The hemorrhagin catrocollastatin inhibits collagen-induced platelet aggregation by binding to collagen via its disintegrin-like domain

Catrocollastatin, a 50 kDa snake venom protein purified from Crotalus atrox, specifically inhibits platelet-collagen adhesion and collagen-induced aggregation. Catrocollastatin is composed of an N-terminal domain, a metalloproteinase domain, a disintegrin-like domain and a cysteine-rich C-terminal domain. The present studies show that catrocollastatin exerts its effect by binding to collagen. Based on the amino acid sequence and homology analysis, a cyclic oligopeptide corresponding to a conservative fragment containing the sequence SECD in the disintegrin-like domain has been synthesized. Like its protein parent, the synthetic peptide inhibits collagen-induced aggregation and possesses the ability to bind to collagen. This is the first snake venom protein with a disintegrin-like structure shown to bind to an integrin ligand matrix molecule instead of an integrin.

Molecular biomarkers of occupational lung cancer

Occupational exposures to certain metals, hydrocarbons and ionizing radiation are associated with increased lung cancer in workers; because these exposures continue, lung cancer remains an important problem in industrialized nations. The gravity of the lung cancer, specifically the low cure rate associated with the disease, has forced researchers to focus efforts at developing biological indicators (biomarkers) of carcinogen exposure and early, reversible effects. This review examines critically the development of these biomarkers for occupational and environmental exposures to polycyclic aromatic hydrocarbons (PAH), a ubiquitous class of lung carcinogens. Biomarkers of several different stages of the carcinogenic process have been proposed. Industrial hygiene and occupational health emphasize exposure and disease prevention. For this reason, biomarkers useful in industrial hygiene practice are those which measure events prior to the initiation phase of carcinogenesis; markers of later events which have a greater positive predictive value may measure irreversible effects and are more appropriate for disease screening and epidemiology. One of the strengths of biological monitoring is that exposures and effects can be measured regardless of route. Data indicates that the dermal route may be a significant pathway for delivery of PAH to the lung. This finding has important ramifications because as airborne exposure limits decrease the relative impact of dermal absorption is increased.

Core promoter-specific function of a mutant transcription factor TFIID defective in TATA-box binding

In conjunction with other general initiation factors, the TATA box-binding protein (TBP) can direct basal transcription by RNA polymerase II from TATA-containing promoters, but its stable interaction with TBP-associated factors (TAFs) in the TFIID complex is required both for activator-dependent transcription and for basal transcription directed by an initiator element. We have generated a TATA-binding-defective TFIID complex containing an amino acid substitution in the DNA-binding surface of its TBP subunit. This mutated TFIID is defective in both basal and activated transcription from core promoters containing only a TATA box but supports transcription from initiator-containing promoters independently of the presence or absence of a TATA sequence. Our results show that a functional initiator element is needed to bypass the requirement for an active TATA DNA-binding surface in TFIID and imply that gene-specific transcription can be achieved by modulating distinct core promoter-specific TFIID functions--e.g., TBP-TATA versus TAF-initiator interactions.

Adenovirus E1A243 disrupts the ATF/CREB-YY1 complex at the mouse c-fos promoter

The adenovirus E1A243 protein can activate transcription of the mouse c-fos gene in a manner that depends on treatment of cells with inducers or analogs of cyclic AMP (cAMP). Activation requires conserved region 1 and the N-terminal domain of E1A243 and is mediated by a 22-bp E1A response element containing a cAMP response element (CRE) at -67 and a binding site for transcription factor YY1 at -54. In the absence of E1A243, YY1 represses CRE-dependent transcription of c-fos by physically interacting with ATF/CREB proteins bound to the -67 CRE. Here we present evidence that expression of E1A243 leads to relief of YY1-mediated repression by a disruption of the ATF/CREB-YY1 complex. Addition of E1A243 to in vitro binding assays prevented binding of ATF-2 to glutathione S-transferase-YY1. Similarly, expression of E1A243 in HeLa cells prevented the association of a YY1-VP16 fusion protein with endogenous ATF/CREB proteins bound to the -67 CRE of a transfected c-fosCAT reporter plasmid. In each case, the N-terminal domain of E1A243, which mediates a direct interaction with YY1, was responsible for disruption of the ATF/CREB-YY1 complex. On the basis of these and previously published results, we present a model for the synergistic transcriptional activation of the c-fos gene by E1A243 and cAMP.

