1
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Van V, Brown JB, O'Shea CR, Rosenbach H, Mohamed I, Ejimogu NE, Bui TS, Szalai VA, Chacón KN, Span I, Zhang F, Smith AT. Iron-sulfur clusters are involved in post-translational arginylation. Nat Commun 2023; 14:458. [PMID: 36709327 PMCID: PMC9884297 DOI: 10.1038/s41467-023-36158-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Accepted: 01/18/2023] [Indexed: 01/30/2023] Open
Abstract
Eukaryotic arginylation is an essential post-translational modification that modulates protein stability and regulates protein half-life. Arginylation is catalyzed by a family of enzymes known as the arginyl-tRNA transferases (ATE1s), which are conserved across the eukaryotic domain. Despite their conservation and importance, little is known regarding the structure, mechanism, and regulation of ATE1s. In this work, we show that ATE1s bind a previously undiscovered [Fe-S] cluster that is conserved across evolution. We characterize the nature of this [Fe-S] cluster and find that the presence of the [Fe-S] cluster in ATE1 is linked to its arginylation activity, both in vitro and in vivo, and the initiation of the yeast stress response. Importantly, the ATE1 [Fe-S] cluster is oxygen-sensitive, which could be a molecular mechanism of the N-degron pathway to sense oxidative stress. Taken together, our data provide the framework of a cluster-based paradigm of ATE1 regulatory control.
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Affiliation(s)
- Verna Van
- Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, MD, 21250, USA
| | - Janae B Brown
- Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, MD, 21250, USA
| | - Corin R O'Shea
- Department of Molecular and Cellular Pharmacology, University of Miami, Miller School of Medicine, Miami, FL, 33136, USA
| | - Hannah Rosenbach
- Institut für Physikalische Biologie, Heinrich-Heine-Universität Düsseldorf, 40225, Düsseldorf, Germany
| | - Ijaz Mohamed
- Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, MD, 21250, USA
| | - Nna-Emeka Ejimogu
- Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, MD, 21250, USA
| | - Toan S Bui
- Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, MD, 21250, USA
| | - Veronika A Szalai
- Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA
| | - Kelly N Chacón
- Department of Chemistry, Reed College, Portland, OR, 97202, USA
| | - Ingrid Span
- Institut für Physikalische Biologie, Heinrich-Heine-Universität Düsseldorf, 40225, Düsseldorf, Germany
| | - Fangliang Zhang
- Department of Molecular and Cellular Pharmacology, University of Miami, Miller School of Medicine, Miami, FL, 33136, USA.,Sylvester Comprehensive Cancer Center, University of Miami Miller School of Medicine, Miami, FL, 33136, USA
| | - Aaron T Smith
- Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, MD, 21250, USA.
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2
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Eldeeb MA. N-Terminal-Dependent Protein Degradation and Targeting Cancer Cells. Anticancer Agents Med Chem 2021; 21:231-236. [PMID: 32814541 DOI: 10.2174/1871520620666200819112632] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Revised: 03/11/2020] [Accepted: 04/19/2020] [Indexed: 11/22/2022]
Abstract
Intracellular protein degradation is mediated selectively by the Ubiquitin-Proteasome System (UPS) and autophagic-lysosomal system in mammalian cells. Many cellular and physiological processes, such as cell division, cell differentiation, and cellular demise, are fine-tuned via the UPS-mediated protein degradation. Notably, impairment of UPS contributes to human disorders, including cancer and neurodegeneration. The proteasome- dependent N-degron pathways mediate the degradation of proteins through their destabilizing aminoterminal residues. Recent advances unveiled that targeting N-degron proteolytic pathways can aid in sensitizing some cancer cells to chemotherapeutic agents. Furthermore, interestingly, exploiting the N-degron feature, the simplest degradation signal in mammals, and fusing it to a ligand specific for Estrogen-Related Receptor alpha (ERRa) has demonstrated its utility in ERRa knockdown, via N-terminal dependent degradation, and also its efficiency in the inhibition of growth of breast cancer cells. These recent advances uncover the therapeutic implications of targeting and exploiting N-degron proteolytic pathways to curb growth and migration of cancer cells.
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Affiliation(s)
- Mohamed A Eldeeb
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, QC, Canada
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3
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An X, Wei Z, Ran B, Tian H, Gu H, Liu Y, Cui H, Zhu S. Histone Deacetylase Inhibitor Trichostatin A Suppresses Cell Proliferation and Induces Apoptosis by Regulating the PI3K/AKT Signalling Pathway in Gastric Cancer Cells. Anticancer Agents Med Chem 2021; 20:2114-2124. [PMID: 32593284 DOI: 10.2174/1871520620666200627204857] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Revised: 03/28/2020] [Accepted: 04/13/2020] [Indexed: 11/22/2022]
Abstract
BACKGROUND Gastric cancer, a common malignant tumour worldwide, has a relatively poor prognosis and is a serious threat to human health. Histone Deacetylase Inhibitors (HDACi) are anticancer agents that are known to affect the cell growth of different cancer types. Trichostatin A (TSA) selectively inhibits the class I and II mammalian Histone Deacetylase (HDAC) family enzymes and regulates many cell processes. Still, the underlying mechanisms of HDACs are not fully understood in gastric cancer. OBJECTIVE This study aims to investigate the antitumor effect and the mechanism of growth modulation of gastric cancer cells by TSA. METHODS The cell proliferation of gastric cancer cells was measured by MTT and BrdU immunofluorescence assays. Soft agar assay was used to detect the colony formation ability of gastric cancer cells. Flow cytometry was used to examine cell cycle and apoptosis. Western blot was employed to detect protein expression of target factors. RESULTS TSA inhibits the proliferation of MKN-45 and SGC-7901 cells and leads to significant repression of colony number and size. Flow cytometry assays show TSA induces cell cycle arrest at G1 phase and apoptosis, and TSA effects the expression of related factors in the mitochondrial apoptotic signalling and cell cycle-related regulatory pathways. Furthermore, TSA increased histone H3K27 acetylation and downregulated the expression of PI3K and p-AKT. CONCLUSION Downregulating PI3K/AKT pathway activation is involved in TSA-mediated proliferation inhibition of gastric cancer.
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Affiliation(s)
- Xinli An
- School of Life Sciences, Southwest University, Chongqing, 400715, China
| | - Zekun Wei
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, 400715, China,Cancer Center, Medical Research Institute, Southwest University, Chongqing 400716, China,Chongqing Engineering and Technology Research Centre for Silk Biomaterials and Regenerative Medicine,
Chongqing 400716, China
| | - Botian Ran
- School of Life Sciences, Southwest University, Chongqing, 400715, China
| | - Hao Tian
- School of Life Sciences, Southwest University, Chongqing, 400715, China
| | - Hongyu Gu
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, 400715, China,Cancer Center, Medical Research Institute, Southwest University, Chongqing 400716, China,Chongqing Engineering and Technology Research Centre for Silk Biomaterials and Regenerative Medicine,
Chongqing 400716, China
| | - Yan Liu
- School of Life Sciences, Southwest University, Chongqing, 400715, China
| | - Hongjuan Cui
- State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, 400715, China,Cancer Center, Medical Research Institute, Southwest University, Chongqing 400716, China,Chongqing Engineering and Technology Research Centre for Silk Biomaterials and Regenerative Medicine,
Chongqing 400716, China
| | - Shunqin Zhu
- School of Life Sciences, Southwest University, Chongqing, 400715, China,State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing, 400715, China,Cancer Center, Medical Research Institute, Southwest University, Chongqing 400716, China,Chongqing Engineering and Technology Research Centre for Silk Biomaterials and Regenerative Medicine,
Chongqing 400716, China
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4
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Park W, Park S, Song G, Lim W. Inhibitory Effects of Osthole on Human Breast Cancer Cell Progression via Induction of Cell Cycle Arrest, Mitochondrial Dysfunction, and ER Stress. Nutrients 2019; 11:nu11112777. [PMID: 31731635 PMCID: PMC6893636 DOI: 10.3390/nu11112777] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Revised: 10/10/2019] [Accepted: 10/11/2019] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND Breast cancer is the most commonly diagnosed cancer and the second leading cause of cancer death in women. Although, recently, the number of pathological studies of breast cancer have increased, it is necessary to identify a novel compound that targets multiple signaling pathways involved in breast cancer. METHODS The effects of osthole on cell viability, apoptosis, mitochondria-mediated apoptosis, production of reactive oxygen species (ROS), and endoplasmic reticulum (ER) stress proteins of BT-474 and MCF-7 breast cancer cell lines were investigated. Signal transduction pathways in both cells in response to osthole were determined by western blot analyses. RESULTS Here, we demonstrated that osthole inhibited cellular proliferation and induced cell cycle arrest through modulation of cell cycle regulatory genes in BT-474 and MCF-7 cells. Additionally, osthole induced loss of mitochondrial membrane potential (MMP), intracellular calcium imbalance, and ER stress. Moreover, osthole induced apoptosis by activating the pro-apoptotic protein, Bax, in both cell lines. Osthole regulated phosphorylation of signaling proteins such as Akt and ERK1/2 in human breast cancer cells. Furthermore, osthole-induced activation of JNK protein-mediated apoptosis in both cell lines. CONCLUSIONS Collectively, the results of the present study indicated that osthole may ameliorate breast cancer and can be a promising therapeutic agent for treatment of breast cancer.
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Affiliation(s)
- Wonhyoung Park
- Department of Biotechnology, Korea University, Seoul 02841, Korea; (W.P.); (S.P.)
| | - Sunwoo Park
- Department of Biotechnology, Korea University, Seoul 02841, Korea; (W.P.); (S.P.)
| | - Gwonhwa Song
- Department of Biotechnology, Korea University, Seoul 02841, Korea; (W.P.); (S.P.)
- Correspondence: (G.S.); (W.L.); Tel.: +82-2-3290-3012 (G.S.); +82-2-910-4773 (W.L.); Fax: +82-2-3290-4994 (G.S.)
| | - Whasun Lim
- Department of Food and Nutrition, Kookmin University, Seoul 02707, Korea
- Correspondence: (G.S.); (W.L.); Tel.: +82-2-3290-3012 (G.S.); +82-2-910-4773 (W.L.); Fax: +82-2-3290-4994 (G.S.)
