Fanconi anaemia proteins: major roles in cell protection against oxidative damage

Fanconi anaemia (FA) is a cancer-prone genetic disorder that is characterised by cytogenetic instability and redox abnormalities. Although rare subtypes of FA (B, D1 and D2) have been implicated in DNA repair through links with BRCA1 and BRCA2, such a role has yet to be demonstrated for gene products of the common subtypes. Instead, these products have been strongly implicated in xenobiotic metabolism and redox homeostasis through interactions of FANCC with cytochrome P-450 reductase and with glutathione S-transferase, and of FANCG with cytochrome P-450 2E1, as well as redox-dependent signalling through an interaction between FANCA and Akt kinase. We hypothesise that FA proteins act directly (via FANCC and FANCG) and indirectly (via FANCA, BRCA2 and FANCD2) with the machinery of cellular defence to modulate oxidative stress. The latter interactions may co-ordinate the link between the response to DNA damage and oxidative stress parameters (3, 6-12).     

Double roles of hydroxycinnamic acid derivatives in protection against lysozyme oxidation

Oxidative damage to protein has been implicated in a number of diseases. Much interest has been focused on preventing oxidative damage to protein. Here we showed that hydroxycinnamic acid derivatives (HCA) were able to inhibit the cross-linking of protein induced by riboflavin-mediated photooxidation. HCA were also found to strongly protect lysozyme from gamma rays irradiation. The antioxidative properties of HCA were further studied by laser flash photolysis. Mechanism of antioxidant activities of HCA on lysozyme oxidation was discussed. HCA were found to protect protein against oxidation by scavenging oxidizing species and repairing the damaged protein.     

Melanopsin and rhodopsin mediate UVA-induced immediate pigment darkening: Unravelling the photosensitive system of the skin

The mammalian skin has a photosensitive system comprised by several opsins, including rhodopsin (OPN2) and melanopsin (OPN4). Recently, our group showed that UVA (4.4?kJ/m²) leads to immediate pigment darkening (IPD) in murine normal and malignant melanocytes. We show the role of OPN2 and OPN4 as UVA sensors: UVA-induced IPD was fully abolished when OPN4 was pharmacologically inhibited by AA9253 or when OPN2 and OPN4 were knocked down by siRNA in both cell lines. Our data, however, demonstrate that phospholipase C/protein kinase C pathway, a classical OPN4 pathway, is not involved in UVA-induced IPD in either cell line. Nonetheless, in both cell types we have shown that: a) intracellular calcium signal is necessary for UVA-induced IPD; b) the involvement of CaMK II, whose inhibition, abolished the UVA-induced IPD; c) the role of CAMK II/NOS/sGC/cGMP pathway in the process since inhibition of either NOS or sGC abolished the UVA-induced IPD. Taken altogether, we show that OPN2 and OPN4 participate in IPD induced by UVA in murine normal and malignant melanocytes through a conserved common pathway. Interestingly, upon knockdown of OPN2 or OPN4, the UVA-driven IPD is completely lost, which suggests that both opsins are required and cooperatively signal in murine both cell lines. The participation of OPN2 and OPN4 system in UVA radiation-induced response, if proven to take place in human skin, may represent an interesting pharmacological target for the treatment of depigmentary disorders and skin-related cancer.     

Natural resistance mechanisms may play a role in protection against chemical carcinogenesis

Summary Mice deprived of B lymphocytes by the chronic administration of anti-IgM antibodies have been shown to possess a heightened natural resistance (NR) to micro-organisms, to parental bone marrow, and to natural killer (NK)-sensitive tumors in vitro and in vivo. Experiments described in this communication indicate that the latent period of primary tumors induced by the injection of methylcholanthrene (MC) is also prolonged in these mice. This observation suggests that NR mechanisms may provide protection against primary chemically induced tumors. Abbreviations used in this paper: MC, methylcholanthrene; NR, natural resistance; NRG, normal rabbit serum pool; NK, natural killer cell     

