Functional impact of PTP1B-mediated Src regulation on oxidative phosphorylation in rat brain mitochondria

Given the presence of Src and PTP1B within rat brain mitochondria, we have investigated whether PTP1B regulates Src activity in mitochondria as in the cytosol. Results showed that Src was stimulated by in vitro addition of ATP to mitochondria, and this stimulation was reversed by a membrane-permeable allosteric inhibitor of PTP1B and by a potent selective Src inhibitor. They also indicated a direct action of PTP1B on phosphorylated tyrosine 527 residue of Src, thus implicating a role for PTP1B in the modulation of Src activity in mitochondria. Putative Src and PTP1B substrates were identified by liquid chromatography tandem mass spectrometry and two-dimensional blue native/SDS-PAGE. Both inhibitors inhibited ADP-stimulated respirations concurrently with Src activation and complex IV activation by ATP, while having no effect or increasing the activity of the other complexes. Our analysis emphasizes the regulatory function of Src and its modulation by PTP1B on oxidative phosphorylation in mitochondria.     

Mitochondrial permeability transition in cardiac ischemia–reperfusion: whether cyclophilin D is a viable target for cardioprotection?

Growing number of studies provide strong evidence that the mitochondrial permeability transition pore (PTP), a non-selective channel in the inner mitochondrial membrane, is involved in the pathogenesis of cardiac ischemia–reperfusion and can be targeted to attenuate reperfusion-induced damage to the myocardium. The molecular identity of the PTP remains unknown and cyclophilin D is the only protein commonly accepted as a major regulator of the PTP opening. Therefore, cyclophilin D is an attractive target for pharmacological or genetic therapies to reduce ischemia–reperfusion injury in various animal models and humans. Most animal studies demonstrated cardioprotective effects of PTP inhibition; however, a recent large clinical trial conducted by international groups demonstrated that cyclosporine A, a cyclophilin D inhibitor, failed to protect the heart in patients with myocardial infarction. These studies, among others, raise the question of whether cyclophilin D, which plays an important physiological role in the regulation of cell metabolism and mitochondrial bioenergetics, is a viable target for cardioprotection. This review discusses previous studies to provide comprehensive information on the physiological role of cyclophilin D as well as PTP opening in the cell that can be taken into consideration for the development of new PTP inhibitors.     

The tyrosine phosphatase SHP-1 negatively regulates cytotrophoblast proliferation in first-trimester human placenta by modulating EGFR activation

Insulin-like growth factors (IGFs) influence placental cell (cytotrophoblast) kinetics. We recently reported that the protein tyrosine phosphatase (PTP) SHP-2 positively regulates IGF actions in the placenta. In other systems, the closely related PTP, SHP-1, functions as a negative regulator of signaling events but its role in the placenta is still unknown. We examined the hypothesis that SHP-1 negatively regulates IGF actions in the human placenta. Immunohistochemical (IHC) analysis demonstrated that SHP-1 is abundant in cytotrophoblast. SHP-1 expression was decreased in first-trimester placental explants using siRNA; knockdown did not alter IGF-induced proliferation but it significantly enhanced proliferation in serum-free conditions, revealing that placental growth is endogenously regulated. Candidate regulators were determined by using antibody arrays, Western blotting, and IHC to examine the activation status of multiple receptor tyrosine kinases (RTKs) in SHP-1-depleted explants; amongst the alterations observed was enhanced activation of EGFR, suggesting that SHP-1 may interact with EGFR to inhibit proliferation. The EGFR tyrosine kinase inhibitor PD153035 reversed the elevated proliferation seen in the absence of SHP-1. This study demonstrates a role for SHP-1 in human trophoblast turnover and establishes SHP-1 as a negative regulator of EGFR activation. Targeting placental SHP-1 expression may provide therapeutic benefits in common pregnancy conditions with abnormal trophoblast proliferation.     

