Specific receptors for phorbol esters in lymphoid cell populations: role in enhanced production of T-cell growth factor

Assessment of fibrin-collagen co-gels for generating microvesselsex vivousing endothelial cell-lined microfluidics and multipotent stromal cell (MSC)-induced capillary morphogenesis

One aspect of the challenge of engineering viable tissues ex vivo is the generation of perfusable microvessels of varying diameters. In this work, we take the approach of using hydrogel-based microfluidics seeded with endothelial cells (ECs) to form small artery/vein-like vessels, in conjunction with using the self-assembly behavior of ECs to form capillary-like vessels when co-cultured with multipotent stromal cells (MSCs). In exploring this approach, we focused on investigating collagen, fibrin, and various collagen-fibrin co-gel formulations for their potential suitability as serving as scaffold materials by surveying their angiogencity and mechanical properties. Fibrin and co-gels successfully facilitated multicellular EC sprouting, whereas collagen elicited a migration response of individual ECs, unless supplemented with the PKC (protein kinase C)-activator, phorbol 12-myristate 13-acetate. Collagen scaffolds were also found to severely contract when embedded with mesenchymal cells, but this contraction could be abrogated with the addition of fibrin. Increasing collagen content within co-gel formulations, however, imparted a higher compressive modulus and allowed for the reliable formation of intact hydrogel-based microchannels which could then be perfused. Given the bioactivity and mechanical benefits of fibrin and collagen, respectively, collagen-fibrin co-gels are a promising scaffold option for generating vascularized tissue constructs.

Biphasic Effects of Ingenol 3,20-Dibenzoate on the Erythropoietin Receptor: Synergism at Low Doses and Antagonism at High Doses

Although ingenol 3,20-dibenzoate (IDB) is known as a selective novel protein kinase C (PKC) agonist, its biologic actions and underlying mechanisms remain incompletely understood. In this study, we identified IDB as a proliferative agent for an erythropoietin (EPO)-dependent cell line, UT-7/EPO, through the screening of a natural compound library. To clarify the underlying mechanism of IDB's EPO-like activities, we thoroughly analyzed the mutual relation between EPO and IDB in terms of in vitro and in vivo activities, signaling molecules, and a cellular receptor. IDB substantially induced the proliferation of UT-7/EPO cells, but not as much as EPO. IDB also lessened the anemia induced by 5-fluorouracil in an in vivo mouse model. Interestingly, IDB showed a synergistic effect on EPO at low concentration, but an antagonistic effect at higher concentration. Physical interaction and activation of PKCs by IDB- and EPO-competitive binding of IDB to EPO receptor (EPOR) explain these synergistic and antagonistic activities, respectively. Importantly, we addressed IDB's mechanism of action by demonstrating the direct binding of IDB to PKCs, and by identifying EPOR as a novel molecular target of IDB. Based on these dual targeting properties, IDB holds promise as a new small molecule modulator of EPO-related pathologic conditions.

Tacrolimus causes a blockage of protein secretion which reinforces its immunosuppressive activity and also explains some of its toxic side-effects

BACKGROUND

Tacrolimus (FK506) is a macrolide immunosuppressant drug from the calcineurin inhibitor family, widely used in solid organ and islet cell transplantation, but produces significant side-effects.

OBJECTIVE

This study examined the effect of FK506 on interleukin-2 (IL-2) and insulin secretion, establishing a novel characteristic of this drug that could explain its diverse adverse effects, and developed an experimental model for the simultaneous analysis of mRNA expression and protein secretion affected by this drug.

METHODS

The IL-2 levels when tacrolimus was administered were analysed by Western blot, immunocytochemistry and RT-PCR in a T lymphocyte cellular line (Jurkat) 24 h post-stimulation. The insulin levels when tacrolimus was administered were analysed 4 h after stimulation of glucose-induced insulin secretion in a pancreatic cellular line (MIN6).

RESULTS

The previously published information describes tacrolimus as only capable of partially blocking IL-2 mRNA expression. In our hands, the cellular content of IL-2 is almost undetectable in stimulated Jurkat cells and can be detected in cellular extracts only when the secretory pathway is blocked by brefeldin A (BFA). BFA added 2 h after the beginning of stimulation was able to inhibit IL-2 secretion, without affecting IL-2 mRNA expression. Therefore BFA utilization allowed us to establish a model to analyze the effect on IL-2 secretion, separately from its expression. Tacrolimus added before stimulation inhibits only IL-2 synthesis, but blocks IL-2 protein secretion when added 2 h after stimulation. Similarly, tacrolimus is also capable of blocking the glucose-stimulated secretion of insulin by MIN6 cells. An increase of the intracellular content can be detected concomitantly with a decrease of the hormone measured in the culture medium.

CONCLUSIONS

Results of this study indicate that tacrolimus possesses another important effect in addition to the inhibition of IL-2 gene transcription, namely the ability to act as a general inhibitor of the protein secretory pathway. These results strongly suggest that the diabetogenic effect of the immune suppressant FK506 could be caused by the blockade of insulin secretion. This novel effect also provides an explanation for other side-effects observed in immunosuppressive treatment.

CD18/ICAM-1-dependent oxidative NF-kappaB activation leading to nitric oxide production in rat Kupffer cells cocultured with syngeneic hepatoma cells

Previous studies have indicated that nitric oxide (NO) released from Kupffer cells modulates biological viability of cocultured hepatoma cells. This study was designed to evaluate the mechanisms by which Kupffer cells synthesize and release NO in reponse to cocultured hepatoma cells. Kupffer cells isolated from male Wistar rats were cocultured with rat hepatoma cell line, AH70 cells. The sum of nitrite and nitrate levels increased in the culture medium of Kupffer cells with AH70 cells as compared with those of Kupffer cells or AH70 cells alone. Increased expressions of iNOS and iNOS mRNA in Kupffer cells cocultured with AH70 cells were detected by an immunofluorescence staining and a fluorescence in situ hybridization study, respectively. A fluorescence in situ DNA-protein binding assay revealed that NF-kappaB activation occurs in Kupffer cells and activated NF-kappaB moved into the nuclei preceding to an increased production of NO. Oxidative stress indicated by dichlorofluorescein fluorescence was observed in Kupffer cells cocultured with AH70 cells. An increased calcium mobilization indicated as increased fluo-3-associated fluorescence was also induced in Kupffer cells after coculture with AH70 cells. Monoclonal antibodies directed against rat CD18 and ICAM-1, as well as TMB-8, a calcium inhibitor, prevented the calcium mobilization, active oxygen production, and NF-kappaB activation in addition to the increased production of NO. Pyrrolidine dithiocarbamate, an inhibitor of oxidative NF-kappaB activation, diphenylene iodonium, an NADPH oxidase inhibitor, and quinacrine, a phospholipase A2 inhibitor, significantly attenuated the increase in dichlorofluorescein fluorescence, NF-kappaB activation, and NO production. Therefore, this study suggests that CD18/ICAM-1-dependent cell-to-cell interaction with hepatoma cells causes calcium mobilization and oxidative activation of NF-kappaB, which may lead to the increased production of NO in Kupffer cells.

