The PLoS community journals

2005 will see the launch of three new open access journals from the Public Library of Science - PLoS Computational Biology, PLoS Genetics, and PLoS Pathogens.     

Differences in monoamine oxidase activity between cultured noradrenergic and cholinergic sympathetic neurons

Two types of monoamine oxidase activity (MAO-A and MAO-B) help regulate the levels of biogenic amines such as catecholamines and serotonin. Although MAO-A has greater activity toward most catecholamines than MAO-B, no direct experiments have determined the types and levels of MAO activity that are normally expressed in noradrenergic neurons. Noradrenergic neurons from neonatal rat superior cervical ganglia were isolated and cultured under conditions that permit either continued expression of the noradrenergic phenotype or promote a transition to a predominantly cholinergic phenotype. After 14-21 days in vitro, neurons from both types of cultures were assayed for the type and amount of monoamine oxidase activity using tryptamine, a common substrate for both MAO-A and MAO-B. Neurons cultured under noradrenergic conditions expressed sevenfold greater MAO activity than neurons cultured under cholinergic conditions. Essentially all MAO activity in the noradrenergic cultures was inhibited by preincubation with 10(-8)-10(-9) M clorgyline, which indicated that this activity was primarily MAO-A. Cultures grown under cholinergic conditions exhibited 6- to 10-fold lower MAO-A activity and an 8- to 10-fold lower level of catecholamine synthesis from labeled precursors compared to neurons grown under noradrenergic conditions. These results directly demonstrate that high MAO-A activity is expressed in noradrenergic neurons in vitro. The corresponding decreases in both MAO-A specific activity and catecholamine synthesis as neurons become cholinergic in vitro suggest that the expression of the noradrenergic phenotype involves the coordinate regulation of degradative as well as synthetic enzymes involved in catecholamine metabolism.     

Correlation of changes in cardiac calcium channels with hemodynamics in Syrian hamster cardiomyopathy and heart failure

We compared hemodynamics with [3H]nitrendipine (calcium channel) binding to cardiac membranes from Bio 14.6 cardiomyopathic Syrian hamsters at 4 and 10 months with their F1B controls. A 50% increase in the number (Bmax) of nitrendipine binding sites (calcium channels) was seen only in the 4 month old myopathic vs controls (Bmax = 468 +/- 11 vs 309 +/- 10 fmol/mg prot with no change in affinity (KD) (KD = .65 +/- .12 vs .75 +/- .14 nM), while no differences in Bmax or KD were seen at 10 months (Bmax = 375 +/- 9 vs 362 +/- 7 fmol/mg prot/KD = .82 +/- .18 vs .89 +/- .17 nM) myopathic vs control respectively. Hemodynamic studies revealed no significant differences in cardiac output, cardiac index, stroke volume, heart rate, mean arterial pressure, peripheral resistance, body weight, heart weight at 4 months, but a significant decrease in peripheral resistance (1120 +/- 360 vs 2080 +/- 240) increase in body weight (118 +/- 2 vs 94 +/- 2 grams) and heart weight (97 +/- 5 vs 78 +/- 2 gms/100 gms body weight) in 10 month myopathic vs control animals. We conclude that the onset of cardiomyopathy at 4 months is associated with a selective increase in calcium channel binding sites and heart failure at 10 months is associated with a relative decrease in these sites.     

Identification of transglutaminase substrates in HT29 colon cancer cells: use of 5-(biotinamido)pentylamine as a transglutaminase-specific probe.

A biotinamine probe, 5-(biotinamido)pentylamine, was used for biotin-labeling of proteins in HT29 colon cancer cell extracts by endogenous transglutaminase activity. The biotin-labeled protein substrates were isolated and recovered by avidin-affinity chromatography. The proteins were separated using SDS-polyacrylamide gel electrophoresis, electroblotted onto a polyvinylidene difluoride membrane, visualized using Coomassie blue, cut out, and sequenced. Amino acid sequence data identified human fructose-1,6-bisphosphate aldolase A, an intracellular protein, as a substrate for cellular transglutaminase.     

Transport of galectin-3 between the nucleus and cytoplasm. I. Conditions and signals for nuclear import

Galectin-3, a factor involved in the splicing of pre-mRNA, shuttles between the nucleus and the cytoplasm. We have engineered a vector that expresses the fusion protein containing the following: (a) green fluorescent protein as a reporter of localization, (b) bacterial maltose-binding protein to increase the size of the reporter polypeptide, and (c) galectin-3, whose sequence we wished to dissect in search of amino acid residues vital for nuclear localization. In mouse 3T3 fibroblasts transfected with this expression construct, the full-length galectin-3 (residues 1-263) fusion protein was localized predominantly in the nucleus. Mutants of this construct, containing truncations of the galectin-3 polypeptide from the amino terminus, retained nuclear localization through residue 128; thus, the amino-terminal half was dispensable for nuclear import. Mutants of the same construct, containing truncations from the carboxyl terminus, showed loss of nuclear localization. This effect was observed beginning with truncation at residue 259, and the full effect was seen with truncation at residue 253. Site-directed mutagenesis of the sequence ITLT (residues 253-256) suggested that nuclear import was dependent on the IXLT type of nuclear localization sequence, first discovered in the Drosophila protein Dsh (dishevelled). In the galectin-3 polypeptide, the activity of this nuclear localization sequence is modulated by a neighboring leucine-rich nuclear export signal.