RNA-dependent RNA polymerase activity of the soluble recombinant hepatitis C virus NS5B protein truncated at the C-terminal region

The hepatitis C virus (HCV) NS5B protein encodes an RNA-dependent RNA polymerase (RdRP), which is the central catalytic enzyme of HCV replicase. We established a new method to purify soluble HCV NS5B in the glutathione S-transferase-fused form NS5Bt from Escherichia coli which lacks the C-terminal 21 amino acid residues encompassing a putative anchoring domain (anino acids 2990-3010). The recombinant soluble protein exhibited RdRP activity in vitro which was dependent upon the template and primer, but it did not exhibit the terminal transferase activity that has been reported to be associated with the recombinant NS5B protein from insect cells. The RdRP activity of purified glutathione S-transferase-NS5Bt and thrombin-cleavaged non-fused NS5Bt shares most of the properties. Substitution mutations of NS5Bt at the GDD motif, which is highly conserved among viral RdRPs, and at the clustered basic residues (amino acids 2919-2924 and 2693-2699) abolished the RdRP activity. The C-terminal region of NS5B, which is dispensable for the RdRP activity, dramatically affected the subcellular localization of NS5B retaining it in perinuclear sites in transiently overexpressed mammalian cells. These results may provide some clues to dissecting the molecular mechanism of the HCV replication and also act as a basis for developing new anti-viral drugs.

Phase-encoded joint transform correlator to reduce the influence of extraneous signals

A technique to reduce the influence of the dc and the complex-conjugate correlation signals that are inherent in a joint transform correlator is proposed. The key part of this technique is the use of a phase mask. The mask contributes only extraneous signals, so the influence of the signals is reduced. The desirable correlation signal is not affected, and its shape is retained. Computer simulations confirm the performance of the proposed phase-encoded joint transform correlator.

Pulmonary toxicity after granulocyte colony-stimulating factor-combined chemotherapy for non-Hodgkin's lymphoma

Sporadic cases have developed pulmonary toxicity after receiving chemotherapy and granulocyte colony-stimulating factor (G-CSF). However, because such cases received chemotherapy that alone frequently causes pulmonary toxicity, the role of G-CSF in this toxicity has been unclear. CHOP therapy (cyclophosphamide, doxorubicin, vincristine and prednisolone) only slightly induces pulmonary toxicity. However, we observed a considerable incidence of this toxicity in non-Hodgkin's lymphoma subjects receiving CHOP therapy and G-CSF (6 out of 52 subjects, 11.5%). In this cohort, among various characteristics, including the dose and interval of CHOP therapy, only the mean peak leucocyte count (MPLC) with each therapy cycle was associated with development of this toxicity (MPLC > or = 23.0 x 10(9) l(-1), 6 out of 29 cases; MPLC < 23.0 x 10(9) l(-1), 0 out of 23 cases; P = 0.020). These findings suggest that the effect of G-CSF is the main determinant of the pulmonary toxicity in these cases. Because the toxicity was associated with a large MPLC and did not recur in cases readministered G-CSF, an idiosyncratic reaction to G-CSF is unlikely to be the pathogenesis of this toxicity. Thus, lowering the G-CSF dose seems to be useful in the prevention of this toxicity. In all six cases, the time course of manifestation of the toxicity was the same, and early application of high-dose corticosteroid led to cure. This knowledge will be helpful in the care of similar cases.

Impact of corticotropin-releasing hormone on gastrointestinal motility and adrenocorticotropic hormone in normal controls and patients with irritable bowel syndrome

BACKGROUND

Corticotropin-releasing hormone (CRH) plays a key role in modulating intestinal motility in stressed animals.

AIMS

To evaluate the effect of CRH on intestinal motility in humans and to determine whether patients with irritable bowel syndrome (IBS) have an exaggerated response to CRH.

SUBJECTS

Ten IBS patients diagnosed by Rome criteria and 10 healthy controls.

