Cell line studies show that HMGB1 is click here strongly up-regulated in breast cancer, colon cancer, melanoma, pancreatic cancer and prostate cancer; upregulated HMGB1 activates TLR2 and TLR4 expressed on immune cells and induces cancer progression and metastasis [20]. We previously reported elevated expression of S100 proteins in melanoma cell lines

relative to normal melanocyte lines. S100 proteins released by melanoma cells stimulated melanoma cells as well as PBLs and acted as an autocrine tumor growth factor [50]. S100A4 is responsible for metastasis and is an indicator of poor prognosis for patients with Epoxomicin datasheet breast cancer [51]. However, although this inflammatory protein is associated with metastatic cancer cells, in the tumor microenvironment it is also expressed by macrophages, lymphocytes and fibroblasts. Elevated interstitial fluid levels of S100A4 in tumors [52] suggest that stromal cells in the tumor microenvironment externalize S100A4, which then activates TLR signals. Recent studies reveal that S100A8 and S100A9 produced by primary tumors can activate serum amyloid A (SAA) 3 in lung tissue prior to pulmonary metastasis. SAA3 has a role in the accumulation of myeloid cells and acts as a positive-feedback regulator for secretion of S100 proteins. SAA3 is a ligand for TLR4 in lung endothelial cells and macrophages. The activation of TLR4

facilitates migration Akt inhibitor of cancer cells from the primary tumor to lung

tissue by creating a tumor microenvironment [53]. Blocking the S100-TLR4 cascade therefore might be an effective strategy for the prevention of pulmonary metastasis. Nucleic Acid Fragments Act as DAMPs During tumor expansion, nucleic acids released from necrotic cancer cells or adjacent injured normal epithelial cells act as DAMPs. Kariko et al. [54] demonstrated that TLR3 expressed in DCs was activated by mRNA released from necrotic cells; subsequent TLR signals upregulated DC maturation, leading to IFN-α secretion. This upregulation could Carnitine dehydrogenase be abolished by pretreatment of necrotic cells with RNase. The mRNA released by cancer cells circulates in the blood [55] and its serum levels have been correlated with disease outcome [56]. In our studies, TLR3 expression was upregulated (24.6–121.3% in mean value) in melanoma cells incubated 12 h with purified total RNA from normal PBL or allogeneic melanoma cells (Fig. 2), and TLR activation promoted melanoma cell migration [5]. Thus, RNA derived from melanoma cells can act as a TLR3 ligand and facilitate migration of melanoma cells, without support from immune cells. Fig. 2 TLR3 ligation and subsequent TLR3 mRNA expression in melanoma cells incubated with purified total RNA from normal donor PBLs or allogeneic melanoma cells. When ME7 and ME1 human melanoma cells were incubated 12 h with total RNA from normal PBL and ME5 melanoma cells, mean TLR3 mRNA expression increased 24.6–121.