mRNA stability and m6A are major determinants of subcellular mRNA localization in neurons.

For cells to perform their biological functions, they need to adopt specific shapes and form functionally distinct subcellular compartments. This is achieved in part via an asymmetric distribution of mRNAs within cells. Currently, the main model of mRNA localization involves specific sequences called "zipcodes" that direct mRNAs to their proper locations. However, while thousands of mRNAs localize within cells, only a few zipcodes have been identified, suggesting that additional mechanisms contribute to localization. Here, we assess the role of mRNA stability in localization by combining the isolation of the soma and neurites of mouse primary cortical and mESC-derived neurons, SLAM-seq, m6A-RIP-seq, the perturbation of mRNA destabilization mechanisms, and the analysis of multiple mRNA localization datasets. We show that depletion of mRNA destabilization elements, such as m6A, AU-rich elements, and suboptimal codons, functions as a mechanism that mediates the localization of mRNAs associated with housekeeping functions to neurites in several types of neurons.

IL-33 controls IL-22-dependent antibacterial defense by modulating the microbiota.

IL-22 plays a critical role in defending against mucosal infections, but how IL-22 production is regulated is incompletely understood. Here, we show that mice lacking IL-33 or its receptor ST2 (IL-1RL1) were more resistant to Streptococcus pneumoniae lung infection than wild-type animals and that single-nucleotide polymorphisms in IL33 and IL1RL1 were associated with pneumococcal pneumonia in humans. The effect of IL-33 on S. pneumoniae infection was mediated by negative regulation of IL-22 production in innate lymphoid cells (ILCs) but independent of ILC2s as well as IL-4 and IL-13 signaling. Moreover, IL-33's influence on IL-22-dependent antibacterial defense was dependent on housing conditions of the mice and mediated by IL-33's modulatory effect on the gut microbiota. Collectively, we provide insight into the bidirectional crosstalk between the innate immune system and the microbiota. We conclude that both genetic and environmental factors influence the gut microbiota, thereby impacting the efficacy of antibacterial immune defense and susceptibility to pneumonia.

Phosphorylation of the Ribosomal Protein RPL12/uL11 Affects Translation during Mitosis.

Emerging evidence indicates that heterogeneity in ribosome composition can give rise to specialized functions. Until now, research mainly focused on differences in core ribosomal proteins and associated factors. The effect of posttranslational modifications has not been studied systematically. Analyzing ribosome heterogeneity is challenging because individual proteins can be part of different subcomplexes (40S, 60S, 80S, and polysomes). Here we develop polysome proteome profiling to obtain unbiased proteomic maps across ribosomal subcomplexes. Our method combines extensive fractionation by sucrose gradient centrifugation with quantitative mass spectrometry. The high resolution of the profiles allows us to assign proteins to specific subcomplexes. Phosphoproteomics on the fractions reveals that phosphorylation of serine 38 in RPL12/uL11, a known mitotic CDK1 substrate, is strongly depleted in polysomes. Follow-up experiments confirm that RPL12/uL11 phosphorylation regulates the translation of specific subsets of mRNAs during mitosis. Together, our results show that posttranslational modification of ribosomal proteins can regulate translation.

The human ZC3H3 and RBM26/27 proteins are critical for PAXT-mediated nuclear RNA decay.

Recruitment of the human ribonucleolytic RNA exosome to nuclear polyadenylated (pA+) RNA is facilitated by the Poly(A) Tail eXosome Targeting (PAXT) connection. Besides its core dimer, formed by the exosome co-factor MTR4 and the ZFC3H1 protein, the PAXT connection remains poorly defined. By characterizing nuclear pA+-RNA bound proteomes as well as MTR4-ZFC3H1 containing complexes in conditions favoring PAXT assembly, we here uncover three additional proteins required for PAXT function: ZC3H3, RBM26 and RBM27 along with the known PAXT-associated protein, PABPN1. The zinc-finger protein ZC3H3 interacts directly with MTR4-ZFC3H1 and loss of any of the newly identified PAXT components results in the accumulation of PAXT substrates. Collectively, our results establish new factors involved in the turnover of nuclear pA+ RNA and suggest that these are limiting for PAXT activity.

