Spermidine regulation of protein synthesis at the level of initiation complex formation of Met-tRNAi, mRNA and ribosomes

Spermidine regulation of protein synthesis (stimulation at low concentrations and inhibition at high concentrations) was studied using a mRNA with a GC-rich 5'-untranslated region. It was found that the initiation complex formation of mRNA, Met-tRNAi, and 40 S ribosomal subunits was regulated by spermidine. The inhibition of initiation complex formation at high spermidine concentrations was greater with 80 S ribosomes than with 40S ribosomal subunits. This was partially explained by the spermidine inhibition of initiation factor-dependent RNA helicase activity.

An aspartate residue in the extracellular loop of the N-methyl-D-aspartate receptor controls sensitivity to spermine and protons

To study the role of acidic residues in modulation of NMDA receptors by spermine, we used site-directed mutagenesis of receptor subunits and voltage-clamp recording in Xenopus oocytes. Sixteen glutamate and aspartate residues, located in the first two thirds of the putative extracellular loop of the NR1A subunit, were individually mutated. This region of NR1A shows homology with bacterial amino acid binding proteins, a bacterial polyamine binding protein, and a bacterial spermidine acetyltransferase. Mutation of D669 to asparagine (D669N), alanine (D669A), or glutamate (D669E) abolished the "glycine-independent" form of spermine stimulation in heteromeric NR1A/NR2B receptors. These mutations also markedly reduced inhibition by ifenprodil and by protons at NR1A/NR2B receptors. Mutations at the equivalent position (D690) in NR1B, which contains the insert encoded by exon 5, reduced the pH sensitivity of NR1B/NR2B receptors. Thus, the effects of mutations at D669 are not prevented by the presence of exon 5, and the influence of exon 5 is not prevented by mutations at D669 (D690 in NR1B). Mutations at NR1A (D669) had little or no effect on the potencies of glutamate and glycine and did not alter voltage-dependent block by Mg2+ or the "glycine-dependent" form of spermine stimulation. Surprisingly, the D669N and D669A mutations, but not the D669E mutation, reduced voltage-dependent block by spermine at NR1A/NR2 receptors. Mutations in NR2B at a position (D668) equivalent to D669 did not alter spermine stimulation or sensitivity to pH and ifenprodil. However, mutations D668N and D668A but not D668E in NR2B reduced voltage-dependent block by spermine. Screening of the negative charges at NR1A(D669) and NR2B(D668) may be involved in voltage-dependent block by spermine. D669 in NR1A could form part of a binding site for polyamines and ifenprodil and/or part of the proton sensor of the NMDA receptor. Alternatively, this residue may be critical for coupling of modulators such as spermine, protons, and ifenprodil to channel gating.

Enhancement of helicase activity and increase of eIF-4E phosphorylation in ornithine decarboxylase-overproducing cells

In mouse FM3A ornithine decarboxylase (ODC) overproducing cells (EXOD-1), the amount of ODC protein was approximately 100-fold that of normal cells. Since it is well known that the translational efficiency of ODC mRNA is very low and that eIF-4E is a limiting factor for the mRNA recognition and the scanning of 40 S ribosomal subunits, we measured the amount and phosphorylation of eIF-4E in EXOD-1 cells. An increase in the phosphorylation of eIF-4E, its association with p220 protein, and an enhancement of RNA helicase activity were observed in the cells. These results support the hypothesis that phosphorylation of eIF-4E enhances RNA helicase activity through eIF-4F (4A, 4E, and p220) complex formation.

Spermidine-preferential uptake system in Escherichia coli. Identification of amino acids involved in polyamine binding in PotD protein

Spermidine-binding sites on PotD protein, substrate-binding protein in periplasm, in the spermidine-preferential uptake system in Escherichia coli were studied by measuring polyamine transport activities of right-side-out membrane vesicles with mutated PotD proteins prepared by site-directed mutagenesis of the potD gene and by measuring polyamine binding activities of these mutated PotD proteins. Polyamine transport activities of the mutated PotD proteins paralleled their polyamine binding activities. It was found that Trp-34, Thr-35, Glu-36, Tyr-37, Ser-83, Tyr-85, Asp-168, Glu-171, Trp-229, Trp-255, Asp-257, Tyr-293, and Gln-327 of PotD protein were involved in the binding to spermidine. When spermidine uptake activities were measured in intact cells expressing the mutated PotD proteins, it was found that Glu-171, Trp-255, and Asp-257 were more strongly involved in the binding of spermidine to PotD protein than the other amino acids listed above. The dissociation constants of spermidine for the mutated PotD proteins at Glu-171, Trp-255, and Asp-257 increased greatly in comparison with those for the other mutated PotD proteins. Since these three amino acids clearly interact with the diaminopropane moiety of spermidine, the results are in accordance with the finding that PotD protein has a higher affinity for spermidine than for putrescine. Putrescine was found to bind at the position of the diaminobutane moiety of spermidine.