METHODS

CRH (2 micrograms/kg) was intravenously administered during duodenal and colonic manometry and plasma adrenocorticotropic hormone (ACTH) was measured by radioimmunoassay.

RESULTS

CRH induced motility of the descending colon in both groups (p < 0.001) and induced greater motility indexes in IBS patients than in controls (p < 0.05). CRH produced duodenal phase III motor activity in 80% of the subjects and duodenal dysmotility in 40% of IBS patients. Abdominal symptoms evoked by CRH in IBS patients lasted significantly longer than those in controls (p < 0.05). CRH induced significant increases in plasma ACTH levels in both groups (p < 0.001) and produced significantly higher plasma ACTH levels in IBS patients than in controls (p < 0.001).

CONCLUSION

Human intestinal motility is probably modulated by exogenous CRH. The brain-gut in IBS patients may have an exaggerated response to CRH.

Neurite outgrowth of neuroblastoma cells overexpressing alpha and beta isoforms of Ca2+/calmodulin-dependent protein kinase II-effects of protein kinase inhibitors

Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) is one of the most abundant protein kinases in the brain and has a broad substrate specificity [M.K. Bennett, N.E. Erondu, M.B. Kennedy, Purification and characterization of a calmodulin-dependent protein kinase that is highly concentrated in brain, J. Biol. Chem. 258 (1983) 12735-12744 [1]; J.R. Goldenring, B. Gonzalez, J.S. McGuire, Jr., R.J. DeLorenzo, Purification and characterization of a calmodulin-dependent kinase from rat brain cytosol able to phosphorylate tubulin and microtubule-associated proteins, J. Biol. Chem. 258 (1983) 12632-12640 [4]; M.B. Kennedy, P. Greengard, Two calcium/calmodulin-dependent protein kinases, which are highly concentrated in brain, phosphorylate protein I at distinct sites, Proc. Natl. Acad. Sci. U.S.A. 78 (1981) 1293-1297 [10]; T. Yamauchi, H. Fujisawa, Evidence for three distinct forms of calmodulin-dependent protein kinases from rat brain, FEBS Lett. 116 (1980) 141-144 [20]; T. Yamauchi, H. Fujisawa, Purification and characterization of the brain calmodulin-dependent protein kinase (kinase II), which is involved in the activation of tryptophan 5-monooxygenase, Eur. J. Biochem. 132 (1983) 15-21 [21]]. The alpha and beta isoforms of CaM kinase II are known to be expressed almost exclusively in the brain [P.I. Hanson, H. Schulman, Ca2+/calmodulin-dependent protein kinases, Annu. Rev. Biochem. 61 (1992) 559-601 [7]]. To elucidate the cellular function of CaM kinase II, we introduced cDNA of wild-type CaM kinase II alpha- or beta-isoform, and of mutant alpha-isoform (Ala-286 kinase) into two different types of neuroblastoma, Neuro2a (Nb2a) and NG108-15, thus generating cell lines stably producing elevated levels of these kinases. The mutant alpha-isoform is markedly suppressed in its autophosphorylation by replacement of Thr-286 with Ala [Y.-L. Fong, W.L. Taylor, A.R. Means, T.R. Soderling, Studies of the regulatory mechanism of Ca2+/calmodulin-dependent protein kinase II. Mutation of threonine 286 to alanine and aspartate, J. Biol. Chem. 264 (1989) 16759-16763 [3]; P.I. Hanson, M.S. Kapiloff, L.L. Lou, M.G. Rosenfeld, H. Schulman, Expression of a multifunctional Ca2+/calmodulin-dependent protein kinase and mutational analysis of its autoregulation, Neuron 3 (1989) 59-70 [6]; S. Ohsako, H. Nakazawa, S. Sekihara, A. Ikai, T. Yamauchi, Role of Threonine-286 as autophosphorylation site for appearance of Ca2+-independent activity of calmodulin-dependent protein kinase II alpha subunit, J. Biochem. 109 (1991) 137-143 [15]]. We provided evidence that CaM kinase II played a role in regulating neurite outgrowth and growth cone motility in these cells, and that the autophosphorylation is essential for the kinase to sufficiently exert its cellular function in vivo [Y. Goshima, S. Ohsako, T. Yamauchi, Overexpression of Ca2+/calmodulin-dependent protein kinase II in Neuro2a and NG108-15 neuroblastoma cell lines promotes neurite outgrowth and growth cone motility, J. Neurosci. 13 (1993) 559-567 [5]]. Neurite outgrowth was further stimulated by treatment with 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) or chelerythrine, inhibitors of protein kinase C [T. Nomura, K. Kumatoriya, Y. Yoshimura, T. Yamauchi, Overexpression of alpha and beta isoforms of Ca2+/calmodulin-dependent protein kinase II in neuroblastoma cells-H-7 promotes neurite outgrowth, Brain Res. 766 (1997) 129-141 [14]]. The morphological change stimulated with protein kinase inhibitors was rapid and was greater in the beta than alpha cells. Some substrates of CaM kinase II related to neurite outgrowth were detected in cells overexpressing the kinase stimulated with H-7. These results suggest that CaM kinase II and protein kinase C play an important role in the control of cell change. (c) 1998 Elsevier Science B.V. All rights reserved.