Long-wave ultraviolet radiation causes increase of membrane-bound fraction of protein kinase C in rat myeloid leukemia cells

We examined the effect of long-wave ultraviolet radiation (UVA) on protein kinase C (PKC) and on the proliferation of rat myeloid leukemia cell line (ChL). Exposure of cells to a single dose of UVA (8 J/cm2 at 372 +/- 10 nm) caused a rapid increase in the quantity of the membrane-bound PKC, as assessed by 3H-phorbol ester (3H-PMA) binding assay (performed at 4 degrees C). Within 2 h of UVA irradiation, three peaks of increased 3H-PMA binding to the ChL cells (by 70-100%) were observed at ca. 20, 60 and 95 min post-irradiation. The exposure of ChL to UVA caused also a rapid, but transient, decline in the cell proliferation rate (by 18% within 24 h). However, the statistically significant decrease in cell numbers was observed only 3 days later (down by 22%). The inhibition of ChL proliferation was not due to alteration of cell viability as determined by trypan blue exclusion assay, and neither was it caused by cell cycle arrest or apoptosis, as determined by flow cytometry analysis of propidium iodide-labelled cells and cell morphology in May-Grünvald-Giemsa-stained cell smears. Phorbol-ester-induced activation of PKC (performed at 37 degrees C) caused inhibition of ChL proliferation similar to that caused by UVA. This suggests that a UVA-induced increase of the membrane-bound fraction of PKC may be responsible for the UVA-induced inhibition of ChL proliferation.

Nocardia fractions, NLD and NWSM, induce tumor necrosis factor-alpha secretion in human monocytes: role of protein kinase C

Nocardia lysozyme digest (NLD) and Nocardia water-soluble mitogen (NWSM) are two fractions derived from Nocardia opaca. In this report, we demonstrated that both fractions elicited significant secretion of tumor necrosis factor-alpha (TNF-alpha) in human monocytes. Supernatants from monocytes stimulated with NWSM and low concentrations of NLD displayed a cytotoxic activity against TNF-alpha-sensitive L929 cells, but supernatants from monocytes stimulated with high concentrations of NLD failed to lyse L929 cells. This latter phenomenon might be related to the secretion of an inactive form of TNF-alpha or the release of an inhibitor of TNF-alpha cytotoxic activity. Since it is well established that protein kinase C (PKC) plays a major role in the signaling of several monocyte activators, we investigated the putative role of PKC in cytokine synthesis induced by NLD and NWSM fractions. TNF-alpha secretion in response to both Nocardia fractions was inhibited by sphingosine, staurosporine and calphostin C, known PKC inhibitors, as well as by a PKC depletion procedure. In addition, NLD and NWSM induced a transient increase in [3H]phorbol dibutyrate binding, which assessed the activation of PKC. The data suggest the involvement of PKC in the signaling of NLD and NWSM fractions leading to the synthesis and the secretion of TNF-alpha by human monocytes.

Phorbol esters inhibit insulin-induced receptor down-regulation in cultured human lymphocytes: association with diminished insulin receptor autophosphorylation

Exposure of cells to phorbol 12-myristate 13-acetate (PMA) has been reported to result in resistance to the acute biological effects of insulin and an associated reduction in insulin-receptor tyrosine kinase activity. To investigate the relationship of insulin receptor autophosphorylation with a longer-term action of insulin the effect of PMA on insulin-stimulated receptor down-regulation was examined in cultured human lymphocytes (IM-9). Lymphocytes bound [3H]phorbol dibutyrate specifically with characteristics typical of binding to protein kinase C (PKC). Acute exposure (30 min) to PMA resulted in a transient decrease of insulin binding which is consistent with a decrease in receptor number. Chronic (18 h) exposure to PMA (5 nM) resulted in inhibition of insulin-induced down-regulation of its cognate receptor. Sphingosine, an inhibitor of PKC, or chronic pre-exposure to a high concentration of PMA (1 microM), which is known to inactivate PKC, blocked the effect of PMA. PMA inhibited insulin-stimulated receptor internalization by 26% and receptor degradation by 82%. Exposure of intact cells to PMA followed by insulin treatment inhibited insulin-receptor autophosphorylation subsequently assayed in vitro, as well as beta-subunit tyrosine phosphorylation in situ. In summary, PMA inhibited insulin-stimulated receptor down-regulation via activation of PKC. This was associated with an inhibition of both receptor internalization and receptor degradation. There was a concomitant inhibition of receptor tyrosine autophosphorylation consistent with a requirement of receptor kinase activation for both short-term and long-term biological effects of insulin.

Dithiocarbamates as potent inhibitors of nuclear factor kappa B activation in intact cells

Dithiocarbamates and iron chelators were recently considered for the treatment of AIDS and neurodegenerative diseases. In this study, we show that dithiocarbamates and metal chelators can potently block the activation of nuclear factor kappa B (NF-kappa B), a transcription factor involved in human immunodeficiency virus type 1 (HIV-1) expression, signaling, and immediate early gene activation during inflammatory processes. Using cell cultures, the pyrrolidine derivative of dithiocarbamate (PDTC) was investigated in detail. Micromolar amounts of PDTC reversibly suppressed the release of the inhibitory subunit I kappa B from the latent cytoplasmic form of NF-kappa B in cells treated with phorbol ester, interleukin 1, and tumor necrosis factor alpha. Other DNA binding activities and the induction of AP-1 by phorbol ester were not affected. The antioxidant PDTC also blocked the activation of NF-kappa B by bacterial lipopolysaccharide (LPS), suggesting a role of oxygen radicals in the intracellular signaling of LPS. This idea was supported by demonstrating that treatment of pre-B and B cells with LPS induced the production of O2- and H2O2. PDTC prevented specifically the kappa B-dependent transactivation of reporter genes under the control of the HIV-1 long terminal repeat and simian virus 40 enhancer. The results from this study lend further support to the idea that oxygen radicals play an important role in the activation of NF-kappa B and HIV-1.

Tumor necrosis factor induces rapid production of 1'2'diacylglycerol by a phosphatidylcholine-specific phospholipase C

Tumor necrosis factor (TNF) is a proinflammatory polypeptide that is able to induce a great diversity of cellular responses via modulating the expression of a number of different genes. One major pathway by which TNF receptors communicate signals from the membrane to the cell nucleus involves protein kinase C (PKC). In the present study, we have addressed the molecular mechanism of TNF-induced PKC activation. To this, membrane lipids of the human histiocytic cell line U937 were labeled by incubation with various radioactive precursors, and TNF-induced changes in phospholipid, neutral lipid, and water-soluble metabolites were analyzed by thin layer chromatography. TNF treatment of U937 cells resulted in a rapid and transient increase of 1'2'diacylglycerol (DAG), a well-known activator of PKC. The increase in DAG was detectable as early as 15 s after TNF treatment and peaked at 60 s. DAG increments were most pronounced (approximately 360% of basal levels) when cells were preincubated with [14C]lysophosphatidylcholine, which was predominantly incorporated into the phosphatidylcholine (PC) pool of the plasma-membranes. Further extensive examination of changes in metabolically labeled phospholipids indicated that TNF-stimulated hydrolysis of PC is accompanied by the generation of phosphorylcholine and DAG. These results suggest the operation of a PC-specific phospholipase C. Since no changes in phosphatidic acid (PA) and choline were observed and the production of DAG by TNF could not be blocked by either propranolol or ethanol, a combined activation of phospholipase D and PA-phosphohydrolase in DAG production appears unlikely. TNF-stimulated DAG production as well as PKC activation could be blocked by the phospholipase inhibitor p-bromophenacylbromide (BPB). Since BPB did not inactivate PKC directly, these findings underscore that TNF activates PKC via formation of DAG. TNF stimulation of DAG production could be inhibited by preincubation of cells with a monoclonal anti-TNF receptor (p55-60) antibody, indicating that activation of a PC-specific phospholipase C is a TNF receptor-mediated event.

