The Na,K-ATPase pump and the lymphocyte adenylate cyclase system]

The effects of the Na(+)-K(+)-pump inhibitor ouabain on the beta 2-adrenoreceptor-coupled adenylate cyclase system were examined in vitro using intact human mononuclear lymphocytes and cell homogenates. Ouabain caused a dose-dependent increase in basal adenylate cyclase (AC) activity from 0.1 to 100 microM. The density of surface binding sites for 125ICYP (4 degrees C) was decreased by almost 25% after ouabain action. Glycoside shifted to the right the dose-response curve for stimulation of the cAMP synthesis by 1-isoproterenol. This shift was due to a decrease in the affinity of beta 2-adrenoreceptors for 1-isoproterenol, as it was shown in the competition experiments with 125ICYP (control--IC50, 1-isoproterenol--0.5 microM, ouabain--1.25 microM). Ouabain did not change the forskolin-stimulated AC activity. The activity measured in the presence of Gpp(NH)p which stimulates AC via Gs-protein was increased by ouabain; lag-period of Gpp(NH)p action did not change after ouabain addition. N-ethylmaleimide which inactivates Gi-protein increased basal, 1-isoproterenol and ouabain-sensitive AC activities. The stimulation of lymphocyte AC activity by ouabain may be due to an enhancement of the activation of Gs-protein.     

Ouabain inhibition of human lymphocyte cytotoxicity.

Ouabain, a specific inhibitor of the membrane Na⁺-K⁺-ATPase, is known to inhibit the proliferation of human lymphocytes in culture induced by any of a variety of agents. Here we show that the cytotoxic activity of human lymphocytes precultured with ouabain for 1 day against antibody-coated target cells (ADCC) was inhibited in a concentration-dependent manner; a 2-day exposure resulted in a drastic and irreversible loss. Ouabain acted synergistically with the respiratory chain inhibitor antimicin A to block killing, but did not act synergistically with the competitive inhibitor of glucose utilization 2-deoxyglucose. T-cell cytotoxicity (CML) was more sensitive to ouabain than was ADCC; it was inhibited when the drug was only present during the assay. We conclude that prolonged exposure to ouabain has a selective effect not only on the proliferation of immunocompetent cells, but also on the different function of cytotoxicity, whether in ADCC or in CML, and that one of the victims of the treatment may be energy production.     

Overexpression of the Polycystin-1 C-Tail Enhances Sensitivity of M-1 Cells to Ouabain

Cells derived from renal cysts of patients with autosomal dominant polycystic kidney disease (ADPKD) are abnormally sensitive to ouabain, responding to physiological ouabain concentrations with enhanced proliferation and increased forskolin-induced transepithelial fluid secretion. This requires activation of the epidermal growth factor receptor (EGFR), Src kinase and the extracellular signal-regulated kinases MEK and ERK. Here, we have determined if the ADPKD phenotype obtained in mouse cortical collecting duct cells by stable overexpression of the C-terminal domain of polycystin-1 (PC-1 C-tail) also elicits the ADPKD-like response to ouabain in the cells. M-1 C20 cells expressing the PC-1 C-tail and M-1 C17 cells lacking expression of this construct were treated with physiological concentrations of ouabain, and cell proliferation, activation of the EGFR-Src-MEK-ERK pathway, forskolin-induced transepithelial Cl^? secretion and the sensitivity of Na,K-ATPase to ouabain were explored. M-1 C20 cells responded to ouabain with increased cell proliferation and ERK phosphorylation. Ouabain also augmented forskolin-induced and cystic fibrosis transmembrane conductance regulator-mediated apical secretion of Cl^? in M-1 C20 cells. These effects required activation of EGFR, Src and MEK. In contrast, ouabain had no significant effects on M-1 C17 cells. Interestingly, approximately 20 % of the Na,K-ATPase from M-1 C20 cells presented an abnormally increased sensitivity to ouabain. Overexpression of PC-1 C-tail in M-1 C20 cells is associated with an ouabain-sensitive phenotype and an increased ability of the cells to proliferate and secrete anions upon ouabain stimulation. This phenotype mimics the ouabain sensitivity of ADPKD cells and may help promote their cystogenic potential.     

