The role of calcium ions in initiating transformation of lymphocytes

Effect of gravity on lymphocyte proliferation

Reports on postflight examination of lymphocytes from crew members of soviet and american spaceships show a depression of reactivity towards mitogens in vitro. The purpose of this communication is to present experimental evidence that gravity can interfere with lymphocyte activation. Lymphocytes were incubated in the presence of concanavalin A in a centrifuge at 2 and 4 g for four days. This environment causes a significant acceleration of the response to the mitogen. In addition, remarkable differences in the ultrastructure of cells grown at 1 g and 4 g are observed by electron microscopy. This investigation is related to the experiment "Effect of weightlessness on lymphocyte proliferation" experiment which will be performed during the first Spacelab mission.

Dietary olive oil enhances murine lymphocyte calcium uptake

BACKGROUND

Dietary lipids enhance immune function and improve outcome from injury or infection in animal models. We tested the hypothesis that amount, type, or both, of dietary lipid increases intracellular calcium concentration, a surrogate for lymphocyte activation.

METHODS

Mice were fed 2 weeks on semipurified diets with 5% (by weight [w/w]), 10% (w/w), or 20% (w/w) dietary fat consisting of coconut, olive, safflower, or linseed oil. Changes in intracellular calcium concentration after mitogen stimulation of splenic lymphocytes was estimated by using flow cytometry.

RESULTS

Olive oil diets increase intracellular calcium concentration after concanavalin A, lipopolysaccharide, and CD3 stimulation. On the other hand, linseed oil (which is high in omega-3 fatty acids, which have been shown in other studies to enhance immune function) depresses intracellular calcium levels. The amount of dietary fat had no effect on intracellular calcium.

CONCLUSION

Olive oil merits further study in the application of nutritional pharmacology to immunomodulation of the critically injured, because it may enhance lymphocyte function.

[8-(Diethylamino)octyl-3,4,5-trimethoxybenzoate, HCl], the inhibitor of intracellular calcium mobilization, blocked mitogen-induced T cell proliferation by interfering with the sustained phase of protein kinase C activation

The physiological role of IP(3)-dependent Ca(2+) release in T cell activation was in question due to the contradictory findings that [8-(Diethylamino)octyl-3,4,5-trimethoxybenzoate, HCl] (TMB-8), an inhibitor of intracellular Ca(2+) mobilization, blocked T cell proliferation, curtailing specifically the level of released Ca(2+) did not affect T cell activation and T cell line lacking IP(3) receptor was defective in IL-2 production in response to TCR/CD3 ligand. In the present study we found that TMB-8 inhibited Concanavalin A (Con A)- but not PMA/Ionomycin-induced T cell proliferation in a reversible and dose-dependent manner. The kinetic study revealed that TMB-8 exerted the inhibitory effect at a very early step of T cell activation. The Ca(2+) ionophore ionomycin augmented instead of overcoming the inhibitory effect of TMB-8, although the same doses of ionomycin alone had no effect on Con A-induced T cell proliferation. PMA the metabolically stable, but not diacylglycerol (DAG) the metabolically labile, activator of protein Kinase C (PKC) completely overcome the antiproliferative effect of TMB-8. A specific DAG lipase inhibitor RHC80267 also overcome the effect of TMB-8. Taken together, these results showed that the process of Ca(2+) release through IP(3) receptor, not the released Ca(2+), is essential for the sustained phase of PKC activation during T cell proliferation.

Decrease of hormone binding capacity of estrogen receptor by calcium

We have addressed the question as to whether calcium may modify the [3H]estradiol ([3H]E2) binding properties of the estrogen receptor (ER). A human recombinant full length ER (yER) expressed in yeast was used to limit the potential interference of ER-associated proteins and proteases present in the target tissues. Ca++ (0.1-10 mM) always produced an important loss of [3H]E2 binding capacity without any effect on the hormone binding affinity of residual receptors. This loss was reflected in a decrease of immunoreactivity for monoclonal antibodies raised against the hormone binding domain. An ER recombinant expressing solely this domain confirmed that the ion operated at this level. Binding of [125I]Z-17 alpha-(2-iodovinyl)-11 beta-chloromethyl estradiol-17 beta (an compound with very high selectivity for ER) as well as [125I]tamoxifen aziridine were similarly affected. Size-exclusion chromatography failed to reveal the emergence of any ER isoforms of low molecular weight rejecting the hypothesis of a Ca(++)-induced proteolysis. In agreement with this conclusion, EDTA reversed the loss of [3H]E2 binding capacity. Phosphoamino acids (PY, PT and PS) partly antagonized the effect of Ca++ suggesting its interaction with phosphoamino acid residues. Worthy of note, the effect of Ca++ appeared more marked when assessed by DCC than HAP assay. The phosphocalcic nature of the HAP matrix may explain this phenomenon which was observed with cytosolic ER from various origins.

Response of intestinal transglutaminase activity to dietary phytohaemagglutinin

The behaviour of the activity of tissue transglutaminase, a calcium-dependent enzyme, and the levels of polyamines which are physiological substrates for the enzyme, were studied in rat small intestine induced to grow by lectin phytohaemagglutinin. Transglutaminase activity greatly increased in the homogenates and the cytosolic fractions of the intestinal mucosa of lectin-treated rats compared to that of untreated animals. The measurement of enzyme activity in the presence of monodansylcadaverine, a competitive inhibitor of transglutaminase, testified that the assayed enzyme activity was authentic transglutaminase. As regards polyamines, the level of spermine did not change, whereas putrescine and spermidine contents were enhanced. The activation of transglutaminase, which was probably due to Ca2+ accumulation in enterocytes, could have a role in maintaining enterocyte adhesion and intestinal cell homeostasis, and/or repairing lectin-induced damages of microvilli of the gut epithelium.

