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Bujosa P, Reina O, Caballé A, Casas-Lamesa A, Torras-Llort M, Pérez-Roldán J, Nacht AS, Vicent GP, Bernués J, Azorín F. Linker histone H1 regulates homeostasis of heterochromatin-associated cRNAs. Cell Rep 2024; 43:114137. [PMID: 38662543 DOI: 10.1016/j.celrep.2024.114137] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Revised: 12/23/2023] [Accepted: 04/08/2024] [Indexed: 06/01/2024] Open
Abstract
Chromatin-associated RNAs (cRNAs) are a poorly characterized fraction of cellular RNAs that co-purify with chromatin. Their full complexity and the mechanisms regulating their packaging and chromatin association remain poorly understood. Here, we address these questions in Drosophila. We find that cRNAs constitute a heterogeneous group of RNA species that is abundant in heterochromatic transcripts. We show that heterochromatic cRNAs interact with the heterogeneous nuclear ribonucleoproteins (hnRNP) hrp36/hrp48 and that depletion of linker histone dH1 impairs this interaction. dH1 depletion induces the accumulation of RNA::DNA hybrids (R-loops) in heterochromatin and, as a consequence, increases retention of heterochromatic cRNAs. These effects correlate with increased RNA polymerase II (RNAPII) occupancy at heterochromatin. Notably, impairing cRNA assembly by depletion of hrp36/hrp48 mimics heterochromatic R-loop accumulation induced by dH1 depletion. We also show that dH1 depletion alters nucleosome organization, increasing accessibility of heterochromatin. Altogether, these perturbations facilitate annealing of cRNAs to the DNA template, enhancing R-loop formation and cRNA retention at heterochromatin.
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Affiliation(s)
- Paula Bujosa
- Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain
| | - Oscar Reina
- Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain
| | - Adrià Caballé
- Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain
| | - Anna Casas-Lamesa
- Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain
| | - Mònica Torras-Llort
- Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain
| | - Juan Pérez-Roldán
- Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain
| | - Ana Silvina Nacht
- Centre de Regulació Genòmica (CRG), The Barcelona Institute of Science and Technology, Barcelona, Spain
| | - Guillermo P Vicent
- Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Centre de Regulació Genòmica (CRG), The Barcelona Institute of Science and Technology, Barcelona, Spain
| | - Jordi Bernués
- Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain.
| | - Fernando Azorín
- Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain.
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2
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Singh AK. Hsrω and Other lncRNAs in Neuronal Functions and Disorders in Drosophila. LIFE (BASEL, SWITZERLAND) 2022; 13:life13010017. [PMID: 36675966 PMCID: PMC9865238 DOI: 10.3390/life13010017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/15/2022] [Revised: 11/27/2022] [Accepted: 12/14/2022] [Indexed: 12/24/2022]
Abstract
Long noncoding RNAs (lncRNAs) have a crucial role in epigenetic, transcriptional and posttranscriptional regulation of gene expression. Many of these regulatory lncRNAs, such as MALAT1, NEAT1, HOTAIR, etc., are associated with different neurodegenerative diseases in humans. The lncRNAs produced by the hsrω gene are known to modulate neurotoxicity in polyQ and amyotrophic lateral sclerosis disease models of Drosophila. Elevated expression of hsrω lncRNAs exaggerates, while their genetic depletion through hsrω-RNAi or in an hsrω-null mutant background suppresses, the disease pathogenicity. This review discusses the possible mechanistic details and implications of the functions of hsrω lncRNAs in the modulation of neurodegenerative diseases.