Modulation of ACh receptor currents by arachidonic acid

The present study investigated the effects of arachidonic acid on Torpedo (alpha beta gamma delta) and neuronal nicotinic acetylcholine (ACh) receptors (chick alpha7; rat alpha7, alpha3 beta2, alpha3 beta4, alpha4 beta2, and alpha4 beta4). Arachidonic acid (10 microM) depressed currents through normal Torpedo ACh receptors during treatment and afterward, persistently (>/=30 min) potentiated the currents. The potentiation was blocked by the selective protein kinase C (PKC) inhibitor, GF109203X or PKC inhibitor peptide (PKCI). The depression was not inhibited by any protein kinase inhibitor examined here, but greater in Ca2+-free extracellular solution. Arachidonic acid also potentiated currents through mutant Torpedo ACh receptors lacking PKC phosphorylation sites at Ser333 on the alpha subunit and Ser377 on the delta subunit without depression, but otherwise, it depressed currents through mutant receptors replacing of each Ser by negatively charged amino acid residue, possibly that mimics PKC phosphorylation of the receptors. These results suggest that the depression was due to the direct blocking effect on Ca2+-modulatory sites, which was accelerated under conditions of the receptors phosphorylated by PKC, and that the potentiation was caused by PKC activation, independently of PKC phosphorylation of the receptors. Arachidonic acid reduced currents through chick alpha7 receptors by a mechanism independent of protein kinase activation. In contrast, arachidonic acid potentiated currents through rat alpha7, alpha3 beta2, alpha4 beta2, and alpha4 beta4 receptors, perhaps by the same mechanism as the potentiation observed in Torpedo ACh receptors, although it had no effect on rat alpha3 beta4 receptors. The results of the present study thus demonstrate that arachidonic acid exerts diverse actions on nicotinic ACh receptors by different mechanisms.

Antigen receptor cross-linking by anti-immunoglobulin antibodies coupled to cell surface membrane induces rapid apoptosis of normal spleen B cells

Cross-linking of surface immunoglobulin (sIg) has been shown to induce either activation or apoptosis of mature B cells presumably depending on the nature of antigens. However, the nature of antigens for induction of mature B-cell apoptosis is not yet fully understood. We cross-linked sIg of mature B cells with various amounts of either anti-Ig antibodies in the soluble form or anti-Ig coupled to erythrocytes or myeloma cells as surrogate membrane-bound antigens. Anti-Ig antibodies coupled to cell surface membrane induced rapid and extensive apoptosis of normal spleen B cells even in the absence of signalling via the Fc receptor. In contrast, soluble anti-Ig induced proliferation or apoptosis of mature B cells depending on the concentration of anti-Ig. The extent of apoptosis induced by soluble anti-Ig was limited compared to that induced by membrane-bound anti-Ig. These results suggest that mature B cells undergo apoptosis or proliferation depending on whether antigens are soluble or membrane-bound and on antigen doses.

