XPO5 is required for miRNA biogenesis and promotes primary miRNA processing independent of RanGTP
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ABSTRACT: XPO5 mediates nuclear export of miRNA hairpin precursors in a RanGTP-dependent manner. However, the requirement of XPO5 for global miRNA biogenesis and mammalian development and XPO5-associated RNA species are not determined. Here we show that XPO5 is required for mouse embryonic development and morphogenesis of skin and brain. Loss of XPO5 compromises the biogenesis of most miRNAs and that leads to severe developmental defects. Surprisingly, XPO5 not only associates with miRNA hairpin precursors but also pervasively binds to double-stranded RNA (dsRNA) regions found in many cellular RNAs and some clustered pri-miRNAs. The binding of XPO5 to miR-17~92 pri-miRNAs is RanGTP-independent. Pre-incubation with XPO5 enhances the processing efficiency of the DROSHA/DGCR8 microprocessor. Together, our studies demonstrate the requirement of XPO5 for miRNA biogenesis and mouse development, reveal an unexpected role of XPO5 for recognizing and facilitating the nuclear cleavage of clustered pri-miRNAs and identify numerous cellular RNAs as novel XPO5 subtracts.
Project description:Biogenesis of canonical microRNAs (miRNAs) involves multiple steps: nuclear processing of primary miRNA (pri-miRNA) by DROSHA, nuclear export of precursor miRNA (pre-miRNA) by Exportin 5 (XPO5), and cytoplasmic processing of pre-miRNA by DICER. To gain a deeper understanding of the contribution of each of these maturation steps, we deleted DROSHA, XPO5, and DICER in the same human cell line, and analyzed their effects on miRNA biogenesis. Canonical miRNA production was completely abolished in DROSHA-deleted cells while we detected a few DROSHA-independent miRNAs including three previously unidentified noncanonical miRNAs (miR-7706, miR-3615, and miR-1254). In contrast to DROSHA knockout, many canonical miRNAs were still detected without DICER albeit at markedly reduced levels. In the absence of DICER, pre-miRNAs are loaded directly onto AGO and trimmed at the 3â² end, yielding miRNAs from the 5â² strand (5p miRNAs). Interestingly, in XPO5 knockout cells, most miRNAs are affected only modestly, suggesting that XPO5 is necessary but not critical for miRNA maturation. Our study demonstrates an essential role of DROSHA and an important contribution of DICER in the canonical miRNA pathway, and reveals that the function of XPO5 can be complemented by alternative mechanisms. Thus, this study allows us to understand differential contributions of key biogenesis factors, and provides with valuable resources for miRNA research. Two independent sequencing experiments (set 1 and set 2, respectively) were performed using 9 samples.
Project description:Biogenesis of canonical microRNAs (miRNAs) involves multiple steps: nuclear processing of primary miRNA (pri-miRNA) by DROSHA, nuclear export of precursor miRNA (pre-miRNA) by Exportin 5 (XPO5), and cytoplasmic processing of pre-miRNA by DICER. To gain a deeper understanding of the contribution of each of these maturation steps, we deleted DROSHA, XPO5, and DICER in the same human cell line, and analyzed their effects on miRNA biogenesis. Canonical miRNA production was completely abolished in DROSHA-deleted cells while we detected a few DROSHA-independent miRNAs including three previously unidentified noncanonical miRNAs (miR-7706, miR-3615, and miR-1254). In contrast to DROSHA knockout, many canonical miRNAs were still detected without DICER albeit at markedly reduced levels. In the absence of DICER, pre-miRNAs are loaded directly onto AGO and trimmed at the 3′ end, yielding miRNAs from the 5′ strand (5p miRNAs). Interestingly, in XPO5 knockout cells, most miRNAs are affected only modestly, suggesting that XPO5 is necessary but not critical for miRNA maturation. Our study demonstrates an essential role of DROSHA and an important contribution of DICER in the canonical miRNA pathway, and reveals that the function of XPO5 can be complemented by alternative mechanisms. Thus, this study allows us to understand differential contributions of key biogenesis factors, and provides with valuable resources for miRNA research.
Project description:Mutations in SOD1 (Superoxide Dismutase 1) gene are associated with amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease. By employing ascorbate peroxidase (APEX)-based proximity labeling, coupled with LC-MS/MS analysis, we uncovered 37 and 28 proteins exhibiting higher abundance in the proximity proteomes of SOD1G85R and SOD1G93A, respectively, than that of the wild-type SOD1. Immunoprecipitation followed by western blot analysis confirmed the preferential binding of one of these proteins, exportin 5 (XPO5), toward the two mutants of SOD1 over its wild-type counterpart. In line with the established function of XPO5 in pre-miRNA transport, we observed diminished nucleocytoplasmic transport of pre-miRNAs in cells with ectopic expression of the two SOD1 mutants over those expressing the wild-type counterpart. On the other hand, RT-qPCR results revealed significant elevations in mature miRNA in cells expressing the two SOD1 mutants, which are attributed to diminished inhibitory effect of XPO5 on Dicer-mediated cleavage of pre-miRNA to mature miRNA. Together, our chemoproteomic approach led to the revelation of a novel mechanism through which ALS-associated mutants of SOD1 perturb miRNA biogenesis, i.e., through aberrant binding toward XPO5.
