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R Axel

Publications and source records attributed to R Axel.

At least 37 records · Page 2Linked to original sources
PubMed1989

Ectopic expression of the serotonin 1c receptor and the triggering of malignant transformation.

Neurotransmitter receptors are usually restricted to neuronal cells, but the signaling pathways activated by these receptors are widely distributed in both neural and non-neural cells. The functional consequences of activating a brain-specific neurotransmitter receptor, the serotonin 5HT1c receptor, in the unnatural environment of a fibroblast were examined. Introduction of functional 5HT1c receptors into NIH 3T3 cells results, at high frequency, in the generation of transformed foci. Moreover, the generation and maintenance of transformed foci requires continued activation of the serotonin receptor. In addition, the injection of cells derived from transformed foci into nude mice results in the generation of tumors. The serotonin 5HT1c receptor therefore functions as a protooncogene when expressed in NIH 3T3 fibroblasts.

Animals↗
PubMed1989

Activation of the beta 2-adrenergic receptor promotes growth and differentiation in thyroid cells.

We have introduced the beta 2-adrenergic receptor into the unnatural environment of a thyroid cell to demonstrate that the activation of this receptor initiates diverse cellular programs in different cell types. The thyroid-stimulating hormone (TSH) receptor and the beta 2-adrenergic receptor stimulate a common signaling pathway in distinct populations of cells. In this study, we demonstrate that the activation of the beta 2-adrenergic receptor, transfected into a thyroid epithelial cell, elicits a program of growth and differentiation normally observed with TSH. In thyroid cells expressing beta 2 receptors, the beta 2 agonist isoproterenol activates adenylate cyclase, induces the expression of a thyroid-specific iodide carrier system, and can substitute for TSH to promote growth. Thus, in thyroid cells expressing beta 2-adrenergic receptors, isoproterenol elicits the entire array of thyroid-specific functions normally activated by TSH.

1-Methyl-3-isobutylxanthine↗
PubMed1989

5-HT1c receptor is a prominent serotonin receptor subtype in the central nervous system.

Neurons in rat central nervous system (CNS) that express 5-HT1c receptor mRNA have been localized by in situ hybridization histochemistry. The 5-HT1c receptor is expressed in a wide variety of cortical and subcortical neurons including hippocampal pyramidal neurons, neurons within most of the central monoaminergic cell groups, neurons in thalamic sensory relay nuclei, and neurons involved in the central processing and regulation of nociceptive transmission. Therefore, the 5-HT1c receptor is a prominent but poorly characterized central subclass of serotonin (5-HT) receptor. The distribution of the 5-HT1c receptor within the CNS is considerably more widespread than that of the structurally and functionally related 5-HT2 receptor.

Animals↗
PubMed1988

HIV infection does not require endocytosis of its receptor, CD4.

The T cell surface molecule CD4 interacts with class II MHC molecules on the surface of target cells as well as with the envelope glycoprotein of human immunodeficiency virus (HIV). Internalization of CD4 molecules is observed after exposure of CD4+ T cells to either phorbol esters or appropriate antigen-bearing target cells. To determine whether HIV entry proceeds via receptor-mediated endocytosis or direct viral fusion with the cell membrane, we have constructed two mutants in the cytoplasmic domain of the CD4 protein that severely impair the ability of CD4 molecules to undergo endocytosis. Quantitative infectivity studies reveal that HeLa cell lines expressing wild-type or mutant CD4 molecules are equally susceptible to HIV infection. In addition, HIV binding does not lead to CD4 endocytosis. These studies indicate that although the CD4 molecule can be internalized, HIV entry proceeds via direct fusion of the viral envelope with the cell membrane.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Molecular characterization of a functional cDNA encoding the serotonin 1c receptor.

Neurons that release serotonin as a neurotransmitter project to most regions of the central and peripheral nervous system and mediate diverse neural functions. The physiological effects of serotonin are initiated by the activation of multiple, distinct receptor subtypes. Cloning in RNA expression vectors was combined with a sensitive electrophysiological assay in Xenopus oocytes in order to isolate a functional cDNA clone encoding the 5HTlc serotonin receptor. Injection of RNA transcribed in vitro from this clone into Xenopus oocytes elicits serotonin sensitivity. Mouse fibroblasts transformed with this clone bind serotonin agonists and antagonists and exhibit an increase in intracellular Ca2+ concentrations in response to serotonin. The sequence of the 5HTlc receptor reveals that it belongs to the family of G protein-coupled receptors, which are thought to traverse the cytoplasmic membrane seven times. Moreover, in situ hybridization and RNA blot analysis indicate that the 5HTlc receptor is expressed in neurons in many regions of the central nervous system and suggest that this subclass of receptor may mediate many of the central actions of serotonin.

Amino Acid Sequence↗
PubMed1988

A soluble form of CD4 (T4) protein inhibits AIDS virus infection.

