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A Giovane

Publications and source records attributed to A Giovane.

At least 37 records · Page 2Linked to original sources
PubMed1994

Docosahexaenoic acid and signaling pathways in rabbit colon.

The effects of one of the main components of fish oil, docosahexaenoic acid (DHA), on prostaglandin (PG) and Ca2+ signaling pathways were examined in intact mucosa and freshly isolated crypt cells of rabbit descending colon. Preincubation of serosal mucosa for 20 min with 1 microM DHA fully suppressed the short-circuit and transepithelial conductance increase induced by serosal addition of 10 microM arachidonic acid (AA). DHA at 1 microM also prevented the Cl- secretion promoted by 10 microM AA, as estimated by unidirectional 36Cl flux measurements (net flux = 0.68 +/- 0.30 versus -1.91 +/- 0.20 microEq/hr/cm2, four experiments, p < 0.001), whereas it did not affect the electrophysiological and ion flux responses to PGE2. Addition of 1 microM DHA to the serosal side of the mucosa also inhibited the PG cascade activation elicited by AA (PG synthesis and second messenger cAMP increase). In vitro assays of colonic cyclooxygenase activity showed that 1 microM DHA inhibited (with a 20-min lag) cyclooxygenase activity to the same extent as 5 microM indomethacin (approximately 82% and 80%, respectively). DHA also affected the Ca2+ signaling pathway; in isolated crypt cells, the cytosolic free Ca2+ concentration ([Ca2+]i) dropped by 49 +/- 7.6% (mean +/- standard error, six experiments) after incubation with 1 microM DHA. The sustained phase of the [Ca2+]i response to 500 nM concentrations of the intracellular Ca(2+)-ATPase inhibitor thapsigargin was also inhibited within 150 sec upon 1 microM DHA addition (141 +/- 5.8 versus 243 +/- 8.2 nM [Ca2+]i mean +/- standard error, eight experiments, p < 0.01). The [Ca2+]i-lowering effect of DHA, which was not achieved by incubation with other free fatty acids, was not prevented by removal of Na+ from the incubation medium (-46 +/- 4.3% versus -47 +/- 3.8%, mean +/- standard error, four experiments), nor it was mediated by cAMP-, protein kinase C-, or calmodulin-dependent mechanisms. The incubation of highly purified basolateral membranes of crypt cells with 1 microM DHA for 1 min produced a 5-fold increase (IC50 = 0.25 microM) in the plasma membrane Ca(2+)-ATPase activity (34.3 +/- 2.73 versus 6.02 +/- 0.50 nmol/mg of protein/min, mean +/- standard error, four experiments, p < 0.0001), thus indicating that the DHA effects on the Ca2+ pathway were mediated mainly by an increase in plasma membrane Ca2+ pump activity. These findings suggest that DHA is a powerful modulator of the cellular response to activation of PG and Ca2+ signaling pathways.

Animals↗
PubMed1993

Characterization of the human CD4 gene promoter: transcription from the CD4 gene core promoter is tissue-specific and is activated by Ets proteins.

We analyzed the 5' transcription control sequences of the human CD4 gene. We located the transcription initiation site and showed that the CD4 core promoter (positions -40 to +16) lacks a classical "TATA" or initiator positioning consensus sequence but directs precise and efficient transcription when coupled to the ubiquitously active simian virus 40 enhancer. The transcriptional activity of the CD4 gene promoter correlated with CD4 expression in various cell types. Interestingly, the CD4 core promoter also displayed a tissue-specific transcriptional activity. Within this fragment, three nucleic acid sequences are completely conserved in the murine CD4 gene. One of these sequences contains a perfect ETS consensus sequence. Another ETS consensus sequence is located 1060 nt upstream. Electrophoretic-mobility-shift assays showed that the core promoter ETS motif binds an Ets-related protein specifically expressed at high levels in CD4+ cells. Moreover, in CD4- cells, overexpression of Ets-1 or Ets-2 efficiently and specifically activated transcription from the CD4 promoter and core promoter. These data indicate that Ets transcription factors play a central role in controlling CD4 gene expression, by binding to both a classical remote site and an unusual proximal activator sequence.

Animals↗
PubMed1993

tRNA fluorescent labeling at 3' end inducing an aminoacyl-tRNA-like behavior.

