Hemoglobin synthesis in murine virus-induced leukemic cells in vitro. 3. Effects of 5-bromo-2'-deoxyuridine, dimethylformamide and dimethylsulfoxide

Protein kinase Calpha plays a critical role in mannosylerythritol lipid-induced differentiation of melanoma B16 cells

Mannosylerythritol lipid (MEL), a novel extracellular glycolipid from yeast, was found to inhibit the proliferation of mouse melanoma B16 cells in a dose-dependent manner and to induce the apoptosis of B16 cells at concentrations higher than 10 microm (Zhao, X., Wakamatsu, Y., Shibahara, M., Nomura, N., Geltinger, C., Nakahara, T., Murata, T., and Yokoyama, K. K. (1999) Cancer Res. 59, 482-486). We show here that exposure of B16 cells to MEL (5 microm) for 2 days resulted in an increase of the levels of differentiation-associated markers of melanoma cells such as melanogenesis and tyrosinase activity, which were accompanied by morphological changes. The MEL-induced differentiation of B16 cells at this concentration was closely associated with arrest of the cell cycle at G(1) phase, but no significant population of apoptotic cells was identified. Expression of protein kinase Calpha (PKCalpha) was enhanced after exposure of B16 cells to MEL for 48 h. Antisense oligodeoxynucleotides against the mouse gene for PKCalpha prevented MEL-induced melanogenesis in B16 cells. Conversely, the effects of the expression of a constitutively active form of PKCalpha mimicked the effects of MEL on B16 cells. These data suggest that MEL, a yeast-derived glycolipid, triggers the differentiation of B16 melanoma cells through a signaling pathway that involves PKCalpha.

Growth-inhibitory and differentiation-inducing activity of dimethylformamide in cultured human malignant glioma cells

OBJECTIVE

To determine the growth-inhibitory and differentiation-inducing activity of dimethylformamide (DMF) on a human glioma cell line (SHG-44). DMF is a type of polar solvent and a potent differentiation-inducing agent in many kinds of human solid tumors, yet its effect on human glioma remains unclear.

METHODS

The effects of DMF on cell proliferation using 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, cell cycle distribution (with flow cytometry), colony-forming efficiency in double-layer soft agar, tumorigenicity in athymic nude mice, morphological changes, and glial fibrillary acidic protein expression were studied.

RESULTS

At dose ranges of 0.25, 0.5, 0.75, and 1.0%, DMF caused a dose-dependent proliferation inhibitory effect in monolayers and a marked dose-dependent suppression of colony-forming efficiency in double-layer soft agar with a complete loss of colony-forming ability in cells exposed to 0.75 and 1.0% DMF. Accumulation of cells in G0/G1 phases was observed in DMF-treated (0.5 and 1.0%) cells, also in a dose-dependent manner. SHG-44 cells exposed to DMF (0.5 and 1.0%) for 15 days changed morphologically from small spindle-shaped to large polygonal and flattened stellate cells with multiple slender processes. These cells were still tumorigenic in athymic nude mice, but the growth of xenografts was remarkably reduced, especially in the 1.0% DMF-treated group. The expression of glial fibrillary acidic protein was notably increased by DMF (0.5 and 1.0%). Washout experiments revealed that the effects of DMF on cell proliferation and cell cycle distribution were reversible.

CONCLUSION

Our results suggest that DMF drove the SHG-44 cells to a more mature phenotype with inhibited growth.

AIDS and transfer factor: myths, certainties and realities

At the end of the 20th century, the triumph of biology is as indisputable as that of physics was at the end of the 19th century, and so is the might of the inductive thought. Virtually all diseases have been seemingly conquered and HIV, the cause of AIDS, has been fully described ten years after the onset of the epidemic. However, the triumph of biological science is far from being complete. The toll of several diseases, such as cancer, continues to rise and the pathogenesis of AIDS remains elusive. In the realm of inductive science, the dominant paradigm can seldom be challenged in a frontal attack, especially when it is apparently successful, and only what Kuhn calls "scientific revolutions" can overthrow it. Thus, it is hardly surprising that the concept of transfer factor is considered with contempt, and the existence of the moiety improbable: over forty years after the introduction of the concept, not only its molecular structure remains unknown, but also its putative mode of action contravenes dogmas of both immunology and molecular biology. And when facts challenge established dogmas, be in religion, philosophy or science, they must be suppressed. Thus, results of heterodox research become henceforth nisi-i.e., valid unless cause is shown for rescinding them, because they challenge the prevalent paradigm. However, when observations pertain to lethal disorders, their suppression in the name of dogmas may become criminal. Because of the failure of medical science to manage the AIDS pandemic, transfer factor, which has been successfully used for treating or preventing viral infections, may today overcome a priori prejudice and rejection more swiftly. In science, as in life, certainties always end up by dying, and Copernicus' vision by replacing that of Ptolemy.

Repression of neu-induced clonogenicity by dimethylsulfoxide correlates with decreased levels of neu-encoded cell-surface p185 and changes in phosphotyrosine content of endogenous proteins

Treatment of neu-transformed fibroblasts with dimethylsulfoxide (DMSO), results in change in morphology and loss of clonogenicity. Although the total amount of neu-encoded p185 protein and mRNA remained constant after DMSO treatment, cell-surface p185 decreased by 60%, indicating that transmembrane p185 protein is not located in its physiological position. The aberrant location of p185 induced by DMSO resulted in increased tyrosine phosphorylation of p185 and concomitant decreased tyrosine phosphorylation of potential substrate proteins of p185 in the cell. However, the autophosphorylation activity of p185 in vitro was unaffected by DMSO. Thus, DMSO-induced loss of clonogenicity may be due to inappropriate location of p185, which prevents interaction between p185 and its substrates and therefore inhibits p185-mediated signal transduction pathway.