[A case of metastatic choriocarcinoma associated with cerebral thrombosis and aneurysmal formation]

A rare case of metastatic choriocarcinoma with cerebral thrombosis and subsequent neoplastic aneurysm formation and rupture is reported. Three months after normal pregnancy and normal delivery, a 16-year-old woman was admitted with the chief complaints of speech disturbance and paresthesia of her right upper extremity on June 4, 1992. Both CT and MRI demonstrated cerebral infarction in the left insula. A cerebral angiogram revealed that the left middle cerebral artery (about 2 mm in diameter) was occluded in the distal M2 segment. On the 34th day, a follow up angiogram demonstrated a fusiform aneurysm at the same point of the arterial occlusion that had been already recanalized. On the 37th day, she suddenly had severe headaches and consciousness disturbance. CT showed subarachnoid hemorrhage. Resection of the aneurysm and left STA-MCA anastomosis were performed. Histological examination revealed that the aneurysmal walls were invaded by choriocarcinoma. On the 60th day, she was transferŕed to the department of obstetrics and gynecology for chemotherapy. On the 65th day and the 71st day, the patient suffered from intracerebral hemorrhage in the left basal ganglia, which originated from a different point of aneurysmectomy. She died because of the rapid growth of liver metastases 7 months after initial admission. Because chest CT and roentgenogram detected no lesion in the lungs, neoplastic embolus was unlikely as a cause of occlusion of the cerebral artery of about 2 mm in diameter. It would be more reasonable to believe that choriocarcinoma metastasized to the cerebral arterial walls initially and formed a thrombus which occluded the artery. As the neoplastic invasion weakened the arterial wall, a fusiform aneurysm was formed when the vessel was recanalized. There has been no case reported in the literature of neoplastic aneurysms of choriocarcinoma in which the course from aneurysmal formation to rupture was followed angiographically.

Protective effects of chlorogenic acid on paraquat-induced oxidative stress in rats

The protective effects of chlorogenic acid on paraquat-induced oxidative stress were examined in rats. The activities of erythrocytes and liver glutathione peroxidase, and of both liver catalase and glutathione reductase, which were increased by feeding paraquat, declined to the levels in the control rats by supplementing chlorogenic acid to the paraquat diet. The activity of superoxide dismutase was not changed by dietary paraquat or by supplementing chlorogenic acid to the paraquat diet. Paraquat in the diet markedly decreased the liver triacylglycerol and phospholipid concentrations, as well as the food intake and body weight gain, while chlorogenic acid protected against these decreases. These in vivo results and the in vitro superoxide anion scavenging activity of chlorogenic acid suggest that chlorogenic acid acted preventively against paraquat-induced oxidative stress.

Mechanism of catechin chemiluminescence in the presence of active oxygen

The photon emission (chemiluminescence; CL) of catechin in the presence of active oxygen species (hydrogen peroxide, hydroxyl radical tert-butyl hydroperoxide and tert-butyl oxyl radical) and acetaldehyde was confirmed to occur non-enzymatically at room temperature in aqueous neutral conditions. The CL intensity [P] in the presence of active oxygen species (X), catalytic species (Y) and receptors (Z) is predicted by [P] = k [X] [Y] [Z]. The calculated photon constants (k) of 8 catechins and gallic acid were 8.23 x 10(6) M-2 s-1 counts ((-)-epigallocatechin), 2.78 x 10(8) ((-)-epigallocatechin gallate), 4.66 x 10(5) ((-)-gallocatechin gallate), 4.36 x 10(5) ((-)-gallocatechin), 2.70 x 10(5) ((-)-epicatechin), 6.44 x 10(4) ((-)-catechin), 585 x 10(4) ((-)-epicatechin gallate), 4.78 x 10(4) (gallic acid) and 3.54 x 10(4) ((-)-catechin gallate), respectively. The system of active oxygen species, catalytic species and receptors is proposed to be a scavenging mechanism for active oxygen species. In the presence of acetaldehyde, (-)-epigallocatechin (maximum k value among catechins tested) reacted with tert-BuOOH to form tert-BuOH as determined by HPLC analysis.

