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Biomedical subjects

R Poulin

Publications and source records attributed to R Poulin.

At least 127 records · Page 7Linked to original sources
PubMed1993

Enhancement of the spermidine uptake system and lethal effects of spermidine overaccumulation in ornithine decarboxylase-overproducing L1210 cells under hyposmotic stress.

The D-R cell subline, an ornithine decarboxylase-overproducing variant of L1210 mouse leukemia cells, shows a growth advantage at low osmolality due to its high putrescine content. We tested the ability of spermidine to fulfill the role of putrescine under hyposmotic conditions. Although spermidine (1-30 microM) had no effect on growth under normosmotic conditions (325 mosm/kg), it was strongly inhibitory to D-R cell proliferation at 150 mosm/kg in a concentration-dependent manner. Hypotonic shock greatly increased the rate of spermidine uptake in D-R cells. The increased spermidine content enhanced total putrescine synthesis through a large induction of cytosolic spermidine/spermine N1-acetyltransferase activity but also promoted the excretion of most of the putrescine synthesized by the cells. Delaying the addition of spermidine until 24 h after hypotonic shock resulted in a much sharper decrease in D-R cell viability and strongly depressed polyamine contents. These lethal effects occurred between 8 and 24 h after spermidine addition and followed a dramatic increase in the rate and extent of spermidine accumulation which overrode the metabolic capacity of the N1-acetyltransferase/polyamine oxidase (PAO) pathway. Inhibition of PAO partly reversed the effect of spermidine on growth when the polyamine was added at the time of hypotonic shock, but not 24 h later. Similar experiments performed with alpha-methylspermidine, a metabolically resistant analog, which can completely fulfill cellular requirements for spermidine in normosmotic media, suggested that the lethal effect of a delayed spermidine addition is caused predominantly by excessive accumulation with a minor contribution resulting from stress due to polyamine oxidase activity. In contrast, in hypotonically shocked L1210 cells, spermidine stimulated cell proliferation (albeit less effectively than putrescine), there was no lethal effect of a delayed addition of alpha-methylspermidine, and there was no time-dependent increase in the rate of alpha-methylspermidine uptake. Thus, the spermidine transport system is strongly enhanced by hyposmotic shock in D-R cells, which can result in extensive cell death from overaccumulation of the polyamine and, to a lesser extent, from stress related to the PAO-catalyzed degradation of N1-acetylspermidine. The absence of these effects in parental L1210 cells indicates that the acquisition of an ornithine decarboxylase-overproducing phenotype also involves major modifications in the expression and/or regulation of polyamine transport.

Animals↗
PubMed1993

The disparity between observed and uniform distributions: a new look at parasite aggregation.

A simple new measure of parasite aggregation is described, the index of discrepancy (D). It quantifies the difference between the observed parasite distribution, and the hypothetical distribution that corresponds to the ideal case where all hosts harbour the same number of parasites. This index, computed for parasite distributions obtained from the literature, is compared to 2 other measures of aggregation, the variance to mean ratio and the parameter k of the negative binomial distribution. Both k and D indicate that aggregation decreases when the prevalence of infection and the mean number of parasites per host increase, while the variance to mean ratio suggests the opposite. Since an increase in prevalence means that parasites exploit a greater proportion of the available hosts and are thus not concentrating in only a few, aggregation should be inversely proportional to prevalence. Unlike k and D, the variance to mean ratio is a host-centered measure that is not very sensitive to the distribution of parasites. The index of discrepancy, on the other hand, is not only much easier to compute than k, but focuses on the difference between an ideal, uniform distribution and the one actually displayed by parasites. Since what it measures is what parasitologists mean by aggregation, the new index appears to be a more adequate measure of aggregation than other measures currently used.

Animals↗
PubMed1993

The relations of emotionality and regulation to preschoolers' social skills and sociometric status.