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5
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Pore SK, Ganguly A, Sau S, Godeshala S, Kanugula AK, Ummanni R, Kotamraju S, Banerjee R. N-end rule pathway inhibitor sensitizes cancer cells to antineoplastic agents by regulating XIAP and RAD21 protein expression. J Cell Biochem 2019; 121:804-815. [PMID: 31407360 DOI: 10.1002/jcb.29326] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 07/15/2019] [Indexed: 12/20/2022]
Abstract
Anticancer drugs exert their effects on cancer cells by deregulating many pathways linked to cell cycle, apoptosis, etc. but cancer cells gradually become resistive against anticancer drugs, thereby necessitating the development of newer generation anticancer molecules. N-end rule pathway has been shown to be involved in the degradation of many cell cycle and apoptosis-related proteins. However, the involvements of this pathway in cancer are not well established. Recently, we developed a non-peptide-based N-end rule pathway inhibitor, RF-C11 for type 1 and 2 recognition domains of E3 ubiquitin ligases. The inhibitor significantly increased the half-life of potential N-degrons leading to significant physiological changes in vivo. We hypothesized RF-C11 may be used to decipher the N-end rule pathway's role in cancer towards the development of anticancer therapeutics. In this study, we showed that RF-C11, barring noncancer cells, significantly sensitizes cancer cells towards different anticancer agents tested. We further find that the profound cellular sensitization to anticancer drugs was affected by (a) downregulation of X-linked inhibitor of apoptosis protein, an antiapoptotic protein and (b) by stabilization of RAD21, and thereby inhibiting metaphase to anaphase promotion. The study shows that RF-C11 or its analogs may be used as a novel additive in combination therapy against cancer.
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Affiliation(s)
- Subrata K Pore
- Department of Applied Biology, CSIR-Indian Institute of Chemical Technology, Hyderabad, India.,Life Science Division, Institute of Advanced Study in Science and Technology, Guwahati, Assam, India
| | - Anirban Ganguly
- Department of Applied Biology, CSIR-Indian Institute of Chemical Technology, Hyderabad, India
| | - Samaresh Sau
- Department of Pharmaceutical Sciences, Wayne State University, Detroit, Michigan
| | - Sudhakar Godeshala
- Department of Chemical Engineering, Arizona State University, Tempe, Arizona
| | - Anantha K Kanugula
- Department of Integrative Medical Sciences, Northeast Ohio Medical University (NEOMED), Rootstown, Ohio
| | - Ramesh Ummanni
- Department of Applied Biology, CSIR-Indian Institute of Chemical Technology, Hyderabad, India
| | - Srigiridhar Kotamraju
- Department of Applied Biology, CSIR-Indian Institute of Chemical Technology, Hyderabad, India
| | - Rajkumar Banerjee
- Department of Applied Biology, CSIR-Indian Institute of Chemical Technology, Hyderabad, India
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6
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7
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Eldeeb MA, Leitao LCA, Fahlman RP. Emerging branches of the N-end rule pathways are revealing the sequence complexities of N-termini dependent protein degradation. Biochem Cell Biol 2017; 96:289-294. [PMID: 29253354 DOI: 10.1139/bcb-2017-0274] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The N-end rule links the identity of the N-terminal amino acid of a protein to its in vivo half-life, as some N-terminal residues confer metabolic instability to a protein via their recognition by the cellular machinery that targets them for degradation. Since its discovery, the N-end rule has generally been defined as set of rules of whether an N-terminal residue is stabilizing or not. However, recent studies are revealing that the N-terminal code of amino acids conferring protein instability is more complex than previously appreciated, as recent investigations are revealing that the identity of adjoining downstream residues can also influence the metabolic stability of N-end rule substrate. This is exemplified by the recent discovery of a new branch of N-end rule pathways that target proteins bearing N-terminal proline. In addition, recent investigations are demonstrating that the molecular machinery in N-termini dependent protein degradation may also target proteins for lysosomal degradation, in addition to proteasome-dependent degradation. Herein, we describe some of the recent advances in N-end rule pathways and discuss some of the implications regarding the emerging additional sequence requirements.
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Affiliation(s)
- Mohamed A Eldeeb
- a Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.,b Department of Chemistry, Faculty of Science, Cairo University, Giza, Cairo, Egypt
| | - Luana C A Leitao
- a Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Richard P Fahlman
- a Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.,c Department of Oncology, University of Alberta, Edmonton, AB T6G 2H7, Canada
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8
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The Cooperative Effect of Genistein and Protein Hydrolysates on the Proliferation and Survival of Osteoblastic Cells (hFOB 1.19). Molecules 2016; 21:molecules21111489. [PMID: 27834834 PMCID: PMC6274156 DOI: 10.3390/molecules21111489] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2016] [Revised: 11/03/2016] [Accepted: 11/04/2016] [Indexed: 11/26/2022] Open
Abstract
Chum salmon skin gelatin, de-isoflavoned soy protein, and casein were hydrolyzed at two degrees of hydrolysis. Genistein, the prepared hydrolysates, and genistein-hydrolysate combinations were assessed for their proliferative and anti-apoptotic effects on human osteoblasts (hFOB 1.19) to clarify potential cooperative effects between genistein and these hydrolysates in these two activities. Genistein at 2.5 μg/L demonstrated the highest proliferative activity, while the higher dose of genistein inhibited cell growth. All hydrolysates promoted osteoblast proliferation by increasing cell viability to 102.9%–131.1%. Regarding etoposide- or NaF-induced osteoblast apoptosis, these hydrolysates at 0.05 g/L showed both preventive and therapeutic effects against apoptosis. In the mode of apoptotic prevention, the hydrolysates decreased apoptotic cells from 32.9% to 15.2%–23.7% (etoposide treatment) or from 23.6% to 14.3%–19.6% (NaF treatment). In the mode of apoptotic rescue, the hydrolysates lessened the extent of apoptotic cells from 15.9% to 13.0%–15.3% (etoposide treatment) or from 13.3% to 10.9%–12.7% (NaF treatment). Gelatin hydrolysates showed the highest activities among all hydrolysates in all cases. All investigated combinations (especially the genistein-gelatin hydrolysate combination) had stronger proliferation, apoptotic prevention, and rescue than genistein itself or their counterpart hydrolysates alone, suggesting that genistein cooperated with these hydrolysates, rendering greater activities in osteoblast proliferation and anti-apoptosis.
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9
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Tsujimura N, Yamada NO, Kuranaga Y, Kumazaki M, Shinohara H, Taniguchi K, Akao Y. A Novel Role of Dickkopf-Related Protein 3 in Macropinocytosis in Human Bladder Cancer T24 Cells. Int J Mol Sci 2016; 17:E1846. [PMID: 27827955 PMCID: PMC5133846 DOI: 10.3390/ijms17111846] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 11/01/2016] [Accepted: 11/02/2016] [Indexed: 01/22/2023] Open
Abstract
Dickkopf-related protein 3 (Dkk-3) is a potential tumor suppressor reported in various cancer entities. However, we found that Dkk-3 was exceptionally upregulated in bladder cancer T24 cells. To validate the biological role of Dkk-3 other than a tumor suppressor, we examined the function of Dkk-3 in T24 cells. Gene silencing of Dkk-3 inhibited cell growth through inducing G₀/G₁ cell-cycle arrest. Furthermore, Dkk-3 knock-down caused macropinocytosis accompanied by autophagy, which were canceled in part by their inhibitors 5-(N-ethyl-N-isopropyl) amiloride (EIPA) and 3-methyladenine (3-MA). The macropinocytosis was induced by the Dkk-3 knock-down when there were sufficient extracellular nutrients. On the other hand, when the nutritional condition was poor, the autophagy was mainly induced by the Dkk-3 knock-down. These data indicated that Dkk-3 has a role in modulating macropinocytotic and autophagic pathways, a distinct function other than a Wnt antagonist.
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Affiliation(s)
- Nonoka Tsujimura
- United Graduate School of Drug Discovery and Medical Information Sciences, Gifu University, 1-1 Yanagido, Gifu-city, Gifu 501-1194, Japan.
| | - Nami O Yamada
- United Graduate School of Drug Discovery and Medical Information Sciences, Gifu University, 1-1 Yanagido, Gifu-city, Gifu 501-1194, Japan.
- Department of Anatomy, Graduate School of Medicine, Gifu University, 1-1 Yanagido, Gifu-city, Gifu 501-1194, Japan.
| | - Yuki Kuranaga
- United Graduate School of Drug Discovery and Medical Information Sciences, Gifu University, 1-1 Yanagido, Gifu-city, Gifu 501-1194, Japan.
| | - Minami Kumazaki
- United Graduate School of Drug Discovery and Medical Information Sciences, Gifu University, 1-1 Yanagido, Gifu-city, Gifu 501-1194, Japan.
| | - Haruka Shinohara
- United Graduate School of Drug Discovery and Medical Information Sciences, Gifu University, 1-1 Yanagido, Gifu-city, Gifu 501-1194, Japan.
| | - Kohei Taniguchi
- United Graduate School of Drug Discovery and Medical Information Sciences, Gifu University, 1-1 Yanagido, Gifu-city, Gifu 501-1194, Japan.
| | - Yukihiro Akao
- United Graduate School of Drug Discovery and Medical Information Sciences, Gifu University, 1-1 Yanagido, Gifu-city, Gifu 501-1194, Japan.
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10
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Lenci E, Innocenti R, Biagioni A, Menchi G, Bianchini F, Trabocchi A. Identification of Novel Human Breast Carcinoma (MDA-MB-231) Cell Growth Modulators from a Carbohydrate-Based Diversity Oriented Synthesis Library. Molecules 2016; 21:molecules21101405. [PMID: 27775632 PMCID: PMC6273552 DOI: 10.3390/molecules21101405] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Revised: 10/12/2016] [Accepted: 10/15/2016] [Indexed: 01/16/2023] Open
Abstract
The application of a cell-based growth inhibition on a library of skeletally different glycomimetics allowed for the selection of a hexahydro-2H-furo[3,2-b][1,4]oxazine compound as candidate inhibitors of MDA-MB-231 cell growth. Subsequent synthesis of analogue compounds and preliminary biological studies validated the selection of a valuable hit compound with a novel polyhydroxylated structure for the modulation of the breast carcinoma cell cycle mechanism.
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Affiliation(s)
- Elena Lenci
- Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 13, 50019 Sesto Fiorentino, Florence, Italy.
| | - Riccardo Innocenti
- Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 13, 50019 Sesto Fiorentino, Florence, Italy.
| | - Alessio Biagioni
- Department of Clinical and Experimental Biomedical Science "Mario Serio", University of Florence, Viale Morgagni 50, 50134 Florence, Italy.
| | - Gloria Menchi
- Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 13, 50019 Sesto Fiorentino, Florence, Italy.
| | - Francesca Bianchini
- Department of Clinical and Experimental Biomedical Science "Mario Serio", University of Florence, Viale Morgagni 50, 50134 Florence, Italy.
| | - Andrea Trabocchi
- Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 13, 50019 Sesto Fiorentino, Florence, Italy.