[Malignant recurrence of solitary fibrous tumor of the pleura developed 20 years after the surgery: a case report of re-extirpation]

A 63-year-old female developed the chest wall tumor protruding into the right thoracic cavity. She consulted our hospital complaining of chest pain. 20 years before this episode, she had undergone tumor extirpation combined with the partial resection of adherent anterior chest wall and the diaphragm for large benign solitary fibrous tumor of the pleura. Because of the difficulty in making diagnosis by needle biopsy, operation (re-tumor extirpation combined with the chest wall) was done. Histological examination revealed that the tumor was malignant solitary fibrous tumor. We concluded that the tumor was the malignant recurrence of the benign solitary fibrous tumor resected 20 years before. Occasionally, benign solitary fibrous tumor of the pleura recurs and behaves more aggressively than primary, but such a long latent period as 20 years is quite uncommon. So we present the case and the review of the literature.

Purification, cDNA cloning, and expression of UDP-Gal: glucosylceramide beta-1,4-galactosyltransferase from rat brain

Lactosylceramide synthase is an enzyme that catalyzes the transfer of galactose from UDP-Gal to glucosylceramide, and thus participates in the biosynthesis of most glycosphingolipids in mammals. We purified this enzyme over 61,000-fold to near homogeneity with a 29. 7% yield from rat brain membrane fractions. The isolation procedure included solubilization with Triton X-100, affinity chromatography on wheat germ agglutinin-agarose and UDP-hexanolamine-agarose, and hydroxylapatite column chromatography, followed by ion exchange chromatography. The final preparation migrated as a broad band with an apparent molecular mass of 61 kDa on SDS-polyacrylamide gel electrophoresis. This apparent molecular mass was reduced to 51 kDa by N-glycanase digestion, suggesting that the enzyme has a glycoprotein nature. The enzyme required Mn2+ for its activity, and glucosylceramide was its preferred substrate. The cDNA for the enzyme was cloned from a rat brain cDNA library. The cDNA insert encoded a polypeptide of 382 amino acid residues, with a molecular weight of 44,776. The polypeptide contained eight putative glycosylation sites and a 20-amino acid residue transmembrane domain at its N terminus. Amino acid sequence homology analysis revealed that this enzyme shared 39% homology with mouse beta-1, 4-galactosyltransferase (EC 2.4.1.38), which catalyzes the transfer of Gal to beta-1,4-GlcNAc in glycoproteins.

ATP produces potassium currents via P3 purinoceptor in the follicle cell layer of Xenopus oocytes

Purinoceptor agonists produced potassium currents with the order of potency: ATP > adenosine = ADP = AMP > beta,gamma-methylene ATP, while a small response or no response was induced by 2-methylthio ATP, UTP, or alpha,beta-methylene ATP. The response induced by beta,gamma-methylene ATP was completely inhibited in the presence of alpha,beta-methylene ATP, suggesting that the relevant receptor for these agonists was a P3 purinoceptor. ATP induced currents with a latency of 24 s and the currents were not induced in defolliculated oocytes. The currents were not affected by either the Gi/o-protein inhibitor, pertussis toxin (PTX), or the selective cAMP-dependent protein kinase inhibitor, H-89, or the phospholipase C (PLC) inhibitor, neomycin, or the phospholipase A2 (PLA2) inhibitor, 4-bromophenacyl bromide. The currents were enhanced by the selective protein kinase C (PKC) inhibitor, GF109203X, but otherwise, they were reduced by the potent PKC activator, 12-O-tetradecanoylphorbol-13-acetate. The results of the present study suggest that a P3 purinoceptor in the follicle cell layer of oocytes is involved in activation of potassium channels and that the evoked currents are regulated by PLC/PLA2-independent PKC activation.