Role of Ca2+ in the early stages of murine adipocyte differentiation as evidenced by calcium mobilizing agents

We have investigated the effect of the endoplasmic reticulum Ca(2+)-ATPase inhibitor thapsigargin and the calcium ionophore A23187 on the differentiation of 3T3-L1 preadipocytes. Treatment of 3T3-L1 preadipocytes with either agent resulted in a dose-dependent inhibition of adipocyte differentiation. The cells accumulated neither fat droplets nor the adipocyte-specific mRNAs encoding stearoyl-CoA desaturase 1 (SCD1) and adipocyte-P2 (aP2). These late markers of differentiation were specifically affected, because thapsigargin and A23187 did not inhibit the expression of beta-tubulin mRNA. No inhibition of differentiation or the expression of the mRNAs occurred when the drugs were added either prior to or 2 days after the initiation of differentiation. Thapsigargin and A23187 were also shown to dramatically block cell proliferation and DNA replication, which occur early in differentiation. Furthermore, during the first 48 h, thapsigargin and A23187 mediated an elevated and prolonged expression of the immediate-early gene corresponding to c-myc, and altered intracellular levels of calcium. Our results suggests that changes in intracellular calcium levels elicited by thapsigargin and A23187 prevent differentiation of 3T3-L1 preadipocytes into adipocytes by blocking the postconfluent mitotic phase of the differentiation process and also by mediating c-myc gene expression.

Role of intracellular calcium as a priming signal for the induction of nitric oxide synthesis in murine peritoneal macrophages

Because the role of intracellular Ca2+ in the two-signal process for the induction of nitric oxide (NO) synthesis is controversial, this study was undertaken to examine the role of Ca2+ in the transcriptional regulation of inducible NO synthase (iNOS) in murine peritoneal macrophages. Treatment of the cells with thapsigargin (TG) or 2,5-di-(t-butyl)-1,4-benzodihydroquinone (tBuBHQ), which are the specific and potent Ca(2+)-ATPase inhibitors of endoplasmic reticulum (ER), showed modest effects on tumoricidal function, whereas TG or tBuBHQ in combination with interferon-gamma (IFN-gamma) or lipopolysaccharide (LPS) showed marked effects on tumoricidal function of the cells. The tumoricidal effects of the activated macrophages were correlated with the amount of NO synthesis, and totally abrogated by the use of NOS inhibitor, NG-monomethyl-L-arginine (NGMMA). The increases in NO synthesis was reflected as increased amounts of iNOS mRNA by Northern blotting. To confirm that iNOS induction was due to the changes in the intracellular Ca2+ level, the acetoxymethyl ester of 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM), an intracellular Ca2+ chelator, was used. Blocking the increase of cytosolic free Ca2+ significantly decreased the induction of NO synthesis. To demonstrate that intracellular Ca2+ acts as a 'priming' signal rather than a 'triggering' signal on the induction of NO synthesis by murine peritoneal macrophages, we designed several experiments. When the cells were treated with TG 6 hr after the treatment with IFN-gamma, there was no increase in NO synthesis. In addition, when the cells were treated with TG or LPS 6 hr after treatment with tBuBHQ, a synergistic increase on NO synthesis was shown only in the case of LPS. When phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, was added to the cells 6 hr after the treatment with TG, there was a marked co-operative induction of NO synthesis, even though PMA alone has no effect. Based on the results obtained in this study, we suggest that cytosolic Ca2+ might be enough for the expression of iNOS gene as a priming signal and PKC might be involved in the induction of NO synthesis as a triggering signal by post-transcriptional modification of iNOS mRNA or iNOS itself in the activated murine peritoneal macrophages.

FK 506: effects on glomerular hemodynamics and on mesangial cells in culture

FK 506 is a new immunosuppressive drug that, like cyclosporine A (CsA), presents nephrotoxicity. Glomerular hemodynamic studies showed that acute FK 506 infusion (N = 9, 3 mg/kg body wt, i.v. in bolus) caused a 57% reduction in glomerular filtration rate (GFR) (0.74 +/- 0.03 to 0.32 +/- 0.02 ml/min, P < 0.05) and a 40% reduction in single nephron glomerular filtration rate (SNGFR; 43.0 +/- 5.2 to 26.0 +/- 2.5 nl/min, P < 0.05) due to a 25% reduction in glomerular plasma flow rate (QA) (133.4 +/- 19.8 to 99.8 +/- 12.0 nl/min) and a 22% reduction in glomerular ultrafiltration coefficient (Kf; 0.1009 +/- 0.0203 to 0.0790 +/- 0.0130 nl/sec. mm Hg). After 10 days of FK treatment (N = 8, 0.6 mg/kg body wt, i.p.), we observed a reduction of 23% in GFR (0.97 +/- 0.02 to 0.75 +/- 0.04 ml/min, P < 0.05) and of 23% in SNGFR (37.9 +/- 3.0 to 29.1 +/- 1.9 nl/min, P < 0.05) due to a 42% reduction in Kf (0.1486 +/- 0.0101 to 0.0870 +/- 0.0110 nl/sec.mm Hg, P < 0.05) and a 38% reduction in QA (117.6 +/- 10.2 to 73.5 +/- 6.1 nl/min, P < 0.05). The latter was consequent to the increment of 72% in total arteriolar resistance (RT) (3.1 +/- 0.2 to 5.2 +/- 0.5 +/- 0.5 10(10).dyn.sec.cm-5, P < 0.05). Thus, the pattern of FK 506 effect on glomerular hemodynamics was similar in both acute and chronic treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Impaired cytosolic free calcium response in splenic T-cells from mice fed with ethanol-containing diet