Ouabain induces cell proliferation through calcium-dependent phosphorylation of Akt (protein kinase B) in opossum kidney proximal tubule cells

Cardiotonic glycosides, like ouabain, inhibit Na⁺-K⁺-ATPase. Recent evidence suggests that low molar concentrations of ouabain alter cell growth. Studies were conducted to examine the effect of ouabain on Akt phosphorylation and rate of cell proliferation in opossum kidney (OK) proximal tubule cells. Cells exposed to 10 nM ouabain displayed increased Akt Ser⁴⁷³ phosphorylation, as evidenced by an increase in phospho-Akt Ser⁴⁷³ band density. Ouabain-stimulated Akt Ser⁴⁷³ phosphorylation was inhibited by pretreatment with phosphatidylinositol 3-kinase (PI3K) inhibitors (LY294002 and wortmannin), a PLC inhibitor (edelfosine), and an Akt inhibitor. Moreover, ouabain-mediated Akt Ser⁴⁷³ phosphorylation was suppressed by reduction of extracellular calcium (EGTA) or when intracellular calcium was buffered by BAPTA-AM. An inhibitor of calcium store release (TMB-8) and an inhibitor of calcium entry via store-operated calcium channels (SKF96365) also suppressed ouabain-mediated Akt Ser⁴⁷³ phosphorylation. In fura-2 AM-loaded cells, 10 nM ouabain increased capacitative calcium entry (CCE). Ouabain at 10 nM did not significantly alter baseline cytoplasmic calcium concentration in control cells. However, treatment with 10 nM ouabain caused a significantly higher ATP-mediated calcium store release. After 24 h, 10 nM ouabain increased the rate of cell proliferation. The Akt inhibitor, BAPTA-AM, SKF96365, and cyclopiazonic acid suppressed the increase in the rate of cell proliferation caused by 10 nM ouabain. Ouabain at 10 nM caused a detectable increase in ⁸⁶Rb uptake but did not significantly alter Na⁺-K⁺-ATPase (ouabain-sensitive pNPPase) activity in crude membranes or cell sodium content. Taken together, the results point to a role for CCE and Akt phosphorylation, in response to low concentrations of ouabain, that increase the rate of cell proliferation without inhibiting Na⁺-K⁺-ATPase-mediated ion transport. Na⁺-K⁺-ATPase; opossum kidney cells     

Phorbol esters augment polyamine transport by influencing Na(+)-K+ pump in murine leukemia cells.

In this report, we elucidate the role of Na(+)-K+ pump in the regulation of polyamine spermidine (Spd) transport in murine leukemia (L 1210) cells in culture. Ouabain, known to bind extracellularly to the alpha-subunit of the Na(+)-K+ pump, inhibits the pump activity. The L 1210 cells were found to possess ouabain binding sites at 7.5 fmol/10(6) cells. Ouabain significantly inhibited the Spd uptake in a dose-dependent manner. The maximum inhibition of Spd uptake by ouabain was observed beyond 200 microM. Spd transport was inversely correlated with the [3H]ouabain binding to L 1210 cells: an increase in the saturation of ouabain binding to L 1210 cells resulted in a decrease of the Spd uptake process. Treatment of L 1210 cells with protein kinase C activator phorbol esters increased the Spd transport and, also, ouabain-sensitive 86Rb+ uptake, a measure of the activity of the Na(+)-K+ pump. H-7, a protein kinase C inhibitor, significantly inhibited the ouabain-sensitive 86Rb+ uptake by L 1210 cells. Phorbol esters stimulated the level, but not the rate, of 22Na+ influx. Addition of H-7 to L 1210 cells inhibited the 22Na+ influx process. A concomitant phorbol ester-induced increase in 22Na+ influx, [14C]Spd uptake, together with the functioning of Na(+)-K+ pump, indicates the role of the "Na+ cycle" in the regulation of the polyamine transport process.     

