Biomedical subjects

N Nelson

Publications and source records attributed to N Nelson.

At least 109 records · Page 6Linked to original sources

PubMed1994

Molecular characterization of the gene for human interleukin-1 beta converting enzyme (IL1BC).

Interleukin-1 beta (IL-1 beta) mediates a wide range of immune and inflammatory responses. The active cytokine is generated by proteolytic cleavage of an inactive precursor by a protease called the IL-1 beta converting enzyme (ICE). A cDNA encoding this protease was recently isolated. A human genomic clone containing the ICE gene (IL1BC) was isolated using the cDNA as a probe. The gene consists of 10 exons spanning at least 10.6 kb. 5'-anchored polymerase chain reaction indicated a single transcription start site approximately 33 bp upstream of the initiator Met codon. The 5'-flanking region does not have an apparent TATA box but may contain an initiator (Inr) promoter element. However, transcriptional activity could not be detected with a fusion gene containing the 5'-flanking region linked to the bacterial chloramphenicol acetyltransferase gene (CAT) when transfected into the human acute monocytic leukemia cell line THP-1. Using the genomic IL1BC clone, we have confirmed the localization of the gene to chromosome 11 band q22.2-q22.3 by fluorescence in situ hybridization.

Amino Acid Sequence↗

PubMed1994

Clinical and histologic appearance in enamel of primary teeth in relation to neonatal blood ionized calcium values.

The purpose of this investigation was to study the relationship between low values of blood ionized calcium measured in the first days of life postpartum and the clinical and histologic appearance of enamel of primary teeth. Twenty-five healthy children selected on the basis of optimality with known blood values of ionized calcium from the first days of life participated in a dental examination at the age of 5 yr. Twenty-four of the children contributed one exfoliated tooth each, which was histologically examined. The infants had lower mean values of ionized blood calcium on days 1 and 3 than day 5 postpartum. Thirteen of the 25 children had enamel aberrations, mainly on one tooth each. The histologic examination showed normal overall enamel morphology. The neonatal line was present in all teeth, and these lines were mostly thin. The registered findings about the enamel morphology could not, in any case, be correlated with the measured values of neonatal blood ionized calcium.

Calcium↗

PubMed1994

Porters and neurotransmitter transporters.

Uptake of neurotransmitters involves multiple transporters acting in different brain locations under different physiological conditions. The vesicular transporters are driven by a proton-motive force generated by a V-ATPase and their substrates are taken up via proton/substrate exchange. The plasma membrane transporters are driven by an electrochemical gradient of sodium generated by a Na+/K(+)-ATPase. Two distinct families of transporters were identified in this group. One cotransports sodium with glutamate and other amino acids and requires additionally an outwardly directed potassium gradient. The second cotransports sodium, chloride and a variety of neurotransmitters, including gamma-aminobutyric acid (GABA), glycine and monoamines. Genes and cDNA encoding several members of the latter family have been cloned and studied in detail. The structure and function as well as the evolutionary relationships among these neurotransmitter transporters are discussed.

Animals↗

PubMed1994

Structure, function and brain localization of neurotransmitter transporters.

We studied four different cDNAs encoding GABA transporters and three different cDNAs encoding glycine transporters in mouse and rat brains. A genomic clone of two of the glycine transporters (GLYT1a and GLYT1b) revealed that they derive from differential splicing of a single gene. The third glycine transporter (GLYT2) is encoded by a separate gene. Antibodies were raised against seven of these neurotransmitter transporters and their cytochemical localization in the mouse brain was studied. In general, we observed a deviation from the classical separation of neuronal and glial transporters. It seems that each of the neurotransmitter transporters is present in specific places in the brain and is expressed in a different way in very specific areas. For example, the GABA transporter GAT4, which also transports beta-alanine, was localized to neurons. However, GAT1, which is specific for GABA, was localized not only to neurons but also to glial cells. The recently discovered glycine transporter GLYT2 was of particular interest because of its deviation from the general structure by a very extended N terminus containing multiple potential phosphorylation sites. Western analysis and immunocytochemistry in frozen sections of mouse brain demonstrated a clear caudal-rostral gradient of GLYT2 distribution, with massive accumulation in the spinal cord and brainstem and less in the cerebellum. Its distribution is typically neuronal and it is present in processes with varicosities. A correlation as observed between the pattern we obtained and that observed previously from strychnine binding studies. The results indicate that GLYT2 is involved in the termination of glycine neurotransmission at the classical inhibitory system in the hindbrain. The availability of four different GABA transporters made it possible to look for specific binding sites upon the neurotransmitter transporters. An extensive program of site-directed mutagenesis led us to identify a potential neurotransmitter binding site on the GABA transporters.

