The global Protein-RNA interaction map of ESRP1 defines a post-transcriptional program that is essential for epithelial cell function

Esrp1 and Esrp2 regulate the stability of tmc1/2a mRNAs in zebrafish sensory hair cells

RNA-binding proteins (RBPs) are important for post-transcriptional RNA processing, including pre-mRNA alternative splicing, mRNA stability, and translation. Several RBPs have been shown to play pivotal roles in the inner ear, whose dysfunction leads to auditory and/or balance impairments. Epithelial splicing-regulatory protein 1 (ESRP1) regulates alternative splicing and mRNA stability, and mutations in ESRP1 gene have been associated with sensorineural hearing loss in humans. In Esrp1 knockout mouse embryos, alternative splicing of its target genes such as Fgfr2 is impaired, which eventually result in cochlear development deficits. However, Esrp1 knockout mice die soon after birth because of complications from cleft-lip and palate defects, impeding further investigations at later postnatal ages. In the present study, we explored the role of ESRP1 in hearing using zebrafish as a model. We showed that esrp1 and its paralog esrp2 are expressed in the inner ear and certain anterior lateral line (ALL) neuromasts. Furthermore, our data suggested that Esrp1 and Esrp2 are required for the mechano-electrical transduction (MET) function of hair cells. RNA sequencing results indicated a significant decrease in the levels of several mRNAs in esrp1/2 double knockout larvae. Among the dysregulated genes are tmc1 and tmc2a, which encode essential subunits of the MET complex. Further investigations demonstrated that Esrp1/2 could directly bind to tmc1 and tmc2a mRNAs and affect their stability. Taken together, we showed here that Esrp1 and Esrp2 regulate the MET function of zebrafish sensory hair cells by modulating the stability of tmc1 and tmc2a mRNAs.Significance statement ESRP1 is an important RNA-binding protein, whose malfunction has been associated with hearing loss in humans. Esrp1 knockout affects alternative splicing of its target mRNAs such as Fgfr2, eventually leading to cochlear development deficits in mice. However, Esrp1 knockout mice die soon after birth, precluding further investigations at later postnatal ages. In this study, we explored the role of ESRP1 in hearing using zebrafish as a model. Our results demonstrated that esrp1 and its paralog esrp2 are expressed in the zebrafish inner ear, and that esrp1/esrp2 double knockout compromised the mechano-electrical transduction (MET) function of hair cells. Additionally, we successfully identified tmc1 and tmc2a mRNAs as the targets of Esrp1/2, which encode essential subunits of the MET complex.

Full-length transcriptome atlas of gallbladder cancer reveals trastuzumab resistance conferred by ERBB2 alternative splicing

Aberrant RNA alternative splicing in cancer generates varied novel isoforms and protein variants that facilitate cancer progression. Here, we employed the advanced long-read full-length transcriptome sequencing on gallbladder normal tissues, tumors, and cell lines to establish a comprehensive full-length gallbladder transcriptomic atlas. It is of note that receptor tyrosine kinases were one of the most dynamic components with highly variable transcript, with Erb-B2 receptor tyrosine kinase 2 (ERBB2) as a prime representative. A novel transcript, designated ERBB2 i14e, was identified for encoding a novel functional protein, and its protein expression was elevated in gallbladder cancer and strongly associated with worse prognosis. With the regulation of splicing factors ESRP1/2, ERBB2 i14e was alternatively spliced from intron 14 and the encoded i14e peptide was proved to facilitate the interaction with ERBB3 and downstream signaling activation of AKT. ERBB2 i14e was inducible and its expression attenuated anti-ERBB2 treatment efficacy in tumor xenografts. Further studies with patient derived xenografts models validated that ERBB2 i14e blockage with antisense oligonucleotide enhanced the tumor sensitivity to trastuzumab and its drug conjugates. Overall, this study provides a gallbladder specific long-read transcriptome profile and discovers a novel mechanism of trastuzumab resistance, thus ultimately devising strategies to improve trastuzumab therapy.