Transcriptional activation of early-response genes by hydrogen peroxide in a mouse osteoblastic cell line

H2O2, like other oxidants, is known to act as a mitogen at low concentrations in resting Balb/3T3 or mouse epidermal JB6 cells. We described previously that H2O2 induces some early response genes in Balb/3T3 cells. We extended these observations using another cell line, MC3T3 (mouse osteoblastic) cells by examination of transcriptional activity of these genes and by using inhibitors of protein kinases. H2O2 increased the expressions of c-fos, c-jun, egr-1 and JE genes which are known to be early response genes and are induced by mitogenic stimuli in many types of cells. Exogenous addition of H2O2 increased the mRNA levels of these genes, the kinetics of increase being similar to those of their inductions by a phorbol ester or serum. Nuclear run-on transcription showed that this induction occurred at the transcriptional level. H2O2 at 0.1-0.2 mM induced maximal expressions of c-fos and c-jun, whereas 0.3 mM H2O2 was required for induction of stress-induced heme oxygenase mRNA. The inductions of c-fos and c-jun were inhibited by 50 microM H7, a protein kinase inhibitor that is relatively specific for protein kinase C, but were not affected by H9, relatively specific for cAMP-dependent protein kinase. In cells pretreated with 12-O-tetradecanoylphorbol 13-acetate, however, in which protein kinase was supposed to be downregulated, H2O2 induced c-fos and heme oxygenase as efficiently as in untreated cells. H2O2 did not increase the phosphorylation of p80 protein, which is known to be a substrate for protein kinase C. Thus, H2O2 seemed to induce c-fos and c-jun by activating protein kinases distinct from protein kinase C. Activity of the chloramphenicol acetyltransferase gene under control of the serum-response element of human c-fos genes was increased by H2O2 treatment, whereas that under control of cAMP-response element was not affected. These results indicate that the inductions by H2O2 of c-fos and possibly other early response genes are mediated through activation of the serum-response element in their enhancer.

Phorbol ester receptors in cerebral cortex of cats with GM1 gangliosidosis

The pathogenesis of neuronal dysfunction in the gangliosidoses is poorly understood. Studies of the feline gangliosidoses and in vitro experiments implicate ganglioside inhibition of protein kinase C (PKC) in the pathogenesis of these neurological diseases. Therefore, in the present study, the binding of [3H]phorbol-12, 13 dibutyrate was measured to determine the levels of PKC in cerebral cortex of cats with GM1 gangliosidosis (mutant) and age matched normal siblings. This binding of ([3H]PDB) to cerebral cortex homogenates in both normal and mutant cats was highly specific. The specificity of receptors was ascertained also from displacement studies using nonradioactive phorbol ester analogues to displace [3H]PDB bound to its receptors. In both mutant and normal cat brain, phorbol 12,13-dibutyrate (PDB), 4-beta-phorbol 12,13-didecanoate (beta-PDD) and 4-beta-phorbol 12,13-dibenzoate (beta-PDBz) were highly potent (approximately to same degree) and effective in displacing [3H]PDB. On the other hand, 4-beta phorbol 12,13-diacetate (beta-PDA) was a weak displacer and 4-alpha-phorbol did not displace the bound [3H]PDB in either normal or mutant brain. Scatchard analysis of the binding data indicated a homogenous single class of binding sites in normal and mutant brain (Normal: Kd = 1.42 x 10(-7) M, Bmax = 8.40 pmoles/mg protein. Mutant: Kd = 1.60 x 10(-7) M, Bmax = 10.00 pmoles/mg protein). Sphingosine inhibited the binding to approximately the same extent in normal and mutant cortex. These studies demonstrate the presence of highly specific, homogenous, single type phorbol ester receptors in cerebral cortex of cats with GM1 gangliosidosis which are qualitatively and quantitatively similar to normal cat brain.

Effect of phorbol myristate acetate on T cell colony formation, interleukin-2 (IL-2) receptor expression and IL-2 production by cells from patients at all stages of HIV infection

We and others have shown that several T cell responses induced by the mitogen phytohaemagglutinin (PHA), including T cell colony formation, IL-2 receptor (IL-2R) expression, and IL-2 production are impaired in patients with AIDS and lymphadenopathy syndrome (LAS). We investigated whether phorbol myristate acetate (PMA) could act in synergy with PHA (as it does in healthy subjects) to enhance in vitro T cell responses of patients at all stages of infection by HIV. In AIDS patients with opportunistic infections (AIDS/OI), PHA + IL-2 + PMA led to a total disappearance of T cell colonies in 10/11 patients, among whom six already displayed very low numbers of colonies induced by PHA + IL-2 (less than 50 colonies/5 x 10(4) cells). In contrast, T cell colony formation induced by PHA + IL-2 + PMA was maintained or increased, compared with that induced by PHA + IL-2, in five out of six AIDS patients with Kaposi's sarcoma (AIDS/KS), 10/14 LAS and six out of seven HIV-seropositive asymptomatic (HIV+/AS) homosexuals. In these three groups of patients, a low percentage of colony cells induced by PHA + IL-2 + PMA expressed CD3 and CD4 molecules, but 50-89% of cells were IL-2R (Tac) positive, as in healthy controls. Studies on T cell activation and IL-2 production were performed on a selected group of 12 HIV-infected patients for whom sufficient numbers of lymphocytes could be obtained. PMA induced CD4 down-modulation in controls and in HIV-infected patients. However, CD3 down-modulation and induction of the Tac chain of IL-2R by PMA were significantly impaired in patients, compared with controls, and these two parameters were correlated. Although PHA alone induced virtually normal levels of Tac antigen on patients' cells, Tac induction by PHA + PMA was significantly decreased in patients versus controls. Cells from five out of 10 patients tested failed to produce detectable amounts of IL-2 after PHA stimulation, whereas IL-2 production increased significantly in all patients tested (n = 9) after PHA + PMA, with a level of IL-2 activity significantly higher than in controls. No correlation was found in this group of patients between the effects of PMA + PHA on T cell colony formation, Tac expression, or IL-2 production, as compared with PHA alone. Taken together, our results indicate that in vitro T cell functional studies with PMA may be useful to evaluate better the defects of T cell activation in HIV-infected patients.

Regulation of IL-4 lymphokine gene expression and cellular proliferation in murine T helper type II cells

Activation of T cells results in the production of lymphokines and cellular proliferation. Protein kinase C (PKC) plays a key role in this process. It has been shown that this enzyme is essential to elicit a response to Con A or specific antigen in CD4+ T helper type 1 (Th 1) cells that secrete IL-2. We have now explored the signal transduction pathway that leads to transcription of the IL-4 gene and proliferation in murine CD4+ T helper type 2 (Th 2) cells. Surprisingly, we have found in two independently derived Th 2 clones that neither cellular proliferation nor IL-4 lymphokine production is affected by blocking or depletion of PKC. This differential mechanism of signal transmission leading to cellular activation implies a new distinction between murine Th 1 and Th 2 cells.

