Protein A induces NO production: involvement of tyrosine kinase, phospholipase C, and protein kinase C

Immunomodulatory effects of polar lichens on the function of macrophages in vitro

Lichen species were collected from King George Island (Antarctica) and were screened for their immunomodulatory effect. Among the lichens tested, the methanol extract (CR-ME) of Caloplaca regalis showed the highest nitric oxide (NO) production in murine peritoneal macrophages. Therefore, this study further examined the ability of C. regalis to induce secretory and cellular responses in macrophages. Macrophages were treated with various concentrations of CR-ME for 18 h. The CR-ME treatment induced tumoricidal activity and increased the production of tumor necrosis factor-alpha (TNF-alpha) and nitric oxide by macrophages. However, CR-ME had a little effect on the levels of reactive oxygen species, interleukin-1 and IFN-gamma in CR-ME-treated macrophages. The CR-ME-induced tumoricidal activity was partially abrogated by a NO inhibitor and the anti-TNF-alpha antibody. Thus, the tumoricidal effect of CR-ME appeared to be mainly mediated by NO and TNF-alpha production from macrophages. Treating the macrophages with a p38 mitogen-activated protein kinase (MAPK) inhibitor partially blocked the tumoricidal activation induced by CR-ME, whereas inhibitors of the other kinases did not have an inhibitory effect. These results suggest that CR-ME induces the tumoricidal activity via the p38 MAPK-dependent pathway. Furthermore, electrophoretic mobility shift assay analyses revealed that the CR-ME treatment induced the activation of the NF-kappaB transcription factor. Overall, these results indicate that the tumoricidal activity induced by CR-ME is mainly due to TNF-alpha and NO production, and the activation of macrophage by CR-ME is mediated probably via the p38 MAPK and NF-kappaB pathway. Our results may also provide some leads in the development of new immunomodulating drugs.

RETRACTED: Activation of murine peritoneal macrophages by sulfated exopolysaccharide from marine microalga Gyrodinium impudicum (strain KG03): involvement of the NF-kappa B and JNK pathway

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor-in-Chief, as there are concerns about inappropriate re-use of published figures. In this study, the same Western blot has been used to represent different studies with different drugs (methoxychalcone vs ganodermanondiol), cell extracts (macrophages versus hepatocytes) and different targets (Nrf2 vs LKB1). The concern was initially raised in PubPeer, the response from author on PubPeer was not acceptable. The journal Editor in Chief requested the author to provide the explanation, however, the author was not able to fulfil this request. PubPeer - Activation of murine peritoneal macrophages by sulfated exop… [pubpeer.com]

Acidic polysaccharides isolated from Phellinus linteus induce phenotypic and functional maturation of murine dendritic cells

Acidic polysaccharides (PL) isolated from Phellinus linteus are known to stimulate the proliferation of T lymphocytes and humoral immune functions to act as a polyclonal activator of B cells, and to inhibit tumor growth and metastasis. However, little is known about their immunomodulating effects or the effects of its mechanisms on murine bone marrow (BM)-derived dendritic cells (DC). In this study, it profoundly increased CD80, CD86, MHC I, and MHC II expression in murine, GM-CSF and IL-4 stimulated, BM-derived myeloid DC. The ability of unstimulated DC to uptake dextran was higher than that of PL- or LPS-stimulated DC. We analyzed the concentration of IL-12 secreted by DC using flow cytometry and ELISA. Untreated DC secreted a low concentration of IL-12, while PL- or LPS-stimulated DC secreted higher levels of IL-12 than untreated DC. There were no remarkable differences in the concentrations of IL-12 produced by PL- or LPS-stimulated DC. However, polymyxin B (PB; an LPS inhibitor) effectively inhibited the surface molecules and IL-12 production induced by LPS, but had no effect on the PL in DC. PL-treated DC were much more potent antigen-presenting cells in allogeneic immune response than untreated DC. PL treatment not only formed morphologically mature DC but also induced predominant migration to lymphoid tissues. Moreover, the inhibitors of protein tyrosine kinase (PTK) or protein kinase C (PKC) significantly blocked the expression of surface molecules and IL-12 production in PL-stimulated DC. Treatment of DC with PL directly induced PKC activity and phosphorylated PTK. Furthermore, CD11b and/or CD18 partially mediated PL-induced DC maturation.

