Transmembrane-truncated alphavbeta3 integrin retains high affinity for ligand binding: evidence for an 'inside-out' suppressor?

The molecular mechanisms of alphavbeta3 integrin affinity regulation have important biological implications in tumour development, wound repair and angiogenesis. We expressed, purified and characterized recombinant forms of human alphavbeta3 (r-alphavbeta3) and compared the activation state of these with alphavbeta3 in its cellular environment. The ligand specificity and selectivity of recombinant full-length and double transmembrane truncations of r-alphavbeta3 cloned in BacPAK6 vectors and expressed in Sf9 and High Five insect cells were compared with those of native placental alphavbeta3 and the receptor in situ on the cell surface. r-alphavbeta3 integrins were purified by affinity chromatography from detergent extracts of cells (full-length), and from the culture medium of cells expressing double-truncated r-alphavbeta3. r-alphavbeta3 had the same epitopes, ligand-binding specificities, bivalent cation requirements and susceptibility to RGD-containing peptides as native alphavbeta3. On M21-L4 melanoma cells, alphavbeta3 mediated binding to vitronectin, but not to fibrinogen unless activated with Mn2+. Non-activated alphaIIbbeta3 integrin as control in M21-L-IIb cells had the opposite profile, mediating binding to fibrinogen, but not to vitronectin unless activated with Mn2+. Thus these receptors had moderate to low ligand affinity. In marked contrast, purified alphavbeta3 receptors, with or without transmembrane and cytoplasmic domains, were constitutively of high affinity and able to bind strongly to vitronectin, fibronectin and fibrinogen under physiological conditions. Our data suggest that, in contrast with the positive regulation of alphaIIbbeta3 in situ, intracellular controls lower the affinity of alphavbeta3, and the cytoplasmic domains may act as a target for negative regulators of alphavbeta3 activity.

Contiguous phosphorylated and non-phosphorylated domains along axonal neurofilaments

I have investigated the phosphorylation state of the medium molecular mass neurofilament protein (NF-M) along axonal neurofilaments. Cultured embryonic sensory neurons were treated with non-ionic detergent to cause the cytoskeletal polymers to splay apart from each other. Neurofilaments were visualized by double-label immunofluorescence microscopy and the proportion of their length that stained with various NF-M antibodies was determined using digital image analysis techniques. Monoclonal antibody RMO255, which binds to NF-M independently of phosphorylation state, stained an average of 98% of the neurofilament length. In contrast, monoclonal antibody RMO55, which binds specifically to a phosphorylated epitope on NF-M, stained some neurofilaments completely, some not at all, and some along part of their length. These partly stained neurofilaments exhibited single or multiple discrete segments of staining along their length separated by segments that were unstained. The average proportion of the neurofilament length that stained with this antibody was lowest proximally (12–22%, n=3) and increased along the axon to reach a maximum distally (58–87%, n=3). A converse pattern (77–87% proximally and 2–9% distally, n=3) was observed for neurons stained with monoclonal antibody FNP7, which binds to specifically to a non-phosphorylated epitope in both NF-M and the high molecular mass neurofilament protein, NF-H. Analysis of the staining of individual neurofilaments revealed a bimodal frequency distribution in which neurofilaments were more likely to be phosphorylated along either all or none of their length than along part of their length. These observations indicate that: (a) phosphorylated and non-phosphorylated neurofilaments can coexist side-by-side in these axons, (b) neurofilaments can be composed of single or multiple contiguous phosphorylated and non-phosphorylated epitope domains along their length, (c) the proportion of the neurofilament length that is phosphorylated at these epitopes increases along the axon in a proximal-to-distal manner, and (d) the pattern of phosphorylation is non-random, generating populations of phosphorylated and non-phosphorylated neurofilaments and discrete phosphorylated and non-phosphorylated domains along individual neurofilaments.

Correlation analysis of somatosensory evoked potential waveforms: clinical applications

OBJECTIVE

To assess the validity of the correlation coefficient (CC) as a diagnostic tool in evaluating somatosensory evoked potential (SEP) waveforms.