Amino Acid Sequence↗

PubMed1994

Energizing porters by proton-motive force.

It is generally accepted that the chemistry of water was the most crucial determinant in shaping life on earth. Among the more important chemical features of water is its dissociation into protons and hydroxyl ions. The presence of relatively high proton concentrations in the ambient solution resulted in the evolution of proton pumps during the dawn of life on earth. These proton pumps maintained neutral pH inside the cells and generated electrochemical gradients of protons (proton-motive force) across their membranes. The existence of proton-motive force enabled the evolution of porters driven by it that are most probably among the more primitive porters in the world. The directionality of the substrate transport by the porters could be to both sides of the membranes because they can serve as proton symporters or antiporters. One of the most important subjects of this meeting is the mechanism by which proton-motive and other ion-motive forces drive the transport processes through porters. Is there a common mechanism of action for all proton-driven porters? Is there some common partial reaction by which we can identify the way that porters are energized by proton-motive force? Is there a common coupling between proton movement and uptake or secretion of certain molecules? Even a partial answer to one of these questions would advance our knowledge... or confusion. As my mentor Efraim Racker used to say: 'If you are not totally confused you do not understand the issue'.

Animals↗

PubMed1994

Leukemia in patients with breast cancer following adjuvant chemotherapy and/or postoperative radiation therapy.

We investigated the possible etiological role of adjuvant chemotherapy and postoperative radiation therapy in the development of leukemia. A case-control design with four controls matched to each case of leukemia from a cohort of women who had been treated for breast cancer during the years from 1970 to 1985 was used. Thirteen (0.23%) of the women in this cohort developed leukemia over varying lengths of follow-up time, ranging from 3 to 14 years. A higher percentage of the leukemia cases previously had adjuvant chemotherapy compared to their matched controls (54% versus 13%). The relative odds estimate of developing leukemia after chemotherapy compared to no chemotherapy was 14.8 (95% C.I. (1.8; 125.3) p < 0.01). This estimate and the test of statistical significance was based on the likelihood function for matched sets with one case and more than one control. Approximately the same percentage of leukemia cases as their controls had received postoperative regional radiation therapy (28% versus 23%). No significant association was found between postoperative radiation therapy and development of leukemia. A combination of adjuvant chemotherapy and postoperative radiation therapy was found more frequently in the leukemia cases than in their matched controls (33% versus 9%). The leukemia developing in patients having received adjuvant chemotherapy was frequently therapy resistant, resulting in a short survival.

Aged↗

PubMed1994

Breast cancer screening: recent trends in the use of mammography in Nebraska.

Although the efficacy of screening mammography has been surrounded in controversy of late, the evidence that it can reduce breast cancer mortality among women 50-74 years of age is extremely sound. In Nebraska, data from the state's Behavioral Risk Factor Survey show, that during the years 1988 to 1992, the percentage of women age 50 years and older who had ever had a mammogram rose from 50% to 65%, while the percentage of women of the same age who had had a mammogram within the past year rose from 24% to 34%. Nebraska BRFS data also show that the percentage of women 50 years of age and older who have had a mammogram within the past year varies considerably by age, income, education, and county of residence. Among women who have not had a mammogram within the past year, 66% reported that they had seen a physician within the past year for a routine check-up. Prompt and appropriate follow-up of abnormal findings by both physicians and health-care organizations is also essential to ensure the maximum benefit of screening mammography.

Aged↗

PubMed1994

Breast cancer screening: recent trends in the use of mammography in Nebraska.

Aged↗

PubMed1993

Cloning and expression of a spinal cord- and brain-specific glycine transporter with novel structural features.

