Anti-inflammatory effects of moxifloxacin on IL-8, IL-1beta and TNF-alpha secretion and NFkappaB and MAP-kinase activation in human monocytes stimulated with Aspergillus fumigatus

OBJECTIVES

We have previously shown that moxifloxacin conferred protective anti-inflammatory effects against Candida pneumonia in immunosuppressed mice. Further in vitro studies showed anti-inflammatory effects of moxifloxacin in LPS and cytokine-stimulated monocytic and epithelial cells. In the present study, concentrating on a more challenging pathogen of immunosuppressed hosts, we studied the effect of moxifloxacin on cytokine secretion and signal transduction mechanisms in monocytic cells stimulated with Aspergillus fumigatus.

METHODS

Human peripheral blood monocytes (PBMCs) and a human monocytic cell line (THP-1) were incubated with 1.5x10(6)/mL conidia of a clinical isolate of A. fumigatus. Cytokine secretion and activation of NFkappaB and the MAP-kinases ERK1/2 and p38 were measured with and without the addition of moxifloxacin (5-20 mg/L).

RESULTS

Stimulation of PBMCs and THP-1 cells with A. fumigatus increased IL-8, IL-1beta and TNF-alpha secretion (4.1-, 8.3- and 7-fold, and 5.4-, 3.7- and 17.8-fold, respectively). Addition of moxifloxacin (5-20 mg/L) inhibited cytokine secretion up to 45.7+/-5%, 72+/-13% and 73+/-10% in PBMCs and up to 35.6+/-0.5%, 30+/-2.4% and 19+/-4% in THP-1 cells (P<0.05). Signal transduction studies showed that incubation of THP-1 cells with A. fumigatus increased ERK1/2 and p38 phosphorylation and p65-NFkappaB protein expression by 1.6-, 1.3- and 1.8-fold, respectively. Addition of moxifloxacin inhibited ERK1/2, p38 and p65-NFkappaB by up to 69+/-14%, 58+/-3% and 75+/-15%, respectively.

CONCLUSIONS

Our results indicate that moxifloxacin acts as an anti-inflammatory agent in monocytic cells stimulated with A. fumigatus conidia. Whether these effects may be protective as in the Candida pneumonia model is unknown and merits in vivo studies in models of pulmonary aspergillosis.

Jun: stealth, stability, and transformation

A recent paper by Wei and collaborators in Cancer Cell sheds light on the effects of one of the mutations in v-Jun and has broad implications for our understanding of control mechanisms that direct the timing of important cell cycle functions (Wei et al., 2005).

Reversion of the Jun-induced oncogenic phenotype by enhanced synthesis of sialosyllactosylceramide (GM3 ganglioside)

In the mouse fibroblast cell line C3H 10T1/2 and the chicken fibroblast cell line DF1, the ganglioside GM3 is the major glycosphingolipid component of the plasma membrane. Expression of the viral oncoprotein Jun (v-Jun) induces transformed cell clones with greatly reduced levels of GM3 and GM3 synthase (lactosylceramide alpha2,3-sialyltransferase) mRNA in both 10T1/2 and DF1 cell cultures. Compared with nontransformed controls, v-Jun transfectants show enhanced ability of anchorage-independent growth, and their growth rates as adherent cells are increased. When the mouse GM3 synthase gene is transfected with the pcDNA vector into v-Jun-transformed 10T1/2 cells, the levels of GM3 synthase and corresponding mRNA are restored to those of control cells. Reexpression of GM3 correlates with a reduced ability of the cells to form colonies in nutrient agar. Similarly, when the newly cloned chicken GM3 synthase gene is transfected into v-Jun-transformed DF1 with the pcDNA vector, the GM3 synthase level is restored to that of control cells, and the ability of the cells to form agar colonies is reduced. The levels of GM3 in the cell also affect membrane microdomains. The complex of GM3 with tetraspanin CD9 and integrin alpha5beta1 inhibits motility and invasiveness. The amounts of this complex are greatly reduced in transformed cells. Expression of GM3 and consequent reversion of the transformed phenotype results in increased levels of that microdomain complex.

