Y-Box-Binding Proteins Have a Dual Impact on Cellular Translation.

Y-box-binding proteins (YB proteins) are multifunctional DNA- and RNA-binding proteins that play an important role in the regulation of gene expression. The high homology of their cold shock domains and the similarity between their long, unstructured C-terminal domains suggest that Y-box-binding proteins may have similar functions in a cell. Here, we consider the functional interchangeability of the somatic YB proteins YB-1 and YB-3. RNA-seq and Ribo-seq are used to track changes in the mRNA abundance or mRNA translation in HEK293T cells solely expressing YB-1, YB-3, or neither of them. We show that YB proteins have a dual effect on translation. Although the expression of YB proteins stimulates global translation, YB-1 and YB-3 inhibit the translation of their direct CLIP-identified mRNA targets. The impact of YB-1 and YB-3 on the translation of their mRNA targets is similar, which suggests that they can substitute each other in inhibiting the translation of their mRNA targets in HEK293T cells.

HOCOMOCO in 2024: a rebuild of the curated collection of binding models for human and mouse transcription factors.

We present a major update of the HOCOMOCO collection that provides DNA binding specificity patterns of 949 human transcription factors and 720 mouse orthologs. To make this release, we performed motif discovery in peak sets that originated from 14 183 ChIP-Seq experiments and reads from 2554 HT-SELEX experiments yielding more than 400 thousand candidate motifs. The candidate motifs were annotated according to their similarity to known motifs and the hierarchy of DNA-binding domains of the respective transcription factors. Next, the motifs underwent human expert curation to stratify distinct motif subtypes and remove non-informative patterns and common artifacts. Finally, the curated subset of 100 thousand motifs was supplied to the automated benchmarking to select the best-performing motifs for each transcription factor. The resulting HOCOMOCO v12 core collection contains 1443 verified position weight matrices, including distinct subtypes of DNA binding motifs for particular transcription factors. In addition to the core collection, HOCOMOCO v12 provides motif sets optimized for the recognition of binding sites in vivo and in vitro, and for annotation of regulatory sequence variants. HOCOMOCO is available at https://hocomoco12.autosome.org and https://hocomoco.autosome.org.

RNA-Seq data of ALKBH5 and FTO double knockout HEK293T human cells.

N6-methyladenosine (m6A) is the most abundant, highly dynamic mRNA modification that regulates mRNA splicing, stability, and translation. The m6A epigenetic mark is erased by RNA demethylases ALKBH5 (AlkB Homolog 5) and FTO (Fat mass and obesity-associated protein). The ALKBH5 and FTO RNA demethylases recognize m6A in similar nucleotide contexts. Therefore, these proteins can partially substitute for each other. To assess the impact of total m6A demethylation failure we performed high-throughput sequencing of cytoplasmic RNA from ALKBH5 and FTO double knockout and wild type HEK293T cells. The RNA-Seq libraries were sequenced on Illumina NextSeq 500, trimmed, and mapped to the human genome. The consequent read counting and differential expression analysis in the R environment detected 5871 differentially expressed and 166 alternatively spliced genes comparing double knockout against wild type HEK293T cells. Raw data are deposited in NCBI Gene Expression Omnibus (GEO) repository under GEO accession GSE198050.

Diverse Regulation of YB-1 and YB-3 Abundance in Mammals.

YB proteins are DNA/RNA binding proteins, members of the family of proteins with cold shock domain. Role of YB proteins in the life of cells, tissues, and whole organisms is extremely important. They are involved in transcription regulation, pre-mRNA splicing, mRNA translation and stability, mRNA packaging into mRNPs, including stress granules, DNA repair, and many other cellular events. Many processes, from embryonic development to aging, depend on when and how much of these proteins have been synthesized. Here we discuss regulation of the levels of YB-1 and, in part, of its homologs in the cell. Because the amount of YB-1 is immediately associated with its functioning, understanding the mechanisms of regulation of the protein amount invariably reveals the events where YB-1 is involved. Control over the YB-1 abundance may allow using this gene/protein as a therapeutic target in cancers, where an increased expression of the YBX1 gene often correlates with the disease severity and poor prognosis.

Enhanced C/EBP binding to G·T mismatches facilitates fixation of CpG mutations in cancer and adult stem cells.