DDX54 regulates transcriptome dynamics during DNA damage response.

The cellular response to genotoxic stress is mediated by a well-characterized network of DNA surveillance pathways. The contribution of post-transcriptional gene regulatory networks to the DNA damage response (DDR) has not been extensively studied. Here, we systematically identified RNA-binding proteins differentially interacting with polyadenylated transcripts upon exposure of human breast carcinoma cells to ionizing radiation (IR). Interestingly, more than 260 proteins, including many nucleolar proteins, showed increased binding to poly(A)+ RNA in IR-exposed cells. The functional analysis of DDX54, a candidate genotoxic stress responsive RNA helicase, revealed that this protein is an immediate-to-early DDR regulator required for the splicing efficacy of its target IR-induced pre-mRNAs. Upon IR exposure, DDX54 acts by increased interaction with a well-defined class of pre-mRNAs that harbor introns with weak acceptor splice sites, as well as by protein-protein contacts within components of U2 snRNP and spliceosomal B complex, resulting in lower intron retention and higher processing rates of its target transcripts. Because DDX54 promotes survival after exposure to IR, its expression and/or mutation rate may impact DDR-related pathologies. Our work indicates the relevance of many uncharacterized RBPs potentially involved in the DDR.

The mRNA-bound proteome and its global occupancy profile on protein-coding transcripts.

Protein-RNA interactions are fundamental to core biological processes, such as mRNA splicing, localization, degradation, and translation. We developed a photoreactive nucleotide-enhanced UV crosslinking and oligo(dT) purification approach to identify the mRNA-bound proteome using quantitative proteomics and to display the protein occupancy on mRNA transcripts by next-generation sequencing. Application to a human embryonic kidney cell line identified close to 800 proteins. To our knowledge, nearly one-third were not previously annotated as RNA binding, and about 15% were not predictable by computational methods to interact with RNA. Protein occupancy profiling provides a transcriptome-wide catalog of potential cis-regulatory regions on mammalian mRNAs and showed that large stretches in 3' UTRs can be contacted by the mRNA-bound proteome, with numerous putative binding sites in regions harboring disease-associated nucleotide polymorphisms. Our observations indicate the presence of a large number of mRNA binders with diverse molecular functions participating in combinatorial posttranscriptional gene-expression networks.

Expanding the map of protein-RNA interaction sites via cell fusion followed by PAR-CLIP.

PAR-CLIP (photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation) facilitates the identification and mapping of protein/RNA interactions. So far, it has been limited to select cell-lines as it requires efficient 4SU uptake. To increase transcriptome complexity and thus identify additional RNA-protein interaction sites we fused HEK 293 T-Rex cells (HEK293-Y) that express the RNA binding protein YBX1 with PC12 cells expressing eGFP (PC12-eGFP). The resulting hybrids enable PAR-CLIP on a neuronally expanded transcriptome (Fusion-CLIP) and serve as a proof of principle. The fusion cells express both parental marker genes YBX1 and eGFP and the expanded transcriptome contains human and rat transcripts. PAR-CLIP of fused cells versus the parental HEK293-Y identified 768 novel RNA targets of YBX1. We were able to trace the origin of the majority of the short PAR-CLIP reads as they differentially mapped to the human and rat genome. Furthermore, Fusion-CLIP expanded the CAUC RNA binding motif of YBX1 to UCUUUNNCAUC. The fusion of HEK293-Y and PC12-eGFP cells resulted in cells with a diverse genome expressing human and rat transcripts that enabled the identification of novel YBX1 substrates. The technique allows the expansion of the HEK 293 transcriptome and makes PAR-CLIP available to fusion cells of diverse origin.

Transcriptome-wide analysis of protein-RNA interactions using high-throughput sequencing.

