Fine structural alterations induced in erythocytes by phorbol myristate acetate.

Prevous studies have demonstrated that PMA is a potent membrane-active agent causing cell-wall derived vacuole formation in neutrophils and granule labilization in platelets. The present investigation demonstrates that PMA also has marked effects on red blood cells. Erythrocytes exposed to PMA were converted into stomatocytes and stomatospherocytes. The effects of PMA on red cells were concentration-dependent, required removal of plasma, and occurred maximally at 37 C. Although the response of the red cell to PMA was not identical to that of other blood cells tested previously; the similarities suggest that the capacity of the agent to produce membrane invagination may be fundamental to its mode of action.     

Acute lung inflammation in rats induced by phorbol myristate acetate (PMA)

Intratracheal administration of PMA produces acute lung injury in part due to the generation of O₂-derived free radicals. This study evaluated the role of the antioxidant enzyme superoxide dismutase (SOD) in PMA-induced lung injury in the rat. PMA was instilled into rats intratracheally (20–60 g/kg), and the lungs were lavaged 4 hr later. Total number of cells recovered from lavage after PMA treatment was not different from the total number recovered from controls; lavagable PMNs increased in a dose-dependent manner. Albumin in lavage fluid (an index of lung vascular permeability) was significantly increased at 60 g/kg PMA. SOD (10,000 U)+PMA (60 g/kg) reduced the albumin level but significantly increased both total number of cells and number of PMNs recovered from lavage fluid. To investigate the possibility that SOD decreases the ability of PMNs to adhere, PMN aggregation was measuredin vitro. The results indicated that 10,000 U SOD can inhibit PMA-induced aggregation by 50%. In contrast, aggregation to other stimuli (e.g., fMet-Leu-Phe, A23187) was unaffected by SOD. We conclude SOD prevents PMA-induced lung permeability and diminishes PMN adherence.     

Two distinct cytolytic mechanisms of macrophages and monocytes activated by phorbol myristate acetate

Pulmonary alveolar macrophages (PAM) and peripheral blood monocytes (PBMO) of the miniature swine can be converted to cytolytically active effector cells by treating with phorbol myristate acetate (PMA) as determined by enhancement of cytotoxicity to various target cells. Kinetics of the PMA-activated PAM and PBMO in cytotoxicity show that the effective PMA concentration ranges from 10 to 1,000 ng/ml. Induction of cytotoxic macrophages and monocytes occurred as early as 30 min and to their maximum cytotoxicity after 1 hr exposure to PMA and the enhanced cytotoxic activity persisted up to 24 to 40 hr when PMA was removed by washing after 1 hr exposure, but prolonged exposure to PMA for more than 6 hr resulted in a drastic decrease of cytolytic activities suggesting the prolonged exposure to PMA causes macrophages and monocytes to become refractory to PMA stimulation. Target cells displayed varying degrees of cytotoxic sensitivity to the PMA-activated PAM and PBMO; PRBC, SRBC, and K562 were sensitive, WEHI-164 and U937 were relatively sensitive, and SB was very resistant to these activated effector cells. The mechanisms of PMA-induced cytotoxicity could largely be divided into two categories. One was the H2O2 mediated killing as shown by complete reduction of cytotoxicity after adding catalase in the assay. The other was the proteases mediated cytolysis, which could be blocked by protease inhibitors, Phenyl methyl sulfonyl fluoride (PMSF), and N- alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK). H2O2 was the only mediator produced in large enough quantities from PBMO to kill target cells, whereas PAM could produce both mediators (H2O2 and proteases). PRBC, SRBC, and K562 appeared to be killed by H2O2 produced by PAM and PBMO. In contrast, U937 and WEHI-164 appeared to be killed by proteases in PAM mediated cytolysis but by H2O2 in PBMO-mediated cytolysis. These results suggest that the observed cytolytic mechanisms can be differed by type of target cells as well as the source of mononuclear phagocytes within the individual animal.     