Cytoskeleton-dependent surface blebbing induced by the polar solvent N-methylformamide

In vivo and in vitro studies performed on the polar solvent N-methylformamide (NMF), as well as on its association with chemotherapeutic agents or X rays, have clearly demonstrated that this compound is capable of inducing changes in biological characteristics of tumor cells, e.g., cell differentiation. However, the mechanism of action of NMF is far from being elucidated. Hence, in order to better clarify such a mechanism an in vitro study was carried out by using mouse fibroblasts in primary culture (MEF) and human melanoma cultured cells (M14). Results obtained by immunocytochemical and ultrastructural methods with doses of NMF ranging from 0.1 to 7% are reported here. As a general rule, a different sensitivity (in terms of cytopathologic changes induced by NMF) was found between the cell types considered. In fact, melanoma cells appeared to be highly susceptible to the action of the drug, undergoing severe morphological modifications represented mainly by a reversible dose and time-dependent cell rounding and surface blebbing. In contrast, NMF-induced injury in MEF cells was characterized mainly by a simple retraction of the cell body. A cytochemical analysis of the expression of certain membrane antigens (e.g., glycoproteins, epidermal growth factor receptor, B2 microglobulin) in NMF-treated M14 cells undergoing blebbing was also carried out. A randomly distributed labeling of such molecules was observed. Accordingly, freeze-fracturing electron microscopic analysis also displayed a random distribution of intramembrane particles over the plasma membrane. When subcellular changes induced by the drug were investigated, a remarkable modification of cytoskeletal components was detected in both cell types. In particular, cross-linked actin microfilament bundles were easily observed in NMF-exposed MEF cells. Finally, when different experimental conditions which perturb calcium ion homeostasis or restore protein thiol group reduced state were analyzed, a noticeable impairment of the blebbing phenomenon was observed. Thus, a target effect of NMF on the microfilament system, probably leading, in turn, to several subcellular changes and cell surface blebbing, can be hypothesized. Such a cytoskeletal element-dependent cytopathology appears to be related to changes of the oxidized state of such molecules as well as to calcium ion perturbations.

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.

Anti-tumor and differentiation-inducing activity of N,N-dimethylformamide (DMF) in head-and-neck cancer xenografts

The anti-tumor activity of the putative differentiation-inducing agent dimethylformamide (DMF) was assessed in 7 head-and-neck xenograft (HNX) lines transplanted into nude mice. The drug was administered intra-peritoneally at the maximum tolerated dose. A significant growth-inhibitory effect was observed in 3 out of 7 tumor lines tested. When compared with 5 conventional drugs active in patients with squamous-cell carcinoma of the head and neck (HNSCC), DMF was as effective as the most active drugs (cisplatin and bleomycin). The most sensitive xenograft line, the poorly differentiated tumor HNX-14C, was used to test the hypothesis that differentiation induction might play a role in the anti-tumor activity of DMF. Light microscopic examination did not show clear-cut alteration of differentiation characteristics such as keratin and keratin pearl formation. Furthermore, we used a monoclonal antibody to study the expression of cytokeratin 10 which is useful as a differentiation marker of human HNSCC tumors. Keratin 10, not present in HNX-14C tumors grown under control conditions, became expressed in some cells upon DMF treatment. Further evidence for a differentiation-inducing activity of DMF was found in electron-microscopic studies. In treated HNX-14C tumors, in addition to cells with normal ultrastructural features, better-differentiated cells were observed, as manifested by an increase in the number of tonofilaments and desmosomes. The results show that DMF has a potential value for the treatment of patients with head-and-neck cancer, and that differentiation induction might play a role in the anti-tumor action of the drug.

Anion transport during maturation of erythroblastic cells

Bromide uptake was measured in single maturing erythroblastic cells of rabbits by means of X-ray microanalysis. Increase in bromide uptake as the cells matured was observed. The order of cells from low to high bromide uptake was: early erythroblast less than late erythroblast less than marrow red cells less than peripheral red blood cells. The transition from low to high bromide uptake is correlated to the accumulation of iron which begins in the late erythroblast. A decrease in rubidium uptake also occurs as iron accumulates in the cell. These results indicate that the anion and cation transport changes during maturation are parallel in time course but opposite in direction. In addition, the increase in bromide uptake can be accounted for by the increase in surface-to-volume ratios of the cells. Surface-to-volume ratios were estimated by morphometric techniques.

Modulation of cyclic AMP levels and differentiation by adenosine analogs in mouse erythroleukemia cells

Friend virus-transformed mouse erythroleukemia (MEL) cells can be induced to undergo erythroid differentiation by a variety of compounds, including dimethyl sulfoxide (DMSO) and the adenosine analog xylosyladenine. The present studies have monitored the effects of the stable adenosine receptor ligand N6-phenylisopropyladenosine (PIA) on induction of MEL cell differentiation. PIA has been previously shown to stimulate adenylate cyclase activity in rat hepatic and mouse Leydig 1-10 cells as well as inhibit adenylate cyclase in adipocytes. In the present study, PIA was ineffective as an inducer of the differentiated MEL cell phenotype. However, the results demonstrate that PIA inhibits the induction of MEL cell differentiation by DMSO and xylosyladenine. The extent of this inhibition as determined by benzidine staining, induction of globin RNA, and loss of self-renewal capacity was dependent on PIA concentration. The results also demonstrate that PIA induces a rapid and sustained increase in cyclic AMP (cAMP) levels. Furthermore, there was a highly significant correlation between cAMP levels and inhibition of xylosyladenine-induced differentiation (r = 0.962, P less than 0.0005). This relationship is further supported by the demonstration that prostaglandins E1 and E2 increase MEL cell cAMP levels and inhibit induction of the differentiated MEL cell phenotype. Moreover, PIA inhibited induction of MEL cell differentiation by butyric acid, diazepam, hypoxanthine, and the aminonucleoside analog of puromycin. These results suggest that cAMP may act as a negative regulatory signal in the induction of MEL cell differentiation.

