1
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Romero G, Martin B, Gabris B, Salama G. Relaxin suppresses atrial fibrillation, reverses fibrosis and reduces inflammation in aged hearts. Biochem Pharmacol 2024; 227:116407. [PMID: 38969298 DOI: 10.1016/j.bcp.2024.116407] [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: 03/19/2024] [Revised: 06/18/2024] [Accepted: 07/02/2024] [Indexed: 07/07/2024]
Abstract
Healthy aging results in cardiac structural and electrical remodeling that increase susceptibility to cardiovascular diseases. Relaxin has shown broad cardioprotective effects including anti-fibrotic, anti-arrhythmic and anti-inflammatory outcomes in multiple models. This paper focuses on the cardioprotective effects of Relaxin in a rat model of aging. Sustained atrial or ventricular fibrillation are readily induced in the hearts of aged but not young control animals. Treatment with Relaxin suppressed this arrhythmogenic response by increasing conduction velocity, decreasing fibrosis and promoting substantial cardiac remodeling. Relaxin treatment resulted in a significant increase in the levels of: Nav1.5, Cx43, βcatenin and Wnt1 in rat hearts. In isolated cardiomyocytes, Relaxin increased Nav1.5 expression. These effects were mimicked by CHIR 99021, a pharmacological activator of canonical Wnt signaling, but blocked by the canonical Wnt inhibitor Dickkopf1. Relaxin prevented TGF-β-dependent differentiation of cardiac fibroblasts into myofibroblasts while increasing the expression of Wnt1; the effects of Relaxin on cardiac fibroblast differentiation were blocked by Dickkopf1. RNASeq studies demonstrated reduced expression of pro-inflammatory cytokines and an increase in the expression of α- and β-globin in Relaxin-treated aged males. Relaxin reduces arrhythmogenicity in the hearts of aged rats by reduction of fibrosis and increased conduction velocity. These changes are accompanied by substantial remodeling of the cardiac tissue and appear to be mediated by increased canonical Wnt signaling. Relaxin also exerts significant anti-inflammatory and anti-oxidant effects in the hearts of aged rodents. The mechanisms by which Relaxin increases the expression of Wnt ligands, promotes Wnt signaling and reprograms gene expression remain to be determined.
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Affiliation(s)
- Guillermo Romero
- Departments of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
| | - Brian Martin
- Departments of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - Beth Gabris
- Departments of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - Guy Salama
- Departments of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
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2
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Jiao L, Liu Y, Yu XY, Pan X, Zhang Y, Tu J, Song YH, Li Y. Ribosome biogenesis in disease: new players and therapeutic targets. Signal Transduct Target Ther 2023; 8:15. [PMID: 36617563 PMCID: PMC9826790 DOI: 10.1038/s41392-022-01285-4] [Citation(s) in RCA: 49] [Impact Index Per Article: 49.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Revised: 12/01/2022] [Accepted: 12/08/2022] [Indexed: 01/10/2023] Open
Abstract
The ribosome is a multi-unit complex that translates mRNA into protein. Ribosome biogenesis is the process that generates ribosomes and plays an essential role in cell proliferation, differentiation, apoptosis, development, and transformation. The mTORC1, Myc, and noncoding RNA signaling pathways are the primary mediators that work jointly with RNA polymerases and ribosome proteins to control ribosome biogenesis and protein synthesis. Activation of mTORC1 is required for normal fetal growth and development and tissue regeneration after birth. Myc is implicated in cancer development by enhancing RNA Pol II activity, leading to uncontrolled cancer cell growth. The deregulation of noncoding RNAs such as microRNAs, long noncoding RNAs, and circular RNAs is involved in developing blood, neurodegenerative diseases, and atherosclerosis. We review the similarities and differences between eukaryotic and bacterial ribosomes and the molecular mechanism of ribosome-targeting antibiotics and bacterial resistance. We also review the most recent findings of ribosome dysfunction in COVID-19 and other conditions and discuss the consequences of ribosome frameshifting, ribosome-stalling, and ribosome-collision. We summarize the role of ribosome biogenesis in the development of various diseases. Furthermore, we review the current clinical trials, prospective vaccines for COVID-19, and therapies targeting ribosome biogenesis in cancer, cardiovascular disease, aging, and neurodegenerative disease.
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Affiliation(s)
- Lijuan Jiao
- grid.263761.70000 0001 0198 0694Institute for Cardiovascular Science and Department of Cardiovascular Surgery, First Affiliated Hospital and Medical College of Soochow University, Collaborative Innovation Center of Hematology, Soochow University, Suzhou, Jiangsu 215123 P. R. China
| | - Yuzhe Liu
- grid.452829.00000000417660726Department of Orthopedics, the Second Hospital of Jilin University, Changchun, Jilin 130000 P. R. China
| | - Xi-Yong Yu
- grid.410737.60000 0000 8653 1072Key Laboratory of Molecular Target & Clinical Pharmacology and the NMPA State Key Laboratory of Respiratory Disease, Guangzhou Medical University, Guangzhou, Guangdong 511436 P. R. China
| | - Xiangbin Pan
- grid.506261.60000 0001 0706 7839Department of Structural Heart Disease, National Center for Cardiovascular Disease, China & Fuwai Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, P. R. China ,Key Laboratory of Cardiovascular Appratus Innovation, Beijing, 100037 P. R. China
| | - Yu Zhang
- grid.263761.70000 0001 0198 0694Institute for Cardiovascular Science and Department of Cardiovascular Surgery, First Affiliated Hospital and Medical College of Soochow University, Collaborative Innovation Center of Hematology, Soochow University, Suzhou, Jiangsu 215123 P. R. China
| | - Junchu Tu
- grid.263761.70000 0001 0198 0694Institute for Cardiovascular Science and Department of Cardiovascular Surgery, First Affiliated Hospital and Medical College of Soochow University, Collaborative Innovation Center of Hematology, Soochow University, Suzhou, Jiangsu 215123 P. R. China
| | - Yao-Hua Song
- Cyrus Tang Hematology Center, Collaborative Innovation Center of Hematology, Soochow University, National Clinical Research Center for Hematologic Diseases, the First Affiliated Hospital of Soochow University, Suzhou, P. R. China. .,State Key Laboratory of Radiation Medicine and Protection, Soochow University, Suzhou, 215123, P. R. China.
| | - Yangxin Li
- Institute for Cardiovascular Science and Department of Cardiovascular Surgery, First Affiliated Hospital and Medical College of Soochow University, Collaborative Innovation Center of Hematology, Soochow University, Suzhou, Jiangsu, 215123, P. R. China.