The ntpJ gene in the Enterococcus hirae ntp operon encodes a component of KtrII potassium transport system functionally independent of vacuolar Na+-ATPase

The ntpJ gene, the tail end in the vacuolar type Na+-ATPase (ntp) operon of Enterococcus hirae, encodes a putative 49-kDa hydrophobic protein resembling K+ transporter protein in Saccharomyces cerevisiae (Takase, K., Kakinuma, S., Yamato, I., Konishi, K., Igarashi, K., and Kakinuma, Y. (1994) J. Biol. Chem. 269, 11037-11044). Northern blotting experiment revealed that the ntpJ gene was transcribed as a cistron in the ntp operon. We constructed an Enterococcus strain in which the ntpJ gene was disrupted by cassette mutagenesis with erythromycin resistance gene. The growth of this mutant was normal at low pH. However, the mutant did not grow at high pH in K+-limited medium (less than 1 mM), while the wild type strain grew well; the internal K+ concentration of this mutant was as low as 7% of that of the wild type strain, suggesting that the K+ accumulation at high pH was inactivated by disruption of the ntpJ gene. Potassium uptake activity via the KtrII system, which had been proposed as the proton potential-independent, Na+-ATPase-coupled system working at high pH (Kakinuma, Y., and Harold, F. M. (1985) J. Biol. Chem. 260, 2086-2091), was missing in this mutant strain. However, this mutant retained as high activities of Na+-ATPase and Na+ pumping as the wild type strain. From these results, we conclude that the NtpJ is a membraneous component of the KtrII K+ uptake system but not a functional subunit of vacuolar Na+-ATPase complex; the interplay between the KtrII system and the Na+-ATPase was discussed.

Crystal structure of PotD, the primary receptor of the polyamine transport system in Escherichia coli

PotD protein is a periplasmic binding protein and the primary receptor of the polyamine transport system, which regulates the polyamine content in Escherichia coli. The crystal structure of PotD in complex with spermidine has been solved at 2.5-A resolution. The PotD protein consists of two domains with an alternating beta-alpha-beta topology. The polyamine binding site is in a central cleft lying in the interface between the domains. In the cleft, four acidic residues recognize the three positively charged nitrogen atoms of spermidine, while five aromatic side chains anchor the methylene backbone by van der Waals interactions. The overall fold of PotD is similar to that of other periplasmic binding proteins, and in particular to the maltodextrin-binding protein from E. coli, despite the fact that sequence identity is as low as 20%. The comparison of the PotD structure with the two maltodextrin-binding protein structures, determined in the presence and absence of the substrate, suggests that spermidine binding rearranges the relative orientation of the PotD domains to create a more compact structure.

Inhibition of alpha interferon but not gamma interferon signal transduction by phorbol esters is mediated by a tyrosine phosphatase

Previous studies have indicated that the expression of viral oncoproteins, cell transformation, or phorbol ester treatment of cells can inhibit alpha/beta interferon (IFN-alpha/beta)-induced gene expression. The mechanisms by which these promoters of cell growth exert their inhibitory effects vary, but in most instances they involve a disruption of the IFN-alpha/beta-induced transcription complex ISGF3 such that the DNA-binding component of this complex (the 48-kDa ISGF3gamma protein) does not bind to the interferon-stimulated response element (ISRE). In this report, we demonstrated that phorbol ester treatment of human peripheral blood monocytes dramatically inhibits activation of IFN-alpha/B-stimulated early response genes but by a mechanism which does not involve abrogation of the ISRE binding of ISGF3gamma. Phorbol ester treatment of monocytes inhibited IFN alpha-stimulated tyrosine phosphorylation of the transcription factors Stat1alpha, Stat2, and Stat3 and of the tyrosine kinase Tyk2 but had no effect on IFN-gamma activation of Stat1alpha. IFNalpha-stimulated tyrosine phosphorylation of Jak1 and the alpha subunit of the IFN-alpha receptor were unaffected by phorbol 12-myristate 13-acetate (PMA). Moreover, PMA caused the dephosphorylation of Tyk2 but not of Jak1, which was activated by IFN. Pretreatment of cells with vanadate prevented the effects of PMA with regard to PMA-induced Tyk2 dephosphorylation. These observations suggest that PMA exerts its inhibitory effects by activation of a tyrosine phosphatase which selectively regulates Tyk2 but not Jak1 activity.

