Activation of the phosphatidylinositol metabolic pathway by low molecular weight B cell growth factor

Cyclosporin A inhibits 2-chloroadenosine-induced DNA cleavage in mouse thymocytes

Incubation of mouse thymocytes with the adenosine analogue 2-chloroadenosine resulted in enhanced internucleosomal DNA fragmentation which could be inhibited by the immunosuppressive drug cyclosporin A. In order to be effective, cyclosporin A had to be added to thymocyte preparations at the same time as 2-chloroadenosine. Since cyclosporin A is a selective inhibitor of calcineurin, our data suggest a possible role for calcineurin as a signaling intermediate in the apoptotic pathway activated in thymocytes through adenosine receptors. However, at the present time we cannot exclude the possibility that the inhibitory effect of cyclosporin A on 2-chloroadenosine-induced apoptosis may be mediated through a calcineurin-independent process.

Actions of interleukin-4 on prostaglandin biosynthesis by human amnion cells

The effects of interleukin-4 (IL-4) on amnion prostaglandin (PG) production have been determined. Human amnion cells from term placentae were grown to confluence and incubated with IL-4 either alone or with various concentrations of epidermal growth factor (EGF) of ionomycin. PGE2 production was determined using a specific radioimmunoassay. IL-4 alone stimulated PGE2 production in amnion cells in a concentration-related manner. IL-4 significantly enhanced the stimulatory actions of ionomycin and EGF on amnion cell PGE2 production. Ionomycin and IL-4 acted synergistically in their effects on PGE2 production by amnion cells whereas EGF and IL-4 acted more additively in this respect. We suggest that IL-4 production by immune effector cells in gestational tissues may contribute to the mechanisms of labor at term and preterm.

Interferon alpha and intracytoplasmic free calcium in hairy cell leukemia cells

Hairy cell leukemia (HCL) is a B-cell tumor affecting the pre-plasma stage of B cell differentiation. One of the most striking characteristics of this disease is its remarkable responsiveness to alpha-interferon (IFN-alpha) therapy. Interferons constitute a heterologous family of multifunctional cytokines displaying anti-viral, anti-proliferative and immunoregulatory properties. These activities have been extensively studied in hairy cells, but the mechanism of action of IFN-alpha in hairy cell leukemia remains unknown. Our approach to investigate the mode action of IFN-alpha in HCL has been to identify abnormalities which occur in these tumor cells and then to ascertain whether these abnormalities can be rectified by IFN-alpha treatment. A high level of free Ca2+ in the cytoplasm of hairy cells was identified. Increases in cytosolic Ca2+ are believed to be a pivotal signal in regulating cell proliferation, cell differentiation and cell death. These high Ca2+ levels in hairy cells could be reduced upon treatment with IFN-alpha either in vitro or in vivo, probably acting by reducing Ca2+ influx into the leukemic cells. Moreover, the effect of IFN-alpha on [Ca2+]i seems to be correlated with down-regulation of CD20 phosphorylation, a B cell specific phosphoprotein involved in Ca2+ influx across the plasma membrane. The possible origins and implications of Ca2+ deregulation and the possible mechanisms or sites of action of IFN-alpha in tumor cells from HCL are explored in this review.

Actions of interleukin-4 on prostaglandin biosynthesis at the chorion-decidual interface

OBJECTIVE

We determined the effects of interleukin-4 on chorion and decidual prostaglandin production.

STUDY DESIGN

Chorion and decidual cells from term placentas were grown to confluence. Cells were then incubated with interleukin-4 either alone or with other known stimulants of prostaglandin production: interleukin-1 beta, epidermal growth factor, ionomycin, or phorbol 12-myristate 13-acetate. Prostaglandin E2 production was determined with a specific radioimmunoassay.

RESULTS

Interleukin-4 alone stimulated prostaglandin E2 production in chorion and decidual cells. Interleukin-4 significantly enhanced the stimulatory actions of phorbol 12-myristate 13-acetate, ionomycin, and epidermal growth factor but not interleukin-1 beta on prostaglandin E2 production.

CONCLUSION

Interleukin-4 stimulates prostaglandin E2 production by chorion and decidual cells. These data suggest that interleukin-4 production by immune effector cells in gestational tissues may contribute to the pathophysiologic features of preterm labor.

Adenosine stimulates Ca2+ fluxes and increases cytosolic free Ca2+ in cultured rat mesangial cells

