Publications by authors named "Shih-Yin Tsai"

10 Publications

  • Page 1 of 1

Sarcopenia: Tilting the Balance of Protein Homeostasis.

Proteomics 2020 03 4;20(5-6):e1800411. Epub 2019 Dec 4.

Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, 2 Medical Drive, MD9 Admin Office, Singapore, 117597, Singapore.

Sarcopenia, defined as age-associated decline of muscle mass and function, is a risk factor for mortality and disability, and comorbid with several chronic diseases such as type II diabetes and cardiovascular diseases. Clinical trials showed that nutritional supplements had positive effects on muscle mass, but not on muscle function and strength, demonstrating our limited understanding of the molecular events involved in the ageing muscle. Protein homeostasis, the equilibrium between protein synthesis and degradation, is proposed as the major mechanism underlying the development of sarcopenia. As the key central regulator of protein homeostasis, the mammalian target of rapamycin (mTOR) is proposed to be essential for muscle hypertrophy. Paradoxically, sustained activation of mTOR complex 1 (mTORC1) is associated with a loss of sensitivity to extracellular signaling in the elderly. It is not understood why sustained mTORC1 activity, which should induce muscle hypertrophy, instead results in muscle atrophy. Here, recent findings on the implications of disrupting protein homeostasis on muscle physiology and sarcopenia development in the context of mTOR/protein kinase B (AKT) signaling are reviewed. Understanding the role of these molecular mechanisms during the ageing process will contribute towards the development of targeted therapies that will improve protein metabolism and reduce sarcopenia.
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http://dx.doi.org/10.1002/pmic.201800411DOI Listing
March 2020

Dosage-dependent copy number gains in E2f1 and E2f3 drive hepatocellular carcinoma.

J Clin Invest 2017 Mar 30;127(3):830-842. Epub 2017 Jan 30.

Disruption of the retinoblastoma (RB) tumor suppressor pathway, either through genetic mutation of upstream regulatory components or mutation of RB1 itself, is believed to be a required event in cancer. However, genetic alterations in the RB-regulated E2F family of transcription factors are infrequent, casting doubt on a direct role for E2Fs in driving cancer. In this work, a mutation analysis of human cancer revealed subtle but impactful copy number gains in E2F1 and E2F3 in hepatocellular carcinoma (HCC). Using a series of loss- and gain-of-function alleles to dial E2F transcriptional output, we have shown that copy number gains in E2f1 or E2f3b resulted in dosage-dependent spontaneous HCC in mice without the involvement of additional organs. Conversely, germ-line loss of E2f1 or E2f3b, but not E2f3a, protected mice against HCC. Combinatorial mapping of chromatin occupancy and transcriptome profiling identified an E2F1- and E2F3B-driven transcriptional program that was associated with development and progression of HCC. These findings demonstrate a direct and cell-autonomous role for E2F activators in human cancer.
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http://dx.doi.org/10.1172/JCI87583DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5330731PMC
March 2017

Increased 4E-BP1 Expression Protects against Diet-Induced Obesity and Insulin Resistance in Male Mice.

Cell Rep 2016 08 4;16(7):1903-14. Epub 2016 Aug 4.

Buck Institute for Research on Aging, Novato, CA 94945, USA. Electronic address:

Obesity is a major risk factor driving the global type II diabetes pandemic. However, the molecular factors linking obesity to disease remain to be elucidated. Gender differences are apparent in humans and are also observed in murine models. Here, we link these differences to expression of eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1), which, upon HFD feeding, becomes significantly reduced in the skeletal muscle and adipose tissue of male but not female mice. Strikingly, restoring 4E-BP1 expression in male mice protects them against HFD-induced obesity and insulin resistance. Male 4E-BP1 transgenic mice also exhibit reduced white adipose tissue accumulation accompanied by decreased circulating levels of leptin and triglycerides. Importantly, transgenic 4E-BP1 male mice are also protected from aging-induced obesity and metabolic decline on a normal diet. These results demonstrate that 4E-BP1 is a gender-specific suppressor of obesity that regulates insulin sensitivity and energy metabolism.
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http://dx.doi.org/10.1016/j.celrep.2016.07.029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4988876PMC
August 2016

A Pilot Study of Ceramic Powder Far-Infrared Ray Irradiation (cFIR) on Physiology: Observation of Cell Cultures and Amphibian Skeletal Muscle.

Chin J Physiol 2011 Aug;54(4):247-54

Department of Diagnostic Radiology, Taipei Medical University Hospital, Taipei 11042, Taiwan, Republic of China.

