Structural characterization of the gene for human histidine-rich glycoprotein, reinvestigation of the 5'-terminal region of cDNA and a search for the liver specific promoter in the gene

Genomic DNA libraries were screened for the human histidine-rich glycoprotein (HRG) gene and a sequence of 15,499 nucleotides was determined. The gene is composed of 7 exons and 6 introns, and all the exon-intron boundaries match the consensus GT/AG sequence for donor and acceptor splice sites. Each of cystatin-like domains I and II of HRG is encoded by three exons, exons I to III and exons IV to VI, respectively, like those of other members of the cystatin superfamily. The entire C-terminal half of the molecule is encoded by the largest exon, VII. The first 103 nucleotides of the cDNA sequence reported for human HRG [Koide, T., Foster, D., Yoshitake, S. , and Davie, E.W. (1986) Biochemistry 25, 2220-2225] could not be found in the determined gene sequence. A homology search of this sequence against a database showed the complete matching to a part of the yeast mitochondrial DNA encoding 21S ribosomal RNA. Rapid amplification of cDNA 5' ends (5'-RACE) analysis revealed that the cDNA has multiple 5'-ends and that a possible starting point is nucleotide 104 of the reported cDNA sequence. These results suggest that the first 103 nucleotides of the cDNA sequence reported for human HRG originated from yeast mitochondrial DNA and were incidentally incorporated into the HRG cDNA in the process of the construction of a cDNA library. Various fragments obtained on restriction endonuclease digestion of the 5'-noncoding region of the HRG gene were ligated to the chloramphenicol acetyltransferase (CAT) gene and then transfected into HepG2 and 293 cells to analyze the promoter activity. The sequence between -262 and -21 from the putative translation initiation site supported the expression of CAT in HepG2 cells but not in 293 cells, suggesting that this segment promotes the liver-specific transcription of the human HRG gene.

Protein kinase C-dependent regulation of Na+/Ca2+ exchanger isoforms NCX1 and NCX3 does not require their direct phosphorylation

We compared the phosphorylation-dependent regulation of three mammalian Na+/Ca2+ exchanger isoforms (NCX1-NCX3) expressed in CCL39 fibroblasts that have little endogenous activity. Na+i-dependent 45Ca2+ uptake into NCX1- or NCX3-expressing cells, but not that into NCX2-expressing cells, was significantly enhanced by phorbol 12-myristate 13-acetate (PMA) or platelet-derived growth factor-BB, which was abolished by pretreatment of cells with calphostin C or a prior long exposure to PMA. This suggests that NCX1 or NCX3, but not NCX2, is stimulated by a pathway involving protein kinase C (PKC). Immunoprecipitation experiments using [32P]orthophosphate-labeled cells revealed that both NCX2 and NCX3 proteins were phosphorylated to a much lesser extent than the NCX1 protein in unstimulated cells and that the extent of phosphorylation was not increased by treatment with PKC activators, although NCX1 phosphorylation was enhanced significantly. Using site-directed mutagenesis, we identified three phosphorylation sites in the NCX1 protein in the PMA-stimulated cells to be Ser-249, Ser-250, and Ser-357 with Ser-250 being predominantly phosphorylated. We found that the NCX1 mutant with these serine residues substituted with alanine still maintained a normal response to PMA. In contrast, the NCX1 or NCX3 mutant, with the large central cytoplasmic loop deleted, lost the responsiveness to PMA. These results suggest that the PKC-dependent regulation of NCX1 or NCX3 requires the central cytoplasmic loop but does not require the direct phosphorylation of the exchanger.

Posthyperventilatory steal response in chronic cerebral hemodynamic stress: a positron emission tomography study

BACKGROUND AND PURPOSE

The alteration of regional cerebral blood flow (CBF) during and after hyperventilation was measured using positron emission tomography (PET) to determine the circulatory response induced by daily respiratory changes in the cerebral area under chronic hemodynamic stress.

METHODS

Three normal volunteers and 12 patients with an obstruction of major cerebral arteries underwent PET measurements of the CBF after an injection of H2(15)O: (1) in the resting condition, (2) during hyperventilation (HV scan), (3) 1 to 3 minutes after hyperventilation (post-HV scan), (4) during the inhalation of 5% CO2, and (5) after an injection of acetazolamide. Eleven patients also underwent a 15O gas study to measure CBF, oxygen extraction fraction (OEF), and cerebral blood volume (CBV).

