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R Torres

Publications and source records attributed to R Torres.

At least 73 records · Page 4Linked to original sources
PubMed1994

Imidazo[1,5-a]pyrimidine and benzo[4,5]imidazo-[1,2-a]pyrimidine derivatives as calcium antagonists.

Several bicyclic dihydropyrimidines were synthesized and evaluated for their calcium antagonistic activities by comparison with the usual 1,4-dihydropyridine calcium antagonist reference compound nifedipine. The solid-state structure of the isopropyl 2-methyl-4-(3'-nitrophenyl)-1,4-dihydrobenzo[4,5]imidazo[1,2- a]pyrimido-3-carboxylate shows that these compounds can adopt the most important structural features of the 1,4-dihydropyridine and 1,4-dihydropyrimidine calcium channel blockers. The high-potassium depolarized rat aorta assay was used for testing the compounds as calcium channel blockers. Some compounds showed interesting vasorelaxant activity.

Animals↗
PubMed1994

Evolutionary relationships and functional conservation among vertebrate Max-associated proteins: the zebra fish homolog of Mxi1.

In mammals, current evidence supports the view that Myc-responsive activities are regulated in part through an intracellular balance between levels of transcriptionally-active Myc/Max heterodimers and those of transcriptionally-inert Max/Max, Mad/Max and Mxi1/Max complexes. To gain insight into the roles of Mad and Mxi1 in cellular growth and differentiation and to fortify key structure-function relationships from an evolutionary standpoint, low stringency hybridization screens were used to identify potential homologs of these Max-associated proteins in the zebra fish genome. A single class of cDNA clones that cross-hybridized both to human mad and mxi1 probes was shown to encode a putative protein with significantly greater homology to mammalian Mxi1 than to Mad, particularly in the basic and helix-loop-helix (bHLH) regions. The high degree of structural relatedness between vertebrate Mxi1 proteins apparent in molecular modelling studies was consistent with the findings that the HLH/leucine zipper (LZ) region of zMxi1 exhibited the same profile of dimerization specificities as its mammalian counterpart in the two-hybrid system and that zmxi1 could, like human mxi1 (Lahoz et al., 1994), suppress the oncogenic potential of mouse c-myc in a mammalian cell. Finally, a comparison of steady-state zc-myc and zmxi1 mRNA levels during zebra fish embryogenesis demonstrated (i) high levels of zc-myc relative to zmxi1 mRNA during initiation of organogenesis, a period characterized by intense growth and active differentiation and (ii) rising levels of zmxi1 mRNA during progression towards the terminally differentiated state. These contrasting patterns of developmental expression together with the capacity of zmxi1 to repress myc-induced transformation support a model for the regulation, by Max-associated proteins, of Myc functions in the control of normal cell development and neoplastic growth.

Amino Acid Sequence↗
PubMed1993

Antibodies to murine CD40 stimulate normal B lymphocytes but inhibit proliferation of B lymphoma cells.

A rat anti-mouse CD40 antiserum has been prepared by hyperimmunisation of Lewis rats with a highly purified preparation of the recombinant extracellular domain of murine CD40. This antiserum specifically binds CD40-expressing L cell transfectants, but not untransfected L cells, and induces vigorous proliferation of highly purified small dense B cells obtained from the spleens of unstimulated mice. Anti-CD40-induced B cell proliferation can be augmented by the addition of IL-4 and is inhibited by purified recombinant soluble mouse CD40. Interestingly the same anti-CD40 antiserum specifically inhibits the in vitro growth of A.20 murine B lymphoma cells. The specificity of this inhibition can be demonstrated by reversing the effect with purified recombinant soluble mouse CD40. These data implicate CD40 as a possible target for therapeutic intervention in the treatment of B lymphomas.

Animals↗
PubMed1993

Influence of dietary myoinositol on myocardial vulnerability and norepinephrine release in a diabetic animal model.

