Biomedical subjects

D E Axelrod

Publications and source records attributed to D E Axelrod.

32 records · Page 2Linked to original sources

PubMed1984

Interferon-induced growth modulation: low dose maintenance of the antiproliferative response.

Treatment of the Burkitt's lymphoma-derived Daudi cell line with human beta interferon (HuIFN-beta) results in a dose-dependent antiproliferative response. We have defined three phases including: (1) initiation, (2) maintenance, and (3) termination of the antiproliferative state. Each phase is characterized by specific growth modulatory properties. Initiation of the antiproliferative state with a single interferon dose requires 200 International Reference Units (IRU) per ml, depending on such factors including cell density, serum content in the medium and the length of IFN exposure. Initiation of the IFN response occurred within a 4 h incubation period. Even following this short exposure, the vast majority of cells would be sequestered in the G0/G1 cell cycle compartment. As measured by cytofluorimetry there was a 16-20 h delay in the initiation of the antiproliferative response. The antiproliferative response, as measured by changes in the distribution of cells in the cell cycle, was maximal at 24 h after treatment. This delay was equal to the doubling time of the Daudi cell. The antiproliferative response initiated by 200 IRU/ml of IFN was reversible if the IFN was removed and not replenished. Cells showed renewed growth approximately 40 h after treatment. The antiproliferative state could be maintained by additional interferon, but, even after such treatment, the antiproliferative state decayed in a dose-dependent fashion. This decay was proportional to the decrease in the biological activity of the interferon molecule itself. Finally, we showed that the antiproliferative state could be maintained by using only 40 IRU/ml. These cells were maintained in the antiproliferative state for an extended period of time.

Burkitt Lymphoma↗

PubMed1983

Dimethyl sulfoxide affects the amount of extrachromosomal spleen focus-forming virus DNA in murine erythroleukemia cells.

We used Southern blot hybridization to titrate and map restriction enzyme cleavage sites of a 6.3-kilobase-pair species of extrachromosomal viral DNA found in derivatives of the 745A line of murine erythroleukemia cells, which vary in their ability to be induced to differentiate by dimethyl sulfoxide (DMSO). Greater than an eightfold variation was observed in the amount of this DNA, with the largest amounts being found in cells that were resistant to the induction of differentiation by DMSO. This increase in the level of extrachromosomal viral DNA was found to be dependent upon the continued presence of DMSO in the culture medium. The increase was shown not to be due to an immediate stimulatory effect of this agent on the synthesis or maintenance of this DNA, since cell lines sensitive to the differentiation-inducing effects of DMSO were shown to undergo a transient reduction in the amount of extrachromosomal viral DNA after the addition of DMSO to the culture medium. In addition to the 6.3-kilobase-pair linear form found in the cytoplasm, in some preparations two hybridizing bands were observed that migrated in agarose gels in the position expected of covalently closed circular species of viral DNA. Restriction enzyme mapping of the cytoplasmic linear form indicated a close relationship of this DNA to two polycythemic strains of spleen focus-forming virus that have been molecularly cloned by other workers. No obvious change in the number or arrangement of chromosomal viral sequences could be detected after treating cells with DMSO. Thus, the exposure of murine erythroleukemia cells to DMSO caused an obvious change in the amount of extrachromosomal spleen focus-forming virus DNA but no obvious change in the integration of the provirus.

Animals↗

PubMed1983

Phenotypic variation associated with molecular alterations at a cluster of thymidine kinase genes.

Genetic variation was studied in several mouse L cell lines containing tandemly repeated herpes simplex virus thymidine kinase (TK) genes introduced by DNA-mediated gene transfer. Variants were obtained after alternate positive and negative selection for TK expression. Three classes of molecular alteration are described. One class consisted of a concerted wave of hypermethylation affecting many sites in all or nearly all of the TK genes. This resulted in genetically stable TK- variants. Of five TK+ transformants from independent transfer experiments, only one, named HM, showed this class of methylation. Hypermethylation was a reproducible phenomenon in HM, yielding TK- variants after selection with either bromodeoxyuridine or acycloguanosine [Acyclovir or 9-(2-hydroxyethy-oxymethyl)guanine]. A second class of alteration consisted of methylation affecting some, but not all, genes in the cluster. This happened in all TK+ (HAT [hypoxanthine-aminopterin-thymidine]-resistant) cell lines investigated, and this second class of methylation was incapable of generating TK- variants. Neither type of methylation was accompanied by genomic rearrangements. The third class of molecular alteration was found among TK+ (HAT-resistant) back revertants of hypermethylated HM TK- derivatives. It consisted of a 10-fold amplification of the hypermethylated TK genes. Demethylation of hypermethylated HM variants was not observed. Thus, hypermethylation in this system can be compensated for by amplification but cannot be reversed.

