Terbium ion binding to Limuluspolyphemus hemocyanin

Terbium ion binds to calcium-free $\text{Limulus}$ hemocyanin at pH 7.0 and 8.9, and promotes the aggregation of hemocyanin subunits, a phenomenon associated with calcium binding. An excitation maximum for the bound terbium at 293 nm and the results of treating the hemocyanin with N-bromosuccinimide indicate that energy transfer from tryptophan to the bound terbium is responsible for the enhancement of terbium fluorescence. At pH 8.9, addition of calcium to hemocyanin containing bound terbium results in only a partial loss of terbium fluorescence, suggesting heterogeneity in the terbium binding sites. Titration of hemocyanin with terbium also indicates multiple binding sites.     

New dual inhibitors of EGFR and HER2 protein tyrosine kinases

A novel series of dual EGFR and HER2 inhibitors based on the pyrrolo[2,1-f][1,2,4]triazine nucleus is described. A general route toward their synthesis, which enables functionalization at multiple sites, has been developed. Biological evaluation in enzymatic and cell-based assays has identified a series of C-6 carbamates with potent biochemical and cellular activities.     

Insulation of the chicken beta-globin chromosomal domain from a chromatin-condensing protein,MENT

Active genes are insulated from developmentally regulated chromatin condensation in terminally differentiated cells. We mapped the topography of a terminal stage-specific chromatin-condensing protein, MENT, across the active chicken beta-globin domain. We observed two sharp transitions of MENT concentration coinciding with the beta-globin boundary elements. The MENT distribution profile was opposite to that of acetylated core histones but correlated with that of histone H3 dimethylated at lysine 9 (H3me2K9). Ectopic MENT expression in NIH 3T3 cells caused a large-scale and specific remodeling of chromatin marked by H3me2K9. MENT colocalized with H3me2K9 both in chicken erythrocytes and NIH 3T3 cells. Mutational analysis of MENT and experiments with deacetylase inhibitors revealed the essential role of the reaction center loop domain and an inhibitory affect of histone hyperacetylation on the MENT-induced chromatin remodeling in vivo. In vitro, the elimination of the histone H3 N-terminal peptide containing lysine 9 by trypsin blocked chromatin self-association by MENT, while reconstitution with dimethylated but not acetylated N-terminal domain of histone H3 specifically restored chromatin self-association by MENT. We suggest that histone H3 modification at lysine 9 directly regulates chromatin condensation by recruiting MENT to chromatin in a fashion that is spatially constrained from active genes by gene boundary elements and histone hyperacetylation.     

Free fatty acid-induced peripheral insulin resistance augments splanchnic glucose uptake in healthy humans

To investigate the effect of elevated plasma free fatty acid (FFA) concentrations on splanchnic glucose uptake (SGU), we measured SGU in nine healthy subjects (age, 44 +/- 4 yr; body mass index, 27.4 +/- 1.2 kg/m(2); fasting plasma glucose, 5.2 +/- 0.1 mmol/l) during an Intralipid-heparin (LIP) infusion and during a saline (Sal) infusion. SGU was estimated by the oral glucose load (OGL)-insulin clamp method: subjects received a 7-h euglycemic insulin (100 mU x m(-2) x min(-1)) clamp, and a 75-g OGL was ingested 3 h after the insulin clamp was started. After glucose ingestion, the steady-state glucose infusion rate (GIR) during the insulin clamp was decreased to maintain euglycemia. SGU was calculated by subtracting the integrated decrease in GIR during the period after glucose ingestion from the ingested glucose load. [3-(3)H]glucose was infused during the initial 3 h of the insulin clamp to determine rates of endogenous glucose production (EGP) and glucose disappearance (R(d)). During the 3-h euglycemic insulin clamp before glucose ingestion, R(d) was decreased (8.8 +/- 0.5 vs. 7.6 +/- 0.5 mg x kg(-1) x min(-1), P < 0.01), and suppression of EGP was impaired (0.2 +/- 0.04 vs. 0.07 +/- 0.03 mg x kg(-1) x min(-1), P < 0.01). During the 4-h period after glucose ingestion, SGU was significantly increased during the LIP vs. Sal infusion study (30 +/- 2 vs. 20 +/- 2%, P < 0.005). In conclusion, an elevation in plasma FFA concentration impairs whole body glucose R(d) and insulin-mediated suppression of EGP in healthy subjects but augments SGU.     

