RNA-protein coevolution study of Gemin5 uncovers the role of the PXSS motif of RBS1 domain for RNA binding

Evolution of the RNA alternative decay cis element into a high-affinity target for the immunomodulatory protein Roquin

RNA cis elements play pivotal roles in regulatory processes, e.g. in transcriptional and translational regulation. Two stem-looped cis elements, the constitutive and alternative decay elements (CDE and ADE, respectively) are shape-specifically recognized in mRNA 3' untranslated regions (UTRs) by the immune-regulatory protein Roquin. Roquin initiates mRNA decay and contributes to balanced transcript levels required for immune homoeostasis. While the interaction of Roquin with several CDEs is described, our knowledge about ADE complex formation is limited to the mRNA of Ox40, a gene encoding a T-cell costimulatory receptor. The Ox40 3'UTR comprises both a CDE and ADE, each sufficient for Roquin-mediated control. Opposed to highly conserved and abundant CDE structures, ADEs are rarer, but predicted to exhibit a greater structural heterogeneity. This raises the question of how and when two structurally distinct cis elements evolved as equal target motifs for Roquin. Using an interdisciplinary approach, we here monitor the evolution of sequence and structure features of the Ox40 ADE across species. We designed RNA variants to probe en-detail determinants steering Roquin-RNA complex formation. Specifically, those reveal the contribution of a second RNA-binding interface of Roquin for recognition of the ADE basal stem region. In sum, our study sheds light on how the conserved Roquin protein selected ADE-specific structural features to evolve a second high-affinity mRNA target cis element relevant for adaptive immune regulation. As our findings also allow expanding the RNA target spectrum of Roquin, the approach can serve a paradigm for understanding RNA-protein specificity through back-tracing the evolution of the RNA element.

Understanding GEMIN5 Interactions: From Structural and Functional Insights to Selective Translation

GEMIN5 is a predominantly cytoplasmic protein, initially identified as a member of the survival of motor neurons (SMN) complex. In addition, this abundant protein modulates diverse aspects of RNA-dependent processes, executing its functions through the formation of multi-component complexes. The modular organization of structural domains present in GEMIN5 enables this protein to perform various functions through its interaction with distinct partners. The protein is responsible for the recognition of small nuclear (sn)RNAs through its N-terminal region, and therefore for snRNP assembly. Beyond its role in spliceosome assembly, GEMIN5 regulates translation through the interaction with either RNAs or proteins. In the central region, a robust dimerization domain acts as a hub for protein-protein interaction, while a non-canonical RNA-binding site is located towards the C-terminus. Interestingly, GEMIN5 regulates the partitioning of mRNAs into polysomes, likely due to its RNA-binding capacity and its ability to bind native ribosomes. Understanding the functional and structural organization of the protein has brought an increasing interest in the last years with important implications in human disease. Patients carrying GEMIN5 biallelic variants suffer from neurodevelopmental delay, hypotonia, and cerebellar ataxia. This review discusses recent relevant works aimed at understanding the molecular mechanisms of GEMIN5 activity in gene expression, and also the challenges to discover new functions.

Convergent evolution of allele-specific gene expression that leads to non-small cell lung cancer in different human populations

Phenotypical innovations during evolution are caused by novel mutations, which are usually heterozygous at the beginning. The gene expressions on two alleles of these mutation sites are not necessarily identical, leading to flexible allele-specific regulation in cell systems. We retrieve the transcriptome data of normal and non-small cell lung cancer (NSCLC) tissues from 47 African Americans (AA) and 50 European Americans (EA). We analyze the differentially expressed genes (DEGs) in NSCLC as well as the tumor-specific mutations. Expression and mutation profiles show convergent evolution in AA and EA populations. The tumor-specific mutations are poorly overlapped, but many of them are located in the same genes, mainly oncogenes and tumor suppressor genes. The DEGs in tumors are majorly caused by the mutated alleles rather than normal alleles. The relative expressions of mutated alleles are highly correlated between AA and EA. The differential expression in NSCLC is predominantly mediated by the mutated alleles on heterozygous sites. This molecular mechanism underlying NSCLC oncogenesis is conserved across different human populations, exhibiting convergent evolution. We present this novel angle that differential expression analysis should be performed separately for different alleles. Our ideas should greatly benefit the cancer community.