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Affiliation(s)
- Anand Kumar Singh
- Interdisciplinary School of Life Sciences, Institute of Science, Banaras Hindu University, Varanasi 221005, India
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3
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Kwon PK, Kim HM, Kang B, Kim SW, Hwang SM, Im SH, Roh TY, Kim KT. hnRNP K supports the maintenance of RORγ circadian rhythm through ERK signaling. FASEB J 2021; 35:e21507. [PMID: 33724572 DOI: 10.1096/fj.202002076r] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2020] [Revised: 02/11/2021] [Accepted: 02/22/2021] [Indexed: 11/11/2022]
Abstract
Retinoic acid-related orphan receptor γ (RORγ) maintains the circadian rhythms of its downstream genes. However, the mechanism behind the transcriptional activation of RORγ itself remains unclear. Here, we demonstrate that transcription of RORγ is activated by heterogeneous nuclear ribonucleoprotein K (hnRNP K) via the poly(C) motif within its proximal promoter. Interestingly, we confirmed the binding of endogenous hnRNP K within RORγ1 and RORγ2 promoter along with the recruitment of RNA polymerase 2 through chromatin immunoprecipitation (ChIP). Furthermore, an assay for transposase accessible chromatin (ATAC)-qPCR showed that hnRNP K induced higher chromatin accessibility within the RORγ1 and RORγ2 promoter. Then we found that the knockdown of hnRNP K lowers RORγ mRNA oscillation amplitude in both RORγ and RORγ-dependent metabolic genes. Moreover, we demonstrated that time-dependent extracellular signal-regulated kinase (ERK) activation controls mRNA oscillation of RORγ and RORγ-dependent metabolic genes through hnRNP K. Taken together, our results provide new insight into the regulation of RORγ by hnRNP K as a transcriptional activator, along with its physiological significance in metabolism.
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Affiliation(s)
- Paul Kwangho Kwon
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Republic of Korea
| | - Hyo-Min Kim
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang, Republic of Korea
| | - Byunghee Kang
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang, Republic of Korea
| | - Sung Wook Kim
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang, Republic of Korea
| | - Sung-Min Hwang
- Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang, Republic of Korea
| | - Sin-Hyeog Im
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Republic of Korea.,Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang, Republic of Korea
| | - Tae-Young Roh
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Republic of Korea.,Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang, Republic of Korea
| | - Kyong-Tai Kim
- Department of Life Sciences, Pohang University of Science and Technology, Pohang, Republic of Korea.,Division of Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang, Republic of Korea
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4
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hnRNP K Supports High-Amplitude D Site-Binding Protein mRNA ( Dbp mRNA) Oscillation To Sustain Circadian Rhythms. Mol Cell Biol 2020; 40:MCB.00537-19. [PMID: 31907279 DOI: 10.1128/mcb.00537-19] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Accepted: 12/20/2019] [Indexed: 01/24/2023] Open
Abstract
Circadian gene expression is defined by the gene-specific phase and amplitude of daily oscillations in mRNA and protein levels. D site-binding protein mRNA (Dbp mRNA) shows high-amplitude oscillation; however, the underlying mechanism remains elusive. Here, we demonstrate that heterogeneous nuclear ribonucleoprotein K (hnRNP K) is a key regulator that activates Dbp transcription via the poly(C) motif within its proximal promoter. Biochemical analyses identified hnRNP K as a specific protein that directly associates with the poly(C) motif in vitro Interestingly, we further confirmed the rhythmic binding of endogenous hnRNP K within the Dbp promoter through chromatin immunoprecipitation as well as the cycling expression of hnRNP K. Finally, knockdown of hnRNP K decreased mRNA oscillation in both Dbp and Dbp-dependent clock genes. Taken together, our results show rhythmic protein expression of hnRNP K and provide new insights into its function as a transcriptional amplifier of Dbp.
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5
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Emerging roles for hnRNPs in post-transcriptional regulation: what can we learn from flies? Chromosoma 2014; 123:515-27. [PMID: 24913828 DOI: 10.1007/s00412-014-0470-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2014] [Revised: 05/21/2014] [Accepted: 05/23/2014] [Indexed: 12/13/2022]
Abstract
Heterogeneous nuclear ribonucleoproteins (hnRNPs) are a highly conserved family of RNA-binding proteins able to associate with nascent RNAs in order to support their localization, maturation and translation. Research over this last decade has remarked the importance of gene regulatory processes at post-transcriptional level, highlighting the emerging roles of hnRNPs in several essential biological events. Indeed, hnRNPs are key factors in regulating gene expression, thus, having a number of roles in many biological pathways. Moreover, failure of the activities catalysed by hnRNPs affects various biological processes and may underlie several human diseases including cancer, diabetes and neurodegenerative syndromes. In this review, we summarize some of hnRNPs' roles in the model organism Drosophila melanogaster, particularly focusing on their participation in all aspects of post-transcriptional regulation as well as their conserved role and involvement in the aetiology of human pathologies.
