1
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Naraki Y, Watanabe M, Takeya K. Inhibitory effects of rubratoxin A, a potent inhibitor of protein phosphatase 2, on the Ca 2+-dependent contraction of skinned carotid artery from guinea pig. J Smooth Muscle Res 2020; 55:14-22. [PMID: 31006724 PMCID: PMC6473161 DOI: 10.1540/jsmr.55.14] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Rubratoxin A, a potent inhibitor of PP2A, is known to suppress smooth muscle contraction.
The inhibitory role of PP2A in smooth muscle contraction is still unclear. In order to
clarify the regulatory mechanisms of PP2A on vascular smooth muscle contractility, we
examined the effects of rubratoxin A on the Ca2+-induced contraction of β-escin
skinned carotid artery preparations from guinea pigs. Rubratoxin A at 1 µM and 10 µM
significantly inhibited skinned carotid artery contraction at any Ca2+
concentration. The data fitting to the Hill equation in [Ca2+]-contraction
relationship indicated that rubratoxin A decreased Fmax-Ca2+ and increased
[Ca2+]50, indices of Ca2+ sensitivity for the force and
myosin-actin interaction, respectively. These results suggest that PP2A inhibition causes
downregulation of the myosin light chain phosphorylation and direct interference with
myosin-actin interaction.
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Affiliation(s)
- Yasuyuki Naraki
- Department of Frontier Health Sciences, Graduate School of Human Health Sciences, Tokyo Metropolitan University, 7-2-10 Higashiogu, Arakawa-ku, Tokyo 116-8551, Japan
| | - Masaru Watanabe
- Department of Frontier Health Sciences, Graduate School of Human Health Sciences, Tokyo Metropolitan University, 7-2-10 Higashiogu, Arakawa-ku, Tokyo 116-8551, Japan
| | - Kosuke Takeya
- Department of Veterinary Biochemistry, Faculty of Veterinary Medicine, Okayama University of Science, Imabari-shi, Ehime 794-8555, Japan
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2
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Swingle MR, Honkanen RE. Inhibitors of Serine/Threonine Protein Phosphatases: Biochemical and Structural Studies Provide Insight for Further Development. Curr Med Chem 2019; 26:2634-2660. [PMID: 29737249 PMCID: PMC10013172 DOI: 10.2174/0929867325666180508095242] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2017] [Revised: 02/05/2018] [Accepted: 03/29/2018] [Indexed: 11/22/2022]
Abstract
BACKGROUND The reversible phosphorylation of proteins regulates many key functions in eukaryotic cells. Phosphorylation is catalyzed by protein kinases, with the majority of phosphorylation occurring on side chains of serine and threonine residues. The phosphomonoesters generated by protein kinases are hydrolyzed by protein phosphatases. In the absence of a phosphatase, the half-time for the hydrolysis of alkyl phosphate dianions at 25º C is over 1 trillion years; knon ~2 x 10-20 sec-1. Therefore, ser/thr phosphatases are critical for processes controlled by reversible phosphorylation. METHODS This review is based on the literature searched in available databases. We compare the catalytic mechanism of PPP-family phosphatases (PPPases) and the interactions of inhibitors that target these enzymes. RESULTS PPPases are metal-dependent hydrolases that enhance the rate of hydrolysis ([kcat/kM]/knon ) by a factor of ~1021, placing them among the most powerful known catalysts on earth. Biochemical and structural studies indicate that the remarkable catalytic proficiencies of PPPases are achieved by 10 conserved amino acids, DXH(X)~26DXXDR(X)~20- 26NH(X)~50H(X)~25-45R(X)~30-40H. Six act as metal-coordinating residues. Four position and orient the substrate phosphate. Together, two metal ions and the 10 catalytic residues position the phosphoryl group and an activated bridging water/hydroxide nucleophile for an inline attack upon the substrate phosphorous atom. The PPPases are conserved among species, and many structurally diverse natural toxins co-evolved to target these enzymes. CONCLUSION Although the catalytic site is conserved, opportunities for the development of selective inhibitors of this important group of metalloenzymes exist.
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Affiliation(s)
- Mark R Swingle
- Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile AL 36688, United States
| | - Richard E Honkanen
- Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile AL 36688, United States
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3
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Chen M, Wan L, Zhang J, Zhang J, Mendez L, Clohessy JG, Berry K, Victor J, Yin Q, Zhu Y, Wei W, Pandolfi PP. Deregulated PP1α phosphatase activity towards MAPK activation is antagonized by a tumor suppressive failsafe mechanism. Nat Commun 2018; 9:159. [PMID: 29335436 PMCID: PMC5768788 DOI: 10.1038/s41467-017-02272-y] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2016] [Accepted: 11/17/2017] [Indexed: 12/22/2022] Open
Abstract
The mitogen-activated protein kinase (MAPK) pathway is frequently aberrantly activated in advanced cancers, including metastatic prostate cancer (CaP). However, activating mutations or gene rearrangements among MAPK signaling components, such as Ras and Raf, are not always observed in cancers with hyperactivated MAPK. The mechanisms underlying MAPK activation in these cancers remain largely elusive. Here we discover that genomic amplification of the PPP1CA gene is highly enriched in metastatic human CaP. We further identify an S6K/PP1α/B-Raf signaling pathway leading to activation of MAPK signaling that is antagonized by the PML tumor suppressor. Mechanistically, we find that PP1α acts as a B-Raf activating phosphatase and that PML suppresses MAPK activation by sequestering PP1α into PML nuclear bodies, hence repressing S6K-dependent PP1α phosphorylation, 14-3-3 binding and cytoplasmic accumulation. Our findings therefore reveal a PP1α/PML molecular network that is genetically altered in human cancer towards aberrant MAPK activation, with important therapeutic implications.
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Affiliation(s)
- Ming Chen
- Cancer Research Institute, Beth Israel Deaconess Cancer Center, Department of Medicine and Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, 02215, USA
| | - Lixin Wan
- Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, 02115, USA
- Department of Molecular Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, 33612, USA
| | - Jiangwen Zhang
- School of Biological Sciences, The University of Hong Kong, Hong Kong, 999077, China
| | - Jinfang Zhang
- Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, 02115, USA
| | - Lourdes Mendez
- Cancer Research Institute, Beth Israel Deaconess Cancer Center, Department of Medicine and Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, 02215, USA
| | - John G Clohessy
- Cancer Research Institute, Beth Israel Deaconess Cancer Center, Department of Medicine and Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, 02215, USA
| | - Kelsey Berry
- Cancer Research Institute, Beth Israel Deaconess Cancer Center, Department of Medicine and Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, 02215, USA
| | - Joshua Victor
- Cancer Research Institute, Beth Israel Deaconess Cancer Center, Department of Medicine and Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, 02215, USA
| | - Qing Yin
- Department of Molecular Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, 33612, USA
| | - Yuan Zhu
- Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, 02115, USA
| | - Wenyi Wei
- Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, 02115, USA
| | - Pier Paolo Pandolfi
- Cancer Research Institute, Beth Israel Deaconess Cancer Center, Department of Medicine and Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, 02215, USA.
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4
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Quach R, Furkert DP, Brimble MA. Gold catalysis: synthesis of spiro, bridged, and fused ketal natural products. Org Biomol Chem 2017; 15:3098-3104. [DOI: 10.1039/c7ob00496f] [Citation(s) in RCA: 69] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
This review summarises the application of gold catalysis for the syntheses of spiro, bridged and fused ketal natural products.
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Affiliation(s)
- Rachelle Quach
- The School of Chemical Sciences
- University of Auckland
- Auckland 1010
- New Zealand
| | - Daniel P. Furkert
- The School of Chemical Sciences
- University of Auckland
- Auckland 1010
- New Zealand
| | - Margaret A. Brimble
- The School of Chemical Sciences
- University of Auckland
- Auckland 1010
- New Zealand
- Maurice Wilkins Centre for Molecular Biodiscovery
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5
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Chattopadhyay D, Swingle MR, Salter EA, Wood E, D'Arcy B, Zivanov C, Abney K, Musiyenko A, Rusin SF, Kettenbach A, Yet L, Schroeder CE, Golden JE, Dunham WH, Gingras AC, Banerjee S, Forbes D, Wierzbicki A, Honkanen RE. Crystal structures and mutagenesis of PPP-family ser/thr protein phosphatases elucidate the selectivity of cantharidin and novel norcantharidin-based inhibitors of PP5C. Biochem Pharmacol 2016; 109:14-26. [PMID: 27002182 DOI: 10.1016/j.bcp.2016.03.011] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Accepted: 03/15/2016] [Indexed: 12/24/2022]
Abstract
Cantharidin is a natural toxin and an active constituent in a traditional Chinese medicine used to treat tumors. Cantharidin acts as a semi-selective inhibitor of PPP-family ser/thr protein phosphatases. Despite sharing a common catalytic mechanism and marked structural similarity with PP1C, PP2AC and PP5C, human PP4C was found to be insensitive to the inhibitory activity of cantharidin. To explore the molecular basis for this selectivity, we synthesized and tested novel C5/C6-derivatives designed from quantum-based modeling of the interactions revealed in the co-crystal structures of PP5C in complex with cantharidin. Structure-activity relationship studies and analysis of high-resolution (1.25Å) PP5C-inhibitor co-crystal structures reveal close contacts between the inhibitor bridgehead oxygen and both a catalytic metal ion and a non-catalytic phenylalanine residue, the latter of which is substituted by tryptophan in PP4C. Quantum chemistry calculations predicted that steric clashes with the bulkier tryptophan side chain in PP4C would force all cantharidin-based inhibitors into an unfavorable binding mode, disrupting the strong coordination of active site metal ions observed in the PP5C co-crystal structures, thereby rendering PP4C insensitive to the inhibitors. This prediction was confirmed by inhibition studies employing native human PP4C. Mutation of PP5C (F446W) and PP1C (F257W), to mimic the PP4C active site, resulted in markedly suppressed sensitivity to cantharidin. These observations provide insight into the structural basis for the natural selectivity of cantharidin and provide an avenue for PP4C deselection. The novel crystal structures also provide insight into interactions that provide increased selectivity of the C5/C6 modifications for PP5C versus other PPP-family phosphatases.