DESIGN

SEP waveforms were recorded over the spine and scalp in response to tibial nerve stimulation at the ankle for 30 patients.

SETTING

A general community, ambulatory, private referral center.

PATIENTS

Patients were all ambulatory and were selected randomly from among existing patient records at the medical center.

MAIN OUTCOME MEASURE

The test for validity uses the CC to verify reproducibility. The test for side-to-side symmetry uses the CC to obtain a measure of similarity between left and right tibial scalp responses. For both tests, a table is presented with CCs for normal subjects. If the CC for each patient falls below the appropriate critical value from the table, then the CC is taken to be abnormal; p values are provided at specific levels in this table.

RESULTS

A new data base for the means and critical values of CCs with corresponding p values is established for normal subjects. Most of the patient data reveal significant CC nonreproducibility and lack of symmetry in tibial scalp SEP waveforms.

CONCLUSION

The CC provides objective and quantitative waveform information that complements latency and amplitude measurements in the clinical interpretation of tibial scalp SEP waveforms.

Systematic study of the six cysteines of the E1 subunit of the pyruvate dehydrogenase multienzyme complex from Escherichia coli: none is essential for activity

Variants of the Escherichia coli 1-lip pyruvate dehydrogenase multienzyme complex (1-lip PDHc) with the C259N and C259S substitutions in the putative thiamin diphosphate-(ThDP-) binding motif of the pyruvate dehydrogenase component (E1, EC 1.2.4.1) were characterized. Single substitutions were made at the five remaining cysteines of the E1 component, creating the C120A, C575A, C610A, C654A, and C770S variants to test the hypothesis that the activity loss that accompanies exposure of the enzyme to fluoropyruvate, bromopyruvate, and 2-oxo-3-butynoic acid is the result of the modification of approximately one cysteine residue per E1 monomer. Surprisingly, all single cysteine E1 variants could be reconstituted with E2-E3 subcomplex and showed PDHc activity ranging from 74% to 96% that of the parental enzyme. The specific activities of C259N and C259S variants of 1-lip PDHc were 58% and 27% relative to that of the parental 1-lip PDHc. All five single cysteine E1 variants, along with the C259N and C259S variants of 1-lip PDHc, could also (1) be inactivated with fluoropyruvate and 2-oxo-3-butynoic acid, (2) were subject to inactivation by the monoclonal antibody 18A9 reported from one of our laboratories, and (3) were subject to regulation by pyruvate and acetyl-CoA. It was therefore concluded that none of the six cysteine residues is essential for the activity of the E1 component or of the complex. When tested with the putative transition-state analogue, thiamin 2-thiothiazolone diphosphate, all but the C259S and C259N variants were very potently inhibited, the stoichiometry for parental E1 being about 1.6 mol of inhibitor/mol of E1 subunit. The C259S and C259N E1 variants required at least 25-fold greater inhibitor concentration to achieve the same level of inhibition. C259 is located in the putative thiamin diphosphate-binding motif of the enzyme [more exactly, it is adjacent to a ligand to the Mg(II) ion]. It is therefore concluded that thiamin 2-thiothiazolone diphosphate is not a transition-state analogue; rather, it is a potent inhibitor of the complex because of a specific interaction with the C259 residue.

The Human PAX6 Mutation Database

The Human PAX6 Mutation Database contains details of 94 mutations of the PAX6 gene. A Microsoft Access program is used by the Curator to store, update and search the database entries. Mutations can be entered directly by the Curator, or imported from submissions made via the World Wide Web. The PAX6 Mutation Database web page at URL http://www.hgu.mrc.ac.uk/Softdata/PAX6/ provides information about PAX6, as well as a fill-in form through which new mutations can be submitted to the Curator. A search facility allows remote users to query the database. A plain text format file of the data can be downloaded via the World Wide Web. The Curation program contains prior knowledge of the genetic code and of the PAX6 gene including cDNA sequence, location of intron/exon boundaries, and protein domains, so that the minimum of information need be provided by the submitter or Curator.

