Human glycine decarboxylase gene (GLDC) and its highly conserved processed pseudogene (psiGLDC): their structure and expression, and the identification of a large deletion in a family with nonketotic hyperglycinemia

Mutations in the glycine decarboxylase gene (GLDC) cause nonketotic hyperglycinemia (NKH), an in-born error of metabolism characterized by severe neurological disturbance. We have determined the structure of GLDC and of its pseudogene (psiGLDC) and studied their expression for a molecular analysis of NKH. The GLDC gene spans at least 135 kb and consists of 25 exons. All donor and acceptor sites adhere to the canonical GT-AG rule, except for the donor site of intron 21, where a variant form GC is used instead of GT. The transcription initiation site has been assigned to a residue 163 bp upstream from the translation initiation triplet by primer extension analysis. The psiGLDC gene has no intron and shares 97.5% homology with the coding region of functional GLDC, suggesting that psiGLDC is a processed pseudogene that arose from the GLDC transcript about 4-8 million years ago. RNA blotting analysis has revealed that GLDC is expressed in human liver, kidney, brain, and placenta. We have also examined a patient with NKH with no detectable GLDC mRNA in his lymphoblasts. Exons 1-3 of the functional GLDC gene from this patient are not amplified by polymerase chain reaction (PCR), whereas those from control subjects are. These results suggest a large homozygous deletion (at least 30 kb) in the patient. Furthermore, we have devised a semi-quantitative PCR to estimate the number of GLDC alleles by using psiGLDC as an internal control and have confirmed the homozygosity and heterozygosity of the deletion in the patient and his parents, respectively. Structural information of GLDC and psiGLDC should facilitate the molecular analysis of NKH.

Antitumor activity of dextran derivatives immobilizing platinum complex (II)

The in vivo antitumor activity and toxicity of a newly synthesized polymeric prodrug of cisplatin was investigated and also compared with plain cisplatin. The prodrug included a dicarboxymethyl-dextran conjugate of cisplatin (DCM-Dex/CDDP). DCM-Dex/CDDP was i.v. injected in mice bearing s.c. Colon 26 mouse colon cancer cells. The tissue distribution of platinum was thereafter determined by flameless atomic absorption spectrophotometry. The platinic concentration of the organs showed a high rate of retention at 24 h after injection in the DCM-Dex/CDDP-treated mice. No biochemical or hematologically adverse effects were observed. In addition, DCM-Dex/CDDP showed a significantly higher antitumor activity than cisplatin alone. These results indicate that DCM-Dex/CDDP may therefore be a potentially effective cancer chemotherapy.

Prenylation of Rho1p is required for activation of yeast 1, 3-beta-glucan synthase

One of the essential protein substrates of geranylgeranyl transferase type I in the budding yeast Saccharomyces cerevisiae is a rho-type GTPase, Rho1p, which is a regulatory subunit of 1, 3-beta-glucan synthase. Previous studies have indicated that modification of Rho1p is significantly reduced in a mutant of the beta subunit of geranylgeranyl transferase type I called cal1-1. Here we present genetic and biochemical evidence showing that modification of Rho1p is required for activity of 1,3-beta-glucan synthase. The 1,3-beta-glucan synthase activity of the cal1-1 membrane was significantly reduced compared with that of the wild-type membrane. The impaired activity was partly due to the reduced amount of Fks1p, a putative catalytic subunit of 1, 3-beta-glucan synthase, but also partly due to reduced affinity between unmodified Rho1p and Fks1p. Glutathione S-transferase (GST)-Rho1 proteins with or without the C-terminal motif required for the modification were purified and used to analyze the interaction. The modified form of GST-Rho1p was specifically able to restore the 1,3-beta-glucan synthase of the rho1-3 membrane. Gel overlay analysis indicated that an unmodified form of GST-Rho1p fails to interact with Fks1p. These results indicated that the geranylgeranylation of Rho1p is a prerequisite to the assembly and activation of 1,3-beta-glucan synthase in vitro. Increased cytoplasmic levels of divalent cations such as Ca(2+) restored both Rho1p modification and the 1,3-beta-glucan synthase activity of cal1-1, suggesting that cytoplasmic levels of the divalent cations affect geranylgeranyl transferase type I activity in vivo.

