Toll-like receptor 4 signaling promotes tumor growth. J Immunother. 2010;33:73-82. [PMID: 19952954 DOI: 10.1097/CJI.0b013e3181b7a0a4]

Hypoxia-inducible factor-1 up-regulates the expression of Toll-like receptor 4 in pancreatic cancer cells under hypoxic conditions

BACKGROUND & AIMS

Hypoxia is a common characteristic of solid tumors. Recent studies confirmed that Toll-like receptor 4 (TLR4) plays a significant role in cancer invasion and progression. In this study, the correlation between the expression of TLR4 and the change of the protein level of Hypoxia-inducible factor-1 alpha (HIF-1α) was studied.

METHODS

We examined 84 human pancreatic cancer tissues for expression of HIF-1α and TLR4 proteins. Panc-1 cells were exposed to normoxia (20% O(2)) or hypoxia (<1% O(2)) or treated with CoCl(2). TLR4 protein was analyzed by flow cytometry and immunostaining. Growth studies were conducted on cells with the HIF-1α inhibition isolated from stable transfected cell lines. Finally, TLR4 protein was detected by immunohistochemistry in vivo tumors.

RESULTS

There was a positive correlation between TLR4 and HIF-1α protein in pancreatic cancer tissues. Hypoxic stress induced TLR4 mRNA and protein expression in Panc-1 cells. Cells transfected with HIF-1α siRNA showed attenuation of hypoxia stress-induced TLR4 expression. In vivo growth decreased in response to TLR4 and HIF-1α inhibiton. Transient HIF-1α siRNA treatment could effectively curb tumor growth in vivo.

CONCLUSION

These results suggest that TLR4 expression in pancreatic cancer cells is up-regulated via HIF-1α in response to hypoxic stress and underscore the crucial role of HIF-1α-induced TLR4 in tumor growth.

Exogenous or endogenous Toll-like receptor ligands: which is the MVP in tumorigenesis?

Toll-like receptors (TLRs) are a class of pattern recognition receptors sensing microbial components and triggering an immune response against pathogens. In addition to their role in anti-infection immunity, increasing evidence indicates that engagement of TLRs can promote cancer cell survival and proliferation, induce tumor immune evasion, and enhance tumor metastasis and chemoresistance. Recent studies have demonstrated that endogenous molecules or damage-associated molecular patterns released from damaged/necrotic tissues are capable of activating TLRs and that the endogenous ligands-mediated TLR signaling is implicated in the tumor development and affects the therapeutic efficacy of tumors. Since both exogenous and endogenous TLR ligands can initiate TLR signaling, which is the most valuable player in tumor development becomes an interesting question. Here, we summarize the effect of TLR signaling on the development and progression of tumors, and discuss the role of exogenous and endogenous TLR ligands in the tumorigenesis.

Resveratrol inhibits LPS-induced epithelial-mesenchymal transition in mouse melanoma model

Epithelial to mesenchymal transition (EMT) has been linked to metastasis. Resveratrol exhibits potential antitumor activities; however, the inhibitory effects of resveratrol on the EMT of melanoma have not been demonstrated. Here, a new role for LPS in promoting EMT is described. LPS-induced EMT was identified by examining the markers of EMT. To assess the activation of NF-κB signal transduction pathway, we performed a reporter assay by using tumor cells transfected with the luciferase gene under the control of NF-κB response elements. The antitumor effects of resveratrol were evaluated in an experimental mouse metastasis tumor model. LPS increased N-cadherin and Snail expression and decreased zonula occludens-1 expression in a dose- and time-dependent manner. Meanwhile, LPS stimulated cell migration through activation of TLR4/NF-κB signal pathway. LPS-induced EMT is critical for inflammation-initiated metastasis. Nuclear translocation and transcriptional activity of p65 NF-κB, an important inducer of EMT, were inhibited by resveratrol. Resveratrol inhibited LPS-induced tumor migration and markers of EMT, significantly prolonged animal survival and reduced the tumor size. Thus, resveratrol plays an important role in the inhibition of LPS-induced EMT in mouse melanoma through the down-regulation of NF-κB activity. The data provide an insight into the mechanisms on the function of resveratrol during the processes of EMT.