Alkylformamides as inducers of tumour cell differentiation--a mini-review

The induction of terminal differentiation in tumour cells represents a possible therapeutic strategy for treating cancer. The alkylformamides are 1 group of experimental compounds which have been shown to induce terminal differentiation in human HL-60 leukemia and murine Friend erythroleukemia cells in vitro. Their mechanism of action is unknown. Dimethylformamide has been used as a model inducer in carcinoma and fibroblastic models. Analysis of the relationship between structure and inducing activity of the alkylformamides in vitro reveals that no specificity of structure exists and that their properties as inducers of terminal differentiation extend to related compounds, e.g. the alkylacetamides and alkylureas. This is in contrast to the marked specificity of N-methylformamide (NMF) as an in vivo antitumour agent. The potency of these compounds as inducers of differentiation is predictable and correlated with their molecular weight. High concentrations of NMF are required to induce differentiation in vitro and these concentrations are not achievable in vivo. However, while NMF is unlikely to be a useful inducer in vivo many of its higher MW analogues are very much more potent as inducers in vitro and yet no more toxic (to the host) in vivo. Some of these (e.g. tetramethylurea or 1,3-dimethylurea) may be capable of achieving inducing concentrations in vivo.

The anti-proliferative effect of lithium chloride on melanoma cells and its reversion by myo-inositol

The effect of LiCl on melanoma cell growth and differentiation was studied in mouse and human melanoma cell lines. LiCl markedly inhibited B16 and HT-144 melanoma cell growth in vitro. Clonogenicity in soft agar of the melanoma cells was also markedly inhibited by LiCl. Pretreatment of B16 mouse melanoma cells with LiCl delayed the appearance of melanoma tumours in syngeneic mice. Growth inhibition of cells was accompanied by morphological and biochemical alterations. LiCl induced cell enlargement and formation of dendrite-like structures. The activity of NADPH cytochrome c reductase, an enzymatic marker of endoplasmic reticulum was significantly (2-3 fold) increased. Addition of myo-inositol to cell cultures partially reversed the anti-proliferative and morphological effects of LiCl on melanoma cells. This finding may suggest that the anti-proliferative effect of LiCl is related to its effect on phosphatidylinositol metabolism.

Inhibitory effects of theophylline and dibutyryl cAMP on murine erythroleukemia cell differentiation

Murine erythroleukemia cells can be induced to differentiate by a variety of compounds. We have previously shown that 5'-methylthioadenosine, an inhibitor of cAMP phosphodiesterase, blocks induction of these cells. The present study demonstrates that theophylline, another cAMP phosphodiesterase inhibitor, also blocks murine erythroleukemia cell differentiation in a concentration-dependent manner. Northern blot analysis indicates that this agent inhibits accumulation of alpha- and beta-globin transcripts. These findings are extended by demonstrating that dibutyryl cAMP exerts similar effects. Furthermore, theophylline and dibutyryl cAMP are synergistic in inhibiting appearance of the mature erythroid phenotype. The results thus suggest that cAMP regulates induction of murine erythroleukemia cell differentiation.

Biological effects of acetamide, formamide, and their monomethyl and dimethyl derivatives

The industrial use of certain acetamides and formamides (particularly DMAC and DMF) for their solvent properties has resulted in rather extensive examination of their biological properties. Both DMAC and DMF are rapidly absorbed through biological membranes and are metabolized by demethylation first to monomethyl derivatives and then to the parent acetamide or formamide. Relatively high single doses to various species following oral, dermal, i.p., i.v., or inhalation exposures generally are required to produce mortality. The liver is the primary target following acute high level exposure, but massive doses can also produce damage to other organs and tissues. Repeated sublethal treatment by various routes also shows the liver to be the target organ with the degree of damage being proportional to the amount absorbed. With MMF, the potential usefulness as a cancer chemotherapeutic agent needs to be measured against the hepatotoxic effects produced in man. Acetamides and formamides are generally inactive in mutagenicity tests. Mammalian test systems do not appear to be genetically sensitive and DMF has been recommended for use as the vehicle in microbial assays designed to test for genetic activity of hard-to-dissolve chemicals. Embryotoxicity can be demonstrated at high doses; doses which generally show toxicity to the maternal animals. Structural abnormalities in sensitive species such as the rabbit are produced following exposure at near-lethal levels. The spectrum of abnormalities seen is broad and fails to show any time or site specificity in terms of developing organs/organ systems. Inhalation exposures to DMAC and DMF at levels producing some maternal toxicity in rats have produced no teratogenic response and only slight evidence of embryotoxicity. Long-term feeding of relatively high levels of acetamide produces liver cancer in rats. DMAC and DMF appear to be noncarcinogenic. The environmental toxicity of these chemicals is low. Liver damage can be produced by overexposure to these chemicals in man. Airborne concentrations need to be controlled and care should be taken to avoid excessive liquid contact as the chemicals are absorbed through the skin. A relationship exists between the amount of DMAC or DMF absorbed and the amount of MMAC or MMF excreted in the urine so that biomonitoring of the urinary metabolites can indicate situations in which total exposures, both dermal and inhalation, are excessive. An interaction between DMF and ethanol occurs such that signs, including severe facial flushing, appear when DMF-exposed individuals consume alcoholic beverages.

