SUMMARY Just as reference genome sequences revolutionized human genetics, reference maps of interactome networks will be critical to fully understand genotype-phenotype relationships. Here, we describe a systematic map of ~14,000 high-quality human binary protein-protein interactions. At equal quality, this map is ~30% larger than what is available from small-scale studies published in the literature in the last few decades. While currently available information is highly biased and only covers a relatively small portion of the proteome, our systematic map appears strikingly more homogeneous, revealing a “broader” human interactome network than currently appreciated. The map also uncovers significant inter-connectivity between known and candidate cancer gene products, providing unbiased evidence for an expanded functional cancer landscape, while demonstrating how high quality interactome models will help “connect the dots” of the genomic revolution.

Whereas individual steps of protein-coding gene expression in eukaryotes can be studied in isolation in vitro, it has become clear that these steps are intimately connected within cells. Connections not only ensure quality control but also fine-tune the gene expression process, which must adapt to environmental changes while remaining robust. In this review, we systematically present proven and potential mechanisms by which sequence-specific DNA-binding transcription factors can alter gene expression beyond transcription initiation and regulate pre-mRNA splicing, and thereby mRNA isoform production, by (i) influencing transcription elongation rates, (ii) binding to pre-mRNA to recruit splicing factors, and/or (iii) blocking the association of splicing factors with pre-mRNA. We propose various mechanistic models throughout the review, in some cases without explicit supportive evidence, in hopes of providing fertile ground for future studies.

The largely nuclear cap-binding complex (CBC) binds to the 5 ′ caps of RNA polymerase II (RNAPII)-synthesized transcripts and serves as a dynamic interaction platform for a myriad of RNA processing factors that regulate gene expression. While influence of the CBC can extend into the cytoplasm, here we review the roles of the CBC in the nucleus, with a focus on protein-coding genes. We discuss differences between CBC function in yeast and mammals, covering the steps of transcription initiation, release of RNAPII from pausing, transcription elongation, cotranscriptional pre-mRNA splicing, transcription termination, and consequences of spurious transcription. We describe parameters known to control the binding of generic or gene-specific cofactors that regulate CBC activities depending on the process(es) targeted, illustrating how the CBC is an ever-changing choreographer of gene expression.The nuclear cap-binding complex (CBC), which is a heterodimer conserved from Saccharomyces cerevisiae to Homo sapiens, is composed of two cap-binding proteins (CBPs). CBP20 directly binds the m 7 G cap at the 5 ′ end of RNA polymerase II (RNAPII)-synthesized transcripts, while CBP80 stabilizes the binding of CBP20 to the cap and serves as an interaction platform for numerous factors that control virtually every step of gene expression (Gonatopoulos-Pournatzis and Cowling 2014; Müller-McNicoll and Neugebauer 2014). RNAPII-synthesized transcripts bound by the CBC include precursor and processed mRNAs, long noncoding RNAs (lncRNAs), promoter upstream transcripts (PROMPTs), enhancer RNAs (eRNAs), immature small nuclear RNAs (snRNAs), small nucleolar RNAs (snoRNAs) of intergenic origin, and primary-micro-RNAs (pri-miRNAs). Whereas our lab discovered and con-tributed to elucidating the role of the CBC in the cytoplasm during the pioneer round of translation and nonsense-mediated mRNA decay (NMD) (for review, see Maquat et al. 2010;Ryu and Kim 2017;Kurosaki et al. 2019), our current research focuses on the role of the CBC during gene transcription by RNAPII (Cho et al. 2018). Here, we review known roles of the CBC in the nucleus during the transcription of genes that encode proteins, stitching together past studies from diverse groups to describe the continuum of CBC-mediated checks and balances in eukaryotic cells. Chromatin-associated steps in the synthesis and processing of protein-coding transcriptsThe transcription of eukaryotic protein-coding genes is a stepwise process that can be divided into fundamental stages, all of which are regulated by the CBC: preinitiation complex assembly, transcription initiation, promoterproximal pausing, processive transcription elongation, and transcription termination coupled to pre-mRNA 3 ′ end processing. The process of pre-mRNA splicing, being largely cotranscriptional, is also presented in this review. Preinitiation complex assemblyThe first step of gene transcription is assembly at the core promoter of a preinitiation complex (PIC) composed of RNAPII and general transcription factors (GTFs). ...

