mRNA chr11 escape 4. Disease relevance spans both immunology and oncology. CLNS1A deletion in CD4 T cells impairs proliferation and effector function by disrupting genome stability and cell cycle progression, protecting mice from experimental autoimmune encephalomyelitis and inflammatory bowel disease 5. In non-small cell lung cancer, CLNS1A overexpression correlates with poor survival and promotes chemoresistance through both chloride channel-dependent drug efflux and FAK-SRC-RAC1 pathway activation 6. CLNS1A depletion impairs detained intron splicing regulation, representing a therapeutic vulnerability in cancer cells dependent on proper PRMT5-mediated splicing 7. These findings establish CLNS1A as both a fundamental RNA processing factor and emerging therapeutic target.