Superoxide as a signal for increase in intracellular pH

We examined the role of superoxide in the increase in intracellular pH (pHi) of human histiocytic leukemia U937 cells treated with 4 beta-phorbol-12,13-didecanoate (4 beta-PDD) or serum. 4 beta-PDD or serum induced a rapid increase in pHi, and antioxidants such as superoxide dismutase (SOD), vitamin E, and butylated hydroxyanisole (BHA) were found to inhibit the amiloride-sensitive increase in pHi induced by 4 beta-PDD. SOD inhibited the increase in pHi caused by serum, and essentially the same was found in concanavalin A-stimulated mouse thymocytes. Also, a superoxide-generating system, xanthine-xanthine oxidase (X-XOD), increased pHi of U937 cells as much as 4 beta-PDD or serum. From these findings, it appears that superoxide is the basis for the modulation of pHi.

Modulation of leukotriene release from human polymorphonuclear leucocytes by PMA and arachidonic acid

Stimulation of human neutrophils (PMN) with Ca ionophore A23187, opsonized zymosan and formyl-L-methionyl-L-leucyl-phenylalanine (FMLP) led to a time- and dose-dependent release of LTB4, 20-OH-LTB4, 20-COOH-LTB4, 6-trans-LTB4, 12-epi-6-trans LTB4 and LTC4, as detected by reverse-phase HPLC. Preincubation of the PMN suspension in the presence of Ca2+ and Mg2+ with phorbol-12-myristate-13-acetate (PMA) did not release leukotrienes by itself, but modulated the subsequent Ca ionophore-induced leukotriene release. The release of LTC4, 20-OH-LTB4 and 20-COOH-LTB4 was significantly decreased. Lesser effects were observed for the release of LTB4 and the non-enzymatic LTB4 isomers. In contrast, opsonized zymosan and FMLP enhanced the release of LTB4 and LTB4-omega-oxidation products from cells pretreated with PMA. With arachidonic acid as prestimulus, the amounts of the LTB4 isomers (6-trans-LTB4 and 12-epi-6-trans-LTB4) were enhanced significantly on subsequent stimulation with Ca ionophore. Prestimulation of lymphocytes, monocytes and basophilic granulocytes (LMB) with PMA had no significant effects on the ionophore-induced release of LTC4 and LTB4. PMN, but not LMB, suspensions prestimulated with PMA convert exogenously added LTC4 to LTB4 isomers and LTC4 sulphoxide. Our data suggest that preincubation of human granulocytes with PMA modified leukotriene release by activation or inhibition of different metabolic pathways for LTC4 and LTB4.

Characterization of lymphocyte stimulation by phorbol related compounds

1. The stimulation of (3H)-thymidine incorporation by lymphocytes in response to phorbol and seven other phorbol related compounds was investigated. 2. Lymphocytes from each of a small group of individuals were treated with the test compounds over wide concentration ranges. 3. All the tested compounds, including the most active, 12-0-tetradecanoylphorbol-13-acetate, were far less effective lymphocyte mitogens than the plant lectin phytohaemagglutinin. 4. Inter-individual differences were detected in the maximum response to the phorbols but not in their stimulating potency, as estimated by the concentration producing a half maximal response. 5. The rank order of the lymphocyte stimulating potency of the tested compounds was similar to the rank order of both tumour promoting activity and irritant potency in mouse skin. 6. Lymphocyte stimulation was paralleled equally well by these two mouse skin responses.

The cellular regulation of vesicle exocytosis by Entamoeba histolytica

We studied the cellular regulation of vesicle exocytosis by Entamoeba histolytica utilizing release of endocytosed 125iodine (125I) labeled tyrosine conjugated dextran; 125I-dextran entered the acid pH vesicles of the amebae and was not degraded during these studies. Exocytosis was temperature dependent with 74%, 36%, 4%, and 0% of 125I-dextran released after 120 min at 37 degrees C, 31 degrees C, 25 degrees C, and 4 degrees C, respectively (P less than 0.01 for each). Exocytosis at 37 degrees C was inhibited by cytochalasin D (10 micrograms/ml), EDTA (10 mM), or the putative intracellular calcium antagonist TMB-8 (250 microM) (P less than 0.01 for each at greater than or equal to 60 min). Calcium ionophore A23187 (1 microM) enhanced exocytosis at 5 and 15 min (P less than 0.01). Elevation of vesicle pH with NH4Cl (10 mM) had no effect on release of 125I-dextran; phorbol myristate acetate (10(-6) M) increased exocytosis by 46% at 30 min (P less than 0.01). Centrifugation of amebae with target Chinese hamster ovary cells resulted in decreased 125I-dextran release into the cell supernatant after 30 and 60 min at 37 degrees C (by 40% and 42%, respectively, P less than 0.01); release of 125I-dextran returned to control values with addition of 1.0 g% galactose or GalNac but not with mannose or N-acetyl-D-glucosamine. Amebic phagocytosis of serum-exposed latex beads had no effect on release of dextran by amebae (n = 16). Exocytosis of acid pH vesicles by E. histolytica is temperature-, microfilament-, and calcium-dependent, and stimulated by phorbol esters.

Changes in protein kinase C and cAMP-dependent kinase in lymphocytes after treatment with 12-O-tetradecanoylphorbol-13-acetate or concanavalin A: quantitation of activities with an in situ gel assay

Primary lymphocytes can be stimulated to proliferate by mitogenic lectins such as concanavalin A (Con A). While the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) alone is not mitogenic for these cells, it can enhance the response to Con A. Previously, protein kinases and phosphorylation have been reported to be important in lymphocyte proliferation. More recently TPA has been found to bind and activate protein kinase C. Therefore, we examined kinase activity in lymphocytes stimulated with the complete mitogen Con A and the comitogen TPA. In order to monitor more than one kinase we used an in situ gel assay and developed the system to compare both protein kinase C and cAMP-dependent kinases. When total cell extracts were assayed in the presence of histone five major bands of activity were detected by autoradiography of the gel. The bands corresponding to protein kinase C and to cAMP-dependent kinases were identified by partial purification of the enzymes, by binding of [20-3H(N)]7-phorbol-12, 13-dibutyrate (3H-PDBU), and by photoaffinity labelling with 8-azidoadenosine-3':5'-cyclic monophosphate (8-N3-[32P]cAMP). Differential extraction of cell lysate allowed comparison of soluble and particulate kinases. We found that when the preparations from either TPA- or Con A-treated lymphocytes were assayed, protein kinase C activity increased three- to four-fold in the particulate fraction within 5 min after treatment. A concurrent decrease of 30-50% occurred in the cytosol. In contrast, cytosolic cAMP-dependent protein kinase II increased 1.4-fold in the same period with Con A. PKI and PKII showed the most significant changes after 24 h of stimulation by Con A when the activity of the holoenzyme decreased to half that of the unstimulated cells. Therefore, although TPA and Con A separately can affect protein kinase C this alone is not sufficient for proliferation to occur.

Cytotoxic T lymphocytes: blocked differentiation at the 'poised' stage

The effect of different concentrations of phorbol myristate acetate (PMA) on the development of cytotoxic cells was studied. PMA was selectively able to prevent the development of cytotoxic cells in a mixed leucocyte culture, while allowing the responding cells to proliferate. The higher concentration of PMA (10(-5)M) blocked both direct cytotoxicity and lytic activity in the presence of lectin, while the lower concentration (10(-8) M) only prevented direct lytic function. The removal of PMA and subsequent addition of recombinant interleukin 2 (IL-2) or IL-2-containing supernatants effectively reversed the effect of PMA with recovery of antigen-specific lytic function of cells treated with 10(-8) M, while cells treated with 10(-5)M PMA only recovered lectin-dependent cytotoxic ability.