RESULTS

(1) In 9 patients, the CBF value in the post-HV scan was lower than that in the HV scan in 1 or more regions in the area of the obstructed arteries, although the PaCO2 level during the post-HV scan was higher than that during the HV scan in all patients. All control regions in the patients and in the normal volunteers showed an elevated CBF in the post-HV scan compared with the HV scan. (2) The negative post-HV response (posthyperventilatory steal) was prominent in 4 patients with moyamoya vessels and in another 5 patients with atherosclerotic disease who had PET evidence of hemodynamic stress (elevated CBV or OEF). (3) The regional pre- to post-HV change in CBF was significantly correlated with the CBF responses to acetazolamide and CO2.

CONCLUSIONS

Vasodilatation after the termination of hyperventilation in the normal areas induces a steal response in the cerebral area suffering from hemodynamic stress and may cause profound hypoperfusion in everyday situations. This phenomenon may be important to our understanding of the clinical symptoms and the natural course of chronic cerebral occlusive disease bearing hemodynamic stress.

Na+/Ca2+ exchanger overexpression impairs calcium signaling in fibroblasts: inhibition of the [Ca2+] increase at the cell periphery and retardation of cell adhesion

We examined the Ca2+ handling property and cell function of CCL39 fibroblasts highly overexpressing the cardiac isoform (NCX1) of Na+/ Ca2+ exchanger. In NCX1 transfectants in 146 mM Na+, ionomycin, alpha-thrombin or thapsigargin only produced a small transient increase in [Ca2+]i compared to the large increase seen in control cells, although resting [Ca2+]i was not significantly different between these cells. In Na+-free medium, in contrast, the [Ca2+]i responses in NCX1 transfectants and control cells stimulated with these agents were not different, indicating that the Ca2+ content of the intracellular store(s) does not decrease on NCX1 transfection. The expression levels of the endoplasmic reticulum and plasma membrane Ca2+-ATPases, and thrombin- or serum-stimulated cell growth were not altered in NCX1 transfectants. The latter finding suggests that Ca2+ signaling in the nucleus is not impaired appreciably. On fluorescence imaging and confocal microscopy, we found that [Ca2+] did not increase in the peripheral cytoplasm of these cells treated with alpha-thrombin in Na+-containing medium. In these NCX1 transfectants, activation of the plasma membrane Ca2+-activated K+ channels by thrombin or ionomycin was markedly suppressed, and the integrin-mediated adhesion to substrate was significantly delayed compared with control cells. NCX1-overexpressing CCL39 cells thus seem to be a good model with which we can study the Ca2+-regulated membrane processes under physiologically relevant conditions.

Regulation of the Na+/H+ exchanger in fibroblasts overexpressing the Na+/Ca2+ exchanger

To assess the role of Ca2+ in regulation of the Na+/H+ exchanger (NHE1),we used CCL-39 fibroblasts overexpressing the Na+/Ca2+ exchanger (NCX1). Expression of NCX1 markedly inhibited the transient cytoplasmic Ca2+ rise and long-lasting cytoplasmic alkalinization (60-80% inhibition) induced by alpha-thrombin. In contrast, coexpression of NCX1 did not inhibit this alkalinization in cells expressing the NHE1 mutant with the calmodulin (CaM)-binding domain deleted (amino acids 637-656), suggesting that the effect of NCX1 transfection involves Ca2+-CaM binding. Expression of NCX1 only slightly inhibited platelet-derived growth factor BB-induced alkalinization and did not affect hyperosmolarity- or phorbol 12-myristate 13-acetate-induced alkalinization. Downregulation of protein kinase C (PKC) inhibited thrombin-induced alkalinization partially in control cells and abolished it completely in NCX1-transfected cells, suggesting that the thrombin effect is mediated exclusively via Ca2+ and PKC. On the other hand, deletion mutant study revealed that PKC-dependent regulation occurs through a small cytoplasmic segment (amino aids 566-595). These data suggest that a mechanism involving direct Ca2+-CaM binding lasts for a relatively long period after agonist stimulation, despite apparent short-lived Ca2+ mobilization, and further support our previous conclusion that Ca2+- and PKC-dependent mechanisms are mediated through distinct segments of the NHE1 cytoplasmic domain.

Evaluation of carbon-11-labeled KF17837: a potential CNS adenosine A2a receptor ligand

The 11C-labeled KF17837 ([7-methyl-11C](E)-8-(3,4-dimethoxystyryl)-1,3-dipropyl-7-methylxa nthine) was evaluated as a PET ligand for mapping adenosine A2a receptors in the central nervous system (CNS).

METHODS

The regional brain distribution of [11C]KF17837 and the effect of adenosine antagonists on the distribution were measured in mice by the tissue sampling method. In rats, the regional brain uptake of [11C]KF17837 and the effect of carrier KF17837 was visualized by autoradiography. Imaging of the monkey brain with [11C]KF17837 was performed by PET.

