Biomedical subjects

C G Davis

Publications and source records attributed to C G Davis.

At least 19 recordsLinked to original sources

PubMed1997

Childhood adversity and adult psychiatric disorder in the US National Comorbidity Survey.

BACKGROUND: Survey data are presented on the associations between retrospectively reported childhood adversities and subsequent onset and persistence of DSM-III-R disorders. METHODS: Data come from the US National Comorbidity Survey, a large survey of the US household population. RESULTS: Twenty-six adversities were considered, including loss events (e.g. parental divorce), parental psychopathologies (e.g. maternal depression), interpersonal traumas (e.g. rape) and other adversities (e.g. natural disaster). These adversities were consistently associated with onset, but not persistence, of DSM-III-R mood disorders, anxiety disorders, addictive disorders and acting out disorders. Most bivariate associations with onset attenuated in models that controlled for clustering of adversities and for lifetime co-morbidities among psychiatric disorders. Multivariate effects of adversities in logistic models were additive, which means that they have multiplicative effects on probability of disorder onset. Adversities showed little specificity. An analysis of time decay showed that the effects of childhood adversities on disorder onset persist beyond childhood. CONCLUSIONS: The existence of strong clustering among childhood adversities and lifetime co-morbidity among adult disorders means that caution is needed in interpreting the results of previous single-adversity single-disorder studies as documenting unique effects of specific childhood adversities on specific adult disorders. Future studies need to assess a broader range of adversities and disorders and to explore the existence and effects of commonly occurring adversity clusters. Replication is needed to verify that the effects of childhood adversities are mostly on first onset rather than on the creation of vulnerabilities that lead to increased risk of persistence.

Adolescent↗

PubMed1997

Functional transplant of megabase human immunoglobulin loci recapitulates human antibody response in mice.

We constructed two megabase-sized YACs containing large contiguous fragments of the human heavy and kappa (kappa) light chain immunoglobulin (Ig) loci in nearly germline configuration, including approximately 66 VH and 32 V kappa genes. We introduced these YACs into Ig-inactivated mice and observed human antibody production which closely resembled that seen in humans in all respects, including gene rearrangement, assembly, and repertoire. Diverse Ig gene usage together with somatic hypermutation enables the mice to generate high affinity fully human antibodies to multiple antigens, including human proteins. Our results underscore the importance of the large Ig fragments with multiple V genes for restoration of a normal humoral immune response. These mice are likely to be a valuable tool for the generation of therapeutic antibodies.

Amino Acid Sequence↗

PubMed1997

The familial aggregation of common psychiatric and substance use disorders in the National Comorbidity Survey: a family history study.

BACKGROUND: Most family studies of psychiatric disorders examine one syndrome at a time, and identify probands in clinical rather than epidemiological settings. METHOD: In the National Comorbidity Survey, 5877 respondents were asked about the history of five psychiatric disorders in their parents: major depression (MD), generalised anxiety disorder (GAD), antisocial personality disorder (ASP), alcohol abuse/dependence (AAD) and drug abuse/dependence (DAD). RESULTS: Significant familial aggregation was seen for all disorders. Controlling for other disorders produced only modest reductions in the odds ratios for MD, GAD and AAD and larger reductions for ASP and DAD. The familial transmission of these disorders can be explained by underlying vulnerabilities to internalising and to externalising disorders transmitted across generations with moderate fidelity. CONCLUSIONS: Familial aggregation of common psychiatric and substance use disorders is substantial in epidemiologic samples. The examined environmental adversities account for little of the observed parent-offspring transmission of these conditions.

Adolescent↗

PubMed1996

Interleukin-12 and B7.1 co-stimulation cooperate in the induction of effective antitumor immunity and therapy of established tumors.

Interleukin-12 (IL-12) promotes specific and long-lasting anti-tumor immunity mediated by T cells in a variety of murine tumor models. IL-12 also synergizes with B7.1 (CD80) co-stimulation to induce proliferation and cytokine production by both human and murine T cells in vitro. We evaluated the combined anti-tumor efficacy of IL-12 and B7.1 gene delivery in two apparently poorly immunogenic tumor models (TS/A and MCA207). In both of these models, expression of B7.1 and production of IL-12 in the inoculum led to improved anti-tumor immunity, with up to 80% long-term tumor-free animals (vs 0-20% of mice remaining tumor free when inoculated with either B7.1- or IL-12-transfected tumors alone). Tumor-free mice were capable of rejecting a subsequent rechallenge with the wild-type tumor in 66% of the cases. Cooperativity was dependent upon the level of IL-12 secreted by engineered cells. IL-12 delivery required B7 expression of therapeutic effects to be observed in these models. Vaccines provided at a site distal to a control, non-transfected tumor slowed (TS/A) or abrogated (MCA207) the progression of wild-type tumors. The synergistic anti-tumor effects associated with combined application of B7.1- and IL-12-transfected tumors were partially negated by systemic administration of the CD28-B7.1/B7.2 antagonist CTLA4-Ig or by inoculation with neutralizing antibodies directed against murine interferon-gamma or tumor necrosis factor-alpha, two cytokines elicited in response to IL-12 stimulation. These data support the potential clinical utility of combined gene therapy using IL-12- and B7.1-engineered autologous cells (tumor or fibroblasts) as a vaccine to elicit specific anti-tumor immunity.

