Beta-defensins: linking innate and adaptive immunity through dendritic and T cell CCR6

Defensins contribute to host defense by disrupting the cytoplasmic membrane of microorganisms. This report shows that human beta-defensins are also chemotactic for immature dendritic cells and memory T cells. Human beta-defensin was selectively chemotactic for cells stably transfected to express human CCR6, a chemokine receptor preferentially expressed by immature dendritic cells and memory T cells. The beta-defensin-induced chemotaxis was sensitive to pertussis toxin and inhibited by antibodies to CCR6. The binding of iodinated LARC, the chemokine ligand for CCR6, to CCR6-transfected cells was competitively displaced by beta-defensin. Thus, beta-defensins may promote adaptive immune responses by recruiting dendritic and T cells to the site of microbial invasion through interaction with CCR6.

LL-37, the neutrophil granule- and epithelial cell-derived cathelicidin, utilizes formyl peptide receptor-like 1 (FPRL1) as a receptor to chemoattract human peripheral blood neutrophils, monocytes, and T cells

We have previously shown that antimicrobial peptides like defensins have the capacity to mobilize leukocytes in host defense. LL-37 is the cleaved antimicrobial 37-residue, COOH-terminal peptide of hCAP18 (human cationic antimicrobial protein with a molecular size of 18 kD), the only identified member in humans of a family of proteins called cathelicidins. LL-37/hCAP18 is produced by neutrophils and various epithelial cells. Here we report that LL-37 is chemotactic for, and can induce Ca(2+) mobilization in, human monocytes and formyl peptide receptor-like 1 (FPRL1)-transfected human embryonic kidney 293 cells. LL-37-induced Ca(2+) mobilization in monocytes can also be cross-desensitized by an FPRL1-specific agonist. Furthermore, LL-37 is also chemotactic for human neutrophils and T lymphocytes that are known to express FPRL1. Our results suggest that, in addition to its microbicidal activity, LL-37 may contribute to innate and adaptive immunity by recruiting neutrophils, monocytes, and T cells to sites of microbial invasion by interacting with FPRL1.

Role of angiogenesis in patients with cerebral ischemic stroke

BACKGROUND AND PURPOSE

Stroke is one of the most common causes of mortality and morbidity in the Western world. It results from the occlusion of a cerebral artery followed by severe disturbances in blood supply through microvessels to brain tissue. Despite an extensive literature its pathophysiology is poorly understood, and this has severely impeded the logical development of therapy.

METHODS

Brains were obtained from 10 patients aged 46 to 85 years with survival times of 5 to 92 days after their stroke. Infarcted areas and representative control tissues from the contralateral uninvolved brain hemisphere were collected. Microvessel density was measured microscopically. A total of 6520 microvessels were scored in 10,801 areas. The level of activation of the endothelial cells was studied by immunohistochemistry using three monoclonal antibodies, viz, E-9, raised against activated endothelial cells; IG11, recognizing vascular cell adhesion molecule-1; and anti-proliferating cell nuclear antigen. Angiogenic activity in tissue extracts was examined using an in vivo chicken chorioallantoic membrane assay.

RESULTS

There was a statistically significant increase in the number of microvessels (Wilcoxon log-rank test; P < or = .01) in 9 of 10 infarcted brain tissues when compared with their contralateral normal hemisphere. In these patients the higher blood vessel counts correlated with longer survival, as ascertained by Spearman's p analysis (P < .02). The number of microvessels filled with blood cells was significantly lower in the infarcted hemispheres (P < .01). In contrast, statistically significant increased numbers of empty microvessels occurred in infarcted tissues compared with the contralateral hemisphere. Monoclonal antibody E-9 reacted weakly with normal-brain vascular endothelial cells; anti-proliferating cell nuclear antigen and IG11 were virtually negative. All three antibodies strongly stained the blood vessels of stroke tissues. The stroke tissues contained angiogenic activity, as shown by the induction of new blood vessels in a chorioallantoic membrane assay.

CONCLUSIONS

We have shown that stroke causes active angiogenesis that is more developed in the penumbra. Further experiments are needed to determine if this angiogenesis has beneficial effect.