Acidic polysaccharide isolated from Phellinus linteus induces nitric oxide-mediated tumoricidal activity of macrophages through protein tyrosine kinase and protein kinase C

Mushroom polysaccharides are increasingly being utilized to treat a wide variety of diseases. Aqueous extracts from the Phellinus linteus have been reported to have anti-tumor and immunomodulatory properties. In particular, acidic polysaccharide (PL) isolated from P. linteus induced a secretory and cellular macrophage response. However, the exact mechanism by which PL regulates the macrophage functions remains unclear. PL-treated murine peritoneal macrophages in vitro and in vivo dramatically induced the production of NO. PL enhanced the lytic death of B16 cells through the production of NO. The present study examined signal molecules that may participate in PL-elicited responses by macrophages. The data demonstrated that a protein kinase C (PKC) inhibitor, staurosporine, and a protein tyrosine kinase (PTK) inhibitor, genistein, inhibited the tumoricidal activity of macrophages induced by PL. In addition, these inhibitors blocked the production of NO and the expression of surface molecules in PL-stimulated macrophages. Furthermore, CD11b/CD18 possibly mediates PL-induced cell activation. These results suggest that PL stimulates NO production for tumoricidal activity and induces cell-mediated immunity by increasing surface molecules, and the process may be a mechanism by which PL produces its therapeutic effects.

Differential expression of protein kinase C isoenzymes related to high nitric oxide synthase activity in a T lymphoma cell line

Protein kinase C (PKC) is critical for T lymphocyte activation and proliferation, while nitric oxide synthase (NOS) may function both as an activator or inhibitor of T cell apoptosis. Both enzymatic activities were studied in T lymphoma cells in comparison to normal and activated T lymphocytes. Here we show a higher translocation of PKC in BW5147 lymphoma cells than in mitogen-stimulated T lymphocytes. Tumor cells overexpressed PKC zeta isoform, while high levels of the PKC beta isotype were found in mitogen-stimulated T lymphocytes. Moreover, tumoral T cells showed high NOS activity, almost undetectable in normal or stimulated T lymphocytes. PKC and NOS inhibitors or the intracellular delivery of an anti-PKC zeta antibody diminished both NO production and proliferation in tumor cells. These results suggest that atypical PKC zeta isoform expression and its association with NOS activity regulation would participate in the multistep process leading to BW5147 cell malignant transformation.

The role of nitric oxide in the phosphorylation of cyclic adenosine monophosphate—responsive element-binding protein in the spinal cord after intradermal injection of capsaicin

We investigated the involvement of nitric oxide (NO) in the phosphorylation of cyclic adenosine monophosphate-responsive element-binding protein (CREB) in the spinal cord of rats during central sensitization after intradermal capsaicin injection. CREB and phosphorylated CREB (p-CREB) were measured by immunoblotting. The level of p-CREB increased by 20 minutes, peaked between 20 and 60 minutes after capsaicin injection, and started to decrease after 150 minutes. CREB itself did not show an obvious change after capsaicin injection. The p-CREB expression on the ipsilateral side of the spinal dorsal horn, but not on the contralateral side, increased significantly after capsaicin injection. The increase in p-CREB induced by capsaicin injection was partially blocked by pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor, administered through a microdialysis fiber placed across the spinal cord. D-NAME, an inactive form of L-NAME, had no effect. CREB phosphorylation, not the level of CREB, was induced within 20 minutes by microdialysis administration of SIN-1, an NO donor. These results indicate that CREB phosphorylation in the spinal cord results from both endogenous and exogenous NO release and that p-CREB may play a role in central sensitization or in longer-term changes in gene expression induced by strong peripheral noxious stimulation.