The purpose of this study was to examine the relations of emotionality (intensity and negative emotion) and regulation (coping and attentional regulation) to preschoolers' social skills (as rated by adults) and sociometric status. Teachers' ratings of children's constructive coping and attentional control were positively related to boys' social skills and peer status, whereas negative affect was negatively related. Acting out (vs. avoidant) coping and emotional intensity were negatively related to girls' and boys' social skills and boys' peer status. In addition, mothers' reports of boys' coping by seeking social support and low emotional intensity were associated with boys' positive social functioning, whereas avoidant coping was positively related to girls' rated social skills. The results are discussed in relation to research on emotion regulation and coping with emotion in interpersonal contexts.

Adaptation, Psychological↗
PubMed1992

Mechanism of the irreversible inactivation of mouse ornithine decarboxylase by alpha-difluoromethylornithine. Characterization of sequences at the inhibitor and coenzyme binding sites.

Mouse ornithine decarboxylase (ODC) was expressed in Escherichia coli and the purified recombinant enzyme used for determination of the binding site for pyridoxal 5'-phosphate and of the residues modified in the inactivation of the enzyme by the enzyme-activated irreversible inhibitor, alpha-difluoromethylornithine (DFMO). The pyridoxal 5'-phosphate binding lysine in mouse ODC was identified as lysine 69 of the mouse sequence by reduction of the purified holoenzyme form with NaB[3H]4 followed by digestion of the carboxymethylated protein with endoproteinase Lys-C, radioactive peptide mapping using reversed-phase high pressure liquid chromatography and gas-phase peptide sequencing. This lysine is contained in the sequence PFYAVKC, which is found in all known ODCs from eukaryotes. The preceding amino acids do not conform to the consensus sequence of SXHK, which contains the pyridoxal 5'-phosphate binding lysine in a number of other decarboxylases including ODCs from E. coli. Using a similar procedure to analyze ODC labeled by reaction with [5-14C]DFMO, it was found that lysine 69 and cysteine 360 formed covalent adducts with the inhibitor. Cysteine 360, which was the major adduct accounting for about 90% of the total labeling, is contained within the sequence -WGPTCDGL(I)D-, which is present in all known eukaryote ODCs. These results provide strong evidence that these two peptides form essential parts of the catalytic site of ODC. Analysis by fast atom bombardment-mass spectrometry of tryptic peptides containing the DFMO-cysteine adduct indicated that the adduct formed in the enzyme was probably the cyclic imine S-(2-(1-pyrroline)methyl)cysteine. This is readily oxidized to S-((2-pyrrole)methyl)cysteine or converted to S-((2-pyrrolidine)methyl)cysteine by NaBH4 reduction. This adduct is consistent with spectral evidence showing that inactivation of the enzyme with DFMO does not entail the formation of a stable adduct between the pyridoxal 5'-phosphate, the enzyme, and the inhibitor.

Amino Acid Sequence↗
PubMed1992

Determinants of host-specificity in parasites of freshwater fishes.

Factors responsible for interspecific variability in host-specificity were investigated within 15 genera (including 176 species) of metazoan parasites found in Canadian freshwater fish. For each species in a genus, the parasite's number of known hosts was determined from published host-parasite records. The effects of the total number and mean size of potential hosts (i.e. all fish species belonging to the family or families that include a parasite's known hosts) on number of hosts of congeneric species were evaluated using multiple regressions. Since parasite species that have been recorded often tend to have greater numbers of known hosts than do seldom-recorded parasites, it was necessary to control for the confounding effect of study intensity. In all parasite genera, whether from highly specific taxa such as monogeneans or from less host-specific ones, there was a positive relationship between the number of potential hosts and the number of known hosts. However, no consistent relationships were observed between the mean size of potential hosts and number of known hosts. These results suggest that the availability of suitable host species may have been a key factor limiting the colonization of new hosts by fish parasites.

Animals↗
PubMed1992

Toxic pollution and parasitism in freshwater fish.

