Differential effects of PKC inhibitors on gelatinase B and interleukin 6 production in the mouse macrophage

Information theoretic approach to complex biological network reconstruction: application to cytokine release in RAW 264.7 macrophages

BACKGROUND

High-throughput methods for biological measurements generate vast amounts of quantitative data, which necessitate the development of advanced approaches to data analysis to help understand the underlying mechanisms and networks. Reconstruction of biological networks from measured data of different components is a significant challenge in systems biology.

RESULTS

We use an information theoretic approach to reconstruct phosphoprotein-cytokine networks in RAW 264.7 macrophage cells. Cytokines are secreted upon activation of a wide range of regulatory signals transduced by the phosphoprotein network. Identifying these components can help identify regulatory modules responsible for the inflammatory phenotype. The information theoretic approach is based on estimation of mutual information of interactions by using kernel density estimators. Mutual information provides a measure of statistical dependencies between interacting components. Using the topology of the network derived, we develop a data-driven parsimonious input-output model of the phosphoprotein-cytokine network.

CONCLUSIONS

We demonstrate the applicability of our information theoretic approach to reconstruction of biological networks. For the phosphoprotein-cytokine network, this approach not only captures most of the known signaling components involved in cytokine release but also predicts new signaling components involved in the release of cytokines. The results of this study are important for gaining a clear understanding of macrophage activation during the inflammation process.

Cationic liposomal lipids: from gene carriers to cell signaling

Cationic lipids are positively charged amphiphilic molecules which, for most of them, form positively charged liposomes, sometimes in combination with a neutral helper lipid. Such liposomes are mainly used as efficient DNA, RNA or protein carriers for gene therapy or immunization trials. Over the past decade, significant progress has been made in the understanding of the cellular pathways and mechanisms involved in lipoplex-mediated gene transfection but the interaction of cationic lipids with cell components and the consequences of such an interaction on cell physiology remains poorly described. The data reported in the present review provide evidence that cationic lipids are not just carriers for molecular delivery into cells but do modify cellular pathways and stimulate immune or anti-inflammatory responses. Considering the wide number of cationic lipids currently available and the variety of cellular components that could be involved, it is likely that only a few cationic lipid-dependent functions have been identified so far.

PKC412 (CGP41251) modulates the proliferation and lipopolysaccharide-induced inflammatory responses of RAW 264.7 macrophages

PKC412 (CGP41251) is a multitarget protein kinase inhibitor with anti-tumor activities. Here, we investigated the effects of PKC412 on macrophages. PKC412 inhibited the proliferation of murine RAW 264.7 macrophages through induction of G2/M cell cycle arrest and apoptosis. At non-toxic drug concentrations, PKC412 significantly suppressed the lipopolysaccharide (LPS)-induced release of TNF-alpha and nitric oxide, while instead enhancing IL-6 secretion. PKC412 attenuated LPS-induced phosphorylations of MKK4 and JNK, as well as AP-1 DNA binding activities. Furthermore, PKC412 suppressed LPS-induced Akt and GSK-3beta phosphorylations. These results suggest that the anti-proliferative and immunomodulatory effects of PKC412 are, at least in part, mediated through its interference with the MKK4/JNK/AP-1 and/or Akt/GSK-3beta pathways. Since macrophages contribute significantly to the development of both acute and chronic inflammation, PKC412 may have therapeutic potential and applications in treating inflammatory and/or autoimmune diseases.

Inhibition of angiogenesis and endothelial cell functions are novel sulforaphane-mediated mechanisms in chemoprevention

