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E V Prochownik

Publications and source records attributed to E V Prochownik.

63 records · Page 4Linked to original sources
PubMed1977

Cell generation and type C virus expression in the human embryonic cell strain HEL-12.

The spontaneous expression of a type C virus in a diploid strain of human embryonic lung fibroblast-like cells (HEL-12) was examined during serial culture. Virus antigen expression was determined by indirect immunofluorescenc with antisera to disrupted simian sarcoma virus and the 28000 mol. wt. internal antigen of the endogenous cat virus RD-114. Virus production was examined by reverse transcriptase assays of culture fluids. Virus antigens were not detected for 25 days after frozen, primary HEL-12 cells were reinstated in culture. The cells expressed virus antigens but did not release virus particles between 25 and 80 days. Spontaneous virus release and maximal antigen expression occurred in cells grown for 80 to 120 days. Virus particles were not detected after 120 days although virus antigens persisted until the experiment was terminated. The HEL-12 virus was infectious for cell cultures of human, rhesus monkey, dog and rabbit cells. The proportion of SiSV-like and RD-114-like antigenic components of HEL-12 virus were altered by passage through heterologous cells suggesting heterogeneity of the HEL-12 virus population.

Antigens, Viral↗
PubMed1975

Isolation of type C virions from a normal human fibroblast strain.

Type C virions were spontaneously released from cultures of a diploid human cell strain. The varions have properties of known type C RNA tumor viruses and share antigenic determinants with the major interspecies-specific antigen (p30) of simian sarcoma virus. Antiserum to reverse transcriptase of gibbon ape leukemia virus inhibits the reverse transcriptase of the putative human virions and that of simian sarcoma virus, but has no effect on the corresponding enzymes of avian or murine RNA tumor viruses.

Antigens, Viral↗
PubMed1975

Biological and physical modifications of a murine oncornavirus by 2-deoxy-D-glucose.

2-Deoxy-D-glucose (2-DG) inhibited the release of transforming Kirsten murine sarcoma-leukemia virus [KiMSV(KiMuLV)] from transformed rat kidney (NRK-K) cells. At a concentration of 30 mM 2-DG, RNA synthesis in NRK-K cells was inhibited by approximately 30 percent and protein synthesis was inhibited by as much as 80 percent of control levels. RNA synthesis was not inhibited in nontransformed normal rat kidney (NRK) cells, although protein synthesis was equally suppressed in NRK and NRK-K cells. After treatment with 2-DG, the release of physical particles of KiMSV(KiMuLV) from NRK-K cels was not reduced as determined by equilibrium density gradient centrifugation and assays for RNA-dependent DNA polymerase of culture fluids. The ability to detect virion-associated radioactivity in equilibrium density gradients was dependent on the conditions of labeling. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of KiMSV(KiMulLV) proteins revealed marked structural alterations after propagation of the virus in 30 mM 2-DG. These alterations may account for the observed loss of transforming ability of KiMSV(KiMuLV).

Animals↗
PubMed1975

Induction of type C virions from normal rat kidney cells by 2-deoxy-D-glucose.

The sugar 2-deoxy-D-glucose (2-DG) induced the release of type C virions from an established line of normal rat kidney (NRK) cells. Within 20 h after the addition of 5 mg of 2-DG per ml to exponentially growing NRK clutures, more than 80% of the cells expressed the mammalian type C virus interspecies-specific antigen (p30) as determined by indirect cytoplasmic immunofluorescence. Maximal virion release occurred 1 to 2 days after 2-DG was added for 24 h to the growth medium although a low level of virion production was detected as early as 2.5 h after 2-DG treatment. Studies with inhibitors of RNA synthesis indicated a requirement for de novo RNA synthesis after the addition of 2-DG. Sensitivity of NRK cells to type C virion induction was limited to a relatively short period of in vitro growth and preceded spontaneous virion release by 8 to 10 subculture generations. A model is presented for the sequential derepression of latent type C virus information in serially propagated NRK cells.

Animals↗
PubMed1975

The interferon refractory state. II. Biological characterization of a refractoriness-inducing protein.