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Heterochromatin protein 1 (HP1a) positively regulates euchromatic gene expression through RNA transcript association and interaction with hnRNPs in Drosophila. PLoS Genet 2009; 5:e1000670. [PMID: 19798443 PMCID: PMC2743825 DOI: 10.1371/journal.pgen.1000670] [Citation(s) in RCA: 121] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2009] [Accepted: 09/02/2009] [Indexed: 11/19/2022] Open
Abstract
Heterochromatin Protein 1 (HP1a) is a well-known conserved protein involved in heterochromatin formation and gene silencing in different species including humans. A general model has been proposed for heterochromatin formation and epigenetic gene silencing in different species that implies an essential role for HP1a. According to the model, histone methyltransferase enzymes (HMTases) methylate the histone H3 at lysine 9 (H3K9me), creating selective binding sites for itself and the chromodomain of HP1a. This complex is thought to form a higher order chromatin state that represses gene activity. It has also been found that HP1a plays a role in telomere capping. Surprisingly, recent studies have shown that HP1a is present at many euchromatic sites along polytene chromosomes of Drosophila melanogaster, including the developmental and heat-shock-induced puffs, and that this protein can be removed from these sites by in vivo RNase treatment, thus suggesting an association of HP1a with the transcripts of many active genes. To test this suggestion, we performed an extensive screening by RIP-chip assay (RNA–immunoprecipitation on microarrays), and we found that HP1a is associated with transcripts of more than one hundred euchromatic genes. An expression analysis in HP1a mutants shows that HP1a is required for positive regulation of these genes. Cytogenetic and molecular assays show that HP1a also interacts with the well known proteins DDP1, HRB87F, and PEP, which belong to different classes of heterogeneous nuclear ribonucleoproteins (hnRNPs) involved in RNA processing. Surprisingly, we found that all these hnRNP proteins also bind heterochromatin and are dominant suppressors of position effect variegation. Together, our data show novel and unexpected functions for HP1a and hnRNPs proteins. All these proteins are in fact involved both in RNA transcript processing and in heterochromatin formation. This suggests that, in general, similar epigenetic mechanisms have a significant role on both RNA and heterochromatin metabolisms. Heterochromatin Protein 1 (HP1a) is a very well known prototype protein of a general model for heterochromatin formation and epigenetic gene silencing in different species including humans. Here, we report our experiments showing that HP1a is also required for the positive regulation of more than one hundred euchromatic genes by its association with the corresponding RNA transcripts and by its interaction with heterogeneous nuclear ribonucleoproteins (hnRNPs) belonging to different classes. Importantly, we also found that all the tested hnRNP proteins bind to the heterochromatin and are dominant suppressors of position effect variegation, thus suggesting they also have a role in heterochromatin organization. Taken together, our data show novel and important functions, not only for HP1a, but also for hnRNPs, which were previously believed to participate only in RNA processing. These results shed new light on the epigenetic mechanisms of gene silencing and gene expression. They also establish a link between RNA transcript metabolism and heterochromatin formation and change several aspects of the canonical views about these apparently different processes.