A novel glycine transporter (GLYT2) was cloned from a rat brain cDNA library. GLYT2 is about 48 and 50% homologous to the previously cloned mouse glycine transporter (GLYT1) and rat proline transporter (PROT), respectively. GLYT2 differs from GLYT1 in molecular structure, tissue specificity, and pharmacological properties. The cDNA of GLYT2 encodes for 799 amino acid residues with an extended amino-terminal peptide containing 200 amino acids before the first transmembrane domain. Potential phosphorylation sites for protein kinase C, cAMP-dependent kinase, and calmodulin-dependent kinase were identified in the amino-terminal region. GLYT2 mRNA was shown to be specifically localized in spinal cord, brain stem, and to a lesser extent in the cerebellum. In contrast, GLYT1 mRNA distribution in the brain has been found previously to be more ubiquitous. Xenopus oocytes injected with GLYT2 cRNA transport glycine with a Km of 17 microM, and the uptake of glycine is resistant to inhibition by sarcosine. The experimental data suggests GLYT2 might play a major role in the termination of the inhibitory effect of glycine in the brain stem and spinal cord of vertebrates. On the other hand, the main function of GLYT1 may be in the modulation of excitatory nerve terminals. Two types of GLYT1 cDNA, GLYT1a and GLYT1b, were cloned from the mouse brain library. They differ only at their amino-terminal sequences, and GLYT1b contains two additional potential phosphorylation sites for proline-dependent kinase. Cloning of the gene encoding the GLYT1 revealed that the two variants resulted from a differential splicing.

Amino Acid Sequence↗

PubMed1993

The nuclear-encoded polypeptide Cfo-II from spinach is a real, ninth subunit of chloroplast ATP synthase.

Proton-translocating F-ATP synthases from chloroplasts contain a nuclear-coded subunit, CFo-II, that lacks an equivalent in the corresponding E. coli complex. Three recombinant phages that code for the entire precursor of this subunit have been isolated from lambda gt11 cDNA expression libraries made from polyadenylated spinach RNA using a two-step strategy. The reading frame of 222 amino acid residues includes 147 residues for the mature protein (M(r) 16.5 kDa) and a transit sequence of 75 residues (M(r) 8.0 kDa). Secondary structure predictions indicate a bitopic protein, anchored by a single N-terminal transmembrane segment and a C-terminal hydrophilic region that probably reaches into CF1. CFo-II precursor made in vitro can be imported into isolated, intact chloroplasts and assembled into ATP synthase. This protein is a real subunit of the plastid enzyme and a distinctive characteristic of ATP synthases involved in photosynthetic processes. Unique features are (i) that the gene for CFo-II (atpG) appears to be a duplication of atpF encoding CFo-I, the homologues of the genes for subunits b' and b in photosynthetic bacteria, (ii) that it represents the first instance that one copy of the various duplicated loci found in plastid chromosomes has been phylogenetically translocated to the nucleus, and (iii) that it operates with a bipartite (import/thylakoid-targeting) transit peptide but without an intermediate cleavage site for the stroma protease, suggestive of a way of membrane integration different from that of its plastome-encoded counterpart CFo-I. With these data, the first complete sequence for a chloroplast ATP synthase of a higher plant (spinach) is available.

Amino Acid Sequence↗

PubMed1993

Vacuolar ATPase mutants accumulate precursor proteins in a pre-vacuolar compartment.

The vacuole of the yeast Saccharomyces cerevisiae contains a proton-translocating ATPase that acidifies the vacuolar lumen and generates an electrochemical potential across the vacuole membrane. Strains with chromosomal disruptions of the genes encoding the A, B, and c subunits of the vacuolar ATPase accumulate precursor forms of the vacuolar membrane protein alkaline phosphatase, and the soluble vacuolar hydrolases carboxypeptidase Y and proteinase A. We have found that the intracellular precursors in delta vat strains accumulate within the secretory pathway at some point before delivery to the vacuole but after transit to the Golgi complex. Purified vacuoles from delta vat cells do not contain the precursor forms of carboxypeptidase Y or alkaline phosphatase. In addition, vacuolar hydrolase-invertase hybrid proteins are inefficiently delivered to the vacuole in delta vat strains as demonstrated by vacuole isolation. Further subcellular fractionation to separate organelles indicate that significant amounts of the carboxypeptidase Y-invertase and alkaline phosphatase-invertase hybrid proteins are located in the late Golgi complex and/or post Golgi compartments.

