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Free mRNA in excess upon polysome dissociation is a scaffold for protein multimerization to form stress granules.

ABSTRACT: The sequence of events leading to stress granule assembly in stressed cells remains elusive. We show here, using isotope labeling and ion microprobe, that proportionally more RNA than proteins are present in stress granules than in surrounding cytoplasm. We further demonstrate that the delivery of single strand polynucleotides, mRNA and ssDNA, to the cytoplasm can trigger stress granule assembly. On the other hand, increasing the cytoplasmic level of mRNA-binding proteins like YB-1 can directly prevent the aggregation of mRNA by forming isolated mRNPs, as evidenced by atomic force microscopy. Interestingly, we also discovered that enucleated cells do form stress granules, demonstrating that the translocation to the cytoplasm of nuclear prion-like RNA-binding proteins like TIA-1 is dispensable for stress granule assembly. The results lead to an alternative view on stress granule formation based on the following sequence of events: after the massive dissociation of polysomes during stress, mRNA-stabilizing proteins like YB-1 are outnumbered by the burst of nonpolysomal mRNA. mRNA freed of ribosomes thus becomes accessible to mRNA-binding aggregation-prone proteins or misfolded proteins, which induces stress granule formation. Within the frame of this model, the shuttling of nuclear mRNA-stabilizing proteins to the cytoplasm could dissociate stress granules or prevent their assembly.

SUBMITTER: Bounedjah O

PROVIDER: S-EPMC4117795 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Liquid- and solid-like RNA granules form through specific scaffold proteins and combine into biphasic granules.

Project description:RNA granules consist of membrane-less RNA-protein assemblies and contain dynamic liquid-like shells and stable solid-like cores, which are thought to function in numerous processes in mRNA sorting and translational regulation. However, how these distinct substructures are formed, whether they are assembled by different scaffolds, and whether different RNA granule scaffolds induce these different substructures remains unknown. Here, using fluorescence microscopy-based morphological and molecular-dynamics analyses, we demonstrate that RNA granule scaffold proteins (scaffolds) can be largely classified into two groups, liquid and solid types, which induce the formation of liquid-like and solid-like granules, respectively, when expressed separately in cultured cells. We found that when co-expressed, the liquid-type and solid-type scaffolds combine and form liquid- and solid-like substructures in the same granules, respectively. The combination of the different types of scaffolds reduced the immobile fractions of the solid-type scaffolds and their dose-dependent ability to decrease nascent polypeptides in granules, but had little effect on the dynamics of the liquid-type scaffolds or their dose-dependent ability to increase nascent polypeptides in granules. These results suggest that solid- and liquid-type scaffolds form different substructures in RNA granules and differentially affect each other. Our findings provide detailed insight into the assembly mechanism and distinct dynamics and functions of core and shell substructures in RNA granules.

| S-EPMC6416441 | biostudies-literature

Scaffold-Free Endometrial Organoids Respond to Excess Androgens Associated With Polycystic Ovarian Syndrome.

Project description:ContextPolycystic ovary syndrome (PCOS) is a prevalent disorder in reproductive aged women associated with a number of endocrine and metabolic complications, including increased risk of endometrial cancer.ObjectiveTo study the effect of the characteristic increased androgen levels in PCOS on the endometrium, a novel scaffold-free multicellular endometrial organoid was established.DesignHuman endometrial organoids were constructed using primary endometrial epithelial and stromal cells from endometrial tissues. Organoids were treated for 14 days with physiologic levels of estradiol and testosterone to mimic a normal follicular phase or PCOS hormone profiles. Organoids were harvested for immunostaining and ribonucleic acid sequencing.SettingAcademic institution.PatientsEndometrial tissues from 10 premenopausal women undergoing hysterectomy for benign pathologies were obtained following written consent.Main outcome measuresOrganoid architecture, cell specific markers, functional markers, proliferation, and gene expression were measured.ResultsA method to generate scaffold-free endometrial organoids containing epithelial and stromal cells was established. These organoids exhibited distinct organization with epithelial cells lining the outer surface and stromal cells in the center of the organoids. Epithelial cells were polarized, organoids expressed cell type specific and functional markers, as well as androgen, estrogen, and progesterone receptors. Treatment with PCOS hormones increased cell proliferation and dysregulated genes in endometrial organoids.ConclusionsA new multicellular, scaffold-free endometrial organoid system was established that resembled physiology of the native endometrium. Excess androgens in PCOS promoted cell proliferation in endometrial organoids, revealing new mechanisms of PCOS-associated with risk of endometrial neoplasia.