The purpose of this research was to assess the potential for far-infrared ray irradiation from ceramic powder to improve exercise performance at room temperature. We designed experiments with murine myoblast cells (C2C12) to study the effect of cFIR irradiation on cell viability and lactate dehydrogenase release under H2O2-mediated oxidative stress and evaluated intracellular levels of nitric oxide and calmodulin. We also used electro-stimulation of amphibian skeletal muscle. Our results show that cFIR strengthened C2C12 under oxidative stress and delayed onset of fatigue induced by muscle contractions. We discuss possible mechanisms including anti-oxidation and prevention of acid build-up in muscle tissue based, and expect to see more applications of cFIR in the future.
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http://dx.doi.org/10.4077/CJP.2011.AMM044DOI Listing
August 2011

TOR and ageing: a complex pathway for a complex process.

Philos Trans R Soc Lond B Biol Sci 2011 Jan;366(1561):17-27

Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.

Studies in invertebrate model organisms have led to a wealth of knowledge concerning the ageing process. But which of these discoveries will apply to ageing in humans? Recently, an assessment of the degree of conservation of ageing pathways between two of the leading invertebrate model organisms, Saccharomyces cerevisiae and Caenorhabditis elegans, was completed. The results (i) quantitatively indicated that pathways were conserved between evolutionarily disparate invertebrate species and (ii) emphasized the importance of the TOR kinase pathway in ageing. With recent findings that deletion of the mTOR substrate S6K1 or exposure of mice to the mTOR inhibitor rapamycin result in lifespan extension, mTOR signalling has become a major focus of ageing research. Here, we address downstream targets of mTOR signalling and their possible links to ageing. We also briefly cover other ageing genes identified by comparing worms and yeast, addressing the likelihood that their mammalian counterparts will affect longevity.
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http://dx.doi.org/10.1098/rstb.2010.0198DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3001303PMC
January 2011

Emerging roles of E2Fs in cancer: an exit from cell cycle control.

Nat Rev Cancer 2009 Nov;9(11):785-97

Human Cancer Genetics Program, Department of Molecular Virology, Immunology and Medical Genetics and Department of Molecular Genetics, The Ohio State University, Columbus, Ohio 43210, USA.

Mutations of the retinoblastoma tumour suppressor gene (RB1) or components regulating the RB pathway have been identified in almost every human malignancy. The E2F transcription factors function in cell cycle control and are intimately regulated by RB. Studies of model organisms have revealed conserved functions for E2Fs during development, suggesting that the cancer-related proliferative roles of E2F family members represent a recent evolutionary adaptation. However, given that some human tumours have concurrent RB1 inactivation and E2F amplification and overexpression, we propose that there are alternative tumour-promoting activities for the E2F family, which are independent of cell cycle regulation.
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http://dx.doi.org/10.1038/nrc2696DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3616489PMC
November 2009

E2f3a and E2f3b contribute to the control of cell proliferation and mouse development.

Mol Cell Biol 2009 Jan 17;29(2):414-24. Epub 2008 Nov 17.

Human Cancer Genetics Program, Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University, Columbus, Ohio 43210, USA.

The E2f3 locus encodes two Rb-binding gene products, E2F3a and E2F3b, which are differentially regulated during the cell cycle and are thought to be critical for cell cycle progression. We targeted the individual inactivation of E2f3a or E2f3b in mice and examined their contributions to cell proliferation and development. Chromatin immunoprecipitation and gene expression experiments using mouse embryo fibroblasts deficient in each isoform showed that E2F3a and E2F3b contribute to G(1)/S-specific gene expression and cell proliferation. Expression of E2f3a or E2f3b was sufficient to support E2F target gene expression and cell proliferation in the absence of other E2F activators, E2f1 and E2f2, suggesting that these isoforms have redundant functions. Consistent with this notion, E2f3a(-/-) and E2f3b(-/-) embryos developed normally, whereas embryos lacking both isoforms (E2f3(-/-)) died in utero. We also find that E2f3a and E2f3b have redundant and nonredundant roles in the context of Rb mutation. Analysis of double-knockout embryos suggests that the ectopic proliferation and apoptosis in Rb(-/-) embryos is mainly mediated by E2f3a in the placenta and nervous system and by both E2f3a and E2f3b in lens fiber cells. Together, we conclude that the contributions of E2F3a and E2F3b in cell proliferation and development are context dependent.
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http://dx.doi.org/10.1128/MCB.01161-08DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2612501PMC
January 2009

Mouse development with a single E2F activator.

Nature 2008 Aug 25;454(7208):1137-41. Epub 2008 Jun 25.

Department of Molecular Genetics, College of Biological Sciences, The Ohio State University, Columbus, Ohio 43210, USA.