CD4 (T4) is a glycoprotein of relative molecular mass 55,000 (Mr 55K) on the surface of T lymphocytes which is thought to interact with class II MHC (major histocompatibility complex) molecules, mediating efficient association of helper T cells with antigen-bearing targets. The CD4 protein is also the receptor for HIV, a T-lymphotropic RNA virus responsible for the human acquired immune deficiency syndrome (AIDS) (refs 4-7). To define the mechanisms of interaction of CD4 with the surface of antigen-presenting cells and with HIV, we have isolated the CD4 gene and expressed this gene in several different cellular environments. Here we describe an efficient expression system in which a recombinant, soluble form of CD4 (sCD4) is secreted into tissue culture supernatants. This sCD4 retains the structural and biological properties of CD4 on the cell surface, binds to the envelope glycoprotein (gp110) of HIV and inhibits the binding of virus to CD4+ lymphocytes, resulting in a striking inhibition of virus infectivity.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1987

Alternative splicing in individual Aplysia neurons generates neuropeptide diversity.

The neuron R15 is a peptidergic cell within the abdominal ganglion of Aplysia that participates in two neural circuits governing physiological and behavioral programs. We have cloned and characterized the major gene product expressed in this neuron. The R15 cDNA encodes a polyprotein precursor that is cleaved to yield a set of small neuropeptides. One peptide, R15 alpha 1, may act on different target cells to generate distinct but complementary physiological alterations that contribute to a program of cardiovascular changes in Aplysia. We have found that the RNA encoding the R15 polyprotein is spliced differently in different neurons. Our results suggest that alternative splicing of RNAs encoding polyproteins may provide a mechanism to generate distinct but overlapping sets of peptides that govern distinct but related physiological or behavioral programs.

Animals↗
PubMed1987

Structure and expression of the human and mouse T4 genes.

The T4 molecule may serve as a T-cell receptor recognizing molecules on the surface of specific target cells and also serves as the receptor for the human immunodeficiency virus. To define the mechanisms of interaction of T4 with the surface of antigen-presenting cells as well as with human immunodeficiency virus, we have further analyzed the sequence, structure, and expression of the human and mouse T4 genes. T4 consists of an extracellular segment comprised of a leader sequence followed by four tandem variable-joining (VJ)-like domains, a transmembrane domain, and a cytoplasmic segment. The structural domains of the T4 protein deduced from amino acid sequence are precisely reflected in the intron-exon organization of the gene. Analysis of the expression of the T4 gene indicates that T4 RNA is expressed not only in T lymphocytes, but in B cells, macrophages, and granulocytes. T4 is also expressed in a developmentally regulated manner in specific regions of the brain. It is, therefore, possible that T4 plays a more general role in mediating cell recognition events that are not restricted to the cellular immune response.

Amino Acid Sequence↗
PubMed1987

Characterization of two members of the rho gene family from the yeast Saccharomyces cerevisiae.

The rho genes comprise an evolutionarily conserved family with significant homology to the ras oncogene family. Two members of the rho family were isolated from the yeast Saccharomyces cerevisiae and characterized by DNA sequence analysis. The yeast genes RHO1 and RHO2 are 70% and 57% identical, respectively, to the rho gene of the marine snail Aplysia, and they are 53% identical to each other. Inactivation of these genes showed that RHO1 is required for cell viability, while RHO2 is not an essential gene. A mutant allele of RHO1 (RHO1-His68) was constructed with a mutation analogous to one that activates the transforming potential of the human HRAS gene. Diploid strains containing RHO1-His68 in either low or high copy number are unable to sporulate, and the mutant allele is dominant over wild-type RHO1. The requirement for RHO1 cannot be circumvented by introduction of high copy number plasmids containing either the gene encoding the catalytic subunit of cAMP-dependent protein kinase or the mutant allele RAS2-Val19. Despite the conservation between the rho and ras gene families, the finding that RHO1 functions independently of the adenylate cyclase cAMP-dependent protein kinase cascade suggests that rho and ras are involved in distinct biochemical pathways.

Alleles↗
PubMed1987

Glucocorticoids enhance stability of human growth hormone mRNA.

We have studied the control of expression of the human growth hormone (hGH) gene introduced into the chromosomes of mouse fibroblasts. Cell lines transformed with the hGH gene expressed low levels of intact hGH mRNA and secreted hGH protein into the medium. Although the level of expression of hGH mRNA was low, the gene remained responsive to induction by glucocorticoid hormones. To localize the sequences responsible for induction and to determine the mechanism by which these cis-acting sequences enhance gene expression, we have constructed a series of fusion genes between the hGH gene and the herpes simplex virus (HSV) thymidine kinase (tk) gene. We have demonstrated that a fusion gene in which hGH cDNA is flanked at its 5' terminus by an HSV tk promoter and is flanked at its 3' terminus by 3' HSV tk DNA remains inducible by glucocorticoids. Our studies indicate that the hGH exons contain sequences which are responsible for glucocorticoid hormone induction. Pulse-chase experiments, in vitro nuclear transcription, and approach to steady-state measurements indicate that the mechanisms responsible for induction of the hGH cDNA fusion gene operate posttranscriptionally to enhance the stability of hGH mRNA. Moreover, this increased stability was associated with an increase in the length of the 3' poly(A) tail on hGH mRNA.

Animals↗
PubMed1986

A bipotential neuroendocrine precursor whose choice of cell fate is determined by NGF and glucocorticoids.