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11
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Posttranslational arginylation enzyme Ate1 affects DNA mutagenesis by regulating stress response. Cell Death Dis 2016; 7:e2378. [PMID: 27685622 PMCID: PMC5059882 DOI: 10.1038/cddis.2016.284] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Revised: 08/01/2016] [Accepted: 08/10/2016] [Indexed: 01/06/2023]
Abstract
Arginyltransferase 1 (Ate1) mediates protein arginylation, a poorly understood protein posttranslational modification (PTM) in eukaryotic cells. Previous evidence suggest a potential involvement of arginylation in stress response and this PTM was traditionally considered anti-apoptotic based on the studies of individual substrates. However, here we found that arginylation promotes cell death and/or growth arrest, depending on the nature and intensity of the stressing factor. Specifically, in yeast, mouse and human cells, deletion or downregulation of the ATE1 gene disrupts typical stress responses by bypassing growth arrest and suppressing cell death events in the presence of disease-related stressing factors, including oxidative, heat, and osmotic stresses, as well as the exposure to heavy metals or radiation. Conversely, in wild-type cells responding to stress, there is an increase of cellular Ate1 protein level and arginylation activity. Furthermore, the increase of Ate1 protein directly promotes cell death in a manner dependent on its arginylation activity. Finally, we found Ate1 to be required to suppress mutation frequency in yeast and mammalian cells during DNA-damaging conditions such as ultraviolet irradiation. Our study clarifies the role of Ate1/arginylation in stress response and provides a new mechanism to explain the link between Ate1 and a variety of diseases including cancer. This is also the first example that the modulation of the global level of a PTM is capable of affecting DNA mutagenesis.
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12
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N-end rule pathway inhibition assists colon tumor regression via necroptosis. MOLECULAR THERAPY-ONCOLYTICS 2016; 3:16020. [PMID: 27556106 PMCID: PMC4980110 DOI: 10.1038/mto.2016.20] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/29/2015] [Revised: 06/14/2016] [Accepted: 06/16/2016] [Indexed: 12/23/2022]
Abstract
Recent study has shown that N-end rule pathway, an ubiquitin dependent proteolytic system, counteracts cell death by degrading many antisurvival protein fragments like BCLxL, BRCA1, RIPK1, etc. Inhibition of the N-end rule pathway can lead to metabolic stabilization of proapoptotic protein fragments like RIPK1, thereby sensitizing cells to programmed cell death. Receptor interacting serine-threonine protein kinase-1 (RIPK1) is one of the upstream regulators of programmed necrosis known as necroptosis. Necroptosis is particularly gaining attention of cancer biologists as it provides an alternate therapeutic modality to kill cancer cells, which often evolve multiple strategies to circumvent growth inhibition by apoptosis. Utilizing the over expression of biotin receptor in cancer cells, herein, we report that coadministration of synthetic hetero-bivalent N-end rule inhibitor RFC11 and anticancer drug shikonin solubilized in a stable biotin receptor-targeted liposome exhibited significant synergistic antitumor effect in both subcutaneous and orthotopic mouse colon tumor model through induction of necroptosis with distinctive upregulation of RIPK1. Besides developing a newly targeted formulation for necroptosis induction, this report is the first in vivo evidence demonstrating that potent inhibition of N-end rule pathway can enhance therapeutic efficacy of conventional chemotherapeutics.
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13
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Ubr3 E3 ligase regulates apoptosis by controlling the activity of DIAP1 in Drosophila. Cell Death Differ 2014; 21:1961-70. [PMID: 25146930 DOI: 10.1038/cdd.2014.115] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Revised: 07/15/2014] [Accepted: 07/15/2014] [Indexed: 12/31/2022] Open
Abstract
Apoptosis has essential roles in a variety of cellular and developmental processes. Although the pathway is well studied, how the activities of individual components in the pathway are regulated is less understood. In Drosophila, a key component in apoptosis is Drosophila inhibitor of apoptosis protein 1 (DIAP1), which is required to prevent caspase activation. Here, we demonstrate that Drosophila CG42593 (ubr3), encoding the homolog of mammalian UBR3, has an essential role in regulating the apoptosis pathway. We show that loss of ubr3 activity causes caspase-dependent apoptosis in Drosophila eye and wing discs. Our genetic epistasis analyses show that the apoptosis induced by loss of ubr3 can be suppressed by loss of initiator caspase Drosophila Nedd2-like caspase (Dronc), or by ectopic expression of the apoptosis inhibitor p35, but cannot be rescued by overexpression of DIAP1. Importantly, we show that the activity of Ubr3 in the apoptosis pathway is not dependent on its Ring-domain, which is required for its E3 ligase activity. Furthermore, we find that through the UBR-box domain, Ubr3 physically interacts with the neo-epitope of DIAP1 that is exposed after caspase-mediated cleavage. This interaction promotes the recruitment and ubiquitination of substrate caspases by DIAP1. Together, our data indicate that Ubr3 interacts with DIAP1 and positively regulates DIAP1 activity, possibly by maintaining its active conformation in the apoptosis pathway.
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14
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Dou QP, Zonder JA. Overview of proteasome inhibitor-based anti-cancer therapies: perspective on bortezomib and second generation proteasome inhibitors versus future generation inhibitors of ubiquitin-proteasome system. Curr Cancer Drug Targets 2014; 14:517-36. [PMID: 25092212 PMCID: PMC4279864 DOI: 10.2174/1568009614666140804154511] [Citation(s) in RCA: 207] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Revised: 06/16/2014] [Accepted: 07/11/2014] [Indexed: 02/07/2023]
Abstract
Over the past ten years, proteasome inhibition has emerged as an effective therapeutic strategy for treating multiple myeloma (MM) and some lymphomas. In 2003, Bortezomib (BTZ) became the first proteasome inhibitor approved by the U.S. Food and Drug Administration (FDA). BTZ-based therapies have become a staple for the treatment of MM at all stages of the disease. The survival rate of MM patients has improved significantly since clinical introduction of BTZ and other immunomodulatory drugs. However, BTZ has several limitations. Not all patients respond to BTZ based therapies and relapse occurs in many patients who initially responded. Solid tumors, in particular, are often resistant to BTZ. Furthermore, BTZ can induce dose-limiting peripheral neuropathy (PN). The second generation proteasome inhibitor Carfizomib (CFZ; U.S. FDA approved in August 2012) induces responses in a minority of MM patients relapsed from or refractory to BTZ. There is less PN compared to BTZ. Four other second-generation proteasome inhibitors (Ixazomib, Delanzomib, Oprozomib and Marizomib) with different pharmacologic properties and broader anticancer activities, have also shown some clinical activity in bortezomib-resistant cancers. While the mechanism of resistance to bortezomib in human cancers still remains to be fully understood, targeting the immunoproteasome, ubiquitin E3 ligases, the 19S proteasome and deubiquitinases in pre-clinical studies represents possible directions for future generation inhibitors of ubiquitin-proteasome system in the treatment of MM and other cancers.
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Affiliation(s)
| | - Jeffrey A Zonder
- Barbara Ann Karmanos Cancer Institute and Department of Oncology, Wayne State University School of Medicine, 540.1 HWCRC, 4100 John R Road, Detroit, MI 48201.
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15
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Parisien M, Wang X, Pan T. Diversity of human tRNA genes from the 1000-genomes project. RNA Biol 2013; 10:1853-67. [PMID: 24448271 DOI: 10.4161/rna.27361] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The sequence diversity of individual human genomes has been extensively analyzed for variations and phenotypic implications for mRNA, miRNA, and long non-coding RNA genes. TRNA (tRNA) also exhibits large sequence diversity in the human genome, but tRNA gene sequence variation and potential functional implications in individual human genomes have not been investigated. Here we capitalize on the sequencing data from the 1000-genomes project to examine the diversity of tRNA genes in the human population. Previous analysis of the reference human genome indicated an unexpected large number of diverse tRNA genes beyond the necessity of translation, suggesting that some tRNA transcripts may perform non-canonical functions. We found 24 new tRNA sequences in>1% and 76 new tRNA sequences in>0.2% of all individuals, indicating that tRNA genes are also subject to evolutionary changes in the human population. Unexpectedly, two abundant new tRNA genes contain base-pair mismatches in the anticodon stem. We experimentally determined that these two new tRNAs have altered structures in vitro; however, one new tRNA is not aminoacylated but extremely stable in HeLa cells, suggesting that this new tRNA can be used for non-canonical function. Our results show that at the scale of human population, tRNA genes are more diverse than conventionally understood, and some new tRNAs may perform non-canonical, extra-translational functions that may be linked to human health and disease.
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Affiliation(s)
- Marc Parisien
- Department of Biochemistry and Molecular Biology; University of Chicago; Chicago, IL USA Keywords: tRNA, isodecoder, SNP, 1000 genomes project
| | - Xiaoyun Wang
- Department of Biochemistry and Molecular Biology; University of Chicago; Chicago, IL USA Keywords: tRNA, isodecoder, SNP, 1000 genomes project
| | - Tao Pan
- Department of Biochemistry and Molecular Biology; University of Chicago; Chicago, IL USA Keywords: tRNA, isodecoder, SNP, 1000 genomes project
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16
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Imamura T, Oshima Y, Hikita A. Regulation of TGF-β family signalling by ubiquitination and deubiquitination. J Biochem 2013; 154:481-9. [PMID: 24165200 DOI: 10.1093/jb/mvt097] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Members of the transforming growth factor-β (TGF-β) family, including TGF-βs, activin and bone morphogenetic proteins (BMPs), are multifunctional proteins that regulate a wide variety of cellular responses, such as proliferation, differentiation, migration and apoptosis. TGF-β family signalling is mainly mediated by membranous serine/threonine kinase receptors and intracellular Smad proteins. This signalling is tightly regulated by various post-translational modifications including ubiquitination. Several E3 ubiquitin ligases play a crucial role in the recognition and ubiquitin-dependent degradation of TGF-β family receptors, Smad proteins and their interacted proteins to regulate positively and negatively TGF-β family signalling. In contrast, non-degradative ubiquitin modifications also regulate TGF-β family signalling. Recently, in addition to protein ubiquitination, deubiquitination by deubiquitinating enzymes has been reported to control TGF-β family signalling pathways. Interestingly, more recent studies suggest that TGF-β signalling is not only regulated via ubiquitination and/or deubiquitination, but also it relies on ubiquitination for its effect on other pathways. Thus, ubiquitin modifications play key roles in TGF-β family signal transduction and cross-talk between TGF-β family signalling and other signalling pathways. Here, we review the current understandings of the positive and negative regulatory mechanisms by ubiquitin modifications that control TGF-β family signalling.
