To further validate activation of GFAP induced by STAT3 binding, a ChIP analysis was performed to examine the recruitment of RNA polymerase II. A comparison of undifferentiated NTera-2 cells with differentiated cells revealed increased recruitment of RNA polymerase II to the GFAP gene transcription start site (primer set e) after differentiation, consistent with enhanced transcription (Fig. 5B) . Previous studies suggested that H3 Lys4 trimethylated (H3K4me3) nucleosomes occur near transcription start sites of actively transcribed genes. Moreover, several large-scale and genome-wide analyses revealed that about 91% of all RNA polymerase II-binding sites are correlated with H3K4me3-binding sites and were positively correlated with gene expression levels [54, 55] . Using a ChIP assay, we also found that H3K4me3 was enriched at sites of transcription initiation (primer sets e-g), with maximal enrichment immediately downstream of the start site (primer sets e and f) and overlapping the peak of RNA polymerase II at the transcription start site (primer set e) in differentiated cells compared to undifferentiated cells (Fig. 5C) . These results suggest a close correlation among STAT3-mediated chromatin remodeling, RNA polymerase II recruitment, and GFAP activation. Figure 2B and 2C show that activated STAT3 was coimmunoprecipitated with p300. Furthermore, it was reported that STAT proteins activate transcription by recruiting the transcription co-activator, CBP/p300 [56, 57] , and CBP/p300-induced acetylation on histone tails is coupled with chromatin remodeling, thereby enhancing target gene expression [58, 59] . We next examined whether the CBP/p300 co-activator was also associated with the activated GFAP promoter along with an increase in the histone acetylation level in the same region. Notably, we did not detect a significant association between CBP/p300 proteins and the STAT3-binding site at the GFAP promoter (primer sets a-c), as indicated by the ChIP analyses (Fig. 5D) . Conversely, upon cellular differentiation, robust recruitment of CBP/p300 proteins was observed in the vicinity of the exon 1 coding region (primer sets e-g with the CBP antibody and primer sets d, f, and g with the p300 antibody) (Fig. 5D ). Since there is no report of DNA-binding ability of CBP/p300 in these regions, this result suggested that CBP/p300 was brought to the vicinity of exon 1 by transcription factors such as STAT3 (Fig. 5A ) after cell differentiation. We further inspected the status of histone acetylation before and after differentiation to survey the influence of CBP/p300 deposition on exon 1. ChIP assays were conducted with specific antibodies against acetyl-H3K9 (H3K9Ac) and acetyl-H3K14 (H3K14Ac) in undifferentiated NTera-2 cells and differentiated cells. The results showed that there were significant increases in active markers of H3K9Ac (primer sets b and c) and H3K14Ac (primer sets a and b) around the STAT3binding site at the GFAP promoter region, particularly the STAT3binding site (primer set b), but not in the exon 1 coding region (Fig. 5E ). In addition, in a separate experiment (Liao, CH and Yu, J. unpublished observation), we found that treatment of NTera-2 cells with HDAC inhibitors led to an increase in the acetylated H3K9 and H3K14 using specific antibodies and also GFAP gene expression. Therefore, our results raise the possibility that the chromatin structure of the GFAP promoter may undergo dramatic changes in organization during cell differentiation.