Astrocyte-specific Expression of the α1-Antichymotrypsin and Glial Fibrillary Acidic Protein Genes Requires Activator Protein-1

Abstract

An amyloid-associated serine proteinase inhibitor (serpin), ␣ 1 -antichymotrypsin (ACT), is encoded by a gene located within the distal serpin subcluster on human chromosome 14q32.1. The expression of these distal serpin genes is determined by tissue-specific chromatin structures that allow their ubiquitous expression in hepatocytes; however, their expression is limited to a single ACT gene in astrocytes. In astrocytes and glioma cells, six specific DNase I-hypersensitive sites (DHSs) were found located exclusively in the 5-flanking region of the ACT gene. We identified two enhancers that mapped to the two DHSs at ؊13 kb and ؊11.5 kb which contain activator protein-1 (AP-1) binding sites, both of which are critical for basal astrocyte-specific expression of ACT reporters. In vivo, these elements are occupied by c-jun homodimers in unstimulated cells and c-jun/c-fos heterodimers in interleukin-1-treated cells. Moreover, functional c-jun is required for the expression of ACT in glioma cells because both transient and stable inducible overexpression of dominant-negative c-jun(TAM67) specifically abrogates basal and reduces cytokine-induced expression of ACT. Expression-associated methylation of lysine 4 of histone H3 was also lost in these cells, but the DHS distribution pattern and global histone acetylation were not changed upstream of the ACT locus. Interestingly, functional AP-1 is also indispensable for the expression of glial fibrillary acidic protein (GFAP), which is an astrocyte-specific marker. We propose that AP-1 is a key transcription factor that, in part, controls astrocyte-specific expression of genes including the ACT and GFAP genes.The 11 genes encoding the serine proteinase inhibitors (serpins) 2 are clustered on human chromosome 14q32.1 and occupy the ϳ370 kb region (1, 2). This serpin cluster can be divided into three subclusters that contain 4, 3, and 4 genes, respectively. The distal subcluster consists of the genes encoding the ␣ 1 -antichymotrypsin (ACT), kallistatin, protein C inhibitor, and the recently identified kallistatin-like protein (2). All of these genes are highly transcribed in hepatocytes and hepatoma cells, and their promoters are accessible to DNase I digestion (3). In contrast, only the ACT gene is expressed in brain astrocytes and glioma cells (3). Selective expression of ACT in these cells correlates with DNase I accessibility at the 5Ј-flanking region of the gene, whereas nonexpressed protein C inhibitor and kallistatin genes are localized in DNase I-inaccessible chromatin (3).In the liver, hepatocyte-specific gene expression is determined by transcription factors belonging to the hepatocyte nuclear factor (HNF) and CAAT enhancer-binding protein (C/EBP) families, with HNF-1 and HNF-4 being critical, but not sufficient, for the expression of the genes from the proximal serpin subcluster (4). The presence of binding sites for these transcription factors near the promoters of the distal serpin genes suggests that they play a critical role in their expression in hepatic cells. ...

Nuclear Factor-1-X Regulates Astrocyte-specific Expression of the α1-Antichymotrypsin and Glial Fibrillary Acidic Protein Genes

“…We have recently reported that the AP-1 complex is needed for the basal astrocyte-specific expression of the ACT and GFAP genes (10). However, the precise mechanism that allows this ubiquitous transcription factor to determine astrocyte-specific expression is not known.…”

“…Hence, NFI is critical for intrinsic astrocyte-specific expression of the ACT and GFAP genes. (10) resulted in a drastic suppression of ACT expression in glioma cells, we analyzed the 14-kb long 5Ј-flanking region of the ACT gene for the . Expression of the AC T and GFAP genes requires NFI in U373 cells.…”

“…Its expression in hepatocytes is likely determined by liver-specific transcription factors belonging to the hepatocyte nuclear factor and CAAT enhancer-binding protein families (9). In contrast to hepatocytes, the constitutive astrocyte-specific expression of ACT requires the activator protein-1 (AP-1) transcription factor, which is composed of the Jun and Fos family members (10). Two AP-1 binding sites have recently been identified at Ϫ13 kb and Ϫ11.5 kb in the 5Ј-flanking region of the ACT gene, which are critical for astrocyte-specific expression (4,10).…”

“…Two AP-1 binding sites have recently been identified at Ϫ13 kb and Ϫ11.5 kb in the 5Ј-flanking region of the ACT gene, which are critical for astrocyte-specific expression (4,10). However, glioma cells overexpressing dominant-negative c-jun(TAM67), which quenches functional AP-1 complexes and abolishes basal ACT expression, retained the astrocyte-specific chromatin structure of the distal serpin subcluster (10). Several models have been hypothesized to explain this phenomenon, including the one that proposes the presence of an additional transcription factor(s) that, by virtue of its cooperation with AP-1, determine both astrocyte-specific chromatin structure and ACT gene expression.…”

“…In contrast to hepatocytes, the constitutive astrocyte-specific expression of ACT requires the activator protein-1 (AP-1) transcription factor, which is composed of the Jun and Fos family members (10). Two AP-1 binding sites have recently been identified at Ϫ13 kb and Ϫ11.5 kb in the 5Ј-flanking region of the ACT gene, which are critical for astrocyte-specific expression (4,10). However, glioma cells overexpressing dominant-negative c-jun(TAM67), which quenches functional AP-1 complexes and abolishes basal ACT expression, retained the astrocyte-specific chromatin structure of the distal serpin subcluster (10).…”