Activation of cell membrane enzymes in the stimulation of cell division

Effects of growth factors on the enzymes of purine metabolism in culture of regenerating rat liver cells

Hepatocytes are affected by many cytokines and growth factors during liver regeneration. In regenerating rat liver cells cultures, liver cell growth factor (LCGF), hepatic stimulator substance (HSS), interleukin-1 beta (IL-1 beta), as well as their combination, were tested for their ability to activate the enzymes involved in purine metabolism. The enzymes tested were 5' nucleotidase, AMP deaminase, adenosine deaminase and xanthine oxidase. The cytokines alone or in combination, activated 5' nucleotidase and adenosine deaminase. Activity of AMP deaminase was stimulated by IL-1 beta associated with LCGF, HSS and IL-1 beta. Xanthine oxidase was stimulated by IL-1 beta but not with HSS and LCGF. Associated with IL-1 beta these two substances decreased its activity. A novel approach to the understanding of the mechanisms involved in the regulation of purine metabolism during liver regeneration, is proposed.

Membrane fractions display different lipid and enzyme content in three cell types in 16-cell stage embryos of sea urchins

Three cell types were isolated from dissociated 16-cell sea urchin embryos. Four membrane density fractions from discontinuous gradients have different proportions of lipids, surfacer markers and enzymes for the three cell types. Assays of lipid content, CH/PLIPID and SPH/PC ratios, acyl chain length, level of unsaturation by proton NMR and assays of enzyme activity revealed variation at the same density between the three cell types and among different densities from one cell type. There were also differences between whole embryos and dissociated embryo cells. There was no typical membrane domain at a particular density common to the cell types. Cell surface characteristics and polarity of adult cells rely on which lipid domains and enzymes are present, their association with cytoskeleton and how they are localized. At the 16-cell stage these characteristics are still very dynamic as revealed by cytochemical localization of Na+/K(+)-ATPase which varied with cell type and suggests endocytosis at set times in the division cycle. Polarity has not been permanently set for Na+/K(+)-ATPase yet. Membrane enzyme and lipid distributions unique to the three cell types seen in this study suggest parcelling out or insertion of new membrane domains occurs during early sea urchin cleavage. Perturbation of membrane density distribution and lipid content occurs after treatment of embryos with animalizing and vegetalizing teratogens which alter development.

5-nucleotidase activity in cultured cell lines. Effect of different assay conditions and correlation with cell proliferation

The 5-AMPase activity of the ectoenzyme 5-nucleotidase has been measured in a variety of cell lines, using intact cells. Human cell types showed two orders of magnitude higher enzyme activity than mouse cell lines. The ectoenzyme is inhibited by adenosine 5-(alpha, beta-methylene) diphosphate and Concanavalin A. A different extent of 5-nucleotidase lectin inhibition was observed in the studied cell lines, suggesting that the corresponding ectoenzymes are glycoproteins with a different type or degree, or both, of glycosylation. The 5-nucleotidase activity increased during subculture and decreased after cell transformation. Generally, the 5-nucleotidase activity was two- to five-fold higher in monolayer than in suspension cell culture. A relation between cell growth and 5-AMPase activity was also observed. Enzyme activity increased at the end of the lag phase (glioblastoma cells) or during the exponential phase (the other two cell lines). After confluence, the activity decreased to the initial or even lower range of activity. Observed activity variations with cell proliferation correlate with modifications of 5-AMPase activity during subculture.

Reduced Na+ + K+-ATPase activity in peripheral nerve of streptozotocin-diabetic rats: a role for protein kinase C?