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3
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Guo N, Zheng D, Sun J, Lv J, Wang S, Fang Y, Zhao Z, Zeng S, Guo Q, Tong J, Wang Z. NAP1L5 Promotes Nucleolar Hypertrophy and Is Required for Translation Activation During Cardiomyocyte Hypertrophy. Front Cardiovasc Med 2021; 8:791501. [PMID: 34977198 PMCID: PMC8718910 DOI: 10.3389/fcvm.2021.791501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Accepted: 11/29/2021] [Indexed: 11/13/2022] Open
Abstract
Pathological growth of cardiomyocytes during hypertrophy is characterized by excess protein synthesis; however, the regulatory mechanism remains largely unknown. Using a neonatal rat ventricular myocytes (NRVMs) model, here we find that the expression of nucleosome assembly protein 1 like 5 (Nap1l5) is upregulated in phenylephrine (PE)-induced hypertrophy. Knockdown of Nap1l5 expression by siRNA significantly blocks cell size enlargement and pathological gene induction after PE treatment. In contrast, Adenovirus-mediated Nap1l5 overexpression significantly aggravates the pro-hypertrophic effects of PE on NRVMs. RNA-seq analysis reveals that Nap1l5 knockdown reverses the pro-hypertrophic transcriptome reprogramming after PE treatment. Whereas, immune response is dominantly enriched in the upregulated genes, oxidative phosphorylation, cardiac muscle contraction and ribosome-related pathways are remarkably enriched in the down-regulated genes. Although Nap1l5-mediated gene regulation is correlated with PRC2 and PRC1, Nap1l5 does not directly alter the levels of global histone methylations at K4, K9, K27 or K36. However, puromycin incorporation assay shows that Nap1l5 is both necessary and sufficient to promote protein synthesis in cardiomyocyte hypertrophy. This is attributable to a direct regulation of nucleolus hypertrophy and subsequent ribosome assembly. Our findings demonstrate a previously unrecognized role of Nap1l5 in translation control during cardiac hypertrophy.
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Affiliation(s)
- Ningning Guo
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, China
- Shenzhen Key Laboratory of Cardiovascular Disease, Fuwai Hospital, Chinese Academy of Medical Sciences, Shenzhen, China
- State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Disease, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Di Zheng
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, China
| | - Jiaxin Sun
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, China
| | - Jian Lv
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, China
- Shenzhen Key Laboratory of Cardiovascular Disease, Fuwai Hospital, Chinese Academy of Medical Sciences, Shenzhen, China
- State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Disease, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Shun Wang
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, China
| | - Yu Fang
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, China
- Shenzhen Key Laboratory of Cardiovascular Disease, Fuwai Hospital, Chinese Academy of Medical Sciences, Shenzhen, China
- State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Disease, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Zhenyi Zhao
- Shenzhen Key Laboratory of Cardiovascular Disease, Fuwai Hospital, Chinese Academy of Medical Sciences, Shenzhen, China
- State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Disease, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
- Health Science Center, School of Pharmacy, Shenzhen University, Shenzhen, China
| | - Sai Zeng
- Shenzhen Key Laboratory of Cardiovascular Disease, Fuwai Hospital, Chinese Academy of Medical Sciences, Shenzhen, China
- State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Disease, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Qiuxiao Guo
- Shenzhen Key Laboratory of Cardiovascular Disease, Fuwai Hospital, Chinese Academy of Medical Sciences, Shenzhen, China
- State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Disease, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
| | - Jingjing Tong
- School of Life Sciences, Central China Normal University, Wuhan, China
- *Correspondence: Jingjing Tong
| | - Zhihua Wang
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, China
- Shenzhen Key Laboratory of Cardiovascular Disease, Fuwai Hospital, Chinese Academy of Medical Sciences, Shenzhen, China
- State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Disease, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
- Zhihua Wang
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Figueiredo VC, D'Souza RF, Van Pelt DW, Lawrence MM, Zeng N, Markworth JF, Poppitt SD, Miller BF, Mitchell CJ, McCarthy JJ, Dupont‐Versteegden EE, Cameron‐Smith D. Ribosome biogenesis and degradation regulate translational capacity during muscle disuse and reloading. J Cachexia Sarcopenia Muscle 2021; 12:130-143. [PMID: 33231914 PMCID: PMC7890271 DOI: 10.1002/jcsm.12636] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 09/02/2020] [Accepted: 09/16/2020] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND Translational capacity (i.e. ribosomal mass) is a key determinant of protein synthesis and has been associated with skeletal muscle hypertrophy. The role of translational capacity in muscle atrophy and regrowth from disuse is largely unknown. Therefore, we investigated the effect of muscle disuse and reloading on translational capacity in middle-aged men (Study 1) and in rats (Study 2). METHODS In Study 1, 28 male participants (age 50.03 ± 3.54 years) underwent 2 weeks of knee immobilization followed by 2 weeks of ambulatory recovery and a further 2 weeks of resistance training. Muscle biopsies were obtained for measurement of total RNA and pre-ribosomal (r)RNA expression, and vastus lateralis cross-sectional area (CSA) was determined via peripheral quantitative computed tomography. In Study 2, male rats underwent hindlimb suspension (HS) for either 24 h (HS 24 h, n = 4) or 7 days (HS 7d, n = 5), HS for 7 days followed by 7 days of reloading (Rel, n = 5) or remained as ambulatory weight bearing (WB, n = 5) controls. Rats received deuterium oxide throughout the study to determine RNA synthesis and degradation, and mTORC1 signalling pathway was assessed. RESULTS Two weeks of immobilization reduced total RNA concentration (20%) and CSA (4%) in men (both P ≤ 0.05). Ambulatory recovery restored total RNA concentration to baseline levels and partially restored muscle CSA. Total RNA concentration and 47S pre-rRNA expression increased above basal levels after resistance training (P ≤ 0.05). In rats, RNA synthesis was 30% lower while degradation was ~400% higher in HS 7d in soleus and plantaris muscles compared with WB (P ≤ 0.05). mTORC1 signalling was lower in HS compared with WB as was 47S pre-rRNA (P ≤ 0.05). With reloading, the aforementioned parameters were restored to WB levels while RNA degradation was suppressed (P ≤ 0.05). CONCLUSIONS Changes in RNA concentration following muscle disuse and reloading were associated with changes in ribosome biogenesis and degradation, indicating that both processes are important determinants of translational capacity. The pre-clinical data help explain the reduced translational capacity after muscle immobilization in humans and demonstrate that ribosome biogenesis and degradation might be valuable therapeutic targets to maintain muscle mass during disuse.