Physiological regulatory networks: ecological roles and evolutionary constraints

Ecological and evolutionary physiology has traditionally focused on one aspect of physiology at a time. Here, we discuss the implications of considering physiological regulatory networks (PRNs) as integrated wholes, a perspective that reveals novel roles for physiology in organismal ecology and evolution. For example, evolutionary response to changes in resource abundance might be constrained by the role of dietary micronutrients in immune response regulation, given a particular pathogen environment. Because many physiological components impact more than one process, organismal homeostasis is maintained, individual fitness is determined and evolutionary change is constrained (or facilitated) by interactions within PRNs. We discuss how PRN structure and its system-level properties could determine both individual performance and patterns of physiological evolution.     

rWind: download,edit and include wind data in ecological and evolutionary analysis

1) Wind connectivity has been identified as a key factor driving many biological processes. 2) Existing software available for managing wind data are often overly complex for studying many ecological processes and cannot be incorporated into a broad framework. 3) Here we present rWind, an R language package to download and manage surface wind data from the Global Forecasting System and to compute wind connectivity between locations. 4) Data obtained with rWind can be used in a general framework for analysis of biological processes to develop hypotheses about the role of wind in driving ecological and evolutionary patterns.     

The roles of IFN gamma in protection against tumor development and cancer immunoediting

Interferon-gamma (IFN gamma) is a cytokine that plays physiologically important roles in promoting innate and adaptive immune responses. The absence of IFN gamma production or cellular responsiveness in humans and experimental animals significantly predisposes the host to microbial infection, a result that validates the physiologic importance of this cytokine in preventing infectious disease. Recently, an additional role for IFN gamma in preventing development of primary and transplanted tumors has been identified. Although there now appears to be a consensus that IFN gamma promotes host responses to tumors, the mechanisms by which this cytokine achieves its effects remain unclear. In this review, we briefly discuss key issues of the molecular cell biology of IFN gamma and its receptor that are most relevant to IFN gamma-dependent anti-tumor effects and then focus on the data implicating IFN gamma as a critical immune system component that regulates tumor development. Potential mechanisms underlying IFN gamma's anti-tumor effects are discussed and a preliminary integrative model of IFN gamma's actions on tumors is proposed. Finally, the capacity of IFN gamma and lymphocytes to not only provide protection against tumor development but also to sculpt the immunogenic phenotype of tumors that develop in an immunocompetent host is presented and introduced as a "cancer immunoediting" process.     

G80A reduced folate carrier SNP modulates cellular uptake of folate and affords protection against thrombosis via a non homocysteine related mechanism

Dietary folate is absorbed in the jejunum by the 'Reduced Folate Carrier' binding protein. This protein also sequesters extracellular folate for use by many cells in the body. As several biosynthetic pathways require folate for critical life processes, any change in the properties of this protein could lower folate bioavailability, cellular levels of the vitamin, and thus influence health. Since folate lowers thrombogenic homocysteine, we examined the prevalence of a common genetic polymorphism encoding the Reduced Folate Carrier (G80A RFC) to see if it acts as a risk factor for thrombotic vascular disease via an effect on homocysteine disposition in a cohort of 156 patients. The odds ratio indicates a significant protective effect of the mutant A allele against thrombosis: OR = 0.56(95% CI; 0.34-0.92). chi2; p = 0.022 (Yates corrected chi2; p = 0.031). The polymorphism had no impact on homocysteine, but did increase the level of extracellular to intracellular folate as might be predicted by the biological role of the expressed protein. This, and not homocysteine level, may be what affords protection against thrombosis.     

Streptozotocin may provide protection against subsequent oxidative stress of endotoxin or streptozotocin in rats