Sulforaphane, an aliphatic isothiocyanate, is a known cancer chemopreventive agent. Aiming to investigate antiangiogenic potential of sulforaphane, we here report a potent decrease of newly formed microcapillaries in a human in vitro antiangiogenesis model, with an IC50 of 0.08 micromol/L. The effects of sulforaphane on endothelial cell functions essential for angiogenesis were investigated in HMEC-1, an immortalized human microvascular endothelial cell line. Molecular signaling pathways leading to activation of endothelial cell proliferation and degradation of the basement membrane were analyzed by reverse transcription-PCR. Sulforaphane showed time- and concentration-dependent inhibitory effects on hypoxia-induced mRNA expression of vascular endothelial growth factor and two angiogenesis-associated transcription factors, hypoxia-inducible factor-1alpha and c-Myc, in a concentration range of 0.8 to 25 micromol/L. In addition, the expression of the vascular endothelial growth factor receptor KDR/flk-1 was inhibited by sulforaphane at the transcriptional level. Sulforaphane could also affect basement membrane integrity, as it suppressed transcription of the predominant endothelial collagenase matrix metalloproteinase-2 and its tissue inhibitor of metalloproteinase-2. Migration of HMEC-1 cells in a wound healing assay was effectively prevented by sulforaphane at submicromolar concentrations, and we determined an IC50 of 0.69 micromol/L. In addition, within 6 hours of incubation, sulforaphane inhibited tube formation of HMEC-1 cells on basement membrane matrix at 0.1, 1, and 10 micromol/L concentrations. These effects were not due to inhibition of HMEC-1 cell proliferation; however, after 72 hours of incubation, sulforaphane nonselectively reduced HMEC-1 cell growth with an IC50 of 11.3 micromol/L. In conclusion, we have shown that sulforaphane interferes with all essential steps of neovascularization from proangiogenic signaling and basement membrane integrity to endothelial cell proliferation, migration, and tube formation. These novel antiangiogenic activities of sulforaphane are likely to contribute to its cancer chemopreventive and therapeutic potential.

Differential effects of staurosporine and its analogues on chemokine release by promyelocytic leukemia cell line NB-4

The protein kinase inhibitor staurosporine elicits multiple responses in various systems. We evaluated nine naturally occurring staurosporine derivatives as modulators of chemokine production by monitoring the secretion of interleukin-8 (IL-8) and monocyte chemotactic protein-1 (MCP-1) in the cell line NB-4. Several staurosporines increased, dose- and time-dependently, the IL-8 and MCP-1 concentration in the cell culture supernatants and three derivatives strongly inhibited proliferation of the NB-4 cells. By comparing the efficiency of these analogues at the same concentration, the lead compound staurosporine (STS-1) was the best inducer of chemokine secretion, whereas 3-hydroxystaurosporine (STS-3) was the most potent growth inhibitor. Besides the staurosporines, also 12-O-tetradecanoyl phorbol acetate (TPA) and tumor necrosis factor-alpha (TNFalpha) strongly increased the IL-8 and MCP-1 secretion of NB-4 cells. Several staurosporine analogues clearly inhibited the TPA-induced but enhanced the TNFalpha-mediated chemokine increase. These effects, namely the increase of chemokines in untreated or TNFalpha-treated cells and the inhibition of chemokine release in TPA-treated cells, cannot be explained by the exclusive inhibition of protein kinase C (PKC). It may indicate that staurosporines are additionally involved in activation of the PKC-triggered chemokine production.

Macrophages and post-burn immune dysfunction

The activation of a pro-inflammatory cascade after burn injury appears to be important in the development of subsequent immune dysfunction, susceptibility to sepsis and multiple organ failure. Macrophages are major producers of pro-inflammatory mediators and their productive capacity for these mediators is markedly enhanced following thermal injury. Thus, macrophage hyperactivity (as defined by increased productive capacity for pro-inflammatory mediators) appears to be of critical importance in the development of post-burn immune dysfunction. This review will focus on the current state of knowledge with regards to the role of macrophages in the development of post-burn immune dysfunction. Particular areas of discussion include: nitric oxide synthase (NOS) and cyclooxygenase (COX) enzyme systems, macrophages and the T-helper (Th)-1/Th-2 cytokine responses, alterations in macrophages signal transduction and a potential role for gamma/delta T-cells in the development of macrophage hyperactivity following thermal injury. A more comprehensive understanding of the relationship between macrophage activity and post-burn immune dysfunction will hopefully provide the basis for improved therapeutic regimes in the treatment of burn patients.

