Structural and functional characteristics of activated human factor IX after chemical modification of gamma-carboxyglutamic acid residues

Activated human factor IX (factor IXa) was treated under mildly acidic conditions with a mixture of formaldehyde and morpholine. This reagent has been shown to react preferentially with gamma-carboxyglutamyl (Gla) residues and to convert these residues to gamma-methyleneglutamyl residues (Wright, S.F., Bourne, C.D., Hoke, R.A., Koehler, K.A., and Hiskey, R.G. (1984) Anal. Biochem. 139, 82-90). The modified enzyme was evaluated for coagulant activity and calcium-dependent fluorescence quenching. [14C]Formaldehyde was employed to allow quantitation of the modification and to facilitate localization of the modified residues in the primary structure of factor IXa. In the presence of the [14C]formaldehyde/morpholine reagent, factor IXa rapidly lost coagulant activity, which corresponded to incorporation of radiolabel. Examination of the relationship between protein modification (radiolabel incorporation) and the loss of coagulant activity suggested that modification of 1 mol of Gla/mol of factor IXa results in complete loss of factor IXa coagulant activity. Primary structure analysis of the radioactivity labeled factor IXa suggested that modification of any one of 11 Gla residues was responsible for the loss of coagulant activity. In the presence of calcium, modified factor IXa exhibited a smaller Gla-dependent decrease in protein fluorescence than native factor IXa, but the Gla-independent fluorescence change was the same for both proteins. It therefore appears that the Gla domain of factor IXa must be completely intact for the enzyme to undergo a functionally important calcium-dependent conformational change necessary for coagulant activity.     

Enhanced catabolism of low density lipoproteins in rat by lactosaminated Fab fragment. A new carrier of macromolecules to the liver

Proteins conjugated with lactose residues exhibit enhanced hepatic uptake mediated by the galactose receptor. In this study, we demonstrate that lactosaminated Fab fragments (lac-Fab) of IgG can induce hepatic catabolism of specific antigens, especially low density lipoproteins (LDL). lac-Fab and human LDL-lac-Fab complex exhibited specific uptake in isolated rat hepatocytes. In vivo in the rat, lactosamination enhanced plasma clearance of Fab fragments 2-fold and hepatic localization 20-fold. Fab fragments retained their affinity after lactosamination. Hepatic uptake of rat 125I-IgG complexed in vitro with anti-rat lac-Fab was increased almost 5-fold, compared to rat 125I-IgG alone. Injection of rats with anti-LDL lac-Fab induced plasma clearance and hepatic uptake of tracer amounts of previously injected human 125I-LDL, which decreased 50% 10 min after injection of lac-Fab, with 30% present in the liver. Asialofetuin completely inhibited these processes. After a bolus of 6 mg of human LDL, administration of anti-LDL lac-Fab reduced the serum cholesterol of rats to basal values within 2.5 h. These findings suggest that lactosaminated Fab fragments of specific IgGs are effective reagents for inducing hepatic uptake of macromolecules through the galactose receptor. lac-Fab specific for LDL may be an effective hypocholesterolemic agent in vivo.     

A model evaluation of estimates of breath-to-breath alveolar gas exchange

A mathematical model has been implemented for evaluation of methods for estimating breath-to-breath alveolar gas exchange during exercise in humans. This model includes a homogeneous alveolar gas exchange compartment, a dead space compartment, and tissue spaces for CO2 (alveolar and dead space). The dead space compartment includes a mixing portion surrounded by tissue and an unmixed (slug flow) portion which is partitioned between anatomical and apparatus contributions. A random sinusoidal flow pattern generates a breath-to-breath variation in pulmonary stores. The Auchincloss algorithm for estimating alveolar gas exchange (Auchincloss et al., J. Appl. Physiol. 21: 810-818, 1966) was applied to the model, and the results were compared with the simulated gas exchange. This comparison indicates that a compensation for changes in pulmonary stores must include factors for alveolar gas concentration change as well as alveolar volume change and thus implies the use of end-tidal measurements. Although this algorithm yields reasonable estimates of breath-to-breath alveolar gas exchange, it does not yield a "true" indirect measurement because of inherent error in the estimation of a homogeneous alveolar gas concentration at the end of expiration.     

Tenax-GC Extraction Technique for Residual Polychlorinated Biphenyl and Polyaromatic Hydrocarbon Analysis in Biodegradation Assays

A rapid Tenax-GC extraction technique has been evaluated for use in conjunction with aqueous biodegradation assays for polyaromatic hydrocarbons and polychlorinated biphenyls. The method was quantitatively efficient and reproducible for phenanthrene, but variable and not quantitative for Aroclor 1254 (polychlorinated biphenyls). Aqueous sample volumes and varying concentrations of organic matter influenced polychlorinated biphenyl and polyaromatic hydrocarbon extraction efficiency. Phenanthrene recovery was decreased by soil extract but unaffected by spent bacteriological culture medium. Both types of organic matter caused significant reduction of Aroclor 1254 recovery. Polyaromatic hydrocarbon and polychlorinated biphenyl biodegradation assays, performed with reservoir samples, supported the laboratory evaluation. The study demonstrated the utility of the Tenax-GC extraction technique for phenanthrene analysis in biodegradation assessment; however, Tenax-GC extraction was not appropriate for Aroclor 1254 biodegradation studies.     