A fluorescent tRNA derivative labeled at 3'-O position of the ultimate adenosine residue by reaction, under mild conditions, of tRNA with isatoic anhydride [3,1-benzoxazine-2,4(1H)-dione] was obtained. The labeling selectivity was determined by several criteria: digestion with RNase, followed by HPLC of the digest, produces only one labeled nucleoside, identified as 3'-O-anthraniloyladenosine; the ratio of the absorbance at 260 nm to 332 nm also suggests a 1:1 molar ratio between the nucleic acid and the fluorophore; finally, the incapacity of the labeled tRNA to be charged by the specific aminoacyltransferase further demonstrates the engagement of the 3'-O position. Although the 3'-O-anthraniloyl-labeled tRNA does not seem to be functionally active, as far as the aminoacyl charging activity is concerned, surprisingly we found that it is able to form the ternary complex with elongation factor Tu (EF-Tu) and GTP with an affinity consistently higher than uncharged tRNA. From fluorescence anisotropy measurements the ternary complex dissociation constant was estimated as 73 nM for Escherichia coli and 140 nM for yeast anthraniloyl-tRNA(Phe). These results may be interpreted in terms of the particular structure of the anthraniloyl group that makes the labeled tRNA similar to an aminoacyl-tRNA.

Escherichia coli↗
PubMed1993

The Ets family of transcription factors.

Interest in the Ets proteins has grown enormously over the last decade. The v-ets oncogene was originally discovered as part of a fusion protein expressed by a transforming retrovirus (avian E26), and later shown to be transduced from a cellular gene. About 30 related proteins have now been found in species ranging from flies to humans, that resemble the vEts protein in the so-called 'ets domain'. The ets domain has been shown to be a DNA-binding domain, that specifically interacts with sequences containing the common core trinucleotide GGA. Furthermore, it is involved in protein-protein interactions with co-factors that help determine its biological activity. Many of the Ets-related proteins have been shown to be transcription activators, like other nuclear oncoproteins and anti-oncoproteins (Jun, Fos, Myb, Myc, Rel, p53, etc.). However, Ets-like proteins may have other functions, such as in DNA replication and a general role in transcription activation. Ets proteins have been implicated in regulation of gene expression during a variety of biological processes, including growth control, transformation, T-cell activation, and developmental programs in many organisms. Signals regulating cell growth are transmitted from outside the cell to the nucleus by growth factors and their receptors. G-proteins, kinases and transcription factors. We will discuss how several Ets-related proteins fit into this scheme, and how their activity is regulated both post- and pre-translationally. Loss of normal control is often associated with conversion to an oncoprotein. vEts has been shown to have different properties from its progenitor, which might explain how it has become oncogenic. Oncogene-related products have been implicated in the control of various developmental processes. Evidence is accumulating for a role for Ets family members in Drosophila development, Xenopus oocyte maturation, lymphocyte differentiation, and viral infectious cycles. An ultimate hope in studying transformation by oncoproteins is to understand how cells become cancerous in humans, which would lead to more effective treatments. vEts induces erythroblastosis in chicken. Cellular Ets-family proteins can be activated by proviral insertion in mice and, most interestingly, by chromosome translocation in humans. We are at the beginning of understanding the multiple facets of regulation of Ets activity. Future work on the Ets family promises to provide important insights into both normal control of growth and differentiation, and deregulation in illness.

Amino Acid Sequence↗
PubMed1993

Role of calcium in chloride secretion mediated by cAMP pathway activation in rabbit distal colon mucosa.

Effects of Ca2+ on adenosine 3',5'-cyclic monophosphate (cAMP)-mediated Cl- secretion were investigated in intact mucosa and isolated crypt cells of rabbit descending colon. Addition of 10 microM prostaglandin (PG)E2 or forskolin to tissues incubated in Ca(2+)-free medium increased the size of short-circuit current (Isc) and Cl- secretion as estimated by unidirectional 36Cl flux measurements (net flux = -2.31 +/- 0.24 vs. -1.22 +/- 0.10 mueq.h-1.cm-2, n = 4, P < 0.001). Addition of 10 microM PGE2 to tissues incubated in 1.2 mM Ca2+ Ringer induced a 7-fold increase in mean cAMP level, whereas it produced an 11-fold increase in tissues exposed to Ca(2+)-free medium. Membrane preparations from whole mucosa incubated in Ca(2+)-free medium displayed a cyclic nucleotide phosphodiesterase activity significantly lower than controls (18.76 +/- 0.54 vs. 31.20 +/- 0.39 pmol cAMP. mg protein-1.min-1, means +/- SE, n = 4, P < 0.001). Ca2+ removal also affected adenylate cyclase (AC) responsiveness to agonists; AC activity increased in controls by 54 and 226% after stimulation with 10 microM PGE2 and forskolin, respectively, but it increased more (77 and 325%, respectively) after incubation in Ca(2+)-free solutions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1992

Salmonella typhimurium porins stimulate platelet-activating factor synthesis by human polymorphonuclear neutrophils.

