Showing papers by "Howard Hughes Medical Institute published in 1994"
TL;DR: The ob gene product may function as part of a signalling pathway from adipose tissue that acts to regulate the size of the body fat depot.
Abstract: The mechanisms that balance food intake and energy expenditure determine who will be obese and who will be lean. One of the molecules that regulates energy balance in the mouse is the obese (ob) gene. Mutation of ob results in profound obesity and type II diabetes as part of a syndrome that resembles morbid obesity in humans. The ob gene product may function as part of a signalling pathway from adipose tissue that acts to regulate the size of the body fat depot.
12,394 citations
TL;DR: P27 Kip1 as mentioned in this paper is a cyclin-dependent kinase inhibitor implicated in G1 phase arrest by TGFβ and cell-cell contact, and it has been shown to be highly conserved and broadly expressed in human tissues, and its mRNA levels are similar in proliferating and quiescent cells.
2,194 citations
TL;DR: Insight gained from studies of the signaling pathways downstream of TCR and BCR stimulation is likely to contribute significantly to future understanding of mechanisms responsible for lymphocyte differentiation and for the discrimination of self from nonself in developing and mature cells.
2,122 citations
TL;DR: Results suggest that the MAb may obstruct the interaction of CTLA-4 with its natural ligand and block a negative signal, or directly signal T cells to down-regulate immune function.
2,086 citations
TL;DR: A mammalian FKBP–rapamycin-associated protein (FRAP) is isolate whose binding to structural variants of rapamycin complexed to FK BP12 correlates with the ability of these ligands to inhibit cell-cycle progression.
Abstract: THE structurally related natural products rapamycin and FK506 bind to the same intracellular receptor, FKBP12, yet the resulting complexes interfere with distinct signalling pathways1,2. FKBP12–rapamycin inhibits progression through the Gl phase of the cell cycle in osteosarcoma3, liver4, 5 and T cells6, 7 as well as in yeast8 and interferes with mitogenic signalling pathways that are involved in Gl progression9, 10 namely with activation of the protein p70S6k (refs 5,11–13) and cyclin-dependent kinases3, 14–16. Here we isolate a mammalian FKBP–rapamycin-associated protein (FRAP) whose binding to structural variants of rapamycin complexed to FKBP12 correlates with the ability of these ligands to inhibit cell-cycle progression. Peptide sequences from purified bovine FRAP were used to isolate a human cDNA clone that is highly related to the DRR1/TOR1 and DRR2/TOR2 gene products from Saccharomyces cerevisiae8, 17, 18. Although it has not been previously demonstrated that either of the DRR/TOR gene products can bind the FKBP–rapamycin complex directly17, 19 these yeast genes have been genetically linked to a rapamycin-sensitive pathway and are thought to encode lipid kinases17–20.
1,960 citations
TL;DR: A new member of the p16INK4 family is isolated, p15INK4B, which is induced ∼30-fold in human keratinocytes by treatment with TGF-β, suggesting that pi5 may act as an effector of T GF-β-mediated cell cycle arrest.
Abstract: TRANSFORMING growth factor-beta (TGF-β) inhibits cell proliferation by inducing a Gl-phase cell cycle arrest1. Normal progression through Gl is promoted by the activity of the cyclin-dependent protein kinases CDK4 and CDK6 (ref. 2), which are inhibited by the protein p16INK4. We have isolated a new member of the p16INK4 family, p15INK4B. p15 expression is induced ∼30-fold in human keratinocytes by treatment with TGF-β, suggesting that pi5 may act as an effector of TGF-β-mediated cell cycle arrest. The gene encoding p15 is located on chromosome 9 adjacent to the p16 gene at a frequent site of chromosomal abnormality in human tumours (9p21).
1,830 citations
TL;DR: It is shown that p21 directly inhibits PCNA-dependent DNA replication in the absence of a cyclin/CDK, and blocks the ability of PCNA to activateDNA polymerase δ, the principal replicative DNA polymerase.
Abstract: The p53 tumour-suppressor protein controls the expression of a gene encoding the p21 cyclin-dependent protein kinase (CDK) regulator. Levels of p21 protein are increased in senescent cells and p21 overexpression blocks the growth of tumour cells. In normal human cells, but not in many tumour cells, p21 exists in a quaternary complex with a cyclin, a CDK, and the proliferating-cell nuclear antigen (PCNA). p21 controls CDK activity, thereby affecting cell-cycle control, whereas PCNA functions in both DNA replication and repair. Here we use simian virus 40 DNA replication in vitro to show than p21 directly inhibits PCNA-dependent DNA replication in the absence of a cyclin/CDK. Furthermore, p21 blocks the ability of PCNA to activate DNA polymerase delta, the principal replicative DNA polymerase. This regulation results from a direct interaction between p21 and PCNA. Thus, during p53-mediated suppression of cell proliferation, p21 and PCNA may be important for coordinating cell-cycle progression, DNA replication and repair of damaged DNA.
