PubMed

Recent Publications

Regulatory Expansion in Mammals of Multivalent hnRNP Assemblies that Globally Control Alternative Splicing.

Read Full Article on External Site Related Articles

Regulatory Expansion in Mammals of Multivalent hnRNP Assemblies that Globally Control Alternative Splicing.

Cell. 2017 Jul 13;170(2):324-339.e23

Authors: Gueroussov S, Weatheritt RJ, O'Hanlon D, Lin ZY, Narula A, Gingras AC, Blencowe BJ

Abstract
Alternative splicing (AS) patterns have diverged rapidly during vertebrate evolution, yet the functions of most species- and lineage-specific splicing events are not known. We observe that mammalian-specific AS events are enriched in transcript sequences encoding intrinsically disordered regions (IDRs) of proteins, in particular those containing glycine/tyrosine repeats that mediate formation of higher-order protein assemblies implicated in gene regulation and human disease. These evolutionary changes impact nearly all members of the hnRNP A and D families of RNA binding proteins. Regulation of these events requires formation of unusual, long-range mammalian-specific RNA duplexes. Differential inclusion of the alternative exons controls the formation of tyrosine-dependent multivalent hnRNP assemblies that, in turn, function to globally regulate splicing. Together, our results demonstrate that AS control of IDR-mediated interactions between hnRNPs represents an important and recurring mechanism underlying splicing regulation. Furthermore, this mechanism has expanded the regulatory capacity of mammalian cells.

PMID: 28709000 [PubMed - indexed for MEDLINE]



▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄

Quantitative analysis of protein interaction network dynamics in yeast.

Quantitative analysis of protein interaction network dynamics in yeast.

Mol Syst Biol. 2017 Jul 13;13(7):934

Authors: Celaj A, Schlecht U, Smith JD, Xu W, Suresh S, Miranda M, Aparicio AM, Proctor M, Davis RW, Roth FP, St Onge RP

Abstract
Many cellular functions are mediated by protein-protein interaction networks, which are environment dependent. However, systematic measurement of interactions in diverse environments is required to better understand the relative importance of different mechanisms underlying network dynamics. To investigate environment-dependent protein complex dynamics, we used a DNA-barcode-based multiplexed protein interaction assay in Saccharomyces cerevisiae to measure in vivo abundance of 1,379 binary protein complexes under 14 environments. Many binary complexes (55%) were environment dependent, especially those involving transmembrane transporters. We observed many concerted changes around highly connected proteins, and overall network dynamics suggested that "concerted" protein-centered changes are prevalent. Under a diauxic shift in carbon source from glucose to ethanol, a mass-action-based model using relative mRNA levels explained an estimated 47% of the observed variance in binary complex abundance and predicted the direction of concerted binary complex changes with 88% accuracy. Thus, we provide a resource of yeast protein interaction measurements across diverse environments and illustrate the value of this resource in revealing mechanisms of network dynamics.

PMID: 28705884 [PubMed - in process]



▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄

Syp1 regulates the clathrin-mediated and clathrin-independent endocytosis of multiple cargo proteins through a novel sorting motif.

Related Articles

Syp1 regulates the clathrin-mediated and clathrin-independent endocytosis of multiple cargo proteins through a novel sorting motif.

Mol Biol Cell. 2017 Jul 12;:

Authors: Apel AR, Hoban K, Chuartzman S, Tonikian R, Sidhu S, Schuldiner M, Wendland B, Prosser D

Abstract
Internalization of proteins from the plasma membrane (PM) allows for cell-surface composition regulation, signaling network modulation, and nutrient uptake. Clathrin-mediated endocytosis (CME) is a major internalization route for PM proteins. During CME, endocytic adaptor proteins bind cargos at the cell surface and link them to the PM and clathrin coat. Muniscins are a conserved family of endocytic adaptors, including Syp1 in budding yeast and its mammalian ortholog, FCHo1. These adaptors bind cargo via a C-terminal ì-homology domain (ìHD); however, few cargos exhibiting muniscin-dependent endocytosis have been identified, and the sorting sequence recognized by the μHD is unknown. To reveal Syp1 cargo-sorting motifs, we performed a phage display screen and used biochemical methods to demonstrate that the Syp1 μHD binds DxY motifs in the previously identified Syp1 cargo, Mid2, and the v-SNARE, Snc1. We also executed an unbiased visual screen, which identified the peptide transporter, Ptr2, and the ammonium permease, Mep3, as Syp1 cargos containing DxY motifs. Finally, we determined that, in addition to regulating cargo entry through CME, Syp1 can promote internalization of Ptr2 through a recently identified clathrin-independent endocytic pathway that requires the Rho1 GTPase. These findings elucidate the mechanism of Syp1 cargo recognition and its role in trafficking.