LPS-induced lung injury in neonatal rats: changes in gelatinase activities and consequences on lung growth

Postnatal lung growth disorders may involve imbalance between metalloproteinases and their inhibitors. Inflammatory cell 92-kDa gelatinase overactivity has been reported in adults with lung injury but has not been looked for in neonates. We compared gelatinase activity in neonatal and adult rats and evaluated postnatal lung growth after lipopolysaccharide (LPS)-induced lung injury. Significant intra-alveolar inflammatory cell recruitment occurred in adults and neonates; cell counts increased 16-fold in adults and 2.7-fold in neonates. Total 92-kDa gelatinase activity was increased in neonates and adults and was significantly correlated to inflammatory cell counts. For a given cell count, 92-kDa gelatinase increased more in neonates than in adults. Morphometric neonatal lung analysis showed that LPS-injured lungs had decreases in absolute values of lung volume (P < 0.03), alveolar surface (P < 0.004), and air space volume (P < 0.03). Doxycycline, a nonspecific metalloproteinase inhibitor, partly inhibited LPS-induced 92-kDa gelatinase overactivity but did not improve LPS-induced alveolar growth disorders. LPS-mediated lung injury in neonatal rats induced both gelatinase B overactivity and alveolar growth disorders, although no causal link between these two effects was demonstrated.

Differential regulation of MMP-1/9 and TIMP-1 secretion in human monocytic cells in response to Mycobacterium tuberculosis

In tuberculosis, matrix metalloproteinase (MMP) secretion is involved in leukocyte migration to sites of infection but in excess may contribute to tissue destruction. We demonstrate that human monocytic THP-1 cells and primary monocytes secrete MMP-1 (52 kD collagenase) when phagocytosing live, virulent M. tuberculosis but not inert latex. The magnitude of MMP-1 secretion was approximately 10-fold less when compared to MMP-9 (92 kD gelatinase) secretion. MMP-1 secretion was also relatively delayed (detected at 24 h vs. 4 h). M. tuberculosis, zymosan or latex stimulate similar TIMP-1 secretion within 8 h and increasing over 24 h. MMP-1/9 secretion was decreased by inhibitors of protein kinase (PK) C, PKA or tyrosine kinases (PTK) in a concentration-dependent manner. In contrast, TIMP-1 secretion was not affected by PKC or PTK blockade and only somewhat reduced by high level PKA inhibition. In summary, M. tuberculosis-infected monocytes secrete MMP-1 at lower concentrations than MMP-9 and such MMP secretion is regulated by multiple upstream signalling pathways which do not control TIMP-1 secretion. Divergent effects of i on MMP and TIMP secretion from monocytes may be important in influencing matrix degradation in vivo.

Expression of gelatinase B in trachomatous conjunctivitis

BACKGROUND/AIMS

Gelatinase B is a matrix metalloproteinase involved in extracellular matrix (ECM) breakdown often associated with scarring and other pathological disorders. It was investigated whether gelatinase B is involved in the pathogenesis of ECM degradation associated with trachomatous conjunctivitis.

METHODS

Conjunctival biopsy specimens obtained from six patients with active trachoma, six patients with active vernal keratoconjunctivitis (VKC), and seven control subjects were studied. Immunohistochemical techniques and a specific monoclonal antibody against human gelatinase B were used, and a monoclonal antibody against macrophage CD68 to identify mononuclear cells with gelatinase B immunoreactivity. In addition, quantitative zymography was used to compare the activity of gelatinase B in conjunctival biopsy specimens from seven patients with active trachoma and seven control subjects.

RESULTS

Gelatinase B was detected by immunohistochemistry only in polymorphonuclear cells located in the vascular lumens in three normal conjunctival biopsy specimens. In all trachoma specimens and in five VKC specimens, gelatinase B was localised in monocyte/macrophage cells, positive for the CD68 marker, and in polymorphonuclear cells. The majority of the latter cell type was located in intravascular spaces. Compared with VKC specimens, trachoma specimens showed significantly more immunoreactive gelatinase B monocyte/macrophage cells (52.3 (21.9) v 8.2 (6.4); p <0.001) and polymorphonuclear cells (23.2 (14.2) v 6.3 (5.4); p = 0. 013). Activated macrophages with giant cell morphology clearly stained with the gelatinase B specific monoclonal antibody were observed in trachoma specimens. Zymography revealed that gelatinase B levels in trachoma specimens were significantly higher than the levels found in normal conjunctiva (1739.6 (1078.3) v 609.3 (395.9) scanning units; p = 0.0127).

CONCLUSIONS

The increased activity of gelatinase B and numbers of inflammatory cells containing gelatinase B in trachoma specimens suggest that this enzyme plays a part in the pathogenesis of conjunctival scarring in trachoma.