Somatic mutations in regulatory sites of human stem cells affect cell identity or cause malignant transformation. By mining the human genome for co-occurrence of mutations and transcription factor binding sites, we show that C/EBP binding sites are strongly enriched with [C > T]G mutations in cancer and adult stem cells, which is of special interest because C/EBPs regulate cell fate and differentiation. In vitro protein-DNA binding assay and structural modeling of the CEBPB-DNA complex show that the G·T mismatch in the core CG dinucleotide strongly enhances affinity of the binding site. We conclude that enhanced binding of C/EBPs shields CpG·TpG mismatches from DNA repair, leading to selective accumulation of [C > T]G mutations and consequent deterioration of the binding sites. This mechanism of targeted mutagenesis highlights the effect of a mutational process on certain regulatory sites and reveals the molecular basis of putative regulatory alterations in stem cells.

Assessing Ribosome Distribution Along Transcripts with Polarity Scores and Regression Slope Estimates.

During translation, the rate of ribosome movement along mRNA varies. This leads to a non-uniform ribosome distribution along the transcript, depending on local mRNA sequence, structure, tRNA availability, and translation factor abundance, as well as the relationship between the overall rates of initiation, elongation, and termination. Stress, antibiotics, and genetic perturbations affecting composition and properties of translation machinery can alter the ribosome positional distribution dramatically. Here, we offer a computational protocol for analyzing positional distribution profiles using ribosome profiling (Ribo-Seq) data. The protocol uses papolarity, a new Python toolkit for the analysis of transcript-level short read coverage profiles. For a single sample, for each transcript papolarity allows for computing the classic polarity metric which, in the case of Ribo-Seq, reflects ribosome positional preferences. For comparison versus a control sample, papolarity estimates an improved metric, the relative linear regression slope of coverage along transcript length. This involves de-noising by profile segmentation with a Poisson model and aggregation of Ribo-Seq coverage within segments, thus achieving reliable estimates of the regression slope. The papolarity software and the associated protocol can be conveniently used for Ribo-Seq data analysis in the command-line Linux environment. Papolarity package is available through Python pip package manager. The source code is available at https://github.com/autosome-ru/papolarity .

YB-1 Phosphorylation at Serine 209 Inhibits Its Nuclear Translocation.

YB-1 is a multifunctional DNA- and RNA-binding protein involved in cell proliferation, differentiation, and migration. YB-1 is a predominantly cytoplasmic protein that is transported to the nucleus in certain conditions, including DNA-damaging stress, transcription inhibition, and viral infection. In tumors, YB-1 nuclear localization correlates with high aggressiveness, multidrug resistance, and a poor prognosis. It is known that posttranslational modifications can regulate the nuclear translocation of YB-1. In particular, well-studied phosphorylation at serine 102 (S102) activates YB-1 nuclear import. Here, we report that Akt kinase phosphorylates YB-1 in vitro at serine 209 (S209), which is located in the vicinity of the YB-1 nuclear localization signal. Using phosphomimetic substitutions, we showed that S209 phosphorylation inhibits YB-1 nuclear translocation and prevents p-S102-mediated YB-1 nuclear import.

The Reduced Level of Inorganic Polyphosphate Mobilizes Antioxidant and Manganese-Resistance Systems in Saccharomyces cerevisiae.

Inorganic polyphosphate (polyP) is crucial for adaptive reactions and stress response in microorganisms. A convenient model to study the role of polyP in yeast is the Saccharomyces cerevisiae strain CRN/PPN1 that overexpresses polyphosphatase Ppn1 with stably decreased polyphosphate level. In this study, we combined the whole-transcriptome sequencing, fluorescence microscopy, and polyP quantification to characterize the CRN/PPN1 response to manganese and oxidative stresses. CRN/PPN1 exhibits enhanced resistance to manganese and peroxide due to its pre-adaptive state observed in normal conditions. The pre-adaptive state is characterized by up-regulated genes involved in response to an external stimulus, plasma membrane organization, and oxidation/reduction. The transcriptome-wide data allowed the identification of particular genes crucial for overcoming the manganese excess. The key gene responsible for manganese resistance is PHO84 encoding a low-affinity manganese transporter: Strong PHO84 down-regulation in CRN/PPN1 increases manganese resistance by reduced manganese uptake. On the contrary, PHM7, the top up-regulated gene in CRN/PPN1, is also strongly up-regulated in the manganese-adapted parent strain. Phm7 is an unannotated protein, but manganese adaptation is significantly impaired in Δphm7, thus suggesting its essential function in manganese or phosphate transport.

Inhibition of Transcription Induces Phosphorylation of YB-1 at Ser102 and Its Accumulation in the Nucleus.

