Linker histone subtype composition and affinity for chromatin in situ in nucleated mature erythrocytes

The replacement linker histones H1(0) and H5 are present in frog and chicken erythrocytes, respectively, and their accumulation coincides with cessation of proliferation and compaction of chromatin. These cells have been analyzed for the affinity of linker histones for chromatin with cytochemical and biochemical methods. Our results show a stronger association between linker histones and chromatin in chicken erythrocyte nuclei than in frog erythrocyte nuclei. Analyses of linker histones from chicken erythrocytes using capillary electrophoresis showed H5 to be the subtype strongest associated with chromatin. The corresponding analyses of frog erythrocyte linker histones using reverse-phase high performance liquid chromatography showed that H1(0) dissociated from chromatin at somewhat higher ionic strength than the three additional subtypes present in frog blood but at lower ionic strength than chicken H5. Which of the two H1(0) variants in frog is expressed in erythrocytes has thus far been unknown. Amino acid sequencing showed that H1(0)-2 is the only H1(0) subtype present in frog erythrocytes and that it is 100% acetylated at its N termini. In conclusion, our results show differences between frog and chicken linker histone affinity for chromatin probably caused by the specific subtype composition present in each cell type. Our data also indicate a lack of correlation between linker histone affinity and chromatin condensation.     

The matrix metalloproteinase 9 (mmp-9) hemopexin domain is a novel gelatin binding domain and acts as an antagonist

Matrix metalloproteinases (MMPs) are involved in the remodeling processes of the extracellular matrix and the basement membrane. Most MMPs are composed of a regulatory, a catalytic, and a hemopexin subunit. In many tumors the expression of MMP-9 correlates with local tumor growth, invasion, and metastasis. To analyze the role of the hemopexin domain in these processes, the MMP-9 hemopexin domain (MMP-9-PEX) was expressed as a glutathione S-transferase fusion protein in Escherichia coli. After proteolytic cleavage, the isolated PEX domain was purified by size exclusion chromatography. In a zymography assay, MMP-9-PEX was able to inhibit MMP-9 activity. The association and dissociation rates for the interaction of MMP-9-PEX with gelatin were determined by plasmon resonance. From the measured rate constants, the dissociation constant was calculated to be K(d) = 2,4 x 10(-8) m, demonstrating a high affinity between MMP-9-PEX and gelatin. In Boyden chamber experiments the recombinant MMP-9-PEX was able to inhibit the invasion of melanoma cells secreting high amounts of MMP-9 in a dose-dependent manner. These data demonstrate for the first time that the hemopexin domain of MMP-9 has a high affinity binding site for gelatin, and the particular recombinant domain is able to block MMP-9 activity and tumor cell invasion. Because MMP-9 plays an important role in metastasis, this antagonistic effect may be utilized to design MMP inhibition-based cancer therapy.     

Cholera toxin B pretreatment of macrophages and monocytes diminishes their proinflammatory responsiveness to lipopolysaccharide

The cholera toxin B chain (CTB) has been reported to suppress T cell-dependent autoimmune diseases and to potentiate tolerance of the adaptive immune system. We have analyzed the effects of CTB on macrophages in vitro and have found that preincubation with CTB (10 microg/ml) suppresses the proinflammatory reaction to LPS challenge, as demonstrated by suppressed production of TNF-alpha, IL-6, IL-12(p70), and NO (p < 0.01) in cells of macrophage lines. Pre-exposure to CTB also suppresses LPS-induced TNF-alpha and IL-12(p70) formation in human PBMC. Both native and recombinant CTB exhibited suppressive activity, which was shared by intact cholera toxin. In cells of the human monocyte line Mono Mac 6, exposure to CTB failed to suppress the production of IL-10 in response to LPS. Control experiments excluded a role of possible contamination of CTB by endotoxin or intact cholera toxin. The suppression of TNF-alpha production occurred at the level of mRNA formation. Tolerance induction by CTB was dose and time dependent. The suppression of TNF-alpha and IL-6 production could be counteracted by the addition of Abs to IL-10 and TGF-beta. IFN-gamma also antagonized the actions of CTB on macrophages. In contrast to desensitization by low doses of LPS, tolerance induction by CTB occurred silently, i.e., in the absence of a measurable proinflammatory response. These findings identify immune-deviating properties of CTB at the level of innate immune cells and may be relevant to the use of CTB in modulating immune-mediated diseases.     