Calcium-dependent signal transduction pathways of T-cell proliferation have been extensively studied in the past years. However, little is known about effects of ethanol on the calcium-dependent signal transduction pathway in T-cell proliferation. Thus, a murine model was used to determine effects of ethanol in vivo on T-cell proliferation and the intracellular free calcium concentration [Ca2+]i in response to Concanavalin A (Con A) and recombinant IL2 (rIL2) in T-cells. Splenic cells from young C57BL/6 mice, that had been fed on 3 different diets (ethanol-, maltose substitute- and standard liquid-diet) for 7-8 weeks were tested for their proliferative responses to Con A and rIL2. Concurrently, measurement was also made of [Ca2+]i in the nylon-wool-enriched resting T-cells induced by Con A and in Con-A-activated blast T-cells induced by rIL2. Our results showed that [Ca2+]i increases were seen in the splenic T-cells from three different groups of mice following Con A, but not rIL2 stimulation. However, this increase was much smaller in the splenic T-cells from ethanol-fed mice as compared to mice on maltose- or standard-diet. Furthermore, we also demonstrated that the impaired [Ca2+]i increase was seen in the T-cells of the same ethanol-fed mice having decreased the proliferative response to Con A. This reduced proliferation did not result from the presence of excessive suppressor T-cell activity. Finally, we also demonstrated that both the number of IL2 binding sites/cell and the Kd values of the low- and high-affinity IL2R on the T-cells from ethanol-fed mice were unaltered. Because evidence indicates that (1) a normal level of [Ca2+]i increase is a prerequisite for the production of IL2 by mitogen-stimulated T-cells, and (2) T-cells from ethanol-fed mice have normal capacities to produce IL2 that is the crucial growth factor controlling T-cells to progress through the cell cycle, these lines of evidence taken together with the results of this study suggest that the impairment in [Ca2+]i increases in T-cells from ethanol-fed mice may not be the primary factor contributing to the diminished T-cell proliferation in the same mice.

Towards the molecular bases of polymerase dynamics

One aspect of the strong relationship that is known to exist between the processes of DNA replication and transcription is manifest in the coupling of the rates of movement of the replication fork (rf) and RNA polymerase (rt). We address two issues concerning the largely unexplored area of polymerase dynamics: (i) The validity of an approximate kinematic formula linking rf and rt suggested by experiments in which transcription is inhibited in some prokaryotes with the antibiotic streptolydigin, and (ii) What are the molecular bases of the kinematic formula? An analysis of the available data suggests possible molecular bases for polymerase dynamics. In particular, we are led to a hypothesis: In active chromatin rt may depend on the length (lambda t) of the transcript of the primary messenger RNA (pre-mRNA). This new effect is subject to experimental verification. We discuss possible experiments that may be performed in order to test this prediction.

Accumulation of hyporesponsive, calcium extruding memory T cells as a key feature of age-dependent immune dysfunction

In this review I propose a hypothesis with a number of testable predictions: that the age-dependent decline in T lymphocyte function is largely the result of the accumulation of memory T lymphocytes with over-active plasma membrane calcium pumps. This idea is consistent with much, though not all, of the currently available data. I will start by presenting the evidence that suggested and most clearly supports this idea, then discuss apparently contrary data (some of it still difficult to reconcile with the model), and lastly consider the implications of the model for our understanding of late life development of the T cell immune system.

Cholesterol oxides and carcinogenesis

Experimental evidence indicates a relationship between cholesterol alpha-epoxide and skin cancer, and exposure of skin fibroblasts to ultraviolet radiation enduces formation of significant levels of this oxide. Colon cancer is also etiologically linked to cholesterol oxidation products. Higher than normal levels of cholestanetriol have been found in patients with colon cancer and also in those with precancerous disorders such as adenomatous polyps and ulcerative colitis. Higher than normal levels of cholesterol alpha-epoxide have been found in breast fluid aspirates of women with benign breast disease, with or without atypical hyperplasia of the epithelium, and this may be a factor in the increased incidence of breast cancer associated with hyperplasia. Similarly, the observed increased levels of cholesterol alpha and beta-epoxides in prostatic fluid of men with benign prostatic hypertrophy may be associated with subsequent development of prostate cancer. Cholesterol alpha-epoxide has been found to be mutagenic to fibroblasts in culture and to induce morphological transformation in hamster embryo cells and in mouse C3H cells. 25-Hydroxycholesterol and 20 alpha-hydroxycholesterol are potent suppressors of generation and proliferation of tumor-specific cytotoxic T lymphocytes. Although investigations into the role of cholesterol oxidation products in cancer are still in the early stages, evidence to date indicates a potentially significant role in the induction of some types of cancer.

Dissociation of unidirectional influx of external Ca2+ and release from internal stores in activated human T lymphocytes

Addition of lectin or antibody to the T cell receptor complex of human T cells results in a rapid increase in the concentration of cytoplasmic free Ca2+ ([Ca2+]i). This response is biphasic and results from contributions of Ca2+ from internal stores, uptake of Ca2+ across the plasma membrane and possibly a decrease in Ca2+ efflux. These responses have been linked through the activity of inositol 1,4,5-trisphosphate in releasing Ca2+ from internal stores and potentially mediating Ca2+ uptake across the plasma membrane. Following addition of phytohemagglutinin or anti-CD3 antibody to resting T cells or Jurkat cells, we have been able to dissociate the [Ca2+]i responses by loading cells with the Ca2+ chelator 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetate (BAPTA). In BAPTA-loaded T cells, we have shown that Ca2+ mobilized from intracellular stores following activation is effectively buffered, while stimulated Ca2+ uptake and associated changes in [Ca2+]i were relatively unaffected. In this report, we show that the sustained increase in [Ca2+]i is due to increased unidirectional influx of external Ca2+ without changes in efflux and that it is the entry of extracellular Ca2+ which is sensitive to the transmembrane potential.

Effects of calcium channel modulators on the proliferation of mouse spleen lymphocytes in vitro

The effects of nimodipine (voltage-dependent calcium channel blocker), CGP 28392 and BAY K 8644 (novel dihydropyridine derivatives that are considered as calcium entry stimulators) on the spontaneous proliferation of mouse spleen lymphocytes were studied in vitro. [3H]-thymidine incorporation into DNA of lymphocytes was used as an sensitive index of the cell proliferation. It has been found that nimodipine (10(-4) M-10(-6) M) significantly inhibited the [3H]-thymidine uptake in a dose dependent fashion with ED50 value of 2.4 x 10(-5) M. Unexpectedly, CGP 28392 (10(-4) M-10(-7) M) acts as a calcium entry blocker and produces a strong inhibitory effect on lymphocyte proliferation (ED50-2 x 10(-5) M). BAY K 8644 at a high concentration (10(-4) M) also has an inhibitory effect but at a lower concentration (10(-6) M-10(-10) M) significantly increased [3H]-thymidine uptake and abolished the inhibitory effect of nimodipine. This effect of nimodipine was also reversed by 5 x 10(-3) M calcium chloride. These findings indicate that calcium channel modulators can regulate the proliferation of mouse spleen lymphocytes in vitro.