Chondrocyte activation by interleukin-1: Synergism with fibroblast growth factor and phorbol myristate acetate

Exposure to synovial factors or purified interleukin-1 (IL-1) induces the production of prostaglandin E₂ (PGE₂) and the neutral proteinases (NP) collagenase, gelatinase and stromelysin by lapine articular chondrocytes. Having frequently found our partially purified synovial preparations to elicit this process of chondrocyte activation more strongly than recombinant IL-1, Phadke's report [1] of synergism between IL-1 and fibroblast growth factor (FGF) intrigued us. In our hands, basic FGF (1 ng/ml–1 μg/ml) did not activate chondrocytes but, in a dose-dependent manner, enhanced the production of PGE₂ and NP by chondrocytes exposed to IL-1α or IL-1β (1–10 U/ml). Further examination determined that the basic FGF was a better synergist than acidic FGF. In view of reports that FGF activates protein kinase C, we tested whether phorbol myristate acetate (PMA) could substitute for FGF as a synergist. Not only did it do so, but PMA alone (0.1 ng/ml–100 ng/ml), unlike FGF, provoked the production of PGE₂ by chondrocytes. The Ca²⁺ ionophore A23187 could not substitute for FGF in enhancing induction of the NP. Using a cDNA probe, we confirmed that the synergistic effects of both FGF and PMA upon IL-1 mediated collagenase induction, were associated with an increased abundance of collagenase mRNA.     

Induction of human T-lymphocyte colonies by phorbol myristate acetate

Colony growth of human lymphocytes by phorbol myristate acetate (PMA) was studied. PMA was able to induce lymphocyte colony growth in methylcellulose semi-solid cultures in the absence of lectin mitogens, phytohaemagglutinin or concanavalin A. PMA-induced colonies were found in cultures of mononuclear cells, monocyte-depleted mononuclear cells and the T-enriched cell fraction, whereas no colonies were obtained from the non-T cell fraction. At least one million mononuclear cells were required to form colonies by PMA. The colony cells were mainly T cells as judged from sheep red blood cell rosette formation. Surface immunoglobulin positive cells and peroxidase positive cells were not detected in colony cells. Non-specific esterase positive cells were only found to be less than 1% of colony cells. T cells formed more colonies than did mononuclear cells, presumably because of a concentration of colony forming cells and/or co-operating cells. Colony formation by PMA was induced from monocyte-depleted mononuclear cells and monocyte-depleted T cells, suggesting independence of monocytes. When mononuclear cells were precultured at 37 degrees for 5 min or 30 min with PMA and then cultured in the semi-solid medium without PMA, only a small number of colonies grew. Further studies of PMA-induced T-cell colonies will provide information the identification and characterization of immunological states in various immunological diseases.     

Polymorphonuclear leukocyte chemiluminescence induced by formylmethionyl-leucyl-phenylalanine and phorbol myristate acetate: Effects of catalase and superoxide dismutase

The effects of pristane (2,6,10,14-tetramethylpentadecane) on the cellular DNA of lymphoid cells from Copenhagen rats were examined by flow cytometry. Significant reductions in the mean relative fluorescent intensities of propidium iodide (PI) stained lymphocytes from peripheral blood, spleen, thymus and lymph nodes were observed after a single intraperitoneal injection of pristane. The altered PI staining characteristics were observed as early as 4 days and reached a maximum decrease between 1–4 weeks (depending upon the lymphoid cells examined) post pristane treatment. The pristane-induced effects on peripheral blood lymphocytes were observed to be dose dependent, transient and reinducible by a subsequent exposure to pristane. Further analyses, using gas-liquid chromatography to detect pristane in the blood and lymphoid tissues of treated rats, indicated, significant increases over normal amounts of pristane. Furthermore, correlations existed between the times of maximum decrease in the fluorescence of PI stained cells and the amounts of pristane detected within the respective lymphoid tissues. By contrast no changes in the PI staining characteristics of kidney cells were observed, even though appreciable amounts of pristane, were detected in this organ. Diphenylamine analyses indicated no differences in the amounts of DNA in lymphoid cells from pristane treated and untreated rats. Furthermore, lymphocytes from pristane-treated rats did not exhibit decreased fluorescence when fixed at pH 10 rather than pH 7.4 prior to PI staining. Collectively these results suggest that pristane, may preferentially induce qualitative rather than quantitative changes in the DNA of lymphocytes.This investigation was supported by PHS grant numbers CA33111 and AI22607.     

Induction of human autorosette forming cells by phorbol myristate acetate.