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Affiliation(s)
| | - Mark R Swingle
- Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, AL 36688, USA
| | - Edward A Salter
- Department of Chemistry, University of South Alabama, Mobile, AL 36688, USA
| | - Eric Wood
- Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, AL 36688, USA; Department of Chemistry, University of South Alabama, Mobile, AL 36688, USA
| | - Brandon D'Arcy
- Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, AL 36688, USA
| | - Catherine Zivanov
- Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, AL 36688, USA; Department of Chemistry, University of South Alabama, Mobile, AL 36688, USA
| | - Kevin Abney
- Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, AL 36688, USA
| | - Alla Musiyenko
- Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, AL 36688, USA
| | - Scott F Rusin
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Lebanon, NH 03756, USA
| | - Arminja Kettenbach
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Lebanon, NH 03756, USA; Norris Cotton Cancer Center, Geisel School of Medicine at Dartmouth, Lebanon, NH 03756, USA
| | - Larry Yet
- Department of Chemistry, University of South Alabama, Mobile, AL 36688, USA
| | - Chad E Schroeder
- Department of Medicinal Chemistry, University of Kansas Specialized Chemistry Center, Lawrence, KS 66047, USA
| | - Jennifer E Golden
- Department of Medicinal Chemistry, University of Kansas Specialized Chemistry Center, Lawrence, KS 66047, USA
| | - Wade H Dunham
- Centre for Systems Biology, Lunenfeld-Tanenbaum Research Institute at Mount Sinai Hospital, Toronto, Ontario M5G 1X5, Canada; Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Anne-Claude Gingras
- Centre for Systems Biology, Lunenfeld-Tanenbaum Research Institute at Mount Sinai Hospital, Toronto, Ontario M5G 1X5, Canada; Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Surajit Banerjee
- Northeastern Collaborative Access Team (NE-CAT) Cornell University, Lemont, IL, USA
| | - David Forbes
- Department of Chemistry, University of South Alabama, Mobile, AL 36688, USA
| | - Andrzej Wierzbicki
- Department of Chemistry, University of South Alabama, Mobile, AL 36688, USA
| | - Richard E Honkanen
- Department of Biochemistry and Molecular Biology, University of South Alabama, Mobile, AL 36688, USA.
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6
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Ishida M, Takeya K, Miyazu M, Yoshida A, Takai A. Force-inhibiting effect of Ser/Thr protein phosphatase 2A inhibitors on bovine ciliary muscle. J Smooth Muscle Res 2015; 51:10-21. [PMID: 26004377 PMCID: PMC5137268 DOI: 10.1540/jsmr.51.10] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Ciliary muscle is a smooth muscle characterized by a rapid response to muscarinic receptor stimulation and sustained contraction. Although it is evident that these contractions are Ca(2+)-dependent, detailed molecular mechanisms are still unknown. In order to elucidate the role of Ser/Thr protein phosphatase 2A (PP2A) in ciliary muscle contraction, we examined the effects of okadaic acid and other PP2A inhibitors on contractions induced by carbachol (CCh) and ionomycin in bovine ciliary muscle strips (BCM). Okadaic acid inhibited ionomycin-induced contraction, while it did not cause significant changes in CCh-induced contraction. Fostriecin showed similar inhibitory effects on the contraction of BCM. On the other hand, rubratoxin A inhibited both ionomycin- and CCh-induced contractions. These results indicated that PP2A was involved at least in ionomycin-induced Ca(2+)-dependent contraction, and that BCM had a unique regulatory mechanism in CCh-induced contraction.
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Affiliation(s)
- Minori Ishida
- Department of Physiology, Asahikawa Medical University, Hokkaido, Japan
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7
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Yumoto M, Watanabe M. Blebbistatin, a myosin II inhibitor, suppresses Ca(2+)-induced and "sensitized"-contraction of skinned tracheal muscles from guinea pig. J Smooth Muscle Res 2014; 49:89-98. [PMID: 24662474 PMCID: PMC5137305 DOI: 10.1540/jsmr.49.89] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Blebbistatin, a potent inhibitor of myosin II, has inhibiting effects on Ca(2+)-induced contraction and contractile filament organization without affecting the Ca(2+)-sensitivity to the force and phosphorylation level of myosin regulatory light chain (MLC20) in skinned (cell membrane permeabilized) taenia cecum from the guinea pig (Watanabe et al., Am J Physiol Cell Physiol. 2010; 298: C1118-26). In the present study, we investigated blebbistatin effects on the contractile force of skinned tracheal muscle, in which myosin filaments organization is more labile than that in the taenia cecum. Blebbistatin at 10 μM or higher suppressed Ca(2+)-induced tension development at any given Ca(2+) concentration, but had little effects on the Ca(2+)- induced myosin light chain phosphorylation. Also blebbistatin at 10 μM and higher significantly suppressed GTP-γS-induced "sensitized" force development. Since the force inhibiting effects of blebbistatin on the skinned trachea were much stronger than those in skinned taenia cecum, blebbistatin might directly affect myosin filaments organization.
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8
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Zhang M, Yogesha SD, Mayfield JE, Gill GN, Zhang Y. Viewing serine/threonine protein phosphatases through the eyes of drug designers. FEBS J 2013; 280:4739-60. [PMID: 23937612 DOI: 10.1111/febs.12481] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Revised: 07/03/2013] [Accepted: 08/02/2013] [Indexed: 01/04/2023]
Abstract
Protein phosphatases, as the counterpart to protein kinases, are essential for homeostatic balance of cell signaling. Small chemical compounds that modulate the specific activity of phosphatases can be powerful tools to elucidate the biological functions of these enzymes. More importantly, many phosphatases are central players in the development of pathological pathways where inactivation can reverse or delay the onset of human diseases. Therefore, potent inhibitors for such phosphatases can be of great therapeutic benefit. In contrast to the seemingly identical enzymatic mechanism and structural characterization of eukaryotic protein kinases, protein phosphatases evolved from diverse ancestors, resulting in different domain architectures, reaction mechanisms and active site properties. In this review, we discuss for each family of serine/threonine protein phosphatases their involvement in biological processes and corresponding strategies for small chemical intervention. Recent advances in modern drug discovery technologies have markedly facilitated the identification of selective inhibitors for some members of the phosphatase family. Furthermore, the rapid growth in knowledge about structure-activity relationships related to possible new drug targets has aided the discovery of natural product inhibitors for the phosphatase family. This review summarizes the current state of investigation of the small molecules that regulate the function of serine/threonine phosphatases, the challenges presented and also strategies to overcome these obstacles.