Hex: a homeobox gene revealing peri-implantation asymmetry in the mouse embryo and an early transient marker of endothelial cell precursors

The divergent homeobox gene Hex exhibits three notable expression patterns during early mouse development. Initially Hex is expressed in the primitive endoderm of the implanting blastocyst but by 5.5 dpc its transcripts are present only in a small patch of visceral endoderm at the distal tip of the egg cylinder. Lineage analysis shows that these cells move unilaterally to assume an anterior position while continuing to express Hex. The primitive streak forms on the opposite side of the egg cylinder from this anterior Hex expression domain approximately 24 hours after the initial anterior movement of the distal visceral endoderm. Thus, Hex expression marks the earliest unequivocal molecular anteroposterior asymmetry in the mouse embryo and indicates that the anteroposterior axis of the embryo develops from conversion of a proximodistal asymmetry established in the primitive endoderm lineage. Subsequently, Hex is expressed in the earliest definitive endoderm to emerge from the streak and its expression within the gut strongly suggests that the ventral foregut is derived from the most anterior definitive endoderm and that the liver is probably the most anterior gut derivative. Hex is also an early marker of the thyroid primordium. Within the mesoderm, Hex is transiently expressed in the nascent blood islands of the visceral yolk sac and later in embryonic angioblasts and endocardium. Comparison with flk-1 (T. P. Yamaguchi et al., Development 118, 489–498, 1993) expression indicates that Hex is also an early marker of endothelial precursors but its expression in this progenitor population is much more transient than that of flk-1, being downregulated once endothelial cell differentiation commences.

Does pancreatic enzyme supplementation reduce pain in patients with chronic pancreatitis: a meta-analysis

OBJECTIVE

Pancreatic enzyme therapy is widely used in the treatment of pain in chronic pancreatitis. The aim of our study was to perform a meta-analysis to determine whether pancreatic enzyme supplementation significantly decreases abdominal pain in patients with chronic pancreatitis.

METHODS

From a MEDLINE search, we identified, evaluated, and subjected to a meta-analysis, six randomized, double-blind, placebo-controlled trials. Important features of data extraction included the method of subject inclusion, definition of disease, enzyme preparation, response to pancreatic enzyme therapy versus placebo, and modality for measuring response.

RESULTS

In the meta-analysis, the pooled estimate of the percentage of patients per study who preferred enzymes relative to placebo was 52% (95% confidence interval, 45-60%). A test of homogeneity indicated that there was no statistically significant heterogeneity across studies in the percentage of patients preferring enzymes.

CONCLUSION

Statistical analysis demonstrates no significant benefit of supplemental pancreatic enzyme therapy to relieve pain associated with chronic pancreatitis.

RNA aptamers to the peptidyl transferase inhibitor chloramphenicol

BACKGROUND

The problem of how macromolecules adopt specific shapes to recognize small molecules in their environment is readily addressed through in vitro selections (the SELEX protocol). RNA-antibiotic interactions are particularly attractive systems for study because they provide an opportunity to expand our understanding of molecular recognition by RNA and to facilitate ribosomal modeling. Specifically, the antibiotic chloramphenicol (Cam) naturally binds bacterial ribosomes in the 'peptidyl transferase loop' of 23S ribosomal RNA to inhibit peptide bond formation.

RESULTS

We identified Cam-binding RNA molecules ('aptamers') from two independent initial random RNA populations. Boundary determinations, ribonuclease S1 sensitivity analyses and the activity of truncated minimal RNAs identified a structural motif that is shared by sequences from both selections. The pseudosymmetric motif consists of a highly conserved central helix of five to six base pairs flanked by A-rich bulges and additional helices. Addition of Cam prior to ribonuclease S1 protected nucleotides in the conserved cores from cleavage. Reselection from a pool of mutated variants of the minimal aptamer further refined the sequence requirements for binding. Finally, we used proton nuclear magnetic resonance (NMR) to establish a 1:1 RNA: Cam stoichiometry of the complex. Both the protection and NMR data both show that Cam stabilizes the active fold of this aptamer.