High incidence of esophageal cancer in esophageal achalasia by the oral administration of N-amyl-N-methylnitrosamine and its prevention by nicardipine hydrochloride in mice

Esophageal achalasia (EA) is a rare disease in man and animals and there are many discussions on its higher risk of esophageal cancer. N-Amyl-N-methylnitrosamine (AMN) which specifically induces esophageal tumors in mice and rats was given to three mutant mouse strains, i.e. 101/N, STX/Le and BXH-8, which develop a high incidence of EA. The incidence of EA in 101/N, STX/Le, BXH-8 and normal C57BL/6J mice was 38.5% (110/286), 30.1% (43/143), 91.8% (190/207) and 0% (0/167), respectively. The average numbers of AMN-induced esophageal tumors in EA(+) were significantly higher than those of EA(-) in all of the 101/N, STX/Le and BXH-8 mice. Furthermore, significantly larger size tumors and invasive squamous cell carcinomas were found in EA(+) mice than in EA(-) mice. These results indicate the higher sensitivity of EA for both tumor induction and promotion, possibly due to the longer retention of AMN. In fact, relaxation of the lower esophagus by a smooth muscle relaxing calcium-channel blocker, nicardipine hydrochloride, significantly prevented the induction of esophageal tumors.

Minimal residual disease in acute myelogenous leukemia with PML/RAR alpha or AML1/ETO mRNA and phenotypic analysis of possible T and natural killer cells in bone marrow

Here we studied minimal residual disease (MRD) of patients with acute myeloid leukemia (AML) who have PML/RAR alpha or AML1/ETO as well as the phenotypic analysis of lymphocyte subsets involved in antitumor immunity. Eight patients in long-term (LT; 3 to 15 years) and 15 patients in short-term (ST; up to 3 years) remission were studied. Using the reverse transcription-polymerase chain reaction (RT) assay, the limit of detection was 10(-5) to 10(-6) for PML/RAR alpha transcript and 10(-4) to 10(-5) for the AML1/ETO transcript. Simultaneously, T lymphocyte subsets and NK cells from the peripheral blood (PB) and bone marrow (BM) were investigated by flow cytometric analysis. Four of the eight patients in LT and 7 of the 15 patients in ST remission were MRD-positive. Although all MRD-positive patients in LT remission are still until now event-free, 3 of the 7 MRD-positive (MRD+) patients in ST remission soon relapsed. The total populations of CD4+, CD8+ and CD56+ [possible T-cell and natural killer (T/NK) populations] in the BM of ST patients and MRD+/LT patients were significantly (p < .01) low. The CD8+ CD28+ population showed the same tendency (p < .01-.02). The T/NK subsets in the BM of MRD-negative (MRD-) LT (MRD-/LT) patients showed similar numbers of cells as normal volunteers. Basically, the total percentage of the CD4+, CD8+ and CD56+ cell populations in the BM was increased and in the following order: MRD-/LT patients, normal volunteers, MRD+/LT patients and MRD+ or -/ST patients. The percentages of the T/NK-cell subsets in the PB were not significantly different among these groups. Thus, the difference of the possible T/NK-cell phenotype in the BM may strongly influence clinical and molecular remission. These results still remain to be confirmed by further studies of the functional anti-tumor immunity of T/NK cells of AML in remission.

Antitumor-promoting naphthoquinones from Catalpa ovata

Bioassay-directed fractionation of an extract of the stem-bark of Catalpa ovata led to the isolation of three new naphthoquinones: 8-methoxydehydroiso-alpha-lapachone (1), 9-methoxy-4-oxo-alpha-lapachone (2), and (4S,4aR,10R,10aR)-4, 10-dihydroxy-2,2-dimethyl-2,3,4,4alpha,10, 10alpha-hexahydrobenzo[g]chromen-5-one (3), which is a 1,4-reductive form of 6. The known compounds 3-hydroxydehydroiso-alpha-lapachone (4), 4,9-dihydroxy-alpha-lapachone (5), 4-hydroxy-alpha-lapachone (6), and 9-methoxy-alpha-lapachone (7), and catalpalactone (8) were also isolated. Their structures were elucidated by spectral methods. These compounds all exhibited significant inhibitory activity against 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced Epstein-Barr virus early antigen (EBV-EA) activation in Raji cells.