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Affiliation(s)
- Vandré C. Figueiredo
- Liggins InstituteThe University of AucklandAucklandNew Zealand
- Department of Physical Therapy, College of Health SciencesUniversity of KentuckyKYUSA
- Center of Muscle BiologyUniversity of KentuckyKYUSA
| | | | - Douglas W. Van Pelt
- Department of Physical Therapy, College of Health SciencesUniversity of KentuckyKYUSA
- Center of Muscle BiologyUniversity of KentuckyKYUSA
| | - Marcus M. Lawrence
- Aging and Metabolism Research ProgramOklahoma Medical Research Foundation (OMRF)Oklahoma CityOKUSA
| | - Nina Zeng
- Liggins InstituteThe University of AucklandAucklandNew Zealand
| | | | - Sally D. Poppitt
- School of Biological SciencesThe University of AucklandAucklandNew Zealand
| | - Benjamin F. Miller
- Aging and Metabolism Research ProgramOklahoma Medical Research Foundation (OMRF)Oklahoma CityOKUSA
| | - Cameron J. Mitchell
- Liggins InstituteThe University of AucklandAucklandNew Zealand
- School of KinesiologyUniversity of British ColumbiaVancouverCanada
| | - John J. McCarthy
- Center of Muscle BiologyUniversity of KentuckyKYUSA
- College of MedicineUniversity of KentuckyKYUSA
| | - Esther E. Dupont‐Versteegden
- Department of Physical Therapy, College of Health SciencesUniversity of KentuckyKYUSA
- Center of Muscle BiologyUniversity of KentuckyKYUSA
| | - David Cameron‐Smith
- Liggins InstituteThe University of AucklandAucklandNew Zealand
- Human Potential Translational Research Programme, Yong Loo Lin School of MedicineNational University of SingaporeSingapore
- Singapore Institute for Clinical SciencesAgency for Science, Technology and ResearchSingapore
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5
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Ribeiro AS, Zaleta-Rivera K, Ashley EA, Pruitt BL. Stable, covalent attachment of laminin to microposts improves the contractility of mouse neonatal cardiomyocytes. ACS APPLIED MATERIALS & INTERFACES 2014; 6:15516-26. [PMID: 25133578 PMCID: PMC4160263 DOI: 10.1021/am5042324] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The mechanical output of contracting cardiomyocytes, the muscle cells of the heart, relates to healthy and disease states of the heart. Culturing cardiomyocytes on arrays of elastomeric microposts can enable inexpensive and high-throughput studies of heart disease at the single-cell level. However, cardiomyocytes weakly adhere to these microposts, which limits the possibility of using biomechanical assays of single cardiomyocytes to study heart disease. We hypothesized that a stable covalent attachment of laminin to the surface of microposts improves cardiomyocyte contractility. We cultured cells on polydimethylsiloxane microposts with laminin covalently bonded with the organosilanes 3-glycidoxypropyltrimethoxysilane and 3-aminopropyltriethoxysilane with glutaraldehyde. We measured displacement of microposts induced by the contractility of mouse neonatal cardiomyocytes, which attach better than mature cardiomyocytes to substrates. We observed time-dependent changes in contractile parameters such as micropost deformation, contractility rates, contraction and relaxation speeds, and the times of contractions. These parameters were affected by the density of laminin on microposts and by the stability of laminin binding to micropost surfaces. Organosilane-mediated binding resulted in higher laminin surface density and laminin binding stability. 3-glycidoxypropyltrimethoxysilane provided the highest laminin density but did not provide stable protein binding with time. Higher surface protein binding stability and strength were observed with 3-aminopropyltriethoxysilane with glutaraldehyde. In cultured cardiomyocytes, contractility rate, contraction speeds, and contraction time increased with higher laminin stability. Given these variations in contractile function, we conclude that binding of laminin to microposts via 3-aminopropyltriethoxysilane with glutaraldehyde improves contractility observed by an increase in beating rate and contraction speed as it occurs during the postnatal maturation of cardiomyocytes. This approach is promising for future studies to mimic in vivo tissue environments.
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Affiliation(s)
- Alexandre
J. S. Ribeiro
- Department of Mechanical Engineering and Stanford Cardiovascular Institute, Stanford University, Stanford, California United
States
| | - Kathia Zaleta-Rivera
- Department of Mechanical Engineering and Stanford Cardiovascular Institute, Stanford University, Stanford, California United
States
- Department of Cardiovascular Medicine, Stanford University School of Medicine, Stanford, California United States
| | - Euan A. Ashley
- Department of Mechanical Engineering and Stanford Cardiovascular Institute, Stanford University, Stanford, California United
States
- Department of Cardiovascular Medicine, Stanford University School of Medicine, Stanford, California United States
| | - Beth L. Pruitt
- Department of Mechanical Engineering and Stanford Cardiovascular Institute, Stanford University, Stanford, California United
States
- E-mail: . Fax: +1 650 725 1587. Phone: +1 650 723 2300
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6
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Hannan KM, Sanij E, Rothblum LI, Hannan RD, Pearson RB. Dysregulation of RNA polymerase I transcription during disease. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1829:342-60. [PMID: 23153826 DOI: 10.1016/j.bbagrm.2012.10.014] [Citation(s) in RCA: 100] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Revised: 10/30/2012] [Accepted: 10/31/2012] [Indexed: 12/13/2022]
Abstract
Transcription of the ribosomal RNA genes by the dedicated RNA polymerase I enzyme and subsequent processing of the ribosomal RNA are fundamental control steps in the synthesis of functional ribosomes. Dysregulation of Pol I transcription and ribosome biogenesis is linked to the etiology of a broad range of human diseases. Diseases caused by loss of function mutations in the molecular constituents of the ribosome, or factors intimately associated with RNA polymerase I transcription and processing are collectively termed ribosomopathies. Ribosomopathies are generally rare and treatment options are extremely limited tending to be more palliative than curative. Other more common diseases are associated with profound changes in cellular growth such as cardiac hypertrophy, atrophy or cancer. In contrast to ribosomopathies, altered RNA polymerase I transcriptional activity in these diseases largely results from dysregulated upstream oncogenic pathways or by direct modulation by oncogenes or tumor suppressors at the level of the RNA polymerase I transcription apparatus itself. Ribosomopathies associated with mutations in ribosomal proteins and ribosomal RNA processing or assembly factors have been covered by recent excellent reviews. In contrast, here we review our current knowledge of human diseases specifically associated with dysregulation of RNA polymerase I transcription and its associated regulatory apparatus, including some cases where this dysregulation is directly causative in disease. We will also provide insight into and discussion of possible therapeutic approaches to treat patients with dysregulated RNA polymerase I transcription. This article is part of a Special Issue entitled: Transcription by Odd Pols.