Structural and Functional Analysis of the Differential Effects of c-Jun and v-Jun on Prolactin Gene Expression

The protooncogene c-Jun and its oncogenic isoform v-Jun are members of the activator protein 1 family of transcription factors that have been shown to have differential transcriptional effects that are both promoter specific and cell type specific. Previously, we have demonstrated that whereas c-Jun inhibits pituitary-specific rat prolactin (rPRL) promoter activity, expression of v-Jun stimulates the rPRL promoter in GH4 pituitary cells. In this report, we have conducted an extensive structure-function analysis of c-Jun vs. v-Jun to determine which regions of these proteins are responsible for their differential transcriptional effects in this pituitary model system. We show that isoform-specific responses are mediated by complex interactions between the delta-domain, serine 243, and the amino-terminal transcriptional activation domains. Thus, in contrast to previous reports, no single domain is responsible for the differential transcriptional activities of c-Jun and v-Jun. Mutation of c-Jun serine 243 to phenylalanine and replacement of the c-Jun amino terminus with the corresponding region from v-Jun, thereby removing the delta-domain, are necessary and sufficient to confer a functional switch from the c-Jun-inhibitory to the v-Jun-activating phenotype. Thus, we propose that isoform-specific subdomains in c-Jun and v-Jun dictate discrete interactions with distinct protein partners, which underlie the differential Jun-dependent transcriptional responses of the rPRL promoter.

Jun, the oncoprotein

Cellular Jun (c-Jun) and viral Jun (v-Jun) can induce oncogenic transformation. For this activity, c-Jun requires an upstream signal, delivered by the Jun N-terminal kinase (JNK). v-Jun does not interact with JNK; it is autonomous and constitutively active. v-Jun and c-Jun address overlapping but not identical sets of genes. Whether all genes essential for transformation reside within the overlap of the v-Jun and c-Jun target spectra remains to be determined. The search for transformation-relevant targets of Jun is moving into a new stage with the application of DNA microarrays technology. Genetic screens and functional tests remain a necessity for the identification of genes that control the oncogenic phenotype.

v-Jun sensitizes cells to apoptosis by a mechanism involving mitochondrial cytochrome C release

v-Jun shares the ability of the Myc, E1A, and E2F oncogenes to both sustain cell cycle progression and promote apoptosis in the absence of mitogenic stimulation. To gain an insight into the mechanism of apoptosis sensitization, we examined the possible involvement of key regulatory proteins previously implicated in oncogene-induced cell death during v-Jun-induced apoptosis triggered by serum withdrawal. We observed that ectopic expression of the anti-apoptotic Bcl-2 protein, or of two downstream effectors of growth factor signalling, v-PI 3-Kinase and v-Src, partially or completely suppressed apoptosis. Apoptosis was also observed in the presence of serum growth factors when endogenous PI3K activity was blocked using the synthetic inhibitor LY294002, further suggesting an important role for PI3-K in cell survival. Cytochrome C was released into the cytosol of apoptotic v-Jun expressing cells, and this release was inhibited by Bcl-2, suggesting an important role for mitochondrial dysfunction in v-Jun induced apoptosis. In contrast, inhibition of Fas signalling using dominant negative FADD did not inhibit apoptosis, nor was there any evidence for accumulation or activation of p53 in v-Jun transformed cells. Consistent with this latter observation, inhibition of p53 function by HPV16 E6 protein had no effect on v-Jun induced cell death. Taken together, these results suggest that mitochondrial dysfunction is an important component of the mechanism through which v-Jun sensitizes cells to apoptosis, but that the apoptotic signals elicited by v-Jun upstream of the mitochondria do not depend on increased levels of p53 activity or Fas signalling.

Transcriptional control of SPARC by v-Jun and other members of the AP1 family of transcription factors

Transformation of chick embryo fibroblasts by the v-Jun oncoprotein correlates with a down-regulation of the extracellular matrix protein SPARC and repression of the corresponding mRNA. Alteration in SPARC expression has been repeatedly reported in human cancers of various origin, and is thought to contribute to the remodeling of the extracellular matrix during neoplastic progression. Transcriptional control of SPARC is poorly understood. We show here that (i) v-Jun-mediated repression of the endogenous SPARC gene is enhanced by Fra2 but alleviated by ATF2, Fra2 and ATF2 being the two major partners of v-Jun in the transformed cells; (ii) high basal activity as well as repression by v-Jun and modulation by Fra2 and ATF2 is restricted to a small proximal fragment (-124/+16) of the chicken SPARC promoter; (iii) the activity of this minimal promoter is modulated by all the AP1 family members known in chickens (c-Jun and JunD; c-Fos and Fra2; ATF2; c-Maf, MafA, and MafB). Taken together these data demonstrate that, at least in avian primary cells, SPARC expression is under the control of the AP1 transcription factor. Further studies with the minimal (-124/+16) promoter fragment are needed to understand how this control takes place at the molecular level.