nature structural & molecular biology advance online publication a r t i c l e sAlthough undisputable evidence has clearly demonstrated that the nuclear steps of mRNA processing are mechanistically linked to transcription, a conceptual evolution in gene regulation has come with the realization that transcription might also be functionally connected to more remote processes occurring in the cytoplasm, such as mRNA decay 1,2 . Cytoplasmic mRNA decay is initiated by deadenylation, a rate-limiting event during which the poly(A) tail of the transcript is trimmed off by the CCR4-NOT complex, the main deadenylation machinery in eukaryotes 3 . The degradation of specific mRNAs, a key process in the regulation of eukaryotic gene expression, is achieved through the recruitment of the CCR4-NOT complex by sequence-specific RNA-binding proteins (RBPs) or by the microRNA machinery 3,4 . Poly(A)-shortened mRNAs, along with factors involved in the deadenylation, decapping and mRNA-degradation machineries, accumulate in microscopic mRNA-protein complex (mRNP) aggregates called processing bodies (PBs) 5 .The idea of coupling between mRNA synthesis and degradation has recently emerged. Genome-wide expression studies in yeast have shown that mRNA synthesis and decay are mechanistically and functionally coordinated, thus supporting the existence of common molecular effectors [6][7][8][9] . In particular, the CCR4-NOT deadenylation complex was first described as a transcriptional regulator and has been implicated in initiation and elongation by RNA polymerase II 10,11 . More surprisingly, it has also been shown that degradation of yeast mRNAs is determined by cis-acting sequence elements in promoters 12,13 . These findings have led to the concept of mRNA imprinting, in which sequence-specific DNA-binding factors might orchestrate mRNA synthesis and decay. This decay would occur via loading of factors regulating cytoplasmic mRNA degradation onto the transcribing mRNA 14 . However, the identity of these DNA-binding mRNA coordinators is still obscure, and it remains to be tested whether such coupling between transcription and decay also exists in higher eukaryotes. E26 (Ets) proteins, a family of 28 helix-loop-helix transcription factors (TFs) in metazoans, are characterized by a highly conserved DNA-binding ETS domain 15 . Through this domain, Ets factors bind specific gene promoters and act as key regulators in many biological processes including cellular proliferation, apoptosis, differentiation and survival 16 . ERG, FLI1 and the more structurally divergent FEV compose the Erg subfamily of Ets factors and have been identified as driving factors in prostate cancer, Ewing's tumors and leukemias 15,17 . Using ERG as a paradigm, we sought to investigate the possibility that eukaryotic transcription factors might be directly involved in cytoplasmic mRNA decay. We demonstrate that ERG triggers degradation of mRNAs connected to Aurora signaling by recruiting RBPs and the CCR4-NOT deadenylation complex and that this activity is important fo...

Although peroxisome proliferator-activated receptor-γ (PPARγ) coactivator 1α (PGC-1α) is a well-established transcriptional coactivator for the metabolic adaptation of mammalian cells to diverse physiological stresses, the molecular mechanism by which it functions is incompletely understood. Here we used in vitro binding assays, X-ray crystallography, and immunoprecipitations of mouse myoblast cell lysates to define a previously unknown cap-binding protein 80 (CBP80)-binding motif (CBM) in the C terminus of PGC-1α. We show that the CBM, which consists of a nine-amino-acid α helix, is critical for the association of PGC-1α with CBP80 at the 5' cap of target transcripts. Results from RNA sequencing demonstrate that the PGC-1α CBM promotes RNA synthesis from promyogenic genes. Our findings reveal a new conduit between DNA-associated and RNA-associated proteins that functions in a cap-binding protein surveillance mechanism, without which efficient differentiation of myoblasts to myotubes fails to occur.