Alkaline Phosphatase↗

PubMed1993

Importance of the amino terminus of the interleukin-8 receptor in ligand interactions.

Interleukin-8 (IL-8) and growth regulatory gene/melanoma growth stimulatory activity (GRO/MGSA) are small polypeptide molecules involved in the chemotactic response of certain cell types. Two receptors have been described which interact with IL-8, designated type 1 and type 2. IL-8 binds with high affinity to both receptors, whereas GRO/MGSA and neutrophil-activating peptide-2 demonstrate a high degree of binding only to the type 2 receptor. The two forms of IL-8 receptor are members of the rhodopsin seven-helix membrane-spanning superfamily, and share a high degree of overall homology, although the amino termini are very divergent. By using conserved restriction enzyme sites, a series of chimeric IL-8 receptor molecules were constructed between the type 1 and type 2 receptors and transfected into human 293 kidney epithelial cells. These chimeric molecules altered regions of the receptor presented to the ligand. The ability of the chimeric receptors to bind IL-8 was determined, as well as the ability of IL-8 and GRO/MGSA to inhibit radiolabeled IL-8 binding. The amino terminus of the IL-8 receptors was found to be important for differential binding of GRO/MGSA and IL-8. In addition, a series of peptides was also constructed to further investigate which residues of IL-8 receptor interact with IL-8. These peptides also identified the amino-terminal sequence of the IL-8 receptors as being important in interacting with IL-8.

Amino Acid Sequence↗

PubMed1993

The atp2 operon of the green bacterium Chlorobium limicola.

The operon (atp2) encoding the beta and epsilon subunits of F-ATPase from Chlorobium limicola was cloned and sequenced. In contrast with purple bacteria these genes are arranged in a separate operon similar to the cyanobacteria. The operon terminates with a pronounced stem-loop structure. About 0.8 kb upstream of the beta subunit a gene encoding the enzyme phospho enol pyruvate carboxykinase was identified. This gene is transcribed in the opposite direction of the atp2 operon and also ends with a stem-loop structure. These genes of green bacteria are among the first to be sequenced, and therefore the genetic distance between these genes and corresponding genes from other bacteria and eukaryotes was studied. Even though the operon structure resembles that of cyanobacteria, the evolutionary tree compiled from these data places the chlorobium gene close to purple bacteria. Chlorobium limicola beta and epsilon subunits complemented Escherichia coli mutants defective in the corresponding subunits, indicating that the hybrid enzyme formed from subunits of the two bacteria is active in ATP synthesis.

Amino Acid Sequence↗

PubMed1993

Molecular characterization of four pharmacologically distinct gamma-aminobutyric acid transporters in mouse brain [corrected].

Two novel gamma-aminobutyric acid (GABA) transporters, GAT3 and GAT4, were cloned from the mouse neonatal brain cDNA library and expressed in Xenopus oocytes. Sequence analysis indicated they were members of the Na(+)-dependent neurotransmitter transporter family. The GABA uptake activities were measured in cRNA injected Xenopus oocytes. The Km for GABA uptake by GAT3 was 18 microM and by GAT4 was 0.8 microM. GAT3 also transports beta-alanine and taurine with Km of 28 and 540 microM, respectively. Similarly, GAT4 transports beta-alanine with Km of 99 microM and taurine with a Km of 1.4 mM. The newly cloned GABA transporters were compared with two previously cloned GABA transporters, GAT1 and GAT2, in terms of molecular and pharmacological properties. While GAT1 and GAT4 gene expression were neural specific, GAT2 and GAT3 mRNAs were detected in other tissues such as liver and kidney, in which GAT3 mRNA was especially abundant. The expression of GAT3 mRNA in mouse brain is developmentally regulated, and its mRNA is abundant in neonatal brain but not in adult brain. High affinity GABA transporters GAT1 and GAT4 were more sensitive to inhibition by nipecotic acid. Low affinity GABA transporters GAT2 and GAT3 were inhibited most effectively by betaine and beta-alanine, respectively. The differential tissue distribution and distinct pharmacological properties of those four GABA transporters suggest functional specialization in the mechanisms of GABA transmission termination.