Abatacept↗

PubMed1994

Spinal cord ischemia and reperfusion metabolism: the effect of hypothermia.

PURPOSE: The metabolic and neurologic functional effects of regional hypothermia induced by cold (4 degrees C) heparinized saline perfusion on spinal cord ischemia were evaluated in 35 rabbits. METHODS: Spinal cord ischemia was induced for 20 minutes by infrarenal aortic occlusion in anesthetized animals. Regional spinal cord hypothermia was obtained by perfusing the lumbar arteries supplying the spinal cord through an infrarenal aortic catheter. The lumbar spinal cord was "snap frozen" in situ with liquid nitrogen and harvested immediately at the conclusion of the ischemic period or after 24 hours of normothermic reperfusion and neurologic observation. Spinal cord metabolic studies included determination of the energy charge and the intracellular concentrations of adenosine triphosphate, glucose, lactate, glutamate, and aspartate. RESULTS: Postoperative neurologic function was normal in all but one animal treated with hypothermia, while normothermic ischemia resulted in paralysis in all animals (p = 0.002). Spinal cord temperature during 20 minutes of ischemia and hypothermic perfusion decreased from 37.5 degrees +/- 0.43 degrees C to 22.8 degrees +/- 0.00 degrees C (p = 0.0001) compared to a fall in systemic temperature from 38.8 to 36.1 (p = 0.0001). Hypothermia reduced the decline in energy charge, adenosine triphosphate concentration and glucose concentration during ischemia but had no effect on markedly elevated levels of lactate acid. High-energy phosphates were restored after reperfusion in both normothermic and hypothermic animals and were not predictive of postoperative paraplegia. Intracellular glutamate and aspartate concentrations were unchanged during normothermic ischemia but decreased after reperfusion in all paralyzed animals. Intracellular glutamate and aspartate concentrations increased during hypothermic perfusion and remained elevated after reperfusion in animals with a normal or mildly abnormal neurologic examination result. CONCLUSIONS: We conclude that spinal cord hypothermia induced by cold heparinized saline perfusion is a simple technique that prevents paraplegia after 20 minutes of ischemia and preserves intracellular concentrations of important metabolites.

Adenosine Triphosphate↗

PubMed1991

The cytoplasmic tail of CD4 targets chimeric molecules to a degradative pathway.

Many different cell surface receptors undergo endocytosis via coated pits. Once having entered the cell, the receptors are sorted into diverse pathways. Which path a given receptor will follow is determined by signals inherent in the receptor's structure. The nature of these structural features is not yet known. In this study, we have taken the approach of constructing chimeric molecules to localize the domain of the T-cell surface molecule CD4 which is responsible for targeting it for degradation. Chimeric molecules bearing the cytoplasmic domain of CD4 and the extracellular domain of either the low-density lipoprotein receptor or a major histocompatibility complex (MHC) class I molecule were both internalized in response to phorbol 12-myristate 13-acetate and were subsequently degraded, indicating that the cytoplasmic tail of CD4 contains all the information required for both processes. The ability to modulate the level of MHC class I molecules on the cell surface offers an approach to investigating quantitative aspects of antigen presentation, the initial possibilities of which are explored herein.

CD4 Antigens↗

PubMed1990

The value of psychosocial Level II fieldwork.

The shortage of occupational therapists choosing to practice in mental health and the increase of therapists electing to specialize in other areas led to a pilot study designed to gather information regarding the value of psychosocial Level II fieldwork. A survey was mailed to 152 practicing occupational therapists who had graduated from Colorado State University in Fort Collins between 1983 and 1988; of the surveys returned, 116 were used in this study. The results indicate that the psychosocial Level II fieldwork experience provides therapists with valuable training and experience regardless of their current area of practice or specialization. The results also suggest that to preserve the holistic approach that occupational therapists offer their clients, psychosocial Level II fieldwork must remain a requirement of occupational therapy programs.