Project description:Hairpin-containing pre-miRNAs are precursors of microRNAs (miRNAs) that play important roles in cellular processes and various human diseases. Pre-miRNAs are produced from longer primary transcripts (pri-miRNAs). The falsity in cellular expression and sequences of pre-miRNAs might cause cellular defects or human diseases. However, the current pre-miRNA quantification methods by qPCR cannot discriminate between pre-miRNAs and their parental pri-miRNAs. In addition, the ligation of the sequencing adapter to 5’-end of pre-miRNAs is inefficient, therefore, pre-miRNA sequencing is highly impractical. Here, we developed a method, called the intramolecular ligation method (iLIME) for pre-miRNA quantification and sequencing. This method utilized T4 RNA ligase 1 to convert hairpin-pre-miRNAs into circularized RNAs that do not naturally exist in cells. The resulting circuliarized RNAs allow us to design unique primers to quantify pre-miRNAs by qPCR specicially, and thus this qPCR can distinguish pre-miRNA from pri-miRNAs. In addition, the iLIME also allows us to sequence pre-miRNAs using next-generation sequencing. The iLIME method offers a simple and effective way to quantify and sequence pre-miRNAs. This will be useful in investigating pre-miRNAs for addressing research questions for medical applications. The iLIME can be potentially extended to other hairpin-containing RNAs, such as tRNAs and snRNAs.
Project description:Microprocessor initiates processing of microRNAs (miRNAs) from hairpin regions of primary transcripts (pri-miRNAs). Pri-miRNAs often contain multiple miRNA hairpins, and this clustered arrangement can assist processing of otherwise defective hairpins. We find that miR-451, which derives from a hairpin with a suboptimal terminal loop and a suboptimal stem length, accumulates to 40-fold higher levels when clustered with a helper hairpin. This phenomenon tolerates changes in hairpin order, linker lengths, and the identities of the helper hairpin, the recipient hairpin, the linker-sequence, and the RNA polymerase that transcribes the hairpins. It can act reciprocally and need not occur co-transcriptionally. It requires Microprocessor recognition of the helper hairpin and linkage of the two hairpins, yet predominantly manifests after helper-hairpin processing. It also requires Enhancer of Rudimentary Homology (ERH), which copurifies with Microprocessor and can dimerize and interact with other proteins that can dimerize, suggesting a model in which Microprocessor recruits another Microprocessor.
Project description:Microprocessor is responsible for conversion of pri-miRNA transcripts into pre-miRNA hairpins in miRNA biogenesis. The in vivo properties of this process remain enigmatic. Here, we present the first study of in vivo transcriptome-wide pri-miRNA processing using next-generation sequencing of chromatin-associated pri-miRNAs. We identify a distinctive Microprocessor signature in the transcriptome profile, from which efficiency of the endogenous processing event can be accurately quantified. This analysis reveals differential susceptibility to Microprocessor cleavage as a key regulatory step in miRNA biogenesis. Processing is highly variable among pri-miRNAs and a better predictor of miRNA abundance than primary transcription itself. Processing is also largely stable across three cell lines, suggesting a major contribution of sequence determinants. Based on differential processing efficiencies we define functionality for short sequence features adjacent to the pre-miRNA hairpin. In conclusion, we identify Microprocessor as the main hub for diversified miRNA output and suggest a role for uncoupling miRNA biogenesis from host gene expression.
Project description:MicroRNAs (miRNAs) are a family of short, noncoding RNAs that regulate translation of mRNAs by mechanisms involving the binding of complementary sequences. The influence of miRNAs on the proteome and cellular events is extensive as they regulate an estimated 60% of the transcriptome and play key roles in differentiation, plasticity, circadian rhythm, immunity, and disease. The post-transcriptional biogenesis of most miRNAs involves a sequential cleavage process mediated by RNase III family enzymes. Primary transcripts (pri-miRNAs) are first cleaved by Drosha in the nucleus to yield ~70nt hairpin precursors (pre-miRNAs). These intermediates are transported to the cytoplasm where ~22mer dsRNAs are excised by Dicer. Typically, one strand of the dsRNAs is inserted as a mature miRNA into the RNA-induced silencing complex (RISC), which contains members of the Argonaute (Ago) protein family that contribute to translational regulation. Recent studies indicate that some RNA-binding proteins (RNA-BPs) can regulate discrete processing steps, differentially blocking or promoting the formation of specific miRNAs to control cellular proliferation and differentiation. Elegant examples of this mechanism include the attenuation of let-7 biogenesis in embryonic stem cells by the pluripotency factor LIN28, and the selective enhancement of miR-18a biogenesis from a polycistronic transcript by hnRNPA1. Mature miRNA expression profiles in B104 cells were measured after siRNA-mediated knockdown of RBM3 in the B104 neuronal cell line. Mock treated B104 cells were used as a control. Experiments were replicated in duplicates.