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7
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Ji Y, Tulin AV. Poly(ADP-ribosyl)ation of heterogeneous nuclear ribonucleoproteins modulates splicing. Nucleic Acids Res 2009; 37:3501-13. [PMID: 19346337 PMCID: PMC2699505 DOI: 10.1093/nar/gkp218] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The biological functions of poly(ADP-ribosyl)ation of heterogeneous nuclear ribonucleoproteins (hnRNPs) are not well understood. However, it is known that hnRNPs are involved in the regulation of alternative splicing for many genes, including the Ddc gene in Drosophila. Therefore, we first confirmed that poly(ADP-ribose) (pADPr) interacts with two Drosophila hnRNPs, Squid/hrp40 and Hrb98DE/hrp38, and that this function is regulated by Poly(ADP-ribose) Polymerase 1 (PARP1) and Poly(ADP-ribose) Glycohydrolase (PARG) in vivo. These findings then provided a basis for analyzing the role of pADPr binding to these two hnRNPs in terms of alternative splicing regulation. Our results showed that Parg null mutation does cause poly(ADP-ribosyl)ation of Squid and hrp38 protein, as well as their dissociation from active chromatin. Our data also indicated that pADPr binding to hnRNPs inhibits the RNA-binding ability of hnRNPs. Following that, we demonstrated that poly(ADP-ribosyl)ation of Squid and hrp38 proteins inhibits splicing of the intron in the Hsrω-RC transcript, but enhances splicing of the intron in the Ddc pre-mRNA. Taken together, these findings suggest that poly(ADP-ribosyl)ation regulates the interaction between hnRNPs and RNA and thus modulates the splicing pathways.
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Affiliation(s)
| | - Alexei V. Tulin
- *To whom correspondence should be addressed. Tel: +1 215 728 7408; Fax: +1 215 728 2412;
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8
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Jolly C, Lakhotia SC. Human sat III and Drosophila hsr omega transcripts: a common paradigm for regulation of nuclear RNA processing in stressed cells. Nucleic Acids Res 2006; 34:5508-14. [PMID: 17020918 PMCID: PMC1636489 DOI: 10.1093/nar/gkl711] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Exposure of cells to stressful conditions elicits a highly conserved defense mechanism termed the heat shock response, resulting in the production of specialized proteins which protect the cells against the deleterious effects of stress. The heat shock response involves not only a widespread inhibition of the ongoing transcription and activation of heat shock genes, but also important changes in post-transcriptional processing. In particular, a blockade in splicing and other post-transcriptional processing has been described following stress in different organisms, together with an altered spatial distribution of the proteins involved in these activities. However, the specific mechanisms that regulate these activities under conditions of stress are little understood. Non-coding RNA molecules are increasingly known to be involved in the regulation of various activities in the cell, ranging from chromatin structure to splicing and RNA degradation. In this review, we consider two non-coding RNAs, the hsrω transcripts in Drosophila and the sat III transcripts in human cells, that seem to be involved in the dynamics of RNA-processing factors in normal and/or stressed cells, and thus provide new paradigms for understanding transcriptional and post-transcriptional regulations in normal and stressed cells.
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9
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Mikula M, Dzwonek A, Karczmarski J, Rubel T, Dadlez M, Wyrwicz LS, Bomsztyk K, Ostrowski J. Landscape of the hnRNP K protein-protein interactome. Proteomics 2006; 6:2395-406. [PMID: 16518874 DOI: 10.1002/pmic.200500632] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The heterogeneous nuclear ribonucleoprotein K is an ancient RNA/DNA-binding protein that is involved in multiple processes that compose gene expression. The pleiotropic action of K protein reflects its ability to interact with different classes of factors, interactions that are regulated by extracellular signals. We used affinity purification and MS to better define the repertoire of K protein partners. We identified a large number of new K protein partners, some typically found in subcellular compartments, such as plasma membrane, where K protein has not previously been seen. Electron microscopy showed K protein in the nucleus, cytoplasm, mitochondria, and in vicinity of plasma membrane. These observations greatly expanded the view of the landscape of K protein-protein interaction and provide new opportunities to explore signal transduction and gene expression in several subcellular compartments.
