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L H Davis

Publications and source records attributed to L H Davis.

11 recordsLinked to original sources
PubMed1992

Ankyrin regulation: an alternatively spliced segment of the regulatory domain functions as an intramolecular modulator.

This study of two forms of ankyrin (protein 2.1 and 2.2) from human erythrocytes has revealed a role for alternate exon usage at the level of regulation of protein interactions. The smaller form of ankyrin (protein 2.2), which lacks a portion of the regulatory domain due to alternative splicing of pre-mRNA, exhibits increased affinity for the cytoplasmic domain of the anion exchanger, spectrin, and tubulin. Direct evidence that at least one of these associations is modulated by the alternatively spliced segment of the regulatory domain is provided by experiments utilizing a polypeptide that is comprised of residues 1513-1674 corresponding to the portion of the regulatory domain missing from protein 2.2. Addition of this regulatory domain polypeptide to binding assays reversed the increase in affinity of protein 2.2 for the anion exchanger. The inhibitory activity of the regulatory domain polypeptide in these assays is accompanied by a direct interaction with a site that is available on the smaller form of ankyrin and is distinct from the binding site for the anion exchanger. These results support the idea that the alternatively spliced segment within the regulatory domain of erythrocyte ankyrin performs a repressor function and acts through an allosteric mechanism involving interaction(s) at a site separate from the binding site for the anion exchanger.

Allosteric Regulation↗
PubMed1991

Specific 33-residue repeat(s) of erythrocyte ankyrin associate with the anion exchanger.

Erythrocyte ankyrin contains an 89-kDa domain (residues 2-827) comprised almost entirely of 22 tandem repeats of 33 amino acids which are responsible for the high affinity interaction of ankyrin with the anion exchanger (Davis, L., and Bennett, V. (1990) J. Biol. Chem. 265, 10589-10596). The question of whether the repeats are equivalent with respect to binding to the anion exchanger was addressed using defined regions of erythrocyte and brain ankyrins expressed in bacteria. The conclusion is that the repeats are not interchangeable and that the 44 residues from 722 to 765 are essential for high affinity binding between erythrocyte ankyrin and the anion exchanger. Residues 348-765 were active whereas a polypeptide of the same size (residues 305-721) but missing the 44 residues was not active. The difference between the active and inactive polypeptides was not caused by the degree of folding based on circular dichroism spectra. The 44 residues from 722 to 765 were not sufficient for binding since deletions of residues from 348 to 568 resulted in a 10-fold loss of activity. However, the role of residues 348-568 may be at the level of folding rather than a direct contact since the deleted sequences were not active in the absence of 722-765 and since circular dichroism spectra revealed significant loss of structure in the smaller polypeptides. Further evidence that the 33-residue repeats are not equivalent in ability to bind to the anion exchanger is that a region of human brain ankyrin containing 18 33-residue repeats with 67% overall sequence identity to erythrocyte ankyrin was 8-fold less active than a region of erythrocyte ankyrin containing only 12 repeats. The fact that the anion exchanger binds to certain repeats suggests that the other 33-amino acid repeats could interact with proteins distinct from the anion exchanger and provide ankyrin with the potential for considerable diversity in association with membrane proteins as well as cytoplasmic proteins. Tubulin was identified as one example of a protein that can interact with ankyrin repeats that are not recognized by the anion exchanger.

Amino Acid Sequence↗
PubMed1990

Mapping the binding sites of human erythrocyte ankyrin for the anion exchanger and spectrin.

This report describes initial characterization of the binding sites of ankyrin for spectrin and the anion exchanger using defined subfragments isolated from purified ankyrin domains. The spectrin-binding domain of ankyrin is comprised of two subdomains: an acidic, proline-rich region (pI = 4) involving the amino-terminal 80 residues from 828 to 908 and a basic region (pI = 8.8) that extends from 898 to 1386. The amino-terminal 70 amino acids of the spectrin-binding domain are critical for association with spectrin, since a subfragment missing this region is only 5% as active as the intact domain in displacing binding of spectrin to inside-out membrane vesicles, while deletion of the first 38 residues of the acidic domain results in a 10-fold reduction in activity. The anion exchanger-binding site is confined to an 89-kDa domain that was isolated and characterized as a globular molecule with approximately 30% alpha-helical configuration. A subfragment of the 89-kDa domain extending from residues 403 to 779 (or possibly 740) retains ability to associate with the anion exchanger. The 89-kDa domain is comprised of a series of tandem repeats of 33 amino acids that extend from residues 35 to 778 (Lux, S., John, K., and Bennett, V. (1990) Nature 344, 36-42). The activity of residues 403-779 demonstrates that the 33-amino acid repeats of the 89-kDa domain are responsible for association between ankyrin and the anion exchanger. The 33-amino acid repeating sequence of ankyrin represents an ancient motif also found in proteins of Drosophila, yeast, and Caenor habditis elegans. The finding that the 33-amino acid repeating sequence is involved in interaction with the anion exchanger implies that this motif may perform a role in molecular recognition in diverse proteins.