Complementation analysis in PtdInsP kinase-deficient yeast mutants demonstrates that Schizosaccharomyces pombe and murine Fab1p homologues are phosphatidylinositol 3-phosphate 5-kinases

Phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P(2)) is widespread in eukaryotic cells. In Saccharomyces cerevisiae, PtdIns(3,5)P(2) synthesis is catalyzed by the PtdIns3P 5-kinase Fab1p, and loss of this activity results in vacuolar morphological defects, indicating that PtdIns(3,5)P(2) is essential for vacuole homeostasis. We have therefore suggested that all Fab1p homologues may be PtdIns3P 5-kinases involved in membrane trafficking. It is unclear which phosphatidylinositol phosphate kinases (PIPkins) are responsible for PtdIns(3,5)P(2) synthesis in higher eukaryotes. To clarify how PtdIns(3,5)P(2) is synthesized in mammalian and other cells, we determined whether yeast and mammalian Fab1p homologues or mammalian Type I PIPkins (PtdIns4P 5-kinases) make PtdIns(3,5)P(2) in vivo. The recently cloned murine (p235) and Schizosaccharomyces pombe FAB1 homologues both restored basal PtdIns(3,5)P(2) synthesis in Deltafab1 cells and made PtdIns(3,5)P(2) in vitro. Only p235 corrected the growth and vacuolar defects of fab1 S. cerevisiae. A mammalian Type I PIPkin supported no PtdIns(3,5)P(2) synthesis. Thus, FAB1 and its homologues constitute a distinct class of Type III PIPkins dedicated to PtdIns(3,5)P(2) synthesis. The differential abilities of p235 and of SpFab1p to complement the phenotypic defects of Deltafab1 cells suggests that interaction(s) with other protein factors may be important for spatial and/or temporal regulation of PtdIns(3,5)P(2) synthesis. These results also suggest that p235 may regulate a step in membrane trafficking in mammalian cells that is analogous to its function in yeast.

An FH domain-containing Bnr1p is a multifunctional protein interacting with a variety of cytoskeletal proteins in Saccharomyces cerevisiae

Proteins containing formin homology domains, FH1 and FH2, are involved in cytokinesis or establishment of cell polarity in a variety of organisms. Bni1p and Bnr1p are FH proteins and potential targets of the Rho family small GTP-binding proteins in S. cerevisiae. We have shown that Bnr1p is localized at the bud neck to interact with Hof1p, involved in cytokinesis. We report here that the overexpression of BNR1 causes a cytokinesis deficiency which is similar to the phenotypes of the septin mutants, including cdc3, cdc10, cdc11, and cdc12. The region required for the septin mutant phenotypes was mapped to Bnr1p (35-500), which coincided with the region required for the bud-neck localization. To further isolate a gene interacting with BNI1 or BNR1, a multicopy suppressor of the bni1 bnr1 mutant was isolated. This gene encoded Smy1p, a kinesin-related protein. Bnr1p, but not Bni1p, directly interacted with the C-terminal region of Smy1p. The Smy1p-interacting region of Bnr1p was mapped to a region containing the FH2 domain. Bnr1p also directly interacted with Bud6p, a novel actin-binding protein. Bnr1p is thus a multifunctional protein which interacts with the septin system, a microtubule-dependent motor protein, and the actin system, to regulate cytoskeletal functions in S. cerevisiae.

Preparation of a Completely Oriented Molecular Sieve Membrane

Growth of oriented seed crystals on a substrate led to a completely oriented and continuous membrane of LTA-type zeolite. The seed crystals of cubic morphology were dip-coated onto a tilted substrate (see schematic diagram) with the zeolite channels normal to the surface. The substrate was hydrothermally treated in a reaction mixture containing the organic ligand 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol, which lowers the degree of supersaturation of [Al(OH)(4)](-) ions and preferentially facilitates the intergrowth of the seed crystals.

Sodium-potassium pump current in smooth muscle cells from mesenteric resistance arteries of the guinea-pig