Unidirectional valve patch for repair of cardiac septal defects with pulmonary hypertension

BACKGROUND

Congenital septal defects with a large left-to-right shunt often cause pulmonary hypertension, which complicates surgical repair of the defects.

METHODS

Twenty-four patients with congenital cardiac septal defects and severe pulmonary hypertension had operation to close the septal defect using a unidirectional valve patch during a 3-year period. The ratio of systolic pulmonary artery pressure to systolic arterial blood pressure was near to or more than 1.0 in all patients.

RESULTS

Two patients died in the hospital after operation, and there have been no deaths during intermediate term follow-up. Mean pulmonary artery pressure decreased from 80 +/- 12 mm Hg to 56 +/- 18 mm Hg. The ratio of pulmonary artery pressure to systemic arterial pressure dropped from 1.1 +/- 0.1 mm Hg to 0.7 +/- 0.1 mm Hg. The unidirectional valve patch functioned allowing right to left shunting in 4 patients with a systolic pulmonary artery pressure more than systolic arterial blood pressure immediately after closure of a septal defect. The patch sealed or was effectively closed by the third postoperative day. There was impressive improvement in symptoms and exercise tolerance after operation during the 3-month to 3-year (mean, 1.1 year) follow-up period.

CONCLUSIONS

The unidirectional valve patch is useful for management of patients having operation to close cardiac septal defects in the presence of severe pulmonary hypertension.

Sodium pivalate reduces cardiac carnitine content and increases glucose oxidation without affecting cardiac functional capacity

This study determined how selected functional, metabolic, and contractile properties were impacted by sodium pivalate, a compound which creates a secondary carnitine deficiency. Young male rats received either sodium pivalate (20 mM, PIV) or sodium bicarbonate (20 mM, CONTR) in their drinking water. After 11-12 weeks cardiac function and glucose oxidation rates were measured in isolated, perfused working heart preparations. Hearts were also analyzed for carnitine content, activities of hexokinase (HK), citrate synthase (CS), and B-hydroxyacyl CoA dehydrogenase (HOAD), and myosin isoenzyme distribution. Sodium pivalate treatment significantly reduced cardiac carnitine content and increased glucose oxidation but did not alter cardiac functional capacity. HK activity was increased in the PIV group (p < 0.05), and HOAD activity decreased (p < 0.05). CS activity and myosin isoform distribution (VI > 85%) remained unchanged. These results demonstrate that pivalate treatment of this duration and the accompanying carnitine deficiency shift cardiac substrate utilization without compromising cardiac functional capacity.

Secondary structure of holo- and apo-aminoacylase from prediction, circular dichroism, and FT-Raman spectroscopy

The secondary structures of native (Holo-) and Zn(2+)-free (Apo-) aminoacylase were examined by circular dichroism (CD) and Fourier transform Raman (FT-Raman) spectroscopic techniques and prediction methods. Quantitative analysis of the conformationally sensitive amide I band indicates that Holo- and Apo-enzyme contain 19.3 and 17.2% helical structure, respectively. Far-UV CD spectra of Holo- and Apo-enzyme show that they contain 20.1 and 17.6% alpha-helix, respectively. Secondary structure prediction of aminoacylase indicates that it contains approximately 20.9% alpha-helical structure including 10 alpha-helix segments. The results show that after removal of Zn2+ in aminoacylase, the extent of ordered structure was decreased markedly. The conformation at or near the active site of aminoacylase may contain more ordered structure and the presence of Zn2+ may help to maintain the catalytically active conformation at the active site.