RESULTS

In mice, a high uptake of [11C]KF17837 was found in the striatum in which A2a receptors were highly enriched. The uptake was decreased by co-injection of carrier KF17837 or a xanthine-type A2a antagonist CSC but not by nonxanthine-type A2a antagonists ZM 241385 or SCH 58261, or an A1 antagonist KF15372. In the rat brain, [11C]KF17837 was accumulated higher in the striatum than in other brain regions, and the uptake was blocked by co-injection of carrier KF17837. In a monkey PET study, a high striatal uptake of radioactivity was observed.

CONCLUSION

Carbon-11-KF17837 binds to adenosine A2a receptors in the striatum. However, the presence of an unknown but specific binding site for xanthine-type compounds also was suggested in the other brain regions. The results also suggested that the in vivo receptor-binding sites of xanthine-type ligands are slightly different from those of nonxanthine-type A2a antagonists.

HRG Tokushima: molecular and cellular characterization of histidine-rich glycoprotein (HRG) deficiency

Previously, we found the first congenital deficiency of histidine-rich glycoprotein (HRG) in a Japanese woman with thrombosis. To elucidate the genetic basis of this deficiency, we first performed Southern blot analysis and found no gross deletion or insertion in the proband's HRG gene. We then examined the nucleotide sequences of all seven exons of the proband's HRG gene. A single nucleotide substitution, G to A at nucleotide position 429, which mutates Gly85 to Glu in the first cystatin-like domain, was found in exon 3 in 13 of 22 amplified clones. This mutation generates a unique Taq I site. Exon 3 was amplified from the proband, her family members, and 50 unrelated normal Japanese individuals, and Taq I fragmentation was examined. Fragmentation of exon 3 was observed in one allele of the genes from the proband and the family members who also have decreased plasma levels of HRG. Fifty unrelated normal Japanese individuals had a normal HRG gene, indicating that the G to A mutation is not a common polymorphism. To elucidate the identified mutation as a cause for the secretion defect of HRG in the proband's plasma, we constructed and transiently expressed the recombinant Tokushima-type HRG mutant (Gly85 to Glu) in baby hamster kidney (BHK) cells, and examined an intracellular event of the mutant protein. The results showed that only about 20% of the Tokushima-type HRG was secreted into the culture medium, and intracellular degradation of the mutant was observed. Thus, the present study strongly suggests that the HRG deficiency is caused by intracellular degradation of the Gly85 to Glu mutant of HRG in the proband.

Change of mechanical activity to contraction from the relaxation induced by the intracellular Ca2+ antagonist KT-362; effects of alkylation of side chain, and substitution of 2,3,4,5-tetrahydro-1,5-benzothiazepine derivatives

KT-362 (5-[3-[2-(3,4-Dimethoxyphenyl)ethyl]aminopropionyl]-2,3,4, 5-tetrahydro-1,5-benzothiazepine fumarate) is an intracellular Ca2+ antagonist. The compound obtained by introducing methyl groups onto the nitrogen (R2) of the side chain of KT-362 showed vasoconstrictive activity. Therefore we synthesized various derivatives, and examined their activities. Substitution at position R2 of the side chain resulted in potent contractile activity, and the optimal alkyl length was two or three carbons. The potency was further increased by the introduction of a chloro group at the R1 position of 2,3,4,5-tetrahydro-1,5-benzothiazepines. One of the synthesized compounds, 8-chloro-5-¿N-ethyl-N-[2-(3,4-dimethoxyphenyl)ethyl]aminopropionyl¿-2,3,4, 5-tetrahydro-1,5-benzothiazepine fumarate (9b), showed an EC50 value of 3.47 x 10(-8) M for contraction of rabbit iliac artery. The action of compound 9b was antagonized competitively by an H1-histamine receptor antagonist, diphenhydramine, and the pA2 value was 7.82. The maximum constriction was inhibited by a Ca2+ entry blocker, nicardipine, but not by an alpha 1-adrenoreceptor antagonist, prazosin. In a Ca(2+)-free medium, tonic constriction induced by 9b disappeared, and only a phasic constriction was observed. Though this phasic constriction was inhibited by diphenhydramine, it was not inhibited by prazosin or nicardipine.

