Polyribosome Profiles and Polyribosome-Associated RNA of Friend Leukaemia Cells Following DMSO-induced Differentiation

HHV-6 inhibition by two polar compounds

Dimethyl sulphoxide and dimethyl formamide, two polar compounds and powerful cell differentiation inducers, inhibit HHV-6 infection when added to HHV-6-infected HSB2 cultures. This was established by a delay in the time-course of infection and in the development of virus-induced cytopathic effects. Furthermore, viral titration of supernatants showed a significant reduction (3 log10) of the number of infectious particles. Electron microscopy confirmed that viable cells and extracellular virions were present in the cultures containing the polar compounds, while in the non-treated cultures all cells were lysed and no extracellular virus was evident. The mode of action of these compounds is still unclear and warrants further investigation.

Induction of differentiation in Friend erythroleukemia cells with dimethyl sulfoxide, hexamethylene bisacetamide and sodium butyrate is not accompanied by changes in proviral DNA or its expression

The integration pattern, copy number and DNA expression of the Friend virus genome was examined in Friend erythroleukemia cells induced to differentiate with dimethyl sulfoxide, hexamethylene bisacetamide and sodium butyrate. The integrated proviral DNA in Friend erythroleukemia cells was examined by Southern hybridization with a cloned Friend virus (F-MuLV) probe at days 1 and 4 following inducer treatment, as well as on day 6 at which time the cells had remained for 48 h in inducer free medium. KpnI fragments 9 and 5.7 kb long were observed. The copy number of each fragment remained constant throughout the erythroid differentiation process. EcoRI digestion of DNA isolated from cells at different times following the inducer treatment demonstrated multiple integration sites of the proviral genome, which also remained constant during the differentiation process. Proviral DNA expression was examined at 4 h and 4 days following inducer treatment as well as on day 6 by which time cells remained for 48 h in inducer free medium. Northern blot hybridization to the F-MuLV probe indicated no change in the provirus gene expression independent of the class of inducers. These observations reinforce our conclusions that the viral genome and its transcription product do not play a major role in the differentiation process of Friend erythroleukemic cells.

The plasma pharmacokinetics and tissue distribution of dimethyl sulfoxide in mice

We defined the plasma and tissue concentrations and pharmacokinetics of dimethyl sulfoxide (DMSO) in 22-34 g male Swiss Webster mice injected i.v. with 15% DMSO at a dosage of 1.5 mg per g. Concentrations of DMSO in alkalinized, perchloric acid extracts of tissue and plasma were determined by gas-liquid chromatography. Plasma concentrations of DMSO declined in a biexponential fashion that was well described by the equation Ct = 2.36 exp(-0.449 t) + 1.28 exp(-0.00768 t), indicating a t 1/2 (alpha) of 1.5 min and t 1/2 (beta) of 90 min. DMSO was rapidly and extensively distributed through tissues and was not concentrated in any particular tissue, although at 1 min after injection, the brain contained the lowest concentration of DMSO of any tissue studied. By 8 hr after injection, there was little DMSO in plasma or any tissue. Intravenous injection of DMSO produced neuro-muscular disturbances, hemolysis, and hemoglobinuria in all animals. Intravenous injection of DMSO produced little increase in plasma osmolality and did not produce any histological evidence of central nervous system or renal tubular damage.

Polysomal and nonpolysomal messenger RNA of noninduced and induced Friend erythroleukemic cells: analysis by cell-free translation

Polyadenylated and nonpolyadenylated mRNA were prepared from polysomes and from the postribosomal supernatant of noninduced and DMSO-induced Friend cells. The mRNA preparations were translated in a wheat germ cell-free system and the in vitro synthesized proteins, fractionated by polyacrylamide gel electrophoresis, were compared by fluorography. The electrophoretic analysis shows that four preparations of poly (A) + RNA code for many different peptides and that most of these peptides are present in each of the poly (A) + RNA translation products. However, the electrophoretic patterns of these translation products differ in the relative amounts of peptides comigrating in the gel electrophoresis. After DMSO treatment, Friend cells show significative differences in the polysomal and nonpolysomal mRNA pools. With induction, globin becomes the most abundant product of the polysomal poly (A) + RNA, while the relative amounts of peptides coded by nonglobin polysomal poly (A) + RNA are reduced. In parallel, the electrophoretic pattern of the in vitro products on the nonpolysomal poly (A) + RNA changes in the relative amounts of the fractionated peptides; moreover, in induced cells, the nonpolysomal poly (A) + RNA codes for peptides not detected in the polysomal poly (A) + RNA of the same cells. These data were interpreted assuming that in DMSO-induced cells, protein synthesis is regulated at both the transcriptional and translational levels. Polysomal poly (A)-RNA codes mostly for the five main histone classes; with DMSO treatment the amount of H2b MRNA bound to polysomes is increased with respect to the other polysomal histone mRNA.

X-linked control of globin mRNA and hemoglobin production in erythroleukemia-lymphoma cell hybrids

In somatic cell hybrids formed by the fusion of mouse erythroleukemic cells with cultured mouse lymphoma cells, retention of the X chromosome donated by the lymphoma parent is correlated with inhibition of hemoglobin accumulation in response to dimethyl sulfoxide. The inhibition of hemoglobin production was due to an inhibition of globin mRNA accumulation. Heme can partially overcome the effects of the lymphoma X chromosome and induce globin mRNA and hemoglobin accumulation in the dimethylsulfoxide-treated hybrid cells. The data suggests that the X chromosome contributed by the lymphoma cells inhibits hemoglobin production by inhibiting both inducible globin mRNA accumulation as well as inducible heme biosynthesis, most likely at a step after the formation of delta-aminolevulinic acid. The properties of erythroleukemia x lymphoma cell hybrids are compared with those of a series of erythroleukemia x bone marrow cell hybrids. The data indicate the possibility of multiply loci on the X chromosome capable of regulating the expression of erythroid characteristics.