Further characterization of the human cell multiprotein DNA replication complex

Evidence for multiprotein complexes playing a role in DNA replication has been growing over the years. We have previously reported on a replication-competent multiprotein form of DNA polymerase isolated from human (HeLa) cell extracts. The proteins that were found at that time to co-purify with the human cell multiprotein form of DNA polymerase included: DNA polymerase alpha, DNA primase, topoisomerase I, RNase H, PCNA, and a DNA-dependent ATPase. The multiprotein form of the human cell DNA polymerase was further purified by Q-Sepharose chromatography followed by glycerol gradient sedimentation and was shown to be fully competent to support origin-specific and large T-antigen dependent simian virus 40 (SV40) DNA replication in vitro [Malkas et al. (1990b): Biochemistry 29:6362-6374]. In this report we describe the further characterization of the human cell replication-competent multiprotein form of DNA polymerase designated MRC. Several additional DNA replication proteins that co-purify with the MRC have been identified. These proteins include: DNA polymerase delta, RF-C, topoisomerase II, DNA ligase I, DNA helicase, and RP-A. The replication requirements, replication initiation kinetics, and the ability of the MRC to utilize minichromosome structures for DNA synthesis have been determined. We also report on the results of experiments to determine whether nucleotide metabolism enzymes co-purify with the human cell MRC. We recently proposed a model to represent the MRC that was isolated from murine cells [Wu et al. (1994): J Cell Biochem 54:32-46]. We can now extend this model to include the human cell MRC based on the fractionation, chromatographic and sedimentation behavior of the human cell DNA replication proteins. A full description of the model is discussed. Our experimental results provide further evidence to suggest that DNA synthesis is mediated by a multiprotein complex in mammalian cells.

Transcriptional repression of the c-fos gene by YY1 is mediated by a direct interaction with ATF/CREB

Transcriptional activation of the mouse c-fos gene by the adenovirus 243-amino-acid E1A protein requires a binding site for transcription factor YY1 located at -54 of the c-fos promoter. YY1 normally represses transcription of c-fos, and this repression depends on the presence of a cyclic AMP (cAMP) response element located immediately upstream of the -54 YY1 DNA-binding site. This finding suggested that the mechanism of transcriptional repression by YY1 might involve a direct interaction with members of the ATF/CREB family of transcription factors. In vitro and in vivo binding assays were used to demonstrate that YY1 can interact with ATF/CREB proteins, including CREB, ATF-2, ATFa1, ATFa2, and ATFa3. Structure-function analyses of YY1 and ATFa2 revealed that the C-terminal zinc finger domain of YY1 is necessary and sufficient for binding to ATFa2 and that the basic-leucine zipper region of ATFa2 is necessary and sufficient for binding to YY1. Overexpression of YY1 in HeLa cells resulted in repression of a mutant c-fos chloramphenicol acetyltransferase reporter that lacked binding sites for YY1, suggesting that repression can be triggered through protein-protein interactions with ATF/CREB family members. Consistent with this finding, repression was relieved upon removal of the upstream cAMP response element. These data support a model in which YY1 binds simultaneously to its own DNA-binding site in the c-fos promoter and also to adjacent DNA-bound ATF/CREB proteins in order to effect repression. They further suggest that the ATF/CREB-YY1 complex serves as a target for the adenovirus 243-amino-acid E1A protein.

