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R Tremblay

Publications and source records attributed to R Tremblay.

At least 37 records · Page 2Linked to original sources
PubMed1995

N-methyl-D-aspartate- or glutamate-mediated toxicity in cultured rat cortical neurons is antagonized by FPL 15896AR.

The neuroprotective action of (S)-alpha-phenyl-2-pyridineethanamine dihydrochloride (FPL 15896AR), a novel noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, was examined in primary rat cortical neuronal cultures. Exposure of cortical cultures to NMDA (50 microM) or glutamate (50 microM) for 15 min resulted in the death of 85-95% of the neurons during the next 24 h. This neurotoxicity was completely eliminated by adding FPL 15896AR (50 microM) to the cultures during the time of NMDA or glutamate exposure. Neuroprotective concentrations of FPL 15896AR also inhibited other acute effects of NMDA. FPL 15896AR (50 microM) prevented the loss of membrane-associated protein kinase C activity that developed by 4 h after transient exposure to 50 microM NMDA or 50 microM glutamate. FPL 15896AR also reduced by approximately 35% the magnitude of NMDA-triggered increases in intracellular free Ca2+ concentration in the cortical cultures. These data indicate that NMDA-mediated toxicity in cultured cortical neurons can be blocked by the NMDA antagonist FPL 15896AR.

Animals↗
PubMed1994

Evidence that the activation of an inactive pool of membrane-associated protein kinase C is linked to the IL-2-dependent survival of T lymphocytes.

The activation of protein kinase C (PKC) is believed to result from the translocation of inactive cytosolic enzyme to the lipid environment of membranes. However, by using a novel method for measuring PKC activity directly in isolated membranes, we have previously shown that a significant proportion of the PKC present in a variety of cells associates with membranes in an inactive state, and that this pool of inactive PKC can be stimulated specifically in cells in the absence of translocation. IL-2 did not stimulate the translocation of PKC to membranes in the IL-2-dependent mouse T cell line, CTLL-2. Nevertheless, a transient, two approximately threefold increase in membrane PKC activity was observed within 10 min of IL-2 addition to these cells. This increase was entirely caused by the activation of a pool of inactive membrane PKC previously associated with the membrane. The inhibition of PKC activity by the specific inhibitors bisindolylmaleimide (BIS) and 1-O-hexadecyl-2-O-methyl-rac-glycerol (AMG) blocked the ability of IL-2 to suppress the onset of apoptosis in IL-2 and serum-deprived CTLL-2 cells. The inhibition of this important function of IL-2 was most pronounced when the PKC inhibitors were added to the medium within 2 h of stimulating the cells with IL-2. The results suggest that transient activation of inactive membrane PKC is linked to the IL-2 receptor signaling, and may be an important step in the mechanism(s) by which the cytokine suppresses cell death in T lymphocytes.

Animals↗
PubMed1994

Purinergic receptor-mediated intracellular Ca2+ oscillations in chicken granulosa cells.

These studies were designed to investigate the effects of extracellular ATP on intracellular calcium ion concentration ([Ca2+]i) and progesterone secretion in granulosa cells obtained from the two largest preovulatory follicles (F1 and F2) of hens. [Ca2+]i was measured in cells loaded with the Ca(2+)-responsive fluorescent dye fura-2. The resting [Ca2+]i in these cells was 99 +/- 7 nM (n = 22). There was a 5.7 +/- 0.7-fold increase in [Ca2+]i in all (n = 140) of the cells within 5 sec of adding a maximally stimulatory concentration (100 microM) of extracellular ATP. The initial spike was followed by [Ca2+]i oscillations that returned to the resting level between spikes. The frequency and amplitude of the [Ca2+]i oscillations were varied and persisted for 1-40 min. [Ca2+]i oscillations were also triggered by 100 microM UTP, UDP, GTP, GDP, ADP, and the nonhydrolyzable analog ATP gamma S. Adenosine, AMP, GMP, and UMP (all at 100 microM) were ineffective. The lowest ATP concentration to trigger a [Ca2+]i response was 1 microM. The sustained oscillatory phase of the response, but not the initial spike, was inhibited by incubating the cells in Ca(2+)-free medium containing 2 mM EGTA. The nucleotide-triggered [Ca2+]i oscillations were not affected by adding the dihydropyridine Ca2+ channel blockers verapamil (100 microM), methoxy-verapamil (D600; 100 microM), or nifedipine (10 microM), before or during the response. However, the oscillations, but not the initial spike, were prevented by pretreating the cells with a general Ca2+ channel blocker, lanthanum (1 mM) or cobalt (5 mM). Lanthanum and cobalt also promptly stopped the [Ca2+]i oscillations when added during the oscillatory phase. The nucleotide-triggered [Ca2+]i response was also abolished by pretreating the cells with an inhibitor of inositol phospholipid hydrolysis, neomycin (1.5 mM). In 3-h incubations, adenosine (100 microM) or ATP (100 microM) did not affect basal or LH (20 or 100 ng/ml)-stimulated progesterone production. These studies demonstrate that chicken granulosa cells display P2 purinergic receptors on their surfaces. Activation of these receptors triggers [Ca2+]i oscillations that follow the release of Ca2+ from internal stores and depend on Ca2+ influx through dihydropyridine-insensitive Ca2+ channels. The physiological function(s) of P2 purinergic receptors on granulosa cells is not known.