Potentiation of lipopolysaccharide-induced IL-6 release by uridine triphosphate in macrophages: cross-interaction with cyclooxygenase-2-dependent prostaglandin E(2) production

Our previous study has demonstrated the potentiation by uridine triphosphate (UTP) of nitric oxide (NO) and prostaglandin E(2) (PGE(2)) production in lipopolysaccharide (LPS)-stimulated murine J774 macrophages. In this study, we found that the amount of interleukin-6 (IL-6) release in response to LPS stimulation was greatly enhanced in the presence of UTP. This enhancement exhibited concentration dependence and occurred after 8 h of treatment with LPS. RT-PCR analysis indicated that the steady-state level of IL-6 mRNA induced by LPS was apparently increased upon co-addition of UTP. The potentiation by UTP was inhibited by the treatment with U73122 (a phosphatidylinositol-phospholipase C inhibitor), BAPTA/AM (an intracellular Ca(2+) chelator), KN-93 (a selective inhibitor of calmodulin-dependent protein kinase) or PDTC (a nuclear factor kappaB inhibitor). To understand the cross-regulation among NO, PGE(2) and IL-6, all of which are dramatically induced after LPS stimulation, the effects of L-NAME (a nitric oxide synthase inhibitor), indomethacin (a cyclooxygenase inhibitor), NS-398 (a cycloxygenase-2 inhibitor) and IL-6 antibody were tested. The results revealed the positive regulation between PGE(2) and IL-6 synthesis because NS-398 and indomethacin inhibited LPS plus UTP-induced IL-6 release, and IL-6 antibody attenuated LPS plus UTP-induced PGE(2) release. Taken together these results reinforce the role of UTP as a regulatory element in inflamed sites by demonstrating the capacity of this nucleotide to potentiate LPS-induced release of inflammatory mediators.

Protein kinase C-alpha modulates lipopolysaccharide-induced functions in a murine macrophage cell line

Lipopolysaccharide (LPS), a potent modulator of macrophage functional activity, binds to CD14 and triggers the activation of several protein kinases, leading to the secretion of variety of immunomodulatory molecules such as nitric oxide and proinflammatory cytokines. In this study, we have examined the role of the alpha isoenzyme of protein kinase C (PKC) in the regulation of LPS-initiated signal transduction in macrophages. To this end, we have stably overexpressed a dominant-negative (DN) version of PKC-alpha (DN PKC-alpha) in the murine macrophage cell line RAW 264. 7. Clones overexpressing DN PKC-alpha were indistinguishable from the parental line with respect to morphology and growth characteristics. At the functional level, DN PKC-alpha overexpression strongly inhibited LPS-induced interleukin-1alpha mRNA accumulation, and to a lesser extent inducible nitric oxide synthase and tumor necrosis factor-alpha expression. DN-PKC-alpha overexpression did not cause a general unresponsiveness to LPS, as secretion of the matrix metalloproteinase-9 was up-regulated in our DN PKC-alpha-overexpressing clones. Moreover, LPS-induced phosphorylation and degradation of IkappaBalpha, NF-kappaB activation, as well as p38 mitogen-activated protein kinase and Jun N-terminal kinase phosphorylation, were not affected by DN PKC-alpha overexpression. Collectively, these data provide evidence that PKC-alpha regulates selective LPS-induced macrophage functions involved in host defense and inflammation.

Overexpression of protein kinase C alpha enhances lipopolysaccharide-induced nitric oxide formation in vascular smooth muscle cells