In a canine model of diabetes enhanced ventricular vulnerability (VFT) has been associated with reduced myocardial myoinositol and increased release of norepinephrine (NE). To assess the role of the polyol, a dietary supplement of myoinositol was fed for 1 year to a diabetic group. Diabetes was induced with alloxan, 30 mg/kg. Controls (Group 1) were compared with diabetics without (Group 2) and with the inositol supplement (Group 3). After 1 year the animals were anesthetized to assess VFT. Basal heart rate and arterial pressure were comparable. The VFT in Group 1 was 43 +/- 2.6 ma, 26.7 +/- 2.8 ma in Group 2 (P < 0.02) and 39 +/- 3.5 ma in Group 3 (P < 0.02 vs. Group 2). Since the cardiac sympathetic system may promote arrhythmogenesis, the release of NE into the coronary sinus (CS) has been determined. To assess basal NE release serial arterial (A) and (CS) samples were taken at 5 min intervals for 20 min during infusion of 3H-NE. There was no significant difference between the diabetic groups in the level of arterial NE (HPLC). The mean for NEA-CS was higher in Group 2 (-228 +/- 33 pg/ml) compared to normals (-75 +/- 19 P < 0.02). In Group 3 the mean NE in the coronary venous effluent was -33 +/- 9 pg/ml, significantly less than Group 2. Infusion of 3H-NE was attended by significantly higher 3H-NEcs levels in Group 2. While dihydroxyphenylglycol (DHPG) was increased, 3H DHPG was not, suggesting that an impaired uptake mechanism contributed to the increased NEcs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Parathyroid hormone related peptide (1-34) and 1,25-dihydroxyvitamin D, have no additive effects on bone tartrate resistant acid phosphatase activity in fetal rat calvaria cultures.

Parathyroid hormone related peptide (PTHrP) and 1,25-dihydroxyvitamin D are known to be resorptive agents which could contribute to the development of hypercalcemia in humoral hypercalcemia of malignancy (HHM) syndrome in Walker 256 tumor bearing rats. In order to clarify some aspects about the relative contribution of these factors to bone resorption, we have determined the effects produced by PTHrP (1-34) and/or 1,25(OH)2D3 on tartrate resistant acid phosphatase (TRAP), a biochemical marker of bone resorption, in fetal rat calvaria cultures. At the same time, bovine parathyroid hormone (PTH) (1-34) was used as a control in the experiments in order to compare its effects with those produced by the other two agonists. In the present work, 10(-7) M PTH (1-34), 10(-7) M PTHrP (1-34) and 10(-8) M or 10(-10) M 1,25(OH)2D3 produced a significant increase in TRAP activity, when these agonists were added to the calvaria culture. Surprisingly, and in spite of the different ways of action of PTH, PTHrP and 1,25(OH)2D3, their actions are not additive in our experiment. The results of the present work suggest that any of the two implicated factors PTHrP or 1,25(OH)2D3 could be individually responsible for the high rate of bone resorption that takes place in HHM syndrome in Walker 256 carcinosarcoma bearing rats, although other different agents, like TGF, could also be implicated.

Acid Phosphatase↗
PubMed1993

Genetic construction and functional analysis of hybrid polyketide synthases containing heterologous acyl carrier proteins.

The gene that encodes the acyl carrier protein (ACP) of the actinorhodin polyketide synthase (PKS) of Streptomyces coelicolor A3(2) was replaced with homologs from the granaticin, oxytetracycline, tetracenomycin, and putative frenolicin polyketide synthase gene clusters. All of the replacements led to expression of functional synthases, and the recombinants synthesized aromatic polyketides similar in chromatographic properties to actinorhodin or to shunt products produced by mutants defective in the actinorhodin pathway. Some regions within the ACP were also shown to be interchangeable and allow production of a functional hybrid ACP. Structural analysis of the most abundant polyketide product of one of the recombinants by electrospray mass spectrometry suggested that it is identical to mutactin, a previously characterized shunt product of an actVII mutant (deficient in cyclase and dehydrase activities). Quantitative differences in the product profiles of strains that express the various hybrid synthases were observed. These can be explained, at least in part, by differences in ribosome-binding sites upstream of each ACP gene, implying either that the ACP concentration in some strains is rate limiting to overall PKS activity or that the level of ACP expression also influences the expression of another enzyme(s) encoded by a downstream gene(s) in the same operon as the actinorhodin ACP gene. These results reaffirm the idea that construction of hybrid polyketide synthases will be a useful approach for dissecting the molecular basis of the specificity of PKS-catalyzed reactions. However, they also point to the need for reducing the chemical complexity of the approach by minimizing the diversity of polyketide products synthesized in strains that produce recombinant polyketide synthases.