Protein-RNA interactions are emerging as an important functional element in the regulation of gene expression. Cross-linking of proteins to RNA by UV irradiation followed by immunoprecipitation (CLIP) has provided a crucial tool for research in this field. Initially, the bottleneck of the method was the relatively low number of identified RNA binding sites. It was only the arrival of next-generation sequencing that allowed a comprehensive and unbiased description of the cross-linked protein-RNA fragments. Here, we summarize recent progress in the study of protein-RNA interactions, as well as some of the important findings obtained using different CLIP approaches in cultured cells and organisms. These efforts allowed the identification of functional RNA-binding sites for a wide range of RNA-interacting proteins. Experimental and bioinformatic progress will further advance this dynamic area of research. The combination of high-resolution protein-RNA interaction maps with transcriptome-wide data describing the stability, modifications and structures of RNAs, in addition to protein expression profiling, will provide deeper insight into post-transcriptional and translational regulatory events and mechanisms.

Transcriptome analysis reveals involvement of thiopurine S-methyltransferase in oxidation-reduction processes.

Thiopurine S-methyltransferase (TPMT) is an important enzyme involved in the deactivation of thiopurines and represents a major determinant of thiopurine-related toxicities. Despite its well-known importance in thiopurine metabolism, the understanding of its endogenous role is lacking. In the present study, we aimed to gain insight into the molecular processes involving TPMT by applying a data fusion approach to analyze whole-genome expression data. The RNA profiling was done on whole blood samples from 1017 adult male and female donors to the Estonian biobank using Illumina HTv3 arrays. Our results suggest that TPMT is closely related to genes involved in oxidoreductive processes. The in vitro experiments on different cell models confirmed that TPMT influences redox capacity of the cell by altering S-adenosylmethionine (SAM) consumption and consequently glutathione (GSH) synthesis. Furthermore, by comparing gene networks of subgroups of individuals, we identified genes, which could have a role in regulating TPMT activity. The biological relevance of identified genes and pathways will have to be further evaluated in molecular studies.

Robust detection of clinically relevant features in single-cell RNA profiles of patient-matched fresh and formalin-fixed paraffin-embedded (FFPE) lung cancer tissue.

PURPOSE: Single-cell transcriptional profiling reveals cell heterogeneity and clinically relevant traits in intra-operatively collected patient-derived tissue. So far, single-cell studies have been constrained by the requirement for prospectively collected fresh or cryopreserved tissue. This limitation might be overcome by recent technical developments enabling single-cell analysis of FFPE tissue. METHODS: We benchmark single-cell profiles from patient-matched fresh, cryopreserved and archival FFPE cancer tissue. RESULTS: We find that fresh tissue and FFPE routine blocks can be employed for the robust detection of clinically relevant traits on the single-cell level. Specifically, single-cell maps of fresh patient tissues and corresponding FFPE tissue blocks could be integrated into common low-dimensional representations, and cell subtype clusters showed highly correlated transcriptional strengths of signaling pathway, hallmark, and clinically useful signatures, although expression of single genes varied due to technological differences. FFPE tissue blocks revealed higher cell diversity compared to fresh tissue. In contrast, single-cell profiling of cryopreserved tissue was prone to artifacts in the clinical setting. CONCLUSION: Our analysis highlights the potential of single-cell profiling in the analysis of retrospectively and prospectively collected archival pathology cohorts and increases the applicability in translational research.

Clinically used broad-spectrum antibiotics compromise inflammatory monocyte-dependent antibacterial defense in the lung.

