Project description:In previous studies, we identified a sequence motif (GDCGG) in almost all microRNAs downregulated in the serum of patients with amyotrophic lateral sclerosis. We found that FMR1, FXR1 and FXR2 directly and specifically interact with microRNAs containing the GDCGG motif via their RGG/RG-domains. Here, we compare the specificities for microRNAs of the RGG/RG-domains of FMR1, FXR1 and FXR2 on a transcriptome-wide scale using the Affymetrix GeneChip™ miRNA 3.0 Arrays.
Project description:FXR1 is an essential RNA-binding protein. This chromosome 3q26-28 gene is overexpressed in many epithelial tumors. FXR1 controls the turnover and translation of multiple mRNAs and is involved in cellular transformation. We identified critical residues in the protein that are post-translationally modified. These regulate the stability of FXR1 protein, its RNA-binding function, cell growth, and proliferation. Here we show that PRMT5-mediated arginine methylation of FXR1 increases the protein's binding to G-quadruplex RNAs in vivo and controls their expression in cancer cells. Independent point mutations of specific arginine residues in the nuclear export signal (R386, R388) and arginine-glycine rich (R453, R455, R459) domains of FXR1 abrogate the RNA-binding in vitro. Genetic and small molecule inhibition of PRMT5 minimizes methylation and levels of FXR1 and suppresses oral tumor growth and proliferation. RNA-seq analyses of FXR1 KD cells show an increase in the expression of PLK2, TCN2, and TRAF4 along with FXR1’s well-known target CDKN1A. Like CDKN1A, these targets possess strong G4 sequences. FXR1 and G4-RNA interactions provide new insights into the molecular mechanism of FXR1 and its interaction with target mRNAs. Furthermore, an increased expression of FXR1 and PRMT5 is colocalized in cancer tissues, leading to a poor patient prognosis. Thus, our data demonstrate that PRMT5-mediated arginine methylation of FXR1 arginine residues in the NES and RGG domains plays a critical role in binding and controlling G4-RNAs, which encode tumor suppressors and promote cancer cell growth and proliferation.
Project description:The RBP, FXR1, is overexpressed in many epithelial tumors containing a canonical RGG box domain. FXR1 controls post-transcriptional gene regulation through changes in mRNA turnover and translation of target genes. Here we show that arginine methyltransferase PRMT5- mediated specific arginine methylation of FXR1 increases its stability in cancer cells. FXR1-dependent gene signatures show decreased expression and instability of G4-rich sequences containing mRNAs such as CDKN1A, PLK2, TCN2, and TRAF4. Furthermore, structural features of FXR1 and G4-RNA interactions provide novel insights into the critical arginine amino acids of FXR1 essential for G4-RNA-binding and turnover activity. In addition, analysis of the eCLIP data provides various RNA targets and the G-rich sequence motifs of FXR1 in head and neck cancer cell line. Thus, our results indicate that PRMT5-mediated methylation of FXR1 binding with G4-RNAs favors mRNA stability and turnover, contributing to cancer cell growth and proliferation.
Project description:The Fragile X Mental Retardation-Related 1 gene (FXR1) belongs to the Fragile X Related gene family, together with FMR1 and FXR2. While inactivation of FMR1 causes Fragile X syndrome, the most common form of inherited mental retardation, inactivation of FXR1 in various animal models suggest a critical role for the RNA-binding protein FXR1P during myogenesis. Seven alternatively spliced FXR1 transcripts have been identified, three of them being muscle-specific. We previously reported a reduction of these isoforms in myoblasts from Fascio Scapulo Humeral Distrophy (FSHD) myopathic patients. However, so far, no mRNA target of FXR1P has been linked to the drastic muscular phenotypes caused by its absence and the exact molecular role of FXR1P in muscular development remains unknown. In the present study, gene expression profiling of C2C12 myoblasts reveals that transcripts involved in cell cycle and muscular development pathways are modulated by Fxr1-depletion. In addition, Fxr1-depletion translates physiologically into a premature cell cycle exit of myoblasts, accompanied by a robust up-regulation of the cyclin-dependant kinase inhibitor p21/Cdkn1a/Waf/Cip1 mRNA. Importantly, we also observe this P21 increase in FSHD human myoblasts depleted in FXR1P muscular isoforms. Our data further indicate that FXR1P muscle-specific isoforms are involved in the post-transcriptional control of p21 mRNA levels via direct interaction with a conserved G-quadruplex structure located in its 3’ untranslated region. This study has crucial implications for the understanding of FXR1P role during myogenesis and the pathophysiology of FSHD. 2 independent experiments performed in a one color design, corresponding to 2 conditions: si-control and si-fxr1, for a total of 4 samples.