Calmodulin-binding autoinhibitory domain controls "pH-sensing" in the Na+/H+ exchanger NHE1 through sequence-specific interaction

The calmodulin (CaM)-binding domain reduces the affinity of the Na+/H+ exchanger NHE1 for intracellular H+ by exerting an autoinhibitory function in quiescent cells. We replaced this domain (aa 637-656) with homologous segments from other NHE isoforms (NHE2 and 4) or functionally similar regions from other sources (Na+/Ca2+ exchanger, CaM-dependent protein kinase II, plasma membrane Ca2+-pump, or CaM-binding peptide Trp3). The NHE-1-, NHE2-, and NHE4-segments bound CaM with Kds of 16, 130, and 27 nM, respectively. These chimeric molecules were expressed in the exchanger-deficient cell PS120. NHE1 with incorporated NHE2-segment was activated in response to Ca2+-mobilizing agents ionomycin and thrombin resulting in an alkaline shift of the intracellular pH (pHi)-dependence of 22Na+ uptake, as was the case with the intact rat NHE2. In contrast, incorporation of the NHE4-segment or other CaM-binding segments induced a constitutive alkaline shift of pHi-dependence with concomitant abolishment of Ca2+-dependent activation, indicating that these segments could not function as an autoinhibitory domain in NHE1. Detailed analyses revealed that Leu639, Lys651 and Tyr652, conserved in the NHE1- and NHE2-segments, but not in the NHE4-segment, are important for the autoinhibition. Furthermore, 125I-labeled CaM-binding peptide from NHE1 was efficiently crosslinked to the NHE1 protein, suggesting that the inhibitory domain physically interacts with part(s) of the molecule. Together, these findings support the notion that the reduction of H+ affinity in Na+/H+ exchange occurs through a mechanism involving a highly sequence-specific interaction of the inhibitory domain with its putative acceptor in NHE1.

Three-dimensional imaging of cortical structure, function and glioma for tumor resection

A three-dimensional brain imaging protocol with PET and MRI was used to visualize the cortical structure in relation to brain function and glioma infiltration to determine tumor resectability.

METHODS

Sixteen patients with glioma had a PET scan with 11C-methionine to visualize tumor infiltration. The PET images were co-registered to the patients' own MRI reconstructed to the three-dimensional brain surface images to indicate the gyral structure and the extent of tumor infiltration. Thirteen patients, who bore tumors adjacent to the language or motor cortex, had H2 15O activation study to locate the eloquent cortex. The area of tumor infiltration was superimposed on the brain surface images together with the language and/or motor cortex.

RESULTS

When a tumor was located within a single gyrus without influencing surface cortical gyrus pattern, the motor and language areas were identified morphologically by three-dimensional surface image alone. However, when the tumor caused swelling and deformation of cortical structure, functional mapping with H2(15)O activation technique was essential in locating them correctly. In such cases, the combined mapping of the facial motor area with oral movement and the language area with word repetition was the most useful method to identify the parasylvian structure in the dominant hemisphere. Total or near total resection of low-grade glioma in eight patients and the effective decompression of the active part of the malignant glioma in four patients was completed without causing functional neurological deterioration.

CONCLUSION

The three-dimensional expression of cortical structure and function combined with PET glioma imaging with 11C-methionine is useful for radical resection of cerebral glioma.

Brain incorporation of [1-11C]arachidonate in normocapnic and hypercapnic monkeys, measured with positron emission tomography

Positron emission tomography (PET) was used to determine brain incorporation coefficients k* of [1-11C]arachidonate in isoflurane-anesthetized rhesus monkeys, as well as cerebral blood flow (CBF) using [15O]water. Intravenously injected [1-11C]arachidonate disappeared from plasma with a half-life of 1.1 min, whereas brain radioactivity reached a steady-state by 10 min. Mean values of k* were the same whether calculated by a single-time point method at 20 min after injection began, or by least-squares fitting of an equation for total brain radioactivity to data at all time points. k* equalled 1.1-1.2 x 10(-4) ml x s(-1) x g(-1) in gray matter and was unaffected by a 2.6-fold increase in CBF caused by hypercapnia. These results indicate that brain incorporation of [1-11C]arachidonate can be quantified in the primate using PET, and that incorporation is flow-independent.

Characterization of the 5'-flanking regions of plasminogen-related genes A and B

We examined the promoter activity of two homologous plasminogen-related genes (PRGA and PRGB) employing HepG2 cells. The 5'-flanking regions of these genes were sequenced first, then inserted into the upstream region of the CAT gene in an expression vector. CAT assays revealed that the promoter activity of PRGA was 3-fold that of plasminogen, while the activity of PRGB was 5-fold. Deletion analysis of these genes demonstrated that a region between -283 and +153 bp relative to the transcription initiation site was essential for their expression, and that there were regions with either negative or positive effects on expression farther upstream.