1,703 citations
TL;DR: It is established that the Ftz-F1 gene is essential for sexual differentiation and formation of the primary steroidogenic tissues.
1,578 citations
TL;DR: Low pH induces a conformational change in the influenza virus haemagglutinin, which then mediates fusion of the viral and host cell membranes, and reveals a major refolding of the secondary and tertiary structure of the molecule.
Abstract: Low pH induces a conformational change in the influenza virus haemagglutinin, which then mediates fusion of the viral and host cell membranes. The three-dimensional structure of a fragment of the haemagglutinin in this conformation reveals a major refolding of the secondary and tertiary structure of the molecule. The apolar fusion peptide moves at least 100 A to one tip of the molecule. At the other end a helical segment unfolds, a subdomain relocates reversing the chain direction, and part of the structure becomes disordered.
1,577 citations
TL;DR: The developmental programs of lymphoid and myeloid lineages require a common genetic function likely acting at the level of a multipotential progenitor, and mice carrying a mutation in the PU.1 locus were generated by gene targeting.
Abstract: The transcription factor PU.1 is a hematopoietic-specific member of the ets family. Mice carrying a mutation in the PU.1 locus were generated by gene targeting. Homozygous mutant embryos died at a late gestational stage. Mutant embryos produced normal numbers of megakaryocytes and erythroid progenitors, but some showed an impairment of erythroblast maturation. An invariant consequence of the mutation was a multilineage defect in the generation of progenitors for B and T lymphocytes, monocytes, and granulocytes. Thus, the developmental programs of lymphoid and myeloid lineages require a common genetic function likely acting at the level of a multipotential progenitor.
1,546 citations
TL;DR: An influenza virus peptide binds to HLA-DR1 in an extended conformation with a pronounced twist, providing a universal mode of peptide binding, distinct from the strategy used by class I histocompatibility proteins.
Abstract: An influenza virus peptide binds to HLA-DR1 in an extended conformation with a pronounced twist. Thirty-five per cent of the peptide surface is accessible to solvent and potentially available for interaction with the antigen receptor on T cells. Pockets in the peptide-binding site accommodate five of the thirteen side chains of the bound peptide, and explain the peptide specificity of HLA-DR1. Twelve hydrogen bonds between conserved HLA-DR1 residues and the main chain of the peptide provide a universal mode of peptide binding, distinct from the strategy used by class I histocompatibility proteins.
TL;DR: Skin appears to possess a p53-dependent 'guardian-of-the-tissue' response to DNA damage which aborts precancerous cells, and if this response is reduced in a single cell by a prior p53 mutation, sunburn can select for clonal expansion of the p 53-mutated cell into the AK.
Abstract: Squamous cell carcinoma of the skin (SCC) can progress by stages: sun-damaged epidermis, with individual disordered keratinocytes; actinic keratosis (AK), spontaneously regressing keratinized patches having aberrant cell differentiation and proliferation; carcinoma in situ; SCC and metastasis. To understand how sunlight acts as a carcinogen, we determined the stage at which sunlight mutates the p53 tumour-suppressor gene and identified a function for p53 in skin. The p53 mutations induced by ultraviolet radiation and found in > 90% of human SCCs were present in AKs. Inactivating p53 in mouse skin reduced the appearance of sunburn cells, apoptotic keratinocytes generated by overexposure to ultraviolet. Skin thus appears to possess a p53-dependent 'guardian-of-the-tissue' response to DNA damage which aborts precancerous cells. If this response is reduced in a single cell by a prior p53 mutation, sunburn can select for clonal expansion of the p53-mutated cell into the AK. Sunlight can act twice: as tumour initiator and tumour promoter.
TL;DR: It is proposed that synaptotagmin I is the major low affinity Ca2+ sensor mediating Ca2-regulation of synchronous neurotransmitter release in hippocampal neurons and not essential for asynchronous or Ca(2+)-independent release.
TL;DR: The data suggest that tissue-specific responsiveness to peroxisome proliferators, including certain fatty acids, is in part a consequence of differential expression of multiple, pharmacologically distinct PPAR isoforms.
