| hnRNP D/AUF1 is a ubiquitously expressed RNA‑binding protein of the heterogeneous nuclear ribonucleoprotein family that functions as a multi‑isoform regulator of post‑transcriptional gene expression, with a primary role in controlling mRNA stability and turnover for transcripts bearing AU‑rich and U/GU‑rich elements. The protein is produced as four isoforms by alternative splicing and contains tandem RNA recognition motifs plus an arginine‑glycine‑glycine (RGG) domain, an architecture that supports high‑affinity binding to AU‑rich elements in 3′UTRs, to defined 5′‑UUAG‑containing RNA sequences, and to specific single‑stranded telomeric DNA repeats, allowing AUF1 to participate in both cytoplasmic mRNP complexes and nuclear nucleic acid regulation. Binding of AUF1 to AU‑rich, mRNA‑destabilizing sequences recruits or cooperates with deadenylation and decay machineries, including components that act at the major coding‑region determinant of instability in FOS mRNA, and typically accelerates mRNA decay, although some targets show increased stability or altered translation depending on isoform and context. AUF1 interacts functionally with other ARE‑binding proteins and decay regulators such as tristetraprolin and poly(A)‑binding proteins, forming higher‑order ribonucleoprotein assemblies that tune the half‑life and translational output of cytokine, proto‑oncogene and growth factor mRNAs during stress responses and homeostatic adjustments. Transcriptome‑wide PAR‑CLIP mapping has shown that AUF1 engages a broad spectrum of targets, including mRNAs, miRNAs and lncRNAs, and that its binding can either promote decay or, for selected transcripts, enhance stability or translation, linking AUF1 activity to diverse cellular processes such as genome integrity maintenance, circadian clock control and stress adaptation. For example, AUF1 directly binds the 3′UTR of CRY1 and PER2 mRNAs and induces rhythmic translation of these core clock components, inserting AUF1 into the machinery that enforces circadian timing at the post‑transcriptional level. AUF1 also represses VEGF expression through 3′UTR‑dependent mechanisms, illustrating its capacity to modulate angiogenic signaling by controlling the output of key growth factor transcripts. Beyond RNA, AUF1 can bind double‑ and single‑stranded DNA, and RRM1 binding to telomeric 5′‑TTAGGG‑3′ repeats inhibits formation of G‑quadruplex structures, a property that may influence telomere elongation and chromatin architecture. Isoform‑specific properties and post‑translational modifications, including phosphorylation and other regulatory switches, alter AUF1 subcellular localization and binding preferences, and these changes shape its impact on immune-related genes, where AUF1 regulates mRNAs encoding cytokines, inflammatory receptors and GPCRs and is strongly expressed in lymphoid tissues. Dysregulated AUF1 expression or activity is linked to chronic inflammation, neoplastic and cardiac diseases through aberrant control of labile transcripts, and viral proteases from picornaviruses cleave AUF1 to reprogram host mRNA decay in favor of viral replication, underscoring its importance as a node in host–pathogen and inflammatory signaling networks. |