Suppression of mitogen- and antigen-induced lymphocyte proliferation by lanthanides

Lanthanide ions (Ln3+) inhibited the proliferative response of human lymphocytes to various polyclonal mitogens and the 'purified protein derivative' (PPD) of the tuberculin antigen. Of the four Ln3+ ions tested lanthanum (La3+) was the strongest inhibitor; erbium (Er3+) and lutetium (Lu3+) were only weakly active, while samarium (Sm3+) had intermediate potency. At a concentration of 1 mM, La3+ almost completely inhibited the uptake of [3H]-thymidine by lymphocytes exposed to mitogenic agents. Trypan blue exclusion tests confirmed that the La3+ ions were not toxic. These findings may bear upon the reported anti-inflammatory properties of the lanthanides.

A comparison of the effects of various stimulatory agents on t-PA secretion by normal and malignant cell lines

Succinyl con A and acetyl con A both stimulated epithelial cells to produce similar yields of tissue plasminogen activator (t-PA) to those previously obtained with native con A. However, unlike con A, the derivatized lectins did not adversely affect cell morphology and viability, and cells treated with succinyl con A could secrete t-PA for a prolonged period. Con A and the two derivatives produced similar morphological effects in Bowes melanoma cells, but t-PA production was not increased. Elevated cyclic nucleotide concentrations did not affect t-PA production from epithelial cells, but calcium ionophore treatment generated t-PA yields similar to those obtained with lectins. Azacytidine, which enhanced t-PA production from epithelial cells, did not increase yields from Bowes melanoma cells, and also sodium butyrate, reported to increase t-PA yields from human endothelial cells, had no effect on either cell line.

Regulation of levels of IL-1 mRNA in human fibroblasts

Interleukin-1 (IL-1) has a crucial role in host defenses, inflammatory processes, and tissue homeostasis. A wide variety of cells produce this protein in response to a number of extracellular stimuli including microorganisms, antigenic stimuli, and products from other cells. Regulation of IL-1 production at the molecular level is poorly understood. We studied expression, intracellular signals, and posttranscriptional regulation of IL-1 mRNA in human mesenchymal cells by using Northern blot analysis. Tumor necrosis factor alpha (TNF alpha) and activators of protein kinase C including 12-O-tetradecanoylphorbol-13-acetate (TPA) and teleocidin induced the accumulation of IL-1 beta mRNA in human fibroblasts (WI-38). Effect of TNF alpha was not blocked by inhibitors of either protein synthesis (cycloheximide) or protein kinase C activity. Accumulation of IL-1 beta mRNA was also increased by a calcium ionophore (A23187) and an inhibitor of the Na+/K+ pump (ouabain); both compounds are known to increase cytoplasmic levels of Ca++. Stability of IL-1 beta mRNA in fibroblasts exposed to TPA was more than fourfold greater than after fibroblasts were exposed to either TNF alpha or cycloheximide. This suggests that posttranscriptional stabilization of IL-1 beta mRNA is a major mechanism leading to accumulation of IL-1 beta mRNA after activation of PKC in fibroblasts. Fibroblasts did not express IL-1 alpha mRNA after exposure to stimuli which induced the accumulation of IL-1 beta mRNA. In summary, several different pathways regulate levels of IL-1 beta mRNA in human mesenchymal cells.

Epidemiologic and toxicologic evidence for chronic health effects and the underlying biologic mechanisms involved in sub-lethal exposures to acidic pollutants

Since the 1880s, a disparate and extensive literature has evolved examining the biologic effects of acidification on cells. More recently, effects on the health of human and other species of acidic agents contained, for example, in pollutants have been suggested, particularly relating to long-term exposures. This paper provides a review of the epidemiologic and toxicologic evidence concerning health effects--particularly carcinogenicity--attributable to sub-lethal acid exposure. Underlying biologic mechanisms that explain adverse health outcomes include pH modulation of toxicity for a number of xenobiotics (including carcinogens, genotoxins, and teratogens), and low-pH-induced changes of cells involving, for example, alterations in mitotic and enzyme regulation. More focused research is recommended to test the relationship between long-term exposures to acidic agents (with a consequent lowered cellular pH) and various health effects.

Effects of inhibitors and activators of protein kinase C on late erythroid progenitor (CFU-e) colony formation in vitro

Protein kinase C (PKC) plays a central role in external signal transduction for many cell types. To examine the involvement of PKC in the control of erythropoiesis, we tested the effects of PKC inhibitors on in vitro colony formation by late erythroid progenitors (CFU-e) from normal and Friend virus-infected mice. Inhibitors of PKC and other kinases (H-7 and H-8) inhibited CFU-e at concentrations which inhibit PKC. HA1004, an inhibitor of the cyclic nucleotide-dependent kinases and a weak inhibitor of PKC, had little effect on CFU-e. In the absence of erythropoietin, a combination of phorbol ester and Ca++ ionophore significantly increased normal CFU-e. These results suggest PKC plays a role in the transduction of regulatory signals for the growth of CFU-e.