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Affiliation(s)
- Michał Mikula
- Department of Gastroenterology, Medical Center for Postgraduate Education and Maria Skłodowska-Curie Memorial Cancer Center and Institute of Oncology, Warsaw, Poland
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10
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Gortchakov AA, Eggert H, Gan M, Mattow J, Zhimulev IF, Saumweber H. Chriz, a chromodomain protein specific for the interbands of Drosophila melanogaster polytene chromosomes. Chromosoma 2005; 114:54-66. [PMID: 15821938 DOI: 10.1007/s00412-005-0339-3] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2004] [Revised: 03/15/2005] [Accepted: 03/16/2005] [Indexed: 01/04/2023]
Abstract
Polytene interphase chromosomes are compacted into a series of bands and interbands reflecting their organization into independent chromosomal domains. In order to understand chromosomal organization, we set out to study the role of proteins that are selective for interbands. Here we describe the Drosophila melanogaster chromodomain protein Chriz that is coimmunoprecipitated with the zinc finger protein Z4. Both proteins colocalize exclusively to the interbands on Drosophila polytene chromosomes. Like Z4, Chriz is ubiquitously expressed throughout development and is associated with chromatin in all interphase nuclei. Following dissociation from chromatin, early in mitosis Chriz binds to the centrosomes and to the mitotic spindle. Newly induced amorphic Chriz alleles are early lethal, and ubiquitous overexpression of Chriz is lethal as well. Available Chriz hypomorphs which survive until pupal stage have a normal chromosomal phenotype. Reducing Z4 protein does not affect Chriz binding to polytene chromosomes and vice versa. Z4 is still chromosomally bound when Chriz protein is depleted by RNA interference.
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Affiliation(s)
- A A Gortchakov
- Institute of Cytology and Genetics, Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia
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11
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Kiesler E, Hase ME, Brodin D, Visa N. Hrp59, an hnRNP M protein in Chironomus and Drosophila, binds to exonic splicing enhancers and is required for expression of a subset of mRNAs. ACTA ACUST UNITED AC 2005; 168:1013-25. [PMID: 15781475 PMCID: PMC2171850 DOI: 10.1083/jcb.200407173] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
Here, we study an insect hnRNP M protein, referred to as Hrp59. Hrp59 is relatively abundant, has a modular domain organization containing three RNA-binding domains, is dynamically recruited to transcribed genes, and binds to premRNA cotranscriptionally. Using the Balbiani ring system of Chironomus, we show that Hrp59 accompanies the mRNA from the gene to the nuclear envelope, and is released from the mRNA at the nuclear pore. The association of Hrp59 with transcribed genes is not proportional to the amount of synthesized RNA, and in vivo Hrp59 binds preferentially to a subset of mRNAs, including its own mRNA. By coimmunoprecipitation of Hrp59–RNA complexes and microarray hybridization against Drosophila whole-genome arrays, we identify the preferred mRNA targets of Hrp59 in vivo and show that Hrp59 is required for the expression of these target mRNAs. We also show that Hrp59 binds preferentially to exonic splicing enhancers and our results provide new insights into the role of hnRNP M in splicing regulation.
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Affiliation(s)
- Eva Kiesler
- Department of Molecular Biology and Functional Genomics, Stockholm University, SE-10691 Stockholm, Sweden
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12
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Abstract
Since its original identification as a component of the heterogeneous nuclear ribonucleoprotein (hnRNP) complex, K protein has been found not only in the nucleus but also in the cytoplasm and mitochondria and is implicated in chromatin remodeling, transcription, splicing and translation processes. K protein contains multiple modules that, on one hand, bind kinases while, on the other hand, recruit chromatin, transcription, splicing and translation factors. Moreover, the K- protein-mediated interactions are regulated by signaling cascades. These observations are consistent with K protein acting as a docking platform to integrate signaling cascades by facilitating cross-talk between kinases and factors that mediate nucleic-acid-directed processes. Comparison of K across species reveals that it is an essential factor in metazoans, but not in yeast. Although some of the K protein interactions and functions are conserved in eukaryotes from yeast to man, the mammalian protein seems to play a wider role. The greater diversity of mammalian K protein interactions and function may reflect gain of novel docking sites and expansion evolutionary of gene expression networks.
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Affiliation(s)
- Karol Bomsztyk
- Department of Medicine, University of Washington, Seattle, WA 98195, USA.