Adenosine↗
PubMed1993

A translation-based generation effect in bilingual recall and recognition.

Two experiments were performed with incidental study procedures in which generation effects were observed for relatively balanced French-English bilingual subjects on measures of both free recall and recognition. Experiment 1 used a within-subject design, and Experiment 2 used a between-subject design. In both experiments, reading translations and reading same-language repetitions generally resulted in similar amounts of retention. Experiment 2 and Experiment 3 also showed that the generation effect was abolished under intentional study procedures because of an enhancement of reading-based retention. The results suggested that previous failures to obtain a translation-based generation effect may have been due to the use of intentional study procedures. The pattern of effects was explained in terms of a single-code model of bilingual linguistic representation and an individual-item processing interpretation of the generation effect.

Adult↗
PubMed1992

Evidence that a novel human differentiation-inhibiting protein blocks the dimethyl sulfoxide-induced differentiation of erythroleukemia cells by inhibiting the activation of membrane protein kinase C.

We have previously reported (J. P. Durkin et al., Blood, 79: 1161-1171, 1992) the isolation of a human differentiation-inhibiting protein (DIP) which selectively inhibits and blocks the differentiation of erythroid burst-forming unit progenitor cells in bone marrow colony assay, and the dimethyl sulfoxide (DMSO)-induced differentiation of cultured murine erythroleukemia (MEL) cells. DIP blocks MEL cell differentiation directly, without affecting the ability of the cells to proliferate. In the present study, DIP (at < 1 ng/ml) inhibited MEL cell differentiation only when added to the culture medium within 1 h after DMSO induction, indicating that it blocked an early, critical step in erythroleukemia cell differentiation. The protein kinase C (PKC) inhibitor H-7 also maximally inhibited the differentiation of MEL cells during this same period following induction, suggesting that DIP may have blocked an early PKC-dependent process. Indeed, DIP was found to abolish a transient increase in membrane PKC activity which was triggered in MEL cells within 10-30 min after DMSO addition. This increase in membrane PKC activity resulted from the activation of an inactive pool of PKC residing on membranes, and not from the translocation of cytosolic PKC to membranes. DMSO also stimulated membrane PKC activity and differentiation in human erythroleukemia cells and HL-60 myeloid leukemia cells. As was the case with MEL cells, DIP prevented the early activation of PKC and the differentiation of human erythroleukemia cells. However, it did not inhibit the early increase in PKC activity in HL-60 cells or the subsequent differentiation of these cells. These results suggest that DIP blocks erythroleukemia cell differentiation by inhibiting an early and critical activation of inactive membrane PKC.

Amino Acid Sequence↗
PubMed1992

The activation of inactive membrane-associated protein kinase C is associated with DMSO-induced erythroleukemia cell differentiation.

The rapid redistribution of cytosolic protein kinase C (PKC) to membranes and its subsequent proteolytic activation to PKM have been implicated in the DMSO/HMBA-induced differentiation of murine erythroleukemia (MEL) cells. However, DMSO was found not to induce detectable changes in PKC distribution in a MEL cell subline (MEL1) which differentiated normally in response to the agent. Nevertheless, the differentiation of MEL1 cells appeared dependent on an early PKC-related event because hemoglobinization was partially blocked by the PKC inhibitor H-7 added to cells within the first 2 h after DMSO induction. Indeed, a rapid (15-60 min) increase in membrane PKC activity was detected in DMSO-treated MEL1 cells using a novel method which quantitates the amount of 'active' PKC in intact membranes. This transient PKC increase resulted from the activation of 'inactive' enzyme already associated with membranes, and not from the translocation of cytosolic PKC. Conventional PKC assays cannot distinguish between active and inactive membrane PKC pools. DMSO also activated inactive membrane PKC in HL-60 cells, but not in S49T-lymphoma and WEHI-231 B-lymphoma cells which do not differentiate in response to DMSO. The results suggest that a rapid and transient increase in membrane PKC activity may be an important early step in DMSO-induced differentiation of erythroleukemia cells.

Animals↗
PubMed1992

The identification and characterization of a novel human differentiation-inhibiting protein that selectively blocks erythroid differentiation.

We have isolated a novel inhibitor of erythropoietic differentiation from the plasma of a patient suffering from idiopathic pure red cell aplasia. This differentiation-inhibiting protein (DIP) specifically blocked the differentiation of human burst-forming unit-erythroid (BFU-E), but not colony-forming unit-erythroid (CFU-E) cells. DIP also blocked the maturation of murine BFU-E cells, but not CFU-E or CFU-granulocyte-macrophage cells, and it inhibited the dimethyl sulfoxide (DMSO)-induced differentiation of Friend murine erythroleukemia cells (FLC) at levels between 10(-10) and 10(-12) mol/L. DIP activity was not detectable in the plasma of normal, healthy subjects. Unlike other known inhibitors of hematopoiesis, DIP appears to directly inhibit erythropoietic differentiation, because it did not affect the proliferation of untreated FLC and it effectively blocked FLC hemoglobinization without affecting the ability of the blocked cells to proliferate. DIP blocked FLC differentiation only when added to the culture medium within 1 hour of inducing the cells with DMSO, suggesting that the protein inhibited an early, but critical, DMSO-induced cellular process. DIP appears to be at least partially responsible for the patient's anemia, and its unique activity suggests a role in the early development of some erythroleukemias.