Functional analysis of ESRP1/2 gene variants and CTNND1 isoforms in orofacial cleft pathogenesis

Orofacial cleft (OFC) is a common human congenital anomaly. Epithelial-specific RNA splicing regulators ESRP1 and ESRP2 regulate craniofacial morphogenesis and their disruption result in OFC in zebrafish, mouse and humans. Using esrp1/2 mutant zebrafish and murine Py2T cell line models, we functionally tested the pathogenicity of human ESRP1/2 gene variants. We found that many variants predicted by in silico methods to be pathogenic were functionally benign. Esrp1 also regulates the alternative splicing of Ctnnd1 and these genes are co-expressed in the embryonic and oral epithelium. In fact, over-expression of ctnnd1 is sufficient to rescue morphogenesis of epithelial-derived structures in esrp1/2 zebrafish mutants. Additionally, we identified 13 CTNND1 variants from genome sequencing of OFC cohorts, confirming CTNND1 as a key gene in human OFC. This work highlights the importance of functional assessment of human gene variants and demonstrates the critical requirement of Esrp-Ctnnd1 acting in the embryonic epithelium to regulate palatogenesis.

Functional analysis of ESRP1/2 gene variants and CTNND1 isoforms in orofacial cleft pathogenesis

Orofacial cleft (OFC) is a common human congenital anomaly. Epithelial-specific RNA splicing regulators ESRP1 and ESRP2 regulate craniofacial morphogenesis and their disruption result in OFC in zebrafish, mouse and humans. Using esrp1/2 mutant zebrafish and murine Py2T cell line models, we functionally tested the pathogenicity of human ESRP1/2 gene variants. We found that many variants predicted by in silico methods to be pathogenic were functionally benign. Esrp1 also regulates the alternative splicing of Ctnnd1 and these genes are co-expressed in the embryonic and oral epithelium. In fact, over-expression of ctnnd1 is sufficient to rescue morphogenesis of epithelial-derived structures in esrp1/2 zebrafish mutants. Additionally, we identified 13 CTNND1 variants from genome sequencing of OFC cohorts, confirming CTNND1 as a key gene in human OFC. This work highlights the importance of functional assessment of human gene variants and demonstrates the critical requirement of Esrp-Ctnnd1 acting in the embryonic epithelium to regulate palatogenesis.

Alternative splicing in EMT and TGF-β signaling during cancer progression

Epithelial to mesenchymal transition (EMT) is a physiological process during development where epithelial cells transform to acquire mesenchymal characteristics, which allows them to migrate and colonize secondary tissues. Many cellular signaling pathways and master transcriptional factors exert a myriad of controls to fine tune this vital process to meet various developmental and physiological needs. Adding to the complexity of this network are post-transcriptional and post-translational regulations. Among them, alternative splicing has been shown to play important roles to drive EMT-associated phenotypic changes, including actin cytoskeleton remodeling, cell-cell junction changes, cell motility and invasiveness. In advanced cancers, transforming growth factor-β (TGF-β) is a major inducer of EMT and is associated with tumor cell metastasis, cancer stem cell self-renewal, and drug resistance. This review aims to provide an overview of recent discoveries regarding alternative splicing events and the involvement of splicing factors in the EMT and TGF-β signaling. It will emphasize the importance of various splicing factors involved in EMT and explore their regulatory mechanisms.