Adrenal medullary endocrine (chromaffin) cells and sympathetic neurons both derive from the neural crest. We have found that the embryonic adrenal medulla and sympathetic ganglia are both initially populated by precursors expressing neural-specific genes. By birth, however, the medulla consists largely of chromaffin cells. In primary culture, the medullary precursors have three developmental fates: in NGF they continue to mature into neurons and survive, whereas in glucocorticoid they either extinguish their neuronal properties and exhibit an endocrine phenotype, or else continue to develop into neurons but then die. These data suggest that, in vivo, the adrenal medulla develops through both the glucocorticoid-induced differentiation of bipotential progenitors and the degeneration of committed neuronal precursors, which have migrated into the gland.

Adrenal Medulla↗
PubMed1986

The T4 gene encodes the AIDS virus receptor and is expressed in the immune system and the brain.

The isolation of clones encoding the human surface protein T4, and the expression of the T4 gene in new cellular environments, have enabled us to examine the role of this protein in the pathogenesis of AIDS. Our studies support a mechanism of AIDS virus infection that initially involves the specific interaction of the AIDS virus with T4 molecules on the cell surface. This association can be demonstrated on T4+ transformed T and B lymphocytes as well as epithelial cells. Furthermore, the presence of T4 on the surface of all human cells examined is sufficient to render these cells susceptible to AIDS virus infection. Our data suggest that the T4-AIDS virus complex is then internalized by receptor-mediated endocytosis. Finally, we find that the T4 gene is expressed in the brain as well as in lymphoid cells, providing an explanation for the dual neurotropic and lymphotropic character of the AIDS virus. In this manner, a T lymphocyte surface protein important in mediating effector cell-target cell interactions has been exploited by a human retrovirus to specifically target the AIDS virus to populations of T4+ cells.

Ammonium Chloride↗
PubMed1986

Nucleosomes are phased along the mouse beta-major globin gene in erythroid and nonerythroid cells.

We have used the chemical cleavage reagent methidiumpropyl-EDTA-Fe(II) to determine the location of the nucleosomes along the mouse beta-major globin gene in erythroid and nonerythroid cells. In mouse L cells, in which the globin gene is inactive, the nucleosomes are precisely positioned with respect to the underlying DNA sequence from positions -3000 to +1500 relative to the cap site. In uninduced and induced murine erythroleukemia cells, the same phasing persists but is interrupted from positions -200 to +500. This gap in the phased distribution of nucleosomes appears to be protected from MPE-Fe(II) digestion, and is bounded on both sides by hypersensitive sites. These results define at least two structural states for the globin gene: an inactive state in which the gene is covered with a continuous array of phased nucleosomes and an active state in which this array is disrupted over the 5' half of the structural gene.

Animals↗
PubMed1986

Molecular cloning and nucleotide sequence of the streptavidin gene.

Using synthetic oligonucleotides as probes we have cloned the streptavidin gene from a genomic library of Streptomyces avidinii. Nucleotide sequence analysis indicated that a 2 Kb DNA-fragment contained the entire coding region, a signal peptide region and the 3' and 5' flanking regions of the gene. The deduced amino acid sequence shows several interrupted blocks of homology with the amino acid sequence of chicken egg-white avidin. Analysis of the secondary structure suggests a high content of beta-structure in both proteins and considerable overall structural similarity between them.

Amino Acid Sequence↗
PubMed1986

The gene encoding the T-cell surface protein T4 is located on human chromosome 12.

The surface glycoproteins T4 and T8 define functionally distinct populations of T lymphocytes. We have obtained cDNA and genomic clones encoding the T4 molecule and used these as probes to determine the chromosomal location of this gene. Genomic blotting experiments, along with in situ hybridization analyses, indicate that the T4 gene resides on the short arm of human chromosome 12, at region p12-pter. Thus, the T4 gene is not linked to any known member of the immunoglobulin gene family, including its counterpart gene, T8, which resides on human chromosome 2 immediately distal to the immunoglobulin kappa locus.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1986

The T4 glycoprotein is a cell-surface receptor for the AIDS virus.

Taken together, our studies suggest a mechanism of AIDS virus infection that initially involves the specific association of the AIDS virus with T4 molecules on the cell surface. This association does not require additional T-cell-specific molecules and can be demonstrated on both B lymphocytes and epithelial cell lines. The T4-AIDS virus complex is likely to be internalized in endosomes via receptor-mediated endocytosis. The virus can then fuse with the vacuolar membrane, releasing the viral nucleocapsid into the cytoplasm to undergo uncoating. Viral replication does not appear to require the environment of a T lymphocyte because active infection is also observed in human T4+ B lymphocytes and epithelial cell lines. Moreover, the T4 gene is expressed in the brain as well as in lymphocytes, providing an explanation for the dual neurotropic and lymphotropic character of the virus. In this manner, a T-lymphocyte surface protein thought to be important in mediating effector cell-target cell interactions has been exploited by a human lymphotropic virus to target the AIDS virus specifically to populations of T4+ cells.

Acquired Immunodeficiency Syndrome↗