Functional dichotomy of a 20-mer and 16-mer peptide derived from Staphylococcus aureus protein A: importance of amino acid sequence

Protein A (PA) of Staphylococcus aureus possesses a wide variety of biological properties such as antitumor, antitoxic, anticarcinogenic, immunomodulatory, antifungal and antiparasitic. Since PA is a foreign protein, it is quite logical to assume that it may be cleaved into smaller peptide fragments in vivo, which may be responsible for the diverse biological activities of whole PA. We have shown that two proteolytic peptide fragments (20-mer and 16-mer) of PA mimics IgG binding and some of the immunomodulatory properties of PA. In the present study, we investigated upon the functional similarity and dissimilarity in these two peptides. The 16-mer peptide induces the production of IL6, IL10, TNFalpha and IL1alpha but it does not have any effect on secretion of IFNgamma and IL4. Whereas 20-mer peptide induces production of TNFalpha, IL1alpha along with induction of IFNgamma but it downregulates IL4, IL6 and IL10 production. IFNgamma to IL4 ratio clearly indicates that the 20-mer peptide induces Th1 type response, whereas 16-mer peptide induces Th0 type response. The 20-mer peptide retains the antitumor property of the native protein (PA) in Ehrlich ascitis tumor model, whereas 16-mer peptide does retain the same property only in vitro. The 16-mer peptide however can activate macrophages to kill Ehrlich ascitis tumor cells in vitro more efficiently than that of 20-mer peptide. Thus both the peptides although derived from same native protein and has had 13 aminoacid residues in common, appears to evoke different reactivites in the immune system. Thus it appears that the IgG binding ability which is seen with the native protein A molecule and also with both 16-mer and 20-mer peptides do not automatically confer upon them the antitumor property, and cytokine producing activities. Thus it appears that all different properties associated with Protein A may not be necessarily associated with its IgG binding abilities.

Superantigen-induced apoptotic death of tumor cells is mediated by cytotoxic lymphocytes, cytokines, and nitric oxide

The bacterial superantigen staphylococcal enterotoxin A (SEA) is a potent inducer of CTL activity and cytokine production in vivo. Protein A (PA) of Staphylococcal aureus has been found to have diverse biological response modifying properties and to possess antitumor, antitoxic and antiparasitic effects. In this study we examined the anti-tumor effect of these two superantigens used separately as well as in combination in mice carrying the Ehrlich ascites tumor. With combined treatment, DNA cell cycle analysis of tumor cells showed a significant (P < 0.05) percentage of tumor cell death. Levels of the soluble mediators TNF-alpha, IFN-gamma and IL-1 as well as NO were elevated. Additionally, CD4(+) and CD8(+) specific T cells in spleen, thymus and PBMC in tumor carrying mice were increased (P < 0.01). Our data altogether suggests that enhanced tumor cell death is caused by the increased CTL activity, cytokine and nitric oxide levels, in response to the combined effect of SEA + PA.

Repeated treatment with S. aureus superantigens expands the survival rate of Ehrlich ascites tumor bearing mice

The bacterial superantigen Staphylococcal enterotoxin-A (SEA), produced by some strains of Staphylococcus aureus, causes proliferation of cytotoxic T-lymphocytes and cytokine production in vivo. SEA has been shown to be highly efficient for antibody-targeted superantegen immunotherapy for different tumor models. A candidate B-cell superantigen that has received considerable attention these days is staphylococcal protein-A (PA). It has been shown to possess multiple immunological responses. The anti-tumor property of PA is well documented in the literature in various transplantable tumors of rats and mice. In the present study, we have shown that the T-cell superantigen SEA and B-cell superantigen PA induce immunomodulatory and anti-tumor activity which is strongly protentiated by PA + SEA co-administration. Combination treatment with PA and SEA prolongs the immune response in vivo, limits the development of immunological unresponsiveness and promotes maximum anti-tumor effects to tumor carrying animals, as compared with PA or SEA alone. The immune response after combined therapy is characterized by substantially augmented IFN-gamma, TNF-alpha, Nitric oxide and strong CTL activity. Our data demonstrate that combined PA + SEA therapy induces long-term survival of the animals, carrying the Ehrlich ascites tumor.

Involvement of protein kinase C and tyrosin kinase in tumoricidal activation of macrophage induced by Streptococcus pneumoniae type II capsular polysaccharide

Capsular polysaccharide type 2 (PS) from Streptococcus pnemoniae induced the secretory and cellular macrophage response. However, the exact mechanism by which PS regulates the macrophage functions remains unclear. In this study, we examined signal molecules which may participate in PS-elicited responses by macrophages. Our data demonstrated that tumoricidal activation of macrophages induced by PS was inhibited by either protein kinase C (PKC) inhibitor, H7 or protein tyrosine kinase (PTK) inhibitor, genistein. In addition, these inhibitors blocked the production of TNF-alpha and NO in PS-stimulated macrophages. Furthermore, PS-induced cell activation is possibly mediated by Toll-like receptor 2. These data suggest that PKC and PTK are involved in the activation of macrophages with PS.