Human peripheral blood lymphocytes were examined for rosette formation with autologous erythrocytes. When normal human lymphocytes were stimulated with phorbol myristate acetate (PMA) in the presence of autologous serum, the levels of autorosette forming cells (ARFC) were strongly enhanced. Pre-culture was necessary for the generation of ARFC by PMA and the maximal level of ARFC was observed at 72 hr of culture. ARFC appear to belong to a T cell subset and the induction of ARFC by PMA was noted in monocyte depleted lymphocyte fractions, indicating monocyte independency.     

Impaired release of colony stimulating activity by monocytes from Hodgkin's disease in response to phorbol myristate acetate activation

We assessed the humoral effect of resting and phorbol esters preincubated monocytes from Hodgkin's disease patients (HDMo) and healthy subjects (nMo), on granulocyte progenitors (CFU-dG) growth using a double diffusion chamber technique. The release of colony stimulating activity and indomethacin-dependent inhibitors by resting HDMo and nMo was found to be cell-concentration dependent. However, phorbol myristate acetate preincubated HDMo (PMA-HDMo) in contrast to nMo at low concentrations (2.5 x 10(4] were unable to increase the CFU-dG growth stimulation. On the other hand, at a higher cell number (5 x 10(4], phorbol treated HDMo stimulated the myeloid colony formation, whereas nMo suppressed the CFU-dG proliferation. Further enhancement of HDMo and nMo concentrations induced a pronounced inhibition of CFU-dG-derived colony formation, caused by an increased PGE2 production. After incubation with the cyclooxygenase inhibitor-indomethacin, PMA-HDMo showed considerably more granulocyte colony formation than nMo. Our results suggest that the observed abnormalities in the function of HDMo could be associated with an excessive production of PGE2 and a general dysfunction of these cells in Hodgkin's disease.     

Neutrophil-mediated nonoxidative tumor lysis stimulated by high concentrations of phorbol myristate acetate

The mechanism of neutrophil-mediated lysis of tumor targets was investigated. Tumor lysis was directly related to the concentration of phorbol myristate acetate (PMA) used to stimulate PMNs. Lysis increased as the PMA concentration increased between 10(-7) and 10(-4) M. In contrast, the production of H2O2 plateaued between concentrations of 10(-5) and 10(-4) M. The K562 erythroleukemia cell, the target used in this study, was found to be relatively resistant to preformed H2O2, with an LD50 of 8.3 X 10(-3) M. Myeloperoxidase was not capable of enhancing K562 lysis. Although resistant to preformed H2O2, K562 lysis mediated by PMNs stimulated with 10(-7) M PMA was oxidative in nature. It was sensitive to inhibition by catalase and was not significant when PMNs from patients with chronic granulomatous disease were used. In contrast, PMN lysis stimulated by 10(-4) M PMA was nonoxidative in nature. The inhibitors catalase and superoxide dismutase had no effect on lysis, lysis was significant when the assay was performed in an anaerobic atmosphere, and PMNs from patients with chronic granulomatous disease were comparable to control PMNs in tumor lysis. A single-cell conjugate and cytotoxicity assay demonstrated that PMA was both able to increase the ability of PMNs to bind to tumor targets and to enhance their lysis of bound targets. These data indicate that PMNs are capable of achieving tumor lysis by nonoxidative pathways under certain conditions. The high-dose PMA model may be valuable as a tool for investigating these alternative mechanisms of tumor lysis.     

The differential mobilization of human neutrophil granules. Effects of phorbol myristate acetate and ionophore A23187.

Phorbol myristate acetate (PMA, 2 to 100 ng/ml) and ionophore A23187 (10(-7) to 10(-6) M) cause human neutrophils to release up to 50% of the granule-associated enzyme lysozyme extracellularly without release of beta-glucuronidase or the cytoplasmic enzyme LDH. When azurophil and specific granules are separated from neutrophil lysates by sucrose density centrifugation, it is found that lysozyme release from neutrophils exposed to PMA or to A23187 reflects a selective disappearance of the small, peroxidase-negative (specific) granules from the cells. These studies demonstrate that neutrophils can mobilize the specific and azurophil granules independently. These studies also demonstrate that under certain conditions the specific granules of human neutrophils behave like the storage granules of secretory cells. Finally, these studies show that techniques of separating neutrophil granules according to their sedimentation characteristics successfully divide these granules into populations that are distinct not only by cytochemical and morphologic criteria but also according to their availability for mobilization and extracellular release. (APM J Pathol 87:273-284, 1977).     