Identification of cytoplasmic subdomains that control pH-sensing of the Na+/H+ exchanger (NHE1): pH-maintenance, ATP-sensitive, and flexible loop domains

To precisely identify the cytoplasmic subdomains that are responsible for the intracellular pH (pHi)-sensitivity, ATP depletion-induced inhibition and Ca2+ activation of the Na+/H+ exchanger (NHE1), we generated a set of deletion mutants of carboxyl-terminated cytoplasmic domain and expressed them in the exchanger-deficient cell line PS120. We evaluated pHi-sensitivity of these mutants by measuring the resting pHi in cells placed in an acidic medium (pH 6.0) and pHi-dependence of 5-(N-ethyl-N-isopropyl)amiloride-sensitive 22Na+ uptake. Detailed analysis revealed that the cytoplasmic domain of NHE1 is consists of at least four subdomains in terms of pHi-sensitivity of the unstimulated NHE1: I, aa 516-590/595; II, aa 596-635; III aa 636-659; and IV, aa 660-815. Subdomains II and IV were silent for pHi-sensitivity. Subdomain I had a pHi-maintenance function, preserving pHi-sensitivity in a physiological range, whereas subdomain III, overlapping with the high affinity calmodulin (CaM)-binding site, exhibited an autoinhibitory function. Deletion of subdomain I abolished the decrease of pHi-sensitivity induced by cell ATP depletion, indicating that domain I plays a crucial role in this phenomenon. Deletion of subdomain III rendered the inhibition by ATP depletion less efficient, suggesting the possible interaction between subdomains I and III. On the other hand, tandem elongation of subdomain II by insertion did not affect either the inhibitory function of domain III or the removal of this inhibition by ionomycin or thrombin. However, deletion of subdomain II partially abolished the inhibitory effect of subdomain III. Subdomain II thus seems to function as a mobile "flexible loop," permitting the CaM-binding subdomain III to exert its normal function. These findings, together with our previous data, support a concept that cell ATP, Ca2+, and growth factors regulate NHE1 via a mechanism involving direct or indirect interactions of specific cytoplasmic subdomains with the "H(+)-modifier site.".

Expression and induction by IL-6 of the normal and variant genes for human plasminogen

We examined the promoter activity of the gene for human plasminogen (PLG) employing its 1.1 kb fragment of the 5'-flanking region inserted in front of a reporter gene. Deletion analysis revealed that a region surrounding the transcription start site was essential for the PLG expression. Since the PLG gene has three sequences for the interleukin-6 (IL-6) responsive element, we examined the effect of IL-6 on the PLG expression. IL-6 stimulation of PLG resulted in a 2.5-fold increase in its transcription. This is also true for the PLG gene of a case with dysplasminogenemia. Although the patient's gene had six mutations in the 5'-flanking region, its promoter activity was 1.8-fold that of normal PLG.

Molecular physiology of vertebrate Na+/H+ exchangers

This review describes recent progress concerning the molecular aspects of the Na+/H+ exchanger. The Na+/H+ exchanger is an important regulator for intracellular pH, cell volume, and transepithelial Na+ transport. It exists in virtually all cells with cell type-dependent pattern of isoform expression, and it is regulated in response to a variety of extracellular stimuli, among them not only agonists such as growth factors and hormones but also mechanical stimuli such as osmotic stress and cell spreading. Thus this transporter is also an excellent model to study the signal transduction. Since the first molecular cloning of the Na+/H+ exchanger, detailed studies revealed many interesting features of this transporter. At present, at least five different isoforms of the Na+/H+ exchanger are known. These isoforms differ in tissue localization, sensitivity of inhibitors, and mode of transcriptional and posttranscriptional regulation, allowing them to participate in different physiological processes. We have only started to understand an intriguing mechanism underlying these functional differences among the exchanger isoforms. Because the Na+/H+ exchanger is relatively simple in terms of its kinetic features, e.g., a simple 1:1 stoichiometry of Na+ and H+ and no input of metabolic energy such as ATP hydrolysis, the study of its structural and mechanistic aspects would also serve as a good model to understand the general mechanism of various ion transporters.