Six weeks after induction of diabetes, the rate of ouabain-sensitive 86Rb+ accumulation, a parameter which reflects Na+ + K+-ATPase pumping activity, was significantly reduced in endoneurial preparations of sciatic nerve from untreated diabetic rats compared with that in control rats (Trial, 1, 0.19 +/- 0.09 versus 0.48 +/- 0.13 pmol/min per mg wet weight of tissue, p less than 0.001; Trial 2, 0.27 +/- 0.16 versus 0.47 +/- 0.18, p less than 0.01). This decrease in ouabain-sensitive 86Rb+ uptake was not observed in nerves from diabetic rats maintained on sorbinil (an aldose reductase inhibitor) or myo-inositol diets. Protein kinase C activity was demonstrated in the soluble fraction of a sciatic nerve homogenate by assaying for lipid-activated, Ca+-dependent phosphorylation of calf thymus histone. No significant difference in the time course of kinase C activity was observed between cytosol fractions of nerve homogenates from control and diabetic rats (control, 6.22 +/- 0.97 pmol 32P incorporated/mg cytosol protein in 50 min; diabetic, 5.32 +/- 0.71). Three low molecular weight neural proteins (each with Mr less than 29,000) were identified as substrates for protein kinase C.

Alteration of calcium transport by tumor promoters, 12-O-tetradecanoyl phorbol-13-acetate and p,p'-dichlorodiphenyltrichloroethane, in the Chinese hamster V79 fibroblast cell line

Effects of two tumor promoters, 12-O-tetradecanoyl phorbol-13-acetate (TPA) and p,p'-dichlorodiphenyltrichloroethane (DDT), on cellular calcium regulatory mechanisms were studied by using the Chinese hamster V79 fibroblast cell line. Both compounds at concentrations known to inhibit cell-cell communication, increased the cellular 45Ca2+ uptake and inhibited its efflux. DDT inhibited Ca,Mg-ATPase of the plasma membrane, while TPA stimulated cellular uptake of Ca2+. A working hypothesis has been proposed that the increase in intracellular concentration of Ca2+ by the action of these chemicals directly results in the closure of the central opening of the gap junction, and thereby causing a cessation of gap junction-mediated intercellular communication.

Lack of correlation between effects of tumor promoter TPA on plasminogen activator production, phosphatidyl choline synthesis, and hexose transport in mammalian cell culture systems

We have investigated the effects of the tumor promoter 12-0-tetradecanoyl-phorbol-13-acetate (TPA) on plasminogen activator production, hexose transport and metabolism, and the incorporation of choline into the acid soluble pool and into phosphatidylcholine in suspension cultures of mouse L, mouse P388 leukemia, human HeLa, and Chinese hamster ovary cells, and in monolayer cultures of baby hamster kidney (BHK), mouse 3T3, mouse 3T6, and mouse P388D1 macrophage-like cells. BHK, 3T3, P388D1, and P388 cells produced plasminogen activator constitutively, but no significant production was observed in the other cell lines. Plasminogen activator production was induced or stimulated by TPA only in P388 cells (10- to 20-fold by 100 ng TPA/ml). On the other hand, phosphatidylcholine synthesis was stimulated by TPA only in HeLa cells, and hexose transport, as measured with 3-0-methyl-D-glucose, only in 3T3 and P388D1 cells, as well as in human lymphocytes. The stimulation of hexose transport occurred more rapidly than the induction of plasminogen activator production and seemed to be part of the mitogenic response of cells to TPA treatment. A stimulation of deoxyglucose uptake was similarly limited to 3T3 and P388D1 cells. A significant decarboxylation of carbon 1 of deoxyglucose occurred in P388 and P388D1 cells, but not in Novikoff cells, and any decarboxylation that occurred was not stimulated by TPA. The results indicate that the various investigated responses of cells to TPA are unrelated and occur independent of each other. The time courses of the biochemical responses also differ significantly.

Binding of phorbol-12-myristate-13-acetate to cultured myoblasts

The tumor promoter phorbol 12-myristate 13-acetate (PMA) binds in a rapid (maximal at 30 min), reversible, and non-saturable manner to cultured embryonic chick myoblasts. Serum was not required for binding although it promoted the release of PMA from the cells. This appears to be due to PMA binding to serum proteins. At any concentration tested, approx. 10% of the total PMA was bound at 5 min and 30% was bound at 30 min. It is estimated that a PMA concentration in the cell membrane of only 1 molecule of PMA/5000 molecules of membrane lipid elicits maximal biological responses in these cells.