Differentiation of the U-937 promonocytic cell line induced by phorbol myristate acetate or retinoic acid: Effect of aurothiomalate

Tissue macrophages, which participate in chronic synovial inflammation, differentiate from haemopoietic precursors in bone marrow and subsequently in tissue. During this process, they acquire attributes which are essential for their function in inflammation. Modulation of this process may represent a means of regulating inflammatory competence of macrophages in inflammatory joint disease. The action of aurothiomalate (ATM), an anti-rheumatic gold compound, on the differentiation of a promonocytic cell line (U937) was, therefore, examined inin vitro systems. U937 cells exposed to retinoic acid (RA) for 4 days or to phorbol myristate acetate (PMA) for 2 days acquired characteristics of macrophages, including the capacity to produce superoxide (O ₂ ^– ), responsiveness to formyl-methionyl-leucyl-phenylalanine (fMLP) and reduced proliferation. The activity of transglutaminase also increased in RA-exposed cultures. The effect of ATM exposure on acquisition of these characteristics was small and differed between RA- and PMA-stimulated cells.     

Oxygen metabolites induced by phorbol myristate acetate increase lateral diffusion of wheat germ agglutinin-labeled glycoconjugates in human polymorphonuclear leukocytes

To assess the general effects of protein kinase C (PKC) activation on cell membrane receptor mobility in human neutrophilic polymorphonuclear leukocytes (PMNLs), the lateral diffusion of fluoresceinated succinylated wheat germ agglutinin (S-WGA-FITC)-labeled membrane glycoconjugates was measured using fluorescence recovery after photobleaching (FRAP). Activation of PKC was achieved by incubating the PMNLs with different concentrations (5–100 nM) of phorbol myristate acetate (PMA). The membrane effects of dimethyl sulfoxide (DMSO), another possible membrane perturbant, were also studied. We found that PMA treatment ( 10 nM) increased the glycoconjugate diffusion coefficient (D) 2–2.5-fold. The mobile fraction (R) remained constant, around 30%. With DMSO, no effect on the diffusion was seen. The increase in lateral mobility due to cell stimulation with PMA was totally inhibited by catalase (200 units/ml) but only partly with superoxide dismutase (2000 units/ml). Exogenous hydrogen peroxide (0.01–5 mM) had no effect on glycoconjugate mobility in unstimulated cells. We therefore propose that activation of PKC mediates augmented mobility of glycoconjugate receptors in PMNL, a reaction that seems to be critically dependent on formation of reactive oxygen metabolites. The results indicate that endogenous formation of reactive metabolites upon receptor stimulation may have a general effect on receptor mobility.     

Effects of tumour promoter phorbol myristate acetate on mouse lymphocytes: selective inhibition of B cell activation by mitogens and antigens.

The effect of the tumour promoter phorbol myristate acetate (PMA) on the responses of mouse lymphocytes to various stimuli was studied in vitro. Nanomolar concentrations of PMA inhibited B cell proliferation induced by lipopolysaccharide and by anti-Ig antibodies, and the polyclonal antibody response to lipopolysaccharide. Specific antibody responses to both T-dependent and T-independent antigens were similarly affected. In marked contrast, T cell proliferation elicited by various mitogens was 10- to 1000-fold more resistant to inhibition. Cell fractionation experiments suggest that the effects on B cell responses are the results of a direct anti-proliferative effect of PMA on responding B lymphocytes.     

Lymphocyte stimulation with phorbol myristate acetate in atopic and non-atopic individuals.

Phorbol myristate acetate (PMA) was found to be a potent stimulator of DNA synthesis in human whole blood cell cultures. Stimulation with pokeweed mitogen was strongly enhanced by addition of PMA-activated cells. PMA responsiveness varied with age, being low or absent in newborns and very pronounced in adults. In atopic children, PMA responsiveness was normal or increased. The ratio of phytohemagglutinin to PMA responsiveness was significantly reduced in cultures from such children. This finding would be compatible with the hypothesis of a relative suppressor cell deficiency in atopic disease. The results of tests designed to detect suppressor and helper cell activity, added further support to this hypothesis.     

