Irreversible inactivation of soybean lipoxygenase-1 by hydrophobic thiols

Soybean lipoxygenase-1 is inactivated by micromolar concentrations of the following hydrophobic thiols: 1-octanethiol, 12(S)-mercapto-9(Z)-octadecenoic acid (S-12-HSODE), 12(R)-mercapto-9(Z)-octadecenoic acid (R-12-HSODE), and 12-mercaptooctadecanoic acid (12-HSODA). In each case, inactivation is time-dependent and not reversed by dilution or dialysis. Inactivation requires 13-hydroperoxy-9(Z),11(E)-octadecadienoic acid (13-HPOD), which suggests that it is specific for the ferric form of the enzyme. Lipoxygenase catalyzes an oxygenation reaction on each of the aforementioned thiols, as judged by the consumption of O(2). These reactions also require 13-HPOD. 1-Octanethiol is converted to 1-octanesulfonic acid, which was identified by GC/MS of its methyl ester. The rates of oxygen uptake for R- and S-12-HODE are about 5- and 2.5-fold higher than the rate with 1-octanethiol. The stoichiometries of inactivation imply that inactivation occurs on approximately 1 in 18 turnovers for 12-HSODA, 1 in 48 turnovers for 1-octanethiol, 1 in 63 turnovers for S-12-HSODE, and 1 in 240 turnovers for R-12-HSODE. These data imply that close resemblance to lipoxygenase substrates is not a crucial requirement for either oxidation or inactivation. Under the conditions of our experiments, inactivation was not observed with several more polar thiols: mercaptoethanol, dithiothreitol, L-cysteine, glutathione, N-acetylcysteamine, and captopril. The results imply that hydrophobic thiols irreversibly inactivate soybean lipoxygenase by a mechanism that involves oxidation at sulfur.     

Oxidative stress/damage induces multimerization and interaction of Fanconi anemia proteins

Fanconi anemia (FANC) is a heterogeneous genetic disorder characterized by a hypersensitivity to DNA-damaging agents, chromosomal instability, and defective DNA repair. Eight FANC genes have been identified so far, and five of them (FANCA, -C, -E, -F, and -G) assemble in a multinuclear complex and function at least in part in a complex to activate FANCD2 by monoubiquitination. Here we show that FANCA and FANCG are redox-sensitive proteins that are multimerized and/or form a nuclear complex in response to oxidative stress/damage. Both FANCA and FANCG proteins exist as monomers under non-oxidizing conditions, whereas they become multimers following H2O2 treatment. Treatment of cells with oxidizing agent not only triggers the multimeric complex of FANCA and FANCG in vivo but also induces the interaction between FANCA and FANCG. N-Ethylmaleimide treatment abolishes multimerization and interaction of FANCA and FANCG in vitro. Taken together, our results lead us to conclude that FANCA and FANCG uniquely respond to oxidative damage by forming complex(es) via intermolecular disulfide linkage(s), which may be crucial in forming such complexes and in determining their function.     

Visible light-induced destabilization of endocytosed liposomes

The potential biomedical utility of the photoinduced destabilization of liposomes depends in part on the use of green to near infrared light with its inherent therapeutic advantages. The polymerization of bilayers can be sensitized to green light by associating selected amphiphilic cyanine dyes, i.e. the cationic 1,1'-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine (DiI), or the corresponding anionic disulfonated DiI (DiI-DS), with the lipid bilayer. The DiI sensitization of the polymerization of 1, 2-dioleoyl-sn-glycero-3-phosphoethanolamine/1,2-bis[10-(2', 4'-hexadienoyloxy)-decanoyl]-sn-glycero-3-phosphocholine liposomes caused liposome destabilization with release of encapsulated aqueous markers. In separate experiments, similar photosensitive liposomes were endocytosed by cultured HeLa cells. Exposure of the cells and liposomes to 550 nm light caused a net movement of the liposome-encapsulated 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) from low pH compartment(s) to higher pH compartment(s). This suggests that photolysis of DiI-labelled liposomes results in delivery of the contents of the endocytosed liposomes to the cytoplasm. The release of HPTS into the cytoplasm appears to require the photoactivated fusion of the labelled liposomes with the endosomal membrane. These studies aid in the design of visible light sensitive liposomes for the delivery of liposome-encapsulated reagents to the cytoplasm.     

Rapid identification of cyst (Heterodera spp., Globodera spp.) and root-knot (Meloidogyne spp.) nematodes on the basis of ITS2 sequence variation detected by PCR-single-strand conformational polymorphism (PCR-SSCP) in cultures and field samples