PMID: 28701344 [PubMed - as supplied by publisher]



▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄

Phosphatidylserine dictates the assembly and dynamics of caveolae in the plasma membrane.

Read Full Article on External Site Read Full Article on External Site Related Articles

Phosphatidylserine dictates the assembly and dynamics of caveolae in the plasma membrane.

J Biol Chem. 2017 Aug 25;292(34):14292-14307

Authors: Hirama T, Das R, Yang Y, Ferguson C, Won A, Yip CM, Kay JG, Grinstein S, Parton RG, Fairn GD

Abstract
Caveolae are bulb-shaped nanodomains of the plasma membrane that are enriched in cholesterol and sphingolipids. They have many physiological functions, including endocytic transport, mechanosensing, and regulation of membrane and lipid transport. Caveola formation relies on integral membrane proteins termed caveolins (Cavs) and the cavin family of peripheral proteins. Both protein families bind anionic phospholipids, but the precise roles of these lipids are unknown. Here, we studied the effects of phosphatidylserine (PtdSer), phosphatidylinositol 4-phosphate (PtdIns4P), and phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) on caveolar formation and dynamics. Using live-cell, single-particle tracking of GFP-labeled Cav1 and ultrastructural analyses, we compared the effect of PtdSer disruption or phosphoinositide depletion with caveola disassembly caused by cavin1 loss. We found that PtdSer plays a crucial role in both caveola formation and stability. Sequestration or depletion of PtdSer decreased the number of detectable Cav1-GFP puncta and the number of caveolae visualized by electron microscopy. Under PtdSer-limiting conditions, the co-localization of Cav1 and cavin1 was diminished, and cavin1 degradation was increased. Using rapamycin-recruitable phosphatases, we also found that the acute depletion of PtdIns4P and PtdIns(4,5)P2 has minimal impact on caveola assembly but results in decreased lateral confinement. Finally, we show in a model of phospholipid scrambling, a feature of apoptotic cells, that caveola stability is acutely affected by the scrambling. We conclude that the predominant plasmalemmal anionic lipid PtdSer is essential for proper Cav clustering, caveola formation, and caveola dynamics and that membrane scrambling can perturb caveolar stability.

PMID: 28698382 [PubMed - indexed for MEDLINE]



▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄

Oncogenic Activation of the RNA Binding Protein NELFE and MYC Signaling in Hepatocellular Carcinoma.

Read Full Article on External Site Related Articles

Oncogenic Activation of the RNA Binding Protein NELFE and MYC Signaling in Hepatocellular Carcinoma.

Cancer Cell. 2017 Jul 10;32(1):101-114.e8

Authors: Dang H, Takai A, Forgues M, Pomyen Y, Mou H, Xue W, Ray D, Ha KCH, Morris QD, Hughes TR, Wang XW

Abstract
Global transcriptomic imbalance is a ubiquitous feature associated with cancer, including hepatocellular carcinoma (HCC). Analyses of 1,225 clinical HCC samples revealed that a large numbers of RNA binding proteins (RBPs) are dysregulated and that RBP dysregulation is associated with poor prognosis. We further identified that oncogenic activation of a top candidate RBP, negative elongation factor E (NELFE), via somatic copy-number alterations enhanced MYC signaling and promoted HCC progression. Interestingly, NELFE induces a unique tumor transcriptome by selectively regulating MYC-associated genes. Thus, our results revealed NELFE as an oncogenic protein that may contribute to transcriptome imbalance in HCC through the regulation of MYC signaling.

PMID: 28697339 [PubMed - indexed for MEDLINE]



▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄

Tracing the origins of relapse in acute myeloid leukaemia to stem cells.

Related Articles

Tracing the origins of relapse in acute myeloid leukaemia to stem cells.