Porins, a family of hydrophobic proteins located in the outer membrane of cell-wall of Gram-negative bacteria, were shown to stimulate the synthesis and release of platelet-activating factor (PAF), a 1-O-alkyl-2-acetyl-sn-glycerol-3-phosphorylcholine mediator of inflammation and endotoxic shock produced by polymorphonuclear neutrophils. PAF synthesis was independent either from contamination by LPS or generation of TNF. Experiments with labeled precursors demonstrated that PAF was synthesized via the remodeling pathway that involves acetylation of 1-O-alkyl-sn-glyceryl-3-phosphorylcholine generated from 1-O-alkyl-2-acyl-sn-glyceryl-3-phosphorylcholine by phospholipase A2 (PLA2) activity. Porins, indeed, induced a sustained PLA2-dependent mobilization of [14C]arachidonic acid that was inhibited by p-bromodiphenacylbromide. p-Bromodiphenacylbromide, an inhibitor of PLA2, also blocked PAF synthesis by preventing the mobilization of 2-lyso-PAF, the substrate for PAF-specific acetyltransferase. The addition of 2-lyso-PAF restored PAF synthesis. The activity of acetyl CoA:2-lyso-PAF acetyltransferase was transiently increased in porin-stimulated PMN and the [3H]acetyl group was incorporated in the synthetized PAF after cell preincubation with [3H]acetyl CoA. The activation of PAF synthesis by porins as well as its release were dependent on extracellular Ca2+. Porins by forming trans-membrane channels determined a sustained influx of 45Ca2+ into the cytosol. As shown by inhibitors of Ca(2+)-calmodulin complexes, calmodulin mediated the Ca(2+)-dependent activation of enzymes involved in PAF synthesis.

Arachidonic Acid↗
PubMed1992

Galactokinase activity in patients with idiopathic presenile and senile cataract.

The activity of galactokinase in red blood cells of 30 patients affected by idiophatic presenile and senile cataract, and of 20 age-matched controls with perfectly transparent lenses, was investigated. The results obtained show a partial deficiency of the galactokinase activity in the patients affected by presenile idiopathic cataract. There is, moreover, a significant relationship between the cortical form of cataract and enzymatic reduction.

Adult↗
PubMed1992

Antiflammins suppress the A23187- and arachidonic acid-dependent chloride secretion in rabbit distal colonic mucosa.

Antiflammins are synthetic peptides with sequence homology to proteins inhibitory for phospholipase A2. The effects of antiflammins on chloride secretion induced by the calcium ionophore A23187, arachidonic acid (AA) and prostaglandin E2 (PGE2) were investigated in distal rabbit colonic mucosa mounted in Ussing-type chambers. 100 nM AF-2 (antiflammin 2, peptide HDMNKVLDL) fully prevented the increase in Isc, net chloride secretion, tissue PGE2 and second messenger cAMP induced by 5 microM A23187. AF-1 (antiflammin 1, peptide MQMKKVLDS) also inhibited, although to a lesser extent, the A23187-mediated increase in Isc. AF-2 inhibition began at doses of 100 nM (delta Isc -0.20 +/- 0.08, microEq h-1 cm-2, mean +/- S.E.M., N = 3) and was maximal at doses comprised between 200 and 250 nM (delta Isc -0.51 +/- 0.12, microEq h-1 cm-2, mean +/- S.E.M., N = 3). AF-2 also inhibited the increase in Isc and chloride secretion induced by the incubation with 10 microM AA and bradykinin but it was ineffective when tissues were stimulated with 10 microM PGE2. 100 nM AF-2 brought about an inhibition of the increase in AA-mediated increases in PGs and cAMP comparable to that of 10 microM of the cyclooxygenase inhibitor indomethacin. In vitro assay of colonic cyclooxygenase activity showed that 100 nM AF-2 and AF-1 inhibited cyclooxygenase activity (73 and approximately 30%, respectively), but they did not modify the in vitro activity of porcine phospholipase A2.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1991

Arachidonic acid metabolites and chloride secretion in rabbit distal colonic mucosa.