Hospital-acquired pneumonia (HAP) is associated with high mortality and costs, and frequently caused by multidrug-resistant (MDR) bacteria. Although prior antimicrobial therapy is a major risk factor for HAP, the underlying mechanism remains incompletely understood. Here, we demonstrate that antibiotic therapy in hospitalized patients is associated with decreased diversity of the gut microbiome and depletion of short-chain fatty acid (SCFA) producers. Infection experiments with mice transplanted with patient fecal material reveal that these antibiotic-induced microbiota perturbations impair pulmonary defense against MDR Klebsiella pneumoniae. This is dependent on inflammatory monocytes (IMs), whose fatty acid receptor (FFAR)2/3-controlled and phagolysosome-dependent antibacterial activity is compromized in mice transplanted with antibiotic-associated patient microbiota. Collectively, we characterize how clinically relevant antibiotics affect antimicrobial defense in the context of human microbiota, and reveal a critical impairment of IM´s antimicrobial activity. Our study provides additional arguments for the rational use of antibiotics and offers mechanistic insights for the development of novel prophylactic strategies to protect high-risk patients from HAP.

HDLBP binds ER-targeted mRNAs by multivalent interactions to promote protein synthesis of transmembrane and secreted proteins.

The biological role of RNA-binding proteins in the secretory pathway is not well established. Here, we describe that human HDLBP/Vigilin directly interacts with more than 80% of ER-localized mRNAs. PAR-CLIP analysis reveals that these transcripts represent high affinity HDLBP substrates and are specifically bound in their coding sequences (CDS), in contrast to CDS/3'UTR-bound cytosolic mRNAs. HDLBP crosslinks strongly to long CU-rich motifs, which frequently reside in CDS of ER-localized mRNAs and result in high affinity multivalent interactions. In addition to HDLBP-ncRNA interactome, quantification of HDLBP-proximal proteome confirms association with components of the translational apparatus and the signal recognition particle. Absence of HDLBP results in decreased translation efficiency of HDLBP target mRNAs, impaired protein synthesis and secretion in model cell lines, as well as decreased tumor growth in a lung cancer mouse model. These results highlight a general function for HDLBP in the translation of ER-localized mRNAs and its relevance for tumor progression.

CRNKL1 Is a Highly Selective Regulator of Intron-Retaining HIV-1 and Cellular mRNAs.

The HIV-1 Rev protein is a nuclear export factor for unspliced and incompletely spliced HIV-1 RNAs. Without Rev, these intron-retaining RNAs are trapped in the nucleus. A genome-wide screen identified nine proteins of the spliceosome, which all enhanced expression from the HIV-1 unspliced RNA after CRISPR/Cas knockdown. Depletion of DHX38, WDR70, and four proteins of the Prp19-associated complex (ISY1, BUD31, XAB2, and CRNKL1) resulted in a more than 20-fold enhancement of unspliced HIV-1 RNA levels in the cytoplasm. Targeting of CRNKL1, DHX38, and BUD31 affected nuclear export efficiencies of the HIV-1 unspliced RNA to a much larger extent than splicing. Transcriptomic analyses further revealed that CRNKL1 also suppresses cytoplasmic levels of a subset of cellular mRNAs, including some with selectively retained introns. Thus, CRNKL1-dependent nuclear retention is a novel cellular mechanism for the regulation of cytoplasmic levels of intron-retaining HIV-1 mRNAs, which HIV-1 may have harnessed to direct its complex splicing pattern.IMPORTANCE To regulate its complex splicing pattern, HIV-1 uses the adaptor protein Rev to shuttle unspliced or partially spliced mRNA from the nucleus to the cytoplasm. In the absence of Rev, these RNAs are retained in the nucleus, but it is unclear why. Here we identify cellular proteins whose depletion enhances cytoplasmic levels of the HIV-1 unspliced RNA. Depletion of one of them, CRNKL1, also increases cytoplasmic levels of a subset of intron-retaining cellular mRNA, suggesting that CRNKL1-dependent nuclear retention may be a basic cellular mechanism exploited by HIV-1.

Loss of m1acp3Ψ Ribosomal RNA Modification Is a Major Feature of Cancer.