Holistic Health↗

PubMed1990

The many faces of epidermal growth factor repeats.

Epidermal growth factor (EGF) is a short peptide with a distinctive motif of six cysteines. This motif is found in many different proteins of diverse functions. One approach to determining the functional utility of EGF repeats is to undertake a methodical analysis of each individual protein. While this approach has met with some success, it has been applied to only a small fraction of all the EGF repeat-bearing proteins. A second approach is to consider all these proteins as a whole but give particular attention to structural and functional similarities. This review attempts a broad, although not comprehensive, survey of the families of proteins containing EGF repeats, with particular emphasis on the relative distribution of calcium-binding and noncalcium-binding EGF repeats.

Amino Acid Sequence↗

PubMed1987

Self-association of the low density lipoprotein receptor mediated by the cytoplasmic domain.

When the low density lipoprotein (LDL) receptor was solubilized from bovine adrenal cortex membranes and subjected to electrophoresis in the absence of reducing agents, a disulfide-bonded dimeric species was demonstrated. Formation of these covalent bonds was blocked when the tissue was homogenized in the presence of sulfhydryl alkylating agents, indicating that the native receptor was self-associated noncovalently and that the disulfide bond formation occurred only after homogenization. The disulfide-linked dimers were disrupted and the receptor was restored to a monomeric form when inside-out adrenal vesicles were treated with trypsin, suggesting that the disulfide bond formation involved the 50-amino acid cytoplasmic domain of the receptor. When the receptor was solubilized from bovine adrenal cortex membranes and then purified by ion exchange and affinity chromatography, it could be covalently coupled into dimers and trimers in the presence of bivalent cross-linking agents. Receptor dimers could also be demonstrated by chemical cross-linking of intact cells that were transfected with an expressible cDNA encoding the normal human LDL receptor. Dimer formation was markedly reduced in transfected cells expressing mutated cDNAs that had premature termination codons at positions 792, 807, and 812, which produced shortened receptors that retained 2, 17, and 22 of the original 50 amino acids of the cytoplasmic domain, respectively. The first two mutant receptors, which did not form oligomers, did not enter coated pits and were not rapidly internalized by cells. However, the mutant receptor that terminates at position 812 was internalized normally even though oligomer formation was greatly reduced. Moreover, a mutant receptor with a cysteine substituted for a tyrosine at position 807, which internalized very slowly, showed a normal susceptibility to chemical cross-linking. Deletion of external domains of the LDL receptor, including the epidermal growth factor homology region and the O-linked sugar domain, did not alter susceptibility to chemical cross-linking. We conclude that the cytoplasmic domain of the LDL receptor is responsible both for self-association into oligomers and for clustering in coated pits, but the available data do not establish a causal connection between these two events.

Adrenal Cortex↗

PubMed1987

The low density lipoprotein receptor. Identification of amino acids in cytoplasmic domain required for rapid endocytosis.

The 50-residue cytoplasmic domain of the low density lipoprotein receptor (amino acids 790-839) directs the receptor to coated pits, thereby facilitating rapid endocytosis of bound low density lipoprotein. To determine the structural features required for this targeting, we produced 24 mutations in the cytoplasmic domain through use of oligonucleotide-directed mutagenesis. The first 22 amino acids of the cytoplasmic domain (residues 790-811) are sufficient for rapid internalization. The amino acid at position 807 is especially critical. Aromatic residues (tyrosine, phenylalanine, or tryptophan) at this position allow rapid internalization. Charged or uncharged aliphatic residues do not substitute. Although the requirements at the neighboring positions (806 and 808) are less stringent, the insertion of proline at position 806 is detrimental. These specificities suggest that the juxtamembranous region of the cytoplasmic domain participates in protein:protein interactions that allow the low density lipoprotein receptor to cluster in coated pits.

Amino Acid Sequence↗

PubMed1987

The Lebanese allele at the low density lipoprotein receptor locus. Nonsense mutation produces truncated receptor that is retained in endoplasmic reticulum.