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Affiliation(s)
- K M Hannan
- Oncogenic Signalling and Growth Control Program, Peter MacCallum Cancer Centre, Locked Bag 1, A'Beckett St, Melbourne, Victoria 8006, Australia
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7
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Ritchie RH, Irvine JC, Rosenkranz AC, Patel R, Wendt IR, Horowitz JD, Kemp-Harper BK. Exploiting cGMP-based therapies for the prevention of left ventricular hypertrophy: NO* and beyond. Pharmacol Ther 2009; 124:279-300. [PMID: 19723539 DOI: 10.1016/j.pharmthera.2009.08.001] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2009] [Accepted: 08/14/2009] [Indexed: 02/07/2023]
Abstract
Left ventricular hypertrophy (LVH), an increased left ventricular (LV) mass, is common to many cardiovascular disorders, initially developing as an adaptive response to maintain myocardial function. In the longer term, this LV remodelling becomes maladaptive, with progressive decline in LV contractility and diastolic function. Indeed LVH is recognised as an important blood-pressure independent predictor of cardiovascular morbidity and mortality. The clinical efficacy of current treatments for LVH is reduced, however, by their tendency to slow disease progression rather than induce its reversal, and thus the development of new therapies for LVH is paramount. The signalling molecule cyclic guanosine-3',5'-monophosphate (cGMP), well-recognised for its role in regulating vascular tone, is now being increasingly identified as an important anti-hypertrophic mediator. This review is focused on the various means by which cGMP can be stimulated in the heart, such as via the natriuretic peptides, to exert anti-hypertrophic actions. In particular we address the limitations of traditional nitric oxide (NO*) donors in the face of the potential therapeutic advantages offered by novel alternatives; NO* siblings, ligands of the cGMP-generating enzymes, soluble (sGC) and particulate guanylyl cyclases (pGC), and phosphodiesterase inhibitors. Further impact of cGMP within the cardiovascular system is also discussed with a view to representing cGMP-based therapies as innovative pharmacotherapy, alone or concurrent with standard care, for the management of LVH.
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Affiliation(s)
- Rebecca H Ritchie
- Heart Failure Pharmacology, Baker IDI Heart & Diabetes Institute Melbourne, Victoria, Australia.
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8
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Stefanovsky V, Langlois F, Gagnon-Kugler T, Rothblum LI, Moss T. Growth factor signaling regulates elongation of RNA polymerase I transcription in mammals via UBF phosphorylation and r-chromatin remodeling. Mol Cell 2006; 21:629-39. [PMID: 16507361 DOI: 10.1016/j.molcel.2006.01.023] [Citation(s) in RCA: 165] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2005] [Revised: 12/14/2005] [Accepted: 01/17/2006] [Indexed: 01/21/2023]
Abstract
Synthesis of the 45S rRNA by RNA polymerase I limits cell growth. Knowledge of the mechanism of its regulation is therefore key to understanding growth control. rRNA transcription is believed to be regulated solely at initiation/promoter release. However, we found that stimulation of endogenous 45S rRNA synthesis by epidermal growth factor (EGF) and serum failed to induce an increase in RNA polymerase I engagement on the rRNA genes, despite robust enhancement of 45S rRNA synthesis. Further, endogenous transcription elongation rates were measured and found to be directly proportional to 45S rRNA synthesis. Thus, elongation is a rate-limiting step for rRNA synthesis in vivo. ERK phosphorylation of the HMG boxes of UBF, an RNA polymerase I factor essential for transcription enhancement, was shown to directly regulate elongation by inducing the remodeling of ribosomal gene chromatin. The data suggest a mechanism for coordinating the cotranscriptional assembly of preribosomal particles.
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Affiliation(s)
- Victor Stefanovsky
- Cancer Research Centre and Department of Medical Biology, Laval University, Hôtel-Dieu de Québec, 11 côte du Palais, G1R 2J6 Québec, Canada
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9
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Goodfellow SJ, Innes F, Derblay LE, MacLellan WR, Scott PH, White RJ. Regulation of RNA polymerase III transcription during hypertrophic growth. EMBO J 2006; 25:1522-33. [PMID: 16541106 PMCID: PMC1440310 DOI: 10.1038/sj.emboj.7601040] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2005] [Accepted: 02/20/2006] [Indexed: 01/19/2023] Open
Abstract
The cell division-independent growth of terminally differentiated cardiomyocytes is commonly associated with cardiovascular disease. We demonstrate that it is accompanied by a substantial rise in transcription by RNA polymerase (pol) III, which produces essential components of the biosynthetic apparatus, including 5S rRNA and tRNAs. This increase in transcription is achieved by changes in both the activity and level of the essential pol III-specific transcription factor TFIIIB. Erk and c-Myc, which directly activate TFIIIB in proliferating fibroblasts, also induce pol III transcription in growing cardiomyocytes. Furthermore, hypertrophic stimulation increases expression of the essential TFIIIB subunit Brf1, an effect not seen when fibroblasts proliferate. Erk mediates this induction of Brf1 expression and therefore contributes in at least two ways to pol III transcriptional activation during hypertrophy. Increased production of tRNA and 5S rRNA will contribute to the enhanced translational capacity required to sustain hypertrophic growth.
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Affiliation(s)
- Sarah J Goodfellow
- Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK
| | - Fiona Innes
- Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK
| | - Louise E Derblay
- Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK
| | - W Robb MacLellan
- Cardiovascular Research Laboratory, David Geffen School of Medicine, UCLA, Los Angeles, CA, USA
| | - Pamela H Scott
- Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK
| | - Robert J White
- Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, UK
- Beatson Institute for Cancer Research, Bearsden, Glasgow, UK
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10
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Poortinga G, Hannan KM, Snelling H, Walkley CR, Jenkins A, Sharkey K, Wall M, Brandenburger Y, Palatsides M, Pearson RB, McArthur GA, Hannan RD. MAD1 and c-MYC regulate UBF and rDNA transcription during granulocyte differentiation. EMBO J 2004; 23:3325-35. [PMID: 15282543 PMCID: PMC514509 DOI: 10.1038/sj.emboj.7600335] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2004] [Accepted: 06/28/2004] [Indexed: 01/10/2023] Open
Abstract
The regulation of cell mass (cell growth) is often tightly coupled to the cell division cycle (cell proliferation). Ribosome biogenesis and the control of rDNA transcription through RNA polymerase I are known to be critical determinants of cell growth. Here we show that granulocytic cells deficient in the c-MYC antagonist MAD1 display increased cell volume, rDNA transcription and protein synthesis. MAD1 repressed and c-MYC activated rDNA transcription in nuclear run-on assays. Repression of rDNA transcription by MAD1 was associated with its ability to interact directly with the promoter of upstream binding factor (UBF), an rDNA regulatory factor. Conversely, c-MYC activated transcription from the UBF promoter. Using siRNA, UBF was shown to be required for c-MYC-induced rDNA transcription. These data demonstrate that MAD1 and c-MYC reciprocally regulate rDNA transcription, providing a mechanism for coordination of ribosome biogenesis and cell growth under conditions of sustained growth inhibition such as granulocyte differentiation.