1. The Na+-K+ pump current was studied in smooth muscle cells from mesenteric resistance arteries of guinea-pigs by the use of the perforated patch-clamp technique in the presence of blockers for various ion channels and exchangers. 2. When the Na+ concentration in the pipette solution ([Na+]i) was 50 mM, an increase in the extracellular K+ concentration ([K+]o) from 0 to 10 mM caused an outward current. Both the removal of K+ from the bath solution and the application of 10 microM ouabain abolished this current. Thus, this K+-induced and ouabain-sensitive current was considered to be the Na+-K+ pump current. 3. The amplitude of the Na+-K+ pump current increased as the membrane potential was made more positive until around 0 mV, while the amplitude saturated at more positive potentials than 0 mV. 4. An increase in [K+]o or [Na+]i amplified the Na+-K+ pump current. For [K+]o, the binding constant (Kd) was 1.6+/-0.3 mM and the Hill coefficient (nH) was 1.1+/-0.2 (n = 6). For [Na+]i, Kd was 22+/-5 mM and nH was 1.7+/-0.5 (n = 4-19). 5. The presence of various monovalent cations other than Na+ in the bath solution also evoked the Na+-K+ pump current. The order of potency was K+ >= Rb+ > Cs+ >> Li+. 6. Ouabain inhibited the Na+-K+ pump current in a dose-dependent manner with a Kd of 0.35+/-0.03 microM and an nH of 1.2+/-0.1 (n = 6-8). 7. The Na+-K+ pump current increased as temperature increased. The temperature coefficient (Q10; 26-36 C) was 1.87 (n = 9). 8. In summary the present study characterized for the first time the Na+-K+ pump current in vascular smooth muscle cells by the use of the voltage-clamp method. The use of this method should provide essential information for Na+,K+-ATPase-mediated changes in the cell functions of vascular smooth muscle cells.

Evaluation of the staphylococcal exotoxins and their specific IgE in childhood atopic dermatitis

BACKGROUND

Superantigenic exotoxins produced by Staphylococcus aureus and their specific IgE antibodies are thought to be important precipitating factors of atopic dermatitis (AD), but there are few reports evaluating these 2 factors at the same time.

OBJECTIVE

We examined whether the presence of the exotoxins sampled from the skin of patients with AD and the levels of anti-exotoxin IgE antibodies in their sera correlated with their severity of AD.

METHODS

Patients with mild-to-severe AD, 1 to 22 years of age, were evaluated by using Leicester's scoring system. Specific IgE antibodies against these exotoxins were determined by using ELISA. S aureus was isolated from 3 different areas of the skin. We examined whether the exotoxin (staphylococcal enterotoxin [SE]A, SEB, SEC, SED, and toxic shock syndrome toxin-1) could be detected.

RESULTS

The levels of SEB-specific IgE were correlated with the severity of AD. Five of 6 patients having very high SEB-specific IgE antibody titers were under 6 years of age, and SEB was most frequently isolated (41%). There was no difference in severity between patients with or without exotoxin-producing S aureus. The severity of 9 patients who had both exotoxin-producing S aureus on the skin and specific IgE antibody against the same exotoxin in sera was significantly higher than that of the other patients.

CONCLUSIONS

Anti-SEB IgE titers correlate well with the severity of AD. The presence of exotoxin-producing S aureus may precipitate AD through its specific IgE antibody.

In vitro characteristics and in vivo plasma disposition of cisplatin conjugated with oxidized and dicarboxymethylated dextrans

In vitro release behavior and cytotoxic activity, and in vivo plasma disposition of newly synthesized macromolecular derivatives of cisplatin (CDDP) were investigated and compared with CDDP. The derivatives included oxidized dextran conjugate of CDDP (OX-Dex/CDDP) and dicarboxymethylated dextran conjugate of CDDP (DCM-Dex/CDDP). In vitro release of platinum complex from dextran conjugated CDDP was determined by an equilibrium dialysis method. These dextran conjugates showed sustained release of the platinum complex. In vitro release half-life for DCM-Dex/CDDP was significantly longer (4.5 times) than that for OX-Dex/CDDP. In vitro cytotoxic activity of CDDP and dextran conjugated CDDP against colon 26, mouse colon cancer cell line, was measured using the MTT assay method. OX-Dex/CDDP showed a similar cytotoxic activity to CDDP. However, both cytotoxic activities were markedly decreased when preincubated with the medium containing serum. On the other hand, DCM-Dex/CDDP retained residual cytotoxic activity at a significantly higher level than OX-Dex/CDDP after preincubation with the medium containing serum, although it showed the lowest cytotoxic activity. This indicated longer maintenance of the in vitro antitumor activity of DCM-Dex/CDDP in serum compared with OX-Dex/CDDP. Plasma disposition of CDDP and dextran conjugated CDDP was determined by intravenous administration to rats. Although the total platinum plasma concentration-time profile for OX-Dex/CDDP was similar to that for CDDP, its markedly higher profile was achieved when DCM-Dex/CDDP was administered. The values of the total platinum AUC and MRT, where AUC is the area under the platinum concentration-time curve and MRT is the mean residence time, for DCM-Dex/CDDP were 11.2 times and 4.8 times significantly higher than with OX-Dex/CDDP in plasma, respectively. DCM-Dex/CDDP also showed a significantly lower total clearance compared with OX-Dex/CDDP. These results from the in vivo experiments revealed that retention of DCM-Dex/CDDP in blood circulation was much greater than that for OX-Dex/CDDP. DCM-Dex/CDDP thus has potential as a macromolecular derivative of CDDP for passive tumor targeting.