As aquatic habitats throughout the world are increasingly contaminated with toxic chemicals, toxicologist strive to determine what impact these substances will have an biological systems. So far, the effects of this type of pollution on fish parasites has received little attention, despite their important status as determinants of fish health. Robert Poulin discusses the many ways in which toxic pollution may affect infections of metazoan parasites in freshwater fish. Effects on fish immunity, parasites survival and intermediate host populations are not independent, and currently the outcome of toxic pollution and parasitism in fish is impossible to predict. Future research will have to answer several questions if we are to understand and forecast pollution-mediated changes in parasitism, an urgent challenge for ecotoxicologists and fish parasitologists alike.

Journal Article↗
PubMed1992

Androgens and breast cancer.

We have recently demonstrated that physiological levels of androgens exert direct and potent inhibitory effects on the growth of human breast cancer ZR-75-1 cells in vivo in nude mice as well as in vitro under both basal and estrogen-stimulated conditions. The inhibitory effect of androgens has also been confirmed on the growth of dimethylbenz(a)anthracene (DMBA)-induced mammary carcinoma in the rat. Such observations are in close agreement with the clinical data showing that androgens and the androgenic compound medroxyprogesterone acetate (MPA) have beneficial effects in breast cancer in women comparable to other endocrine therapies, including tamoxifen. Although the inhibitory action of androgens on cell proliferation in estrogen-induced ZR-75-1 cells results, in part, from their suppressive effect on expression of the estrogen receptor, the androgens also exert a direct inhibitory effect independent of estrogens. Androgens cause a global slowing effect on the duration of the cell cycle. These observations support clinical data showing that androgenic compounds induce an objective remission after failure of antiestrogen therapy as well as those indicating that the antiproliferative action of androgens is additive to that of antiestrogens. We have also recently demonstrated in ZR-75-1 human breast cancer cells the antagonism between androgens and estrogens on the expression of GCDFP-15 and GCDFP-24 which are two major proteins secreted in human gross cystic disease fluid. The effects of androgens and estrogens as well as those of progestins and glucocorticoids on GCDFP-15 and GCDFP-24 mRNA levels and secretion are opposite to those induced by the same steroids on cell growth in ZR-75-1 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgens↗
PubMed1991

An early enlargement of the putrescine pool is required for growth in L1210 mouse leukemia cells under hypoosmotic stress.

Hypoosmotic stress is a potent inducer of ornithine decarboxylase (ODC) activity in a variety of mammalian cells, but the physiological relevance of this response has not been determined. To test whether an increased putrescine content confers a growth advantage at lower osmolarities, we compared the ability of L1210 mouse leukemia cells and of ODC-overproducing variants obtained from this cell line (D-R cells) to proliferate after a hypotonic shock (325----130 mosmol/kg). The growth rate of D-R cells at 130 mosmol/kg was greater than or equal to 5-fold higher than in L1210 cells; and unlike the ODC-overproducing strain, L1210 cells underwent up to a 90% loss of viability over time as seen after restoration of normosmotic growth conditions and by trypan blue exclusion tests. The addition of putrescine or L-ornithine stimulated the proliferation of both cell sublines up to 5-fold in a concentration-dependent manner, with a maximal effect observed at about 10 and 100 microM, respectively. Putrescine restored virtually normal growth rates in both sublines at osmolarities as low as 190 mosmol/kg. No other alpha,omega-diamine was active in that respect whereas spermidine was markedly inhibitory. Furthermore, D-R cells incubated at 130 mosmol/kg showed a marked growth inhibition by 1-aminooxy-3-aminopropane (potent ODC inhibitor to which they are resistant in isotonic media) as a result of putrescine but not spermidine depletion. Whereas ODC was strongly and rapidly induced by hypotonic shock there was a precipitous decline in S-adenosylmethionine decarboxylase activity. Putrescine synthesis and accumulation were nevertheless reduced in D-R cells incubated at 130 mosmol/kg because of a decreased availability of L-ornithine. When either putrescine or L-ornithine was added to hypotonic media, D-R cells accumulated putrescine massively for extended periods together with a reduction in spermidine and spermine contents. Putrescine transport patterns were altered by hypotonic shock, net excretion of the diamine being reduced by about 80%, with a concurrent enlargement of the intracellular pool. Finally, parental L1210 cells incubated with an irreversible inhibitor of S-adenosylmethionine decarboxylase for 24 h until hypotonic shock and supplemented with putrescine in the presence of the drug thereafter exhibited a greatly exaggerated growth stimulation by the diamine. These results demonstrate an essential role for an early increase in putrescine content in the growth adaptation of a mammalian cell line to a lower osmolarity.

