| HuD (ELAVL4) is a neuron-enriched member of the ELAV family of RNA-binding proteins, featuring three RNA recognition motifs that enable preferential cytoplasmic localization and selective binding to AU-rich elements within the 3′ untranslated regions of numerous neuronal mRNAs. The protein’s N-terminal tandem RRMs and a third C-terminal RRM confer specificity for U-rich and AU-rich sequences, and this modular organization allows HuD to simultaneously engage multiple cis-elements in target 3′UTRs and to assemble higher-order ribonucleoprotein complexes with other RNA-binding proteins and translation factors. Through binding to AU-rich elements, HuD stabilizes neuronal transcripts by antagonizing mRNA decay mechanisms, which extends transcript half-life and increases steady-state protein expression of key factors involved in neurite extension, dendritic growth, synaptic plasticity, and injury-induced regeneration, establishing HuD as a central post-transcriptional regulator in neuronal development and adult neural plasticity. In neuroblastoma, HuD is specifically expressed in neuroblastic N- and I-type cells, where it interacts with multiple AU-rich destabilizing elements within the MYCN 3′UTR; overexpression of HuD in these cells blocks mRNA decay mediated by these elements and increases MYCN mRNA stability in vivo, raising steady-state MYCN levels, which connects HuD activity directly to the maintenance of an oncogenic transcription factor that supports cell proliferation and tumor aggressiveness. HuD is also a principal neuronal autoantigen in paraneoplastic encephalomyelitis and sensory neuropathy associated with small cell lung cancer, as ectopic expression of HuD in tumor cells provokes anti-Hu immune responses that cross-react with neuronal Hu proteins, linking HuD’s neuronal specificity to paraneoplastic neuroimmunological disease. |