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Affiliation(s)
- Mengmeng Zhang
- Department of Chemistry and Biochemistry, University of Texas at Austin, TX, USA
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9
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Cirak Y, Varol U, Atmaca H, Kisim A, Sezgin C, Karabulut B, Uzunoglu S, Uslu R, Karaca B. Zoledronic acid in combination with serine/threonine phosphatase inhibitors induces enhanced cytotoxicity and apoptosis in hormone-refractory prostate cancer cell lines by decreasing the activities of PP1 and PP2A. BJU Int 2012; 110:E1147-54. [DOI: 10.1111/j.1464-410x.2012.11392.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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10
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Sutherland C, Walsh MP. Myosin regulatory light chain diphosphorylation slows relaxation of arterial smooth muscle. J Biol Chem 2012; 287:24064-76. [PMID: 22661704 DOI: 10.1074/jbc.m112.371609] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The principal signal to activate smooth muscle contraction is phosphorylation of the regulatory light chains of myosin (LC(20)) at Ser(19) by Ca(2+)/calmodulin-dependent myosin light chain kinase. Inhibition of myosin light chain phosphatase leads to Ca(2+)-independent phosphorylation at both Ser(19) and Thr(18) by integrin-linked kinase and/or zipper-interacting protein kinase. The functional effects of phosphorylation at Thr(18) on steady-state isometric force and relaxation rate were investigated in Triton-skinned rat caudal arterial smooth muscle strips. Sequential phosphorylation at Ser(19) and Thr(18) was achieved by treatment with adenosine 5'-O-(3-thiotriphosphate) in the presence of Ca(2+), which induced stoichiometric thiophosphorylation at Ser(19), followed by microcystin (phosphatase inhibitor) in the absence of Ca(2+), which induced phosphorylation at Thr(18). Phosphorylation at Thr(18) had no effect on steady-state force induced by Ser(19) thiophosphorylation. However, phosphorylation of Ser(19) or both Ser(19) and Thr(18) to comparable stoichiometries (0.5 mol of P(i)/mol of LC(20)) and similar levels of isometric force revealed differences in the rates of dephosphorylation and relaxation following removal of the stimulus: t(½) values for dephosphorylation were 83.3 and 560 s, and for relaxation were 560 and 1293 s, for monophosphorylated (Ser(19)) and diphosphorylated LC(20), respectively. We conclude that phosphorylation at Thr(18) decreases the rates of LC(20) dephosphorylation and smooth muscle relaxation compared with LC(20) phosphorylated exclusively at Ser(19). These effects of LC(20) diphosphorylation, combined with increased Ser(19) phosphorylation (Ca(2+)-independent), may underlie the hypercontractility that is observed in response to certain physiological contractile stimuli, and under pathological conditions such as cerebral and coronary arterial vasospasm, intimal hyperplasia, and hypertension.
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Affiliation(s)
- Cindy Sutherland
- Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada
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11
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Abstract
It has been a long journey since tautomycin (TTM) was isolated in 1987 and the discovery that it inhibited protein phosphatase 1 (PP1) more strongly than PP2A until finally the cocrystal structure of TTM and PP1 was presented early in 2009. The fact that TTM shows preference to inhibit PP1 over PP2A makes this compound unique among the known PP1 and PP2A inhibitors. A number of groups were involved in work aiming to unravel TTM's interactions with PP1 and by doing so hoping to disentangle the secrets as to why TTM is a better inhibitor of PP1 than PP2A. This Focus Review looks back at the work conducted with TTM in order to establish its point of interaction with PP1 prior to X-ray structure. Finally the conclusions before the X-ray structure are compared with the real situation.
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Affiliation(s)
- Magne O Sydnes
- Laboratory of Organic Chemistry, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8601, Japan
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12
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Leading tip drives soma translocation via forward F-actin flow during neuronal migration. J Neurosci 2010; 30:10885-98. [PMID: 20702717 DOI: 10.1523/jneurosci.0240-10.2010] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Neuronal migration involves coordinated extension of the leading process and translocation of the soma, but the relative contribution of different subcellular regions, including the leading process and cell rear, in driving soma translocation remains unclear. By local manipulation of cytoskeletal components in restricted regions of cultured neurons, we examined the molecular machinery underlying the generation of traction force for soma translocation during neuronal migration. In actively migrating cerebellar granule cells in culture, a growth cone (GC)-like structure at the leading tip exhibits high dynamics, and severing the tip or disrupting its dynamics suppressed soma translocation within minutes. Soma translocation was also suppressed by local disruption of F-actin along the leading process but not at the soma, whereas disrupting microtubules along the leading process or at the soma accelerated soma translocation. Fluorescent speckle microscopy using GFP-alpha-actinin showed that a forward F-actin flow along the leading process correlated with and was required for soma translocation, and such F-actin flow depended on myosin II activity. In migrating neurons, myosin II activity was high at the leading tip but low at the soma, and increasing or decreasing this front-to-rear difference accelerated or impeded soma advance. Thus, the tip of the leading process actively pulls the soma forward during neuronal migration through a myosin II-dependent forward F-actin flow along the leading process.
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13
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Sakon M, Kambayashi JI, Murata KH. The Involvement of Protein Phosphatases in Platelet Activation. Platelets 2009; 5:130-4. [DOI: 10.3109/09537109409005524] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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14
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Optimization of culture conditions for tautomycin production in shaking flasks with Streptomyces spiroverticillatus. J Biotechnol 2008. [DOI: 10.1016/j.jbiotec.2008.07.637] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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15
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Zhang TT, Platholi J, Heerdt PM, Hemmings HC, Tung HYL. Protein phosphatase-2A is activated in pig brain following cardiac arrest and resuscitation. Metab Brain Dis 2008; 23:95-104. [PMID: 18197471 DOI: 10.1007/s11011-007-9074-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/10/2007] [Accepted: 09/25/2007] [Indexed: 12/22/2022]
Abstract
Protein phosphatase-2A (PP-2A) interacts with several regulators of cell death pathways and is therefore a potential component of signaling pathways linking global cerebral ischemia to cell death. Using a novel procedure to quantify PP-2A activity, we find that cardiac arrest with resuscitation and reperfusion leads to activation of PP-2A by 1.6-fold in pig brain extract and by 3.4-fold after partial purification of PP-2A. This is the first demonstration of PP-2A activation in a clinically relevant model of transient global cerebral ischemia. These results suggest that inhibition of PP-2A activity may be neuroprotective in global cerebral ischemia.
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Affiliation(s)
- Tao T Zhang
- Institute for Neuronal Cell Signaling, Department of Anesthesiology, Weill Medical College of Cornell University, New York, NY 10021, USA
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16
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Sydnes MO, Kuse M, Kurono M, Shimomura A, Ohinata H, Takai A, Isobe M. Protein phosphatase inhibitory activity of tautomycin photoaffinity probes evaluated at femto-molar level. Bioorg Med Chem 2008; 16:1747-55. [DOI: 10.1016/j.bmc.2007.11.034] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2007] [Revised: 11/06/2007] [Accepted: 11/06/2007] [Indexed: 10/22/2022]
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17
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Differential modulation of agonist and antagonist structure activity relations for rat TRPV1 by cyclosporin A and other protein phosphatase inhibitors. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 2008; 377:149-57. [PMID: 18259730 DOI: 10.1007/s00210-007-0258-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2006] [Accepted: 12/21/2007] [Indexed: 10/22/2022]
Abstract
The transient receptor potential V1 channel (vanilloid receptor, TRPV1) represents a promising therapeutic target for inflammatory pain and other conditions involving C-fiber sensory afferent neurons. Sensitivity of TRPV1 is known to be subject to modulation by numerous signaling pathways, in particular by phosphorylation, and we wished to determine whether TRPV1 structure activity relations could be differentially affected. We demonstrate here that the structure activity relations of TRPV1, as determined by (45)Ca(2) uptake, were substantially altered by treatment of the cells with cyclosporin A, an inhibitor of protein phosphatase 2B. Whereas the potency of resiniferatoxin for stimulation of (45)Ca(2) was not altered by cyclosporin A treatment, the potencies of some other agonists were increased up to 8-fold. Among the antagonists examined, potencies were reduced to a lesser extent, ranging from 1- to 2.5-fold. Finally, the efficacy of partial agonists was increased. In contrast to cyclosporin A, okadaic acid, an inhibitor of protein phosphatases 1 and 2A, had little effect on agonist potencies, and calyculin A, an inhibitor of protein phosphatases 1 and 2A but with somewhat different selectivity from that of okadaic acid, caused changes in structure activity relations distinct from those induced by cyclosporin A. Because phosphatase activity differentially modulates the structure activity relations of TRPV1 agonists and antagonists, our findings predict that it may be possible to design agonists and antagonists selective for TRPV1 in a specific regulatory environment. A further implication is that it may be desirable to tailor screening approaches for drug discovery to reflect the desired regulatory state of the targeted TRPV1.
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Chen X, Zheng Y, Shen Y. Natural Products with Maleic Anhydride Structure: Nonadrides, Tautomycin, Chaetomellic Anhydride, and Other Compounds. Chem Rev 2007; 107:1777-830. [PMID: 17439289 DOI: 10.1021/cr050029r] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Xiaolong Chen
- Institute of Bioengineering, Zhejiang University of Technology, Hangzhou 310032, P. R. China
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Chatfield K, Eastman A. Inhibitors of protein phosphatases 1 and 2A differentially prevent intrinsic and extrinsic apoptosis pathways. Biochem Biophys Res Commun 2004; 323:1313-20. [PMID: 15451440 DOI: 10.1016/j.bbrc.2004.09.003] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2004] [Indexed: 11/16/2022]
Abstract
Inhibitors of serine/threonine protein phosphatases can inhibit apoptosis. We investigated which protein phosphatases are critical for this protection using calyculin A, okadaic acid, and tautomycin. All three phosphatase inhibitors prevented anisomycin-induced apoptosis in leukemia cell models. In vitro, calyculin A does not discriminate between PP1 and PP2A, while okadaic acid and tautomycin are more selective for PP2A and PP1, respectively. Increased phosphorylation of endogenous marker proteins was used to define concentrations that inhibited each phosphatase in cells. Concentrations of each inhibitor that prevented anisomycin-induced apoptosis correlated with inhibition of PP2A. The inhibitors prevented Bax translocation to mitochondria, indicating inhibition upstream of mitochondria. Tautomycin and calyculin A, but not okadaic acid, also prevented apoptosis induced through the CD95/Fas death receptor, and this protection correlated with inhibition of PP1. The inhibitors prevented Fas receptor oligomerization, FADD recruitment, and caspase 8 activation. The differential effects of PP1 and PP2A in protection from death receptor and mitochondrial-mediated pathways of death, respectively, may help one to define critical steps in each pathway, and regulatory roles for serine/threonine phosphatases in apoptosis.
