Advancing Functional Utility of PAR-CLIP by Quantifying Background Binding to mRNAs and lncRNAs
ABSTRACT: We developed a method for measuring non-specific background in PAR-CLIP data demonstrating that covalently crosslinked background binding is common, reproducible and apparently universal. Furthermore, we show that quantitative determination of background is essential for identifying targets of weakly binding RNA-binding proteins and can substantially improve motif analysis. To define background binding events in PAR-CLIP data we performed the standard PAR-CLIP protocol (Hafner et al., Cell 2010.) on lysates expressing a commonly used non-RBP control, FLAG-GFP. After FLAG-tag immunopurification of UV 365nm irradiated lysates prepared from cells supplemented with 4-thiouridine (4SU), RNA was partially digested with RNase T1, radiolabeled and separated by SDS-PAGE. Reads were sequenced by Illumina HiSeq. PAR-CLIP was also performed for HuR. Included as well is a total from lysates treated like PAR-CLIP, but without immunoprecipitation (see sample description for more detail).
Project description:Precise control of mRNA decay is fundamental for robust yet not exaggerated inflammatory responses to pathogens. Parameters determining the specificity and extent of mRNA degradation within the entire inflammation-associated transcriptome remain incompletely understood. Using transcriptome-wide high resolution occupancy assessment of the mRNA-destabilizing protein TTP, a major inflammation-limiting factor, we qualitatively and quantitatively characterize TTP binding positions and functionally relate them to TTP-dependent mRNA decay in immunostimulated macrophages. We identify pervasive TTP binding with incompletely penetrant linkage to mRNA destabilization. A necessary but not sufficient feature of TTP-mediated mRNA destabilization is binding to 3’ untranslated regions (UTRs). Mapping of binding positions of the mRNA-stabilizing protein HuR in activated macrophages revealed that TTP and HuR binding sites in 3’ UTRs occur mostly in different transcripts implicating only a limited co-regulation of inflammatory mRNAs by these proteins. Remarkably, we identify robust and widespread TTP binding to introns of stable transcripts. Nuclear TTP is associated with spliced-out introns and maintained in the nucleus throughout the inflammatory response. Our study establishes a functional annotation of binding positions dictating TTP-dependent mRNA decay in immunostimulated macrophages. The findings allow navigating the transcriptome-wide landscape of RNA elements controlling inflammation. PAR-iCLIP for TTP (3 replicates) and for HuR (2 replicates)
Project description:The conserved human LIN28 RNA-binding proteins function in development, maintenance of pluripotency and oncogenesis. We used PAR-CLIP and a newly developed variant of this method, iDo-PAR-CLIP, to identify LIN28B targets as well as sites bound by the individual RNA binding domains of LIN28B in the human transcriptome at nucleotide resolution. The position of target binding sites reflected the known structural relative orientation of individual LIN28B binding domains, validating iDo-PAR-CLIP. Our data suggest that LIN28B directly interacts with most expressed mRNAs and members of the let-7 microRNA family. The Lin28 binding motif detected in pre-let-7 was enriched in mRNA sequences bound by LIN28B. Upon LIN28B knock down, cell proliferation and the cell cycle were strongly impaired. Quantitative shotgun proteomics of LIN28B depleted cells revealed significant reduction of protein synthesis from its RNA targets that function in translation, mRNA splicing and cell cycle control. Computational analyses provided evidence that the strength of protein synthesis reduction correlated with the location of LIN28B binding sites within target transcripts. We used PAR-CLIP and a newly developed variant of this method, iDo-PAR-CLIP, to identify LIN28B targets as well as sites bound by the individual RNA binding domains of LIN28B in the human transcriptome at nucleotide resolution.