Chaos and spectral analyses of heart rate variability during head-up tilting in essential hypertension

To investigate nonlinear and linear components of heart rate variability (HRV) in essential hypertension (EHT), we analyzed HRV by chaos and spectral analyses in patients with EHT (n = 18) and normotensives (n = 10) during head-up tilting. We used the correlation dimension (CD) and Lyapunov exponents as the parameters of chaos. The CD, an index of complexity, was lower at rest in EHT group than in normotensives, and did not change in EHT group in response to head-up tilting, but decreased in normotensives. Head-up tilting did not change the Lyapunov exponents, an index of sensitive dependence on initial condition, a hallmark of chaos, in both groups. In the spectral analysis, the normalized high-frequency component (%HF) was decreased in EHT group at rest, and head-up tilting increased the low- to high-frequency ratio (L/H) and reduced the %HF in both groups. The CD and Lyapunov exponents at rest were correlated with the %HF and L/H. These results suggest that chaos analysis can assess the different aspect of HRV from spectral analysis and that nonlinear components of HRV may be associated with hypertension through an impaired dynamic regulation of HRV.

The Rho1 effector Pkc1, but not Bni1, mediates signalling from Tor2 to the actin cytoskeleton

In Saccharomyces cerevisiae, the phosphatidylinositol kinase homologue Tor2 controls the cell-cycle-dependent organisation of the actin cytoskeleton by activating the small GTPase Rho1 via the exchange factor Rom2 [1,2]. Four Rho1 effectors are known, protein kinase C 1 (Pkc1), the formin-family protein Bni1, the glucan synthase Fks and the signalling protein Skn7 [2,3]. Rho1 has been suggested to signal to the actin cytoskeleton via Bni1 and Pkc1; rho1 mutants have never been shown to have defects in actin organisation, however [2,4]. We have further investigated the role of Rho1 in controlling actin organisation and have analysed which of the Rho1 effectors mediates Tor2 signalling to the actin cytoskeleton. We show that some, but not all, rho1 temperature-sensitive (rho1ts) mutants arrest growth with a disorganised actin cytoskeleton. Both the growth defect and the actin organisation defect of the rho1-2ts mutant were suppressed by upregulation of Pkc1 but not by upregulation of Bni1, Fks or Skn7. Overexpression of Pkc1, but not overexpression of Bni1, Fks or Skn7, also rescued a tor2ts mutant, and deletion of BNI1 or SKN7 did not prevent the suppression of the tor2ts mutation by overexpressed Rom2. Furthermore, overexpression of the Pkc1-controlled mitogen-activated protein (MAP) kinase Mpk1 suppressed the actin defect of tor2ts and rho1-2ts mutants. Thus, Tor2 signals to the actin cytoskeleton via Rho1, Pkc1 and the cell integrity MAP kinase cascade.

Importance of phenylalanine residues of yeast calmodulin for target binding and activation

Recent genetic studies of yeast calmodulin (yCaM) have shown that alterations of different sets of Phe residues result in distinct functional defects (Ohya, Y., and Botstein, D. (1994) Science 263, 963-966). To examine the importance of Phe residues for target binding and activation, we purified mutant yCaMs containing single or double Phe to Ala substitutions and determined their ability to bind and activate two target proteins, calcineurin and CaM-dependent protein kinase (CaMK). Binding assays using the gel overlay technique and quantitative analyses using surface plasmon resonance measurements indicated that the binding of yCaM to calcineurin is impaired by either double mutations of F16A/F19A or a single mutation of F140A, while binding to CaMK is impaired by F89A, F92A, or F140A. These same mutant yCaMs fail to activate calcineurin and CaMK, respectively, in vitro. In addition, F19A exhibited a severe defect in activation of both enzymes. F12A activated calcineurin to only 50% of the level achieved by wild-type calmodulin but fully activated CaMK. These results suggest that each target protein requires a specific and distinct subset of Phe residues in yCaM for target binding and activation.