CONCLUSIONS

There are many different RNA sequences that can bind Cam. The Cam aptamers that we examined have a well-defined secondary structure with a binding pocket that appears to be stabilized by Cam. This RNA motif superficially resembles the Cam-binding site in 23S rRNA, although further work is needed to establish the significance of these similarities.

Visual organization test performance in an African American population with acute unilateral cerebral lesions

Controversy abounds as to whether the Hooper Visual Organization Test (VOT) is a measure of hemisphere-specific, region-specific, or non-specific brain damage. The present study examines this issue in a group of African Americans with acute unilateral brain damage and non-brain-injured controls. Consistent with the idea that the VOT is a measure of "organic" cerebral pathology, non-brain damaged controls earned significantly higher VOT scores than brain-damaged patients. While other studies have noted that the VOT is primarily sensitive to damage in the right parietal region of the brain, the present study shows that VOT performance is especially vulnerable to acute lesions in the right anterior quadrant of the brain. This latter finding supports the idea that VOT performance is differentially sensitive to regional cerebral pathology, but challenges the region specific claim of poorer VOT performance among patients with right posterior cerebral damage.

Unilateral brain lesions and performance on Russell's version of the Wechsler Memory Scale in an African American population

Studies of patients with unilateral lesions report hemisphere-specific and locus-specific impairments on Russell's (1975) Revision of the Wechsler Memory Scale (RWMS). In the current investigation "race-homogeneous" and "race-comparative" paradigms provide the context in which the generalizability of RWMS findings are examined in a population of African Americans with unilateral lesions. The performances of brain-damaged patients were impaired relative to normal controls on five of the six RWMS measures. However, patients with left and right hemisphere damage in our sample did not differ systematically on RWMS subtests. Likewise, among patients with lesions confined to one of the quadrants in the brain, there were no quadrant group differences in performance on RWMS subtests. But, right posteriors were impaired relative to controls on immediate and delayed VR subtests. The relative merits of the race-comparative and race-homogeneous paradigms are considered in the context of these findings.

Domestic violence. Working with the spouse abuser

Reported "success rates" for abuser treatment programs vary greatly, from as low as 5% to as high as 67%. Regardless of statistics, intervention cannot be overlooked if domestic violence is to be addressed. The primary concern must always be safety for the victim, but the cycle of violence will not stop without treatment interventions for the abuser. Effective screening and referral of potential abusers are crucial to breaking the cycle. Working under the provisions of NC General Statute 50B-3(a), the North Carolina Council for Women works with abuser treatment programs in order to establish eligibility requirements for abusers. These programs, listed in Health Watch (pages 345-8), provide individual and group counseling for a set fee, which the abuser pays. For more information call Joyce W. Allen, NC Council For Women, 919/733-2455.

The effects of maternal protein deprivation on the fetal rat pancreas: major structural changes and their recuperation

There is evidence that low birth weight and poor growth in early life cause a long-term predisposition to non-insulin-dependent diabetes. Morphological changes were assessed in fetal rat pancreas subjected to both pre- and post-natal maternal protein deprivation (LP). Further groups were subjected to purely prenatal maternal protein deprivation (preLP) and purely postnatal maternal protein deprivation (postLP), as well as a control group. The results show that the LP and postLP groups had fewer but larger islets than the control group, while the preLP group had more numerous, smaller islets. All three low protein groups had more irregularly shaped islets than the control group. There was a reduction in the amount of beta cells within each islet in all three protein-deprived groups. The LP and postLP groups showed a reduction in the percentage of islet tissue and beta cells per pancreas, but the percentage of islet tissue expressed per unit body weight was similar in all four groups. These results show that in maternal protein deprivation, homeostatic mechanisms ensure a constant amount of pancreatic endocrine tissue per unit of body weight. However, there remain major structural changes in the size, shape, and composition of the islets. These results support the theory that early development profoundly affects the structure of the pancreas and may play a role in the later development of adult diseases, such as non-insulin-dependent diabetes mellitus.