Recombinant human interferon-inducible protein 10 is a chemoattractant for human monocytes and T lymphocytes and promotes T cell adhesion to endothelial cells

The human cytokine interferon-inducible protein 10 (IP-10) is a small glycoprotein secreted by activated T cells, monocytes, endothelial cells, and keratinocytes, and is structurally related to a family of chemotactic cytokines called chemokines. Although this protein is present in sites of delayed-type hypersensitivity reactions and lepromatous leprosy lesions, the biological activity of IP-10 remains unknown. We report here that recombinant human IP-10 stimulated significant in vitro chemotaxis of human peripheral blood monocytes but not neutrophils. Recombinant human IP-10 also stimulated chemotaxis of stimulated, but not unstimulated, human peripheral blood T lymphocytes. Phenotypic analysis of the stimulated T cell population responsive to IP-10 demonstrated that stimulated CD4+ and CD29+ T cells migrated in response to IP-10. This resembles the biological activity of the previously described T cell chemoattractant RANTES. Using an endothelial cell adhesion assay, we demonstrated that stimulated T cells pretreated with optimal doses of IP-10 exhibited a greatly enhanced ability to bind to an interleukin 1-treated endothelial cell monolayer. These results demonstrate that the IP-10 gene encodes for an inflammatory mediator that specifically stimulates the directional migration of T cells and monocytes as well as potentiates T cell adhesion to endothelium.

Inhibition of STAT3 signaling leads to apoptosis of leukemic large granular lymphocytes and decreased Mcl-1 expression

Large granular lymphocyte (LGL) leukemia is characterized by the expansion of antigen-activated cytotoxic T lymphocytes. These leukemic cells are resistant to Fas-mediated apoptosis despite expressing high levels of Fas. We found that leukemic LGL from 19 patients displayed high levels of activated STAT3. Treatment of leukemic LGL with the JAK-selective tyrosine kinase inhibitor AG-490 induced apoptosis with a corresponding decrease in STAT-DNA binding activity. Moreover, using an antisense oligonucleotide approach to diminish STAT3 expression, we found that Fas sensitivity was restored in leukemic LGL. AG-490-induced apoptosis in leukemic LGL was independent of Bcl-xL or Bcl-2 expression. However, we found that the Bcl-2-family protein Mcl-1 was significantly reduced by AG-490 treatment. Activated STAT3 was shown to bind an SIE-related element in the murine mcl-1 promoter. Using a luciferase reporter assay, we demonstrated that v-src overexpression in NIH3T3 induced STAT3-dependent transcriptional activity from the mcl-1 promoter and increased endogenous Mcl-1 protein levels. We conclude that STAT3 activation contributed to accumulation of the leukemic LGL clones. These findings suggest that investigation should focus on novel strategies targeting STAT3 in the treatment of LGL leukemia.

Granulocyte- and granulocyte-macrophage-colony stimulating factors induce human endothelial cells to migrate and proliferate

Granulocyte-colony stimulating factor (G-CSF) and granulocyte-macrophage-colony stimulating factor (GM-CSF) belong to a family of glycoprotidic growth factors required for the survival, growth and differentiation of haematopoietic precursors and which affect the function of circulating mature cells. They are produced by resting or stimulated stromal cells of the haematopoietic microenvironment (fibroblasts and endothelium) and by immunocompetent cells (T cells and monocytes/macrophages). The action of these CSF molecules was thought to be restricted to cells of haematopoietic origin. Here, we report that G-CSF and GM-CSF influence the migration and proliferation of human endothelial cells suggesting that these molecules may act as regulatory signals outside the haematopoietic system.

Identification of defensin-1, defensin-2, and CAP37/azurocidin as T-cell chemoattractant proteins released from interleukin-8-stimulated neutrophils