Cyst and root-knot nematodes show high levels of gross morphological similarity. This presents difficulties for the study of their ecology in natural ecosystems. In this study, cyst and root-knot nematode species, as well as some ectoparasitic nematode species, were identified using the second internal transcribed spacer (ITS2) sequence variation detected by polymerase chain reaction-single-strand conformational polymorphism (PCR-SSCP). The ITS2 region was sufficiently variable within the taxa investigated to allow species to be separated on the basis of minor sequence variation. The PCR primers used in this study were effective for 12 species with three genera within the Heteroderinae (Globodera pallida, G. rostochiensis, Heterodera arenaria/avenae, H. ciceri, H. daverti, H. hordecalis, H. mani, H. schachtii, H. trifolii, Meloidogyne ardenensis, M. duytsi and M. maritima). However, pathotypes of Globodera pallida and G. rostochiensis could not be distinguished. The method was tested at two coastal dune locations in The Netherlands (one in the lime-poor dunes of the north and one in calcareous dunes of the south) to determine the population structure of cyst nematodes. At each site, cyst nematodes were associated with three plant species: two plant species on the foredune (Elymus farctus and Ammophila arenaria) and one plant species occurring further inland (Calamagrostis epigejos). Two species of cyst nematodes, H. arenaria and H. hordecalis, were found. H. arenaria associated with vigorous A. arenaria and H. hordecalis in association with degenerating A. arenaria and C. epigejos. The field survey demonstrated that in coastal dunes abiotic factors may be the important affecting the distribution of cyst nematodes.     

Prolactin-like hormone in the nematode Trichinella spiralis larvae

Expression of prolactin (PRL) or prolactin-like hormone has been reported in invertebrates. We investigated the larval phase of Trichinella spiralis: (a) to express 23 kDa PRL, (b) to define its localization and (c) to test its possible biological activity. Immunostaining in isolated larvae demonstrated positive material to 23 kDa PRL by all along the stichosome, specifically in the stichocytes. Homogenized immunoblot larvae showed a 23 kDa protein band. To assess PRL release and its biological activity, larvae were incubated in culture medium and the excretory/secretory products were analyzed by the Nb2 cells bioassay. A cellular growth equivalent until 10 nM PRL and using antibody against 23 kDa PRL, the growth was blocked. In conclusion our result provides evidence that PRL-like hormone is expressed and secreted by the larvae of T. spiralis.     

Nuclear translocation of calcineurin Abeta but not calcineurin Aalpha by platelet-derived growth factor in rat aortic smooth muscle

Calcineurin regulates the proliferation of many cell types through activation of the nuclear factor of activated T cells (NFAT). Two main isoforms of the calcineurin catalytic subunit [calcineurin A (CnA) and CnA] have been identified, although their expression and function are largely unknown in smooth muscle. Western blot analysis and confocal imaging were performed in freshly isolated and cultured rat aortic myocytes to identify these CnA isoforms and elucidate the effect of PDGF on their cellular distribution and interaction with NFAT isoforms. CnA and CnA isoforms displayed differential cellular distribution, with CnA being evenly distributed between the nucleus and cytosol and CnA being restricted to the cytosol. In contrast with the rat brain, we found no evidence for particulate/membrane localization of calcineurin. PDGF caused significant nuclear translocation of CnA and induced smooth muscle cell proliferation, with both effects being abrogated by the calcineurin inhibitor cyclosporin A, the novel NFAT inhibitors A-285222 and inhibitor of NFAT-calcineurin association-6, and the adenylyl cyclase activator forskolin. PDGF also caused cyclosporin A-sensitive translocation of NFATc3, with no apparent effect on either CnA or NFATc1 distribution. Moreover, 87% of nuclear CnA was found to colocalize with NFATc3, consistent with the finding that CnA bound more avidly than CnA to a glutathione S-transferase-NFATc3 fusion protein. Based on their differential distribution in aortic muscle, our results suggest that CnA and CnA are likely to have different cellular functions. However, CnA appears to be specifically activated by PDGF, and we postulate that calcineurin-dependent nuclear translocation of NFATc3 is involved in smooth muscle proliferation induced by this mitogen. nuclear factor of activated T cells c3; confocal imaging; cell proliferation; inhibitor of nuclear factor activated T cells-calcineurin association-6; A-285222     

Effects of prolactin deficiency during the early postnatal period on the development of maternal behavior in female rats: Mother's milk makes the difference

During early life, prolactin (PRL) ingested by the pups through the milk participates in the development of neuroendocrine, immunological and reproductive systems. The present study tested whether a deficiency in PRL in the dam's milk during early lactation affected the offspring in terms of the maternal responsiveness in the sensitization paradigm and behavioral response to a novel environment in the offspring. Thus, lactating rats were injected (sc) on postnatal days (PND) 2–5 with bromocriptine (125 μg/day), bromocriptine + ovine PRL (125 μg + 300 μg/day), or vehicle. As juveniles (at PND 24) or adults (PND 90–100), one female from each litter was exposed to 5 foster pups continuously for 8 days and their maternal responsiveness was recorded. Female offspring were also tested in an open field arena. Adult, but not juvenile, female offspring of bromocriptine-treated mothers showed an increased latency to become maternal, in comparison to latencies displayed by the offspring of control mothers. Furthermore, the proportion of adult, but not juvenile, offspring of bromocriptine-treated mothers that became maternal was lower than that showed by the offspring of vehicle-treated mothers. In comparison to female offspring of vehicle-treated mothers, female offspring of bromocriptine-treated mothers spent less time hovering over the pups (as juvenile females), body licking (as both juvenile and adult females), and in close proximity to pups (as adult females) during the maternal behavior test. Simultaneous administration of ovine PRL and bromocriptine reversed almost all the negative effects of bromocriptine. These data suggest that maternally-derived PRL participates during the early postnatal period in the development of neural systems that underlie the control of maternal behavior.     

