Nitric oxide-mediated modulation of interleukin-8 production by a human glioblastoma cell line, T98G, cocultured with myeloid and monocytic cell lines

[Study of cytokine signaling: the quest for immunomodulatory drugs interacting with cytokine production and activity]

I have been engaged in research and education in the fields of immunology and biochemistry at a medical college and college of pharmacy for 40 years. The original reasons why I began studying cytokines and some of the interests that have motivated me to continue working in the field of cytokine research are described: 1) the roles of cytokines in various immunological and inflammatory diseases (e.g., chemokines in bacterial infections and inflammatory diseases, particularly the role of interleukin-5 and eotaxins in eosinophilia); 2) the role of focal adhesion kinase in antiapoptosis and metastasis of melanoma; 3) recent findings on the role of JAK2/STAT pathways, particularly how JAK2V617F mutation induces dysregulated proliferation and tumorigenesis; and 4) the interactions of various chemical compounds and natural products in cytokine gene activation and signaling. Previous discoveries and published findings by my research group are described, along with comments and discussion pertaining to recent developments in the field.

Glycyrrhiza inflata-derived chalcones, Licochalcone A, Licochalcone B and Licochalcone D, inhibit phosphorylation of NF-kappaB p65 in LPS signaling pathway

Licorice root has been used as a traditional medicine for the treatment of gastric ulcer, bronchial asthma and inflammation. Licochalcone A is a major component of Xinjiang licorice, Glycyrrhiza inflata. Previously we showed that Licochalcone A significantly inhibited LPS-induced NF-kappaB transcriptional activation by abrogating the phosphorylation of NF-kappaB p65 at serine 276. Glycyrrhiza inflata contains not only Licochalcone A but also Licochalcone B, Licochalcone C, Licochalcone D, Echinatin and Isoliquiritigenin, harboring the common structure of chalcones. No chalcones had any effect on LPS-induced IkappaB degradation, nuclear translocation and DNA binding activity of NF-kappaB p65; however, we observed that Licochalcone B and Licochalcone D significantly inhibited LPS-induced phosphorylation at serine 276 and transcriptional activation of NF-kappaB, the same as Licochalcone A. Interestingly, we also found that Licochalcone A, Licochalcone B and Licochalcone D effectively inhibited LPS-induced activation of PKA, which is required for the phosphorylation of NF-kappaB p65 at serine 276. Consequently, Licochalcone B and Licochalcone D significantly reduced the LPS-induced production of NO, TNFalpha and MCP-1. On the other hand, Licochalcone C, Echinatin and Isoliquitigenin failed to inhibit LPS-induced NF-kappaB activation. These findings suggest that the anti-inflammatory effect of Glycyrrhiza inflata is ascribable to the potent inhibition of NF-kappaB by Licochalcone A, Licochalcone B and Licochalcone D.

Licochalcone A significantly suppresses LPS signaling pathway through the inhibition of NF-kappaB p65 phosphorylation at serine 276

Licorice root, Glycyrrhiza inflata, has been used as a traditional medicine for the treatment of bronchial asthma and inflammation; however, the mechanism of its anti-inflammatory activity has not been clarified. Here, we investigated the effect of Licochalcone A, a major component of G. inflata, on the LPS signaling pathway. We found that Licochalcone A remarkably inhibited LPS-induced NO production, and TNFalpha expression and MCP-1 expression in both RAW264.7 cells and primary macrophages. Furthermore, when injected with Licochalcone A prior to injection of LPS, the serum level of TNFalpha and MCP-1 in C57BL/6 mice was clearly decreased, indicating that Licochalcone A has a potent anti-inflammatory effect both in vitro and in vivo. Strikingly, Licochalcone A significantly inhibited LPS-induced NF-kappaB transcriptional activation; however, it had no effect on not only the phosphorylation and degradation of IkappaBalpha but also nuclear translocation and DNA binding activity of NF-kappaB p65. Interestingly, Licochalcone A markedly inhibited the phosphorylation of p65 at serine 276. As a result, it reduced NF-kappaB transactivation by preventing the interaction of p65 with p300. Taken together, Licochalcone A might contribute to the potent anti-inflammatory effect of G. inflata through the unique mechanism of NF-kappaB inhibition.