Reports that interleukin-8 (IL-8) induces the infiltration of neutrophils followed by T-cells into injection sites led us to postulate that by stimulation of neutrophil degranulation IL-8 may cause the release of factors with chemoattractant activity for T-lymphocytes. Extracts of human neutrophil granules were chromatographed to isolate and purify T-lymphocyte chemoattractant factors. Two major peaks of T-cell chemotactic activity were purified by C18 reversed phase high pressure liquid chromatography (HPLC). The first peak was resolved further by C4 reversed phase HPLC and yielded an active fraction shown by NH2-terminal amino acid sequence analysis to contain defensins HNP-1, HNP-2, and HNP-3. Purified defensins HNP-1 and HNP-2 (kindly provided by Dr. R. I. Lehrer, UCLA) were also potent chemoattractants for human T-cells, while HNP-3 was inactive. The second peak of T-cell chemoattractant activity was also further purified to homogeneity by C4 reversed phase HPLC and identified by NH2-terminal sequence analysis as CAP37/azurocidin, a protein with sequence homology to serine proteases. 0.1 100 ng of defensins and 1.0 100 ng/ml CAP37 were able to stimulate in vitro T-cell chemotaxis. Neutrophil activating factors, i.e. IL-8, phorbol 12-myristate 13-acetate/ionomycin, and formylmethionylleucylphenylalanine each induced the release of CAP37 and defensins from neutrophil granules. Subcutaneous administration of defensins or CAP37/azurocidin into BALB/c mice resulted in a moderate neutrophil and mononuclear cell infiltrate by 4 h, which was greater by 24 h at the site of injection. Additionally, subcutaneous injection of defensins into chimeric huPBL-SCID mice resulted in significant infiltration by human CD3+ cells within 4 h. These results identify the antimicrobial proteins, CAP37/azurocidin and defensins HNP-1 and HNP-2, as potent neutrophil-derived chemoattractants for T-cells. These proteins represent primordial antimicrobial peptides which may have evolved into acute inflammatory cell-derived signals that mobilize immunocompetent T-cells and other inflammatory cells.

Serum amyloid A is a chemoattractant: induction of migration, adhesion, and tissue infiltration of monocytes and polymorphonuclear leukocytes

Serum amyloid A (SAA) is an acute phase protein that in the blood is bound to high density lipoproteins; SAA is secreted mainly by hepatocytes, and its concentration increases in the blood up to 1000 times during an inflammatory response. At present, its biological function is unclear. Since some forms of secondary amyloidosis are caused by deposition in tissues of peptides derived from the SAA and leukocytes seem to be involved in this process, we investigated the effect of human SAA on human monocytes and polymorphonuclear cells (PMN). When recombinant human SAA (rSAA) was used at concentrations corresponding to those found during the acute phase (> 0.8 microM), it induced directional migration of monocytes and polymorphonuclear leukocytes. Preincubation of rSAA with high density lipoproteins blocked this chemoattractant activity for both monocytes and PMN. rSAA also regulated the expression of the adhesion proteins CD11b and leukocyte cell adhesion molecule 1 and induced the adhesion of PMN and monocytes to umbilical cord vein endothelial cell monolayers. When subcutaneously injected into mice, rSAA recruited PMN and monocytes at the injection site. On the basis of these data, we suggest that SAA may participate in enhancing the migration of monocytes and PMN to inflamed tissues during an acute phase response.

A seven-transmembrane, G protein-coupled receptor, FPRL1, mediates the chemotactic activity of serum amyloid A for human phagocytic cells

We have previously reported (Badolato, R., J.M. Wang, W.J. Murphy, A. R. Lloyd, D.F. Michiel, L.L. Bausserman, D.J. Kelvin, and J.J. Oppenheim. 1994. J. Exp. Med. 180:203; Xu, L., R. Badolato, W.J. Murphy, D.L. Longo, M. Anver, S. Hale, J.J. Oppenheim, and J.M. Wang. 1995. J. Immunol. 155:1184.) that the acute phase protein serum amyloid A (SAA) is a potent chemoattractant for human leukocytes in vitro and mouse phagocytes in vivo. To identify the signaling mechanisms, we evaluated patterns of cross-desensitization between SAA and other leukocyte chemoattractants. We found that the chemotactic bacterial peptide, N-formyl- methionyl-leucyl-phenylalanine (fMLP), was able to specifically attenuate Ca2+ mobilization in human phagocytes induced by SAA, but only at very high concentrations, suggesting that SAA uses a low affinity fMLP receptor. Here we demonstrate that SAA selectively induced Ca2+ mobilization and migration of HEK cells expressing FPRL1, a human seven-transmembrane domain phagocyte receptor with low affinity for fMLP, and high affinity for lipoxin A4. Furthermore, radiolabeled SAA specifically bound to human phagocytes and FPRL1-transfected 293 cells. In contrast, SAA was not a ligand or agonist for FPR, the high affinity fMLP receptor. Thus, SAA is the first chemotactic ligand identified for FPRL1. Our results suggest that FPRL1 mediates phagocyte migration in response to SAA.