Human Breast Tumor Cells Are More Resistant to Cardiac Glycoside Toxicity Than Non-Tumorigenic Breast Cells

Cardiotonic steroids (CTS), specific inhibitors of Na,K-ATPase activity, have been widely used for treating cardiac insufficiency. Recent studies suggest that low levels of endogenous CTS do not inhibit Na,K-ATPase activity but play a role in regulating blood pressure, inducing cellular kinase activity, and promoting cell viability. Higher CTS concentrations inhibit Na,K-ATPase activity and can induce reactive oxygen species, growth arrest, and cell death. CTS are being considered as potential novel therapies in cancer treatment, as they have been shown to limit tumor cell growth. However, there is a lack of information on the relative toxicity of tumor cells and comparable non-tumor cells. We have investigated the effects of CTS compounds, ouabain, digitoxin, and bufalin, on cell growth and survival in cell lines exhibiting the full spectrum of non-cancerous to malignant phenotypes. We show that CTS inhibit membrane Na,K-ATPase activity equally well in all cell lines tested regardless of metastatic potential. In contrast, the cellular responses to the drugs are different in non-tumor and tumor cells. Ouabain causes greater inhibition of proliferation and more extensive apoptosis in non-tumor breast cells compared to malignant or oncogene-transfected cells. In tumor cells, the effects of ouabain are accompanied by activation of anti-apoptotic ERK1/2. However, ERK1/2 or Src inhibition does not sensitize tumor cells to CTS cytotoxicity, suggesting that other mechanisms provide protection to the tumor cells. Reduced CTS-sensitivity in breast tumor cells compared to non-tumor cells indicates that CTS are not good candidates as cancer therapies.     

All-trans retinoic acid (ATRA) induces miR-23a expression,decreases CTSC expression and granzyme B activity leading to impaired NK cell cytotoxicity

NK cell is an innate immune system lymphocyte lineage with natural cytotoxicity. Its optimal use in the clinic requires in vitro expansion and activation. Cytokines and encounter with target cells activate NK cells and induce proliferation, and this could depend on the presence of other immune cells. Here we activated PBMCs during 5 days with IL-2, with IL-2 plus the tumor cell line K562 and with the lymphoblastoid cell line R69 and perform integrated analyses of microRNA and mRNA expression profiles of purified NK cells. The samples cluster depending on the stimuli and not on the donor, indicating that the pattern of NK cell stimulation is acutely well conserved between individuals. Regulation of mRNA expression is tighter than that of miRNA expression. All stimuli induce a common preserved genetic remodeling. In addition, encounter with target cells mainly activates pathways related to metabolism. Different target cells induce different NK cell remodeling which affects cytokine response and cytotoxicity, supporting the notion that encounter with different target cells significantly changing the activation pattern. We validate our analysis by showing that activation down regulates miR-23a, which is a negative regulator of cathepsin C (CTSC) mRNA, a gene up regulated by all stimuli. The peptidase CTSC activates the granzymes, the main effector proteases involved in NK cell cytotoxicity. All-trans retinoic acid (ATRA), which induces miR-23a expression, decreases CTSC expression and granzyme B activity leading to impaired NK cell cytotoxicity in an in vivo mouse model.     

Modulation of natural killer-mediated lysis by red blood cells

Natural killer (NK)-mediated cytotoxicity is significantly enhanced in the presence of red blood cells (RBC). The enhancement is dose dependent on the number of RBC present and can be induced by autochthonous, allogeneic, or xenogeneic RBC. The enhancement was demonstrated in cytotoxicity against two different NK-sensitive tumor target cell lines, K562 and U937, and by three different assay systems, chromium release, lactate dehydrogenase release, and inhibition of thymidine incorporation. RBC directly enhance the cytotoxic activity of NKH-1/Leu19+ large granular lymphocyte NK cells. Intact RBC have to be present during the cytotoxicity assay to induce the enhancement, which probably occurs at a postbinding, preprogramming phase. The anti-CD2 antibody Leu5 cannot block the enhancement at a concentration inhibitory to lymphocyte rosetting with sheep RBC, suggesting that the enhancement is not induced by interaction through the CD2 antigen. These results indicate that RBC are a potent modulator of NK cytotoxicity and suggest that in vitro NK studies using purified lymphocytes may not always truly reflect NK activity in the blood stream.     

