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Biomedical subjects

N M Dean

Publications and source records attributed to N M Dean.

At least 73 records · Page 4Linked to original sources
PubMed1991

Personality profiles of Iditarod mushers as compared by finish group.

This study uses a personality profile questionnaire to determine what it is about a person's character that makes them unique to their finish place in the Iditarod Trail Sled Dog Race using data collected from 1988 and 1989. It is the purpose of this study to determine differences in personality that make a musher a top ten finisher as opposed to those who finished in other groups. Mushers were divided into five groups: 1) top ten, 2) 11 to 20, 3) 21 to 30, 4) 31 to last, and 5) scratches. Data was subjected to an analysis of variance (ANOVA) and a Pearson Product-Moment Correlation to determine if any significant distinctions occurred among these groups. A main effect is found in Factor E, Factor F, Factor L, and Factor Q2. In Factor E, Group 1 (top ten finishers) was found to be more aggressive. This group is also more enthusiastic (Factor F). Top mushers are more suspicious and hard to fool (whereas those who finish last are more trusting [Factor L]). Top ten finishers are more group-oriented than the rest of the mushers, inferring that they get along with others and are more helping (Factor Q2). These data suggest that to place in the top ten pack of Iditarod mushers, one must be aggressive, enthusiastic, and calculating.

Adult↗
PubMed1990

Angiotensin II causes phosphatidylinositol turnover and increases 1,2-diacylglycerol mass but is not mitogenic in rat liver T51B cells.

Proliferation in rat liver T51B cells has previously been shown to be initiated by the tyrosine-kinase activator epidermal growth factor. We have found that T51B cells also contain angiotensin II receptors, and, as the transforming mas oncogene has been identified as a functional angiotensin receptor [Jackson, Blair, Marshall, Goedert & Hanley (1988) Nature (London) 335, 437-440], we have investigated the possibility that angiotensin II might also regulate proliferation of T51B cells. Angiotensin II at concentrations up to 10 microM did not promote DNA synthesis, even in the presence of the co-mitogens serum (1%) or 12-O-tetradecanoylphorbol 13-acetate (TPA) (50 ng/ml). The addition of 1 microM angiotensin II to myo-[3H]inositol-radiolabelled T51B cells did however result in a rapid accumulation of multiple inositol phosphates as well as in an increase in intracellular Ca2+, demonstrating the coupling of the angiotensin receptor in these cells to a polyphosphoinositide-hydrolysing phospholipase C. The increases in both inositol phosphates and intracellular Ca2+ were lower in cells pretreated for 10 min with 50 ng of TPA/ml and potentiated by a 24 h pretreatment with TPA. In addition, angiotensin II increased 1,2-diacylglycerol levels. These results demonstrate that, although angiotensin II is capable of increasing phosphoinositide-derived second messengers in T51B cells, these responses are not sufficient to trigger DNA synthesis.

Angiotensin II↗
PubMed1990

PDGF-induced activation of phospholipase C is not required for induction of DNA synthesis.

Platelet-derived growth factor (PDGF) induction of DNA synthesis is believed to involve activation of phospholipase C (PLC) and subsequent accumulation of inositol 1,4,5-triphosphate [I(1,4,5)P3], increase in intracellular Ca2+, activation of protein kinase C (PKC), and receptor down regulation. Generation of these events is triggered by the tyrosine protein kinase (TPK) activity of the PDGF receptor. The TPK inhibitor genistein blocked PDGF induction of these events, including DNA synthesis, with the exception of receptor down regulation. PDGF-induced phosphotyrosine phosphorylations, including receptor autophosphorylation, were inhibited by genistein. Removal of genistein and PDGF resulted in DNA synthesis without the occurrence of PLC activation. These findings indicate that these early events, with the exception of receptor down regulation, are not necessary for PDGF-induced DNA synthesis.

Animals↗
PubMed1990

Retinyl acetate inhibits platelet-derived growth factor-induced Ca2+ signals in C3H 10T1/2 fibroblasts.