Abstract: To gain insight into the function of peroxisome proliferator-activated receptor (PPAR) isoforms in mammals, we have cloned and characterized two PPAR alpha-related cDNAs (designated PPAR gamma and -delta, respectively) from mouse. The three PPAR isoforms display widely divergent patterns of expression during embryogenesis and in the adult. Surprisingly, PPAR gamma and -delta are not activated by pirinixic acid (Wy 14,643), a potent peroxisome proliferator and activator of PPAR alpha. However, PPAR gamma and -delta are activated by the structurally distinct peroxisome proliferator LY-171883 and linoleic acid, respectively, indicating that each of the isoforms can act as a regulated activator of transcription. These data suggest that tissue-specific responsiveness to peroxisome proliferators, including certain fatty acids, is in part a consequence of differential expression of multiple, pharmacologically distinct PPAR isoforms.
TL;DR: The recent discovery that CD28 and B7 are each members of larger gene families suggests that the regulation of co-stimulation is more complex than previously imagined.
TL;DR: The crystal structure of ribonuclease inhibitor protein has revealed that leucine-rich repeats correspond to beta-alpha structural units, which are arranged so that they form a parallel beta-sheet with one surface exposed to solvent, so that the protein acquires an unusual, nonglobular shape.
TL;DR: In this article, the authors have purified from embryonic chick brain two proteins, Netrin-1 and netrin-2, that each possess commissural axon outgrowth-promoting activity and also identified a distinct activity that potentiates their effects.
TL;DR: The structure reveals the determinants of substrate preference for tyrosine rather than serine or threonine and a novel autoinhibition mechanism whereby one of the tyrosines that is autophosphorylated in response to insulin, Tyr 1,162, is bound in the active site.
Abstract: The X-ray crystal structure of the tyrosine kinase domain of the human insulin receptor has been determined by multiwavelength anomalous diffraction phasing and refined to 2.1 A resolution. The structure reveals the determinants of substrate preference for tyrosine rather than serine or threonine and a novel autoinhibition mechanism whereby one of the tyrosines that is autophosphorylated in response to insulin, Tyr 1,162, is bound in the active site.
TL;DR: Analysis of molecular markers for neural, epidermal, and neural crest cells indicates that CNS expansion occurs as early as neural plate formation, and inhibition of DNA synthesis shows that additional CNS tissue does not depend on cell division--rather it reflects conversion of prospective neural crest andEpidermal cells to a neural fate.
Abstract: In Drosophila, the proneural genes of the achaete-scute complex encode transcriptional activators that can commit cells to a neural fate. We have isolated cDNAs for two Xenopus achaete-scute homologs, ASH3a and ASH3b, which are expressed in a subset of central nervous system (CNS) neuroblasts during early neurogenesis. After expressing either ASH3 protein in developing Xenopus embryos, we find enlargement of the CNS at the expense of adjacent non-neural ectoderm. Analysis of molecular markers for neural, epidermal, and neural crest cells indicates that CNS expansion occurs as early as neural plate formation. ASH3-dependent CNS enlargement appears to require neural induction, as it does not occur in animal cap explants. Inhibition of DNA synthesis shows that additional CNS tissue does not depend on cell division--rather it reflects conversion of prospective neural crest and epidermal cells to a neural fate. The differentiation of the early forming primary neurons also seems to be prevented by ASH3 expression. This may be secondary to the observed activation of Xotch transcription by ASH3.
TL;DR: A gene, reaper (rpr), that appears to play a central control function for the initiation of programmed cell death (apoptosis) in Drosophila was identified and suggests that the basic cell death program is intact although it was not activated in mutant embryos.
Abstract: A gene, reaper (rpr), that appears to play a central control function for the initiation of programmed cell death (apoptosis) in Drosophila was identified. Virtually all programmed cell death that normally occurs during Drosophila embryogenesis was blocked in embryos homozygous for a small deletion that includes the reaper gene. Mutant embryos contained many extra cells and failed to hatch, but many other aspects of development appeared quite normal. Deletions that include reaper also protected embryos from apoptosis caused by x-irradiation and developmental defects. However, high doses of x-rays induced some apoptosis in mutant embryos, and the resulting corpses were phagocytosed by macrophages. These data suggest that the basic cell death program is intact although it was not activated in mutant embryos. The DNA encompassed by the deletion was cloned and the reaper gene was identified on the basis of the ability of cloned DNA to restore apoptosis to cell death defective embryos in germ line transformation experiments. The reaper gene appears to encode a small peptide that shows no homology to known proteins, and reaper messenger RNA is expressed in cells destined to undergo apoptosis.
TL;DR: This model, involving inactivation of one allelic array and cis control of the active array, provides a mechanism such that individual neurons express one or a small number of receptors.
TL;DR: The results suggest that LIM homeobox genes contribute to the generation of motor neuron diversity and may confer subclasses of motor neurons with the ability to select specific axon pathways, thereby initiating the topographic organization of motor projections.