The relationships between arachidonic acid (AA) metabolism and chloride secretion were investigated in mucosal preparations of rabbit distal colon. Tissues displayed a significant cyclooxygenase activity already in nonstimulated conditions and incubation with exogenous AA and calcium ionophore A23187 produced a predominant prostaglandin F2 alpha (PGF2 alpha) profile [PGF2 alpha greater than PGE2 greater than thromboxane B2 (TxB2) greater than 6-keto-PGF1 alpha] as assessed by HPLC of tissue homogenates, whereas 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) was not detected in AA- or A23187-stimulated tissues. Radioimmunological assays showed that PGE2 synthesis was time dependent, plateaued at 10 min, and proceeded at rates 15-20 times over TxB2 and 6-keto-PGF1 alpha. Among the PGs produced by colonic mucosa, only PGE2 and, to a lower extent, PGF2 alpha were found to stimulate chloride secretion and cAMP synthesis. Pretreatment with 10 microM 5,8,11,14-eicosatetraynoic acid, a cyclo- and lipoxygenase inhibitor, prevented AA-induced chloride secretion and PG and cAMP synthesis with the same strength as the cyclooxygenase inhibitor indomethacin. No effects were found after preincubation with nordihydroguaiaretic acid, a lipoxygenase blocker with moderate cyclooxygenase inhibitory properties, and caffeic acid, a lipoxygenase inhibitor. 5-HETE (5 microM) had no effect on short-circuit currents (Isc) and chloride transport, but it significantly reduced the increase in Isc, chloride secretion, and PGE2 synthesis elicited by AA or A23187. Platelet-activating factor, reported to stimulate rabbit colon Isc through an indomethacin-sensitive pathway, was not detected at concentrations as low as 10(-10) M.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1991

Mechanism of arachidonic acid transport across rabbit distal colonic mucosa.

The initial rate of [1-14C]arachidonic acid (AA) entry in the serosal side of rabbit distal colonic mucosa mounted in Ussing-type chambers is linear and independent of intracellular metabolism. When the maximal AA uptake was plotted as a function of medium AA concentration in ranges between 50 and 500 nM, saturation of the AA uptake with increasing concentrations was observed. The time course of the uptake of oleic acid and palmitic acid was similar to that observed with AA, and their separate addition to incubation medium strongly reduced the AA uptake. The influx of arachidonate was largely inhibited by ouabain and by incubation with mucosal sodium-free solution and amiloride, while it was increased when colonic mucosa was exposed to luminal amphotericin B. However, voltage-clamp studies showed that the AA entry rate appeared to be linearly related (r = 0.99) to transepithelial potential difference (PD) and suggested that the sodium dependence of AA translocation is an indirect effect of the changes in transepithelial PD induced by sodium transport shifts. These features provide evidence that there is a common entry pathway for AA and other long-chain free fatty acids mediated by a mechanism of facilitated diffusion driven by transmembrane PD.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1990

A glycoprotein inhibitor of pectin methylesterase in kiwi fruit (Actinidia chinensis).

The finding of a powerful inhibitor of pectin methylesterase in ripe kiwi fruit is reported. The inhibitor was revealed to be a glycoprotein. It was purified to homogeneity and found to have a molecular mass of about 28 kDa, as estimated by gel filtration chromatography, SDS/PAGE and analytical ultracentrifugation. The sugar portion is composed of galactose, arabinose and rhamnose, the latter being much less represented. The amino acid composition showed a very high content of acidic residues compared to basic ones, which is the reason for the very low isoelectric point of the protein (less than 3.5). The kind of inhibition on kiwi pectin methylesterase was found to be competitive with an apparent Ki of 0.22 microM, using citrus pectin as a substrate. Moreover, the inhibitor is effective in inhibiting pectin methylesterase in the pH range 3.5-7.5. Kiwi inhibitor appears to be specific for pectin methylesterase, inasmuch as it was found to be ineffective against other polysaccharide-degrading enzymes, such as polygalacturonase and amylase. Conversely, it appears to be completely aspecific as far as the pectin methylesterase source is concerned. In fact, it was found to inhibit this enzyme effectively from all the sources we assayed, i.e. orange, tomato, apple, banana, potato.

Amino Acids↗
PubMed1990

[Measurement of the erythrocyte galactokinase activity in patients with presenile and senile idiopathic cataract. Preliminary study].

The activity of galactokinase in red blood cells, has been assayed in 17 patients with idiopathic senile and presenile cataract and in 12 age-matched subjects with perfectly transparent lenses. 3 of the idiopathic cataract patients (17.6%) showed low erythrocytes GK activity, while nobody in the control group showed reduced GK activity. Although preliminary, our results seem to support the possibility that a chronic disorder of galactose metabolism may be involved in the pathogenesis of the idiopathic senile and presenile cataract.

Adult↗
PubMed1989

Conformation and reactivity changes induced by N-methylkirromycin (aurodox) in elongation factor Tu.