Lipopolysaccharide-induced monocyte chemotactic protein-1 is enhanced by suppression of nitric oxide production, which depends on poor CD14 expression on the surface of skeletal muscle

It is known that lipopolysaccharide (LPS)-induced monocyte chemotactic protein (MCP)-1 secretion from tissues recruits monocytes from the circulation, but the mechanism of the LPS-induced MCP-1 production in skeletal muscle is largely unexplained. To clarify the effect of LPS on MCP-1 production in skeletal muscle cells, C2C12 cells from a mouse skeletal muscle cell line, and RAW 264.7 cells from a mouse macrophage cell line, were used to assess production of LPS-induced MCP-1, nitric oxide (NO) and interferon (IFN)-beta. In addition, we evaluated inducible NO synthases (iNOS) mRNA expression using RT-PCR, and cell surface expression of CD14 and toll-like receptor (TLR) 4 using flow cytometry. In C2C12 cells, LPS stimulation increased MCP-1 production (p < 0.01), but combined treatment with LPS and NO inducer, diethylammonium (Z)-1-(N,N-diethylamino) diazen-1-ium-1,2-diolate (NONOate), significantly inhibited its production (p < 0.01). LPS stimulation neither induced production of NO nor of IFN-beta, which is an NO inducer. Recombinant IFN-beta stimulation, on the other hand, enhanced LPS-induced NO production (p < 0.01). Interestingly, we found that surface expression of CD14, which regulates IFN-beta production, in C2C12 cells was much lower than that in RAW 264.7 cells, although TLR4 expression on C2C12 cells was similar to that on RAW 264.7 cells. These data suggest that the reduced NO production in response to LPS may depend on low expression of CD14 on the cell surface of skeletal muscle, and that it may enhance LPS-induced MCP-1 production. Together, these functions of skeletal muscle could decrease the risk of bacterial infection by recruitment of monocytes.

Inhibition by (+/-)-indenestrol A of interferon gamma-stimulated nitric oxide formation in murine macrophage RAW 264.7 cells

We examined the effects of (+/-)-indenestrol A (IA), an antioxidative and superoxide-producing metabolite of diethylstilbestrol (DES), on the activation of murine macrophages (RAW 264.7 cells) in vitro, particularly with regard to interferon (IFN)-gamma-induced nitric oxide (NO) production. (+/-)-IA inhibited NO production more strongly than DES as assessed by a nitrite assay. The inhibitory effect of (+/-)-IA on IFN-gamma-induced intracellular NO production was confirmed by direct staining of intracellular NO with diaminofluorescein-2 diacetyl. Inhibition of NO production was confirmed by Western blot analysis of IFN-gamma-induced NO synthase. Under IFN-gamma-stimulated conditions, the IFN-gamma activation site (GAS), which was the most important transcription factor, was significantly inhibited by (+/-)-IA. (+/-)-IA also promoted the activation of NF-kappaB. (+/-)-IA at 1 and 3 microM delayed the onset of apoptosis. Our results suggest that (+/-)-IA inhibited the activation of macrophages, resulting in the suppression of NO-mediated apoptosis. These results suggest a novel mechanism for the carcinogenic promoting activity of DES via its metabolite, (+/-)-IA.

Suppression of monocyte chemoattractant protein 1, but not IL-8, by alprazolam: effect of alprazolam on c-Rel/p65 and c-Rel/p50 binding to the monocyte chemoattractant protein 1 promoter region

Alprazolam is a hypnotic/tranquilizer that has been shown to specifically inhibit the platelet-activating factor (PAF)-induced aggregation of human platelets. The goal of this study was to elucidate whether alprazolam modulates IL-1alpha-initiated responses. For this purpose we investigated the effects of alprazolam on the IL-1alpha-induced production of inflammatory cytokines (IL-8 and monocyte chemoattractant protein 1 (MCP-1)) in a human glioblastoma cell line, T98G, and explored the signaling pathways involved. We found that alprazolam inhibited IL-1alpha-elicited MCP-1 production within a range of 0.1-3 micro M. In contrast, it did not inhibit IL-1alpha-induced IL-8 production. Although NF-kappaB is involved in regulating the IL-1alpha-induced expression of MCP-1 and IL-8, the degradation of IkappaB-alpha stimulated by IL-1alpha was not inhibited by alprazolam. Alprazolam prevented NF-kappaB from binding to the MCP-1 promoter region (the A2 and A1 oligonucleotide probes), but binding of NF-kappaB to IL-8/NF-kappaB was not inhibited. Moreover, alprazolam inhibited c-Rel/p50 binding to the A2 oligonucleotide probe, but not p50/p65 from binding to the IL-8/NF-kappaB site. While AP-1 is involved in regulating the IL-1alpha-induced expression of IL-8, but not MCP-1, alprazolam potentiated the binding of c-Jun/c-Fos to the AP-1 oligonucleotide probe. These results show that the inhibition of IL-1alpha-mediated MCP-1 production by alprazolam is mainly due to inhibition of c-Rel/p65 and c-Rel/p50 binding to the MCP-1 promoter region, since alprazolam did not affect the IL-1alpha-mediated activation of NF-kappaB (p50/p65) or AP-1 (c-Jun/c-Fos) binding to the IL-8 promoter region. In conclusion, a new action of alprazolam was elucidated, as shown in the inhibition of c-Rel/p65- and c-Rel/p50-regulated transcription.