Amino Acid Sequence↗
PubMed1990

Activation of glycogen phosphorylase in rat pheochromocytoma PC12 cells and isolated hepatocytes by organophosphates.

Several organophosphates including diisopropylfluorophosphonate (DPF) and a variety of compounds used as chemical warfare agents produced dose- and time-dependent increases in phosphorylase-a, the phosphorylated form of glycogen phosphorylase in rat pheochromocytoma cells, PC12, and isolated hepatocytes. Increases in phosphorylase-a did not occur in cells exposed to the carbamates, physostigmine or pyridostigmine, or to O-ethyl S-2-diisopropylaminoethylmethyl-phosphonathiolate (VX), an organophosphate which is protonated at physiological pH. When extracellular pH was increased to pH 8, VX acted like the other organophosphates and increased phosphorylase-a activity. The possibility that organophosphates increase phosphorylase-a in intact cells by releasing Ca2+ from intracellular binding sites is supported by the following findings: organophosphate-induced increases in phosphorylase-a did not correlate with changes in cyclic AMP in the two cell types studied; in PC12 cells, increases in this activity occurred in the absence of extracellular calcium and were not inhibited by the calcium channel blocker, verapamil; fluorescence of the calcium sensitive dye, Quin-2, in PC12 cells preloaded with the acetoxymethyl ester of the dye was increased by soman; finally, addition of the calcium ionophore, A23187, to PC12 cells maintained in calcium-free medium caused sarin-stimulated phosphorylase-a activity to return rapidly to basal levels. Collectively, these data argue strongly that organophosphates increase phosphorylase-a activity in intact cells via a novel mechanism involving release of calcium from intracellular binding sites.

Adenine Nucleotides↗
PubMed1988

Effects of organophosphates and nerve growth factor on muscarinic receptor binding number in rat pheochromocytoma PC12 cells.

Muscarinic receptor binding in PC12 cells is influenced by both nerve growth factor (NGF) and organophosphates. Treatment of PC12 cells with a single dose of NGF (50 ng, 7S NGF/ml) increased [3H]N-methylscopolamine ([3H]-NMS) binding sites approximately two-fold at 48 hr but did not change the Kd for this ligand. Exposure of PC12 cells to soman, 50 microM, decreased [3H]-NMS binding in both undifferentiated and NGF-treated cells; however, decreases in muscarinic binding induced by the organophosphate were only minimal after the first hour after treatment and were maximal at about 24 hr. Other organophosphates including sarin, tabun, and VX as well as the carbamate, pyridostigmine, also reduced [3H]-NMS binding in PC12 cells measured 24-48 hr after treatment. The order of potency of organophosphates in lowering [3H]-NMS binding was soman greater than sarin greater than VX greater than tabun greater than DFP. High amounts of VX (200 microM) but not the other organophosphates inhibited [3H]-NMS binding when added to cells during the course of binding assays. Decreases in muscarinic receptor binding induced by the organophosphates differed markedly from that produced by carbamylcholine, which decreased [3H]-NMS binding maximally 30 min after addition to the cells. Decreases in [3H]-NMS binding produced by carbamylcholine were antagonized by atropine, but reductions in muscarinic binding produced by the organophosphates were not reversed by atropine. Thus, decreases in muscarinic receptor binding induced in PC12 cells by organophosphates occur via a novel mechanism that does not involve agonist-induced receptor desensitization.

Animals↗
PubMed1987

Metabolism via the pentose phosphate pathway in rat pheochromocytoma PC12 cells: effects of nerve growth factor and 6-aminonicotinamide.