Endotoxin lipopolysaccharide (LPS) and streptozotocin-induced diabetes are known to cause oxidative stress in vivo. There is some evidence that a sublethal dose of LPS provides protection against subsequent oxidative stress. Because of its wide use as a diabetogenic agent, this study was undertaken to determine if streptozotocin can likewise provide a protective effect against further oxidative stress in rats. Female Sprague–Dawley rats were given streptozotocin (50 mg/kg intraperitoneally once) prior to exposure to either bacterial endotoxin from Salmonella abortus equii (5 mg/kg intraperitoneally) or three additional daily doses of streptozotocin (50 mg/kg intraperitoneally). One week after LPS or streptozotocin treatments, oxidative stress was determined by measuring changes in antioxidant activity (glutathione peroxidase, glutathione reductase, superoxide dismutase, catalase, glutathione S-transferase, and γ-glutamyltranspeptidase) and in concentrations of glutathione, nitrite, and thiobarbituric acid reactants in liver, kidney, intestine, and spleen. High levels of some antioxidants in the LPS-control and streptozotocin-control rats, in contrast to normal levels found in diabetes + LPS and multidose-streptozotocin rats, suggest that streptozotocin, like LPS, may confer a protective effect against subsequent oxidative stress. © 1998 John Wiley & Sons, Inc. J Biochem Toxicol 12: 143–149, 1998     

The flexible evolutionary anchorage-dependent Pardee's restriction point of mammalian cells: how its deregulation may lead to cancer

Living cells oscillate between the two states of quiescence and division that stand poles apart in terms of energy requirements, macromolecular composition and structural organization and in which they fulfill dichotomous activities. Division is a highly dynamic and energy-consuming process that needs be carefully orchestrated to ensure the faithful transmission of the mother genotype to daughter cells. Quiescence is a low-energy state in which a cell may still have to struggle hard to maintain its homeostasis in the face of adversity while waiting sometimes for long periods before finding a propitious niche to reproduce. Thus, the perpetuation of single cells rests upon their ability to elaborate robust quiescent and dividing states. This led yeast and mammalian cells to evolve rigorous Start [L.H. Hartwell, J. Culotti, J. Pringle, B.J. Reid, Genetic control of the cell division cycle in yeast, Science 183 (1974) 46-51] and restriction (R) points [A.B. Pardee, A restriction point for control of normal animal cell proliferation, Proc. Natl. Acad. Sci. U. S. A. 71 (1974) 1286-1290], respectively, that reduce deadly interferences between the two states by enforcing their temporal insulation though still enabling a rapid transition from one to the other upon an unpredictable change in their environment. The constitutive cells of multi-celled organisms are extremely sensitive in addition to the nature of their adhering support that fluctuates depending on developmental stage and tissue specificity. Metazoan evolution has entailed, therefore, the need for exceedingly flexible anchorage-dependent R points empowered to assist cells in switching between quiescence and division at various times, places and conditions in the same organism. Programmed cell death may have evolved concurrently in specific contexts unfit for the operation of a stringent R point that increase the risk of deadly interferences between the two states (as it happens notably during development). But, because of their innate flexibility, anchorage-dependent R points have also the ability to readily adjust to a changing structural context so as to give mutated cells a chance to reproduce, thereby encouraging tumor genesis. The Rb and p53 proteins, which are regulated by the two products of the Ink4a-Arf locus [C.J. Sherr, The INK4a/ARF network in tumor suppression, Nat. Rev., Mol. Cell Biol. 2 (2001) 731-737], govern separable though interconnected pathways that cooperate to restrain cyclin D- and cyclin E-dependent kinases from precipitating untimely R point transit. The expression levels of the Ink4a and Arf proteins are especially sensitive to changes in cellular shape and adhesion that entirely remodel at the time when cells shift between quiescence and division. The Arf proteins further display an extremely high translational sensitivity and can activate the p53 pathway to delay R point transit, but, only when released from the nucleolus, 'an organelle formed by the act of building a ribosome' [T. Mélèse, Z. Xue, The nucleolus: an organelle formed by the act of building a ribosome, Curr. Opin. Cell Biol. 7 (1995) 319-324]. In this way, the Ink4a/Rb and Arf/p53 pathways emerge as key regulators of anchorage-dependent R point transit in mammalian cells and their deregulation is, indeed, a rule in human cancers. Thus, by selecting the nucleolus to mitigate cell cycle control by the Arf proteins, mammalian cells succeeded in forging a highly flexible R point enabling them to match cell division with a growth rate imposed by factors controlling nucleolar assembling, such as nutrients and adhesion. It is noteworthy that nutrient control of critical size at Start in budding yeast has been shown recently to be governed by a nucleolar protein interaction network [P. Jorgensen, J.L. Nishikawa, B.-J. Breitkreutz, M. Tyers, Systematic identification of pathways that couple cell growth and division in yeast, Science 297 (2002) 395-400].     