The E2F family is conserved from Caenorhabditis elegans to mammals, with some family members having transcription activation functions and others having repressor functions. Whereas C. elegans and Drosophila melanogaster have a single E2F activator protein and repressor protein, mammals have at least three activator and five repressor proteins. Why such genetic complexity evolved in mammals is not known. To begin to evaluate this genetic complexity, we targeted the inactivation of the entire subset of activators, E2f1, E2f2, E2f3a and E2f3b, singly or in combination in mice. We demonstrate that E2f3a is sufficient to support mouse embryonic and postnatal development. Remarkably, expression of E2f3b or E2f1 from the E2f3a locus (E2f3a(3bki) or E2f3a(1ki), respectively) suppressed all the postnatal phenotypes associated with the inactivation of E2f3a. We conclude that there is significant functional redundancy among activators and that the specific requirement for E2f3a during postnatal development is dictated by regulatory sequences governing its selective spatiotemporal expression and not by its intrinsic protein functions. These findings provide a molecular basis for the observed specificity among E2F activators during development.
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http://dx.doi.org/10.1038/nature07066DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4288824PMC
August 2008

Specific tumor suppressor function for E2F2 in Myc-induced T cell lymphomagenesis.

Proc Natl Acad Sci U S A 2007 Sep 19;104(39):15400-5. Epub 2007 Sep 19.

Human Cancer Genetics Program, Department of Molecular Virology, Immunology, and Medical Genetics, College of Medicine and Public Health, Ohio State University, Columbus, OH 43210, USA.

Deregulation of the Myc pathway and deregulation of the Rb pathway are two of the most common abnormalities in human malignancies. Recent in vitro experiments suggest a complex cross-regulatory relationship between Myc and Rb that is mediated through the control of E2F. To evaluate the functional connection between Myc and E2Fs in vivo, we used a bitransgenic mouse model of Myc-induced T cell lymphomagenesis and analyzed tumor progression in mice deficient for E2f1, E2f2, or E2f3. Whereas the targeted inactivation of E2f1 or E2f3 had no significant effect on tumor progression, loss of E2f2 accelerated lymphomagenesis. Interestingly, loss of a single copy of E2f2 also accelerated tumorigenesis, albeit to a lesser extent, suggesting a haploinsufficient function for this locus. The combined ablation of E2f1 or E2f3, along with E2f2, did not further accelerate tumorigenesis. Myc-overexpressing T cells were more resistant to apoptosis in the absence of E2f2, and the reintroduction of E2F2 into these tumor cells resulted in an increase of apoptosis and inhibition of tumorigenesis. These results identify the E2f2 locus as a tumor suppressor through its ability to modulate apoptosis.
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http://dx.doi.org/10.1073/pnas.0706307104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2000495PMC
September 2007

Interaction of Saccharomyces Cdc13p with Pol1p, Imp4p, Sir4p and Zds2p is involved in telomere replication, telomere maintenance and cell growth control.

Nucleic Acids Res 2004 23;32(2):511-21. Epub 2004 Jan 23.

Institute of Biopharmaceutical Science, National Yang-Ming University, Shih-Pai 112, Taipei, Taiwan, Republic of China.

Telomeres are the physical ends of eukaryotic chromosomes. They are important for maintaining the integrity of chromosomes and this function is mediated through a number of protein factors. In Saccharomyces cerevisiae, Cdc13p binds to telomeres and affects telomere maintenance, telomere position effects and cell cycle progression through G(2)/M phase. We identified four genes encoding Pol1p, Sir4p, Zds2p and Imp4p that interact with amino acids 1-252 of Cdc13p using a yeast two-hybrid screening system. Interactions of these four proteins with Cdc13p were through direct protein-protein interactions as judged by in vitro pull-down assays. Direct protein-protein interactions were also observed between Pol1p-Imp4p, Pol1p-Sir4p and Sir4p-Zds2p, whereas no interaction was detected between Imp4p-Sir4p and Zds2p-Imp4p, suggesting that protein interactions were specific in the complex. Pol1p was shown to interact with Cdc13p. Here we show that Zds2p and Imp4p also form a stable complex with Cdc13p in yeast cells, because Zds2p and Imp4p co-immunoprecipitate with Cdc13p, whereas Sir4p does not. The function of the N-terminal 1-252 region of Cdc13p was also analyzed. Expressing Cdc13(252-924)p, which lacks amino acids 1-252 of Cdc13p, causes defects in progressive cell growth and eventually arrested in the G(2)/M phase of the cell cycle. These growth defects were not caused by progressive shortening of telomeres because telomeres in these cells were long. Point mutants in the amino acids 1-252 region of Cdc13p that reduced the interaction between Cdc13p and its binding proteins resulted in varying level of defects in cell growth and telomeres. These results indicate that the interactions between Cdc13(1-252)p and its binding proteins are important for the function of Cdc13p in telomere regulation and cell growth. Together, our results provide evidence for the formation of a Cdc13p-mediated telosome complex through its N-terminal region that is involved in telomere maintenance, telomere length regulation and cell growth control.
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http://dx.doi.org/10.1093/nar/gkh203DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC373330PMC
April 2004