Oligomerization regulates the interaction of Gemin5 with members of the SMN complex and the translation machinery

RNA-binding proteins are multifunctional molecules impacting on multiple steps of gene regulation. Gemin5 was initially identified as a member of the survival of motor neurons (SMN) complex. The protein is organized in structural and functional domains, including a WD40 repeats domain at the N-terminal region, a tetratricopeptide repeat (TPR) dimerization module at the central region, and a non-canonical RNA-binding site at the C-terminal end. The TPR module allows the recruitment of the endogenous Gemin5 protein in living cells and the assembly of a dimer in vitro. However, the biological relevance of Gemin5 oligomerization is not known. Here we interrogated the Gemin5 interactome focusing on oligomerization-dependent or independent regions. We show that the interactors associated with oligomerization-proficient domains were primarily annotated to ribosome, splicing, translation regulation, SMN complex, and RNA stability. The presence of distinct Gemin5 protein regions in polysomes highlighted differences in translation regulation based on their oligomerization capacity. Furthermore, the association with native ribosomes and negative regulation of translation was strictly dependent on both the WD40 repeats domain and the TPR dimerization moiety, while binding with the majority of the interacting proteins, including SMN, Gemin2, and Gemin4, was determined by the dimerization module. The loss of oligomerization did not perturb the predominant cytoplasmic localization of Gemin5, reinforcing the cytoplasmic functions of this essential protein. Our work highlights a distinctive role of the Gemin5 domains for its functions in the interaction with members of the SMN complex, ribosome association, and RBP interactome.

Novel compound heterozygous mutation and phenotype in the tetratricopeptide repeat-like domain of the GEMIN5 gene in two Chinese families

BACKGROUND

GEMIN5 is an RNA-binding protein that regulates multiple molecular functions, including splicing, localisation, translation, and mRNA stability. GEMIN5 mutations present a syndrome centred on cerebellar dysplasia, including motor dysfunction, developmental delay, cerebellar atrophy, and hypotonia.

CASES

We report three patients from two families with novel compound heterozygous mutations in the tetratricopeptide repeat-like domain of the GEMIN5 gene who presented with motor dysfunction, developmental delay, and ataxia syndrome. Novel variants were identified: c.2551_c.2552delCT (Leu851Glufs*30) and c.2911 C > G (Gln971Glu) in Family 1, and c.3287 T > C (Leu1096Pro) and c.2882 G > C (Trp961 Ser) in Family 2, which were inherited from their parents. Moreover, infantile spasms syndrome(ISs) was diagnosed in the family.

CONCLUSION

We report the first case of ISs caused by GEMIN5 gene mutations. Our cases expand on GEMIN5 variants and neurological phenotypes, reinforcing the crucial impact of tetratricopeptide repeat-like domain variants in the GEMIN5 gene.

A full repertoire of Hemiptera genomes reveals a multi-step evolutionary trajectory of auto-RNA editing site in insect Adar gene

Adenosine-to-inosine (A-to-I) RNA editing, mediated by metazoan ADAR enzymes, is a prevalent post-transcriptional modification that diversifies the proteome and promotes adaptive evolution of organisms. The Drosophila Adar gene has an auto-recoding site (termed S>G site) that forms a negative-feedback loop and stabilizes the global editing activity. However, the evolutionary trajectory of Adar S>G site in many other insects remains largely unknown, preventing us from a deeper understanding on the significance of this auto-editing mechanism. In this study, we retrieved the well-annotated genomes of 375 arthropod species including the five major insect orders (Lepidoptera, Diptera, Coleoptera, Hymenoptera and Hemiptera) and several outgroup species. We performed comparative genomic analysis on the Adar auto-recoding S>G site. We found that the ancestral state of insect S>G site was an uneditable serine codon (unSer) and that this state was largely maintained in Hymenoptera. The editable serine codon (edSer) appeared in the common ancestor of Lepidoptera, Diptera and Coleoptera and was almost fixed in the three orders. Interestingly, Hemiptera species possessed comparable numbers of unSer and edSer codons, and a few 'intermediate codons', demonstrating a multi-step evolutionary trace from unSer-to-edSer with non-synchronized mutations at three codon positions. We argue that the evolution of Adar S>G site is the best genomic evidence supporting the 'proteomic diversifying hypothesis' of RNA editing. Our work deepens our understanding on the evolutionary significance of Adar auto-recoding site which stabilizes the global editing activity and controls transcriptomic diversity.