Nature. 2017 Jun 28;:

Authors: Shlush LI, Mitchell A, Heisler L, Abelson S, Ng SWK, Trotman-Grant A, Medeiros JJF, Rao-Bhatia A, Jaciw-Zurakowsky I, Marke R, McLeod JL, Doedens M, Bader G, Voisin V, Xu C, McPherson JD, Hudson TJ, Wang JCY, Minden MD, Dick JE

Abstract
In acute myeloid leukaemia, long-term survival is poor as most patients relapse despite achieving remission. Historically, the failure of therapy has been thought to be due to mutations that produce drug resistance, possibly arising as a consequence of the mutagenic properties of chemotherapy drugs. However, other lines of evidence have pointed to the pre-existence of drug-resistant cells. For example, deep sequencing of paired diagnosis and relapse acute myeloid leukaemia samples has provided direct evidence that relapse in some cases is generated from minor genetic subclones present at diagnosis that survive chemotherapy, suggesting that resistant cells are generated by evolutionary processes before treatment and are selected by therapy. Nevertheless, the mechanisms of therapy failure and capacity for leukaemic regeneration remain obscure, as sequence analysis alone does not provide insight into the cell types that are fated to drive relapse. Although leukaemia stem cells have been linked to relapse owing to their dormancy and self-renewal properties, and leukaemia stem cell gene expression signatures are highly predictive of therapy failure, experimental studies have been primarily correlative and a role for leukaemia stem cells in acute myeloid leukaemia relapse has not been directly proved. Here, through combined genetic and functional analysis of purified subpopulations and xenografts from paired diagnosis/relapse samples, we identify therapy-resistant cells already present at diagnosis and two major patterns of relapse. In some cases, relapse originated from rare leukaemia stem cells with a haematopoietic stem/progenitor cell phenotype, while in other instances relapse developed from larger subclones of immunophenotypically committed leukaemia cells that retained strong stemness transcriptional signatures. The identification of distinct patterns of relapse should lead to improved methods for disease management and monitoring in acute myeloid leukaemia. Moreover, the shared functional and transcriptional stemness properties that underlie both cellular origins of relapse emphasize the importance of developing new therapeutic approaches that target stemness to prevent relapse.

PMID: 28658204 [PubMed - as supplied by publisher]



▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄

Evaluation and Design of Genome-Wide CRISPR/SpCas9 Knockout Screens.

Related Articles

Evaluation and Design of Genome-Wide CRISPR/SpCas9 Knockout Screens.

G3 (Bethesda). 2017 Jun 27;:

Authors: Hart T, Tong AHY, Chan K, Van Leeuwen J, Seetharaman A, Aregger M, Chandrashekhar M, Hustedt N, Seth S, Noonan A, Habsid A, Sizova O, Nedyalkova L, Climie R, Tworzyanski L, Lawson K, Sartori MA, Alibai S, Tieu D, Masud S, Mero P, Weiss A, Brown KR, Ušaj M, Billmann M, Rahman M, Costanzo M, Myers CL, Andrews BJ, Boone C, Durocher D, Moffat J

Abstract
The adaptation of CRISPR/SpCas9 technology to mammalian cell lines is transforming the study of human functional genomics. Pooled libraries of CRISPR guide RNAs (gRNAs) targeting human protein-coding genes and encoded in viral vectors have been used to systematically create gene knockouts in a variety of human cancer and immortalized cell lines, in an effort to identify whether these knockouts cause cellular fitness defects. Previous work has shown that CRISPR screens are more sensitive and specific than pooled library shRNA screens in similar assays, but currently there exists significant variability across CRISPR library designs and experimental protocols. In this study, we re-analyze 17 genome-scale knockout screens in human cell lines from three research groups using three different genome-scale gRNA libraries. Using the Bayesian Analysis of Gene Essentiality (BAGEL) algorithm to identify essential genes, we refine and expand our previously defined set of human core essential genes from 360 to 684 genes. We use this expanded set of reference Core Essential Genes (CEG2) plus empirical data from six CRISPR knockout screens to guide the design of a sequence-optimized gRNA library, the Toronto KnockOut version 3.0 (TKOv3) library. We then demonstrate the high effectiveness of the library relative to reference sets of essential and nonessential genes as well as other screens using similar approaches. The optimized TKOv3 library, combined with the CEG2 reference set, provide an efficient, highly optimized platform for performing and assessing gene knockout screens in human cell lines.

