Inactivation of tyrosinase photoinduced by pterin

Tyrosinase catalyzes in mammals the first and rate-limiting step in the biosynthesis of the melanin, the main pigment of the skin. Pterins, heterocyclic compounds able to photoinduce oxidation of DNA and its components, accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder in which the protection against UV radiation fails due to the lack of melanin. Aqueous solutions of tyrosinase were exposed to UV-A irradiation (350nm) in the presence of pterin, the parent compound of oxidized pterins, under different experimental conditions. The enzyme activity in the irradiated solutions was determined by spectrophotometry and HPLC. In this work, we present data that demonstrate unequivocally that the enzyme is photoinactivated by pterin. The mechanism of the photosensitized process involves an electron transfer from tyrosinase to the triplet excited state of pterin, formed after UV-A excitation of pterin. The biological implications of the results are discussed.     

Hemopoietic cell expression of the chemokine decoy receptor D6 is dynamic and regulated by GATA1

D6 scavenges inflammatory chemokines and is essential for the regulation of inflammatory and immune responses. Mechanisms explaining the cellular basis for D6 function have been based on D6 expression by lymphatic endothelial cells. In this study, we demonstrate that functional D6 is also expressed by murine and human hemopoietic cells and that this expression can be regulated by pro- and anti-inflammatory agents. D6 expression was highest in B cells and dendritic cells (DCs). In myeloid cells, LPS down-regulated expression, while TGF-beta up-regulated expression. Activation of T cells with anti-CD3 and soluble CD28 up-regulated mRNA expression 20-fold, while maturation of human macrophage and megakaryocyte precursors also up-regulated D6 expression. Competition assays demonstrated that chemokine uptake was D6 dependent in human leukocytes, whereas mouse D6-null cells failed to uptake and clear inflammatory chemokines. Furthermore, we present evidence indicating that D6 expression is GATA1 dependent, thus explaining D6 expression in myeloid progenitor cells, mast cells, megakaryocytes, and DCs. We propose a model for D6 function in which leukocytes, within inflamed sites, activate D6 expression and thus trigger resolution of inflammatory responses. Our data on D6 expression by circulating DCs and B cells also suggest alternative roles for D6, perhaps in the coordination of innate and adaptive immune responses. These data therefore alter our models of in vivo D6 function and suggest possible discrete, and novel, roles for D6 on lymphatic endothelial cells and leukocytes.     

Differential Regulation and Function of CD73, a Glycosyl-Phosphatidylinositol–linked 70-kD Adhesion Molecule, on Lymphocytes and Endothelial Cells

CD73, otherwise known as ecto-5′-nucleotidase, is a glycosyl-phosphatidylinositol–linked 70-kD molecule expressed on different cell types, including vascular endothelial cells (EC) and certain subtypes of lymphocytes. There is strong evidence for lymphocyte CD73 having a role in several immunological phenomena such as lymphocyte activation, proliferation, and adhesion to endothelium, but the physiological role of CD73 in other cell types is less clear. To compare the biological characteristics of CD73 in different cell types, we have studied the structure, function, and surface modulation of CD73 on lymphocytes and EC. CD73 molecules on lymphocytes are shed from the cell surface as a consequence of triggering with an antiCD73 mAb, mimicking ligand binding. In contrast, triggering of endothelial CD73 does not have any effect on its expression. Lymphocyte CD73 is susceptible to phosphatidylinositol phospholipase, whereas only a small portion of CD73 on EC could be removed by this enzyme. Furthermore, CD73 on EC was unable to deliver a tyrosine phosphorylation inducing signal upon mAb triggering, whereas triggering of lymphocyte CD73 can induce tyrosine phosphorylation. Despite the functional differences, CD73 molecules on lymphocytes and EC were practically identical structurally, when studied at the protein, mRNA, and cDNA level. Thus, CD73 is an interesting example of a molecule which lacks structural variants but yet has a wide diversity of biological functions. We suggest that the ligand- induced shedding of lymphocyte CD73 represents an important and novel means of controlling lymphocyte– EC interactions.     

Molecular Cloning of Silicatein Gene from Marine Sponge <Emphasis Type="Italic">Petrosia ficiformis</Emphasis> (Porifera,Demospongiae) and Development of Primmorphs as a Model for Biosilicification Studies

In some sponges peculiar proteins called silicateins catalyze silica polymerization in ordered structures, and their study is of high interest for possible biotechnological applications in the nanostructure industry. In this work we describe the isolation and the molecular characterization of silicatein from spicules of Petrosia ficiformis, a common Mediterranean sponge, and the development of a cellular model (primmorphs) suitable for in vitro studies of silicatein gene regulation. The spicule of P. ficiformis contains an axial filament composed of 2 insoluble proteins, of 30 and 23 kDa. The 23-kDa protein was characterized, and the full-length cDNA was cloned. The putative amino acid sequence has high homology with previously described silicateins from other sponge species and also is very similar to cathepsins, a cystein protease family. Finally, P. ficiformis primmorphs express the silicatein gene, suggesting that they should be a good model for biosilicification studies.     

The impact of a fox‐ and cat‐free safe haven on the bird fauna of remnant vegetation in southwestern Australia

Introduced predators are a serious threat to Australian vertebrates. However, the consequences of predation for an area's avifauna have rarely been quantified. We took advantage of the establishment of a 7,832 ha fox‐ and cat‐free safe haven at Mt Gibson, in Western Australia, to assess the consequences of excluding introduced mammal predators on the bird fauna. Bird surveys were conducted over 6 years, before and after the establishment of the introduced predator‐free safe haven. After 3 years, half the sites were enclosed by the fence that excluded introduced predators, while the remainder of sites remained outside the fence and were exposed to fox and cat activity. The sites were stratified by four major vegetation types. A total of 91 bird species were variously detectable with the survey approach, but were typically more detectable during morning surveys. Site occupancy varied considerably among species, but overall, occupancy by all species was most likely to be either not impacted or positively impacted by the safe haven. The most notable change was that avifaunal richness appeared to increase in woodland and shrubland habitats within, as compared to outside, the safe haven. We conclude that: (1) the safe haven had an overall positive impact on bird occupancy; and (2) there were no consistent trends with respect to the kinds of species whose occupancy was positively impacted, beyond them all being small‐ to medium‐sized birds and mostly insectivorous. However, these conclusions must be tempered by the poor detection probability of many species.     

Altered White Matter Architecture in BDNF Met Carriers

Brain-derived neurotrophic factor (BDNF) modulates the pruning of synaptically silent axonal arbors. The Met allele of the BDNF gene is associated with a reduction in the neurotrophin''s activity-dependent release. We used diffusion-weighted imaging to construct structural brain networks for 36 healthy subjects with known BDNF genotypes. Through permutation testing we discovered clear differences in connection strength between subjects carrying the Met allele and those homozygotic for the Val allele. We trained a Gaussian process classifier capable of identifying the subjects'' allelic group with 86% accuracy and high predictive value. In Met carriers structural connectivity was greatly increased throughout the forebrain, particularly in connections corresponding to the anterior and superior corona radiata as well as corticothalamic and corticospinal projections from the sensorimotor, premotor, and prefrontal portions of the internal capsule. Interhemispheric connectivity was also increased via the corpus callosum and anterior commissure, and extremely high connectivity values were found between inferior medial frontal polar regions via the anterior forceps. We propose that the decreased availability of BDNF leads to deficits in axonal maintenance in carriers of the Met allele, and that this produces mesoscale changes in white matter architecture.