Biomedical subjects
Publications and source records attributed to E T David.
Thorium dioxide is a deleterious substance that was employed as a vascular contrast medium during the early 20th century. Our report entails a unique neoplastic complication of thorium administration.
Rat embryo cells were infected with adenovirus type 5 mutants that code for only one of the two early E1A proteins, mutants with defects in one of the two conserved regions common to the two proteins, or mutants with defects in the 46-amino-acid region unique to the 289-amino-acid E1A protein. Cells were scored for altered cell cycle progression, disruption of actin stress fibers, and activation of E2A expression. Mutants lacking either E1A protein were able to cause all of these effects; but mutants lacking a 243-amino-acid protein had less effect, and mutants lacking a 289-amino-acid protein much less effect, than wild-type virus. A mutation in any of the three conserved regions caused a defect in each E1A effect. To investigate the reported function of conserved domain 2 in mitosis, we monitored by fluorescence-activated cell sorter the reduction in Hoechst 33342 fluorescence that occurs when cells divide after undergoing a round of DNA replication in 5-bromodeoxyuridine. A smaller percentage of adenovirus-infected cells than mock-infected cells divided within a given period after completing a round of DNA replication. Viruses with mutations in conserved domain 2 were defective for initiation of cellular DNA replication, as were all other E1A mutants we have examined, but had no specific defect in cell division compared with wild-type virus. Thus, although there may be some specialization of function between the two E1A proteins and between their conserved domains, it was not apparent in the aspects of E1A function and the mutants that we examined.
The identification of unstable cervical spine injury (UCSI) in blunt high-energy transfer injury (BHETI) patients is critical to management. In a prospective study of BHETI patients identified to be at high risk for UCSI, the use of lateral cervical spine view (LCV), three-view cervical spine series (FCS), and limited computerized tomography (CT) in the initial evaluation of these patients was analyzed. Thirteen of 204 patients sustained UCSI. Sensitivity of the LCV alone was 0.85 and the predictive value of the negative test was 0.97. Sensitivity and predictive value of a negative study were maximized by the use of FCS combined with CT when plain X-rays were inadequate. We conclude that technically adequate, normal FCS can be safely used to eliminate the presence of UCSI. If these studies are technically inadequate, the addition of a limited CT can be used to "clear" the spine.
Altered control of the rat cell cycle induced by adenovirus requires expression of transformation region E1A, but not of E1B, E2A, E2B, or late genes. We show here that neither E3 nor E4 is required, so the effect results directly from an E1A product. Mutants with defects in the 289-amino-acid (aa) E1A product had little or no effect on the rat cell cycle even at 1,000 IU per cell. A mutant (pm975) lacking the 243-aa E1A product altered cell cycle progression, but less efficiently than did wild-type virus. The 289-aa E1A protein is therefore essential for cell cycle effects; the 243-aa protein is also necessary for the full effect but cannot act alone. Mutants with altered 289-aa E1A proteins showed different extents of leak expression of viral early region E2A as the multiplicity was increased; each leaked more in human than in rat cells. dl312, with no E1A products, failed to produce E2A mRNA or protein at 1,000 IU per cell in rat cells but did so in some experiments in human cells. There appears to be a very strict dependence of viral early gene expression on E1A in rat cells, whereas dependence on E1A is more relaxed in HeLa cells, perhaps due to a cellular E1A-like function. Altered cell cycle control is more dependent on E1A function than is early viral gene expression.
The effects of varying concentrations of ethanol on reactions involved in protein biosynthesis have been examined using a cell-free system from Chinese hamster ovary cells that actively translates natural mRNAs in order to detect those components most sensitive to alcohol. Ethanol, at relatively low concentrations (0.2 M or lower) inhibited the translation of endogenous polysomal mRNAs and, in mRNA-depleted extracts, of exogenous natural mRNA. Ethanol markedly inhibited leucyl-tRNA synthetase, and it inhibited Phe- and Glu-tRNA synthetases to some extent, but had only a small effect on several other aminoacyl-tRNA synthetases, elongation factors 1 and 2, ribosomes, or the formation of eukaryotic initiation factor 2 . GTP . Met-tRNAr ternary complex. Methanol inhibited slightly the translation of mRNA and Leu-tRNA synthetase, but isobutyl alcohol and isopropyl alcohol strongly depressed these activities. Ethanol inhibited the interaction of leucine with Leu-tRNA synthetase competitively, whereas isobutyl alcohol and acetaldehyde inhibited the leucine interaction in a noncompetitive manner. Leu-tRNA synthetase from Chinese hamster ovary cells was more sensitive to ethanol than that from yeast.
Saturating concentrations of the initiation-specific inhibitors poly(I) and T-2 toxin inhibit protein synthesis by over 35% and cause ribosome 'run-off' from the polyribosomes. The elongation-specific inhibitor cycloheximide totally prevents protein synthesis and 'freezes' the ribosomes in the pattern of unincubated controls. These results prove that our Tetrahymena extracts are capable of protein-synthesis initiation, a conclusion which is confirmed by a 30% inhibition of synthesis by the mRNA cap analogue, 7-methylguanosine 5'-monophosphate.
1. We have examined methods necessary for preparing post-mitochondrial supernatants from Tetrahymena pyriformis strain HSM that are capable of efficient cell-free protein synthesis. 2. The requirements for optimum synthesis in these extracts are described. 3. Data relating to the kinetics of protein synthesis and the initiation capacity of these supernatants are presented.