The Y-box binding protein 1 (YB-1) is an RNA/DNA-binding protein regulating gene expression in the cytoplasm and the nucleus. Although mostly cytoplasmic, YB-1 accumulates in the nucleus under stress conditions. Its nuclear localization is associated with aggressiveness and multidrug resistance of cancer cells, which makes the understanding of the regulatory mechanisms of YB-1 subcellular distribution essential. Here, we report that inhibition of RNA polymerase II (RNAPII) activity results in the nuclear accumulation of YB-1 accompanied by its phosphorylation at Ser102. The inhibition of kinase activity reduces YB-1 phosphorylation and its accumulation in the nucleus. The presence of RNA in the nucleus is shown to be required for the nuclear retention of YB-1. Thus, the subcellular localization of YB-1 depends on its post-translational modifications (PTMs) and intracellular RNA distribution.

Transportin-1-dependent YB-1 nuclear import.

The DNA/RNA-binding protein YB-1 (Y-box binding protein 1) performs multiple functions both in the cytoplasm and the nucleus of the cell. Generally localized to the cytoplasm, under certain conditions YB-1 is translocated to the nucleus. Here we report for the first time a transport factor that mediates YB-1 nuclear import - transportin-1. The YB-1/transportin-1 complex can be isolated from HeLa cell extract. Nuclear import of YB-1 and its truncated form YB-1 (1-219) in in vitro transport assay was diminished in the presence of a competitor substrate and ceased in the presence of transportin-1 inhibitor M9M. Inhibitors of importin ß1 had no effect on YB-1 transport. Furthermore, transport of YB-1 (P201A/Y202A) and YB-1 (1-219) (P201A/Y202A) bearing inactivating mutations in the transportin-1-dependent nuclear localization signal was practically abolished. Together, these results indicate that transportin-1 mediates YB-1 nuclear translocation.

Negative selection maintains transcription factor binding motifs in human cancer.

BACKGROUND: Somatic mutations in cancer cells affect various genomic elements disrupting important cell functions. In particular, mutations in DNA binding sites recognized by transcription factors can alter regulator binding affinities and, consequently, expression of target genes. A number of promoter mutations have been linked with an increased risk of cancer. Cancer somatic mutations in binding sites of selected transcription factors have been found under positive selection. However, action and significance of negative selection in non-coding regions remain controversial. RESULTS: Here we present analysis of transcription factor binding motifs co-localized with non-coding variants. To avoid statistical bias we account for mutation signatures of different cancer types. For many transcription factors, including multiple members of FOX, HOX, and NR families, we show that human cancers accumulate fewer mutations than expected by chance that increase or decrease affinity of predicted binding sites. Such stability of binding motifs is even more exhibited in DNase accessible regions. CONCLUSIONS: Our data demonstrate negative selection against binding sites alterations and suggest that such selection pressure protects cancer cells from rewiring of regulatory circuits. Further analysis of transcription factors with conserved binding motifs can reveal cell regulatory pathways crucial for the survivability of various human cancers.

Architectural proteins Pita, Zw5,and ZIPIC contain homodimerization domain and support specific long-range interactions in Drosophila.

According to recent models, as yet poorly studied architectural proteins appear to be required for local regulation of enhancer-promoter interactions, as well as for global chromosome organization. Transcription factors ZIPIC, Pita and Zw5 belong to the class of chromatin insulator proteins and preferentially bind to promoters near the TSS and extensively colocalize with cohesin and condensin complexes. ZIPIC, Pita and Zw5 are structurally similar in containing the N-terminal zinc finger-associated domain (ZAD) and different numbers of C2H2-type zinc fingers at the C-terminus. Here we have shown that the ZAD domains of ZIPIC, Pita and Zw5 form homodimers. In Drosophila transgenic lines, these proteins are able to support long-distance interaction between GAL4 activator and the reporter gene promoter. However, no functional interaction between binding sites for different proteins has been revealed, suggesting that such interactions are highly specific. ZIPIC facilitates long-distance stimulation of the reporter gene by GAL4 activator in yeast model system. Many of the genomic binding sites of ZIPIC, Pita and Zw5 are located at the boundaries of topologically associated domains (TADs). Thus, ZAD-containing zinc-finger proteins can be attributed to the class of architectural proteins.

Alternative forms of Y-box binding protein 1 and YB-1 mRNA.

