PRMT5 Modulates Splicing in Hematopoietic Stem Cells
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ABSTRACT: This study aimed to clarify the role of PRMT5 in the hematopoietic stem cell (HSC) compartment, and elucidate the functional relevance of PRMT5-mediated splicing in HSCs. We confirm the cell intrinsic requirement for PRMT5 in HSC maintenance, and present evidence suggesting that PRMT5 deficiency perturbs HSC proteostasis. Notably, we also uncover a critical role for PRMT5 in maintaining HSC genomic integrity by modulating splicing of genes involved in DNA repair; loss of which leads to unresolved DNA damage, p53 activation and rapid HSC exhaustion. Overall, these findings establish PRMT5-mediated splicing as a major determinant of HSC fate, and highlight the need to maintain an adequate level of PRMT5 activity in HSCs.
Project description:Maintaining proteostasis is key to resisting stress and to promoting healthy aging. Proteostasis is necessary to preserve stem cell function, but little is known about the mechanisms that regulate proteostasis during stress in stem cells, and whether disruptions in proteostasis contribute stem cell aging is largely unexplored. We determined that ex vivo cultured mouse and human hematopoietic stem cells (HSCs) rapidly increase protein synthesis. This challenge to HSC proteostasis was associated with nuclear accumulation of Hsf1, and deletion of Hsf1 impaired HSC maintenance ex vivo. Strikingly, supplementing cultures with small molecules that enhance Hsf1 activation partially suppressed protein synthesis, rebalanced proteostasis, and supported retention of HSC serial reconstituting activity. Although Hsf1 was dispensable for young adult HSCs in vivo, Hsf1 deficiency increased protein synthesis and impaired the reconstituting activity of middle-aged HSCs. Hsf1 thus promotes proteostasis and the regenerative activity of HSCs in response to culture stress and aging.
Project description:Maintaining proteostasis is key to resisting stress and to promoting healthy aging. Proteostasis is necessary to preserve stem cell function, but little is known about the mechanisms that regulate proteostasis during stress in stem cells, and whether disruptions in proteostasis contribute stem cell aging is largely unexplored. We determined that ex vivo cultured mouse and human hematopoietic stem cells (HSCs) rapidly increase protein synthesis. This challenge to HSC proteostasis was associated with nuclear accumulation of Hsf1, and deletion of Hsf1 impaired HSC maintenance ex vivo. Strikingly, supplementing cultures with small molecules that enhance Hsf1 activation partially suppressed protein synthesis, rebalanced proteostasis, and supported retention of HSC serial reconstituting activity. Although Hsf1 was dispensable for young adult HSCs in vivo, Hsf1 deficiency increased protein synthesis and impaired the reconstituting activity of middle-aged HSCs. Hsf1 thus promotes proteostasis and the regenerative activity of HSCs in response to culture stress and aging.
Project description:Protein Arginine MethylTransferase 5 (PRMT5) is known to mediate epigenetic control on chromatin and to functionally regulate components of the splicing machinery. In this study we show that selective deletion of PRMT5 in different organs leads to cell cycle arrest and apoptosis. At the molecular level, PRMT5 depletion results in reduced methylation of Sm proteins, aberrant constitutive splicing and in the Alternative Splicing (AS) of specific mRNAs. We identify Mdm4 as one of these mRNAs, which due to its weak 5’-Donor site, acts as a sensor of splicing defects and transduces the signal to activate the p53 response, providing a mechanistic explanation of the phenotype observed in PRMT5 conditional knockout mice. Our data demonstrate a key role of PRMT5, together with p53, as guardians of the transcriptome. This will have fundamental implications in our understanding of PRMT5 activity, both in physiological conditions, as well as pathological conditions, including cancer and neurological diseases. Total RNA was extracted from control and Prmt5 depleted Neural Stem/Progenitors Cells (NPCs) and Mouse Embryonic Fibroblasts (MEFs). Prmt5 depleted cells were treated with 4-OHT 24 hours before splitting to induce PRMT5 knockout and final libraries were sequenced in triplicates on Illumina HiSeq 2000.