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13
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Rajendra TK, Prasanth KV, Lakhotia SC. Male sterility associated with overexpression of the noncoding hsromega gene in cyst cells of testis of Drosophila melanogaster. J Genet 2001; 80:97-110. [PMID: 11910129 DOI: 10.1007/bf02728335] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Of the several noncoding transcripts produced by the hsromega gene of Drosophila melanogaster, the nucleus-limited >10-kb hsromega-n transcript colocalizes with heterogeneous nuclear RNA binding proteins (hnRNPs) to form fine nucleoplasmic omega speckles. Our earlier studies suggested that the noncoding hsromega-n transcripts dynamically regulate the distribution of hnRNPs in active (chromatin bound) and inactive (in omega speckles) compartments. Here we show that a P transposon insertion in this gene's promoter (at -130 bp) in the hsromega05421; enhancer-trap line had no effect on viability or phenotype of males or females, but the insertion-homozygous males were sterile. Testes of hsromega05421; homozygous flies contained nonmotile sperms while their seminal vesicles were empty. RNA:RNA in situ hybridization showed that the somatic cyst cells in testes of the mutant male flies contained significantly higher amounts of hsromega-n transcripts, and unlike the characteristic fine omega speckles in other cell types they displayed large clusters of omega speckles as typically seen after heat shock. Two of the hnRNPs, viz. HRB87F and Hrb57A, which are expressed in cyst cells, also formed large clusters in these cells in parallel with the hsromega-n transcripts. A complete excision of the P transposon insertion restored male fertility as well as the fine-speckled pattern of omega speckles in the cyst cells. The in situ distribution patterns of these two hnRNPs and several other RNA-binding proteins (Hrp40, Hrb57A, S5, Sxl, SRp55 and Rb97D) were not affected by hsromega mutation in any of the meiotic stages in adult testes. The present studies, however, revealed an unexpected presence (in wild-type as well as mutant) of the functional form of Sxl in primary spermatocytes and an unusual distribution of HRB87F along the retracting spindle during anaphase telophase of the first meiotic division. It appears that the P transposon insertion in the promoter region causes a misregulated overexpression of hsromega in cyst cells, which in turn results in excessive sequestration of hnRNPs and formation of large clusters of omega speckles in these cell nuclei. The consequent limiting availability of hnRNPs is likely to trans-dominantly affect processing of other pre-mRNAs in cyst cells. We suggest that a compromise in the activity of cyst cells due to the aberrant hnRNP distribution is responsible for the failure of individualization of sperms in hsromega05421; mutant testes. These results further support a significant role of the noncoding hsromega-n transcripts in basic cellular activities, namely regulation of the availability of hnRNPs in active (chromatin bound) and inactive (in omega speckles) compartments.
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Affiliation(s)
- T K Rajendra
- Cytogenetics Laboratory, Department of Zoology, Banaras Hindu University, Varanasi 221 005, India
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14
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Habelhah H, Shah K, Huang L, Burlingame AL, Shokat KM, Ronai Z. Identification of new JNK substrate using ATP pocket mutant JNK and a corresponding ATP analogue. J Biol Chem 2001; 276:18090-5. [PMID: 11259409 DOI: 10.1074/jbc.m011396200] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Modification of the ATP pocket on protein kinases allows selective use of an ATP analogue that exhibits high affinity for the altered kinases. Using this approach, we altered the ATP-binding site on JNK and identified N(6)-(2-phenythyl)-ATP, a modified form of ATP that exhibits high specificity and affinity for the modified, but not the wild type form, of JNK. Using modified JNK and its ATP analogue enables the detection of novel JNK substrates. Among substrates identified using this approach is heterogeneous nuclear ribonucleoprotein K, which is involved in transcription and post-transcriptional mRNA metabolism. The newly identified substrate can be phosphorylated by JNK on amino acids 216 and 353, which contribute to heterogeneous nuclear ribonucleoprotein K mediated transcriptional activities.