Project description:mRNAs are key molecules in gene expression and subject to diverse regulatory events. Regulation is accomplished by distinct sets of trans-acting factors that interact with mRNAs and form defined mRNA-protein complexes (mRNPs). The resulting “mRNP code” determines the fate of any given mRNA and thus controlling gene expression at the post-transcriptional level. The La-related protein 4B (LARP4B) belongs to an evolutionarily conserved family of RNA binding proteins characterized by the presence of a La-module implicated in direct RNA binding. Biochemical experiments have shown previously direct interactions of LARP4B with factors of the translation machinery. This finding along with the observation of an association with actively translating ribosomes suggested that LARP4B is a factor contributing to the mRNP code. To gain insight into the function of LARP4B in vivo we tested its mRNA association at the transcriptome level and its impact on the proteome. PAR-CLIP analyses allowed us to identify the in vivo RNA targets of LARP4B. We show that LARP4B binds to a distinct set of cellular mRNAs by contacting their 3´UTRs. Biocomputational analysis combined with in vitro binding assays identified the LARP4B binding motif on mRNA targets. The reduction of cellular LARP4B levels leads to a marked destabilization of its mRNA targets and consequently their reduced translation. Our data identify LARP4B as a component of the mRNP code that influences the expression of its mRNA targets by affecting their stability. PAR-CLIP experiments for LARP4B in HEK293cells in two biological replicates
Project description:PAPD5 is one of the seven members of non-canonical poly(A) polymerases in human cells. There are previous reports about polyadenylation dependent degradation of pre-ribosomal RNAs and uridylation dependent degradation of histone mRNAs in vivo. In this study, we observed polyadenylation but not polyuridylation activity of PAPD5 with in vitro assays. We aimed to get genome-wide targets of PAPD5 and used PAR-CLIP and deep sequencing for this purpose. Recombinant version of PAPD5 is expressed in HEK293 human cell lines and its genome wide targets are obtained with PAR-CLIP and deep sequencing as two replicate experiments. The short reads in the deep sequencing libraries of PAPD5 replicates and an unrelated protein to polymerization from a previous study, IGF2BP1, are aligned to the hg18 human genome assembly. The biological variance of the read counts in overlapping 100-nucleotide-long-windows is estimated between the PAPD5 replicates and further used in the differential expression estimations between the 100-nucleotide windows in PAPD5 replicates and IGF2BP1. The top differentially expressed windows in PAPD5 and IGF2BP1 are further annotated using gene and repeat tracks from UCSC.
Project description: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. Close to one third of these proteins, were neither previously annotated nor could be functionally predicted to bind 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 unexpected mRNA-binders with novel molecular functions participating in combinatorial post-transcriptional gene-expression networks. PARCLIP was performed as in Hafner et al. 2010 Cell 141, 129–141, with HEK293 cell lines stably expressing HIS/FLAG/HA-tagged ALKBH5, C17orf85, C22orf28, CAPRIN1, and ZC3H7B. We used 4-thiouridine (4SU) to enhance the crosslink and generated two PAR-CLIP cDNA libraries per protein.
Project description:Dicer is a deeply conserved endoribonuclease with key functions in small RNA biogenesis. Here we employed PAR-CLIP/iPAR-CLIP to identify direct Dicer binding sites in the transcriptomes of human cells and human. We found hundreds of novel miRNAs and non-canonical Dicer substrates with high sensitivity. Small RNA production depended on structure of the binding site and is globally biased towards the 5' arm of hairpins. Unexpectedly, in both species Dicer bound numerous hairpins inside mRNAs without observable small RNA production. Our data revealed ~100 mRNAs of protein coding genes to be targeted in both human and worm. These mRNAs significantly overlapped with the RNAi pathway. We also, unexpectedly, found that mitochondrial transcripts are Dicer targets in both species. We demonstrate functional consequences of Dicer binding by perturbation analysis. Taken together,we provide the first genome-wide catalog of direct Dicer targets. Our results suggest widespread function outside of miRNA biogenesis. PAR-CLIP basically as described previously (Hafner et al. 2010).