The antiapoptotic gene mcl-1 is up-regulated by the phosphatidylinositol 3-kinase/Akt signaling pathway through a transcription factor complex containing CREB

mcl-1 is an immediate-early gene activated by the granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 3 (IL-3) signaling pathways and plays an important role in the viability response of these cytokines. In this study, we demonstrated that cytokine stimulation of mcl-1 mRNA and protein expression were attenuated by pretreatment of cells with phosphatidylinositol 3-kinase (PI3-K) inhibitors. Reporter gene assays further showed that the PI3-K/Akt signaling pathway was involved in IL-3 activation of mcl-1 gene transcription. Analysis of the mcl-1 promoter revealed that both promoter elements, SIE at position -87 and CRE-2 at -70, contribute to IL-3 stimulation of mcl-1 gene expression. Although either the SIE site or the CRE-2 site alone was sufficient to confer IL-3 inducibility on a heterologous promoter, only IL-3 activation of the CRE-2 reporter was mediated via the PI3-K/Akt pathway. The SIE binding activity was constitutively high in cells deprived of or stimulated by IL-3. In contrast, the CRE-2 binding activity was low in cytokine-starved cells and was strongly induced within 1 h following cytokine treatment of cells. In addition, cytokine induction of the CRE-2 but not of the SIE binding activity was dependent on activation of the PI3-K/Akt signaling pathway. Lastly, we showed that CREB was one component of the CRE-2 binding complex and played a role in IL-3 activation of the mcl-1 reporter gene. Taken together, our results suggest that both PI3-K/Akt-dependent and -independent pathways contribute to the IL-3 activation of mcl-1 gene expression. Activation of mcl-1 by the PI3-K/Akt-dependent pathway is through a transcription factor complex containing CREB.

Genetic relationship of populations in China

Despite the fact that the continuity of morphology of fossil specimens of modern humans found in China has repeatedly challenged the Out-of-Africa hypothesis, Chinese populations are underrepresented in genetic studies. Genetic profiles of 28 populations sampled in China supported the distinction between southern and northern populations, while the latter are biphyletic. Linguistic boundaries are often transgressed across language families studied, reflecting substantial gene flow between populations. Nevertheless, genetic evidence does not support an independent origin of Homo sapiens in China. The phylogeny also suggested that it is more likely that ancestors of the populations currently residing in East Asia entered from Southeast Asia.

Human recombinant monocyte chemotactic protein and other C-C chemokines bind and induce directional migration of dendritic cells in vitro

Because dendritic cells (DC) are the most potent antigen-presenting cells involved in many pathophysiological responses, we investigated the effect of chemokines on the migration of these cells in an effort to determine whether chemokines may contribute to the initiation of immune responses. CD34+ progenitor cells isolated from umbilical cord blood were grown in suspension cultures with cytokines and expanded 50- to 100-fold. A variable proportion of the cells expressed markers consistent with DC. The proportion of CD1a+ DC was increased when the cells were cultured with interleukin-4 (IL-4). These cells expressed specific binding sites for C-C and C-X-C chemokines. Cells cultured with or without IL-4 had similar binding profiles. All C-C chemokines tested, including monocyte chemotactic protein (MCP)-1, MCP-2, MCP-3, macrophage inflammatory protein-1 alpha (MIP1 alpha), MIP-1 beta, and RANTES, induced migration of DC-enriched cells cultured with or without IL-4 with MCP-3 being the most potent chemoattractant. Phenotypic analysis of cell migrating in response to C-C chemokines showed that CD1a+ cells were indeed attracted across the polycarbonate filters, and there was no preferential attraction of contaminating CD14+ monocytes by C-C chemokines. DC-enriched cells also expressed specific binding sites for IL-8 and NAP2, which failed to induce cell migration. Our results suggest that C-C chemokines may participate in the recruitment of DC to amplify host defense.