Amino Acid Sequence↗

PubMed1993

A rat brain cDNA encoding the neurotransmitter transporter with an unusual structure.

A rat cDNA clone encoding the novel membrane protein of the neurotransmitter transporters family was cloned and sequenced. The cDNA was identified as a transcript of the gene NTT4 of which a partial genomic clone was previously sequenced. Alignment of the amino acid sequence of NTT4 with other members of the neurotransmitter transporter family revealed a marked deviation from the conserved structure of all other members of the family. The largest extracellular loop with a potential glycosylation site was identified between membrane segments 7 and 8. The protein retains the common glycosylated loop between transmembrane helices 3 and 4 in all members of the family. The transcript of NTT4 was found exclusively in the central nervous system and is more abundant in the cerebellum and the cerebral cortex.

Amino Acid Sequence↗

PubMed1993

The murine homologue of the human interleukin-8 receptor type B maps near the Ity-Lsh-Bcg disease resistance locus.

Interleukin-8 (IL-8), a member of the chemokine alpha subfamily, is a chemoattractant for neutrophils. Cell surface receptors for IL-8 have been cloned from rabbits and humans. Two related but different IL-8 receptors (IL-8R) have been characterized from humans. IL-8RA and IL-8RB bind IL-8 at high affinity but IL-8RB also binds GRO/MGSA and NAP-2 at high affinity. Using the human IL-8RB cDNA as a probe, we have determined that the homologous murine gene maps near the Ity-Lsh-Bcg disease resistance locus. A murine homologue of the human IL-8RB was isolated from a genomic library. This gene would encode a protein of 359 amino acids and would have a 68 and 71% amino acid identity with human IL-8RA and IL-8RB, respectively. Additional mapping data using the murine gene revealed the following genetic distances (in cM +/- 1 standard error) from the centromere: Mylf--7.9 +/- 2.7--Lsh-Ity-Bcg--1.9 +/- 1.4--Il8rb--1.9 +/- 1.4--Vil-- 5.9 +/- 2.3--Acrg--2.9 +/- 1.7--Bcl-2.

Amino Acid Sequence↗

PubMed1993

Molecular characterization of receptors for human interleukin-8, GRO/melanoma growth-stimulatory activity and neutrophil activating peptide-2.

Interleukin-8 (IL-8), neutrophil activating peptide-2 (NAP-2), and growth regulated gene (GRO, also known as melanoma growth stimulatory activity) are members of a family of peptides which are chemotactic agents for inflammatory cells such as neutrophils. Receptors have been identified for IL-8, GRO and NAP-2 on human neutrophils and granulocytic cell lines, and it has been observed that these cytokines can cross-compete for binding to a common receptor. Using the recently characterized rabbit IL-8 receptor as a probe, two classes of cDNAs, termed type 1 and type 2, were isolated from a human neutrophil library. The type 1 receptor binds only IL-8 while the type 2 receptor binds IL-8, GRO and NAP-2 at high affinity when respective cDNAs are expressed in COS-7 cells. The two cDNAs encode proteins that have an amino acid sequence identity of 77% while the type 1 and 2 receptors have an identity of 84 and 74% with the rabbit IL-8 receptor. These receptors also show significant homology with receptors for other chemotactic agents and with potential coding regions from the human cytomegalovirus genome.

Amino Acid Sequence↗

PubMed1993

Presynaptic events involved in neurotransmission.

Vacuolar H(+)-ATPase (V-ATPase) plays a key role in neurotransmission. It provides the energy for the uptake and storage of neurotransmitters in synaptic vesicles and granules. It also may play a role in the biogenesis of synaptic vesicles as well as in neurosecretion. This is one of the most conserved fundamental enzymes in nature, but functions in a wide variety or organelles and membranes. Its structure, function, molecular biology and biogenesis is discussed in relation to its role in neurotransmission. Termination of neurotransmission is carried out by neurotransmitter transporters that function in the reuptake of the neurotransmitters into the presynaptic cells. We cloned, sequenced and expressed several cDNAs encoding neurotransmitter transporters. Their specificity and site of synthesis revealed some new aspects of neurotransmission.

Amino Acid Sequence↗