Induced interleukin-8 expression in gliomas by tumor-associated macrophages

The tumor microenvironment affects tumor initiation, progression, and metastasis. However, it is still not clear how stromal cells interact with the tumor cells. By using a cytokine array immunoblot assay, we showed that interleukin (IL)-8, IL-6, and RANTES (regulated upon activation normal T-cell expressed and secreted) proteins were up-regulated in GBM8401 glioma cells after coculture with human THP-1-derived macrophages. IL-8 is a chemokine with leukocyte chemotactic, tumorigenic, and proangiogenic properties. To evaluate the correlation of IL-8 expression with tumor-associated macrophages and angiogenesis, 43 glioma specimens were studied. The results showed that the IL-8 mRNA expression and microvessel count in glioma surgical specimens correlated positively with the density of tumor-associated macrophages. We further showed that IL-8 mRNA expression in GBM8401 cells increased dramatically, by 2(8)-2(10)-fold, after being cocultured with macrophages. This increase could also be induced by macrophage-conditioned medium, tumor necrosis factor-alpha, IL-1alpha, and IL-1beta, and could be suppressed by anti-inflammatory agents including pyrrolidine dithiocarbamate, pentoxifylline, or dexamethasone. These findings imply that macrophage infiltration may be the common feature shared by cancer and inflammation, and macrophages could play a role in promoting glioma growth and angiogenesis by inducing IL-8 expression in glioma cells via inflammatory stimuli or the nuclear factor kappa B pathway.