SHIP-1 is an inositol phosphatase predominantly expressed in hematopoietic cells. Over the ten past years, SHIP-1 has been described as an important regulator of immune functions. Here, we characterize a new inhibitory function for SHIP-1 in NOD2 signaling. NOD2 is a crucial cytoplasmic bacterial sensor that activates proinflammatory and antimicrobial responses upon bacterial invasion. We observed that SHIP-1 decreases NOD2-induced NF-κB activation in macrophages. This negative regulation relies on its interaction with XIAP. Indeed, we observed that XIAP is an essential mediator of the NOD2 signaling pathway that enables proper NF-κB activation in macrophages. Upon NOD2 activation, SHIP-1 C-terminal proline rich domain (PRD) interacts with XIAP, thereby disturbing the interaction between XIAP and RIP2 in order to decrease NF-κB signaling.

Staufen1 (STAU1) is an RNA-binding protein (RBP) that interacts with double-stranded RNA structures and has been implicated in regulating different aspects of mRNA metabolism. Previous studies have indicated that STAU1 interacts extensively with RNA structures in coding regions (CDSs) and 3′-untranslated regions (3′UTRs). In particular, duplex structures formed within 3′UTRs by inverted-repeat Alu elements (IRAlus) interact with STAU1 through its double-stranded RNA-binding domains (dsRBDs). Using 3′ region extraction and deep sequencing coupled to ribonucleoprotein immunoprecipitation (3′READS + RIP), together with reanalyzing previous STAU1 binding and RNA structure data, we delineate STAU1 interactions transcriptome-wide, including binding differences between alternative polyadenylation (APA) isoforms. Consistent with previous reports, RNA structures are dominant features for STAU1 binding to CDSs and 3′UTRs. Overall, relative to short 3′UTR counterparts, longer 3′UTR isoforms of genes have stronger STAU1 binding, most likely due to a higher frequency of RNA structures, including specific IRAlus sequences. Nevertheless, a sizable fraction of genes express transcripts showing the opposite trend, attributable to AU-rich sequences in their alternative 3′UTRs that may recruit antagonistic RBPs and/or destabilize RNA structures. Using STAU1-knockout cells, we show that strong STAU1 binding to mRNA 3′UTRs generally enhances polysome association. However, IRAlus generally have little impact on STAU1-mediated polysome association despite having strong interactions with the protein. Taken together, our work reveals complex interactions of STAU1 with its cognate RNA substrates. Our data also shed light on distinct post-transcriptional fates for the widespread APA isoforms in mammalian cells.

ORF9p (homologous to herpes simplex virus 1 [HSV-1] VP22) is a varicella-zoster virus (VZV) tegument protein essential for viral replication. Even though its precise functions are far from being fully described, a role in the secondary envelopment of the virus has long been suggested. We performed a yeast two-hybrid screen to identify cellular proteins interacting with ORF9p that might be important for this function. We found 31 ORF9p interaction partners, among which was AP1M1, the μ subunit of the adaptor protein complex 1 (AP-1). AP-1 is a heterotetramer involved in intracellular vesicle-mediated transport and regulates the shuttling of cargo proteins between endosomes and the -Golgi network via clathrin-coated vesicles. We confirmed that AP-1 interacts with ORF9p in infected cells and mapped potential interaction motifs within ORF9p. We generated VZV mutants in which each of these motifs was individually impaired and identified leucine 231 in ORF9p to be critical for the interaction with AP-1. Disrupting ORF9p binding to AP-1 by mutating leucine 231 to alanine in ORF9p strongly impaired viral growth, most likely by preventing efficient secondary envelopment of the virus. Leucine 231 is part of a dileucine motif conserved among alphaherpesviruses, and we showed that VP22 of Marek's disease virus and HSV-2 also interacts with AP-1. This indicates that the function of this interaction in secondary envelopment might be conserved as well. Herpesviruses are responsible for infections that, especially in immunocompromised patients, can lead to severe complications, including neurological symptoms and strokes. The constant emergence of viral strains resistant to classical antivirals (mainly acyclovir and its derivatives) pleads for the identification of new targets for future antiviral treatments. Cellular adaptor protein (AP) complexes have been implicated in the correct addressing of herpesvirus glycoproteins in infected cells, and the discovery that a major constituent of the varicella-zoster virus tegument interacts with AP-1 reveals a previously unsuspected role of this tegument protein. Unraveling the complex mechanisms leading to virion production will certainly be an important step in the discovery of future therapeutic targets.