Synergistic immunopotentiating effects induced by T-cell and B-cell superantigen in mice

Staphylococcal Enterotoxin-A(SEA), a 27kDa monomeric protein, produced by some strains of Staphylococcus aureus, is a prototype T-cell superantigen which causes proliferation of cytotoxic T-lymphocytes and produces cytokines like TNF-alpha and IFN-gamma. Recently Protein A (PA), a 42 kDa membrane protein of the Staphylococcus aureus Cowan-I strain, has been termed a B-cell super antigen. It has been shown to cause multiple immunological responses. In the present study we examined the effect of these two superantigens used separately as well as combination in a normal mouse system. It has been shown that combination treatment of PA and SEA is more effective than that of each individual one. FACS analyses of cell cycles showed that a finely turned cellular collaboration occurred in various phases of cell growth and proliferative response compared with controls (P<0.01). It has also been shown that the percentage of various cell types bearing different clusters of differentiation markers, e.g., CD8+, CD34+ increases considerably due to the combined effect of PA and SEA. We also observed that co-administration of both the elicits different soluble mediators like cytokines (TNF-alpha, INF-gamma, IL-1beta). No apoptotic phenomenon was observed (from the cell cycle analysis) for the dose of PA and SEA, used for the experiments, suggesting that these doses of PA and SEA should be non-toxic.

Solution structure of an immunoactive peptide fragment of Staphylococcal protein-A

Staphylococcal protein-A (SpA) is known to bind the Fc fragment of immunoglobin G in vitro and induce a myriad of immunogenic responses in vivo. The latter is ascribed to be due to the interaction of Fc and SpA. It has also been proposed that in vivo proteolytically cleaved fragments of SpA may be functioning in the same manner. One such fragment (EQQNAFYEILHLPNLNEEQR), fragment 8-27 of the B-domain (SpA-B), was recently shown to exhibit in vivo immunogenic response [Sinha, P., Sengupta, J., and Ray, P. K. (1999) Biochem. Biophys. Res. Commun. 258, 141-147]. As a first step towards understanding the mode of interaction of this peptide with the Fc fragment, we have studied the solution conformation of this isolated peptide by CD and NMR. The peptide, with 7 contact residues in the crystal structure of the SpA-B/Fc complex and comprising of mostly helixI and part of helixII of the 3-helix bundle of SpA-B, was found to be present predominantly in extended structure. However it showed nascent turn/helix like conformations around F14 & Y15. These two residues are known to play a vital role in SpA-B/Fc interaction as deciphered from crystal structure and NMR studies of SpA-B/Fc complex and mutational studies. The implications of our results, especially the nascent conformations found around F14 & Y15, in design of SpA-B mimetic small molecules are discussed.

Mechanisms of protein A superantigen-induced signal transduction for proliferation of mouse B cell

Apart from many of the biological properties of protein A (PA) of Staphylococcus aureus, it has been recognized recently as a B-cell superantigen. Therefore, we investigated the molecular mechanisms of PA superantigen-induced mice splenic B-cell proliferation. Treatment of resting B cells with PA-evoked cell proliferation. Binding of PA to B cells led to a cascade of signal transduction mechanisms involving tyrosine kinase that activated phospholipase C, which in turn activated protein kinase C (PKC), and translocated it from cytosol to membrane. Mitogen-activated protein (MAP) kinase has been found to be activated down-stream of PKC in this signal pathway, which ultimately caused an activation of serum-responsive factor (SRF). Inhibition at any step of this signaling cascade could block B-cell proliferation. PA could also stimulate the Bcl-2 gene expression at protein level thereby supporting the pro-proliferative effect of PA. Thus, the molecular mechanisms related to PA-induced B cell proliferation has been delineated in this report as tyrosine kinase > PLC > PKC > MAP kinase > SRF > Bcl-2. Knowledge gathered from these observations might be of immense help to study the immune cell proliferation as a part of immunoactivation process. Also, the development of suitable inhibitors of the signaling pathway outlined here might provide clues as to how to abrogate pathologic antibody production in many disease processes.