Interleukin-8 and human cancer biology

The aggressive nature of metastatic human cancer has been shown to be related to numerous abnormalities in growth factors and their receptors. These perturbations confer a tremendous growth advantage to the malignant cells. Interleukin-8 (IL-8), originally discovered as a chemotactic factor for leukocytes, has recently been shown to contribute to human cancer progression through its potential functions as a mitogenic, angiogenic, and motogenic factor. While it is constitutively detected in human cancer tissues and established cell lines, IL-8 expression is regulated by various tumor microenvironment factors, such as hypoxia, acidosis, nitric oxide, and cell density. Understanding the mechanisms of both inducible and constitutive IL-8 expression will be helpful in designing potential therapeutic strategies of targeting IL-8 to control tumor growth and metastasis. In this review, the role and regulation of IL-8 expression in the growth and metastasis of human cancer with a focus on human pancreatic adenocarcinoma will be discussed.

Regulation of interleukin-8 expression by tumor-associated stress factors

Tumor and host cells frequently express interleukin-8 (IL-8). IL-8 has been shown to be motogenic, mitogenic, and angiogenic and to play important roles in human tumor progression. IL-8 expression can be induced by numerous stress factors present in the tumor environment, such as hypoxia, acidosis, hyperglycemia, hyperosmotic pressure, high cell density, hyperthermia, radiation, and chemotherapeutic agents. Understanding the mechanisms of IL-8 expression and regulation will be helpful in designing potential therapeutic modalities targeting IL-8 to control tumor growth and metastasis.

Regulation of interleukin-8 expression by nitric oxide in human pancreatic adenocarcinoma

The regulation of interleukin-8 (IL-8) expression by nitric oxide (NO) was determined in human pancreatic cancer cell lines. CaPan-2 and FG human pancreatic adenocarcinoma cells were incubated for 24 h in medium alone or medium containing a cytokine mixture in the presence or absence of an NO synthase (NOS) inhibitor, N(G)-monomethyl-L-arginine (NMA). The NOS activity and level of IL-8 expression were determined. IL-8 expression was induced in the two cell lines. A low level of NOS activity was detectable only in CaPan-2 cells. Moreover, the presence of NMA did not reverse the induction of IL-8. The FG cells were then engineered to produce a physiologic level of NO and incubated in medium alone or medium containing 1 mM NMA. No significant IL-8 expression was induced in those producing a low level of NO, whereas IL-8 expression was induced in those producing a high level of NO. Inhibition of NO production by NMA reversed this effect. Incubation of FG cells with an NO donor, S-nitroso-D,L.-acetyl-penicillamine (SNAP), led to a concentration-dependent and time-dependent induction of IL-8 expression. This NO-mediated upregulation of IL-8 expression correlated with an increase in IL-8 gene transcription and mRNA stability. Our results indicate that NO is involved in the regulation of IL-8 expression in and contributes to the progression of human pancreatic cancer.

Differential induction of JE/MCP-1 in subclones from a murine macrophage cell line, RAW 264.7: role of kappaB-3 binding protein

The JE/MCP-1 gene is an immediate-early gene, and its product is a CC chemokine that attracts monocytes, basophils and T lymphocytes. JE/MCP-1 gene expression is induced by various inflammatory stimuli, but its transcriptional mechanism is not fully understood. To address this question, we obtained two subclones from a parental RAW264.7 cell line, one subline with low JE/MCP-1-producing capacity (named RAW.c11) and the other with high JE/MCP-1-producing capacity (named RAW.c25), in response to lipopolysaccharide (LPS). These subclones have no significant differences in CD14 expression, nitric oxide production, or production of other cytokines, including TNF-alpha or IL-1alpha/beta. In electrophoretic mobility shift assays (EMSA), there were no significant differences in DNA binding to the NF-kappaB-consensus sequence and interferon regulatory factor (IRF)-1,2 binding sequences. However, significantly higher binding activity to the NF-kappaB-like sequence (kappaB-3), which is located in the promoter region of the JE/MCP-1 gene, was shown by a high producer subclone than by a low producer subclone. Transient transfection analysis using deletion mutants of a 0.5-kb region from -467 to +59 identified an LPS-responsive region in a kappaB-3 site (from -169 to -132) in the high producer subclone. Mutation of this site markedly reduced sensitivity to LPS in the high producer subclone. These data suggest that a yet undefined nuclear factor may be involved in differential JE/MCP-1 gene transcription.