Background: Tumor necrosis factor alpha (TNFα) has been used to treat certain tumors in clinic trials. However, the curative effect of TNFα has been undermined by the induced-NF-κB activation in many types of tumor. Maslinic acid (MA), a pharmacological safe natural product, has been known for its important effects as anti-oxidant, anti-inflammatory, and anti-viral activities. The aim of this study was to determine whether MA potentiates the anti-tumor activity of TNFα though the regulation of NF-κB activation. Results: In this study, we demonstrate that MA significantly enhanced TNFα-induced inhibition of pancreatic cancer cell proliferation, invasion, and potentiated TNFα-induced cell apoptosis by suppressing TNFα-induced NF-κB activation in a dose- and time-dependent manner. Addition of MA inhibited TNFα-induced IκBα degradation, p65 phosphorylation, and nuclear translocation. Furthermore, MA decreased the expression levels of NF-κB-regulated genes, including genes involved in tumor cell proliferation (Cyclin D1, COX-2 and c-Myc), apoptosis (Survivin, Bcl-2, Bcl-xl, XIAP, IAP-1), invasion (MMP-9 and ICAM-1), and angiogenesis (VEGF). In athymic nu/nu mouse model, we further demonstrated that MA significantly suppressed pancreatic tumor growth, induced tumor apoptosis, and inhibited NF-κB-regulated anti-apoptotic gene expression, such as Survivin and Bcl-xl. Conclusions: Our data demonstrate that MA can potentiate the anti-tumor activities of TNFα and inhibit pancreatic tumor growth and invasion by activating caspase-dependent apoptotic pathway and by suppressing NF-κB activation and its downstream gene expression. Therefore, MA together with TNFα could be new promising agents in the treatment of pancreatic cancer.

Extracellular nucleotides that constitute a “danger signal” play an important role in the regulation of immune responses. However, the function and mechanism of extracellular UDP and P2Y₆ in antiviral immunity remain unknown. In this study, we demonstrated the in vitro and in vivo protection of UDP/P2Y₆ signaling in vesicular stomatitis virus (VSV) infection. First, we demonstrated that VSV-infected cells secrete UDP from the cytoplasm as a danger signal to arouse surrounding cells. Meanwhile, expression of the UDP-specific receptor P2Y₆ also was enhanced by VSV. Consequently, UDP protects RAW 264.7 cells, murine embryonic fibroblasts, bone marrow–derived macrophages, and L929 cells from VSV and GFP lentivirus infection. This protection can be blocked by the P2Y₆ selective antagonist MRS2578 or IFN-α/β receptor–blocking Ab. VSV-induced cell death and virus replication were both enhanced significantly by knocking down and knocking out P2Y₆ in different cells. Mechanistically, UDP facilitates IFN-β secretion through the p38/JNK- and ATF-2/c-Jun–signaling pathways, which are crucial in promoting antiviral immunity. Interestingly, UDP was released through a caspase-cleaved pannexin-1 channel in VSV-induced apoptotic cells and protected cells from infection through P2Y₆ receptor in an autocrine or paracrine manner. Furthermore, UDP also protected mice from VSV infection through P2Y₆ receptors in an acute neurotropic infection mouse model. Taken together, these results demonstrate the important role of extracellular UDP and P2Y₆ as a danger signal in antiviral immune responses and suggest a potential therapeutic role for UDP/P2Y₆ in preventing and controlling viral diseases.