Effects of adrenochrome and epinephrine on human arterial endothelial cells in vitro

The effects of adrenochrome and epinephrine were investigated in cultured human umbilical arterial endothelial cells. The cells were exposed to either adrenochrome or epinephrine at levels of 50 and 200 microM, respectively, up to 24 hrs. At 3, 5, 7 and 24 hrs of the designed harvesting time, [3H]thymidine incorporation, protein content, [3H]cholesterol uptake, prostacyclin production and lipid peroxidation were measured. We found that adrenochrome at a level of 200 microM inhibited [3H]thymidine incorporation, decreased protein content, stimulated [3H]cholesterol uptake, and decreased prostacyclin production after 3, 5, 24 and 5 hrs of exposure, respectively, compared with control. It took 24 hrs however for epinephrine at a level of 200 microM to inhibit [3H]thymidine incorporation and prostacyclin production. When the concentration was reduced to 50 microM, only adrenochrome inhibited [3H]thymidine incorporation after 24 hrs of treatment. Both adrenochrome and epinephrine had no effect on lipid peroxidation. We suggest that atherogenic changes found in severe hypertension may be due to abnormal high concentration of epinephrine, especially oxidized epinephrine, on endothelial cell functions, such as DNA synthesis, cholesterol uptake and prostacyclin production.

Immunocytochemical and in situ hybridization approaches to the optimization of brain slice preparations

Methods are described for determining the expression of specific mRNAs and proteins in brain slices, in order to elucidate changes in gene expression during preparation of vibratome slices from hippocampus of adult rats. In situ hybridization with 35S-labeled oligonucleotides was used to evaluate the level and distribution of c-fos and hsp72 mRNAs in 15-microns frozen sections prepared from these slices. Commercially available antibodies were used to examine the distribution of induced Fos and Jun proto-oncogenes as well as expression of the neuronal cytoskeletal protein, microtubule-associated protein 2 (MAP2), in 50-microns vibratome sections from immersion-fixed slices. These studies confirm the induction of c-fos and hsp72 mRNAs during routine incubation, as previously observed in hippocampal slices obtained with a tissue chopper and incubated under somewhat different conditions, indicating that such responses are likely to be common features of many slice preparations. Accumulation of Fos and Jun immunoreactivities in neurons and glia was generally consistent with the distribution of c-fos mRNA induction observed in slices, and the neuronal component of this response was comparable to the expression of these proteins observed after transient ischemia in vivo. MAP2 immunoreactivity detected in the dendritic processes of neurons tended to show an increase in staining intensity during slice incubation, although loss of dendritic staining in specific regions was occasionally observed in association with the absence of Fos and Jun expression and histological evidence of neuron damage. These results support the use of MAP2 immunoreactivity as a sensitive indicator of neuronal integrity in slices.(ABSTRACT TRUNCATED AT 250 WORDS)

Variables related to nausea and vomiting during pregnancy

Seventy to 90 percent of all pregnant women experience nausea, and 50 percent have at least one episode of vomiting or retching. A continuous measure was used to quantify symptoms of nausea with or without vomiting or retching during pregnancy in 126 women. Relationships between symptoms and selected variables were evaluated. Nausea with or without vomiting or retching was associated with maternal age, occupation, parity, cigarette smoking, infant gender, and the personality trait of independence. Significant associations were entered into multiple regression equations. Fourteen percent of the variation in symptoms overall, 25.1 percent of the variation in nausea symptoms, and 16.6 percent of the variation in vomiting or retching symptoms were explained by a combination of these selected independent variables. Although this study found associations, independent variables contributed little to predicting or explaining the presence and severity of nausea and vomiting during pregnancy. More sensitive measures and evaluation are required to understand and treat this perplexing phenomenon.

The effects of magnesium deficiency on DNA and lipid synthesis in cultured human umbilical arterial endothelial cells