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Affiliation(s)
- Gretchen Poortinga
- Division of Research, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia
| | - Katherine M Hannan
- Division of Research, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia
| | - Hayley Snelling
- Division of Research, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia
| | - Carl R Walkley
- Division of Research, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia
- Department of Medicine, St Vincent's Hospital, University of Melbourne, Fitzroy, Victoria, Australia
| | - Anna Jenkins
- Division of Research, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia
| | - Kerith Sharkey
- Division of Research, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia
| | - Meaghan Wall
- Division of Research, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia
| | | | - Manuela Palatsides
- Division of Research, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia
| | - Richard B Pearson
- Division of Research, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia
- Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria, Australia
| | - Grant A McArthur
- Division of Research, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia
- Department of Medicine, St Vincent's Hospital, University of Melbourne, Fitzroy, Victoria, Australia
- Division of Haematology/Medical Oncology, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia
- These two authors contributed equally to this work
- Molecular Oncology Laboratory, Trescowthick Research Laboratories, Peter MacCallum Cancer Centre, St Andrew's Place, East Melbourne 3002, Victoria, Australia. Tel.: +61 3 9656 1195; Fax: +61 3 9656 1411; E-mail:
| | - Ross D Hannan
- Division of Research, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia
- Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria, Australia
- These two authors contributed equally to this work
- Growth Control Laboratory, Trescowthick Research Laboratories, Peter Mac Callum Cancer Centre, St Andrew's Place, east Melbourne 3002, Victoria, Australia. Tel.: +61 3 9656 1747; Fax: +61 3 9656 1411; E-mail:
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11
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James MJ, Zomerdijk JCBM. Phosphatidylinositol 3-kinase and mTOR signaling pathways regulate RNA polymerase I transcription in response to IGF-1 and nutrients. J Biol Chem 2003; 279:8911-8. [PMID: 14688273 DOI: 10.1074/jbc.m307735200] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Regulation of ribosomal RNA gene transcription by RNA polymerase I (Pol I) is fundamental to ribosome biogenesis and therefore protein translation capacity and cell growth, yet little is known of the key signaling cascades involved. We show here that insulin-like growth factor-1 (IGF-1)-induced Pol I transcription in HEK293 cells is entirely dependent on phosphatidylinositol 3-kinase (PI3K) activity and, additionally, is modulated by the mammalian target of rapamycin (mTOR), which coordinates Pol I transcription with the availability of amino acids. The mitogen-activated protein kinase (MAPK) pathway is weakly stimulated by IGF-1 in these cells and partly contributes to Pol I transcription regulation. Activation of Pol I transcription by IGF-1 results from enhancement of the activity of the Pol I transcription machinery and increased occupancy by SL1 of the endogenous tandemly repeated ribosomal promoters in vivo. The inputs from PI3K, mTOR, and MAPK pathways converge to direct appropriate rRNA gene expression by Pol I in the nucleolus of mammalian cells in response to environmental cues, such as growth factors and nutrients.
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Affiliation(s)
- Martyn J James
- Division of Gene Regulation and Expression, Wellcome Trust Biocentre, Faculty of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
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12
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Hannan KM, Brandenburger Y, Jenkins A, Sharkey K, Cavanaugh A, Rothblum L, Moss T, Poortinga G, McArthur GA, Pearson RB, Hannan RD. mTOR-dependent regulation of ribosomal gene transcription requires S6K1 and is mediated by phosphorylation of the carboxy-terminal activation domain of the nucleolar transcription factor UBF. Mol Cell Biol 2003; 23:8862-77. [PMID: 14612424 PMCID: PMC262650 DOI: 10.1128/mcb.23.23.8862-8877.2003] [Citation(s) in RCA: 343] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Mammalian target of rapamycin (mTOR) is a key regulator of cell growth acting via two independent targets, ribosomal protein S6 kinase 1 (S6K1) and 4EBP1. While each is known to regulate translational efficiency, the mechanism by which they control cell growth remains unclear. In addition to increased initiation of translation, the accelerated synthesis and accumulation of ribosomes are fundamental for efficient cell growth and proliferation. Using the mTOR inhibitor rapamycin, we show that mTOR is required for the rapid and sustained serum-induced activation of 45S ribosomal gene transcription (rDNA transcription), a major rate-limiting step in ribosome biogenesis and cellular growth. Expression of a constitutively active, rapamycin-insensitive mutant of S6K1 stimulated rDNA transcription in the absence of serum and rescued rapamycin repression of rDNA transcription. Moreover, overexpression of a dominant-negative S6K1 mutant repressed transcription in exponentially growing NIH 3T3 cells. Rapamycin treatment led to a rapid dephosphorylation of the carboxy-terminal activation domain of the rDNA transcription factor, UBF, which significantly reduced its ability to associate with the basal rDNA transcription factor SL-1. Rapamycin-mediated repression of rDNA transcription was rescued by purified recombinant phosphorylated UBF and endogenous UBF from exponentially growing NIH 3T3 cells but not by hypophosphorylated UBF from cells treated with rapamycin or dephosphorylated recombinant UBF. Thus, mTOR plays a critical role in the regulation of ribosome biogenesis via a mechanism that requires S6K1 activation and phosphorylation of UBF.
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Affiliation(s)
- Katherine M Hannan
- Trescowthick Research Laboratories, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, USA
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13
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Hannan RD, Jenkins A, Jenkins AK, Brandenburger Y. Cardiac hypertrophy: a matter of translation. Clin Exp Pharmacol Physiol 2003; 30:517-27. [PMID: 12890171 DOI: 10.1046/j.1440-1681.2003.03873.x] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
1. Left ventricular hypertrophy (LVH) of the heart is an adaptive response to sustained increases in blood pressure and hormone imbalances. Left ventricular hypertrophy is associated with programmed responses at the molecular and biochemical level in different subsets of cardiac cells, including the cardiac muscle cells (cardiomyocytes), fibroblasts, conductive tissue and coronary vasculature. 2. Regardless of the initiating cause, the actual increase in chamber enlargement is, in each case, due to an increase in size of a pre-existing cardiomyocyte population, with little or no change in their number; a process referred to as cellular hypertrophy. 3. An accelerated rate of global protein synthesis is the primary mechanism by which protein accumulation increases during cardiomyocyte hypertrophy. In turn, increased rates of synthesis are a result of increased translational rates of existing ribosomes (translational efficiency) and/or synthesis and recruitment of additional ribosomes (translational capacity). 4. The present review examines the relative importance of translational capacity and translational efficiency in the response of myocytes to acute and chronic demands for increased protein synthesis and the role of these mechanisms in the development of LVH.