Regression of carotid wall thickening after corticosteroid therapy in Takayasu's arteritis evaluated by B-mode ultrasonography: report of 2 cases

We describe 2 young Japanese female patients with active Takayasu's arteritis whose diagnosis was mainly based on the characteristic ultrasonographic finding, that is, a circumferential vascular wall thickening in common carotid arteries. Following corticosteroid therapy, serial ultrasonographic examination documented the improvement of their thickened carotid walls (in Case 1 from 1.4 to 0.5 mm after 2 months of therapy, in Case 2 from 1.5 to 0.9 mm after 9 months of therapy). These cases emphasize that ultrasonography is useful for evaluation of the therapeutic effect as well as for the diagnosis of Takayasu's arteritis in its early stage.

Identification of functional connections between calmodulin and the yeast actin cytoskeleton

One of four intragenic complementing groups of temperature-sensitive yeast calmodulin mutations, cmd1A, results in a characteristic functional defect in actin organization. We report here that among the complementing mutations, a representative cmd1A mutation (cmd1-226: F92A) is synthetically lethal with a mutation in MYO2 that encodes a class V unconventional myosin with calmodulin-binding domains. Gel overlay assay shows that a mutant calmodulin with the F92A alteration has severely reduced binding affinity to a GST-Myo2p fusion protein. Random replacement and site-directed mutagenesis at position 92 of calmodulin indicate that hydrophobic and aromatic residues are allowed at this position, suggesting an importance of hydrophobic interaction between calmodulin and Myo2p. To analyze other components involved in actin organization through calmodulin, we isolated and characterized mutations that show synthetic lethal interaction with cmd1-226; these "cax" mutants fell into five complementation groups. Interestingly, all the mutations themselves affect actin organization. Unlike cax2, cax3, cax4, and cax5 mutations, cax1 shows allele-specific synthetic lethality with the cmd1A allele. CAX1 is identical to ANP1/GEM3/MCD2, which is involved in protein glycosylation. CAX4 is identical to the ORF YGR036c, and CAX5 is identical to MNN10/SLC2/BED1. We discuss possible roles for Cax proteins in the regulation of the actin cytoskeleton.

Troglitazone, an insulin sensitizer, increases forearm blood flow in humans

To test whether troglitazone, a thiazolidinedione insulin sensitizer, increases the peripheral blood flow, the changes in forearm blood flow (FBF) were evaluated by venous occlusion plethysmography in 11 lean healthy male volunteers (age range, 24 to 39 years) after a single oral dose of 200 mg of troglitazone. Forearm vascular resistance (FVR) was calculated from FBF and blood pressure. Two hours after the dose, FBF increased from 3.66+/-0.31 to 4.81+/-0.57 mL/100 mL/min (P < .01), and FVR decreased from 24.7+/-2.2 to 20.2+/-2.2 units (P < .01), whereas both these values did not change during the control recordings obtained without troglitazone. Blood pressure, blood glucose levels, and serum immunoreactive insulin levels did not change significantly during the observation period. Serum concentrations of nitrate ions decreased from 27.0+/-3.5 mmol/L to 23.1+/-2.7 mmol/L (P < .01) after the administration. These results suggest that troglitazone increases muscular blood flow through vasodilation induced by a mechanism other than the correction of hyperinsulinemia or the increase in nitric oxide. The present study provides the first evidence that troglitazone dilates the vasculature in humans.

Metalloproteinase-like, disintegrin-like, cysteine-rich proteins MDC2 and MDC3: novel human cellular disintegrins highly expressed in the brain

Cellular disintegrins are a family of membrane-anchored proteins structurally related to snake venom disintegrins, and are potential regulators of cell-cell and cell-matrix interactions. The members of this protein family are also called ADAMs (a disintegrin and metalloproteinase) or MDC proteins (metalloproteinase-like disintegrin-like cysteine-rich), because they all contain disintegrin-like and metalloproteinase-like domains. In this paper, we report the cloning and sequence analysis of two novel additional members of this family, which we have termed MDC2 and MDC3. The deduced amino acid sequences reveal that the two proteins possess typical cellular disintegrin structures [that is, pro-, metalloproteinase-like, disintegrin-like, cysteine-rich, epidermal growth factor-like, transmembrane, and cytoplasmic domains] and exhibit high sequence similarity with human MDC/ADAM11 protein [Katagiri, Harada, Emi and Nakamura (1995) Cytogenet. Cell Genet. 68, 39-44]. A zinc-binding motif, which is critical for proteinase activity, is disrupted in the metalloproteinase-like domain of MDC2 and MDC3, as well as MDC/ADAM11. In the disintegrin-like domain of snake venom short disintegrins, the RDG-containing loops are critical for integrin binding. These three MDCs do not contain the RDG sequences, but the corresponding loops in these proteins are similar to each other. Northern blot analysis revealed that the mRNAs of MDC2, MDC3 and MDC/ADAM11 are highly expressed in the brain. These findings suggest that these proteins may function as integrin ligands in the brain.