Niemann-Pick C1 disease gene: homology to mediators of cholesterol homeostasis

Niemann-Pick type C (NP-C) disease, a fatal neurovisceral disorder, is characterized by lysosomal accumulation of low density lipoprotein (LDL)-derived cholesterol. By positional cloning methods, a gene (NPC1) with insertion, deletion, and missense mutations has been identified in NP-C patients. Transfection of NP-C fibroblasts with wild-type NPC1 cDNA resulted in correction of their excessive lysosomal storage of LDL cholesterol, thereby defining the critical role of NPC1 in regulation of intracellular cholesterol trafficking. The 1278-amino acid NPC1 protein has sequence similarity to the morphogen receptor PATCHED and the putative sterol-sensing regions of SREBP cleavage-activating protein (SCAP) and 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase.

Murine model of Niemann-Pick C disease: mutation in a cholesterol homeostasis gene

An integrated human-mouse positional candidate approach was used to identify the gene responsible for the phenotypes observed in a mouse model of Niemann-Pick type C (NP-C) disease. The predicted murine NPC1 protein has sequence homology to the putative transmembrane domains of the Hedgehog signaling molecule Patched, to the cholesterol-sensing regions of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and SREBP cleavage-activating protein (SCAP), and to the NPC1 orthologs identified in human, the nematode Caenorhabditis elegans, and the yeast Saccharomyces cerevisiae. The mouse model may provide an important resource for studying the role of NPC1 in cholesterol homeostasis and neurodegeneration and for assessing the efficacy of new drugs for NP-C disease.

2-Oxo-3-alkynoic acids, universal mechanism-based inactivators of thiamin diphosphate-dependent decarboxylases: synthesis and evidence for potent inactivation of the pyruvate dehydrogenase multienzyme complex

A new class of compounds, the 2-oxo-3-alkynoic acids with a phenyl substituent at carbon 4 was reported by the authors as potent irreversible and mechanism-based inhibitors of the thiamin diphosphate- (ThDP-) dependent enzyme pyruvate decarboxylase [Chiu, C.-F., & Jordan, F. (1994) J. Org. Chem. 59, 5763-5766]. The method has been successfully extended to the synthesis of the 4-, 5-, and 7-carbon aliphatic members of this family of compounds. These three compounds were then tested on three ThDP-dependent pyruvate decarboxylases: the Escherichia coli pyruvate dehydrogenase multienzyme complex (PDHc) and its E1 (ThDP-dependent) component, pyruvate oxidase (POX, phosphorylating; from Lactobacillus plantarum),and pyruvate decarboxylase (PDC) from Saccharomycescerevisiae. All three enzymes were irreversibly inhibited by the new compounds. The 4-carbon acid is the best substrate-analog inactivator known to date for PDHc, more potent than either fluoropyruvate or bromopyruvate. The following conclusions were drawn from extensive studies with PDHc: (a) The kinetics of inactivation of PDH complexes and of resolved E1 by 2-oxo-3-alkynoic acids is time- and concentration-dependent. (b) The 4-carbon acid has a Ki 2 orders of magnitude stronger than the 5-carbon acid, clearly demonstrating the substrate specificity of PDHc. (c) The rate of inactivation of PDH complexes and of resolved E1 by 2-oxo-3-alkynoic acids is enhanced by the addition of ThDP and MgCl2. (d) Pyruvate completely protects E1 and partially protects PDHc from inactivation by 2-oxo-3-butynoic acid. (e) E1 but not E2-E3 is the target of inactivation by 2-oxo-3-butynoic acid. (f) Inactivation of E1 by 2-oxo-3-butynoic acid is accompanied by modification of 1.3 cysteines/E1 monomer. The order of reactivity with the 4-carbon acid was PDHc > POX > PDC. While the order of reactivity with PDHc and POX was 2-oxo-3-butynoic acid > 2-oxo-3-pentynoic acid > 2-oxo-3-heptynoic acid, the order of reactivity was reversed with PDC.