Low molecular weight protein tyrosine phosphatases: small,but smart

Low molecular weight protein tyrosine phosphatases (LMW-PTPs) are a family of 18-kDa enzymes involved in cell growth regulation. Despite very limited sequence similarity to the PTP superfamily, they display a conserved signature motif in the catalytic site. LMW-PTP associates and dephosphorylate many growth factor receptors, such as platelet-derived growth factor receptor (PDGF-r), insulin receptor and ephrin receptor, thus downregulating many of the tyrosine kinase receptor functions that lead to cell division. In particular, LMW-PTP acts on both growth-factor-induced mitosis, through dephosphorylation of activated PDGF-r, and on cytoskeleton rearrangement, through dephosphorylation of p190RhoGAP and the consequent regulation of the small GTPase Rho. LMW-PTP activity is modulated by tyrosine phosphorylation on two specific residues, each of them with specific characteristics. LMW-PTP activity on specific substrates depends also on its localization. Moreover, LMW-PTP is reversibly oxidized during growth factor signaling, leading to inhibition of its enzymatic activity. Recovery of phosphatase activity depends on the availability of reduced glutathione and involves the formation of an S–S bridge between the two catalytic site cysteines. Furthermore, studies on the redox state of LMW-PTP in contact-inhibited cells and in mature myoblasts suggest that LMW-PTP is a general and versatile modulator of growth inhibition. Received 17 January 2002; received after revision 22 March 2002; accepted 26 March 2002     

Receptor and nonreceptor protein tyrosine phosphatases in the nervous system

Protein tyrosine phosphatases (PTPs) have emerged as a new class of signaling molecules that play important roles in the development and function of the central nervous system. They include both tyrosine-specific and dual-specific phosphatases. Based on their cellular localization they are also classified as receptor-like or intracellular PTP. However, the intracellular mechanisms by which these PTPs regulate cellular signaling pathways are not well understood. Evidence gathered to date provides some insight into the physiological function of these PTPs in the nervous system. In this review, we outline what is currently known about the functional role of PTPs expressed in the brain.Received 31 March 2003; received after revision 7 May 2003; accepted 22 May 2003     

TULA-2, a novel histidine phosphatase, regulates bone remodeling by modulating osteoclast function

Bone is a dynamic tissue that depends on the intricate relationship between protein tyrosine kinases (PTK) and protein tyrosine phosphatases (PTP) for maintaining homeostasis. PTKs and PTPs act like molecular on and off switches and help modulate differentiation and the attachment of osteoclasts to bone matrix regulating bone resorption. The protein T cell ubiquitin ligand-2 (TULA-2), which is abundantly expressed in osteoclasts, is a novel histidine phosphatase. Our results show that of the two family members, only TULA-2 is expressed in osteoclasts and that its expression is sustained throughout the course of osteoclast differentiation, suggesting that TULA-2 may play a role during early as well late stages of osteoclast differentiation. Skeletal analysis of mice that do not express TULA or TULA-2 proteins (DKO mice) revealed that there was a decrease in bone volume due to increased osteoclast numbers and function. Furthermore, in vitro experiments indicated that bone marrow precursor cells from DKO mice have an increased potential to form osteoclasts. At the molecular level, the absence of TULA-2 in osteoclasts results in increased Syk phosphorylation at the Y352 and Y525/526 residues and activation of phospholipase C gamma 2 (PLCγ2) upon engagement of immune-receptor-tyrosine-based-activation-motif (ITAM)—mediated signaling. Furthermore, expression of a phosphatase-dead TULA-2 leads to increased osteoclast function. Taken together, these results suggest that TULA-2 negatively regulates osteoclast differentiation and function.     

