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An Intrinsically Disordered RNA Binding Protein Modulates mRNA Translation and Storage.

Proteins with intrinsically disordered regions (IDR) play diverse functions in regulating gene expression in the cell. Many of these proteins interact with cytoplasmic ribosomes. However, the molecular functions related to the interactions are largely unclear. In this study, using an abundant RNA-binding protein, Sbp1, with a structurally well-defined RNA recognition motif and an intrinsically disordered RGG domain as a model system, we investigated how an RNA binding protein with IDR modulates mRNA storage and translation. Using genomic and molecular approaches, we show that Sbp1 slows ribosome movement on cellular mRNAs and promotes polysome stacking or aggregation. Sbp1-associated polysomes display a ring-shaped structure in addition to a beads-on-string morphology visualized under the electron microscope, likely to be an intermediate slow translation state between actively translating polysomes and the translation-sequestered RNA granule. Moreover, the binding of Sbp1 to the 5'UTRs of mRNAs represses both cap-dependent and cap-independent translation initiation of proteins, many are functionally important for general protein synthesis in the cell. Finally, post-translational modifications at the arginine in the RGG motif change the Sbp1 protein interactome and play important roles in directing cellular mRNAs to either translation or storage. Taken together, our study demonstrates that under physiological conditions, intrinsically disordered RNA binding proteins promote polysome aggregation and regulate mRNA translation and storage using multiple distinctive mechanisms. This research also establishes a framework with which functions of other IDR-containing proteins can be investigated and defined.

RNA-Binding Proteins

Translation by bacterial cells of messenger RNA for interferon of animal origin.

Escherichia coli, strain AB 1157, cells are capable of translating human, mouse, and chicken messenter RNA for interferon with production of interferon of the corresponding specifity. This translation occurs in the presence of serum. The activity of the resulting interferon decreased in parallel to dilution of the original mRNA preparation, upon multiple ulitization of the mRNA solution, as well as upon reduction of the interferon- producing activity of cells-donors of mRNA due to prolonged storage of the cells. Unlike animal cells, the bacteria do not require pre-treatment with actinomycin D. The interferon translated by bacteria is inactivated by trypsin and resistant to ribonuclease.

Animals

Effects of a chromatin low molecular weight peptidic fraction on differentiation markers and virus production in Friend leukemia cells.

Low molecular weight chromatin peptides exert a dose-dependent inhibition of Dimethylsulfoxide (DMSO)-induced erythroid differentiation of murine Friend Leukemia Cells (FLC). This effect correlates with the degree of purification of the peptide fractions. Crot analysis of globin mRNA amounts in DMSO-treated FLC given the peptides showed a 4-5-fold decrease of messenger RNA in the cytoplasma with no nuclear storage of globin transcripts. Spectrin accumulation in "induced" FLC is inhibited as well. The effects of the peptides on erythroid markers are reversible upon removal of the compounds. They also appear to be specific for induced gene expression as (1) no effects are observed on cell growth and RNA synthesis in normal non-differentiating cell lines; and (2) no changes have been detected with regard to the expression of integrated viral genes coding for continuous shedding of viral particles.

Animals

Retinal hypoxia reversal with PLGA-oxygen nanobubbles.

Pathologies associated with retinal hypoxia, including diabetic retinopathy, central/branch retinal artery occlusion (CRAO/BRAO), central/branch retinal vein occlusion (CRVO/BRVO), retinopathy of prematurity, sickle cell retinopathy, etc., have limited effective therapeutic intervention strategies. To address this shortcoming, herein we propose a biocompatible and biodegradable poly (lactic-co-glycolic acid) shell-based oxygen nanobubbles (PLGA-ONBs) platform, formulated with PLGA, polyvinyl alcohol (PVA), and NaHCO3. The formulation of a novel PLGA-ONBs was proposed, and the synthesis process was optimized with respect to dependent (sonication power, PVA, and NaHCO3 concentrations) and response (hydrodynamic diameter and oxygen capacity) variables. The optimized formulation has a concentration of (13.8 ± 0.01) × 1010 particles per ml with a hydrodynamic diameter of 142.83 ± 11.46 nm, and oxygen loading capacity of 47.2 ± 2.4 mg L-1. After 4 weeks of storage, the ONBs were found to have an oxygen concentration of 38.9 ± 2.9 mg L-1, indicating excellent oxygen retention capability. The PLGA-ONBs tested in vitro in Muller and R28 retinal cell lines demonstrated excellent biocompatibility and potential to mitigate hypoxia. In addition, the PLGA-ONBs treatment on hypoxic cells demonstrated restoration of mRNA expression of three key hypoxic genes (HIF-1α, PAI-1, and VEGF-A) to normoxic states, indicating hypoxia reversal potential. Biosafety of the PLGA-ONBs was demonstrated in a rabbit model, demonstrating promise in clinical translation. The PLGA-ONBs developed exhibited excellent oxygen loading and retention, potential in hypoxia mitigation, and a safety profile that could be a promising route to treating ischemic diseases of the eye.

Polylactic Acid-Polyglycolic Acid Copolymer

Delayed diagnosis of mild mucopolysaccharidosis type IVA.