| S-EPMC7112974 | biostudies-literature

Polysome-associated mRNA levels upon glucose repletion

2011-09-05 | GSE31220 | GEO

Polysome-associated mRNA levels upon glucose repletion

Project description:Cell survival in changing environments requires appropriate regulation of gene expression, including post-transcriptional gene regulatory mechanisms. Based on reporter gene studies in glucose-starved yeast, it was proposed that translationally silenced eukaryotic mRNAs accumulate in P-bodies and can return to active translation. We present evidence contradicting the notion that this model is a widespread and general phenomenon. First, genome-wide measurements of mRNA abundance, translation, and ribosome occupancy following glucose withdrawal show that most mRNAs are lost from the cell coincident with their loss from polysomes. Second, only a very limited sub-population of translationally repressed transcripts, comprising fewer than 400 genes, can be reactivated for translation upon glucose re-addition in the absence of new transcription. This highly selective post-transcriptional regulation could be a mechanism for cells to minimize the energetic costs of reversing gene-regulatory decisions in rapidly changing environments by transiently preserving a pool of transcripts whose translation is rate-limiting for growth. Sigma 1278b yeast were grown to OD600=1.0-1.1 in YPD in baffled flasks at 30C with vigorous shaking. Cells were treated with thiolutin to a final concentration of 3ug/mL, harvested by centrifugation, and resuspended in pre-warmed YPA medium lacking glucose. Cells were returned to 30C for shaking for 10 minutes. For the refed samples, glucose was added to a final concentration of 2% and samples were taken after 5 minutes. Polysome preparation and RNA isolation were as described in Experimental Procedues. A common RNA sample, polysomal RNA from cells grown in YPD, was used for one channel of each array.

2011-09-04 | E-GEOD-31220 | biostudies-arrayexpress

Correction: Polysome Fractionation to Analyze mRNA Distribution Profiles.

Project description:[This corrects the article PMC5431591.].

| S-EPMC6482963 | biostudies-literature

A solanesol-derived scaffold for multimerization of bioactive peptides.

Project description:A flexible molecular scaffold bearing varying numbers of terminal alkyne groups was synthesized in five steps from solanesol. R(CO)-MSH(4)-NH(2) ligands, which have a relatively low affinity for binding at the human melanocortin 4 receptor (hMC4R), were prepared by solid phase synthesis and were N-terminally acylated with 6-azidohexanoic acid. Multiple copies of the azide N(3)(CH(2))(5)(CO)-MSH(4)-NH(2) were attached to the alkyne-bearing, solanesol-derived molecular scaffold via the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. Control studies showed that the binding affinity of the triazole-containing ligand, CH(3)(CH(2))(3)(C(2)N(3))(CH(2))(5)(CO)-MSH(4)-NH(2), was not significantly diminished relative to the corresponding parental ligand, CH(3)(CO)-MSH(4)-NH(2). In a competitive binding assay with a Eu-labeled probe based on the superpotent ligand NDP-alpha-MSH, the monovalent and multivalent constructs appear to bind to hMC4R as monovalent species. In a similar assay with a Eu-labeled probe based on MSH(4), modest increases in binding potency with increased MSH(4) content per scaffold were observed.

| S-EPMC2929268 | biostudies-literature

A sucrose-derived scaffold for multimerization of bioactive peptides.