The fibrinolytic receptor for urokinase activates the G protein-coupled chemotactic receptor FPRL1/LXA4R

The function of urokinase and its receptor is essential for cell migration in pathological conditions, as shown by the analysis of knockout mice phenotypes. How a protease of a fibrinolytic pathway can induce migration is not understood and no link between this protease and migration-promoting G protein-coupled receptors has been described. We now show that FPRL1/LXA4R, a G protein-coupled receptor for a number of polypeptides and for the endogenous lipoxin A4 (LXA4), is the link between urokinase-type plasminogen activator (uPA) and migration as it directly interacts with an activated, soluble, cleaved form of uPA receptor (uPAR) (D2D3(88-274)) to induce chemotaxis. In this article we show that (i) both uPAR and FPRL1/LXA4R are necessary for the chemotactic activity of uPA whereas FPRL1/LXA4R is sufficient to mediate D2D3(88-274)-induced cell migration. (ii) Inhibition or desensitization of FPRL1/LXA4R by antibodies or specific ligands specifically prevents chemotaxis induced by D2D3(88-274) in THP-1 cells and human peripheral blood monocytes. (iii) Desensitization of FPRL1/LXA4R prevents the activation of tyrosine kinase Hck induced by D2D3(88-274). (iv) D2D3(88-274) directly binds to FPRL1/LXA4R and is competed by two specific FPRL1/LXA4R agonists, the synthetic MMK-1 peptide and a stable analog of LXA4. Thus, a naturally produced cleaved form of uPAR is a unique endogenous chemotactic agonist for FPRL1/LXA4R receptor and its activity can be antagonized by specific ligands. These results provide the first direct link, to our knowledge, between the fibrinolytic machinery and the inflammatory response, demonstrating that uPA-derived peptide fragments can activate a specific chemotactic receptor.

Chemokines and their role in tumor growth and metastasis

Chemokines are a superfamily of pro-inflammatory polypeptide cytokines that selectively attract and activate different cell types. Many patho-physiological conditions require the participation of chemokines, including inflammation, infection, tissue injury, allergy, cardiovascular diseases, as well as malignant tumors. Chemokines activate cells through their binding to shared or unique cell surface receptors which belong to the seven-transmembrane, G-protein-coupled Rhodopsin superfamily. The role of chemokines in malignant tumors is complex: while some chemokines may enhance innate or specific host immunity against tumor implantation, others may favor tumor growth and metastasis by promoting tumor cell proliferation, migration or neovascularization in tumor tissue. In this review, the authors summarize some of the recent advances in chemokine research and emphasis is made on the effect of chemokines in tumor growth and metastasis.

In vitro and in vivo activation of endothelial cells by colony-stimulating factors

This study was designed to identify the set of functions activated in cultured endothelial cells by the hematopoietic growth factors, granulocyte colony-stimulating factor (G-CSF) and granulocyte macrophage-colony-stimulating factor (GM-CSF), and to compare them with those elicited by prototypic cytokines active on these cells. Moreover, indications as to the in vivo relevance of in vitro effects were obtained. G-CSF and GM-CSF induced endothelial cells to proliferate and migrate. In contrast, unlike appropriate reference cytokines (IL-1 and tumor necrosis factor, IFN-gamma), G-CSF and GM-CSF did not modulate endothelial cell functions related to hemostasis-thrombosis (production of procoagulant activity and of platelet activating factor), inflammation (expression of leukocyte adhesion molecule-1 and production of platelet activating factor), and accessory function (expression of class II antigens of MHC). Other colony-stimulating factors (IL-3 and macrophage-colony-stimulating factor) were inactive on all functions tested. In comparison to basic fibroblast growth factor (bFGF), G-CSF and GM-CSF induced lower maximal proliferation of endothelial cells, whereas migration was of the same order of magnitude. G-CSF and GM-CSF stimulated repair of mechanically wounded endothelial monolayers. Exposure to both cytokines induced shape changes and cytoskeletal reorganization consistent with a migratory phenotype. To explore the in vivo relevance of the in vitro effects of these cytokines on endothelium, we studied the angiogenic activity of human G-CSF in the rabbit cornea. G-CSF, but not the heat-inactivated molecule, had definite angiogenic activity, without any sign of inflammatory reactions. G-CSF was less active than bFGF. However, the combination of a nonangiogenic dose of bFGF with G-CSF resulted in an angiogenic response higher than that elicited by either individual cytokines. Thus, G-CSF and GM-CSF induce endothelial cells to express an activation/differentiation program (including proliferation and migration) related to angiogenesis.

