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Biomedical subjects

Jill Thompson

Publications and source records attributed to Jill Thompson.

32 records · Page 2Linked to original sources
PubMed2004

Testing the conservation of the translational machinery over evolution in diverse environments: assaying Thermus thermophilus ribosomes and initiation factors in a coupled transcription-translation system from Escherichia coli.

Ribosomes from the extreme thermophile Thermus thermophilus are capable of translation in a coupled transcription-translation system derived from Escherichia coli. At 45 degrees C, T.thermophilus ribosomes translate at approximately 25-30% of the maximal rate of E.coli ribosomes, and synthesize full-length protein. T.thermophilus and E.coli subunits can be combined to effect translation, with the spectrum of proteins produced depending upon the source of the 30S subunit. In this system, T.thermophilus ribosomes function in concert with E.coli translational factors and tRNAs, with elongation and release factors being supplied from the E.coli extract, and purified initiation factors (IFs) being added exogenously. Cloned and purified T.thermophilus IF1, IF2 and IF3 supported the synthesis of the same products in vitro as the E.coli factors, although the relative levels of some polypeptides were factor dependent. We conclude that, at least between these two phylogenetically distant species, translational factor function and subunit-subunit interactions are conserved. This functional compatibility is remarkable given the extreme and highly divergent environments to which these species have adapted.

Escherichia coli↗
PubMed2004

The A2453-C2499 wobble base pair in Escherichia coli 23S ribosomal RNA is responsible for pH sensitivity of the peptidyltransferase active site conformation.

Peptide bond formation, catalyzed by the ribosomal peptidyltransferase, has long been known to be sensitive to monovalent cation concentrations and pH. More recently, we and others have shown that residue A2451 in the peptidyltransferase center of the Escherichia coli 50S ribosomal subunit changes conformation in response to alterations in pH, depending on ionic conditions and temperature. Two wobble pairs, A2453-C2499 and A2450-C2063, have been proposed as potential candidates to convey pH-dependent flexibility to the peptidyltransferase center. Each is presumed to possess a near-neutral pK(a), and both lie in proximity to A2451. We show through mutagenesis and chemical probing that the identity of the A2453-C2499 base pair, but not the A2450-C2063 base pair, is critical for the pH-dependent structural rearrangement of A2451. We conclude that, while the A2453-C2499 base pair may be important for maintaining the structure of the active site in the E.coli peptidyltransferase center, its lack of conservation makes it, and consequently its near-neutral pK(a), unlikely to contribute to function during peptide bond formation.

Adenine↗
PubMed2004

A simple method to cure established tumors by inflammatory killing of normal cells.

We describe a simple technology used to cure an established metastatic disease. Intradermal injection of plasmid DNA encoding a transcriptionally targeted cytotoxic gene, along with hsp70, not only promoted tissue-specific, inflammatory killing of normal melanocytes, but also induced a CD8(+) T-cell-dependent, antigen-specific response in mice that eradicated systemically established B16 tumors. This CD8(+) T cell response was subsequently suppressed in vivo within a few days. The data demonstrate that deliberate destruction of normal tissue can be exploited to generate immunity against a malignant disease originating from that tissue. This approach obviates the need to identify tumor antigens and does not require complex isolation of tumor cells or their derivatives. In addition, it provides a model system for studying the mechanisms underlying the etiology and control of autoimmune diseases. Finally, despite targeting normal tissue, therapy could be separated from development of overt autoimmune symptoms, suggesting that the strategy may be valuable against tumors derived from both non-essential and essential tissue types.

Animals↗
PubMed2004

Thiostrepton-resistant mutants of Thermus thermophilus.

Ribosomal protein L11 and its associated binding site on 23S rRNA together comprise one of the principle components that mediate interactions of translation factors with the ribosome. This site is also the target of the antibiotic thiostrepton, which has been proposed to act by preventing important structural transitions that occur in this region of the ribosome during protein synthesis. Here, we describe the isolation and characterization of spontaneous thiostrepton-resistant mutants of the extreme thermophile, Thermus thermophilus. All mutations were found at conserved positions in the flexible N-terminal domain of L11 or at conserved positions in the L11-binding site of 23S rRNA. A number of the mutant ribosomes were affected in in vitro EF-G-dependent GTP hydrolysis but all showed resistance to thiostrepton at levels ranging from high to moderate. Structure probing revealed that some of the mutations in L11 result in enhanced reactivity of adjacent rRNA bases to chemical probes, suggesting a more open conformation of this region. These data suggest that increased flexibility of the factor binding site results in resistance to thiostrepton by counteracting the conformation-stabilizing effect of the antibiotic.