Functional consequences of cAMP accumulation in human natural killer cells. Implications for IL-2 and IL-4 signal transduction

To approach the mechanisms whereby IL-2 activates human NK cells, we have compared the effects of IL-4 and of Bt2cAMP on this activation. Both agents block completely the proliferation induced by IL-2 on highly purified CD3-negative human NK cells. We also report that the net LAK response of PBL is inhibited by IL-4 and cAMP. However, kinetics analysis showed that IL-4 appears to inhibit an early stage of IL-2-induced activation of NK cells. IL-4 does not affect the cytotoxicity of freshly isolated NK cells against the K562 target and is ineffective on IL-2-preactivated cells. In contrast, cAMP primarily blocks the lytic effector phase, whether cells have been cultured in IL-2 or not, and its effect appears independent of time of addition. These differences between the activity of IL-4 and cAMP suggested that cAMP was not directly involved in IL-4 signal transduction in human NK cells. Consistent with this interpretation, we did not observe any variation in the level of intracellular cAMP concentrations when NK cells were stimulated with IL-4, or when they are stimulated with IL-2 or IL-2 plus IL-4. In addition, we also demonstrate that NK cell cytotoxic activation induced by IL-2 is still demonstrable in the presence of Bt2cAMP under conditions in which NK cell proliferation is blocked. These results clearly indicate that the differentiative effect of IL-2 on NK cells is independent of cell proliferation. Furthermore, the p70-75 IL-2R-initiated signal transduction pathway that leads to increased cytotoxicity appears not to be susceptible to inhibition by cAMP in human NK cells.     

Differential effects of ouabain on human cell-mediated cytotoxicity. I. Inhibition of mitogen-induced cellular cytotoxicity and antibody-dependent cellular cytotoxicity against chicken red cell targets.

The effects of ouabain, a known inhibitor of lymphoproliferation, were studied in relation to the cytotoxic effector function of human peripheral blood mononuclear leukocytes (MNL) against chicken red blood cell (CRC) targets. MNL effectors lysed ⁵¹Cr-labeled CRC targets in the presence of PHA (mitogen-induced cellular cytotoxicity—MICC) or rabbit anti-CRC antibody (antibody-dependent cellular cytotoxicity—ADCC) in the absence of ouabain. The addition of ouabain to the cytotoxic reaction caused profound diminution of MICC with greater than 90% suppression of killing at ouabain concentrations of 5 × 10^?4M; ADCC was much more resistant to the effects of ouabain with only 60 to 70% inhibition of killing at similar ouabain concentrations (P < 0.01). Similar ouabain inhibition of MICC occurred whether the effector cell populations were unseparated MNL, depleted of monocytes, enriched for T cells, or depleted of T cells, suggesting a generalized activity by ouabain against all effector cells active in MICC. Ouabain inhibition of MICC could be overcome by increasing PHA concentrations, indicating that ouabain inhibition was not due to irreversible toxic effects on effector cells. Increasing the concentration of anti-CRC antibody resulted in increased killing in this ADCC system and, paradoxically, ADCC cultures with the highest antibody concentrations were more completely inhibited by ouabain. This enhanced inhibitory effect of ouabain on ADCC cultures with the highest antibody concentrations was not observed when the effector cell population was first depleted of phagocytic cells, suggesting a preferential inhibitory action by ouabain against monocyte effectors in ADCC. Thus, the differential inhibitory effects of ouabain on MICC and ADCC against CRC targets may be in part explained by the differing ouabain sensitivities of the various effector cell subpopulations involved in these cell-mediated cytotoxic events.     

Characterization of temperature-sensitive mutants of animal cells

An early increase in lymphocyte plasma membrane K⁺ transport is essential for PHA stimulated lymphocytes to divide. Little is known about the specific source and amount of energy required to support the increased transport by activated lymphocytes. Since ouabain, a cardiac glycoside, specifically inhibits the transport ATPase, we have measured the decrement in glycolysis and tricarboxylic acid cycle activity when untreated and PHA treated lymphocytes were exposed to ouabain. This metabolic decrement represents the portion of metabolism associated with monovalent cation transport and closely related processes. Since TCA cycle activity accounted for only 0.2% of glucose consumption, aerobic glycolysis was the major source of energy, i.e., ATP, for increased transport. Approximately one-third of the total lactate production in both control and PHA stimulated lymphocytes was ouabain-sensitive. Ouabain sensitive lactate production in control, 105 μmol/10¹⁰ cells/hour, increased 1.8-fold to 193 μmol/10¹⁰ cells/hour after PHA treatment. Active K⁺ influx in similar cell populations increased from 40 μmol/10¹⁰ cells/hour to 74 μmol/10¹⁰ cells/hour (1.9-fold) after PHA treatment. The increment in ouabain-sensitive energy production and K⁺ transport were closely correlated and, therefore, 0.38 moles of K⁺ are transported for each mole of ATP generated in both control and PHA treated cells. The increased requirement for transport related energy is provided by increasing the ouabain-sensitive ATP production rather than altering the efficiency of ATP transduction.     

