Induction of proinflammatory cytokines in response to malignant cells is an integral component of immune response to control tumor development. However, recent evidences have suggested that tumor cells may evade the immune system and exploit inflammatory responses to enhance its own growth. An exemplary example is the highly invasive and tumor necrosis factor (TNF)a-resistant glioblastoma, whose growth is associated with TNFa expression. We thus examined whether the tumor takes advantage of TNFa overexpression to enhance its invasiveness. To delineate the contribution of inflammation in tumor migration, we demonstrated that the role of proinflammatory cytokines on matrix metalloproteinases-3 (MMP-3) expression, and its consequent effects on the invasiveness of a human glioma cell-line, T98G. By using Matrigel Invasion Chamber, T98G cell migration was significantly enhanced in response to TNFa. In contrast, interferon-c (IFNc) reduced both basal and TNFa-enhanced cell invasion. To investigate the mechanisms involved, we demonstrated that TNFa upregulated mRNA and protein expression of MMP-3 in T98G cells, whereas IFNc downregulated the MMP-3 expression. The role of MMP-3 in glioma invasiveness was further confirmed by transfecting MMP-3 siRNA in T98G to abrogate the TNFa-enhanced cell invasion. To delineate the mechanisms further, we showed that IFNc exerts an inhibitory effect on the binding of TNFa-activated Ets-1 and NFjB to their respective enhancer elements found in MMP-3 promoter. In summary, our results indicated that TNFa enhances the invasiveness of T98G glioma cells through MMP-3 induction, and such enhancement of cell migration can be inhibited by IFNc. ' 2007 Wiley-Liss, Inc.Key words: MMP-3; IFNc; TNFa; invasiveness; glioma Glioblastoma is a malignant and highly invasive form of astrocyte-derived brain tumor, which accounts for more than 40% of all central nervous system neoplasm.1 Because of its relative resistance to radiation and chemotherapy, the prognosis for malignant glioblastoma remains poor.2 In addition, most of glioblastoma cells are resistant to tumor necrosis factor (TNF)-induced cytotoxic effects 3 and high invasiveness of these tumor cells makes the complete surgical resection nearly impossible in most cases. Glioblastoma consists of both neoplastic cells (glioma) and non-neoplastic cellular elements including fibroblasts, endothelial cells, lymphocytes and macrophages surrounded by extracellular matrix.4 During tumor development, changes in the milieu provoke cytokine expression, which in turn stimulates leukocyte infiltration leading to the release of more cytokines.Induction of proinflammatory cytokines in various preneoplastic and malignant diseases is commonly believed to be the host immune response against tumor development and progression. However, growing evidences have suggested that inflammation is actually an indispensable participant in the neoplastic process, nurturing proliferation, survival and migration of cancer cells. 5,6 Therefore, within this microenvironment, cytok...