Adenosine has been associated with cellular Ca2+ metabolism in some cell types. Since adenosine is able to contract glomerular mesangial cells in culture, and since Ca2+ is the main messenger mediating contractile responses, we studied the effect of adenosine on 45Ca2+ movements into and out of mesangial cells and on the cytosolic free Ca2+ concentration ([Ca2+]i). Adenosine at 0.1 mM increased 45Ca2+ uptake (basal, 9993 +/- 216; + adenosine, 14823 +/- 410 d.p.m./mg; P less than 0.01) through verapamil-sensitive Ca2+ channels. These channels seem to be of the A1-adenosine receptor subtype. Adenosine also stimulated 45Ca2+ efflux from 45Ca(2+)-loaded mesangial cells. This effect was accompanied by a net depletion of intracellular 45Ca2+ content under isotopic equilibrium conditions (basal, 24213 +/- 978; + adenosine, 18622 +/- 885 d.p.m./mg; P less than 0.05). The increase in 45Ca2+ efflux was inhibited by a Ca(2+)-free medium or in the presence of 10 microM-verapamil. However, the intracellular Ca(2+)-release blocker TMB-8 (10 microM) only partially inhibited the adenosine-stimulated 45Ca2+ efflux. In addition, adenosine induced an elevation in [Ca2+]i in mesangial cells with an initial transient peak within 15 s (basal, 113 +/- 7; adenosine, 345 +/- 46 nM), and a secondary increase which was slower (3-4 min) and of lower magnitude than the initial peak (250 +/- 21 nM). In summary, adenosine elevates [Ca2+]i and stimulates both Ca2+ uptake from the extracellular pool and Ca2+ efflux from intracellular pools in mesangial cells. The Ca2+ release from internal stores is produced by a combination of a TMB-8-inhibitable and a non-TMB-8-inhibitable mechanism, and seems to be dependent on Ca2+ influx.

Effect of bacterial toxins on human B cell activation. II. Mitogenic activity of the B subunit of cholera toxin

The B subunit of cholera toxin (CT) but not the entire CT was found to induce the proliferation of resting human B lymphocytes. A significant mitogenic effect was observed for B subunit concentrations greater than 1 microgram/ml and reached a maximum of stimulation at 10 micrograms/ml. As already described for B lymphocytes preactivated with Staphylococcus aureus Cowan Strain I (SAC). B lymphocytes preactivated with the B subunit of CT, but not with the entire CT, were able to proliferate in response to exogenous interleukin 2 (IL 2) and to the low-molecular weight B cell growth factor (BCGF). To determine the transmembrane signaling system used by the B subunit of CT to mediate its biological effects, we compared the transmembrane signals used by the entire CT, its B subunit and SAC. In comparison to the entire CT, which directly activates adenylate cyclase and increases intracellular cAMP levels, neither the B subunit nor SAC modified the cAMP content. In contrast, although SAC induced inositol phosphate generation neither CT nor the separate subunits were able to induce such a production. Moreover, changes in the fluorescence of indo-1-loaded B lymphocytes revealed that mitogenic doses of either the B subunit or SAC induced a rapid and sustained increase in cytoplasmic free Ca2+ concentration ([Ca2+]i). The effect of the B subunit appeared to be largely dependent on the presence of extracellular Ca2+, because in Ca2(+)-free medium no [Ca2+]i uptake was observed. In contrast, the SAC-induced [Ca2+]i uptake is substantially, but not totally, inhibited in Ca2(+)-free medium, suggesting that part of the rise in [Ca2+]i was due to the release from internal stores. Moreover, fluorimetric measurements on loaded cells with 2',7'-bis(carboxyethyl)-5(6')-carboxyfluorescein revealed that SAC induced a rapid cytoplasmic alkalinization via activation of Na+/H+ exchange, whereas the entire CT and its B subunit had no effect on intracellular pH. Taken together, these data suggest that, in comparison to SAC, the mitogenic effect of the B subunit of CT was mediated through different intracellular biochemical pathways.

The involvement of protein kinase C, calcium, and 5-lipoxygenase in the production of tumor necrosis factor by a cloned interleukin-3 dependent cell line with natural cytotoxic activity

The cloned interleukin-3 dependent cell line, M1-A5 was studied to determine whether protein kinase C, calcium mobilization, and 5-lipoxygenase activity were involved in the signal transduction pathways required for the production of TNF. TNF release was stimulated by 10 ng/ml phorbol myristate acetate (PMA), 2 microM calcium ionophore A23187, and 1 microgram/ml lipopolysaccharide (LPS) with synergism seen between PMA and A23187. All signals were blocked by phloretin and the PMA signal was blocked by H-7, both drugs acting as protein kinase C inhibitors. Desensitization of protein kinase C by PMA (1 microgram/ml for 24 h) provided evidence that both PMA- and LPS-stimulated TNF production were protein kinase C-dependent while A23187-stimulated TNF production was not. Both the calcium chelator, EGTA, and the intracellular calcium antagonist, TMB-8, inhibited TNF production stimulated by all agents, indicating that TNF stimulation by all agents was calcium dependent. Finally, the 5-lipoxygenase inhibitors, ketoconazole and L-656,224, but not the cyclo-oxygenase inhibitor ASA, inhibited TNF stimulated by all agents. These findings indicate that, although TNF production by M1-A5 cells can be stimulated either by a calcium/protein kinase C- or by a calcium-dependent signal, there is a convergence of signals at the level of 5-lipoxygenase activation.