Identification and characterization of genes upregulated in cells transformed by v-Jun

The transcription factor Jun (c-Jun) functions as a recipient of extracellular growth signals and converts them into patterns of gene expression. An oncogenic variant of c-Jun was isolated from the acutely transforming retrovirus ASV17. Overexpression of this viral Jun (v-Jun) induces transformation of chicken embryo fibroblasts (CEF) in culture and fibrosarcomas in chickens. v-Jun is a constitutively active form of c-Jun and transforms cells presumably by deregulating the expression of specific target genes. In this report, we describe six genes whose transcripts are upregulated in v-Jun-transformed CEF. Three of these genes show homology to known mammalian genes, to MAP kinase phosphatase 2 (MKP-2), to reversion-induced LIM protein (RIL) and to cytokine-inducible SH2-containing protein (CIS). Northern blot analysis, using CEF infected with various Jun mutants or an estrogen-regulatable Jun chimera, revealed distinct induction patterns of individual targets by v-Jun. The chicken RIL homolog showed an expression pattern tightly correlated with the activity of v-Jun. Its expression is also transformation-dependent, suggesting a role for this gene in v-Jun transformation. The newly identified v-Jun targets can serve as molecular markers in the v-Jun transformation process. Oncogene (2000) 19, 3537 - 3545

Tumor induction by v-Jun homodimers in chickens

To study the contribution of v-Jun homodimers to oncogenesis, we constructed artificial v-Jun derivatives in which the natural dimerization domain of v-Jun was replaced by an heterologous homodimerization domain from either the viral EB1 or the yeast GCN4 transcription factor. The resulting v-Jun chimeric proteins, called v-Juneb1 and v-Jungcn4, which can no longer dimerize with Jun or Fos, should only form homodimers in the cell. Helper-independent retroviruses expressing v-Jun, v-Juneb1 and v-Jungcn4 were generated. All three viruses transformed primary cultures of chick embryo cells with the same high efficiency and promoted local tumor growth after subcutaneous injection of infected cells in young animals. In contrast, after intravenous injection of viral suspensions into chick embryos, only the chimeric proteins produced internal tumors that were lethal. These tumors were leiomyosarcomas located within the liver and along the digestive tract. Thus, in vivo, v-Juneb1 and v-Jungcn4 are more potent oncoproteins than v-Jun. These data demonstrate that when forced to accumulate, v-Jun homodimers can induce tumors efficiently. They also show that the oncogenic potential of v-Jun can be regulated through the properties of its dimerization domain.

The glucocorticoid receptor synergizes with Jun homodimers to activate AP-1-regulated promoters lacking GR binding sites

Jun/Fos (AP-1) and steroid hormone receptors (SHR) are distinct families of transcription factors that convert extracellular signals into long-term genetic responses. Despite clear differences in their modes of activation and DNA binding specificities, a regulatory cross-talk between AP-1 and SHR such as the glucocorticoid receptor (GR), has been established. Here, we show that the hormone-activated GR negatively or positively modulates the expression of AP-1-dependent genes, depending on the subunits of the dimeric AP-1 complex. This type of regulation does not depend on the presence of a GR binding site in the promoter and is mediated through the DNA binding domain of Jun. Since individual subunits of AP-1 exhibit small differences in sequence specificity, specific subsets of AP-1-dependent genes may be regulated by steroid hormones in different directions.

