Intestinal iodide secretion and its dependence upon mucosal I- permeability

Iodide secretion across different regions of rat small intestine has been investigated in vitro using the standard Wilson-Wiseman technique. Net I- secretion was observed along the entire small intestine, being significantly higher in the central region. Anaerobic conditions, ouabain (2 mM) and Na+ free Ringer solution prevented net I- secretion, whilst both theophylline (1 mM) and carbachol (0,1 mM) enhanced the observed basal intestinal I- secretion. Furthermore, Ca2+-deprived bathing solutions significantly reduced intestinal I- secretion. Epithelial I- uptake from both mucosal and serosal sides was measured by using a Ussing-type chamber technique. The initial rate of I- uptake across the mucosal membrane was significantly higher in the central region than in the proximal part of rat small intestine. No significant differences were observed in the rate of I- uptake from the serosal side. These studies suggest that mucosal I- permeability might determine the direction of net I- intestinal transport and that cytosolic Ca2+ may be a physiological regulator of intestinal I- transport.     

Role of calcium in the phloretin effects on sugar transport in rat small intestine

The effect of phloretin on D-galactose transport in rat small intestine has been investigated. Phloretin enhanced tissue sugar accumulation and reduced mucosal to serosal D-galactose fluxes. Calcium-deprived bathing solutions and verapamil significantly reduced, but did not abolish, the phloretin-effects on intestinal galactose transport. Furthermore in the presence of the anticalmodulin drugs, RMI 12330A and trifluoperazine, phloretin was without effect on D-galactose transport. These findings suggest that phloretin may reduce serosal sugar permeability via an increase in Ca2+-calmodulin complex.     

Sex hormone changes induced by the parasite lead to feminization of the male host in murine Taenia crassiceps cysticercosis

Female mice are more susceptible to Taenia crassiceps (TC) infection than males. However, after a month parasite load increases massively in both genders reaching thousands of parasites per host. The possibility of hormonal changes in the infected mice was envisaged. Sex hormones levels were assayed after different periods of infection, the parasites present in the peritoneal cavity were collected and gonads, uterus and seminal vesicles were weighed. In male mice, serum estradiol increased to levels 200 times their normal values whilst those of testosterone decreased 90% relative to controls. The weight of seminal vesicles was significantly diminished. Infected female mice also showed a slight increase in estrogen blood levels after 8 weeks of infection and the weight of the uterus was significantly increased relative to controls. Serum estradiol and testosterone were almost undetectable after gonadectomy. Cytokines such as IL-6 are capable of stimulating aromatase activity and we found that splenocytes from infected mice produced amounts of IL-6 higher than control as measured by ELISA. In conclusion T. crassiceps infection triggers a feminization process in the infected hosts. The gonads are required for the parasite to induce higher estrogen synthesis. IL-6 could be involved in the immunoendocrine mechanism used by the parasite to maintain a highly permissive environment for its rapid growth.     

Anabolic actions of a mixed beta-adrenergic agonist on nitrogen retention and protein turnover.

Subcutaneous administration of a mixed beta-agonist induced increases in muscle (+13%) and heart (+17%) weights, which were accompanied by a reduction in back (-13%) and perirenal (-27%) fat stores in young male rats, while no changes in liver were observed. The values of nitrogen retention (mg/day) were significantly higher in the beta-agonist treated animals (+16%) as well as those of muscle DNA content (+8%). On the other hand, no statistically significant changes in muscle protein synthetic activity (g protein synthetized/g RNA) were detected (control: 13.4 vs treated: 14.6), while muscle proteolytic activity was decreased (-9%) in those rats administered with the repartitioning agent. In this context, it is suggested that the anabolic effect of metaproterenol should be attributed to a reduction in muscle protein degradation rather than to changes in protein synthesis.     

Immunological mediation of gonadal effects on experimental murine cysticercosis caused by Taenia crassiceps metacestodes.

Female BALB/c mice are naturally more susceptible than males to intraperitoneal experimental infection with Taenia crassiceps metacestodes. Gonadectomy tends to equalize susceptibility between sexes by reducing in half the mean individual intensity of females and by tripling that of males. The effect of gonadectomy is seen only in mice with intact immune systems but not in irradiated mice. Purified sex hormones (17-beta estradiol, testosterone, and progesterone) do not affect cysticercus reproduction or growth in vitro. Thus, gonadal effect on mouse susceptibility to cysticercosis appears to be mediated via the immune system, and it is probably not the consequence of the major sex steroids acting directly upon the parasites. Because sublethal irradiation increases the intensity in gonadectomized females and intact males, whereas that of gonadectomized males and intact females remains unchanged, irradiation results are consistent with the hypothesis that immunological events that participate in controlling the growth of cysticerci are inhibited by ovaries and stimulated by testes.     