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Affiliation(s)
- Takeshi Imamura
- Department of Molecular Medicine for Pathogenesis, Ehime University Graduate School of Medicine; Division of Bio-imaging, Proteo-Science Center, Ehime University; Translational Research Center, Ehime University Hospital; and Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Shitsukawa, Toon, Ehime 791-0295, Japan
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17
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Traverso JA, Micalella C, Martinez A, Brown SC, Satiat-Jeunemaître B, Meinnel T, Giglione C. Roles of N-terminal fatty acid acylations in membrane compartment partitioning: Arabidopsis h-type thioredoxins as a case study. THE PLANT CELL 2013; 25:1056-77. [PMID: 23543785 PMCID: PMC3634677 DOI: 10.1105/tpc.112.106849] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Revised: 02/22/2013] [Accepted: 03/04/2013] [Indexed: 05/18/2023]
Abstract
N-terminal fatty acylations (N-myristoylation [MYR] and S-palmitoylation [PAL]) are crucial modifications affecting 2 to 4% of eukaryotic proteins. The role of these modifications is to target proteins to membranes. Predictive tools have revealed unexpected targets of these acylations in Arabidopsis thaliana and other plants. However, little is known about how N-terminal lipidation governs membrane compartmentalization of proteins in plants. We show here that h-type thioredoxins (h-TRXs) cluster in four evolutionary subgroups displaying strictly conserved N-terminal modifications. It was predicted that one subgroup undergoes only MYR and another undergoes both MYR and PAL. We used plant TRXs as a model protein family to explore the effect of MYR alone or MYR and PAL in the same family of proteins. We used a high-throughput biochemical strategy to assess MYR of specific TRXs. Moreover, various TRX-green fluorescent protein fusions revealed that MYR localized protein to the endomembrane system and that partitioning between this membrane compartment and the cytosol correlated with the catalytic efficiency of the N-myristoyltransferase acting at the N terminus of the TRXs. Generalization of these results was obtained using several randomly selected Arabidopsis proteins displaying a MYR site only. Finally, we demonstrated that a palmitoylatable Cys residue flanking the MYR site is crucial to localize proteins to micropatching zones of the plasma membrane.
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Affiliation(s)
- José A. Traverso
- Centre National de la Recherche Scientifique, Centre de Recherche de Gif, Institut des Sciences du Végétal, F-91198 Gif-sur-Yvette cedex, France
- Consejo Superior de Investigaciones Científicas, Estación Experimental del Zaidín, C/ Profesor Albareda 1, Granada, Spain
| | - Chiara Micalella
- Centre National de la Recherche Scientifique, Centre de Recherche de Gif, Institut des Sciences du Végétal, F-91198 Gif-sur-Yvette cedex, France
| | - Aude Martinez
- Centre National de la Recherche Scientifique, Centre de Recherche de Gif, Institut des Sciences du Végétal, F-91198 Gif-sur-Yvette cedex, France
| | - Spencer C. Brown
- Centre National de la Recherche Scientifique, Centre de Recherche de Gif, Institut des Sciences du Végétal, F-91198 Gif-sur-Yvette cedex, France
| | - Béatrice Satiat-Jeunemaître
- Centre National de la Recherche Scientifique, Centre de Recherche de Gif, Institut des Sciences du Végétal, F-91198 Gif-sur-Yvette cedex, France
| | - Thierry Meinnel
- Centre National de la Recherche Scientifique, Centre de Recherche de Gif, Institut des Sciences du Végétal, F-91198 Gif-sur-Yvette cedex, France
| | - Carmela Giglione
- Centre National de la Recherche Scientifique, Centre de Recherche de Gif, Institut des Sciences du Végétal, F-91198 Gif-sur-Yvette cedex, France
- Address correspondence to
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18
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Xu Z, Payoe R, Fahlman RP. The C-terminal proteolytic fragment of the breast cancer susceptibility type 1 protein (BRCA1) is degraded by the N-end rule pathway. J Biol Chem 2012; 287:7495-502. [PMID: 22262859 PMCID: PMC3293596 DOI: 10.1074/jbc.m111.301002] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2011] [Revised: 01/05/2012] [Indexed: 01/27/2023] Open
Abstract
The breast cancer susceptibility type 1 gene product (BRCA1) is cleaved by caspases upon the activation of apoptotic pathways. After proteolysis the C-terminal fragment has been reported to translocate to the cytoplasm and promote cell death. Here we report that the C-terminal fragment is unstable in cells as it is targeted for degradation by the N-end rule pathway. The data reveals that mutating the wild type N-terminal aspartate, of the C-terminal fragment, to valine stabilizes the fragment. If the N terminus is mutated to another N-terminal destabilizing residue, like arginine, the C-terminal fragment remains unstable in cells. Last, the C-terminal fragment of BRCA1 is stable in cells lacking ATE1, a component of the N-end rule pathway.
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Affiliation(s)
- Zhizhong Xu
- From the Departments of Biochemistry and
- Oncology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | | | - Richard P. Fahlman
- From the Departments of Biochemistry and
- Oncology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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19
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Sriram SM, Kim BY, Kwon YT. The N-end rule pathway: emerging functions and molecular principles of substrate recognition. Nat Rev Mol Cell Biol 2011; 12:735-47. [PMID: 22016057 DOI: 10.1038/nrm3217] [Citation(s) in RCA: 152] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The N-end rule defines the protein-destabilizing activity of a given amino-terminal residue and its post-translational modification. Since its discovery 25 years ago, the pathway involved in the N-end rule has been thought to target only a limited set of specific substrates of the ubiquitin-proteasome system. Recent studies have provided insights into the components, substrates, functions and structural basis of substrate recognition. The N-end rule pathway is now emerging as a major cellular proteolytic system, in which the majority of proteins are born with or acquire specific N-terminal degradation determinants through protein-specific or global post-translational modifications.
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Affiliation(s)
- Shashikanth M Sriram
- Center for Pharmacogenetics and Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
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20
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Wang H, Clem RJ. The role of IAP antagonist proteins in the core apoptosis pathway of the mosquito disease vector Aedes aegypti. Apoptosis 2011; 16:235-48. [PMID: 21274634 DOI: 10.1007/s10495-011-0575-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
While apoptosis regulation has been studied extensively in Drosophila melanogaster, similar studies in other insects, including disease vectors, lag far behind. In D. melanogaster, the inhibitor of apoptosis (IAP) protein DIAP1 is the major negative regulator of caspases, while IAP antagonists induce apoptosis, in part, by binding to DIAP1 and inhibiting its ability to regulate caspases. In this study, we characterized the roles of two IAP antagonists, Michelob_x (Mx) and IMP, in apoptosis in the yellow fever mosquito Aedes aegypti. Overexpression of Mx or IMP caused apoptosis in A. aegypti Aag2 cells, while silencing expression of mx or imp attenuated apoptosis. Addition of recombinant Mx or IMP, but not cytochrome c, to Aag2 cytosolic extract caused caspase activation. Consistent with this finding, AeIAP1 bound and inhibited both initiator and effector caspases from A. aegypti, and Mx and IMP competed with caspases for binding to AeIAP1. However, a difference was observed in the BIR domains responsible for Dronc binding by AeIAP1 versus DIAP1. These findings demonstrate that the mechanisms by which IAP antagonists regulate apoptosis are largely conserved between A. aegypti and D. melanogaster, although subtle differences exist.
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Affiliation(s)
- Hua Wang
- Molecular, Cellular, and Developmental Biology Program, Arthropod Genomics Center, Division of Biology, Kansas State University, Manhattan, KS 66506, USA
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21
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Varshavsky A. The N-end rule pathway and regulation by proteolysis. Protein Sci 2011; 20:1298-345. [PMID: 21633985 PMCID: PMC3189519 DOI: 10.1002/pro.666] [Citation(s) in RCA: 517] [Impact Index Per Article: 39.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Revised: 05/16/2011] [Accepted: 05/18/2011] [Indexed: 01/12/2023]
Abstract
The N-end rule relates the regulation of the in vivo half-life of a protein to the identity of its N-terminal residue. Degradation signals (degrons) that are targeted by the N-end rule pathway include a set called N-degrons. The main determinant of an N-degron is a destabilizing N-terminal residue of a protein. In eukaryotes, the N-end rule pathway is a part of the ubiquitin system and consists of two branches, the Ac/N-end rule and the Arg/N-end rule pathways. The Ac/N-end rule pathway targets proteins containing N(α) -terminally acetylated (Nt-acetylated) residues. The Arg/N-end rule pathway recognizes unacetylated N-terminal residues and involves N-terminal arginylation. Together, these branches target for degradation a majority of cellular proteins. For example, more than 80% of human proteins are cotranslationally Nt-acetylated. Thus most proteins harbor a specific degradation signal, termed (Ac)N-degron, from the moment of their birth. Specific N-end rule pathways are also present in prokaryotes and in mitochondria. Enzymes that produce N-degrons include methionine-aminopeptidases, caspases, calpains, Nt-acetylases, Nt-amidases, arginyl-transferases and leucyl-transferases. Regulated degradation of specific proteins by the N-end rule pathway mediates a legion of physiological functions, including the sensing of heme, oxygen, and nitric oxide; selective elimination of misfolded proteins; the regulation of DNA repair, segregation and condensation; the signaling by G proteins; the regulation of peptide import, fat metabolism, viral and bacterial infections, apoptosis, meiosis, spermatogenesis, neurogenesis, and cardiovascular development; and the functioning of adult organs, including the pancreas and the brain. Discovered 25 years ago, this pathway continues to be a fount of biological insights.
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Affiliation(s)
- Alexander Varshavsky
- 1Division of Biology, California Institute of Technology, Pasadena, California 91125.
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22
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Kumar B, Lecompte KG, Klein JM, Haas AL. Ser(120) of Ubc2/Rad6 regulates ubiquitin-dependent N-end rule targeting by E3{alpha}/Ubr1. J Biol Chem 2010; 285:41300-9. [PMID: 21041297 DOI: 10.1074/jbc.m110.169136] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In CHO cells, CDK1/2-dependent phosphorylation of Ubc2/Rad6 at Ser(120) stimulates its ubiquitin conjugating activity and can be replicated by a S120D point mutant (Sarcevic, B., Mawson, A., Baker, R. T., and Sutherland, R. L. (2002) EMBO J. 21, 2009-2018). In contrast, we find that ectopic expression of wild type Ubc2b but not Ubc2bS120D or Ubc2bS120A in T47D human breast cancer cells specifically stimulates N-end rule-dependent degradation but not the Ubc2-independent unfolded protein response pathway, indicating that the former is E2 limiting in vivo and likely down-regulated by Ser(120) phosphorylation, as modeled by the S120D point mutation. In vitro kinetic analysis shows the in vivo phenotype of Ubc2bS120D and Ubc2bS120A is not due to differences in activating enzyme-catalyzed E2 transthiolation. However, the Ser(120) mutants possess marked differences in their abilities to support in vitro conjugation by the N-end rule-specific E3α/Ubr1 ligase that presumably accounts for their in vivo effects. Initial rate kinetics of human E3α-catalyzed conjugation of the human α-lactalbumin N-end rule substrate shows Ubc2bS120D is 20-fold less active than wild type E2, resulting from an 8-fold increase in K(m) and a 2.5-fold decrease in V(max), the latter reflecting a decreased ability to support the initial step in target protein conjugation; Ubc2bS120A is 8-fold less active than wild type E2 due almost exclusively to a decrease in V(max), reflecting a defect in polyubiquitin chain elongation. These studies suggest a mechanism for the integrated regulation of diverse ubiquitin-dependent signaling pathways through E2 phosphorylation that yields differential effects on its cognate ligases.