Tumour promoter uncouples beta-adrenergic receptor from adenyl cyclase in mouse epidermis

Alterations in beta-adrenergic receptor number and function and in the hormonal responsiveness of adenylate cyclase have been observed in transformed cells, and tumours. Phorbol myristate acetate (PMA), a potent tumour promoter in mouse skin, induces a dramatic loss of epidermal responsiveness to catecholamines in vivo, although basal levels of cyclic AMP are not affected. In other work we have shown that PMA treatment does not alter the number or affinity of epidermal beta-receptors, although accumulation of cyclic AMP in response to isoprenaline injection is sharply inhibited. Evidence is presented here that PMA exerts this effect by uncoupling epidermal beta-receptors from adenylate cyclase.

Tumor promoters induce changes in the chick embryo fibroblast cytoskeleton

We have examined the effect of the tumor promoter, 12-0-tetradecanoyl phorbol-13-acetate (TPA), on the actin-containing elements of the cytoskeleton of chick embryo fibroblasts (CEF). TPA at concentrations as low as 7.3 times 10-10M indices a reversible change in the cytoskeleton as visualized by indirect immunofluorescence using anti-actin antibodies. Cells incubated with TPA lose the ordered actin-containing structures found in normal cells and resemble Rous sarcoma virus-transformed cells in that the immunofluorescent actin pattern is diffuse. The TPA effects are both dose-and time-dependent. Analogs of TPA which are inactive as tumor promoters do not induce cytoskeletal changes at the concentrations tested, while a second tumor promoter, PDD, is also able to cause alterations in actin-containing structures. The action of TPA requires de novo synthesis of both RNA and protein. The direct cytoskeletal changes are neither plasmin-dependent nor subject to inhibition by incubating the cells with high levels of protease inhibitors during the exposure to TPA. However, plasminogen does increase the sensitivity of cells to TPA.

Inhibition of phorbol ester-accelerated amino acid transport in bovine lymphocytes

12-O-Tetradecanoylphorbol-13-acetate, a highly active tumor-promoting agent and lymphocyte comitogen, rapidly accelerates the transport of alpha-aminoisobutyric acid in cultured bovine lymphocytes. Structure-activity studies show that the ability of phorbol diesters to accelerate alpha-aminoisobutyric acid uptake runs parallel to their potency as lymphocyte comitogens and as tumor promoters in mouse skin. This phorbol ester-accelerated, amino acid transport is largely insensitive to the inhibition of RNA and protein synthesis by actinomycin D and cycloheximide, respectively, and is insensitive to the inhibition of membrane movement by cytochalasin B and colchicine. Retinoic acid, an antagonist of the tumor-promoting and comitogenic actions of phorbol esters also inhibits the acceleration of amino acid uptake by 12-O-tetradecanoylphorbol-13-acetate; however, the epoxy derivatives of retinoic acid and structurally related analogs, which are potent antagonists of the other aspects of phorbol ester activation of lymphocytes, are inactive in blocking amino acid uptake. Comparative studies in lymphocytes show that this phorbol ester elicits a number of metabolic responses which appear to originate at the cell membrane and that these are differentially antagonized by retinoic acid, the 5,6-epoxide of retinoic acid, and related retinoid analogs.

Biologically active phorbol esters specifically alter affinity of epidermal growth factor membrane receptors

TPA (12-O-tetradecanoyl-phorbol-13-acetate) reversibly inhibits the binding of (125)I-labelled epidermal growth factor (EGF) to treated mouse and human cells, but does not affect the binding of various other ligands to their membrane receptors. It alters the affinity of the receptors for EGF without changing the total number of available receptors per cell. Those phorbol esters which stimulate cell growth in culture and have tumour-promoting activity in vivo alter the EGF-receptor affinity, while the biologically inactive derivatives fail to change the affinity of EGF for its receptors.