Growth inhibition of murine melanoma by butyric acid and dimethylsulfoxide

Treatment of B16-F10 melanoma cells with dimethylsulfoxide (DMSO) or butyric acid (BA) inhibits cell growth and delays tumor appearance in syngeneic mice. Both agents induce morphological changes in these cells. Treatment of melanoma cells with DMSO results in a marked increase in tyrosinase activity and melanin content. BA, on the other hand, does not increase melanin content and decreases tyrosinase activity. The data show that there are marked differences in the effect of DMSO and BA on melanin biosynthesis, whereas both agents inhibit cell growth and cause a delay in tumor appearance. These findings indicate that decreased proliferation of melanoma cells and induction of melanin biosynthesis are not necessarily associated phenomena.

The Hofmeister effect and the behaviour of water at interfaces

Starting from known properties of non-specific salt effects on the surface tension at an air-water interface, we propose the first general, detailed qualitative molecular mechanism for the origins of ion-specific (Hofmeister) effects on the surface potential difference at an air-water interface; this mechanism suggests a simple model for the behaviour of water at all interfaces (including water-solute interfaces), regardless of whether the non-aqueous component is neutral or charged, polar or non-polar. Specifically, water near an isolated interface is conceptually divided into three layers, each layer being I water-molecule thick. We propose that the solute determines the behaviour of the adjacent first interfacial water layer (I1); that the bulk solution determines the behaviour of the third interfacial water layer (I3), and that both I1 and I3 compete for hydrogen-bonding interactions with the intervening water layer (I2), which can be thought of as a transition layer. The model requires that a polar kosmotrope (polar water-structure maker) interact with I1 more strongly than would bulk water in its place; that a chaotrope (water-structure breaker) interact with I1 somewhat less strongly than would bulk water in its place; and that a non-polar kosmotrope (non-polar water-structure maker) interact with I1 much less strongly than would bulk water in its place. We introduce two simple new postulates to describe the behaviour of I1 water molecules in aqueous solution. The first, the 'relative competition' postulate, states that an I1 water molecule, in maximizing its free energy (--delta G), will favour those of its highly directional polar (hydrogen-bonding) interactions with its immediate neighbours for which the maximum pairwise enthalpy of interaction (--delta H) is greatest; that is, it will favour the strongest interactions. We describe such behaviour as 'compliant', since an I1 water molecule will continually adjust its position to maximize these strong interactions. Its behaviour towards its remaining immediate neighbours, with whom it interacts relatively weakly (but still favourably), we describe as 'recalcitrant', since it will be unable to adjust its position to maximize simultaneously these interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructural evidence of dimethylformamide-induced differentiation of cultured human colon carcinoma cells. Increased expression of desmosomes

N,N-dimethylformamide (DMF) induces differentiation of human colon carcinoma (DLD-1) cells in culture and reduces their tumorigenicity in nude mice. The current investigation analyzed DLD-1 (clone D) cells for ultrastructural evidence of differentiation. Examination of treated and untreated confluent monolayers by transmission electron microscopy revealed an occasional intracytoplasmic lumen indicative of adenocarcinoma. DMF-treated cells showed no signs of a toxic reaction. Cytoplasmic organelles were essentially unchanged except for an increase in tonofilaments and associated desmosomes. The number of desmosomes per unit length of contiguous cell border increased almost sixfold in treated monolayers. No other type of cell junction was seen. The increased frequency of desmosomes in DMF-treated cultures is significant because of the direct correlation known to exist between the number of desmosomes and degree of differentiation of some human carcinomas. Desmosomes serve as foci of cell adhesion and are reduced in number in some invasive tumors. Whether the supernumerary desmosomes in DMF-treated cells contribute to the reduction in malignant behavior of these cells in vivo remains to be determined.

The effect of induction of hemoglobin synthesis in cultured Friend cells on the number of initiation sites for replication and transcription

It was found that differentiation of murine erythroleukemia cells can be induced by 5-fluorodeoxyuridine (FudR), amethopterin and alpha-aminoisobutyrate. Each of these compounds is believed to delay the onset of DNA synthesis. Since relief of the FudR block to DNA synthesis by addition of thymidine can increase the number of initiation sites for replication (Taylor, 1977), the effect of various inducers and inhibitors of differentiation of Friend cells upon the relative number of initiation sites for replication and transcription was investigated. Very efficient inducers of hemoglobin synthesis, hexamethylene bisacetamide (HMBA) and dimethylsulfoxide (DMSO), increase the number of initiation sites for transcription and HMBA also increases the number of functional initiation sites for replication. Two other compounds that induce differentiation of Friend cells, low levels of actinomycin D and FudR, did not increase the number of initiation sites for transcription. Compounds that prevent induction of hemoglobin synthesis by HMBA and DMSO include 5-bromodeoxyuridine (BrdU) and novobiocin. Both of these compounds were found to decrease the number of functional initiation sites for transcription and it is known that both compounds reduce the number of initiation sites for replication. The relation between initiation of replication and transcription, and its effect upon differentiation of erythroleukemia cells is discussed.

Factors affecting the CEA secretion of human adenocarcinoma cell lines into the spent medium

CEA producing cell lines were established from human gastric cancer (HGC-Y1), pancreatic cancer (HPC-Y9) and lung cancer (HLC-Y1). The culture medium was used RPMI-1640 supplemented with 10% fetal bovine serum. The secretion of carcinoembryonic antigen (CEA) into the spent medium from these cultured cell lines was modified by several factors, such as theophylline, cyclic AMP (cAMP), dibutyryl cyclic AMP (dbcAMP), Bromodeoxyuridine (BrdUrd), dimethyl sulfoxide (DMSO), Prostaglandin E2 (PGE2) and human interferon (INF). CEA secretion was enhanced by theophylline, cAMP, PGE2 and INF. Theophylline had an optimal dose to maximally enhance CEA secretion. cAMP and INF apparently enhanced CEA secretion dose dependently. PGE2 appeared to enhance CEA secretion, although cell growth was markedly suppressed dose dependently, dbcAMP, DMSO and BrdUrd did not affect CEA secretion. Here, the kinetics of CEA secretion was discussed.