Inhibition of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) endocytosis by ouabain in human endothelial cells

3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) uptake and reduction is widely used to evaluate cell proliferation and viability. MTT is taken up by the cells through endocytosis. We find that ouabain (1-200 nM) inhibits MTT reduction in human umbilical vein endothelial cells (HUVEC) without affecting cell viability. Ouabain does not inhibit MTT reduction when cell lysates substituted for the intact cells. Disruption of caveolae by cholesterol depletion, completely prevents the effect of ouabain. Treatment of HUVEC with Src inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine partially abrogates the inhibitory effect of ouabain. The data suggest that ouabain interaction with caveolar Na/K-ATPase inhibits MTT endocytosis through the activation of signaling proteins such as Src kinase.     

Recombinant interleukin 2 enhanced natural killer cell-mediated cytotoxicity in human lymphocyte subpopulations expressing the Leu 7 and Leu 11 antigens

Highly purified recombinant human interleukin 2 (rIL 2) markedly augments the natural killer (NK) cell-mediated cytotoxicity of peripheral blood lymphocytes. In this study, we examined the cellular and metabolic basis of rIL 2-mediated activation of human lymphocyte subpopulations expressing the NK cell-associated surface antigens Leu 7 and Leu 11. All rIL 2-responsive cytotoxic NK cells were found within the subset of lymphocytes expressing the Leu 11 marker, an antigen associated with the Fc-IgG receptor on human NK cells. Cells lacking the Leu 11 antigen, including cells expressing another NK cell-associated marker, Leu 7, did not express NK cell-mediated cytotoxicity either before or after rIL 2 treatment. By contrast, rIL 2 augmented the NK activity of both Leu7-,11+ and Leu 7+,11+ subpopulations. Activation of Leu 11+ NK cells resulted from a direct effect of rIL 2 on these cells and neither required nor was amplified by the presence of T lymphocytes. Enhanced NK cell-mediated cytotoxicity occurred within 4 hr after exposure to rIL 2, and was blocked by the protein synthesis inhibitor cyclohexamide, but not by the DNA synthesis inhibitor mitomycin C or 1500 rad of x-irradiation. Neither Tac antigen, a high-affinity receptor for IL 2, nor other activation markers, such as transferrin receptor or HLA-DR antigen, were detectable on a significant proportion of Leu 11+ cells, either before or after incubation with rIL 2 for 48 hr. In addition, saturating concentrations of antibodies to each of these markers had no effect on the enhancement of NK activity by rIL 2. Finally, preliminary experiments with neutralizing antibodies to gamma- and alpha-interferons also failed to prevent rIL 2 enhancement of NK cell-mediated cytotoxicity, suggesting that rIL 2 does not mediate its effect via release of these cytokines.     

A subset of CD16-natural killer cells without antibody-dependent cellular cytotoxicity function

The low affinity IgG receptor, CD16 (Fc gamma RIII), is expressed on almost all peripheral blood natural killer (NK) cells. A small subset of CD3- CD16- CD56+ NK cells, representing less than 1% of peripheral blood lymphocytes, expands during in vivo IL-2 treatment. To analyze this CD16- NK cell subset in more detail, NK clones have been generated. One of them (TNK2) has been used to study the function of these cells in more detail. It is demonstrated that TNK2 exerts normal NK activity and displays large granular lymphocyte morphology. Since this clone lacks CD16 expression, antibody-dependent cellular cytotoxicity cannot be exerted. CD16 monoclonal antibodies fail to induce cytotoxic activity against NK-resistant target cells. These studies reveal that the lack of CD16 detection is not due to the modulation or the stage of activation of these NK cells. TNK2 is representative of this small subset of peripheral blood NK cells, expanded during IL-2 treatment, which does not express Fc gamma RIII and therefore cannot perform antibody-dependent cellular cytotoxicity.     