Therapeutic effect of egualen sodium (KT1-32), a new antiulcer agent, on chronic gastritis induced by sodium taurocholate in rats

We investigated the therapeutic effects of egualen sodium (KT1-32), a new antiulcer agent, on chronic erosive and atrophic gastritis induced by 5 months' administration of sodium taurocholate (TCA; 5 mM) in rats. The chronic gastritis was manifested by mucosal surface injuries (erosions), reduced mucosal thickness, reduction of the number of parietal cells, infiltration of inflammatory cells, and proliferation of collagenous fiber. Egualen sodium, (10-100 mg/kg, t.i.d.) administered orally to the rats for 2 weeks after the withdrawal of TCA, dose-dependently and significantly decreased the total length of erosions. The indicators of atrophic gastritis, i.e., reduced mucosal thickness and reduction in the number of parietal cells, were improved dose-dependently by the administration of this agent. Egualen sodium also reduced the inflammatory cell infiltration and the proliferation of collagenous fiber in the gastric mucosa in a dose-dependent manner. The reduced staining of neutral gastric mucus was improved by a high dose (100 mg/kg) of egualen sodium. The therapeutic effects of egualen sodium on experimental gastritis were superior to those of sofalcone and sodium guaiazulene 3-sulfonate. These results suggest that egualen sodium may be a promising agent for the treatment of erosive and atrophic gastritis.

Phosphorylation-dependent regulation of cardiac Na+/Ca2+ exchanger via protein kinase C

The cardiac Na+/Ca2+ exchanger (NCX1) plays a major role in the extrusion of Ca2+ from cardiomyocytes. We studied the role of protein phosphorylation in the regulation of cardiac NCX1 using CCL39 stably overexpressing the canine cardiac NCX1 and rat neonatal cardiomyocytes. In both cell types, the NCX1 protein immunoprecipitated with a chicken anti-NCX1 antibody exhibited a significant basal phosphorylation that was further enhanced by treatment with endothelin-1, acidic fibroblast growth factor, phorbol 12-myristate 13-acetate, or okadaic acid. In contrast, calphostin C, K252a, or EGTA inhibited the phosphorylation. The phosphorylation occurred on two major tryptic phosphopeptides (P1 and P2) exclusively on serine residues. Evidence is presented suggesting that P2 was derived from an N-terminal half (amino acids 240-475) of the central cytoplasmic domain of NCX1 and was phosphorylated directly by protein kinase C (PKC). The agents that increased NCX1 phosphorylation significantly enhanced both the forward and reverse modes of Na+/Ca2+ exchange. This exchange activation exhibited a very good correlation with the NCX1 phosphorylation. In NCX1-transfected cells, PKC down-regulation following prolonged exposure to phorbol 12-myristate 13-acetate abolished the acidic fibroblast growth factor-induced activation of exchange activity. On the other hand, cell ATP depletion reduced the exchange activity and abolished the effects of the above agents on exchange activity. These results indicate that the cardiac NCX1 is up-regulated by PKC-catalyzed phosphorylation. The cardiac NCX1 thus could play an important role in the previously reported negative inotropic actions of phorbol esters and other PKC-activating agents.

Azulene derivatives as TXA2/PGH2 receptor antagonists--II. Synthesis and biological activity of 6-mono- and 6-dihydroxylated-isopropylazulenes

In order to examine the correlation between activity and hydrophilicity of the side chain of sodium 3-[4-(4-chlorobenzenesulfonylamino)butyl]-6-isopropylazulene -1-sulfonate (KT2-962), a non-prostanoid TXA2/PGH2 receptor antagonist, one or two hydroxyl groups were introduced into the isopropyl moiety. A series of 6-hydroxylated-isopropylazulenes were synthesized by regioselective oxidation of 6-isopropylazulenes and their in vitro and in vivo antagonistic activities were studied. Both the primary and tertiary alcohols, monohydroxylated derivatives, exhibited potent biological activities comparable to unmodified 6-isopropylazulenes both in vitro and in vivo. In contrast, the activities of 1,2- and 1,3-diols of 6-substituted derivatives, markedly decreased, but recovered by O-isopropylidenation of the dihydroxyl moiety. These findings indicate that the moderate hydrophobicity of substituent at the 6-position of the azulene ring might be required for the activity and the size of the substituent at this position, not so rigid for keeping potent biological activity.