When L929 cells were treated with samples collected from cells or mice producing interferon, almost complete refractoriness to subsequent interferon induction was observed. The relationship of this refractoriness-inducing product (RIP) to the antiviral activity of the samples was determined. Using interferon in the pretreatment sample as a measure of RIP concentration, a semilog plot of the pretreatment interferon titer and interferon subsequently produced, resulted in an approximately linear relationship between 10 and 100 units of interferon in the pretreatment sample. This relationship was largely independent of multiplicity of Newcastle disease virus (NDV) used to produce interferon in the treated monolayers. A 2- to 6-fold temporal differentiation in the refractoriness-inducing activity and the antiviral activities was obtained both in vitro and in vivo. Supernatants collected 48 hr after NDV infection of L929 cells had 2- to 4-fold more refractoriness-inducing activity than those collected earlier. In serum of ICR mice given poly rIn:rCn-poly-D-lysine, a quantitatively similar temporal increase in refractoriness-inducing activity was observed. Treatment of L929 cells with cycloheximide resulted in a 4-fold increase in interferon production. At equivalent interferon concentrations, supernatants from the cycloheximide-treated monolayers inhibited interferon production 4-fold less than did comparable supernatants from non-cycloheximide-treated monolayers. Soluble cell extracts inhibited interferon production to a greater degree than did extracellular preparations. The protein nature of the refractoriness-inducing activity was suggested by its trypsin sensitivity. These findings suggest that the refractoriness-inducing and antiviral activities of interferon preparations result from different proteins.

Antiviral Agents↗
PubMedDate not supplied

Relationship between an enhancer element in the human antithrombin III gene and an immunoglobulin light-chain gene enhancer.

Enhancers, cis-acting transcriptional control elements have been described in both viral and cellular genes. They influence transcription in a quantitative fashion, act over relatively large distances (several kilobases, kb) and behave independently of their position and orientation. Enhancers have been described in immunoglobulin, chymotrypsin and insulin genes. They bear little homology with each other except for an 8-base pair (bp) 'consensus' core element, GTGGAAATTTG (refs 10, 11), but even this element is sometimes non-homologous. I have searched for such elements in the human antithrombin III (AT-III) gene. AT-III is an important coagulation protein which inactivates thrombin. It is produced by the liver and, to a lesser extent, by the kidney. Here, I report that the 5' flanking region of the AT-III gene encodes a segment homologous with the enhancer containing the joining-constant kappa (J kappa-C kappa) intron of immunoglobulin kappa-chain genes. This extensive homology suggests the existence of regulatory factors that recognize common DNA sequences in lymphoid tissues and in those which express AT-III.

Acetyltransferases↗
PubMedDate not supplied

Deregulated expression of c-myc by murine erythroleukaemia cells prevents differentiation.

Friend murine erythroleukaemia (F-MEL) cells are a permanent line of primitive erythroid precursors originally derived from the spleens of mice infected with the Friend strain of murine leukaemia virus. F-MEL cells differentiate in vitro in response to various chemical inducers. Concomitantly with induction, a biphasic regulation of c-myc oncogene transcripts is observed. Within one hour of the addition of dimethyl sulphoxide (DMSO) or hypoxanthine (Hyp), the levels of c-myc transcripts fall dramatically and remain virtually undetectable for the next few hours. Between 8 and 24 hours after induction, c-myc transcripts return to pre-induction levels and then decline again between 3 and 5 days as most of the cells undergo terminal differentiation. To explore the potential relationship between c-myc expression and F-MEL terminal differentiation, we have investigated here whether reversing the early fluctuations in c-myc transcript levels affects the ability of F-MEL cells to differentiate. We therefore constructed an amplifiable plasmid vector containing a full-length mouse c-myc complementary DNA and introduced it stably into recipient F-MEL cells. The exogenous c-myc sequences are transcribed in F-MEL cells and the transcript levels do not change significantly in response to inducing agents. The net result is continued c-myc expression following DMSO or Hyp induction and a complete or partial inhibition of F-MEL differentiation.

Animals↗