Our previous studies showed that lipopolysaccharide (LPS)-induced nitric oxide (NO) synthesis in cardiovascular tissues is attenuated by protein kinase C (PKC) inhibitors. In the current study, we identify a specific PKC isotype involved in the LPS signal transduction pathway that leads to NO formation in rat vascular smooth muscle cells (VSMC). VSMC were transfected with a mammalian expression vector containing a full length PKCalpha cDNA insert, and a stable transfectant overexpressing PKCalpha was obtained as evidenced by increased expression of PKCalpha mRNA and protein. In response to 100 ng/ml LPS stimulation, the PKCalpha transfectants showed a 1.8-fold increase in PKC activity at 30 min and a twofold increase in NO production over 24 hr compared with cells transfected with control plasmids. The LPS-stimulated increase in NO synthesis in PKCalpha transfectants was blocked by the specific PKCalpha inhibitor Gö 6976. After 6 hr LPS treatment, PKCalpha-transfected and control cells showed equivalent increases in mRNA and protein for the inducible NO synthase. NO synthase activity of the cell extracts assayed in the presence of excess substrate and cofactors was not significantly different between PKCalpha-transfected and control cells after LPS stimulation. However, mRNA levels for GTP cyclohydrolase I, a key enzyme in (6R)-tetrahydro-L-biopterin synthesis, and cationic amino acid transporter-2, involved in L-arginine transport, was enhanced in cells overexpressing PKCalpha compared with control cells. These results suggest that PKCalpha plays an important role in LPS-induced NO formation and that a significant portion of this effect may be by means of enhanced substrate availability to the inducible nitric oxide synthase enzyme.

Modulatory effects of PKC activity on increased 92-kDa gelatinase secretion by neonatal alveolar macrophages

We previously demonstrated that alveolar macrophages (AMs) from neonatal rats can secrete more 92-kDa gelatinase than AMs from adult rats. In this study, we investigated the role of the protein kinase C (PKC) pathway in the transductional regulation of 92-kDa gelatinase secretion by rat AMs, and we also evaluated maturational changes in this role with increasing postnatal age. After AM stimulation by phorbol 12-myristate 13-acetate (PMA), we observed a dose-dependent increase in gelatinase secretion that was significantly more marked in AMs from 6-day-old rats than in AMs from adult rats and that was inhibited by the PKC inhibitor calphostin C. Adenosine 3',5'-cyclic monophosphate mimetics or concanavalin A failed to induce an increase in gelatinase secretion by AMs. Time-dependent variations in PKC activity after PMA stimulation differed significantly between 6-day-old rats and adult rats; PKC activity decreased in adult AMs (50%) but remained stable in 6-day-old AMs. We therefore investigated age-related differences in the intracellular proteolytic degradation of PKC, which is thought to be mediated by calpains. Leupeptin, used as a calpain inhibitor, inhibited the decrease in PKC activity after exposure of adult AMs to PMA and induced a greater than threefold increase in PMA-induced gelatinase secretion. Calpain activity was significantly lower in AM extracts from 6-day-old than from adult rats. The physiological implication of these developmental changes in 92-kDa gelatinase regulation was demonstrated by investigation of AMs from 1-day-old rats that showed a high level of spontaneous PKC-dependent gelatinase secretion coexisting with very low calpain activity. We conclude that sustained PKC activity is a key factor in the increased gelatinase secretion by AMs seen during the postnatal period and is due, at least in part, to reduced PKC degradation.

Anti-inflammatory activity of cationic lipids

1. The effect of liposome phospholipid composition has been assumed to be relatively unimportant because of the presumed inert nature of phospholipids. 2. We have previously shown that cationic liposome formulations used for gene therapy inhibit, through their cationic component, the synthesis by activated macrophages of the pro-inflammatory mediators nitric oxide (NO) and tumour necrosis factor-alpha (TNF-alpha). 3. In this study, we have evaluated the ability of different cationic lipids to reduce footpad inflammation induced by carrageenan and by sheep red blood cell challenge. 4. Parenteral (i.p. or s.c) or local injection of the positively charged lipids dimethyldioctadecylammomium bromide (DDAB), dioleyoltrimethylammonium propane (DOTAP), dimyristoyltrimethylammonium propane (DMTAP) or dimethylaminoethanecarbamoyl cholesterol (DC-Chol) significantly reduced the inflammation observed in both models in a dose-dependent manner (maximum inhibition: 70-95%). 5. Cationic lipids associated with dioleyol- or dipalmitoyl-phosphatidylethanolamine retained their anti-inflammatory activity while cationic lipids associated with dipalmitoylphosphatidylcholine (DPPC) or dimyristoylphosphatidylglycerol (DMPG) showed no anti-inflammatory activity, indicating that the release of cationic lipids into the macrophage cytoplasm is a necessary step for anti-inflammatory activity. The anti-inflammatory activity of cationic lipids was abrogated by the addition of dipalmitoylphosphatidylethanolamine-poly(ethylene)glycol-2000 (DPPE-PEG2000) which blocks the interaction of cationic lipids with macrophages. 6. Because of the significant role of protein kinase C (PKC) in the inflammatory process we have determined whether the cationic lipids used in this study inhibit PKC activity. The cationic lipids significantly inhibited the activity of PKC but not the activity of a non-related protein kinase, PKA. The synthesis of interleukin-6 (IL-6), which is not dependent on PKC activity for its induction in macrophages, was not modified in vitro or in situ by cationic lipids. The synthesis of NO and TNF-alpha in macrophages, both of which are PKC-dependent, was downregulated by cationic lipids. 7. These results demonstrate that cationic lipids can be considered as novel anti-inflammatory agents. The downregulation of pro-inflammatory mediators through interaction of cationic lipids with the PKC pathway may explain this anti-inflammatory activity. Furthermore, since cationic lipids have intrinsic anti-inflammatory activity, cationic liposomes should be used with caution to deliver nucleic acids for gene therapy in vivo.