Ethanol inhibits insulin expression and actions in the developing brain

Ethanol-induced cerebellar hypoplasia is associated with inhibition of insulin-stimulated survival signaling. The present work explores the mechanisms of impaired insulin signaling in a rat model of fetal alcohol syndrome. Real-time quantitative RT-PCR demonstrated reduced expression of the insulin gene in cerebella of ethanol-exposed pups. Although receptor expression was unaffected, insulin and insulin-like growth factor (IGF-I) receptor tyrosine kinase (RTK) activities were reduced by ethanol exposure, and these abnormalities were associated with increased PTP1b activity. In addition, glucose transporter molecule expression and steady-state levels of ATP were reduced in ethanol-exposed cerebellar tissue. Cultured cerebellar granule neurons from ethanol-exposed pups had reduced expression of genes encoding insulin, IGF-II, and the IGF-I and IGF-II receptors, and impaired insulin- and IGF-I-stimulated glucose uptake and ATP production. The results demonstrate that ethanol inhibits insulin-mediated actions in the developing brain by reducing local insulin production and insulin RTK activation, leading to inhibition of glucose transport and ATP production.Received 30 December 2004; received after revision 1 March 2005; accepted 10 March 2005     

Expression of the Stp1 LMW-PTP and inhibition of protein CK2 display a cooperative effect on immunophilin Fpr3 tyrosine phosphorylation and <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> growth

Although the yeast genome does not encode bona fide protein tyrosine kinases, tyrosine-phosphorylated proteins are numerous, suggesting that besides dual-specificity kinases, some Ser/Thr kinases are also committed to tyrosine phosphorylation in Saccharomyces cerevisiae. Here we show that blockage of the highly pleiotropic Ser/Thr kinase CK2 with a specific inhibitor synergizes with the overexpression of Stp1 low-molecular-weight protein tyrosine phosphatase (PTP) in inducing a severe growth-defective phenotype, consistent with a prominent role for CK2 in tyrosine phosphorylation in yeast. We also present in vivo evidence that immunophilin Fpr3, the only tyrosine-phosphorylated CK2 substrate recognized so far, interacts with and is dephosphorylated by Spt1. These data disclose a functional correlation between CK2 and LMW-PTPs, and suggest that reversible phosphorylation of Fpr3 plays a role in the regulation of growth rate and budding in S. cerevisiae.Received 15 January 2004; received after revision 20 February 2004; accepted 4 March 2004     

Identification of tyrosine-phosphorylated proteins of the mitochondrial oxidative phosphorylation machinery

The role of some serine/threonine kinases in the regulation of mitochondrial physiology is now well established, but little is known about mitochondrial tyrosine kinases. We showed that tyrosine phosphorylation of rat brain mitochondrial proteins was increased by in vitro addition of ATP and H₂O₂, and also during in situ ATP production at state 3, and maximal reactive oxygen species production. The Src kinase inhibitor PP2 decreased tyrosine phosphorylation and respiratory rates at state 3. We found that the 39-kDa subunit of complex I was tyrosine phosphorylated, and we identified putative tyrosine-phosphorylated subunits for the other complexes. We also have strong evidence that the FoF1-ATP synthase α chain is probably tyrosine-phosphorylated, but demonstrated that the β chain is not. The tyrosine phosphatase PTP 1B was found in brain but not in muscle, heart or liver mitochondria. Our results suggest that tyrosine kinases and phosphatases are involved in the regulation of oxidative phosphorylation.Received 7 January 2005; received after revision 19 April 2005; accepted 22 April 2005     

Oxidation and tyrosine phosphorylation: synergistic or antagonistic cues in protein tyrosine phosphatases