Kirromycin and related antibiotics inhibit protein synthesis in bacteria by acting on elongation factor Tu (EF-Tu). We have studied the effects of N-methylkirromycin (aurodox) on some molecular properties of this protein. The binding of the antibiotic causes a dramatic variation in the protein fluorescence emission spectrum with the appearance of a new maximum at around 340 nm. Addition of aurodox to trypsinized EF-Tu resulted in an emission spectrum similar to that of the denatured intact factor. Fluorescence lifetime analysis performed by a multifrequency phase fluorometer indicated that the fluorescence emission of the factor is heterogeneous with the major component having a lifetime near 4.8 ns in the absence and 6.6 ns in the presence of the antibiotic. These results were interpreted in terms of an antibiotic-induced environmental modification of the unique tryptophan residue of the protein leading to an increase in its quantum yield. However, aurodox did not modify the solvent exposure of this residue, as judged by fluorescence quenching experiments. Moreover, 1-anilino-8-naphthalenesulfonate (ANS) binding studies, as well as analysis of the protein reactivity toward the sulfhydryl group reagent 5,5'-dithiobis(2-nitrobenzoate) (DTNB), showed that, in the presence of aurodox, the behavior of the EF-Tu-GDP complex nears that of EF-Tu.GTP. These results strongly support the hypothesis that aurodox not only confers a "GTP-like" conformation to the EF-Tu.GDP complex but also produces a less stable folding of the protein around the tryptophan residue that may contribute to the multiple functional effects of this antibiotic.

Anti-Bacterial Agents↗
PubMed1988

Evidence of a yeast proteinase specific for elongation factor 2.

Two proteinases active on elongation factor 2 have been found in yeast. The former hydrolyzes the factor producing a single ADP-ribosylatable fragment, whereas it does not produce any fragment when incubated with different proteins. The latter, less specific, is active in cleaving both EF-2 and other proteins giving rise to a noticeable number of fragments. Moreover, when native EF-2 is incubated with the most specific of the two proteinases, the amount of the ADP-ribosylatable fragment increases with time, while no fragments are evident when ADP-ribosylation of EF-2 comes before its incubation with the proteolytic enzyme. A possible regulatory role of this proteinase on EF-2 turnover is hypothesized.

Adenosine Diphosphate Ribose↗
PubMed1987

Purification of elongation factor 2 from human placenta and evidence of its fragmentation patterns in various eukaryotic sources.

While preparing human placenta elongation factor 2 (EF-2), whose purification and some molecular properties are reported, we noticed the presence of numerous protein fractions which did not have EF-2 activity, but were ADP-ribosylated by diphtheria toxin in the presence of NAD+. All these proteins, like EF-2, were selectively retained by a heparin-Sepharose column, which we used as an affinity-chromatography step. This was also observed when EF-2 was prepared, by this purification step, from other sources, i.e. ox liver and two species of yeasts. In order to assess whether these proteins were a degradation product of EF-2, independent proteins or a mixture of both, they were analysed by subjecting them, after [14C]ADP-ribosylation, to exhaustive trypsinolysis. Only one radioactive peptide was found, thus suggesting that those proteins originate from EF-2 by some proteolytic process. Our findings indicate that this proteolysis does not occur after cell disruption, but is more or less active in the intact cell, depending on the system considered.

Adenosine Diphosphate Ribose↗
PubMed1985

1-N6-Etheno-ADP-ribosylation of elongation factor-2 by diphtheria toxin.

Diphtheria toxin fragment A is able to inhibit protein synthesis in the eukaryotic cell by ADP-ribosylating the diphthamide residue of elongation factor-2 (EF-2) [(1980) J. Biol. Chem. 255, 10710-10720]. The reaction requires NAD as ADP-ribose donor. This work reports on the capacity of an NAD analog, the nicotinamide 1-N6-ethenoadenine dinucleotide (epsilon NAD), to be a substrate of diphtheria toxin fragment A in the transferring reaction of the fluorescent moiety, the epsilon ADP-ribose, to the EF-2. As a consequence of the transfer of the epsilon ADP-ribosyl moiety to the EF-2, there is an increase in the emission intensity of the fluorophore and a blue shift in its emission maximum. The epsilon ADP-ribosylated EF-2, like ADP-ribosylated EF-2, retains the capacity to bind GTP and ribosome. The utility of introducing a fluorescent probe in a well defined point of the EF-2 molecule for conformational or binding studies is discussed.

Adenosine Diphosphate↗
PubMed1984

Conformational stability and basal metabolic rate: reexamination of the case of myoglobin.

The free energy of unfolding of several myoglobins from different animal species has been determined from their denaturation pattern by using the ligand binding model. The results indicate that no simple correlation exists between the free energy of unfolding of myoglobin and the basal metabolic rate of the animal species from which the myoglobin was isolated.

Animals↗