A monoclonal antibody inhibiting leucocyte adhesion blocks induction of IL-2 production but not IL-2 receptor expression

Monoclonal antibody 60.3 defines the leucocyte antigen CD 18 and recognizes a cell surface glycoprotein with an apparent molecular weight (MW) of 90,000 expressed by most human peripheral blood and bone marrow cells. This antibody can, among other things, block phorbol ester-induced adhesion among human mononuclear leucocytes. We show in this study that phorbol esters alone can induce peripheral blood mononuclear cells (PBL) to secrete interleukin-2 (IL-2) and that the IL-2-dependent cell line CTLL can be used for measuring this lymphokine without influence of the phorbol esters themselves. These findings make it possible to analyse the capacity of antibody 60.3 to interfere with IL-2 production and receptor expression by phorbol ester or phytohaemagglutinin (PHA)-treated human PBL. A significant positive correlation between blockage of induced cell aggregation by antibody 60.3 and reduction in IL-2 release was observed. The addition of interleukin-1 (IL-1) restored IL-2 secretion in PHA-treated, but not in 4-beta-phorbol 12, 13-dibutyrate [P(Bu)2]-treated, cells in the presence of this antibody. In parallel, IL-2 receptor expression was determined by immunofluorescence using biotinylated anti-IL-2 receptor (Tac) antibodies. FACS analysis showed that IL-2 receptor expression was unaffected by antibody 60.3, whereas DNA synthesis of the same P(Bu)2-treated PBL was inhibited. However, addition of external recombinant IL-2 overcame this proliferation blockade. These results indicate that a cell-to-cell adhesion step is necessary for the production of IL-2, but not for the expression of its receptor on both PHA- and P(Bu)2-treated human PBL.

Phorbol ester binding and phorbol ester-induced arachidonic acid metabolism in a highly responsive murine fibrosarcoma cell line and in a less-responsive variant

Phorbol ester binding was examined in two lines of murine fibrosarcoma cells. The two cell lines were isolated from the same parent tumor but respond differentially to stimulation with phorbol esters. In one of the lines, these agents stimulate a rapid attachment and spreading response and induce directional migration. The other cell line does not migrate in response to stimulation with phorbol esters and the attachment and spreading response is slow. The cell line which responds actively to phorbol ester stimulation is highly malignant when injected into syngeneic animals while the other line is of low tumorigenicity and is virtually non-metastatic. In spite of these differences, both lines were found in the present study to bind [3H]4 beta-phorbol-12 beta, 13 alpha-dibutyrate in a receptor-mediated fashion. The characteristics of binding were virtually identical between the two cell lines. In additional studies, arachidonic acid metabolism was examined in the same two lines. In the highly responsive line, PMA stimulated a rapid release of [3H]arachidonic acid and its conversion into cyclooxygenase and lipoxygenase products. In the less-responsive line, PMA stimulated a slower release of [3H]arachidonic acid from prelabeled cells. The quantity of arachidonic acid metabolites produced was also much less. These studies suggest that the disparity between the two cell lines in their response to phorbol ester stimulation is not the result of differences in the initial interaction between the cells and ligand but may result from alterations in their signal transductance mechanism. This may be the result of inherent differences in capacity for arachidonic acid metabolism.

Phorbol ester enhances deoxynucleoside incorporation while inhibiting proliferation of K-562 cells

Recently a new technique has been developed to study bromodeoxyuridine incorporation into DNA as a function of the cell cycle phase distribution. We have made the observation that treatment of the hematopoietic cell line K-562 results in a complete and immediate cessation of cell growth, although tritiated thymidine incorporation is markedly elevated for as long as 5 days. We have made use of that newly described technique to study this phenomenon.

Phorbol ester-induced adhesion (binding) among human mononuclear leukocytes requires extracellular Mg++ and is sensitive to protein kinase C, lipoxygenase, and ATPase inhibitors

Under gentle shaking, the phorbol 12,13-dibutyrate (P(Bu)2)-induced adhesion among human blood mononuclear leukocytes started within a few minutes, increased with time and was almost complete after 12 h. During this moment and thereafter more than 60% of the cells were in aggregates. Induction of the cell aggregation by 20 min treatment with P(Bu)2 did not occur in Ca++/Mg++-free medium but was almost complete with Mg++ alone and reached its maximal manifestation with both divalent cations present. The intracellular Ca++ antagonist 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate had a minimal inhibitory effect, and simultaneous treatment of the cells with Ca++ ionophore A23187 and P(Bu)2 did not increase the intercellular binding, whereas A23187 alone induced some cell aggregation. Retinal, a protein kinase C inhibitor, inhibited the intercellular adhesion by more than 50%, and treatment of intact cells with 1-oleoyl-2-acetyl-glycerol, an activator of the enzyme, induced some cell aggregation that was slightly increased when A23187 was added simultaneously. Nordihydroguaiaretic acid, 5,8,11-eicosatriynoic acid and 5,8,11,14-eicosatetraynoic acid, which inhibit lipoxygenation of arachidonic acid, reduced the cell aggregation in contrast to indomethacin and acetylsalicylic acid that had no effect. Cellular ATPases, inhibited by quercetin, but not the ouabain-sensitive Na+, K+-ATPase, appeared to participate, whereas the amiloride-sensitive plasma membrane Na+/H+ exchanger and the intracellular levels of cGMP did not seem to influence the system.

Identification of a cell surface protein complex mediating phorbol ester-induced adhesion (binding) among human mononuclear leukocytes

Phorbol esters rapidly induce aggregation of human mononuclear leukocytes in vitro. Previous studies have indicated that cell surface proteins are involved. We report now that the monoclonal antibody 60.3, either as purified IgG or as Fab' fragments, to an antigen common to leukocytes completely inhibited the phorbol ester-induced intercellular adhesion (binding). No inhibition of cell aggregation was observed with monoclonal antibodies to common leukocyte antigen T 200, T-cell-associated antigen, monocyte-granulocyte antigen, brain granulocyte-T-lymphocyte antigen, transferrin receptor, mature T-cell antigens (mol.wt either 67,000 or 19,000/29,000), T helper/inducer cell antigen, sheep erythrocyte receptor, class I or class II antigens, or T cytotoxic/suppressor cell antigen. The antibody 60.3 did not inhibit stimulation of the cells since the characteristic phorbol ester-induced morphological changes and phorbol ester-enhanced cap formation of membrane glycoproteins were readily observed. Two major cell surface polypeptides with apparent molecular weights of 90,000 and 160,000 were immunoprecipitated. We conclude that this protein complex, or at least one of its components, mediates adhesion among mononuclear leukocytes.