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Affiliation(s)
- Kathryn Chatfield
- Norris Cotton Cancer Center, Dartmouth Medical School, Lebanon, NH 03756, USA
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20
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Kurono M, Isobe M. A practical semi-synthesis of tautomycin using a hydrolysate of natural tautomycin. Tetrahedron 2003. [DOI: 10.1016/j.tet.2003.09.097] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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21
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Liu W, Sheppeck JE, Colby DA, Huang HB, Nairn AC, Chamberlin AR. The selective inhibition of phosphatases by natural toxins: the anhydride domain of tautomycin is not a primary factor in controlling PP1/PP2A selectivity. Bioorg Med Chem Lett 2003; 13:1597-600. [PMID: 12699763 DOI: 10.1016/s0960-894x(03)00105-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Analogues of the potent and moderately selective PP1/PP2A inhibitor tautomycin (TM) were prepared with modifications in the C1'-C7' anhydride moiety. While all retain varying degrees of activity within a 3000-fold range of potencies, they also show remarkable constancy in their IC(50) ratios, suggesting that the anhydride moiety is not critical in controlling the selectivity of inhibition.
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Affiliation(s)
- Wen Liu
- Department of Chemistry, University of California at Irvine, Irvine, CA 92697, USA
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22
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Colby DA, Liu W, Sheppeck JE, Huang HB, Nairn AC, Chamberlin AR. A new model of the tautomycin-PP1 complex that is not analogous to the corresponding okadaic acid structure. Bioorg Med Chem Lett 2003; 13:1601-5. [PMID: 12699764 DOI: 10.1016/s0960-894x(03)00106-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A revised model of PP1-tautomycin (TM) complex suggests that this toxin does not bind in a conformation analogous to its structural cousin okadaic acid (OA), as has been assumed, but instead more resembles the mode of binding adopted by calyculin. This model rationalizes the unexpected potency of a truncated TM analogue lacking the bicyclic ketal common to TM and OA.
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Affiliation(s)
- David A Colby
- Department of Chemistry, University of California at Irvine, Irvine, CA 92697, USA
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23
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Larsen AKR, Møller MTN, Blankson H, Samari HR, Holden L, Seglen PO. Naringin-sensitive phosphorylation of plectin, a cytoskeletal cross-linking protein, in isolated rat hepatocytes. J Biol Chem 2002; 277:34826-35. [PMID: 12095991 DOI: 10.1074/jbc.m205028200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To identify phosphoproteins that might play a role in naringin-sensitive hepatocellular cytoskeletal disruption and apoptosis induced by algal toxins, hepatocyte extracts were separated by gel electrophoresis and immunostained with a phosphothreonine-directed antibody. Use of dilute (5%) polyacrylamide gels containing 6 m urea allowed the resolution of one very large (approximately 500-kDa) okadaic acid- and naringin-sensitive phosphoprotein, identified by tryptic fingerprinting, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and immunostaining as the cytolinker protein, plectin. The naringin-sensitive phosphorylation induced by okadaic acid and microcystin-LR probably reflected inhibition of a type 2A protein phosphatase, whereas the naringin-resistant phosphorylation induced by calyculin A, tautomycin, and cantharidin probably involved a type 1 phosphatase. Okadaic acid caused a collapse of the plectin-immunostaining bile canalicular sheaths and the general cytoskeletal plectin network into numerous medium-sized plectin aggregates. Inhibitors of protein kinase C, cAMP-dependent protein kinase, or Ca(2+)/calmodulin-dependent kinase II had moderate or no protective effects on plectin network disruption, whereas naringin offered 86% protection. Okadaic acid induced a naringin-sensitive phosphorylation of AMP-activated protein kinase (AMPK), the stress-activated protein kinases SEK1 and JNK, and S6 kinase. The AMPK-activating kinase (AMPKK) is likely to be the target of inhibition by naringin, the other kinases serving as downstream components of an AMPKK-initiated signaling pathway.
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Affiliation(s)
- Ann-Kristin Ruud Larsen
- Proteomics and Mammalian Cell Biology Section, Department of Cell Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Montebello, 0310 Oslo, Norway
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Niiro N, Ikebe M. Zipper-interacting protein kinase induces Ca(2+)-free smooth muscle contraction via myosin light chain phosphorylation. J Biol Chem 2001; 276:29567-74. [PMID: 11384979 DOI: 10.1074/jbc.m102753200] [Citation(s) in RCA: 147] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The inhibition of myosin phosphatase evokes smooth muscle contraction in the absence of Ca(2+), yet the underlying mechanisms are not understood. To this end, we have cloned smooth muscle zipper-interacting protein (ZIP) kinase cDNA. ZIP kinase is present in various smooth muscle tissues including arteries. Triton X-100 skinning did not diminish ZIP kinase content, suggesting that ZIP kinase associates with the filamentous component in smooth muscle. Smooth muscle ZIP kinase phosphorylated smooth muscle myosin as well as the isolated 20-kDa myosin light chain in a Ca(2+)/calmodulin-independent manner. ZIP kinase phosphorylated myosin light chain at both Ser(19) and Thr(18) residues with the same rate constant. The actin-activated ATPase activity of myosin increased significantly following ZIP kinase-induced phosphorylation. Introduction of ZIP kinase into Triton X-100-permeabilized rabbit mesenteric artery provoked a Ca(2+)-free contraction. A protein phosphatase inhibitor, microcystin LR, also induced contraction in the absence of Ca(2+), which was accompanied by an increase in both mono- and diphosphorylation of myosin light chain. The observed sensitivity of the microcystin-induced contraction to various protein kinase inhibitors was identical to the sensitivity of isolated ZIP kinase to these inhibitors. These results suggest that ZIP kinase is responsible for Ca(2+) independent myosin phosphorylation and contraction in smooth muscle.
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Affiliation(s)
- N Niiro
- Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA
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25
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Kumagai A, Dunphy WG. Claspin, a novel protein required for the activation of Chk1 during a DNA replication checkpoint response in Xenopus egg extracts. Mol Cell 2000; 6:839-49. [PMID: 11090622 DOI: 10.1016/s1097-2765(05)00092-4] [Citation(s) in RCA: 325] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have identified Claspin, a novel protein that binds to Xenopus Chk1 (Xchk1). Binding of Claspin to Xchk1 is highly elevated in the presence of DNA templates that trigger a checkpoint arrest of the cell cycle in Xenopus egg extracts. Xchk1 becomes phosphorylated during a checkpoint response, and we demonstrate directly that this phosphorylation results in the activation of Xchk1. Immunodepletion of Claspin from egg extracts abolishes both the phosphorylation and activation of Xchk1. Furthermore, Claspin-depleted extracts are unable to arrest the cell cycle in response to DNA replication blocks. Taken together, these findings indicate that Claspin is an essential upstream regulator of Xchk1.
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Affiliation(s)
- A Kumagai
- Division of Biology, Howard Hughes Medical Institute, California Institute of Technology, Pasadena 91125, USA
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26
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Herzig S, Neumann J. Effects of serine/threonine protein phosphatases on ion channels in excitable membranes. Physiol Rev 2000; 80:173-210. [PMID: 10617768 DOI: 10.1152/physrev.2000.80.1.173] [Citation(s) in RCA: 202] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This review deals with the influence of serine/threonine-specific protein phosphatases on the function of ion channels in the plasma membrane of excitable tissues. Particular focus is given to developments of the past decade. Most of the electrophysiological experiments have been performed with protein phosphatase inhibitors. Therefore, a synopsis is required incorporating issues from biochemistry, pharmacology, and electrophysiology. First, we summarize the structural and biochemical properties of protein phosphatase (types 1, 2A, 2B, 2C, and 3-7) catalytic subunits and their regulatory subunits. Then the available pharmacological tools (protein inhibitors, nonprotein inhibitors, and activators) are introduced. The use of these inhibitors is discussed based on their biochemical selectivity and a number of methodological caveats. The next section reviews the effects of these tools on various classes of ion channels (i.e., voltage-gated Ca(2+) and Na(+) channels, various K(+) channels, ligand-gated channels, and anion channels). We delineate in which cases a direct interaction between a protein phosphatase and a given channel has been proven and where a more complex regulation is likely involved. Finally, we present ideas for future research and possible pathophysiological implications.