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Affiliation(s)
- Brajesh Kumar
- Department of Biochemistry and Molecular Biology and the Stanley S Scott Cancer Center, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112, USA
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23
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Toxin-based therapeutic approaches. Toxins (Basel) 2010; 2:2519-83. [PMID: 22069564 PMCID: PMC3153180 DOI: 10.3390/toxins2112519] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2010] [Revised: 10/25/2010] [Accepted: 10/26/2010] [Indexed: 01/08/2023] Open
Abstract
Protein toxins confer a defense against predation/grazing or a superior pathogenic competence upon the producing organism. Such toxins have been perfected through evolution in poisonous animals/plants and pathogenic bacteria. Over the past five decades, a lot of effort has been invested in studying their mechanism of action, the way they contribute to pathogenicity and in the development of antidotes that neutralize their action. In parallel, many research groups turned to explore the pharmaceutical potential of such toxins when they are used to efficiently impair essential cellular processes and/or damage the integrity of their target cells. The following review summarizes major advances in the field of toxin based therapeutics and offers a comprehensive description of the mode of action of each applied toxin.
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Abstract
The homologous to the E6-associated protein carboxyl terminus (HECT) domain E3 ubiquitin ligase Smurf1 is the first E3 ligase to be implicated in regulating bone cell function. The involvement of Smurf1 in multiple signaling pathways and pathological conditions is presently an area of extensive scientific interest. This review highlights recent works exploring Smurf-regulated biological processes in bone cells and highlights recent discoveries surrounding the regulatory mechanisms modulating its catalytic activity and substrate recognition capability. Moreover, we discuss the relevance of targeting the HECT E3s through the development of small-molecule inhibitors as an anticancer therapeutic strategy.
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Affiliation(s)
- Lianping Xing
- Department of Pathology, University of Rochester School of Medicine, Rochester, New York 14642, USA
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25
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Gou LT, Tong AP, Yan F, Yuan Z, He F, Wang W, Zhou Y, Chen LJ, Tang MH, Yang JL. Altered protein-expressing profile in hPNAS4-induced apoptosis in A549 human lung adenocarcinoma cells. J Cell Biochem 2010; 108:1211-9. [PMID: 19795389 DOI: 10.1002/jcb.22353] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Human PNAS4 (hPNAS4) is a recently identified pro-apoptosis gene, which is able to induce apoptosis in A549 human lung adenocarcinoma cells following its overexpression. In this work, we investigated the changes of protein profile in hPNAS4-induced apoptosis in A549 cells through proteomic strategy consisting of two-dimensional electrophoresis (2-DE) coupled with MALDI-Q-TOF mass spectrometry. A total of 20 different proteins with more than 3.0-fold change in expression, including 5 up-regulated and 15 down-regulated proteins were successfully identified by database search. The mRNA transcription levels of the different proteins were further examined by RT-PCT. Functional analyses showed these different proteins are involved in diverse biological processes including metabolism, proteolysis, signal transduction, apoptosis, and redox regulation. Two essential apoptosis-associated protein, annexin A1 and prothymosin alpha, were confirmed by Western blot and showed consistent changes with proteomic detection. Our data provide molecular evidence and possible associated pathway in hPNAS4-induced apoptosis through proteomic strategy, which should be contributed to further investigation on biological function of hPNAS4.
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Affiliation(s)
- Lan-Tu Gou
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, West China Medical School, Sichuan University, Chengdu 610041, Sichuan Province, China
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26
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Graciet E, Wellmer F. The plant N-end rule pathway: structure and functions. TRENDS IN PLANT SCIENCE 2010; 15:447-453. [PMID: 20627801 DOI: 10.1016/j.tplants.2010.04.011] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2010] [Revised: 04/25/2010] [Accepted: 04/29/2010] [Indexed: 05/29/2023]
Abstract
The N-end rule pathway is a protein degradation pathway that relates the stability of a protein to the nature of its N-terminal amino acid residue. This pathway is part of the ubiquitin-proteasome system in eukaryotes and has been shown to be involved in a multitude of cellular and developmental processes in animals and fungi. However, in plants, its structure and functions have long been enigmatic. In this review, we discuss recent advances in the identification of the enzymatic components that mediate protein degradation through the N-end rule pathway in plants. We further describe the known functions of this pathway in the control of plant growth and development and outline open questions that will likely be the focus of future research.
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Affiliation(s)
- Emmanuelle Graciet
- Smurfit Institute of Genetics, Trinity College Dublin, Dublin 2, Ireland.
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27
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The ubiquitin proteasome system and its involvement in cell death pathways. Cell Death Differ 2009; 17:1-3. [PMID: 20010850 DOI: 10.1038/cdd.2009.189] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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Brush JM, Kim K, Sayre JW, McBride WH, Iwamoto KS. Imaging of radiation effects on cellular 26S proteasome function in situ. Int J Radiat Biol 2009; 85:483-94. [PMID: 19401903 DOI: 10.1080/09553000902883794] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
PURPOSE The classical radiobiological paradigm is that DNA is the target for cell damage caused by ionising radiation. However, evidence is accumulating that other constituents, such as the membrane, organelles, and proteins, are also important targets. We have shown that the isolated 26S proteasome is one such target and here we wish to substantiate it within the cell, in situ. MATERIALS AND METHODS We used confocal microscopy to quantitatively detect and subcellularly localise radiation-induced 26S proteasome inhibition in cells expressing an ornithine decarboxylase degron that targets a fused Zoanthus species green (ZsGreen) fluorescent protein reporter specifically to the 26S proteasome. RESULTS Exposure of cells to a range of radiation doses, even as low as 0.05 Gy inhibited 26S activity within minutes. Initially, punctate nuclear ZsGreen fluorescence was observed that became cytoplasmic after seven hours -- a pattern distinct from the diffuse homogeneous fluorescence of cells incubated in the conventional proteasome inhibitor MG-132. CONCLUSIONS Our study clearly indicates that the 26S proteasome is a radiation target with physiological consequences and introduces a new perspective in mechanistic investigations of cellular responses to stresses.
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Affiliation(s)
- James M Brush
- Department of Radiation Oncology, David Geffen School of Medicine at UCLA, Los Angeles, California 90095-1714, USA
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29
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Tasaki T, Zakrzewska A, Dudgeon DD, Jiang Y, Lazo JS, Kwon YT. The substrate recognition domains of the N-end rule pathway. J Biol Chem 2008; 284:1884-95. [PMID: 19008229 DOI: 10.1074/jbc.m803641200] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The N-end rule pathway is a ubiquitin-dependent system where E3 ligases called N-recognins, including UBR1 and UBR2, recognize type-1 (basic) and type-2 (bulky hydrophobic) N-terminal residues as part of N-degrons. We have recently reported an E3 family (termed UBR1 through UBR7) characterized by the 70-residue UBR box, among which UBR1, UBR2, UBR4, and UBR5 were captured during affinity-based proteomics with synthetic degrons. Here we characterized substrate binding specificity and recognition domains of UBR proteins. Pull-down assays with recombinant UBR proteins suggest that 570-kDa UBR4 and 300-kDa UBR5 bind N-degron, whereas UBR3, UBR6, and UBR7 do not. Binding assays with 24 UBR1 deletion mutants and 31 site-directed UBR1 mutations narrow down the degron-binding activity to a 72-residue UBR box-only fragment that recognizes type-1 but not type-2 residues. A surface plasmon resonance assay shows that the UBR box binds to the type-1 substrate Arg-peptide with Kd of approximately 3.4 microm. Downstream from the UBR box, we identify a second substrate recognition domain, termed the N-domain, required for type-2 substrate recognition. The approximately 80-residue N-domain shows structural and functional similarity to 106-residue Escherichia coli ClpS, a bacterial N-recognin. We propose a model where the 70-residue UBR box functions as a common structural element essential for binding to all known destabilizing N-terminal residues, whereas specific residues localized in the UBR box (for type 1) or the N-domain (for type 2) provide substrate selectivity through interaction with the side group of an N-terminal amino acid. Our work provides new insights into substrate recognition in the N-end rule pathway.
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Affiliation(s)
- Takafumi Tasaki
- Center for Pharmacogenetics and Department of Pharmaceutical Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
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30
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Carrico I. Unexpected N-terminal editing: a cysteine protease that cuts and pastes. Nat Chem Biol 2008; 4:525-6. [DOI: 10.1038/nchembio0908-525] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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31
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Xia Z, Webster A, Du F, Piatkov K, Ghislain M, Varshavsky A. Substrate-binding sites of UBR1, the ubiquitin ligase of the N-end rule pathway. J Biol Chem 2008; 283:24011-28. [PMID: 18566452 DOI: 10.1074/jbc.m802583200] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Substrates of a ubiquitin-dependent proteolytic system called the N-end rule pathway include proteins with destabilizing N-terminal residues. N-recognins, the pathway's ubiquitin ligases, contain three substrate-binding sites. The type-1 site is specific for basic N-terminal residues (Arg, Lys, and His). The type-2 site is specific for bulky hydrophobic N-terminal residues (Trp, Phe, Tyr, Leu, and Ile). We show here that the type-1/2 sites of UBR1, the sole N-recognin of the yeast Saccharomyces cerevisiae, are located in the first approximately 700 residues of the 1,950-residue UBR1. These sites are distinct in that they can be selectively inactivated by mutations, identified through a genetic screen. Mutations inactivating the type-1 site are in the previously delineated approximately 70-residue UBR motif characteristic of N-recognins. Fluorescence polarization and surface plasmon resonance were used to determine that UBR1 binds, with a K(d) of approximately 1 microm, to either type-1 or type-2 destabilizing N-terminal residues of reporter peptides but does not bind to a stabilizing N-terminal residue such as Gly. A third substrate-binding site of UBR1 targets an internal degron of CUP9, a transcriptional repressor of peptide import. We show that the previously demonstrated in vivo dependence of CUP9 ubiquitylation on the binding of cognate dipeptides to the type-1/2 sites of UBR1 can be reconstituted in a completely defined in vitro system. We also found that purified UBR1 and CUP9 interact nonspecifically and that specific binding (which involves, in particular, the binding by cognate dipeptides to the UBR1 type-1/2 sites) can be restored either by a chaperone such as EF1A or through macromolecular crowding.