Control of plasma cholesterol-lowering action of probucol with various lipid carrier systems

In order to explore the relationship between the pharmacokinetic properties and pharmacological actions of lipophilic drugs injected with lipid carrier systems, probucol was selected as a model drug with high lipophilicity, and the effect of disposition control on cholesterol-lowering activities was evaluated. Both large emulsion, with mean diameter of 280 nm, and long-circulating type small emulsion containing egg sphingomyelin with mean diameter of 100 nm, showed stable incorporation of probucol. The former produced rapid accumulation of probucol in the liver, while the latter demonstrated prolonged systemic circulation and gradual hepatic uptake. On the other hand, injection of a micellar solution with HCO-60 (polyoxyethylene hydrogenated castor oil) showed a rapid decrease in plasma concentration and a high hepatic uptake of probucol, similar to injections with serum, suggesting the rapid release of the drug from the micelles. However, probucol in a micellar solution showed higher cholesterol-lowering action than that in emulsion formulations. These results suggested that the pharmacological action of probucol in the liver might be affected by the uptake mode and sequential disposition in the organ, depending on the drug retention properties of the lipid carrier particles.

Effect of mouse intestinal bacteria on incidence of colorectal tumors induced by 1,2-dimethylhydrazine injection in gnotobiotic transgenic mice harboring human prototype c-Ha-ras genes

We produced transgenic (Tg) gnotobiotic (GB) mice carrying human prototype c-Ha-ras genes and compared the incidence of colorectal tumors induced by 1,2-dimethylhydrazine (DMH) injection. At 7 to 11 weeks of age, germfree (GF) CB6F1-Tg Hras2 mice were inoculated with various mouse fecal suspensions or mixtures of bacteria isolated from mouse feces. Three weeks after bacterial inoculation, DMH was administered by subcutaneous injection at 20 mg per kg body weight for 20 weeks. Mice were euthanized 5 weeks after the last injection to investigate the number of colorectal tumors. The incidence of colorectal tumors was high in both Tg- and non-Tg-GF mice (100%). In Tg-specific pathogen-free (SPF) mice and Tg-GB-4 mice associated with basic mouse flora consisting of Escherichia coli, lactobacilli, Bacteroides and clostridia, the incidence of colorectal tumors was as high as that in GF mice. In Tg-SPF mice, the tumor score was higher than in Tg-GF mice (p < 0.01), but no colorectal tumors were detected in non-Tg groups of SPF, and the tumor incidence was remarkably low in non-Tg-GB-4 mice. The tumor incidence and score in Tg- and non-Tg-GB mice varied depending on the bacterial combination in their intestine. These results indicate that the presence of human c-Ha-ras genes and intestinal bacteria substantially modify colorectal tumorigenesis induced by DMH.

Reduction of a model for an Onchidium pacemaker neuron

The eight-variable model for the giant neuron localized in the esophageal ganglia of the marine pulmonate mollusk Onchidium verruculatum is reduced to four- and-three-dimensional systems by regrouping variables with similar time scales. These reduced models replicate the complex behavior including beating, periodic bursting and aperiodic bursting displayed by the original full model when the parameter Iext representing the intensity of the constant DC current stimulation is varied across a wide range. The complex behavior of the full model arises from the interaction of fast and slow dynamics, and depends on the time scale Cs of the slow dynamics. The four-variable reduced model is constructed independently from the parameter Cs so that it reproduces the two-dimensional bifurcation structure of the full model for the two parameters Iext and Cs. The three-variable reduced model is derived for a specific value of Cs. The parameters of this model are tuned so that its one-parameter bifurcation diagram for Iext closely matches that of the full model. Correspondence between bifurcation structures ensures that both reduced models reproduce the various discharge patterns of the full model. Similarity between the full and reduced models is also confirmed by comparing mean firing frequencies and membrane potential waveforms in various regimes. The reduction exposes the factors essential for reproducing the dynamics of the full model; indeed, it shows that the eight variables representing the membrane potential and seven gating variables of six ionic currents in the full model account, in fact, for three basic processes responsible for excitability, post-discharge refractoriness and slow membrane modulation.