Project description:The Photo-Activatable Ribonucleoside-enhanced CrossLinking and ImmunoPrecipitation (PAR-CLIP) method was recently developed for global identification of RNAs interacting with proteins. The strength of this versatile method results from induction of specific T to C transitions at sites of interaction. However, current analytical tools do not distinguish between non-experimentally and experimentally induced transitions. Furthermore, geometric properties at potential binding sites are not taken into account. To surmount these shortcomings, we developed a two-step algorithm consisting of a non-parametric two-component mixture model and a wavelet-based peak calling procedure. Our algorithm can reduce the number of false positives up to 24% thereby identifying high confidence interaction sites. We successfully employed this approach in conjunction with a modified PAR-CLIP protocol to study the functional role of nuclear MOV10, a putative RNA helicase interacting with Argonaute2 and Polycomb. Our method, available as the R package wavClusteR, is generally applicable to any substitution-based inference problem in genomics. The data comprises one MOV10 PAR-CLIP data file and one nuclear RNA-seq file
Project description:Background: In recent years, a variety of small RNAs derived from other RNAs with well-known functions such as tRNAs and snoRNAs, have been identified. The functional relevance of these RNAs is largely unknown. To gain insight into the complexity of snoRNA processing and the functional relevance of snoRNA-derived small RNAs, we sequenced long and short RNAs, small RNAs that co-precipitate with the Argonaute 2 protein and RNA fragments obtained in photoreactive nucleotide-enhanced crosslinking and immunoprecipitation (PAR-CLIP) of core snoRNA-associated proteins. Results: Analysis of these data sets revealed that many loci in the human genome reproducibly give rise to C/D box-like snoRNAs, whose expression and evolutionary conservation are typically less pronounced relative to the snoRNAs that are currently catalogued. We further found that virtually all C/D box snoRNAs are specifically processed inside the regions of terminal complementarity, retaining in the mature form only 4-5 nucleotides upstream of the C box and 2-5 nucleotides downstream of the D box. Sequencing of the total and Argonaute 2-associated populations of small RNAs revealed that despite their cellular abundance, C/D box-derived small RNAs are not efficiently incorporated into the Ago2 protein. Conclusions: We conclude that the human genome encodes a large number of snoRNAs that are processed along the canonical pathway and expressed at relatively low levels. Generation of snoRNA-derived processing products with alternative, particularly miRNA-like, functions appears to be uncommon. PAR-CLIP profiling for snoRNP core proteins NOP56, NOP58, Fibrillarin, and Dyskerin in HEK293 cells. Small RNA profiling using RNA-seq in HEK293 and HeLa cells, small RNA profiling using IP-seq of Ago2 associated small RNAs.
Project description:We employed PAR-CLIP, a recently developed method based on RNA-protein crosslinking, to identify Cirbp and Rbm3 binding sites at transcriptome-level. Genome-wide RNA-seq analysis indicated that cold temperature leads to extensive 3’UTR lengthening whereas the loss of Cirbp or Rbm3 resulted in 3’UTR shortening. Combining with PAR-CLIP results, we found that these two RBPs repress the polyadenylation adjacent to their binding sites. Examination of the binding sites of Cirbp and Rbm3 by PAR-CLIP and their influence on the transcriptome by RNA-seq. PARCLIP was performed as in Hafner et al. 2010 Cell 141, 129–141, with MEFs cell lines stably expressing FLAG-tagged Cirbp and Rbm3. We used 4-thiouridine (4SU) to enhance the crosslink. For RNA-seq, polyadenylated RNA from the mock-transfected cells at 37°C or 32°C with two replicates, siCirbp-1, siCirbp-2, siRbm3-1 and siRbm3-2 MEFs at 37°C were sequenced on Solexa GAII using 76bp single-end kits according to the manufacturer’s instructions.
Project description:We explored the RNA binding properties of LINE-1 ORF1p, both free and in the L1 RNP, using a recently developed photoactivatable-ribonucleoside-enhanced crosslinking and immunoprecipitation technique (PAR-CLIP) to comprehensively identify ORF1p binding sites in the transcriptome of human cells (HEK293T). Our results show that ORF1p binds to a wide range of cellular mRNAs, with an enrichment for binding at the 3’ UTR. Our data also show that ORF1p binds very strongly with retrotransposable RNA, i.e., L1, Alu and SVA. PAR-CLIP analysis of L1 RNPs and free ORF1p RNA binding profiles, comparison to HuR RNA binding profile