Ultrastructural study of biochemically modulated ADCC in HSV-1 infected and uninfected Chang liver cells

The effect of cytochalasin B, ouabain and 25-OH cholesterol on specific lysis due to antibody dependent cellular cytotoxicity (ADCC) in allogeneic and xenogeneic systems was studied using Herpes simplex I infected Chang liver cells. Cytochalasin B reduced both cytotoxicity and lymphocyte/target (LT) binding in the allogeneic system whereas cytotoxicity but not LT binding was reduced in the xenogeneic system. Ouabain inhibited ADCC in both systems as well as LT binding in the allogeneic system; however, binding in the xenogeneic system was not significantly reduced. The 25-OH cholesterol produced a marked decrease in ADCC in both systems but had no significant effect on LT binding in either system. The biochemical and ultrastructural data suggest that the modulators act at different stages in the ADCC response and that there may be more than one mechanism of ADCC to handle different types of target antigens.     

Effect of anti-human pan-T monoclonal antibodies on lymphocyte proliferative and cytotoxic functions

Effects of anti-human pan-T-specific monoclonal antibodies of the Second International Workshop on Human Leucocyte Differentiation Antigens were investigated in a number of lymphocyte functional tests. Monoclonal antibodies blocking antibody-dependent cytotoxicity (ADCC), PWM-induced IL-2 release, or Con A- and PWM-induced lymphocyte proliferation were found among anti-CD2 and CD3 reagents. Inhibition of lectin-dependent cellular cytotoxicity (LDCC) was found as an exclusive effect of anti-CD2 (the sheep red cell receptor) antibodies. Several anti-CD2s blocked natural killer (NK) activity and/or PWM-induced interferon production. These two effects were exerted by antibodies against epitopes on resting T cells but not by those directed to activation epitopes. The inhibitory activity of individual antibodies in the LDCC and NK tests showed a good correlation. Also, PHA-mediated cytotoxicity (LDCC) and proliferation were in good correlation. Concerning anti-CD3 (T3) reagents, some effects were characteristic for the majority of the antibodies in this group. Namely, induction of proliferation, enhancement of IL-2-dependent cell division, IL-2 consumption by antibody-triggered cells, inhibition of mitogen-induced proliferation but not IL-2 and interferon production were observed. None of the CD3-specific reagents exerted all of these effects. In general, no correlation of the effects with immunoglobulin subclass or CD3 subcluster specificity could be found. Further epitope analysis and affinity data may be required to understand the basis of heterogeneity in functional effects of monoclonal antibodies to the CD3 molecule.     

Selective expansion and partial activation of human NK cells and NK receptor-positive T cells by IL-2 and IL-15.

IL-2 and IL-15 are lymphocyte growth factors produced by different cell types with overlapping functions in immune responses. Both cytokines costimulate lymphocyte proliferation and activation, while IL-15 additionally promotes the development and survival of NK cells, NKT cells, and intraepithelial lymphocytes. We have investigated the effects of IL-2 and IL-15 on proliferation, cytotoxicity, and cytokine secretion by human PBMC subpopulations in vitro. Both cytokines selectively induced the proliferation of NK cells and CD56(+) T cells, but not CD56(-) lymphocytes. All NK and CD56(+) T cell subpopulations tested (CD4(+), CD8(+), CD4(-)CD8(-), alphabetaTCR(+), gammadeltaTCR(+), CD16(+), CD161(+), CD158a(+), CD158b(+), KIR3DL1(+), and CD94(+)) expanded in response to both cytokines, whereas all CD56(-) cell subpopulations did not. Therefore, previously reported IL-15-induced gammadelta and CD8(+) T cell expansions reflect proliferations of NK and CD56(+) T cells that most frequently express these phenotypes. IL-15 also expanded CD8alpha(+)beta(-) and Valpha24Vbeta11 TCR(+) T cells. Both cytokines stimulated cytotoxicity by NK and CD56(+) T cells against K562 targets, but not the production of IFN-gamma, TNF-alpha, IL-2, or IL-4. However, they augmented cytokine production in response to phorbol ester stimulation or CD3 cross-linking by inducing the proliferation of NK cells and CD56(+) T cells that produce these cytokines at greater frequencies than other T cells. These results indicate that IL-2 and IL-15 act at different stages of the immune response by expanding and partially activating NK receptor-positive lymphocytes, but, on their own, do not influence the Th1/Th2 balance of adaptive immune responses.     