Emerging roles of RNA-binding proteins in fatty liver disease

A rampant and urgent global health issue of the 21st century is the emergence and progression of fatty liver disease (FLD), including alcoholic fatty liver disease and the more heterogenous metabolism-associated (or non-alcoholic) fatty liver disease (MAFLD/NAFLD) phenotypes. These conditions manifest as disease spectra, progressing from benign hepatic steatosis to symptomatic steatohepatitis, cirrhosis, and, ultimately, hepatocellular carcinoma. With numerous intricately regulated molecular pathways implicated in its pathophysiology, recent data have emphasized the critical roles of RNA-binding proteins (RBPs) in the onset and development of FLD. They regulate gene transcription and post-transcriptional processes, including pre-mRNA splicing, capping, and polyadenylation, as well as mature mRNA transport, stability, and translation. RBP dysfunction at every point along the mRNA life cycle has been associated with altered lipid metabolism and cellular stress response, resulting in hepatic inflammation and fibrosis. Here, we discuss the current understanding of the role of RBPs in the post-transcriptional processes associated with FLD and highlight the possible and emerging therapeutic strategies leveraging RBP function for FLD treatment. This article is categorized under: RNA in Disease and Development > RNA in Disease.

ESRP1 controls biogenesis and function of a large abundant multiexon circRNA

While the majority of circRNAs are formed from infrequent back-splicing of exons from protein coding genes, some can be produced at quite high level and in a regulated manner. We describe the regulation, biogenesis and function of circDOCK1(2-27), a large, abundant circular RNA that is highly regulated during epithelial-mesenchymal transition (EMT) and whose formation depends on the epithelial splicing regulator ESRP1. CircDOCK1(2-27) synthesis in epithelial cells represses cell motility both by diverting transcripts from DOCK1 mRNA production to circRNA formation and by direct inhibition of migration by the circRNA. HITS-CLIP analysis and CRISPR-mediated deletions indicate ESRP1 controls circDOCK1(2-27) biosynthesis by binding a GGU-containing repeat region in intron 1 and detaining its splicing until Pol II completes its 157 kb journey to exon 27. Proximity-dependent biotinylation (BioID) assay suggests ESRP1 may modify the RNP landscape of intron 1 in a way that disfavours communication of exon 1 with exon 2, rather than physically bridging exon 2 to exon 27. The X-ray crystal structure of RNA-bound ESRP1 qRRM2 domain reveals it binds to GGU motifs, with the guanines embedded in clamp-like aromatic pockets in the protein.

Epithelial specific splicing regulator proteins as emerging oncogenes in aggressive prostate cancer

Prostate cancer progression is connected to the activity of conventional oncogenes and tumour suppressors and driven by circulating steroid hormones. A key issue has been how to identify and care for aggressively developing prostate tumours. Here we discuss how expression of the splicing regulators ESRP1 and ESRP2, and how their role as "masterminds" of epithelial splicing patterns, have been identified as markers of aggressively proliferating prostate primary tumours. We suggest that the origin of prostate cancer within epithelial cells, and the subsequent association of ESRP1 and ESRP2 expression with more aggressive disease progression, identify ESRP1 and ESRP2 as lineage survival oncogenes. To move this field on in the future it will be important to identify the gene expression targets controlled by ESRP1/2 that regulate prostate cancer proliferation. Potential future therapies could be designed to target ESRP1 and ESRP2 protein activity or their regulated splice isoforms in aggressive prostate tumours. Design of these therapies is potentially complicated by the risk of producing a more mesenchymal splicing environment that might promote tumour metastasis.

The discovery, function, and regulation of epithelial splicing regulatory proteins (ESRP) 1 and 2

Alternative splicing is a broad and evolutionarily conserved mechanism to diversify gene expression and functionality. The process relies on RNA binding proteins (RBPs) to recognize and bind target sequences in pre-mRNAs, which allows for the inclusion or skipping of various alternative exons. One recently discovered family of RBPs is the epithelial splicing regulatory proteins (ESRP) 1 and 2. Here, we discuss the structure and physiological function of the ESRPs in a variety of contexts. We emphasize the current understanding of their splicing activities, using the classic example of fibroblast growth factor receptor 2 mutually exclusive splicing. We also describe the mechanistic roles of ESRPs in coordinating the splicing and functional output of key signaling pathways that support the maintenance of, or shift between, epithelial and mesenchymal cell states. In particular, we highlight their functions in the development of mammalian limbs, the inner ear, and craniofacial structure while discussing the genetic and biochemical evidence that showcases their conserved roles in tissue regeneration, disease, and cancer pathogenesis.