Protein tyrosine phosphatases (PTPs) have been generally recognised as key modulators of cell proliferation, differentiation, adhesion and motility. During signalling, several PTPs undergo two posttranslational modifications that greatly affect their enzymatic activity: tyrosine phosphorylation and cysteine oxidation. Although these modifications share their reversibility depending on the intracellular environment, their effects on enzymatic activity are opposite, tyrosine phosphorylation being correlated to enzyme activation and thiol oxidation to complete inactivation. Several papers have suggested that both these modifications occur in response to the same stimuli i.e. cell proliferation induced by numerous growth factors and cytokines. Conversely, the possibility that these two regulation mechanisms act simultaneously on PTPs has not been established and very few reports investigated this dual regulation of PTPs. To underline the relevance of the question, we discuss several possibilities: (i) that tyrosine phosphorylation and cysteine oxidation of PTPs may share the same target molecules but with different kinetics; (ii) that PTP phosphorylation and oxidation may take place on different subcellular pools of the same protein and (iii) that these two modifications, although having divergent effects on enzyme activity, cooperate in the integrated and coordinated function of PTPs during receptor tyrosine kinase signalling. We believe that our perspective will open new perspectives on an ancient problem – the apparent contradiction of opposing enzymatic regulation of many PTPs – thus clarifying their role as positive or negative transducers (or both) of many extracellular stimuli.Received 11 October 2004; received after revision 26 January 2005; accepted 10 February 2005 Available online 29 March 2005     

Astrology

As a divinatory practice, astrology is without equal in both its colorful history and modern day popularity. Astrology has grown, over thousands of years, into a huge and ornate superstructure that lacks a central design. Although astrology has been dimly veiled by its occult mystique for centuries, the light of modern day inquiry has shown its substance to be mostly illusionary and revealed its foundation to be the shakiest possible: that of self-justification and anecdotal evidence. Despite the many claims of its practitioners and followers, extensive investigation has revealed astrology to be a great teetering monument to human gullibility.     

Cytochrome P450 2U1, a very peculiar member of the human P450s family

Cytochrome P450 2U1 (CYP2U1) exhibits several distinctive characteristics among the 57 human CYPs, such as its presence in almost all living organisms with a highly conserved sequence, its particular gene organization with only five exons, its major location in thymus and brain, and its protein sequence involving an unusually long N-terminal region containing 8 proline residues and an insert of about 20 amino acids containing 5 arginine residues after the transmembrane helix. Few substrates, including fatty acids, N-arachidonoylserotonin (AS), and some drugs, have been reported so far. However, its biological roles remain largely unknown, even though CYP2U1 mutations have been involved in some pathological situations, such as complicated forms of hereditary spastic paraplegia. These data together with its ability to hydroxylate some fatty acids and AS suggest its possible role in lipid metabolism.     

Astrology

Summary As a divinatory practice, astrology is without equal in both its colorful history and modern day popularity. Astrology has grown, over thousands of years, into a huge and ornate superstructure that lacks a central design. Although astrology has been dimly veiled by its occult mystique for centuries, the light of modern day inquiry has shown its substance to be mostly illusionary and revealed its foundation to be the shakiest possible: that of self-justification and anecdotal evidence. Despite the many claims of its practitioners and followers, extensive investigation has revealed astrology to be a great teetering monument to human gullibility.     

The dual role model for p53 in maintaining genomic integrity

The tumour suppressor p53 is a potent mediator of cellular responses against genotoxic insults. In this review we describe the multiple functions of p53 in response to DNA damage, with an emphasis on p53's role in DNA repair. We summarize data demonstrating that p53 actively participates in various processes of DNA repair and DNA recombination via its ability to interact with components of the repair and recombination machinery, and by its various biochemical activities. An important aspect in evaluating p53 functions is provided by the finding that the core domain of p53 harbours two mutually exclusive biochemical activities, sequence-specific DNA binding required for its transactivation function, and 3'-5' exonuclease activity, possibly involved in aspects of DNA repair. Based on the finding that modifications of p53 which lead to activation of its sequence-specific DNA-binding activity result in inactivation of its 3'-5' exonuclease activity, we propose that p53 exerts its functions as a 'guardian of the genome' at various levels: in its noninduced state, p53 should not be regarded as a 'dead' protein but, for example, via its exonuclease activity might be actively involved in prevention and repair of endogenous DNA damage. Upon induction through exogenous DNA damage, p53 will exert its well-documented functions as a superior response element in various types of cellular stress. This dual role model for p53 in maintaining genomic integrity significantly enhances p53's possibilities as a guardian of the genome.     