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.

Effects of dexamethasone and phorbol myristate acetate on the induction of differentiation in mouse erythroleukemic cells by dimethyl sulfoxide, proteases, and other compounds

Lines DS-19 and 5-86, each derived from line 745, when tested for their responses to various inducers and inhibitors of differentiation, shared some characteristics, but differed in others. In particular, DS-19 was markedly induced to differentiate by actinomycin D whereas 5-86 was only slightly affected. The patterns of the ability of PMA to influence induction and cell multiplication by various inducing agents differed in the two lines. The pattern of DEX inhibition of differentiation was similar in the two lines. Notably, DEX markedly inhibited induction due to all of the inducers tested except protease V8, actinomycin D, PGE1, and butyrate and its fatty acid analogues that were tested. DEX stimulated growth during its inhibition of induction by DMSO and many other inducers, but reduced cell multiplication in the presence of butyrate. PMA inhibited induction by most of the inducers tested in DS-19 cells except for some of the fatty acids. The inhibition by PMA generally was accompanied by cytotoxicity in DS-19 cells, but not in 5-86 cells. PMA markedly inhibited differentiation by only 5 of the inducing agents tested in 5-86 cells, but was not as cytotoxic in this line. Proteases, which have been shown to stimulate both MEL cell differentiation and growth, are inhibited with respect to their effects on differentiation, but not with respect to those on growth by DEX and/or PMA. DEX did not have the same effect on induction stimulated by the two proteases studied. Many of these findings indicate that at least some effects by inducers on cell multiplication in this system are not inextricably linked to differentiation. It is hoped that the further study of induction by proteases, which have known enzymatic activities, as well as of inhibitors of induction, will shed light on the molecular mechanism(s) of action of DMSO and other low molecular weight inducers.

Induction of leukemia cell differentiation by chemotherapeutic agents

The antineoplastic agents marcellomycin (and related anthracycline antibiotics) and 6-thioguanine are effective inducers of the differentiation of cultured leukemia cells. Studies designed to investigate the relationship between structure and activity conducted with the anthracyclines in HL-60 human acute promyelocytic leukemia cells indicated a dissociation between cytotoxicity and maturation-inducing properties of these agents. In an analogous manner, 6-thioguanine induced effective erythroid and granulocytic differentiation of Friend and HL-60 leukemias, respectively, only in hypoxanthine-guanine phosphoribosyltransferase deficient cells. These findings suggest that 6-thioguanine need not be metabolized to a nucleotide to be active as an inducer of differentiation, and that the concentration of the 6-thiopurine required to initiate the commitment to maturation is greater than that producing cytotoxicity. Erythrodifferentiation of HGPRT negative Friend murine leukemia cells by 6-thioguanine was antagonized by tetracaine, d, 1-propranolol and 12-O-tetradecanoylphorbol-13-acetate, providing evidence for a cell membrane mediated component in the action of the purine antimetabolite. This suggests that the biochemical events that produce differentiation after exposure to 6-thioguanine may differ from those responsible for the toxic actions of the drug. Studies such as these, designed to gain an understanding of the target sites of inducers of differentiation, may lead to the development of new agents of potential therapeutic benefit in the treatment of certain forms of cancer based on the conversion of malignant cells to their non-proliferating mature counterparts.

Perturbation of the switch-on of transcriptase activity in intermediate subviral particles from reovirus

Intermediate subviral particles (ISVP) derived from reovirus represent a simple model system for the switch-on of transcriptase function. In such particles the endogenous transcriptase is present in a switched-off form, one step removed from the switched-on state. Switch-on of transcriptase function is an active process in this system and can be triggered by K+ions. A variety of agents which affect gene expression in cells were tested for an effect on switch-on in ISVP. Marked effects on switch-on in ISVP were observed with a diverse group of test agents, including DMSO and other solvents, BUdR, TdR, caffeine, theophylline, and temperature. The correlation in response between ISVP and cells suggests that the ISVP system may be useful as a model for studying the biochemical mechanisms underlying the perturbative effects of such agents on gene expression in cells.

Modification of the response of mouse skin to x-irradiation by a polar solvent, N,N-dimethylformamide

The modification of the response of mouse skin to either single or split (24 hrs) graded doses of X rays by topically applied N,N-dimethylformamide (DMF) was investigated. DMF was applied daily for 5 days prior to irradiation. At a radiation dose level producing dry desquamation, DMF enhanced the X ray response by a factor of 1.3. Also, at the same level of response, the fraction of X ray dose repaired in 24 hours was 0.57, whereas for the DMF-treated and irradiated skin, this factor was 0.41, indicating a reduction of about 28% in subeffective damage repair. The times of maximal involvement of the skin reactions were not different in the X ray plus DMF treated mice versus mice receiving x-irradiation only. The data indicate that DMF is able to modify intrinsic radiation sensitivity of mouse skin epithelial cells, possibly through a reduction in the magnitude of the shoulder region of the survival curve.