Two-stage malignant transformation in hamster embryo cells

Transformation of primary hamster embryo cells was investigated using 3-methylcholanthrene (MCA), a combination of MCA and 12-O-tetradecanoylphorbol-13-acetate (TPA), and initiation with MCA or dibenz(a,h)anthracene (DBA) followed by promotion with TPA. Evidence for transformation was (a) abnormal cellular morphology, (b) increased lifespan, (c) growth in soft agar, and (d) tumour induction by s.c. inoculation into suckling hamsters.Cells treated with either MCA or MCA+TPA showed the same latent period to morphological transformation, although their tumorigenic potential varied. Cells did not form tumours when TPA was administered 7 days after treatment with either MCA or DBA. However, when administration of TPA was delayed to 27 days after treatment with a transforming dose of MCA or a subthreshold dose of DBA, the cells transformed and produced tumours in hamsters.Our results show that TPA may act as an inhibitor or promoter, depending on the length of time between treatment of the hamster embryo cells with the carcinogen and administration of the TPA. It appears that treatment of cells with TPA before the initiating event is complete inhibits or delays the development of their ability to induce tumours in animals or grow in soft agar. However, with a sufficient interval between the application of the initiating carcinogen and the promoter, transformation occurs, and the ability of cells treated with subthreshold doses of DBA to form tumours is enhanced.

Inhibition of the mixed lymphocyte proliferative response by phorbol esters

The phorbol diester, 12-O-tetradecanoyl-phorbol-13-acetate, a potent cocarcinogen in mice, blocks the induction of DNA synthesis in lymphocytes undergoing the mixed lymphocyte response. At 10(-7) M diester, the induced DNA synthesis is inhibited almost completely (99%). This action of the diester affects some early step in the response which is necessary for the triggering of cell replication; on-going DNA replication is not significantly affected. Phorbol 12,13-diacetate, a less potent analogue in tumor promotion in vivo, is also a less potent inhibitor of the mixed lymphocyte response (75% inhibition at 10(-6) M). Phorbol, the parent alcohol, is not effective in either system. The use of phorbol diesters in the molecular dissection of mixed lymphocyte responses is discussed.

Qualitative and quantitative separation of a series of phorbol-ester tumor promoters by high-pressure liquid chromatography

A high-pressure liquid chromatographic (HPLC) method using a micro-particulate silica column and gradient elution was developed that separated 12-O-tetradecanoylphorbol-13-acetate (TPA) from 20-oxo-TPA; 12-O-tetradecanoylphorbol (TP); 13-O-acetylphorbol (PA), and from the diterpene alcohol, phorbol (P). A series of other phorbol-ester tumor promoters were also separated via HPLC. Spectrophotometric determination at 232 nm allowed detection sensitivities of 0.05 microgram of TPA. When tritiated TPA was applied to mouse skin, the majority of the tritiated product recovered was TPA, indicating only minimal metabolism of TPA and no need for metabolic activation for tumor promotion.

Induction of cell division in BALB/c-3T3 cells by phorbol myristate acetate or bovine serum: effects of inhibitors of cyclic AMP phosphodiesterase and Na+-K+-ATPase

Cell division is induced in stationary cultures of BALB/c-3T3 mouse embryo cells without renewal of medium by addition of the tumor promoter, phorbol myristate acetate (PMA), or bovine serum. The addition of dbcAMP (10(-3) M) or other inhibitors of cAMP phosphodiesterase, papaverine (6.7 X 10(-6) M), Persantin (5 X 10(-5) M) or RO-20-1724 (10(-4) M), prevents cell replication induced by PMA or serum. In contrast, ouabain (10(-4) M) and N,N'-dicyclohexylcarbodiimide (10(-5) M), inhibitors of Na+-K+-ATPase activity, block the PMA-stimulated effect but do not inhibit serum-stimulated cell division. Several stages in the cell cycle are sensitive to dbcAMP addition. One is early in the G1 phase at the time of reinitiation of the cell cycle from a stationary (Go) phase, a second is associated with the G1-S transition, and a third with passage of cells from a post-S phase to mitosis. Based on observations of early morphological changes, responses of plasma membrane enzymes and effects of enzyme inhibitors, the stimulation of cell division in BALB/c-3T3 cells by PMA or serum appears to involve several membrane functions which may act in a cooperative manner.