Mitogenic stimulation of density-arrested C3H 10T1/2 mouse fibroblasts by serum or purified platelet-derived growth factor (PDGF) was potently inhibited by retinyl acetate (RAc; IC50 = 0.1 microgram/ml, 0.3 x 10(-6) M) when administered during the first 2 hours of mitogen exposure. This inhibitory effect of RAc coincided with a period early in the cell growth-division cycle when density-arrested C3H 10T1/2 cells stimulated by PDGF were found to require physiological levels of extracellular Ca2+ for the transition from G0 to G1 of the cell cycle. To determine if the inhibitory effect of RAc was mediated through alterations in the Ca2+ signaling pathway induced by mitogens, we examined Fura-2-loaded fibroblasts for changes in the Ca2+ response elicited by PDGF. Addition of PDGF (5 ng/ml) induced a transient increase in the [Ca2+]i that was not significantly effected by the extracellular Ca2+ concentration. Treatment of cells with RAc caused a concentration- and time-dependent inhibition of this PDGF-stimulated Ca2+ flux (IC50 = 0.45 microgram/ml or 1.5 x 10(-6) M; t1/2 = 15 min), whereas release of intracellularly stored Ca2+ by thrombin was unaffected by RAc (1.2 micrograms/ml, 4 x 10(-6) M). Treatment with RAc did not significantly affect PDGF binding to cell surface receptors or the generation of inositol phosphates. These results suggest that the mechanism by which RAc inhibits PDGF- or serum-induced mitogenesis is through modulation of the Ca2+ signal stimulated by PDGF, and thereby depriving the cell of a rise in intracellular Ca2+ necessary for progression through the cell cycle.

Animals↗
PubMed1990

Okadaic acid: a reversible inhibitor of neoplastic transformation of mouse fibroblasts.

Okadaic acid (OA) is a potent inhibitor of serine/threonine-specific protein phosphatases types 1 and 2A at nanomolar concentrations in cell-free assays and has tumor promoting activity in vivo. We have found that at non-toxic, nanomolar concentrations, OA concentration dependently inhibits the induction of focus-forming transformed cells by the "complete" and "two-stage" protocols in the C3H/10T1/2 mouse fibroblast transformation assay. This inhibitory effect was fully reversible upon removal of OA from the culture medium of carcinogen-treated cells, indicating that OA was not selectively toxic to initiated or transformed cells. Additional treatment with the phorbol ester tumor promoter, TPA, was required to promote the induction of transformed cells after the removal of OA in the two-stage transformation assay. At concentrations that inhibited neoplastic transformation, OA inhibited a type 2A-like phosphohistone protein phosphatase in homogenates of C3H/10T1/2 cells. It is postulated that OA inhibited an early protein phosphatase-sensitive event in the process of in vitro neoplastic transformation by C3H/10T1/2 fibroblasts and had the effect of maintaining carcinogen-treated cells in an initiated state.

Animals↗
PubMed1989

Effects of the tyrosine-kinase inhibitor genistein on DNA synthesis and phospholipid-derived second messenger generation in mouse 10T1/2 fibroblasts and rat liver T51B cells.

We have examined the effects of the tyrosine kinase inhibitor genistein on hormone dependent cell proliferation and intracellular signalling in mouse 10T1/2 fibroblasts and rat liver T51B epithelial cells. Genistein inhibits both PDGF and EGF induced mitogenesis with an IC50 of 40 uM and 10 uM respectively. Genistein also inhibits inositol phosphate generation and calcium signalling in response to PDGF, and 1,2-diacylglycerol generation and calpactin II translocation in response to EGF. By contrast genistein does not inhibit inositol phosphate production, Ca2+ signalling or 1,2-diacylglycerol generation in response to ATP or angiotensin II. These data demonstrate that genistein selectively inhibits tyrosine kinase dependent processes without effecting similar responses obtained to hormones which are not dependent upon tyrosine kinase activation.

Animals↗
PubMed1989

Methods for the analysis of inositol phosphates.

Interest in the inositol phospholipids was stimulated by the simultaneous discoveries that the products of hydrolysis of these lipids could serve as messengers to activate to synergistic signaling pathways in hormonally responsive cells, namely, inositol 1,4,5-trisphosphate which causes the release of Ca2+ from intracellular stores and diacylglycerol which promotes the activation of protein kinase C. At the same time, Berridge and co-workers introduced relatively simple approaches to study the inositol phospholipid cycle. These included the use of [3H]inositol to label the inositol metabolites, all of which are confined to this cycle, and of Li+ to decrease the rate of degradation of the inositol phosphates. Water-soluble inositol phosphates and chloroform-soluble inositol phospholipids could then be separated by solvent partition and the inositol phosphates further separated by use of an anion-exchange resin. However, the subsequent application of high-performance liquid chromatography as a separation technique indicated the existence of many isomers of the inositol phosphates formed by different pathways of dephosphorylation and phosphorylation. Mapping of these metabolic pathways may be substantially complete, but novel pathways may still be discovered. We review both old and new methods of analysis of the inositol phosphates for the measurement of mass and radioactivity. Although the complexity of the cycle sometimes demands the use of sophisticated methods of separation and rigorous identification, older and inexpensive methods may still be useful for some purposes.