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Affiliation(s)
- Zanxian Xia
- Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA
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Meinnel T, Giglione C. Tools for analyzing and predicting N-terminal protein modifications. Proteomics 2008; 8:626-49. [DOI: 10.1002/pmic.200700592] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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Kovesdi E, Czeiter E, Tamas A, Reglodi D, Szellar D, Pal J, Bukovics P, Doczi T, Buki A. Rescuing neurons and glia: is inhibition of apoptosis useful? PROGRESS IN BRAIN RESEARCH 2007; 161:81-95. [PMID: 17618971 DOI: 10.1016/s0079-6123(06)61006-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Abstract
Traumatic brain injury (TBI) represents a leading cause of death in western countries. Despite all research efforts we still lack any pharmacological agent that could effectively be utilized in the clinical treatment of TBI. Detailed unraveling of the pathobiological processes initiated by/operant in TBI is a prerequisite to the development of rational therapeutic interventions. In this review we provide a summary of those therapeutic interventions purported to inhibit the cell death (CD) cascades ignited in TBI. On noxious stimuli three major forms of CD, apoptosis, autophagia and necrosis may occur. Apoptosis can be induced either via the mitochondrial (intrinsic) or the receptor mediated (extrinsic) pathway; endoplasmic reticular stress is the third trigger of caspase-mediated apoptotic processes. Although, theoretically pan-caspase inhibition could be an efficient tool to limit apoptosis and thereby the extent of TBI, potential cross-talk between various avenues of CD suggests that more upstream events, particularly the preservation of the cellular energy homeostasis (cyclosporine-A, poly ADP ribose polymerase (PARP) inhibition, hypothermia treatment) may represent more efficient therapeutic targets hopefully also translated to the clinical care of the severely head injured.
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Affiliation(s)
- E Kovesdi
- Department of Neurosurgery, University Medical School, Pécs University, Pécs, Hungary, Rét u. 2. H-7624, Hungary
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Tasaki T, Kwon YT. The mammalian N-end rule pathway: new insights into its components and physiological roles. Trends Biochem Sci 2007; 32:520-8. [PMID: 17962019 DOI: 10.1016/j.tibs.2007.08.010] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2007] [Revised: 08/21/2007] [Accepted: 08/21/2007] [Indexed: 12/30/2022]
Abstract
The N-end rule pathway is a ubiquitin-dependent proteolytic system, in which destabilizing N-terminal residues of short-lived proteins function as an essential determinant of an N-terminal degradation signal (N-degron). An N-degron can be created from a pre-N-degron through specific N-terminal modifications, providing a means conditionally to destabilize otherwise stable polypeptides. The pathway has been found in all organisms examined, from prokaryotes to eukaryotes. Recent biochemical and proteomic studies identified many components of the mammalian N-end rule pathway, including a family of substrate recognition ubiquitin ligases and their substrates. The genetic dissection in animals and humans revealed its essential role in various vital physiological processes, ranging from cardiovascular development and meiosis to the pathogenesis of human genetic diseases. These discoveries have provided new insights into the components, functions and mechanics of this unique proteolytic system.
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Affiliation(s)
- Takafumi Tasaki
- Center for Pharmacogenetics and Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, Pittsburgh, PA 15261, USA
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Watanabe K, Toh Y, Suto K, Shimizu Y, Oka N, Wada T, Tomita K. Protein-based peptide-bond formation by aminoacyl-tRNA protein transferase. Nature 2007; 449:867-71. [PMID: 17891155 DOI: 10.1038/nature06167] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2007] [Accepted: 08/13/2007] [Indexed: 11/08/2022]
Abstract
Eubacterial leucyl/phenylalanyl-tRNA protein transferase (LF-transferase) catalyses peptide-bond formation by using Leu-tRNA(Leu) (or Phe-tRNA(Phe)) and an amino-terminal Arg (or Lys) of a protein, as donor and acceptor substrates, respectively. However, the catalytic mechanism of peptide-bond formation by LF-transferase remained obscure. Here we determine the structures of complexes of LF-transferase and phenylalanyl adenosine, with and without a short peptide bearing an N-terminal Arg. Combining the two separate structures into one structure as well as mutation studies reveal the mechanism for peptide-bond formation by LF-transferase. The electron relay from Asp 186 to Gln 188 helps Gln 188 to attract a proton from the alpha-amino group of the N-terminal Arg of the acceptor peptide. This generates the attacking nucleophile for the carbonyl carbon of the aminoacyl bond of the aminoacyl-tRNA, thus facilitating peptide-bond formation. The protein-based mechanism for peptide-bond formation by LF-transferase is similar to the reverse reaction of the acylation step observed in the peptide hydrolysis reaction by serine proteases.
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Affiliation(s)
- Kazunori Watanabe
- Institute of Biological Resources and Functions, National Institute of Advanced Industrial Sciences and Technology, 1-1-1, Higashi, Tsukuba-shi, Ibaraki 305-8566, Japan
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Qian F, Zhen F, Xu J, Huang M, Li W, Wen Z. Distinct functions for different scl isoforms in zebrafish primitive and definitive hematopoiesis. PLoS Biol 2007; 5:e132. [PMID: 17472439 PMCID: PMC1858710 DOI: 10.1371/journal.pbio.0050132] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2006] [Accepted: 03/12/2007] [Indexed: 01/20/2023] Open
Abstract
The stem-cell leukemia (SCL, also known as TAL1) gene encodes a basic helix-loop-helix transcription factor that is essential for the initiation of primitive and definitive hematopoiesis, erythrocyte and megakarocyte differentiation, angiogenesis, and astrocyte development. Here we report that the zebrafish produces, through an alternative promoter site, a novel truncated scl (tal1) isoform, scl-beta, which manifests a temporal and spatial expression distinct from the previously described full-length scl-alpha. Functional analysis reveals that while scl-alpha and -beta are redundant for the initiation of primitive hematopoiesis, these two isoforms exert distinct functions in the regulation of primitive erythroid differentiation and definitive hematopoietic stem cell specification. We further demonstrate that differences in the protein expression levels of scl-alpha and -beta, by regulating their protein stability, are likely to give rise to their distinct functions. Our findings suggest that hematopoietic cells at different levels of hierarchy are likely governed by a gradient of the Scl protein established through temporal and spatial patterns of expression of the different isoforms.
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Affiliation(s)
- Feng Qian
- Laboratory of Molecular and Developmental Immunology, Institute of Molecular and Cell Biology, Singapore, Singapore
| | - Fenghua Zhen
- Laboratory of Molecular and Developmental Immunology, Institute of Molecular and Cell Biology, Singapore, Singapore
- Department of Biological Sciences National University of Singapore, Singapore, Singapore
| | - Jin Xu
- Laboratory of Molecular and Developmental Immunology, Institute of Molecular and Cell Biology, Singapore, Singapore
- Department of Biological Sciences National University of Singapore, Singapore, Singapore
| | - Mei Huang
- Laboratory of Molecular and Developmental Immunology, Institute of Molecular and Cell Biology, Singapore, Singapore
| | - Wanyu Li
- Laboratory of Molecular and Developmental Immunology, Institute of Molecular and Cell Biology, Singapore, Singapore
| | - Zilong Wen
- Laboratory of Molecular and Developmental Immunology, Institute of Molecular and Cell Biology, Singapore, Singapore
- Department of Biological Sciences National University of Singapore, Singapore, Singapore
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Tasaki T, Sohr R, Xia Z, Hellweg R, Hörtnagl H, Varshavsky A, Kwon YT. Biochemical and genetic studies of UBR3, a ubiquitin ligase with a function in olfactory and other sensory systems. J Biol Chem 2007; 282:18510-18520. [PMID: 17462990 DOI: 10.1074/jbc.m701894200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Our previous work identified E3 ubiquitin ligases, termed UBR1-UBR7, that contain the approximately 70-residue UBR box, a motif important for the targeting of N-end rule substrates. In this pathway, specific N-terminal residues of substrates are recognized as degradation signals by UBR box-containing E3s that include UBR1, UBR2, UBR4, and UBR5. The other E3s of this set, UBR3, UBR6, and UBR7, remained uncharacterized. Here we describe the cloning and analyses of mouse UBR3. The similarities of UBR3 to the UBR1 and UBR2 E3s of the N-end rule pathway include the RING and UBR domains. We show that HR6A and HR6B, the E2 enzymes that bind to UBR1 and UBR2, also interact with UBR3. However, in contrast to UBR1 and UBR2, UBR3 does not recognize N-end rule substrates. We also constructed UBR3-lacking mouse strains. In the 129SvImJ background, UBR3-/- mice died during embryogenesis, whereas the C57BL/6 background UBR3-/- mice exhibited neonatal lethality and suckling impairment that could be partially rescued by litter size reduction. The adult UBR3-/- mice had female-specific behavioral anosmia. Cells of the olfactory pathway were found to express beta-galactosidase (LacZ) that marked the deletion/disruption UBR3- allele. The UBR3-specific LacZ expression was also prominent in cells of the touch, vision, hearing, and taste systems, suggesting a regulatory role of UBR3 in sensory pathways, including olfaction. By analogy with functions of the UBR domain in the N-end rule pathway, we propose that the UBR box of UBR3 may recognize small compounds that modulate the targeting, by this E3, of its currently unknown substrates.
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Affiliation(s)
- Takafumi Tasaki
- Center for Pharmacogenetics and Department of Pharmaceutical Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Reinhard Sohr
- Institute of Pharmacology and Toxicology, Charité-University Medicine Berlin, Campus Mitte, Dorotheenstrasse 94, D-10117 Berlin, Germany
| | - Zanxian Xia
- Division of Biology, California Institute of Technology, Pasadena, California 91125
| | - Rainer Hellweg
- Department of Psychiatry and Psychotherapy, Charité-University Medicine Berlin, Campus Benjamin Franklin, Eschenallee 3, D-14050 Berlin, Germany
| | - Heide Hörtnagl
- Institute of Pharmacology and Toxicology, Charité-University Medicine Berlin, Campus Mitte, Dorotheenstrasse 94, D-10117 Berlin, Germany
| | - Alexander Varshavsky
- Division of Biology, California Institute of Technology, Pasadena, California 91125
| | - Yong Tae Kwon
- Center for Pharmacogenetics and Department of Pharmaceutical Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
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Mogk A, Schmidt R, Bukau B. The N-end rule pathway for regulated proteolysis: prokaryotic and eukaryotic strategies. Trends Cell Biol 2007; 17:165-72. [PMID: 17306546 DOI: 10.1016/j.tcb.2007.02.001] [Citation(s) in RCA: 207] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2006] [Revised: 01/08/2007] [Accepted: 02/02/2007] [Indexed: 01/02/2023]
Abstract
The N-end rule states that the half-life of a protein is determined by the nature of its N-terminal residue. This fundamental principle of regulated proteolysis is conserved from bacteria to mammals. Although prokaryotes and eukaryotes employ distinct proteolytic machineries for degradation of N-end rule substrates, recent findings indicate that they share common principles of substrate recognition. In eukaryotes substrate recognition is mediated by N-recognins, a class of E3 ligases that labels N-end rule substrates via covalent linkage to ubiquitin, allowing the subsequent substrate delivery to the 26S proteasome. In bacteria, the adaptor protein ClpS exhibits homology to the substrate binding site of N-recognin. ClpS binds to the destabilizing N-termini of N-end rule substrates and directly transfers them to the ClpAP protease.
