NMR-derived secondary structure of the full-length Ox40 mRNA 3'UTR and its multivalent binding to the immunoregulatory RBP Roquin

Unrestrained cleavage of Roquin-1 by MALT1 induces spontaneous T cell activation and the development of autoimmunity

Constitutive activation of the MALT1 paracaspase in conventional T cells of Malt1TBM/TBM (TRAF6 Binding Mutant = TBM) mice causes fatal inflammation and autoimmunity, but the involved targets and underlying molecular mechanisms are unknown. We genetically rendered a single MALT1 substrate, the RNA-binding protein (RBP) Roquin-1, insensitive to MALT1 cleavage. These Rc3h1Mins/Mins mice showed normal immune homeostasis. Combining Rc3h1Mins/Mins alleles with those encoding for constitutively active MALT1 (TBM) prevented spontaneous T cell activation and restored viability of Malt1TBM/TBM mice. Mechanistically, we show how antigen/MHC recognition is translated by MALT1 into Roquin cleavage and derepression of Roquin targets. Increasing T cell receptor (TCR) signals inactivated Roquin more effectively, and only high TCR strength enabled derepression of high-affinity targets to promote Th17 differentiation. Induction of experimental autoimmune encephalomyelitis (EAE) revealed increased cleavage of Roquin-1 in disease-associated Th17 compared to Th1 cells in the CNS. T cells from Rc3h1Mins/Mins mice did not efficiently induce the high-affinity Roquin-1 target IκBNS in response to TCR stimulation, showed reduced Th17 differentiation, and Rc3h1Mins/Mins mice were protected from EAE. These data demonstrate how TCR signaling and MALT1 activation utilize graded cleavage of Roquin to differentially regulate target mRNAs that control T cell activation and differentiation as well as the development of autoimmunity.

Advances, Applications, and Perspectives in Small-Angle X-ray Scattering of RNA

RNAs exhibit a plethora of functions far beyond transmitting genetic information. Often, RNA functions are entailed in their structure, be it as a regulatory switch, protein binding site, or providing catalytic activity. Structural information is a prerequisite for a full understanding of RNA-regulatory mechanisms. Owing to the inherent dynamics, size, and instability of RNA, its structure determination remains challenging. Methods such as NMR spectroscopy, X-ray crystallography, and cryo-electron microscopy can provide high-resolution structures; however, their limitations make structure determination, even for small RNAs, cumbersome, if at all possible. Although at a low resolution, small-angle X-ray scattering (SAXS) has proven valuable in advancing structure determination of RNAs as a complementary method, which is also applicable to large-sized RNAs. Here, we review the technological and methodological advancements of RNA SAXS. We provide examples of the powerful inclusion of SAXS in structural biology and discuss possible future applications to large RNAs.

1H, 13C, 15N backbone chemical shift assignments of the extended ARID domain in human AT-rich interactive domain protein 5a (Arid5a)

The family of AT-rich interactive domain (ARID) containing proteins -Arids- contains 15 members that have almost exclusively been described as DNA-binding proteins. Interestingly, a decade ago the family member Arid5a was found to bind and stabilize mRNAs of immune system key players and thereby account for driving inflammatory and autoimmune diseases. How exactly binding to DNA and RNA is coordinated by the Arid5a ARID domain remains unknown, mainly due to the lack of atom-resolved information on nucleic acid-binding. This in particular applies to the protein's ARID domain, despite the comfortable size of its core unit for NMR-based investigations. Furthermore, the core domain of ARID domains is found to be extended by functionally relevant, often flexible stretches, but whether such elongations are present and crucial for the versatile Arid5a functions is unknown. We here provide a near-complete NMR backbone resonance assignment of the Arid5a ARID domain with N- and C-terminal extensions, which serves as a basis for further studies of its nucleic acid-binding preferences and targeted inhibition by means of NMR. Our data thus significantly contribute to unravelling mechanisms of Arid5a-mediated gene regulation and diseases.

Insight into the Structural Basis for Dual Nucleic Acid-Recognition by the Scaffold Attachment Factor B2 Protein

The family of scaffold attachment factor B (SAFB) proteins comprises three members and was first identified as binders of the nuclear matrix/scaffold. Over the past two decades, SAFBs were shown to act in DNA repair, mRNA/(l)ncRNA processing and as part of protein complexes with chromatin-modifying enzymes. SAFB proteins are approximately 100 kDa-sized dual nucleic acid-binding proteins with dedicated domains in an otherwise largely unstructured context, but whether and how they discriminate DNA and RNA binding has remained enigmatic. We here provide the SAFB2 DNA- and RNA-binding SAP and RRM domains in their functional boundaries and use solution NMR spectroscopy to ascribe DNA- and RNA-binding functions. We give insight into their target nucleic acid preferences and map the interfaces with respective nucleic acids on sparse data-derived SAP and RRM domain structures. Further, we provide evidence that the SAP domain exhibits intra-domain dynamics and a potential tendency to dimerize, which may expand its specifically targeted DNA sequence range. Our data provide a first molecular basis of and a starting point towards deciphering DNA- and RNA-binding functions of SAFB2 on the molecular level and serve a basis for understanding its localization to specific regions of chromatin and its involvement in the processing of specific RNA species.

A comprehensive review of methods to study lncRNA-protein interactions in solution

The long non-coding RNAs (lncRNAs) other than rRNA and tRNA were earlier assumed to be 'junk genomic material'. However, recent advancements in genomics methods have highlighted their roles not only in housekeeping but also in the progression of diseases like cancer as well as viral infections. lncRNAs owing to their length, have both short-range and long-range interactions resulting in complex folded structures that recruit various biomolecules enabling lncRNAs to undertake their various biological functions. Using cell lysate pull-down assays increasing number of lnRNAs-interacting proteins are being identified. These interactions can be further exploited to develop targeted novel therapeutic strategies to inhibit lncRNA-protein interactions. This review attempts to succinctly techniques that can identify and characterize the lnRNAs-protein interactions (i.e. affinity, stoichiometry, and thermodynamics). Furthermore, using other sophisticated biophysical techniques, one can also perform size estimations, and determine low-resolution structures. Since these methods study the biomolecules in solution, large-scale structural observations can be performed in real-time. This review attempts to briefly introduce the readers to biochemical and biophysical techniques, such that they can utilize these methods to obtain a holistic characterization of the biomolecules of interest. Additionally, it should be noted that the use of these methods is not limited to the characterization of the interacting molecules but can also be used to determine the efficacy of the therapeutic molecules to disrupt these interactions.

The silencing of ets-4 mRNA relies on the functional cooperation between REGE-1/Regnase-1 and RLE-1/Roquin-1

Regnase-1 is an evolutionarily conserved endoribonuclease. It degrades diverse mRNAs important for many biological processes including immune homeostasis, development and cancer. There are two competing models of Regnase-1-mediated mRNA silencing. One model postulates that Regnase-1 works together with another RNA-binding protein, Roquin-1, which recruits Regnase-1 to specific mRNAs. The other model proposes that the two proteins function separately. Studying REGE-1, the Caenorhabditis elegans ortholog of Regnase-1, we have uncovered its functional relationship with RLE-1, the nematode counterpart of Roquin-1. While both proteins are essential for mRNA silencing, REGE-1 and RLE-1 appear to associate with target mRNA independently of each other. Thus, although the functional interdependence between REGE-1/Regnase-1 and RLE-1/Roquin-1 is conserved, the underlying mechanisms may display species-specific variation, providing a rare perspective on the evolution of this important post-transcriptional regulatory mechanism.