Use of stable isotopically labeled tracers to measure very low density lipoprotein-triglyceride turnover

Tracer methods for VLDL-TG kinetics vary in their ability to account for the effect of tracer recycling, which can influence the calculation of VLDL-TG fractional catabolic rates (FCRs). We evaluated a novel approach, involving stable isotopically labeled glycerol or palmitate tracers in conjunction with compartmental modeling, for measuring VLDL-TG kinetics in normolipidemic human subjects. When administered as a bolus simultaneously, both tracers provided identical VLDL-TG FCRs when the data were analyzed by a compartmental model that accounted for hepatic lipid tracer recycling, but not by non-compartmental analysis. The model-derived FCR was greater than that determined using a non-compartmental approach, and was 2- to 3-fold higher than that usually reported by using a bolus of radioactive [3H]glycerol. When palmitate tracer was given as a constant infusion, VLDL-TG turnover appeared 5-fold slower, because tracer recycling through hepatic lipid pools could not be resolved with the infusion protocol. We conclude that accounting for tracer recycling, particularly the contribution of hepatic glycerolipid pools, is essential to accurately measure VLDL-TG kinetics, and that bolus injection of stable isotopically labeled glycerol or palmitate tracers in conjunction with compartmental modeling analysis offers a reliable approach for measuring VLDL-TG kinetics.     

A partial skeleton of Prodeinotherium bavaricum (Proboscidea, Mammalia) from the Middle Miocene of Unterzolling (Upper Freshwater Molasse, Germany)

Here, a partial skeleton of Prodeinotherium bavaricum from Unterzolling (Southern Germany) is documented. The following elements are preserved and described for the first time: cervical vertebrae 1-2 and 5-7, the first thoracic vertebra, one lumbar vertebra, trapezium, metacarpals 1-5, tibia, calcaneus, endo- and mesocuneiform, cuboid, the fourth metatarsal, and some phalanges. Comparisons with the skeletons of P. bavaricum from Franzensbad (Czech Republic) and Deinotherium giganteum from Eserovo (Bulgaria) show osteological differences that are described and discussed.     

Drought until death do us part: a case study of the desiccation-tolerance of a tropical moist forest seedling-tree,Licania platypus (Hemsl.) Fritsch

Studies of the desiccation tolerance of 15-month-old Licania platypus (Hemsl.) Fritsch seedlings were performed on potted plants. Pots were watered to field capacity and then dehydrated for 23-46 d to reach various visible wilting stages from slightly-wilted to dead. Root hydraulic conductance, k(r), was measured with a high-pressure flow meter and whole-stem hydraulic conductance, k(ws), was measured by a vacuum chamber method. Leaf punches were harvested for measurement of leaf water potential by a thermocouple psychrometer and for measurement of fresh- and dry-weight. L. platypus was surprisingly desiccation-tolerant, suggesting that most species of central Panama may be well adapted to the seasonality of rainfall in the region. The slightly-wilted stage corresponded to leaf water potentials and relative water contents of -2.7 MPa and 0.85, respectively, but plants did not die until these values fell to -7.5 MPa and 0.14, respectively. As desiccation proceeded k(r) and k(ws) declined relative to irrigated controls, but k(ws) was more sensitive to desiccation than k(r). Values of k(ws) declined by 70-85% in slightly-wilted to dead plants, respectively. By comparison, k(r) showed no significant change in slightly-wilted plants and fell by about 50% in plants having severely-wilted to dead shoots.     

Identification of K(+) channels in the plasma membrane of maize subsidiary cells

The stomatal complex of Zea mays consists of two guard cells with the pore in between them and two flanking subsidiary cells. Both guard cells and subsidiary cells are important elements for stoma physiology because a well-coordinated transmembrane shuttle transport of potassium and chloride ions occurs between these cells during stomatal movement. To shed light upon the corresponding transport systems from subsidiary cells, subsidiary cell protoplasts were enzymatically isolated and in turn, analyzed with the patch-clamp technique. Thereby, two K(+)-selective channel types were identified in the plasma membrane of subsidiary cells. With regard to their voltage-dependent gating behavior, they may act as hyperpolarization-dependent K(+) uptake and depolarization-activated K(+) release channels during stomatal movement. Interestingly, the K(+) channels from subsidiary cells and guard cells similarly responded to membrane voltage as well as to changes in the K(+) gradient. Further, the inward- and outward-rectifying K(+) current amplitude decreased upon a rise in the intracellular free Ca(2+) level from 2 nM to the micro M-range. The results indicate that the plasma membrane of subsidiary cells and guard cells has to be inversely polarized in order to achieve the anti-parallel direction of K(+) fluxes between these cell types during stomatal movement.