Increase in serum vascular endothelial growth factor levels during altitude training

The present study was performed to evaluate the effects of physical exercise at altitudes on serum vascular endothelial growth factor (VEGF) levels. Eight subjects underwent intensive swimming training for 21 days at 1886 m. After altitude training commenced, red blood cell (RBC) counts and erythropoietin levels increased, but both haemoglobin and haematocrit levels did not change significantly. The serum level of VEGF, measured by means of a highly sensitive chemiluminescence (ELISA), showed a transient decrease 10 days after start of the altitude training, thereafter increasing significantly to reach a peak level 19 days later, rising from 23.0 +/- 5.3 to 46.0 +/- 14.6 pg mL-1 (P < 0.05 vs. before). On return to low altitude in Japan, the level of VEGF decreased, and 1 month later had returned to initial levels. Endurance training at altitudes increases serum VEGF levels; this could be an adaptive reaction to hypoxic conditions. This result suggests that VEGF may provide a new physiological parameter for hypoxic stress imposed by high altitude training.

Pharmacokinetic characteristics and therapeutic effects of mitomycin C-dextran conjugates after intratumoural injection

The pharmacokinetics and therapeutic effects of macromolecular prodrugs of mitomycin C (MMC), MMC-dextran conjugates (MMC-D) were studied after intratumoural injection in rats bearing Walker 256 carcinosarcoma. As the first step, the intratumoural disposition characteristics of these drugs were delineated in perfusion experiments employing a tissue-isolated tumour preparation. While MMC immediately disappeared from the tumour preparation following direct intratumoural injection, cationic and anionic MMC-D were retained in the tumour longer, demonstrating that the intratumoural clearance of MMC can be greatly retarded by dextran conjugation. The effect was more pronounced in the case of the cationic conjugate. Venous outflow data in the perfusion experiments were analyzed based on a compartment model in which the tumour tissue was assumed to consist of two compartments, one well- and the other poorly-perfused. The pharmacokinetic analysis revealed that macromolecular conjugation reduced elimination of MMC from the poorly-perfused region rather than well-perfused region. Simulation of conjugated and free MMC levels in the tissue using the calculated parameters clearly showed that intratumoural injection of MMC-D, especially the cationic form, can maintain a certain level of active free MMC in the tissue for a much longer time period. The long retention of cationic MMC-D in tumour after intratumoural injection was also confirmed by an in vivo pharmacokinetic study and whole body autoradiography in rats bearing subcutaneous Walker 256 carcinosarcoma. In addition, superior antitumour activity of cationic MMC-D was observed against subcutaneous tumours after intratumoural injection. Together with the finding that MMC is selectively toxic to hypoxic tumour cells at low concentrations, these pharmacokinetic studies strongly support the therapeutic efficacy of the macromolecular prodrugs.

Frequent p53 mutations at dipyrimidine sites in patients with pyothorax-associated lymphoma

A high incidence of non-Hodgkin's lymphoma of the pleural cavity has developed in Japanese patients with long-standing pyothorax (38 years on average) resulting from artificial pneumothorax for the treatment of pulmonary tuberculosis or tuberculous pleuritis. Patients with pyothorax-associated lymphoma (PAL) have long been exposed to antituberculous drugs, antibiotics, bacterial or viral products, and frequent diagnostic radiation for the confirmation of pneumothorax and pyothorax. We analyzed p53 mutations on paraffin-embedded specimens from 21 patients with PAL by PCR-single-strand conformational polymorphism followed by direct sequencing. An unusually high frequency of p53 mutations (14 of 21 cases, 67%) was detected in the PAL specimens, and mutations consisted of 13 nucleotide substitutions and 1 deletion. Furthermore, 10 of 13 substitutions (77%) occurred at dipyrimidine sites (CC:GG to CT:GA substitution). Such specificity has not been reported, except for solar light-related skin cancer and AIDS-related lymphoma in some parts. An UV light mimetic agent may be produced in the long history of chronic inflammation in tuberculosis or immunodeficient patients.