Priming of mouse macrophages with the macrophage colony-stimulating factor (CSF-1) induces a variety of pathways that regulate expression of the interleukin 6 (Il6) and granulocyte-macrophage colony-stimulating factor (Csfgm) genes

Recent data have indicated that resident mouse peritoneal macrophages (PMo) transcribed the interleukin 6 (Il6) and granulocyte-macrophage colony-stimulating factor (Csfgm) genes in response to stimulation with the monocyte-macrophage colony-stimulating factor (CSF-1) but only Il6 mRNA was translated into secreted protein. In this paper, we extend these observations. It is shown that resident PMo incubated with protein kinase (PK)C inhibitors, staurosporine (SP) and its derivative GF109203-X, showed a several fold increase in the levels of Il6 mRNA in control and CSF-1-primed PMo and a parallel release of large amounts of protein. In contrast, SP was shown to have no effect on the release of GM-CSF from control or CSF-1-primed PMo, although it increased by approximately twofold the amount of Csfgm mRNA in CSF-1-primed Mo. When SP was added 4 h after CSF-1 priming to block CSF-1-induced protein kinase pathways, an increased amount of IL-6 release was again seen but without any increase in Il6 mRNA levels. Under these conditions, Csfgm gene expression was relatively unaffected. Activation of PKC by phorbol myristate acetate (PMA) also resulted in increased Il6 gene expression by control and CSF-1-primed PMo. PMA had no apparent effect on Csfgm transcription but appeared to influence translation at a low level, as measured by the release of small amounts of GM-CSF protein. The addition of lipopolysaccharide (LPS) to CSF-1-primed PMo resulted in a synergistic increase in the expression of both genes at the levels of transcription and protein release. The addition of SP to CSF-1-primed Mo before LPS, however, further enhanced IL-6 release but not GM-CSF release from the cells. The data indicate that CSF-1-priming drives a number of pathways involved in the regulation of expression of both genes and renders PMo highly susceptible to appropriate secondary stimulatory agents that transform the PMo into secretory inflammatory cells.

CSF-1-induced and constitutive Il6 gene expression in mouse macrophages: evidence for PKC-dependent and -independent pathways

It has been recently shown that CSF-1 enhanced the constitutive expression of the Il6 gene in resident mouse peritoneal macrophages (PM phi) but little is known about the pathways involved. In this report, we show that both constitutive and CSF-1-induced IL-6 release were enhanced and prolonged in the presence of the PKC inhibitors, staurosporine (SP) and its derivative, GF-109203X. Enhancement of constitutive IL-6 release required higher concentrations of inhibitors, while enhanced CSF-1-induced release was diminished when inhibitor concentrations exceeded defined limits. SP was also shown to activate constitutive IL-6 release by blood monocytes and elicited PM phi but had no effect on their responsiveness to CSF-1. Activation of PKC by exposure of resident PM phi to phorbol myristate acetate (PMA) also resulted in enhanced IL-6 release and PMA was shown to synergize with CSF-1. These data indicate that CSF-1 does not induce Il6 gene expression by amplifying the constitutive pathway in all mononuclear phagocyte subpopulations. It exerts its effects independently of PKC, which may activate Il6 gene expression in its own right by an alternative pathway. While CSF-1 and PKC are involved in separate pathways, the synergistic IL-6 response seen when PMA and CSF-1 interact suggests convergence of the two pathways. It is also apparent that multiple PKs, excluding PKC, may be involved in repressing constitutive and CSF-1-induced Il6 gene expression.