Phosphatidylinositol-4-phosphate 5-kinase localized on the plasma membrane is essential for yeast cell morphogenesis

Phosphatidylinositol 4,5-biphosphate (PtdIns(4,5)P2), an important element in eukaryotic signal transduction, is synthesized either by phosphatidylinositol-4-phosphate 5-kinase (PtdIns(4)P 5K) from phosphatidylinositol 4-phosphate (PtdIns(4)P) or by phosphatidylinositol-5-phosphate 4-kinase (PtdIns(5)P 4K) from phosphatidylinositol 5-phosphate (PtdIns(5)P). Two Saccharomyces cerevisiae genes, MSS4 and FAB1, are homologous to mammalian PtdIns(4)P 5Ks and PtdIns(5)P 4Ks. We show here that MSS4 is a functional homolog of mammalian PtdIns(4)P 5K but not of PtdIns(5)P 4K in vivo. We constructed a hemagglutinin epitope-tagged form of Mss4p and found that Mss4p has PtdIns(4)P 5K activity. Immunofluorescent and fractionation studies of the epitope-tagged Mss4p suggest that Mss4p is localized on the plasma membrane, whereas Fab1p is reportedly localized on the vacuolar membrane. A temperature-sensitive mss4-1 mutant was isolated, and its phenotypes at restrictive temperatures were found to include increased cell size, round shape, random distribution of actin patches, and delocalized staining of cell wall chitin. Thus, biochemical and genetic analyses on Mss4p indicated that yeast PtdIns(4)P 5K localized on the plasma membrane is required for actin organization.

Single L-type calcium channels in smooth muscle cells from resistance arteries of spontaneously hypertensive rats

The amplitude of the whole-cell L-type Ca2+ channel current recorded from vascular smooth muscle cells is reportedly greater in spontaneously hypertensive rats (SHR) than in Wistar-Kyoto rats (WKY). However, no study has examined properties of single Ca2+ channels in arterial cells from these strains. To further test the hypothesis that activation of L-type Ca2+ channels in arterial smooth muscle cells would be enhanced in SHR, we recorded single Ca2+ channel currents in resistance mesenteric artery cells from SHR and WKY (8 to 9 weeks of age) using a cell-attached patch clamp technique. With 50 mmol/L Ba2+ in the recording pipette, the depolarizing pulse from a holding potential of -40 mV evoked the single L-type Ca2+ channel current. Opening of the single channels was more frequent in cells from SHR than from WKY. Single-channel conductance (20 pS) and open time (1 ms at 0 mV) did not differ in the two strains. The results suggest that an increased amplitude of the whole-cell current can be attributed to the enhanced opening of single Ca2+ channels in the arterial smooth muscle cells from SHR compared with WKY.

Amino acid residues that define both the isoprenoid and CAAX preferences of the Saccharomyces cerevisiae protein farnesyltransferase. Creating the perfect farnesyltransferase

Studies of the yeast protein farnesyltransferase (FTase) have shown that the enzyme preferentially farnesylates proteins ending in CAAX (C = cysteine, A = aliphatic residue, X = cysteine, serine, methionine, alanine) and to a lesser degree CAAL. Furthermore, like the type I protein geranylgeranyltransferase (GGTase-I), FTase can also geranylgeranylate methionine- and leucine-ending substrates both in vitro and in vivo. Substrate overlap of FTase and GGTase I has not been determined to be biologically significant. In this study, specific residues that influence the substrate preferences of FTase have been identified using site-directed mutagenesis. Three of the mutations altered the substrate preferences of the wild type enzyme significantly. The ram1p-74D FTase farnesylated only Ras-CIIS and not Ras-CII(M,L), and it geranylgeranylated all three substrates as well or better than wild type. The ram1p-206DDLF FTase farnesylated Ras-CII(S,M,L) at wild type levels but could no longer geranylgeranylate the Ras-CII(M,L) substrates. The ram1p-351FSKN FTase farnesylated Ras-CIIS and Ras-CIIM but not Ras-CIIL. The ram1p-351FSKN FTase was not capable of geranylgeranylating the Ras-CII(M,L) substrates, giving this mutant the attributes of the dogmatic FTase that only farnesylates non-leucine-ending CAAX substrates and does not geranylgeranylate any substrate. These results suggest that the isoprenoid and protein substrate specificities of FTase are interrelated. The availability of a mutant FTase that lacked substrate overlap with the protein GGTase-I made possible an analysis of the role of substrate overlap in normal cellular processes of yeast, such as mating and growth at elevated temperatures. Our findings suggest that neither farnesylation of leucine-ending CAAX substrates nor geranylgeranylation by the FTase is necessary for these cellular processes.