Acyl Carrier Protein↗
PubMed1993

Comparative analysis of the expression and oncogenic activities of Xenopus c-, N-, and L-myc homologs.

A polymerase chain reaction-based cloning strategy allowed for the isolation of two distinct Xenopus L-myc genes, as well as previously isolated xc- and xN-myc genes, thus demonstrating that these three well-defined members of the mammalian myc gene family are present in lower vertebrates as well. Comparison of the Xenopus and mammalian Myc families revealed a high degree of structural relatedness at the gene and protein levels; this homology was consistent with the ability of the xc-myc1 and xN-myc1 genes to function as oncogenes in primary mammalian cells. In contrast, the xL-myc1 gene was found to be incapable of transforming rat embryo fibroblast cells, and this inactivity may relate to localized but significant differences in its putative transactivation domain. Analysis of xc-, xN-, and xL-myc gene expression demonstrated that (i) all three genes were highly expressed during oogenesis and their transcripts accumulated as abundant maternal mRNAs, (ii) each gene exhibited a distinctive pattern of expression during embryogenesis and in adult tissues, and (iii) the xL-myc1 and xL-myc2 genes were coordinately expressed in the maternal and zygotic genomes. The markedly high expression of the Xenopus myc gene family in differentiated tissues, such as the central nervous system and kidney, contrasts sharply with the low levels observed in mammalian adult tissues. These differences may reflect unique functions of the Myc family proteins in processes specific to amphibians, such as tissue regeneration.

Amino Acid Sequence↗
PubMed1993

Zebra fish myc family and max genes: differential expression and oncogenic activity throughout vertebrate evolution.

To gain insight into the role of Myc family oncoproteins and their associated protein Max in vertebrate growth and development, we sought to identify homologs in the zebra fish (Brachydanio rerio). A combination of a polymerase chain reaction-based cloning strategy and low-stringency hybridization screening allowed for the isolation of zebra fish c-, N-, and L-myc and max genes; subsequent structural characterization showed a high degree of conservation in regions that encode motifs of known functional significance. On the functional level, zebra fish Max, like its mammalian counterpart, served to suppress the transformation activity of mouse c-Myc in rat embryo fibroblasts. In addition, the zebra fish c-myc gene proved capable of cooperating with an activated H-ras to effect the malignant transformation of mammalian cells, albeit with diminished potency compared with mouse c-myc. With respect to their roles in normal developing tissues, the differential temporal and spatial patterns of steady-state mRNA expression observed for each zebra fish myc family member suggest unique functions for L-myc in early embryogenesis, for N-myc in establishment and growth of early organ systems, and for c-myc in increasingly differentiated tissues. Furthermore, significant alterations in the steady-state expression of zebra fish myc family genes concomitant with relatively constant max expression support the emerging model of regulation of Myc function in cellular growth and differentiation.

Amino Acid Sequence↗
PubMed1993

Evaluation of penicillin acylase production by two strains of Bacillus megaterium.

Penicillin acylase is a key enzyme for the production of semisynthetic beta-lactam antibiotics. The intracellular enzyme from Escherichia coli has been thoroughly studied and characterized. The extracellular enzyme from Bacillus megaterium, despite its potential advantages, has received less attention in the recent scientific literature. A comparative study is presented for the production of penicillin acylase with two strains of Bacillus megaterium in batch fermentation in previously optimized complex and defined media. The enzyme produced by the selected strain has been recovered, partially purified and its kinetic behaviour determined.

Bacillus megaterium↗
PubMed1993

Cardiodepressor effects of 7-O-demethylisothalicberine, bisbenzylisoquinoline alkaloid isolated from Berberis chilensis.

7-O-demethylisothalicberine (7-O-DI), an alkaloid isolated from Berberis chilensis Gillies ex Hook, induces a negative inotropism and chronotropism on guinea pig isolated atria (IC50 = 1.5 x 10(-4) and 1.8 x 10(-4) M, respectively). As these effects were not antagonized by propranolol, 7-O-DI inhibition of isoproterenol-induced atrial activation seems to be attained through a mechanism distinct of beta-receptor blockade. A probable cholinergic mechanism of action was also ruled out. 7-O-DI atrial effects were completely reversed by a 50% increase of calcium concentration. The spontaneous frequency of rat sinus node was also deeply modified by 7-O-DI, in accordance with previous results obtained in frog cardiac pacemaker cells. It is concluded that 7-O-DI should perform its pharmacological action through calcium entry blockade. These results open expectations for future research about probable therapeutic use for 7-O-DI.