Structural basis for Gemin5 decamer-mediated mRNA binding

Gemin5 in the Survival Motor Neuron (SMN) complex serves as the RNA-binding protein to deliver small nuclear RNAs (snRNAs) to the small nuclear ribonucleoprotein Sm complex via its N-terminal WD40 domain. Additionally, the C-terminal region plays an important role in regulating RNA translation by directly binding to viral RNAs and cellular mRNAs. Here, we present the three-dimensional structure of the Gemin5 C-terminal region, which adopts a homodecamer architecture comprised of a dimer of pentamers. By structural analysis, mutagenesis, and RNA-binding assays, we find that the intact pentamer/decamer is critical for the Gemin5 C-terminal region to bind cognate RNA ligands and to regulate mRNA translation. The Gemin5 high-order architecture is assembled via pentamerization, allowing binding to RNA ligands in a coordinated manner. We propose a model depicting the regulatory role of Gemin5 in selective RNA binding and translation. Therefore, our work provides insights into the SMN complex-independent function of Gemin5.

Structural biology, complemented by biochemistry experiments and RNA-binding assays show that the Gemin5 C-terminal region adopts a decamer architecture. Gemin5 decamerization is essential for its role in regulating mRNA translation.

Gemin5-dependent RNA association with polysomes enables selective translation of ribosomal and histone mRNAs

Selective translation allows to orchestrate the expression of specific proteins in response to different signals through the concerted action of cis-acting elements and RNA-binding proteins (RBPs). Gemin5 is a ubiquitous RBP involved in snRNP assembly. In addition, Gemin5 regulates translation of different mRNAs through apparently opposite mechanisms of action. Here, we investigated the differential function of Gemin5 in translation by identifying at a genome-wide scale the mRNAs associated with polysomes. Among the mRNAs showing Gemin5-dependent enrichment in polysomal fractions, we identified a selective enhancement of specific transcripts. Comparison of the targets previously identified by CLIP methodologies with the polysome-associated transcripts revealed that only a fraction of the targets was enriched in polysomes. Two different subsets of these mRNAs carry unique cis-acting regulatory elements, the 5’ terminal oligopyrimidine tracts (5’TOP) and the histone stem-loop (hSL) structure at the 3’ end, respectively, encoding ribosomal proteins and histones. RNA-immunoprecipitation (RIP) showed that ribosomal and histone mRNAs coprecipitate with Gemin5. Furthermore, disruption of the TOP motif impaired Gemin5-RNA interaction, and functional analysis showed that Gemin5 stimulates translation of mRNA reporters bearing an intact TOP motif. Likewise, Gemin5 enhanced hSL-dependent mRNA translation. Thus, Gemin5  promotes polysome association of only a subset of its targets, and as a consequence, it favors translation of the ribosomal and the histone mRNAs. Together, the results presented here unveil Gemin5 as a novel translation regulator of mRNA subsets encoding proteins involved in fundamental cellular processes.

Autosomal Recessive Cerebellar Atrophy and Spastic Ataxia in Patients With Pathogenic Biallelic Variants in GEMIN5

The hereditary ataxias are a heterogenous group of disorders with an increasing number of causative genes being described. Due to the clinical and genetic heterogeneity seen in these conditions, the majority of such individuals endure a diagnostic odyssey or remain undiagnosed. Defining the molecular etiology can bring insights into the responsible molecular pathways and eventually the identification of therapeutic targets. Here, we describe the identification of biallelic variants in the GEMIN5 gene among seven unrelated families with nine affected individuals presenting with spastic ataxia and cerebellar atrophy. GEMIN5, an RNA-binding protein, has been shown to regulate transcription and translation machinery. GEMIN5 is a component of small nuclear ribonucleoprotein (snRNP) complexes and helps in the assembly of the spliceosome complexes. We found that biallelic GEMIN5 variants cause structural abnormalities in the encoded protein and reduce expression of snRNP complex proteins in patient cells compared with unaffected controls. Finally, knocking out endogenous Gemin5 in mice caused early embryonic lethality, suggesting that Gemin5 expression is crucial for normal development. Our work further expands on the phenotypic spectrum associated with GEMIN5-related disease and implicates the role of GEMIN5 among patients with spastic ataxia, cerebellar atrophy, and motor predominant developmental delay.

