Although malignant gliomas are highly invasive tumors, a characteristic that contributes to the commonly observed therapeutic failures and local disease recurrences, the molecular events that regulate invasion in these tumors remain poorly understood. Because the transcription factor RelA/NF- mu B has been shown to regulate invasion during several cellular processes, we have examined immunohistochemically expression of the constitutively activated RelA/NF- mu B in tissues obtained from 49 astrocytic tumors 8 diffuse astrocytomas, 9 anaplastic astrocytomas (AAs) and 32 glioblastomas (GBMs). In addition, we examined the in vitro effects of antisense oligonucleotides and curcumin on the expression and activation of RelA/NF- mu B, urokinase-type plasminogen activator (u-PA) expression, migration, and invasion in the T98G glioma cell line. Expression of the constitutively activated RelA/NF- mu B was observed in 2 (25%) of 8 cases of diffuse astrocytomas, 5 (55.6%) of 9 cases of AAs, and 30 (93.8%) of 32 cases of GBMs. This expression was significantly correlated with the malignant potential in astrocytic tumors (P < 0.001). Moreover, antisense oligonucleotides and curcumin inhibited phorbol-12-myristate-13-acetate (PMA)-induced RelA/NF- mu B expression or activation (or both), down-regulated u-PA expression, and reduced the migration and invasive potentials of T98G glioma cells. Thus, the expression of constitutively activated RelA/NF- mu B is associated with malignancy potential in astrocytic tumors and may play a critical role in the regulation of u-PA expression and invasiveness in gliomas. RelA/NF- mu B may therefore be an intriguing candidate for studies aimed at understanding and prevention of the invasiveness of gliomas.