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Affiliation(s)
- S Herzig
- Institut für Pharmakologie, Universität Köln, Köln, Germany.
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27
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Weber LP, Van Lierop JE, Walsh MP. Ca2+-independent phosphorylation of myosin in rat caudal artery and chicken gizzard myofilaments. J Physiol 1999; 516 ( Pt 3):805-24. [PMID: 10200427 PMCID: PMC2269290 DOI: 10.1111/j.1469-7793.1999.0805u.x] [Citation(s) in RCA: 124] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
1. Smooth muscle contraction is activated primarily by the Ca2+-calmodulin (CaM)-dependent phosphorylation of the 20 kDa light chains (LC20) of myosin. Activation can also occur in some instances without a change in intracellular free [Ca2+] or indeed in a Ca2+-independent manner. These signalling pathways often involve inhibition of myosin light chain phosphatase and unmasking of basal kinase activity leading to LC20 phosphorylation and contraction. 2. We have used demembranated rat caudal arterial smooth muscle strips and isolated chicken gizzard myofilaments in conjunction with the phosphatase inhibitor microcystin-LR to investigate the mechanism of Ca2+-independent phosphorylation of LC20 and contraction. 3. Treatment of Triton X-100-demembranated rat caudal arterial smooth muscle strips with microcystin at pCa 9 triggered a concentration-dependent contraction that was slower than that induced by pCa 4.5 or 6 but reached comparable steady-state levels of tension. 4. This Ca2+-independent, microcystin-induced contraction correlated with phosphorylation of LC20 at serine-19 and threonine-18. 5. Whereas Ca2+-dependent LC20 phosphorylation and contraction were inhibited by a synthetic peptide (AV25) based on the autoinhibitory domain of myosin light chain kinase (MLCK), Ca2+-independent, microcystin-induced LC20 phosphorylation and contraction were resistant to AV25. 6. Ca2+-independent LC20 kinase activity was also detected in chicken gizzard smooth muscle myofilaments and catalysed phosphorylation of endogenous myosin LC20 at serine-19 and/or threonine-18. This is in contrast to MLCK which phosphorylates threonine-18 only after prior phosphorylation of serine-19. 7. Gizzard Ca2+-independent LC20 kinase could be separated from MLCK by differential extraction from myofilaments and by CaM affinity chromatography. Its activity was resistant to AV25. 8. We conclude that inhibition of smooth muscle myosin light chain phosphatase (MLCP) unmasks the activity of a Ca2+-independent LC20 kinase associated with the myofilaments and distinct from MLCK. This kinase, therefore, probably plays a role in Ca2+ sensitization and Ca2+-independent contraction of smooth muscle in response to stimuli that act via Ca2+-independent pathways, leading to inhibition of MLCP.
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Affiliation(s)
- L P Weber
- Smooth Muscle Research Group and Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Calgary, 3330 Hospital Drive N.W., Calgary, Alberta, Canada T2N 4N1
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28
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Dietrich J, Bäckström T, Lauritsen JP, Kastrup J, Christensen MD, von Bülow F, Palmer E, Geisler C. The phosphorylation state of CD3gamma influences T cell responsiveness and controls T cell receptor cycling. J Biol Chem 1998; 273:24232-8. [PMID: 9727047 DOI: 10.1074/jbc.273.37.24232] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The T cell receptor (TCR) is internalized following activation of protein kinase C (PKC) via a leucine (Leu)-based motif in CD3gamma. Some studies have indicated that the TCR is recycled back to the cell surface following PKC-mediated internalization. The functional state of recycled TCR and the mechanisms involved in the sorting events following PKC-induced internalization are not known. In this study, we demonstrated that following PKC-induced internalization, the TCR is recycled back to the cell surface in a functional state. TCR recycling was dependent on dephosphorylation of CD3gamma, probably mediated by the serine/threonine protein phosphatase-2A, but independent on microtubules or actin polymerization. Furthermore, in contrast to ligand-mediated TCR sorting, recycling of the TCR was independent of the tyrosine phosphatase CD45 and the Src tyrosine kinases p56(Lck) and p59(Fyn). Studies of mutated TCR and chimeric CD4-CD3gamma molecules demonstrated that CD3gamma did not contain a recycling signal in itself. In contrast, the only sorting information in CD3gamma was the Leu-based motif that mediated lysosomal sorting of chimeric CD4-CD3gamma molecules. Finally, we found a correlation between the phosphorylation state of CD3gamma and T cell responsiveness. Based on these observations a physiological role of CD3gamma and TCR cycling is proposed.
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MESH Headings
- Amino Acid Sequence
- Antigens, CD/metabolism
- Biotinylation
- CD4 Antigens/metabolism
- Calcium/metabolism
- Cell Membrane/immunology
- Cytosol/metabolism
- Humans
- Jurkat Cells/drug effects
- Jurkat Cells/immunology
- Kinetics
- Leucine
- Leukocyte Common Antigens/metabolism
- Lysosomes/immunology
- Molecular Sequence Data
- Phorbol 12,13-Dibutyrate/pharmacology
- Phosphoprotein Phosphatases/metabolism
- Phosphorylation
- Protein Phosphatase 2
- Protein-Tyrosine Kinases/metabolism
- Receptor-CD3 Complex, Antigen, T-Cell/chemistry
- Receptor-CD3 Complex, Antigen, T-Cell/physiology
- Receptors, Antigen, T-Cell/physiology
- Receptors, Antigen, T-Cell, gamma-delta/chemistry
- Receptors, Antigen, T-Cell, gamma-delta/physiology
- Recombinant Fusion Proteins/metabolism
- Sequence Alignment
- Sequence Homology, Amino Acid
- T-Lymphocytes/drug effects
- T-Lymphocytes/immunology
- Transfection
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Affiliation(s)
- J Dietrich
- Institute of Medical Microbiology and Immunology, University of Copenhagen, The Panum Institute, Building 18.3, Blegdamsvej 3C, DK-2200 Copenhagen, Denmark.
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29
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Kawamura T, Matsuzawa S, Mizuno Y, Kikuchi K, Oikawa H, Oikawa M, Ubukata M, Ichihara A. Different moieties of tautomycin involved in protein phosphatase inhibition and induction of apoptosis. Biochem Pharmacol 1998; 55:995-1003. [PMID: 9605423 DOI: 10.1016/s0006-2952(97)00539-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The effects of tautomycin and its derivatives on protein phosphatases PP1 and PP2A and their apoptosis-inducing activity toward human leukemia Jurkat cells were examined, and the relationship between chemical structure and function was discussed. Among the compounds we examined, tautomycin was the most potent inhibitor and the most effective inducer of apoptosis. It inhibited PP1 and PP2A enzymatic activity concentration-dependently with IC50 values of 20 and 75 pM, respectively, in the presence of 0.01% Brij-35, and an LC50 value of 1 microM. Esterification of the anhydride moiety of tautomycin markedly increased the IC50 for the protein phosphatases. The C1'-C7' fragment of tautomycin had no inhibitory effect, but the fragment containing the C22-C26 moiety was inhibitory. These results suggest that the C22-C26 moiety is essential for inhibition of protein phosphatase activity and that the anhydride moiety enhances the inhibition. However, the esterification of the anhydride did not decrease, nor did the inclusion of the C22-C26 moiety increase the apoptosis-inducing activity. On the other hand, the C1-C18 moiety of tautomycin was essential for induction of apoptosis, and the conformation and the arrangement of functionalities of the C18-C26 carbon chain affected the apoptosis activity. However, modification of C1-C18, C1-C21, or C1-C26 compounds had little effect on phosphatase inhibitory activity. Our results strongly suggest that different moieties of tautomycin are involved in protein phosphatase inhibition and induction of apoptosis.
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Affiliation(s)
- T Kawamura
- Section of Biochemistry, Institute of Immunological Science, Hokkaido University, Sapporo, Japan
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30
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Walsh AH, Cheng A, Honkanen RE. Fostriecin, an antitumor antibiotic with inhibitory activity against serine/threonine protein phosphatases types 1 (PP1) and 2A (PP2A), is highly selective for PP2A. FEBS Lett 1997; 416:230-4. [PMID: 9373158 DOI: 10.1016/s0014-5793(97)01210-6] [Citation(s) in RCA: 168] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Fostriecin, an antitumor antibiotic produced by Streptomyces pulveraceus, is a strong inhibitor of type 2A (PP2A; IC50 3.2 nM) and a weak inhibitor of type 1 (PP1; IC50 131 microM) serine/threonine protein phosphatases. Fostriecin has no apparent effect on the activity of PP2B, and dose-inhibition studies conducted with whole cell homogenates indicate that fostriecin also inhibits the native forms of PP1 and PP2A. Studies with recombinant PP1/PP2A chimeras indicate that okadaic acid and fostriecin have different binding sites.