Utilization of DNA as a Sole Source of Phosphorus, Carbon, and Energy by Shewanella spp.: Ecological and Physiological Implications for Dissimilatory Metal Reduction

The solubility of orthophosphate (PO₄³⁻) in iron-rich sediments can be exceedingly low, limiting the bioavailability of this essential nutrient to microbial populations that catalyze critical biogeochemical reactions. Here we demonstrate that dissolved extracellular DNA can serve as a sole source of phosphorus, as well as carbon and energy, for metal-reducing bacteria of the genus Shewanella. Shewanella oneidensis MR-1, Shewanella putrefaciens CN32, and Shewanella sp. strain W3-18-1 all grew with DNA but displayed different growth rates. W3-18-1 exhibited the highest growth rate with DNA. While strain W3-18-1 displayed Ca²⁺-independent DNA utilization, both CN32 and MR-1 required millimolar concentrations of Ca²⁺ for growth with DNA. For S. oneidensis MR-1, the utilization of DNA as a sole source of phosphorus is linked to the activities of extracellular phosphatase(s) and a Ca²⁺-dependent nuclease(s), which are regulated by phosphorus availability. Mass spectrometry analysis of the extracellular proteome of MR-1 identified one putative endonuclease (SO1844), a predicted UshA (bifunctional UDP-sugar hydrolase/5′ nucleotidase), a predicted PhoX (calcium-activated alkaline phosphatase), and a predicted CpdB (bifunctional 2′,3′ cyclic nucleotide 2′ phosphodiesterase/3′ nucleotidase), all of which could play important roles in the extracellular degradation of DNA under phosphorus-limiting conditions. Overall, the results of this study suggest that the ability to use exogenous DNA as the sole source of phosphorus is widespread among the shewanellae, and perhaps among all prokaryotes, and may be especially important for nutrient cycling in metal-reducing environments.     

Lactation-associated redistribution of the glial fibrillary acidic protein within the supraoptic nucleus

Summary Three clones of myeloproliferative virus (MPV)-transformed rat fibroblasts (NRK) with different growth properties and morphology were transplanted to athymic nude mice. Presence of carbohydrate-binding proteins was inferred by fluorescence microscopy using fluorescent, glycosylated markers. Salt and detergent extracts of tumors from this model system were fractionated under identical conditions on different sets of Sepharose columns, to which lactose, asialofetuin, melibiose, mannan and fucose had been covalently linked. Successive elution by chelating reagent and specific sugar resulted in isolation of the different Ca²⁺-dependent and Ca²⁺-independent endogenous carbohydrate-binding proteins that were assayable as agglutinins. In comparison, the different tumors displayed a pattern with qualitative and quantitative alterations. Since protein-carbohydrate interaction mediated by carbohydrate-binding proteins (lectins) is of importance for cognitive processes, it is remarkable that the pattern of membrane glycoproteins, isolated by affinity chromatography on resins with immobilized plant lectins, had also been found to reveal certain individual properties for receptors specific for peanut agglutinin (PNA) and Ulex europaeus agglutinin (UEA). These demonstrated differences within the system of protein-carbohydrate interaction suggest that endogenous lectins and their ligands have potential significance as markers defining a certain phenotype within this tumor model system.Dedicated to Prof. Dr. W. Lamprecht on the occasion of his 60th birthday     

A role for cAMP in angiotensin II mediated inhibition of cell growth in AT1A receptor-transfected CHO-K1 cells

G-protein coupled Angiotensin II receptors (AT_1A), mediate cellular responses through multiple signal transduction pathways. In AT_1A receptor-transfected CHO-K1 cells (T3CHO/AT_1A), angiotensin II (AII) stimulated a dose-dependent (EC₅₀=3.3 nM) increase in cAMP accumulation, which was inhibited by the selective AT₁, nonpeptide receptor antagonist EXP3174. Activation of protein kinase C, or increasing intracellular Ca²⁺ with ATP, the calcium ionophore A23187 or ionomycin failed to stimulate cAMP accumulation. Thus, AII-induced cAMP accumulation was not secondary to activation of a protein kinase C- or Ca²⁺/calmodulin-dependent pathway. Since cAMP has an established role in cellular growth responses, we investigated the effect of the AII-mediated increase in cAMP on cell number and [³H]thymidine incorporation in T3CHOA/AT_1A cells. AII (1 M) significantly inhibited cell number (51% at 96 h) and [³H]thymidine incorporation (68% at 24 h) compared to vehicle controls. These effects were blocked by EXP3174, confirming that these responses were mediated through the AT₁ receptor. Forskolin (10 M) and the cAMP analog dibutyryl-cAMP (1 mM) also inhibited [³H]thymidine incorporation by 55 and 25% respectively. We extended our investigation on the effect of AII-stimulated increases in cAMP, to determine the role for established growth related signaling events, i.e., mitogen-activated protein kinase activity and tyrosine phosphorylation of cellular proteins. AII-stimulated mitogen-activated protein kinase activity and phosphorylation of the 42 and 44 kD forms. These events were unaffected by forskolin stimulated increases in cAMP, thus the AII-stimulated mitogen-activated protein kinase activity was independent of cAMP in these cells. AII also stimulated tyrosine phosphorylation of a number of cellular proteins in T3CHO/AT_1A cells, in particular a 127 kD protein. The phosphorylation of the 127 kD protein was transient, reaching a maximum at 1 min, and returning to basal levels within 10 min. The dephosphorylation of this protein was blocked by a selective inhibitor of cAMP dependent protein kinase A, H89-dihydrochloride and preexposure to forskolin prevented the AII-induced transient tyrosine phosphorylation of the 127 kD protein. These data suggest that cAMP, and therefore protein kinase A can contribute to AII-mediated growth inhibition by stimulating the dephosphorylation of substrates that are tyrosine phosphorylated in response to AII.     

