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Biomedical subjects

S Panem

Publications and source records attributed to S Panem.

At least 37 records · Page 2Linked to original sources
PubMed1978

Time-dependent resistance or susceptibility of tumor cells to cytotoxic antibody after exposure to a chemotherapeutic agent.

We report that a chemotherapeutic agent (melphalan) can affect the sensitivity of tumor cells to cytotoxic antibody. Depending on the time interval between drug treatment and subsequent exposure to antibody and complement, the tumor cells can be either more resistant or more susceptible to antibody when compared to control cells. The number of tumor cells surviving the combined treatment was determined by a colony inhibition assay. The two antisera used in this study were directed against either virus-specific or myeloma protein-specific antigens on the surface of S107 murine myeloma cells; identical results were obtained with both sera. Twenty-four hours after exposure to the drug, the number of tumor cells surviving the antibody treatment increased. During this period of increased resistance, the tumor cells were temporarily arrested in the G(2) phase of the cell cycle. After this period of maximal resistance, the effect of cytotoxic antibody on the cells changed such that 4 days after melphalan treatment the cells were significantly more susceptible to the antibody than were the sham-treated control cells. The period of increased susceptibility correlated with an increased density of S107 myeloma protein and viral antigens on the surface of the tumor cells. Eight days after the drug treatment, the susceptibility of the tumor cells and the density of surface antigens both returned to normal levels. This study shows that the correct time interval between exposure to a drug and subsequent treatment with antibody is critical for maximal killing of the tumor cells. The basis for the differential sensitivity of the tumor cells to anti-body may be related to the drug-induced changes in the cell cycle and in antigen expression on the cell surface.

Antibodies, Viral↗
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↗
PubMed1976

C-type virus expression in systemic lupus erythematosus.

Kidneys from patients with lupus nephropathy, non-lupus immune-complex glomerulonephritis and other renal diseases were examined by indirect immunofluorescence for antigens related to a C-type virus from human cells (HEL-12 virus). All 11 specimens of lupus nephropathy contained HEL-12 virus antigens deposited in the same pattern as the immune complexes. The intensity of immunofluorescence with anti-HEL-12 virus serum correlated with the extent of immune-complex deposition. In contrast, nine renal lesions other than lupus nephropathy and seven normal tissues did not react with anti-HEL-12 virus serum. Antibody eluted from one kidney with lupus nephropathy reacted by indirect immunofluorescence with human and dog cells infected with HEL-12 virus but not with uninfected control cells. These findings demonstrate a specific association of lupus nephropathy with a C-type viral antigen that is deposited as antigen-antiviral antibody complex.

Antibodies, 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

Distribution and virogenic effects of 5-bromodeoxyuridine in synchronized rat embryo cells.

Rat embryo cell cultures were synchronized by a double thymidine block. The DNA replication phase (S) was divided into an early, middle, and late period. Cell cultures in the early, middle, or late S phase were pulsed with 0.1 muM 5-bromo[(3)H]deoxyuridine (BrdU) or equimolar [(3)H]dT. DNA-DNA reassociation experiments of each sample revealed that [(3)H]BrdU was more concentrated in the intermediate repetitive than the repetitive or unique DNA sequences of the early and middle S phase. In contrast, [(3)H]dT was nearly uniformly jistributed throughout all nucleotide sequences during the entire S phase. synchronized rat cells were pulsed during various portions of the S phase with unlabeled 0.1 mM or 0.1 muM BrdU and examined for sytoplasmic immumofluorescence against the 30,000 molecular weight group-specific antigen (p30) of Friend mouse leukemia virus. Equally strong fluorescence was detected 12 hr later in cells treated with each concentration of BrdU. Furthermore, incorporation of BrdU during late S phase was suffieient to elicit maximal antigen expression.

Animals↗
PubMed1975

Proteins of Kirsten murine leukaemia-sarcoma virus: localization within the virus particle by iodination and fractionation techniques.

The protein and glycoprotein composition of Kirsten murine leukaemia-sarcoma virus (KiMSV(KiMuLV) was studied using SDS-polyacrylamide gel electrophoresis. Twenty-three polypeptides and three glycoproteins were detected following electrophoresis by staining with Coomassie blue and PAS or by autoradiography of isotopically labelled virus. Protein components were assigned positions in the virus particle, envelope, nucleoid or intermediate area based on iodination with lactoperoxidase and sedimentation in potassium citrate equilibrium gradients. The KiMSV (KiMuLV) envelope contained 11 polypeptides and three glycoproteins. The virus nucleoid and intermediate area were each composed of six proteins. The protein composition of KiMSV(KiMuLV) was highly reproducible when virus was harvested from cells of the same subcluture generation. However, the protein profiles were altered with repeated in vitro passages of the virus-producing cell line.

Autoradiography↗
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↗