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Affiliation(s)
- Axel Mogk
- ZMBH, Universität Heidelberg, Im Neuenheimer Feld 282, Heidelberg D-69120, Germany
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Yamaguchi M, Obama T, Kuyama H, Nakayama D, Ando E, Okamura TA, Ueyama N, Nakazawa T, Norioka S, Nishimura O, Tsunasawa S. Specific isolation of N-terminal fragments from proteins and their high-fidelity de novo sequencing. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2007; 21:3329-36. [PMID: 17879392 DOI: 10.1002/rcm.3215] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
A new method to determine N-terminal amino acid sequences of multiple proteins at low pmol level by a parallel processing has been developed. The method contains the following five steps: (1) reduction, S-alkylation and guanidination for targeted proteins; (2) coupling with sulfosucccimidyl-2-(biotinamido)ethyl-1,3-dithiopropionate(sulfo-NHS-SS-biotin) to N(alpha)-amino groups of proteins; (3) digestion of the modified proteins by an appropriate protease; (4) specific isolation of N-terminal fragments of proteins by affinity capture using the biotin-avidin system; (5) de novo sequence analysis of peptides by MALDI-TOF-/MALDI-TOF-PSD mass spectrometry with effective utilization of the CAF (chemically assisted fragmentation) method.1 This method is also effective for N-terminal sequencing of each protein in a mixture of several proteins, and for sequencing components of a multiprotein complex. It is expected to become an essential proteomics tool for identifying proteins, especially when used in combination with a C-terminal sequencing method.
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Affiliation(s)
- Minoru Yamaguchi
- Life Science Laboratory, Shimadzu Corporation, Kyoto 604-8511, Japan.
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Werner ME, Chen F, Moyano JV, Yehiely F, Jones JCR, Cryns VL. Caspase proteolysis of the integrin beta4 subunit disrupts hemidesmosome assembly, promotes apoptosis, and inhibits cell migration. J Biol Chem 2006; 282:5560-9. [PMID: 17178732 PMCID: PMC2819670 DOI: 10.1074/jbc.m603669200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Caspases are a conserved family of cell death proteases that cleave intracellular substrates at Asp residues to modify their function and promote apoptosis. In this report we identify the integrin beta4 subunit as a novel caspase substrate using an expression cloning strategy. Together with its alpha6 partner, alpha6beta4 integrin anchors epithelial cells to the basement membrane at specialized adhesive structures known as hemidesmosomes and plays a critical role in diverse epithelial cell functions including cell survival and migration. We show that integrin beta4 is cleaved by caspase-3 and -7 at a conserved Asp residue (Asp(1109)) in vitro and in epithelial cells undergoing apoptosis, resulting in the removal of most of its cytoplasmic tail. Caspase cleavage of integrin beta4 produces two products, 1) a carboxyl-terminal product that is unstable and rapidly degraded by the proteasome and 2) an amino-terminal cleavage product (amino acids 1-1109) that is unable to assemble into mature hemidesmosomes. We also demonstrate that caspase cleavage of integrin beta4 sensitizes epithelial cells to apoptosis and inhibits cell migration. Taken together, we have identified a previously unrecognized proteolytic truncation of integrin beta4 generated by caspases that disrupts key structural and functional properties of epithelial cells and promotes apoptosis.
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Affiliation(s)
- Michael E. Werner
- Cell Death Regulation Laboratory, Northwestern University, Chicago, Illinois 60611
- Department of Medicine, Northwestern University, Chicago, Illinois 60611
- Department of Cell and Molecular Biology, Northwestern University, Chicago, Illinois 60611
- Robert H. Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611
| | - Feng Chen
- Cell Death Regulation Laboratory, Northwestern University, Chicago, Illinois 60611
- Department of Medicine, Northwestern University, Chicago, Illinois 60611
- Department of Cell and Molecular Biology, Northwestern University, Chicago, Illinois 60611
- Robert H. Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611
| | - Jose V. Moyano
- Cell Death Regulation Laboratory, Northwestern University, Chicago, Illinois 60611
- Department of Medicine, Northwestern University, Chicago, Illinois 60611
- Department of Cell and Molecular Biology, Northwestern University, Chicago, Illinois 60611
- Robert H. Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611
| | - Fruma Yehiely
- Cell Death Regulation Laboratory, Northwestern University, Chicago, Illinois 60611
- Department of Medicine, Northwestern University, Chicago, Illinois 60611
- Department of Cell and Molecular Biology, Northwestern University, Chicago, Illinois 60611
- Robert H. Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611
| | - Jonathan C. R. Jones
- Department of Cell and Molecular Biology, Northwestern University, Chicago, Illinois 60611
- Robert H. Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611
| | - Vincent L. Cryns
- Cell Death Regulation Laboratory, Northwestern University, Chicago, Illinois 60611
- Department of Medicine, Northwestern University, Chicago, Illinois 60611
- Department of Cell and Molecular Biology, Northwestern University, Chicago, Illinois 60611
- Robert H. Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611
- To whom correspondence should be addressed: Departs. of Medicine and Cell and Molecular Biology, Lurie 4-113, Feinberg School of Medicine, Northwestern University, 303 E. Superior St., Chicago, IL 60611. Tel.: 312-503-0644; Fax: 312-908-9032;
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Hu X, Addlagatta A, Lu J, Matthews BW, Liu JO. Elucidation of the function of type 1 human methionine aminopeptidase during cell cycle progression. Proc Natl Acad Sci U S A 2006; 103:18148-53. [PMID: 17114291 PMCID: PMC1838721 DOI: 10.1073/pnas.0608389103] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Processing of the N-terminal initiator methionine is an essential cellular process conserved from prokaryotes to eukaryotes. The enzymes that remove N-terminal methionine are known as methionine aminopeptidases (MetAPs). Human MetAP2 has been shown to be required for the proliferation of endothelial cells and angiogenesis. The physiological function of MetAP1, however, has remained elusive. In this report we demonstrate that a family of inhibitors with a core structure of pyridine-2-carboxylic acid previously developed for the bacterial and yeast MetAP1 is also specific for human MetAP1 (HsMetAP1), as confirmed by both enzymatic assay and high-resolution x-ray crystallography. Treatment of tumor cell lines with the MetAP1-specific inhibitors led to an accumulation of cells in the G(2)/M phase, suggesting that HsMetAP1 may play an important role in G(2)/M phase transition. Overexpression of HsMetAP1, but not HsMetAP2, conferred resistance of cells to the inhibitors, and the inhibitors caused retention of N-terminal methionine of a known MetAP substrate, suggesting that HsMetAP1 is the cellular target for the inhibitors. In addition, when HsMetAP1 was knocked down by gene-specific siRNA, cells exhibited slower progression during G(2)/M phase, a phenotype similar to cells treated with MetAP1 inhibitors. Importantly, MetAP1 inhibitors were able to induce apoptosis of leukemia cell lines, presumably as a consequence of their interference with the G(2)/M phase checkpoint. Together, these results suggest that MetAP1 plays an important role in G(2)/M phase of the cell cycle and that it may serve as a promising target for the discovery and development of new anticancer agents.
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Affiliation(s)
- Xiaoyi Hu
- *Department of Pharmacology and Molecular Sciences and
| | - Anthony Addlagatta
- Institute of Molecular Biology, Howard Hughes Medical Institute and Department of Physics, University of Oregon, Eugene, OR 97403-1229
| | - Jun Lu
- *Department of Pharmacology and Molecular Sciences and
| | - Brian W. Matthews
- Institute of Molecular Biology, Howard Hughes Medical Institute and Department of Physics, University of Oregon, Eugene, OR 97403-1229
- To whom correspondence may be addressed. E-mail: or
| | - Jun O. Liu
- *Department of Pharmacology and Molecular Sciences and
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205; and
- To whom correspondence may be addressed. E-mail: or
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Suto K, Shimizu Y, Watanabe K, Ueda T, Fukai S, Nureki O, Tomita K. Crystal structures of leucyl/phenylalanyl-tRNA-protein transferase and its complex with an aminoacyl-tRNA analog. EMBO J 2006; 25:5942-50. [PMID: 17110926 PMCID: PMC1698881 DOI: 10.1038/sj.emboj.7601433] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2006] [Accepted: 10/17/2006] [Indexed: 11/09/2022] Open
Abstract
Eubacterial leucyl/phenylalanyl-tRNA protein transferase (L/F-transferase), encoded by the aat gene, conjugates leucine or phenylalanine to the N-terminal Arg or Lys residue of proteins, using Leu-tRNA(Leu) or Phe-tRNA(Phe) as a substrate. The resulting N-terminal Leu or Phe acts as a degradation signal for the ClpS-ClpAP-mediated N-end rule protein degradation pathway. Here, we present the crystal structures of Escherichia coli L/F-transferase and its complex with an aminoacyl-tRNA analog, puromycin. The C-terminal domain of L/F-transferase consists of the GCN5-related N-acetyltransferase fold, commonly observed in the acetyltransferase superfamily. The p-methoxybenzyl group of puromycin, corresponding to the side chain of Leu or Phe of Leu-tRNA(Leu) or Phe-tRNA(Phe), is accommodated in a highly hydrophobic pocket, with a shape and size suitable for hydrophobic amino-acid residues lacking a branched beta-carbon, such as leucine and phenylalanine. Structure-based mutagenesis of L/F-transferase revealed its substrate specificity. Furthermore, we present a model of the L/F-transferase complex with tRNA and substrate proteins bearing an N-terminal Arg or Lys.
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Affiliation(s)
- Kyoko Suto
- Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
| | - Yoshihiro Shimizu
- Department of Medical Genome Sciences, Graduate School of Frontier Sciences, University of Tokyo, Kashiwa, Chiba, Japan
| | - Kazunori Watanabe
- Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
| | - Takuya Ueda
- Department of Medical Genome Sciences, Graduate School of Frontier Sciences, University of Tokyo, Kashiwa, Chiba, Japan
| | - Shuya Fukai
- Department of Biological Information, Graduate School of Bioscience and Technology, Tokyo Institute of Technology, Nagatsuda-cho, Midori-ku, Yokohama, Kanagawa, Japan
| | - Osamu Nureki
- Department of Biological Information, Graduate School of Bioscience and Technology, Tokyo Institute of Technology, Nagatsuda-cho, Midori-ku, Yokohama, Kanagawa, Japan
| | - Kozo Tomita
- Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
- Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1, Higashi, Tsukuba, Ibaraki 305-8566, Japan. Tel.: +81 29 861 6085; Fax: +81 29 861 6095; E-mail:
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Ardley HC, Robinson PA. The role of ubiquitin-protein ligases in neurodegenerative disease. NEURODEGENER DIS 2006; 1:71-87. [PMID: 16908979 DOI: 10.1159/000080048] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2003] [Accepted: 02/19/2004] [Indexed: 12/17/2022] Open
Abstract
Alzheimer's disease and Parkinson's disease are the most common neurodegenerative conditions associated with the ageing process. The pathology of these and other neurodegenerative disorders, including polyglutamine diseases, is characterised by the presence of inclusion bodies in brain tissue of affected patients. In general, these inclusion bodies consist of insoluble, unfolded proteins that are commonly tagged with the small protein, ubiquitin. Covalent tagging of proteins with chains of ubiquitin generally targets them for degradation. Indeed, the ubiquitin/proteasome system (UPS) is the major route through which intracellular proteolysis is regulated. This strongly implicates the UPS in these disease-associated inclusions, either due to malfunction (of specific UPS components) or overload of the system (due to aggregation of unfolded/mutant proteins), resulting in subsequent cellular toxicity. Protein targeting for degradation is a highly regulated process. It relies on transfer of ubiquitin molecules to the target protein via an enzyme cascade and specific recognition of a substrate protein by ubiquitin-protein ligases (E3s). Recent advances in our knowledge gained from the Human Genome Mapping Project have revealed the presence of potentially hundreds of E3s within the human genome. The discovery that parkin, mutations in which are found in at least 50% of patients with autosomal recessive juvenile parkinsonism, is an E3 further highlights the importance of the UPS in neurological disease. To date, parkin is the only E3 confirmed to have a direct causal role in neurodegenerative disorders. However, a number of other (putative) E3s have now been identified that may cause disease directly or interact with neurological disease-associated proteins. Many of these are either lost or mutated in a given disease or fail to process disease-associated mutant proteins correctly. In this review, we will discuss the role(s) of E3s in neurodegenerative disorders.