Quality control of protein C: protein C synthesized in the presence of warfarin is selectively degraded in the endoplasmic reticulum

Warfarin is known to disrupt the microsomal vitamin K cycle, which results in a decrease of the plasma level of protein C, an anticoagulant factor, as well as some other vitamin K-dependent coagulation factors. We examined the effect of warfarin on secretion of recombinant protein C expressed in human kidney 293 or BHK cells. In transient expression, warfarin caused a two- to four-fold decrease in the quantity of protein C secreted, compared to findings with vitamin K-treated cells. Pulse-chase experiments using stable cells showed that, although recombinant protein C was secreted in the presence of vitamin K, the decrease in total amount of the radioactivity in the warfarin-treated cells suggested intracellular degradation. This degradation depended on the concentration of warfarin and was not inhibited by an endoplasmic reticulum (ER)-Golgi transport inhibitor or by lysosomotropic inhibitors. Thus, protein C synthesized in the presence of warfarin is selectively degraded and the degradation occurs in a pre-Golgi, nonlysosomal compartment. Among the protease inhibitors tested, N-acetyl-Leu-Leu-methioninal and N-acetyl-Leu-Leu-norleucinal blocked the degradation of protein C synthesized in the presence of warfarin and the protein C accumulated intracellularly, in a dose-dependent manner. Both inhibitors, however, did not disturb the secretion of protein C in the vitamin K-treated cells. Thus, a cysteine protease(s) appeared to be responsible for the degradation. These results suggest that protein C synthesized in the presence of warfarin was selectively degraded by a cysteine protease(g) in the ER through a "quality control" mechanism.

[New intracellular calcium antagonists. I. Synthesis and pharmacological evaluation of 2,3,4,5-tetrahydro-1,5-benzothiazepine analogs]

A series of 2,3,4,5-tetrahydro-1,5-benzothiazepine and related compounds were prepared, and the intracellular Ca2+ inhibitory effects were examined using methoxamine- or caffeine-induced contraction of isolated rabbit arteries. Structure-activity relationship studies of these compounds are discussed and the results suggest that novel 5-[3-[2-(3,4-dimethoxyphenyl)ethyl]aminopropionyl]-2,3,4,5- tetrahydro-1,5-benzothiazepine fumarate (20d) showed the most potent inhibitory action on the intracellular Ca2+ release.

Identification and genetic analysis of a common molecular variant of histidine-rich glycoprotein with a difference of 2kD in apparent molecular weight

Two forms of histidine-rich glycoprotein (HRG) were detected on SDS-PAGE by silver staining and immunoblotting after isolation of the protein from pooled plasma using immuno-affinity chromatography followed by chromatography with heparin-Sepharose. Both forms were single-chain molecules and the apparent molecular weights of form 1 and form 2 were 77 kD and 75 kD respectively. Mendelian inheritance of both HRG forms was observed in four families with 24 informative meioses, strongly suggesting that the two forms are encoded by different alleles. The frequency of form 1 and form 2 in a group of 36 individuals was 0.35 and 0.65 respectively. The difference between the two molecular variants was studied by direct sequence analysis of amplified exons of the HRG gene from 6 individuals who were homozygous either for form 1 or form 2. Five amino acid polymorphisms in three different exons were observed: Ile/Thr in exon4; Pro/Ser in exon 5; His/Arg, Arg/Cys and Asn/Ile in exon 7. Analysis of these polymorphisms in 20 volunteers showed that only the Pro/Ser polymorphism at position 186 in exon 5 was coupled to the form of the HRG protein. Ser was found in form 1 and Pro in form 2. The presence of Ser at position 186 introduces a consensus sequence for a N-glycosylation site (Asn-X-Ser/Thr). By removing N-linked sugars with N-glycanase, it could be demonstrated that the difference between the two forms of HRG is caused by an extra carbohydrate group at Asn 184 in form 1.

Incorporation of [1-carbon-11]palmitate in monkey brain using PET

We determined regional incorporation coefficients (k*) of plasma [1-11C]palmitate into stable brain lipids of anesthetized monkeys with PET.

METHODS

Carbon-11-palmitate was injected intravenously in untreated animals and in animals pretreated with methyl palmoxirate (MEP), an inhibitor of beta-oxidation of palmitate in the brain and periphery. Plasma radioactivity was followed, and brain radioactivity was determined at various times using PET. A least-squares method was used to fit the data to an operational equation to obtain regional values of k* and of cerebral blood volume (Vb) in individual experiments.

RESULTS

MEP significantly decreased the integral of plasma [11C]CO2 following 11C-palmitate infusion. Mean values of k* in monkeys not given MEP were 4.9, 4.2, 4.9, 4.0 and 2.9 x 10(-5) ml/sec.g for the temporal, frontal, parietal and occipital cortices and white matter, respectively. With the exception of k* in white matter, which was increased by MEP, k* in the other brain regions was not significantly changed by MEP. The Vb ranged from 0.035 ml/g to 0.048 ml/g in gray matter regions and equaled 0.022 ml/g in white matter.

CONCLUSION

PET can be used to determine regional incorporation coefficients of 11C-palmitate into the primate brain in vivo. Combined with MEP, 11C-palmitate could be used with PET to examine regional brain phospholipid metabolism in humans in normal and pathological conditions.