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Affiliation(s)
- R D Hannan
- Gene Transcription Laboratory, Baker Medical Research Institute, Melbourne, Victoria, Australia
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14
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Brandenburger Y, Arthur JF, Woodcock EA, Du XJ, Gao XM, Autelitano DJ, Rothblum LI, Hannan RD. Cardiac hypertrophy in vivo is associated with increased expression of the ribosomal gene transcription factor UBF. FEBS Lett 2003; 548:79-84. [PMID: 12885411 DOI: 10.1016/s0014-5793(03)00744-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The ribosomal DNA transcription-specific factor, UBF, is a key target for the regulation of ribosomal RNA synthesis and hypertrophic growth of isolated neonatal cardiomyocytes. In this study, we have examined whether UBF expression is also an important determinant of cardiac growth rates in vivo. We show that rDNA transcription, rRNA synthesis and UBF expression in left ventricular myocytes isolated from mice 1-6 weeks following transverse aortic constriction were significantly increased (2.5-3.5-fold) compared to the levels in myocytes from the left ventricle of sham-operated mice.
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Affiliation(s)
- Yves Brandenburger
- Molecular Cardiology, Baker Heart Research Institute, P.O. Box 6492, St Kilda Road Central, Melbourne, Vic., 8008, Australia
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15
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Abstract
Skeletal muscle hypertrophy is characterized, in part, by increases in protein mass per fiber. This increased accumulation of protein results from a net increase in protein synthesis relative to breakdown. Increases in rates of protein synthesis (translation) have been reported across different models of resistance exercise and across all species studied. However, although an increase in protein synthesis after exercise is reported commonly, the mechanisms underlying this response are not understood clearly. Therefore, the aim of the current review was to select areas of research within which translational control has been well-studied. The logic is that the mechanisms described in this review have the potential to contribute to the changes seen in protein synthesis after high-resistance exercise. The field of translational control has seen rapid growth in the past 5 to 10 years and although attempts have been made to include all contributing studies, apologies are given from the start because many have undoubtedly been overlooked.
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Affiliation(s)
- Gustavo A Nader
- Muscle Biology Laboratory, School of Kinesiology (M/C 194), University of Illinois, 901 W. Roosevelt Road, Chicago, IL 60608-1516, USA
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16
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Xu ZP, Tsuji T, Riordan JF, Hu GF. The nuclear function of angiogenin in endothelial cells is related to rRNA production. Biochem Biophys Res Commun 2002; 294:287-92. [PMID: 12051708 DOI: 10.1016/s0006-291x(02)00479-5] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Angiogenin is a potent angiogenic protein whose inhibition is known to prevent human tumor growth in athymic mice. It is secreted by both tumor and normal cells; and interacts with endothelial and smooth muscle cells to induce a wide range of cellular responses including cell migration and invasion, proliferation, and formation of tubular structures. Angiogenin is rapidly endocytosed and translocated to the cell nucleus where it accumulates in the nucleolus and binds to DNA. Although nuclear translocation is necessary for its angiogenic activity, the nuclear function of angiogenin is unclear. Here we report that exogenous angiogenin enhances the production of 45S rRNA in endothelial cells, and reduction of endogenous angiogenin inhibits its transcription. In a nuclear run-on assay, angiogenin stimulates RNA synthesis including that containing the initiation site sequences of 45S rRNA. This suggests that the nuclear function of angiogenin relates to its capacity to induce rRNA synthesis. Because rRNA transcription is essential for the synthesis of new ribosomes that are necessary for protein translation and cell growth, inhibition of angiogenin-stimulated transcription of rRNA may inhibit angiogenesis and therefore, would serve as a molecular target for therapeutic intervention.
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MESH Headings
- Amanitins/pharmacology
- Cell Line
- Cell Nucleus/chemistry
- Cell Nucleus/drug effects
- Cell Nucleus/metabolism
- Endothelium, Vascular/cytology
- Endothelium, Vascular/drug effects
- Endothelium, Vascular/metabolism
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/metabolism
- Neovascularization, Physiologic/physiology
- Nucleic Acid Synthesis Inhibitors/pharmacology
- Oligonucleotides, Antisense/pharmacology
- RNA, Ribosomal/biosynthesis
- Ribonuclease, Pancreatic/antagonists & inhibitors
- Ribonuclease, Pancreatic/genetics
- Ribonuclease, Pancreatic/metabolism
- Ribonuclease, Pancreatic/pharmacology
- Transcription, Genetic/drug effects
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Affiliation(s)
- Zheng-ping Xu
- Center for Biochemical and Biophysical Sciences and Medicine, Harvard Medical School, One Kendall Square, Building 600, 3rd Floor, Cambridge, MA 02139, USA
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17
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Stefanovsky VY, Pelletier G, Hannan R, Gagnon-Kugler T, Rothblum LI, Moss T. An immediate response of ribosomal transcription to growth factor stimulation in mammals is mediated by ERK phosphorylation of UBF. Mol Cell 2001; 8:1063-73. [PMID: 11741541 DOI: 10.1016/s1097-2765(01)00384-7] [Citation(s) in RCA: 184] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ribosomal transcription in mammals is regulated in response to growth, differentiation, disease, and aging, but the mechanisms of this regulation have remained unresolved. We show that epidermal growth factor induces immediate, ERK1/2-dependent activation of endogenous ribosomal transcription, while inactivation of ERK1/2 causes an equally immediate reversion to the basal transcription level. ERK1/2 was found to phosphorylate the architectural transcription factor UBF at amino acids 117 and 201 within HMG boxes 1 and 2, preventing their interaction with DNA. Mutation of these sites inhibited transcription activation and abrogated the transcriptional response to ERK1/2. Thus, growth factor regulation of ribosomal transcription likely acts by a cyclic modulation of DNA architecture. The data suggest a central role for ribosome biogenesis in growth regulation.
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Affiliation(s)
- V Y Stefanovsky
- Cancer Research Centre and Department of Medical Biology, Laval University, Hôtel-Dieu de Québec, 11 côte du Palais, G1R 2J6, Québec, Canada
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18
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Hirschler-Laszkiewicz I, Cavanaugh A, Hu Q, Catania J, Avantaggiati ML, Rothblum LI. The role of acetylation in rDNA transcription. Nucleic Acids Res 2001; 29:4114-24. [PMID: 11600700 PMCID: PMC60214 DOI: 10.1093/nar/29.20.4114] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2001] [Accepted: 08/27/2001] [Indexed: 12/14/2022] Open
Abstract
Treatment of NIH 3T3 cells with trichostatin A (TSA), an inhibitor of histone deacetylase (HDAC), resulted in a dose-dependent increase in transcription from a rDNA reporter and from endogenous rRNA genes. Chromatin immunoprecipitation using anti-acetyl-histone H4 antibodies demonstrated a direct effect of TSA on the acetylation state of the ribosomal chromatin. TSA did not reverse inhibition of transcription from the rDNA reporter by retinoblastoma (Rb) protein, suggesting that the main mechanism by which Rb blocks rDNA transcription may not involve recruitment of deacetylases to rDNA chromatin. Overexpression of histone transacetylases p300, CBP and PCAF stimulated transcription in transfected NIH 3T3 cells. Recombinant p300, but not PCAF, stimulated rDNA transcription in vitro in the absence of nucleosomes, suggesting that the stimulation of rDNA transcription by TSA might have a chromatin-independent component. We found that the rDNA transcription factor UBF was acetylated in vivo. Finally, we also demonstrated the nucleolar localization of CBP. Our results suggest that the organization of ribosomal chromatin of higher eukaryotes is not static and that acetylation may be involved in affecting these dynamic changes directly through histone acetylation and/or through acetylation of UBF or one of the other components of rDNA transcription.