Modulation of integrin-mediated intercellular adhesion during the interaction of thymocytes with stromal cells expressing VLA-4 and LFA-1 ligands

Mature peripheral T cells closely regulate their intercellular interactions by modulating integrin adhesion functions. The ability of members of the integrin family to mediate intercellular adhesion is dependent on signals from within the cells (inside-out signaling) that increase the avidity of integrins for their ligands. These changes in avidity are independent of the quantitative changes on the number of receptors, and there is evidence to suggest that phosphorylation events play a predominant role in the regulation of the avidity state of the integrins. Whether such regulatory mechanisms are operative during T cell development had hitherto been an opened question. In the present work, we have used an in vitro adhesion assay between thymocytes and target cells expressing VLA-4 and LFA-1 counter ligands to determine how thymocytes can discriminate between integrin-specific signals during T cell development. Our findings are that VLA-4, but not LFA-1, is constitutively expressed in its high-avidity state during the early stages of T cell development, and that the high-avidity state of thymocytes for VCAM-1-expressing cells is closely regulated by signaling through protein kinase C and protein tyrosine kinase pathways. At later stages of development, mature thymocytes prior to leaving the thymus turn off both VLA-4 and LFA-1 adhesion functions. Our results show that the low-affinity state of integrins on peripheral mature T cells is established before mature thymocytes leave the thymus. Only when mature T cells recognize antigenic peptides in the context of major histocompatibility complex in the periphery will they turn on the adhesion function of VLA-4 and/or LFA-1 integrins.

Pharmacological inhibition of gelatinase B induction and tumor cell invasion

The 92 kDa matrix metalloproteinase (gelatinase B, MMP-9) plays a major role in the facilitation of tumor metastasis and in inflammatory disorders characterized by excessive matrix protein destruction. MMP-9 is transcriptionally induced in multiple cell types by exposure to the inflammatory mediators bacterial endotoxin, interleukin-1 (IL-1) or tumor necrosis factor-alpha (TNF-alpha). CT-2519, (1-(5-isothiocyanatohexyl)-3,7-dimethylxanthine), a synthetic small molecule from an anti-inflammatory compound library, was evaluated for its effect on endotoxin and cytokine-induced MMP-9 synthesis by a monocytic leukemic cell line, THP-1, and a monocyte/macrophage line, RAW 264.7. CT-2519 dose-dependently inhibited endotoxin and cytokine-induced synthesis of MMP-9 by these cells. Furthermore, both MMP-9 secretion and matrix invasion by cells of a human fibrosarcoma cell line, HT-1080, were inhibited by CT-2519 in a dose-dependent manner. Northern blot analyses and studies utilizing MMP-9 promoter constructs indicated that the inhibitory action of CT-2519 occurs at the level of transcriptional suppression. Given the observation that cellular activation by endotoxin, IL-1 and TNF-alpha may be mediated, at least in part, through induction of certain species of phosphatidic acid (PA), the effect of CT-2519 on lipid levels was analyzed. CT-2519 effectively reduced endotoxin-mediated increases in particular cellular lipid levels. Pharmacologic modulation of cytokine-dependent gene products, such as MMP-9, may offer an important therapeutic approach to the treatment of neoplastic and inflammatory disorders.

Synergistic and selective stimulation of gelatinase B production in macrophages by lipopolysaccharide, trans-retinoic acid and CGP 41251, a protein kinase C regulator