Animals↗

PubMed1980

Tumorigenicity of Friend murine erythroleukemia cell lines differing in spontaneous differentiation rates.

The relationship between tumorigenicity and in vitro differentiation was studied in four Friend erythroleukemia cell lines. The cell lines were isolated by repeated subcloning of an unmutagenized population (sib selection). The cell lines differed in their ability to form tumors when 10(3) cells were injected subcutaneously into syngeneic mice (8 to 56% animals with tumors). The ability of cell lines to form tumors was not proportional to their ability to be induced to differentiate by dimethylsulfoxide. The cell lines had indistinguishable chromosome numbers, plating efficiencies, number of cycling cells, population doubling times and spontaneous mutation rates to drug resistance. However, the cell lines had different spontaneous differentiation rates in the absence of dimethylsulfoxide (0.87 to 16.0 X 10(-4) per cell per generation). The ability of cell lines to form tumors was inversely proportional to their spontaneous differentiation rate. Apparently cells which are most efficiently blocked in differentiation have the highest probability of forming tumors.

Animals↗

PubMed1979

Cell differentiation rates of Friend murine erythroleukemia variants isolated by sib selection.

Variants of Friend erythroleukemia cells were isolated which produced a high frequency (98%) or low frequency (2%) of hemoglobinized cells after induction with dimethylsulfoxide. Repeated subcloning and sib selection allowed enrichment of different cell lines without the use of mutagens or drug selection. The cell lines do not differ in growth rates, plating efficiencies, or chromosome numbers. The differences in inducibility phenotype were stable for more than 260 cell generations. In addition to differences in induction by dimethylsulfoxide and butyric acid, the cell lines also differ in spontaneous rates of cell differentiation. These results suggest that differences in differentiation rates are an inherited property of cells which is amplified in the presence of nonphysiological inducing agents.

Animals↗

PubMed1978

Maintenance of hemoglobin inducibility in somatic cell hybrids of tetraploid (2S) mouse erythroleukemia cells with mouse or human fibroblasts.

It has previously been reported that Friend mouse erythroleukemia (MEL) cells synthesize hemoglobin when exposed to 2% dimethylsulfoxide, and that hybrids between MEL cells and fibroblasts (or other nonerythroid cells) do not synthesize hemoglobin. We have been successful in obtaining hybrids (3/15) between MEL cells and mouse L-cell fibroblasts that maintain hemoglobin inducibility by preserving nonadherent cells after fusion. The proportion of hemoglobin inducible hybrids can be increased (8/11) by using a stable 2S (pseudotetraploid) MEL parent in addition to preserving nonadherent cells after fusion. All hybrids which were nonadherent were hemoglobin inducible, and all hybrids which were adherent were not. Five nonadherent hybrid clones were analyzed from fusions between a stable 2S MEL parent and a human fibroblast (WI-38, VA-2). All these clones were inducible for hemoglobin. It is concluded that gene dosage is effective in increasing the proportion of hemoglobin inducible hybrids, but hybrid morphology is the phenotype characteristic that correlates most closely with expression of hemoglobin inducibility.

Animals↗

PubMed1978

Sporulation competence in Aspergillus nidulans: a role for iron in development.

There is a difference in the response of DNA from mycelial extracts of Aspergillus nidulans to hot acid hydrolysis depending upon the state of sporulation competence. The DNA in incompetent culture mycelia is not hydrolyzable while the DNA in competent culture is hydrolyzable. The inhibition of DNA hydrolysis is due to the presence of iron. Although the concentration of iron decreases in mycelia during growth, there is sufficient iron present in competent mycelia to inhibit DNA hydrolysis. The change in DNA hydrolyzability may be the result of a change in intracellular iron distribution, or a change in an iron binding component. We suggest that these changes are related to the altered capacity for gene expression which occurs at the time of acquisition of sporulation competence.

Aspergillus nidulans↗

PubMed1978