The multifunctional eukaryotic protein YB-1 (Y-box binding protein 1) plays a role in DNA reparation, transcription regulation, splicing, and mRNA translation, thereby participating in many crucial events in cells. Its effect is dependent mostly on its amount, and hence, on regulation of its synthesis. Published data on regulation of synthesis of YB-1 mediated by its mRNA 5' UTR, and specifically on the 5' UTR length and the presence of TOP-like motifs in this region, are contradictory. Here we report that 5' UTRs of major forms of human, rabbit, and mouse YB-1 mRNAs are about 140 nucleotides long and contain no TOP-like motifs mentioned in the literature. Also, we have found that YB-1 specifically interacts with the 5' UTR of its own mRNA within a region of about 100 nucleotides upstream from the start codon. Apart from YB-1, translation of YB-1 mRNA in a cell free system gives an additional product with an extended N-terminus and lower electrophoretic mobility. The start codon for synthesis of the additional product is AUC at position -(60-58) of the same open reading frame as that for the major product. Also, in the cell there is an alternative YB-1 mRNA with exon 1 replaced by a part of intron 1; YB-1 synthesized in vitro from this mRNA contains, instead of its N-terminal A/P domain, 10-11 amino acids encoded by intron 1.

How to determine the size of folding nuclei of protofibrils from the concentration dependence of the rate and lag-time of aggregation. II. Experimental application for insulin and LysPro insulin: aggregation morphology, kinetics, and sizes of nuclei.

Insulin is a commonly used protein for studies of amyloidogenesis. There are a few insulin analogues with different pharmacokinetic characteristics, in particular the onset and duration of action. One of them is LysPro insulin. The behavior of LysPro insulin in the process of amyloid formation has not been studied in detail yet. To quantitatively investigate the differences between insulin and LysPro insulin in the aggregation reaction, we used thioflavin T fluorescence assay, electron microscopy, X-ray diffraction methods, and theoretical modeling. Kinetic experimental data for both insulin samples demonstrated the increase of the lag-time for LysPro insulin at low concentrations of monomers, particularly at 2 and 4 mg/mL, which corresponds to the pharmaceutical concentration. However, the morphology of insulin and LysPro insulin fibrils and their X-ray diffraction patterns is identical. Mature fibrils reach 10-12 µm in length and about 3-4 nm in diameter. The obtained analytical solution allow us to determine the sizes of the primary and secondary nuclei from the experimentally obtained concentration dependences of the time of growth and the ratio of the lag-time duration to the time of growth of amyloid protofibrils. In the case of insulin and LysPro insulin, we have exponential growth of amyloid protofibrils following the "bifurcation + lateral growth" scenario. In accord with the developed theory and the experimental data, we obtained that the size of the primary nucleus is equal to one monomer and the size of the secondary nucleus is zero in both insulin and LysPro insulin.

YB-1 protein: functions and regulation.

The Y-box binding protein 1 (YB-1, YBX1) is a member of the family of DNA- and RNA-binding proteins with an evolutionarily ancient and conserved cold shock domain. It falls into a group of intrinsically disordered proteins that do not follow the classical rule 'one protein-one function' but introduce a novel principle stating that a disordered structure suggests many functions. YB-1 participates in a wide variety of DNA/RNA-dependent events, including DNA reparation, pre-mRNA transcription and splicing, mRNA packaging, and regulation of mRNA stability and translation. At the cell level, the multiple activities of YB-1 are manifested as its involvement in cell proliferation and differentiation, stress response, and malignant cell transformation. WIREs RNA 2014, 5:95-110. doi: 10.1002/wrna.1200 CONFLICT OF INTEREST: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

Specific PABP effect on translation of YB-1 mRNA is neutralized by polyadenylation through a "mini-loop" at 3' UTR.

YB-1 is a multifunctional cold shock domain containing protein that is involved virtually in all DNA- and mRNA-dependent cellular events. Its amount is regulated at the level of both transcription and translation. We showed previously that translation of poly A(-) YB-1 mRNA in vitro is selectively controlled by two proteins, YB-1 and PABP, through their specific and competitive binding to a regulatory element (RE) within 3' UTR of this mRNA. Here, we describe effects of these two proteins on translation of poly A(+) as compared with poly A(-) YB-1 mRNA in a rabbit reticulocyte cell-free translation system. We have found that YB-1 inhibits translation of both poly A(+) and poly A(-) YB-1 mRNAs at the same comparatively low YB-1/mRNA ratio. PABP has no positive effect on translation of poly A(+) YB-1 mRNA, although it has a stimulating effect on translation of poly A(-) YB-1 mRNA. A positive PABP effect on translation of poly A(+) YB-1 mRNA arose after removal of a portion of the sequence between RE and the poly(A) tail and disappeared after its replacement by another non-specific sequence of the same length. We also report that the RE fragment forms a complex with the poly(A) fragment in the presence of rabbit reticulocyte lysate (RRL) proteins. For its formation PABP is necessary but not sufficient. These results are in agreement with the proposed model implying formation of a mini-loop at 3' UTR of YB-1 mRNA that includes RE, RRL proteins and the poly(A) tail.