Glutamate carboxypeptidase II and folate deficiencies result in reciprocal protection against cognitive and social deficits in mice: implications for neurodevelopmental disorders

Interactions between genetic and environmental risk factors underlie a number of neuropsychiatric disorders, including schizophrenia (SZ) and autism (AD). Due to the complexity and multitude of the genetic and environmental factors attributed to these disorders, recent research strategies focus on elucidating the common molecular pathways through which these multiple risk factors may function. In this study, we examine the combined effects of a haplo-insufficiency of glutamate carboxypeptidase II (GCPII) and dietary folic acid deficiency. In addition to serving as a neuropeptidase, GCPII catalyzes the absorption of folate. GCPII and folate depletion interact within the one-carbon metabolic pathway and/or of modulate the glutamatergic system. Four groups of mice were tested: wild-type, GCPII hypomorphs, and wild-types and GCPII hypomorphs both fed a folate deficient diet. Due to sex differences in the prevalence of SZ and AD, both male and female mice were assessed on a number of behavioral tasks including locomotor activity, rotorod, social interaction, prepulse inhibition, and spatial memory. Wild-type mice of both sexes fed a folic acid deficient diet showed motor coordination impairments and cognitive deficits, while social interactions were decreased only in males. GCPII mutant mice of both sexes also exhibited reduced social propensities. In contrast, all folate-depleted GCPII hypomorphs performed similarly to untreated wild-type mice, suggesting that reduced GCPII expression and folate deficiency are mutually protective. Analyses of folate and neurometabolite levels associated with glutamatergic function suggest several potential mechanisms through which GCPII and folate may be interacting to create this protective effect.     

Microsomal glutathione S-transferase 1 in the retinal pigment epithelium: protection against oxidative stress and a potential role in aging

High oxygen tension, exposure to light, and the biochemical events of vision generate significant oxidative stress in the retina and the retinal pigment epithelium (RPE). Understanding the mechanisms and basis of susceptibility to progressive retinal diseases involving oxidative damage such as age-related macular degeneration (AMD) remains a major challenge. Here microsomal glutathione S-transferase (MGST1) is shown to be a dominant, highly expressed enzyme in bovine and mouse RPE microsomes that displays significant reduction activity toward synthetic peroxides, oxidized RPE lipids, and oxidized retinoids. This enzymatic reduction activity (GPx) can be partially neutralized with a monoclonal anti-MGST1 antibody developed in this study. MGST1-transfected HEK293 cells exhibited greater viability (70 +/- 4% survival) compared with untransfected control cells (46 +/- 4% survival) when challenged with 20 microM H(2)O(2), and greater viability of MGST1-transfected cells following challenge with oxidized docosahexaenoic acid was also observed. Cultured ARPE19 cells transfected with silencing MGST1 siRNAs exhibited lower expression of MGST1 (12% and 26% of the controls) and significantly lower GPx activity (44 +/- 13%) and, thus, were more susceptible to oxidative damage. Immunoblotting revealed that the in vivo expression of MGST1 in mouse RPE decreases 3-4-fold with age, to trace levels in 18-month-old mice. GPx activity in the RPE was also found to be reduced in 12-month-old mice to approximately 67%. These results support an important protective function for MGST1 against oxidative insult in the RPE that decreases with age and suggest that this enzyme may play a role in the development of age-related diseases such as AMD.     

The glutamyl-tRNA synthetase of Escherichia coli: substrate-induced protection against its thermal inactivation.