Alkaloids↗
PubMed1993

Effects of the (1-34) fragment of synthetic parathyroid hormone-related protein on tartrate-resistant acid phosphatase and alkaline phosphatase and alkaline phosphatase activities, and on osteocalcin synthesis, in cultured fetal rat calvaria.

In the last years, a parathyroid hormone (PTH)-related peptide (PTHrP) has been isolated from tumors associated with humoral hypercalcemia with malignancy (HHM). In the present work, we studied the effect of bovine PTH (bPTH)(1-34) and PTHrP(1-34) on tartrate-resistant acid phosphatase (TRAP), a marker of bone resorption, and alkaline phosphatase (AP) activities, and basal and vitamin D-stimulated osteocalcin (BGP) synthesis (markers of bone formation) in fetal rat calvaria cultures. After a 48-hour incubation period, both bPTH(1-34) and PTHrP(1-34) caused an increase in TRAP activity liberated in the medium with respect to control cultured calvaria. On the other hand, while after 2 or 4 h of incubation both bPTH(1-34) and PTHrP(1-34) caused a decrease in the AP activity liberated in the medium, after 48 h of incubation both peptides caused a significant increase in the AP liberated in the medium with respect to control cultures. With respect to BGP synthesis, both bPTH(1-34) and PTHrP(1-34) antagonized the 1,25-dihydroxyvitamin D3 stimulatory effect in calvaria cultures. We conclude that PTHrP(1-34) causes similar effects on bone, in organ cultures, to those caused by bPTH(1-34), namely an increase in both bone resorption and formation and a decrease in the vitamin D-stimulated BGP synthesis.

Acid Phosphatase↗
PubMed1992

Genomic structure and chromosomal mapping of the murine CD40 gene.

The B cell-associated surface molecule, CD40, is likely to play a central role in the expansion of Ag-stimulated B cells, and their interaction with activated Th cells. In our study we have isolated genomic clones of murine CD40 from a mouse liver genomic DNA library. Comparison with the murine CD40 cDNA sequence revealed the presence of nine exons that together contain the entire murine CD40 coding region, and span approximately 16.3 kb of genomic DNA. The intron/exon structure of the CD40 gene resembles that of the low affinity nerve growth factor receptor gene, a close homolog of both human and murine CD40. In both cases the functional domains of the receptor molecules are separated onto different exons throughout the genes. Southern blot analysis demonstrated that murine CD40 is a single copy gene that maps in the distal region of mouse chromosome 2.

Amino Acid Sequence↗
PubMed1992

Baboon T cell lymphomas expressing the B cell-associated surface proteins CD40 and Bgp95.

Papio hamadryas baboons in the Sukhumi colony develop enzootic outbreaks of malignant lymphomas with an incidence of about 1.5% per year among adults of the high-risk stock. We investigated the surface phenotypes of cells from normal and lymphomatous animals using antibodies against human lymphocyte antigens. We found that more than 80% of the lymphomas that developed during the last 3 years were characterized histologically to be of the peripheral T cell type. Generally, the lymphomatous cells also expressed high levels of MHC class II DR protein, CD18 (LFA-1 beta chain), and CD45RO. Surprisingly, these cells also expressed on their surface two proteins previously characterized as being relatively B cell-restricted: CD40 and Bgp95. These proteins were never found on the peripheral blood T cells from normal animals. The expression of these two gene products was confirmed by RNA blotting and immunoprecipitation. In most cases, the two B cell-associated proteins were expressed on the predominant T cell subsets; we found both B cell proteins on CD4+, CD8+ as well as on the CD4/8 double-positive cells when these subsets were expressed at high levels. About 90% of these animals are seropositive for Herpesvirus papio and human T cell leukemia virus-1 (HTLV-1) before developing outright lymphomas. In all of the lymphoma samples, HTLV-1 tax DNA sequences were detected by PCR amplification. Whether or not HTLV-1 or the Herpesvirus papio gene products influence the surface expression of CD40 and Bgp95 remains to be determined.

Animals↗
PubMed1992

Myocardial inositol and sodium in diabetes.