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Affiliation(s)
- I Hirschler-Laszkiewicz
- The Henry Hood Research Program, Sigfried and Janet Weis Center for Research, The Geisinger Clinic, 100 North Academy Avenue, Danville, PA 17822-2618, USA
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19
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Hannan KM, Kennedy BK, Cavanaugh AH, Hannan RD, Hirschler-Laszkiewicz I, Jefferson LS, Rothblum LI. RNA polymerase I transcription in confluent cells: Rb downregulates rDNA transcription during confluence-induced cell cycle arrest. Oncogene 2000; 19:3487-97. [PMID: 10918607 DOI: 10.1038/sj.onc.1203690] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
When 3T6 cells are confluent, they withdraw from the cell cycle. Concomitant with cell cycle arrest a significant reduction in RNA polymerase I transcription (80% decrease at 100% confluence) is observed. In the present study, we examined mechanism(s) through which transcription of the ribosomal genes is coupled to cell cycle arrest induced by cell density. Interestingly with an increase in cell density (from 3 - 43% confluence), a significant accumulation in the cellular content of hyperphosphorylated Rb was observed. As cell density increased further, the hypophosphorylated form of Rb became predominant and accumulated in the nucleoli. Co-immunoprecipitation experiments demonstrated there was also a significant rise in the amount of hypophosphorylated Rb associated with the rDNA transcription factor UBF. This increased interaction between Rb and UBF correlated with the reduced rate of rDNA transcription. Furthermore, overexpression of recombinant Rb inhibited UBF-dependent activation of transcription from a cotransfected rDNA reporter in either confluent or exponential cells. The amounts or activities of the rDNA transcription components we examined did not significantly change with cell cycle arrest. Although the content of PAF53, a polymerase associated factor, was altered marginally (decreased 38%), the time course and magnitude of the decrease did not correlate with the reduced rate of rDNA transcription. The results presented support a model wherein regulation of the binding of UBF to Rb and, perhaps the cellular content of PAF53, are components of the mechanism through which cell cycle and rDNA transcription are linked. Oncogene (2000) 19, 3487 - 3497
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Affiliation(s)
- K M Hannan
- Department of Cellular and Molecular Physiology, The Pennsylvania State University, College of Medicine, Hershey, PA 17033, USA
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20
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Xu Y, Hopfner RL, McNeill JR, Gopalakrishnan V. Vasopressin accelerates protein synthesis in neonatal rat cardiomyocytes. Mol Cell Biochem 1999; 195:183-90. [PMID: 10395082 DOI: 10.1023/a:1006961330375] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Arginine vasopressin (AVP) has been shown to promote vascular smooth muscle cell hypertrophy and hyperplasia of fibroblasts. The present study examines the effect of AVP and endothelin-1 (ET-1) on protein, DNA, and RNA synthesis in primary cultures of serum deprived neonatal rat cardiomyocytes (RC) as assessed by changes in [3H] phenylalanine, [3H] thymidine, and [14C] uridine incorporation respectively. Both AVP and ET-1 evoked significant increases in protein synthesis in RC of 36 +/- 12% (p < 0.05) and 53 +/- 22% (p < 0.01) respectively. The stimulating action of AVP on [3H] phenylalanine incorporation was abolished by pretreatment with 2-nitro-4carboxyphenyl-N, N-diphenylcarbamate (NCDC), a phospholipase C (PLC) inhibitor. [14C] uridine incorporation was significantly higher in cells incubated with ET-1 (95 +/- 12%) but not AVP (9 +/- 11%). Neither AVP nor ET-1 significantly affected cell number or [3H]thymidine incorporation, suggesting a lack of a hyperplastic effect. AVP evoked an increase in [Ca2+]i levels (162 +/- 12 nmol/L from a basal value of 77 +/- 6 nmol/L) which was completely abolished by pretreatment with either NCDC or cyclopiazonic acid (sarcoplasmic reticulum (SR) Ca2+ pump inhibitor) but unaffected by ryanodine (ryanodine sensitive SR Ca2+ store depletor). Taken together, these data suggest that AVP, in a PLC dependent manner, both stimulates protein synthesis and augments [Ca2+]i release in RC from ryanodine insensitive (IP3 sensitive) Ca2+ stores. Thus, AVP may promote cardiac hypertrophy via direct effects on cardiomyocyte protein synthesis secondary to IP3 mediated [Ca2+]i release.
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Affiliation(s)
- Y Xu
- Department of Pharmacology, College of Medicine, University of Saskatchewan, Saskatoon, Canada
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21
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Kihm AJ, Hershey JC, Haystead TA, Madsen CS, Owens GK. Phosphorylation of the rRNA transcription factor upstream binding factor promotes its association with TATA binding protein. Proc Natl Acad Sci U S A 1998; 95:14816-20. [PMID: 9843972 PMCID: PMC24532 DOI: 10.1073/pnas.95.25.14816] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/1998] [Accepted: 10/16/1998] [Indexed: 11/18/2022] Open
Abstract
rRNA synthesis by RNA polymerase I requires both the promoter selectivity factor 1, which is composed of TATA binding protein (TBP) and three TBP-associated factors, and the activator upstream binding factor (UBF). Whereas there is strong evidence implicating a role for phosphorylation of UBF in the control of growth-induced increases in rRNA transcription, the mechanism of this effect is not known. Results of immunoprecipitation studies with TBP antibodies showed increased recovery of phosphorylated UBF from growth-stimulated smooth muscle cells. Moreover, using an immobilized protein-binding assay, we found that phosphorylation of UBF in vivo in response to stimulation with different growth factors or in vitro with smooth muscle cell nuclear extract increased its binding to TBP. Finally, we demonstrated that UBF-TBP binding depended on the C-terminal 'acidic tail' of UBF that was hyperphosphorylated at multiple serine sites after growth factor stimulation. Results of these studies suggest that phosphorylation of UBF and subsequent binding to TBP represent a key regulatory step in control of growth-induced increases in rRNA synthesis.