Separation of functional domains for the alpha-1,4 and alpha-1,6 hydrolytic activities of a Bacillus amylopullulanase by limited proteolysis with papain

An amylopullulanase (APase) from alkalophilic Bacillus sp. KSM-1378 hydrolyzes both alpha-1,6 linkages in pullulan and alpha-1,4 linkages in other polysaccharides, each maximally active at an alkaline pH, to generate oligosaccharides. We analyzed proteolytic fragments that were produced by exposing pure APase to various proteases, to identify its catalytic domain(s). The intact, pure 210-kDa APase was partially digested with papain for a short time, yielding simultaneously two smaller non-overlapping active fragments, designated amylose-hydrolyzing fragment (AHF114, 114 kDa) and pullulan-hydrolyzing fragment (PHF102, 102 kda). The two truncated protein fragments, each containing a single catalytic domain, were purified to homogeneity. The purified AHF114 and PHF102 had similar enzymatic properties to the amylase and pullulanase activities, respectively, of intact APase. The partial amino-terminal sequences of APase and AHF114 were both Glu-Thr-Gly-Asp-Lys-Arg-Ile-Glu-Phe-Ser-Tyr-Glu-Arg-Pro and that of PHF102 was Thr-Val-Pro-Leu-Ala-Leu-Val-Ser-Gly-Glu-Val-Leu-Ser-Asp-Lsy-Leu. These results were direct evidence that the alpha-1,6 and alpha-1,4 hydrolytic activities were associated with two different active sites in this novel enzyme. Our alkaline APase is obviously a "biheaded enzyme".

Endothelin-1 and vasopressin activate Ca(2+)-permeable non-selective cation channels in aortic smooth muscle cells: mechanism of receptor-mediated Ca2+ influx

The effects of vasopressin and endothelin-1 on cultured aortic smooth muscle cell lines (A7r5) were investigated by measurements of intracellular calcium [Ca2+]i and the patch-clamp techniques. Vasopressin and endothelin-1 (100 nM) evoked an initial peak followed by a smaller sustained rise of [Ca2+]i in the presence of extracellular calcium [Ca2+]o. In the absence of [Ca2+]o, only the initial peak of [Ca2+]i was observed. Therefore, the initial peak of [Ca2+]i was mainly due to calcium release from the storage sites, whereas the later sustained rise of [Ca2+]i was due to the calcium entry from outside. The sustained rise of [Ca2+]i was unaffected by nifedipine (10 microM) significantly, but was completely abolished by La3+ (1 mM). Under current clamp conditions with K(+)-internal solution, vasopressin and endothelin-1 (100 nM) produced hyperpolarization, then followed by depolarization. Under voltage clamp conditions at a holding potential of -40 mV, both vasopressin and endothelin-1 first activated the outward current, then followed by a long-lasting inward current with a high noise level. The first outward current was abolished by charybdotoxin (100 nM), Cs+ in the patch pipette and high EGTA (10 mM) in the pipette, suggesting that it was a Ca(2+)-sensitive K+ current (IK.Ca). The inward current was still elicited with the patch pipette containing Cs(+)-internal solution, and reversed at about 0 mV. The reversal potential was not significantly altered by the replacement of [Cl-]i or [Cl-]o, proposing that the inward current is a cation selective channel (IN.S.). The inward current was also observed even when extracellular cations are Ca2+. La3+ (1 mM), Cd2+ (1 mM) completely abolished the vasopressin-induced (IN.S.), however, nifedipine (10 microM) failed to inhibit it significantly. Single channel activities were recorded in the cell-attached configurations when vasopressin or endothelin-1 was applied to the bathing solution. The unitary conductance of the channels was approximately 20 pS with 140 mM Na+, Cs+, or K+ in the pipette, but was 15 pS with 110 mM Ca2+ in the pipette. Permeabilities sequence calculated from the reversal potentials was Na+ not equal to Cs+ not equal to K+ > Ca+. These results provide evidence that calcium entry and membrane depolarization elicited by vasopressin or endothelin-1 are mediated by a receptor-mediated Ca(2+)-permeable non-selective cation channel in aortic smooth muscle cells.