Drugs of the future: the hormone relaxin

The peptide hormone relaxin is emerging as a multi-functional factor in a broad range of target tissues including several non-reproductive organs, in addition to its historical role as a hormone of pregnancy. This review discusses the evidence that collectively demonstrates the many diverse and vital roles of relaxin: the homeostatic role of endogenous relaxin in mammalian pregnancy and ageing; its gender-related effects; the therapeutic effects of relaxin in the treatment of fibrosis, inflammation, cardioprotection, vasodilation and wound healing (angiogenesis) amongst other pathophysiological conditions, and its potential mechanism of action. Furthermore, translational issues using experimental models (to humans) and its use in various clinical trials, are described, each with important lessons for the design of future trials involving relaxin. The diverse physiological and pathological roles for relaxin have led to the search for its significance in humans and highlight its potential as a drug of the future. Received 12 December 2006; received after revision 12 February 2007; accepted 15 March 2007     

日本染料敏化太阳能电池最新研究动向

染料敏化太阳能电池(DSC)由于具有理论转换效率高，透明性高，制备工艺简单，成本低等众多优点，近年来成为世界各国争相开发研究的热点。本文在回顾了DSC的发展进程，分析了DSC的现存问题后，重点介绍了日本近几年来在开发用于DSC的光电材料和促进DSC实用化方面的研究成果。     

Heaps of moles? – Mediating macroscopic and microscopic measurement of chemical substances

In this paper I take a close look at the SI base quantity “amount of substance”, and its unit, the mole. The mole was introduced as a base unit in the SI in 1971, and there is currently a proposal to change its definition. The current definition of the mole shows a certain ambiguity regarding the nature of the quantity “amount of substance”. The proposed new definition removes the ambiguity, but at a cost: it becomes difficult to justify treating amount of substance as having its own dimension, and hence its own unit, the mole. I argue that the difficulties with amount of substance result from its role as a mediator between macroscopic and microscopic scales. To understand why amount of substance might have its own dimension, we need to connect amount of substance to mass, contra current proposals to separate them.     

Chemistry and Chemists at the London Institution 1807-1912

The London Institution, established in the City of London in 1807, was devoted, as its full title proclaimed, to the 'advancement of Literature and the Diffusion of Useful Knowledge'. With its extensive lecture programme, splendid reference library, reading rooms, laboratory and other amenities, it provided for its members a scientific and cultural centre, modelled on the highly successful and fashionable Royal Institution in London's West End. Among its scientific activities, chemistry long maintained a leading role, in terms of both the sheer volume and variety of its presentations, and the high standing of its lecturers; they included Faraday, Playfair, Hofmann, Roscoe, Odling, Norman Lockyer, Meldola, and Sir William Ramsay, as well as other visiting lecturers, specially selected for their ability to present their subject in an interesting and attractive fashion to a wider lay public. The laboratory of the Institution, although limited in size and facilities, was the scene of instruction in practical chemistry, and between 1863 and 1884 attained the reputation of a significant centre of chemical research during the successive tenure of the professorship in chemistry by J. A. Wanklyn and H. E. Armstrong. Their publications, appearing under the device 'From the Laboratory of the London Institution', were a frequent feature of the leading chemical periodicals. Thus, within its many-sided activities, the Institution promoted significantly the public appreciation of the function of chemistry, as a contributor both to pure knowledge, and to technical and economic progress. It achieved this in an environment of influential City merchants, manufacturers and financiers and doubtless led to beneficient, if unrecorded, consequences. It was only towards the close of the nineteenth century, when the universities had become increasingly concerned with the systematic study of the discipline, that chemistry lost its direct impact in the London Institution, but continued to maintain a presence within its cultural framework.