Effects of phorbol myristate acetate on the metabolism and ultrastructure of neutrophils in chronic granulomatous disease

Previous investigations have demonstrated that phorbol myristate acetate (PMA), the active principle of croton oil, stimulates alterations in normal polymorphonuclear leukocytes (PMN) that resemble closely the changes that develop in the cells after phagocytosis of bacteria. The present study has compared the effects of PMA and heat-killed bacteria on the oxygen uptake, glucose oxidation, nitroblue tetrazolium (NBT) reduction, and ultrastructure of normal neutrophils and PMN from six patients with chronic granulomatous disease (CGD). PMA stimulated oxygen consumption, hexose monophosphate shunt activity, and NBT reduction in normal cells but failed to produce similar effects in CGD neutrophils. However, PMA did induce formation of cytoplasmic vacuoles in the CGD cells similar to those observed in normal neutrophils. The results indicate that PMA is a useful nonparticulate agent for distinguishing between normal and CGD neutrophils and for studying basic mechanisms of phagocytosis in normal and abnormal PMN.

The tumor-promoter phorbol ester (12-O-tetradecanoyl-phorbol-13-acetate), a potent aggregating agent for blood platelets

The phorbol ester 12-0-tetradecanoyl-phorbol-13-acetate, a potent tumor-promoting agent, caused irreversible platelet aggregation when more than 0.02 microM was stirred with human citrated or heparinized platelet-rich plasma (PRP). With washed platelets, 1 nM was effective. The alcohol phorbol, which has little tumor-promoting activity, failed to cause platelet aggregation. With all but low concentrations of phorbol ester, aggregation was succeeded by a rapid phase. The latter was prevented or reduced by enzymes which destroy ADP and by aspirin, was associated with a change in platelet shape, and was presumably due to released ADP. At higher concentrations, only a rapid phase was seen, and these inhibitors were not effective. Low concentrations did not aggregate platelets in PRP containing sufficient EDTA or EGTA to chelate ionized calcium or in PRP from thrombasthenic patients; higher concentrations caused slight aggregation. Both the primary, non-ADP-dependent aggregation and the rapid ADP-dependent aggregation were markedly inhibited by substances which increase cyclic AMP, metabolic inhibitors, and the sulfhydryl inhibitor N-ethylmaleimide. Phorbol ester reduced platelet cyclic AMP only when it had been previously elevated by prostaglandin E(1). 1 microM did not release beta-glucuronidase, lactic dehydrogenase, or inflammatory material from platelets in 4-5 min despite marked aggregation, but liberated all three in 30 min. The possibility is discussed that low phorbol ester concentrations cause primary aggregation by a direct action on platelet actomyosin.

Mechanism for the regulation of cell division in Agmenellum

We describe a nonlethal temperature-conditional mutant of Agmenellum quadruplicatum which allows dissociation of the processes of growth and cell division. With this system, evidence has been obtained for the regulation of one step in the process of cell division by a small effector molecule. The effector molecule is apparently released into the surrounding medium and can be obtained from lyophilized spent medium by extraction with 80% ethanol. The addition of this extract to serpentine filaments of the SN29 mutant strain stimulates cell division in these filaments and leads to the production of cells approximating normal dimensions within one generation time. The degree of stimulation of cell division is directly related to the amount of extract added. A general hypothesis is presented for the positive regulation of the initiation of cell wall and cell membrane invagination in this organism.