We here describe a mutant low density lipoprotein receptor gene that produces a shortened receptor protein lacking three domains: the region of clustered O-linked carbohydrates, the membrane-spanning region, and the cytoplasmic tail. The defect is attributable to a single nucleotide substitution that creates a premature termination codon at amino acid 660, eliminating 180 residues from the mature protein. The truncated protein retains only two domains: a complete ligand-binding region (residues 1-292) and a partial epidermal growth factor precursor homology region (residues 293-659). The termination codon occurs in the middle of a cysteine-rich sequence that is part of the epidermal growth factor precursor homology domain. The mutant protein is present in markedly reduced amounts and may be translated at a reduced rate. After synthesis, most of the receptor remains within the cell for several hours with its N-linked carbohydrate in an unprocessed endoglycosidase H-sensitive form. This finding suggests that the shortened receptor leaves the endoplasmic reticulum at an abnormally slow rate, which is likely attributable to abnormal folding of the truncated protein. The mutation creates a new restriction site for the enzyme HinfI, thus permitting diagnosis by Southern blotting of genomic DNA. Two copies of this mutant gene were present in each of four unrelated Arab patients with homozygous familial hypercholesterolemia (three from Lebanon and one from Syria). We believe that this mutation, hereafter referred to as the "Lebanese allele," is responsible for the extraordinarily high incidence of familial hypercholesterolemia in Lebanon.

Base Sequence↗

PubMed1987

The LDL receptor: oligonucleotide-directed mutagenesis of the cytoplasmic domain.

Mutations at many different sites in the gene for the low density lipoprotein (LDL) receptor can cause the disease familial hypercholesterolaemia. A particularly interesting class of mutations includes those producing 'internalization-defective' receptors-receptors which are expressed on the cell surface and which bind LDL normally, but which fail to cluster in coated pits. This defect was first observed in fibroblasts from patient J.D. Cloning and sequencing of the terminal exons of J.D.'s internalization-defective LDL receptor gene revealed a single point mutation which caused the substitution of cysteine for tyrosine at residue 807. On the basis of this observation, we have used techniques of oligonucleotide-directed mutagenesis to make an extensive series of mutations in the full-length LDL receptor cDNA. Stable cell-lines expressing these mutant receptors have been analysed for receptor function. Of 13 different amino acids expressed at residue 807, only the aromatics tyrosine, phenylalanine and tryptophan allowed rapid internalization. Position 807 seems to be a particularly sensitive site, since neither substitution of a cysteine for residue 806 or 808 nor deletion of two triplets downstream had any effect on receptor internalization. In addition, a series of truncations localize the signals for internalization to the membrane-proximal 22 amino acid residues.

Amino Acid Sequence↗

PubMed1986

The J.D. mutation in familial hypercholesterolemia: amino acid substitution in cytoplasmic domain impedes internalization of LDL receptors.

Genomic DNA encompassing the terminal exons of the gene for the low density lipoprotein (LDL) receptor was isolated from J.D., a patient with familial hypercholesterolemia whose receptor fails to cluster in coated pits. The DNA sequence revealed a substitution of a cysteine codon for a tyrosine codon at residue 807 in the cytoplasmic domain of the receptor. We reproduced this substitution through oligonucleotide-directed mutagenesis of the normal human receptor cDNA. Upon transfection into receptor-deficient hamster cells, the cDNA specified a receptor that bound LDL normally, but entered the cell slowly. Electron microscopy showed that this receptor was distributed diffusely over the cell surface, whereas the receptor produced by the normal cDNA was concentrated in coated pits. These results support the hypothesis that cytoplasmic domains direct receptors to coated pits, thereby determining the high rate of receptor internalization in animal cells.

Alleles↗

PubMed1986

Deletion of clustered O-linked carbohydrates does not impair function of low density lipoprotein receptor in transfected fibroblasts.

A single exon in the gene for the receptor for plasma low density lipoprotein (LDL) encodes a region of clustered serine and threonine residues that is immediately external to the membrane-spanning sequence. This region has been proposed as the site of clustered O-linked carbohydrate chains. In the current studies we have deleted the 144 base pairs (48 amino acids) that encode this serine- and threonine-rich region from the cDNA for the human LDL receptor. Upon transfection into receptor-deficient hamster fibroblasts, this mutated cDNA encoded a shortened receptor that no longer showed an anomalously high molecular weight on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Labeling with [3H]glucosamine confirmed the lack of clustered O-linked sugars and further revealed that the shortened receptor and the normal receptor both contained isolated O-linked carbohydrate chains attached to the NH2-terminal portion of the protein. The ratio of clustered to isolated O-linked sugar chains in the normal receptor was estimated to be approximately 4-6 to 1. Despite the loss of clustered O-linked carbohydrate, the LDL receptor encoded by the deletion-bearing cDNA bound and internalized LDL normally. It also recycled normally and exhibited a normal half-life. We conclude that: 1) the serine- and threonine-rich region of the LDL receptor is the site for addition of clustered O-linked carbohydrates; 2) the receptor contains a small number of isolated chains of O-linked carbohydrates in addition to the clustered chains; and 3) the clustered O-linked carbohydrates are not essential for LDL receptor function in cultured hamster fibroblasts.