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Affiliation(s)
- Helen C Ardley
- Molecular Medicine Unit, University of Leeds, St. James's University Hospital, Leeds, UK.
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Abstract
E3 ubiquitin ligases are a large family of proteins that are engaged in the regulation of the turnover and activity of many target proteins. Together with ubiquitin-activating enzyme E1 and ubiquitin-conjugating enzyme E2, E3 ubiquitin ligases catalyze the ubiquitination of a variety of biologically significant protein substrates for targeted degradation through the 26S proteasome, as well as for nonproteolytic regulation of their functions or subcellular localizations. E3 ubiquitin ligases, therefore, play an essential role in the regulation of many biologic processes. Increasing amounts of evidence strongly suggest that the abnormal regulation of some E3 ligases is involved in cancer development. Furthermore, some E3 ubiquitin ligases are frequently overexpressed in human cancers, which correlates well with increased chemoresistance and poor clinic prognosis. In this review, E3 ubiquitin ligases (such as murine double minute 2, inhibitor of apoptosis protein, and Skp1-Cullin-F-box protein) will be evaluated as potential cancer drug targets and prognostic biomarkers. Extensive study in this field would lead to a better understanding of the molecular mechanism by which E3 ligases regulate cellular processes and of how their deregulations contribute to carcinogenesis. This would eventually lead to the development of a novel class of anticancer drugs targeting specific E3 ubiquitin ligases, as well as the development of sensitive biomarkers for cancer treatment, diagnosis, and prognosis.
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Affiliation(s)
- Yi Sun
- Division of Cancer Biology, Department of Radiation Oncology, University of Michigan Comprehensive Cancer Center, Ann Arbor, MI 48109-0936, USA.
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45
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Hu RG, Brower CS, Wang H, Davydov IV, Sheng J, Zhou J, Kwon YT, Varshavsky A. Arginyltransferase, its specificity, putative substrates, bidirectional promoter, and splicing-derived isoforms. J Biol Chem 2006; 281:32559-73. [PMID: 16943202 DOI: 10.1074/jbc.m604355200] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Substrates of the N-end rule pathway include proteins with destabilizing N-terminal residues. Three of them, Asp, Glu, and (oxidized) Cys, function through their conjugation to Arg, one of destabilizing N-terminal residues that are recognized directly by the pathway's ubiquitin ligases. The conjugation of Arg is mediated by arginyltransferase, encoded by ATE1. Through its regulated degradation of specific proteins, the arginylation branch of the N-end rule pathway mediates, in particular, the cardiovascular development, the fidelity of chromosome segregation, and the control of signaling by nitric oxide. We show that mouse ATE1 specifies at least six mRNA isoforms, which are produced through alternative splicing, encode enzymatically active arginyltransferases, and are expressed at varying levels in mouse tissues. We also show that the ATE1 promoter is bidirectional, mediating the expression of both ATE1 and an oppositely oriented, previously uncharacterized gene. In addition, we identified GRP78 (glucose-regulated protein 78) and protein-disulfide isomerase as putative physiological substrates of arginyltransferase. Purified isoforms of arginyltransferase that contain the alternative first exons differentially arginylate these proteins in extract from ATE1(-/-) embryos, suggesting that specific isoforms may have distinct functions. Although the N-end rule pathway is apparently confined to the cytosol and the nucleus, and although GRP78 and protein-disulfide isomerase are located largely in the endoplasmic reticulum, recent evidence suggests that these proteins are also present in the cytosol and other compartments in vivo, where they may become N-end rule substrates.
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Affiliation(s)
- Rong-Gui Hu
- Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA
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Abstract
Accumulating evidence indicates that there is a critical role of the ubiquitin/proteasome pathway in the regulation of apoptosis. Among the important molecules that couple these two fundamental cellular activities are members of the inhibitor of apoptosis (IAP) protein family. In addition to their well-studied ability to directly bind and inhibit caspases, many IAPs contain RING domains that are necessary and sufficient to cause ubiquitylation and subsequent proteasome-mediated proteolysis. This review summarizes recent findings about the ubiquitin protein ligase activity of IAPs, and considers possible mechanisms for substrate selectivity.
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Affiliation(s)
- Ting Ni
- College of Life Science, Sichuan University, Sichuan Province, P. R. China
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47
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Affiliation(s)
- J Chloë Bulinski
- Department of Biological Sciences and the Department of Pathology and Cell Biology, Columbia University, 1212 Amsterdam Avenue, New York, NY 10027-2450, USA.
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Liu X, Huang W, Li C, Li P, Yuan J, Li X, Qiu XB, Ma Q, Cao C. Interaction between c-Abl and Arg tyrosine kinases and proteasome subunit PSMA7 regulates proteasome degradation. Mol Cell 2006; 22:317-27. [PMID: 16678104 DOI: 10.1016/j.molcel.2006.04.007] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2005] [Revised: 09/07/2005] [Accepted: 04/10/2006] [Indexed: 11/15/2022]
Abstract
Proteasome-mediated proteolysis is a primary protein degradation pathway in cells. The present study demonstrates that c-Abl and Arg (abl-related gene) tyrosine kinases associate with and phosphorylate the proteasome PSMA7 (alpha4) subunit at Tyr-153. Consequently, proteasome-dependent proteolysis is compromised. Notably, cells expressing a phosphorylation mutant of PSMA7(Y153F) display impaired G1/S transition and S/G2 progression, highlighting the biological significance of tyrosine phosphorylation of a proteasome subunit as an important cellular regulatory control.
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Affiliation(s)
- Xuan Liu
- Beijing Institute of Biotechnology, Beijing 100850, China
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Walling LL. Recycling or regulation? The role of amino-terminal modifying enzymes. CURRENT OPINION IN PLANT BIOLOGY 2006; 9:227-33. [PMID: 16597508 DOI: 10.1016/j.pbi.2006.03.009] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2006] [Accepted: 03/22/2006] [Indexed: 05/08/2023]
Abstract
Post-translational modifications are essential for a variety of functions, such as the translocation, activation, regulation, and, ultimately, degradation of proteins. The amino-terminal (N-terminal) region is a particularly active area for such alterations. Three types of reactions predominate: limited proteolysis to remove one or more amino acids; modification of the alpha-amino group; and side-chain-specific changes. The N-terminal peptidases expose penultimate residues, providing new substrates for peptidase or transferase action. These enzymes can act sequentially or competitively to influence a protein's longevity, location or activity. N-terminal modifying enzymes (NTMEs) might target a protein for ubiquitination and degradation or protect a protein from rapid turnover. The N-terminal peptidases might also have important roles in processing the peptides that are released from the proteasome. Plant NTMEs have roles in senescence, meiosis and defense, and proposed roles in polar auxin transport.
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Affiliation(s)
- Linda L Walling
- Department of Botany and Plant Sciences, Center for Plant Cell Biology, University of California, Riverside, California 92521, USA.
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50
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An JY, Seo JW, Tasaki T, Lee MJ, Varshavsky A, Kwon YT. Impaired neurogenesis and cardiovascular development in mice lacking the E3 ubiquitin ligases UBR1 and UBR2 of the N-end rule pathway. Proc Natl Acad Sci U S A 2006; 103:6212-7. [PMID: 16606826 PMCID: PMC1458857 DOI: 10.1073/pnas.0601700103] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. A subset of degradation signals recognized by the N-end rule pathway comprises the signals, called N-degrons, whose determinants include destabilizing N-terminal residues. Our previous work identified a family of at least four mammalian E3 ubiquitin ligases, including UBR1 and UBR2, that share the UBR box and recognize N-degrons. These E3 enzymes mediate the multifunctional N-end rule pathway, but their individual roles are just beginning to emerge. Mutations of UBR1 in humans are the cause of Johanson-Blizzard syndrome. UBR1 and UBR2 are 46% identical and appear to be indistinguishable in their recognition of N-degrons. UBR1-/- mice are viable but have defects that include pancreatic insufficiency, similarly to UBR1-/- human patients with Johanson-Blizzard syndrome. UBR2-/- mice are inviable in some strain backgrounds and are defective in male meiosis. To examine functional relationships between UBR1 and UBR2, we constructed mouse strains lacking both of these E3s. We report here that UBR1-/-UBR2-/- embryos die at midgestation, with defects in neurogenesis and cardiovascular development. These defects included reduced proliferation as well as precocious migration and differentiation of neural progenitor cells. The expression of regulators such as D-type cyclins and Notch1 was also altered in UBR1-/-UBR2-/- embryos. We conclude that the functions of UBR1 and UBR2 are significantly divergent, in part because of differences in their expression patterns and possibly also because of differences in their recognition of protein substrates that contain degradation signals other than N-degrons.
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Affiliation(s)
- Jee Young An
- *Center for Pharmacogenetics and Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, Pittsburgh, PA 15261; and
| | - Jai Wha Seo
- *Center for Pharmacogenetics and Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, Pittsburgh, PA 15261; and
| | - Takafumi Tasaki
- *Center for Pharmacogenetics and Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, Pittsburgh, PA 15261; and
| | - Min Jae Lee
- *Center for Pharmacogenetics and Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, Pittsburgh, PA 15261; and
| | - Alexander Varshavsky
- Division of Biology, California Institute of Technology, Pasadena, CA 91125
- To whom correspondence may be addressed. E-mail:
or
| | - Yong Tae Kwon
- *Center for Pharmacogenetics and Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, Pittsburgh, PA 15261; and
- To whom correspondence may be addressed. E-mail:
or
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