Adenosylmethionine Decarboxylase↗
PubMed1991

Personality and socialization correlates of vicarious emotional responding.

The relations of personality and family characteristics to adults' negative vicarious emotional responses to sympathy and distress films were examined. Ss reported more sympathy and less personal distress and exhibited less skin conductance as well as heart rate deceleration when viewing a sympathy-evoking film. Dispositional emotional intensity and fantasy empathy were associated with greater self-reported emotional responding and higher skin conductance. Dispositional perspective taking and personal distress were positively and negatively correlated, respectively, with reported vicarious responding to the sympathy film when Ss were administered instructions to imagine the emotions of those in the films. Family cohesiveness was associated with reported sympathy and sadness in reaction to the sympathy film, whereas the expression of negative subordinate and positive emotional states in the home of origin was associated with women's reported responsivity.

Adult↗
PubMed1990

Regulation of ornithine decarboxylase expression by anisosmotic shock in alpha-difluoromethylornithine-resistant L1210 cells.

Ornithine decarboxylase (ODC) activity is known to be strongly enhanced in mammalian cells by a sudden reduction in ambient osmolality. The effect of hypoosmotic shock on the regulation of ODC protein and mRNA levels was studied in a variant L1210 mouse leukemia cell line (D-R cells) which expresses ODC at greater than or equal to 100-fold higher levels than the parental cells. Hypoosmotic stress increased ODC activity in proportion with the osmotic gradient imposed to both D-R cells and their normal counterparts. A 60% decrease in medium osmolality increased ODC activity and the amount of immunoreactive ODC protein from 20- to 30-fold after 4 h without any detectable change in ODC mRNA contents in D-R cells. ODC induction was sustained up to 48 h after hypoosmotic shock, with maximal activity levels being observed at 24 h. Hypotonic shock dramatically increased (up to 36-fold) the rate of ODC synthesis as measured by 10-min pulses with 35S-labeled methionine, in agreement with kinetic constants predicted from the changes observed for the enzyme activity. Moreover, hypoosmotic stress extended the half-life of ODC activity from 35 +/- 10 to 212 +/- 67 min and blocked any degradation of the radiolabeled immunoreactive protein, which had a half-life of 28 +/- 6 min under isotonic conditions, for at least 120 min after addition of cycloheximide. The induction of ODC by hypoosmotic stress was quickly reversed by a sudden upshift of osmolality through a very rapid inhibition of ODC biosynthesis and an increase in the rate of enzyme degradation. Thus, hypoosmotic stress activates the expression of ODC exclusively through post-transcriptional mechanisms in D-R cells. The osmotically induced accumulation of ODC molecules is quite unique as shown by the fact that ODC is the major protein (approximately 25% of total) synthesized during the first 4 h following a 60% hypotonic shock, despite a 30-50% reduction of the rate of labeled precursor incorporation into soluble proteins.

Animals↗
PubMed1990

Wide spectrum of steroids serving as substrates for the formation of lipoidal derivatives in ZR-75-1 human breast cancer cells.

Recently, several natural steroids have been found to be esterified to long-chain fatty acids (FAE) in various mammalian tissues. The purpose of the present study was to determine the ability of a series of 3H-labeled steroids to serve as substrates for the formation and accumulation of such non-polar derivatives in intact cells, using the hormone-responsive ZR-75-1 human breast cancer cell line as model. All 14 steroids tested were found to be converted, directly or following further metabolism, to lipoidal ester derivatives. The percentage of intracellular steroids recovered as FAE derivatives was usually substantial (14-90%), especially in the case of C-19 steroids (75-90%). The composition of the lipoidal steroid fractions recovered from the labeled cell extracts was characterized by chromatographic comparison with synthetic steroid FAEs and by saponification of the steroid FAEs and identification of the released steroidal moieties. Following metabolism, most steroid substrates were converted into multiple lipoidal esters. Furthermore, 5 alpha-androstane-3 alpha, 17 beta-diol, 5 alpha-androstane-3 beta, 17 beta-diol, as well as androst-5-ene-3 beta, 17 beta-diol formed lipoidal diesters in addition to the monoester form. The high level of intracellular steroid FAE accumulation reported in this study suggests that these yet poorly known steroid derivatives may play important functions in the regulation of steroid hormone metabolism and action.