This study investigated the effects of magnesium deficiency on thymidine incorporation and lipid synthesis in human umbilical arterial endothelial cells. To study [3H]thymidine incorporation, the cells were exposed for 12 to 96 h to experimental media containing decreasing magnesium concentrations of 237, 118 and 5 microM. A magnesium concentration of 949 microM was used as control. At 48 h of exposure to the experimental media, magnesium was restored to 949 microM in half of the magnesium-deficient cultures. To determine [14C]acetic acid distributions among cholesterol, phospholipid and triglyceride, the cells were treated with decreased magnesium media at the levels mentioned above for 12 to 48 h. The results showed that [3H]thymidine incorporation into DNA was inhibited by magnesium deficiency. The inhibition was augmented correspondingly with decreased magnesium concentrations and increased exposure periods. When magnesium in the medium was enhanced to normal level, incorporation was no longer inhibited. Incorporation of [14C]acetic acid into phospholipid was inhibited, its incorporation into triglyceride was stimulated, but its incorporation into cholesterol was not affected by magnesium deficiency. We suggest (i) that with the restoration of adequate magnesium, the inhibiting effect of magnesium deficiency on thymidine incorporation is reversible; (ii) that magnesium deficiency can result in a redistribution of [14C]acetic acid between phospholipid and triglyceride.

Maternal consumption of a low vitamin D diet retards metabolic and contractile development in the neonatal rat heart

During the fetal and suckling periods of mammalian development, the mother serves as the sole nutritional source for the offspring. As such, the quality of the maternal diet effects growth and development of the offspring during these periods. This study sought to determine if a maternal vitamin D deficiency altered the well characterized development of the neonatal heart. Weaned rat pups (21-day-old) were obtained from mothers who had consumed either a vitamin D-supplemented diet (3000 IU of vitamin D/kg) or a low vitamin D diet (< 200 IU of vitamin D/kg) prior to becoming pregnant and throughout pregnancy and suckling. These pups were sacrificed, hearts excised, and the hearts biochemically analysed for metabolic and contractile protein properties. The pups of dams fed the low vitamin D diet were slightly hypocalcemic relative to those on the supplemented diet (2.28 v 2.41 mumol/l, P < 0.05), had significantly lower body weights (43 v 55 g), heart weights (143 v 174 mg), citrate synthase activity (106 v 147 mumol g-1 min-1), and 3-hydroxyacyl CoA dehydrogenase activity (59 v 91 mumol g-1 min-1). Hexokinase activity (1.98 v 2.02 mumol g-1 min-1), and the distribution of cardiac myosin among its three isoforms (> 85% V1), were unaffected by this dietary deficiency, however myofibrillar protein content was approximately 15% lower in the experimental hearts. These data demonstrate that maternal consumption of a low vitamin D diet results in a general but significant slowing of neonatal cardiac development.

Numerical approximation of light scattering from tenuous cylindrical membranes at normal incidence

A numerical method has been developed to calculate the scattered field from a complex matrix of cylindrical membranes that are thin relative to wavelength with a refractive index close to that of the medium. The membranes are broken into a collection of adjacent parallel thin fibers, each fiber is assigned an internal field, and vector summation of the fields scattered by each fiber is used to calculate the total scattered field. For an incident wave in the TM mode the internal field of each membrane fiber is chosen to be equal to the incident field (the Born approximation). For the TE mode the internal field is determined by the local membrane orientation (φ) and relative refractive index (m) according to A sin 2φ for the component in the direction of incidence and 1 - A(1 - cos 2φ)for the transverse component, where A = (m(2) - 1)/2m(2). The method has application to light scattering by cell membranes in bundles of nerve axons.

Molecular cloning and expression of catrocollastatin, a snake-venom protein from Crotalus atrox (western diamondback rattlesnake) which inhibits platelet adhesion to collagen