Ca++-ionophore-induced dissipation of intracellular proton gradients in rat thymocytes

Rat thymocytes incorporate large amounts of acridine orange at concentrations of approximately 10 microM in about 10 minutes at 37 degrees C. The addition of (NH4)2SO4 (at a final concentration of several mMolars) releases about 30% of the incorporated dye into the medium. The NH4+-releasable dye uptake is almost completely abolished by 20 minutes' incubation with 4 microM of the Ca++-ionophore A23187. Dye uptake is associated with an absorbance change at 492 mm and thus may be followed spectrophotometrically. However, NH4+ at the above concentrations or nigericin (0.5 mg/ml) completely annul this change in absorbance, indicating that it reflects only the accumulation of the dye within the acidic cellular compartments. In a Ca++-containing physiological saline, the addition of A23187 (at a final concentration of 8 microM) at the end of the dye uptake phase initiated a reversal in the absorbance change; in the absence of Ca++, reversal occurred at a much lower rate. Incubation of cells for 30 minutes with 2 microM A23187 in Ca++-containing saline completely abolished NH4+-sensitive dye uptake; less A23187 (0.5 microM) and like or a longer incubation period brought about a striking decrease in NH4+-sensitive dye uptake. Similar results were obtained with cells suspended in RPLM 1640 medium. In the absence of external Ca++, A23187 impaired cell capacity to incorporate dye in a delta pH-dependent manner, but a longer incubation time or higher concentrations of the ionophore were required to obtain a comparable effect. It is thus concluded that the ionophore dissipates intracellular pH gradients by an intracellular divalent cation (Ca++ or also Mg++)-H+ exchange.

Control of DNA replication and cell growth by inhibiting the export of mitochondrially derived citrate

When citrate export from mitochondria is blocked with 1,2,3-benzenetricarboxylate (BTC) during the G1/S phase of the cell cycle, both DNA synthesis and cell growth are dramatically inhibited in suspension-grown 70Z/3 murine lymphoma cell cultures sustained under otherwise optimal conditions. Synchronized (G0/G1 or G1/S) and unsynchronized cultures are susceptible to this phenomenon. BTC prevents two requirements from being met. (1) It deprives the cytosol of the acetyl CoA necessary for operation of the cholesterogenesis pathway, thereby depleting the supply of mevalonate (MVA) implicated as a requirement for triggering DNA synthesis. (2) It behaves as a nonmetabolizable divalent cation chelator, reducing the availability of Ca2+ and Mg2+, which, in whole cells are both required for DNA synthesis. Such inhibitions are reversible. In whole cells, removal of the inhibitor yields rapid and complete recovery of DNA synthesis. During the prolonged presence of BTC, the addition of MVA plus the Ca2+ ionophore A23187 allows partial recovery of DNA synthesis. In isolated, DNA synthesizing nuclei, on the other hand, the slight inhibition of DNA synthesis by BTC is reversed merely by addition of Mg2+. We conclude that the uninterrupted production of citrate-derived MVA via the mitochondria, at the G1/S boundary of the cell cycle (i.e., subsequent to peak cholesterol synthesis), is mandatory for initiating the duplication of the cell genome. Consequently, by its mitochondrial site of action, BTC can severely limit the otherwise continuous supply of MVA during late G1, which in turn, prevents entry into the S phase, and thereby cell proliferation.

Inhibitory effect of calcium channel blockers on proliferation of human glioma cells in vitro

The effects of 2 specific calcium channel blockers, verapamil and nimodipine, on the proliferation of human glioma tumour cells were investigated in vitro. Tumour tissues for primary cell cultures were obtained bioptically from 3 patients with the histopathological diagnosis of glioblastoma. The [3H]-thymidine incorporation into glioma tumour cells DNA was used as a sensitive index of the cell proliferation. It was found that verapamil (10(-4)-10(-5) M) and nimodipine (10(-4)-10(-6) M) significantly inhibited the [3H]-thymidine uptake in a dose-related manner. The inhibitory effect of both calcium channel antagonists was reversed by simultaneous addition of calcium chloride (5 x 10(-3) M). These results indicate that verapamil and nimodipine may exert an antiproliferative effect on glioma cells growth acting through a blockade of specific voltage-dependent calcium channels.

Inhibition of the CD3-mediated calcium signal by protein kinase C activators in human T (Jurkat) lymphoblastoid cells

The changes in the cytoplasmic free calcium concentrations (Cai) were investigated in human T (Jurkat) lymphoblastoid cells, loaded with the calcium-sensitive fluorescent dye Indo-1. A rapid increase in Cai could be evoked by monoclonal antibodies (mAb) directed against the CD3 antigen, as well as by the mitogenic lectin concanavalin A (conA). The protein kinase C (pKC) activators TPA and DiC8 did not increase Cai, but the addition of any of these two compounds prior to mAb eliminated the mAb-induced calcium signal. In contrast, the calcium signal evoked by ConA was not blocked by TPA or DiC8. These results suggest that the CD3-dependent calcium signal is selectively down-regulated by the activation of pKC.

Cytoplasmic calcium response to fluid shear stress in cultured vascular endothelial cells

Vascular endothelial cells modulate their structure and functions in response to changes in hemodynamic forces such as fluid shear stress. We have studied how endothelial cells perceive the shearing force generated by blood flow and the substance(s) that may mediate such a response. We identify cytoplasmic-free calcium ion (Ca++), a major component of an internal signaling system, as a mediator of the cellular response to fluid shear stress. Cultured monolayers of bovine aortic endothelial cells loaded with the highly fluorescent Ca++-sensitive dye Fura 2 were exposed to different levels of fluid shear stress in a specially designed flow chamber, and simultaneous changes in fluorescence intensity, reflecting the intracellular-free calcium concentration [( Ca++]i), were monitored by photometric fluorescence microscopy. Application of shear stress to cells by fluid perfusion led to an immediate severalfold increase in fluorescence within 1 min, followed by a rapid decline for about 5 min, and finally a plateau somewhat higher than control levels during the entire period of the stress application. Repeated application of the stress induced similar peak and plateau levels of [Ca++]i but at reduced magnitudes of response. These responses were observed even in Ca++-free medium. Thus, a shear stress transducer might exist in endothelial cells, which perceives the shearing force on the membrane as a stimulus and mediates the signal to increase cytosolic free Ca++.

