in all cell lines, except in U-343 MG-Cl2:6 and somewhat inconsistently in U-251 MG. Thus, irrespective of the differences in gene expression patterns, it was confirmed that HSF1 is a target for NFIX in many cell lines. Results NFIX regulates genes involved in stress response To identify the functions of NFIX, we suppressed it by transient siRNA transfections. By real time quantitative RTPCR we confirmed that NFIA, NFIB and NFIC were not affected. As an NFIX peptide has never been demonstrated before, we also characterized the NFIX peptide and its intracellular localization. We also found that tyrosine phosphorylation affects intracellular localization of NFIX. Thus we identified a 60 KDa nuclear peptide which could be immunoprecipitated and was down-regulated by NFIX-siRNA. To detect transcriptional targets of NFIX, total RNA from control- or NFIX-siRNA transfected U-251 MG cells were profiled using cDNA microarrays in six pairs of dye-swap hybridizations representing six different transfection experiments. Using a very stringent B value threshold. Of these, 55 were down-regulated and 95 up-regulated by NFIXsiRNA suggesting that NFIX has more repressive effect on transcription than activating. While the genes with altered transcript levels were involved in diverse cellular GLPG-0634 site processes, the largest functional group of the these genes coded for proteins involved in unfolded protein response, such as HSPA1A, HSPA8 HSP90B1, XBP1, ATF4, PDIA4, DDIT3, SYVN1, TXNDC4, DERL2, HYOU1 and HERPUD1. The changed expression of these genes was confirmed by qRTPCR in the same RNA samples used for microarray hybridizations. To check if the regulation of stress-related genes by NFIX is a more general phenomenon or NFI-binding sites do not dictate transcriptional regulation by NFIX Next we investigated if the transcriptional deregulation observed 
after NFIX-siRNA treatment is a direct effect of loss of NFIX binding to its target sequences or not. A TransFac search for commonly occurring transcription factor binding sites did not reveal any significant differences between the genes with altered transcript levels and a set of genes on the microarray which did not exhibit altered transcript levels. Since the NFI-binding site matrix used by TransFac is based on the half 18334597 NFI-binding sites, we asked if the full palindromic NFI-binding sites existed in the promoter regions of genes with altered transcript levels. 3 Kb regions spanning upstream of the transcription start sites of 91 genes with altered transcript levels and 137 control genes were extracted and searched for the presence of full NFI-binding sites, with different stringencies. The sequence motifs YGGMGCCAA, TGGMCCAA and TGGMCCA were found in 6.6, 17.6 and 53.8% of genes with altered transcript levels and in 2.2, 10.2 and 42.3% of control genes respectively. Even if the genes with altered transcript levels consistently had a higher percentage of genes containing NFI-binding site in their promoters than the control genes, there was still a substantial number 10604535 of genes on the microarrays, which were associated with NFI-binding sites and did not exhibit altered transcript levels. The genes with altered transcript levels HSPA8, MSN and LOX had NFI-binding sites in their promoters and NFIX binding to those sites in U-2987 MG cells was studied by chromatin immunoprecipitation PCR using NFIX antibody. NFIX was found to bind to the MSN and LOX promoters, but not the HSPA8 promoter. The HSF1 promoter was also anal