Asymptomatic moyamoya disease associated with coronary and renal artery stenoses--a case report

Moyamoya disease is an occlusive intracranial arteriopathy with abnormal cerebral vascular collateral networks. Although this disease is known to be associated with stenosis of extracranial arteries, such as the renal artery, a case associated with stenoses of the coronary and renal arteries has not been reported. We described here a 23-year-old man who had effort angina, renovascular hypertension, and asymptomatic moyamoya disease. Arterioangiography revealed bilateral occlusion of the intracranial carotid arteries and stenoses in the left coronary artery and the left renal artery.

Inhibitory action of insulin-sensitizing agents on calcium channels in smooth muscle cells from resistance arteries of guinea-pig

1. The actions of troglitazone, pioglitazone, metformin and bezafibrate, agents that improve insulin-resistance, on voltage-dependent Ca2+ channels in arterial smooth muscle cells were examined by use of the conventional and nystatin-perforated whole-cell clamp methods. Single cells were freshly isolated from resistance mesenteric arteries of guinea-pigs. The actions of these agents on 77 mM K+-induced contraction of the isolated arteries were also examined with the use of isometric tension recording. 2. The thiazolidinedione derivatives, troglitazone and pioglitazone, inhibited whole-cell Ca2+ currents in a dose-dependent manner with dissociation constants of 3.0 microM and 44.9 microM and Hill coefficients of 0.61 and 0.68, respectively. These two agents inhibited the 77 mM K+-induced contraction with similar potencies as those inhibiting the Ca2+ currents. Metformin and bezafibrate had no apparent effects on the Ca2+ current or high K+-induced contraction. 3. The inhibitory action of troglitazone on Ca2+ currents was not affected by the command potential, the holding potential, or the stimulation frequency, suggesting that its mode of the action differs from that of known organic Ca2+ channel antagonists. 4. The inhibitory action of troglitazone on Ca2+ currents was not affected by the addition of insulin to, or the removal of glucose from, the solutions. 5. In conclusion, the thiazolidinedione derivatives directly inhibited the voltage-dependent Ca2+ channels in a different manner from that of organic Ca2+ channel antagonists. This inhibitory action on Ca2+ channels was not a common feature of insulin-sensitizing agents.

Stretch-activated channels in arterial smooth muscle of genetic hypertensive rats

Electrical and contractile responses of small arteries to mechanical stress are reportedly enhanced in spontaneously hypertensive rats (SHR), compared with those in Wistar Kyoto rats (WKY). We have previously shown that stretch-activated cation channels exist in arterial smooth muscle membrane, of which opening causes Na+ and Ca2+ influx and membrane depolarization. We thus hypothesize that activation of stretch-activated channels is enhanced in arterial smooth muscle of SHR compared with WKY. To test this hypothesis, stretch-activated currents were recorded in single smooth muscle cells of resistance mesenteric arteries from SHR and WKY (16 to 24 weeks of age). In the whole-cell recording, membrane stretch was applied by inflating the cell with positive pressure to the recording pipette. Cell-inflation evoked Gd3+-sensitive cation currents. This current appeared with less stretch stimulation and its amplitude was larger in SHR cells compared with WKY cells. In the cell-attached recording, suction to the recording pipette evoked single stretch-activated channel currents (conductance of 32 pS with 150 mmol/L Na+), which were blocked by Gd3+. Channels were activated with less negative pressure and their availability was greater in SHR cells than in WKY cells. Results suggest that the activation of stretch-activated channels is enhanced in smooth muscle of resistance arteries from SHR compared with WKY, which may contribute to the enhanced vascular responses to mechanical stress in SHR.