Recombinant human interleukin 5 is a selective eosinophil chemoattractant

Human recombinant interleukin (IL) induced migration across polycarbonate filters of human peripheral blood eosinophils. The contribution of chemotaxis vs. chemokinesis was investigated using a checkerboard design with both polycarbonate and nitrocellulose filters. When different cytokine concentrations were seeded above and below the filter, maximal induction of migration required a positive concentration gradient between the lower and upper compartments of the chamber, though some gradient-independent augmentation of migration occurred. These results indicate that induction of eosinophil migration across filter involves actual chemotaxis. The effect of IL5 was selective for eosinophils with no effect on neutrophils and monocytes. Conversely, granulocyte-macrophage colony-stimulating factor elicited migration of both eosinophils and neutrophils. Thus, human IL5 is a potent and selective chemoattractant for human eosinophils. Eosinophils are selectively localized in tissues under a variety of physiological and pathological conditions. Locally produced IL5 may play a role in the selective recruitment of eosinophils from the blood compartment.

Protective effect of Hibiscus anthocyanins against tert-butyl hydroperoxide-induced hepatic toxicity in rats

Hibiscus anthocyanins (HAs), a group of natural pigments occurring in the dried flowers of Hibiscus sabdariffa L., which is a local soft drink material and medical herb, were studied for antioxidant bioactivity. The preliminary study showed that HAs were able to quench the free radicals of 1,1-diphenyl-2-picrylhydrazyl. This antioxidant bioactivitiy was further evaluated using the model of tert-butyl hydroperoxide (t-BHP)-induced cytotoxicity in rat primary hepatocytes and hepatotoxicity in rats. The results demonstrated that HAs, at the concentrations of 0.10 and 0.20 mg/ml, significantly decreased the leakage of lactate dehydrogenase and the formation of malondialdehyde induced by a 30-min treatment of t-BHP (1.5 mM). The in vivo investigation showed that the oral pretreatment of HAs (100 and 200 mg/kg) for 5 days before a single dose of t-BHP (0.2 mmol/kg, ip) significantly lowered the serum levels of hepatic enzyme markers (alanine and aspartate aminotransferase) and reduced oxidative liver damage. The histopathological evaluation of the liver revealed that Hibiscus pigments reduced the incidence of liver lesions including inflammatory, leucocyte infiltration, and necrosis induced by t-BHP in rats. Based on the results described above, we speculate that Hibiscus pigments may play a role in the prevention of oxidative damage in living systems.

Identification of human neutrophil-derived cathepsin G and azurocidin/CAP37 as chemoattractants for mononuclear cells and neutrophils

Macrophage infiltration into inflammatory sites is generally preceded by neutrophils. This suggests neutrophils may be the source of chemotactic factors for monocytes. To identify these putative monocyte attractants, we have systematically prepared neutrophil granules, lysed them, and sequentially purified the released proteins by several reverse phase chromatography procedures. Assays for monocyte chemotactic activity of the chromatography fractions yielded a major peak of activity associated with a protein of 30 kD, according to SDS-PAGE analysis. NH2-terminal sequence of the protein revealed this to be identical to cathepsin G. The monocyte chemotactic activity of human cathepsin G was dose dependent with optimal concentration at 0.5-1 microg/ml. Cathepsin G is chemotactic rather than chemokinetic for monocytes, as demonstrated by checkerboard analysis. Cathepsin G-induced monocyte chemotaxis is partially pertussis toxin sensitive implying the involvement of a G protein-coupled receptor. Enzymatic activity of cathepsin G is associated with its monocyte chemotactic activity, since DFP- or PMSF-inactivated cathepsin G no longer induced monocyte migration. The chemotactic activity of cathepsin G can also be completely blocked by alpha1 antichymotrypsin, a specific inhibitor of chymotrypsin-like proteinases present in human plasma. In addition, cathepsin G is also a potent chemoattractant for neutrophils and a chemokinetic stimulant for T cells. In the course of pursuing these in vitro studies, we established that the T cell chemoattractant, azurocidin/CAP37 from human neutrophil granules, at doses of 0.05 to 5 microg/ml, was chemotactic for monocytes and neutrophils. As predicted from the in vitro chemotactic activity, subcutaneous injection of cathepsin G into BALB/c mice led to infiltration of both mononuclear cells and neutrophils. Thus, the transition of inflammatory exudate from neutrophil to mononuclear cells can be mediated, at least in part, by extracellular release of neutrophil granule proteins such as cathepsin G and azurocidin/CAP37.

