PABPN1 is a nuclear RNA-binding protein that plays critical roles in mRNA 3'-end processing and quality control. The protein stimulates poly(A) polymerase activity and controls poly(A) tail length during mRNA maturation 1. PABPN1 facilitates splicing of terminal introns, particularly those with weak 3' splice sites, through a poly(A) tail-dependent mechanism involving recruitment of splicing factors like RBM26/27 1. The protein also prevents nuclear export of incompletely spliced mRNAs containing retained introns, functioning as a quality control mechanism independent of nuclear RNA decay pathways 2. PABPN1 regulates alternative polyadenylation (APA) by suppressing proximal polyadenylation site usage, with reduced PABPN1 levels leading to APA-shifts that primarily affect muscle transcripts 3. Disease-causing alanine expansions in PABPN1 lead to oculopharyngeal muscular dystrophy (OPMD), where the mutant protein forms nuclear aggregates containing chaperones like HSP70 and novel components including GRP78/BiP, RPL24, and p62 4. The pathogenesis involves both toxic gain-of-function from aggregates and loss-of-function effects, with APA-shifts correlating with reduced expression of specific PABPN1 isoforms rather than aggregate formation 3. PABPN1 also demonstrates oncogenic properties in hepatocellular carcinoma through modulation of complement component C5 and NF-κB signaling 5.