PMID: 28655737 [PubMed - as supplied by publisher]



▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄

RNAcompete-S: combined RNA sequence/structure preferences for RNA binding proteins derived from a single-step in vitro selection.

Related Articles

RNAcompete-S: combined RNA sequence/structure preferences for RNA binding proteins derived from a single-step in vitro selection.

Methods. 2017 Jun 23;:

Authors: Cook KB, Vembu S, Ha KCH, Zheng H, Laverty KU, Hughes TR, Ray D, Morris QD

Abstract
RNA-binding proteins recognize RNA sequences and structures, but there is currently no systematic and accurate method to derive large (>12 base) motifs de novo that reflect a combination of intrinsic preference to both sequence and structure. To address this absence, we introduce RNAcompete-S, which couples a single-step competitive binding reaction with an excess of random RNA 40-mers to a custom computational pipeline for interrogation of the bound RNA sequences and derivation of SSMs (Sequence and Structure Models). RNAcompete-S confirms that HuR, QKI, and SRSF1 prefer binding sites that are single stranded, and recapitulates known 8-10 bp sequence and structure preferences for Vts1p and RBMY. We also derive an 18-base long SSM for Drosophila SLBP, which to our knowledge has not been previously determined by selections from pure random sequence, and accurately discriminates human replication-dependent histone mRNAs. Thus, RNAcompete-S enables accurate identification of large, intrinsic sequence-structure specificities with a uniform assay.

PMID: 28651966 [PubMed - as supplied by publisher]



▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄

Recent advances in understanding contextual TGFβ signaling.

Related Articles

Recent advances in understanding contextual TGFβ signaling.

F1000Res. 2017;6:749

Authors: Ayyaz A, Attisano L, Wrana JL

Abstract
The appearance of the first animal species on earth coincides with the emergence of transforming growth factor β (TGFβ) pathways. The evolution of these animals into more complex organisms coincides with a progressively increased TGFβ repertoire through gene duplications and divergence, making secreted TGFβ molecules the largest family of morphogenetic proteins in humans. It is therefore not surprising that TGFβ pathways govern numerous aspects of human biology from early embryonic development to regeneration, hematopoiesis, neurogenesis, and immunity. Such heavy reliance on these pathways is reflected in the susceptibility to minor perturbations in pathway components that can lead to dysregulated signaling and a diverse range of human pathologies such as cancer, fibrosis, and developmental disorders. Attempts to comprehensively resolve these signaling cascades are complicated by the long-recognized paradoxical role the pathway plays in cell biology. Recently, several groups have probed examples of the disparate aspects of TGFβ biology in a variety of animal models and uncovered novel context-dependent regulatory mechanisms. Here, we briefly review recent advancements and discuss their overall impact in directing future TGFβ research.

PMID: 28649369 [PubMed - in process]



▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄

Effectively infinite optical path-length created using a simple cubic photonic crystal for extreme light trapping.

Related Articles

Effectively infinite optical path-length created using a simple cubic photonic crystal for extreme light trapping.

Sci Rep. 2017 Jun 23;7(1):4171

Authors: Frey BJ, Kuang P, Hsieh ML, Jiang JH, John S, Lin SY

Abstract
A 900 nm thick TiO2 simple cubic photonic crystal with lattice constant 450 nm was fabricated and used to experimentally validate a newly-discovered mechanism for extreme light-bending. Absorption enhancement was observed extending 1-2 orders of magnitude over that of a reference TiO2 film. Several enhancement peaks in the region from 600-950 nm were identified, which far exceed both the ergodic fundamental limit and the limit based on surface-gratings, with some peaks exceeding 100 times enhancement. These results are attributed to radically sharp refraction where the optical path length approaches infinity due to the Poynting vector lying nearly parallel to the photonic crystal interface. The observed phenomena follow directly from the simple cubic symmetry of the photonic crystal, and can be achieved by integrating the light-trapping architecture into the absorbing volume. These results are not dependent on the material used, and can be applied to any future light trapping applications such as phosphor-converted white light generation, water-splitting, or thin-film solar cells, where increased response in areas of weak absorption is desired.

PMID: 28646167 [PubMed - in process]



▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄ ▄

Back to Top