Calcium and SLY genes suppress the temperature-sensitive secretion defect of Saccharomyces cerevisiae uso1 mutant

Saccharomyces cerevisiae uso1-1 mutant stops the transport of secretory proteins from the endoplasmic reticulum to the Golgi apparatus at 37 degrees C. We found that this temperature-sensitive defect was suppressed either by increasing the concentration of calcium ion in the medium or by introducing in the cell the SLY genes which suppress the defect of Ypt1 protein, a small GTP-binding protein. The common phenotype and suppression of the mutants suggest that Uso1 and Ypt1 proteins function in the same process of protein transport, i.e., targeting or fusion of the transport vesicles to the Golgi membrane.

Participation of a medium chain acyl-CoA synthetase in glycine conjugation of the benzoic acid derivatives with the electron-donating groups

Glycine conjugation of a series of benzoic acid derivatives was investigated in bovine liver mitochondria. Benzoic acids with chlorine, methyl, methoxy or ethoxy substituents in the para-or meta-positions of the benzene ring showed a high degree of glycine conjugation. In contrast, the acids with cyano, nitro, amino, or acetylamino groups were conjugated to a small extent with glycine. A medium chain acyl-CoA synthetase that activates carboxylic acids was purified from bovine liver mitochondria. The purified medium chain acyl-CoA synthetase accepted not only medium chain fatty acids but also aromatic and arylacetic acids as substrates. There was a good correlation between the activity of the purified medium chain acyl-CoA synthetase and glycine conjugation of ten benzoic acids with electron-donating substituents. These findings indicate that the purified medium chain acyl-CoA synthetase is a major enzyme for glycine conjugation of benzoic acids with electron-donating groups in bovine live mitochondria.

[Neurophysiological mechanism of jaw-tongue reflex in man]

The present study was carried out to examine if the jaw-tongue reflex (JTR) could be elicited in man and if afferent fibers from the jaw-closing muscles were involved in this reflex. Electromyographic (EMG) activities were simultaneously recorded from the genioglossus (GG), the tongue retruding (TR) muscles, and the anterior temporal (TA), the posterior temporal (TP), the masseteric (Mass) and the digastric (Dig) muscles under various conditions. The results were as follows: 1. EMG activities of the GG and the TR muscles were increased during clenching, voluntary and passive jaw-opening, and chin-tapping. 2. Electrical stimulation of the deep temporal and masseteric nerves evoked H-reflex in the TA and the Mass muscles. EMG activities in the GG and the TR muscles were detected as the intensity of the electrical stimulation were increased. 3. The tonic vibration reflex (TVR) was induced in the jaw-closing muscles by applying vibratory stimulation to the bellies of the TA and the Mass muscles. EMG activities of the GG and the TR muscles were increased as the TA muscle activity was increased. It is concluded that the JTR is elicited in man and suggested that low threshold afferent fibers from the jaw-closing muscles, mainly the temporal muscle, were involved in eliciting the JTR in man.

Analysis of neurotrophin-3 expression using the lacZ reporter gene suggests its local mode of neurotrophic activity

We replaced the mouse neurotrophin-3 gene with the Escherichia coli-derived lacZ gene by means of homologous recombination. The mice with this mutation were useful models for studying the distribution of neurotrophin-3 expression in vivo, because visualization by 5-bromo-4-chloro-3-indoyl-beta-D-galactopyranoside (X-Gal) staining was simple and rapid compared with in situ hybridization or immunohistochemistry. Whole-mount staining of mutant embryos at embryonic day 10 revealed that lacZ, a reporter for the neurotrophin-3 gene, was expressed in the mesencephalon, mandibular arch and somites. In the embryos at days 13-17, lacZ was markedly expressed in the peripheral target tissues of sensory and sympathetic neurons. We also found that spinal motor neurons and sensory neurons in trigeminal and dorsal root ganglia express lacZ. Some of these X-Gal staining regions overlapped with the sites expressing trkC, a high-affinity receptor for neurotrophin-3. The distribution of X-Gal staining in heterozygotes and homozygotes was similar to that of neurotrophin-3 messenger RNA detected by in situ hybridization. However, there was less lacZ expression in the dorsal root ganglia of homozygotes than neurotrophin-3 expression in wild-type mice. These results suggest that the neurotrophin-3 produced in the dorsal root ganglia also plays a role in the survival of some of the neurotrophin-3-positive neurons and that the local mode of neurotrophic activity is widely distributed.

