ABSTRACT
The nuclear Cap-Binding Complex (CBC), consisting of Nuclear Cap-Binding Protein 1 (NCBP1) and 2 (NCBP2), associates with the nascent 5'cap of RNA polymerase II transcripts and impacts RNA fate decisions. Recently, the C17orf85 protein, also called NCBP3, was suggested to form an alternative CBC by replacing NCBP2. However, applying protein-protein interaction screening of NCBP1, 2 and 3, we find that the interaction profile of NCBP3 is distinct. Whereas NCBP1 and 2 identify known CBC interactors, NCBP3 primarily interacts with components of the Exon Junction Complex (EJC) and the TRanscription and EXport (TREX) complex. NCBP3-EJC association in vitro and in vivo requires EJC core integrity and the in vivo RNA binding profiles of EJC and NCBP3 overlap. We further show that NCBP3 competes with the RNA degradation factor ZC3H18 for binding CBC-bound transcripts, and that NCBP3 positively impacts the nuclear export of polyadenylated RNAs and the expression of large multi-exonic transcripts. Collectively, our results place NCBP3 with the EJC and TREX complexes in supporting mRNA expression.
Subject(s)
RNA, Messenger/genetics , RNA-Binding Proteins/genetics , RNA/genetics , Transcription, Genetic , Active Transport, Cell Nucleus/genetics , Cell Nucleus/genetics , Exons , Gene Expression Regulation/genetics , Humans , Nuclear Cap-Binding Protein Complex/genetics , RNA Cap-Binding Proteins/genetics , RNA Polymerase II/genetics , RNA Stability/genetics , RNA Transport/genetics , Transcription Factors/geneticsABSTRACT
Activation of the innate immune pattern recognition receptor NOD2 by the bacterial muramyl-dipeptide peptidoglycan fragment triggers recruitment of the downstream adaptor kinase RIP2, eventually leading to NF-κB activation and proinflammatory cytokine production. Here we show that full-length RIP2 can form long filaments mediated by its caspase recruitment domain (CARD), in common with other innate immune adaptor proteins. We further show that the NOD2 tandem CARDs bind to one end of the RIP2 CARD filament, suggesting a mechanism for polar filament nucleation by activated NOD2. We combine X-ray crystallography, solid-state NMR and high-resolution cryo-electron microscopy to determine the atomic structure of the helical RIP2 CARD filament, which reveals the intermolecular interactions that stabilize the assembly. Using structure-guided mutagenesis, we demonstrate the importance of RIP2 polymerization for the activation of NF-κB signalling by NOD2. Our results could be of use to develop new pharmacological strategies to treat inflammatory diseases characterised by aberrant NOD2 signalling.
Subject(s)
NF-kappa B/metabolism , Nod2 Signaling Adaptor Protein/metabolism , Receptor-Interacting Protein Serine-Threonine Kinase 2/metabolism , Caspase Activation and Recruitment Domain , HEK293 Cells , Humans , Protein Conformation , Receptor-Interacting Protein Serine-Threonine Kinase 2/geneticsABSTRACT
The previously published version of this Article contained an error in Figure 1. In panel d, the Arabidopsis SERRATE protein was incorrectly labelled 'Human SERRATE' and should have been labelled 'SERRATE'. The error has been corrected in both the PDF and HTML versions of the Article.
ABSTRACT
ARS2 is a highly conserved metazoan protein involved in numerous aspects of nuclear RNA metabolism. As a direct partner of the nuclear cap-binding complex (CBC), it mediates interactions with diverse RNA processing and transport machineries in a transcript-dependent manner. Here, we present the human ARS2 crystal structure, which exhibits similarities and metazoan-specific differences to the plant homologue SERRATE, most notably an additional RRM domain. We present biochemical, biophysical and cellular interactome data comparing wild type and mutant ARS2 that identify regions critical for interactions with FLASH (involved in histone mRNA biogenesis), NCBP3 (a putative cap-binding protein involved in mRNA export) and single-stranded RNA. We show that FLASH and NCBP3 have overlapping binding sites on ARS2 and that CBC-ARS2-NCBP3 form a ternary complex that is mutually exclusive with CBC-ARS-PHAX (involved in snRNA export). Our results support that mutually exclusive higher-order CBC-ARS2 complexes are critical in determining Pol II transcript fate.
Subject(s)
Nuclear Proteins/chemistry , RNA Transport/physiology , RNA, Messenger/metabolism , RNA, Small Nuclear/metabolism , Transcription, Genetic/physiology , Animals , Apoptosis Regulatory Proteins/metabolism , Binding Sites/genetics , Calcium-Binding Proteins/metabolism , Crystallography, X-Ray , Humans , Nuclear Cap-Binding Protein Complex/metabolism , Nuclear Proteins/physiology , Protein Domains , RNA Polymerase II/metabolism , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolismABSTRACT
Pol II transcribes diverse classes of RNAs that need to be directed into the appropriate nuclear maturation pathway. All nascent Pol II transcripts are 5'-capped and the cap is immediately sequestered by the nuclear cap-binding complex (CBC). Mutually exclusive interactions of CBC with different partner proteins have been implicated in transcript fate determination. Here, we characterise the direct interactions between CBC and NELF-E, a subunit of the negative elongation factor complex, ARS2 and PHAX. Our biochemical and crystal structure results show that the homologous C-terminal peptides of NELF-E and ARS2 bind identically to CBC and in each case the affinity is enhanced when CBC is bound to a cap analogue. Furthermore, whereas PHAX forms a complex with CBC and ARS2, NELF-E binding to CBC is incompatible with PHAX binding. We thus define two mutually exclusive complexes CBC-NELF-E and CBC-ARS2-PHAX, which likely act in respectively earlier and later phases of transcription.