Metastasis is one of the main causes of death for patients with malignant tumors. Aberrant expression of matrix metalloproteinase-9 (MMP-9) has been implicated in the invasion and metastasis of various cancer cells. Here, we found that caffeic acid 3,4-dihydroxy-phenethyl ester (CADPE) could inhibit the migration and invasion of human gastric carcinoma cells in Transwell migration assays. To understand the underlying mechanism, we showed that CADPE significantly inhibited phorbol 12-myristate 13-acetate (PMA)–induced increases in MMP-9 expression and activity in a dose-dependent manner. The inhibitory effect of CADPE on MMP-9 expression correlated well with the suppression of MMP-9 promoter activity and the reduction of MMP-9 mRNA. Reporter gene assay and electrophoretic mobility shift assay showed that CADPE inhibited MMP-9 expression by suppressing the activation of the nuclear transcription factor activator protein-1 (AP-1) and c-Fos, but not NF-κB. Moreover, CADPE inhibited PMA-induced phosphorylation of protein kinases involved in AP-1 activation, such as focal adhesion kinase (FAK), mitogen-activated protein kinase/extracellular signal–regulated kinase (ERK) kinase (MEK), and ERK1/2, whereas CADPE had little effect on the phosphorylation of p38 and c-jun NH₂-terminal kinase. Taken together, our findings indicate that CADPE could be a unique antitumor agent that specifically inhibits MMP-9 activity by targeting the activation of FAK/MEK/ERK protein kinases and AP-1 transcription factor. Mol Cancer Res; 8(11); 1477–88. ©2010 AACR.

Extracellular ATP (eATP), released as a “danger signal” by injured or stressed cells, plays an important role in the regulation of immune responses, but the relationship between ATP release and innate immune responses is still uncertain. In this study, we demonstrated that ATP was released through Toll-like receptor (TLR)-associated signaling in bothEscherichia coli-infected mice and lipopolysaccharide (LPS)- or Pam3CSK4-treated macrophages. This ATP release could be blocked completely only byN-ethylmaleimide (NEM), not by carbenoxolone (CBX), flufenamic acid (FFA), or probenecid, suggesting the key role of exocytosis in this process. Furthermore, LPS-induced ATP release could also be reduced dramatically through suppressing calcium mobilization by use of U73122, caffeine, and thapsigargin (TG). In addition, the secretion of interleukin-1β (IL-1β) and CCL-2 was enhanced significantly by ATP, in a time- and dose-dependent manner. Meanwhile, macrophage-mediated phagocytosis of bacteria was also promoted significantly by ATP stimulation. Furthermore, extracellular ATP reduced the number of invading bacteria and protected mice from peritonitis by activating purinergic receptors. Mechanistically, phosphorylation of AKT and ERK was overtly increased by ATP in antibacterial immune responses. Accordingly, if we blocked the P2X- and P2Y-associated signaling pathway by using suramin and pyridoxal phosphate-6-azo(benzene-2,4-disulfonic acid), tetrasodium salt (PPADS), the ATP-enhanced immune response was restrained significantly. Taken together, our findings reveal an internal relationship between danger signals and TLR signaling in innate immune responses, which suggests a potential therapeutic significance of calcium mobilization-mediated ATP release in infectious diseases.

G protein–coupled receptor 54 (GPR54), the key receptor for the neuropeptide hormone kisspeptin, plays essential roles in regulating puberty development and cancer metastasis. However, its role in the antiviral innate immune response is unknown. We report that virus-induced type I interferon (IFN-I) production was significantly enhanced in Gpr54-deficient cells and mice and resulted in restricted viral replication. We found a marked increase of kisspeptin in mouse serum during viral infection, which, in turn, impaired IFN-I production and antiviral immunity through the GPR54/calcineurin axis. Mechanistically, kisspeptin/GPR54 signaling recruited calcineurin and increased its phosphatase activity to dephosphorylate and deactivate TANK [tumor necrosis factor receptor-associated factor (TRAF) family member-associated NF-κB activator]–binding kinase 1 (TBK1) in a Ca²⁺-dependent manner. Thus, our data reveal a kisspeptin/GPR54/calcineurin-mediated immune evasion pathway exploited by virus through the negative feedback loop of TBK1 signaling. These findings also provide insights into the function and cross-talk of kisspeptin, a known neuropeptide hormone, in antiviral innate immune response.