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Affiliation(s)
- A H Walsh
- Department of Biochemistry and Molecular Biology, College of Medicine, University of South Alabama, Mobile 36688, USA
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31
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Sheppeck JE, Gauss CM, Chamberlin AR. Inhibition of the Ser-Thr phosphatases PP1 and PP2A by naturally occurring toxins. Bioorg Med Chem 1997; 5:1739-50. [PMID: 9354230 DOI: 10.1016/s0968-0896(97)00146-6] [Citation(s) in RCA: 133] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The okadaic acid class of naturally occurring toxins is a structurally diverse group of molecules that inhibit the protein phosphatases PP1 and PP2A. Studies providing information about the mode of binding between the toxins and the phosphatases contribute to an overall understanding of the signal transduction pathways in which the phosphatases are involved.
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Affiliation(s)
- J E Sheppeck
- Department of Chemistry, University of California at Irvine 92697, USA
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32
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Tsuchiya T, Ikeda N, Obara K, Hartshorne DJ. A Type 2A Protein Phosphatase from Clam Smooth Muscle. Use of 4-Methylumbelliferyl Phosphate as Substrate. Comp Biochem Physiol B Biochem Mol Biol 1997. [DOI: 10.1016/s0305-0491(97)00005-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Favre B, Turowski P, Hemmings BA. Differential inhibition and posttranslational modification of protein phosphatase 1 and 2A in MCF7 cells treated with calyculin-A, okadaic acid, and tautomycin. J Biol Chem 1997; 272:13856-63. [PMID: 9153244 DOI: 10.1074/jbc.272.21.13856] [Citation(s) in RCA: 259] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Calyculin-A (CA), okadaic acid (OA), and tautomycin (TAU) are potent inhibitors of protein phosphatases 1 (PP1) and 2A (PP2A) and are widely used on cells in culture. Despite their well characterized selectivity in vitro, their exact intracellular effects on PP1 and PP2A cannot be directly deduced from their extracellular concentration because their cell permeation properties are not known. Here we demonstrate that, due to the tight binding of the inhibitors to PP1 and/or PP2A, their cell penetration could be monitored by measuring PP1 and PP2A activities in cell-free extracts. Treatment of MCF7 cells with 10 nM CA for 2 h simultaneously inhibited PP1 and PP2A activities by more than 50%. A concentration of 1 microM OA was required to obtain a similar time course of PP2A inhibition in MCF7 cells to that observed with 10 nM CA, whereas PP1 activity was unaffected. PP1 was predominantly inhibited in MCF7 cells treated with TAU but even at 10 microM TAU PP1 inhibition was much slower than that observed with 10 nM CA. Furthermore, binding of inhibitors to PP2Ac and/or PP1c in MCF7 cells led to differential posttranslational modifications of the carboxyl termini of the proteins as demonstrated by Western blotting. OA and CA, in contrast to TAU, induced demethylation of the carboxyl-terminal Leu309 residue of PP2Ac. On the other hand, CA and TAU, in contrast to OA, elicited a marked decrease in immunoreactivity of the carboxyl terminus of the alpha-isoform of PP1c, probably reflecting proteolysis of the protein. These results suggest that in MCF7 cells OA selectively inhibits PP2A and TAU predominantly affects PP1, a conclusion supported by their differential effects on cytokeratins in this cell line.
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Affiliation(s)
- B Favre
- Friedrich Miescher-Institut, P. O. Box 2543, CH-4002 Basel, Switzerland
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35
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Sheppeck JE, Liu W, Chamberlin AR. Total Synthesis of the Serine/Threonine-Specific Protein Phosphatase Inhibitor Tautomycin(1). J Org Chem 1997; 62:387-398. [PMID: 11671414 DOI: 10.1021/jo961633s] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A convergent, asymmetric synthesis of the protein phosphatase inhibitor, tautomycin, is described. The natural product was constructed by joining two major fragments of comparable complexity at the C21-C22 bond. Absolute stereochemistry of the C1-C21 ketone originates from (S)-citronellene and (2R,3S)-geraniol epoxide. The anti stereochemical relationships at C6-C7 and C18-C19 were introduced with Duthaler's chiral titanium propionic enolate. Syn stereochemical relationships at C13-C14 and C23-C24 were established using an Evan's oxazolidinone chiral auxiliary. The spiroketal was efficiently constructed via a one-pot double-alkylation-spirocyclization sequence with acetone N,N-dimethylhydrazone serving as the central linchpin. Final coupling of the two halves using a chelation-controlled Mukaiyama aldol addition followed by deprotection yielded synthetic tautomycin that is identical to the natural product.
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Affiliation(s)
- James E. Sheppeck
- Department of Chemistry, University of California, Irvine, California 92717
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36
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Sasahara Y, Kobayashi T, Onodera H, Onoda M, Ohnishi M, Kato S, Kusuda K, Shima H, Nagao M, Abe H, Yanagawa Y, Hiraga A, Tamura S. Okadaic Acid Suppresses Neural Differentiation-dependent Expression of the Neurofilament-L Gene in P19 Embryonal Carcinoma Cells by Post-transcriptional Modification. J Biol Chem 1996. [DOI: 10.1074/jbc.271.42.25950] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
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37
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38
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Walsh MP, Horowitz A, Clément-Chomienne O, Andrea JE, Allen BG, Morgan KG. Protein kinase C mediation of Ca(2+)-independent contractions of vascular smooth muscle. Biochem Cell Biol 1996; 74:485-502. [PMID: 8960355 DOI: 10.1139/o96-053] [Citation(s) in RCA: 118] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Tumour-promoting phorbol esters induce slow, sustained contractions of vascular smooth muscle, suggesting that protein kinase C (PKC) may play a role in the regulation of smooth muscle contractility. In some cases, e.g., ferret aortic smooth muscle, phorbol ester induced contractions occur without a change in [Ca2+]i or myosin phosphorylation. Direct evidence for the involvement of PKC came from the use of single saponin-permeabilized ferret aortic cells. A constitutively active catalytic fragment of PKC induced a slow, sustained contraction similar to that triggered by phenylephrine. Both responses were abolished by a peptide inhibitor of PKC. Contractions of similar magnitude occurred even when the [Ca2+] was reduced to close to zero, implicating a Ca(2+)-independent isoenzyme of PKC. Of the two Ca(2+)-independent PKC isoenzymes, epsilon and zeta, identified in ferret aorta, PKC epsilon is more likely to mediate the contractile response because (i) PKC epsilon, but not PKC zeta, is responsive to phorbol esters; (ii) upon stimulation with phenylephrine, PKC epsilon translocates from the sarcoplasm to the sarcolemma, whereas PKC zeta, translocates from a perinuclear localization to the interior of the nucleus; and (iii) when added to permeabilized single cells of the ferret aorta at pCa 9, PKC epsilon, but not PKC zeta, induced a contractile response similar to that induced by phenylephrine. A possible substrate of PKC epsilon is the smooth muscle specific, thin filament associated protein, calponin. Calponin is phosphorylated in intact smooth muscle strips in response to carbachol, endothelin-1, phorbol esters, or okadaic acid. Phosphorylation of calponin in vitro by PKC (a mixture of alpha, beta, and gamma isoenzymes) dramatically reduces its affinity for F-actin and alleviates its inhibition of the cross-bridge cycling rate. Calponin is phosphorylated in vitro by PKC epsilon but is a very poor substrate of PKC zeta. A signal transduction pathway is proposed to explain Ca(2+)-independent contraction of ferret aorta whereby extracellular signals trigger diacylglycerol production without a Ca2+ transient. The consequent activation of PKC epsilon would result in calponin phosphorylation, its release from the thin filaments, and alleviation of inhibition of cross-bridge cycling. Slow, sustained contraction then results from a slow rate of cross-bridge cycling because of the basal level of myosin light chain phosphorylation (approximately 0.1 mol Pi/mol light chain). We also suggest that signal transduction through PKC epsilon is a component of contractile responses triggered by agonists that activate phosphoinositide turnover; this may explain why smooth muscles often develop more force in response, e.g., to alpha 1-adrenergic agonists than to K+.
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Affiliation(s)
- M P Walsh
- Smooth Muscle Research Group, Faculty of Medicine, University of Calgary, AB, Canada.
