Functional interplay between TTP/ZFP36 and HuR/ELAVL1 in cancer: a post-transcriptional regulatory network

Post-transcriptional regulation of gene expression has emerged as a fundamental determinant of cancer initiation, progression, and therapeutic response. Among the RNA-binding proteins (RBPs) involved in mRNA turnover and translational regulation, tristetraprolin (TTP), encoded by the ZFP36 gene, and "Human antigen R" (HuR), encoded by ELAVL1, represent two functionally antagonistic regulators of AU-rich element (ARE)-containing transcripts. TTP promotes the degradation of target mRNAs through recruitment of deadenylation and decay complexes, whereas HuR generally stabilizes and enhances the translation of overlapping mRNA subsets. Because many oncogenic, inflammatory, angiogenic, and metastasis-associated transcripts contain AREs within their 3 ' untranslated regions, the balance between TTP-mediated decay and HuR-mediated stabilization critically influences tumor biology. Accumulating evidence demonstrates that loss of TTP expression or activity and cytoplasmic accumulation of HuR are recurrent features across multiple cancer types, including breast, colorectal, pancreatic, gastric, liver, ovarian, and lung cancers. Importantly, several studies indicate that the reciprocal interplay between these proteins establishes a post-transcriptional rheostat controlling cancer-associated RNA regulons. This review summarizes current knowledge regarding the molecular biology of TTP and HuR, emphasizing their opposing functions in mRNA metabolism and cancer progression. We discuss mechanisms regulating their expression, localization, phosphorylation, and RNA-binding activity; analyze cancer-specific evidence; and examine models in which both proteins are co-expressed or functionally interconnected. Finally, we evaluate therapeutic strategies aimed at restoring TTP function or inhibiting HuR activity and discuss future perspectives for targeting post-transcriptional regulatory networks in oncology.