Animals↗
PubMed1988

Inositol 1,3,4,5-tetrakisphosphate induces Ca2+ sequestration in rat liver cells.

Inositol 1,4,5-trisphosphate [I(1,4,5)P3] is a second messenger generated along with diacylglycerol upon the binding of various physiological agents with their cell surface receptors. I(1,4,5)P3 mobilizes Ca2+ from intracellular storage sites through a receptor-coupled mechanism, and the subsequent increased intracellular free calcium ion concentration [( Ca2+]i) activates a multitude of cellular responses. Electropermeabilized neoplastic rat liver epithelial (261B) cells were used to study Ca2+ sequestration, a process that reverses the elevated [Ca2+]i to resting levels and replenishes intracellular Ca2+ pools. Although I (1,4,5)P3-mobilized Ca2+ is readily sequestered into storage pools by the action of Ca2+-adenosine triphosphatases, Ca2+ mobilized by addition of the nonmetabolized inositol trisphosphate isomer I(2,4,5)P3 is not sequestered, suggesting that metabolism is necessary to eliminate the stimulus for Ca2+ release. Several inositol phosphate compounds were examined for their ability to lower the buffer [Ca2+] to determine if a specific I(1,4,5)P3 metabolite might be involved in stimulating Ca2+ sequestration; of these, I(1,3,4,5)P4 alone was found to induce Ca2+ sequestration, demonstrating a physiological role for this inositol trisphosphate metabolite.

Animals↗
PubMed1988

Formation of inositol 1,4,5-trisphosphate and inositol 1,3,4-trisphosphate from inositol 1,3,4,5-tetrakisphosphate and their pathways of degradation in RBL-2H3 cells.

Previous studies with antigen-stimulated rat basophilic leukemia (RBL-2H3) cells indicated the formation of multiple isomers of each of the various categories of inositol phosphates. The identities of the different isomers have been elucidated by selective labeling of [3H]inositol 1,3,4,5-tetrakisphosphate with [32P]phosphate in the 3'-or 4',5'-positions and by following the metabolism of different radiolabeled inositol phosphates in extracts of RBL-2H3 cells. We report here that inositol 1,3,4,5-tetrakisphosphate, when incubated with the membrane fraction of extracts of RBL-2H3 cells, was converted to inositol 1,4,5-trisphosphate and inositol 1,3,4-trisphosphate. Further dephosphorylation of the inositol polyphosphates proceeded rapidly in whole extracts of cells, although the process was significantly retarded when ATP (2 mM) levels were maintained by an ATP-regenerating system. The degradation of inositol 1,4,5-trisphosphate proceeded with the sequential formation of inositol 1,4-bisphosphate, the inositol 4-monophosphate (with smaller amounts of the 1-monophosphate), and finally inositol. Inositol 1,3,4-trisphosphate, on the other hand, was converted to inositol 1,3-bisphosphate and inositol 3,4-bisphosphate and subsequently to inositol 4-monophosphate and inositol 1-monophosphate (stereoisomeric forms were undetermined). The possible implications of the apparent interconversion between inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate in regulating histamine secretion in the RBL-2H3 cells are discussed.

Animals↗
PubMed1988

Metabolism of inositol bis-, tris-, tetrakis- and pentakis-phosphates in GH3 cells.

Previous studies demonstrated a multiplicity of isomers of inositol phosphates in GH3 rat pituitary tumour cells. In order to determine their origin, we have investigated the metabolism of radiolabelled inositol phosphates (IPn) in GH3 cell homogenates by using h.p.l.c. I(1,4,5)P3 is either phosphorylated to I(1,3,4,5)P4 (in the presence of ATP) or dephosphorylated to I(1,4)P2 (in the absence of ATP). I(1,4)P2 is dephosphorylated to I(4)P (greater than 95%). I(1,3,4,5)P4 hydrolysis yields two products. By using dual-labelled [32P, 3H]I(1,3,4,5)P4 with 32P in either the 3 or the 4/5 position, we have identified the probable configuration of these isomers. The predominant (greater than 97%) IP3 formed is I(1,3,4)P3, with a minor I(1,4,5)P3 peak. Subsequent I(1,3,4)P3 hydrolysis yields two IP2 isomers [the major (approximately equal to 85%) is I(3,4)P2; the minor (approximately equal to 15%) is I(1,3)P2] and two IP isomers (the major (approximately equal to 90%) is I(3)P [L-I(1)P], the minor I(4)P). IP5 is very slowly dephosphorylated to and IP4 of undetermined isomeric configuration. We have also examined GH3 cell lipids for the presence of phosphoinositides either more highly phosphorylated than PIP2 (as potential sources of the IP4/IP5 and IP6 in these cells) or phosphorylated in positions other than 1, 4 and 5, and have been unable to find evidence of either. These data suggest two main routes of metabolism for I(1,4,5)P3 in GH3 cells: either (1) phosphorylation to I(1,3,4,5)P4, and the subsequent consecutive dephosphorylation to I(1,3,4)P3, I(3,4)P2 and finally L-I(1)P [D-I(3)P]; or (2) dephosphorylation to I(1,4)P2 and, subsequently, I(4)P.