The substrates-induced protection against the heat-inactivation of the glutamyl-tRNA synthetase has been investigated. tRNAGlu and ATP protect efficiently the enzyme, whereas glutamate does not. In the presence of tRNAGlu, glutamate induces an additional protection to that given by the tRNAGlu alone. A weak synergism was observed between ATP and tRNAGlu, whereas no synergism was detected between ATP and glutamate. These results suggest that tRNAGlu and ATP, but not glutamate are able to bind to the free enzyme form; glutamate binds only to the Enzyme.tRNAGlu and to the Enzyme.tRNAGlu.ATP complexes. The presence of the three substrates induces a higher stabilization of the enzyme than that expected from the protection observed for the various other substrates combinations, suggesting the existence of a marked synergism between the three substrates against the heat-inactivation of the enzyme. The protection constants determined from this study are similar to the dissociation constants determined by direct binding experiments and to the Km values determined kinetically.     

Population dynamics and evolutionary processes: the manifold roles of habitat selection

Summary Any character that has a substantial effect on a species' distribution and abundance can exert a variety of indirect effects on evolutionary processes. It is suggested that an organism's capacity for habitat selection is just such a character. Habitat selection can constrain the selective environment experienced by a population. Habitat selection can also indirectly influence the relative importance of natural selection, drift, and gene flow, through its effect on population size and growth rate. In many circumstances (but not all), habitat selection increases population size and growth rate, and thereby makes selection in a local environment more effective than drift and gene flow.     

Folding changes in membrane-inserted diphtheria toxin that may play important roles in its translocation.

Diphtheria toxin membrane penetration is triggered by the low pH within the endosome lumen. Subsequent exposure to the neutral pH of the cytoplasm is believed to aid in translocation of the catalytic A domain of the toxin into the cytoplasm. To understand the effects of low pH and subsequent exposure to neutral pH on translocation, we studied toxin conformation in solution and in toxin inserted in model membranes. Two conformations were found at low pH. One form, L', predominates below 25-30 degrees C, and the other, L", predominates above 25-30 degrees C and is formed from the L' state by an unfolding event. Both forms are hydrophobic and penetrate deeply into membranes. After pH neutralization, the L' and L' conformations give rise to two new conformations, R' and R', respectively. The R' and R" conformations differ from each other in that in the R' state the A domain remains folded, whereas in the R" state the A domain is unfolded. This is confirmed by the finding that only the R' state possesses the capacity to bind and hydrolyze NAD+. It is also supported by the finding that the R' state can also be formed by thermal unfolding of the R' state. The R conformations differ from the low-pH L conformations in that although they remain largely membrane-inserted, it appears that a large portion of the toxin is no longer in contact with the hydrophobic core of the bilayer.(ABSTRACT TRUNCATED AT 250 WORDS)     

The roles of thioredoxin in protection against oxidative stress-induced apoptosis in SH-SY5Y cells.

Using models of serum deprivation and 1-methyl-4-phenylpyridinium (MPP(+)), we investigated the mechanism by which thioredoxin (Trx) exerts its antiapoptotic protection in human neuroblastoma cells (SH-SY5Y) and preconditioning-induced neuroprotection. We showed that SH-SY5Y cells are highly sensitive to oxidative stress and responsive to both extracellularly administered and preconditioning-induced Trx. Serum deprivation and MPP(+) produced an elevation in the hydroxyl radicals, malondialdehyde and 4-hydroxy-2,3-nonenal (HNE), causing the cells to undergo mitochondria-mediated apoptosis. Trx in the submicromolar range blocked the observed apoptosis via a multiphasic protection mechanism that includes the suppression of cytochrome c release (most likely via the induction of Bcl-2), the inhibition of procaspase-9 and procaspase-3 activation, and the elevated level of Mn-SOD. The reduced form of Trx suppresses the serum-free-induced hydroxyl radicals, lipid peroxidation, and apoptosis, indicating that H(2)O(2) is removed by Trx peroxidase. The participation of Trx in preconditioning-induced neuroprotection is supported by the observation that inhibition of Trx synthesis with antisense oligonucleotides or of Trx reductase drastically reduced the hormesis effect. This effect of Trx-mediated hormesis against oxidative stress-induced apoptosis is striking. It induced a 30-fold shift in LD(50) in the MPP(+)-induced neurotoxicity.