CD3 pathway of T-cell activation. II. Role of HLA-class I molecules in early events

The role of distinct regions of HLA class I molecules in regulating T-cell activation via the CD3-antigen receptor complex was investigated. Monoclonal antibodies (MoAbs) which recognize monomorphic and polymorphic epitopes on HLA Class I molecules were shown to inhibit T-cell proliferation to OKT3. These MoAbs have differential effects on the synthesis of interleukin-2 (IL-2) and IL-2 receptor expression. Cell cycle analysis demonstrated that these MoAbs function both in inhibiting cell cycle entry (G0-G1 shift) and in blocking cell cycle progression (G1-S shift) of activated T cells. Furthermore, these MoAbs have regulatory effects on the alternate pathway of T-cell activation via the CD2 molecule, T-cell activation induced by PHA, and activation induced by the phorbol ester PMA in conjunction with the calcium ionophore Ionomycin. Thus these MoAbs have different effects depending upon the pathway of T-cell activation. The results indicate that HLA class I molecules are selectively involved in the sequence of intracellular events leading to T-cell activation and proliferation.

Uptake of extracellular Ca2+ and not recruitment from internal stores is essential for T lymphocyte proliferation

Changes in free cytosolic calcium concentrations ([Ca2+]i) are thought to be important initiating events in the activation of T lymphocytes. Mitogen-induced increases in [Ca2+]i may result from net influx across the plasma membrane and/or release of Ca2+ from intracellular stores. In human T lymphocytes loaded with the fluorescent indicator indo-1, addition of phytohemagglutinin (PHA) or the anti-CD3 antibody UCHT-1 elicits a biphasic [Ca2+]i response. A major component of the initial transient peak was due to release from internal stores whereas the lower plateau phase was sustained by Ca2+ influx. Previous work suggested that Ca2+ influx is essential for interleukin 2 (IL 2) secretion and cell proliferation. To determine the relative effects of the initial and sustained phases of [Ca2+]i change, IL 2 secretion and cell proliferation, we introduced into the cell 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), a high affinity intracellular Ca2+ chelator which neither contributes to nor interferes with the fluorescence determinations of [Ca2+]i. In cells preloaded with BAPTA, both PHA and UCHT-1 antibody failed to elicit the transient [Ca2+]i overshoot. Only the plateau phase could be observed in the presence of extracellular Ca2+. In contrast, BAPTA-loaded cells were found to be fully functional when assessed for IL 2 receptor expression, IL 2 secretion and cell proliferation. Thus, the mitogen-induced, maximal but transient increase in [Ca2+]i, contributed to mainly by release of Ca2+ from internal stores, does not appear to be essential for these T cell responses.

Diminished mitogen-induced calcium uptake by lymphocytes from Alzheimer patients

Recent studies demonstrate diminished calcium uptake by cultured skin fibroblasts from Alzheimer patients. To determine if altered calcium homeostasis is also present in tissue taken from Alzheimer patients, calcium homeostasis was assessed in mitogen-stimulated lymphocytes. Calcium uptake by lymphocytes from Alzheimer patients was 10%-15% lower (p less than 0.002) than that of lymphocytes from age-matched controls. However, neither superficially bound nor total calcium was altered by Alzheimer's disease. These small differences in uptake may reflect larger differences in cytosolic calcium, in later calcium-mediated events, or in the response of particular subsets of lymphocytes. Their biological significance remains to be determined.

Transmembrane signaling by the B subunit of cholera toxin: increased cytoplasmic free calcium in rat lymphocytes

It has previously been shown that the B subunit of cholera toxin, which binds solely to the plasma membrane ganglioside GM1, stimulates the proliferation of rat thymic lymphocytes (Spiegel, S., P. H. Fishman, and R. J. Weber, 1985, Science [Wash. DC], 230:1285-1287). The purpose of this study was to identify which transmembrane signaling system(s) are activated by the B subunit of cholera toxin. We compared the effects of B subunit and concanavalin A (Con A), a potent mitogenic lectin, on a number of second messenger systems that are putative mediators of T cell activation. Changes in the fluorescence of quin2-loaded cells revealed that mitogenic doses of either B subunit or Con A induced rapid and sustained increases in cytoplasmic free Ca2+ ([Ca2+]i). Within 5 min, [Ca2+]i increased from a basal level of 69 +/- 4 to 136 +/- 17 and 185 +/- 24 nM, respectively. The effects of B subunit and Con A were additive and largely dependent on the presence of extracellular Ca2+, though release of Ca2+ from intracellular stores could be detected for Con A, but not B subunit, using indo-1. The B subunit had no effect on either inositol phosphate levels or on the distribution of protein kinase C, indicating that, unlike Con A, the B subunit does not activate phosphoinositide hydrolysis. Fluorimetric measurements on cells loaded with bis(carboxyethyl)-5,6-carboxyfluorescein revealed that Con A induced a rapid cytoplasmic alkalinization via activation of Na+/H+ exchange, whereas B subunit had no effect on intracellular pH. Finally, by monitoring bis-oxonol fluorescence, we found that Con A induced a small hyperpolarization of the membrane potential, whereas B subunit had no acute effect. These data suggest that the biological effects of B subunit are mediated by an increase in [Ca2+]i resulting from a net influx of extracellular Ca2+.

Biphasic effects of dibutyryl cyclic adenosine 3',5'-monophosphate on synergistic stimulation of DNA synthesis by diacylglycerol, and the ionophore A23187 in guinea pig lymphocytes

When guinea pig lymphocytes were cultured with 1-oleoyl-2-acetylglycerol (OAG) and the ionophore A23187 for 8 h, [3H]-thymidine incorporation into the acid-insoluble fraction of the cells was stimulated synergistically. Further addition of dibutyryl cAMP caused a biphasic effect on the synergistic stimulation. Dibutyryl cAMP augmented the synergistic stimulation when A23187 was at the concentration of 0.075 micrograms/ml, but inhibited it when the ionophore was at 0.25 micrograms/ml. At the higher concentration of A23187, dibutyryl cAMP stimulated the [3H]thymidine incorporation when culture was for 4 h, but inhibited it when culture was for 8 h. The results were the same when 12-0-tetradecanoylphorbol-13-acetate (TPA) was used instead of OAG. Butyrate could replace dibutyryl cAMP for stimulation of [3H]thymidine incorporation in combination with TPA and A23187, but not with OAG and A23187 at the lower ionophore concentration. Dibutyryl cAMP but not butyrate stimulated ornithine decarboxylase induction caused by TPA and A23187. These results suggest that the effect of dibutyryl cAMP on DNA synthesis induced by OAG and A23187 was biphasic and depended on the concentration of A23187 and on the time of culture, and that the stimulation mechanism of butyrate is different from that of dibutyryl cAMP.