Lipid composition of Friend leukemia cells following induction of erythroid differentiation by dimethyl sulfoxide

The effects of dimethyl sulfoxide (DMSO)-induced differentiation of Friend leukemia cells in vitro on the lipid composition of these cells have been examined. DMSO had no early effect on the incorporation of either [14C]glycerol or [3H]methyl choline chloride into the total lipids or individual phospholipids of Friend cells up to 240 min after addition of the inducer. Examination of DMSO-differentiated Friend cell phospholipids revealed a percentage composition which was similar to control cells, with phosphatidylcholine and phosphatidylethanolamine in both uninduced and differentiated cells accounting for over 75% of the total phospholipid. Sphingomyelin levels were significantly lower in Friend cells than in normal adult mouse erythrocytes, and differentiation of murine erythroleukemia cells resulted in a further lowering of this phospholipid. In contrast, a significant increase in the level of phosphatidylethanolamine occurred as a result of maturation. Fatty acid analysis of major lipid classes of differentiated Friend cells showed significant reduction in saturation, but no alteration in chain length in comparison to undifferentiated cells. A pronounced decrease in the cellular content of both free and esterified cholesterol, which resulted in a 45% decrease in the ratio of cholesterol/phospholipids, occurred in cells differentiated by the polar solvent. The findings indicate that erythrodifferentiation induced by DMSO results in a variety of changes in the lipid composition of the membranes of Friend leukemia cells.

The effect of hexamethylene-bis-acetamide on multiparameter analysis of Friend leukemia cells

Friend leukemia cells were induced to differentiate by hexamethylene-bis-acetamide (HMBA). The relationship between cell growth cell volume distribution, fluorescence intensity and fluorescence anisotropy of the membrane probe 1,6 diphenyl 1,3,5 hexatriene (DPH) was analyzed in differentiated and undifferentiated cells with the aid of the fluorescence activated cell sorter (FACS II). The induction of a differentiated state was associated with a decrease in cell volume and an increase of fluorescence anisotrophy. The inhibition of this induction by dexamethasone prevented the decrease of cell volume without affecting the increase of fluorescence anisotropy. We conclude therefore that the high degree of anisotropy is not correlated to the differentiated state nor with the volume of the cells.

Induction by butyrate of differentiated properties in cloned murine rhabdomyosarcoma cells

A cell line derived from the murine rhabdomyosarcoma BW10139 (Dexter, Cancer Res. 37: 3136, 1977) was subcloned and examined with respect to growth and myogenic characteristics in the presence and absence of 1 mM butyrate. Without butyrate, these cells behave as typical transformed cells: they grow rapidly and chaotically, do not form multinucleated muscle fibers and have little or no creatine kinase activity. In the presence of 1 mM sodium butyrate or butyric acid, growth slows, cells become arranged in whorl patterns, and creatine kinase activities increase to levels comparable to those found in normal chick myoblasts immediately prior to cell fusion. The increase in creatine kinase activity is detectable within 2 h exposure to butyrate, reaches a maximum by 24 h, and the elevated level can be maintained for at least six weeks. The induction is reversible upon sequential addition, deletion, and readdition of butyrate to the culture medium. Isoenzyme analyses demonstrated that only the BB form of creatine kinase is induced; MM creatine kinase was not detected. Although formation of multinucleated cells increases after exposure to butyrate, no typical myotubes form. The results suggest that this rhabdomyosarcoma cell line can, under appropriate conditions, re-express some properties characteristic of skeletal muscle, but not the complete muscle phenotype.

Variations in the response of cloned murine friend erythroleukemia cells to different inducers

Cells of the line 3BM-78 derived from murine bone marrow cells infected in vitro with polycythemic Friend leukemia virus (FLV-P) produce virus with spleen focus-forming activity (SFFV) and can be induced to synthesize hemoglobin. Fifteen clones, isolated from this line, have been analyzed in detail for the effect of different inducing agents (dimethyl-sulfoxide, DMSO; hexamethylene bisacetamide, HMBA; and sodium butyrate, SB) on the synthesis of hemoglobin and virus at the clonal level. All the clones proved to be inducible with one or more of the agents, but the degree of the response depended on the type and concentration of the agent used. In general, the effectiveness of the agent--within the usual range of concentration for induction--both for hemoglobin and for virus synthesis, was in the order HMBA greater than DMSO greater than SB. Reverse transcriptase activity was, however, more easily induced than hemoglobin synthesis in that stimulation was seen at lower concentrations of the same inducing agent. This clonal analysis confirmed that virus and hemoglobin production are regulated independently in these erythroleukemic cells chronically infected with FLV-P.

Membrane dynamics of Friend leukaemic cells. II. Changes associated with cell differentiation

In a previous study, using fluorescence polarization (P) with diphenyl hexatriene (DPH), it was shown that growing and resting cells have different P-values. This property has now been used to investigate the membrane action of dimethylsulfoxide (DMSO) and hexamethylene bisacetamide (HMBA), two inducers of Friend leukaemic cell (FLC) differentiation. Both an inducible cell line (FLC) and a resistant variant cell line (RFLC), had the same characteristics regarding P-values. During the differentiation process in the FLC cell line, further changes in P-values were observed. In the resistant cell line, these changes in P-value were not seen. This suggests that these inducers of differentiation are acting at the cell membrane.

Hypomethylation of DNA during differentiation of Friend erythroleukemia cells

DNA from mammalian cells has been shown to contain significant amounts of 5-methyl cytosine resulting from enzymatic transfer of methyl groups from s-adenosylmethionine to cytosine residues in the DNA polymer. The function of this modification is not known. We have found that DNA synthesized during chemically induced differentiation of friend erythroleukemia cells is hypomethylated, as measured by its ability to accept methyl groups transferred by homologous DNA methyltransferases in vitro. The extent of hypomethylation detected by this sensitive method is small, a decrease of less than 1.6 percent in 5-methylcytosine content. Hypomethylated DNA can be isolated from friend erythroleukemia cells grown in the presence of dimethyl sulfoxide, butyrate, hexamethylene-bis- acetamide, pentamethylene-bis acetamide, and ethionine. However, hypomethylated DNA is found only under conditions where differentiation is actually induced. DNA isolated from cells of a dimethyl sulfoxide- resistant subclone grown in the presence of that agent is not hypomethylated, although DNA of these cells becomes hypomethylated after growth in the presence of inducers that can trigger their differentiation. We also find that the DNA of friend erythroleukemia cells does not become hypomethylated when the cells are exposed to inducing agents in the presence of substances that inhibit differentiation. These results suggest a close link between genome modification by methylation and differentiation of friend erythroleukemia cells.