Project description:Protein Arginine MethylTransferase 5 (PRMT5) is known to mediate epigenetic control on chromatin and to functionally regulate components of the splicing machinery. In this study we show that selective deletion of PRMT5 in different organs leads to cell cycle arrest and apoptosis. At the molecular level, PRMT5 depletion results in reduced methylation of Sm proteins, aberrant constitutive splicing and in the Alternative Splicing (AS) of specific mRNAs. We identify Mdm4 as one of these mRNAs, which due to its weak 5’-Donor site, acts as a sensor of splicing defects and transduces the signal to activate the p53 response, providing a mechanistic explanation of the phenotype observed in PRMT5 conditional knockout mice. Our data demonstrate a key role of PRMT5, together with p53, as guardians of the transcriptome. This will have fundamental implications in our understanding of PRMT5 activity, both in physiological conditions, as well as pathological conditions, including cancer and neurological diseases. Total RNA was extracted from control Prmt5F/F, and Prmt5 depleted Prmt5F/FNes (Nestin-Cre) Neural Stem/Progenitors Cells (NPCs). The final cRNA samples were hybridized to Illumina MouseRef-8 V2 arrays in quadruplicates.
Project description:Protein Arginine Methyltransferase (PRMT) 5 is the major type 2 methyltransferase catalyzing symmetric dimethylation (SDM) of arginine. PRMT5 inhibition or deletion in CD4 Th cells reduces TcR engagement-induced IL-2 production and Th cell expansion and confers protection against experimental autoimmune encephalomyelitis (EAE), the animal model of Multiple Sclerosis. However, the mechanisms by which PRMT5 modulates T helper (Th) cell proliferation are still not completely understood and neither are the methylation targets in T cells. In this manuscript, we uncover the role of PRMT5 on alternative splicing (AS) in activated T cells and identify several targets of PRMT5 SDM involved in splicing. In addition, we find a possible link between PRMT5 mediated AS of Trpm4 (Transient Receptor Potential Cation Channel Subfamily M Member 4) and TcR/NFAT signaling/IL-2 production. This understanding may guide development of drugs targeting these processes to benefit patients with T cell-mediated diseases.
Project description:Hematopoietic stem cells (HSCs) regenerate blood cells throughout life. To preserve their fitness, HSCs are particularly dependent on maintaining protein homeostasis (proteostasis). However, how HSCs purge misfolded proteins is unknown. Here we show that in contrast to most cells that primarily utilize the proteasome to degrade misfolded proteins, HSCs preferentially traffic misfolded proteins to aggresomes in a Bag3-dependent manner, and depend on aggrephagy, a selective form of autophagy, to maintain proteostasis in vivo. When autophagy is disabled, HSCs compensate by increasing proteasome activity, but proteostasis is ultimately disrupted as protein aggregates accumulate and HSC function is impaired. Bag3-deficiency blunts aggresome formation in HSCs, resulting in protein aggregate accumulation, myeloid-biased differentiation, and diminished self-renewal activity. Furthermore, HSC aging is associated with a severe loss of aggresomes and reduced autophagic flux. Protein degradation pathways are thus specifically configured in young adult HSCs to preserve proteostasis and fitness, but become dysregulated during aging.
Project description:CRISPR was utilized to deplete either PRMT5 or WDR77 in HSC-5 cells. Subsequently, RNA-seq was performed to identify changes in the transcriptome following the loss of PRMT5 or WDR77 in these cells. Critically, Gene Set Enrichment Analysis (GSEA) was conducted to screen and identify a list of genes co-regulated by PRMT5 and WDR77.