Ion channels and B cell mitogenesis

Given the presence of ionic channels at the membrane of lymphocytes, we have analyzed the effect of various channels blockers on B lymphocytes activation. TEA and 4-AP, two K+ channels blockers, quinine, a blocker of Ca2(+)-activated K+ channels, nickel and verapamil, two Ca2+ channels blockers, all inhibited LPS-induced B cell proliferation. However, these drugs neither inhibited the induction of Ia and Fc gamma RII expression nor cell enlargement and early RNA synthesis, indicating that the entry of B lymphocytes into G1 phase was not affected. In contrast, both late RNA synthesis and the induction of the TfR, which occur while the cell progress through G1, were inhibited by these blockers. These data show that TEA, quinine and verapamil block B lymphocyte activation during the G1 phase, probably between G1A and G1B. To question whether these effects were due to the block of voltage-activated K+ channels, we compared the ability of TEA, quinine, verapamil, 4-AP and nickel to block proliferation and K+ channels. A striking correlation was found for all the drugs but less for 4-AP. Moreover, TMA, a TEA analog unable to block K+ currents, did not affect B cell proliferation. Taken together, our data suggests that functional voltage-gated K+ channels are required at a precise stage of the G1 phase of the B cell cycle.

Effect of bacterial toxins on human B cell activation. I. Mitogenic activity of pertussis toxin

Pertussis toxin (PT) was found to elicit an increased thymidine uptake in resting B lymphocytes purified from human peripheral blood. A significant mitogenic effect was detected for toxin concentrations greater than 100 ng/ml (1nM) and a plateau of stimulation was reached at 1000 ng/ml (10 nM). B cell blasts, activated by a first signal such as Staphylococcus aureus Cowan I or insolubilized anti-mu chain antibody, were also stimulated to DNA synthesis by PT in the same range of concentrations. At lower sub-mitogenic concentrations, the toxin potentiated the response to the low-molecular weight B cell growth factor (LMW-BCGF or 12-kDa BCGF), a progression factor for activated B cells. The "A" or catalytic subunit was devoid of any activity on B cells, suggesting the stimulatory effect of the toxin might be associated with the binding or "B" subunit, as it has been shown for T cells. This hypothesis was strengthened by the observation that, as in T cell, the whole toxin but not the "A" promoter, was able to induce calcium influx in these cells. In addition, the purified "B" oligomer alone was found to promote DNA synthesis in B cells. Finally, a fragment of the soluble cleaved form of the CD23 molecule (Fc epsilon RII) could be involved in the process of PT mitogenicity for B cells.

Extracellular but not intracellular calcium mobilization is required for Epstein-Barr virus-containing supernatant-induced B cell activation

Changes in intracytosolic free calcium concentration ([Ca2+]i) are though to be an important trigger for the initiation of the cellular events culminating in B cell activation. After exposure of human B lymphocytes loaded with the fluorescent indicator quin-2 to the Epstein-Barr virus (EBV)-containing supernatant of B95-8 cell line, a rise in [Ca2+]i is observed. To determine the respective contribution of the intra- and extracellular Ca2+ pools in EBV-induced B cell activation, the pharmacologic modulation of these processes was investigated using an intracellular calcium chelator, 1,2-bis(o-aminophenoxy)ethane- N,N,N',N'-tetraacetic (BAPTA) or the calcium channel blocking drugs. When the extracellular Ca2+ contribution was minimized in the presence of calcium channel-blocking drugs or incubation of the cells in Ca2+-free medium, the EBV-induced human B cell activation was fully inhibited. When the calcium channel-blocking drugs, either verapamil or diltiazem, were withdrawn or when exogenous Ca2+ was added to the Ca2+-free medium, EBV-induced B cell activation was noted, demonstrating the reversibility of the inhibition. On the contrary, when the intracellular Ca2+ contribution was reduced after loading the cell with BAPTA, no alteration of the EBV-induced B cell activation was observed. Thus, the EBV-induced rise of [Ca2+]i required in the activation of human B cells appears to be essentially related to the entry of extracellular Ca2+ and not to the release of Ca2+ from internal stores.

Potentiation of the proliferative response of human B lymphocytes to low molecular weight B cell growth factor (LMW-BCGF) by fibroblast growth factors (FGFs)

Both acidic and basic fibroblast growth factor (FGF), although devoid alone of growth-promoting ability on resting or activated human lymphoid B cells, were found to markedly increase the proliferative response of anti-mu-chain or SAC preactivated B cell blasts to the low molecular weight B cell growth factor (LMW-BCGF) and to enhance the costimulatory response of resting B cells to anti-mu-chain and LMW-BCGF. This potentiating effect was also observed for a LMW-BCGF-dependent B cell tumor derived from a lymphocytic nodular lymphoma. Other growth factors acting on fibroblasts, such as epidermal growth factor, alpha-thrombin, platelet-derived growth factor, and insulin-like growth factor-I did not display such enhancing effect on LMW-BCGF-driven proliferation. Activated, but not resting B cells were found to bear receptor sites for FGFs and from kinetics experiments, it is suggested that LMW-BCGF induces competence expression for FGFs in those cells. Moreover, the LMW-BCGF-elicited generation of inositoltrisphosphate resulting from polyphosphoinositides hydrolysis was increased in the presence of FGF.