The effect of hexose ratios on metabolite production in Saccharomyces cerevisiae strains obtained from the spontaneous fermentation of mezcal

Mezcal from Tamaulipas (México) is produced by spontaneous alcoholic fermentation using Agave spp. musts, which are rich in fructose. In this study eight Saccharomyces cerevisiae isolates obtained at the final stage of fermentation from a traditional mezcal winery were analysed in three semi-synthetic media. Medium M1 had a sugar content of 100 g l^?1 and a glucose/fructose (G/F) of 9:1. Medium M2 had a sugar content of 100 g l^?1 and a G/F of 1:9. Medium M3 had a sugar content of 200 g l^?1 and a G/F of 1:1. In the three types of media tested, the highest ethanol yield was obtained from the glucophilic strain LCBG-3Y5, while strain LCBG-3Y8 was highly resistant to ethanol and the most fructophilic of the mezcal strains. Strain LCBG-3Y5 produced more glycerol (4.4 g l^?1) and acetic acid (1 g l^?1) in M2 than in M1 (1.7 and 0.5 g l^?1, respectively), and the ethanol yields were higher for all strains in M1 except for LCBG-3Y5, -3Y8 and the Fermichamp strain. In medium M3, only the Fermichamp strain was able to fully consume the 100 g of fructose l^?1 but left a residual 32 g of glucose l^?1. Regarding the hexose transporters, a high number of amino acid polymorphisms were found in the Hxt1p sequences. Strain LCBG-3Y8 exhibited eight unique amino acid changes, followed by the Fermichamp strain with three changes. In Hxt3p, we observed nine amino acid polymorphisms unique for the Fermichamp strain and five unique changes for the mezcal strains.     

Translocation properties of primitive molecular machines and their relevance to the structure of the genetic code

We address the question, related with the origin of the genetic code, of why are there three bases per codon in the translation to protein process. As a follow-up to our previous work (Aldana et al., 1998, Martínez-Mekler et al., 1999a,b), we approach this problem by considering the translocation properties of primitive molecular machines, which capture basic features of ribosomal/messenger RNA interactions, while operating under prebiotic conditions. Our model consists of a short one-dimensional chain of charged particles (rRNA antecedent) interacting with a polymer (mRNA antecedent) via electrostatic forces. The chain is subject to external forcing that causes it to move along the polymer which is fixed in a quasi-one-dimensional geometry. Our numerical and analytic studies of statistical properties of random chain/polymer potentials suggest that, under very general conditions, a dynamics is attained in which the chain moves along the polymer in steps of three monomers. By adjusting the model in order to consider present-day genetic sequences, we show that the above property is enhanced for coding regions. Intergenic sequences display a behavior closer to the random situation. We argue that this dynamical property could be one of the underlying causes for the three-base codon structure of the genetic code     

Renewed hope for a vaccine against the intestinal adult Taenia solium

Review of experimental and observational evidence about various cestode infections of mammalian hosts revives hope for the development of an effective vaccine against adult intestinal tapeworms, the central protagonists in their transmission dynamics. As for Taenia solium, there are abundant immunological data regarding cysticercosis in humans and pigs, but information about human taeniasis is scarce. A single publication reporting protection against T. solium taeniasis by experimental primo infection and by vaccination of an experimental foster host, the immunocompetent female hamster, kindles the hope of a vaccine against the tapeworm to be used in humans, its only natural definitive host.     

Poly(A)-Binding Protein 1 Partially Relocalizes to the Nucleus during Herpes Simplex Virus Type 1 Infection in an ICP27-Independent Manner and Does Not Inhibit Virus Replication