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Affiliation(s)
- A J Kihm
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA 22908-0011, USA
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22
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Larsen TH, Saetersdal T. Translocation of 60S ribosomal subunit in spreading cardiac myocytes. J Histochem Cytochem 1998; 46:963-70. [PMID: 9671446 DOI: 10.1177/002215549804600810] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Cardiac myocytes in culture undergo considerable structural reorganization. The remodeling of the myofibrils and the nonmyofibrillar cytoskeleton that occurs in the spreading cardiac myocytes resembles the cellular features observed in the hypertrophying heart. In this study we examined the distribution of the large 60S ribosomal subunit in freshly isolated cardiac myocytes and during the course of attachment and spreading in culture. Initially, anti-60S immunolabeling was scattered widely throughout the sarcoplasm of the dissociated cardiac myocytes. After attachment to the substrate, the 60S ribosomal subunit attained wide sarcoplasmic localization before a sarcomere-related staining pattern appeared in the spreading cell. Double labeling experiments with alpha-actinin confirmed co-localization of the 60S ribosomal subunit with nascent and mature myofibrils. These findings demonstrate that translocation of the 60S ribosomal subunit coincides with the cytoskeletal reorganization taking place in these cells. Moreover, the close association between the myofibrils indicates a particular role for the ribosomes in maintenance and growth of the contractile apparatus. (J Histochem Cytochem 46:963-969, 1998)
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Affiliation(s)
- T H Larsen
- Experimental Cardiology Unit, Departments of Radiology, University of Bergen, Bergen, Norway
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23
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Kim JK, Summer SN, Wood WM, Schrier RW. Osmotic and non-osmotic regulation of arginine vasopressin (AVP) release, mRNA, and promoter activity in small cell lung carcinoma (SCLC) cells. Mol Cell Endocrinol 1996; 123:179-86. [PMID: 8961255 DOI: 10.1016/s0303-7207(96)03912-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Arginine vasopression (AVP) is synthesized in the magnocellular neurons of the hypothalamus and stored in the posterior pituitary. It has been shown that hypothalamic AVP mRNA is increased during experimental stimulation of osmotic and non-osmotic stimulation of AVP release. The mechanisms underlying the stimulation of AVP biosynthesis in these conditions are not known. The present study was, therefore, performed to measure AVP release, AVP mRNA level, and AVP gene promoter activity during osmotic and non-osmotic stimulation of AVP secretion in the small cell lung carcinoma (SCLC) cells. AVP release was measured by radioimmunoassay, steady state levels of AVP mRNA by solution hybridization, and AVP gene promoter activity exhibited by a 1.5 kb 5'-flanking AVP gene fragment fused to a luciferase reporter after SCLC cells were subjected to osmotic or non-osmotic conditions. High media osmolality (330 mOsm) significantly increased AVP release (control (C) 1.42 +/- 0.27 vs. High Osm 3.67 +/- 0.39 pg/2 x 10(6) cells, N = 9, P < 0.002); AVP mRNA (C 173.6 +/- 16.8 vs. High Osm 280.1 +/- 19.4 pg/2 x 10(6) cells, N = 7, P < 0.001); and AVP gene promoter activity (C 1353 +/- 99 vs. High Osm 2026 +/- 134 L.U./10(-4) U beta-gal, N = 8, P < 0.001). Non-osmotic stimulators. 0.1 microM endothelin 3 (ET3), 1 microM angiotensin II (AII), and 10 microM acetylcholine (Ach) significantly increased AVP release; ET3 (C 1.78 +/- 0.20 vs. ET3 6.85 +/- 1.86 pg/2 x 10(6) cells, N = 8, P < 0.02); AII (C 1.29 +/- 0.38 vs. AII 27.80 +/- 7.09 pg/2 x 10(6) cells, N = 5, P < 0.05) and Ach (C 1.14 +/- 0.33 vs. Ach 2.68 +/- 0.58 pg/2 x x10(6) cells, N = 6, P < 0.05). However, only ET3 significantly increased AVP mRNA (C 166.6 +/- 19.6 vs. ET3 254.4 +/- 25.6 pg/p x 10(6) cells, N = 5, P < 0.05) and AVP promoter activity (C 1515 +/- 163 vs. ET3 2389 +/- 342 L.U./10(-4) U beta-gal, N = 6, P < 0.05). To localize the region of the AVP promoter that mediates the osmotic stimulation and the effect of ET3, 5' deletions of the AVP promoter fragments terminating at -532, -211, and -102, was assessed. Only the promoter activity of the 1.5 kb construct, but not the deletion constructs, was significantly increased by ET3 or high osmolality. These results suggest that modulation of AVP gene transcription is, at least in part, responsible for increased AVP synthesis and release in response to osmotic and non-osmotic stimulation, and that the region of 5' flanking sequence between -1500 and -532 contains the elements responsible for the effects.
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Affiliation(s)
- J K Kim
- Department of Medicine, School of Medicine, University of Colorado, Denver 80262, USA
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24
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Hannan RD, Stefanovsky V, Taylor L, Moss T, Rothblum LI. Overexpression of the transcription factor UBF1 is sufficient to increase ribosomal DNA transcription in neonatal cardiomyocytes: implications for cardiac hypertrophy. Proc Natl Acad Sci U S A 1996; 93:8750-5. [PMID: 8710943 PMCID: PMC38745 DOI: 10.1073/pnas.93.16.8750] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The accelerated protein accumulation characteristic of cardiomyocyte hypertrophy results from increased cellular protein synthetic capacity (elevated ribosome content). The rate limiting step in ribosome accumulation is transcription of the rRNA genes. During neonatal cardiomyocyte hypertrophy induced by norepinephrine or spontaneous contraction, changes in the expression of a ribosomal DNA transcription factor, UBF, correlated with increased rates of ribosome biogenesis. We hypothesized that elevated expression of UBF was part of the mechanism by which these hypertrophic stimuli effected increases in the rate of transcription from the rDNA promoter. In this study, we have examined directly the effect of overexpressing UBF on rDNA transcription in neonatal cardiomyocytes in culture. In control experiments, a novel reporter construct for rDNA transcription (pSMECAT) showed similar increases in activity in response to hypertrophic stimuli (10(-4) M phenylephrine, 10(-7) M endothelin, and spontaneous contraction) as did the endogenous rRNA genes. When contraction-arrested cardiomyocytes were cotransfected with pSMECAT and increasing amounts of a UBF1 expression vector; a dose-dependent (3-5 fold) increase in rDNA transcription was observed. Western blot analysis confirmed that the overexpressed, FLAG-tagged UBF accumulated in the cardiomyocyte nuclei. The observation that overexpression of UBF1 is sufficient to increase rDNA transcription in neonatal cardiomyocytes provides evidence in support of the hypothesis that the regulation of UBF is a key component of the increased ribosome biogenesis and protein accumulation associated with cardiomyocyte hypertrophy.
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Affiliation(s)
- R D Hannan
- Sigfried and Janet Weis Center for Research, Geisinger Clinic, Danville, PA 17822, USA
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