Project description:The protein arginine methyl transferase PRMT5 is an enzyme expressed in oligodendrocyte lineage cells and responsible for the symmetric methylation of arginine residues on histone tails. Previous work from our laboratory identified PRMT5 as critical for myelination, due to its transcriptional regulation of survival and early stages of differentiation. However, besides its nuclear localization, PRMT5 is found at high levels in the cytoplasm of oligodendrocyte progenitor cells (OPCs) and yet, its interacting partners and non-histone substrates in this lineage, remain elusive. By using mass spectrometry on protein eluates from extracts generated from OPC and immunoprecipitated with PRMT5 antibodies, we identified 1116 proteins as PRMT5 interacting partners. These proteins are related to molecular functions such as RNA binding, ribosomal structure, nucleotide binding, cadherin and actin binding, GTP and GTPase activity. We then investigated PRMT5 substrates using iTRAQ-based proteomics on protein samples isolated from CRISPR-PRMT5 knockdown immortalized oligodendrocyte progenitors compared to CRISPR-EGFP controls. This analysis identified 169 peptides with statistically different symmetric methylation of arginine residues in the two groups. Those peptides led to 30 unique non-histone substrates of PRMT5. The majority of these proteins were consistent with PRMT5 substrates, previously identified in distinct cancer cell lines (e.g. the transcription factor ZN326), and were functionally related to RNA processing and transport, splicing, regulation of mRNA stability and transcription. In addition, we detected three substrates as unique to the oligodendrocyte lineage and not identified in cancer cells. They included the proline-rich protein PRC2C, involved in methyl-RNA binding, the RNA binding protein KHDR2, regulating splicing events and the heterogeneous nuclear RNA binding protein HNRPD, involved in regulation of RNA stability. Together, these results highlight a cell-specific role of PRMT5 in regulating, not only transcription, but RNA processing and translation in OPCs. (287 WORDS)
Project description:Many pathways regulating blood formation have been elucidated, yet how each coordinates with embryonic biophysiology to modulate the spatio-temporal production of hematopoietic stem cells (HSCs) is currently unresolved. Here, we report that glucose metabolism impacts the onset and magnitude of HSC induction in vivo. In zebrafish, transient elevations in physiological glucose levels elicited dose-dependent effects on HSC development, including enhanced runx1 expression and hematopoietic cluster formation in the Aorta-Gonad-Mesonephros (AGM) region; embryonic-to-adult transplantation studies confirmed glucose increased functional HSCs. Glucose uptake was required to mediate the enhancement in HSC development; likewise, metabolic inhibitors diminished nascent HSC production and reversed glucose-mediated effects on HSCs. Increased glucose metabolism preferentially impacted hematopoietic and vascular targets, as determined by gene expression analysis, through mitochondrial-derived reactive oxygen species (ROS)-mediated stimulation of hypoxia inducible factor 1α (hif1α); epistasis assays demonstrated hif1α regulates HSC formation in vivo and mediates the dose-dependent effects of glucose metabolism on the timing and magnitude of HSC production. We propose this fundamental metabolic-sensing mechanism enables the embryo to respond to changes in environmental energy input and adjust hematopoietic output to maintain embryonic growth and ensure viability. We performed microarray analysis to explore the changes in gene expression that occur in repsonse to altered metabolism during the induction of developmental hematopoeisis. We compared RNA from zebrafish raised in a solution of 1% glucose from 12-36hpf vs controls. Two biological replicates for each condition were performed.
Project description:Protein arginine methyltransferase 5 (PRMT5) belongs to the class II arginine methyltransferases and catalyzes monomethylation and symmetrical dimethylation of arginines on proteins. It has recently emerged as a promising cancer drug target, and three PRMT5 inhibitors are currently in clinical trials for a range of malignancies. In this study, we aimed to further elucidate the role of PRMT5 in acute myeloid leukemia (AML). Using an enzymatic dead version of PRMT5 as well as a PRMT5-specific inhibitor, we demonstrated the requirement of the catalytic activity of PRMT5 for the survival of AML cells. By using multiplexed quantitative proteomics, we identified PRMT5 substrates and investigated their role in the survival of AML cells. We found that the function of the splicing regulator SRSF1 relies on its methylation by PRMT5. Consistent with this, we found that loss of PRMT5 led to changes in alternative splicing. This analysis revealed multiple affected essential genes, linking PRMT5 activity to its loss of function phenotype. Our results show that PRMT5 regulates binding of SRSF1 to mRNAs and proteins in leukemia and provide potential biomarkers for the treatment response to PRMT5 inhibitors.