Efficient induction of fibrosarcomas by v-jun requires mutations in the DNA binding region and the transactivation domain

v-jun is the transforming gene of ASV 17, a retrovirus isolated from a spontaneous chicken fibrosarcoma. There are three mutations in the viral Jun protein (v-Jun) as compared to its cellular progenitor c-Jun: a deletion in the transactivation domain (called delta) and two amino acid substitutions in and near the DNA binding region. The effect of each of these mutations on fibrosarcoma development is described. All three mutations contribute towards tumor formation, and their cumulative effect makes v-Jun more tumorigenic compared to Jun proteins that carry only one or two of the mutations. Viruses rescued from tumors induced by c-Jun carrying the two amino acid substitutions in the DNA binding region have increased transforming and tumorigenic potential. These increases are probably due to further mutations that result in the expression of a rearranged Jun protein. Taken together the results show that the evolution of the c-Jun oncoprotein to an efficient carcinogen requires mutations in the transactivation and DNA binding regions.

Transcriptional activation by the v-Jun oncoprotein is independent of positive regulatory phosphorylation

Growth factors, phorbol esters, and oncogenes such as ras, src, and sis are believed to stimulate c-Jun transcriptional activation by inducing increased phosphorylation at two serine residues (S63 and S73) within the N-terminal transactivation domain. Although S63 and S73 are conserved in the mutant v-Jun oncoprotein, they are not phosphorylated by two enzymes which target the corresponding residues in c-Jun in vitro; namely a partially purified c-Jun kinase from TPA-stimulated U937 cells and purified p54 mitogen activated protein (MAP) kinase. In addition, v-Jun activates transcription more strongly than c-Jun when fused to the Gal4 DNA-binding domain, and transcriptional activation by Gal4-v-Jun is unaffected when S63, S73, or both, are replaced with non-phosphorylatable alanine residues, amino acid substitutions which severely impair transcriptional activation by Gal4-c-Jun. The novel biochemical and transcriptional properties of v-Jun result from deletion of a 27 amino acid segment, termed delta, which is important for transforming activity. On the basis of these results we propose that unlike c-Jun, v-Jun transcriptional activation is independent of positive regulatory phosphorylation and that this may contribute to oncogenesis by v-Jun.

Amino acid substitutions modulate the effect of Jun on transformation, transcriptional activation and DNA replication

The retroviral oncogene v-jun and its cellular counterpart code for proteins that function as major components of the transcription factor complex AP-1. Jun proteins bind to the AP-1 consensus sequence as homodimers or heterodimers with members of the Fos protein family. This report compares the ability of viral and cellular Jun proteins (v-Jun and c-Jun) to activate transcription and to stimulate DNA synthesis. The effect of amino acid substitutions on cellular transformation is also described. In F9 cells c-Jun is a more effective transactivator than v-Jun, which carries two amino acid substitutions in the carboxy-terminal region that together down-regulate transactivation. The delta deletion, present in the amino-terminal region of v-Jun, does not affect transactivation in F9 cells; however, it does modulate the stimulation of DNA synthesis. When delta is deleted, the amino acid substitutions are without consequence on DNA synthesis. In the presence of delta the amino acid substitutions down-regulate DNA synthesis. Deletion of the Jun transactivation domain, which is required for cellular transformation, abolishes both transactivation and stimulation of DNA synthesis. We conclude that transformation, transactivation and stimulation of DNA synthesis all depend on the presence of the transactivation domain. The three functions are, however, not tightly correlated, and further work is needed to define the role of the biochemical activities of Jun in oncogenesis.

Mutation of a phosphorylation site in the DNA-binding domain is required for redox-independent transactivation of AP1-dependent genes by v-Jun

The ability of the nuclear oncoprotein Jun to activate transcription is controlled both by level of DNA binding and by the activity of its transactivation domain. Control of DNA binding is achieved by two mechanisms: phosphorylation and redox regulation. Mutation of Ser-226 inhibits phosphorylation of the DNA binding, resulting in enhanced DNA-binding and transactivation activity of Jun. In contrast, mutation of Cys-252, which is the target for repression of DNA-binding activity under oxidative conditions, results in a strong decrease of Jun-specific activation of transcription. However, transactivation by c-Jun-Cys-252 is fully restored upon mutation of Ser-226. Both mutations are also found in the oncogenic counterpart of c-Jun, v-Jun, and are the only differences between these proteins in the DNA-binding domain, suggesting that v-Jun escapes down-modulation of DNA binding by both mechanisms. However, inhibition of phosphorylation of Ser-226 is absolutely required for the ability of v-Jun to activate transcription of AP-1-dependent genes in a redox-independent manner.