Amino Acid Sequence↗
PubMed2004

Thermus thermophilus L11 methyltransferase, PrmA, is dispensable for growth and preferentially modifies free ribosomal protein L11 prior to ribosome assembly.

The ribosomal protein L11 in bacteria is posttranslationally trimethylated at multiple amino acid positions by the L11 methyltransferase PrmA, the product of the prmA gene. The role of L11 methylation in ribosome function or assembly has yet to be determined, although the deletion of Escherichia coli prmA has no apparent phenotype. We have constructed a mutant of the extreme thermophile Thermus thermophilus in which the prmA gene has been disrupted with the htk gene encoding a heat-stable kanamycin adenyltransferase. This mutant shows no growth defects, indicating that T. thermophilus PrmA, like its E. coli homolog, is dispensable. Ribosomes prepared from this mutant contain unmethylated L11, as determined by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), and are effective substrates for in vitro methylation by cloned and purified T. thermophilus PrmA. MALDI-TOF MS also revealed that T. thermophilus L11 contains a total of 12 methyl groups, in contrast to the 9 methyl groups found in E. coli L11. Finally, we found that, as with the E. coli methyltransferase, the ribosomal protein L11 dissociated from ribosomes is a more efficient substrate for in vitro methylation by PrmA than intact 70S ribosomes, suggesting that methylation in vivo occurs on free L11 prior to its incorporation into ribosomes.

Bacterial Proteins↗
PubMed2003

Expression of inflammatory chemokines combined with local tumor destruction enhances tumor regression and long-term immunity.

Expression of chemokines within tumors can be used to recruit immature dendritic cells (DCs) for the initiation of antitumor T-cell responses. Here, we describe the chemokine receptor expression on murine bone marrow-derived immature DCs. On the basis of these receptor studies, we chose to express the chemokines CCL3 (Mip-1alpha) or CCL20 (Mip-3alpha) in tumors. We show that expression of these chemokines in the colorectal tumor model CMT93 significantly decreases tumorigenesis. This decrease is associated with an increase in CD8 T cells, natural killer cells, and Class II DCs in the tumor within the first 24 h. Furthermore, studies in immunodeficient mice show that both natural killer cells and T cells are required for this decrease in immunogenicity. CCL3 and CCL20 expression alone did not significantly inhibit the development of the B16 melanoma tumor. However, coexpression of the Herpes Simplex Virus thymidine kinase gene (HSVtk) and CCL20, cured large established tumors where HSVtk expression alone was not sufficient. Finally, coexpression of HSVtk with either CCL3 or CCL20 was able to significantly increase protection against subsequent tumor rechallenge.

Animals↗
PubMed2003

Pharmacologically regulated production of targeted retrovirus from T cells for systemic antitumor gene therapy.

We aimed to use cell-based carriers to direct vector production to target sites for systemic therapy. We used T cells engineered to express a chimeric T cell receptor that can specifically recognize target cells expressing the tumor-associated carcinoembryonic antigen (CEA). These T cells were modified to produce a retrovirus under tight pharmacological control using the rapamycin-inducible transcriptional regulatory system. The retroviral vectors produced were transcriptionally targeted to CEA-expressing target cells. We found that vector production and transgene expression from these T cells in vitro was dependent on pharmacological induction and expression of CEA in target cells, respectively. Mice bearing metastatic tumors that received cell carriers delivering the HSVtk gene demonstrated a significant increase in survival, but only in response to pharmacological induction of vector production. Interestingly, the therapeutic effect required the presence of the tumor-specific chimeric receptor on T cells. Further studies demonstrated that systemic delivery of tumor-specific T cells to mice bearing metastatic tumors caused recruitment of nonspecific T cells to the tumor site. We hypothesize that this enhanced targeting to tumor sites is responsible for the efficiency of T cell-mediated retroviral gene transfer and that this principle can be used to enhance systemic therapies using immune-cell carriers.