Control of lysozyme gene expression in differentiating HL-60 cells

We have investigated the control of lysozyme gene expression in HL-60 cells induced to differentiate into macrophage-like cells with phorbol myristate acetate (PMA). Differentiation, as evidenced by cellular adherence, and morphological changes corresponded temporally to an increase in nonspecific esterase activity. The lysozyme concentration in the medium of uninduced HL-60 cells was 10 micrograms/10(7) cells, increasing to a maximum of 46 micrograms/10(7) cells after 48 h incubation with PMA (16 nM). At 72 h the lysozyme concentration decreased to 16 micrograms/10(7) cells. Intracellular lysozyme activity remained constant throughout differentiation. If HL-60 cells were exposed to PMA for 24 h, washed, then maintained in normal medium, they differentiated normally, confirming their irreversible commitment to differentiate. The increase in lysozyme secretion by these cells, however, is markedly blunted suggesting that continued PMA treatment of differentiated cells is required for their secretion of lysozyme. There is no change in the rate of extracellular degradation of lysozyme during differentiation. The level of lysozyme mRNA does not correlate directly with the amount of lysozyme secreted into the medium. Hybridization of uninduced HL-60 cell RNA with a chicken lysozyme cDNA probe demonstrates moderate hybridization. There is a modest (five-fold) increase in lysozyme mRNA between 0 and 36 h of exposure to PMA, corresponding to the burst of lysozyme secretion by these cells. The lysozyme mRNA decreases to a level which is lower than the original baseline by 72 h, when the cells are still secreting substantial amounts of lysozyme. These data suggest that both transcriptional and post-transcriptional controls are operative in the control of lysozyme gene expression during the differentiation of HL-60 cells. They also imply that lysozyme secretion is not a necessary component in the macrophage-monocyte differentiation of these cells.

Structural correlations of phorbol-ester-induced stimulation of PGE2 production by human rheumatoid synovial cells

Eight phorbol esters were studied for their ability to stimulate prostaglandin production in human rheumatoid synovial cells over the dose range 0.1 ng to 1.0 micrograms. These derivatives were based upon phorbol, 4-deoxyphorbol, and 12-deoxyphorbol nuclei. This activity was structurally dependent and, although it did not correlate with the actions of the same compounds to induce erythema in vivo, it did correlate with their ability to stimulate human lymphocyte mitogenesis. Stimulation of PGE2 production by a phorbol and a 12-deoxyphorbol analog was inhibited in this system by both indomethacin and dexamethasone.

Analysis of human T lymphocyte activation in a T cell tumor model system

The human T leukemia line Jurkat maintains functional characteristics of normal T cells in responding to inducing stimuli by the release of interleukin 2 (IL 2). Presence of a phorbol ester during stimulation eliminated the requirement for specialized accessory cells in the response to cell mitogenic agents such as the lectin concanavalin A or treatment with neuraminidase and galactose oxidase. Antibodies directed against the T cell receptor-associated antigen T3 served as efficient stimuli, especially if aided by agents that cross-link immunoglobulin, indicating that a triggering signal is received by a T cell via aggregation of its antigen receptor complex. A Burkitt lymphoma cell line, Raji, was found to selectively trigger Jurkat cells, suggesting the ability of those cells to respond to certain foreign stimuli. The Jurkat cell line has been instrumental in the purification of IL 2 and cloning of the corresponding gene. Our data suggest it can also serve as a useful model for induction of T cell responses.

Induction of IL-2 production, IL-2 receptor expression and proliferation of T3- T-PLL cells by phorbol ester

Leukemic T cells from the peripheral blood of a patient with T-prolymphocytic leukemia (T-PLL) were investigated for their potential to differentiate in vitro upon exposure to 12-O-tetradecanoyl-phorbol-13-acetate (TPA). The T-PLL cells, identified as typical PLL cells by nuclear morphology, were typed as E+slg-OKT1+3-4+6-8-11+ cells lacking reactivity with OKI-1 or OKM-1. In addition, between 3% and 10% of the cells reacted with monoclonal antibodies against T10. In contrast to normal T cells, the T-PLL cells could not be induced to proliferate by mitogenic lectins or alloantigens in the presence or absence of human interleukin-1 (IL-1), interleukin-2(IL-2) or allogeneic monocytes and did not produce IL-2. They also failed to proliferate in response to TPA or TPA in the presence of phytohemagglutinin (PHA), but under these conditions T-PLL cells secreted high levels of IL-2 activity. Incubation in the presence of PHA + TPA or TPA for 48 h induced T-PLL cells to become blasts exhibiting enhanced protein synthesis, and induced a 10-fold increase in the percentage of cells reactive with monoclonal antibodies against T10. At the same time, about 15% of the cells developed receptors for IL-2 as monitored by their reactivity with anti-Tac monoclonal antibody. Washing of these T-PLL cells to remove TPA resulted in the induction of proliferation upon subsequent culture in the presence of IL-2 or in medium only. Since proliferating T-PLL cells still failed to express T3 antigens, it was concluded that these leukemic cells represent a T-cell differentiation stage or a T-cell subset which can be activated via a T3-independent pathway.

The E receptor regulates interferon-gamma production: four-receptor model for human lymphocyte activation

The E receptor (binds sheep erythrocytes) is found on virtually all human T cells. Here we show that a monoclonal antibody 9.6, which recognizes and binds the E receptor, inhibited interferon-gamma production by human peripheral blood mononuclear leukocytes induced with the mitogens phytohemagglutinin, concanavalin A, Staphylococcal enterotoxin A and the monoclonal antibody OKT3. Metabolic activation (RNA and DNA synthesis) in human peripheral blood mononuclear leukocytes in response to mitogens was also sharply inhibited by 9.6. This inhibitory effect occurred early during the induction phase since 9.6 had much diminished inhibitory effects when added 15-24 h after induction; peak IFN-gamma production and DNA synthesis occurred 3-4 days post induction. An early event inhibited by 9.6 appeared to be interleukin 2 (IL 2) receptor formation since: (a) the ability of mitogen-stimulated peripheral blood mononuclear leukocytes to absorb IL 2 was inhibited by 9.6, and (b) lines of T lymphocytes which already expressed IL 2 receptors were largely resistant to the inhibitory effects of 9.6 on IFN-gamma production and DNA synthesis. The tumor promoters 12-O-tetradecanoyl phorbol-13-acetate and teleocidin largely reversed the inhibition by 9.6 of IFN-gamma production and metabolic activation induced by mitogens. A model for the control of IFN-gamma induction involving four receptors, those for mitogens, tumor promoter, IL 2 and erythrocyte, is proposed.

12-O-Tetradecanoylphorbol-13-acetate (TPA) directly inhibits spontaneous immunoglobulin secretion by in vivo antigen-induced human lymphoblastoid B cells

Tetanus toxoid (Tet) booster immunization induces the transient appearance in the circulation of lymphoblastoid (LB) B cells which spontaneously produce anti-tetanus toxoid IgG antibody (IgG-Tet) during a 3-day in vitro culture. In this study we have examined the effects of TPA on the ability of LB cells to secrete antibody and have found that as little as 10 ng/ml of TPA provoked a marked inhibition of the induced LB cells' IgG-Tet production. This inhibitory effect was observed only when TPA was added early in the culture and could be achieved by pretreating the B cells with TPA for as little as 1 hr. Only marginal inhibition of IgG-Tet production was observed if the addition of TPA was delayed 14-24 hr. The TPA inhibition was not mediated by contaminant T cells as the addition of increasing numbers of T cells to LB cell cultures proportionally reversed the TPA inhibitory effect. Likewise, the inhibition of antibody synthesis was not due to a monocyte-dependent mechanism since (1) substantial depletion of adherent cells did not reverse the inhibition of antibody synthesis, (2) the addition of a monocyte-enriched population to monocyte-depleted B cells did not enhance, but in fact partially reversed, the inhibition caused by TPA, and (3) the addition of monocyte populations pretreated with TPA to monocyte-depleted B-cell fractions did not inhibit subsequent IgG-Tet production by the LB cells.