Breast Neoplasms↗
PubMed1990

Responses of the fish ectoparasite Salmincola edwardsii (Copepoda) to stimulation, and their implication for host-finding.

The short-lived infective copepodid stages of the copepod Salmincola edwardsii, ectoparasitic on brook trout, Salvelinus fontinalis, are under strong selective pressure to evolve efficient host-finding mechanisms. In laboratory experiments, we quantified the effects of visual and mechanical stimulation on the activity of the copepodids. We found that shadows passing above the copepodids and shock waves passing through the water generated marked increases in the rate and length of upward swimming bursts, which resulted in more time spent suspended in the water column and greater distances travelled. However, we found no strong evidence for a relationship between the magnitude of the copepodids' response and the intensity of stimulation. Although these responses are not host-specific, they allow the parasites to conserve their limited energy stores by increasing their host-finding activity only when potential hosts are nearby.

Analysis of Variance↗
PubMed1990

Interactions between estrogens, androgens, progestins, and glucocorticoids in ZR-75-1 human breast cancer cells.

The human breast cancer cell line ZR-75-1 possesses androgen, estrogen, progesterone, and glucocorticoid receptors, thus offering a good model to study the specific role of each class of steroids in the control of breast cancer growth. Although the stimulatory action of classical estrogens (E2 and estrone) is well known, we have found a potent mitogenic effect of the adrenal estrogen androst-5-ene-3 beta,17 beta-diol (delta 5-diol) at concentrations within the range of those found in the serum of adult women, thus suggesting that delta 5-diol might be the most important estrogen in women. Androgens, on the other hand, exert a potent inhibitory effect on basal ZR-75-1 cell growth and completely reverse the stimulatory effect of estrogens on the same parameter. The antiproliferative effect of androgens was completely prevented by the antiandrogen OH-FLU, thus suggesting an action mediated by the androgen receptor. Part of the effect of androgens can be explained by the marked inhibition of estrogen receptor binding and mRNA levels by androgens. The antiproliferative effect of androgens is additive to that exerted by antiestrogens. Progestins, on the other hand, exert a specific antiproliferative effect in the presence of estrogens, the effect of progestins being antagonized by the stimulatory action of insulin on cell growth. Medroxyprogesterone acetate (MPA), a compound frequently used in the treatment of breast cancer in women, exerts its main inhibitory action through an androgen receptor-mediated action, whereas its glucocorticoid-like activity could play an additional role at high concentrations. All four classes of steroids are present, to various extents, as lipophilic esters of long-chain fatty acids. It is of interest to mention that all steroids that inhibit ZR-75-1 breast cancer cell growth (androgens, progestins, and glucocorticoids) stimulate the secretion and mRNA levels of gross cystic disease fluid protein-15 (GCDFP-15), whereas estrogens have the opposite effects, thus suggesting that GCDFP-15 could well be a good marker for monitoring the response to androgens, progestins, and antiestrogens during the course of breast cancer therapy.

Androgens↗
PubMed1990

Identification of a 51-kilodalton calmodulin binding protein that changes during estrogen-stimulated cell growth.

Calmodulin-binding proteins (CaMBPs) were analyzed during estrogen-stimulated growth in the human breast cancer cell line ZR-75-1. A variety of Ca2(+)-dependent and -independent CaMBPs were observed to be present in these cells. Calmodulin (CaM) binding to a 51-kilodalton protein was shown to be Ca2(+)-dependent. Moreover, binding to this protein was reduced in the estrogen-treated cells. This effect occurred early during estrogen-stimulated cell growth and was maintained during exponential growth in the presence of estrogen. 125I-labeled CaM overlay procedure of two-dimensional polyacrylamide gels reveals that this 51-kilodalton protein is composed of at least two distinct isoforms with different isoelectric points. Subcellular localization demonstrates that this protein resides exclusively in the microsomal fraction.