The RBS1 domain of Gemin5 is intrinsically unstructured and interacts with RNA through conserved Arg and aromatic residues

Gemin5 is a multifaceted RNA-binding protein that comprises distinct structural domains, including a WD40 and TPR-like for which the X-ray structure is known. In addition, the protein contains a non-canonical RNA-binding domain (RBS1) towards the C-terminus. To understand the RNA binding features of the RBS1 domain, we have characterized its structural characteristics by solution NMR linked to RNA-binding activity. Here we show that a short version of the RBS1 domain that retains the ability to interact with RNA is predominantly unfolded even in the presence of RNA. Furthermore, an exhaustive mutational analysis indicates the presence of an evolutionarily conserved motif enriched in R, S, W, and H residues, necessary to promote RNA-binding via π-π interactions. The combined results of NMR and RNA-binding on wild-type and mutant proteins highlight the importance of aromatic and arginine residues for RNA recognition by RBS1, revealing that the net charge and the π-amino acid density of this region of Gemin5 are key factors for RNA recognition.

RNA-Binding Proteins at the Host-Pathogen Interface Targeting Viral Regulatory Elements

Viral RNAs contain the information needed to synthesize their own proteins, to replicate, and to spread to susceptible cells. However, due to their reduced coding capacity RNA viruses rely on host cells to complete their multiplication cycle. This is largely achieved by the concerted action of regulatory structural elements on viral RNAs and a subset of host proteins, whose dedicated function across all stages of the infection steps is critical to complete the viral cycle. Importantly, not only the RNA sequence but also the RNA architecture imposed by the presence of specific structural domains mediates the interaction with host RNA-binding proteins (RBPs), ultimately affecting virus multiplication and spreading. In marked difference with other biological systems, the genome of positive strand RNA viruses is also the mRNA. Here we focus on distinct types of positive strand RNA viruses that differ in the regulatory elements used to promote translation of the viral RNA, as well as in the mechanisms used to evade the series of events connected to antiviral response, including translation shutoff induced in infected cells, assembly of stress granules, and trafficking stress.

Uncovering targets of the Leader protease: Linking RNA-mediated pathways and antiviral defense

RNA viruses have developed specialized mechanisms to subvert host RNA‐binding proteins (RBPs) favoring their own gene expression. The Leader (L) protein of foot‐and‐mouth disease virus, a member of the Picornaviridae family, is a papain‐like cysteine protease that self‐cleaves from the polyprotein. Early in infection, the L protease cleaves the translation initiation factors eIF4GI and eIF4GII, inducing the shutdown of cap‐dependent translation. However, the cleavage sites on the viral polyprotein, eIF4GI, and eIF4GII differ in sequence, challenging the definition of a consensus site for L targets. Identification of Gemin5 and Daxx proteolytic products in infected cells unveiled a motif centered on the RKAR sequence. The RBP Gemin5 is a member of the survival of motor neurons complex, a ribosome interacting protein, and a translation downregulator. Likewise, the Fas‐ligand Daxx is a multifunctional adaptor that plays key roles in transcription control, apoptosis, and innate immune antiviral response. Remarkably, the cleavage site on the RNA helicases MDA5 and LGP2, two relevant immune sensors of the retinoic acid‐inducible gene‐I (RIG‐I)‐like receptors family, resembles the L target site of Gemin5 and Daxx, and similar cleavage sites have been reported in ISG15 and TBK1, two proteins involved in type I interferon response and signaling pathway, respectively. In this review we dissect the features of the L cleavage sites in essential RBPs, eventually helping in the discovery of novel L targets.

This article is categorized under:

RNA in Disease and Development > RNA in Disease

Translation > Translation Regulation