The ribosome is an RNA-protein complex that is essential for translation in all domains of life. The structural and catalytic core of the ribosome is its ribosomal RNA (rRNA). While mutations in ribosomal protein (RP) genes are known drivers of oncogenesis, oncogenic rRNA variants have remained elusive. We identify a cancer-specific single-nucleotide variation in 18S rRNA at nucleotide 1248.U in up to 45.9% of patients with colorectal carcinoma (CRC) and present across >22 cancer types. This is the site of a unique hyper-modified base, 1-methyl-3-α-amino-α-carboxyl-propyl pseudouridine (m1acp3Ψ), a >1-billion-years-conserved RNA modification at the peptidyl decoding site of the ribosome. A subset of CRC tumors we call hypo-m1acp3Ψ shows sub-stoichiometric m1acp3Ψ modification, unlike normal control tissues. An m1acp3Ψ knockout model and hypo-m1acp3Ψ patient tumors share a translational signature characterized by highly abundant ribosomal proteins. Thus, m1acp3Ψ-deficient rRNA forms an uncharacterized class of "onco-ribosome" which may serve as a chemotherapeutic target for treating cancer patients.

Surface active stabilizer tyloxapol in colloidal dispersions exerts cytostatic effects and apoptotic dismissal of cells.

Solid lipid nanoparticles (SLN) have been praised for their advantageous drug delivery properties such as biocompatibility, controlled release and passive drug targeting. However, the cytotoxicity of SLN and their ingredients, especially over a longer time period, has not been investigated in detail. We examined the critical issues regarding the use of a surface active stabilizer Tyloxapol (Tyl) for the preparation of solid lipid particles (SLP) and their effects on cellular functions and viability. SLP composed of behenate, phospholipids and a stabilizer, Tyloxapol or Lutrol (Lut), were prepared by the lipid melt method, labeled with a fluorescent dye and tested on Jurkat or HEK293 cells. The nano-sized particles were rapidly internalized and exhibited cytoplasmic localization. Incubation of cells with SLP-Tyl resulted in a dose- and time-dependent cytostatic effect, and also caused moderate and delayed cytotoxicity. Tyloxapol solution or SLP-Tyl dispersion caused the detachment of HEK293 cells, a decrease in cell proliferation and alterations in cellular morphology. Cell cycle analysis revealed that, while the unfavourable effects of SLP-Tyl and Tyloxapol solution are similar initially, longer incubation results in partial recovery of cells incubated with the dispersion of SLP-Tyl, whereas the presence of Tyloxapol solution induces apoptotic cell death. These findings indicate that Tyloxapol is an unfavourable stabilizer of SLP used for intracellular delivery and reinforce the role of stabilizers in a design of SLP with minimal cytotoxic properties.

A novel gene delivery system for stable transfection of thiopurine-S-methyltransferase gene in versatile cell types.

A novel gene delivery system termed artificial viral particles (AVPs) containing a plasmid coding for a recombinant fusion protein of enhanced green fluorescent protein (EGFP) with thiopurine-S-methyltransferase (TPMT) was designed for transfection of selected cell lines to establish stable clones which express recombinant EGFP-TPMT protein for further in vitro investigation of toxic effect of thiopurine drugs. Various AVPs based on a complex of the cationic polymer polyethylenimine (PEI) and anionic liposomes were formulated and transfection conditions were adapted in order to transfect the human Jurkat, HepG2 and HEK 293 cell lines. An adequate transfection rate was achieved with AVP containing branched low molecular weight PEI at a PEI:DNA charge ratio of 4.5:1 and liposomes composed of DOPS, DLPE, cholesterol and an activated N-glutaryl-DOPE membrane anchor. Stably transfected clones were successfully established and expression of recombinant EGFP-TPMT in homogeneous cell populations was demonstrated by flow cytometry, fluorescence microscopy and immunoblotting. The level of the expressed protein in stable clones was highest in HEK 293, followed by HepG2 and Jurkat. The enzymatic activity of the TPMT moiety was demonstrated by decreased sensitivity to 6-thioguanine and increased sensitivity to 6-mercaptopurine in HEK 293 cells expressing EGFP-TPMT. Formulation of AVP as transfection vector succeeded in establishing human cell lines stably expressing EGFP-TPMT, thereby proving a successful delivery system and providing an initial step to enable investigation of the role of the clinically important drug metabolizing enzyme TPMT.