17β-estradiol induced Ca2+ influx via L-type calcium channels activates the Src/ERK/cyclic-AMP response element binding protein signal pathway and BCL-2 expression in rat hippocampal neurons: A potential initiation mechanism for estrogen-induced neuroprotection

Our group and others have demonstrated that 17beta-estradiol (E2) induces neurotrophic and neuroprotective responses in hippocampal and cortical neurons which are dependent upon the Src/extracellular signal-regulated kinase (ERK) signaling pathways. The purpose of this study was to determine the upstream mechanism(s) that initiates the signaling cascade leading to E2-inducible neuroprotection. We tested the hypothesis that E2 activates rapid Ca(2+) influx in hippocampal neurons, which would lead to activation of the Src/ERK signaling cascade and up-regulation of Bcl-2 protein expression. Using fura-2 ratiometric Ca(2+) imaging, we demonstrated that E2 induced a rapid rise of intracellular Ca(2+) concentration ([Ca(2+)](i)) within minutes of exposure which was blocked by an L-type Ca(2+) channel antagonist. Inhibition of L-type Ca(2+) channels resulted in a loss of E2 activation of the Src/ERK cascade, activation of cyclic-AMP response element binding protein (CREB) and subsequent increase in Bcl-2. Real-time intracellular Ca(2+) imaging combined with pERK immunofluorescence, demonstrated that E2 induced [Ca(2+)](i) was coincident with ERK activation in the same neuron. Small interfering RNA knockdown of CREB resulted in a loss of E2 activation of CREB and subsequent E2-induced increase of Bcl-2 expression. We further demonstrated the presence of specific membrane E2 binding sites in hippocampal neurons. Together, these data indicate that E2-induced Ca(2+) influx via the L-type Ca(2+) channel is required for E2 activation of the Src/ERK/CREB/Bcl-2 signaling. Implications of these data for understanding estrogen action in brain and use of estrogen therapy for prevention of neurodegenerative disease are discussed.

The flavonoid baicalin exhibits anti-inflammatory activity by binding to chemokines

Baicalin (BA) is a flavonoid compound purified from the medicinal plant Scutellaria baicalensis Georgi and has been reported to possess anti-inflammatory and anti-viral activities. In order to elucidate the mechanism(s) of action of BA, we tested whether BA could interfere with chemokines or chemokine receptors, which are critical mediators of inflammation and infection. We observed that BA inhibited the binding of a number of chemokines to human leukocytes or cells transfected to express specific chemokine receptors. This was associated with a reduced capacity of the chemokines to induce cell migration. Co-injection of BA with CXC chemokine interleukin-8 (IL-8) into rat skin significantly inhibited IL-8 elicited neutrophil infiltration. BA did not directly compete with chemokines for binding to receptors, but rather acted through its selective binding to chemokine ligands. This conclusion was supported by the fact that BA cross-linked to oxime resin bound chemokines of the CXC (stromal cell-derived factor (SDF)-1alpha, IL-8), CC (macrophage inflammatory protein (MIP)-1beta, monocyte chemotactic protein (MCP)-2), and C (lymphotactin (Ltn)) subfamilies. BA did not interact with CX3C chemokine fractalkine/neurotactin or other cytokines, such as TNF-alpha and IFN-gamma, indicating that its action is selective. These results suggest that one possible anti-inflammatory mechanism of BA is to bind a variety of chemokines and limit their biological function.

mcl-1 is an immediate-early gene activated by the granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling pathway and is one component of the GM-CSF viability response

mcl-1, a bcl-2 family member, was originally identified as an early gene induced during differentiation of ML-1 myeloid leukemia cells. In the present study, we demonstrate that Mcl-1 is tightly regulated by the granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling pathway. Upon deprivation of survival factor from TF-1 myeloid progenitor cells, Mcl-1 levels quickly dropped prior to visible detection of apoptosis of these cells. Upon restimulation of these deprived cells with GM-CSF, the mcl-1 mRNA was immediately induced and its protein product was accordingly resynthesized. Analysis with Ba/F3 cells expressing various truncation mutants of the GM-CSF receptor revealed that the membrane distal region between amino acids 573 and 755 of the receptor beta chain was required for mcl-1 induction. Transient-transfection assays with luciferase reporter genes driven by various regions of the mcl-1 promoter demonstrated that the upstream sequence between -197 and -69 is responsible for cytokine activation of the mcl-1 gene. Overexpression of mcl-1 delayed but did not completely prevent apoptosis of cells triggered by cytokine withdrawal. Its down regulation by antisense constructs overcame, at least partially, the survival activity of GM-CSF and induced the apoptosis of TF-1 cells. Taken together, these results suggest that mcl-1 is an immediate-early gene activated by the cytokine receptor signaling pathway and is one component of the GM-CSF viability response.