The production of gelatinase B by macrophages is relevant in the immunological and migratory functions of macrophages. CGP 41251, an inhibitor of protein kinase C (PKC), was found to stimulate the expression of gelatinase B in macrophages, as shown by the study of two different monocytic/macrophagic cell lines, mouse RAW 264.7 and human THP-1 cells. When human monocytes and rat peritoneal macrophages were treated with CGP 41251, insignificant increases of 10 and 25% were obtained. This can possibly be due to the presence of contaminating cells in these two enriched populations, since the CGP 41251 treatment of non-macrophagic cell lines inhibited their PMA-induced gelatinase B production. Taken together, these results suggest that the stimulatory effect of CGP 41251 is specific to cells of the monocytic lineage. Using RAW 264.7 cells as a model, the effect of CGP 41251 is additive to that obtained using lipopolysaccharide (LPS) and phorbol 12-myristate 13-acetate (PMA), as revealed by gelatin zymography and Northern blot analysis. The stimulatory effect of CGP 41251 on gelatinase B production in RAW 264.7 was: (a) inhibited by calphostin C (as is the LPS-induced response), indicating a PKC-dependence; (b) inhibited by dexamethasone (as opposed to the LPS-induced response); and (c) enhanced by addition of trans-retinoic acid (RA). In fact, RA can induce gelatinase B production, either alone or in synergy with LPS and/or CGP 41251, since the combination of the three agents gives the highest gelatinase B response, at both the protein and the mRNA levels. This represents an important observation considering the RA is now being tested as an anti-cancer agent and proposed for prevention studies.

Differential modulation of natural and adaptive immunity in Fischer rats exposed for 6 weeks to 60 Hz linear sinusoidal continuous-wave magnetic fields

Two separate, independent experiments were conducted to evaluate the effect of 60 Hz linearly polarized, sinusoidal, continuous-wave magnetic fields (MFs) on immune system performances in rats born and raised under these fields. Each experiment lasted for 6 weeks. A total of 96 animals, divided into groups of eight animals each, was exposed for 20 h/day to MFs of different intensities, i.e., sham (< 0.02 microT) and 2, 20, 200, and 2000 microT. Another group of animals, which was housed in a separate room, served as cage controls (CC). These animals were exposed to ambient MFs of < 0.02 microT. The following immune responses were evaluated in both experiments total T and B cells; CD4+ and CD8+ subpopulation and natural killer (NK) cell activity in splenic lymphocytes; hydrogen peroxide (H2O2), nitrous oxide (NO), and tumor necrosis factor (TNF) production by peritoneal macrophages. Our results show that a 6 week exposure to MFs induced a significant decrease in the number of CD5+, CD4+, and CD8+ populations. These changes were even more significant in rats that were exposed to fields of 2000 microT. A lower, although significant, decrease in the CD5+ population was also observed in animals that were exposed to fields of 200 microT. Linear regression analysis demonstrated a dose effect with MF intensity. B lymphocyte (Ig+ cell) populations also showed a 12% decrease (P < .05) in the groups that were exposed to fields of 20 and 200 microT. However, these results were not significant, and no relation with MF intensities could be demonstrated. In contrast, evaluation of splenic NK cell activity revealed a 50% increase (P < .05) in animals that were exposed to fields of 2000 microT. No significant results were obtained from the evaluation of TNF activity and NO secretion in peritoneal macrophages. Phorbol 12-myristate 13-acetate (PMA)-stimulated and net H2O2 productions for a minor subpopulation of peritoneal cells showed positive dose-response correlations by linear regression analysis. Taken together, our results suggest that an in vivo exposure of rats for 6 weeks to 60 Hz MFs can induce significant immunological perturbations on effector cells of both natural and adaptive immunity in a dose-dependent fashion.

Prevention of acute autoimmune encephalomyelitis and abrogation of relapses in murine models of multiple sclerosis by the protease inhibitor D-penicillamine

The in vitro activity of gelatinase B, an enzyme whose appearance in the cerebrospinal fluid is associated with inflammatory diseases of the central nervous system, was dose-dependently inhibited by the antirheumatic D-penicillamine. Inhibition of gelatinase B in electrophoretically pure preparations and in cell culture supernatants and human body fluids was obtained at dosages reached in the circulation of patients treated with a peroral dosis of 750 mg D-penicillamine per day. In mice, developing acute demyelination, D-penicillamine significantly reduced the mortality and morbidity rates of experimental allergic encephalomyelitis (EAE). In chronic relapsing EAE in Biozzi AB/H mice, an animal model for relapses in multiple sclerosis (MS), it attenuated the exacerbations, even when the treatment was started after the primary full-blown disease had developed. We infer protease inhibition as the mechanism of action of D-penicillamine and suggest that its use may be effective as peroral treatment for MS.