Breast Neoplasms↗
PubMed1989

Effect of S-adenosyl-1,12-diamino-3-thio-9-azadodecane, a multisubstrate adduct inhibitor of spermine synthase, on polyamine metabolism in mammalian cells.

The effects of the potent spermine synthase inhibitor S-adenosyl-1,12-diamino-3-thio-9-azadodecane (AdoDatad) on polyamine biosynthesis have been studied in transformed mouse fibroblasts (SV 3T3 cells) and in mouse leukemia cells (L1210). A dose-dependent decrease in intracellular spermine concentration was observed in both cell lines when grown in the presence of the inhibitor. A major difference in the effects seen in these two cell lines was the cytotoxicity observed in L1210 cells exposed to the inhibitor, which contrasted with little or no effects on growth of SV 3T3 cells treated similarly. Oxidative metabolism of the drug in L1210 cells was suggested by the fact that addition of aminoguanidine, an amine oxidase inhibitor, to the cell cultures ablated the cytotoxic effects of the inhibitor. Complete analysis of intracellular polyamines was carried out, together with analysis of S-adenosylmethionine, decarboxylated S-adenosylmethionine, and the inhibitor. These analyses revealed that, although the inhibitor had a dramatic effect on spermine biosynthesis in the cells studied, a compensatory increase in spermidine biosynthesis was observed. This resulted in no change in total polyamine concentrations in cells treated with inhibitors of either spermine synthase or spermidine synthase (Pegg et al., 1982) alone or in combination. In all cases, the concentration of the aminopropyl donor decarboxylated S-adenosylmethionine increased dramatically, thus allowing for the observed maintenance of total polyamine levels even in the presence of either one or both potent inhibitors of the aminopropyltransferases. Oxidative metabolism of the inhibitor complicates the interpretation of experiments carried out in the absence of amine oxidase inhibitors such as aminoguanidine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1989

Effect of 1-amino-oxy-3-aminopropane on polyamine metabolism and growth of L1210 cells.

1-Amino-oxy-3-aminopropane (AOAP) was reported to inhibit several mammalian polyamine-biosynthetic enzymes in vitro, including ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC) [Khomutov, Hyvönen, Karvonen, Kauppinen, Paalanen, Paulin, Eloranta, Pajula, Andersson & Pösö (1985) Biochem. Biophys. Res. Commun. 130, 596-602]. In order to clarify its mechanism of action in intact cells, the inhibitory properties of AOAP on the growth and polyamine metabolism of L1210 cells were compared with those seen in a variant subline (D-R cells) which overproduces ODC. As little as 20 microM-AOAP completely blocked proliferation of L1210 cells, and this effect was reversed by the concomitant addition of exogenous putrescine or spermidine. Growth of D-R cells was not affected by AOAP at concentrations up to 0.5 mM. There was no difference in the uptake of AOAP between the L1210 and the D-R cells. Exposure of L1210 or D-R cells to AOAP greatly decreased ODC activity in undialysed cell extracts, but did not decrease AdoMetDC. Activities of both enzymes were increased severalfold by AOAP treatment when activity was measured in dialysed extracts. Treatment with AOAP depleted intracellular putrescine and spermidine contents of L1210 cells, while inducing a massive accumulation of decarboxylated AdoMet. The 8-fold higher putrescine pool present in untreated D-R cells was depleted in a dose-dependent manner by AOAP, but a significant decrease in spermidine and accumulation of decarboxylated AdoMet required 10 times higher drug concentrations, and the changes were much less dramatic than in L1210 cells. These results indicate that in L1210 cells AOAP behaves primarily as a reversible inhibitor of ODC.

Adenosylmethionine Decarboxylase↗