Cytoplasmic domain of the ubiquitous Na+/H+ exchanger NHE1 can confer Ca2+ responsiveness to the apical isoform NHE3

The Na+/H+ exchanger isoforms NHE1 and NHE3 are regulated differently by various stimuli. Calcium has been recognized as one of the major second messengers in such exchanger regulation. We previously proposed that Ca(2+)-induced activation of NHE1 occurs via displacement of its autoinhibitory domain from the H+ modifier site due to direct binding of Ca2+/calmodulin. To further validate this hypothesis, the functional role of the cytoplasmic domain was studied in both wild-type and chimeric exchangers, i.e. NHE1, NHE3, NHE1 with the cytoplasmic domain of NHE3 (N1N3), and NHE3 with the cytoplasmic domain of NHE1 (N3N1). After expression in exchanger-deficient fibroblasts (PS120), early response (< 80 s) to external stimuli was assessed as 5-(N-ethyl-N-isopropyl)amiloride-sensitive 22Na+ uptake. Among stimuli tested (ionomycin, alpha-thrombin, phorbol ester, hyperosmotic stress, and platelet-derived growth factor) that are all known to activate NHE1, only ionomycin and thrombin induced a significant intracellular Ca2+ mobilization and early activation of 22Na+ uptake, implying that Ca2+ is a main regulator of NHE1 in the early phase of the agonist response. However, all the stimuli did not activate NHE3 or N1N3. In contrast, a significant stimulation of 22Na+ uptake in response to ionomycin and thrombin was observed in N3N1, accompanied by an alkaline shift of pHi sensitivity (approximately 0.2 pH units). Deletion of the cytoplasmic calmodulin-binding domain within N3N1 resulted in a constitutive alkaline shift of pHi sensitivity and abolished the activation by ionomycin and thrombin. Together, these data reinforce our concept of Ca(2+)-induced activation of NHE1. Furthermore, they provide evidence for a functional interaction of the autoinhibitory domain of NHE1 with the H(+)-modifier site of a different isoform, NHE3.

Detachment of cultured cells from the substratum induced by the neutrophil-derived oxidant NH2Cl: synergistic role of phosphotyrosine and intracellular Ca2+ concentration

The neutrophil-derived, membrane-permeating oxidant, NH2Cl, (but not the non-membrane-permeating chloramine, taurine-NHCl) induced detachment of fetal mouse cardiac myocytes and other cell types (fibroblasts, epithelial cells, and endothelial cells) from the culture dish, concomitant with cell shrinkage ("peeling off"). Stimulated human neutrophils also induced peeling off of cultured mouse cardiac myocytes when the latter were pretreated with inhibitors of .OH and elastase. Immunofluorescence microscopy revealed that the NH2Cl-induced peeling off of WI-38 fibroblasts is accompanied by disorganization of integrin alpha 5 beta 1, vinculin, stress fibers, and phosphotyrosine (p-Tyr)-containing proteins. Decrease in the content of the p-Tyr-containing proteins of the NH2Cl-treated cells was analyzed by immunoblotting techniques. Coating of fibronectin on the culture dish prevented both NH2Cl-induced peeling off and a decrease in p-Tyr content. Preincubation with a protein-tyrosine phosphatase inhibitor, sodium orthovanadate (Na3VO4), also prevented NH2Cl-induced peeling off, suggesting that dephosphorylation of p-Tyr is necessary for peeling off. NH2Cl-induced peeling off was accompanied by an increase in intracellular Ca2+ concentration ([Ca2+]i) in mouse cardiac myocytes and WI-38 fibroblasts. The absence of extracellular Ca2+ prevented both NH2Cl-induced peeling off and increased [Ca2+]i, both of which did occur on subsequent incubation of the cells in Ca2+-containing medium. These observations suggest that an increase in [Ca2+]i is also necessary for peeling off. Depletion of microsomal and cytosolic Ca2+ by incubation with the microsomal Ca2+-ATPase inhibitor 2',5'-di(tert-butyl)-1,4-benzohydroquinone (BHQ) plus EGTA prevented both NH2Cl-induced increases in [Ca2+]i and peeling off. Direct inhibition of microsomal Ca2+ pump activity by NH2Cl may participate in the NH2Cl-induced [Ca2+]i increment. A combination of p-Tyr dephosphorylation by genistein (an inhibitor of tyrosine kinase) and an increase in [Ca2+]i by BHQ could also induce peeling off. All these observations suggest a synergism between p-Tyr dephosphorylation and increased [Ca2+]i in NH2Cl-induced peeling off.