Characterization of sarcoma cell lines from v-jun transgenic mice

Wounding is a prerequisite for tumor formation in v-jun transgenic mice. The progression from wound to dermal sarcoma is a multistep process which, at some stage, results in an increase in transgene mRNA expression in tumor tissue. However, transgene expression in individual sarcoma cells stained for Jun protein cultures is heterogeneous. We cloned several cell lines from wound-related v-jun transgenic tumors to determine whether a relationship existed between the cellular growth properties and structure, expression, or function of the transgene. Cell lines with very high v-jun expression had a high cloning efficiency in soft agar and tumorigenicity in nude mice. However, for cell lines with an intermediate or low level of transgene expression there was no correlation between transgene expression and the transformed phenotype. There was also no correlation between transgene expression and individual cell line morphologies, growth rates, transgene genomic DNA copy number, or mRNA expression of jun-related genes. The tumor cell subclones (1-20.2, 3-24.3) with very low transgene expression, very poor cloning efficiency, and low tumorigenicity also showed reduced activator protein 1 DNA binding activity and had an increased expression of endogenous c-jun when compared to other tumor cell lines. Transfection of a v-jun expression vector into cell lines with poor cloning efficiency and low tumorigenicity enhanced both in vitro cloning and in vivo tumor formation. However, such overexpressed v-jun had no effect on NIH3T3 cells. Our studies show that expression of the v-jun transgene contributes to the transformed phenotype of tumor cell lines but that there are additional factors that determine growth properties in culture and in the animal.

Skeletal muscle arises as a late event during development of wound sarcomas in v-jun transgenic mice

Mice carrying an H-2K-v-jun transgene develop malignant sarcomas by a multistage mechanism following wounding. Here we show that these malignancies are often heterogeneous in composition, containing both undifferentiated mesenchymal cells as well as focal areas of skeletal muscle. Such myogenic areas are not detectable in premalignant precursor lesions, suggesting that cells competent for muscle differentiation arise at a late stage of tumorigenesis. Immunohistochemical staining of transgenic sarcomas reveals that levels of v-Jun correlate inversely with muscle-specific gene expression, suggesting that high levels may be inhibitory to myogenesis. Consistent with this idea, we demonstrate that whereas high levels of v-Jun are able to block MyoD-dependent gene expression in vitro, the levels of v-Jun in sarcoma-derived myogenic cells are below the threshold required to produce this effect. The cell of origin of v-jun wound sarcomas, as well as the relationship between myogenic determination and multistage tumorigenesis, are discussed in the light of these results.

So what's new with jun?

Cancer causing oncogenes are found in specific locations within the cell. Although a great deal is known about the function of the transforming genes that reside on the plasma membrane, less is known about the function of the oncogenes that reside in the nucleus. Studies performed over the last three years on the jun and fos oncogenes have taught us a great deal about how these cancer causing genes function in the nucleus. The products of the jun and fos protooncogenes appear to enhance the transcription of specific genes. The proteins form a heterodimer that binds to specific DNA sequences upstream from the start site of transcription and stimulate the production of messenger RNA. Recent data may explain how jun protein becomes transforming. Unlike normal jun protein, transforming jun protein lacks 30 amino acids. These 30 amino acids appear to bind a protein that inhibits the ability of the jun protoncogene to activate gene transcription. The change of cells from normal to transformed may be mediated partially by unrestrained activation of transcription. These findings suggest possible new targets for chemotherapy to inhibit cancer cell growth.

The genetics of jun

Mutational analyses of Jun show that the leucine zipper mediates dimerization with other Jun molecules or with the Fos protein and determines the three-dimensional orientation of the adjacent basic region, facilitating interaction with DNA. The basic region of Jun is the DNA contact surface. Substitution of certain basic residues in this region leads to loss of DNA binding. Some basic region mutants also act as transdominant lethals: they are able to tie up wild type protein in inactive complexes. The definition of transactivator domains with deletion mutants of Jun appears to depend on the assay for transcriptional activation. CAT assays suggest multiple transactivator regions in the N-terminal third of Jun, while in vitro transcription assays detect a negative regulator of transcription in this region. Another transactivator domain appears to be located close to the basic region in both c-Jun and JunD. The genetics of Jun supports a hierarchical order of Jun functions in which dimerization is a prerequisite for both DNA binding and transcriptional activation, and DNA binding is needed for transcriptional activation.