Systematic Detection of Poly(A)+ RNA-Interacting Proteins and Their Differential Binding.

RNA-binding proteins are dynamic posttranscriptional regulators of gene expression. Identification of mRNA-binding proteins in a given experimental setting is thus of great importance. We describe a procedure to enrich for direct poly(A)+ RNA protein binders by 4-thiouridine-enhanced UV cross-linking and oligo(dT) purification. Subsequent nuclease-mediated release of RNA-binding proteins (RBPs) from mRNA allows for detection of eluted proteins by mass spectrometry. In addition, we provide a comparative approach to detect differences in RBP binding activity upon a biological stimulus.

Association of ITPA genotype with event-free survival and relapse rates in children with acute lymphoblastic leukemia undergoing maintenance therapy.

Although the treatment of acute lymphoblastic leukemia (ALL) has improved significantly over recent decades, failure due to treatment-related toxicities and relapse of the disease still occur in about 20% of patients. This retrospective study included 308 pediatric ALL patients undergoing maintenance therapy and investigated the effects of genetic variants of enzymes involved in the 6-mercaptopurine (6-MP) metabolism and folate pathway on survival and relapse rates. The presence of at least one of the non-functional ITPA alleles (94C>A and/or IVS2+21A>C variant) was associated with longer event-free survival compared to patients with the wild-type ITPA genotype (p = 0.033). Furthermore, patients carrying at least one non-functional ITPA allele were shown to be at a lower risk of suffering early (p = 0.003) and/or bone marrow relapse (p = 0.017). In conclusion, the ITPA genotype may serve as a genetic marker for the improvement of risk stratification and therapy individualization for patients with ALL.

Post-translational stabilization of thiopurine S-methyltransferase by S-adenosyl-L-methionine reveals regulation of TPMT*1 and *3C allozymes.

Thiopurine S-methyltransferase (TPMT; EC 2.1.1.67) plays a pivotal role in thiopurine treatment outcomes. However, little has been known about its intracellular regulation. Here, we describe the effect of fluctuations in physiological levels of S-adenosyl-L-methionine (SAM) and related metabolites on TPMT activity levels in cell lines and erythrocytes from healthy donors. We determined higher TPMT activity in wild-type TPMT*1/*1 individuals with high SAM concentrations (n=96) compared to the low SAM level group (n=19; P<0.001). These findings confirm the results of our in vitro studies, which demonstrated that the restriction of L-methionine (Met) in cell growth media reversibly decreased TPMT activity and protein levels. Selective inhibition of distinct components of Met metabolism was used to demonstrate that SAM is implicitly responsible for direct post-translational TPMT stabilization. The greatest effect of SAM-mediated TPMT stabilization was observed in the case of wild-type TPMT*1 and variant *3C allozymes. In addition to TPMT genotyping, SAM may serve as an important biochemical marker in individualization of thiopurine therapy.

MTHFR and TYMS genotypes influence TPMT activity and its differential modulation in males and females.

OBJECTIVES: TPMT catalyzes the deactivation of the cytostatic drug 6-mercaptopurine used in treatment of cancer. Patients with low levels of TPMT more often experience severe toxic effects when treated with standard doses of 6-mercaptopurine than patients with high levels who, in turn, may experience inadequate treatment. It is therefore very important to assess factors that could influence TPMT activity. DESIGN AND METHODS: Red blood cell TPMT activity was measured by means of HPLC and genotypes of 86 healthy individuals were analyzed using TaqMan and PCR-RFLP methods, in order to investigate the effect of TPMT, MTHFR and TYMS genotypes on TPMT activity. RESULTS: TPMT activity was higher in TPMT wild-type males than females (p=0.028). Three-way ANOVA interaction analysis revealed a significant interaction effect between MTHFR genotype and gender on TPMT activity (p=0.023). CONCLUSION: Males have higher TPMT activity than females and the trend of influence of MTHFR genotype on TPMT activity is different in the two gender groups.