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Tojyo Y, Tanimura A, Matsumoto Y. Suppression of capacitative Ca2+ entry by serine/threonine phosphatase inhibitors in rat parotid acinar cells. JAPANESE JOURNAL OF PHARMACOLOGY 1995; 69:381-9. [PMID: 8786642 DOI: 10.1254/jjp.69.381] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The effects of three serine/threonine protein phosphatase inhibitors, calyculin-A, tautomycin and okadaic acid, on the Ca2+ entry across the plasma membrane was studied in Fura-2-loaded rat parotid acinar cells. These protein phosphatase inhibitors did not affect the peak elevation of cytosolic free Ca2+ concentration ([Ca2+]i) just after stimulation with the muscarinic agonist carbachol (CCh), but they suppressed the sustained increase in [Ca2+]i. In the absence of extracellular Ca2+, CCh produced a transient increase in [Ca2+]i due to Ca2+ release from intracellular Ca2+ stores, and this increase in [Ca2+]i was unaffected by the phosphatase inhibitors. When Ca2+ was added to the external medium after the transient [Ca2+]i response, the increase in [Ca2+]i in the cells treated with the phosphatase inhibitors was significantly smaller than that in the control cells, indicating that the Ca2+ entry was reduced. Similar suppression of Ca2+ entry by the phosphatase inhibitors was observed when intracellular Ca2+ stores were previously depleted by the microsomal Ca(2+)-ATPase inhibitor thapsigargin (TG). In addition, the phosphatase inhibitors reduced the Mn2+ (Ca2+ surrogate) influx following the addition of CCh or TG. The enhancement of Ca2+ entry by the protein kinase inhibitor staurosporine was significantly attenuated by the phosphatase inhibitors. These results suggest that the phosphatase inhibitors suppressed the Ca2+ entry mechanism activated by depletion of intracellular Ca2+ stores in rat parotid acinar cells. The capacitative Ca2+ entry may be regulated by protein phosphorylation/dephosphorylation.
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Affiliation(s)
- Y Tojyo
- Department of Dental Pharmacology, Health Sciences University of Hokkaido, Japan
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Suganuma M, Okabe S, Sueoka E, Nishiwaki R, Komori A, Uda N, Isono K, Fujiki H. Tautomycin: an inhibitor of protein phosphatases 1 and 2A but not a tumor promoter on mouse skin and in rat glandular stomach. J Cancer Res Clin Oncol 1995; 121:621-7. [PMID: 7559747 DOI: 10.1007/bf01197780] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Tautomycin isolated from Streptomyces spiroverticillatus is an inhibitor of protein phosphatases 1 and 2A. Tautomycin induced hyperphosphorylation of cytokeratin peptides in human keratinocytes (PHK 16-I cells) 30 times less strongly than did okadaic acid. Repeated applications of tautomycin (30 micrograms, 40 nmol/application) did not induce tumor promotion in a two-stage carcinogenesis experiment on mouse skin initiated with 7,12-dimethylbenz[a]anthracene, whereas okadaic acid (1 microgram, 1.2 nmol/application) as a control induced tumor promotion strongly. As for mucosa of rat glandular stomach, tautomycin induced ornithine decarboxylase 4 h after intubation into the stomach. The tumor-promoting activity of tautomycin was next studied in the glandular stomach initiated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Administration of tautomycin in the diet (1 mg rat-1 day-1), from week 9 to week 52 of the experiment, inhibited rather than enhanced tumor development in the glandular stomach initiated with MNNG. The percentages of tumor-bearing rats of the groups treated with MNNG plus tautomycin, MNNG alone, and tautomycin alone were 20.0%, 40.6%, and 0% respectively in week 52. The reason for the absence of tumor-promoting activity of tautomycin was studied in relation to tumor necrosis factor alpha (TNF alpha), an endogenous tumor promoter. We found that tautomycin neither enhanced TNF alpha mRNA expression in mouse skin nor induced TNF alpha release in a human stomach cancer cell line (KATO III cells), whereas okadaic acid did both. These results indicate that not all inhibitors of protein phosphatases are tumor promoters, and suggest that tumor promotion of the okadaic acid class of compounds is mediated by TNF alpha.
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Affiliation(s)
- M Suganuma
- Saitama Cancer Center Research Institute, Japan
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41
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Matsuzawa S, Suzuki T, Suzuki M, Matsuda A, Kawamura T, Mizuno Y, Kikuchi K. Thyrsiferyl 23-acetate is a novel specific inhibitor of protein phosphatase PP2A. FEBS Lett 1994; 356:272-4. [PMID: 7805852 DOI: 10.1016/0014-5793(94)01281-4] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Thyrsiferyl 23-acetate (TF23A), a cytotoxic compound from marine red alga, has been shown to potently and specifically inhibit serine/threonine protein phosphatase 2A (PP2A) with IC50 values of 4-16 microM, depending on the enzyme concentration. TF23A did not affect activity of protein phosphatase 1 (PP1), 2B (PP2B), 2C (PP2C), or protein tyrosine phosphatases (PTP) up to 1 mM. It inhibited PP2A activity in a crude extract of a human T cell line, Jurkat cell, as well as the purified catalytic subunit. Thus, TF23A proved to be a novel useful probe for clearly distinguishing the activity of PP2A from those of the other protein phosphatases in crude cell extracts and identification of cellular processes that are regulated by PP2A.
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Affiliation(s)
- S Matsuzawa
- Section of Biochemistry, Institute of Immunological Science, Hokkaido University, Sapporo, Japan
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42
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Murphy CT, Westwick J. Role of type 1 and type 2A phosphatases in signal transduction of platelet-activating-factor-stimulated rabbit platelets. Biochem J 1994; 301 ( Pt 2):531-7. [PMID: 8042999 PMCID: PMC1137113 DOI: 10.1042/bj3010531] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Calyculin A, the potent inhibitor of type 1 (PP1) and type 2A (PP2A) phosphatases, has been employed in order to investigate the role of endogenously activated PP1/PP2A in the signal-transduction pathway of platelet-activating-factor (PAF)-stimulated platelets. Calyculin A alone caused an increase in protein phosphorylation in unstimulated platelets, with the detection of a number of newly phosphorylated proteins, whereas in PAF-stimulated platelets phosphorylation of the major substrates of protein kinase C and myosin light-chain kinase were no longer transient, but phosphorylation was sustained. PP1/PP2A appear to play a role in Ca2+ homoeostasis, as inhibition of PP1/PP2A caused an inhibition of Ca2+ mobilization and Ca2+ influx through the plasma membrane in PAF-stimulated platelets. The effect of calyculin A on Ca2+ mobilization correlated with the observed inhibition of the production of the signal molecule Ins(1,4,5)P3. The release reaction (which is a Ca(2+)-dependent event) was also inhibited by calyculin A. The results are discussed in relation to the possible role of protein kinase C in mediating the events leading to the effects observed with calyculin A.
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Affiliation(s)
- C T Murphy
- School of Pharmacy and Pharmacology, University of Bath, Avon, U.K
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Oikawa H, Oikawa M, Ueno T, Ichihara A. Total synthesis of tautomycin: Efficient aldol coupling of two large subunits. Tetrahedron Lett 1994. [DOI: 10.1016/s0040-4039(00)76974-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Nakamura SI, Shibasaki M. Synthetic studies on tautomycin. Stereoselective construction of the C1–C26 region. Tetrahedron Lett 1994. [DOI: 10.1016/s0040-4039(00)73135-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Koike Y, Ozaki Y, Qi R, Satoh K, Kurota K, Yatomi Y, Kume S. Phosphatase inhibitors suppress Ca2+ influx induced by receptor-mediated intracellular Ca2+ store depletion in human platelets. Cell Calcium 1994; 15:381-90. [PMID: 8033196 DOI: 10.1016/0143-4160(94)90013-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The effects of three phosphatase inhibitors including okadaic acid, calyculin A and tautomycin were evaluated on platelet Ca2+ mobilization. Calyculin A and tautomycin at appropriate concentrations appeared to have a selective inhibitory effect on thrombin-induced Ca2+ influx, but not on [Ca2+]i release from intracellular Ca2+ storage sites. In contrast, pretreatment with okadaic acid at concentrations that effectively lowered Ca2+ influx also suppressed Ca2+ release from intracellular Ca2+ stores. In a system that specifically evaluates the effects of agents on Ca2+ influx induced by the Ca(2+)-depleted state of intracellular Ca2+ storage sites, the three phosphatase inhibitors attenuated Ca2+ influx in a dose dependent manner and showed complete inhibition at appropriate concentrations. These findings suggest that protein phosphorylation/dephosphorylation plays an important role in mediating signals to open Ca2+ channels when Ca2+ depletion in intracellular Ca2+ stores is caused by thrombin. In contrast, Ca2+ influx induced by thapsigargin, a Ca(2+)-ATPase inhibitor, was only partially suppressed by pretreatment with each of the three phosphatase inhibitors. Based on these findings, we suggest that the Ca(2+)-depleted state of intracellular Ca2+ stores by thapsigargin induces the opening of Ca2+ channels via phosphatase inhibitor-insensitive pathways. All the phosphatase inhibitors, at the highest concentrations tested in the present study, only partially inhibited Mn2+ entry induced by thrombin. These findings suggest that there are at least two types of divalent ion channels on platelet plasma membranes and that one of them, that preferentially allows Mn2+ entry, is resistant to the inhibitory effects of phosphatase inhibitors.