Ploidy race distributions since the Last Glacial Maximum in the North American desert shrub, Larrea tridentata

• 1 A classic biogeographic pattern is the alignment of diploid, tetraploid and hexaploid races of creosote bush (Larrea tridentata) across the Chihuahuan, Sonoran and Mohave Deserts of western North America. We used statistically robust differences in guard cell size of modern plants and fossil leaves from packrat middens to map current and past distributions of these ploidy races since the Last Glacial Maximum (LGM).
• 2 Glacial/early Holocene (26–10 ¹⁴C kyr bp or thousands of radiocarbon years before present) populations included diploids along the lower Rio Grande of west Texas, 650 km removed from sympatric diploids and tetraploids in the lower Colorado River Basin of south‐eastern California/south‐western Arizona. Diploids migrated slowly from lower Rio Grande refugia with expansion into the northern Chihuahuan Desert sites forestalled until after ~4.0 ¹⁴C kyr bp . Tetraploids expanded from the lower Colorado River Basin into the northern limits of the Sonoran Desert in central Arizona by 6.4 ¹⁴C kyr bp . Hexaploids appeared by 8.5 ¹⁴C kyr bp in the lower Colorado River Basin, reaching their northernmost limits (~37°N) in the Mohave Desert between 5.6 and 3.9 ¹⁴C kyr bp .
• 3 Modern diploid isolates may have resulted from both vicariant and dispersal events. In central Baja California and the lower Colorado River Basin, modern diploids probably originated from relict populations near glacial refugia. Founder events in the middle and late Holocene established diploid outposts on isolated limestone outcrops in areas of central and southern Arizona dominated by tetraploid populations.
• 4 Geographic alignment of the three ploidy races along the modern gradient of increasingly drier and hotter summers is clearly a postglacial phenomenon, but evolution of both higher ploidy races must have happened before the Holocene. The exact timing and mechanism of polyploidy evolution in creosote bush remains a matter of conjecture.

     

Laminin-10/11 and fibronectin differentially prevent apoptosis induced by serum removal via phosphatidylinositol 3-kinase/Akt- and MEK1/ERK-dependent pathways

Cell adhesion to the extracellular matrix inhibits apoptosis, but the molecular mechanisms underlying the signals transduced by different matrix components are not well understood. Here, we examined integrin-mediated antiapoptotic signals from laminin-10/11 in comparison with those from fibronectin, the best characterized extracellular adhesive ligand. We found that the activation of protein kinase B/Akt in cells adhering to laminin-10/11 can rescue cell apoptosis induced by serum removal. Consistent with this, wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase, or ectopic expression of a dominant-negative mutant of Akt selectively accelerated cell death upon serum removal. In contrast to laminin-10/11, fibronectin rescued cells from serum depletion-induced apoptosis mainly through the extracellular signal-regulated kinase pathway. Cell survival on fibronectin but not laminin was significantly reduced by treatment with PD98059, a specific inhibitor of mitogen- or extracellular signal-regulated kinase kinase-1 (MEK1) and by expression of a dominant-negative mutant of MEK1. Laminin-10/11 was more potent than fibronectin in preventing apoptosis induced by serum depletion. These results, taken together, demonstrate laminin-10/11 potency as a survival factor and demonstrate that different extracellular matrix components can transduce distinct survival signals through preferential activation of subsets of multiple integrin-mediated signaling pathways.