Project description:A spherical molecular scaffold bearing eight terminal alkyne groups was synthesized in one step from sucrose. One or more copies of a tetrapeptide azide, either N(3)(CH(2))(5)(CO)-His-DPhe-Arg-Trp-NH(2) (MSH4) or N(3)(CH(2))(5)(CO)-Trp-Met-Asp-Phe-NH(2) (CCK4), were attached to the scaffold via the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. Competitive binding assays using Eu-labeled probes based on the superpotent ligands Ser-Tyr-Ser-Nle-Glu-His-DPhe-Arg-Trp-Gly-Lys-Pro-Val-NH(2) (NDP-?-MSH) and Asp-Tyr-Met-Gly-Trp-Met-Asp-Phe-NH(2) (CCK8) were used to study the interactions of monovalent and multivalent MSH4 and CCK4 constructs with Hek293 cells engineered to overexpress MC4R and CCK2R. All of the monovalent and multivalent MSH4 constructs exhibited binding comparable to that of the parental ligand, suggesting that either the ligand spacing was inappropriate for multivalent binding, or MSH4 is too weak a binder for a second 'anchoring' binding event to occur before the monovalently-bound construct is released from the cell surface. In contrast with this behavior, monovalent CCK4 constructs were significantly less potent than the parental ligand, while multivalent CCK4 constructs were as or more potent than the parental ligand. These results are suggestive of multivalent binding, which may be due to increased residence times for monovalently bound CCK4 constructs on the cell surface relative to MSH4 constructs, the greater residence time being necessary for the establishment of multivalent binding.

| S-EPMC3197697 | biostudies-literature

Cell-free formation of RNA granules: low complexity sequence domains form dynamic fibers within hydrogels.

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| S-EPMC6347373 | biostudies-literature

MCF-7 Human Breast Cancer Cells Form Differentiated Microtissues in Scaffold-Free Hydrogels.

Project description:Three-dimensional (3D) cultures are increasing in use because of their ability to represent in vivo human physiology when compared to monolayer two-dimensional (2D) cultures. When grown in 3D using scaffold-free agarose hydrogels, MCF-7 human breast cancer cells self-organize to form directionally-oriented microtissues that contain a luminal space, reminiscent of the in vivo structure of the mammary gland. When compared to MCF-7 cells cultured in 2D monolayer culture, MCF-7 microtissues exhibit increased mRNA expression of luminal epithelial markers keratin 8 and keratin 19 and decreased expression of basal marker keratin 14 and the mesenchymal marker vimentin. These 3D MCF-7 microtissues remain responsive to estrogens, as demonstrated by induction of known estrogen target mRNAs following exposure to 17?-estradiol. Culture of MCF-7 cells in scaffold-free conditions allows for the formation of more differentiated, estrogen-responsive structures that are a more relevant system for evaluation of estrogenic compounds than traditional 2D models.

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Rbfox2 dissociation from stress granules suppresses cancer progression.

Project description:Stress granules (SGs) are stalled translation initiation complexes comprising untranslated mRNAs and RNA-binding proteins (RBPs). RBP fox-1 homolog 2 (Rbfox2), a component of SGs, binds to retinoblastoma 1 (RB1) mRNA, which is closely related to cancer progression; however, the role of Rbfox2 in cancer progression remains largely unknown. In this study, we confirmed that Rbfox2, which is present in the nucleus as a splicing regulator, localizes to the cytoplasm of human colon cancer tissues and that induction of Rbfox2 dissociation from SGs by resveratrol treatment inhibits cancer progression. We also observed that Rbfox2 in SGs inhibited RB1 protein expression and promoted cell cycle progression. Additionally, resveratrol treatment inhibited SG-mediated Rbfox2 localization, further inhibiting RB1 protein expression, and inhibited specific Rbfox2 localization to the cytoplasm in melanoma B16-F10 cells, thereby effectively inhibiting metastasis and tumor growth ability. These results indicate that Rbfox2 dissociation from SGs attenuates cancer progression and offer insight into the mechanism associated with Rbfox2 dissociation, thereby marking Rbfox2 as a potential candidate target for cancer therapy.

| S-EPMC6486603 | biostudies-literature

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