Effect of astilbin in tea processed from leaves of Engelhardtia chrysolepis on the serum and liver lipid concentrations and on the erythrocyte and liver antioxidative enzyme activities of rats

The effects of astilbin in Kohki tea, which is produced from the leaves of Engelhardtia chrysolepis Hance (Chinese name, huang-qui), and of an aglycone of astilbin, taxifolin, on the serum and liver lipid concentrations, and on the erythrocyte and liver antioxidative enzyme activities were determined with rats fed on a cholesterol-free diet. The total liver cholesterol concentration tended to be decreased by feeding with astilbin, and significantly decreased by feeding with taxifolin. The liver phospholipid concentration was decreased by feeding with both astilbin and taxifolin. In addition, astilbin and taxifolin lowered the serum and liver TBARS concentrations, but did not influence the serum and liver antioxidative enzyme activities, suggesting the possibility that these compounds acted to lower the TBARS concentration by their direct antioxidative action in vivo, almost without influencing the antioxidative enzyme activities.

Abundant expression of erythroid transcription factor P45 NF-E2 mRNA in human peripheral granurocytes

Transcription factor NF-E2 is crucial for regulation of erythroid-specific gene expression. p45 subunit of NF-E2 contains a basic-leucine zipper domain and dimerizes with the small Maf family protein to form functional NF-E2 complex. While p45 expression was shown to be restricted to erythroid cells, megakaryocytes and mast cells in hematopoietic lineage, we found in this study that p45 mRNA is abundantly transcribed in the granulocyte fraction of human peripheral blood cells. As neutrophils occupy approximately 92% of the cells in granulocyte fraction of human peripheral blood cells. As neutrophils occupy approximately 92% of the cells in this fraction, the cells expressing p45 is most likely to be neutrophils. p45 mRNA is also expressed in HL-60 promyelocytes, albeit the expression level is much lower than that of the granulocyte fraction. HL-60 cells were found to express mafK mRNA, indicating the presence of genuine NF-E2 complex in the cells. Although p45 mRNA is transcribed from two different promoters, aNF-E2 promoter and fNF-E2 promoter, in erythroid and megakaryocytic lineage cells, p45 mRNA is transcribed only from aNF-E2 promoter. The expression of p45 megakaryocytic lineage cells, p45 mRNA is transcribed only from aNF-E2 promoter. The expression of p45 mRNA in the neutrophils declined rapidly after transfer of the cells to in vitro culture and G-CSF could not sustain the expression from the down-regulation, suggesting the E2 may also participate in the regulation of neutrophil-specific gene expression.

Mesodermal- vs. neuronal-specific expression of MafK is elicited by different promoters

BACKGROUND

Small members of the Maf family of transcriptional regulatory proteins share similar basic-leucine zipper domains but have no intrinsic ability to activate transcription. One member of the family (MafK) has been shown to mediate both negative and positive regulation: in addition to forming a homodimer which represses transcription, MafK can also form a heterodimer with p45 (the large subunit of erythroid transcription factor NF-E2) to activate transcription.

RESULTS

We examined the expression of mafK during murine development. mafK mRNA was first detected in 7.5 days post coitus (dpc) embryonic mesoderm and persisted in mesodermal derivatives (mesenchymal and haematopoietic cells) thereafter. However, around 13 dpc mafK was also strongly induced in neuronal cells and it is broadly expressed in neurones in postnatal mouse. The neuronal expression of mafK is directed by a distinct promoter located 6 kbp 3' to the mesoderm-specific promoter. mafK in neurones associates with a different partner molecule from p45. In transgenic mice, a regulatory domain in the immediate vicinity of the mesodermal promoter was found to direct mesenchymal, but not haematopoietic, expression of mafK.

CONCLUSION

The cell type- and developmental stage-specific expression of MafK suggests that, in addition to its demonstrated role in erythroid transcriptional regulation, MafK also plays an important regulatory role in other mesodermally and neuroectodermally derived tissues during mouse embryonic development.