A 50 kDa protein that inhibits platelet adhesion to collagen has been isolated from snake venom of Crotalus atrox (western diamondback rattlesnake) and has been named 'catrocollastatin'. The cDNA cloning of catrocollastatin has been accomplished. A full-length cDNA of 2310 bp with an open reading frame between nucleotides 51 and 1880 was obtained. The deduced amino acid sequence consists of 609 amino acids. The cDNA-predicted amino acid sequence is highly similar to that of haemorrhagic metalloproteinase jararhagin from Bothrops jararaca venom, HR1B from Trimeresurus flavoviridis, Ht-e from C. atrox and trigramin from T. gramineus. Like jararhagin and HR1B, catrocollastatin is a multidomain molecule composed of an N-terminal domain, a metalloproteinase domain, a disintegrin-like domain and a cysteine-rich C-terminal domain. In the disintegrin-like domain, the frequently seen RGD (Arg-Gly-Asp) sequence is replaced by SECD (Ser-Glu-Cys-Asp). This cDNA was expressed in Spodoptera frugiperda (fall armyworm) (Sf9) insect cells using a baculovirus expression system. Like native catrocollastatin, the expressed protein is capable of selectively blocking collagen-induced platelet aggregation. This is the first full-length clone of a high-molecular-mass haemorrhagin to be expressed.

Failure of vitamin E to protect cultured human arterial smooth muscle cells against oxysterol-induced cytotoxicity

OBJECTIVE

The cytotoxicity of oxysterols including 7 alpha-hydroxycholesterol (7 alpha OHC), 7 beta-hydroxycholesterol (7 beta OHC), cholesterol 5 alpha,6 alpha-epoxide (alpha epoxyC), cholesterol 5 beta,6 beta-epoxide (beta epoxyC), 7-ketocholesterol (7ketoC), 26-hydroxycholesterol (26OHC), cholesterol-3 beta,5 alpha,6 beta-triol (TriolC) and the possible protecting effect of vitamin E on 26OHC-induced cytotoxicity were investigated in smooth muscle cells isolated from the arteries of human umbilical cords.

METHODS

To study the cytotoxicity of oxysterols, the cells were incubated with each oxysterol at a level of 10 micrograms/ml from 24 to 120 hours, then 45Ca++ uptake, cytosolic free Ca++ level, [3H]thymidine incorporation, total DNA content and viable cell number were measured. Cholesterol was used as a control. For tracing the possible origin of cytotoxicity of 26OHC, cholesterol, phospholipid and 26OHC content in the membrane were investigated from 24 to 72 hours. For determining whether antioxidants had a protective effect against the cytotoxicity of 26OHC, vitamin E and butylated hydroxytoluene (BHT) were used.

RESULTS

The results indicated that the oxysterols elevated 45Ca++ uptake and cytosolic free Ca++ level, but diminished [3H]thymidine incorporation, total DNA content and viable cell number. 26OHC lowered the cholesterol content of the membrane and incorporated into the membrane after 24 hours of the incubation, but did not alter the total phospholipid content of the membrane until 72 hours. Neither vitamin E or BHT significantly protected the cells from the 26OHC-induced alterations.

CONCLUSION

We suggest that the cytotoxicity of oxysterols, which might result in an alteration in Ca++ ion flow into the cell by decreasing cholesterol content and incorporating oxysterol itself into the membranes, could not be protected by vitamin E.

Extracellular ATP stimulates adenylyl cyclase and phospholipase C through distinct purinoceptors in NG108-15 cells