The role of cAMP and calcium in the stimulation of proliferation of immature erythroblasts by erythropoietin

The hypothesis that cAMP or calcium are the second messengers of erythropoietin (Epo) was tested on fractionated, Epo-responsive immature erythroblasts from anemic rabbit bone marrow by examining whether the proliferative effects of the hormone could be mimicked by agents that increase the intracellular concentration of cAMP or Ca2+. None of the compounds tested (including 10(-6)-10(-4) M db-cAMP, forskolin, isoprenaline or 10(-7)-10(-6) M of the calcium ionophore A23187) alone or in combination could either initiate or potentiate the mitogenic action of the hormone. Furthermore, addition of 0.2 U/ml erythropoietin produced no permanent or transient increase in the uptake of 45Ca2+ by erythroblasts at 37 degrees C. However, cells cultured with imidazole or cordycepin (which reduce the level of intracellular cAMP), or with the calcium chelator EGTA, or the drugs verapamil or TMB-8 (which interfere with the utilization of extracellular or intracellular calcium) showed a decreased stimulation of DNA synthesis by Epo. Finally, the tumour promoter phorbol ester TPA could partially mimic the action of Epo when added to cultures containing more immature progenitor cells. We conclude then that an artificial increase in the cytoplasmic concentration of either cAMP or Ca2+ is not sufficient to elicit the proliferation of Epo-responsive cells.

The role of calcium in stimulation of activated T lymphocytes with interleukin 2

In a study of the role of Ca++ in the stimulation of activated T lymphocytes with interleukin 2 (IL-2) it was found that IL-2-induced proliferation can occur independently of extracellular calcium. Further, there was no correlation between triggering of DNA synthesis and an increase in free cytoplasmic calcium. However, IL-2 induced an increased uptake of 45Ca++ from the extracellular medium. Since there is no increase in free cytoplasmic calcium, it must be assumed that this is caused by an increase in membrane-associated calcium. Further, the calcium channel-blocking agent, verapamil, and TMB-8, a putative inhibitor of mobilization of calcium from intracellular pools, both exerted a dose-dependent inhibition of IL-2-induced DNA synthesis in activated T lymphocytes. We conclude that calcium is not a second messenger in activated T lymphocytes stimulated by IL-2, but our results indicate that calcium may play a role at membrane level.

Calcium ionophore A23187 as a regulator of gene expression in mammalian cells

The calcium ionophore A23187 can reversibly induce the expression of two glucose-regulated genes, p3C5 and p4A3. This induction requires a continuous presence of the ionophore for over 2 h. Although extracellular Ca2+ is important for the optimal effect of A23187, it is not necessary for the induction, since a similar response with a lower magnitude can be triggered in cells cultured in low Ca2+ medium buffered with EGTA. Both the basal and induced levels of p3C5 and p4A3 transcripts can be modulated by the calmodulin antagonist W-7, indicating the involvement of Ca2+/calmodulin-associated pathways. In addition, the sensitivity of the A23187 induction to cycloheximide suggests that the induction process is dependent on de novo protein synthesis.

Calcium ionophore A 23 187 in the presence of phorbol ester PMA: a potent inducer of interleukin 2 and interferon-gamma synthesis by human blood cells

Cultures of human blood mononuclear cells incubated with the calcium ionophore A 23 187 in the presence of the tumor promoter phorbol 12-myristate-13-acetate (PMA) produced 5-10 times more of the lymphokines interleukin 2 (IL 2) and interferon-gamma (IFN-gamma) than cultures which were stimulated with other combinations of inducing agents and PMA. Especially at low protein concentrations, the amount of ionophore which is necessary to induce maximal quantities of both lymphokines was determined by the protein content of the culture medium. The synthesis of the two lymphokines was inhibited by low doses of Mn++ which competes with Ca++ for binding to the ionophore. This suggests the importance of Ca++ in the induction process. The synthesis rates of IL 2 were maximal 10-12 h, and those of IFN-gamma 20-40 h after induction. Maximal titers of IL 2 were detected 48 h after the addition of A 23187 and PMA to the cultures, and the highest IFN-gamma levels 12-24 h later.

Stimulation of proliferation of murine lymphocytes by the calcium ionophore A 23187 in the absence of serum: the requirement for thiols

The proliferation of mouse spleen cells and T-lymphocytes, initiated by the calcium ionophore A 23187 was studied by a serum-free culture technique. In contrast to Con A, A 23187 was capable of stimulating cells only if 2-mercaptoethanol, cysteine and glutathione (reduced form), respectively, were present in the culture medium. In the absence of one of these compounds a stimulating activity of A 23187 was observed only with high concentrations of cells (i.e., 10(7)/ml). With glutathione present, the cells could be stimulated only at concentrations of A 23187 which were found to be suboptimal in cultures with 2-mercaptoethanol. Human serum, fetal calf serum and bovine serum albumin shifted the active and optimally stimulating concentrations of A 23187 to higher values. A similar effect was observed with sera- and Con A-treated cells. The effect of sera and albumin was paralleled by a protecting effect of cells against high concentrations of A 23187.