Animals↗
PubMed1987

The kinetics of phosphoinositide hydrolysis in rat basophilic leukemia (RBL-2H3) cells varies with the type of IgE receptor cross-linking agent used.

We have re-examined, by high pressure liquid chromatographic (HPLC) procedures, the hydrolysis of 3H-labeled inositol phospholipids in rat basophilic leukemia (RBL-2H3) cells. Previous studies showed no clear correlation between the release of any particular inositol metabolite and the calcium signal in these cells. Paradoxically no responses were observed when the cells were stimulated with the antigen, aggregated ovalbumin, in the absence of external Ca2+. We report here that in the absence of external Ca2+ aggregation of the IgE receptor by agents other than aggregated ovalbumin causes the release of small amounts of [3H]inositol phosphates and a small increase in levels of cytosol Ca2+ (approximately 25 nM). The response, however, varied with the type of stimulant used. Within seconds after addition of 24 mol of dinitrophenol conjugated with 1 mol of bovine serum albumin to cells primed with dinitrophenol-specific IgE there was a small burst in release of [3H]inositol 1,4,5-triphosphate, [3H]inositol 1,3,4,5-tetrakisphosphate, and [3H]inositol 1,3,4-trisphosphate which was followed by a gradual rise in inositol 1,3,4-trisphosphate, inositol bisphosphate, and inositol monophosphate. Eventually, all inositol phosphates reached different steady state levels which were maintained for at least 40 min. In contrast, the initial response to oligomeric IgE, which aggregates receptors at a relatively slow rate, was muted although the subsequent development of the response was the same. The levels of inositol pentakisphosphate and hexakisphosphate remained unchanged. These and other studies with cell extracts support the conclusion that inositol 1,4,5-trisphosphate, a putative messenger for release of intracellular Ca2+, was converted to inositol 1,3,4,5-tetrakisphosphate and thence to inositol 1,3,4-trisphosphate. Both trisphosphate metabolites were dephosphorylated in sequential fashion by phosphatase enzymes in the cytosolic and membrane fractions. However, the appearance of several isomers of inositol monophosphates and bisphosphates suggested that degradation proceeded through multiple pathways in the intact cell.

Animals↗
PubMed1987

D-myo-inositol (1,4)-bisphosphate 1-phosphate. Partial purification from rat liver and characterization.

A specific 1-phosphatase acting on myo-inositol (1,4)-biphosphate with a high affinity (Km = 0.9 microM) has been purified 49-fold from soluble proteins of rat liver by anion exchange chromatography followed by gel filtration. This enzyme has a molecular weight of 58,000 as estimated by gel filtration, a pH optimum of 7.5, and requires Mg++ for activity. The only product formed from myo-inositol (1,4)-bisphosphate is the 4-monophosphate. Of 7 other inositol phosphates examined only myo-inositol (1,3,4)-triphosphate was a substrate.

Acid Anhydride Hydrolases↗
PubMed1987

Separation of multiple isomers of inositol phosphates formed in GH3 cells.

A high-performance-liquid-chromatography (h.p.l.c.) separation was developed, which resolves isomers of inositol monophosphate (IP), inositol bisphosphate (IP2), and inositol trisphosphate (IP3) in a single run. In GH3 cells labelled with [3H]inositol, treated with Li+ and thyrotropin-releasing hormone (TRH), radiolabelled components identified as inositol 1-phosphate (I1P), inositol 2-phosphate (I2P), inositol 4-phosphate (I4P), inositol 1,4-bisphosphate [I(1,4)P2], inositol 1,3,4-trisphosphate [I(1,3,4)P3] and inositol 1,4,5-trisphosphate [I(1,4,5)P3] are present, as are multiple unidentified IP2 peaks. After TRH stimulation, both I1P and I4P increase, the increase in I4P preceding that of I1P; I(1,4)P2 and an unknown IP2 increase; and both I(1,3,4)P3 and I(1,4,5)P3 increase, the increase in I(1,4,5)P3 being rapid and transient, whereas the increase in I(1,3,4)P3 is slower and more sustained. The most rapidly appearing inositol phosphates produced after TRH stimulation are I(1,4)P2 and I(1,4,5)P3.

Cell Line↗