Augmentation of mixed lymphocyte response. Stimulatory activity by phorbol ester

The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) induces a variety of phenotypic changes on normal and malignant cells. In chronic and acute lymphocytic leukemia we have observed a marked augmentation in mixed lymphocyte reaction stimulatory capacity (MLRs) following pretreatment of leukemia blasts with TPA. We have now characterized the effects of TPA on MLRs utilizing the non-T, non-B lymphoblastic leukemia-cell line, HOON. Following pretreatment with TPA (optimal concentration, 1.6 X 10(-10) M), but not with other phorbol esters, there was a marked increase in MLRs, particularly at lower stimulator-cell concentrations. This effect was maximal following a 44-hr preincubation period and the enhancement in MLRs was not accompanied by changes in levels of Ia expression. This cell line provides a model for determining the molecular basis for the TPA-induced augmentation of stimulatory capacity in the mixed lymphocyte reaction.

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.

Tumor-promoting phorbol esters inhibit the binding of colony-stimulating factor (CSF-1) to murine peritoneal exudate macrophages

L-cell colony-stimulating factor (CSF-1) is a sialoglycoprotein of molecular weight 70,000 daltons that specifically stimulates macrophage colony formation by single committed cells from normal mouse bone marrow and by various classes of more differentiated tissue-derived mononuclear phagocyte colony-forming cells (Stanley et al., 1978). CSF-1 interacts with target cells by direct and specific binding to membrane receptors (CSF-1 receptors) that are present only on cells of the mononuclear phagocyte series and their precursors. We studied the effect of tumor-promoting phorbol esters on the binding of 125I-labeled CSF-1 (125I-CSF-1) to murine peritoneal exudate macrophages (PEM). Biologically active TPA (12-O-tetradecanoyl phorbol-13-acetate) inhibits the binding of 125I-CSF-1 to its receptor on PEM. This inhibition exhibits temperature, time, and concentration dependence. At 37 degrees C, maximum inhibition occurred at about 10(-7) M; inhibition was 50% at 5 X 10(-9) M. At 0 degrees C, the inhibitory activity of TPA is diminished. The action of TPA on PEM is transient. Treated cells recover their 125I-CSF-1-binding activity whether TPA is later removed or not. The process of recovering CSF-1-binding activity is completely blocked by the addition of cycloheximide. When several phorbol derivatives were tested for their inhibitory activities, only biologically active phorbol esters were found to possess such activities. Furthermore, the inhibitory activities of various phorbol esters are proportional to their tumor-promoting activities. Inhibition appears to be due to a reduction in the total number of available CSF-1 receptors rather than a decrease in receptor affinity.

Enhanced expression of human T-cell leukemia/lymphoma virus in neoplastic T cells induced to proliferate by phorbol ester and interleukin-2

Peripheral blood T cells from a patient with T-cell chronic lymphocytic leukemia (T-CLL) failed to respond to mitogenic lectins or alloantigens but could be induced to proliferate by the addition of exogenous interleukin-2 (IL-2). The T-CLL cells also proliferated in response to 12-O-tetradecanoyl phorbol-13-acetate (TPA), or to TPA in combination with phytohemagglutinin (PHA). These TPA-mediated proliferative responses were transient, and only small but significant amounts of IL-2 activity were generated. In contrast, no IL-2 activity was produced after the T-CLL cells had been stimulated with PHA only. The T-CLL cells that were induced to proliferate with PHA and exogenous IL-2 could be maintained in continuous culture by the addition of exogenous IL-2 at regular intervals. These continuously proliferating T-CLL cells failed to produce IL-2 constitutively. However, they could be induced to produce IL-2 activity by stimulation with TPA or TPA plus PHA. Irradiation of the proliferating T-CLL cells prior to incubation with TPA or TPA plus PHA resulted in a 9-fold increase in IL-2 activity, suggesting that the proliferating T-CLL cells were able to consume the IL-2 they produced. Studies on the presence of human T-cell leukemia/lymphoma virus (HTLV) in the fresh and proliferating T-CLL cells revealed that 12% of the fresh cells expressed the HTLV p19 structural core protein. HTLV p19 expression was strongly enhanced in the T-CLL cells induced to proliferate by TPA (66%) and in the continuously growing IL-2-dependent T-CLL cells (82%). In the latter culture, but not in the fresh T-CLL cells, type-C virus particles were observed. These results indicate that HTLV expression correlates with T-CLL cell proliferation but not with IL-2 production by these cells.

Characterization of a specific phorbol ester aporeceptor in mouse brain cytosol

In the presence of phosphatidylserine, [20-3H]-phorbol 12,13-dibutyrate [( 3H]PBt2) bound specifically to a single class of binding sites in mouse brain cytosol (supernatant at 100,000 X g). The dissociation constant for binding was 3.1 X 10(-9) M, and at saturation 23.2 pmol of [3H]PBt2 was bound per mg of cytosolic protein. Less than 1 pmol of [3H]PBt2 per mg bound in the absence of phospholipids. Phosphatidic acid, sphingomyelin, and phosphatidylinositol also were able to reconstitute binding activity, whereas phosphatidylcholine and phosphatidylethanolamine were relatively ineffective. [3H]PBt2 binding was inhibited by phorbol 12-myristate 13-acetate (Ki = 4.4 X 10(-11) M), phorbol 12,13-didecanoate (Ki = 7.7 X 10(-9) M), phorbol 12,13-diacetate (Ki = 4.4 X 10(-7) M) and 4-O-methylphorbol 12-myristate 13-acetate (Ki = 5.1 X 10(-7) M). The apparent Ki values of the phorbol-related diterpenes for inhibiting binding agreed reasonably closely with the values previously determined for mouse brain membrane binding. The biologically inactive derivatives phorbol (30 microM) and 4 alpha-phorbol 12,13-didecanoate (30 microM) did not inhibit binding. The aporeceptor was eluted in one peak during Ultrogel 44 column chromatography, corresponding to a molecular weight of approximately equal to 77,000. Calcium phospholipid-dependent protein kinase C activity was eluted with a profile similar to that of the cytosolic aporeceptor-binding activity.

Identification of high-affinity phorbol ester receptor in cytosol of EL4 thymoma cells: requirement for calcium, magnesium, and phospholipids

A specific high-affinity phorbol ester binding component has been identified in the cytosol of an EL4 mouse thymoma line by using conditions similar to those for demonstrating activity of a calcium/phospholipid-dependent protein kinase. Specific binding is absolutely dependent on acidic phospholipids (maximal binding at 96 micrograms of phosphatidylserine per ml or 200 micrograms of phosphatidylinositol per ml) and is greatly enhanced by addition of calcium (0.5 mM) and magnesium (75 mM). Scatchard analysis of the cytosolic binding component indicated a Kd of 4.2 +/- 2.5 nM with 1.8 +/- 0.6 x 10(4) sites per cell compared to a Kd of 11.9 +/- 4.4 nM and 4.1 +/- 1.0 x 10(4) sites per cell for the membrane receptor. Consistent with the existence of at least two phorbol ester binding sites in EL4 cells was the observation of curvilinear Scatchard plots for binding to whole homogenates. The cytosolic binding showed the same order of potency for binding phorbol ester analogs as has been observed for intact cells. These results further support the similarity between phorbol ester receptors and the calcium/phospholipid-dependent protein kinase and suggest that the cytosolic receptor may be involved in subsequent phorbol ester effects in EL4 cells including loss of the kinase activity from the cytosol and production of T-cell growth factor.