Contribution of the disulfide bond of the A subunit to the action of Escherichia coli heat-labile enterotoxin

Escherichia coli heat-labile enterotoxin (LT) consists of an A subunit and five B subunits. These subunits oligomerize into an assembled holotoxin within the periplasm. Structural analysis of LT has revealed that the A subunit interacts with the B subunit through its carboxy terminus. This indicates that the carboxy-terminal portion of the protein is required for assembly of holotoxin in the periplasm. However, it is not known whether other regions of the A subunit contribute to the assembly. The A subunit constituting the holotoxin contains a disulfide bond between Cys-187 and Cys-199. It has been observed in many proteins that the intramolecular disulfide bond is deeply involved in the function and tertiary structure of the protein. We speculated that the disulfide bond of the A subunit contributes to the assembly in the periplasm, although the bond is not a structural element of the carboxy-terminal portion of the A subunit. We replaced these cysteine residues of the A subunit by oligonucleotide-directed site-specific mutagenesis and analyzed the LTs produced by cells containing the mutant LT genes. The amount of the mutant holotoxin produced was small compared with that of the wild-type strain, indicating that the disulfide bond of the A subunit contributes to the structure which functions as the site of nucleation in the assembly. A reconstitution experiment in vitro supported the notion. Subsequently, we found that the mutant A subunit constituting holotoxin is easily degraded by trypsin and that in cells incubated with mutant LTs, the lag until the intracellular cyclic AMP begins to accumulate is longer than in cells incubated with native LTs. These results might be useful for the analysis of the interaction of LT with target cells at the molecular level.

Generation of immortalized murine forebrain cell lines expressing an alpha isoform of Ca2+/calmodulin-dependent protein kinase II

Immortalized hybrid cells were generated by the somatic fusion of the cells from the forebrain of embryonic mouse with N18TG2 neuroblastoma cells. Three monoclonal hybrid cell lines, designated NF26, NF81, and NF83 (neuroblastoma forebrain hybrid cells), expressing an alpha isoform of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) were isolated, and their expression was demonstrated by immunoblotting and immunocytochemistry using a monoclonal antibody specific to the a isoform of the enzyme. The kinase activity of the hybrid cells was 2- to 3-fold higher than that of the parent neuroblastoma line N18TG2 cells. The neuronal origin of these lines was shown by their immunoreactivity to neurofilament protein, a neuron specific marker. Lines NF26, NF81, and NF83 are the first cell lines to express the gene of the alpha isoform of CaM kinase II in the brain.

Involvement of glutamic acid residue at position 7 in the formation of the intramolecular disulfide bond of Escherichia coli heat-stable enterotoxin Ip in vivo

Escherichia coli heat-stable enterotoxin Ip (STIp) is a small peptide toxin composed of 18 amino acid residues containing three intramolecular disulfide bonds. We found previously that the bonds are formed by the catalysis of DsbA (a oxidoreductase) in periplasm [1]. To interact with DsbA, the STIp in periplasm must have a structure suitable as substrate. However, the amino acid residues contributing to the construction of this structure have not been elucidated. We mutated the codon for the glutamic acid at position 7 of STIp by oligonucleotide site-specific mutagenesis in vivo and analysed the STIp produced from the mutant gene. The intramolecular disulfide bonds were not formed in mutant STIp (Glu-7-->Ala), but were formed in mutant STIp (Glu-7-->Asp). Furthermore, we found that replacing the asparagine residue at position 11 and the proline residue at position 12 did not affect the disulfide bond formation of STIp. The results indicate that a negative charge at position 7 in the sequence of STIp is necessary for STIp to interact with DsbA in periplasm.