Although inhibition of Na(+)-K+ ATPase has been described in the diabetic heart, K+ loss from myocardium has not been observed in a canine model of mild diabetes. The finding of tissue Na+ accumulation and a potential relation to alteration of left ventricular inositol as observed in other tissues in diabetes form the basis of this investigation. Diabetes was induced with alloxan in three groups of male mongrel dogs who were studied after 1 yr. In the initial experiment the tissue compartment volumes, determined with intravenous 51Cr EDTA as a marker, were found to be normal. Calculated cell sodium was increased to 32.8 +/- 2.6 mEq/kg cell H2O vs 18.7 +/- 1.1 in controls (p < 0.01). Cell potassium in diabetes was normal. In the second group, myocardial polyols were analyzed by gas-liquid chromatography. Inositol was diminished in diabetes to 0.61 +/- 23 microM/g of left ventricle, vs the respective control levels of 1.9 +/- 0.57 microM/g (p < 0.02). Sorbitol concentration was unaltered. Left ventricular sodium increments were not associated with altered tissue calcium. In group III the hypothesis that inhibition of Na(+)-K+ ATPase in diabetes might not elicit the expected alteration of K+ transport was assessed during intracoronary infusion of acetyl strophanthidin. No difference in cation responses from control was observed. It is postulated that a change in the conformation of Na(+)-K+ ATPase, with high affinity sodium binding sites facing the intracellular compartment, may render sodium less releasable from cell membrane.

Animals↗
PubMed1992

Myc and Max: a putative transcriptional complex in search of a cellular target.

Biochemical and genetic observations have supported the hypothesis that Myc family proteins function to regulate genes important in cellular growth and differentiation. The recent findings that Myc proteins can associate with other cellular proteins, possess sequence-specific DNA-binding activity and may directly transactivate transcription of several candidate genes have provided an experimental framework in which to test the transcription factor model. Based on principles established for several well characterized viral oncoproteins, a model is presented in which the regulation of Myc function is controlled by specific cellular protein interactions that serve to activate or repress transactivation activity or deny access of the Myc complex to its target sequences.

Animals↗
PubMed1992

Characterization of large-conductance chloride channels in rabbit colonic smooth muscle.

1. A large-conductance Cl- channel was characterized in cell-free membrane patches from the rabbit longitudinal colonic smooth muscle using the patch clamp technique. In addition, the regulation of these channels by neurokinin-1 (NK-1) receptor agonists and G proteins was studied. 2. No spontaneous channel activity was observed in cell-attached patches at the cell resting potential, or in excised patches at pipette potentials (Vp) between -20 and 20 mV. In excised patches, channel activity could be induced in thirty-six out of ninety-six patches by holding the patch at Vp values more negative than -60 mV or more positive than 60 mV. Once induced, the channel showed a bell-shaped voltage activation curve in high symmetric [Cl-], with maximal open probability between 20 and -5 mV. Varying cytosolic calcium concentration ([Ca2+]) between 5 x 10(-8) M and 1.0 mM had no effect on the voltage activation of the channel. 3. In inside-out and outside-out patches, when pipette and bath solutions contained equal [Cl-] (130 mM), the anion channel showed a linear current-voltage (I-V) relationship between -60 and 60 mV with a slope conductance of 309 +/- 20 pS (n = 13). Reversal potential measurements indicated that the channel was selective for Cl- over Na+ and K+ (PCl/PNa = 6:1). 4. Channel openings from the closed state to the full open state as well as transitions through smaller conductance states were observed. The smallest detectable substate had a conductance of 15.6 pS. Based on the similarities in selectivity and linearity of the I-V curve of the smaller conductances with the full open state, and kinetic analysis of channel activity, it is concluded that the large conductance channel is composed of multiple substates which can either open and close independently, or simultaneously via a main gate. 5. The stilbene derivative diiso-thiocyanato-stilbene-disulphonic acid (DIDS) and the diphenylamine-2-carboxylate analogue 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) caused a dose-dependent, reversible flicker block of the small conductance and significantly reduced the macroscopic current flow through the channel. 6. In quiescent outside-out patches, when the pipette contained a 140 mM-CsCl solution with 10(-6) M-CaCl2, 1.2 mM-MgCl2 and 1 mM-GTP, and the bath contained Ringer solution, addition of the NK-1 receptor antagonists substance P methylester resulted in activation of the full conductance state and of smaller substates.(ABSTRACT TRUNCATED AT 400 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