Adenocarcinoma↗
PubMed2003

A conditionally replicating adenovirus targeted to tumor cells through activated RAS/P-MAPK-selective mRNA stabilization.

The expression of various proteins associated with rapid responses to inflammation and/or proliferation can be controlled at the level of mRNA stability. Because tumor cells continually recapitulate intracellular programs of proliferation, we have used tumor cell-selective stabilization of mRNA as a means to control therapeutic gene expression. We describe an adenoviral vector that is conditionally replication competent in which expression of the essential adenoviral early region 1A (E1A) gene is regulated by ligation to the 3' untranslated region (UTR) of PTGS2 (also known as COX2), the gene encoding prostaglandin-endoperoxide synthase 2, allowing activated RAS/P-MAPK-specific stabilization of its mRNA. Induction of activated RAS supports replication, whereas matched cells in which activated RAS/P-MAPK is not expressed are very poor substrates for viral replication both in vitro and in vivo. Further tumor-targeting strategies will also be required to prevent viral replication at extratumoral sites where PTGS2 is normally induced. Many different genes contain 3' UTRs that control selective mRNA stability under different physiological, pathological and tumor-associated conditions. Therefore, generating tumor selectivity at the level of mRNA stability is a strategy with broad potential applicability in vector design.

Adenoviridae↗
PubMed2003

Functional identification of ion binding sites at the internal end of the pore in Shaker K+ channels.

The inner end of the pore in voltage-gated K+ channels is the site of conformational changes related to gating and contains binding sites for permeant ions and pore-blocking molecules including quaternary ammonium ions and drugs. In order to determine the location and affinity of ion binding sites we probed the Shaker K+ channel with the quaternary ammonium analogue, tetrabutyl antimony (TBSb), a compound that is sufficiently electron dense to have been observed to occupy the cavity site in the bacterial K+ channel, KcsA. TBSb has K+ channel blocking properties analogous to those of tetrabutyl ammonium (TBA), and kinetics slow enough to be reliably measured. In the presence of external TEA, the internal TBSb on-rate decreased with increased internal K+ concentration as if these permeant ions prevented TBSb access to its site in the pore. The TBSb off-rate in low K+ was increased with external TEA addition and then reduced with increased internal K+. We found several differences between the behaviour of internal TBSb and TEA suggesting these molecules bind to distinct but interacting sites in the pore. We also found several differences in how K+ and Rb+ ions occupy sites in the inner end of the pore. These data suggest the presence of three sites in the inner end of the pore: (1) a site near the cytoplasmic end that binds TEA and K+ (but not Rb+) ions; K+ ions binding to this site inhibit TBSb exit from the pore; (2) a TBSb site slightly more into the pore that is rarely occupied by K+ or Rb+ ions; (3) a site further into the pore that has a high affinity for K+ and Rb+ ions; occupancy of this site by these permeant ions increases the TBSb off-rate. These results provide information on the fine-structure of ion interactions with the inner end of the pore in K+ channels.

Animals↗
PubMed2003

External TEA block of shaker K+ channels is coupled to the movement of K+ ions within the selectivity filter.

Recent molecular dynamic simulations and electrostatic calculations suggested that the external TEA binding site in K+ channels is outside the membrane electric field. However, it has been known for some time that external TEA block of Shaker K+ channels is voltage dependent. To reconcile these two results, we reexamined the voltage dependence of block of Shaker K+ channels by external TEA. We found that the voltage dependence of TEA block all but disappeared in solutions in which K+ ions were replaced by Rb+. These and other results with various concentrations of internal K+ and Rb+ ions suggest that the external TEA binding site is not within the membrane electric field and that the voltage dependence of TEA block in K+ solutions arises through a coupling with the movement of K+ ions through part of the membrane electric field. Our results suggest that external TEA block is coupled to two opposing voltage-dependent movements of K+ ions in the pore: (a) an inward shift of the average position of ions in the selectivity filter equivalent to a single ion moving approximately 37% into the pore from the external surface; and (b) a movement of internal K+ ions into a vestibule binding site located approximately 13% into the membrane electric field measured from the internal surface. The minimal voltage dependence of external TEA block in Rb+ solutions results from a minimal occupancy of the vestibule site by Rb+ ions and because the energy profile of the selectivity filter favors a more inward distribution of Rb+ occupancy.