In neuroblastoma x glioma hybrid NG108-15 cells, ATP induced a concentration-dependent increase in the intracellular Ca2+ concentration ([Ca2+]i), accompanied by inositol phosphate formation. Under the same conditions, we found a marked increase in cAMP levels produced by ATP at concentrations similar to those required to increase [Ca2+]i. The Ca2+ ionophore A23187 or bradykinin, which evoked inositol phosphate formation and increases in [Ca2+]i, did not increase, and instead slightly decreased, cAMP content, indicating that ATP-induced cAMP accumulation was not due to activation of Ca(2+)-sensitive adenylyl cyclase. The effect of ATP on cAMP production was not dependent on generation of adenosine caused by ATP hydrolysis. Among several P2 purinoceptor agonists, adenosine-5'-O-(3-thio)triphosphate, 5'-adenylylimidodiphosphate, and adenosine-5'-O-(2-thio)diphosphate evoked both cAMP accumulation and Ca2+ mobilization. In contrast, beta,gamma-methylene-ATP selectively elicited cAMP accumulation, whereas 2-methylthio-ATP and UTP induced only Ca2+ mobilization, without affecting cAMP levels. The potent P2x purinoceptor agonist alpha,beta-methylene-ATP did not induce cAMP accumulation or Ca2+ mobilization. The cAMP accumulation induced by ATP was not affected by the P2 receptor antagonist suramin but was inhibited by P1 receptor antagonists such as 8-(p-sulfophenyl)theophylline, 3-isobutyl-1-methylxanthine, and xanthine amine congener. However, the ATP-induced increase in [Ca2+]i was not affected by suramin or xanthine amine congener. Taken together, these results indicate that ATP activates two distinct purinoceptors that are coupled to different signal transduction systems, one being adenylyl cyclase and the other phospholipase C, in NG108-15 cells. Furthermore, pharmacological profiles of the adenylyl cyclase-coupled receptor were quite different from those of any known purinoceptor subtypes, especially in the unusual sensitivity of the receptor to P1 and P2 receptor agonists and antagonists. It is therefore suggested that ATP-induced cAMP accumulation may be mediated by a novel subtype of purinoceptor in NG108-15 cells.

The relation between the reflectance and thickness of the retinal nerve fiber layer

PURPOSE

This study examined quantitatively the commonly held assumption that the reflectance of the retinal nerve fiber layer is proportional to its thickness.

METHODS

The reflectance of the retinal nerve fiber layer of an in vitro vertebrate cyecup preparation was measured with an imaging microreflectometer, an instrument that provided quantitative images of a small retinal area and allowed precise control of the directions of illumination and observation. After an experiment, the eyecup was fixed and embedded for histology. A direct correspondence between the measured images and the histologic sections was established by serial reconstruction of the retinal blood vessel pattern. The thickness of the previously imaged nerve fiber bundles was measured from photomicrographs of the histologic sections.

RESULTS

The reflectance of the retinal nerve fiber layer was proportional to its thickness in areas where nerve fiber bundles were parallel. When bundles were not parallel, the directional reflectance of the retinal nerve fiber layer caused a failure of proportionality for a single illumination angle. When multiple angles of illumination were used to find the peak reflectance, this peak reflectance was again proportional to the thickness of the retinal nerve fiber layer.

CONCLUSION

These results indicate that the reflectance of the retinal nerve fiber layer arises from throughout its thickness, and have implications for assessment methods designed to identify the surface of the retinal nerve fiber layer. In addition, they indicate that control of observation geometry may be an important means to reduce variability in clinical assessment systems.

Potentiating effect of nicorandil, an antianginal agent, on relaxation induced by isoproterenol in isolated rat aorta: involvement of cyclic GMP-inhibitable cyclic AMP phosphodiesterase

In rat aortic rings, isoproterenol (ISO) 10(-9)-3 x 10(-6)M relaxed the contraction induced by phenylephrine (PE) 3 x 10(-7)M. Pretreatment with nicorandil 3 x 10(-7) and 3 x 10(-6) M potentiated the relaxation induced by ISO. Nicorandil 3 x 10(-6) M also potentiated the relaxations induced by forskolin 3 x 10(-9) - 10(-6) M and dibutylyl-cyclic AMP 3 x 10(-6) - 3 x 10(-4) M. Nitroglycerin (NTG) 10(-8) M, but not cromakalim 3 x 10(-8) M, also potentiated the ISO relaxation. Pretreatment with glyburide 10(-6) M or apamin 10(-6) M did not affect the potentiating action of nicorandil 3 x 10(-6) M. Pretreatment with methylene blue (MB) 10(-6) M, but not with NG-monomethyl-L-arginine (NMMA), however, markedly inhibited the potentiating effect of nicorandil. Removal of endothelium impaired the relaxation induced by ISO but did not inhibit the potentiating effect of nicorandil. In addition, in the presence of MCl-154 (10(-7) M), which itself potentiated ISO-induced relaxation, nicorandil 3 x 10(-6) M did not further potentiate the relaxing response to ISO. Furthermore, nicorandil 3 x 10(-6) M potentiated the increase in the tissue level of cyclic AMP caused by ISO 3 x 10(-7) M, whereas the nicorandil-induced increase in cyclic GMP levels were not affected by ISO. These results suggest that the potentiating effect of nicorandil on the relaxation induced by ISO is most likely due to inhibition of phosphodiesterase III (PDE III) by increased cyclic GMP levels.