Alterations in the protein synthetic apparatus of Friend erythroleukemia cells during their erythroid differentiation

The changes in rate of protein synthesis and cell division and the distribution of polyribosomes and globin mRNA on the polyribosomes of Friend erythroleukemia (FL) cells exposed to 2% DMSO and maintained at low cell density, were examined at different times after exposure to DMSO. The rate of protein synthesis and the capacity of cells to divide declined in concert to 50% of the level found in untreated cell cultures at 24 hours after exposure. Thereafter these rates recovered to 70% of the rate found in untreated control cultures until 96 hours post-exposure and then irreversibly declined as the cells lost the capacity to divide. The proportion of ribosomes present as polyribosomes in cells exposed to DMSO paralleled the capacity of these cells to synthesize protein. The distribution of polyribosomes analyzed by sedimentation in sucrose gradients demonstrated that a discrete, abundant class of polyribosomes composed of pentamers to heptamers appeared as early as 48 hours after exposure to DMSO. The appearance of an abundant class of polyribosomes was correlated with globin synthesis by demonstrating that a discrete class of polyribosomes arises in cells treated with the inducers hexamethylene bisacetamide and hemin.

Granulocyte differentiation by Friend leukemia cells

Friend leukemia cells growing in suspension culture are thought to represent a population of primitive erythroid cells which have undergone malignant transformation. We have found that when growing in vivo or in plasma clots in vitro, these suspension culture cells can exhibit morphologic and enzymatic properties which are characteristic of primitive granulocytic cells. The microenvironment in which the tumor cells grow plays a major role in determining the direction of differentiation of these leukemia cells. Hence it appears likely that the Friend cell is in fact a neoplastic pluripotent hematopoietic stem cell.

Site of initial glycosylation of mannoproteins from Saccharomyces cerevisiae

The cellular site of initial glycosylation of proteins from Saccharomyces cerevisiae has been studied. Short pulses of [U-14C]mannose label the ribosomal fraction of the yeast. Most of the label was associated with polysomes; monosomes contained only a small amount of radioactivity. All of the radioactivity present in the polysomal fraction was accounted by mannose and smaller amounts of glucose and glucosamine. Puromycin treatment detached more than 50% of the radioactivity from the polysomes; treatment of polysomes at pH 10.0 also caused the release of radioactivity. These results indicate that initial sugar binding occurs while the nascent polypeptide chains are still growing on the ribosomes. When the cells were preincubated with 2-deoxy-D-glucose, incorporation of [U-14C]mannose into the polysomes and the cell wall was inhibited, whereas its incorporation into membrane fractions was unimpaired. It was concluded that 2-deoxy-D-glucose inhibited the synthesis of glycoproteins by interference with the initial glycosylation steps at the ribosomal level.

Synthesis of erythrocyte-specific proteins in cultured friend leukemia cells

We have studied synthesis of specific proteins in two permanent lines of Friend virus-induced erythroleukemia cells (Friend line 745 and Ostertag line FSD-1, both derived from DBA/2 mice). By 96 hr following treatment with 1-2% dimethyl sulfoxide (Me2SO), up to 25% of the protein being synthesized by both these cultures is hemoglobin. At that time, hemoglobin constitutes up to 10% of the cellular soluble protein. Both lines synthesize heme and globin coordinately, and alpha and beta globin chains in a nearly balanced 1:1 ratio. However, the ratio of betaMajor:betaMinor chains synthesized by these induced Friend leukemia (FL) cells is approximately 9 in the FSD-1 line and 1.3 in the Friend Clone 745 line, whereas it is 4 in normal adult DBA/2 mouse erythrocytes. Evidence for the latter conclusion was obtained by electrophoresis of FL hemoglobins on cellulose acetate membranes, and also by chromatographic separation of alpha, betaMajor, and betaMinor globins on carboxymethylcellulose in 8 M urea at 20 degrees C. Carbonic anhydrase activity per mg protein is 3 times higher in induced than in control cultures. 2,3-diphosphoglyceric acid is not found in induced FL cells. Induced and control FL cells agglutinate strongly and equally with Phaseolus vulgaris phytohemagglutinin. The developmental process in these cultured leukemia cells appears to be an aberrant erythropoiesis.

Differentiation of erythroleukemic cells in vitro: irreversible induction by dimethyl sulfoxide (DMSO)

The inclusion of DMSO in the media of suspension cultures of Friend erythroleukemia cells results in the erythroid differentiation of these cells. The studies reported here were directed towards answering two questions. (1) How long an exposure to DMSO is necessary to induce the differentiation of these cells; and (2) What is the fate of the differentiating cells when DMSO is removed from the medium. Exposure to DMSO for less than 24 hours failed to produce any detectable evidence of erythroid differentiation. On the other hand, culture in the presence of DMSO for 24 hours followed by culture in DMSO-free medium for four additional days produced a small but detectable increment in the proportion of benzidine positive cells in the culture. Once the differentiation of an individual cell was initiated, the process continued after removal of DMSO from the medium. The cell became progressively more differentiated as evidenced by increases in the intensity of benzidine staining as well as the rate of heme synthesis and heme content. However, when cells which had been induced to differentiate by DMSO were cultured in DMSO-free medium for more than 3--4 days, they became vacuolated and apparently died. This latter phenomenon, as well as the more rapid proliferation of the undifferentiated cells in the culture, accounts for the observation that when new cultures are established from cultures which have been grown in the presence of DMSO for several days, the culture which results ultimately contains only differentiated cells.