Localization of globin gene replication in Friend Leukemia cells to a specific interval of the S phase

Murine erythroblastic leukemia cells, infected with Friend leukemia virus, were grown and synchronized in suspension culture by a double-block procedure involving medium depletion and treatment with excess thymidine. Replicating cultures were then caused to synthesize DNA during the early, middle, or late third of the S period with bromodeoxyuridine as a precursor. The bromodeoxyuridine density-labeled DNA and normal DNA were isolated by sedimentation in a cesium chloride density gradient and analyzed for the level of globin-specific DNA by hybridization with radioactive cDNA of the globin messenger RNA. Globin genes were found to be replicated near the end of the middle third of the S phase. The incorporation of bromodeoxyuridine into DNA also resulted in a lowered induction of hemoglobin synthesis in dimethyl sulfoxide-treated cells. In this case, the sensitivity was correlated with the introduction of bromodeoxyuridine into DNA replicated in early S phase. The possibility that this fraction of DNA, which is low in globin gene content, carries genes regulating the erythroid differentiation or the expression of globin genes is discussed.

Chemical inducers of differentiation in Friend leukaemia cells inhibit lymphocyte mitogenesis

Several phorbol esters, the potent tumour-promoting agents isolated from croton oil, induce proliferation of human lymphocytes and enhance the mitogenic effect of lectins on bovine lymphocytes. While studying the mitogenic properties of one of these agents, phorbol myristate acetate (PMA), we found that dimethyl sulphoxide (DMSO), frequently used as a solvent for PMA, markedly inhibits PMA-induced mitogenesis at DMSO concentrations that have little effect on phytohaemagglutinin (PHA)-induced responses. DMSO, as well as a variety of other organic compounds, induce erythroid differentiation in Friend leukaemia (FL) cells. Phorbol esters, on the other hand, are potent inhibitors of both spontaneous and induced cellular differentiation. We therefore investigated the relationship between the potency of compounds to induce erythroid differentiation in FL cells and their potency to inhibit lymphocyte proliferation induced by PMA and other mitogens. We report here that many of the compounds that induce erythroid differentiation in FL cells are similar to DMSO in selectively suppressing PMA-induced lymphocyte mitogenesis.

Induction of differentiation of murine erythroleukemia cells by aminonucleoside of puromycin and inhibition of this induction by purines and purine derivatives

The effect of the aminonucleoside of puromycin (AMS) on Friend erythroleukemia cells in culture was investigated, because purines and purine analogues are known to act as inducers of differentiation. After treatment with 20-30 micro M AMS for 4 days, the cultures contained between 80 and 90% benzidine-positive cells. Stimulation of hemoglobin synthesis was dose and time dependent. Inosine had no stimulatory activity; however, when it was added to the medium together with AMS, erythroid differentiation was almost completely inhibited. The inhibitory effect of inosine on this potent inducer was also dose and time dependent. No cytotoxicity was observed with either compound, alone or in combination. Inhibition of AMS stimulation of erythroid differentiation was also observed in the presence of inosine monophosphate and poly(inosinic acid). Hypoxanthine had a dual effect. At high concentrations (500 microgram/ml) it acted as an inducer, but when added at low concentrations (20 microgram/ml) together with AMS it inhibited differentiation. These findings suggest there is a link between purine biosynthesis and the event(s) required to trigger differentiation. Agonist-antagonist activity of closely related biological compounds has thus been revealed in the erythroleukemia cells.

Inhibition of Friend erythroleukemic cell differentiation by bromodeoxyuridine: correlation with the amount of bromodeoxyuridine in DNA

These studies were undertaken to examine the relationship between the inhibition by 5-bromodeoxyuridine (BrdU) of erythroid differentiation in Friend erythroleukemia cells and the incorporation of BrdU into DNA. Experiments were carried out in which the incorporation of BrdU into DNA and the concentration of BrdU to which the cells were exposed were varied independently of each other. In addition, the ability of deoxycytidine (dC) to reverse the effects of BrdU on hemoglobin production and to reduce the amount of BrdU in DNA was analyzed. Under all the conditions tested, the effects of BrdU were correlated with the amount of BrdU incorporated into nuclear DNA. These results differ from those of recent studies on the inhibition of pigmentation and the induction of mutations by BrdU in Syrian hamster melanoma cells. The results suggest that BrdU may be producing its biological effects by a variety of different mechanisms.

Alterations in chloride transport during differentiation of Friend virus-transformed cells

Friend erythroleukemic cells can be induced by a variety of agents to synthesize hemoglobin and to exhibit other characteristics suggesting erythroid maturation. Upon induction of hemoglobin synthesis with dimethylsulfoxide (DMSO), the chloride flux in Friend cells gradually increases, until after five days of exposure to DMSO (when the hemoglobin content of the cells approaches that of the mature erythrocyte) the flux is three times the value in non-induced cells. A similar flux increase is observed in the presence of a different type of inducer, hypoxanthine, but no increase in flux is seen in the mutant cell line, TG-13, which does not synthesize hemoglobin after DMSO treatment. Thus, the flux increase seems to be associate d with the induction process, rather than being a direct effect of the inducing agent. After DMSO treatment, the sulphate flux decreases and the chloride/sulphate selectivity increases, aswould be expected if the cells were becoming more like red cells. On the other hand, the sensitivity of the chloride flux to the inhibitor, furosemide, and to temperature is the same in the induced as in the non-induced Friend cells, and different from that of the mature red cell. Thus, the anion transport properties of the induced Friend cell are different from those of both the non-induced Friend cell and the mature erythrocyte. Either the system in the induced cell represents an intermediate stage in the development of the mature red cell characteristics, or else the maturation of transport function in the Friend cell differs from that in normal erythrocyte precursors.