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Affiliation(s)
- H Habelhah
- Ruttenberg Cancer Center, Mount Sinai School of Medicine, New York, New York 10029, USA
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15
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Habelhah H, Shah K, Huang L, Ostareck-Lederer A, Burlingame AL, Shokat KM, Hentze MW, Ronai Z. ERK phosphorylation drives cytoplasmic accumulation of hnRNP-K and inhibition of mRNA translation. Nat Cell Biol 2001; 3:325-30. [PMID: 11231586 DOI: 10.1038/35060131] [Citation(s) in RCA: 230] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Heterogeneous nuclear ribonucleoprotein K (hnRNP-K) is one of a family of 20 proteins that are involved in transcription and post-transcriptional messenger RNA metabolism. The mechanisms that underlie regulation of hnRNP-K activities remain largely unknown. Here we show that cytoplasmic accumulation of hnRNP-K is phosphorylation-dependent. Mitogen-activated protein kinase/extracellular-signal-regulated kinase (MAPK/ERK) efficiently phosphorylates hnRNP-K both in vitro and in vivo at serines 284 and 353. Serum stimulation or constitutive activation of ERK kinase (MEK1) results in phosphorylation and cytoplasmic accumulation of hnRNP-K. Mutation at ERK phosphoacceptor sites in hnRNP-K abolishes the ability to accumulate in the cytoplasm and renders the protein incapable of regulating translation of mRNAs that have a differentiation-control element (DICE) in the 3' untranslated region (UTR). Similarly, treatment with a pharmacological inhibitor of the ERK pathway abolishes cytoplasmic accumulation of hnRNP-K and attenuates inhibition of mRNA translation. Our results establish the role of MAPK/ERK in phosphorylation-dependent cellular localization of hnRNP-K, which is required for its ability to silence mRNA translation.
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Affiliation(s)
- H Habelhah
- Ruttenberg Cancer Center, Mount Sinai School of Medicine, New York, New York 10029, USA
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Prasanth KV, Rajendra TK, Lal AK, Lakhotia SC. Omega speckles - a novel class of nuclear speckles containing hnRNPs associated with noncoding hsr-omega RNA in Drosophila. J Cell Sci 2000; 113 Pt 19:3485-97. [PMID: 10984439 DOI: 10.1242/jcs.113.19.3485] [Citation(s) in RCA: 112] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Fluorescence RNA:RNA in situ hybridization studies in various larval and adult cell types of Drosophila melanogaster showed that the noncoding hsr-omega nuclear (hsromega-n) transcripts were present in the form of many small speckles. These speckles, which we name ‘omega speckles’, were distributed in the interchromatin space in close proximity to the chromatin. The only chromosomal site where hsromega-n transcripts localized was the 93D locus or the hsromega gene itself. The number of nucleoplasmic speckles varied in different cell types. Heat shock, which inhibits general chromosomal transcription, caused the individual speckles to coalesce into larger but fewer clusters. In extreme cases, only a single large cluster of hsromega-n transcripts localizing to the hsromega locus was seen in each nucleus. In situ immunocytochemical staining using antibodies against heterogenous nuclear RNA binding proteins (hnRNPs) like HRB87F, Hrp40, Hrb57A and S5 revealed that, in all cell types, all the hnRNPs gave a diffuse staining of chromatin areas and in addition, were present as large numbers of speckles. Colocalization studies revealed an absolute colocalization of the hnRNPs and the omegaspeckles. Heat shock caused all the hnRNPs to cluster together exactly, following the hsromega-n transcripts. Immunoprecipitation studies using the hnRNP antibodies further demonstrated a physical association of hnRNPs and hsromega transcripts. The omegaspeckles are distinct from interchromatin granules since nuclear speckles containing serine/arginine-rich SR-proteins like SC35 and SRp55 did not colocalize with the ω speckles. The speckled distribution of hnRNPs was completely disrupted in hsromega nullosomics. We conclude that the hsromega-n transcripts play essential structural and functional roles in organizing and establishing the hnRNP-containing omega speckles and thus regulate the trafficking and availability of hnRNPs and other related RNA binding proteins in the cell nucleus.
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Affiliation(s)
- K V Prasanth
- Cytogenetics Laboratory, Department of Zoology, Banaras Hindu University, Varanasi 221 005, India
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