Gliomas express many genes that play a role in neural precursor cells (NPCs), but no direct comparison between glioma and stem cell (SC) gene expression profiles has been performed. To investigate the similarities and differences between gliomas and SCs, we compared the microRNA (miRNA) expression signatures of glial tumors, embryonic SCs (ESCs), NPCs, and normal adult brains from both human and mouse tissues. We demonstrated that both human gliomas (regardless of their grade) and methylcholanthrene-induced mouse glioma shared an miRNA expression profile that is reminiscent of NPCs. About half of the miRNAs expressed in the shared profile clustered in seven genomic regions susceptible to genetic/epigenetic alterations in various cancers. These clusters comprised the miR17 family, mir183-182, and the SC-specific clusters mir367-302 and mir371-373, which are upregulated in gliomas, ESCs, and NPCs. The bipartite cluster of 7 + 46 miRNAs on chromosome 14q32.31, which might represent the largest tumor suppressor miRNA cluster, was downregulated in the shared expression profile. This study provides the first evidence for association between these clusters and gliomas. Despite the broad similarity in the miRNA expression profiles, 15 miRNAs showed disparate expression between SC and gliomas. Ten miRNAs belong to the 2 SC-specific clusters and the remaining (mir135b, mir141, mir205, mir200C, and mir301a) have been previously shown to associate with malignancies. Our finding showed that all gliomas displayed NPC-like miRNA signatures, which may have implications for studies of glioma origins. Furthermore, careful study of the 15 miRNAs that differ in expression between SCs and gliomas, particularly those 5 that are not SC-specific, may enhance our understanding of gliomagenesis.

O 6 -Methylguanine-DNA-methyltransferase (MGMT) and nuclear factor KB (NF-KB) are two key effectors associated with the development of resistance to alkylating agent-based chemotherapy. This prompted us to hypothesize that NF-KB might be involved in MGMT regulation. Consistent with this hypothesis, we have discovered two putative NF-KB binding sites within the MGMT promoter region and showed a specific and direct interaction of NF-KB at each of these sites. Forced expression of the NF-KB subunit p65 in HEK293 cells induced an increase in MGMT expression whereas addition of the NF-KB super repressor #NIKB completely abrogated the induction. We also found a significant correlation between the extent of NF-KB activation and MGMT expression in the glioma cell lines and the human glial tumors tested and showed that it was independent of MGMT promoter methylation. Our results are of potential clinical significance because we show that cell lines with ectopic p65 or high constitutive NF-KB activity are less sensitive to nitrosourea treatment and that suppression of MGMT activity with O 6 -benzylguanine completely abolishes the chemoresistance acquired by NF-KB. The findings of our study strongly suggest that NF-KB plays a major role in MGMT regulation and that MGMT is most probably the major player in NF-KB-mediated chemoresistance to alkylating agents.