Pretreatment with phorbol myristate acetate inhibits macrophage activity against intracellular protozoa

To further document the role of toxic oxygen intermediates in mononuclear phagocyte antiprotozoal activity, microbicidal macrophages were depleted of the capacity to generate superoxide anion (O-2) and hydrogen peroxide (H2O2) by pretreatment with phorbol myristate acetate (PMA), a soluble agent which triggers the macrophage respiratory burst. Treating cells for 90 min with 200 ng/ml of PMA inhibited the extracellular release of both O-2 and H2O2 by 90% upon subsequent restimulation with either PMA or opsonized zymosan. This effect persisted for 48 h, and could not be reversed by the addition of lymphokine. Intracellular nitro-blue tetrazolium reduction by PMA-treated cells was also inhibited by 66-95% upon rechallenge with either PMA or inert or viable particulate agents. In parallel, PMA pretreatment abolished or markedly impaired the ability of normal, lymphokine-stimulated, and in vivo activated macrophages to kill three diverse protozoa--Toxoplasma gondii, Leishmania donovani, and Trypanosoma cruzi. These studies illustrate an additional technique for investigating the antiprotozoal effects of macrophage-derived O-2 and H2O2 and reemphasize the importance of an intact respiratory burst mechanism in killing of intracellular parasites.     

Effects of phorbol myristate acetate on interleukin-2 and accompanying interferon production of human leukocytes induced by heat-inactivated Staphylococcus aureus

Interleukin-2 (IL-2) production induced by heat--inactivated Staphylococcus aureus (SAU) was enhanced by simultaneous addition of phorbol myristate acetate (PMA). The effect was optimal at a concentration of 10 ng/ml SAU; in the presence of 10 ng/ml PMA, the amount of SAU required for maximal IL-2 production was lower. The kinetics of SAU and of SAU plus PMA-induced IL-2 production were similar. Stimulated mononuclear cells produced interferon (IFN) in addition to IL-2. The titre of accompanying IFN was decreased in cultures stimulated with the SAU plus PMA combination. Plastic nonadherent sheep erythrocyte-positive cells were the most active in the SAU-induced IL-2 production. In contrast, the bulk of the IFN activity was produced by the nonadherent E rosette-nonforming cells. Neutralization of IFN with specific antibodies and pH 2 treatment indicated that SAU-induced IFN consisted mainly of alpha-IFN.     

Studies on T-lymphocyte activation. I. Is competence inductions in thymocytes by phorbol myristate acetate,an accessory cell-independent event?

The effect of phorbol myristate acetate (PMA) on lectin-induced murine thymocyte activation was studied. PMA itself failed to stimulate thymocyte proliferation, but potentiated concanavalin A (Con A)-induced thymocyte activation. A brief incubation of thymocytes with PMA changed the responsiveness of these cells to an optimal mitogenic dose of Con A present during the entire subsequent culture period. Further studies showed that PMA induced in a dose-dependent way within 30 min. an optimal competence of thymocytes to respond to the T-cell growth factor interleukin-2 (IL-2). In contrast to lectin-triggered competence induction, PMA-triggered induction of competence in thymocytes seemed to be independent of accessory cells.     

High-affinity interleukin 2 receptors on B cell chronic lymphocytic leukemia cells are induced by phorbol myristate acetate but not by calcium ionophore

The role of phorbol myristate acetate (PMA: a protein kinase-C (PKC) activator) and calcium ionophore A23187 in the induction mechanism of the interleukin 2 receptor (IL2R) on B-cell chronic lymphocytic leukemia (B-CLL) cells was studied. B-CLL cells from five patients were cultured with PMA or A23187 for 72 h and used for the following experiments. Interleukin 2 (IL2) cross-linking assays showed that PMA induced the expression of IL2R subunits (p55 and p70/75) in all cases examined, but that A23187 induced neither subunit. Radiolabeled IL2 binding assays also demonstrated that PMA induced both high-affinity IL2R (HA-IL2R) and low-affinity IL2R (LA-IL2R) on B-CLL cells, but that A23187 did not. After treatment with PMA, three of five cases did not respond to IL2 even though they expressed HA-IL2R, suggesting impaired signal transduction. No cases responded to IL2 after treatment with A23187. In conclusion, PMA but not A23187 stimulates B-CLL cells to induce the expression of p55 and p70/75, indicating that the PKC pathway plays a more important role than the calcium pathway in the induction of IL2R subunits in B-CLL cells.