The inhibitory mechanisms of nicorandil in isolated rat urinary bladder and femoral artery

Nicorandil or cromakalim inhibited contractile responses to acetylcholine and KCl in detrusor muscles of rat urinary bladder, whereas nitroglycerin inhibited only the responses to acetylcholine. In the detrusor muscles contracted by electrical stimulations, relaxations caused by nicorandil and cromakalim were inhibited by glyburide, but not by nitroglycerin or apamin. Methylene blue slightly potentiated the nicorandil-relaxation without affecting the cromakalim-relaxation. NG-Monomethyl-L-arginine also did not affect the relaxation induced by nicorandil. The level of cGMP was increased by both nicorandil and nitroglycerin. In rat femoral arteries contracted by phenylephrine, the relaxation induced by nicorandil was inhibited by methylene blue, glyburide and apamin. The relaxation induced by cromakalim was inhibited by glyburide, but not by apamin or methylene blue. These results suggest that the effect of nicorandil is due to activation of KATP channels in rat detrusor muscles and is due to the activation of guanylate cyclase, KATP and KCa channels in rat femoral arteries. The effect of cromakalim is due to the activation of KATP channels in both smooth muscles.

Novel mechanism and factor for regulation by HIV-1 Tat

Tat regulation of human immunodeficiency virus (HIV) transcription is unique because of its specificity for an RNA target, TAR, and its ability to increase the efficiency of elongation by polymerase. A reconstituted reaction that is Tat-specific and TAR-dependent for activation of HIV transcription has been used to identify and partially purify a cellular activity that is required for trans-activation by Tat, but not by other activators. In the reaction, Tat stimulates the efficiency of elongation by polymerase, whereas Sp1 and other DNA sequence-specific transcription factors activate the rate of initiation. Furthermore, while TATA binding protein (TBP)-associated factors (TAFs) in the TFIID complex are required for activation by transcription factors, they are dispensable for Tat function. Thus, Tat acts through a novel mechanism, which is mediated by a specific host cellular factor, to stimulate HIV-1 gene expression.

The yeast TATA-binding protein (TBP) core domain assembles with human TBP-associated factors into a functional TFIID complex

In mammalian and Drosophila cells, the central RNA polymerase II general transcription factor TFIID is a multisubunit complex containing the TATA-binding protein (TBP) and TBP-associated factors (TAFs) bound to the conserved TBP carboxy-terminal core domain. TBP also associates with alternative TAFs in these cells to form general transcription factors required for initiation by RNA polymerases I and III. Although extracts of human HeLa cells contain little TBP that is not associated with TAFs, free TBP is readily isolated from yeast cell extracts. However, recent studies indicate that yeast TBP can also interact with other yeast polypeptides to form multiprotein complexes. We established stable human HeLa cell lines expressing yeast TBP and several yeast-human TBP hybrids to study TBP-TAF interactions. We found that the yeast TBP core domain assembles with a complete set of human TAFs into a stable TFIID complex that can support activated transcription in vitro. The fact that the yeast TBP core, which differs from human TBP core in approximately 20% of its amino acid residues, has the structural features required to form a stable complex with human TAFs implies that Saccharomyces cerevisiae probably contains TAFs that are structurally and functionally analogous to human TAFs. Surprisingly, the non-conserved amino terminus of yeast TBP inhibited association between the yeast core domain and human TAFs.