Animals↗
PubMed2002

The protein synthesis inhibitors, oxazolidinones and chloramphenicol, cause extensive translational inaccuracy in vivo.

The oxazolidinone family is a new class of synthetic antibiotics that bind to the bacterial 50S ribosomal subunit. Two members of the family, linezolid and XA043, were examined for their effects on translational fidelity using a lacZ reporter gene in vivo. Both promoted highly significant frameshifting and nonsense suppression. Chloramphenicol, a peptidyl transferase inhibitor, affected translational fidelity in a similar fashion. Neither the oxazolidinones nor chloramphenicol stimulated misincorporation of amino acid residues at position 461 in the lacZ gene. In contrast, the aminoglycosides gentamicin and paromomycin, which interact with the decoding region of the 30S subunit, caused significant misincorporation but only modest increases in frameshifting or stop codon readthrough of the lacZ gene. We conclude that effects on translational fidelity may play a significant role in the mechanism of action of the oxazolidinones.

Acetamides↗
PubMed2002

Initiation factor IF2, thiostrepton and micrococcin prevent the binding of elongation factor G to the Escherichia coli ribosome.

The bacterial translational GTPases (initiation factor IF2, elongation factors EF-G and EF-Tu and release factor RF3) are involved in all stages of translation, and evidence indicates that they bind to overlapping sites on the ribosome, whereupon GTP hydrolysis is triggered. We provide evidence for a common ribosomal binding site for EF-G and IF2. IF2 prevents the binding of EF-G to the ribosome, as shown by Western blot analysis and fusidic acid-stabilized EF-G.GDP.ribosome complex formation. Additionally, IF2 inhibits EF-G-dependent GTP hydrolysis on 70 S ribosomes. The antibiotics thiostrepton and micrococcin, which bind to part of the EF-G binding site and interfere with the function of the factor, also affect the function of IF2. While thiostrepton is a strong inhibitor of EF-G-dependent GTP hydrolysis, GTP hydrolysis by IF2 is stimulated by the drug. Micrococcin stimulates GTP hydrolysis by both factors. We show directly that these drugs act by destabilizing the interaction of EF-G with the ribosome, and provide evidence that they have similar effects on IF2.

Anti-Bacterial Agents↗
PubMed2002

A randomized controlled trial of early oral analgesia in gynecologic oncology patients undergoing intra-abdominal surgery.

OBJECTIVE: To evaluate the safety and efficacy of early oral analgesia after intra-abdominal surgery in gynecologic oncology patients. METHODS: Over a 2.5-year period, 227 gynecologic oncology patients undergoing intra-abdominal surgery were enrolled in a randomized controlled trial of early oral versus traditional parenteral analgesia. All patients initially received parenteral morphine via a patient-controlled analgesia (PCA) pump with a basal dose of 0.5 mg/h and a PCA dose of 1 mg with a 10-minute lockout. On the first postoperative day, all patients began a clear liquid diet, which was advanced as tolerated. Patients allocated to early oral analgesia were switched from parenteral to oral morphine. They received a scheduled dose of 20 mg every 4 hours with an additional dose of 10 mg every 2 hours as needed for breakthrough pain. Patients allocated to traditional parenteral analgesia continued to receive parenteral morphine via a PCA pump with basal and PCA doses. On the second postoperative day, the scheduled oral and basal parenteral doses were discontinued. The oral and parenteral PCA doses were continued until 24 hours before discharge, at which time the patient was switched to oxycodone 5 mg/acetaminophen 325 mg. RESULTS: There were no significant differences among the groups in any demographic or clinical indices, including age, case distribution, surgery length, blood loss, time to return of bowel function, length of hospital stay, pain, sedation, and satisfaction scores, and incidence of nausea, vomiting, or major postoperative complications. CONCLUSIONS: Early oral analgesia in gynecologic oncology patients undergoing intra-abdominal surgery is safe and efficacious.

Abdomen↗