Project description:DEAD-box RNA-binding proteins (RBPs) play a significant role in RNA metabolism to achieve cellular homeostasis, including miRNA biogenesis and transcription. Hypoxia induces stemness cell-like characteristics in cancer cells and promotes malignant progression. Despite the fact that hypoxia can induce the changes in protein and RNA modification, thereby regulating downstream gene expressions, how modifications at different molecular layers interplay with each other are poorly understood. Here we show that hypoxia induces HectH9-mediated K63-linked polyubiquitination of the DEAD-box protein DDX17 as well as reduces N6-methyladenosine (m6A) marks in pri-miRNAs. While m6A potentiates DDX17 binding to pri-miRNAs, decreased m6A modifications of pri-miRNAs and increased polyubiquitination of DDX17 under hypoxia lead to decreased DDX17 binding to pri-miRNAs binding. These events enhance the association of DDX17 with the ubiquitin receptor p300 and lead to a decrease in miRNA biogenesis, especially for miRNAs regulating stemness and stemness-related genes. In addition, polyubiquitinated DDX17 together with p300 upregulates H3K56Ac levels on the stemness and stemness-related genes, resulting in enhancement of tumor initiating ability. Post-transcriptionally, decreased miRNA production, including those targeting stemness genes or stemness-related genes, also facilitates tumor initiation. Together, hypoxia triggers DDX17 poly-ubiquitination, which orchestrates dual mechanisms to increase tumor initiating ability and promote tumor progression.
Project description:Human Microprocessor cleaves pri-miRNAs to initiate miRNA biogenesis. The accuracy and efficiency of Microprocessor cleavage ensure appropriate miRNA sequence and expression and thus its proper gene regulation. However, Microprocessor cleaves many pri-miRNAs incorrectly, so it requires assistance from its many cofactors. For example, SRSF3 enhances Microprocessor cleavage by interacting with the CNNC motif in pri-miRNAs. However, whether SRSF3 can function with other motifs and/or requires the motifs in a certain secondary structure is unknown. In addition, the function of SRSF7 (a paralog of SRSF3) in miRNA biogenesis still needs to be discovered. Here, we demonstrated that SRSF7 could stimulate Microprocessor cleavage. In addition, by conducting high-throughput pri-miRNA cleavage assays for Microprocessor and SRSF7 or SRSF3, we demonstrated that SRSF7 and SRSF3 function with the CRC and CNNC motifs, adopting certain secondary structures. In addition, SRSF7 and SRSF3 affect the Microprocessor cleavage sites in human cells. Our findings demonstrate the roles of SRSF7 in miRNA biogenesis and provide a comprehensive view of the molecular mechanism of SRSF7 and SRSF3 in enhancing Microprocessor cleavage.
Project description:MicroRNAs (miRNAs) are a family of short, noncoding RNAs that regulate translation of mRNAs by mechanisms involving the binding of complementary sequences. The influence of miRNAs on the proteome and cellular events is extensive as they regulate an estimated 60% of the transcriptome and play key roles in differentiation, plasticity, circadian rhythm, immunity, and disease. The post-transcriptional biogenesis of most miRNAs involves a sequential cleavage process mediated by RNase III family enzymes. Primary transcripts (pri-miRNAs) are first cleaved by Drosha in the nucleus to yield ~70nt hairpin precursors (pre-miRNAs). These intermediates are transported to the cytoplasm where ~22mer dsRNAs are excised by Dicer. Typically, one strand of the dsRNAs is inserted as a mature miRNA into the RNA-induced silencing complex (RISC), which contains members of the Argonaute (Ago) protein family that contribute to translational regulation. Recent studies indicate that some RNA-binding proteins (RNA-BPs) can regulate discrete processing steps, differentially blocking or promoting the formation of specific miRNAs to control cellular proliferation and differentiation. Elegant examples of this mechanism include the attenuation of let-7 biogenesis in embryonic stem cells by the pluripotency factor LIN28, and the selective enhancement of miR-18a biogenesis from a polycistronic transcript by hnRNPA1.