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Affiliation(s)
- Y Koike
- Department of Clinical and Laboratory Medicine, Yamanashi Medical College, Japan
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Honkanen RE, Codispoti BA, Tse K, Boynton AL, Honkanan RE. Characterization of natural toxins with inhibitory activity against serine/threonine protein phosphatases. Toxicon 1994; 32:339-50. [PMID: 8016855 DOI: 10.1016/0041-0101(94)90086-8] [Citation(s) in RCA: 156] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Recent studies suggest that the ability to inhibit the activity of certain serine/threonine protein phosphatases underlies the toxicity of several natural compounds including: okadaic acid, microcystin-LR, nodularin, calyculin A and tautomycin. To characterize further the actions of these toxins, this study compares the inhibitory effects of okadaic acid, chemical derivatives of okadaic acid, microcystin-LR, microcystin-LA, nodularin, calyculin A and tautomycin on the activity of serine/threonine protein phosphatases types 1 (PP1), 2A (PP2A) and a recently identified protein phosphatase purified from bovine brain (PP3). This study shows that, like PP1 and PP2A, the activity of PP3 is potently inhibited by okadaic acid, both microcystins, nodularin, calyculin A and tautomycin. Further characterization of the toxins employing the purified catalytic subunits of PP1, PP2A and PP3 under identical experimental conditions indicates that: (a) okadaic acid, microcystin-LR, and microcystin-LA inhibit PP2A and PP3 more potently than PP1 (order of potency PP2A > PP3 > PP1); (b) nodularin inhibits PP1 and PP3 at a similar concentration that is slightly higher than that which affects PP2A, and (c) both calyculin A and tautomycin show little selectivity among the phosphatases tested. This study also shows that the chemical modification of the (C1) carboxyl group of okadaic acid can have a profound influence on the inhibitory activity of this toxin. Esterification of okadaic acid, producing methyl okadaate, or reduction, producing okadaol, greatly decreases the inhibitory effects against all three enzymes tested. Further reduction, producing 1-nor-okadaone, or acetylation, producing okadaic acid tetraacetate, results in compounds with no inhibitory activity. In contrast, the substitution of alanine (-LA) for arginine (-LR) in microcystin has no apparent effect on the inhibitory activity against PP1, PP2A or PP3.
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Affiliation(s)
- R E Honkanen
- Department of Biochemistry, University of South Alabama, Mobile 36688
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Pugazhenthi S, Yu B, Gali RR, Khandelwal RL. Differential effects of calyculin A and okadaic acid on the glucose-induced regulation of glycogen synthase and phosphorylase activities in cultured hepatocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1179:271-6. [PMID: 8218371 DOI: 10.1016/0167-4889(93)90082-z] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The effects of the phosphatase inhibitors calyculin A and okadaic acid were investigated to determine the roles of protein phosphatases type 1 and 2A in the regulation of the activities of glycogen synthase and phosphorylase by glucose in a primary culture of hepatocytes. Glycogen synthesis, as measured by the incorporation of labelled glucose into glycogen, was inhibited in a dose-dependent manner by calyculin A (IC50 = 2.2 nM) and okadaic acid with (IC50 = 14 nM). Glucose-induced activation of glycogen synthase was inhibited by calyculin A and okadaic acid with IC50 values of 3.7 nM and 90 nM, respectively. Phosphorylase was simultaneously activated by these inhibitors with calyculin A again being more active (P < 0.001) than okadaic acid. The differing potencies (P < 0.001) of these inhibitors on the activities of glycogen synthase and phosphorylase were also observed with varying concentrations of glucose (5.6-60 mM) in the medium and at different incubation periods upto 120 min. It has been previously shown that both inhibitors inhibit protein phosphatase-2A with equal potency and calyculin A is a more potent inhibitor of protein phosphatase-1 than okadaic acid. Heat- and proteinase-treated cytosolic fractions from hepatocytes incubated with calyculin A and okadaic acid showed similar differential inhibitory activities towards purified types 1 and 2-A protein phosphatases. Hence, these data provide further evidence that protein phosphatase type-1 plays a major role in the control of glycogen synthesis by regulating the activities of glycogen synthase and phosphorylase.
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Affiliation(s)
- S Pugazhenthi
- Department of Biochemistry, University of Saskatchewan, Saskatoon, Canada
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Honkanen RE. Cantharidin, another natural toxin that inhibits the activity of serine/threonine protein phosphatases types 1 and 2A. FEBS Lett 1993; 330:283-6. [PMID: 8397101 DOI: 10.1016/0014-5793(93)80889-3] [Citation(s) in RCA: 216] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Cantharidin, a natural toxicant of blister beetles, is a strong inhibitor of protein phosphatases types 1 (PP1) and 2A (PP2A). Like okadaic acid, cantharidin inhibits the activity of the purified catalytic subunit of PP2A (IC50 = 0.16 microM) at a lower concentration than that of PP1 (IC50 = 1.7 microM) and only inhibits the activity of protein phosphatase type 2B (PP2B) at high concentrations. Dose-inhibition studies conducted with whole cell homogenates indicate that cantharidin also inhibits the native forms of these enzymes. Thus, cantharidin, which is economical and readily available, may be useful as an additional probe for studying the functions of serine/threonine protein phosphatases.
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Affiliation(s)
- R E Honkanen
- Department of Biochemistry, College of Medicine, University of South Alabama, Mobile 36688
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Murata K, Sakon M, Kambayashi J, Yukawa M, Yano Y, Fujitani K, Kawasaki T, Shiba E, Mori T. The possible involvement of protein phosphatase 1 in thrombin-induced Ca2+ influx of human platelets. J Cell Biochem 1993; 51:442-5. [PMID: 8388395 DOI: 10.1002/jcb.2400510409] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Protein phosphatase 1 is considered to be involved in thrombin-induced platelet activation (Murata et al., Biochem Int 26:327-334, 1992). To clarify the mechanism, we examined the effects of protein phosphatase 1 and 2A inhibitors (calyculin A, tautomycin, okadaic acid) on Ca2+ influx. In the presence of 1 mM Ca2+, thrombin- (0.1 U/ml) induced platelet aggregation and ATP release were inhibited by calyculin A, while this inhibitory effect was abolished in the absence of Ca2+ (EGTA 1 mM). Furthermore, thrombin-induced Mn2+ influx but not intracellular Ca2+ mobilization was inhibited by calyculin A in a dose-related manner. Calyculin A also blocked the ongoing Ca2+ influx when added 3 min after thrombin stimulation. Similar inhibitory effects were observed with okadaic acid and tautomycin in the same potency sequence as the reported one for protein phosphatase 1 (calyculin A > tautomycin > okadaic acid). These results suggest that the anti-platelet effects of phosphatase inhibitors are due to the inhibition of Ca2+ influx and that protein phosphatase 1 plays a key role in the regulation of receptor operated Ca2+ channel of human platelets.
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Affiliation(s)
- K Murata
- Department of Surgery II, Osaka University Medical School, Japan
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Abstract
The mechanisms by which prostaglandin F2 alpha (PGF2 alpha) can cause contractions at constant intracellular Ca2+ were investigated by the direct measurement of force from single saponin-permeabilized smooth muscle cells from the ferret aorta. The size of PGF2 alpha contractions did not change between pCa 9.0 and pCa 6.6. The remainder of the experiments were carried out at pCa 7.0. At pCa 7.0, PGF2 alpha (0.1-100 microM) induced sustained force in a dose-dependent manner, reaching a maximum (2.61 +/- 0.20 microN, n = 14) in 10 minutes. Both protein kinase C pseudosubstrate inhibitor (3 microM) and staurosporine (1 microM) significantly inhibited PGF2 alpha (100 microM)-induced contractions, but staurosporine was more effective. Staurosporine caused 88.8 +/- 13.3% inhibition, whereas protein kinase C pseudosubstrate inhibitor inhibited 62.3 +/- 9.6% of the PGF2 alpha-induced contraction. An inhibitor of type-1 and type-2A protein phosphatases, microcystin-LR, at a concentration of 1 microM induced a gradual and sustained contraction (1.53 +/- 0.21 microN). A lower concentration of microcystin-LR (100 nM) also induced a small but significant contraction (0.36 +/- 0.26 microN). Pretreatment with both 1 microM and 100 nM microcystin-LR caused significant inhibition of the PGF2 alpha-induced contraction from 2.61 +/- 0.20 microN (n = 14) to 0.32 +/- 0.20 microN (n = 6) (p < 0.01) and 1.52 +/- 0.21 microN (n = 6) (p < 0.01), respectively. These results indicate that the part of the PGF2 alpha-induced contraction that occurs at a constant, low intracellular Ca2+ is the combined result of activation of protein kinase C and phosphatase inhibition.
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Affiliation(s)
- H Katsuyama
- Cardiovascular Division, Beth Israel Hospital, Boston, MA 02215
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