Effect of the multifunctional proteins RPA, YB-1, and XPC repair factor on AP site cleavage by DNA glycosylase NEIL1.

DNA glycosylases are key enzymes in the first step of base excision DNA repair, recognizing DNA damage and catalyzing the release of damaged nucleobases. Bifunctional DNA glycosylases also possess associated apurinic/apyrimidinic (AP) lyase activity that nick the damaged DNA strand at an abasic (or AP) site, formed either spontaneously or at the first step of repair. NEIL1 is a bifunctional DNA glycosylase capable of processing lesions, including AP sites, not only in double-stranded but also in single-stranded DNA. Here, we show that proteins participating in DNA damage response, YB-1 and RPA, affect AP site cleavage by NEIL1. Stimulation of the AP lyase activity of NEIL1 was observed when an AP site was located in a 60 nt-long double-stranded DNA. Both RPA and YB-1 inhibited AP site cleavage by NEIL1 when the AP site was located in single-stranded DNA. Taking into account a direct interaction of YB-1 with the AP site, located in single-stranded DNA, and the high affinity of both YB-1 and RPA for single-stranded DNA, this behavior is presumably a consequence of a competition with NEIL1 for the DNA substrate. Xeroderma pigmentosum complementation group C protein (XPC), a key protein of another DNA repair pathway, was shown to interact directly with AP sites but had no effect on AP site cleavage by NEIL1.

YB-1 synthesis is regulated by mTOR signaling pathway.

YB-1 is a eukaryotic protein with numerous intra- and extracellular functions based on its ability to interact with RNA, DNA, and many proteins. In spite of achievements in studying its functions, regulation of YB-1 synthesis in the cell remains poorly understood. In the current study Western and Northern blotting were used to determine the amounts of YB-1 and YB-1 mRNA in rabbit organs and several cell lines. As found, in the majority of studied eukaryotic cells a considerable proportion of YB-1 mRNA was stored in free mRNPs, i.e., was poorly translated. Also, we demonstrated that YB-1 synthesis depended on conditions that determined the rate of cell division. Specific suppression of YB-1 synthesis resulted from inhibition of the mTOR signaling pathway with inhibitor PP242, but not rapamycin. Experiments on reporter constructs showed that dependence of YB-1 mRNA translation on activity of the mTOR signaling pathway was dictated by 5' untranslated regions of this mRNA, irrelatively of the TOP-like sequences at the beginning of 5' UTR.

Interplay between Y-box-binding protein 1 (YB-1) and poly(A) binding protein (PABP) in specific regulation of YB-1 mRNA translation.

YB-1 is a DNA- and RNA-binding protein that regulates expression of many important genes. Its deficiency or excess may pose threats, including malignant cellular transformation and metastasis, which explains the necessity of strict control over its amount at every level. As we showed previously, the 3' untranslated region (UTR) of YB-1 mRNA contains a regulatory element specifically binding to YB-1 and PABP (PABPC1). Also, we showed that YB-1 selectively inhibits YB-1 mRNA translation, while PABP stimulates it in a poly(A) tail-independent manner. It was suggested that regulation of YB-1 mRNA translation involves competition between PABP and YB-1 for binding to the regulatory element. Here we offer cogent evidence for this model and add novel details to the mechanism of regulation of YB-1 synthesis. In experiments on regulatory element deletion we showed that it is this element that is responsible for a specific effect of YB-1 and PABP on YB-1 mRNA translation. Mutations eliminating only specific YB-1 affinity for this element suppressed the inhibitory effect of YB-1 and concurrently dramatically decreased the PABP stimulating effect. Mutations reducing only specific PABP affinity for this element, as well as spatial separation of the YB-1- and PABP binding sites, did not affect the YB-1 inhibitory action but completely abolished the positive PABP effect. Together, these results unambiguously prove direct inhibitory action of YB-1 on its mRNA translation, while the positive effect of PABP is realized through displacing YB-1 from the regulatory element.