Animals↗
PubMed1991

Characterization of a novel erythropoiesis-inhibiting human protein.

We have isolated an erythropoiesis-inhibiting protein, DIP (differentiation-inhibiting protein), from the blood of a 60-year-old woman suffering from pure red cell aplasia. This protein inhibits the growth and differentiation of normal human and murine BFU-E, but not CFU-E, cells as well as dimethyl sulfoxide-induced hemoglobin synthesis by Friend murine erythroleukemia cells. It appears that DIP primarily affects differentiation rather than proliferation, because it does not inhibit the proliferation of untreated Friend erythroleukemia cells. DIP seems to function like a recently described 45-kDa autocrine differentiation-inhibiting protein factor (ADIF) which is secreted by tsAEV-transformed chicken erythroleukemia cells. Both proteins selectively block the differentiation of normal human and murine BFU-E cells as well as the differentiation (but not the proliferation) of Friend murine erythroleukemia cells. However, the human DIP is not an autocrine product of the patient's bone marrow cells, nor does it affect chicken erythroid cells.

Animals↗
PubMed1990

The role of signal-transducing events in the proliferative response of cells to a mitogenic viral K-ras protein.

Activated oncogenic ras proteins are powerful mitogenic agents which by themselves can initiate and maintain the proliferation of quiescent cells in the absence of any exogenous growth factors. In an attempt to understand how ras proteins induce proliferation we examined the early events in the G0 to G1 transition caused by the activation of a thermolabile K-ras protein in quiescent, serum-starved tsKSV-transformed NRK cells. We show that ras reactivation, in the absence of exogenous growth factors, triggered a rapid surge in free cytosolic Ca2+ and diacylglycerol production, which led to a transient increase in membrane-associated protein kinase C (PKC) activity which was necessary for G1 transit. Unlike TPA-stimulated PKC activity, the ras-induced increase in PKC was readily extracted from membranes by EGTA. These signal transducing events occurred despite the fact that ras activation did not induce the tyrosine phosphorylation of any known surface receptor. The results indicate that the K-ras protein triggers the G0 to G1 transition by an intracellular mechanism and not indirectly via autocrine stimulation.

Animals↗
PubMed1990

Membrane protein kinase C activity rapidly increases in quiescent tsRSV-infected NRK cells upon reactivation of the mitogenic v-src protein kinase.

The viral src protein kinase, pp60v-src, is a powerful intracellular mitogen which can initiate and maintain the proliferation of quiescent cells in the absence of any exogenous growth factors. In an attempt to understand how pp60v-src induces proliferation, we examined the early events in the G0 to G1 transition caused by the activation of a thermolabile v-src protein in quiescent, serum-starved tsRSV-transformed NRK cells. The reactivation of pp60v-src, in the absence of exogenous growth factors, triggered a rapid biphasic surge of membrane-associated protein kinase C (PKC) activity. Unlike TPA-stimulated PKC activity, the pp60v-src-induced increase in PKC was readily extracted from membranes by EGTA. The down-regulation of PKC activity in these quiescent cells by prolonged exposure to TPA strongly inhibited the ability of the reactivated v-src protein to stimulate DNA replication in serum-deficient medium, suggesting that PKC plays a role in the initial signal by which the viral enzyme induces the G0 to G1 transition in NRK cells.

Animals↗
PubMed1987

Molecular cloning and sequence of the cDNA for a 94-amino-acid seminal plasma protein secreted by the human prostate.

The precursor to a seminal plasma protein reported to have inhibin-like activity was characterized through cDNA cloning and sequencing. It is a 114-amino-acid polypeptide which differs from its seminal plasma derivative mainly by the presence of a 20-residue amino-terminal extension, a putative signal sequence, carrying a possible N-glycosylation site. The protein is specified by a single gene per haploid genome. Its mRNA is detectable in the prostate but not in the testis, which suggests that it is primarily a prostatic secretory protein.

Amino Acid Sequence↗
PubMed1977

The control of human WI-38 cell proliferation by extracellular calcium and its elimination by SV-40 virus-induced proliferative transformation.

The proliferative activity of diploid human WI-38 cells in sparse cultures depends on the extracellular concentration of free (or physiologically available) calcium, and cultivation in a medium having a calcium concentration of 0.1 mM or less gradually, but reversibly, arrest their proliferative development in the prereplicative (G1) phase of the cell cycle. Calcium's proliferative control of this cell type is eliminated by proliferative and morphological transformation by the oncogenic SV-40 virus, and the proliferative activity of SV-WI-38 cells in sparse cultures is unaffected by variation of the extracellular free calcium concentration between 0.00 and 1.25 mM.

Calcium↗