Lung cancer and Toll-like receptors

Lung carcinoma is one of the leading causes of death worldwide. It is a non-immunogenic cancer, resistant to immune surveillance. Toll-like receptors (TLRs) connect the innate to the adaptive immune system. Given that cancerous cells evade the immune system, the activation of TLRs could represent a potential target for cancer therapy. The induction of Th1-like and cytotoxic immunity by TLR signalling could lead to tumour cell death, resulting in tumour regression or arrest. However, basic research and clinical trials revealed that the activation of specific TLRs, such as TLR2, TLR4 and TLR9, do not have any anti-tumour activity in lung carcinoma. Increasing evidence suggests that TLRs are important regulators of tumour biology; however, little is known about their function in lung cancer. Thus, in order to develop new therapeutic approaches, further studies are needed to understand the connection between TLRs and lung cancer progression. This review focuses on the potential mechanisms by which TLR ligands can facilitate or not lung cancer and lung metastases establishment/progression.

Inhibition of cartilage damage by pro-opiomelanocortin prohormone overexpression in a rat model of osteoarthritis

Pro-opiomelanocortin (POMC) is a precursor of various neuropeptides. POMC-derived neuropeptides are potent inflammation inhibitors and immunosuppressants. Evidence that osteoarthritis (OA) is an inflammatory disease is accumulating. We assessed whether intra-articular gene delivery of POMC ameliorates experimentally induced OA in a rat model. OA was induced in Wistar rats by anterior cruciate ligament-transection (ACLT) in the knee of one hind limb. Adenoviral vector encoding human POMC (AdPOMC) was injected intra-articularly into the knee joints after ACLT. The transgene expression and the inflammatory responses were evaluated using immunoblotting, immunohistochemistry and enzyme-linked immunosorbent assay. The treated joints were assessed histologically for manifestations of the disease. Human POMC was expressed in the chondrocytes and synovial membrane after the intra-articular injection. POMC gene transfer reduced nuclear factor-κB activity and the levels of interleukin-1β in HTB-94 chondrosarcoma cells and Raw 264.7 macrophages; it also reduced microvessel density in the synovium. Histological examination showed that symptoms of OA in AdPOMC-treated rats were less severe than in rats treated with either empty adenoviral vector (AdNull) or normal saline. Intra-articular injection of adenoviral vectors expressing POMC significantly suppressed the progression and severity of OA, and reduced inflammatory responses and angiogenesis. POMC gene delivery may offer novel therapeutic approach for treating OA.

Inhibition of experimental lung metastasis by systemic lentiviral delivery of kallistatin

Background

Angiogenesis plays an important role in the development and progression of tumors. Kallistatin exerts anti-angiogenic and anti-inflammatory activities that may be effective in inhibiting tumor metastasis. We investigated the antitumor effect of lentivirus-mediated kallistatin gene transfer in a syngeneic murine tumor model.

Methods

Lentiviral vector encoding kallistatin (LV-Kallistatin) was constructed. The expression of kallistatin was verified by enzyme-linked immunosorbent assay (ELISA), and the bioactivity of kallistatin was determined by using cell proliferation, migration, and invasion assays. In addition, antitumor effects of LV-Kallistatin were evaluated by the intravenous injection of virus into tumor-bearing mice.

Results

The conditioned medium from LV-Kallistatin-treated cells inhibited the migration and proliferation of endothelial cells. Meanwhile, it also reduced the migration and invasion of tumor cells. In the experimental lung metastatic model, tumor-bearing mice receiving LV-Kallistatin had lower tumor nodules and longer survival than those receiving control virus or saline. Moreover, the microvessel densities, the levels of vascular endothelial growth factor (VEGF), tumor necrosis factor (TNF)-α, and nuclear factor κB (NF-κB) transcriptional activity were reduced in the LV-Kallistatin-treated mice.

Conclusion

Results of this study showed that systemic administration of lentiviral vectors encoding kallistatin inhibited the growth of metastatic tumor and prolonged the survival of tumor-bearing mice. These results suggest that gene therapy using lentiviruses carrying the kallistatin gene, which exerts anti-angiogenic and anti-inflammatory activities, represents a promising strategy for the treatment of lung cancer.