TL;DR: It is shown that missense mutations in the alpha-tropomyosin gene cause familial hypertrophic cardiomyopathy (FHC), and it is suggested that abnormal stoichiometry of sarcomeric proteins can cause cardiac hypertrophy.
TL;DR: Using an inducible transgene that expresses a dominant negative member of the fly CREB family, LTM was specifically and completely blocked only after induction, while ARM and learning were unaffected, suggesting that LTM formation requires de novo gene expression probably mediated by CREBfamily genes.
TL;DR: A novel protein kinase, called SAPK/ERK kinase-1 (SEK1), which is structurally related to the MAP kinase kinases (MEKs) and is a potent activator of the SAPKs in vitro and in vivo is identified.
Abstract: THE stress-activated protein kinases (SAPKs), which are distantly related to the MAP kinases, are the dominant c-Jun amino-termi-nal protein kinases activated in response to a variety of cellular stresses, including treatment with tumour-necrosis factor-α and interleukin-β (refs 1, 2). SAPK phosphorylation of c-Jun probably activates the c-Jun transactivation function3. SAPKs are part of a signal transduction cascade related to, but distinct from, the MAPK pathway1. We have now identified a novel protein kinase, called SAPK/ERK kinase-1 (SEK1), which is structurally related to the MAP kinase kinases (MEKs)4. SEK1 is a potent activator of the SAPKs in vitro and in vivo. An inactive SEK1 mutant blocks SAPK activation by extracellular stimuli without interfering with the MAPK pathway. Although alternative mechanisms of SAPK activation may exist, as an immediate upstream activator of the SAPKs, SEK1 further defines a signalling cascade that couples cellular stress agonists to the c-Jun transcription factor.
TL;DR: A novel gene, WASP, which is expressed in lymphocytes, spleen, and thymus is isolated and is likely to be a key regulator of lymphocyte and platelet function.
TL;DR: In vivo evidence is provided that p53-dependent apoptosis, occurring in response to oncogenic events, is a critical regulator of tumorigenesis.
TL;DR: Characterization of these complexes by micro-sequencing and immuno- blotting reveals known receptors for modified forms of LDL, multiple GPI-linked proteins, an anion transporter, cytoskeletal elements, and cytoplasmic signaling molecules--including Src-like kinases, hetero- trimeric G-proteins, and three members of the Rap family of small GTPases.
Abstract: Caveolae are 50-100-nm membrane microdomains that represent a subcompartment of the plasma membrane. Previous morphological studies have implicated caveolae in (a) the transcytosis of macromolecules (including LDL and modified LDLs) across capillary endothelial cells, (b) the uptake of small molecules via a process termed potocytosis involving GPI-linked receptor molecules and an unknown anion transport protein, (c) interactions with the actin-based cytoskeleton, and (d) the compartmentalization of certain signaling molecules, including G-protein coupled receptors. Caveolin, a 22-kD integral membrane protein, is an important structural component of caveolae that was first identified as a major v-Src substrate in Rous sarcoma virus transformed cells. This finding initially suggested a relationship between caveolin, transmembrane signaling, and cellular transformation. We have recently developed a procedure for isolating caveolin-rich membrane domains from cultured cells. To facilitate biochemical manipulations, we have applied this procedure to lung tissue--an endothelial and caveolin-rich source-allowing large scale preparation of these complexes. These membrane domains retain approximately 85% of caveolin and approximately 55% of a GPI-linked marker protein, while they exclude > or = 98% of integral plasma membrane protein markers and > or = 99.6% of other organelle-specific membrane markers tested. Characterization of these complexes by micro-sequencing and immuno-blotting reveals known receptors for modified forms of LDL (scavenger receptors: CD 36 and RAGE), multiple GPI-linked proteins, an anion transporter (plasma membrane porin), cytoskeletal elements, and cytoplasmic signaling molecules--including Src-like kinases, hetero-trimeric G-proteins, and three members of the Rap family of small GTPases (Rap 1--the Ras tumor suppressor protein, Rap 2, and TC21). At least a fraction of the actin in these complexes appeared monomeric (G-actin), suggesting that these domains could represent membrane bound sites for microfilament nucleation/assembly during signaling. Given that the majority of these proteins are known molecules, our current studies provide a systematic basis for evaluating these interactions in vivo.
TL;DR: PC hydrolysis by PLA2, PLC or PLD is a widespread response elicited by most growth factors, cytokines, neurotransmitters, hormones and other extracellular signals and the mechanisms can involve G-proteins, PKC, Ca2+ and tyrosine kinase activities.