Radiation-induced aberration in aneuploid vs. diploid swine leukocytes

Swine leukocytes were cultured for 48 h after receiving γ-ray exposures up to 400 R. Cells with one or two less than the diploid number of centromeres consistently contained more chromosome deletions than did diploid cells. This effect was not evident for dicentric and ring aberrations. Both aneuploid frequencies and the proportion of aberrations in aneuploid cells increased in irradiated samples but showed no dose-response relationship.     

Inhibitors of sterol synthesis. Dietary administration of 5 alpha-cholest-8(14)-en-3 beta-ol-15-one inhibits the intestinal absorption of cholesterol in lymph-cannulated rats

The effect of 5 alpha-cholest-8(14)-en-3 beta-ol-15-one, a potent inhibitor of cholesterol synthesis with marked hypocholesterolemic activity, on the intestinal absorption of exogenous cholesterol has been studied in lymph-cannulated rats. Administration of the 15-ketosterol at a level of 0.05% in a rat chow diet for 10 days was associated with a marked decrease (-64%) in the absorption of cholesterol.     

Thyroid hormone treatment of cultured chondrocytes mimics in vivo stimulation of collagen X mRNA by increasing BMP 4 expression

During endochondral bone formation, chondrocytes undergo terminal differentiation, during which the rate of proliferation decreases, cells become hypertrophic, and the extracellular matrix is altered by production of collagen X, as well as proteins required for matrix mineralization. This maturation process is responsible for most longitudinal bone growth, both during embryonic development and in postnatal long bone growth plates. Among the major signaling molecules implicated in regulation of this process are the positive regulators thyroid hormone (T3) and bone morphogenetic proteins (BMPs). Both T3 and BMPs are essential for endochondral bone formation and cannot compensate for each other, suggesting interaction of the two signaling pathways. We have analyzed the temporal and spatial expression patterns of numerous genes believed to play a role in chondrocyte maturation. Our results show that T3 stimulates collagen X gene expression in cultured chondrocytres with kinetics and magnitude similar to those observed in vivo. Stimulation of collagen X gene expression by T3 occurs only after a significant delay, implying that this hormone may act indirectly. We show further that T3 rapidly stimulates production of BMP 4, concomitant with a decrease in the BMP inhibitor Noggin, potentially resulting in a net increase in BMP signaling. Finally, inhibition of BMP signaling with exogenous Noggin prevents T3 stimulation of collagen X expression, indicating that BMP signaling is essential for this process. These data position thyroid hormone at the top of a T3/BMP cascade, potentially explaining why both pathways are essential for chondrocyte maturation. J. Cell. Physiol. 219: 595–605, 2009. © 2009 Wiley‐Liss, Inc.     

Activation of nuclear factor kappa B in mammary epithelium promotes milk loss during mammary development and infection

We investigated whether nuclear factor kappa B (NF‐κB), which exhibits a regulated pattern of activity during murine mammary gland development, plays an important role during lactation and involution, when milk production ceases and the gland undergoes apoptosis and re‐modeling. We generated a doxycycline inducible transgenic mouse model to activate NF‐κB specifically in the mammary epithelium through expression of a constitutively active form of IKK2, the upstream kinase in the classical NF‐κB signaling cascade. We found that activation of NF‐κB during involution resulted in a more rapid reduction in milk levels and increased cleavage of caspase‐3, an indicator of apoptosis. We also found that activation of NF‐κB during lactation with no additional involution signals had a similar effect. The observation that NF‐κB is a key regulator of milk production led us to investigate the role of NF‐κB during mastitis, an infection of the mammary gland in which milk loss is observed. Mammary gland injection of E. coli LPS resulted in activation of NF‐κB and milk loss during lactation. This milk loss was decreased by selective inhibition of NF‐κB in mammary epithelium. Together, our data reveal that activation of NF‐κB leads to milk clearance in the lactating mammary gland. Therefore, targeting of NF‐κB signaling may prove therapeutic during mastitis in humans and could be beneficial for the dairy industry, where such infections have a major economic impact. J. Cell. Physiol. 222:73–81, 2010. © 2009 Wiley‐Liss, Inc.     

Kinetics of activation of the tyrosine kinase of a deletion mutant of epidermal growth factor receptor missing the sites of self-phosphorylation

The addition of epidermal growth factor (EGF) to epidermal growth factor receptor (EGF receptor) dissolved in a solution of the detergent Triton X-100 results in the activation of its protein tyrosine kinase. To investigate the importance of the sites for self-phosphorylation on the enzyme in this process, the kinetics of activation of a deletion mutant missing the last 195 amino acids of the protein, including all of the sites for self-phosphorylation, were followed by monitoring the initial velocity at which the enzyme catalyzes the phosphorylation of the exogenous substrate RRKGSTAENAEYLRV. The activation of the enzymatic activity of this deletion mutant of EGF receptor displays kinetics that are second-order with respect to the concentration of the enzyme as does wild-type EGF receptor. The second-order rate constant for its activation is 36 +/- 10 microM-1 min-1, which is only 3-fold greater than the second-order rate constant for the activation of wild-type EGF receptor under the same conditions (13 +/- 2 microM-1 min-1). These results suggest that the mechanism by which the protein tyrosine kinase of the deletion mutant is activated is the same as that for the activation of the wild-type receptor and that the sites of self-phosphorylation in the wild-type EGF receptor do not participate in the mechanism of activation of the enzyme.