Project description:PRMT5 is the major enzyme that catalyzes the symmetric dimethylation of arginine (sDMA) in mammalian cells. Its activity is crucial for many biological processes including transcriptional regulation, mRNA processing, as well as DNA damage and repair. However, the protein substrates identified for PRMT5 have yet been limited in numbers, hindering the understanding of PRMT5 functions in normal as well as diseased cells. Herein we developed an optimized strategy for proteomic profiling of cellular sDMA and apply it to the discovery of novel PRMT5 substrates. Our results show that a combination of proteolytic digestion by the metalloprotease ulilysin and using electron-transfer dissociation with supplemental activation as the mass spectrometry method significantly increased sDMA site identification and localization after immuno-affinity enrichment. By employing SILAC-based differential quantitative proteomic approach and a PRMT5 specific inhibitor, we identified 325 sDMA sites being regulated by PRMT5, 220 being novel sites, which greatly expanded the number of PRMT5 substrates. Biochemical studies confirmed the newly discovered PRMT5 substrate, Plasminogen activator inhibitor 1 RNA-binding protein (SERBP1) and revealed that the RGG/RG motif in the central region of SERBP1 contains both PRMT5-catalyzed sDMA and Type I PRMT-catalyzed asymmetric dimethylation of arginine (aDMA). Unexpectedly, using the optimized methylarginine profiling strategy, we also discovered arginine trimethylation, a previously unknown type of modification, on the central RGG/RG region of SERBP1. By mutational studies we demonstrated that the trimethyl modification on R172 of SERBP1 regulates its recruitment to stress granule (SG) under oxidative stress, indicating a functional role of arginine trimethylation in the cell. Overall, the optimized profiling strategy not only enabled the identification of extensive, non-overlapping sDMA sites and novel PRMT5 substrates, but also revealed a potentially important new PTM, arginine trimethylation. The work lays the foundation for further investigations on the functional interplay of different methylation modifications on arginines, especially in the heavily methylated RGG/RG motif of many RNA-binding proteins.
Project description:Fragile-X Syndrome (FXS) is a multi-organ disease leading to mental retardation, macro-orchidism in males, and premature ovarian insufficiency in female carriers. FXS is also a prominent monogenic disease associated with autism spectrum disorders (ASD). FXS is typically caused by the loss of FRAGILE X-MENTAL RETARDATION 1 (FMR1) expression, which encodes for the RNA-binding protein (RBP), FMR1 (or FMRP). We report the discovery of the RNA recognition elements (RREs), binding sites, and mRNA targets for wild-type and I304N mutant FMRP isoforms as well as its paralogs, FXR1 and FXR2. RRE frequency, ratio, and distribution determine target mRNA association with FMRP. Among highly-enriched targets, we identified many genes involved in ASD and demonstrate that FMRP can affect their protein levels in cell culture, mice, and human brain. Unexpectedly, we discovered that these targets are also dysregulated in Fmr1-/- mouse ovaries, showing signs of premature follicular overdevelopment. These results indicate that FMRP targets shared signaling pathways across different cellular contexts. As it is become increasingly appreciated that signaling pathways are important to FXS and ASD, our results here provide an invaluable molecular guide towards the pursuit of novel therapeutic targets for these devastating neurological disorders. PAR-CLIP profiling for wild-type and I304N mutant FMRP isoforms as well as paralogs, FXR1 and FXR2.
Project description:Viral proteins are known to be methylated by host protein arginine methyltransferases (PRMTs) playing critical roles during viral infections. Herein, we show that PRMT1 methylates SARS-CoV-2 nucleocapsid (N) protein at residues R95 and R177 within RGG/RG sequences. Arginine methylation of N protein was confirmed by immunoblotting viral proteins extracted from SARS-CoV-2 virions isolated by cell culture. We demonstrate that arginine methylation of N protein is required for its RNA binding capacity, since treatment with a type I PRMT inhibitor (MS023) or substitution of R95K or R177K inhibited interaction with the 5’-UTR of the SARS-CoV-2 genomic RNA. We defined the N interactome in HEK293 cells with or without MS023 treatment and identified PRMT1 and many of its RGG/RG substrates including the known interactor, G3BP1, and other components of stress granules (SG). Methylation of N protein at R95 regulates another function namely its property to suppress the formation of SGs. MS023 treatment or R95K substitution blocked N-mediated suppression of SGs. Also, the co-expression of methylarginine reader TDRD3 quenched N-mediated suppression of SGs in a dose-dependent manner. Finally, pre-treatment of VeroE6 cells with MS023 significantly reduced SARS-CoV-2 replication. With type I PRMT inhibitors being in clinical trials for cancer treatment, inhibiting arginine methylation to target the later stages of the viral life cycle such as viral genome packaging and assembly of virions may be an additional therapeutic application of these drugs.
Project description:The Fragile X Mental Retardation-Related 1 gene (FXR1) belongs to the Fragile X Related gene family, together with FMR1 and FXR2. While inactivation of FMR1 causes Fragile X syndrome, the most common form of inherited mental retardation, inactivation of FXR1 in various animal models suggest a critical role for the RNA-binding protein FXR1P during myogenesis. Seven alternatively spliced FXR1 transcripts have been identified, three of them being muscle-specific. We previously reported a reduction of these isoforms in myoblasts from Fascio Scapulo Humeral Distrophy (FSHD) myopathic patients. However, so far, no mRNA target of FXR1P has been linked to the drastic muscular phenotypes caused by its absence and the exact molecular role of FXR1P in muscular development remains unknown. In the present study, gene expression profiling of C2C12 myoblasts reveals that transcripts involved in cell cycle and muscular development pathways are modulated by Fxr1-depletion. In addition, Fxr1-depletion translates physiologically into a premature cell cycle exit of myoblasts, accompanied by a robust up-regulation of the cyclin-dependant kinase inhibitor p21/Cdkn1a/Waf/Cip1 mRNA. Importantly, we also observe this P21 increase in FSHD human myoblasts depleted in FXR1P muscular isoforms. Our data further indicate that FXR1P muscle-specific isoforms are involved in the post-transcriptional control of p21 mRNA levels via direct interaction with a conserved G-quadruplex structure located in its 3’ untranslated region. This study has crucial implications for the understanding of FXR1P role during myogenesis and the pathophysiology of FSHD.