Spermine suppresses the activation of human neutrophil NADPH oxidase in cell-free and semi-recombinant systems

Spermine, a cellular polyamine, down-regulates O2- generation in human neutrophils stimulated by receptor-linked agonist [Ogata, Tamura and Takeshita (1992) Biochem. Biophys. Res. Commun. 182, 20-26]. In this study, to elucidate the mechanism for the inhibition, the effect of spermine on cell-free activation of the O2- generating enzyme (NADPH oxidase) was examined. Spermine suppressed the SDS-induced activation of NADPH oxidase in a dose-dependent manner with an IC50 of 18 microM. The inhibition was specific for spermine over its precursor amines, spermidine and putrescine. Spermine did not alter the Km for NADPH or the optimal concentration of SDS for activation. The amine was inhibitory only when added before activation, indicating that it affects the activation process rather than the enzyme's activity. An increased concentration of cytosol partly prevented the inhibition by spermine. In semi-recombinant cell-free system, spermine inhibited the activation of NADPH oxidase as effectively as in the cell-free system (IC50 = 13 microM). Pretreatment of each recombinant cytosolic component with spermine revealed that they (especially p67phox) are sensitive to spermine. These results suggest that spermine interacts with cytosolic component(s) and impairs the assembly of NADPH oxidase.

Specific cross-reaction of IgG anti-phospholipid antibody with platelet glycoprotein IIIa

To study the pathological functions of anti-phospholipid (anti-PL) antibodies, we have analyzed their effect on platelet function. We identified an IgG anti-PL mAb, designated PSG3, which cross-reacted specifically with glycoprotein (GP) IIIa in human platelets and inhibited platelet aggregation. PSG3 bound also to certain polyanionic substances, such as double-stranded DNA, heparan sulfate, dextran sulfate and acetylated-LDL, but not to other polyanionic substances. The binding of PSG3 to GPIIIa was completely inhibited by heparan sulfate and dextran sulfate, indicating that PSG3 recognizes a particular array of negative charges expressed on both GPIIIa and the specified polyanionic substances. Since neither neuraminidase- nor endoglycopeptidase F-treatment of GPIIIa had any significant effect on the binding of PSG3, this array must be located within the amino acid sequence of GPIIIa but not in the carbohydrate moiety. Reduction of the disulfide bonds in GPIIIa greatly reduced its reactivity, suggesting that the negative charges in the epitope are arranged in a particular conformation. PSG3 inhibited platelet aggregation induced by either ADP or collagen, it also inhibited fibrinogen binding to activated platelets in a dose-dependent fashion. PSG3, however, did not inhibit the binding of GRGDSP peptide to activated platelets. These results suggest that the PSG3 epitope on GPIIIa contains a particular array of negative charges, and possibly affects the fibrinogen binding to GPIIb/IIIa complex necessary for platelet aggregation.

Human betacellulin, a member of the EGF family dominantly expressed in pancreas and small intestine, is fully active in a monomeric form

Betacellulin (BTC) was found to be expressed mainly in human pancreas and small intestine. This finding suggests that BTC possesses some specific function distinguished from the other members of epidermal growth factor (EGF) family. To clarify this function, the released form of human BTC has been expressed in E.coli, purified, and characterized. The recombinant human BTC was produced as an inclusion body. This material was dissolved in guanidine-HCl under reducing conditions, refolded, and purified through sequential liquid chromatography. Purified BTC was electrophoresed under reducing conditions and a molecular size of 18 kDa was determined, which is the supposed size of a dimer of the peptide. However, chemical analysis failed to show a covalently linked dimer. The molecular mass of BTC analyzed by mass spectrometry revealed it to be 9 kDa, which is consistent with theoretical value for a monomer. Recombinant BTC showed growth promoting activity for mouse fibroblasts and rat aortic smooth muscle cells which was equivalent to EGF On the other hand, BTC was found to exhibit a growth inhibitory effect on the cells overexpressing EGF receptor.

Establishment of a novel embryonic stem cell line by a modified procedure

To generate mutant mice, embryonic stem (ES) cells are used as a vehicle for introducing mutations. The establishment of ES cells is difficult because it requires specific skills and it is time-consuming. We established a novel ES cell line derived from hybrid mice between C57BL/6 and DBA/2 using a modified method. To collect a large number of preimplantational embryos, we collected embryos at the 8-cell stage and cultured them to blastocysts, whereas the usual procedure of preparing the delayed blastocysts demands technical skills. To eliminate unnecessary female cells at an initial stage of inner cell mass culture, male clones were selected by polymerase chain reaction to detect the mouse Sry gene. The established ES cell line efficiently contributed to the germ-line when injected into 8-cell embryos of ICR mice. This potency was maintained after manipulation throughout gene targeting.