BACKGROUND: Mucopolysaccharidosis IVA (MPS IVA) is a lysosomal storage disease caused by biallelic variants in the N-acetylgalactosamine-6-sulfatase (GALNS) gene and is characterized by progressive and multi-system involvements, dominantly with skeletal deformities. A mild form of MPS IVA often presents with atypical symptoms and can go unrecognized for years. METHODS: The diagnosis of MPS IVA was confirmed via GALNS enzyme activity testing in leukocytes. Clinical features were collected. Molecular analysis was performed by next generation sequence and Sanger sequencing of the GALNS gene. The pathogenicity of the deep intron variant was verified by mRNA analyses. RESULTS: Thirteen patients with mild MPS IVA from six families were included. All probands first visit pediatric orthopedists and it took 5.6 years to be diagnosed after the disease onset. The most common symptoms in our series were waddling gait (85%), short neck (69%) and flat feet (62%). Radiologic findings indicated skeletal abnormalities in all patients, especially modification of the vertebral bodies (100%) and acetabular and femoral head dysplasia (100%). Five novel GALNS variants, including c.121-2_121-1insTTTGCTGGCATATGCA, E2 deletion, c.569 A > G, c.898 + 2 T > A, and c.1139 + 2 T > C, were identified. The most common variant, a deep intron variant NM_000512.5: c.121-210 C > T (NM_001323544.2: c.129 C > T, p.G43G), was revealed to result in an 11 bp deletion (c.128_138delGCGATGCTGAG, p.Gly43Aspfs*5) on GALNS mRNA in the GALNS transcript of NM_001323544.2. CONCLUSIONS: This study provides significant insights into the clinical features and molecular characteristics that contribute to the early diagnosis of mild MPS IVA. On the basis of our cohort, orthopedists need to be able to recognize signs and symptoms of mild MPS IVA as well as the molecular and biochemical diagnosis so that an early diagnosis and treatment can be instituted.

Humans

Rescue of common and rare exon 2 skipping variants of the GAA gene using modified U1 snRNA.

BACKGROUND: Pompe disease (PD) is an autosomal recessive lysosomal storage disorder caused by the deficient activity of acid alpha glucosidase (GAA) enzyme due to mutations in the GAA gene. As a result, undigested glycogen accumulates within lysosomes causing their dysfunction. From a clinical point of view, the disease can be classified in infantile-onset (IO) and late-onset (LO) forms. The common GAA c.-32-13T>G variant, found in 40-70% of LO-PD alleles, is a leaky splicing mutation interfering with the correct GAA exon 2 recognition by the spliceosome leading to the production of non-functional GAA transcripts. In this study, we used modified, GAA-tailored U1 snRNAs to correct the aberrant splicing determined by the c.-32-13T>G and other GAA exon 2-skipping mutations. METHODS: A set of constructs expressing 5 different engineered U1 snRNAs was generated. A functional splicing assay using a GAA hybrid minigene carrying different variants known to affect GAA exon 2 splicing was used to test the effect of engineered U1 snRNAs on exon 2 inclusion. The effect on endogenously expressed GAA transcript and GAA enzymatic activity was assessed by transfecting patient-derived fibroblasts bearing the common c.-32-13T>G with the best performing modified U1 snRNA. RESULTS: Modified U1-3, U1+1 and U1+6 snRNAs were all able to increase, in a dose-dependent manner, the inclusion of exon 2 within the transcript derived from the GAA minigene harbouring the c.-32-13T>G variant. The U1+1 was the most effective one (2,5 fold increase). Moreover, U1+1 snRNA partially rescued the correct splicing of GAA minigenes harbouring mutations that affect the 3'ss (c.-32-3C>G, c.-32-2A>G) and the 5'ss (c.546G>A, c.546G>C, c.546G>T). Notably, the treatment of patient-derived fibroblasts carrying the c.-32-13T>G mutation with the U1+1 snRNA increased the amount of normal GAA mRNA by 1,8 fold and the GAA enzymatic activity by 70%. CONCLUSIONS: we provide the proof-of-concept for the use of modified GAA-tailored U1 snRNAs, designed to potentiate the recognition of the GAA exon 2 5'ss, as therapeutic tools to correct the aberrant transcripts carrying variants that affect exon 2 splicing, including the common c.-32-13T>G variant.

Humans

Clinically relevant pseudoexons of the GALNS gene and their antisense-based correction.

BACKGROUND: Biallelic pathogenic variants in the GALNS gene lead to Mucopolysaccharidosis Type IVA (MPS IVA), a rare lysosomal storage disorder. GALNS encodes the enzyme N-acetylgalactosamine-6-sulfatase, whose deficiency causes accumulation of glycosaminoglycans and leads to a broad spectrum of clinical manifestations primarily affecting the osteoarticular system. Several studies have shown that, in 10%-15% of patients with the biochemical phenotype of MPS IVA, standard molecular genetic testing fails to identify one or both causative variants in the GALNS gene. METHODS: We performed an in-depth investigation of GALNS' splicing, with a special focus on deep-intronic mutations that lead to activation of pseudoexons (PEs). Using bioinformatic tools, we analyzed all deep-intronic variants in GALNS available in public databases and subjected the most relevant ones to in vitro analyses using minigenes. RESULTS: We characterized eight PE-activating variants, one of which (c.121-210C > T) represents a recurrent pathogenic variant which has long been hidden behind the mask of a polymorphic variant. In addition, we demonstrate that GALNS' splicing can produce a diverse range of mRNA isoforms containing so-called wild-type PEs, which are present at low levels as part of non-productive splicing, and weak canonical exons which are prone to skipping. We show that PE-activating variants cluster within wild-type PEs, highlighting the need for closer scrutiny of these regions during genetic testing. Finally, we applied modified U7 small nuclear RNAs and circular RNAs to efficiently block the identified PEs and pave the way for personalized antisense-based therapy for MPS IVA patients. CONCLUSION: The results of this study expand the understanding of GALNS gene splicing, indicating hotspots for splicing mutations. The presented data not only help to increase the diagnostic yield for MPS IVA but also unveil new therapeutic approaches for a number of MPS IVA patients.

Humans