Perturbation of growth and differentiation of Friend murine erythroleukemia cells by 5-bromodeoxyuridine incorporation in early S phase

Cultured Friend murine erythroleukemia cells (Friend cells) are induced to undergo erythroid differentiation when grown in the presence of dimethylsulfoxide (DMSO) and other compounds. The effects of unifilar substitution of bromouracil (BU) for thymidine in the DNA (BU-DNA) of Friend cells were examined. Cells were grown in the presence of 5-bromodeoxy-uridine (BrdU) for one generation, then centrifuged and resuspended in medium containing DMSO without BrdU. These cells exhibited a delay in the appearance of heme-producing, benzidine-reative (B+) cells and a decreased rate of cell proliferation in comparison to the control not containing BU-DNA. A transient inhibition of entry into S phase was observed when control cells or cells containing BU-DNA were grown in the presence of DMSO) for 10 to 20 hours. This transient inhibition was increased in the BrdU culture. Thus BU-substitution in Friend cells alters other cellular functions in addition to erythroid differentiation. The rate of increase in the percent of cells committed to differentiate (those forming B+ colonies in plasma clots) was similar in the BrdU and control cultures until 40 to 50 hours. After this time, a delay in the appearance of committed cells was observed in the BrdU culture. The effect of BrdU on the appearance of B+ cells was more pronounced and occurred earlier than its effect on the rate of commitment. Therefore, the delay in the appearance of B+ cells in the BrdU culture was due primarily to perturbation of post-commitment events such as the accumulation of hemoglobin. We also examined the effect on growth and differentiation after BrdU was incorporated during different intervals of S phase in cells synchronized by centrifugal elutriation or by double thymidine block and hydroxyurea treatment. The delay in the appearance of B+ cells and inhibition of cell proliferation were only observed when BrdU was incorporated in the first half of S phase. BrdU (10 muM) had no effect on growth or differentiation when present during late S or G1 and G2. These results, using two very different methods to achieve cell synchrony, indicate that the effects of BrdU on growth and differentiation described above are due to its incorporation into DNA sequences replicating during early S.

Possible role of glucocorticoid receptors in globin gene expression in differentiating Friend cells

Previous studies from this laboratory have shown that the expression of globin genes during the dimethyl sulfoxide-induced differentiation of T3C12 Friend erythroleukemia cells in inhibited by dexamethasone and related glucocorticoids. The present report shows that dexamethasone exerts a similar effect on the accumulation of globin mRNA and hemoglobin in differentiating GM86 Friend cells, but that these cells are less sensitive to this hormone. The higher sensitivity of T3C12 cells has been correlated with the presence of 6 times as many cytoplasmic glucocorticoid receptors as in the GM86 cells. The receptors of T3C12 cells have been shown to have properties in common with glucocorticoid receptors found in other tissues. It is proposed that these receptors may be responsible for the steroid control of the globin genes in Friend cells.

Proteins of BrdU-dependent hamster cell lines as characterized by two-dimensional gel electrophoresis

Cell lines which exhibit the BrdU-dependent phenotype (B4 and HAB) were studied with respect to BrdU-induced alterations in genetic expression by two-dimensional gel electrophoresis. A comparison of the proteins from the HAB cells, in which the DNA is 100% substituted by BrdU, to those of the unsubstituted parent line (3460) showed 55 protein alterations; the synthesis of 15 increased while that of the other 40 decreased. When 3460 cells were grown in BrdU such that their DNA was greater than 50% substituted, 27 protein changes could be detected; of these, the synthesis of 10 increased while that of 17 decreased. A comparison of all these changes in the various cell lines showed six which were common to the BrdU-substituted cell lines. The proteins from another Syrian hamster cell line, BHK-21 (C-13) and those of HAB cells grown in thymidine or BrdC were also examined on two-dimensional gels. Although BrdU has a dramatic effect on many cellular functions, relatively few changes in the pattern of protein synthesis could be detected in these cell lines, perhaps reflecting the specialized action of this analogue on particular cellular functions.

Induction of erythroid differentiation in Friend leukemia cells by bromodeoxyuridine

Treatment of Friend leukemia cells with BrdU, the thymidine analog which interferes with DMSO induced differentiation in these cells as well as the expression of differentiated character in many other cell systems, is capable of inducing erythroid differentiation. Globin mRNA, as assayed by hybridization to globin cDNA, increases 2.5- to 30-fold after appropriate treatment with BrdU. This effect was observed with several different subclones of three independent Friend tumor cell lines. After BrdU treatment, globin mRNA content may reach up to 10-20% of the levels in DMSO induced cultures. The induction of erythroid differentiation is also apparent when accumulated heme content or the appearance of benzidine positive cells is monitored. One Friend cell line (745) we examined was not induced by BrdU although it incorporated an amount of BrdU into its DNA comparable to that incorporated by the other cell lines. In addition, BrdU did interfere with DMSO induction in this cell line. These results suggest that two different mechanisms may be operative in regulating erythroid differentiation in Friend leukemia cells. While BrdU interferes with the mechanism activated by DMSO treatment, this analog could independently activate an alternative mechanism.