Amino Acid Sequence↗

PubMed1986

The LDL receptor in familial hypercholesterolemia: use of human mutations to dissect a membrane protein.

Since the discovery of the LDL receptor 13 years ago, a multidisciplinary approach to its study has revealed much about this important cell-surface protein. Most recently, we have developed tools in the form of full-length cDNAs and cloned genomic DNAs necessary to understand the molecular genetics of this locus. The frequent occurrence of mutations in the LDL receptor gene in patients with FH provides a fertile ground on which to explore the parts of the receptor that are necessary for its function. The analysis of four large deletions has revealed an unexpectedly universal involvement of Alu repeats in their generation. These studies indicate that repetitive DNAs can destabilize a gene through homologous recombination. Inasmuch as the LDL receptor gene is a mosaic of exons shared with at least five other proteins, it is possible that early exon-shuffling events involved recombination between these repetitive elements. Is it possible that the very plasticity that permitted evolution of the LDL receptor also accounts for its frequent disruption by mutation? Further study may help to answer this question. Mutations that disrupt the structure of the protein have been identified. The biochemical and cellular consequences of these mutations reveal crucial aspects of receptor structure. The receptor is clearly divided into quasi-independent domains with discrete functions. Mutations that disrupt the cytoplasmic domain alter the ability of the LDL receptor to cluster in coated pits, but they do not disrupt ligand binding or produce major effects on intracellular transport. Some of the mutations in the external domain disrupt binding but do not affect transport or internalization.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗

PubMed1984

The human LDL receptor: a cysteine-rich protein with multiple Alu sequences in its mRNA.

The nucleotide sequence of a cloned 5.3 kilobase cDNA for the human low density lipoprotein receptor revealed five domains in the 839 amino acid protein: 322 NH2-terminal amino acids, extremely rich in disulfide-bonded cysteine residues (15%) and including an 8-fold repeat of 40 residues that may contain the LDL binding site; 350 residues homologous to the precursor of mouse epidermal growth factor; a region immediately outside the plasma membrane, rich in serine and threonine and the site of O-linked glycosylation; 22 hydrophobic amino acids, spanning the plasma membrane; and 50 COOH-terminal amino acids, projecting into the cytoplasm. The mRNA for the receptor contains a 3' untranslated region of 2.5 kilobases that includes multiple copies of the Alu family of repetitive DNAs. Transfection of simian COS cells with the human LDL receptor cDNA linked to the SV40 early promoter resulted in expression of functional cell surface receptors.

Amino Acid Sequence↗

PubMed1984

Food frequency related to folacin status in adolescents.

Food frequency data for 372 adolescents from urban and rural low-income households were evaluated. The urban group consisted of blacks (N = 161) and Hispanics (N = 32); blacks (N = 58) and whites (N = 121) composed the rural group. A food frequency questionnaire with 24 food groups categorized according to nutrient contribution was completed for each subject by a trained interviewer. Urban blacks selected folacin-dense foods more frequently than urban Hispanics or rural blacks. This difference corresponded with a higher prevalence of poor folacin status in urban Hispanics vs. urban blacks and in rural blacks vs. urban blacks. Rural whites also consumed a higher frequency of folacin-dense food groups than rural blacks, which, again, corresponded with differences in folacin status. The infrequent consumption of vegetables and fruits, particularly by rural black and urban Hispanic adolescents, provides an explanation for the poor folacin status of the adolescents.

Adolescent↗

PubMed1983

Activation of acetylcholine receptors causes the partition of hydrophobic cations into postsynaptic membrane vesicles.

In the continued presence of cholinergic ligands, the acetylcholine receptor-channel complex (AChR) in postsynaptic membranes undergoes a sequence of conformational changes. On addition of the ligand, the receptor rapidly changes from a closed channel to an open channel conformation, then slowly changes to a nonconducting state termed desensitization. The lifetime of the open channel conformation and the rate of desensitization are both dependent on the magnitude of the membrane potential, suggesting that the ligand-induced conformational changes in AChR may involve the movement of electrical charges within the membrane. Measurements of charge redistribution in AChR-containing membranes following ligand binding have not been reported. Recently, measurements of changes in the membrane partition coefficient of hydrophobic ions have been used to detect electrostatic changes in both biological and model membranes. We report here that cholinergic ligands induce changes in the partition coefficient of the hydrophobic cation tetraphenylphosphonium (TPP) into AChR-enriched membranes. The extent and time course of these changes in TPP partition coefficient are accounted for in a kinetic model. We conclude that TPP movement is a monitor of a molecular event which may be associated with the slow component of AChR desensitization.

Animals↗