Induction of cell proliferation and apoptosis: dependence on the dose of the inducer

Protein A (PA) of Staphylococcus aureus is known as an immunomodulator. In a search of the molecular mechanism(s) of PA-induced immunocyte potentiation, we found dose-dependent binding of PA (0.01 to 100 microg/ml PA) to the mice splenic lymphocytes. Interestingly, treatment of 1 microg PA/20 g mice increased the splenic lymphocyte number approximately 5-fold over control but at a 10-microg dose the cell number was decreased compared with a 1-microg dose. Flow cytometric analysis of cell-cycle phase distribution of nuclear DNA in splenic lymphocytes showed that at a 1-microg dose, PA shifted the cell-cycle phases from G0/G1 to S and G2/M supporting the pro-proliferative role of PA. In contrast, the same inducer increased the sub-G1 cell population at a 10-microg dose indicating the breakdown of cellular DNA. These findings were supported by DNA ladder formation and nuclear breakdown at this higher dose. Further studies revealed that at a 1-microg dose, the level of the pro-proliferative/anti-apoptotic protein bcl-2 was increased in splenic lymphocytes whereas at a 10-microg dose it showed a decreasing trend. In contrast, concentrations of proapoptotic proteins, p53 and bax, were increased at a 10-microg dose. A search of the mechanism(s) of such differential action of PA at these two doses revealed that the lower dose of PA upregulated the production of interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) to the extent which has already been reported by our laboratory to be beneficial to the host. However, at a larger dose, much higher release of TNF-alpha and interleukin-2 (IL-2) may account for the apoptosis of splenic cells. All these findings indicated that the cross-talk between all these pro- and anti-apoptotic factors may contribute to maintain a balance between growth and death of cells and may be one of the important factors deciding whether a cell would follow a proliferative pathway or an apoptotic pathway.

A minimized Fc binding peptide from protein A induces immunocyte proliferation and evokes Th1-type response in mice

It is now well established that PA is a potent biological response modifier, showing simultaneously antitumor, antitoxic, anticarcinogenic, antifungal, antiparasitic and immunomodulatory properties. Since PA is a foreign protein, it is quite logical to assume that it may be cleaved into smaller peptide fragments in vivo which may be responsible for biological activities of whole PA molecule. The present study was undertaken to dissect out the structural entities of PA responsible for its biological properties. Protein A (PA) of Staphylococcus aureus has a unique property of binding with immunoglobulins. On the basis of molecular modeling and energy minimization studies a 20-mer tryptic fragment (theoretical) was predicted to retain IgG binding capacity which has been verified by immunoblot. This peptide sequence was selected to carry out experimental studies to show its functional mimicry of PA. We observed in the sera of 20-mer peptide treated mice that the concentrations of IFNgamma, TNFalpha and IL1alpha increase to a peak level by 4 h; on the other hand, there was a decrease in IL4, IL6 and IL10 concentrations at the same time (4 h). The ratio of IFNgamma to IL4 showed Th1 type of response with the peptide as well as with that of PA. The nitric oxide concentration in sera also increases and the peak increase was in 6 h with both the peptide and PA. Cell cycle analysis using FACS shows that 20 micrograms dose of peptide was non-toxic to thymocytes and spleenocytes; on the other hand, it was immunoproliferative, shifting the thymocytes and spleenocytes from G0/G1 to S phase of the cell cycle. Further studies are in progress to evaluate other biological properties of the peptide, to evaluate if this peptide could be used as a substitute of PA to mimic at least some of its biological activities.

Molecular modeling and experimental approaches toward designing a minimalist protein having Fc-binding activity of Staphylococcal protein A

Protein A (PA), a cell wall constituent of Staphylococcus aureus, has got the unique property of binding with the Fc fragment of IgG from various species. The sequence data indicate five highly homologous Fc-binding regions in protein A. Computer sequence analysis provided the tryptic and chymotryptic fragments of IgG-binding domains of protein A. Molecular modeling in conjunction with molecular mechanical calculation has been used to search for the smallest possible proteolytic fragments of PA, still retaining Fc-binding activity. A 20-residue peptide (typtic fragment) and a 16-residue peptide (chymotryptic fragment) have been indicated, by molecular modeling studies, to possess IgG-binding affinity comparable to that of the B domain of Protein A. Binding of a 20-residue peptide has been substantiated experimentally by immunoprecipitation, capillary electrophoresis, and circular dichroism spectroscopic analyses.