Elevation of intracellular calcium reduces voltage-dependent potassium conductance in human T cells

Both voltage-activated potassium channels and the concentration of free intracellular calcium have been implicated in the activation of T lymphocytes. Using the patch-clamp technique, we now show an unexpected relationship between the level of intracellular calcium [Ca]i in human lymphocytes and the amplitude of a voltage-dependent current: the elevation of [Ca]i decreases the potassium conductance. This is in contrast to other systems where [Ca]i activates K+ channels. Our results suggest that the level of intracellular calcium regulates the effective number of K+ channels capable of being activated.

Clinical and laboratory effects of nifedipine in Raynaud's phenomenon

The calcium channel blocking drug nifedipine was shown to be more effective than placebo as a treatment for Raynaud's phenomenon. Given in a dose of 10 mg four times a day it was well tolerated and reduced both the frequency and the severity of vasospastic attacks. There was, however, a large individual variation in response and while approximately half the patients showed marked improvement others showed no improvement at all. Patients with idiopathic Raynaud's phenomenon responded more favourably than those with systemic sclerosis. Nifedipine was shown to inhibit mitogen-induced lymphocyte proliferation but only in patients who responded to the drug clinically. Calcium channel blocking drugs may therefore have potential as immunoregulatory agents.

Interleukin 2 mRNA induction in human lymphocytes: analysis of the synergistic effect of a calcium ionophore A23187 and a phorbol ester

Induction of interleukin 2 (IL2) mRNA in human tonsillar lymphocytes under various conditions was examined by cytoplasmic dot hybridization using a 32P-labeled IL2 cDNA probe to study the signal transduction mechanisms which lead to IL2 gene expression. A tumor-promoting phorbol ester, 12-O-tetradecanoyl-phorbol 13-acetate (TPA), acted synergistically with a Ca2+ ionophore A23187 or phytohemagglutinin (PHA) to induce a high level of IL2 mRNA in lymphocytes, whereas each of them by itself could not induce the mRNA production. In two-step culture experiments the lymphocytes pulse-incubated with TPA for 1 h (the first culture) could efficiently initiate IL2 mRNA production by subsequent culture with A23187 or PHA (the second culture). Results obtained by removal of extracellular Ca2+ from either the first or second culture revealed that Ca2+ was not necessarily required during the first culture with TPA, but it is essential in the second culture with A23187 or PHA, regardless of the presence or absence of Ca2+ in the first culture. A reagent known to be a calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), almost completely inhibited the IL2 mRNA induction in A23187-TPA-stimulated lymphocytes at a concentration of 25 microM, whereas N-(6-aminohexyl)-1-naphthalenesulfonamide that has much lower affinity for calmodulin than W-7 did not inhibit at this concentration. The IL2 mRNA induction was also blocked by the addition of 50 microM of 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate hydrochloride which is known to block the release of Ca2+ from intracellular storage sites. These results show that mobilization of Ca2+ and the calmodulin-dependent regulatory system appear to work synergistically with TPA which probably activates protein kinase C in the pathway to IL2 gene expression.

Calcium ionophore A23187 induces interleukin 2 reactivity in human T cells

In the present study the activation of purified human T lymphocytes by the calcium ionophore A23187 was analysed in the light of current concepts of receptor-linked inositol lipid metabolism. It was found that A23187 was only slightly mitogenic, with a narrow optimum at 400-500 nM. The proliferation could be blocked by anti-Tac ascites at 10(-3) dilution, suggesting an interleukin 2 (IL-2)-dependent pathway of activation. However, an unexpectedly large proportion of A23187-stimulated cells expressed the IL-2 receptor. Reculturing the cells with exogenous IL-2 after removal of A23187 resulted in strongly enhanced proliferation. Phorbol myristic acetate (PMA) at non-mitogenic concentrations exerted an extremely strong synergistic effect on A23187-induced cell proliferation, which was, again, mediated via an IL-2-dependent pathway. Supernatants of A23187-stimulated T cells did not contain detectable amounts of IL-2. Combination of PMA and A23187 resulted in considerable IL-2 production. It is concluded that A23187 induces the expression of IL-2 receptors without concurrent stimulation of IL-2 production, thus allowing only low levels of proliferation. Addition of exogenous IL-2 or of PMA restores the imbalance between the occurrence of IL-2 and its receptor and results in high rates of proliferation.

Voltage-dependent ion channels in T-lymphocytes

The gigaohm seal 'patch-clamp' technique has recently enabled exploration of the electrical properties of cells of the immune system. In this paper we review progress made to date in cataloguing the ion channels present in the cell membranes of T-lymphocytes and present new data on the types of ion channels present in a number of human and murine T-cell-derived cell lines. The ion channels thus far described in these cells are strikingly similar to those found in nerve and muscle cells. Voltage-gated potassium channels resembling delayed rectifier potassium channels in excitable cells are present in most T-lymphocytes, T-lymphocyte-derived cell lines and macrophages. Sodium channels indistinguishable from those in excitable cells are present in a small fraction of T-cells and T-cell lines, and in some natural killer cells. Calcium channels have been reported in B-lymphocyte-derived cell lines, but have not been found in T-lymphocytes or in any T-cell-derived cell line. Potassium channels are required for activation of T-lymphocytes by mitogen, allogeneic cells, or by antigen, for lysis of target cells by natural killer cells, and may be involved in the triggering mechanism for activation of T-cells. The prevailing conception of early events in T-lymphocyte activation, the 'calcium hypothesis', involves an elevation of cytoplasmic free calcium levels as the proposed 'second messenger' in activation, giving rise to a cascade of subsequent events resulting eventually in cell division. A major focus of this paper is to evaluate specific mechanisms which have been proposed to account for experimental evidence, both in the literature and also presented here, pertaining to the calcium hypothesis. One such mechanism involves calcium channels, which have been postulated to account for the early calcium influx in activated T-lymphocytes. Since calcium channels have not been detected in T-cells, we explore the possibility that existing data can be accounted for without calcium channels. In particular, we show that many of the effects of 'calcium channel antagonists' such as verapamil, nifedipine, diltiazem and some polyvalent cations, can be accounted for by their blocking of voltage-gated potassium channels.