Opiates transdeactivate chemokine receptors: delta and mu opiate receptor-mediated heterologous desensitization

An intact chemotactic response is vital for leukocyte trafficking and host defense. Opiates are known to exert a number of immunomodulating effects in vitro and in vivo, and we sought to determine whether they were capable of inhibiting chemokine-induced directional migration of human leukocytes, and if so, to ascertain the mechanism involved. The endogenous opioid met-enkephalin induced monocyte chemotaxis in a pertussis toxin-sensitive manner. Met-enkephalin, as well as morphine, inhibited IL-8-induced chemotaxis of human neutrophils and macrophage inflammatory protein (MIP)-1alpha, regulated upon activation, normal T expressed and secreted (RANTES), and monocyte chemoattractant protein 1, but not MIP-1beta-induced chemotaxis of human monocytes. This inhibition of chemotaxis was mediated by delta and micro but not kappa G protein-coupled opiate receptors. Calcium flux induced by chemokines was unaffected by met-enkephalin pretreatment. Unlike other opiate-induced changes in leukocyte function, the inhibition of chemotaxis was not mediated by nitric oxide. Opiates induced phosphorylation of the chemokine receptors CXCR1 and CXCR2, but neither induced internalization of chemokine receptors nor perturbed chemokine binding. Thus, inhibition of chemokine-induced chemotaxis by opiates is due to heterologous desensitization through phosphorylation of chemokine receptors. This may contribute to the defects in host defense seen with opiate abuse and has important implications for immunomodulation induced by several endogenous neuropeptides which act through G protein-coupled receptors.

Pleiotropic roles of formyl peptide receptors

FPR and FPRL1 belong to the seven-transmembrane, G protein-coupled chemoattractant receptor superfamily. Because of their capacity to interact with bacterial chemotactic formylated peptides, these receptors are thought to play a role in host defense against microbial infection. Recently, a variety of novel agonists have been identified for these receptors, including several host-derived endogenous molecules that are involved in proinflammatory responses. Most notably is the use of FPRL1 by at least three amyloidogenic protein and peptide ligands, the serum amyloid A (SAA), the 42 amino acid form of beta amyloid (Abeta(42)), and the prion peptide PrP106-126, to chemoattract and activate human phagocytic leukocytes. These new findings have greatly expanded the functional scope of the formyl peptide receptors and call for more in-depth investigation of the role of these receptors in pathophysiological conditions.

Flavonoid baicalin inhibits HIV-1 infection at the level of viral entry

Baicalin (BA) is a flavonoid compound purified from medicinal plant Scutellaria baicalensis Georgi and has been shown to possess anti-inflammatory and anti-HIV-1 activities. In an effort to elucidate the mechanism of the anti-inflammatory effect of BA, we recently found that this flavonoid compound was able to form complexes with selected chemokines and attenuated their capacity to bind and activate receptors on the cell surface. These observations prompted us to investigate whether BA could inhibit HIV-1 infection by interfering with viral entry, a process known to involve interaction between HIV-1 envelope proteins and the cellular CD4 and chemokine receptors. We found that BA at the noncytotoxic concentrations, inhibited both T cell tropic (X4) and monocyte tropic (R5) HIV-1 Env protein mediated fusion with cells expressing CD4/CXCR4 or CD4/CCR5. Furthermore, presence of BA at the initial stage of HIV-1 viral adsorption blocked the replication of HIV-1 early strong stop DNA in cells. Since BA did not inhibit binding of HIV-1 gp120 to CD4, we propose that BA may interfere with the interaction of HIV-1 Env with chemokine coreceptors and block HIV-1 entry of target cells. Therefore, BA can be used as a basis for developing novel anti-HIV-1 agents.

Transgenic rescue of defective Cd36 ameliorates insulin resistance in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) display several features of the human insulin-resistance syndromes. Cd36 deficiency is genetically linked to insulin resistance in SHR. We show that transgenic expression of Cd36 in SHR ameliorates insulin resistance and lowers serum fatty acids. Our results provide direct evidence that Cd36 deficiency can promote defective insulin action and disordered fatty-acid metabolism in spontaneous hypertension.