Antihypertensive treatment and the responsiveness to glutamate in ventrolateral medulla

We have recently reported that the cardiovascular responses to excitatory amino acids are augmented in the rostral ventrolateral medulla of spontaneously hypertensive rats (SHR). In the present study, we investigated whether the responsiveness to excitatory amino acids would be normalized by antihypertensive treatment. Thus we treated 4-week-old SHR and age-matched Wistar-Kyoto (WKY) rats with either enalapril (25 mg/kg per day in drinking water) or vehicle for 8 weeks. At 12 weeks of age, systolic blood pressure in the untreated SHR (248+/-9 mm Hg) was significantly (P<.01) higher than that in the enalapril-treated SHR (140+/-4 mm Hg), untreated WKY rats (148+/-4 mm Hg), and enalapril-treated WKY rats (117+/-1 mm Hg). The pressor responses to L-glutamate (2 nmol) microinjected into the rostral ventrolateral medulla were similar in enalapril-treated and untreated SHR (40+/-5 and 47+/-3 mm Hg, respectively, NS), and these responses were significantly greater than that seen in the untreated WKY rats (24+/-2 mm Hg, P<.01). On the other hand, the pressor response to either N-methyl-D-aspartate, an ionotropic glutamate receptor agonist, or (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid, a metabotropic glutamate receptor agonist, in the enalapril-treated SHR was slightly but significantly smaller than that in the untreated SHR but was still markedly greater than those in untreated and enalapril-treated WKY rats. These results suggest that the augmented responsiveness to excitatory amino acids in the rostral ventrolateral medulla of SHR may be at least partly genetically determined and cannot be normalized by the treatment with enalapril.

Design of macromolecular biological response modifier by immobilizing of D-glucose analogue of muramyl dipeptide on carboxymethyl-dextran having mannose branches

It is well known that muramyl dipeptide is a minimum required structure of bacterial peptidoglycan responsible for immunoadjuvant activity. Since mannose receptors exist on the surface of macrophages, polymers with branched mannose residues are expected to target moieties to macrophages. To achieve an efficient delivery of D-glucose analogue of muramyl dipeptide (GADP) via receptor-mediated endocytosis by mannose receptors on the surface of macrophages, GADP/carboxymethyl-dextran (CM-Dex)/Man conjugate was synthesized. Moreover, to study the effect of the introduction of mannose residues, we also synthesized GADP/CM-glucomannan (CM-GM) and GADP/CM-Dex conjugates. The immunological enhancement activities of their conjugates were evaluated by measurements of glucose consumption and beta-D-glucuronidase activity from macrophage-like cells. The GADP/CM-Dex/Man and GADP/CM-GM conjugates showed higher immunological enhancement activity than the GADP/CM-Dex conjugate. The immunological enhancement activity of GADP/CM-Dex/Man and GADP/CM-GM conjugates was decreased to the same level of immunological enhancement activity of GADP/CM-Dex conjugate under the presence of excess mannose. These results suggested that the introduction of mannose residues into GADP/CM-Dex conjugate could increase the affinity against macrophage and the immunological enhancement activity of GADP/CM-Dex conjugate itself.

Cloning of the RHO1 gene from Candida albicans and its regulation of beta-1,3-glucan synthesis

The Saccharomyces cerevisiae RHO1 gene encodes a low-molecular-weight GTPase. One of its recently identified functions is the regulation of beta-1,3-glucan synthase, which synthesizes the main component of the fungal cell wall (J. Drgonova et al., Science 272:277-279, 1996; T. Mazur and W. Baginsky, J. Biol. Chem. 271:14604-14609, 1996; and H. Qadota et al., Science 272:279-281, 1996). From the opportunistic pathogenic fungus Candida albicans, we cloned the RHO1 gene by the PCR and cross-hybridization methods. Sequence analysis revealed that the Candida RHO1 gene has a 597-nucleotide region which encodes a putative 22.0-kDa peptide. The deduced amino acid sequence predicts that Candida albicans Rho1p is 82.9% identical to Saccharomyces Rho1p and contains all the domains conserved among Rho-type GTPases from other organisms. The Candida albicans RHO1 gene could rescue a S. cerevisiae strain containing a rho1 deletion. Furthermore, recombinant Candida albicans Rho1p could reactivate the beta-1,3-glucan synthesis activities of both C. albicans and S. cerevisiae membranes in which endogenous Rho1p had been depleted by Tergitol NP-40-NaCl treatment. Candida albicans Rho1p was copurified with the beta-1,3-glucan synthase putative catalytic subunit, Candida albicans Gsc1p, by product entrapment. Candida albicans Rho1p was shown to interact directly with Candida albicans Gsc1p in a ligand overlay assay and a cross-linking study. These results indicate that Candida albicans Rho1p acts in the same manner as Saccharomyces cerevisiae Rho1p to regulate beta-1,3-glucan synthesis.