Anti-cancer activity and mechanistic features of a NK cell activating molecule

Natural cytotoxicity receptors (NCRs) are major activating receptors involved in NK cytotoxicity. NCR expression varies with the activation state of NK cells, and the expression level correlates with NK cells’ natural cytotoxicity. In this study, we found that Gö6983, a PKC inhibitor, induced a remarkable increase of NCR expression on primary NK cells, but other PKC inhibitors and NK cell stimulators such as IL-2 and PMA, did not. Gö6983 increased the expression of NCR in a time- and concentration-dependent manner. Furthermore, Gö6983 strongly upregulated the surface expression of death ligands FasL and TRAIL, but not cytotoxic molecules perforin and granzyme B. Unlike two other NK stimulating molecules, IL-2, and PMA, Gö6983 did not induce NK cell proliferation. Up-regulation of NCRs and death ligands on NK cells by Gö6983 resulted in a significant enhancement of NK cytotoxicity against various cancer cell lines. Most importantly, administration of Gö6983 effectively inhibited pulmonary tumor metastasis in mice in a dose-dependent manner. These results suggest that Gö6983 functions as an NK cell activating molecule (NKAM); this NKAM is a novel anti-cancer and anti-metastasis drug candidate because it enhances NK cytotoxicity against cancer cells in vivo as well as in vitro.     

Cytotoxicity from cultured cells: analysis of precursors involved in generation of human cells mediating natural and antibody-dependent cell-mediated cytotoxicity.

Natural cell-mediated cytotoxicity of human peripheral blood lymphocytes natural killer (NK) against K-562 and antibody-dependent cellular cytotoxicity (ADCC) against Chang cells, as measured in a 4-hr ⁵¹Cr release assay, were both completely removed by depletion of Fc receptor-positive (FcR+) cells. After in vitro culture for 7 days, however, NK- and ADCC-like activities spontaneously regenerated. The nature of precursor cells was studied by examination of lymphocyte subpopulations required for generation of this cytotoxicity. After depletion of FcR+ cells from PBL, the following subpopulations were prepared: sheep erythrocyte rosette-forming cells (E+), surface membrane immunoglobulin-positive cells (SmIg+), and null cells (lacking E+, SmIg+, or FcR+ markers). Separate cell types or mixtures were cultured in vitro in medium containing 10% fetal calf serum for 7 days and then tested for NK and ADCC. Whereas unseparated FcR-depleted cells developed substantial cytotoxic activity, each of the subpopulations cultured alone was negative or had low activity. Addition of SmIg+ cells to other cell types had no effect; however, mixture of 80% E+ and 20% null cells resulted in optimal NK and ADCC. It is not presently clear which population the precursors were in. However, the requirement for proliferation by the null cell population but not by the E+ cells (as indicated by sensitivity to radiation and mitomycin C) suggested that the precursors for NK cells may be null cells.     

A study of GRM1 monoclonal antibody that reacts with natural killer cells and granulocytes

We have produced a monoclonal antibody, GRM1, against a prolymphocytic leukemia that defines an antigen present in neutrophilic granulocytes (PMN) and a lymphocyte subset with natural killer (NK) activity, which was identified as large granular lymphocytes. This monoclonal antibody recognizes FcR2 (CD16), an antigen composed of two polypeptides of 50 and 60 kilodaltons, respectively. This GRM1 monoclonal antibody was tested against normal T and B cells, neutrophilic granulocytes, monocytes, platelets, acute and chronic leukemias, and was positive only against granulocytes (95%) and cells with NK activity. GRM1 was able to deplete NK cell activity in complement-dependent lysis. However, GRM1 did not block NK activity nor peripheral blood lymphocyte- and PMN-mediated antibody-dependent cytotoxicity in healthy individuals. GRM1 also did not block Fc receptor in an erythrocyte antibody rosette assay. The immunochemical data and cell distribution patterns lead us to conclude that GRM1 recognizes and FcR2 receptor epitope which is not involved in the receptor's function.