ACIN1 is a multifunctional protein with roles in RNA processing and apoptosis regulation. It serves as an auxiliary component of the exon junction complex (EJC), a ribonucleoprotein assembly deposited on mRNAs after splicing. ACIN1 is part of ASAP complexes that bind RNA and regulate intron excision in specific transcription subsets, conferring RNA-binding capacity to these complexes. Beyond its splicing functions, ACIN1 modulates alternative splicing of apoptotic genes, particularly inhibiting formation of pro-apoptotic isoforms of BCL2L1/Bcl-X. Following caspase-3 activation, ACIN1 induces apoptotic chr14 condensation. In colorectal cancer, the SRSF3-MBNL1-ACIN1 axis shifts splicing patterns to reduce DNA fragmentation, promoting cancer cell survival under oxidative stress 1. ACIN1 alterations associate with multiple malignancies. Recurrent ACIN1-NUTM1 fusions occur in non-KMT2A-rearranged infant acute lymphoblastic leukemia (ALL), a subgroup with excellent prognosis 2 3. In hepatocellular carcinoma, ACIN1 is significantly upregulated and likely regulated by miR-674-5p 4. ACIN1 is also implicated as a hub gene in bicalutamide-resistant prostate cancer 5. In cervical cancer, METTL3 enhances ACIN1 mRNA stability through IGF2BP3 to promote tumor progression 6. A founder ACIN1 mutation in normal bladder mucosa expanded clonally during carcinogenesis, suggesting it initiates field effects in bladder cancer 7. These findings position ACIN1 as both a splicing regulator and a cancer-associated gene with context-dependent pathogenic roles.