Exposure of rat pheochromocytoma PC12 cells to 0.1 mM 6-aminonicotinamide (6AN) for 24 hours resulted in a 500-fold increase in 6-phosphogluconate indicating active metabolism of glucose via the oxidative enzymes of the pentose phosphate pathway. Amounts of 6-phosphogluconate that accumulated in 6AN-treated cells at 24 hours were significantly increased by treatment of the cells with nerve growth factor (NGF) (100 ng 7S/ml) suggesting that metabolism of glucose via the pentose pathway at this time was enhanced by NGF. This stimulation of metabolism via the pentose pathway is probably a late response to NGF because initial rates of 6-phosphogluconate accumulation in 6AN-treated cells were the same in the presence and absence of NGF. Moreover, amounts of 14CO2 generated from 1-[14CO2]glucose during the initial six hour incubation period were the same in control and NGF-treated cells. Specific activities of hexose phosphates labeled from 1-[14CO2]glucose were also the same in control and NGF-treated cells. The observation that 6AN inhibited metabolism via the pentose phosphate pathway but failed to inhibit NGF-stimulated neurite outgrowth suggests that NADPH required for lipid biosynthesis accompanying NGF-stimulated neurite outgrowth from PC12 cells can be derived from sources other than, or in addition to, the oxidative enzymes of the pentose phosphate pathway.

6-Aminonicotinamide↗
PubMed1986

Calcium-dependent activation of glycogen phosphorylase in rat pheochromocytoma PC12 cells by nerve growth factor.

Glycogen phosphorylase in PC12 cells exists in two forms analogous to those found in brain and muscle. The active phosphorylated form of the enzyme, phosphorylase-a, represents about 20-30% of total glycogen phosphorylase in these cells. Incubation of PC12 cells with 100 ng 7S nerve growth factor/ml increased phosphorylase-a within minutes. In contrast to nerve growth factor, insulin (6 ng/ml) and epidermal growth factor (6 ng/ml) decreased phosphorylase-a. Activation of phosphorylase-a by nerve growth factor was not accompanied by increases in cyclic AMP; however, removal of extracellular Ca2+ or incubation of cells with calcium channel blockers inhibited activation of glycogen phosphorylase by nerve growth factor.

Adrenal Gland Neoplasms↗
PubMed1985

Role of cell membrane composition in receptor-mediated internalization of vesicular stomatitis virus in human HEp-2 cells.

The role of essential fatty acids in membrane functions related to receptor-mediated endocytosis of vesicular stomatitis virus (VSV) was investigated using a human laryngeal carcinoma cell line (HEp-2) grown in chemically defined serum-free medium (DM) to deplete their essential fatty acid contents. VSV replicated much less effectively in HEp-2 cells grown in DM as compared to serum containing complete medium (CM). Observed reduction in the rate of virus multiplication was, at least in part, due to reduced virus penetration which was monitored using VSV labeled with nitroxyl free radicals as electron spin probe. Surface proteins of VSV were labeled with maleimide spin-label, and succinimide spin-label. Ni2+ was used as a broadening agent to identify the spin-label signals from viruses inside the cell. HEp-2 cells and mouse leukemia cell line L1210 treated with 5-dimethylaminonaphthalene-1-sulfonyl (dansyl) cadaverine, an agent previously shown to inhibit the uptake of VSV in vitro, was used as a positive control in some experiments. VSV penetrated less effectively in both DM-grown cells and in CM-grown cells in the presence of dansylcadaverine. Similar results were obtained by monitoring the uptake of 125I-labeled VSV. When HEp-2 cells grown for several generations in DM were incubated with 10% fetal calf serum for 16 h, the cells supported virus replication to a similar extent as the cells grown in CM. In contrast, addition of arachidonic acid restored VSV growth only partially. Continued growth of HEp-2 cells in DM resulted in a shift in fatty acyl chain composition of phospholipids. The results indicate a finite role for essential fatty acids in receptor-mediated internalization of virus particles.

Animals↗
PubMed1977

Comparative study of the dorsal motor nucleus of the vagus nerve.

Quantitative studies were made of cells in the dorsal motor nucleus of the vagus nerve in the horse, dog, cat, pig, sheep, goat, and calf. This nucleus was larger in ruminants than in nonruminants. Some cells in all parts of the nucleus supplied visceral structures in the head, cervical, thoracic, and abdominal regions; however, a definite topographic localization did exist within the nucleus. Eighty percent of the cells which supplied the abdominal viscera were in the rostral and rostral-middle regions. The cells which supplied the thoracic viscera were distributed almost equally within the rostral three-quarters of the nucleus. Seventy-three percent of the cells which supplied viscera in the head and neck regions were in the caudal-half of the nucleus. The rostral region of the nucleus was much larger in ruminants than in nonruminants. It is proposed that cells in the rostral region of the nucleus supply the highly developed rumen and reticulum.

Animals↗