Infection of cells by herpes simplex virus type 1 (HSV-1) triggers host cell shutoff whereby mRNAs are degraded and cellular protein synthesis is diminished. However, virus protein translation continues because the translational apparatus in HSV-infected cells is maintained in an active state. Surprisingly, poly(A)-binding protein 1 (PABP1), a predominantly cytoplasmic protein that is required for efficient translation initiation, is partially relocated to the nucleus during HSV-1 infection. This relocalization occurred in a time-dependent manner with respect to virus infection. Since HSV-1 infection causes cell stress, we examined other cell stress inducers and found that oxidative stress similarly relocated PABP1. An examination of stress-induced kinases revealed similarities in HSV-1 infection and oxidative stress activation of JNK and p38 mitogen-activated protein (MAP) kinases. Importantly, PABP relocalization in infection was found to be independent of the viral protein ICP27. The depletion of PABP1 by small interfering RNA (siRNA) knockdown had no significant effect on viral replication or the expression of selected virus late proteins, suggesting that reduced levels of cytoplasmic PABP1 are tolerated during infection.The lytic replication cycle of herpes simplex virus type 1 (HSV-1) can be divided into three phases, immediate-early (IE), early (E), and late (L), that occur in a coordinated sequential gene expression program. IE proteins can regulate E and L gene expression, which produces proteins involved in DNA replication, capsid production, and virion assembly. HSV infection results in host cell shutoff to facilitate the efficient production of viral proteins. First, mRNA is degraded by the virion-associated vhs protein, and then ICP27, a multifunctional regulator of gene expression, inhibits pre-mRNA splicing. As most viral mRNAs are intronless, this abrogates the production of stable cellular mRNAs that can be exported to the cytoplasm and compete for translation with viral mRNAs (44).HSV mRNAs are capped and polyadenylated and so are translated via a normal cap-dependent mechanism. Translation initiation, during which translationally active ribosomes are assembled, is a tightly regulated process (21). Eukaryotic initiation factor 4F (eIF4F) (composed of eIF4E, eIF4G, and eIF4A) that binds the cap at the 5′ end of the mRNA promotes the recruitment of the 40S ribosomal subunit and associated factors, including eIF2-GTP initiator tRNA. The recognition of the start codon then promotes large ribosomal subunit joining. Poly(A)-binding protein 1 (PABP1), which binds and multimerizes on mRNA poly(A) tails, enhances translation initiation through interactions with the eIF4G component of the eIF4F cap-binding complex (20, 29, 32, 51) to circularize the mRNA in a “closed-loop” conformation (24). Key protein-RNA and protein-protein interactions in the translation initiation complex are strengthened by this PABP1-mediated circularization (12).HSV-1 maintains active viral translation in the face of host translational shutoff. Infection activates protein kinase R (PKR), which phosphorylates eIF2α, resulting in translation inhibition. However, HSV-1 ICP34.5 redirects protein phosphatase 1α to reverse eIF2α phosphorylation, abrogating the block to translation (17, 38). In addition, the HSV-1 US11 protein inhibits PKR and may also block PKR-mediated eIF2α phosphorylation (40, 42). HSV-1 infection also enhances eIF4F assembly in quiescent cells by the phosphorylation and proteasome-mediated degradation of the eIF4E-binding protein (4E-BP), which, when hypophosphorylated, can negatively regulate eIF4F complex formation (54). However, ICP6 may also contribute to eIF4F assembly by binding to eIF4G (55). Finally, ICP6 is required for Mnk-1 phosphorylation of eIF4E, but the mechanisms behind this remain unclear (54). ICP27 has also been implicated in translation regulation during HSV infection (6, 8, 10, 30) and may also activate p38 mitogen-activated protein (MAP) kinase that can phosphorylate eIF4E (16, 59).PABP1 appears to be a common cellular target of RNA and DNA viruses. PABP1 can undergo proteolysis, intracellular relocalization, or modification of its interaction with other translation factors in response to infection. For example, poliovirus induces host cell shutoff by cleaving PABP1, thus disrupting certain PABP1-containing complexes (28, 29). The rotavirus NSP3 protein can displace PABP1 from translation initiation complexes (41). However, NSP3 also interacts with a cellular protein, RoXaN, which is required to relocate PABP1 to the nucleus (13). Similarly, the Kaposi''s sarcoma herpesvirus (KSHV) SOX protein plays a role in relocating PABP1, its cofactor in cellular mRNA decay, to the nucleus (33). Although steady-state levels of PABP1 are highest in the cytoplasm of normal cells, where it has cytoplasmic functions, it is a nucleocytoplasmic shuttling protein (1). However, it is unclear how PABP1 enters or exits the nucleus, as it contains neither a canonical nuclear export nor an import signal.Here we describe the loss of PABP1 from cap-binding complexes and the partial relocation of PABP1 to the nucleus in HSV-1-infected cells in a time-dependent manner. Relocation is specific for PABP1, as other translation factors remained in the cytoplasm. Cells undergo stress during HSV-1 infection, and analysis of a variety of cell stresses revealed that PABP relocalization was also observed upon oxidative stress. Paxillin, a potential PABP1 nuclear chaperone, was phosphorylated, and the paxillin-PABP1 interaction was reduced during virus infection. However, the interaction was weak and cell type dependent, indicating that other effectors of PABP1 relocation in the infected cell must exist. Recently, the HSV-1 ICP27 protein was suggested to alter the PABP1 cellular location (6). However, infections with ICP27-null mutant viruses clearly demonstrated that ICP27 is not required for PABP1 nuclear relocation in the context of infection. Although HSV-1 mRNAs are translated by a normal cap-dependent mechanism known to be enhanced by PABP1, small interfering RNA (siRNA) knockdown of PABP1 indicated that at late times of infection, the translation of certain virus late proteins tolerates very low levels of PABP1.