Ral Overactivation in Malignant Peripheral Nerve Sheath Tumors

Ras leads an important signaling pathway that is deregulated in neurofibromatosis type 1 and malignant peripheral nerve sheath tumor (MPNST). In this study, we show that overactivation of Ras and many of its downstream effectors occurred in only a fraction of MPNST cell lines. RalA, however, was overactivated in all MPNST cells and tumor samples compared to nontransformed Schwann cells. Silencing Ral or inhibiting it with a dominant-negative Ral (Ral S28N) caused a significant reduction in proliferation, invasiveness, and in vivo tumorigenicity of MPNST cells. Silencing Ral also reduced the expression of epithelial mesenchymal transition markers. Expression of the NF1-GTPase-related domain (NF1-GRD) diminished the levels of Ral activation, implicating a role for neurofibromin in regulating RalA activation. NF1-GRD treatment caused a significant decrease in proliferation, invasiveness, and cell cycle progression, but cell death increased. We propose Ral overactivation as a novel cell signaling abnormality in MPNST that leads to important biological outcomes with translational ramifications.The Ras family of guanine-nucleotide bound proteins exerts a fundamental role in cell biology and constitutes an important area of cancer research due to its significant involvement in the development and progression of malignancies (8, 10, 17, 18, 32). Ras-like (Ral) proteins are crucial members of this family and have been shown to play a pivotal role in human tumors (7, 28, 41, 66, 70). Because Ral guanine nucleotide exchange factors (Ral-GEFs) are direct effectors of Ras, the Ral signaling pathway has been traditionally considered a Ras-effector pathway. Activation of Ras (in resemblance to Ral) is regulated by two classes of proteins: Ras-GEFs (e.g., SOS) and Ras- GTPase activating proteins (Ras-GAPs such as neurofibromin). The latter induces hydrolysis of Ras from the active (GTP) form to the inactive (GDP) form (13). Ral-GEFs include two main groups: the proteins that are stimulated by Ras because of their carboxy-terminal Ras binding domain (RalGDS, RGL1, and RGL2) and the proteins that are activated by substrates of PI3K through a pleckstrin homology domain on their C-terminal (RALGPS1 and RALGPS2) (19). Although highly similar to Ras, Ral proteins (RalA and RalB) involve a series of distinctly different effectors that influence gene expression and translation through interaction with ZO-1-associated nucleic acid binding protein (ZONAB) and RalA binding protein 1 (RalBP1) (11, 23, 33). RalB directly interacts with the SEC5 subunit of exocyst to facilitate the host defense response (48, 58).In addition to overactivation of GEFs, inactivation of GAPs is another mechanism for overactivation of GTP-bound proteins. The lack of neurofibromin (encoded by NF1 on human chromosome 17q11.2), a Ras-GAP protein, is the main molecular event in neurofibromatosis type 1 (NF-1), an autosomal-dominant human genetic disease occurring in approximately 1 in 2,500 to 3,500 births (22, 27, 42). One of the main tumor-causing effects of inactivating mutations in the tumor suppressor NF1 gene is postulated to be the subsequent activation of Ras (3, 29, 53, 57, 69). With two main functional domains, SEC14 and Ras-GAP, neurofibromin is best known for its Ras-GAP function. Although the yeast SEC14p is shown to be involved in regulating intracellular proteins and lipid trafficking, the function of its homologous domain in neurofibromin is unknown (49, 62). Although neurofibromas are the most common tumors in NF-1, 10% of patients with plexiform develop malignant peripheral nerve sheath tumors (MPNSTs), which are typically high grade and often fatal (21, 34, 65).The molecular events involved in the malignant transformation of benign neurofibromas to MPNST are poorly defined. Usually arising in the third through sixth decades of life, these tumors are composed of tightly packed hyperchromatic spindle-shaped cells with frequent mitotic figures. Inactivation of both copies of the NF1 gene has been demonstrated in benign human neurofibromas and shown to cause tumors in murine models (56). Loss of heterozygosity of NF1 and p53 has frequently been observed in human MPNST (35, 47, 54). Recombinant mouse strains (NP mice), which harbor inactivated Nf1 and p53 alleles (cis-Nf1^+/−:p53^+/−), demonstrate the cumulative effects of loss of both Nf1 and p53 genes in the etiology of MPNST (14, 68).In the present study, we show that while both Ras activation and activation of a series of its downstream effector pathways are observed in a fraction of MPNST cells, RalA is activated globally in all studied mouse and human MPNST cells and tumor samples. Our results also explain the involvement of this signaling molecule in a series of key biological functions of MPNST cells, as shown in a variety of in vitro assays and an in vivo model of MPNST. Such information may play a role in designing novel therapies for treatment of MPNST or other tumors with overactivation of the Ral pathway.