Characterization of a high-affinity receptor for phorbol esters in rat alveolar macrophages

Macrophages display varied responses to the tumor promoter, TPA. In this study, a high-affinity receptor for phorbol ester is characterized in a viable alveolar macrophage population. The binding assay is performed using tritiated PDBu and specific binding is demonstrated to be temperature-sensitive. At 37 degrees C, the level of bound ligand reaches maximal binding within 2-5 min but rapidly decays to within 30% of the original specific binding. Equilibrium, however, can be established when the assay is carried out at 4 degrees C. The data indicate that at this temperature maximal binding is reached within 2 h and remains constant thereafter. Scatchard analysis shows that the receptor has an apparent Kd of 21 nM and each macrophage possesses 2 X 10(5) binding sites. Active phorbol derivatives such as TPA and PDBu compete with the labeled ligand for the receptor, whereas the inactive phorbol alcohol does not modulate the specific binding. Mezerein, a related diterpene which has been shown to share some of the properties of phorbol esters, also competes for the binding site. The high-affinity receptor is not affected by zymosan or EIgG phagocytosis. Inflammatory mediators such as prostaglandins E2 and F2 alpha and platelet-activating factor do not compete for the receptor.

Phytohemagglutinin inhibits phorbol diester promotion of UV-irradiation initiated transformation in Syrian hamster embryo cells

Phytohemagglutinin (PHA) or either of its isolectins, erythroagglutinin or leukoagglutinin, causes a dose-dependent decrease in 12-0-tetradecanoylphorbol 13-acetate (TPA)-promoted transformation of Syrian hamster embryo cells, but has no effect on transformation induced by ultraviolet irradiation. The ineffectiveness of concanavalin A indicates that not every lectin inhibits TPA. Galactose, a dominant sugar in receptors for PHA binding, reverses the inhibition of TPA promotion caused by PHA but galactose does not inhibit TPA promotion itself. Therefore, the TPA and PHA binding sites are functionally discrete. The PHA inhibition of TPA-promoted transformation is reversible because PHA is only effective if present with TPA, whereas lymphotoxin, an immunologic hormone, has a persistent anti-carcinogenic effect, regardless of whether it is added before or after TPA. PHA in conjunction with lymphotoxin causes additional inhibition of TPA-promoted transformation. PHA and lymphotoxin affect the biological activity of TPA by diverse mechanisms. Lymphotoxin alters the physiological state of the cell, causing a change in the cellular response to TPA. PHA may affect either the binding of TPA to a critical cellular receptor for promotion or a later step in promotion.

Tumor-promoting phorbol esters selectively abrogate the expression of the T4 differentiation antigen expressed on normal and malignant (Sézary) T helper lymphocytes

12-O-tetradecanoylphorbol-13-acetate (TPA) selectively abrogates, in nanomolar concentrations, the expression of the T4 differentiation antigen, as defined by the monoclonal anti-T4 antibody (1) on Il-2-producing T helper lymphocytes from normal donors and on T helper lymphocytes from a patient with malignant T cell lymphoma (Sézary's syndrome); this compound does not affect the expression of cell surface antigens as defined by the antibodies anti-OKT3, -T6, -T8, -T11, Ia, or anti-surface immunoglobulin. Abrogation of the T4 antigen expression is concentration dependent, completed within 8 h of incubation at 37 degrees C, does not occur at 4 degrees C, and is reversible. Only those phorbol-esters known to have tumor-promoting activity in vivo (2) affect the T4 antigen, whereas nonpromoting compounds are ineffective.

Receptor-mediated modulation of human monocyte, neutrophil, lymphocyte, and platelet function by phorbol diesters

The tumor promoting phorbol diesters elicit a variety of responses from normal and leukemic blood cells in vitro by apparently interacting with cellular receptors. The biologically active ligand [20-(3)H] phorbol 12,13-dibutyrate ([(3)H]PDBu) bound specifically to intact human lymphocytes, monocytes, polymorphonuclear leukocytes (PMN), and platelets, but not to erythrocytes. Binding, which was comparable for all four blood cell types, occurred rapidly at 23 degrees and 37 degrees C, reaching a maximum by 20-30 min usually followed by a 30-40% decrease in cell associated radioactivity over the next 30-60 min. The time course for binding was temperature dependent with equilibrium binding occurring after 120-150 min at 4 degrees C, with no subsequent loss of cell-associated radioactivity at this temperature. Bound [(3)H]PDBu could be eluted by addition of unlabeled PDBu. Scatchard analysis of data from 4 degrees C binding studies revealed linear plots with high affinity receptors in these cell types with dissociation constants and receptors per cell of 60 nM and 7.8 x 10(5)/cell for lymphocytes, 51 nM and 15.5 x 10(5)/cell for monocytes, 38 nM and 4.0 x 10(5)/cell for PMN, and 19 nM and 2.9 x 10(4)/cell for platelets. Structure-activity studies using unlabeled phorbol-related compounds demonstrated a close correlation between their abilities to inhibit binding of [(3)H]PDBu to cells and their abilities to induce cellular responses (monocyte and PMN H(2)O(2) secretion, lymphocyte (3)HTdR incorporation, and platelet tritiated serotonin release); phorbol and 4-alpha phorbol were inactive while phorbol 12-myristate 13-acetate (PMA), PDBu, mezerein, and phorbol 12,13-diacetate (in decreasing order of potency) inhibited [(3)H]PDBu binding and elicited the various responses. Thus, these high affinity, specific receptors for the phorbol diesters, present on monocytes, lymphocytes, PMN, and platelets, mediate the pleiotypic effects induced by these ligands.

Phorbol ester induction of leukemic cell differentiation is a membrane-mediated process

Phorbol esters are potent inducers of macrophage-like differentiation in the HL-60 promyelocytic leukemia cell line. The sequence of events by which they bring about this transition is poorly understood. However, it is known that phorbol esters bind to the surface membrane of HL-60 cells and to various other cells as well. Our studies were directed toward determining the biologic importance of this membrane association. [3H]Phorbol dibutyrate (PBu2) was specifically bound by HL-60 cells with a Kd of 23 nM and with 1.9 X 10(5) binding sites for [3H]PBu2 per cell. There was no internalization of bound [3H]PBu2. Specific binding was fully reversible upon washing in fresh medium, and [3H]PBu2 added thereafter bound normally to its receptor. Within 10 min of binding, PBu2 stimulated [14C]choline incorporation into phosphatidylcholine, with a rapid return to normal upon removal of the PBu2. Membrane-bound PBu2 progressively inhibited DNA synthesis, with 70% inhibition by 8 hr. This process was interrupted if the PBu2 was removed, and little recovery of DNA synthesis occurred in previously inhibited cells. Between 8 and 16 hr, PBu2 induced adherence of cells to plastic, but only in those cells in which phosphatidylcholine synthesis was stimulated, and this process was also interrupted if PBu2 was removed prior to 16 hr. Similarly, nonspecific esterase, which develops after 72 hr of incubation, was induced in cells exposed to PBu2 for the initial 16 hr but not in cells exposed for 5 hr. These studies demonstrate that phorbol esters exert their effects while retained at the cell surface. Inhibition of cell growth and the acquisition of surface and enzymatic properties that characterize macrophages are separable events, each of which proceeds through a receptor-mediated, transmembrane process. The stimulation of phosphatidylcholine synthesis appears to be a part of that process.